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Received 16 Jun 2015 | Accepted 3 Feb 2016 | Published 14 Mar 2016

Here we identify necdin as a potent PGC-1a stabilizer that promotes mitochondrial biogenesis via PGC-1a in mammalian neurons. Expression of genes encoding mitochondria-specic proteins decreases signicantly in necdin-null cortical neurons, where mitochondrial function and expression of the PGC-1a protein are reduced. Necdin strongly stabilizes PGC-1a by inhibiting its ubiquitin-dependent degradation. Forced expression of necdin enhances mitochondrial function in primary cortical neurons and human SH-SY5Y neuroblastoma cells to prevent mitochondrial respiratory chain inhibitor-induced degeneration. Moreover, overexpression of necdin in the substantia nigra in vivo of adult mice protects dopaminergic neurons against degeneration in experimental Parkinsons disease. These data reveal that necdin promotes mitochondrial biogenesis through stabilization of endogenous PGC-1a to exert neuroprotection against mitochondrial insults.

DOI: 10.1038/ncomms10943 OPEN

Promotion of mitochondrial biogenesis by necdin protects neurons against mitochondrial insults

Koichi Hasegawa1, Toru Yasuda2,w, Chinatsu Shiraishi1, Kazushiro Fujiwara1, Serge Przedborski3, Hideki Mochizuki2 & Kazuaki Yoshikawa1

1 Laboratory of Regulation of Neuronal Development, Institute for Protein Research, Osaka University, Suita, Osaka 565-0871, Japan. 2 Department of Neurology, Graduate School of Medicine, Osaka University, Suita, Osaka 565-0871, Japan. 3 Department of Neurology, Pathology and Cell Biology, Columbia University, New York, New York, 10032, USA. w Present address; Department of Human Genetics, National Center for Child Health and

Development, Setagaya, Tokyo 157-8535, Japan. Correspondence and requests for materials should be addressed to K.H. (email: mailto:[email protected]

Web End [email protected] ) or to K.Y. (email: mailto:[email protected]

Web End [email protected] ).

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ARTICLE NATURE COMMUNICATIONS | DOI: 10.1038/ncomms10943

Mammalian neurons require high mitochondrial activities to generate a large amount of ATP for their signalling events such as action potential generation

and excitatory synaptic transmission1. Mitochondria are also involved in neuronal death and contribute to neuroprotection against various detrimental stresses2. Furthermore, mitochondrial abnormalities are suggested to contribute to the pathogenesis of neurodegenerative diseases such as Parkinsons disease (PD), amyotrophic lateral sclerosis (ALS), Alzheimers disease and Huntingtons disease3,4. However, little is known about the regulatory mechanisms of mitochondrial biogenesis in mammalian neurons under physiological and pathological conditions.

The peroxisome proliferator-activated receptor g coactivator-1 (PGC-1) family, which consists of PGC-1a, PGC-1b and PRC, plays a central role in governing a transcriptional regulatory network for mitochondrial biogenesis and respiratory function5. The PGC-1 family transcriptional coactivators enhance the activities of the nuclear respiratory factors NRF1 and NRF2, which induce transactivation of many genes encoding mitochondria-specic proteins involved in respiratory chain, mitochondrial DNA transcription/replication and protein import/assembly6. PGC-1a is the rst identied PGC-1 family member7, and its expression and function have been most extensively studied5. In non-neuronal cells, expression of PGC-1a is dynamically regulated at the transcriptional and post-translational levels in response to various environmental stimuli such as temperature, nutritional status and physical activity5,8. However, there is limited information on the regulation of neuronal PGC-1a and its involvement in mitochondrial biogenesis.

Necdin is a MAGE (melanoma antigen) family protein originally isolated from neurally differentiated embryonal carcinoma cells9. Necdin is expressed in virtually all neurons throughout the nervous system10. The necdin gene (gene symbols; Ndn for mouse, NDN for human) is expressed only from the paternal allele via genomic imprinting, a mammal-specic epigenetic regulation of gene expression11,12. Necdin interacts with the major transcription factors E2F1 and p53 to suppress cell proliferation and apoptosis1316. Moreover, necdin binds to Sirt1, an NAD -dependent protein deacetylase involved in the regulation of energy homeostasis, and facilitates Sirt1-mediated deacetylation of the transcription factors p53 and FoxO1 in neurons16,17. These ndings suggest that necdin interacts with major nuclear proteins to modulate the transcriptional regulation networks in mammalian neurons.

We here report that necdin facilitates neuronal mitochondrial biogenesis via PGC-1a stabilization by suppressing its proteolytic degradation in the ubiquitin-proteasomal system. Necdin forms a stable complex with PGC-1a in the nucleus of cortical neurons to maintain high mitochondrial activities. Furthermore, we demonstrate that necdin exerts potent neuroprotective effects on dopaminergic neurons against mitochondrial complex I inhibitors that are commonly used for modelling PD18. Our ndings will provide a better understanding of the regulatory mechanism underlying neuronal mitochondrial biogenesis under physiological and pathological conditions.

ResultsNecdin promotes neuronal mitochondria-related gene expression. To investigate whether necdin modulates specic gene transcription networks in brain neurons, we performed microarray-based gene expression proling in necdin-null cortical neurons (GEO accession; GSE63498). In gene ontology analysis for reduced gene expression in necdin-null neurons, the term

mitochondrion in the cellular component category was the most signicantly enriched (Fig. 1a). Of 61 downregulated genes (Fig. 1b and Supplementary Table 1), 10 genes encoding mitochondria-specic proteins were selected, and their expression levels were determined by quantitative reverse transcriptionPCR (qRTPCR) (Fig. 1c). In necdin-null neurons, the mRNA levels of Tomm20, Tomm22, Tomm40, Timm9 and Timm50, which encode mitochondrial import receptors, decreased by 4153%, and those of Ndufs3 and Atp5c1, which encode electron transport chain-associated enzyme components, decreased by 24% and 32%, respectively. However, cytochrome c (Cyc1), Atp5d and Atp5f1 mRNA levels were unchanged. We also quantied the expression of mitochondrial biogenesis-regulatory genes by qRTPCR. Nrf1, Gabpa (also known as Nrf2) and Tfam mRNA levels decreased signicantly in necdin-null neurons, whereas no signicant change in PGC-1a (Ppargc1) mRNA expression was observed.

The gene expression signature of necdin-null neurons indicates that necdin promotes mitochondrial biogenesis in cortical neurons.

Necdin promotes neuronal mitochondrial biogenesis. We then examined whether mitochondrial amounts and activities are reduced in necdin-null neurons. The levels of mitochondrial DNA (D-loop) and the mitochondrial marker MitoTracker Green FM, which localizes to mitochondria regardless of mitochondrial membrane potential, were reduced by 46% and 31%, respectively, in necdin-null neurons (Fig. 1d,e). The levels of oxidative phosphorylation complexes IV (CICV) subunits were also reduced in necdin-null neurons by 85% (CI, NDUFB8), 61% (CII, SDHB), 36% (CIII, UQCRC2), 78% (CIV, MTCO1) and 47% (CV, ATP5A) (Fig. 1f,g). These results suggest that endogenous necdin promotes mitochondrial biogenesis in cortical neurons.

We determined the effect of necdin on mitochondrial metabolic activity in primary cortical neurons using 3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide (MTT), a tetrazolium dye metabolized into water-insoluble formazan mainly in mitochondria. Necdin-null primary neurons exhibited normal morphology, but contained reduced MTT-formazan deposits (Fig. 2a). In quantitative MTT assay, MTT-formazan levels in necdin-null neurons decreased by 41% in the conditions where cellular damage was absent as assessed by lactate dehydrogenase (LDH) release (Fig. 2b). We further analysed oxidative phosphorylation complex I activity in primary cortical neurons by immunocapture assay. Complex I activity was reduced in necdin-null neurons by 60% (Fig. 2c,d). Cellular ATP levels were also signicantly reduced in necdin-null neurons, but not in necdin-null neural progenitor cells (NPCs), indicating that necdin promotes the mitochondrial activity predominantly in differentiated neurons (Fig. 2e). We then examined whether mitochondrial membrane potential is reduced in necdin-null neurons. The levels of chloromethyl-X-rosamine, a mitochondrial membrane potential-dependent uorescent probe, were reduced by 28% in necdin-null neurons (Fig. 2f).

PGC-1a serves as a master regulator of mitochondrial biogenesis in mammalian cells5,7. Because we found no signicant change in PGC-1a expression at the mRNA level in necdin-null neurons, we analysed the expression of PGC-1a at the protein level using a novel antibody raised against mouse PGC-1a (PGCAN) (Supplementary Fig. 1). In NPCs and cortical neurons, PGC-1a was detected as a major 128-kDa band by western blotting, and wild-type cortical neurons expressed higher PGC-1a levels than wild-type NPCs and necdin-null cortical neurons (Fig. 2g). Furthermore, the expression level of PGC-1a in necdin-null neurons was 55% of the wild-type control level (Fig. 2h,i). We then analysed the expression of the PGC-1a

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protein in various tissues at embryonic day 14.5 (E14.5) by western blotting (Fig. 2j). PGC-1a was clearly detected in the brain, slightly in the skeletal muscle (gastrocnemius) and hardly

detectable in the heart and liver. ATP levels in the brain and muscle, where necdin was highly expressed, were signicantly lower in necdin-null mice than in wild-type mice at E14.5

Log10 (P-value)

WT KO

1 2 3 1 2 3

14 8

Timm9

Timm5 0

Cyc1

Atp5c1

MitochondrionOrganelleIntracellularRibosomeTranslationRNA bindingCytoplasmBiosynthetic process Protein metabolic process CellNucleolusMetabolic process NucleusNucleic acid binding Primary metabolic process Protein transport Mitochondrion organization Cell cycleElectron carrier activity

Ndufs3

Atp5 d

Atp5f1

Tomm40

Tomm20

Cellular component Biological process Molecular function

WT KO

1.5

Relative mRNA level

***

*** *** ***

1.0

0.5

0 Tomm20

Tomm22

Tomm40

Timm9

Timm50

Ndufs3

Cyc1

Atp5c1

Atp5d

Atp5f1

Nrf1

Gabpa

Tfam

Ppargc1

Tomm22

1.2

0.2

***

WT KO

Relative mtDNA level

1.0

0.8

0.4

0.6

ATP5A

(CV)

MTCO1

(CIV)

SDHB

(CII)

WT KO

kDa 55

***

CIV

***

1.2

***

CII

***

CIII

UQCRC2

(CIII)

1 2 3 4 5 6 7 8

1.0

Relative level

0.8

WT KO

100

***

0.6

0.4

0.2

MT Green+ cells (%)

NDUFB8

(CI)

Necdin

-Tub

0 WT KO

Figure 1 | Necdin promotes the expression of mitochondria-related genes in primary cortical neurons. (a) Gene expression proling of primary cortical neurons prepared from wild-type and necdin-null mice at E14.5 was performed using DNA microarrays. Enriched gene ontology terms of genes whose expression decreased (420% at Po0.05) in necdin-null cortical neurons. P value cutoff (yellow line), 1.3 log10(0.05). (b) Clustered mitochondrion-

related genes whose expression changed signicantly (Po0.05) between wild-type (WT) and necdin-null (knockout; KO) neurons (yellow, up; blue, down; n 3). Full data are in Supplementary Table 1. (c) Expression levels of mitochondria-related genes and mitochondrial biogenesis-regulatory genes in cortical

neurons were determined by qRTPCR (n 36). (d) D-loop DNA (mtDNA) levels were measured by qRTPCR and normalized to nuclear gene Rplp0 levels

(n 4). (e) MitoTracker Green FM (MT Green) uorescence levels were quantied by uorescence-activated cell sorting analysis (n 4). Mean

uorescence intensity: 367 (WT); 268 (KO). (f,g) Expression of oxidative phosphorylation complexes IV subunits was analysed by immunoblotting using antibodies against the enzyme subunits indicated (f), and these bands were quantied by densitometry (n 4) (g). Data represent meanss.e.m.;

*Po0.05, **Po0.01, ***Po0.005, NS, not signicant at PZ0.05; Students t-test.

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a b c d

WT KO

Relative complex I activity

1.4 NS

1.2

0.2

WT KO

1.2

***

1.0

Relative level

1.0

1 2 3 4 5 6 7 8

0.8

0.4

0.6

0.8

0.4

0.6

0.2

0 MTT LDH

0 WT KO

NPC Neuron

WT KO

kDa

***

WT KO

ATP (nmol per 106cells)

***

WT KO

PGC-1 128

CMXRos+cells (%)

1 2 3 4 5 6

PGC-1

Necdin

-Tub

Necdin 43

Actin 42

kDa

128 43 53

Nestin

320

MAP2

280

0 Neuron NPC

WT KO

1.2

WT KO

Relative PGC-1level

ATP (nmol per mg protein)

***

WT KO

1.0

Brain

Muscle

Heart

Liver

Brain

Muscle

Heart

Liver

0.8

0.6

kDa

128

***

0.4

PGC-1

Necdin

0.2

-Tub

0 WT KO

Brain

Muscle Heart Liver

WT KO

E14.5

3 mo

17 mo

E14.5

3 mo

17 mo

***

ATP (nmol per mg protein)

2.5

1.5

0.25

0.15

kDa

2.0

0.2

128

PGC-1

Necdin

MTCO1 53

1.0

0.1

0.5

0.05

-Tub

0 E14.5

0 17 mo

Figure 2 | Necdin deciency reduces neuronal mitochondrial function and PGC-1a protein expression. (a) MTT-formazan deposits in primary cortical neurons from wild-type (WT) and necdin-null (knockout; KO) mice were observed by differential interference contrast microscopy after incubation with

MTT for 90 min. Scale bar, 50 mm. (b) MTT-formazan levels in primary neurons and released LDH levels were measured after incubation with MTT for 4 h (WT, n 5; KO, n 7). (c,d) Complex I (CI, arrowhead) in neuronal extracts of WT and KO mice were immunocaptured for NADH oxidizing activity (c).

The product signals were quantied by densitometry (d) (n 4). (e) ATP levels in neurons and NPCs were measured by chemiluminescence assay (n 4).

(f) CMXRos uorescence levels were quantied by uorescence-activated cell sorting analysis (n 3). Mean uorescence intensity: 116 (WT); 96 (KO).

(g) Expression of PGC-1a, necdin, nestin, MAP2 and actin in NPCs and neurons prepared from E14.5 mouse cortex was analysed by western blotting. (h,i) PGC-1a expression in cortical neurons was analysed by immunoblotting (h) and quantied by densitometry (i) (n 3). (j) PGC-1a and necdin

expression levels in the brain, gastrocnemius muscle, heart and liver prepared from WT and KO mice at E14.5 were analysed by western blotting.(k) ATP levels in the tissues indicated were measured by chemiluminescence assay (n 4). (l) Expression of PGC-1a, MTCO1 and necdin in the brain of

WT and KO mice at different ages was analysed by western blotting. (m) ATP levels in the brain at indicated ages were measured by chemiluminescence assay (n 5). mo, months old. Data represent meanss.e.m.; *Po0.05, **Po0.01, ***Po0.005, NS, not signicant at PZ0.05; Students t-test.

(Fig. 2k). The brain levels of PGC-1a were the highest at E14.5 and postnatal day 0 (P0), and reduced markedly at adult stages (Fig. 2l). Expression levels of MTCO1 and necdin were the highest at E14.5 and decreased during postnatal development. Necdin-null mice had lower levels of PGC-1a and MTCO1 than

wild-type mice throughout brain development. Interestingly, ATP levels in the brain also decreased sharply during development (o10% and o1% of the E14.5 level at P0 and 17 months, respectively) and were signicantly reduced in the brain of necdin-decient mice (Fig. 2m). We further examined the effect

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of necdin on mitochondrial degradation in cortical neurons using carbonyl cyanide m-chlorophenyl hydrazone, a mitochondrial uncoupler, as described previously19. There was no difference in the expression levels of the autophagy marker LC3-II between wild-type and necdin-null neurons treated with carbonyl cyanide m-chlorophenyl hydrazone (Supplementary Fig. 2), suggesting that necdin fails to affect mitochondrial degradation.

Necdin and PGC-1a are colocalized in neuronal nucleus. We next investigated the distribution patterns of necdin and PGC-1a in the neocortex by immunohistochemistry. In E14.5 mouse forebrain, virtually all cortical neurons expressed both PGC-1a and necdin (Fig. 3a). Most PGC-1a-expressing cells overlapped with necdin-expressing cells in the cortical plate where differentiated neurons are present. PGC-1a and necdin were colocalized in the nucleus of primary cortical neurons as analysed by confocal laser-scanning microscopy (Fig. 3b). Furthermore, uorescence microphotometry revealed that PGC-1a and

MTCO1 immunoreactivities were signicantly reduced in the neocortex of necdin-null mice (Fig. 3ce). These reductions were observed in the cortical plate but not in the ventricular/ subventricular zone, where undifferentiated neural precursors are present. Western blot analysis revealed that expression of PGC-1a and MTCO1 decreased by 46% and 77%, respectively, in necdin-null forebrain extracts (Fig. 3f,g). Tissue ATP levels were markedly reduced in the dorsal cortical area, which contains the cortical plate, of necdin-null mice but not in the ventral area containing undifferentiated cell populations (Fig. 3h). These data suggest that necdin upregulates the protein levels of PGC-1a and

MTCO1 in the brain in vivo.

Necdin binds and stabilizes PGC-1a. We next examined the interaction between necdin and PGC-1a by co-immunoprecipitation assay. Endogenous PGC-1a was coprecipitated with necdin in forebrain extracts prepared from wild-type mice, but not from necdin-null mice (Fig. 4a). Co-immunoprecipitation assay using transfected HEK293A cells revealed that PGC-1a was coprecipitated with necdin, which was conversely coprecipitated with PGC-1a (Fig. 4b). Remarkably, PGC-1a expression levels in transfected HEK293A cells were markedly increased by coexpression of necdin, suggesting that the PGC-1a protein expressed in

HEK293A cells is strongly stabilized in the presence of necdin. Necdin bound to the N-terminal region of PGC-1a in immuno-precipitation assay and in vitro pull-down assays (Fig. 4ce). We also analysed the subcellular localization of PGC-1a in transfected

HEK293A cells by immunocytochemistry (Supplementary Fig. 3). Necdin was colocalized with PGC-1a in the nucleus of co-transfected HEK293A cells, and coexpressed necdin signicantly increased nuclear PGC-1a levels. We then examined whether forced expression of necdin and PGC-1a increases mitochondrial biogenesis in HEK293A cells (Fig. 4f). Necdin failed to increase the expression of MTCO1 but promoted PGC-1a-mediated MTCO1 expression (untransfected control, 1.00.2; necdin, 0.90.0; PGC-1a, 2.50.5; necdin PGC-1a, 5.80.7; control versus

PGC-1a, Po0.05; PGC-1a versus necdin PGC-1a, Po0.01, by

analysis of variance with TukeyKramer post hoc test, n 3 per

each group).

We also examined whether necdin affects the stabilization of PGC-1b, another PGC family member expressed in mammalian cortical neurons20,21, using HEK293A cells expressing necdin and Myc-tagged PGC-1b or Myc-tagged PGC-1a (positive control;

Supplementary Fig. 4). PGC-1b, like PGC-1a, was stabilized by necdin, which promoted PGC-1b-mediated MTCO1 expression, suggesting that necdin requires these PGC-1 family proteins for promoting mitochondrial biogenesis.

Necdin inhibits ubiquitin-dependent degradation of PGC-1a. To clarify whether necdin inhibits proteolytic degradation of PGC-1a by the ubiquitin-proteasome pathway, we examined the effects of the protein synthesis inhibitor cycloheximide (CHX) and the proteasome inhibitor MG132 on PGC-1a expression levels in transfected HEK293A cells. Necdin markedly increased the PGC-1a level irrespective of the presence or absence of CHX (Fig. 4g) or MG132 (Fig. 4h), indicating that necdin strongly inhibits the degradation of PGC-1a in the proteasome. We then examined the effect of necdin on ubiquitin-dependent degradation of PGC-1a using Rnf34, a PGC-1a E3 ubiquitin ligase22.

Rnf34 reduced the PGC-1a level, and necdin completely inhibited the reduction (Fig. 4i). In addition, necdin strongly suppressed Rnf34-mediated ubiquitination of PGC-1a (Fig. 4j). Necdin also protected PGC-1a against ubiquitination mediated by Fbxw7, another PGC-1a E3 ubiquitin ligase23 (Fig. 4k). These data indicate that necdin stabilizes PGC-1a by inhibiting its degradation in the ubiquitin-proteasomal system.

Necdin prevents oligomycin-induced neurodegeneration. To examine whether necdin promotes mitochondrial biogenesis and function, we transferred the mouse necdin gene into primary cortical neurons using lentivirus vectors (LVs). LV-mediated overexpression of necdin increased the PGC-1a levels by 49% and 91% in wild-type and necdin-null neurons, respectively, as compared with the Emerald Green Fluorescent Protein (EmGFP) control levels (Fig. 5a,b). Similarly, necdin overexpression increased the MTCO1 levels 2.1- and 2.7-fold in wild-type and necdin-null neurons, respectively (Fig. 5c). We also examined the effects of necdin overexpression on mitochondrial activities in primary cortical neurons. LV-mediated overexpression of necdin increased MTT levels by 43 and 73% in wild-type and necdin-null neurons, respectively (Fig. 5d). Similarly, necdin overexpression increased the ATP levels by 55% and 63% in wild-type and necdin-null neurons, respectively (Fig. 5e). In necdin-null neurons, necdin increased the MTT and ATP levels to those similar to wild-type control levels.

We then examined whether necdin-null cortical neurons are susceptible to oligomycin, a mitochondrial ATP synthase inhibitor. Oligomycin signicantly increased apoptosis of necdin-null neurons during the 424 h period (Fig. 5f), suggesting that endogenous necdin suppresses oligomycin-induced apoptosis of cortical neurons. In the LDH-based cytotoxicity assay, oligomycin increased the LDH levels by B50% in wild-type neurons and2.3-fold in necdin-null neurons under LV-EmGFP-infected conditions (Fig. 5g), indicating that necdin-null neurons are highly susceptible to oligomycin. Remarkably, LV-mediated overexpression of necdin completely protected necdin-null neurons against oligomycin-induced damage. These results indicate that necdin promotes mitochondrial function to prevent oligomycin-induced degeneration of cortical neurons.

Necdin prevents neurodegeneration in experimental PD models. The mitochondrial complex I inhibitor MPP (1-methyl-4-phenylpyridine) and its precursor MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) selectively damage dopaminergic neurons and are commonly used for experimental PD models18. We rst examined whether necdin prevents MPP -induced degeneration of SH-SY5Y cells, a human neuroblastoma cell line susceptible to MPP . LV-mediated overexpression of necdin increased the expression of PGC-1a and MTCO1 in SH-SY5Y cells as analysed by immunocytochemistry and western blotting (Fig. 6a,b). Necdin markedly increased the expression levels of PGC-1a 2.3- and 18.4-fold (compared with EmGFP controls) and those of MTCO1 9.3- and 8.6-fold (compared with EmGFP

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DNA PGC-1 Necdin Merge

PGC-1 (P)

LV CX

Necdin (N)

Merge (P+N)

Merge (P+N+D)

Merge (P+D)

Merge (N+D)

DNA (D)

DNA

DNA Sox2 III-Tub MAP2 Necdin

PGC-1 MTCO1

CPVZ+SVZ

Dorsal Ventra l

PGC-1

WT KO

MTCO1

WT KO

1.2 NS

0 CP VZ+SVZ

1.2 NS

0 CP VZ+SVZ

CPVZ+SVZ

***

PGC-1intensity

MTCO1 intensity

1.0

0.8

0.6

CPVZ+SVZ

0.8

0.6

0.4

0.2

1 2 3 4 5 6 7 8

WT KO

1.2 ***

0 PGC-1 MTCO1

kDa

128

***

1.0

120

Relative level

140

ATP (nmol per mg protein)

0 CX

(dorsal)

PGC-1

Necdin

MTCO1 42

100

0.8

0.6

0.4

0.2

-Tub

(ventral)

Figure 3 | Necdin and PGC-1a are colocalized in the nucleus of cortical neurons. (a) Forebrain sections were prepared from E14.5 mice and double-immunostained for PGC-1a and necdin. Nuclear DNA was counterstained with Hoechst 33342. Boxed areas in the upper and lower panels are magnied in the lower panels and insets, respectively. Scale bars, 500 mm (upper), 100 mm (lower) and 10 mm (insets). (b) Primary neurons were triply stained for

PGC-1a, necdin and DNA, and observed by confocal laser-scanning microscopy. Confocal images with Z-stacks in accessory panels were merged (right). Scale bars, 10 mm. (c) Sox2, bIII-tubulin (bIII-Tub), MAP2, necdin, PGC-1a and MTCO1 in E14.5 mouse cortical region were analysed by uorescence immunohistochemistry. Scale bars; 500 mm (rst) and 50 mm (second). (d,e) Fluorescence intensities of PGC-1a (d) and MTCO1 (e) in the CP and

VZ SVZ areas of wild-type (WT) and necdin-null (KO) E14.5 mice were quantied by uorescence microphotometry (PGC-1a, n 4; MTCO1, n 5;

right). Scale bars, 50 mm. (f,g) PGC-1a and MTCO1 in E14.5 mouse cortex extracts were analysed by immunoblotting (f) and quantied by densitometry (g) (n 4). (h) The cortex of E14.5 mice was manually dissected into the ventral and dorsal parts, and the ATP levels were measured (n 3). Data

represent meanss.e.m.; **Po0.01, ***Po0.005, NS, not signicant at PZ0.05; Students t-test. CP, cortical plate; CX, cortex; GE, ganglionic eminence; KO, knockout; LV, lateral ventricle; VZ, ventricular zone; VZ SVZ, ventricular and subventricular zones.

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b c

PGC-1

IP: Necdin

IB: PGC-1

IB: Necdin

IB: PGC1-

Necdin

+ +

Lysate

Preimmune IgG

Necdin IgG

kDa

Necdin binding

1 797

180 403 677 709

200

130

TR RR

In vivo

In vitro

IP: PGC-1

IB: Necdin

KO WT KO WT KO

PGC-1 128

43 NT

201 400

401 550

551 797

Necdin 43

PCNA 36

e f g

Necdin +

+ + + 6Myc

TR +

IM + CT +

1% input

PGC-1

MTCO1

Necdin

PGC-1

MBP+

Necdin

+ +

kDa

6Myc+

MBP

PGC-1

Necdin CHX

+ +

kDa

His-Necdin

CBB

+ + kDa

kDa

PGC-1

77 69 60

58 49

IP: Necdin

IB: Myc

IB: Necdin

130 Necdin

130

IP: Myc

IB: Necdin 43

-Tub

43 39

j k

FLAG-Ub

IP: PGC-1

IB: V5

IB: PGC-1

IB: Necdin

PGC-1

Necdin

+ +

+ PGC-1

Necdin

FLAG-Ub

+ ++

Rnf34-V5

+ + +

kDa

100

150

Fbxw7-V5

100 IB: PGC-1

kDa

IP: PGC-1

250 IB: FLAG

IB: Necdin

150 IB: FLAG

IB: FLAG

150

+ + +

250

130

PGC-1

Necdin

-Tub

Necdin

Rnf34-V5

130 IB: V5

PGC-1

Necdin MG132

+ + +

+ +

PGC-1

Necdin

-Tub

43 39

kDa

130

130 43

250 150 100 75

250

100

IB: FLAG

Figure 4 | Necdin stabilizes PGC-1a by inhibiting its ubiquitin-proteasomal degradation. (a) Forebrain extracts from E14.5 wild-type (WT) and necdin-null (KO) mice were immunoprecipitated with anti-necdin IgG and control preimmune IgG for endogenous binding between necdin and PGC-1a.

PCNA, negative control. (b) Necdin and PGC-1a expressed in cDNA-transfected HEK293A cells were immunoprecipitated and immunoblotted. (c) Diagram of the PGC-1a deletion mutants. (d) Necdin and 6Myc-tagged PGC-1a deletion mutants in transfected HEK293A cells were immunoprecipitated and immunoblotted. (e) Bacterially synthesized MBP-fused PGC-1a deletion mutants were incubated with His-tagged necdin (His-Necdin). Bound His-Necdin was detected by immunoblotting. Recombinant proteins were stained with Coomassie Brilliant Blue (CBB). Results are summarized in c (right). (f) MTCO1 levels in HEK293A cells transfected with PGC-1a and necdin cDNAs were detected 72 h post transfection. (g,h) PGC-1a levels in transfected HEK293A were analysed 24 h post transfection after treating with CHX for 60 min (CHX ) (g) or MG132 for 3 h (MG132 ) (h) before harvest. (i) HEK293A cells

were transfected with cDNAs for PGC-1a, V5-tagged Rnf34 (Rnf34-V5) and necdin, and incubated for 24 h. PGC-1a, V5, necdin and b-tubulin were detected by immunoblotting. (j,k) Effects of necdin on PGC-1a degradation and PGC-1a ubiquitination mediated by Rnf34 (j) or Fbxw7 (k) were analysed using HEK293A cells transfected with cDNAs for PGC-1a, necdin, V5-tagged Rnf34 (Rnf34-V5), V5-tagged Fbxw7 (Fbxw7-V5) and FLAG-tagged ubiquitin (FLAG-Ub). Ubiquitination of immunoprecipitated PGC-1a was detected with anti-FLAG antibody. CT, C-terminal; IB, immunoblotted; IM, intermediate; IP, immunoprecipitated; KO, knockout; NT, N-terminal; RR, RNA recognition; TA, transcriptional activation; TR, transcriptional repression.

controls) in SH-SY5Y cells in the absence and presence of MPP , respectively. Necdin increased the MTT levels 1.3- and 2.4-fold (compared with EmGFP controls) in the absence and presence of MPP , respectively (Fig. 6c). Similarly, necdin increased the ATP levels in SH-SY5Y cells by 38% and 79% in the absence and presence of MPP , respectively (Fig. 6d). In the cytotoxicity assay, MPP signicantly increased the LDH levels in uninfected and LV-EmGFP-infected SH-SY5Y cells, whereas forced expression of necdin reduced the LDH levels near MPP -untreated levels (Fig. 6e). These results suggest that necdin improves mitochondrial function to reduce MPP -induced damage of SH-SY5Y cells.

We next investigated whether necdin prevents MPTP-induced degeneration of dopaminergic neurons in the substantia nigra

(SN) in vivo using necdin-null mice in the C57BL/6J background, which is susceptible to MPTP. Tyrosine hydroxylase-expressing (TH ) dopaminergic cells in the SN pars compacta (SNpc) were quantied after MPTP treatment (Fig. 7a and Supplementary

Fig. 5a). There was no difference in the number of SNpc TH cells between wild-type and necdin-null mice without MPTP treatment, whereas SNpc TH cells in necdin-null mice were signicantly reduced in number when treated with MPTP (Fig. 7b,c). The numbers of TH dopaminergic neurons were reduced throughout the SNpc area of necdin-null mice. This suggests that endogenous necdin in SNpc dopaminergic neurons is neuroprotective against MPTP toxicity.

Because necdin potentially prevents neuronal apoptosis through suppressing the E2F1-Cdc2 and p53-Bax axes15,16, we

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Figure 5 | Necdin prevents oligomycin-induced neurodegeneration of primary cortical neurons. (a) Primary cortical neurons prepared from wild-type (WT) and necdin-null (knockout; KO) mice at E14.5 were infected with LV expressing EmGFP (LV-EmGFP) or necdin (LV-Ndn), and expression of PGC-1a, MTCO1 and necdin was analysed by western blotting. Control, uninfected neurons. (b,c) PGC-1a (b) and MTCO1 (c) levels were quantied by densitometry (n 4). (d,e) MTT (d) and ATP (e) levels in LV-infected cortical neurons were measured. (f) Oligomycin (OLG)-induced neuronal apoptosis

was analysed by Hoechst 33342 staining for condensed or fragmented nuclei at the times indicated (n 3). Data represent meanss.e.m.; **Po0.01;

Students t-test. (g) LV-infected cortical neurons were treated without ( ) or with ( ) OLG for 6 h, and released LDH levels were measured. Data

represent meanss.e.m. (n 34; be,g); *Po0.05, **Po0.01, NS, not signicant at PZ0.05; analysis of variance with TukeyKramer post hoc test.

OLG treatment (h)

also analysed the mRNA levels of necdin, E2F1, Cdc2 (Cdk1), p53 and Bax in the SN of wild-type and necdin-null mice treated with MPTP (Supplementary Fig. 5b,c). However, there were no signicant differences in the expression levels of these mRNAs between wild-type and necdin-null mice, suggesting that these pathways are not involved in MPTP-induced degeneration of nigral dopaminergic neurons seen in necdin-null mice.

To investigate whether necdin overexpression exerts protective effects on dopaminergic neurons in vivo, we used adeno-associated virus (AAV)-mediated gene delivery into the SN of MPTP-based PD model mice24,25 (Fig. 8a and Supplementary Fig. 6a). MPTP markedly reduced the number of TH neurons in the contralateral SNpc of mice injected with AAV expressing

GFP (AAV-GFP), whereas injection with AAV expressing human necdin gene (AAV-NDN) fully protected TH neurons in the ipsilateral SNpc against MPTP-induced degeneration (Fig. 8b,c and Supplementary Fig. 6b,c). We then analysed the expression levels of PGC-1a and MTCO1 in the AAV-infected SN by western blotting (Fig. 8d). AAV-NDN infection signicantly increased the necdin levels in the SN (relative necdin levels: MPTP-untreated, contralateral, 1.00.3, ipsilateral, 2.00.4; MPTP-treated, contralateral, 1.00.2, ipsilateral, 2.30.4, Po0.05; Students t-test, n 4 per each group). AAV-mediated

necdin overexpression increased the PGC-1a levels by 32% and 43% in the ipsilateral SN (compared with the contralateral SN levels) of untreated and MPTP-treated mice, respectively (Fig. 8e). Similarly, necdin increased the MTCO1 levels 1.6-and 2.8-fold in the ipsilateral SN of untreated and MPTP-treated mice, respectively (Fig. 8f). Furthermore, AAV-NDN-infected mice exhibited higher behavioural performance in the pole test than AAV-GFP-infected mice (Fig. 8g), indicating that necdin improves motor coordination of MPTP-treated mice. These results suggest that AAV-mediated necdin overexpression

suppresses MPTP-induced degeneration of SN neurons in vivo by promoting PGC-1a-mediated mitochondrial biogenesis.

Necdin deciency promotes neurodegeneration. We investigated the neuroprotective effect of endogenous necdin on SN dopaminergic neurons using necdin-null mice. We rst analysed the number of TH neurons in the SNpc of wild-type and necdin-null mice at their adult (17 weeks old) and late adult (60 weeks old) stages (Fig. 9a). Although there was no signicant difference in the number of SNpc TH cells between wild-type and necdin-null mice at 17 weeks of age, the number of SNpc

TH cells was signicantly reduced by 15% in necdin-null mice at 60 weeks of age. We then analysed the expression levels of TH,

PGC-1a and MTCO1 in the SN by western blotting (Fig. 9b,c). Similar to the results of TH neuron counting, the expression level of TH was decreased by 21% in the SNpc of necdin-null mice 60 weeks old (Fig. 9d). Furthermore, the expression levels of PGC-1a and MTCO1 in the SN decreased by 58% and 63%, respectively, in necdin-null mice 60 weeks old, whereas there were no differences in the SN levels of PGC-1a and MTCO1 between wild-type and necdin-null mice 17 weeks old (Fig. 9e,f). On the other hand, PGC-1a and MTCO1 levels in the cortex of necdin-null mice decreased at 17 weeks of age by 66% and 78%, respectively, and at 60 weeks of age by 37% and 67%, respectively. These results suggest that endogenous necdin prevents degeneration of nigral dopaminergic neurons by maintaining the level of mitochondrial biosynthesis.

DiscussionThe present study has shown that necdin upregulates the expression of neuronal PGC-1a at the post-translational level.

In primary cortical neurons and developing brain tissues, the

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Figure 6 | Necdin prevents MPP -induced degeneration of human SH-SY5Y neuroblastoma cells. (a) SH-SY5Y cells were infected with LV expressing EmGFP (LV-GFP) or necdin (LV-Ndn), cultured in the presence of retinoic acid for 4 days for neural differentiation and triply immunostained for PGC-1a, necdin and EmGFP. Arrowheads, LV-infected cells. Scale bar, 10 mm. (b) LV-infected SH-SY5Y cells were treated without (MPP) or with 1 mM MPP ( MPP) for 48 h. Expression of PGC-1a, MTCO1, necdin, GFP and b-tubulin (b-Tub) was analysed by western blotting. (c) LV-infected SH-SY5Y cells

were treated with MTT for 4 h, and MTT-formazan deposits were measured by spectrophotometry (n 4). (d) ATP levels in LV-infected SH-SY5Y cells

were analysed by chemiluminescence assay (n 3). (e) LDH levels released from LV-infected SH-SY5Y cells treated with 1 mM MPP for 48 h were

quantied (n 4). Data represent meanss.e.m. **Po0.01, NS, not signicant at PZ0.05; analysis of variance with TukeyKramer post hoc test.

levels of necdin parallel with those of PGC-1a and the mitochondrial DNA-encoded protein MTCO1. In addition, PGC-1a and MTCO1 levels in the cerebral cortex in vivo are much lower in necdin-null mice than in wild-type mice at adult stages. These results suggest that necdin is an intrinsic positive regulator of PGC-1a-mediated mitochondrial biogenesis. Virus vector-mediated overexpression of necdin in primary cortical neurons and nigral dopaminergic neurons in vivo upregulates the expression of PGC-1a and MTCO1, indicating that endogenous expression levels of those proteins are controllable by exogenous necdin. Thus, necdin is likely to act as a molecular rheostat to control neuronal mitochondrial biogenesis via PGC-1a. We speculate that necdin and PGC-1a, both of which are expressed in virtually all neurons, cooperate to maintain high mitochondrial activities required for neuronal function and survival.

We have employed the mitochondrial oxidative phosphorylation inhibitors in combination with viral vector-mediated necdin gene delivery to demonstrate the neuroprotective effects of necdin. The combination of primary cortical neurons and the ATP synthase inhibitor oligomycin showed that necdin-null neurons are highly susceptible to oligomycin-induced apoptosis, which is fully prevented by overexpression of necdin. To investigate the effects of necdin on neurodegeneration in vivo,

we have selected nigral dopaminergic neurons, which are highly susceptible to the mitochondrial complex I inhibitor MPTP, a lipophilic protoxin metabolized in glial cells to MPP , which is concentrated in dopaminergic neurons via the dopamine transporter18. Before the analysis of in vivo PD model, we conrmed the toxic effect of the active MPTP metabolite MPP on SH-SY5Y neuroblastoma cells, a human catecholaminergic cell line that exhibits apoptotic changes in response to MPP (refs 26,27). Necdin-mediated protection of SH-SY5Y cells against MPP toxicity led to further demonstrate the neuroprotective effect of necdin on nigral dopaminergic neurons in vivo against MPTP-induced degeneration. These ndings implicate that mitochondrial dysfunction-induced neurodegeneration is preventable by enhancing neuronal mitochondrial biogenesis through overexpression of necdin.

The present study claried that necdin strongly stabilizes PGC-1a by inhibiting its degradation in the ubiquitinproteasome system. Necdin interacted with PGC-1a via the N-terminal region that contains the PEST (proline, glutamic acid, serine, threonine) sequence, a domain critical for ubiquitinproteasomal degradation of PGC-1a in the nucleus28,29. Rnf34 (ref. 22), Fbxw7 (ref. 23) and RNF2 (ref. 30) act as PGC-1a E3 ubiquitin ligases. Necdin efciently suppressed Rnf34- and

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Figure 7 | Necdin deciency enhances MPTP-induced degeneration of dopaminergic neurons in vivo. (a) TH-expressing (TH ) neurons in the SN were analysed by immunohistochemistry (magnied in lower panels). Wild-type (WT) and necdin-null (knockout; KO) 13-week-old mice were injected intraperitoneally without (MPTP) or with MPTP ( MPTP) for 5 consecutive days and killed 21 days after injection. Scale bars, 500 mm (upper) and

50 mm (lower). (b,c) SN sections were immunostained for TH, and the number of TH neurons in each section of the SNpc (b) and the total number (c) were presented (15 sections per mouse; n 45). Data represent meanss.e.m.; **Po0.01, NS, not signicant at PZ0.05; analysis of variance

with TukeyKramer post hoc test.

Fbxw7-mediated ubiquitination of PGC-1a. We speculate that necdin forms a stable nuclear complex with PGC-1a in neurons and protects PGC-1a from ubiquitination mediated by these E3 ubiquitin ligases. The N-terminal amino-acid sequences of PGC-1a and PGC-1b are well conserved5, and these PGC-1 family proteins increase mitochondrial density in primary cortical neurons21. Thus, we infer that necdin protects PGC-1a and PGC-1b against proteasomal degradation to promote their effects on mitochondrial biogenesis in mammalian neurons.

A genome-wide expression study revealed that PGC-1a-regulated genes controlling cellular bioenergetics are under-expressed in SN neurons affected by PD31. PGC-1a-null mutant mice exhibit striatal lesions32, and their SN neurons are highly susceptible to MPTP33. Moreover, PGC-1a overexpression protects SN neurons against neurodegenerative insults34,35. These ndings imply that PGC-1a contributes to the resistance of SN dopaminergic neurons against PD-associated neurodegeneration. In contrast to the benecial effects of PGC-1a, sustained overexpression of PGC-1a in the SN induces degeneration of dopaminergic neurons36,37. These inconsistent results suggest that control of exogenous PGC-1a expression levels is crucial for the neuroprotective effects. In contrast, AAV-mediated overexpression of necdin increases

endogenous PGC-1a protein levels by inhibiting its ubiquitinproteasomal degradation at the post-translational level. Thus, we speculate that the necdin gene delivery increases the PGC-1a levels in dopaminergic neurons within a physiologically tolerable extent that is sufcient for effective neuroprotection.

Recombinant AAV displays efcient transduction of SN dopaminergic neurons in vivo and has been often used for analysing the pathogenic mechanism of PD and developing therapeutic strategies. For example, AAV-mediated overexpression of a-synuclein, a major structural component of Lewy bodies seen in neurons undergoing degeneration in PD, induces PD-like neurodegeneration38. AAV-mediated overexpression of Parkin, a ubiquitin E3 ligase whose mutations cause recessively inherited early-onset PD39, ameliorates a-synuclein-mediated or MPTP-induced degeneration of dopaminergic neurons25,40. Moreover, AAV-mediated delivery of PARIS (also known as ZNF746), a substrate of Parkin, induces selective dopaminergic neuron loss, which is prevented by AAV-mediated overexpression of Parkin34. Gene therapy for PD using AAV-mediated gene delivery has reached human clinical trials41. Thus, we propose that AAV-mediated necdin gene delivery provides a novel strategy for mitochondrial biogenesis-based neuroprotection in PD.

Human necdin gene (NDN) is located on chromosome 15q11q12, and its expression is absent in neurons affected by

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Figure 8 | Necdin prevents MPTP-induced degeneration in vivo of dopaminergic neurons in experimental PD. (a) Schedule of AAV-mediated gene transfer into SN neurons and MPTP treatment. (b) TH dopaminergic neurons were analysed by immunohistochemistry (magnied in lower panels).

AAV expressing GFP (AAV-GFP) or human necdin (AAV-NDN) was microinjected into the SN of 13-week-old mice and treated without (MPTP) or with MPTP ( MPTP). CT, contralateral SN; IP, ipsilateral SN. Scale bars, 500 mm (top panel) and 50 mm (second panel). (c) SN sections were immunostained

for TH, and TH neurons in the SNpc were counted (12 sections per mouse; n 35). (d) Expression of PGC-1a and MTCO1 in SN tissue extracts was

analysed by western blotting. (e,f) Expression levels of PGC-1a (e) and MTCO1 (f) were quantied by densitometry and normalized to b-tubulin (b-Tub) levels (n 45). Data represent meanss.e.m.; *Po0.05, **Po0.01, NS, not signicant at PZ0.05; analysis of variance with TukeyKramer post hoc test.

(g) MPTP-induced behavioural changes of AAV-infected mice were assessed by the pole test. Success rates in three consecutive trials were presented (n 911). Data represent means; *Po0.05, **Po0.01, NS, not signicant at PZ0.05; w2-test.

PraderWilli syndrome (PWS), a classic genomic imprinting-associated neurodevelopmental disorder11,12. The present study has shown that the brain levels of mitochondrial proteins and mitochondrial activities are signicantly reduced in necdin-null neurons. These ndings raise the possibility that necdin-null

neurons affected in PWS have low mitochondrial activities and reduced ATP levels during neuronal development. Motor proteins such as myosin, kinesin and dynein families are powered by ATP hydrolysis and play key roles in neuronal morphogenesis and network formation during brain

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Figure 9 | Necdin deciency promotes degeneration of dopaminergic neurons in the SN of late adult mice. (a) TH neurons in the SN of wild-type (WT) and necdin-null (knockout; KO) mice at 17 and 60 weeks of age (wks) were analysed by immunohistochemistry. SN sections were immunostained for

TH, and the total number of TH neurons were presented (15 sections per mouse; n 36). (b,c) Expression of TH, PGC-1a and MTCO1 in SN tissue

extracts was analysed by western blotting. Durations of chemiluminescence detection were adjusted for quantication of each protein band in twoage groups, and representative blot images of mice at 17 (b) and 60 weeks (c) are presented separately. (df) Expression levels of TH (d), PGC-1a (e) and

MTCO1 (f) were quantied by densitometry of western blot signals and normalized to b-tubulin (b-Tub) levels (n 4 each). Values relative to the WT-SN

level ( 1) in each age group are shown. Data represent meanss.e.m.; *Po0.05, ***Po0.005; NS, not signicant at P40.05; Students t-test.

development42. Mice carrying mutated paternal Ndn exhibit a variety of neurodevelopmental abnormalities such as reduced neuron number, impaired neuronal migration and abnormal axon extension in the embryonic brain4349. Although there is limited information about the neuropathological abnormalities in the PWS-affected brain, earlier studies using magnetic resonance imaging have revealed multiple morphological abnormalities such as ventriculomegaly, reduced sizes of specic areas and differences in grey and white matter volumes in the brain of patients with PWS5052. Thus, we speculate that reduced mitochondrial activities in necdin-null neurons contribute, at least in part, to these neurodevelopmental abnormalities seen in PWS.

Our ndings suggest that necdin and PGC-1a cooperate to promote mitochondrial biogenesis in various types of neurons and prevent mitochondria-associated neurodegeneration. Necdin-null mice exhibit low expression of the PGC-1a protein in the brain, where the number of nigral dopaminergic neurons is signicantly reduced in late adulthood. Necdin is abundantly expressed in spinal cord motor neurons10, and their mitochondrial dysfunction causes ALS53. PGC-1a is also suggested to contribute to the pathogeneses of ALS54. Intriguingly, necdin expression in spinal cord motor neurons of SOD1 G93A mutant mice, an SOD1 gene mutant ALS model, increases signicantly at the early presymptomatic stage and decreases at the late symptomatic stage55. We speculate that necdin expression is upregulated for neuroprotection at the early stage of neurodegeneration but declines at the advanced stage. A multi-cohort transcriptional meta-analysis has revealed that necdin expression is specically diminished in major human neurodegenerative diseases56. These ndings raise the possibility that necdin is involved in neuronal resistance or resilience against neurodegenerative insults. Thus, gene therapy using virus vector-

mediated necdin gene delivery into specic neurons at risk will be a promising avenue for prevention or therapeutic intervention of neurodegenerative diseases. The present ndings also warrant further studies on the neuron-specic mechanism of mitochondrial biogenesis and its association with neurodegenerative diseases.

Methods

Ndn knockout mice. Ndn knockout mice (Ndntm/Ky) were generated and maintained as described46. Heterozygous male mice (Ndn m/ p) (425 generations on the ICR background and 20 generations on the C57BL/6J background) were crossed with wild-type (Ndn m/ p) female mice to obtain

Ndn m/ p and Ndn knockout (Ndn m/-p) littermates. Genotypes of all mice were analysed by PCR for mutated Ndn locus. C57BL/6J mice were used for demonstrating MPTP-induced neurodegeneration and phenotypes of Ndn knockout mice (13, 17 and 60 weeks of age). The study was approved by the Animal Experiment Committee (Approval No. 24-04-0) and Recombinant DNA Committee (Approval No. 3642) of Institute for Protein Research, Osaka University, and were performed in accordance with national, institutional and the ARRIVE guidelines.

Cell cultures. Primary cortical neurons were prepared from the forebrain of ICR mice (Japan SLC) at E14.5 as described16. The cortex was dissected and incubated in 0.5 ml of Ca2 /Mg2-free Hanks balanced salt solution with 0.05% trypsin for 5 min at 37 C. Tissues were dissociated with 10% fetal bovine serum (FBS) in Dulbeccos modied eagle medium (DMEM) and centrifuged at 200g for 3 min. Pellets were resuspended in Neurobasal medium (Life Technologies) supplemented with 2 mM L-glutamine, kanamycin/penicillin and B-27 supplement (1:50 dilution, Life Technologies), plated at a density of B1 105 cells per cm2 in culture dishes,

and incubated for 4 days in vitro (4 DIV) before analyses. For preparation of primary NPCs, dissociated cortical cells were cultured as oating neurospheres in DMEM/F12 (Life Technologies) supplemented with B-27 (1:50 dilution),20 ng ml 1 epidermal growth factor (PeproTech) and 20 ng ml 1 basic broblast growth factor (PeproTech) for 48 h at 37 C under humidied 5% CO2 conditions. HEK293A cells (Life Technologies) and SH-SY5Y cells (gift from Dr June Biedler, Memorial Sloan-Kettering Cancer Center)26 were cultured in DMEM containing 10% FBS at 37 C under humidied 5% CO2 conditions.

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DNA microarray. Total RNA was extracted from primary cortical neurons at4 DIV, with phenol and guanidine thiocyanate mixture (TRI Reagent, Molecular Research Center). Expression proling was performed using CodeLink Mouse Whole Genome Bioarray (Applied Microarrays) according to the manufacturers protocol. Total RNA (1 mg) was labelled and used for microarray. Array slides were hybridized at 37 C for 18 h, washed, dried and scanned with a microarray scanner (GenePix 4400A, Molecular Devices). The signal intensities were quantied using CodeLink Expression Analysis Software v5.0 (Applied Microarrays). Gene ontology and clustering of microarray data were analysed using Microarray Data Analysis Tool Ver3.2 (Filgen) and Cluster and TreeView programmes57.

Quantitative reverse transcriptionPCR. Total RNA was extracted with the guanidine thiocyanate mixture, and contaminating DNA was digested with RQ1 RNase-free DNase (Promega). For qRTPCR, total RNA (2 mg) was reverse-transcribed to cDNA using Transcriptor First Strand cDNA Synthesis Kit (Roche Diagnostics). cDNA (10 ng) was used as templates for PCR mixture (LightCycler FastStart DNA MasterPLUS SYBR Green I, Roche Diagnostics) in a real-time PCR system (LightCycler 1.5, Roche Diagnostics). Primers for qRTPCR are described in Supplementary Table 2.

Mitochondrial DNA/mass measurements. Total genomic DNA was extracted from cortical neurons at 4 DIV, and mitochondrial DNA content was quantied by real-time PCR with LightCycler 1.5 using D-loop primers (forward, 50- GGTTCTT

ACTTCAGGGCCATCA-30; reverse, 50-GATTAGACCCGTTACCATCGAGAT-30). Ribosomal protein P0 gene Rplp0 (R36B4) primers (forward, 50-GTGGGTAAT CTCACTGGAAAG-30; reverse, 50-TTGTCCCAGACTAGCTATGG-30) were used as a nuclear genome control for normalizing the D-loop level. For determination of mitochondrial mass in neurons, cortical neurons at 4 DIV were incubated with 100 nM MitoTracker Green FM (Life Technologies) at 37 C for 30 min, and analysed by ow cytometry with FACSCalibur (BD Biosciences).

Western blot analysis. Cells or tissues were homogenized with lysis buffer containing 10 mM Tris-HCl, pH 8.0, 150 mM NaCl, 1 mM EDTA, 1% IGEPAL CA-630 (MP Biomedicals), 10% glycerol and protease inhibitor cocktails (Complete, Roche Diagnostics). The protein concentration was determined by the Bradford method (Bio-Rad). Proteins (210 mg per lane) were separated by 10%

SDSPAGE and electroblotted to polyvinylidene diuoride membranes (Immobilon, Merck Millipore). The membranes were incubated with primary antibodies against the mitochondrial complex IV subunits NDUFB8, SDHB, UQCRC2, MTCO1 and ATP5A (total OXPHOS rodent WB antibody cocktail of antibodies, ab110413, 1:500, Abcam), necdin (NC243, 1:3,000) (ref. 58),b-tubulin (TUB2.1, 1:1,000, Sigma-Aldrich), PGC-1a (1:500, PGCAN), g-tubulin (GTU-88, 1:1,000, Sigma-Aldrich), nestin (ST-1, 1:500) (ref. 59), MAP2 (1:5,000, gift from Dr Michio Niinobe, Osaka University), actin (JLA20, 1:1,000, Sigma-Aldrich), MTCO1 (ab14705, 1:200, Abcam), LC3 (8E10, 1:1,000, MBL), PCNA (PC10, 1:1,000, Santa Cruz Biotechnologies), Myc (9E10, 1:10), V5 (R960-25, 1:5,000, Life Technologies), FLAG (M2, 1:500, Sigma-Aldrich) and GFP (JFP-J1, 1:200, Riken Cell Bank). Anti-PGC-1a antibody (PGCAN) was generated in rabbit against a puried recombinant protein of maltose-binding protein (MBP) fused to N-terminal PGC-1a (amino acids 1120). Characterization of PGCAN is depicted in Supplementary Fig. 1. After incubation with peroxidase-conjugated IgGs (Cappel), proteins were detected by chemiluminescence method (Chemiluminescence Reagent Plus, PerkinElmer). Signal intensities were quantied with ImageJ 1.44 software. Images have been cropped for presentation. Full-size images are presented in Supplementary Fig. 7.

MTT assay. Mitochondrial MTT (3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide) metabolic activity in primary cortical neurons and differentiated SH-SY5Y cells was analysed by Cell Proliferation Kit I (MTT, Roche Diagnostics) according to the manufacturers protocol. For detectionof intracellular MTT-formazan deposits, primary neurons were plated on a 35-mm imaging dish (m-Dish35mm, high, ibidi) precoated with poly-L-ornithine (Sigma-Aldrich), and treated with 1.1 mM MTT. Images were observed with a differential interference contrast microscope (IX70, Olympus). For quantication of MTT metabolic activity, cells were plated on 96-well dishes (BioLite 96-well Multidish, Thermo Scientic) at 5 104 cells, and treated with 1.1 mM MTT for

4 h and lysed for 12 h in the lysis buffer containing 10% SDS. MTT-formazan deposits were solubilized, measured by spectrophotometry as optical density (OD) at wavelength 550/690 nm (OD 550/690).

LDH assay. LDH levels released from damaged cells were measured using Cytotoxicity Detection kit (LDH, Roche Diagnostics) according to the manufacturers protocol. Culture medium of differentiated neurons was centrifuged at 200g for 5 min. The supernatant was collected, incubated with the LDH reaction mixture at room temperature for 30 min, and measured by spectrophotometry at a dual wavelength of 492/690 nm.

Complex I activity assay. Complex I activity was measured using an assaykit based on the immunocapture with immobilized anti-Complex I antibodies combined with in-gel activity measurement (dipstick assay, ab109720, Abcam). Cell lysates (30 mg protein) were used for the assay according to the manufacturers protocol. Complex I activity was measured by incubating with NADH and nitrotetrazolium blue. Signals of resulting blue-purple precipitates on the dipstick were analysed by densitometry and quantied using ImageJ 1.44 software.

ATP assay. ATP levels in cell lysates were analysed by luciferase chemiluminescence-based assays (CellTiter-Glo Luminescent Cell Viability Assay kit, Promega) according to the manufacturers protocols. Briey, cell lysates were mixed with CellTiter-Glo Reagent for 2 min by shaking vigorously and settled for 10 min. Chemiluminescence in reaction mixtures was measured with a luminometer (Lumat LB9501, Berthold).

Mitochondrial membrane potential assay. For determination of mitochondrial membrane potential in neurons, cortical neurons at 4 DIV were incubated with 100 nM chloromethyl-X-rosamine (MitoTracker Red, Life Technologies) at 37 C for 30 min, and analysed by ow cytometry with FACSCalibur (BD Biosciences).

Immunohistochemistry. Brain tissues of mouse embryos at E14.5 were xed with 4% paraformaldehyde in phosphate buffer (pH 7.4) overnight and cryoprotected by immersion in 20% sucrose overnight. Frozen 12-mm-thick tissue sections were incubated with primary antibodies at 4 C overnight and uorescence dye-conjugated secondary antibodies at room temperature for 60 min. The primary antibodies used are rabbit polyclonal antibody against PGC-1a (PGCAN, 1:500),

MAP2 (1:1,000), necdin (NC243, 1:500), guinea pig polyclonal antibody against necdin (GN1, 1:500) (ref. 46) and mouse monoclonal antibodies against Sox2 (245610, 1:300, R and D Systems), bIII-tubulin (1:1,000, Promega) and MTCO1 (ab14705, 1:1,000). The secondary antibodies used are Alexa488-conjugated anti-rabbit IgG (1:1,000, Molecular Probes), Alexa555-conjugated anti-guinea pig IgG (1:1,000, Molecular Probes) and Alexa488-conjugated anti-mouse IgG (1:1,000, Molecular Probes). Nuclear DNA was counterstained with 3.3 mM

Hoechst 33342 (Sigma-Aldrich). Immunouorescence images were observed with a uorescence microscope (BX51, Olympus), taken by CCD (charge-coupled device) camera system (DP73, Olympus), and processed using Adobe PhotoShop CS4 software. For immunostaining of adult mouse brain sections, free-oating sections were incubated with a rabbit polyclonal antibody to TH (1:5,000, Calbiochem) in PBS containing 0.05% Triton X-100 (PBST) and 2% blocking reagent (Block Ace, Sumitomo Dainippon Pharma) at 4 C for 48 h, with biotinylated anti-rabbit IgG secondary antibody (1:500, Vector Laboratories) in PBST containing 2%

Block Ace for 2 h, and with avidinbiotinperoxidase complex (ABC Elite, Vector Laboratories) for 1 h. After reaction, sections were treated with 0.04% diaminobenzidine in 50 mM Tris-HCl (pH 7.6) and 0.02% hydrogen peroxide with0.04% nickel chloride. Images were observed with a light microscope (BZ-9000, Keyence) and processed using Adobe PhotoShop CS4 software.

Immunocytochemistry. Cells were xed with 10% formalin solution at room temperature for 20 min and permeabilized with methanol at room temperature for 20 min. Fixed cells were incubated with primary antibodies at 4 C overnight, and with secondary antibodies at room temperature for 90 min. Primary antibodies used for immunocytochemistry are rabbit polyclonal antibody against PGC-1a (PGCAN, 1:500), guinea pig polyclonal antibody against necdin (GN1, 1:500), mouse monoclonal antibody against Myc (9E10, 1:10) and rat monoclonal GFP (JFP-J1, 1:200). The secondary antibodies Alexa488-conjugated anti-rabbit, anti-mouse and anti-rat IgGs (1:1,000, Molecular Probes), and Alexa555- and Alexa633-conjugated anti-guinea pig IgG (1:1,000, Molecular Probes) were used. Nuclear DNA was counterstained with 3.3 mM Hoechst 33342 (Sigma-Aldrich).

Images were observed with a uorescence microscope (BX51, Olympus) and confocal laser-scanning microscope (FV1000 BX61, Olympus), taken by CCD camera system (DP73, Olympus), and processed using Adobe PhotoShop CS4 software.

Fluorescence microphotometry. Cortical sections or transfected cells were immunostained for PGC-1a and MTCO1. Signal intensities were quantied by uorescence microphotometry as described17. Fluorescence images were captured with a CCD image sensor (CoolSNAP monochrome, Nippon Roper) as 12-bit digital monochrome images. Fluorescence intensities of PGC-1a and MTCO1 were analysed using uorescence image analysis software (Lumina Vision, Mitani).

Co-immunoprecipitation assays. For detection of endogenous binding between necdin and PGC-1a, lysates of mouse embryonic forebrain (1 mg) were incubated with guinea pig anti-necdin antibody (GN1, 1:100). Bound proteins were pelleted with Protein A-Sepharose (nProtein A Sepharose 4 Fast Flow, GE Healthcare), separated by 10% SDSPAGE and detected by western blotting. For detection of binding between necdin and PGC-1a in transfected cells, HEK293A cells were transfected with combinations of expression vectors by the calcium phosphate method and collected after 24 h. Cell lysates (200 mg) were incubated with antibodies at 4 C for 2 h, pelleted with Protein A-Sepharose, separated by 10%

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SDSPAGE and detected by western blotting. PGC-1a expression vector was constructed by subcloning cDNA encoding full-length mouse PGC-1a and PGC-1b (gifts from Dr Akira Kakizuka, Kyoto University) into pcDNA3.1

and 6Myc-tagged pcDNA3.1 . cDNAs encoding PGC-1a deletion mutants of

amino acids 1200 (N-terminal), 201400 (transcriptional repression), 401550 (intermediate) and 551797 (C-terminal) were generated using synthetic oligonucleotide primers and subcloned into the expression vector.

Co-transfection assays. HEK293A cells were transfected with combinations of expression vectors by the calcium phosphate method and collected after 24 h. For CHX treatment, transfected HEK293A cells were incubated with DMEM/10% FBS containing 500 mM CHX (Sigma-Aldrich) for 60 min. HEK293A cells were transfected with combinations of cDNAs and treated with 10 mM MG132 (Peptide Institute) for 3 h before harvest. For PGC-1a ubiquitination assay, full-length cDNAs encoding the PGC-1a E3 ubiquitin ligases Rnf34 (NM_030564) and Fbxw7 (NM_080428) were cloned from E14.5 mouse forebrain cDNAs used as a PCR template, sequenced, attached with the V5-encoding sequence at the 30-end,and subcloned into pcDNA3.1 . Proteins were immunoprecipitated with

anti-PGC-1a antibody (PGCAN,1:50) and analysed by western blotting.

In vitro binding analysis. Deletion mutants of PGC-1a were subcloned into pMAL-C2 vector to make MBP fusion proteins. MBP-fused mutant proteins were afnity puried with amylose resin, and incubated with His-tagged necdin (200 ng) at 4 C for 30 min in 0.5 ml of the binding buffer containing 20 mM Tris-HCl, pH7.5, 200 mM NaCl and 1 mM EDTA as described16. After washing, bound His-tagged necdin was eluted with 20 mM maltose and detected by western blotting with anti-necdin antibody. MBP fusion proteins were detected by Coomassie Brilliant Blue staining.

Viral vectors. Recombinant LVs were produced in HEK293FT cells by transfecting SIN vector plasmids and two or three helper plasmids using calcium phosphate method as described59. Necdin and EmGFP cDNAs were subcloned into pENTR1A entry vector (Life Technologies) to construct the destination vectors CSII-EF1a-necdin-IRES-EmGFP and CSII-EF1a-IRES-EmGFP to make LV-Ndn and LV-EmGFP, respectively. EmGFP (Life Technologies) was used for an expression indicator and negative control for necdin overexpression. The viral titre was measured by serial dilution on HEK293FT cells and determined as GFP-positive cells by uorescence-activated cell sorting analysis. For AAV serotype-1 vector preparation, pAAV-MCS carrying cytomegalovirus promoter (Stratagene) carrying human necdin cDNA (NM_002487) and humanized GFP were used to make AAV-NDN and AAV-GFP, respectively, as described25. For high-titre viral stocks, AAV vectors were puried by ultracentrifugation in a density gradient with OptiPrep (Axis-Shield PoC AS), which was removed by ultraltration using Centricon Plus-20 (10,000 molecular weight cut-off, Millipore). Averaged titres of AAV-NDN and AAV-GFP were 1 1012 genomes per ml.

Oligomycin-induced neurotoxicity assay. Primary cortical neurons were cultured for 4 days and treated with 20 mg ml 1 oligomycin (Sigma-Aldrich). For quantifying apoptotic neurons, cultures were stained with 3.3 mM Hoechst 33342 (Sigma-Aldrich) for 5 min before xation, and cortical neurons carrying condensed or fragmented nuclei were counted. For LV infection, primary cortical cellswere infected with LVs at multiplicity of infection (m.o.i.) of 2, incubated in DMEM/F12-based medium containing 20 ng ml 1 epidermal growth factor and 20 ng ml 1 basic broblast growth factor for 30 min, and cultured for 4 days in

Neurobasal medium for neuronal differentiation. Mean viral infection efciency was more than 92%. For LDH release assay, neurons were treated with oligomycin for 6 h.

MPP-induced cytotoxicity assay. LV vectors were infected into undifferentiated SH-SY5Y cells (gift from Dr June Biedler, Memorial Sloan-

Kettering Cancer Center) at m.o.i. 2. Mean viral infection efciency was 88%. Infected cells were incubated in Neurobasal medium containing 10 mM retinoic acid (Sigma-Aldrich) for 4 days before analyses. Infected SH-SY5Y cells were treated with 1 mM MPP (Sigma-Aldrich) for 48 h.

MPTP-induced neurodegeneration analysis. In necdin-null mice of C57BL/6J background, 13-week-old mice were treated with MPTP-HCl (30 mg per kg body weight per day, Sigma-Aldrich) dissolved in saline for 5 consecutive days. Control mice without MPTP treatment were injected with saline. AAV vectors were stereotaxically injected into the SN of 13-week-old male C57BL/6J mice (Japan SLC) as described25. AAV-infected mice were injected intraperitoneally 42 days after AAV infection, with MPTP for 5 consecutive days. Control mice without MPTP treatment were injected with saline. MPTP-treated mice were killed 21 days after the last injection of MPTP. MPTP was handled in accordance with the guidelines60. For quantifying TH-expressing (TH ) cells, coronal 20-mm-thick brain sections were cut serially using a cryostat (CM1900, Leica Microsystems).

Sections were stained with anti-TH antibody and counterstained with Nissl.

TH- and Nissl-double-positive neurons in the SNpc were analysed by unbiased

stereological counting method25. Cells having optimally visualized nuclei and nucleoli were counted to avoid double counting. TH cells in every fourth 20-mm section were counted so that 15 sections (total 60 sections for B1.2 mm) cover the entire SNpc extent. For western blotting, brain blocks including the entire SN were cut coronally at 2-mm thickness. A ventral part of the midbrain including the SN (B1.2 mm from the ventral end) was dissected horizontally, and immediately frozen in liquid nitrogen for tissue extraction. Pole test was performed 3 days before western blot analysis according to the method described61 at 20:00 . Mice were placed on the top of a 48-cm-long 1-cm-diameter wooden rod. Mice performed three trials with 30-s intervals, and success rates to reach the oor within 80 s were measured.

Statistics. Statistical signicance was tested using an unpaired Students t-test, one-way analysis of variance followed by TukeyKramer post hoc test, or w2-test.

A signicance of Po0.05 was required for rejection of the null hypothesis.

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Acknowledgements

We are grateful to Dr J. Biedler for SH-SY5Y cells, Dr A. Kakizuka for mouse PGC-1a and PGC-1b cDNAs, Drs T. Ohkumo and H. Miyoshi (RIKEN BioResource Center) for LV vectors and Ms K. Imada for technical support. We also thank all the past and present members of the K.Y. group for discussions, research information and experimental materials. This work was supported by Grants-in-Aid for Scientic Research B2 (24300134; to K.Y.) and Young Scientists B (25830053; to K.H.) from the Japan Society for the Promotion of Science.

Author contributions

K.H. and K.Y. conceived and designed the study; K.H. performed most experiments; T.Y., H.M. and S.P. designed the mitochondrial neurotoxin-based PD models; T.Y., H.M. prepared AAV vectors and performed PD mouse experiments; C.S. performed binding assays; K.F. prepared LV vectors; K.H. and K.Y. analysed data and wrote the manuscript; S.P. contributed to the nal manuscript.

Additional information

Accession codes: Microarray data have been deposited to the Gene Expression Omnibus (GEO) under the accession number GSE63498.

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How to cite this article: Hasegawa, K. et al. Promotion of mitochondrial biogenesis by necdin protects neurons against mitochondrial insults. Nat. Commun. 7:10943doi: 10.1038/ncomms10943 (2016).

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Neurons rely heavily on mitochondria for their function and survival. Mitochondrial dysfunction contributes to the pathogenesis of neurodegenerative diseases such as Parkinson's disease. PGC-1α is a master regulator of mitochondrial biogenesis and function. Here we identify necdin as a potent PGC-1α stabilizer that promotes mitochondrial biogenesis via PGC-1α in mammalian neurons. Expression of genes encoding mitochondria-specific proteins decreases significantly in necdin-null cortical neurons, where mitochondrial function and expression of the PGC-1α protein are reduced. Necdin strongly stabilizes PGC-1α by inhibiting its ubiquitin-dependent degradation. Forced expression of necdin enhances mitochondrial function in primary cortical neurons and human SH-SY5Y neuroblastoma cells to prevent mitochondrial respiratory chain inhibitor-induced degeneration. Moreover, overexpression of necdin in the substantia nigra in vivo of adult mice protects dopaminergic neurons against degeneration in experimental Parkinson's disease. These data reveal that necdin promotes mitochondrial biogenesis through stabilization of endogenous PGC-1α to exert neuroprotection against mitochondrial insults.

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Title

Promotion of mitochondrial biogenesis by necdin protects neurons against mitochondrial insults

Author

Hasegawa, Koichi; Yasuda, Toru; Shiraishi, Chinatsu; Fujiwara, Kazushiro; Przedborski, Serge; Mochizuki, Hideki; Yoshikawa, Kazuaki

Pages

10943

Publication year

2016

Publication date

Mar 2016

Publisher

Nature Publishing Group

e-ISSN

20411723

Source type

Scholarly Journal

Language of publication

English

DOI

https://doi.org/10.1038/ncomms10943

ProQuest document ID

1772843483

Promotion of mitochondrial biogenesis by necdin protects neurons against mitochondrial insults

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