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Abstract
A definitive endogenous and chronic mechanism for regulating the activity and trafficking of the norepinephrine transporter (NET) is unknown. The purpose of this dissertation research was to examine the regulation of NET by the synucleins, a family of presynaptic proteins. Three hypotheses were tested: (1) α-synuclein decreases NET activity and trafficking to the plasma membrane, (2) α-synuclein regulation of NET is dependent on interactions with the cytoskeleton, (3) altered α-synuclein and γ-synuclein-mediated regulation of NET contributes to the development of depression. These studies yielded several novel findings. First, α-synuclein regulates NET activity and trafficking in a bimodal manner. Thus, low or high levels of α-synuclein cause an increase or decrease, respectively, in NET activity and cellular localization. This regulation is dependent on an intact microtubule and actin cytoskeleton. In cell lines, α-synuclein mediated regulation of NET activity is eliminated in the presence of cytoskeletal destabilizing agents. In primary neuronal cultures and frontal cortex synaptosomes, NET activity is enhanced following depolymerization of either microtubules or actin. Lastly, in a rodent model of depression, the regulation of NET activity is not dependent on a polymerized microtubule network in the frontal cortex, the expression of γ-synuclein and NET are high, and α-synuclein expression is low. Following chronic treatment with desipramine, a NET selective antidepressant, NET and γ-synuclein expression are decreased, while α-synuclein levels are increased. Furthermore, desipramine treatment causes NET to regain sensitivity to microtubule destabilizing agents. These results indicate that altered interactions between NET, the synucleins, and the cytoskeleton promote the depressive phenotype and are subsequently targeted by desipramine. This dissertation research has determined novel mechanisms by which the synuclein proteins regulate NET in both homeostatic and disease conditions.
