Decreased Na+/K+ ATPase Expression and Depolarized Cell Membrane in Neurons Differentiated from Chorea-Acanthocytosis Patients

Abstract

Loss of function mutations of the chorein-encoding gene VPS13A lead to chorea-acanthocytosis (ChAc), a neurodegenerative disorder with accelerated suicidal neuronal cell death, which could be reversed by lithium. Chorein upregulates the serum and glucocorticoid inducible kinase SGK1. Targets of SGK1 include the Na⁺/K⁺-ATPase, a pump required for cell survival. To explore whether chorein-deficiency affects Na⁺/K⁺ pump capacity, cortical neurons were differentiated from iPSCs generated from fibroblasts of ChAc patients and healthy volunteers. Na⁺/K⁺ pump capacity was estimated from K⁺-induced whole cell outward current (pump capacity). As a result, the pump capacity was completely abolished in the presence of Na⁺/K⁺ pump-inhibitor ouabain (100 µM), was significantly smaller in ChAc neurons than in control neurons, and was significantly increased in ChAc neurons by lithium treatment (24 hours 2 mM). The effect of lithium was reversed by SGK1-inhibitor GSK650394 (24 h 10 µM). Transmembrane potential (V_m) was significantly less negative in ChAc neurons than in control neurons, and was significantly increased in ChAc neurons by lithium treatment (2 mM, 24 hours). The effect of lithium on V_m was virtually abrogated by ouabain. Na⁺/K⁺ α1-subunit transcript levels and protein abundance were significantly lower in ChAc neurons than in control neurons, an effect reversed by lithium treatment (2 mM, 24 hours). In conclusion, consequences of chorein deficiency in ChAc include impaired Na⁺/K⁺ pump capacity.