Impaired Glur2 palmitoylation in cerebellar Purkinje cells of a Friedreich ataxia mouse model.

Friedreich's ataxia (FRDA) is a neurodegenerative disorder caused by frataxin deficiency, characterized by progressive cerebellar dysfunction and neuronal loss. Although synaptic abnormalities are an early feature of FRDA, the molecular mechanisms linking frataxin deficiency to synaptic dysfunction remain incompletely defined. In this study, we investigated post-translational regulation of the AMPA receptor subunit GluR2 in the cerebellum of the frataxin knockdown (FRDAkd) mouse model. GluR2 protein levels are reduced early following frataxin knockdown, despite unchanged mRNA expression and preserved Purkinje cell number. Phosphorylation of GluR2 at regulatory sites (Ser880 and Tyr876) are unchanged relative to total protein, indicating that altered phosphorylation does not account for reduced GluR2 levels. In contrast, acyl-biotin exchange assays and proximity ligation analysis reveal a significant reduction in GluR2 palmitoylation, localized primarily to Purkinje cell somata. This deficit is selective, as palmitoylation of other synaptic proteins is variably affected. Mechanistically, reduced GluR2 palmitoylation associates with decreased expression and palmitoylation of the palmitoyl acyltransferase DHHC3, while levels of depalmitoylating enzymes remain unchanged. In vitro, DHHC3 enhances GluR2 palmitoylation, supporting a direct enzymatic relationship. Partial restoration of frataxin expression rescues GluR2 and DHHC3 protein levels and partially restores GluR2 palmitoylation. These findings identify impaired GluR2 palmitoylation as an early, selective synaptic alteration in FRDA and implicate dysregulated lipid-dependent post-translational modification as a mechanism linking frataxin deficiency to cerebellar synaptic vulnerability.