Purkinje Cell-specific Deficiency in SEL1L-HRD1 Endoplasmic Reticulum-Associated Degradation Causes Progressive Cerebellar Ataxia in Mice

Recent studies have identified multiple genetic variants of SEL1L-HRD1 ER-associated degradation (ERAD) in humans with neurodevelopmental disorders and locomotor dysfunctions, including ataxia. However, the relevance and importance of SEL1L-HRD1 ERAD in the pathogenesis of ataxia remain unexplored. Here we show that SEL1L deficiency in Purkinje cells leads to early-onset progressive cerebellar ataxia with progressive loss of Purkinje cells with age. Mice with Purkinje cell-specific deletion of SEL1L (Sel1LPcp2Cre) exhibit motor dysfunction beginning around 9 weeks of age. Transmission electron microscopy (TEM) analysis reveals dilated ER and fragmented nuclei in Purkinje cells of adult Sel1LPcp2Cre mice, indicative of altered ER homeostasis and cell death. Lastly, loss of Purkinje cells is associated with a secondary neurodegeneration of granular cells, as well as robust activation of astrocytes and proliferation of microglia, in the cerebellum of Sel1LPcp2Cre mice. These data demonstrate the pathophysiological importance of SEL1L-HRD1 ERAD in Purkinje cells in the pathogenesis of cerebellar ataxia.