Resilience to Endoplasmic Reticulum Stress Mitigates Calcium-Dependent Membrane Hyperexcitability Underlying Late Disease Onset in Spinocerebellar Ataxia Type 6

An enduring puzzle in many inherited neurological disorders is the late onset of symptoms despite expression of function-impairing mutant protein early in life. We examined the basis for onset of impairment in Spinocerebellar ataxia type 6 (SCA6), a polyglutamine ataxia with late-onset cerebellar neurodegeneration. In a mouse model of SCA6, we identified a homeostatic response that engages the unfolded protein response early in disease. This protective response provided insight into endoplasmic reticulum (ER) stress-mediated cerebellar Purkinje neuron membrane hyperexcitability as a driver of disease. Age-dependent impairment of chaperone-mediated compensation for ER stress increased calcium-dependent Purkinje neuron membrane excitability. Redundant pathways of the unfolded protein response mediate this resilience to ER stress. ER stress-related decompensation applies also to other late-onset human cerebellar ataxia. These studies elucidate a mechanism of resilience connecting aberrant proteostasis and calcium-dependent intrinsic membrane hyperexcitability to explain delayed disease onset more widely in age-dependent neurodegenerative disease.