ACTION POTENTIAL MISFIRING DRIVES DEGENERATION OF MOLECULARLY DISTINCT PURKINJE NEURONS IN A CRSPR-CAS9 MOUSE MODEL OF SPINOCEREBELLAR ATAXIA TYPE 13 (SCA-13)

Spinocerebellar Ataxias (SCAs) are hereditary movement disorders caused by functional disruption and prgoreassive age-dependent degeneration of Cerebellar Purkinje Neurons (PNs). Despite genetic heterogeneity in target gene expression and sequence length, neurophenotypes often converge on shared pathogenic pathways which remains poorly understood.
SCA-13 is caused by a set of single point mutations rendering the voltage sensing domain of high voltage gated K⁺-channel Kv3.3 sub-units unresponsive to voltage change. This leads to disrupted action potential repolarization, which among other characteristics translates to prolonged AP half-width. Here we describe a novel CRISPR-Cas9 mouse model of SCA-13 expressing the human disease-causing mutation R420H found in a Filipino kindred.
Using our R420H mouse model we have characterized the degenerative properties of the SCA-13 disease phenotype. Immunohistological analyses reveal early onset PN degeneration beginning at around postnatal day 30 accompanied by reduced cell counts and accumulation of several proteinopathic markers characteristic of other commonly studied neurodegenerative conditions. Cleaved Caspase 3 expression pattern reveals a distinct anatomical bias to the degeneration of PNs. Finally, we have identified that PNs with particular molecular characteristics are resistant to R420H driven degeneration.
Subsequently, we use in vitro whole cell electrophysiology in combination with calcium imaging to investigate the neuroprotective role of the divergent PN molecular profile. Based on our findings, we suggest a mechanism by which we can promote the survival of all PNs affected by the disease-causing mutation, linking the disease characteristics to a shared set of pathways integral to the disease progression of around 20 unique SCA sub-types.