Identifying and Restoring Mechanisms Driving DRPLA-Associated Epilepsy.

About This Grant

Dentatorubral-pallidoluysian atrophy (DRPLA) is a rare inherited neurodegenerative disease caused by expansion of a glutamine-coding CAG repeat in the Atrophin-1 (ATN1) gene. The role of ATN1 in the adult central nervous system (CNS) is currently unknown. However, the clinical manifestations of DRPLA lead to a constellation of symptoms that are inversely correlated to CAG-expansion (CAGEX) size, with younger individuals typically carrying the largest number of CAG repeats, experiencing the most severe disease burden. Importantly, young patients with DRPLA face poor cognitive outcomes, including developmental delay, with a prevalence of high-frequency, drug-resistant seizures and epilepsy diagnosis. The mechanisms leading to increased neuronal hyperexcitability and seizure risk in DRPLA patients are presently unknown. Thus, preclinical humanized in vitro and in vivo models of ATN1 CAGEX represent a novel platform to expediently assess innovative therapies for symptomatic seizure control and disease modification. Further, these models allow exquisite translational fidelity to define how ATN1 mutations lead to neuronal hyperexcitability. Indeed, our labs have recently identified both an increased neuronal excitability using a versatile patient-specific induced pluripotent stem cell (iPSC)-derived in vitro system and an altered seizure threshold in vivo using a novel mouse model expressing a humanized ATN1 CAG repeat expansion. In vitro studies in human patient iPSC-derived cortical neurons using live-cell calcium imaging and multi-electrode array recordings demonstrate altered neuronal network activity by manifesting increased calcium spike amplitude and hypersynchronization, both characteristics simulating epileptiform-like phenotypes. Notably, we have preliminarily demonstrated that neuronal hyperexcitability (in vitro) and seizure threshold (in vivo) can be rescued with exogenous administration of investigational ATN1- silencing antisense oligonucleotides (ASOs). Further, circadian behavior of ATN1 CAGEX mice administered the investigational ASO were normalized, indicating a disease-modifying effect in this clinically relevant rodent model of DRPLA. The present proposal thus aims to expand these pilot studies to address the mechanism behind ATN1 CAGEX-dependent spontaneous seizure risk and neuronal hyperexcitability in vitro and in vivo, and to further define the potential seizure-modifying effects of ASO infusion in the early disease course. Aim 1 will utilize patient iPSC-derived neuro-glial model to characterize the physiological and molecular mechanism of the DRPLA epileptiform and asses ASO efficacy in phenotypic rescue. Aim 2 will then expand on these in vitro studies to establish whether Atn1 CAGEX mice exhibit spontaneous recurrent seizures and define the degree to which an investigational ASO infusion influences the occurrence of these events and improves neuropathological burden. This study will deepen our understanding of the impact of ATN1 CAGEX on pathological neuronal activity and seizure risk while establishing proof-of-principle evidence that ASO intervention is a disease-modifying strategy for DRPLA, a progressive myoclonic epilepsy syndrome with no palliative or curative options.