Examining the Pathogenic Role of Molecular Layer Interneurons in Preclinical Models of Spinocerebellar ataxia type 1

Neurodegenerative diseases (NDDs) are characterized by the dysfunction of different neuronal populations and consequent neuronal loss throughout the central nervous system (CNS). It is not clear what causes NDDs, however, genetic mutations and ageing are associated with the development of NDDs. Among these diseases, Spinocerebellar ataxia type 1 (SCA1), is an autosomal dominant, adult-onset, motor-associated neurodegenerative disease characterized by atrophy in cerebellum. The neurons mainly affected by the disease are the Purkinje cells (PC). SCA1 is caused by the expansion of a polyglutamine repeat within the ubiquitously expressed Ataxin-1 protein. The exact cause of this premature degeneration of PCs is still unknown. Unpublished findings from our group show that within the cerebellar cortex there is an enhanced PV expression in Molecular Layer Interneuron (MLIN), potentially leading to enhanced inhibition onto the PCs. Furthermore, we previously shown an imbalance in the excitatory-inhibitory balance within the cerebellar cortex leading to PCs degeneration. The primary objective of this thesis is to investigate the pathogenic role of Molecular Layer Interneuron (MLIN). For our experiments, we used SCA1 154Q/2Q and WT mice model and iPSCs model from SCA1 patient. Firstly, an increase in PV expression, as a marker of neuronal activity in MLINs,was observed from the cerebellar cortex of SCA1 154Q/2Q than WT . The PV expression increased with the increasing age of the mice. We hypothesized that the MLIN might be more active therefore impacting PC physiology, we further evaluate synaptic connectivity onto MLIN and PCs. Moreover, ther results from proteomics analysis of MLINs was validated revealing multiple synaptic proteins downregulated in SCA1154Q/2Q compared to WT. We focused our attention on characterizing Synaptotagmin 1 (Synt 1), a calcium sensor protein involved in neurotransmitter release.Further its role in mouse and human model of SCA1, was validated confirming its downregulation in both human and mouse models of SCA1. Finally, our findings suggests that the MLINs are important modulators of PCs physiology in SCA1, potentially contributing to PCs degeneration.