Cellular and molecular mechanisms underlying UBA1‐mediated motor neuron degeneration in spinal muscular atrophy

Abstract

Background Spinal muscular atrophy (SMA) is a neurodegenerative genetic disease caused by a homozygous deletion of the Survival Motor Neuron 1 gene (SMN1). It is characterized by the degeneration of α lower motor neurons in the anterior horn of the spinal cord, which leads to muscular atrophy. There is currently no effective therapy. Nevertheless, studies targeting ubiquitin-like modifier-activating enzyme 1 (UBA1) pathways on animal models have shown improvements in neuromuscular phenotype. Experiments have shown that there is a reduction of UBA1 in SMA and that mutations in UBA1 can cause X-linked SMA. However, the mechanism by which UBA1 mediates degeneration in SMA is unclear. Objectives & Aims Previous work was performed in the laboratory in order to identify UBA1-dependent pathways by label-free proteomics of HEK-293 cells after knockdown or overexpression of UBA1. With this pathway, specific proteins can be deregulated in SMA. Thus, this project focuses on the downstream targets of UBA1 and how UBA1 is involved. The project aims to investigate UBA1 as a mediator of neuropathological changes in SMA by studying the UBA1 distribution in post mitotic cells such as primary cultured motor neurons, and SMA cultured motor neurons as well as to identify whether UBA1 distribution is disrupted in cell models of SMA. Methodology This project investigated the role of UBA1 in SMA and, more specifically, the relevance of sub-cellular UBA1 distribution in SMA. UBA1 distribution in post-mitotic cells, including cultured primary neurons, was studied to identify whether UBA1 distribution is disrupted in cell models of SMA. UBA1 distribution was also studied in human embryonic kidney cells to confirm the distribution in dividing cells. Results This study confirmed that a change in the distribution of UBA1 was seen in cultured motor neurons over time (Fig. 1). Moreover, there was a pronounced UBA1 reduction in the nucleus in SMA motor neurons in comparison to healthy motor neurons (Fig. 2). Conclusion This research project studied the role of UBA1 distribution and its relevance to SMA. Results have produced a better understanding of UBA1 distribution in post-mitotic cells, such as cultured motor neurons and SMA motor neurons. Results suggest that understanding UBA1 distribution in SMA will be essential to future studies in reaching a therapeutic cure. Future work will include looking at the downstream effect of this change in UBA1 distribution.