Valosin Containing Protein role in the clearance of toxic mutated-SOD1 aggregates in fALS

Amyotrophic Lateral Sclerosis (ALS) is a neurodegenerative disease (ND) that involves upper and lower motoneurons. The degeneration of these neurons brings the patient to die of respiratory failure in 2-5 years after the diagnosis. ALS is classified in sporadic form (sALS) and familial forms (fALS). Different gene mutations have been correlated to forms of fALS starting form 1993 when it was discovered a point mutation of Superoxide Dismutase 1. SOD1-mutant expresses misfolded proteins that form neurotoxic cytoplasmic aggregates. ALS is known as a proteinpathy in fact one of the causes that concurs to neuronal death is the alteration of the protein quality control (PQC) system. This system is composed of chaperons, co-chaperons and degradation pathways. The role of the PQC system is to check protein folding and functioning, to repair any misfolding or, if it fails, to routes to the degradation pathways. In ALS the PQC system can be altered for the mutations of genes that are involved in the system like Valosin Containing Protein (VCP). VCP is an AAA+ ATPase protein that has a key role in various degradation pathways. Mutation of VCP are correlated with the formation of intracellular inclusion in ALS and other NDs. This study is aimed to define VCP role in removing protein aggregates positive to mutated-SOD1 by modulating VCP expression in cell models of ALS. We studied the aggregation levels of the mutated- SOD1 when VCP-WT is overexpressed. By performing a Filter Retardation Assay (FRA) We could determine that VCP-WT overexpression leads to a significant decrease in the levels of mutated-SOD1 aggregates. Moreover, by inhibiting the Ubiquitin Proteasome System (UPS) and the autophagic pathway, that are two main degradation pathway where VCP is found involved, we could determine that VCP contribute is mainly through the UPS. In fact, quantifying mutatetd-SOD1 aggregates with a FRA we could observe that the inhibition of the autophagic flux does not alter VCP functioning whereas the inhibition of UPS partially alter VCP contribute. In parallel we analysed the mutated-SOD1 aggregation in condition of inhibition of VCP. The treatment with DBeQ, a chemical inhibitor of VCP, does not alter mutated-SOD1 aggregation levels. Overall VCP does not seem to be essential for mutated-SOD1 clearance, but these data demonstrate that enhancing VCP-pathway brings to removal of the neurotoxic mutated-SOD1 aggregates. This is an interesting new pathway to further study.