Valosin Containing Protein cooperates in the removal of toxic mutated-SOD-1 aggregates in Neurodegenerative diseases

Neurodegenerative diseases (NDs) are pathologies characterized by the progressive death of neurons. This can lead to the alteration or loss of cerebral, cognitive and behavioural functions and eventually leads to death. Some NDs are also known as “protein misfolded disorders” because a common hallmark is the presence of misfolded protein aggregates which alter normal cellular homeostasis leading to neuronal loss. The formation of protein aggregates could be due to genetic mutations, altered cellular localization, cell stress, improper post-translation and the dysfunction of protein quality control (PQC) system. The PQC system prevents the formation of these aggregates by routing them to the degradative systems like the ubiquitin-proteasome system (UPS) and the autophagic pathway. Valosin Containing Protein (VCP) is AAA+-ATPase that is found mutated in different NDs like Inclusion Body Myopathy Pajet’s Disease and Frontotemporal Dementia (IBMPFD) and Amyotrophic Lateral Sclerosis (ALS). VCP is a chaperon-like protein that is involved in PQC system. Its function is mainly to extract misfolded proteins and route them to the UPS. Recently studies have found a correlation also between VCP and autophagy. We demonstrate that overexpressed VCP is involved in the removal of mutated SOD1-aggregates in NSC34 models transiently expressing mutated SOD1 (SOD1-G93A). This is a known in vitro model of familial ALS (fALS). In fact by performing a Filter Retardation Assay (FRA) we could observe a decreased level of the insoluble aggregates of mutated-SOD1 when wild type VCP is overexpressed. This data was confirmed in Western Blot (WB). Moreover, by inhibiting the main degradation systems (UPS and autophagy), we observe that VCP enhances SOD1-G93A clearance mainly through the UPS system. We also demonstrate that VCP mutants (R155H and R191Q) maintain VCP-functions in basal condition, but lose their function when the degradative systems have been inhibit. In particular, the inhibition of autophagy shows a relevant loss of function of the mutated VCPs compared to the wild type form. These data, that show VCP role in preventing mutated SOD1-aggregates, are the baseline to define the importance of VCP in the clearance of misfolded protein aggregates. The demonstration of VCP role could make it a new potential target for fALS.