VCP modulation ameliorates pathological features in C9orf72 models

Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are devastating neurodegenerative diseases linked by similar pathological mechanisms, which, in some familial forms, may be associated with the same genetic alterations. Among them, the most common is the C9ORF72 (C9) mutation. The C9 mutation consists in an aberrant expansion of the hexanucleotide repeat (G₄C₂)_n that leads to the production and accumulation of toxic dipeptide repeat proteins (DPRs). Some of these C9-DPRs contribute to neuronal dysfunction and degeneration through different mechanisms. One of these involves alterations in the protein quality control (PQC) system, specifically in the autophagy-lysosomal pathway. Valosin-containing protein (VCP) is a critical component of the PQC system, assisting the degradation of misfolded proteins and damaged organelles and the maintenance of cellular homeostasis. In this study, we investigated the role of VCP in modulating pathological features associated with C9 mutation. Using neuronal cell models, we demonstrated that VCP overexpression significantly reduced C9-DPRs levels. This reduction is mediated by mechanisms involving both the ubiquitin-proteasome system (UPS) and autophagy. Additionally, we also observed that C9-DPRs induce lysosomal damage, which is counteracted by VCP overexpression, as indicated by decreased galectin-3 puncta and restored lysosomal pH. We then pharmacologically activated VCP-mediated clearance through SMER28, increasing the clearance of the most toxic DPR, the polyPR. We also determined that in this model, SMER28 activity is mediated by the UPS and is associated with the mitigation of DPR-induced lysosome damage. Additionally, using motor neurons derived from induced pluripotent stem cells (iPSC-MNs) from C9-ALS mutation carriers, we demonstrated that SMER28 treatment significantly decreased polyGA levels, a marker for C9-DPR accumulation. Moreover, SMER28 rescued C9-MNs commitment to differentiation and the alteration in the expression of autophagy-related genes. Taken together, our findings strongly support VCP as a modulator of C9 pathology and highlight its potential as a therapeutic target.