VCP suppresses proteopathic seeding in neurons

Abstract

Background: Neuronal uptake and subsequent spread of proteopathic seeds, such as alphaS (alpha-synuclein), Tau, and TDP-43, contribute to neurodegeneration. The cellular machinery participating in this process is poorly understood. One proteinopathy called multisystem proteinopathy (MSP) is associated with dominant mutations in Valosin Containing Protein (VCP). MSP patients have muscle and neuronal degeneration characterized by aggregate pathology that can include alphaS, Tau and TDP-43. Methods: We performed a fluorescent cell sorting based genome-wide CRISPR-Cas9 screen in alphaS biosensors. alphaS and TDP-43 seeding activity under varied conditions was assessed using FRET/Flow biosensor cells or immuno fluorescence for phosphorylated alphaS or TDP-43 in primary cultured neurons. We analyzed in vivo seeding activity by immunostaining for phosphorylated alphaS following intrastriatal injection of alphaS seeds in control or VCP disease mutation carrying mice. Results: One hundred fifty-four genes were identified as suppressors of alphaS seeding. One suppressor, VCP when chemically or genetically inhibited increased alphaS seeding in cells and neurons. This was not due to an increase in alphaS uptake or alphaS protein levels. MSP-VCP mutation expression increased alphaS seeding in cells and neurons. Intrastriatal injection of alphaS preformed fibrils (PFF) into VCP-MSP mutation carrying mice increased phospho alphaS expression as compared to control mice. Cells stably expressing fluorescently tagged TDP-43 C-terminal fragment FRET pairs (TDP-43 biosensors) generate FRET when seeded with TDP-43 PFF but not monomeric TDP-43. VCP inhibition or MSP-VCP mutant expression increases TDP-43 seeding in TDP-43 biosensors. Similarly, treatment of neurons with TDP-43 PFFs generates high molecular weight insoluble phosphorylated TDP-43 after 5days. This TDP-43 seed dependent increase in phosphorylated TDP-43 is further augmented in MSP-VCP mutant expressing neurons. Conclusion: Using an unbiased screen, we identified the multifunctional AAA ATPase VCP as a suppressor of alphaS and TDP-43 aggregate seeding in cells and neurons. VCP facilitates the clearance of damaged lysosomes via lysophagy. We propose that VCPs surveillance of permeabilized endosomes may protect against the proteopathic spread of pathogenic protein aggregates. The spread of distinct aggregate species may dictate the pleiotropic phenotypes and pathologies in VCP associated MSP.