VCP R155H

# Research Brief: VCP R155H Variant ## Pathogenic Mechanisms The VCP R155H variant disrupts the function of valosin-containing protein (VCP), a AAA+ ATPase critical for cellular protein quality control. VCP's core molecular functions include ATP binding, ATP hydrolysis activity, and ADP binding, which power its roles in aggresome assembly, autophagosome maturation, and ATP metabolism. The R155H substitution likely compromises these fundamental enzymatic activities, potentially affecting the protein's ability to extract ubiquitinated substrates from protein complexes. Literature on VCP mutations broadly demonstrates pathogenic mechanisms through protein quality control dysfunction, hypoxic stress responses, and structural destabilization. The R155 residue's location and the nature of the arginine-to-histidine substitution (loss of positive charge at physiological pH) suggest disruption of critical electrostatic interactions necessary for ATP binding or hydrolysis. Given VCP's extensive interactome including NSFL1C, UBXN6, UBXN7, UBXN2A, and ASPSCR1, the R155H mutation may impair co-factor recruitment or substrate processing efficiency, leading to proteostatic collapse. ## Clinical Significance R155H is a pathogenic variant associated with the VCP disease spectrum, which includes inclusion body myopathy with Paget disease and frontotemporal dementia (IBMPFD), amyotrophic lateral sclerosis (ALS), and frontotemporal dementia (FTD). The establishment of first baseline clinical data collection for VCP R155H carriers represents a crucial milestone in understanding this multi-system degenerative disorder. This baseline documentation is particularly significant given the highly variable onset and progression rates characteristic of VCP-related diseases, enabling identification of pre-symptomatic or early-stage biomarkers. The systematic capture of clinical, biomarker, and functional parameters in R155H carriers will provide essential reference points for tracking disease evolution and establishing therapeutic intervention windows. The variant's clinical impact likely stems from impaired autophagy and protein degradation pathways, leading to toxic protein accumulation in muscle, bone, and neural tissues. ## Therapeutic Landscape Structural analysis identifies a significant aggregation hotspot at residues 265-269 (score: 0.80), suggesting protein misfolding propensity as a targetable feature. The candidate peptide CP-VCP-001 has been computationally designed to target this 265-269 region, potentially stabilizing the protein or preventing pathological aggregation. This therapeutic rationale is supported by VCP's documented role in aggresome assembly and autophagosome maturation—processes that become dysregulated when VCP misfolds or aggregates. The identification of this aggregation-prone region presents opportunities for small molecule stabilizers, molecular chaperone enhancement, or peptide-based interventions. AlphaFold structural modeling provides additional insights into conformational changes induced by R155H, though specific structural data for this variant requires further characterization. Given VCP's ATPase activity is central to its function, ATP-competitive or allosteric modulators that restore enzymatic activity represent additional therapeutic avenues. ## Research Directions Critical knowledge gaps remain regarding R155H-specific pathogenicity. Direct structural characterization of the R155H variant using cryo-EM or X-ray crystallography would clarify how this substitution affects the D1 ATPase domain architecture and nucleotide binding. Functional studies measuring ATP hydrolysis rates, substrate extraction efficiency, and co-factor binding affinity for R155H versus wild-type VCP are essential. The ongoing baseline data collection initiative should incorporate longitudinal biomarker tracking, including proteomic analysis of autophagy markers, serum creatine kinase levels, and neuroimaging parameters. Given the multi-system nature of VCP diseases, patient-derived iPSCs differentiated into myocytes, neurons, and osteoclasts could model tissue-specific pathology. Preclinical validation of CP-VCP-001 in cellular and animal models would assess its ability to prevent aggregation and restore proteostasis. Finally, investigating genetic modifiers and environmental factors influencing phenotypic variability among R155H carriers could identify additional therapeutic targets and enable personalized risk stratification.