RAB3GAP2 is a Regulator of Skeletal Muscle Endothelial Cell Proliferation and Associated with Capillary Density

Skeletal muscle fiber composition and capillary density influence physical performance and whole-body metabolic properties. ~45% of the variance in fiber type is heritable, which motivated us to perform a genome-wide association study of skeletal muscle histology from 656 Swedish men. Four independent variants were associated (p < 5x10− 8) with proportion of type IIx fibers or capillary-to-fiber ratio (C:F). The strongest signal localized to the rs115660502 variant, where the G-allele corresponded with increased C:F and reduced skeletal muscle expression of the proximal gene, RAB3 GTPase Activating Non-Catalytic Protein Subunit 2 (RAB3GAP2). The G-allele was less frequent in elite short-track sprinters and more frequent in endurance athletes than in matched non-athlete (population) controls; RAB3GAP2 expression was reduced by high-intensity intermittent training. RAB3GAP2 protein was not uniformly expressed in muscle tissue but localized to the endothelium and capillaries. Experimental reduction of RAB3GAP2 in human endothelial cells led to increased tube formation in vitro, to regulation of secreted factors promoting angiogenesis and T-cell activation, to reduced intracellular levels of von Willebrand factor (VWF) and, post-implantation, to increased endothelial cell density in vivo in mice. The amount of RAB3GAP2 in skeletal muscle was positively associated with exercise-induced release of VWF in vivo in humans. By regulating the release of protein factors (VWF, CD70, TNC, TNXB, MCP1, IGFBP3, COL1A1, TFPI2 and tPA), RAB3GAP2 influences fitness adaptation after exercise by improving muscle healing and promotion of capillary formation.