Cyclase associated actin cytoskeleton regulatory protein 2 (CAP2) organizes the actin cytoskeleton to influence the biomechanical properties of the ocular lens

Abstract

Cyclase-associated actin cytoskeleton regulatory protein 2 (CAP2) is a conserved actin-binding protein that promotes actin filament (F-actin) turnover by disassembling ADF/cofilin-decorated filaments, supporting F-actin remodeling in differentiating cells and tissues. In the ocular lens, the actin cytoskeleton is critical for maintaining tissue biomechanical properties during fiber cell maturation. To assess CAP2s role in the lens, we examined lens-specific CAP2 knockout (CAP2cKO) mice at cellular and tissue levels. CAP2cKO lenses were normal in size, shape, and transparency but exhibited increased stiffness under compression and enhanced recovery after load removal. While total actin levels and F-actin were unchanged, immunofluorescence revealed higher levels of Tropomodulin 1 (Tmod1, F-actin pointed-end capping), Tropomyosin3.5 (Tpm3.5, F-actin stabilizing), and T-plastin (F-actin bundling) in F-actin-rich membrane protrusions of mature fibers, while -actinin-1 (F-actin cross-linking) was reduced. These findings suggest that CAP2 loss disrupts F-actin remodeling, promoting filament stabilization through Tpm3.5 binding, Tmod1 capping and T-plastin bundling. Consequently, F-actin networks become stiffer and more resilient, altering lens biomechanics. This study provides the first evidence that CAP2 regulates cell biomechanical properties in a non-muscle tissue through modulation of F-actin-associated proteins. Summary statementCAP2 loss alters the actin cytoskeleton through increased F-actin stabilization by Tmod1 and Tpm3.5, and filament bundling by T-plastin, leading to stiffer lenses.