UC San Diego

Vinculin (Vcl) is a membrane-associated protein that has been shown to play key structural roles in cell adhesion sites and may affect myocardial mechanical function in a direction-dependent manner. Previous studies measured the mechanical effects of Vcl disruption using tagged magnetic resonance imaging (MRI) in vivo and reported significant decreases in the transverse systolic strain components in a cardiomyocyte-specific vinculin knockout (cVclKO) mouse model compared with littermate controls [1]. However, there was no change in systolic fiber strain in vivo [1]. One possible mechanism might be alterations in sarcomeric structure; thus, the lattice spacing and sarcomere length were measured in fixed hearts using microscopy. Measurements from optical diffraction patterns generated using FFTs of electron micrographs yielded an average normalized lattice spacing of 0.0113±0.001 (SD) in end- diastolic cVclKO hearts vs. 0.0095±0.001 in controls (P< 0.05, n=3). A similar trend was observed in the barium- contracted hearts. A crossbridge model was used to compute changes in transverse and axial crossbridge forces associated with this increase in myofilament lattice spacing. A finite element model incorporating these changes in systolic material properties recapitulated key mechanical differences seen between control and mutant mice. The results suggest that Vcl ablation increased myofilament lattice spacing, which alters the crossbridge binding angle of myosin heads; this, in turn, increases the transverse component of sarcomere force and consequently decreases systolic cross-fiber strains in vivo. These results with the experimental measurements suggest that Vcl can influence myofilament architecture and systolic force generation in a direction-dependent manner