Integrins αvβ5 and αvβ3 promote latent TGF-β1 activation by human cardiac fibroblast contraction

AIMS: Pathological tissue remodelling by myofibroblast contraction is a hallmark of cardiac fibrosis. Myofibroblasts differentiate from cardiac fibroblasts under the action of transforming growth factor-β1 (TGF-β1), which is secreted into the extracellular matrix as a large latent complex. Integrin-mediated traction forces activate TGF-β1 by inducing a conformational change in the latent complex. The mesenchymal integrins αvβ5 and αvβ3 are expressed in the heart, but their role in the activation of TGF-β1 remains elusive. Here, we test whether targeting αvβ5 and αvβ3 integrins reduces latent TGF-β1 activation by cardiac fibroblasts with the goal to prevent the formation of α-smooth muscle actin (α-SMA)-expressing cardiac myofibroblasts and their contribution to fibrosis. METHODS AND RESULTS: Using a porcine model of induced right ventricular fibrosis and pro-fibrotic culture conditions, we show that integrins αvβ5 and αvβ3 are up-regulated in myofibroblast-enriched fibrotic lesions and differentiated cultured human cardiac myofibroblasts. Both integrins autonomously contribute to latent TGF-β1 activation and myofibroblast differentiation, as demonstrated by function-blocking peptides and antibodies. Acute blocking of both integrins leads to significantly reduced TGF-β1 activation by cardiac fibroblast contraction and loss of α-SMA expression, which is restored by adding active TGF-β1. Manipulating integrin protein levels in overexpression and shRNA experiments reveals that both integrins can compensate for each other with respect to TGF-β1 activation and induction of α-SMA expression. CONCLUSIONS: Integrins αvβ5 and αvβ3 both control myofibroblast differentiation by activating latent TGF-β1. Pharmacological targeting of mesenchymal integrins is a possible strategy to selectively block TGF-β1 activation by cardiac myofibroblasts and progression of fibrosis in the heart.