Inhibition of mechanosensitive signaling in myofibroblasts ameliorates experimental pulmonary fibrosis

TLDR

Matrix stiffening and myofibroblast resistance to apoptosis are cardinal features of chronic fibrotic diseases, yet how altered tissue biomechanics drive progressive fibrosis remains poorly understood. The study aims to define a Rho/ROCK–actin–MKL1 mechanotransduction pathway that regulates myofibroblast differentiation and survival. Using ex vivo and in vivo models, the authors disrupted this pathway with the ROCK inhibitor fasudil, which induced myofibroblast apoptosis by downregulating BCL‑2 and activating the intrinsic mitochondrial apoptotic pathway. Activation of the Rho/ROCK–actin–MKL1 pathway was observed in experimental lung fibrosis and idiopathic pulmonary fibrosis, and pharmacologic inhibition or genetic ablation of this pathway protected mice from fibrosis, indicating that targeting mechanosensitive signaling to trigger intrinsic apoptosis may be an effective antifibrotic strategy.

Abstract

Matrix stiffening and myofibroblast resistance to apoptosis are cardinal features of chronic fibrotic diseases involving diverse organ systems. The interactions between altered tissue biomechanics and cellular signaling that sustain progressive fibrosis are not well defined. In this study, we used ex vivo and in vivo approaches to define a mechanotransduction pathway involving Rho/Rho kinase (Rho/ROCK), actin cytoskeletal remodeling, and a mechanosensitive transcription factor, megakaryoblastic leukemia 1 (MKL1), that coordinately regulate myofibroblast differentiation and survival. Both in an experimental mouse model of lung fibrosis and in human subjects with idiopathic pulmonary fibrosis (IPF), we observed activation of the Rho/ROCK pathway, enhanced actin cytoskeletal polymerization, and MKL1 cytoplasmic-nuclear shuttling. Pharmacologic disruption of this mechanotransduction pathway with the ROCK inhibitor fasudil induced myofibroblast apoptosis through a mechanism involving downregulation of BCL-2 and activation of the intrinsic mitochondrial apoptotic pathway. Treatment with fasudil during the postinflammatory fibrotic phase of lung injury or genetic ablation of Mkl1 protected mice from experimental lung fibrosis. These studies indicate that targeting mechanosensitive signaling in myofibroblasts to trigger the intrinsic apoptosis pathway may be an effective approach for treatment of fibrotic disorders.