Inhibition of the MRTF-A/SRF signaling axis alleviates vocal fold scarring

Vocal fold scarring, the most common cause of poor voice after airway injury, involves the transition of vocal fold fibroblasts to contractile myofibroblasts. Vocal fold myofibroblasts can be characterized by significant extracellular matrix (ECM) secretion and stress fiber formation. Biochemical signals, such as transforming growth factor (TGF)-β1, and biophysical cues, such as matrix stiffening, have been shown to induce the fibroblast-to-myofibroblast transition. To identify key intracellular pathways that may mediate myofibroblast activation, we performed bulk RNA sequencing of human vocal fold fibroblasts treated with or without TGF-β1 and found that genes downstream of myocardin related transcription factor A (MRTF-A) and serum response factor (SRF) were upregulated in TGFβ1-induced myofibroblasts. We then show that both TGF-β1 and ECM stiffening induce MRTF-A and SRF nuclear translocation during vocal fold myofibroblast activation. Inhibition of MRTF-A via CCG-257,081 reduced pro-fibrotic gene expression, the percentage of α-smooth muscle actin (α-SMA)-positive fibroblasts, and cell contractility in vitro. In a murine model of vocal fold scarring, MRTF-A inhibition reduced vocal fold scarring severity, evidenced by reduced epithelial thickening, decreased glycosaminoglycan content, and collagen deposition, and decreased expression of ACTA2. Our study suggests that the MRTF-A/SRF pathway regulates vocal fold myofibroblast activation, and that inhibition of MRTF-A has a protective effect against vocal fold scarring in mice.