THE ROLE OF INTEGRINS IN THE ACTIVATION OF FIBROBLASTS FROM SKIN, LUNG AND BREAST TISSUE

Abstract

Fibroblasts are abundant mesenchymal cells present in all tissues in a quiescent state, which contribute to wound healing when activated. Cytokine transforming growth factor-β1 (TGF-β1) stimulates fibroblast-myofibroblast differentiation, which induces extracellular matrix secretion, tissue contraction and promotes cancer cell migration. Hence, chronic activity of stromal myofibroblasts correlates with a poor prognosis for cancer and organ fibrosis patients. Therefore, modulating myofibroblast activity may reduce the severity of these diseases. Previous research suggests blockade of transmembrane integrin receptors expressed by fibroblasts prevents TGF-β1- induced differentiation, indicating integrins are attractive therapeutic targets. However, fibroblasts derived from different organs exhibit heterogeneity, although their integrin expression and integrin-regulated differentiation has not been directly compared. The aim of my research was 1) to understand and compare how integrins regulate TGF-β1-induced activation of fibroblasts derived from normal skin, lung and breast tissue; 2) to examine the global gene expression of TGF-β1-treated lung fibroblasts; 3) to identify novel therapeutic targets that modulate TGF-β1-induced activation of lung fibroblasts using a drug library. qPCR showed skin, lung and breast fibroblasts differentially expressed TGF-β1- induced activation markers, including ACTA2, FN1, TIMP3, CTGF and SERPINE1, in addition to integrin genes for α1, α4, α11 and β3. Small-molecule inhibitors of αv integrins only reduced the invasion of TGF-β1-exposed skin fibroblasts, but not lung or breast fibroblasts. siRNA against α11, β3 and β5 decreased TGF-β1-induced collagen contraction and activation marker expression in skin and lung fibroblasts, while α1 siRNA prevented collagen contraction by breast fibroblasts only. RNA sequencing of TGF-β1-treated lung fibroblasts revealed pro-inflammatory and profibrotic pathways were significantly enriched, while screening TGF-β1-treated lung fibroblasts with a FDA-approved drug library identified 46 hits that significantly reduced α-smooth muscle actin and fibronectin expression. Overall, genes are differentially expressed in TGF-β1-treated skin, lung and breast fibroblasts, while different integrins in each fibroblast appear to regulate invasion, TGF-β1-induced collagen contraction and gene expression. RNA sequencing revealed TGF-β1 promotes the expression of a pro-tumour signature in lung fibroblasts and several novel therapeutic targets that modulate the activation of lung fibroblasts have been identified. Understanding these integrin-dependent and independent mechanisms will facilitate the generation of myofibroblast-targeted treatments for cancer and organ fibrosis.