Connective tissue growth factor in tissue fibrosis

Systemic Sclerosis (SSc) is a connective tissue disease characterised by inflammation and autoimmunity, vasculopathy, and interstitial remodelling and fibrosis. This thesis focuses on CTGF (CCN2), a member of the CCN family of matricellular proteins, as elevated CTGF expression is a hallmark of chronic fibrotic diseases such as SSc. In addition to the association of CTGF expression and fibrosis in human disease, experimentally, fibroblast-specific overexpression of CTGF has been shown to induce a fibrotic phenotype, as demonstrated in the Col1a2-CTGF transgenic mice. Prominent features of fibrosis included a thickened dermis, as well as excess collagen deposition in the skin and lung. This CTGF overexpression also provoked changes in the alveolar epithelium. In the lung of Col1a2-CTGF mice, immunostaining revealed a marked increase in the number of cells co-expressing the epithelial marker, TTF-1 and mesenchymal cell markers α-SMA and Snai1, indicative of epithelial-to-mesenchymal transition (EMT)-like changes. This suggested a role for the paracrine effects of CTGF in promoting the phenotypic switching of alveolar epithelial cells. EMT is likely to contribute, at least in part, to the accumulation of interstitial fibroblasts during fibrosis. Complementary in vitro studies in alveolar epithelial cells (AECs) showed that CTGF knockdown using siRNA suppressed TGF-β-induced mesenchymal cell proteins while inducing redistribution of the epithelial cell marker E-cadherin. Immunostaining and Western blotting showed that recombinant CTGF induced EMT-like morphological changes and expression of α-SMA in AECs. Finally, we were interested in whether the reduction or absence of CTGF could abrogate fibrosis. Knockdown of CTGF suppressed the induction of fibrotic proteins in TGF-β-treated control fibroblasts and SSc lung fibroblasts. Deletion of the CTGF gene showed reduced bleomycin-induced pulmonary fibrosis in mice. Overall, these results support that CTGF plays a pivotal role in fibrosis and blocking CTGF activity may be useful as a specific target of attenuating fibrosis in SSc.