Cell autonomous ANTXR1-mediated regulation of extracellular matrix components in primary fibroblasts

Our previous studies of Antxr1 knockout mice suggested that fibrotic skin abnormalities in these mice are associated with increased VEGF signaling. Here, based on studies of primary fibroblasts isolated from skin of Antx1+/+ and Antxr1-/- mice at embryonic stage E17.5 and postnatal day P49, we conclude that increased Col1a1 and Fn1 expression in Antxr1-deficient fibroblasts is partly mediated by a cell-autonomous ANTXR1-dependent mechanism. In turn, this may act in parallel with VEGF-dependent regulation of collagen type I and fibronectin production. We demonstrate that shRNA mediated knockdown of VEGF in Antxr1-/- fibroblasts reduces Col1a1 and Fn1 expression to below control levels, and these are restored by exogenous addition of recombinant VEGF. In addition, the increase in protein levels of collagen type I and fibronectin in mutant cells is blocked by VEGF neutralizing antibody. However, expressing the longest isoform of ANTXR1 (sv1) in mutant fibroblasts decreases levels of Ctgf, Col1a1 and Fn1 transcripts, but has no effect on VEGF expression. Taken together, our data suggest that the increased matrix production in Antxr1- deficient fibroblasts primarily occurs via a CTGF-dependent pathway and that other ANTXR1-associated mechanisms contribute to VEGF-dependent increase of collagen type I and fibronectin expression. Our findings provide a basis for further studies of novel ANTXR1-dependent connective tissue homeostatic control mechanisms in healthy individuals, patients with organ fibrosis, and patients with GAPO syndrome.