Connective tissue growth factor domain 4 amplifies fibrotic kidney disease through activation of ldl receptor-related protein 6

Abstract

Connective tissue growth factor (CTGF), a matrix-Associated proteinwith fourdistinct cytokinebindingdomains, has roles in vasculogenesis, wound healing responses, and fibrogenesis and is upregulated in fibroblasts and myofibroblasts in disease. Here, we investigated the role of CTGF in fibrogenic cells. In mice, tissue-specific inducible overexpression of CTGF by kidney pericytes and fibroblasts had no bearing on nephrogenesis or kidney homeostasis but exacerbated inflammation and fibrosis after ureteral obstruction. These effects required the WNT receptor LDL receptor-related protein 6 (LRP6). Additionally, pericytes isolated from these mice becamehypermigratory and hyperproliferative on overexpression ofCTGF. CTGF is cleaved in vivo into distinct domains. Treatment with recombinant domain 1, 1+2 (N terminus), or 4 (C terminus) independently activated myofibroblast differentiation and wound healing responses in cultured pericytes, but domain 4 showed the broadest profibrotic activity. Domain 4 exhibited low-Affinity binding to LRP6 in in vitro binding assays, and inhibition of LRP6 or critical signaling cascades downstream of LRP6, including JNK and WNT/b-catenin, inhibited the biologic activity of domain 4.Administration of blockingantibodies specifically againstCTGF domain 4or recombinant Dickkopf-related protein-1, an endogenous inhibitor of LRP6, effectively inhibited inflammation and fibrosis associated with ureteral obstruction in vivo. Therefore, domain 4 of CTGF and the WNT signaling pathway are important new targets in fibrosis.