Advanced glycosylation end products up-regulate connective tissue growth factor (insulin-like growth factor-binding protein-related protein 2) in human fibroblasts: A potential mechanism for expansion of extracellular matrixin diabetes mellitus

Expansion of extracellular matrix with fibrosis occurs in many tissues as p art of the end-organ complications in diabetes, and advanced glycosylation end products (AGE) are implicated as one causative factor in diabetic tissu e fibrosis. Connective tissue growth factor (CTGF), also known as insulin-l ike growth factor-binding protein-related protein-2 (IGFBP-rP2), is a poten t inducer of extracellular matrix synthesis and angiogenesis and is increas ed in tissues from rodent models of diabetes. The aim of this study was to determine whether CTGF is up-regulated by AGE in vitro and to explore the c ellular mechanisms involved. AGE treatment of primary cultures of nonfetal human dermal fibroblasts in confluent monolayer increased CTGF steady state messenger RNA (mRNA) levels in a time- and dose-dependent manner. In contr ast, mRNAs for other IGFBP superfamily members, IGFBP-rP1 (mac 25) and IGFB P-3, were not up-regulated by AGE. The effect of the AGE BSA reagent on CTG F mRNA was due to nonenzymatic glycosylation of BSA and, using neutralizing antisera to AGE and to the receptor for AGE, termed RAGE, was seen to be d ue to late products of nonenzymatic glycosylation and was partly mediated b y RAGE. Reactive oxygen species as well as endogenous transforming growth f actor-beta1 could not explain the AGE effect on CTGF mRNA. AGE also increas ed GTGF protein in the conditioned medium and cell-associated CTGF. Thus, A GE up-regulates the profibrotic and proangiogenic protein CTGF (IGFBP-rP2), a finding that may have significance in the development of diabetic compli cations.