Expansion of extracellular matrix with fibrosis occurs in many tissues, including skin, as part of the end-organ complications in diabetes. Advanced glycosylation end-products (AGEs) have been implicated as a pathogenic factor in diabetic tissue fibrosis. Connective tissue growth factor (CTGF), also known as IGF-binding protein-related protein-2, induces extracellular matrix. We have recently shown that CTGF mRNA and protein are up-regulated by AGE treatment of cultured human dermal fibroblasts. The aim of this study was to determine whether CTGF is an autocrine mediator in the induction of fibronectin (FN) by AGE. Primary cultures of non-fetal human dermal fibroblasts in confluent monolayer were treated with synthesized soluble AGE BSA, 0-200 μg/ml. Analysis of mRNA, by quantitative real-time RT-PCR and conditioned media from treated cultures, showed that FN mRNA was increased by approximately 4-fold at 48 h, and FN protein levels by Western immunoblot and FN ELISA were doubled, compared with control. In the same system, added recombinant human CTGF (0-500 ng/ml) induced FN mRNA and protein levels dose dependently and in a rapid time course. To test whether AGE BSA acts through cell-derived CTGF to induce FN, a CTGF neutralizing antibody was shown to significantly attenuate, but not fully inhibit, the AGE induction of FN mRNA. A pan-specific PKC inhibitor, GF109203X, at 0.2 μM, inhibited the induction of FN mRNA by AGE BSA. Although the same inhibitor did not significantly affect the induction of CTGF mRNA by AGE, it blocked the induction of FN mRNA by recombinant human CTGF. In summary, the induction of FN by AGE is partly mediated by the AGE-induced up-regulation of cell-derived CTGF and is dependent on PKC activity. These results have potential implications for the expansion of extracellular matrix in diabetes mellitus by advanced glycosylation end products.
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