Connective tissue growth factor mediates high glucose effects on matrix degradation through tissue inhibitor of matrix metalloproteinase type 1: Implications for diabetic nephropathy

High glucose concentration inhibits matrix degradation and affects the activities of the enzymes responsible, the matrix metalloproteinases ( MMPs) and their tissue inhibitors (TIMPs). Connective tissue growth factor ( CTGF) expression is increased in diabetic nephropathy and is a downstream mediator of TGF-beta actions. However, whether CTGF regulates matrix degradation and the mechanism of effect in diabetes has not been reported. Human mesangial cells were cultured in media containing 5 or 25 mM glucose and, in some experiments, with recombinant human (rh) CTGF (0 - 1000 ng/ml) and/or appropriate neutralizing antibodies. Matrix degradation was inhibited by rhCTGF in a dose-dependent manner, and the decrease in matrix degradation caused by high glucose and by TGF-beta was significantly attenuated by addition of CTGF-neutralizing antibody ( by 40.2 and 69.1%, respectively). Similar to 25 mM glucose, addition of rhCTGF increased MMP-2, TIMP-1, and TIMP-3 mRNA by 2.5-, 2.1-, and 1.6-fold, respectively ( P < 0.05) but had no effect on membrane-type (MT) 1-MMP or TIMP-2. Addition of TIMP-1 antibody to conditioned medium abolished the decrease in degradation caused by rhCTGF and partially prevented ( by 79%) the glucose-induced inhibition of matrix degradation. In vivo studies of glomeruli from diabetic and control rats showed that intensive insulin treatment prevented the increase in expression of CTGF and TIMP-1 and attenuated the decreased matrix degradation seen in diabetes. In summary, CTGF inhibits matrix degradation by increasing TIMP-1 expression, and by this action it contributes to the inhibition of matrix breakdown by high glucose, implying that CTGF has a role in the reduced matrix degradation observed in diabetic nephropathy.