THE EFFECTS OF HIGH GLUCOSE ON HUMAN ENDOTHELIAL-CELL GROWTH AND GENE-EXPRESSION ARE NOT MEDIATED BY TRANSFORMING GROWTH-FACTOR-BETA

BACKGROUND: Because accumulation of extracellular matrix is a prominen t characteristic of the microangiopathy that complicates long-term dia betes, a pathogenetic role for transforming growth factor beta (TGF-be ta) is being considered. Having observed that glucose levels mimicking diabetic hyperglycemia induce in vitro endothelial cell overexpressio n of extracellular matrix molecules, decreased replication, and increa sed levels of TGF-beta mRNA, we have examined whether the effects of h igh glucose are mediated by autocrine TGF-beta. EXPERIMENTAL DESIGN: T GF-beta levels were measured by bioassay in the media conditioned by h uman umbilical vein endothelial cells cultured in the presence of high (30 mM) or normal (5 mM) glucose concentrations. The effect of high g lucose was tested on the proliferation of two epithelial cell lines, o ne (Mv1Lu) exquisitely sensitive to TGF-beta and the other (DR mutants ) insensitive to the cytokine. To examine whether high glucose and TGF -beta affect cellular programs in a similar manner, the effects of hig h glucose and exogenous TGF-beta were compared on proliferation and ge ne expression of endothelial cells. RESULTS: Media conditioned by endo thelial cells cultured in high or normal glucose contained similar amo unts of TGF-beta (4.9 +/- 3.5 and 3.7 +/- 2.5 ng/10(6) cells, respecti vely (mean +/- SD)), all in the latent form. The replication of parent al Mv1Lu cells and their DR mutants was decreased by high glucose to t he same extent. Whereas the inhibitory effect of high glucose on endot helial cell replication was reversible, that of TGF-beta was not. Both perturbations induced up-regulation of fibronectin expression, but th e effects were additive. Only TGF-beta induced overexpression of Type IV collagenase. CONCLUSIONS: These combined observations indicate that (a) endothelial cells exposed to high glucose do not secrete TGF-beta in excess of control cells, (b) there are growth-inhibitory effects o f high glucose that are independent of TGF-beta, and (c) high glucose and TGF-beta exert their effects through distinct pathways and at diff erent loci.