Mechanisms by which bradykinin promotes fibrosis in vascular smooth musclecells: role of TGF-beta and MAPK

Accumulation of extracellular matrix (ECM) is a hallmark feature of vascula r disease. We have previously shown that hyperglycemia induces the expressi on of B-2-kinin receptors in vascular smooth muscle cells (VSMC) and that b radykinin (BK) and hyperglycemia synergize to stimulate ECM production. The present study examined the cellular mechanisms through which BK contribute s to VSMC fibrosis. VSMC treated with BK (10(-8) M) for 24 h significantly increased alpha (2) (I) collagen mRNA levels. In addition, BK produced a tw o- to threefold increase in alpha (2) (I) collagen promoter activity in VSM C transfected with a plasmid containing the alpha (2)(I) collagen promoter. Furthermore, treatment of VSMC with BK for 24 h produced a two- to threefo ld increase in the secretion rate of tissue inhibitor of metalloproteinase 1 (TIMP-1). The increase in alpha (2)(I) collagen mRNA levels and alpha (2) (I) collagen promoter activity, as well as TIMP-1 secretion, in response to BK were blocked by anti-transforming growth factor-beta (anti-TGF-beta) ne utralizing antibodies. BK (10(-8) M) increased the endogenous production of TGF-beta1 mRNA and protein levels. Inhibition of the mitogen-activated pro tein kinase (MAPK) pathway by PD-98059 inhibited the increase of alpha (2)( I) collagen promoter activity, TIMP-1 production, and TGF-beta1 protein lev els observed in response to BK. These findings provide the first evidence t hat BK induces collagen type I and TIMP-1 production via autocrine activati on of TGF-beta1 and implicate MAPK pathway as a key player in VSMC fibrosis in response of BK.