Mechanisms by which bradykinin promotes fibrosis in vascular smooth muscle cells: role of TGF-β and MAPK

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Abstract
Accumulation of extracellular matrix (ECM) is a hallmark feature of vascular disease. We have previously shown that hyperglycemia induces the expression of B2-kinin receptors in vascular smooth muscle cells (VSMC) and that bradykinin (BK) and hyperglycemia synergize to stimulate ECM production. The present study examined the cellular mechanisms through which BK contributes to VSMC fibrosis. VSMC treated with BK (10−8 M) for 24 h significantly increased α2(I) collagen mRNA levels. In addition, BK produced a two- to threefold increase in α2(I) collagen promoter activity in VSMC transfected with a plasmid containing the α2(I) collagen promoter. Furthermore, treatment of VSMC with BK for 24 h produced a two- to threefold increase in the secretion rate of tissue inhibitor of metalloproteinase 1 (TIMP-1). The increase in α2(I) collagen mRNA levels and α2(I) collagen promoter activity, as well as TIMP-1 secretion, in response to BK were blocked by anti-transforming growth factor-β (anti-TGF-β) neutralizing antibodies. BK (10−8 M) increased the endogenous production of TGF-β1 mRNA and protein levels. Inhibition of the mitogen-activated protein kinase (MAPK) pathway by PD-98059 inhibited the increase of α2(I) collagen promoter activity, TIMP-1 production, and TGF-β1 protein levels observed in response to BK. These findings provide the first evidence that BK induces collagen type I and TIMP-1 production via autocrine activation of TGF-β1 and implicate MAPK pathway as a key player in VSMC fibrosis in response of BK.

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