Hypoxia activates beta(1)-integrin via ERK 1/2 and p38 MAP kinase in human vascular smooth muscle cells.

Hypoxia plays an important role in vascular remodeling and directly affects vascular smooth muscle cell (VSMC) functions. VSMC adhesion participates in changes of vascular structure; however, little is known about VSMC adhesion under hypoxic conditions. It was the aim of the present study to investigate the effects of hypoxia on adhesion mechanisms in human VSMCs. Compared to normoxic cells, hypoxia (1% O(2), 24h) significantly increased adhesion of VSMCs to collagen I by 30.2% and fibronectin by 58.0%. This effect was completely inhibited in the presence of the pharmacological ERK 1/2 mitogen-activated protein kinase (MAPK) pathway inhibitor PD98059 (30 microM) or the p38 MAPK inhibitor SB203580 (1 microM). Basal adhesion of normoxic cells was not affected by pretreatment with PD98059 and SB203580. Hypoxia induced a time-dependent activation of ERK 1/2 and p38 MAPK activation in human VSMCs, which were completely abolished by PD98059 or SB203580, respectively. Since adhesion of VSMCs to fibronectin and collagen I involves beta(1)-integrin receptors, we used a blocking antibody against beta(1)-integrin (P5D2) to examine potential effects of hypoxia on beta(1)-integrins. P5D2 significantly reduced VSMC adhesion to fibronectin and collagen I in normoxia and hypoxia in a comparable manner; however, beta(1)-integrin protein or mRNA levels were not affected by hypoxia. As evidenced by flow cytometry, hypoxia induced a activation of beta(1)-integrins by exposing an conformationally sensitive epitope on the beta(1)-subunit. These results demonstrate that hypoxia enhances adhesion of VSMC on extracellular matrix proteins by activating beta(1)-integrin.