Cyclic strain stimulates monocyte chemotactic protein-1 mRNA expression in smooth muscle cells

Hemodynamic forces are important determinants for the formation of atherosclerotic plaques. The recruitment of circulating monocytes into the arterial wall is an important step during atherogenesis. Monocyte chemotactic protein-1 (MCP-1) has been shown to be a key factor for monocyte transmigration. This study examined the effects of cyclic strain on MCP-1 mRNA expression levels of cultured rat aortic smooth muscle cells. The MCP-1 mRNA levels of aortic smooth muscle cells first increased as the duration of cyclic strain increased, reaching the maximum at 6-12 h, maintained at high levels throughout the 48-h strain period. To explore signaling pathways mediating cyclic strain-stimulated MCP-1 mRNA expression, we examined the involvement of tyrosine kinase and protein kinase C (PKC). Tyrosine kinase inhibitors, genistein and tyrphostin 51, at 50 mu M blocked cyclic strain-stimulated MCP-1 mRNA expression. Preincubation with a PKC activator, phorbol 12-myristate 13-acetate (PMA), 2 mu M, for 24 h to downregulate PKC did not decrease cyclic strain-induced MCP-1 mRNA expression. A 6-h incubation with 0.1 mu M PMA to activate PKC, which stimulated MCP-1 expression when applied alone, abolished the stimulatory effects of cyclic strain. A specific PKC inhibitor, calphostin C (0.1 CIM), diminished cyclic strain-stimulated MCP-1 mRNA expression. Angiotensin II at 10 or 1,000 nM induced a moderate upregulation of MCP-1 mRNA, and no synergistic effects were observed between angiotensin II and cyclic strain. These results indicate that cyclic strain stimulates MCP-1 mRNA expression in smooth muscle cells through signaling pathway(s) mediated by tyrosine kinase activation. (C) 1999 Wiley-Liss, Inc.