Mechanical Strain Induces Monocyte Chemotactic Protein-1 Gene Expression in Endothelial Cells

Abstract

Monocyte chemotactic protein-1 (MCP-1), a potent monocyte chemoattractant secreted by endothelial cells (ECs), is believed to play a key role in the early events of atherogenesis. Since vascular ECs are constantly subjected to mechanical stresses, we examined how cyclic strain affects the expression of the MCP-1 gene in human ECs grown on a flexible membrane base deformed by sinusoidal negative pressure (peak level, −16 kPa at 60 cycles per minute). Northern blot analysis demonstrated that the MCP-1 mRNA levels in ECs subjected to strain for 1, 5, or 24 hours were double those in control ECs (P<.05). This strain-induced increase was mainly serum independent, and MCP-1 mRNA level returned to its control basal level 3 hours after release of strain. Culture media from strained ECs contained approximately twice the MCP-1 concentration and more than twice the monocyte chemotactic activity of media from control ECs (P<.05). Pretreatment of collected media with anti–MCP-1 antibody suppressed such activity. Monocyte adhesion to ECs subjected to strain for 12 hours was 1.8-fold greater than adhesion to unstrained control ECs (P<.05). A protein kinase C inhibitor, calphostin C, abolished the strain-induced MCP-1 gene expression. In addition, cAMP- or cGMP-dependent protein kinase inhibitors (KT5720 and KT5823, respectively) partially inhibited such expression. Pretreatment with EGTA or the intracellular Ca²⁺ chelator BAPTA/AM strongly suppressed the strain-induced MCP-1 mRNA. Verapamil, a Ca²⁺ channel blocker, greatly reduced MCP-1 mRNA levels in both strained and unstrained ECs. These results indicate that mechanical strain can stimulate monocyte chemotaxis and adhesion by increasing MCP-1 gene expression in ECs. This increased gene expression is predominantly mediated via the protein kinase C pathway and requires Ca²⁺ influx. Such strain-induced MCP-1 expression might contribute to the trapping of monocytes in the subendothelial space. Strain-induced gene expression might provide a molecular mechanism for the role of hypertension in atherogenesis.