Monocyte chemoattractant protein-1 (MCP-1) is a potent chemokine that stimulates the migration of monocytes into the intima of arterial walls. Although many factors that induce MCP-1 expression have been identified, the effect of homocysteine on the expression of MCP-1 in atherogenesis and the underlying mechanisms are not entirely clear. The objective of the present study was to investigate the role of homocysteine in MCP-1 expression in human aorta vascular smooth-muscle cells (VSMCs). After VSMCs were incubated with homocysteine for various time periods, a nuclease protection assay and ELISA were performed. Homocysteine (0.05-0.2 mM) significantly increased the expression of MCP-1 mRNA (up to 2. 7-fold) and protein (up to 3.3-fold) in these cells. The increase in MCP-1 expression was associated with the activation of protein kinase C (PKC) as well as nuclear factor kappaB (NF-kappaB). Further investigation demonstrated that the activation of NF-kappaB was the result of a PKC-mediated reduction in the expression of inhibitory protein (IkappaBalpha) mRNA and protein in homocysteine-treated cells. Oxidative stress might also be involved in the activation of NF-kappaB by homocysteine in VSMCs. In conclusion, the present study has clearly demonstrated that the activation of PKC as well as superoxide production followed by activation of NF-kappaB is responsible for homocysteine-induced MCP-1 expression in VSMCs. These results suggest that homocysteine-stimulated MCP-1 expression via NF-kappaB activation may play an important role in atherogenesis.

Homocysteinemia is an independent risk factor for cardiovascular disorders. The recruitment of monocytes is an important event in atherogenesis. Monocyte chemoattractant protein-1 (MCP-1) is a potent chemokine that stimulates monocyte migration into the intima of arterial walls. The objective of the present study was to investigate the effect of homocysteine on MCP-1 expression in macrophages and the underlying mechanism of such effect. Human monocytic cell (THP-1)-derived macrophages were incubated with homocysteine. By nuclease protection assay and ELISA, homocysteine (0.05-0.2 mM) was shown to significantly enhance the expression of MCP-1 mRNA (up to 2.6-fold) and protein (up to 4.8-fold) in these cells. Homocysteine-induced MCP-1 expression resulted in increased monocyte chemotaxis. The increase in MCP-1 expression was associated with activation of nuclear factor (NF)-kappaB due to increased phosphorylation of the inhibitory protein (IkappaB-alpha) as well as reduced expression of IkappaB-alpha mRNA in homocysteine-treated cells. In conclusion, our results demonstrate that homocysteine, at pathological concentration, stimulates MCP-1 expression in THP-1 macrophages via NF-kappaB activation.

The present study clearly demonstrates that enhanced MCP-1 expression in rat kidney during ischemia/reperfusion injury is mediated by NF-kappaB activation and oxidative stress. Elevated MCP-1 expression might be responsible for increased monocyte infiltration in the injured kidney.

compared with cells treated with PMA alone. Furthertal and Health Sciences Center, University of British Columbia, more, these MEK inhibitor-pretreated cells were still via-Vancouver, British Columbia, V6T 2B5 Canada. ble but showed no process extensions up to 1 week later. Dr. R. L. Stariha and Dr. S. Kikuchi are co-first authors.Therefore, we propose that a threshold level of ERK activ-Abbreviations used: ERK, extracellular signal-regulated protein ity is required for the initiation of OLG process extension. kinase; GaIC, galactocerebroside; MAP2, microtubule-associated Key Words: Extracellular signal-regulated protein kiprotein 2; MAPK, mitogen-activated protein kinase; MBP, myelin nase-Extracellular signal-regulated protein kinase m~~basic protein; MEK, extracellular signal-regulated protein kinase kinase; MS, multiple sclerosis; OLG, oligodendrocyte; PAGE, polyforms-Mitogen-activated protein kinases-Oligodenacrylamide gel electrophoresis; PBS, phosphate-buffered saline; drocytes-Process extension-Protein kinase C activa-PBS~,phosphate-buffered saline containing 5% normal goat serum tion. and 0.2% Triton X-l00; PKC, protein kinase C; PMA, phorbol 12-J. Neurochem. 68, 945-953 (1997). myristate 13-acetate; SDS, sodium dodecyl sulfate. 945 946 R. L STARIHA ET AL

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