Monocyte Chemoattractant Protein–1 Messenger RNA Expression in Rat Ischemic Cortex

Abstract

Previously we demonstrated that focal cerebral ischemia results in an increased expression of several cytokines/chemokines that precede the infiltration of leukocytes into the ischemic cortex after focal stroke induced by occlusion of the middle cerebral artery (MCAO). Monocyte chemoattractant protein-1 (MCP-1) is a potent chemoattractant specific for monocytes. The aim of the present study was to examine whether MCP-1 messenger RNA (mRNA) is expressed in ischemic brain tissue after MCAO. The expression of MCP-1 mRNA in the ischemic cortex was first identified by means of a sensitive reverse transcription and polymerase chain reaction technique. The time course of expression of MCP-1 mRNA in the ischemic and nonischemic cerebral cortex after both permanent MCAO and temporary MCAO (160 minutes) with reperfusion was then examined by means of Northern blot analysis. Almost no expression of MCP-1 mRNA was found in the sham-operated or nonischemic (contralateral) cortex. A significant increase in MCP-1 mRNA expression in the ischemic cortex was observed after either permanent or temporary MCAO. MCP-1 mRNA was elevated at 6 hours (4.4-fold increase over sham; n = 4), reached its highest expression from 12 hours to 2 days (22.7-fold at the peak level; P < .01), and remained elevated up to 5 days (5.6-fold; P < .01) after permanent MCAO. The profile of MCP-1 mRNA expression in the ischemic cortex after MCAO with reperfusion was similar to that of permanent MCAO except that MCP-1 mRNA was increased earlier (ie, 12.5-fold increase at 3 hours; n = 4; P < .01). Also, MCP-1 mRNA expression in the ischemic cortex after permanent MCAO was significantly greater in hypertensive rats than in two normotensive rats (n = 4; P < .05). The demonstration of induced MCP-1 mRNA expression early after focal ischemia suggests that MCP-1 may represent a locally expressed monocyte chemoattractant that plays an important role in monocyte infiltration into ischemic tissue and therefore may contribute to the tissue injury in ischemic stroke. Further studies must concentrate on identifying the induced expression of MCP-1 and its cellular localization in the ischemic brain when the appropriate antibodies become available.