Glial responses, clusterin, and complement in permanent focal cerebral ischemia in the mouse

There is considerable evidence that complement activation occurs within the CNS in inflammatory and degenerative disorders, but little is known about its involvement in the pathophysiology of cerebral ischemia. Our study soug ht to characterize the glial response and the expression of complement fact ors after permanent focal cerebral ischemia in the mouse, using semiquantit ative reverse transcription-polymerase chain reaction (RT-PCR), in situ hyb ridization, and immunohistochemistry. mRNA expression of glial fibrillary a cidic protein (GFAP) increased at day 1 and peaked 3 days after middle cere bral artery (MCA) occlusion in the perifocal area. Immunohistochemical stai ning for GFAP indicated that astroglia were activated the day after MCA occ lusion. Microglial activation, as assessed by lectin-binding experiments, i ncreased by 1 day after MCA occlusion in the perifocal area and peaked at 3 days postocclusion. RT-PCR experiments demonstrated an increased expressio n of clusterin, C1qB, and C4 mRNA in the ischemic cortex, with a peak level at 3 days after MCA occlusion. Clusterin, C1qB, and C4 mRNA were located i n the perifocal area, as assessed by in situ hybridization. Reactive astroc ytes within the cortex medial to the ischemic lesion were found to be stron gly immunoreactive for clusterin. In addition, we observed C1q-positive mac rophage-like cells within the infarcted core at 3 days postocclusion. At 7 days after the onset of ischemia, increased C4 immunostaining was restricte d to perifocal neurons. We conclude that local expression of complement com ponents may contribute to the inflammation observed in this model, thereby representing an important process in secondary injury mechanisms after foca l cerebral ischemia. (C) 2000 Wiley-Liss, Inc.