Expressions of neuropilin-1, neuropilin-2 and semaphorin 3A mRNA in the rat brain after middle cerebral artery occlusion

H Fujita, B Zhang, K Sato, J Tanaka, M Sakanaka
Brain Research 2001 September 28, 914 (1): 1-14
This study investigated the spatial and temporal expressions of mRNA encoding neuropilin (Npn)-1, Npn-2 and semaphorin3A (Sema3A) in the rat brain after occlusion of the middle cerebral artery (MAC) distal to the striate branches. The expression of Npn-1 mRNA was transiently upregulated in layers V and VI of the parietal cortex not entering infarction on the lesion side from 3 to 6 h after MCA occlusion. The transient up-regulation of Npn-1 mRNA expression was presumably accompanied by an increase in Npn-1 protein as shown by immunohistochemistry in combination with in situ hybridization histochemistry. Intense Npn-2 mRNA expression was noted temporarily in layer II of the parietal cortex on the lesion side from 1 to 6 h after MCA occlusion. The expression of Sema3A mRNA was upregulated in layer VI of the non-infarcted parietal cortex on the lesion side at 6 h after MCA occlusion. The above increases in mRNA expression were no longer observed at 12 h after MCA occlusion. The expressions of Npn-1, -2 and Sema3A mRNA were not detected in the ventroposterior thalamic nucleus undergoing secondary degeneration after MCA occlusion. In the infarct lesion or ischemic core, neuronal expressions of Npn-1, -2 and Sema3A disappeared by 3 days after MCA occlusion as the neurons in situ entered apoptosis or necrosis. In contrast, ED-1-positive microglia/macrophages with Npn-1 and Npn-2 mRNA were observed in the infarct lesion at 1 week after MCA occlusion. These findings suggest that the temporal up-regulation of Npn-1 and Sema 3A mRNA expressions in the non-infarcted parietal cortex on the lesion side is insufficient to induce neuronal cell death possibly because the up-regulated mRNA molecules are not fully translated and that the overexpression of Npn-1 and/or Npn-2 in the ischemic core with degenerating neurons enables activated microglial cells to contact the damaged neurons in situ for phagocytosis.

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