TrkA pathway(s) is involved in regulation of TRPM7 expression in hippocampal neurons subjected to ischemic-reperfusion and oxygen-glucose deprivation.

The transient receptor potential melastatin 7 (TRPM7) is recently revealed playing a key role in anoxic neuronal death. Meanwhile, nerve growth factor (NGF), through activating TrkA pathway, has been widely accepted as a crucial factor for neuronal survival during cerebral ischemia. In this study, middle cerebral artery occlusion (MCAO) for 1h and reperfusion for 5, 10, 20 and 30 h revealed an increasing up-regulation of TRPM7 expression in ipsilateral hippocampus after reperfusion and such a change reached a peak at 20 h, with high expression being maintained up to 30 h. Intracerebroventricular injection of NGF (500 ng) 30 min before MCAO, the expression of TRPM7 at 20 h after reperfusion was significantly reduced, and the effect of NGF was completely abolished by co-injection of TrkA inhibitor K252a. Furthermore, TRPM7 was found residing on hippocampal neuronal body and process, and TrkA was concurrently observed on the cell body by immunofluorescence staining. In agreement with in vivo, pre-incubation of cultured hippocampal neurons with NGF markedly down-regulated TRPM7 high expression at 20 h after oxygen-glucose deprivation (OGD), and this effect could be abrogated by K252a. In addition, when inhibitors wortmannin, U73122 and U0126 were introduced to block phosphatidylinositol-3 kinase (PI-3K), phospholipase C-gamma (PLC-gamma) and ras/mitogen-activated protein kinase (MAPK) pathways, respectively, only PI-3K inhibitor wortmannin substantially abolished NGF effects. These results suggest that TrkA, after being activated by NGF, can prevent up-regulation of TRPM7 expression in hippocampal neurons during reperfusion through PI-3K signal pathway. These findings open a new way for further investigations of the potential roles of TRPM7 and NGF in cerebral ischemia-reperfusion.