Insulin-like growth factor-1 secreted by brain microvascular endothelial cells attenuates neuron injury upon ischemia

Insulin-like growth factor (IGF)-1 is essential for the development of the nervous system, and is present in many cell types. Relatively little is known about IGF-1 expression in brain microvascular endothelial cells (BMECs). For in vivo studies, we examined the expression of IGF-1 and insulin-like growth factor-binding protein (IGFBP)-2 after focal cerebral ischemia for 12 h, 24 h, 3 days and 7 days, utilizing a permanent middle cerebral artery occlusion (MCAO) model in rats. For in vitro studies, we examined the levels of IGF-1 and IGFBP-2 in the culture medium or primary culture of BMECs injured by oxygen-glucose deprivation (OGD). Then, we elucidated the protective effects of IGF-1 on cortical neurons injured by OGD and the possible mechanism. In addition, we investigated the effect of BMEC-conditioned medium on IGF-1 receptor expression in neurons. The results showed that IGF-1 expression increased in serum and brain tissue, whereas IGFBP-2 expression decreased in brain tissue of MCAO-injured rats. In primary culture of BMECs, the expression levels of IGF-1 and IGFBP-2 were significantly higher under OGD conditions in culture. IGF-1 administration improved neuron viability upon normoxia or OGD, and upregulated p-Akt expression. This effect was reversed by LY294002, a specific inhibitor of the phosphoinositide 3-kinase-Akt signaling pathway. Furthermore, conditioned medium from OGD-treated BMECs substantially suppressed neuron viability and the expression of IGF-1 receptor simultaneously. These data demonstrate that therapeutic strategies that prioritize the early recovery of the IGF-1 system in BMECs might be promising in ischemic injury.