The Neuroprotective Effects of Insulin-Like Growth Factor 1 via the Hippo/YAP Signaling Pathway is Mediated by the PI3K/AKT Pathway Following Cerebral Ischemia-Reperfusion Injury

Abstract

Insulin-like growth factor 1 (IGF-1) exhibits neuroprotective properties, such as vasodilatory and anti-inflammatory effects following ischemic stroke. However, the specific molecular mechanisms of action of IGF-1 following ischemic stroke remain elusive. We wanted to explore whether IGF-1 regulates Hippo/YAP signaling pathway, potentially via activation of the PI3K/AKT signaling pathway to exert its neuroprotective effects following ischemic stroke. In the in vitro study, we used oxygen–glucose deprivation to injure cultured PC12 and SH-5YSY cells, and cortical primary neurons. Cell viability was measured using CCK-8 assay. For the in vivo analyses, Sprague–Dawley rats were subjected to middle cerebral artery occlusion; neurological function was assessed using the neurological deficit score; infarct volume was measured using triphenyltetrazolium chloride staining, and neuronal death and apoptosis was evaluated by TUNEL staining, H&E staining and Nissl staining. Western blot was used to measure the levels of YAP/TAZ, PI3K and phosphorylated AKT (p-AKT) both in vitro and in vivo. We found that IGF-1 induced activation of YAP/TAZ, which resulted in improved cell viability in vitro, and decreased neurological deficits, neuronal death and apoptosis, and cerebral infarct volume in vivo. Notably, the neuroprotective effects of IGF-1 were reversed by an inhibitor of the PI3K/AKT signaling pathway, LY294002, which not only reduced expressions of PI3K and p-AKT, but also down-regulated expression of YAP/TAZ, leading to aggravation of neurological dysfunction. These findings indicate that neuroprotective effect of IGF-1 is partly realized by up-regulation of YAP/TAZ, which is mediated by activation of the PI3K/AKT signaling pathway following cerebral ischemic stroke.