Activation of Galanin Receptor 1 with M617 Attenuates Neuronal Apoptosis via ERK/GSK-3β/TIP60 Pathway After Subarachnoid Hemorrhage in Rats

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Subarachnoid hemorrhage (SAH) is a devastating cerebrovascular disease. Neuronal apoptosis plays an important pathological role in early brain injury after SAH. Galanin receptor 1 (GalR1) activation was recently shown to be anti-apoptotic in the setting of ischemic stroke. This study aimed to explore the anti-neuronal apoptosis effect of GalR1 activation after SAH, as well as the underlying mechanisms. GalR1 CRISPR and GalR1 selective agonist, M617, was administered, respectively. Extracellular-signal-regulated kinase (ERK) inhibitor (U0126) and glycogen synthase kinase 3-beta (GSK3-β) CRISPR were administered to investigate the involvement of the ERK/GSK3-β pathway in GalR1-mediated neuroprotection after SAH. Outcome assessments included neurobehavioral tests, western blot, and immunohistochemistry. The results showed that endogenous ligand galanin (Gal) and GalR1 were markedly increased in the ipsilateral brain hemisphere at 12 h and 24 h after SAH. GalR1 were expressed mainly in neurons, but expression was also observed in some astrocytes and microglia. GalR1 CRISPR knockdown exacerbated neurological deficits and neuronal apoptosis 24 h after SAH. Moreover, activation of GalR1 with M617 significantly improved short- and long-term neurological deficits but decreased neuronal apoptosis after SAH. Furthermore, GalR1 activation dysregulated the protein levels of phosphorylated ERK and GSK-3β, but downregulated the phosphorylated Tat-interactive protein 60 (TIP60) and cleaved caspase-3 at 24 h after SAH. GalR1 CRISPR, U0126, and GSK-3β CRISPR abolished the beneficial effects of GalR1 activation at 24 h after SAH in rats. Collectively, the present study demonstrated that activation of GalR1 using M617 attenuated neuronal apoptosis through the ERK/GSK-3β/TIP60 pathway after SAH in rats. GalR1 may serve as a promising therapeutic target for SAH patients.