Role of Estrogen-Related Receptor gamma and PGC-1 alpha/SIRT3 Pathway in Early Brain Injury After Subarachnoid Hemorrhage

Estrogen-related receptors (ERRs) were shown to play an important role in the regulation of free radical-mediated pathology. This study aimed to investigate the neuroprotective effect of ERR gamma activation against early brain injury (EBI) after subarachnoid hemorrhage (SAH) and the potential underlying mechanisms. In a rat model of SAH, the time course of ERRs and SIRT3 and the effects of ERR gamma activation were investigated. ERR gamma agonist DY131, selective inhibitor GSK5182, or SIRT3 selective inhibitor 3-TYP were administered intracerebroventricularly (icv) in the rat model of SAH. The use of 3-TYP was for validating SIRT3 as the downstream signaling of ERR gamma activation. Post-SAH assessments included SAH grade, neurological score, Western blot, Nissl staining, and immunofluorescence staining in rats. In an vitro study, the ERR gamma agonist DY131 and ERR gamma siRNA were administered to primary cortical neurons stimulated by Hb, after which cell viability and neuronal deaths were accessed. Lastly, the brain ERR gamma levels and neuronal death were accessed in SAH patients. We found that brain ERR gamma expressions were significantly increased, but the expression of SIRT3 dramatically decreased after SAH in rats. In the brains of SAH rats, ERR gamma was expressed primarily in neurons, astrocytes, and microglia. The activation of ERR gamma with DY131 significantly improved the short-term and long-term neurological deficits, accompanied by reductions in oxidative stress and neuronal apoptosis at 24 h after SAH in rats. DY131 treatment significantly increased the expressions of PGC-1 alpha, SIRT3, and Bcl-2 while downregulating the expressions of 4-HNE and Bax. ERR gamma antagonist GSK5182 and SIRT3 inhibitor 3-TYP abolished the neuroprotective effects of ERR gamma activation in the SAH rats. An in vitro study showed that Hb stimulation significantly increased intracellular oxidative stress in primary cortical neurons, and DY131 reduced such elevations. Primary cortical neurons transfected with the ERR gamma siRNA exhibited notable apoptosis and abolished the protective effect of DY131. The examination of SAH patients' brain samples revealed increases in ERR gamma expressions and neuronal apoptosis marker CC3. We concluded that ERR gamma activation with DY131 ameliorated oxidative stress and neuronal apoptosis after the experimental SAH. The effects were, at least in part, through the ERR gamma/PGC-1 alpha/SIRT3 signaling pathway. ERR gamma may serve as a novel therapeutic target to ameliorate EBI after SAH.