The Akt/mTOR/p70S6K Pathway Is Involved in the Neuroprotective Effect of Erythropoietin on Hypoxic/Ischemic Brain Injury in a Neonatal Rat Model

Abstract

Background: The mTOR (mammalian target of rapamycin) signaling pathway is a master regulator of cell growth and proliferation in the nervous system. However, the effects of erythropoietin (EPO) treatment on the mTOR signaling pathway have not been elucidated in neonates with hypoxic/ischemic (H/I) brain injury. Objectives: We investigated the mechanism underlying the neuroprotective effect of EPO by analyzing the mTOR signaling pathway after H/I injury in a neonatal rat model. Methods: Seven-day-old rats were subjected to left carotid artery ligation and hypoxic exposure (8%) for 90 min (H/I). EPO at a dose of either 3,000 U/kg or a vehicle (V) was administered by intraperitoneal injection 0, 24 and 48 h after H/I. At 72 h after H/I (postnatal day 10), 2,3,5-triphenyltetrazolium chloride staining, myelin basic protein (MBP) immunofluorescence staining and Western blot analysis of the Akt/mTOR/p70S6K pathway were performed. Neuromotor behavioral tests included Rotarod challenge and cylinder rearing test 1 performed 3 and 6 weeks after H/I. Results: EPO treatment resulted in significant off-setting of MBP depletion ipsilateral (p = 0.001) and contralateral (p = 0.003) to ligation. Western blot analysis showed that the relative immunoreactivity of phosphorylated (p)-Akt, p-mTOR and p-p70S6K ipsilateral to ligation was significantly decreased in the H/I+V group compared with the sham-operated groups. However, EPO treatment significantly upregulated Akt/mTOR/p70S6K signals ipsilateral to ligation compared to the H/I+V group. The behavior tests showed that EPO attenuates long-term impairment in Rotarod challenge and cylinder test performance from 3-6 weeks. Conclusion: This study demonstrates an underlying mechanism of the mTOR signaling pathway after EPO treatment, which is a potential target for treating H/I-induced brain injury.