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 offsetting 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.

Warming Up to New Possibilities with the Capsaicin Receptor TRPV1: mTOR, AMPK, and Erythropoietin

“…Critical to mTOR signaling are AMP activated protein kinase (AMPK) (15, 35, 36) and protein kinase B (Akt) (11, 23, 37). AMPK can govern cellular metabolism, cell survival, and inflammation (25, 38–41).…”

“…Both Akt and phosphoinositide 3-kinase (PI 3-K) also have a vital role in the mTOR signaling pathway (15, 37, 48–50). mTOR contains terminal domains that oversee the binding, catalytic activity, and phosphorylation of mTOR (51).…”

“…EPO can phosphorylate Akt at serine 473 to activate Akt (37, 64, 87, 88). EPO signaling through Akt activation has been shown to protect against hypoxia-reoxygenation stress (79) and EPO may control intracellular calcium levels to preserve mitochondrial function (31, 67, 89–91).…”

Erythropoietin and mTOR: A “One-Two Punch” for Aging-Related Disorders Accompanied by Enhanced Life Expectancy

“…In addition to AMPK, phosphoinositide 3-kinase (PI 3-K) and Akt also play significant roles in the mTOR signaling pathway (9, 21, 85). The terminal domains of mTOR oversee the catalytic activity, binding, and phosphorylation of mTOR (90).…”

“…Growth factors are advocated for the treatment of both acute and chronic disorders (71, 195–199). In particular, the growth factor EPO is considered to offer an exciting therapeutic strategy for the treatment of disorders that result in cell injury and cell death especially since it is intimately involved with mTOR signaling (Table 1) (85, 200–207). EPO has the capacity to offer protection against a number of disease entities (208–212) as well as enhanced biological activity (213, 214).…”