mTOR activates hypoxia-inducible factor-1α and inhibits neuronal apoptosis in the developing rat brain during the early phase after hypoxia–ischemia

Abstract

The mammalian target of rapamycin (mTOR) exerts neuroprotective effects under hypoxic or ischemic conditions. To explore whether mTOR participates in neuroprotective signaling through regulation of hypoxia-inducible factor-1α (HIF-1α), vascular endothelial growth factor (VEGF) and neuronal apoptosis in developing rat brain with hypoxia-ischemia (HI), we operated on postnatal day 10 rats by ligating the common carotid artery followed by exposure to systemic hypoxia. Brains were collected at various intervals to detect the expression of mTOR, phosphorylated mTOR (p-mTOR), HIF-1α, VEGF and cleaved caspase 3 (CC3), using immunohistochemistry and Western blot analysis. We also used terminal deoxynucleotidyl transferase-mediated dUTP-nick end labeling (TUNEL) to detect neuronal apoptosis. The p-mTOR protein expression increased at 2 h after HI, peaked at 8 h, lasted 24 h, and then dropped to the basal level. Also, the expression of HIF-1α and VEGF was significantly enhanced and peaked at 8 h after HI. Up-regulated expression of CC3 was observed at 2 h, peaked at 24 h, and lasted 72 h after HI. Increased neuronal apoptosis is associated with reduced HIF-1α and VEGF expression. Furthermore, pretreatment with rapamycin, a mTOR specific inhibitor, significantly inhibited HIF-1α and VEGF protein after HI. The expression of CC3 and the number of TUNEL-positive cells were up-regulated at 8 h and down-regulated at 24 h after HI in the rapamycin-treated group. Our findings suggest that mTOR may participate in the regulation of HIF-1α, VEGF and neuronal apoptosis, serving neuroprotective functions after HI in developing rat brain.

Hypoxia induces a phase transition within a kinase signaling network in cancer cells

“…Furthermore, our measurements (Fig. 3), and other reports (33), indicate that the HIF-1α expression level can be suppressed by addition of PP242 under hypoxia. Thus, because HIF-1α can repress mTORC1, suppression of HIF-1α could potentially promote mTORC1 activity.…”

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

“…However, little is known about the role of the mTOR signaling pathways that protect the nervous system after EPO treatment in neonates with H/I brain injury. The present study addressed the role of mTOR in neonatal rat models of H/I brain injury to determine the exact mechanisms of EPO-induced neuroprotection [10]. Other signaling pathways that have demonstrated the effectiveness of EPO have primarily focused on gray matter injury in immature rats, whereas the mTOR pathway in the present study is predominantly related to myelin expression [19].…”

“…However, its underlying mechanisms in terms of signal transduction pathways remain largely undescribed, particularly in in vivo neonatal rat models of H/I brain injury [9]. There is increased evidence that mTOR (mammalian target of rapamycin), a Ser/Thr protein kinase, integrates the major signals for cell growth under normal conditions and neuroprotection under H/I conditions in the developing brain [10]. However, we lack the pathophysiological understanding of how EPO treatment is involved in mTOR signaling in developing neurons and oligodendrocytes after perinatal brain injury.…”

Increased phosphorylation of mTOR is involved in remote ischemic preconditioning of hippocampus in mice

“…b r a i n r e s e a r c h 1 5 2 6 ( 2 0 1 3 ) 9 4 -1 0 1 Even in developing rat brain, Chen et al demonstrated that increased p-mTOR following hypoxia, induced hypoxiainducible factor-1α (HIF-1α), vascular endothelial growth factor (VEGF) and decreased neuronal apoptosis. All these protective effects were removed in the presence of rapamycin with decreased mTOR phosphorylation (Chen et al, 2012a(Chen et al, , 2012b.…”