The Akt signaling pathway contributes to postconditioning’s protection against stroke; the protection is associated with the MAPK and PKC pathways

Abstract

We previously reported that ischemic postconditioning with a series of mechanical interruptions of reperfusion reduced infarct volume 2 days after focal ischemia in rats. Here, we extend this data by examining long‐term protection and exploring underlying mechanisms involving the Akt, mitogen‐activated protein kinase (MAPK) and protein kinase C (PKC) signaling pathways. Post‐conditioning reduced infarct and improved behavioral function assessed 30 days after stroke. Additionally, postconditioning increased levels of phosphorylated Akt (Ser473) as measured by western blot and Akt activity as measured by an in vitro kinase assay. Inhibiting Akt activity by a phosphoinositide 3‐kinase inhibitor, LY294002, enlarged infarct in postconditioned rats. Postconditioning did not affect protein levels of phosphorylated‐phosphatase and tensin homologue deleted on chromosome 10 or ‐phosphoinositide‐dependent protein kinase‐1 (molecules upstream of Akt) but did inhibit an increase in phosphorylated‐glycogen synthase kinase 3β, an Akt effector. In addition, postconditioning blocked β‐catenin phosphorylation subsequent to glycogen synthase kinase, but had no effect on total or non‐phosphorylated active β‐catenin protein levels. Furthermore, postconditioning inhibited increases in the amount of phosphorylated‐c‐Jun N‐terminal kinase and extracellular signal‐regulated kinase 1/2 in the MAPK pathway. Finally, postconditioning blocked death‐promoting δPKC cleavage and attenuated reduction in phosphorylation of survival‐promoting εPKC. In conclusion, our data suggest that postconditioning provides long‐term protection against stroke in rats. Additionally, we found that Akt activity contributes to postconditioning’s protection; furthermore, increases in εPKC activity, a survival‐promoting pathway, and reductions in MAPK and δPKC activity; two putative death‐promoting pathways correlate with postconditioning’s protection.

Delayed Hypoxic Postconditioning Protects Against Cerebral Ischemia in the Mouse

“…1 To date, early brain ischemic postconditioning has been first reported in focal ischemia, [3][4][5] then delayed postconditioning against focal 6 and in global ischemia. 7 We have previously shown that hypoxic preconditioning (8% O 2 , 1 hour) performed 24 hours before focal cerebral ischemia in adult mice protects the brain.…”

“…The protection has been associated with the activation of the protein kinase Akt. 4,5 Besides ischemic postconditioning, the existence of hypoxic postconditioning has been described in the heart 8 but not in the brain neither in vivo nor in vitro.Therefore, the aim of this study was to search for the existence of hypoxic postconditioning against focal cerebral ischemia in the mouse. We show that a delayed application of chronic intermittent hypoxia after ischemia led to a significant neuroprotection assessed by T2-weighted MRI.…”

“…The protection has been associated with the activation of the protein kinase Akt. 4,5 Besides ischemic postconditioning, the existence of hypoxic postconditioning has been described in the heart 8 but not in the brain neither in vivo nor in vitro.…”

“…Inspired from these studies, the neuroprotective effect of ischemic postconditioning applied immediately after the ischemic insult has been reported in models of focal cerebral ischemia in the rat. [3][4][5] More delayed ischemic postconditioning, starting 6 hours and 24 hours after focal and global cerebral ischemia, respectively, has been also recently described. 6,7 Whereas the molecular mechanisms of cerebral ischemic preconditioning were addressed in many studies, 1 those of postconditioning after focal ischemia were only suggested in a few studies.…”

Akt regulates β-catenin in a rat model of focal cerebral ischemia-reperfusion injury

“…Abundant GSK-3 in the brain is also a negative regulatory factor of signaling cascades, including PI3K/Akt (7). GSK-3β can be deactivated through Akt-mediated phosphorylation at serine 9, which produces antiapoptotic effects (8,9). During GSK-3β phosphorylation, β-catenin dissociates from the anaphase-promoting complex, enters the nucleus and potentiates the transcription of Wnt target genes, thereby promoting cell proliferation and inhibiting apoptosis (10)(11)(12).…”