Protein Kinase B (Akt) and Mitogen-Activated Protein Kinase p38α in Retinal Ischemic Post-Conditioning

Abstract

In previous studies, it was shown that post-conditioning, a transient period of brief ischemia following prolonged severe ischemia in the retina, could provide significant improvement in post-ischemic recovery, attenuation of cell loss, and decreased apoptosis. However, the mechanisms of post-conditioning in the retina have not been elucidated. We hypothesized that two kinases, mitogen-activated protein kinase p38α and protein kinase B (Akt), were involved in the mechanism of post-conditioning. Ischemia was induced in rat retina in vivo. Recovery after ischemia followed by 8 min of post-conditioning early in the reperfusion period after prolonged ischemia was assessed functionally (electroretinography) and histologically at 7 days after ischemia. We examined the role of p38α and Akt subtypes 1–3 in post-conditioning by intravitreal injection of interfering RNA 6 h prior to ischemia and post-conditioning and compared the results to injection of non-silencing interfering RNA sequence. The blockade of p38α significantly decreased the recovery after ischemia and post-conditioning, and enhanced cell loss and disorganization of the retina. Blockade of Akt1, and to a lesser degree, Akt2, significantly decreased the recovery after ischemia and enhanced cell loss and disorganization. These differences in the effects of blockade of Akt subtypes were not explainable by distribution of Akt subtypes in the retina, which were similar. In conclusion, both p38 and Akt are essential components of the neuroprotection induced by post-ischemic conditioning in the retina.

Gene expression in retinal ischemic post-conditioning

“…Given our previously demonstrated essential role of Akt in retinal Post-C [7], it was not surprising that the PI3K-Akt pathway had a large number of differentially regulated genes in ischemia and Post-C. Many of these, such as the growth factors (e.g., Fgf14), the cytokines (e.g., Il6r, Il6), integrins (e.g., Itga4), receptor tyrosine kinase (e.g., Epha2), are involved in binding to cellular receptors and activation of the PI3K and Akt signaling pathways [58].…”

“…Post-C attenuated apoptotic cell death [2]. Also, Post-C required activation of Akt, tied to numerous downstream cell survival mediators [7]. It is likely that multiple signaling pathways and altered gene expression are involved in the neuroprotective mechanism of Post-C.…”

Mesenchymal stem cell-derived extracellular vesicles and retinal ischemia-reperfusion

“…The ERG a-and b-waves were expressed as normalized intensity-response plots with stimulus intensity (log cd s/m 2 ) on the X-axis, and corresponding percent recovery of baseline on the Y-axis, as we previously reported [6,49,50]. Recorded amplitude, time course, and intensity were exported and analyzed in Matlab 2011a (MathWorks, Natick, MA) as previously described [6,[48][49][50]. ERG waveform recovery after ischemia was corrected for day-to-day variation and reference to the non-ischemic eyes as previously described [5,7].…”

Protective effects of remote ischemic conditioning against ischemia/reperfusion-induced retinal injury in rats

“…Several studies have demonstrated that ischemic conditioning protected retinal function and histology from ischemia–reperfusion injury, when applied before experimental retinal ischemia (preconditioning) and after (postconditioning) reperfusion (Fernandez et al, 2009 b ; Dreixler et al, 2011 a , b ). The preconditioning and postconditioning initiate and potentiate endogenous protective mechanisms, which subsequently diminish reperfusion injury through neutralizing ROS (Zhang et al, 2002; Obolensky et al, 2008).…”