Genetic deletion of p66Shc adaptor protein leads to increased myocardial infarction by inhibiting RISK and SAFE prosurvival pathways

Abstract

Background: Formation of reactive oxygen species (ROS) contributes to many pathophysiological processes. Although ROS production is also involved in some physiological processes, the imbalance between their generation and removal, i.e. oxidative stress, plays a major role in particular in myocardial injury caused by ischemia-reperfusion (I/R). The mammalian Shc locus encodes three Shc isoforms: p46Shc, p52Shc and p66Shc. The p66Shc is not involved in mitogenic signals as p46Shc/p52Shc, but it functions as a critical mediator of intracellular oxidative signal transduction. Various studies relate p66Shc to cardiovascular disease; however, few data are available on the role of p66Shc in myocardial I/R. Methods and results: 8-12-week-old male p66Shc deficient (p66Shc-/-) mice and corresponding C57Bl/6 wild-type (WT) control mice were subjected in vivo to different durations of ischemia (30, 45 and 60 min) followed by 24h of reperfusion. Infarct size was assessed morphologically and by MRI. After 30 min of ischemia, p66Shc-/- mice developed markedly larger infarcts as compared to WT (infarct size [I]/area at risk [AAR]: 20.46±5.02% vs. 7.72±1.31%, n=12-14, p < 0.05). This effect was confirmed by in vivo silencing of p66Shc prior to I/R. Both genetic deletion and silencing of p66Shc displayed an increased post-ischemic levels of serum cardiac troponin I (cTnI). However, the observed effect on infarct size was limited to 30 min of ischemia since by increasing ischemia duration to either 45 or 60 min infarct size did no longer differ between p66Shc-/- and WT mice. Moreover, differently from WT, infarct size in p66Shc-/- was not significantly larger with increasing duration of ischemia (from 30 to 60 min). On the molecular level the observed effect was linked to the inhibition of activation by phosphorylation of protein kinase Akt and transcription factor STAT3 – two key members of prosurvival pathways RISK and SAFE, respectively. Conclusions: Our data suggest that genetic deletion of p66Shc leads to an increased sensitivity to myocardial infarction with larger infarcts with shorter, but not prolonged ischemia, and that RISK and SAFE prosurvival pathways are involved. Therefore, activation of p66Shc may provide resistance to ischemia and represent a novel therapeutic target in the early phase of myocardial infarction.