Abstract 17072: Disruption of mTORC2 Integrity Underlies Increased Myocardial Susceptibility to Ischemia/reperfusion Injury in Chronic Renal Failure
Objective: Chronic renal failure (CRF) worsens prognosis after myocardial infarction, but its impact on myocardial injury remains unclear. We recently found that mTORC2, a kinase complex promoting phosphorylation of Akt at Ser473, plays a pivotal role in cardioprotection. Here, we tested the hypothesis that CRF increases myocardial susceptibility to ischemia/reperfusion injury by disrupting mTORC2 activation.
Methods and results: Rats underwent 5/6 nephrectomy (subtotal nephrectomy, SNx) or a sham operation (Sham). Levels of serum creatinine at 4 weeks after the operation were higher in SNx (n=7) than in Sham (n=8) (0.72±0.05 vs. 0.33±0.05 mg/dl, p<0.05), confirming the development of CRF in SNx. Infarct size after 20-min coronary occlusion/2-hr reperfusion was larger in SNx than in Sham (53.2±5.8 vs. 41.1±2.4% of risk area, p<0.05) and was positively correlated with serum creatinine levels (r=0.54, p=0.01), indicating that severity of CRF is a determinant of infarct size. Using separate groups of rats, the effect of CRF on cellular signaling was examined by immunoblotting. Reperfusion-induced phosphorylation of Akt-Ser473 was significantly lower by 32% in SNx than in Sham, with attenuated phosphorylation of p70S6 kinase and GSK3β, downstream substrates of Akt. On the other hand, phosphorylation levels of Jak2, Akt-Thr308, and ERK were comparable between the two groups. Although expression levels of mTORC2 components (mTOR, Rictor, Sin1, and Deptor) and PTEN, a negative regulator of Akt activity, were similar in SNx and Sham, interaction of mTOR and Sin1 determined by immunoprecipitation was 17% less in SNx than in Sham, indicating partial disruption of mTORC2 integrity in CRF. In neonatal cardiomyocytes, mTOR-Sin1 interaction was reduced by treatment with H2O2 (100 μM).
Conclusion: Taken together with previous reports that CRF up-regulates oxidative stress level in the myocardium, the present results suggest that oxidative stress-mediated disruption of mTOC2 integrity, leading to impaired phosphorylation of Akt at Ser473 upon reperfusion, underlies the increased myocardial susceptibility to ischemia/reperfusion injury in CRF.
Author Disclosures: T. Tobisawa: None. T. Yano: None. T. Miki: None. M. Tanno: None. A. Kuno: None. H. Kouzu: None. H. Murase: None. M. Ogasawara: None. S. Muratsubaki: None. M. Mizuno: None. K. Nishizawa: None. S. Ishikawa: None. H. Yoshida: None. T. Miura: None.
- © 2014 by American Heart Association, Inc.