Abstract 16552: Cardiac Deletion of WW45 Abrogates the Deleterious Effects of Mst1 Activation During Ischemia/Reperfusion Through YAP Activation
Mammalian sterile 20-like kinase 1 (Mst1) is a serine/threonine kinase that plays a key role in mediating cardiomyocyte (CM) death during ischemia/reperfusion (I/R). The molecular mechanism by which Mst1 is activated during I/R is not fully understood. In Drosophila, the adaptor protein Salvador is required for activation of Hippo, a homolog of Mst1. We investigated whether the mammalian homolog of Salvador, WW45, is required for the Mst1-dependent myocardial injury during I/R. Mice with cardiac specific WW45 knockout (W-cKO) showed normal cardiac function at 2 months of age. After I/R (30 min/24 h), W-cKO exhibited a significantly smaller infarct size/area at risk (20.4 ± 6.0 vs. 38.2 ± 4.5%; p<0.05) and fewer TUNEL-positive cells (0.53 ± 0.04 fold, p<0.05) than control (CT) mice. WW45 physically interacts with Mst1 in CMs, and W-cKO showed reduced Mst1 phosphorylation (Thr183)/activation after I/R (0.5 fold, p<0.05), indicating that WW45 is required for Mst1 activation. Transgenic mice with cardiac-specific Mst1-overexpression (Tg-Mst1) exhibited larger infarcts than CT after I/R (60.6 ± 3.0 vs. 39.2 ± 5.4%, p<0.05), but Tg-Mst1 crossed with W-cKO exhibited significantly smaller infarcts than Tg-Mst1 (31.3 ± 2.6%, p<0.05), indicating that WW45 is also required for Mst1-induced enhancement of ischemic injury. Mechanistically, YAP, a transcription co-factor which promotes cellular survival and is exported from the nucleus and degraded upon Mst1 signaling-mediated-phosphorylation (Ser127), was down-regulated in the CT heart after I/R (-39%, p<0.05), an effect consistent with Mst1 activation. In contrast, W-cKO exhibited significant upregulation (4.2 fold, p<0.05), reduced phosphorylation (-75%, p<0.05) and increased nuclear localization of YAP, suggesting that YAP activation might mediate the cardioprotective effect of WW45 deletion during I/R. In support of this hypothesis, we observed that adenoviral-mediated overexpression of YAP in CMs significantly reduced CM death after 12 h hypoxia/24 h reoxygenation in vitro (24.0 ± 0.01% vs. 47.3 ± 0.01, p<0.001). In conclusion, endogenous WW45 is required for the activation and function of Mst1, the inactivation of YAP, and the consequent promotion of myocardial damage during I/R.
- © 2012 by American Heart Association, Inc.