Abstract 14048: The Functional Crosstalk Between YAP and FoxO1 in Mediating the Oxidative Stress Response During Ischemia/Reperfusion in the Heart
Lats2, a serine/threonine kinase and a component of the Hippo pathway, plays an important role in mediating myocardial cell death in response to ischemia/reperfusion (I/R) by negatively regulating YAP, a transcription co-factor. Forkhead box protein O1 (FoxO1) upregulates antioxidant genes, including catalase and MnSOD, thereby protecting cardiomyocytes (CMs). In CMs, endogenous YAP physically interacts with FoxO1 in the nucleus, as indicated by in situ proximity ligation assays and co-immunoprecipitation assays. Luciferase reporter assays revealed that YAP dose-dependently activates FoxO1-mediated transcription. Overexpression of Lats2, known to phosphorylate YAP at Ser127 and induce its nuclear exit, significantly inhibited (-70%, p<0.05) FoxO1 transcriptional activity in CMs. Chromatin immunoprecipitation assays showed that endogenous YAP binds to the FoxO1 binding motifs in the promoter regions of catalase and MnSOD, but Lats2 overexpression significantly reduced YAP binding to these sites (catalase: -70%, p<0.05; MnSOD: -60%, p<0.05). Quantitative PCR showed that mRNA levels of both catalase (-45%, p<0.05) and MnSOD (-50%, p<0.05) are decreased by Lats2 overexpression. These data indicate that Lats2 activation suppresses the YAP-FoxO1 complex and decreases antioxidant protein expression in vitro. I/R strongly induced phosphorylation of YAP at Ser127 in control non-transgenic (NTg) mice but not in transgenic mice (Tg) with cardiac specific expression of dominant negative Lats2, suggesting that endogenous Lats2 mediates Ser127 phosphorylation and inactivation of YAP in response to I/R. Catalase and MnSOD protein levels were significantly decreased by I/R in NTg mice (-48% and -63%, p<0.05) but not in Tg mice. The antioxidant capacity of the heart homogenate after I/R was dramatically decreased in NTg mice (-42%, p<0.05) but not in Tg mice. The myocardial infarct size/area at risk (19% and 49%, p<0.01) and the number of TUNEL positive cells (0.04% and 0.11%, p<0.05) were significantly lower in Tg than in NTg mice after I/R. These data suggest that activation of the Hippo pathway suppresses FoxO1 activity through a YAP-dependent mechanism and enhances myocardial damage by downregulating antioxidant protein expression in the heart.
- © 2013 by American Heart Association, Inc.