Abstract P289: Cardiomyocyte-Specific, but Not Systemic, Rassf1A Deletion Is Protective Against Ischemia-Reperfusion Injury in the Heart

Abstract

Our previous work demonstrated Rassf1A to be a critical mediator of Mst1 activation, the chief component of the mammalian Hippo pathway, in heart failure. In the setting of ischemia/reperfusion (I/R) injury, Mst1 is robustly activated in the heart; however, its regulation remains unclear. Further, the role of Rassf1A in I/R injury has not been investigated. Using genetically modified mice in which expression of Rassf1A is altered in a cell type-specific manner, we demonstrate that systemic deletion of rassf1a (KO) does not alter infarct size (36±4% vs 33±3%) or cardiac myocyte apoptosis (1.7±0.2% vs 2.1±0.4%) following I/R versus WT. Conversely, mice harboring deletion of rassf1a in cardiac myocytes (CKO) have smaller infarcts (38±3% vs 23±2%, p<0.05) and less apoptosis (2.0±0.2% vs 0.9±0.2%) after I/R. Importantly, attenuation of Mst1 activation in ventricular homogenates was observed in both deletion models, implicating Rassf1A as a positive regulator of Mst1 during I/R. Langendorff global I/R injury yielded similar results - no protection in KO, yet significant protection in CKO hearts versus control mice, suggesting that native cardiac cells are sufficient to mediate this response. A candidate molecule screen found exaggerated TNF-α expression in KO hearts compared to WT (4.8±0.7% vs 1.0±0.3%), whereas TNF-α expression was attenuated in CKO hearts (0.9±0.2% vs 0.3±0.1%). Finally, WT and KO mice were administered TNF-α neutralizing or control IgG and subjected to I/R. KO hearts treated with TNF-α Ab, but not IgG, had reduced infarcts (19±4% vs 34±5%), but no significant reduction in infarct size was observed in WT mice given TNF-α Ab. Taken together these data suggest that TNF-α blockade prevents the deleterious consequences of Rassf1A deletion in non-myocytes while unmasking the protective effect of Rassf1A deletion in cardiac myocytes following I/R. Further, these results demonstrate the importance of non-myocytes in modulating cardiac myocyte survival and I/R injury.