Cardiac-specific overexpression of HIF-1α during acute myocardial infarction ameliorates cardiomyocyte apoptosis via differential regulation of hypoxia-inducible pro-apoptotic and anti-oxidative genes

HIF-1α acts as the cellular rheostat for oxygen sensing in cardiomyocytes. Overexpression of HIF-1α in the heart during acute myocardial infarction (MI) is known to attenuate cardiac dysfunction by upregulating pro-angiogenic HIF-1α target genes. However, the effect of HIF-1α overexpression on hypoxic cardiomyocyte apoptosis still remains obscure. In this study, we report for the first time that myocardium-targeted nanotized HIF-1α overexpression during MI downregulates cardiomyocyte apoptosis. HIF-1α overexpression attenuates bnip3-mediated apoptosis indirectly by promoting HO-1-induced anti-oxidant response. Chromatin immunoprecipitation experiment revealed that HIF-1α overexpression in hypoxic cardiomyocytes increases binding of HIF-1α to the hypoxia-responsive element in the promoter of its target anti-oxidant gene ho-1 which is known to attenuate ROS accumulation. ROS accumulation in hypoxic cardiomyocytes causes cysteine oxidation of the DNA-binding p50 subunit of NFκB, which hampers NFκB binding to κB-responsive genes like bnip3. Downregulated oxidative stress due to HIF-1α overexpression leads to decline in cysteine oxidation of NFκBp50, causing NFκB to bind to the promoter of bnip3 as a transcriptional repressor. Therefore HIF-1α overexpression-mediated attenuation of cardiomyocyte apoptosis occurs by transcriptional repression of bnip3 by NFκB. Our study thus reveals that downregulation of bnip3-mediated cardiomyocyte apoptosis occurs via ho-1 upregulation upon HIF-1α overexpression during MI, despite both being HIF-1α target genes. The cross-regulation of HIF-1α and NFκB-mediated pathways effectively downregulates apoptosis due to HIF-1α overexpression during MI, which can be exploited for possible therapeutic intervention.