Abstract 324: Translation Determines the Acute Cardiac Response to Ischemia/Reperfusion

Abstract

Listen

Translate article

Introduction: Since transcription is a relatively slow process, translation of preexisting mRNA networks might affect cardiac gene expression thereby rapidly adapting the myocardium to stress before changes in transcription take place. The mTOR kinase links nutrient and energy levels to protein synthesis by regulation of mRNA translation. Inhibition of mTOR complex 1, the responsible pathway for translational regulation, protects against reperfusion injury, however the underlying mechanisms are unknown. Through rapid restoration of myocardial energy levels upon reperfusion an mTOR-dependent translatome could adapt early changes in gene expression inducing a maladaptive gene network, independent from transcription, which mediates reperfusion injury. Hypothesis: Reperfusion induces an mTOR-mediated overshooting protein synthesis response that contributes to reperfusion injury by rapidly and selectively translating preexisting mRNAs. Methods and Results: To induce reperfusion injury mice were subjected to 60 minutes of LAD ligation and increasing times of reperfusion. Puromycin incorporation showed an overshooting protein synthesis response of cardiac myocytes upon reperfusion that was especially prevalent in the peri-infarct region. Protein synthesis was induced by increased formation of the eIF4F translation initiation complex through the mTORC1-4EBP1 signaling axis. Cardiac myocyte specific ribosome profiling combined with RNA-seq of hearts 2 days after reperfusion showed that the acute cardiac response to reperfusion was mediated by translation of specific mRNAs encoding proteins which determine early events of reperfusion such as leukocyte infiltration and inflammation. Inhibition of the mTORC1-4EBP1-eIF4F axis attenuated this specific protein synthesis response. Importantly, 4EGI-1, a specific inhibitor of eIF4F complex formation, bypassed off-target effects of previously used mTOR inhibitors and protected cardiac myocytes from cell death upon reperfusion. Conclusions: During reperfusion protein synthesis is strongly induced in the peri-infarct region by mTORC1 and contributes to reperfusion injury by rapidly translating specific mRNAs that mediate the early gene expression response to reperfusion.