Impact of the cardiomyocyte transcription factor GATA4 for cardiac regeneration

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Myocardial infarction (MI) is one of the main reasons for mortality in Germany. Because of improved outcome in the acute event, the prevalence of heart failure as long-term sequel of MI is currently rising. This is mainly due to the defective regeneration capacity of the adult mammalian myocardium, which leads to scar formation after cardiomyocyte demise rather than the restitution of functional muscle tissue. It was recently demonstrated that newborn mice, in contrast to adult mice, can completely regenerate the myocardium after myocardial apex resection or (cryo)-infarction. This enables examination of regenerative mechanisms in the mammalian myocardium right after birth as well as the identification of reasons for defective regeneration in the adult heart. Genes or regulatory RNAs identified to promote regeneration in the neonatal heart could potentially be used as therapy to improve cardiac regeneration after MI in patients in the future. In preliminary work for this proposal we found that cardiac expression of the cardiomyocyte transcription factor GATA4 is very high at birth, but sharply declines starting at postnatal day 7, when also the regenerative capacity of the myocardium becomes strongly diminished. Because GATA4 promotes cardiomyocyte proliferation during embryonic development, we hypothesize that it might support myocardial regeneration after injury. Therefore, we will analyze heart regeneration after cardiac cryoinjury in neonatal cardiomyocyte specific GATA4 knock-out (GATA4-CKO) and control mice. We will probe the size of the myocardial scar, cardiomyocyte proliferation and hypertrophy, angiogenesis, cardiac inflammation as well as the cardiac transcriptome (by deep-sequencing) at multiple time-points after the induction of injury in both groups of mice. First results revealed a significantly larger scar and reduced cardiomyocyte proliferation in GATA4-CKO mice 7 days after myocardial cryoinjury. In the deep-sequencing analysis, we aim to identify previously unknown GATA4 dependent factors that promote myocardial regeneration. The regenerative potency of identified candidate genes will be examined in cardiac explant culture as well as in isolated fetal and neonatal cardiomyocytes. In addition, we will use adenoviral and AAV9 vectors to overexpress GATA4 in the heart of 7 day old as well as adult wild-type mice, in which endogenous GATA4 expression is dramatically downregulated and will analyze whether this treatment can improve myocardial regeneration. In a similar manner, we aim to overexpress select candidate genes and determine their regenerative potential after cardiac cryoinjury.