The Role of PRDM16 in Cardiac Development and Cardiomyopathy

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Cardiomyopathies are the major cause of morbidity and mortality in children, with death or transplant occurring in nearly half the patients within the first 2 years of diagnosis. Cardiomyopathies are genetically heterogeneous and mutations in genes encoding sarcomeric, cytoskeletal, mitochondrial, and calcium-handling proteins have been associated with the disease. We identified two pediatric patients with de novo non-sense and splice variant mutations in the transcription factor PR domain 16 (PRDM16) presenting with early onset left ventricular non-compaction (LVNC) that progressed to dilated cardiomyopathy (DCM) in one patient. Furthermore, cardiomyocytes-specific loss of Prdm16 in mice causes LVNC and perinatal lethality while heterozygous mice develop cardiac hypertrophy. Similarly, heterozygous CRISPR knock-in of the non-sense mutation also developed cardiac hypertrophy. To overcome the perinatal lethality in these mice and to characterize the role of PRDM16 in adult cardiac cells, we also generated mice with cardiomyocytes-specific tamoxifen inducible deletion of this gene and show that, similar to the germline heterozygous mice and the Prdm16 knock-in mice, these mice also developed cardiac hypertrophy that progressed into cardiac dysfunction with age. Our preliminary characterization of human induced pluripotent stem cell-derived cardiomyocytes from one proband and cardiomyocytes-specific Prdm16 KO mice reveal a dual role for this transcription factor in gene transcription. Lack of Prdm16 repressed metabolic and oxidative phosphorylation genes whereas it increased fibrotic gene expression. The forgoing scientific premise leads us to hypothesize that PRDM16 plays transcriptional roles pertinent to heart development, metabolic programing and cardiac remodeling and its loss results in LVNC/DCM phenotypes in humans and mice. Our specific aims are: (1) to elucidate the mechanisms underlying cardiomyopathy phenotypes consequent to PRDM16 mutations/deletion in humans and mice and (2) to identify transcriptional mechanisms by which PRDM16 regulates different gene programs in the heart. We have assembled a multidisciplinary team to conduct this highly translational research. This study is novel and highly significant as it shows that PRDM16 is an orchestrator of gene expression in the heart and that its loss in humans and in mice causes LVNC/DCM. Identifying PRDM16 targets and their involvement in cardiomyopathies is key towards a better understanding of the etiology of LVNC/DCM and for the development of therapies for these heterogeneous diseases.