The Role of PRDM16 in Cardiac Development and Cardiomyopathy

心肌病是儿童发病率和死亡率的主要原因，在诊断的前2年内，近一半的患者发生死亡或移植。心肌病是遗传异质性的，编码肌节蛋白、细胞骨架蛋白、线粒体蛋白和钙处理蛋白的基因突变与该疾病相关。我们确定了2例转录因子PR结构域16（PRDM 16）中存在新发无义突变和剪接变异突变的儿科患者，其中1例患者表现为早发性左心室致密化不全（LVNC），并进展为扩张型心肌病（DCM）。此外，Prdm 16在小鼠中的心肌细胞特异性损失导致LVNC和围产期死亡，而杂合子小鼠发展为心脏肥大。类似地，无义突变的杂合CRISPR敲入也发生了心脏肥大。为了克服这些小鼠的围产期致死性并表征PRDM 16在成年心脏细胞中的作用，我们还产生了心肌细胞特异性他莫昔芬诱导缺失该基因的小鼠，并表明，与种系杂合小鼠和Prdm 16敲入小鼠相似，这些小鼠也发生了心脏肥大，随着年龄的增长进展为心功能障碍。我们对来自一个先证者和心肌细胞特异性Prdm 16 KO小鼠的人诱导多能干细胞衍生的心肌细胞的初步表征揭示了该转录因子在基因转录中的双重作用。缺乏Prdm 16抑制代谢和氧化磷酸化基因，而它增加了纤维化基因的表达。上述科学前提使我们假设PRDM 16发挥与心脏发育、代谢编程和心脏重塑相关的转录作用，并且其缺失导致人类和小鼠中的LVNC/DCM表型。我们的具体目标是：（1）阐明人类和小鼠中PRDM 16突变/缺失导致的心肌病表型的潜在机制，以及（2）鉴定PRDM 16调节心脏中不同基因程序的转录机制。我们组建了一个多学科团队来进行这项高度转化的研究。这项研究是新颖的和高度重要的，因为它表明PRDM 16是心脏中基因表达的协调者，并且它在人类和小鼠中的缺失导致LVNC/DCM。识别PRDM 16靶标及其在心肌病中的参与是更好地理解LVNC/DCM病因学和开发这些异质性疾病的治疗方法的关键。

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.