The Role of PRDM16 in Cardiac Development and Cardiomyopathy

心肌病是儿童发病和死亡的主要原因，近一半的患者在诊断后的头2年内死亡或移植。心肌病是遗传异质性的，编码肉瘤蛋白、细胞骨架蛋白、线粒体蛋白和钙处理蛋白的基因突变与心肌病有关。我们确定了两名儿童患者，转录因子PR结构域16 （PRDM16）从头无义和剪接变异突变，表现为早发性左心室非压实（LVNC），其中一名患者进展为扩张性心肌病（DCM）。此外，小鼠心肌细胞特异性Prdm16缺失导致LVNC和围产期死亡，而杂合小鼠则发生心脏肥大。同样，非义突变的杂合CRISPR敲入也会导致心脏肥厚。为了克服这些小鼠的围产期致死性，并表征PRDM16在成年心肌细胞中的作用，我们还生成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PRDM16敲入小鼠相似，这些小鼠也出现心脏肥大，并随着年龄的增长进展为心功能障碍。我们对来自一个先证和心肌细胞特异性Prdm16 KO小鼠的人类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Prdm16抑制代谢和氧化磷酸化基因，而增加纤维化基因的表达。上述科学前提使我们假设PRDM16在心脏发育、代谢编程和心脏重塑中发挥转录作用，其缺失导致人类和小鼠的LVNC/DCM表型。我们的具体目标是：(1)阐明人类和小鼠中PRDM16突变/缺失导致的心肌病表型的潜在机制；(2)确定PRDM16调节心脏中不同基因程序的转录机制。我们已经组建了一个多学科团队来进行这项高度转化的研究。这项研究新颖且意义重大，因为它表明PRDM16是心脏基因表达的协调者，其在人类和小鼠中的缺失导致LVNC/DCM。确定PRDM16靶点及其在心肌病中的作用是更好地了解LVNC/DCM病因和开发这些异质性疾病治疗方法的关键。

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.