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，近一半的患者在确诊后的头两年内死亡或移植。心肌病在遗传上是异质性的，编码肌节、细胞骨架、线粒体和钙处理蛋白的基因突变与这种疾病有关。我们发现两名儿童患者在转录因子PR区域16(PRDM16)发生新的无义和剪接变异突变，表现为早期起病的左心室致密化不全(LVNC)，其中一名患者进展为扩张型心肌病(DCM)。此外，小鼠心肌细胞特异性Prdm16基因的缺失会导致LVNC和围产期死亡，而杂合子小鼠则会发展为心肌肥大。类似地，CRISPR无义突变杂合子敲入也发生了心肌肥厚。为了克服这些小鼠的围产期致死性，并确定PRDM16在成年心肌细胞中的作用，我们还产生了心肌细胞特异性他莫昔芬诱导该基因缺失的小鼠，并表明，类似于生殖系杂合小鼠和Prdm16敲入小鼠，这些小鼠也出现了心肌肥大，并随着年龄的增长发展为心功能障碍。我们对一个先证者的人类诱导多能干细胞来源的心肌细胞和心肌细胞特异性Prdm16 KO小鼠的初步表征揭示了该转录因子在基因转录中的双重作用。Prdm16的缺失抑制了代谢和氧化磷酸化基因的表达，而增加了纤维化基因的表达。上述科学前提使我们假设PRDM16在心脏发育、代谢编程和心脏重构方面发挥着相关的转录作用，它的缺失导致了人类和小鼠的LVNC/DCM表型。我们的具体目标是：(1)阐明PRDM16突变/缺失导致人类和小鼠心肌病表型的机制；(2)确定PRDM16调控心脏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翻译的研究。这项研究具有新颖性和高度的意义，因为它表明PRDM16是心脏中基因表达的协调者，它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参与对于更好地了解LVNC/DCM的病因和开发这些异质性疾病的治疗方法是关键。

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.