Department of Anesthesiology & Perioperative Medicine, David Geffen School of Medicine at UCLA, UCLA, Los Angeles, California, USA.
Internal Medicine, Heart Institute, Center for Regenerative Medicine, University of South Florida, Tampa, Florida, USA.
J Biol Chem. 2024 Jul;300(7):107434. doi: 10.1016/j.jbc.2024.107434. Epub 2024 Jun 1.
During postnatal cardiac hypertrophy, cardiomyocytes undergo mitotic exit, relying on DNA replication-independent mechanisms of histone turnover to maintain chromatin organization and gene transcription. In other tissues, circadian oscillations in nucleosome occupancy influence clock-controlled gene expression, suggesting a role for the circadian clock in temporal control of histone turnover and coordinated cardiomyocyte gene expression. We sought to elucidate roles for the master circadian transcription factor, Bmal1, in histone turnover, chromatin organization, and myocyte-specific gene expression and cell growth in the neonatal period. Bmal1 knockdown in neonatal rat ventricular myocytes decreased myocyte size, total cellular protein synthesis, and transcription of the fetal hypertrophic gene Nppb after treatment with serum or the α-adrenergic agonist phenylephrine. Depletion of Bmal1 decreased the expression of clock-controlled genes Per2 and Tcap, as well as Sik1, a Bmal1 target upregulated in adult versus embryonic hearts. Bmal1 knockdown impaired Per2 and Sik1 promoter accessibility as measured by micrococcal nuclease-quantitative PCR and impaired histone turnover as measured by metabolic labeling of acid-soluble chromatin fractions. Sik1 knockdown in turn decreased myocyte size, while simultaneously inhibiting natriuretic peptide B transcription and activating Per2 transcription. Linking these changes to chromatin remodeling, depletion of the replication-independent histone variant H3.3a inhibited myocyte hypertrophy and prevented phenylephrine-induced changes in clock-controlled gene transcription. Bmal1 is required for neonatal myocyte growth, replication-independent histone turnover, and chromatin organization at the Sik1 promoter. Sik1 represents a novel clock-controlled gene that coordinates myocyte growth with hypertrophic and clock-controlled gene transcription. Replication-independent histone turnover is required for transcriptional remodeling of clock-controlled genes in cardiac myocytes in response to growth stimuli.
在出生后心脏肥大期间，心肌细胞经历有丝分裂退出，依赖于组蛋白周转的非 DNA 复制机制来维持染色质组织和基因转录。在其他组织中，核小体占据的昼夜节律波动影响时钟控制基因的表达，表明时钟在组蛋白周转的时间控制和协调心肌细胞基因表达中发挥作用。我们试图阐明主时钟转录因子 Bmal1 在组蛋白周转、染色质组织和心肌细胞特异性基因表达和细胞生长中的作用，以及在新生儿期的作用。在新生大鼠心室肌细胞中敲低 Bmal1 会降低心肌细胞大小、总细胞蛋白合成以及血清或α-肾上腺素能激动剂苯肾上腺素处理后的胎儿肥厚基因 Nppb 的转录。Bmal1 的耗竭降低了时钟控制基因 Per2 和 Tcap 的表达，以及 Bmal1 在成人心肌中上调的靶基因 Sik1 的表达。Bmal1 敲低会损害 Per2 和 Sik1 启动子的可及性，如微球菌核酸酶定量 PCR 所示，并损害组蛋白周转，如通过代谢标记酸溶性染色质分数测量。Sik1 的敲低反过来又降低了心肌细胞的大小，同时抑制了利钠肽 B 的转录并激活了 Per2 的转录。将这些变化与染色质重塑联系起来，非复制依赖性组蛋白变体 H3.3a 的耗竭抑制了心肌细胞肥大并阻止了苯肾上腺素诱导的时钟控制基因转录变化。Bmal1 是新生儿心肌细胞生长、非复制依赖性组蛋白周转和 Sik1 启动子染色质组织所必需的。Sik1 是一种新的时钟控制基因，它协调心肌细胞的生长与肥厚和时钟控制基因的转录。非复制依赖性组蛋白周转是心脏肌细胞对生长刺激的时钟控制基因转录重塑所必需的。
