在出生后的心脏肥大,心肌细胞经历有丝分裂退出,依靠DNA复制非依赖性的组蛋白周转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振荡影响时钟控制的基因表达,提示昼夜节律在组蛋白周转和协调心肌细胞基因表达的时间控制中的作用。阐明主昼夜节律转录因子的作用,Bmal1,在组蛋白周转中,染色质组织,以及新生儿期肌细胞特异性基因表达和细胞生长。Bmal1敲低新生大鼠心室肌细胞(NRVM)减少肌细胞大小,总细胞蛋白质合成,和用血清或α-肾上腺素能激动剂去氧肾上腺素(PE)处理后胎儿肥大基因Nppb的转录。Bmal1的缺失降低了时钟控制基因Per2和Tcap的表达,以及Sik1,一种Bmal1靶标在成人与胚胎心脏中上调。通过MNase-qPCR测量,Bmal1敲低会损害Per2和Sik1启动子的可及性,通过酸溶性染色质级分的代谢标记测量,组蛋白转换受损。Sik1敲低依次减少了心肌细胞的大小,同时抑制Nppb转录和激活Per2转录。将这些变化与染色质重塑联系起来,复制非依赖性组蛋白变体H3.3a的消耗抑制了心肌细胞肥大,并阻止了PE诱导的时钟控制基因转录变化。Bmal1是新生儿心肌细胞生长所必需的,不依赖复制的组蛋白周转,和Sik1启动子处的染色质组织。Sik1代表一种新的时钟控制基因,可协调肥大和时钟控制基因转录的肌细胞生长。不依赖复制的组蛋白周转是心肌细胞中时钟控制基因响应生长刺激的转录重塑所必需的。
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.