BACKGROUND:Exercise-induced physiological cardiac growth regulators may protect the heart from ischemia/reperfusion (I/R) injury. Homeobox-containing 1 (Hmbox1), a homeobox family member, has been identified as a putative transcriptional repressor and is downregulated in the exercised heart. However, its roles in exercise-induced physiological cardiac growth and its potential protective effects against cardiac I/R injury remain largely unexplored.METHODS:We studied the function of Hmbox1 in exercise-induced physiological cardiac growth in mice after 4 weeks of swimming exercise. Hmbox1 expression was then evaluated in human heart samples from deceased patients with myocardial infarction and in the animal cardiac I/R injury model. Its role in cardiac I/R injury was examined in mice with adeno-associated virus 9 (AAV9) vector-mediated Hmbox1 knockdown and in those with cardiac myocyte–specific Hmbox1 ablation. We performed RNA sequencing, promoter prediction, and binding assays and identified glucokinase (Gck) as a downstream effector of Hmbox1. The effects of Hmbox1 together with Gck were examined in cardiomyocytes to evaluate their cell size, proliferation, apoptosis, mitochondrial respiration, and glycolysis. The function of upstream regulator of Hmbox1, ETS1, was investigated through ETS1 overexpression in cardiac I/R mice in vivo.RESULTS:We demonstrated that Hmbox1 downregulation was required for exercise-induced physiological cardiac growth. Inhibition of Hmbox1 increased cardiomyocyte size in isolated neonatal rat cardiomyocytes and human embryonic stem cell–derived cardiomyocytes but did not affect cardiomyocyte proliferation. Under pathological conditions, Hmbox1 was upregulated in both human and animal postinfarct cardiac tissues. Furthermore, both cardiac myocyte–specific Hmbox1 knockout and AAV9-mediated Hmbox1 knockdown protected against cardiac I/R injury and heart failure. Therapeutic effects were observed when sh-Hmbox1 AAV9 was administered after I/R injury. Inhibition of Hmbox1 activated the Akt/mTOR/P70S6K pathway and transcriptionally upregulated Gck, leading to reduced apoptosis and improved mitochondrial respiration and glycolysis in cardiomyocytes. ETS1 functioned as an upstream negative regulator of Hmbox1 transcription, and its overexpression was protective against cardiac I/R injury.CONCLUSIONS:Our studies unravel a new role for the transcriptional repressor Hmbox1 in exercise-induced physiological cardiac growth. They also highlight the therapeutic potential of targeting Hmbox1 to improve myocardial survival and glucose metabolism after I/R injury.

中文翻译：

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缺血/再灌注损伤中 Hmbox1 的抑制通过 Gck 激活促进心肌细胞存活和葡萄糖代谢


背景：运动诱导的生理性心脏生长调节剂可以保护心脏免受缺血/再灌注（I/R）损伤。同源异型盒家族成员同源异型盒 1 (Hmbox1) 已被确定为假定的转录抑制因子，并在运动心脏中下调。然而，其在运动诱导的生理性心脏生长中的作用及其对心脏I/R损伤的潜在保护作用在很大程度上仍未被探索。方法：我们研究了Hmbox1在小鼠游泳运动4周后运动诱导的生理性心脏生长中的功能。然后评估了已故心肌梗塞患者的人类心脏样本和动物心脏 I/R 损伤模型中的 Hmbox1 表达。在腺相关病毒 9 (AAV9) 载体介导的 Hmbox1 敲除小鼠和心肌细胞特异性 Hmbox1 消融小鼠中检查了其在心脏 I/R 损伤中的作用。我们进行了 RNA 测序、启动子预测和结合测定，并确定葡萄糖激酶 (Gck) 是 Hmbox1 的下游效应子。在心肌细胞中检查了 Hmbox1 与 Gck 的作用，以评估其细胞大小、增殖、凋亡、线粒体呼吸和糖酵解。通过体内心脏 I/R 小鼠体内 ETS1 过表达，研究了 Hmbox1 上游调节因子 ETS1 的功能。结果：我们证明 Hmbox1 下调是运动诱导的生理性心脏生长所必需的。抑制 Hmbox1 会增加分离的新生大鼠心肌细胞和人胚胎干细胞衍生的心肌细胞中的心肌细胞大小，但不影响心肌细胞增殖。在病理条件下，Hmbox1 在人和动物梗塞后心脏组织中表达上调。 此外，心肌细胞特异性 Hmbox1 敲除和 AAV9 介导的 Hmbox1 敲除均可预防心脏 I/R 损伤和心力衰竭。 I/R损伤后给予sh-Hmbox1 AAV9观察到治疗效果。抑制 Hmbox1 可激活 Akt/mTOR/P70S6K 通路并上调 Gck 转录，从而减少心肌细胞凋亡并改善线粒体呼吸和糖酵解。 ETS1 充当 Hmbox1 转录的上游负调节因子，其过度表达可预防心脏 I/R 损伤。 结论：我们的研究揭示了转录抑制因子 Hmbox1 在运动诱导的生理性心脏生长中的新作用。他们还强调了靶向 Hmbox1 在改善 I/R 损伤后心肌存活和葡萄糖代谢方面的治疗潜力。