Inhibition of Hmbox1 Promotes Cardiomyocyte Survival and Glucose Metabolism Through Gck Activation in Ischemia/Reperfusion Injury.

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.

Danlou Tablet Protects Against Cardiac Remodeling and Dysfunction after Myocardial Ischemia/Reperfusion Injury through Activating AKT/FoxO3a Pathway.

Myocardial ischemia/reperfusion injury (I/RI) and ventricular remodeling are the critical pathological basis of heart failure. Danlou tablet (Dan) is a kind of Chinese patent medicine used in angina pectoris treatment in China. However, it remains unclear whether and how Dan could protect against cardiac remodeling after myocardial I/RI. In this study, both preventive and therapeutic administration of Dan attenuated ventricular remodeling and cardiac dysfunction at 3 weeks after myocardial I/RI. Dan inhibited Bax/Bcl2 ratio and Caspase3 cleavage in heart tissues and also inhibited apoptosis of human AC16 cells and neonatal rat cardiomyocytes stressed by oxygen and glucose deprivation/reperfusion. Mechanistically, Dan inhibited myocardial apoptosis through phosphorylating AKT and FoxO3a, thereby inhibiting downstream BIM and PUMA expressions. Collectively, these results demonstrate that Dan treatment is effective to protect against cardiac remodeling and dysfunction after myocardial I/RI and provide theoretical basis for its cardioprotection and clinical application in treating ischemic cardiac diseases.

Danlou Tablet Protects Against Myocardial Infarction Through Promoting eNOS-Dependent Endothelial Protection and Angiogenesis.

Myocardial infarction (MI) is one of the leading causes of death worldwide. Danlou tablet (Dan) is an effective traditional Chinese medicine for cardiac protection, although the underlying mechanism was not fully understood. In this study, we used a murine MI model and demonstrated that Dan administration effectively attenuated myocardial apoptosis, cardiac remodeling, and heart failure post MI. Dan increased CD31-positive capillaries in MI hearts, and reduced the apoptosis and oxidative stress in human umbilical vein endothelial cells after oxygen-glucose deprivation stress, simultaneously with the activated HIF-1α/VEGFA/eNOS signaling. Moreover, inhibition of eNOS by L-NAME attenuated Dan-induced protection against MI, and abolished its effect in promoting angiogenesis and reducing endothelial apoptosis and oxidative stress. Collectively, Dan is beneficial to promote eNOS-dependent endothelial protection and angiogenesis thus protecting against MI. A deep understanding of Dan-induced protection might help promote clinical usage of Dan in MI treatment.

A modified apical resection model with high accuracy and reproducibility in neonatal mouse and rat hearts.

Neonatal mouse heart can regenerate after left ventricle (LV) apical resection (AR). Since current AR rodent method is accomplished by resecting LV apex until exposure of LV chamber, it is relatively difficult to operate reproducibly. We aimed to develop a modified AR method with high accuracy and reproducibility and to investigate whether cardiac regenerative capacity could be replicated in neonatal rats. For 15% AR of whole heart weight in 1-day-old (P1) neonatal mice, a modified 10 µL pipette tip cut to 0.48 mm in internal diameter was connected to a vacuum pump working at 0.06 ± 0.005 MPa and gently kept in touch with LV apex for nearly but no more than 12 s. LV apex was resected by a single incision adjacent to the pipette tip. The modified AR method in P1 mice achieved cardiac structural and functional recovery at 21 days post resection (dpr). Data from different operators showed smaller variation of resected LV apex and higher reproducibility using the modified AR method. Furthermore, we showed that 5% AR of whole heart weight in P1 neonatal rats using a modified 200 µL pipette tip cut to 0.63 mm in internal diameter led to complete regeneration of LV apex and full preservation of cardiac function at 42 dpr. In conclusion, the modified AR rodent model leads to accurate resection of LV apex with high homogeneity and reproducibility and it is practically convenient for the study of structural, functional, and molecular mechanisms of cardiac regeneration in both neonatal mice and rats.