Expression profile of microRNAs in the cardiomyocytes derived from mouse embryonic stem cells / 生理学报

Embryonic stem cells (ESCs), derived from the inner cell mass of blastocysts, are self-renewing and pluripotent cells with the ability to differentiate into all derivatives of three primary germ layers, including cardiomyocytes. Recent studies have revealed that posttranscriptional regulations of lineage specific genes by microRNAs (miRNAs) emerge as a new class of cell fate and lineage determinants of ESCs. However, the miRNAs that control ESC differentiation are still largely unexplored. In the present study, we aimed to identify miRNAs that might be involved in cardiac differentiation of ESCs. Using a hanging drop technique, mouse ESCs (mESCs) were differentiated into cardiomyocytes. We then used the Aligent miRNAs chip (miRbase V16.0) to evaluate miRNA expression levels between the ESC-derived beating area enriched with cardiomyocytes and non-beating area. The expression levels of 19 miRNAs changed over 5-fold between two areas (n = 3, P < 0.05). Among them, 5 miRNAs were upregulated and 14 miRNAs were downregulated in the beating area compared with the non-beating area (P < 0.05). Then quantitative real-time-PCR was used to analyze the miRNAs with the differentiated expression level over 10-fold seen in the Aligent miRNAs chip. miR-196a, miR-196b and miR-467e were confirmed to be significantly lower in the beating area than those in the non-beating area (n = 3, P < 0.05). TargetScan analysis further suggested that miR-196a and miR-196b might be negatively related to the cardiomyocytes differentiation. Our findings provide a new clue for exploring roles of miRNAs in cardiac lineage commitment of mESCs.

Expression pattern of E2F6 in physical and chemical hypoxia-induced apoptosis / 生理学报

Apoptosis can be caused by hypoxia, a major factor during ischemic injury, in cardiomyocytes. However, the regulatory mechanisms underlying hypoxia-induced cardiomyocyte apoptosis have not yet been fully understood. E2F6, an identified E2F family member, has been demonstrated to repress DNA damage-induced apoptosis in our recent study. However, it is unclear whether E2F6 is involved in hypoxia-induced apoptosis. In this study, we determined the expression property of E2F6 during hypoxia-induced apoptosis in H9c2 cells, a rat ventricular myoblast cell line. The results showed that physical hypoxia and chemical hypoxia-mimetic agents desferrioxamine (DFO) and cobalt chloride (CoCl(2)) induced apoptosis in H9c2 cells. Physical hypoxia- and CoCl(2)-induced apoptosis was accompanied with a downregulation of endogenous E2F6 mRNA expression, but not protein expression. DFO treatment resulted in a significant downregulation of both mRNA and protein expressions of endogenous E2F6. These results suggest that E2F6 may be involved in DFO-induced apoptosis, while it is less sensitive in physical hypoxia- and CoCl(2)-induced apoptosis in H9c2 cells. In addition, the apoptosis induced by DFO may share different pathways from that induced by physical hypoxia and CoCl(2).

The cardioprotection of intermittent hypoxic adaptation / 生理学报

Intermittent hypoxia (IH), or periodic hypoxia is referred as exposure to hypoxia interrupted by normoxia that occurs under many physiological and pathophysiological conditions. A lot of researches showed that IH adaptation, like ischemic preconditioning (IPC) and long-term high-altitude hypoxic adaptation (LHA), had significant cardioprotective effects including increasing the tolerance of myocardium to ischemia/reperfusion injury, limiting infarction size and morphologic damage, inhibiting apoptosis of myocardial cells, enhancing recovery of cardiac function in ischemia/reperfusion, and antiarrhythmia. However, the precise mechanisms underlying the protective effects of IH against ischemia/reperfusion injury are far from clear. The potential candidates participating in the protective effects of IH include oxygen transport, energy metabolism, neurohumoral regulation, antioxidase, stress protein, adenosine, ATP-sensitive potassium channel, mitochondrion, calcium control, nitric oxide and protein kinase. The effects of IH are affected by the protocol of hypoxic exposure, age and sex of experimental animals. IH adaptation, for longer lasting time than IPC and lesser side effect than LHA, might have a practical value for using.

Developmental regulation of intracellular calcium homeostasis in early cardiac myocytes / 生理学报

The proper intracellular Ca(2+) signaling is essential for normal cell functions and organ development, and the maintaining Ca(2+) homeostasis in cardiac myocytes is of functional importance for the intact heart. As the first functional organ in the vertebrate embryo, the heart is continuously remodeled and maintains its physiologic pumping function in response to increasing circulatory demands. The expressions of Ca(2+) handing proteins in the embryonic heart, however, are different from those in neonatal and adult hearts, which means that the regulation of Ca(2+) transients in embryonic cardiomyocytes is different from that in adult cardiac myocytes. Recent advances in molecular and cellular biology, as well as the application of embryonic stem cell differentiation system, have made progress in uncovering the regulation of Ca(2+) homeostasis during cardiomyogenesis. This paper briefly summarizes the Ca(2+) homeostasis during early development of cardiomyocytes and reviews current knowledge of the regulatory mechanisms controlling Ca(2+) homeostasis during cardiomyocyte development.