Research has demonstrated that hypoxic preconditioning (HP) can enhance the survival and proliferation of cardiac progenitor cells (CPCs); however, the underlying mechanisms are not fully understood. Here, we report that HP of c-kit (+) CPCs inhibits p53 via the PI3K/Akt-DNMT1 pathway. First, CPCs were isolated from the hearts of C57BL/6 mice and further purified by magnetic-activated cell sorting. Next, these cells were cultured under either normoxia (H0) or HP for 6 hours (H6) followed by oxygen–serum deprivation for 24 hours (24h). Flow cytometric analysis and MTT assays revealed that hypoxia-preconditioned CPCs exhibited an increased survival rate. Western blot and quantitative real-time PCR assays showed that p53 was obviously inhibited, while DNMT1 and DNMT3β were both significantly up-regulated by HP. Bisulphite sequencing analysis indicated that DNMT1 and DNMT3β did not cause p53 promoter hypermethylation. A reporter gene assay and chromatin immunoprecipitation analysis further demonstrated that DNMT1 bound to the promoter locus of p53 in hypoxia-preconditioned CPCs. Together, these observations suggest that HP of CPCs could lead to p53 inhibition by up-regulating DNMT1 and DNMT3β, which does not result in p53 promoter hypermethylation, and that DNMT1 might directly repress p53, at least in part, by binding to the p53 promoter locus.

Cardiovascular disease (CVD) is a leading cause of mortality and morbidity among patients with diabetes. Endothelial dysfunction is an early physiological event in CVD. Metformin, a common oral antihyperglycemic agent, has been demonstrated to directly affect endothelial cell function. Brain-derived neurotrophic factor (BDNF), originally discovered in the brain as a neurotrophin, has also been reported to play a protective role in the cardiovascular system. In our study, we demonstrated that high glucose (HG) reduced cell proliferation and induced cell apoptosis via changes in BDNF expression and that metformin reversed the effects of HG injury by upregulating BDNF expression. Furthermore, we found that cyclic AMP response element binding (CREB) phosphorylation was reduced in HG-treated human umbilical vein endothelial cells (HUVECs), and this effect was reversed by the metformin treatment. However, the metformin effect on BDNF levels in HG-incubated HUVECs was blocked by a CREB inhibitor, which indicated that BDNF expression is regulated by metformin through CREB activation. In addition, we found that adenosine monophosphate-activated protein kinase (AMPK) activation is involved in CREB/BDNF regulation in HG-incubated HUVECs treated with metformin and that an AMPK inhibitor impaired the protective effects of metformin on HG-treated HUVECs. In conclusion, this study demonstrated that metformin affects cell proliferation and apoptosis via the AMPK/CREB/BDNF pathway in HG-incubated HUVECs.

BackgroundC-kit-positive cardiac stem cells (CSCs) have been shown to be a promising candidate treatment for myocardial infarction and heart failure. Insulin-like growth factor (IGF)-1 is an anabolic growth hormone that regulates cellular proliferation, differentiation, senescence, and death in various tissues. Although IGF-1 promotes the migration and proliferation of c-kit-positive mouse CSCs, the underlying mechanism remains unclear.MethodsCells were isolated from adult mouse hearts, and c-kit-positive CSCs were separated using magnetic beads. The cells were cultured with or without IGF-1, and c-kit expression was measured by Western blotting. IGF-1 induced CSC proliferation and migration, as measured through Cell Counting Kit-8 (CCK-8) and Transwell assays, respectively. The miR-193a expression was measured by quantitative real-time PCR (qPCR) assays.ResultsIGF-1 enhanced c-kit expression in c-kit-positive CSCs. The activities of the phosphoinositol 3-kinase (PI3K)/AKT signaling pathway and DNA methyltransferases (DNMTs) were enhanced, and their respective inhibitors LY294002 and 5-azacytidine (5-AZA) blunted c-kit expression. Based on the results of quantitative real-time PCR (qPCR) assays, the expression of miR-193a, which is embedded in a CpG island, was down-regulated in the IGF-1-stimulated group and negatively correlated with c-kit expression, whereas c-kit-positive CSCs infected with lentivirus carrying micro-RNA193a displayed reduced c-kit expression, migration and proliferation.ConclusionsIGF-1 upregulated c-kit expression in c-kit-positive CSCs resulting in enhanced CSC proliferation and migration by activating the PI3K/AKT/DNMT signaling pathway to epigenetically silence miR-193a, which negatively modifies the c-kit expression level.Electronic supplementary materialThe online version of this article (10.1186/s13287-017-0762-4) contains supplementary material, which is available to authorized users.

Background: It is clinically important to identify high-risk patients with acute coronary syndrome (ACS) who may require repeat revascularization. This retrospective study identified risk factors for repeat revascularization among ACS patients after first-time successful percutaneous coronary interventions (PCIs).The predictive value of the triglyceride to high-density lipoprotein cholesterol (TG/HDL-C) ratio for repeat revascularization was also evaluated. Methods: We enrolled consecutive ACS patients who had coronary angiography performed during the period from 6 to 12 months after a first-time successful PCI. The primary outcome of the study was to identify the risk factors of repeat revascularization. The subjects were stratified based on repeat PCI events.After comparing various clinical characteristics, univariate and multivariate Cox proportional hazard model analyses were adopted to evaluate the effects of risk factors on repeat revascularization. Results: The patients (n=271) were divided into the event (+) group (n=101) and the event (−) group (n=170). In the event (+) group, target lesion revascularization (TLR) accounted for 20.79% and target vessel revascularization (TVR) accounted for 50.49% of the patients. In contrast, 52.47% of the patients required de novo vessel revascularization (DVR). After adjustment for confounding factors, the TG/HDL-C ratio [hazard ratio (HR) =1.206, 95% confidence interval (CI): 1.016-1.431, P=0.032 for each higher TG/HDL-C ratio unit] and the Gensini score (HR =1.012, 95% CI: 1.005-1.018, P<0.001 for each higher Gensini score unit) were independent risk factors for a repeat PCI. Subgroup analyses showed that higher TG/HDL-C ratios were associated with a significantly higher risk of repeat PCIs in the male, hypertensive, and diabetes mellitus subgroups. Conclusions: The TG/HDL-C ratio and Gensini score could serve as risk factors for repeat revascularization in ACS patients after a first-time successful PCI.

Cardiac c‐kit positive cells are cardiac‐derived cells that exist within the heart and have a great many protective effects. The senescence of cardiac c‐kit positive cells probably leads to cell dysfunction. Bradykinin plays a key role in cell protection. However, whether bradykinin prevents cardiac c‐kit positive cells from high‐glucose‐induced senescence is unknown. Here, we found that glucose treatment causes the premature senescence of cardiac c‐kit positive cells. Bradykinin B2 receptor (B2R) expression was declined by glucose‐induced senescence. Bradykinin treatment inhibited senescence and reduced intracellular oxygen radicals according to senescence‐associated β‐galactosidase staining and 2′,7′‐dichlorodihydrofluorescein diacetate staining. Moreover, the mitochondrial membrane potential was damaged, as measured by JC‐1 staining. The mitochondrial membrane potential was preserved under bradykinin treatment. The concentration of superoxide was decreased, and the concentration of intracellular adenosine triphosphate was increased after bradykinin treatment. Western blot showed that bradykinin leads to AKT and mammalian target of rapamycin (mTOR) phosphorylation and decreased levels of P53 and P16 when compared with glucose treatment alone. Antagonists of B2R, phosphoinositide 3‐kinase (PI3K), mTOR, and B2R small interfering RNA prevented the protective effect of bradykinin. P53 antagonist also inhibited the glucose‐induced senescence of cardiac c‐kit positive cells. In conclusion, bradykinin prevents the glucose‐induced premature senescence of cardiac c‐kit positive cells through the B2R/PI3K/AKT/mTOR/P53 signal pathways.