Meixiang Xiang

Hypoxic preconditioning attenuates hypoxia/reoxygenation-induced apoptosis in mesenchymal stem cells

AbstractAim:Mesenchymal stem cells (MSC) are a promising candidate for cardiac replacement therapies. However, the majority of transplanted MSC are readily lost after transplantation because of poor blood supply, ischemia-reperfusion, and inflammatory factors. We aimed to study the effects of hypoxia preconditioning (HPC) on hypoxia/reoxygenation-induced apoptosis of MSC.Methods:Three generations of MSC were divided into 6 groups, including the normal group, hypoxia-reoxygenation (H/R) group, cyclosporine A (CsA), and the HPC 10 min, 20 min, and 30 min groups. The apoptotic index, cell viability, mitochondrial membrane potential, translocation of Bcl-2 and bax, extracellular regulated kinase (ERK), Akt, hypoxia-inducible factor 1-α, and the vascular endothelial growth factor (VEGF) were tested after H/R treatment.Results:HPC decreased the apoptotic index and increased the viability induced by H/R. Moreover, HPC markedly stabilized mitochondrial membrane potential, upregulated Bcl-2 and VEGF expressions, and increased the phosphorylation of ERK and Akt. As a positive control, CsA has the same function as HPC, except for promoting ERK and Akt phosphorylation and upregulating VEGF.Conclusion:HPC had a protective effect against MSC apoptosis induced by H/R via stabilizing mitochondrial membrane potential, upregulating Bcl-2 and VEGF, and promoting ERK and Akt phosphorylation. HPC has implications for the development of novel stem cell protective strategies.

Angiopoietin-1 protects mesenchymal stem cells against serum deprivation and hypoxia-induced apoptosis through the PI3K/Akt pathway

AbstractAim:The angiopoietin-1 (Ang1)/Tie-2 signaling system not only plays a pivotal role in vessel growth, remodeling, and maturation, but also reduces apoptosis of endothelial cells, neurons, and cardiomyocytes. However, relatively little is known as to whether Ang1 has a protective effect on mesenchymal stem cells (MSC). The aim of the present study was to investigate the protective effect of Ang1/Tie-2 signaling on MSC against serum deprivation and hypoxia-induced apoptosis, and to determine the possible mechanisms.Methods:Hoechst 33342 and terminal deoxynucleotidyl transferase-mediated digoxigenin-dUTP nick-end labeling staining were used to assess the apoptosis of MSC. The expression of Tie-2, Akt, Bcl-2, Bax, and cleaved caspase-9 and -3 was detected by Western blot analysis.Results:This study showed that MSC expressed Tie-2 receptor, and Ang1 induced Tie-2 receptor phosphorylation. The protective effect of Ang1 on MSC was dose-dependent and peaked at 50 μg/L; however, the soluble Tie-2/Fc fusion protein, which acts as an inhibitor by sequestering Ang1, abrogated the anti-apoptotic effect. Ang1 induced Akt phosphorylation, increased the Bcl-2/Bax ratio, and decreased the activation of caspase-9 and -3. All these effects were attenuated by Tie-2/Fc and a phosphatidylinositol 3 kinase (PI3K) inhibitor, wortmannin.Conclusion:These results demonstrate that Ang1 can protect MSC against serum deprivation and hypoxia-induced apoptosis; Ang1/Tie-2 signaling and its downstream PI3K/Akt messenger pathway are crucial in the processes leading to MSC survival.

Cathepsin L Activity Is Essential to Elastase Perfusion–Induced Abdominal Aortic Aneurysms in Mice

Objective—The development of abdominal aortic aneurysms (AAA) requires extensive aortic wall matrix degradation. Human AAA lesions express high levels of cathepsin L (CatL), one of the most potent mammalian elastases. Whether this protease participates directly in AAA pathogenesis, however, is unknown. Methods and Results—We generated experimental AAA with aortic elastase perfusion in mice and established an essential role of CatL in AAA formation. After 14 days postperfusion, most wild-type (Ctsl+/+) mice developed AAA, but none of the CatL-deficient (Ctsl−/−) mice did. AAA lesion macrophage contents, CD4+ T cell numbers, CD31+ and laminin-5 angiogenic fragment &ggr;2+ microvessel numbers, and elastin fragmentation were all significantly lower in Ctsl−/− mice than in Ctsl+/+ mice. While lesions from Ctsl−/− mice contained fewer Ki67+ proliferating cells than did Ctsl+/+ mice, the absence of CatL did not affect lesion apoptotic cell contents or medial smooth-muscle cell loss significantly. Mechanistic studies indicated that the absence of CatL reduced lesion chemokine monocyte chemotactic protein-1 content, macrophage and T-cell in vitro transmigration, and angiogenesis, and altered the expression and activities of matrix metalloproteinases and other cysteinyl cathepsins in inflammatory cells, vascular cells, and AAA lesions. Conclusion—CatL contributes to AAA formation by promoting lesion inflammatory cell accumulation, angiogenesis, and protease expression.

Usefulness of serum tryptase level as an independent biomarker for coronary plaque instability in a Chinese population

Tryptase and chymase are unique mast cell proteases that are essential in atherogenesis. This study establishes a link between serum tryptase and chymase levels and human coronary heart diseases (CHD) in a cohort of 270 subjects. Serum tryptase levels were significantly higher in patients with substantial CHD than in those without substantial CHD (substantial CHD vs. unsubstantial CHD: 7.81 ± 0.52 ng/mL vs. 6.11 ± 0.51 ng/mL, P=0.002). After subgrouping the substantial CHD patients into those with acute myocardial infarction (AMI) and those with unstable or stable angina pectoris (UAP or SAP), we demonstrated that serum tryptase levels were nearly doubled in AMI patients as compared with unsubstantial CHD patients (11.13 ± 1.55 ng/mL vs. 6.11 ± 0.51 ng/mL, P<0.01), and significantly higher than in UAP patients (7.19 ± 0.62 ng/mL, P<0.05) or SAP patients (6.80 ± 0.94 ng/mL, P<0.05). Although Spearmans correlation test showed that serum tryptase correlated significantly with age (P=0.014) and weakly with fasting glucose (P=0.084), total cholesterol (P=0.071), low-density lipoprotein (P=0.063), and triglyceride (P=0.058), serum tryptase levels remained significantly higher in substantial CHD patients than in unsubstantial CHD patients in a multiple linear regression test after adjusting for all these confounders (P=0.008). Serum chymase levels were also higher in AMI patients (27.64 ± 7.57 ng/mL) or UAP patients (24.62 ± 8.06 ng/mL) than in SAP patients (15.20 ± 0.81 ng/mL) or unsubstantial CHD patients (16.84 ± 0.56 ng/mL), although such differences were not statistically significant. Spearmans correlation test revealed that serum chymase levels correlated significantly only with fasting glucose levels (P=0.019), and CHD status did not affect chymase levels before and after adjusting for all confounders. Our observations suggest that serum tryptase is an independent biomarker for coronary plaque stability in this Chinese population.

Meta-Analysis of Cohort Studies of Baseline Prehypertension and Risk of Coronary Heart Disease

Prehypertension is a common condition, but the extent to which it increases the risk for coronary heart disease (CHD) is unclear. The aim of this study was to determine the association between baseline prehypertension and risk for CHD by performing a meta-analysis of prospective cohort studies. A systematic search of published research was conducted through January 2013, using electronic databases and bibliographies of retrieved reports. Studies were included if they reported multivariate-adjusted relative risks (RRs) and corresponding 95% confidence intervals (CIs) of CHD with respect to prehypertension. A random-effects model was used to combine the study-specific risk estimates. Eighteen studies, consisting of 934,106 participants and 14,952 cases, with a median follow-up period of 8.8 years, were included. Prehypertension was associated with a significantly elevated risk for CHD (RR 1.36, 95% CI 1.22 to 1.53). Eight studies consisting of 12 cohorts further provided risk estimates for low-range prehypertension (120/80 to 129/84 mm Hg) and high-range prehypertension (130/85 to 139/89 mm Hg) separately. The risk for CHD increased significantly in high-range prehypertensive populations (RR 1.53, 95% CI 1.19 to 1.97) but not in low-range prehypertensive populations (RR 1.16, 95% CI 0.96 to 1.42). In conclusion, prehypertension is associated with a significantly increased risk for developing CHD, particularly high-range prehypertension. Further well-designed randomized controlled trials are needed to clarify the efficacy of blood pressure reduction in subjects with prehypertension.

Protective paracrine effect of mesenchymal stem cells on cardiomyocytes

ObjectiveThe aim of this study was to test the protective effect of mesenchymal stem cells (MSCs) on cardiomyocytes in vitro and to investigate the anti-apoptotic signaling pathway.MethodsMSCs from Sprague-Dawley (SD) rats were separated and cultured. MSC medium was collected from MSCs cultured in serum-free Dulbecco’s modified eagle medium (DMEM) under hypoxia. Cultured cardiomyocytes from neonatal SD rats were exposed to hypoxia/reoxygenation (H/R) and treated with MSC medium. The apoptotic cardiomyocytes were stained with Annexin-V-fluorescein isothiocyanate (FITC), Hoechst 33342 and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL). The mitochondrial transmembrane potential of cardiomyocytes was assessed using a fluorescence microscope. The expression of Bcl-2, Bax, cytochrome C, apoptosis-induced factor (AIF), and caspase-3 was tested by Western blot analysis.ResultsOur data demonstrated that MSC medium reduced H/R-induced cardiomyocyte apoptosis, increased the Bcl-2/Bax ratio, and reduced the release of cytochrome C and AIF from mitochondria into the cytosol.ConclusionMSCs protected the cardiomyocytes from H/R-induced apoptosis through a mitochondrial pathway in a paracrine manner.

Heat shock protein 90 protects rat mesenchymal stem cells against hypoxia and serum deprivation-induced apoptosis via the PI3K/Akt and ERK1/2 pathways

Mesenchymal stem cell (MSC) transplantation has shown a therapeutic potential to repair the ischemic and infracted myocardium, but the effects are limited by the apoptosis and loss of donor cells in host cardiac microenvironment. The aim of this study is to explore the cytoprotection of heat shock protein 90 (Hsp90) against hypoxia and serum deprivation-induced apoptosis and the possible mechanisms in rat MSCs. Cell viability was determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Apoptosis was assessed by Hoechst 33258 nuclear staining and flow cytometric analysis with annexin V/PI staining. The gene expression of Toll-like receptor-4 (TLR-4) and V-erb-b2 erythroblastic leukemia viral oncogene homolog 2 (ErbB2) was detected by real-time polymerase chain reaction (PCR). The protein levels of cleaved caspase-3, Bcl-2, Bcl-xL, Bax, total-ERK, phospho-ERK, total-Akt, phospho-Akt, and Hsp90 were detected by Western blot. The production of nitric oxide was measured by spectrophotometric assay. Hsp90 improves MSC viability and protects MSCs against apoptosis induced by serum deprivation and hypoxia. The protective role of Hsp90 not only elevates Bcl-2/Bax and Bcl-xL/Bax expression and attenuates cleaved caspase-3 expression via down-regulating membrane TLR-4 and ErbB2 receptors and then activating their downstream PI3K/Akt and ERK1/2 pathways, but also enhances the paracrine effect of MSCs. These findings demonstrated a novel and effective treatment strategy against MSC apoptosis in cell transplantation.

Role of interleukin-6 in regulation of immune responses to remodeling after myocardial infarction.

Abstract Myocardial remodeling following myocardial infarction (MI) is emerging as key causes of chronic infarct mortality. Interleukin-6 is a classic pro-inflammatory cytokine needed to mount an effective immune response. It seems that interleukin-6 acts as an important role in the dynamic and superbly orchestrated process of innate immunity after MI. Interleukin-6 timely suppresses of innate immune signals to prevent the catastrophic consequences of uncontrolled inflammation on cardiac geometry and function, and thus tunes myocardial remodeling. A comprehensive understanding of biological processes of interleukin-6 in innate immunity leading to inflammatory response and disease-related ventricular remodeling is helpful to find the solution of chronic heart failure. To accomplish this, we reviewed the articles of interleukin-6 regard to inflammation, innate immunity, and cardiac remodeling. This review focuses on the role of interleukin-6 that dominates cell-mediated immunity, especially on neutrophils, monocytes, macrophages, and fibroblasts. In addition, we will also briefly discuss other inflammatory cytokines involved in this process within the paper.

Tea consumption and risk of stroke: a dose-response meta-analysis of prospective studies

ObjectiveTo determine the association between tea consumption and the risk of stroke.MethodsWe searched the PubMed database from January 1966 to March 2012 and reviewed reference lists of retrieved articles to identify relevant studies. Studies were included if they reported relative risks (RRs) and corresponding 95% confidence intervals (CIs) of stroke with respect to three or more categories of tea consumption. A random-effects model was used to combine the study-specific risk estimates.ResultsFourteen studies, consisting of 513 804 participants with a median follow-up of 11.5 years, were included in this meta-analysis. We observed a modest but statistically significant inverse association between tea consumption and risk of stroke. An increase of three cups/d in tea consumption was associated with a 13% decreased risk of stroke (RR 0.87; 95% CI, 0.81–0.94). The decreased risk of stroke with tea consumption was consistent among most subgroups. Based on the three studies that provided results for stroke subtypes, tea consumption was also inversely associated with the risk of ischemic stroke (RR 0.76; 95% CI, 0.69–0.84), but not cerebral hemorrhage (RR 0.96; 95% CI, 0.82–1.11) or subarachnoid hemorrhage (RR 0.81; 95% CI, 0.57–1.16).ConclusionsTea consumption is associated with a decreased risk of stroke, particularly ischemic stroke. More well-designed, rigorously conducted studies are needed in order to make confident conclusions about the association between tea consumption and stroke subtypes.

Angiopoietin-1 preconditioning enhances survival and functional recovery of mesenchymal stem cell transplantation.

ObjectiveMesenchymal stem cell (MSC) transplantation is a promising therapy for ischemic heart diseases. However, poor cell survival after transplantation greatly limits the therapeutic efficacy of MSCs. The purpose of this study was to investigate the protective effect of angiopoietin-1 (Ang1) preconditioning on MSC survival and subsequent heart function improvement after transplantation.MethodsMSCs were cultured with or without 50 ng/ml Ang1 in complete medium for 24 h prior to experiments on cell survival and transplantation. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and Hoechst staining were applied to evaluate MSC survival after serum deprivation in vitro, while cell survival in vivo was detected by terminal deoxynucleotidyl transferase biotin-dUPT nick end labeling (TUNEL) assay 24 and 72 h after transplantation. Heart function and infarct size were measured four weeks later by small animal echocardiography and Masson’s trichrome staining, respectively.ResultsAng1 preconditioning induced Akt phosphorylation and increased expression of Bcl-2 and the ratio of Bcl-2/Bax. In comparison with non-preconditioned MSCs, Ang1-preconditioned cell survival was significantly increased while the apoptotic rate decreased in vitro. However, the PI3K/Akt pathway inhibitor, LY294002, abrogated the protective effect of Ang1 preconditioning. After transplantation, the Ang1-preconditioned-MSC group showed a lower death rate, smaller infarct size, and better heart functional recovery compared to the non-preconditioned-MSC group.ConclusionsAng1 preconditioning enhances MSC survival, contributing to further improvement of heart function.