Insulin-induced phosphorylation of a 38 kDa DNA-binding protein in ventricular cardiomyocytes: possible implication of nuclear protein phosphatase activity

Ventricular cardiomyocytes isolated from adult rat heart were used to analyze the effect of insulin on the phosphorylation of DNA-binding nuclear proteins and to elucidate the potential involvement of protein phosphatase-1 (PP-1) and PP-2A in this hormonal action. Cells were labelled with [³³P]orthophosphate, stimulated with insulin (1.7 × 10⁻⁷ M) and processed for the isolation of nuclei and extraction of DNA-binding proteins. Insulin was found to induce a rapid and constant increase in the serine/threonine phosphorylation of a 38 kDa DNA-binding protein, reaching 150% of control after 15 min and 180% after 150 min. Immunoprecipitation and Western blotting experiments revealed the presence of phosphorylated numatrin in the nuclear extract, however, insulin did not modify its phosphorylation state. Treatment of cardiomyocytes with okadaic acid (1 μM) resulted in a large increase (246 ± 30%) in the phosphorylation of the 38 kDa protein. Using ³²P-labelled phosphorylase as a substrate, we observed a significant inhibition of nuclear PP-1 activity to 38.5 ± 7% (n = 3) of control after incubation of cardiomyocytes with insulin for 15 min. PP-2A, which corresponds to about 25% of total phosphatase activity, was also inhibited to the same extent. These data show the presence of an insulin-responsive 38 kDa DNA-binding phosphoprotein in the nucleus of cardiomyocytes, which is at least partly regulated by nuclear phosphatase activity. It is suggested that inhibition of nuclear PP-1 and PP-2A represents a possible mechanism of insulin signalling to the nucleus of target cells.     

雌激素对小鼠心室肌细胞ATP敏感性钾离子通道活性的影响

目的从离子通道水平,观察雌激素(17α-ethynylestradiol and 17β-estradiol)对小鼠心室肌细胞ATP敏感性钾离子通道的影响。方法利用急性酶解法分离小鼠心室肌细胞,采用膜片钳制技术细胞膜内向外及细胞吸附记录模式。结果在钳制电压-60 mV细胞膜内向外记录模式下,向浴液中加入0.1μmol/L、1μmol/L及10μmol/L三种不同浓度雌激素,观察到两种雌激素(17α-ethynylestradiol、17β-estradiol)均对KATP通道有抑制作用,而且呈浓度依赖性,其半数有效浓度分别为0.3μmol/L及0.1 nmol/L。在钳制电压-60mV细胞吸附记录模式下,向浴液中加入pinacidil或2,4-dinitrophenol(DNP)活化KATP通道后,观察3 min,通道活性未见明显影响。在钳制电压-60mV细胞膜内向外记录模式下,向浴液中加入phorbol 12,13-dibutyrate(PDBu)0.001 nmol与处理后,观察到雌激素(10-8、10-3和1μmol/L)对于KATP离子通道活性抑制作用减弱。结论雌激素可通过影响心肌细胞KATP通道活性防止心律失常的产生,从而发挥心肌保护作用。     

Effect of emulsified isoflurane on apoptosis of anoxia-reoxygenation neonatal rat cardiomyocytes

ObjectiveTo explore the effect of emulsified isoflurane (EI) on apoptosis of anoxia-reoxygenation neonatal rat cardiomyocytes and relevant protein expression.MethodsCardiac muscle anoxia-reoxygenation damage model was established with culture in vitro neonatal rat cardiomyocytes. The cardiomyocytes were divided into control group, model group, fat emulsion group and EI group. The cardiomyocytes apoptosis rates and lactic dehydrogenase (LDH), superoxide dismutase (SOD) and malondialdehyde (MDA) index standardization were detected after relevant treatment. The expression of apoptosis-related proteins Bel-2, Bax and Caspase-3 were detected with Western blot approach.ResultsAfter hypoxia/reoxygenation (H/R) model was treated by EI, the cells apoptosis rate decreased and was dramatically below the fat emulsion group (P<0.05). Cardiomyocytes biochemical index detection presented that, compared with the control group that the LDH activity and MDA content dramatically increased (P<0.05), while the SOD activity notably decreased (P<0.05); compared with the H/R group, the SOD activity of the fat emulsion group and EI group increased (P<0.05); while the LDH activity and MDA content decreased (P<0.05). And the change of the EI group was more remarkable than the fat emulsion group (P<0.05). The Western blot analysis presented that, compared with the control group, the Bcl-2 protein expression of the other groups significantly decreased (P<0.05), the expressions of Bax protein and Caspase-3 protein increased significantly (P<0.05); compared with H/R group, cardiomyocytes Bcl-2 protein expression of EI group increased significantly (P<0.05), the expressions of Bax protein and Caspase-3 protein decreased significantly (P<0.05), and the change of EI group was more remarkable than the fat emulsion group (P<0.05).ConclusionsEI can inhabit the apoptosis of anoxia-reoxygenation damage model cardiomyocytes, and may be related to the up-regulation of expression of Bcl-2 and down-regulation of expression of Caspase-3 protein.     

骨髓间充质干细胞体内诱导分化为心肌细胞的初步实验观察

目的：初步观察MSCs墨体内诱导分化为心肌细胞的能力。方法：从大鼠双侧股骨骨髓获得MSCs，在体外纯化、扩增后，DAPI进行细胞标记，然后注射到急性心肌梗塞模型鼠和正常大鼠的心肌组织内，饲养2～4周后，处死动物在注射点获取心肌标本，初步采用肛染色和电镜观察形态学的方法对分化的心肌细胞进行鉴定，并用免疫组化法从组织学上对转化心肌细胞进行心肌特异性抗原的检测。结果：MSC进行DAPI的标记效率高，电镜观察与宿主心肌细胞问形成了闰盘，组化检测有心肌特异性抗原的出现。结论：在宿主心肌组织内，MSCs具有分化为心肌细胞的能力。     

西洋参茎叶总皂苷通过抑制过度内质网应激减轻大鼠心肌细胞缺氧/复氧损伤

目的: 观察西洋参茎叶总皂苷 (PQS) 对缺氧/复氧 (H/R) 心肌细胞的保护作用,并从内质网应激 (ERS)的角度探讨其分子机制。方法: 建立心肌细胞缺氧/复氧 (H/R) 损伤模型,以台盼蓝染色法、乳酸脱氢酶活性以及流式细胞术检测细胞损伤及凋亡情况;以RT-PCR和Western blotting方法,检测ERS标志分子葡萄糖调节蛋白78 (GRP78)、钙网蛋白 (CRT)、C/EBP同源蛋白 (CHOP)、caspase-12及凋亡相关蛋白Bcl-2、Bax的表达。结果: 和H/R组心肌细胞相比,PQS+H/R组:(1) 细胞凋亡率降低4.19% (P<0.05),存活率升高21.2% (P<0.05),LDH活性降低66.58% (P<0.05);(2) Bcl-2 mRNA和蛋白表达分别升高30.9%和48.0% (P<0.05),Bax mRNA和蛋白表达分别降低39.7%和48.4% (P<0.05);(3) GRP78 mRNA和蛋白表达分别降低61.6%和37.7% (P<0.05),CRT mRNA和蛋白表达分别降低35.7%和52.2% (P<0.05); CHOP mRNA和蛋白表达分别降低57.0%和51.7% (P<0.05);剪切后的caspase-12蛋白表达降低34.9% (P<0.05)。结论: PQS可减轻H/R诱导的心肌细胞损伤,其机制是降低H/R诱导的GRP78、CRT mRNA和蛋白表达,抑制CHOP、caspase-12等内质网凋亡通路激活,从而抑制过度ERS介导的细胞凋亡。     

Behavior of cardiomyocytes and skeletal muscle cells on different extracellular matrix components--relevance for cardiac tissue engineering

Myocardial cell transplantation in patients with heart failure is emerging as a potential therapeutic option to augment the function of remaining myocytes. Nevertheless, further investigations on basic issues such as ideal cell type continue to be evaluated. Therefore, the aim of our studies was to compare the performance of skeletal muscle cells and cardiomyocytes with respect to their proliferation rate and viability on different extracellular matrix components (EMCs). Rat cardiomyocytes (RCM) and rat skeletal muscle cells (RSMC) were cultured on EMCs such as collagen type I, type IV, laminin, and fibronectin. The components were used as "single coating" as well as "double coating." Proliferation rates were determined by proliferation assays on days 1, 2, 4, and 8 after inoculation of the cells. The most essential result is that collagen type I enhances the proliferation rate of RSMC but decreases the proliferation of RCM significantly. This effect is independent of the second EMC used for the double-coating studies. Other EMCs also influence cellular behavior, whereas the sequence of the EMCs is essential. Results obtained in our studies reveal the significant different proliferation behavior of RCM and RSMC under identical conditions. As skeletal muscle cells are also used in heart tissue engineering models, these results are essential and should be investigated in further studies to prove the applicability of skeletal muscle cells for heart tissue engineering purposes.     

Metallothionein alleviates oxidative stress-induced endoplasmic reticulum stress and myocardial dysfunction

Oxidative stress and endoplasmic reticulum (ER) stress have been implicated in cardiovascular diseases although the interplay between the two is not clear. This study was designed to examine the influence of oxidative stress through glutathione depletion on myocardial ER stress and contractile function in the absence or presence of the heavy metal scavenger antioxidant metallothionein (MT). FVB and MT overexpression transgenic mice received the GSH synthase inhibitor buthionine sulfoximine (BSO, 30 mM) in drinking water for 2 weeks. Oxidative stress, ER stress, apoptosis, cardiac function and ultrastructure were assessed using GSH/GSSG assay, reactive oxygen species (ROS), immunoblotting, caspase-3 activity, Langendorff perfused heart function (LVDP and ± dP/dt), and transmission electron microscopy. BSO led to a robust decrease in the GSH/GSSG ratio and increased ROS production, consolidating oxidative stress. Cardiac function and ultrastructure were compromised following BSO treatment, the effect of which was obliterated by MT. BSO promoted overt ER stress as evidenced by upregulated BiP, calregulin, phospho-IRE1α and phospho-eIF2α without affecting total IRE1α and eIF2α. BSO treatment led to apoptosis manifested as elevated expression of CHOP/GADD153, caspase-12 and Bax as well as caspase-3 activity, reduced Bcl-2 expression and JNK phosphorylation, all of which was ablated by MT. Moreover, both antioxidant N-acetylcysteine and the ER stress inhibitor tauroursodeoxycholic acid reversed the oxidative stress inducer menadione-elicited depression in cardiomyocyte contractile function. Taken together, these data suggested that ER stress occurs likely downstream of oxidative stress en route to cardiac dysfunction.     

氧化应激与糖尿病心肌细胞凋亡

氧化应激是糖尿病重要的病理生理过程.氧化应激所导致的心肌细胞凋亡是糖尿病患者非缺血性心力衰竭发生的重要原因.线粒体功能障碍、NADH氧化酶异常以及晚期糖基化终末产物增加是心肌细胞活性氧簇的主要来源.产生的活性氧簇通过直接激活线粒体凋亡途径、肿瘤坏死凶子(TNF)α激活死亡受体途径、P53凋亡途径以及p38丝裂原活化蛋白激酶(MAPK)途径,促进心肌细胞凋亡.但是目前针对糖尿病心脏病的抗氧化治疗效果并不理想,因此有必要进一步研究氧化应激导致心肌细胞凋亡的机制,以发现治疗糖尿病心脏病的新方法.     

Development of cardiac physiopathological models from cultured cardiomyocytes

The cultures of neonatal rat cardiomyocytes represent a very useful tool for the observation and the understanding of the cellular aspects of the electrophysiological, contractile, morphological, metabolic and molecular properties of the myocardium. This model is characterized by a homogeneous population of cardiac muscular cells and by vast possibilities of control of the chemical and physical environment of the cells, allowing the in vitro mimicry of a wide range of cardiac pathological situations. The cardiomyocyte cultures are thus suited to very varied experimental protocols, allowing multiparametric analysis of the cardiocellular effects of different stress such as hypoxia-reoxygenation, of ischemia-reperfusion, of the free radical attack and of thermal shock. These investigations can be combined with the study of the effects and of the cytotoxicity of pharmacological agents, not limited to the putatively cardioactive drugs. The present review proposes an outline of the procedures for the isolation, the culture and the use of neonatal cardiomyocytes. To illustrate the potentialities of this preparation, we describe more specifically the protocols and the various consequences at the cellular scale of an in vitro model of myocardial ischemia reperfusion.     

Transplantation of embryonic stem cells into the infarcted mouse heart: formation of multiple cell types

Initial studies have suggested that transplantation of embryonic stem (ES) cells following myocardial infarction (MI) in animal models is beneficial; however, the mechanism of benefit is largely unknown. The present study investigated the fate of mouse ES cells transplanted post-MI to determine if the ES cells give rise to the range of major cell types present in the native myocardium. MI was produced by coronary artery ligation in C57BL/6 mice. Two different mouse ES cell lines, expressing eGFP and beta-galactosidase, respectively, were tested. Post-MI intramyocardial injection of 3 x 10(4) ES cells was compared to injection of media alone. Histochemistry and immunofluorescence were used to track the transplanted ES cells and identify the resulting cell types. Echocardiography assessed the cardiac size and function in a blinded fashion. Two weeks post-MI, engraftment of the transplanted ES cells was demonstrated by eGFP or beta-galactosidase-positive cells in the infarct region without evidence for tumor formation. Co-immunolabeling demonstrated that the transplanted ES cells had become cardiomyocytes, vascular smooth muscle, and endothelial cells. Echocardiographic analysis showed that ES cell transplantation resulted in reduced post-MI remodeling of the heart and improved cardiac function. In conclusion, transplanted mouse ES cells can regenerate infarcted myocardium in part by becoming cardiomyocytes, vascular smooth muscle, and endothelial cells that result in an improvement in cardiac structure and function. Therefore, ES cells hold promise for myocardial cellular therapy.