In high glucose protein kinase C-zeta activation is required for mesangial cell generation of reactive oxygen species

BACKGROUND: We postulated that in mesangial cells exposed to high glucose, protein kinase C-zeta (PKC-zeta) is necessary for the generation of reactive oxygen species (ROS) by nicotinamide adenine dinucleotide phosphate (NADPH) oxidase and that the requirement of PKC-zeta for filamentous (F)-actin disassembly may involve ROS. To identify signaling mechanisms relevant to PKC-zeta activation and ROS generation, including phosphoinositide 3 kinase (PI3 kinase), we examined mesangial cell stimulation with platelet-derived growth factor (PDGF). METHODS: In primary rat mesangial cells cultured in 5.6 mmol/L or 30 mmol/L d-glucose, PKC-zeta expression was identified with immunoblotting and activity was analyzed in cell membrane immunoprecipitates and by confocal immunofluorescence imaging. ROS generation was measured by dichlorofluorescein fluorescence using confocal microscopy and was inhibited by transfection of antisense against NADPH subunits p22(phox) or p47(phox) or with Tempol. F-actin disassembly was observed by dual-channel confocal fluorescence imaging. PI3 kinase activity was detected by immunoblotting of phosphorylated Akt. RESULTS: In high glucose, generation of NADPH oxidase-dependent ROS was dependent on PKC-zeta. Conversely, sustained PKC-zeta activity was dependent on ROS generation, suggesting a positive feedback. PKC-zeta-dependent F-actin disassembly in high glucose required ROS generation. PDGF stimulated NADPH oxidase generation of ROS through a PKC-zeta mechanism that was independent of Akt phosphorylation and remained unchanged in high glucose. CONCLUSION: In high glucose, mesangial cell PKC-zeta is required for ROS generation from NADPH oxidase similar to PDGF stimulation of PKC-zeta-dependent ROS generation through a pathway independent of PI3 kinase. F-actin disassembly in high glucose also requires ROS. A positive feedback loop occurs between ROS and the activation of PKC-zeta in high glucose.     

蛋白激酶C激活在高糖诱导肾系膜细胞中的作用

目的：探讨高糖对系膜细胞蛋白激酶C（PKC）活性的影响及PKC在系膜细胞增殖、细胞外基质积聚中的作用。方法：采用大鼠系膜细胞进行体外培养,高糖作为激动剂,佛波酯（PMA）作为PKC抑制剂,甘露醇作为渗透压对照,用液闪仪测定PKC活性,^3H-TdR渗入法检测细胞增殖,ELISA法测定培养上清中纤维连接蛋白（FN）含量。结果：高糖可增加系膜细胞颗粒部分PKC活性、抑制细胞增殖、促进FN分泌,且与渗透压无关。抑制PKC后,可阻止高糖诱导的FN分泌。结论：高糖可激活系膜细胞PKC,促进细胞外基质积聚和糖尿病肾症的发生。     

Regulation of protein kinase C-delta and -epsilon isoforms by phorbol ester treatment of LLC-PK1 renal epithelia

BACKGROUND: LLC-PK1 renal epithelia are a widely used model for proximal tubular physiology and differentiation. Protein kinase C (PKC) has been observed to play a role in both processes. This study examines the subcellular distribution and down-regulation of PKC-delta and PKC-epsilon isoforms in phorbol ester-treated LLC-PK1 epithelia. METHODS: Cells were treated with 10-7 mol/L 12-O-tetradecanoyl phorbol 13-acetate (TPA) for up to seven days and were extracted as total cell lysates as well as cytosolic, membrane-associated (Triton-X soluble) and a third (Triton-X insoluble) fraction. The expression and cellular localization of PKC-delta and PKC-epsilon isoforms were then detected using Western immunoblot and immunofluorescence. RESULTS: Based on the use of an anti-PKC-delta monoclonal antibody, TPA was observed to cause a rapid decrease in total PKC-delta content, which then returned to near control levels by seven days of treatment. Immunofluorescence indicated that PKC-delta had a cytoskeletal localization within the cells, and a subtle cytoskeletal rearrangement occurred upon exposure to TPA. Western immunoblots showed that PKC-delta did not undergo the expected membrane translocation upon activation by TPA, but simply disappeared immediately from the cytosolic compartment. Conventional cell fractionation procedures such as homogenization and Triton extraction prior to Western immunoblot will, however, fail to evaluate completely PKC-delta in LLC-PK1 epithelia because of the highly stringent measures necessary to extract PKC-delta from the cytoskeletal compartment of these cells. Furthermore, we observed that a second (polyclonal) PKC-delta antibody may recognize phosphorylated forms of PKC-delta, which went unrecognized by the other antibody. PKC-epsilon was present in the cytosol, membrane, and Triton-X-insoluble fractions of the cells. TPA treatment resulted in a partial translocation of PKC-epsilon to both the membrane and Triton-X-insoluble fractions of the cell, but total PKC-epsilon remained essentially unchanged. CONCLUSIONS: The present data indicate that the localization of PKC-delta and subsequent redistribution within the LLC-PK1 cells in response to TPA treatment is highly unique and distinct from that of PKC-epsilon and PKC-alpha. An important methodological finding is that one given antibody may not recognize all phosphoproteins of a given PKC isoform.     

Effect of high glucose on basal intracellular calcium regulation in rat mesangial cell

BACKGROUND: A number of cellular mechanisms are critically dependent on intracellular Ca(2+) homeostasis. A sustained increase in the intracellular Ca(2+) concentration ([Ca(2+)](i)) is capable of activating a number of potentially harmful processes including phenotype change to secretory type, dysregulated cell proliferation, and cell injury and death. Mesangial cells (MCs) play an important role in the pathophysiology of diabetic nephropathy. METHODS: We evaluated the effect of high glucose on basal [Ca(2+)](i) in the unstimulated state and identified its contributing pathways. MCs were isolated and cultured from Sprague-Dawley rats. [Ca(2+)](i) was measured by fluorometric technique with fura-2AM. RESULTS: In a dose-dependent manner, superfusion of MCs with Tyrode's solution containing high glucose (30 and 50 mM) induced a delayed spontaneous increase in [Ca(2+)](i), which was not found in those with normal (5.5 mM) glucose or mannitol. The high glucose-induced increase in [Ca(2+)](i)()occurred through transmembrane influx of extracellular Ca(2+) and was blocked by SKF96365, an inhibitor of store-operated Ca(2+) influx. Na(+)-Ca(2+) exchanger (NCX) activity, a major channel regulating basal [Ca(2+)](i), and the clearing ability of intracellular Ca(2+) were depressed after MCs were cultured in high-glucose medium. Western blot analysis revealed the decreased expression of a 70-kD NCX protein in MCs cultured in high-glucose medium. CONCLUSIONS: A high-glucose concentration induced a spontaneous increase in basal [Ca(2+)](i) of MCs without stimulation. There was a decrease in the activity of NCX in the high-glucose condition, which seems to occur at the level of protein expression. The present results provide a novel insight into the mechanisms of diabetic nephropathy in that intracellular Ca(2+) homeostasis is an important secondary messenger and a mediator in hormonal signaling.     

脱氢抗坏血酸对高糖诱导系膜细胞产生氧自由基的影响

目的 探讨脱氢抗坏血酸(DHA)对高糖诱导系膜细胞产生氧自由基(ROS)的影响。 方法 (1)原代培养大鼠系膜细胞；(2)以Fe3+还原法检测细胞内抗坏血酸(AA)和DHA浓度，观察系膜细胞摄取AA和DHA的情况及葡萄糖、葡萄糖转运蛋白(GLUT)抑制剂细胞松弛素B对其的影响；(3)采用激光扫描共聚焦显微镜检测细胞内ROS，观察高糖诱导系膜细胞ROS产生的情况及不同浓度DHA对其的影响；(4)采用凝胶电泳迁移率法(EMSA)检测活性蛋白1(AP-1)和DNA的结合活性，观察DHA对高糖诱导的系膜细胞内AP-1 活性的影响。结果 (1)AA不能由细胞外进入系膜细胞，而DHA可以进入，并且随着细胞外葡萄糖浓度的增加，其进入速度减慢；细胞松弛素B则完全抑制了DHA进入到系膜细胞。(2)高糖快速诱导系膜细胞ROS产生增多；DHA抑制了高糖的这种作用，并且该抑制作用在≤4 mmol/L的浓度范围内呈浓度依赖性。(3)DHA抑制了高糖诱导的系膜细胞内AP-1 的激活。 结论 (1)系膜细胞是依赖DHA利用Vit C的细胞型；DHA进入该细胞依赖GLUT介导，高糖可抑制其进入细胞。(2)DHA可有效抑制高糖诱导的系膜细胞ROS产生增多，并在一定范围内呈浓度依赖性。(3)DHA在抑制ROS产生的同时，也显著抑制了高糖诱导的AP-1 的激活。     

Regulation of inositol transport by glucose and protein kinase C in mesangial cells.

Since inositol (Ins) depletion appears to be an important mechanism of cell injury in diabetic glomerulopathy, we studied Ins transport in cultured rat mesangial cells during hyperglycemia. High glucose stimulated [3H]-Ins uptake by 50 to 90% within 24 hours in a dose dependent manner. This effect was characterized by an increase in the Vmax of a Na(+)-dependent Ins transporter (10.3 +/- 0.2 vs. 16.4 +/- 0.4 pmol/mg/min, P less than 0.005). Since high glucose also induced activation of protein kinase C (PKC) in permeabilized mesangial cells, we examined the potential role of this enzyme in the stimulation of Ins transport by glucose. Both PKC inhibition with H7 and staurosporine, and down regulation of PKC by prolonged PMA (1.6 microM) treatment inhibited the stimulatory effect of glucose on Ins transport. In conclusion, high glucose stimulates Na(+)-dependent Ins transport in mesangial cells by a mechanism mediated by PKC. This process may represent an important adaptive response of mesangial cells to hyperglycemia.     

霉酚酸酯对高糖所致大鼠肾小球系膜细胞增殖的影响

霉酚酸酯（MMF）是一种新型的免疫抑制剂。本研究旨在探讨MMF对不同浓度葡萄糖所致的系膜细胞增殖及细胞外基质增多是否有抑制作用。     

Extracellular signal-regulated kinase mediates stimulation of TGF-beta1 and matrix by high glucose in mesangial cells

High ambient glucose exerts its injurious effects on renal cells through nonenzymatic and enzymatic pathways, including altered signal transduction and upregulation of the transforming growth factor-beta (TGF-beta) system. Extracellular signal-regulated kinase (ERK), a member of the mitogen-activated protein kinase (MAPK) cascade, is activated in mesangial cells cultured in high glucose and in glomeruli of diabetic rats. However, the biologic consequences of ERK activation in the kidney have not been investigated. To clarify the role of ERK activation, mouse mesangial cells were exposed to normal (5.5 mM) or high (25 mM) glucose with or without addition of PD98059, a specific inhibitor of MAPK/ERK kinase (MEK), an upstream kinase activator of ERK. Cells that were exposed to high glucose exhibited significant increases in ERK activity, TGF-beta1 expression (total protein, mRNA levels, and promoter activity), [(3)H]-proline uptake, and alpha1(I) collagen and fibronectin mRNA levels. Treatment with PD98059 (up to 25 microM) significantly inhibited these parameters. In contrast, 25 microM PD98059 had no significant effect on any of the parameters measured in cells that were exposed to normal glucose. Overexpression of MAPK phosphatase CL 100 prevented TGF-beta1 promoter activation by high glucose, confirming the involvement of the MEK-ERK pathway in response to high glucose. The conclusion is that activation of ERK in mesangial cells is responsible for high-glucose-induced stimulation of TGF-beta1 and contributes to the increased extracellular matrix expression.     

斯伐他汀对糖尿病肾病大鼠肾小球系膜细胞p38信号通路的影响

目的研究糖尿病肾病大鼠肾小球系膜细胞p38丝裂原活化蛋白激酶（MAPK）的表达及斯伐他汀对其的影响。方法分别以高糖、糖基化终产物（AGE）及过氧化氢孵育糖尿病大鼠肾小球系膜细胞（RMC），Western印迹法检测RMC的p38MAPK和TGF—β蛋白表达，p38MAPK特异性抑制剂SB203580及斯伐他汀预处理对其影响。结果高糖、AGE及过氧化氢均可单独激活p38MAPK，增加RMC的磷酸化（P）p38MAPK和TGF—β的蛋白表达；SB203580显著抑制TGF—β的蛋白表达（P〈0．05）；斯伐他汀抑制p38MAPK的活化并减少TGF—β的蛋白表达（P〈0．05）。结论p38MAPK可能是糖尿病肾病发生的始动信号之一。斯伐他汀可能通过抑制p38MAPK磷酸化而减少TGF—β的蛋白表达。     

磷脂酶D对高糖培养的肾小球系膜细胞骨架的影响

目的 研究高糖环境下肾小球系膜细胞（GMC）内磷脂酶D（PLD）的活性改变及其对细胞骨架的影响。方法 对高糖（30mmol/L)刺激48h的大鼠GMC，用酶联比色法测定磷脂酰胆碱专一性磷脂酶D（PC-PLD）活性，底物磷酸化法检测蛋白激酶C（PKC）的活性。用免疫荧光标记和共聚焦显微镜显示并测量F-actin的表达。结果 高糖刺激48h后，GMC内PC-PLD和PKC活性明显增高，而F-actin荧光表达减少，排列紊乱，给予PC-PLD抑制剂后，高糖培养的GMCPKC活性明显下降。F-actin的荧光表达和排列都得到显著改善。结论 高糖时PLD活性增高可以通过PKC途径影响GMC骨架的组装状态。改变系膜细胞收缩功能。     

肾小球系膜细胞蛋白激酶C同工酶的激活与糖尿病肾病

糖尿病肾病(DN)是糖尿病全身微血管并发症之一,以早期肾小球滤过率升高、继以肾小球毛细血管基底膜增厚、系膜区基质沉积,最终弥漫性或结节性肾小球硬化形成为特征.高血糖是DN损害的主要因素,而在高糖环境下肾小球系膜细胞(mesangial cell,MC) 蛋白激酶C (PKC)的激活是进展性DN的中心环节.     

高糖刺激肾小球系膜细胞葡萄糖转运蛋白4及p21的表达及其意义

目的探讨早期糖尿病肾病(DN)肾小球系膜细胞(GMC)中葡萄糖转运蛋白(GLUT)4、p21mRNA表达变化及其与GMC肥大的关系。方法大鼠1097系膜细胞株分为高糖组、甘露醇组、不同浓度胰岛素组、高糖加不同浓度胰岛素组、正常对照组。用RT-PCR法检测各组GLUT4mRNA、p21mRNA的表达。流式细胞仪测各组GMC体积大小。结果正常对照组GMC有一定GLUT4mRNA、p21mRNA表达。高糖组GLUT4mRNA表达明显下降,p21mRNA表达明显增加。胰岛素刺激GMCGLUT4mRNA表达存在浓度依赖关系。p21mRNA表达越高,细胞前向角度散射光(FSC)越强,GMC体积越大。结论高糖刺激导致GMC肥大,GMC的p21mRNA表达上调和GLUT4mRNA表达下调与DN早期GMC肥大-肾小球肥大有关。     

Interleukin 1 and the glomerular mesangium. III. IL-1-dependent stimulation of mesangial cell protein kinase activity

Interleukin 1 (IL-1) exerts a number of biologic actions upon cultured glomerular mesangial cells (MC). These include stimulation of cellular proliferation and induction of prostaglandin and type IV collagenase secretion. It was determined that this activity, as with other polypeptide growth factors, was associated with the activation of specific MC plasma membrane protein kinases. Plasma membranes from cycling MC were incubated with purified IL-1 and (32P) ATP in the absence of calcium and cyclic nucleotides. Macrophage IL-1 stimulated the rapid phosphorylation of several plasma membrane proteins, the most significant of which were 52-55 kd, 46 kd, and 20 kd in size. Macrophage IL-1 induced specific membrane phosphorylation in concentrations as low as 1.5 x 10(-12) M, an effect obtained with equivalent concentrations of purified MC IL-1. The 46 kd phosphoprotein, which was the most prominent, was alkali-resistant and contained phosphotyrosine when examined by phosphoamino acid analysis. The 52-55 kd and 20 kd phosphoproteins were alkali-labile and contained phosphoserine. The 46 kd phosphoprotein was the major phosphoprotein recovered from Con A-Sepharose and IL-1 affinity columns. Induction of plasma membrane-associated protein kinase activity may represent one mechanism whereby IL-1 initiates mesangial cellular activation.     

Inhibitory effects of nicorandil on rat mesangial cell proliferation via the protein kinase G pathway

We investigated the effects of nicorandil, which is a hybrid between a nitrate and an ATP-sensitive potassium channel (K(ATP)) opener, on cultured rat mesangial cell proliferation. Nicorandil (1 microM to 1 mM inhibited [(3)H]thymidine incorporation into rat mesangial cells in a concentration-dependent manner. Nicorandil (1 microM to 1 mM) also inhibited the number of cells. Nicorandil increased cyclic guanosine 3',5'-cyclic monophosphate accumulation in mesangial cells. A protein kinase G inhibitor, KT5823, partially eliminated the inhibition of mesangial cell proliferation by nicorandil. Methylene blue, a guanylate cyclase inhibitor, blocked the inhibitory effect of nicorandil on mesangial cell proliferation. We also examined the effects of K(ATP) mediators. Cromakalim, a K(ATP) activator, and glibenclamide, a K(ATP) inhibitor, had little effect on the proliferation of mesangial cells. These results suggest that the inhibitory effects of nicorandil on mesangial cell proliferation are mediated via the protein kinase G pathway.     

Homocysteine induces mesangial cell apoptosis via activation of p38-mitogen-activated protein kinase

Hyperhomocysteinemia is prevalent among patients with chronic kidney disease (CKD) and has been linked to progressive kidney and vascular diseases. Increased glomerular mesangial cell (MC) turnover, including proliferation and apoptosis, is a hallmark of CKD. Activation of p38-mitogen-activated protein kinase (p38-MAPK) has been linked to apoptosis in many cell lines. Accordingly, we studied the effect of homocysteine (Hcy) on MC p38-MAPK signalling and apoptosis. Hcy (50 microM/24 h) increased MC apoptosis as determined by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate (dUTP) nick end labelling (TUNEL) and single-stranded DNA (ssDNA) analysis. In addition to increases in pro-caspase-3 protein and caspase-3 activity, cells exposed to Hcy manifested enhanced reactive oxygen species content. Hcy increased p38-MAPK activity (fivefold), with maximal effect at 50 microM and 20 min; p38-MAPK activation was attenuated by N-acetylcysteine (Nac) and catalase (Cat), further indicating that the effect was via oxidative stress. Confocal microscopy revealed activation and nuclear translocation of p38-MAPK that was attenuated by Cat. In addition, Hcy-induced apoptosis as determined by TUNEL and ssDNA assay was abrogated by Nac, Cat, and SB203580 (p38-MAPK inhibitor). We conclude that in MC, Hcy (i) activates p38-MAPK and increases p38MAPK nuclear translocation via an oxidative stress dependent mechanism and (ii) induces DNA damage and apoptosis that is dependent on oxidative stress and p38-MAPK activation.     

葡萄糖转运蛋白4及其下游信号分子在高糖刺激下肾小球系膜细胞中的作用

目的 探讨高糖和胰岛素对肾小球系膜细胞（GMC）葡萄糖转运蛋白4（GLUT4）和Cbl相关蛋白（CAP）的mRNA表达及细胞骨架纤维状肌动蛋白F-actin 的影响,探讨糖尿病肾病发生发展中GLUT4 及其下游分子F-actin和CAP的重要作用。 方法 将细胞分为8组：正常对照组、生理浓度胰岛素（10－9 mol/L）组、低浓度胰岛素（10－8 mol/L）组、高浓度胰岛素（10－6 mol/L）组、高糖（30 mmol/L）组、甘露醇组（25 mmol/L甘露醇＋5 mmol/L葡萄糖）、高糖加高浓度胰岛素组、高糖加生理浓度胰岛素组。采用RT-PCR法和免疫组化法,观察不同情况下GMC中GLUT4蛋白和mRNA以及CAP mRNA 的表达及其变化。Rhodamine-phalloidin染色和激光共聚焦显微镜观察F-actin形态及荧光强度。 结果 正常对照组GMC中GLUT4蛋白和mRNA以及CAP mRNA有一定表达,而生理浓度胰岛素组与正常对照组差异均无统计学意义。高糖组GLUT4蛋白（P < 0.01)和mRNA（P < 0.05）以及CAP mRNA（P < 0.01)表达均显著减少,F-actin解聚增加（P < 0.01）;而甘露醇组以上各指标与对照组差异均无统计学意义。低浓度胰岛素组和高浓度胰岛素组GLUT4 mRNA表达分别为生理浓度胰岛素组的2.06倍和2.66倍,GLUT4蛋白表达分别为对照组的1.93倍和2.83倍,CAP mRNA表达分别为对照组的1.91倍和2.15倍,F-actin荧光强度分别为对照组的1.296倍及1.224倍,均呈一定的浓度依赖性。高糖加高浓度胰岛素组GLUT4 mRNA表达为高糖组的2.15倍（P < 0.05）,GLUT4蛋白表达为高糖组的2.08倍（P < 0.01）,CAP mRNA表达为高糖组的2.14倍（P < 0.01）,F-actin荧光强度为高糖组的1.838倍（P < 0.01）。GLUT4 mRNA与CAP mRNA呈正相关（r = 0.905,P = 0.002）;GLUT4与F-actin呈正相关（r = 0.929,P = 0.001）。 结论 （1）正常GMC中GLUT4 mRNA与蛋白、CAP mRNA有一定表达。（2）高糖可抑制GLUT4的蛋白和mRNA以及CAP mRNA表达,促进F-actin解聚。（3）胰岛素能部分拮抗高糖导致系膜细胞中GLUT4的蛋白和mRNA以及CAP mRNA表达的下调作用。（4）GLUT4、CAP和F-actin是糖尿病肾病发生发展的重要影响因子之一。     

TGF-{beta}- and angiotensin-II-induced mesangial matrix protein secretion is mediated by protein kinase C

Background: Glomerulonephritis is characterized by the accumulation of extracellular matrix protein within the glomerulus. This process, when allowed to proceed unimpeded, leads to glomerulosclerosis and eventually to cessation of glomerular filtration. There is evidence that protein kinase C (PKC) activation plays an important role in mediating at least some of the effects of TGF-{beta} in vascular smooth-muscle cells. The current study was undertaken to determine whether PKC activity is required for both TGF-{beta} and angiotensin II (Ang II) to induce mesangial cell matrix protein secretion. Methods: PKC was inhibited by two separate methods, and [³H]thymidine incorporation was assessed in both the presence and the absence of PKC inhibition. Conditioned medium from cells stimulated with TGF-{beta} or Ang II was collected and analysed for secreted matrix proteins and sulphated proteins by SDS-polyacrylamide gel electrophoresis and western blotting. Results: Twenty-four-hour incubation of rat mesangial cells with phorbol-12-myristate-13-acetate (PMA) reduced total PKC activity to basal levels. Both TGF-{beta} and Ang II were mitogenic in mesangial cells, and chronic PMA pre-incubation inhibited this DNA synthesis. TGF-{beta} and Ang II-induced sulphated protein secretion into conditioned medium was markedly attenuated in PKC-downregulated cells. Secretion of the specific matrix proteins laminin and fibronectin by mesangial cells stimulated with either TGF-{beta} or Ang II was also diminished in PKC-downregulated cells and in cells pre-incubated with the specific PKC inhibitor, chelerythrine. There was no evidence of generalized cell toxicity or decreased non-specific protein synthesis caused by these PKC inhibitors. Conclusions: PKC is a key intermediary in the process by which TGF-{beta} and Ang II cause DNA synthesis and mesangial cell matrix protein production. Thus, PKC inhibitors deserve further study as potential therapeutic agents for a variety of glomerular diseases.     

褪黑素对高糖条件下培养的大鼠系膜细胞增殖、凋亡和细胞周期的影响

糖尿病肾病（DN）晚期肾脏细胞凋亡与肾功能恶化程度成正比，抑制凋亡则可延缓肾小球硬化。褪黑素（MT）是松果体分泌的神经内分泌激素，肾脏是其靶器官之一。研究显示MT对DN肾脏有明显的保护作用，但MT对DN晚期肾小球系膜细胞（MC）凋亡的影响尚未检索到有关报道。本试验选用大鼠MC为研究对象，来观察MT对高糖诱导的MC凋亡的影响。