Attenuation of mouse mesangial cell contractility by high glucose and mannitol: involvement of protein kinase C and focal adhesion kinase

Cellular mechanism of action of forsythiaside for the treatment of diabetic kidney disease

Background: Diabetic kidney disease (DKD) becomes the leading cause of death for end-stage renal disease, whereas the potential mechanism is unclear and effective therapy is still rare. Our study was designed to investigate the cellular mechanism of Forsythiaside against DKD. Materials and Methods: The targets of Forsythiaside and the DKD-related targets were obtained from databases. The overlapping targets in these two sets were regarded as potential targets for alleviation of DKD by Forsythiaside. The targets of diabetic podocytopathy and tubulopathy were also detected to clarify the mechanism of Forsythiaside ameliorating DKD from the cellular level. Results: Our results explored that PRKCA and RHOA were regarded as key therapeutic targets of Forsythiaside with excellent binding affinity for treating DKD podocytopathy. Enrichment analysis suggested the underlying mechanism was mainly focused on the oxidative stress and mTOR signaling pathway. The alleviated effects of Forsythiaside on the reactive oxidative species accumulation and PRKCA and RHOA proteins upregulation in podocytes were also confirmed. Conclusion: The present study elucidates that Forsythiaside exerts potential treatment against DKD which may act directly RHOA and PRKCA target by suppressing the oxidative stress pathway in podocytes. And Forsythiaside could be regarded as one of the candidate drugs dealing with DKD in future experimental or clinical researches.

Elevated urinary IL-36α and IL-18 levels are associated with diabetic nephropathy in patients with type 2 diabetes mellitus

BACKGROUND

Inflammatory cytokines have been reported to be pathogenic factors for the development and progression of diabetic nephropathy (DN). Interleukin (IL)-36α is a newly discovered member of the IL-1 cytokine family that has been implicated in animal models of renal impairment. However, little is known about the role of IL-36α in DN in humans. The purpose of the present study was to assess the levels of IL-36α and IL-18 in type 2 diabetic patients (T2DM) patients with and without DN.

METHODS

Subjects were divided into 3 groups: Control (N.=20), T2DM without DN (N.=30), and T2DM with DN (N.=30). Urinary IL-36α and IL-18 levels were assessed using ELISA. Correlation analysis was performed to determine the association of the IL levels with clinical markers of T2DM and DN.

RESULTS

IL-36α and IL-18 levels were significantly elevated in T2DM patients with DN, when compared to T2DM patients without DN (P<0.0001, P=0.0025, respectively) and controls (P<0.0001, for both). IL-36α levels showed a positive correlation with urinary albumin excretion (r=0.754, P<0.0001), HbA1c (r=0.433, P=0.0168), fasting plasma glucose (r=0.433, P=0.0168) and negative correlation with glomerular filtration rate (r=-0.852 P<0.0001).

CONCLUSIONS

The results highlighted the association of IL-36α with DN. However, further extensive studies are suggested for evaluating the association.

High glucose downregulates myocardin expression in rat glomerular mesangial cells via the ERK signaling pathway

Mesangial cells (MCs), which are vascular smooth muscle-derived cells, occupy the central position in the glomerulus. Diabetic nephropathy (DN) is one of the most common diabetes complications and is likely attributed to the loss of MC contractility. Myocardin stimulates downstream vascular smooth muscle genes and regulates the contractility of vascular smooth muscle cells. Therefore, we hypothesized that myocardin is expressed in MCs and that high glucose is involved in the regulation of myocardin and downstream contractile genes in the context of DN. Confocal microscopy revealed that myocardin is expressed in rat MCs. Western blot and RT-qPCR analyses showed that treatment with 30 mM D-glucose significantly downregulated the mRNA and protein levels of myocardin and downstream SM α-actin. As an isotonic contrast, 30 mM mannitol did not affect myocardin mRNA levels but did downregulate myocardin protein levels. Treatment with 30 mM mannitol also downregulated SM α-actin mRNA and protein levels. Conversely, as another isotonic contrast, 30 mM L-glucose also had no effect on myocardin and SM α-actin expression in MCs. The extracellular signal-regulated kinase (ERK) pathway was activated by treatment with 30 mM D-glucose or mannitol, while specific inhibitors of the ERK pathway (PD98059) compromised the downregulation of myocardin and SM α-actin triggered by high glucose or mannitol. Thus we revealed that myocardin is expressed in MCs and that high glucose downregulates myocardin expression and downstream contractile protein SM α-actin via the ERK pathway. Our results suggest a novel mechanism for high glucose inhibition of MC contraction, which contributes to DN pathogenesis.

Hypo- and hyperglycemia impair endothelial cell actin alignment and nitric oxide synthase activation in response to shear stress

Uncontrolled blood glucose in people with diabetes correlates with endothelial cell dysfunction, which contributes to accelerated atherosclerosis and subsequent myocardial infarction, stroke, and peripheral vascular disease. In vitro, both low and high glucose induce endothelial cell dysfunction; however the effect of altered glucose on endothelial cell fluid flow response has not been studied. This is critical to understanding diabetic cardiovascular disease, since endothelial cell cytoskeletal alignment and nitric oxide release in response to shear stress from flowing blood are atheroprotective. In this study, porcine aortic endothelial cells were cultured in 1, 5.55, and 33 mM D-glucose medium (low, normal, and high glucose) and exposed to 20 dynes/cm² shear stress for up to 24 hours in a parallel plate flow chamber. Actin alignment and endothelial nitric oxide synthase phosphorylation increased with shear stress for cells in normal glucose, but not cells in low and high glucose. Both low and high glucose elevated protein kinase C (PKC) levels; however PKC blockade only restored actin alignment in high glucose cells. Cells in low glucose instead released vascular endothelial growth factor (VEGF), which translocated β-catenin away from the cell membrane and disabled the mechanosensory complex. Blocking VEGF in low glucose restored cell actin alignment in response to shear stress. These data suggest that low and high glucose alter endothelial cell alignment and nitric oxide production in response to shear stress through different mechanisms.

Inflammation and oxidative stress in diabetic nephropathy: new insights on its inhibition as new therapeutic targets

Diabetes and insulin resistance can greatly increase microvascular complications of diabetes including diabetic nephropathy (DN). Hyperglycemic control in diabetes is key to preventing the development and progression of DN. However, it is clinically very difficult to achieve normal glucose control in individual diabetic patients. Many factors are known to contribute to the development of DN. These include diet, age, lifestyle, or obesity. Further, inflammatory- or oxidative-stress-induced basis for DN has been gaining interest. Although anti-inflammatory or antioxidant drugs can show benefits in rodent models of DN, negative evidence from large clinical studies indicates that more effective anti-inflammatory and antioxidant drugs need to be studied to clear this question. In addition, our recent report showed that potential endogenous protective factors could decrease inflammation and oxidative stress, showing great promise for the treatment of DN.

Cytokines in diabetic nephropathy

Diabetic nephropathy (DN), the most common cause of end-stage renal disease (ESRD), is increasingly considered an inflammatory process characterized by leukocyte infiltration at every stage of renal involvement. Cytokines act as pleiotropic polypeptides that regulate inflammatory and immune responses, providing important signals in the pathologic and physiologic processes. Inflammation and activation of the immune system are closely involved in the pathogenesis of diabetes and its microvascular complications. Proinflammatory, Th1, Th2, and Th17 cytokines, as well as TGF-beta, all take part in the development and progression of DN. Gene polymorphism of cytokines and their receptors may have functional variations and can be applied to predict the susceptibility and progression to DN. Improved knowledge on recognizing cytokines as significant pathogenic mediators in DN leaves opens the possibility of new potential therapeutic agents for future clinical treatments.

Involvement of F-actin in chaperonin-containing t-complex 1 beta regulating mouse mesangial cell functions in a glucose-induction cell model

The aim of this study is to investigate the role of chaperonin-containing t-complex polypeptide 1 beta (CCT2) in the regulation of mouse mesangial cell (mMC) contraction, proliferation, and migration with filamentous/globular-(F/G-) actin ratio under high glucose induction. A low CCT2 mMC model induced by treatment of small interference RNA was established. Groups with and without low CCT2 induction examined in normal and high (H) glucose conditions revealed the following major results: (1) low CCT2 or H glucose showed the ability to attenuate F/G-actin ratio; (2) groups with low F/G-actin ratio all showed less cell contraction; (3) suppression of CCT2 may reduce the proliferation and migration which were originally induced by H glucose. In conclusion, CCT2 can be used as a specific regulator for mMC contraction, proliferation, and migration affected by glucose, which mechanism may involve the alteration of F-actin, particularly for cell contraction.

Characterization of the mechanisms of the increase in PPARδ expression induced by digoxin in the heart using the H9c2 cell line

BACKGROUND AND PURPOSE

Digoxin has been used as an inotropic agent in heart failure for a long time. Troponin I (TnI) phosphorylation is related to cardiac contractility, and the genes are regulated by peroxisome proliferator-activated receptors (PPARs). Our previous studies indicated that cardiac abnormality related to the depressed expression of PPARδ in the hearts of STZ rats is reversed by digoxin. However, the cellular mechanisms for this effect of digoxin have not been elucidated. The aim of the present study was to investigate possible mechanisms for this effect of digoxin using the H9c2 cell line cultured in high glucose (HG) conditions.

METHODS

The effects of digoxin on PPARδ expression, intracellular calcium and TnI phosphorylation were investigated in cultured H9c2 cells, maintained in a HG medium, by using Western blot analysis.

RESULTS

Digoxin increased PPARδ expression in H9c2 cells subjected to HG conditions, and increase the intracellular calcium concentration. This effect of digoxin was blocked by BAPTA-AM at concentrations sufficient to chelate calcium ions. In addition, the calcineurin inhibitor cyclosporine A and KN93, an inhibitor of calcium/calmodulin-dependent protein kinase, inhibited this action. Digoxin also increased TnI phosphorylation and this was inhibited when PPARδ was silenced by the addition of RNAi to the cells. Similar changes were observed on the contraction of H9c2 cells.

CONCLUSION

The results suggest that digoxin appears, through calcium-triggered signals, to reverse the reduced expression of PPARδ in H9c2 cells caused by HG treatment.

Role of T cells in type 2 diabetic nephropathy

Type 2 diabetic nephropathy (DN) is the most common cause of end-stage renal disease and is increasingly considered as an inflammatory disease characterized by leukocyte infiltration at every stage of renal involvement. Inflammation and activation of the immune system are closely involved in the pathogenesis of diabetes and its microvascular complications. Macrophage has been well recognized to play an important role in type 2 DN, leukocyte infiltration, and participated in process of DN, as was proposed recently. Th1, Th2, Th17, T reg, and cytotoxic T cells are involved in the development and progression of DN. The purpose of this review is to assemble current information concerning the role of T cells in the development and progression of type 2 DN. Specific emphasis is placed on the potential interaction and contribution of the T cells to renal damage. The therapeutic strategies involving T cells in the treatment of type 2 DN are also reviewed. Improving knowledge of the recognition of T cells as significant pathogenic mediators in DN reinforces the possibility of new potential therapeutic targets translated into future clinical treatments.

Molecular role of GATA binding protein 4 (GATA-4) in hyperglycemia-induced reduction of cardiac contractility

Background

Diabetic cardiomyopathy, a diabetes-specific complication, refers to a disorder that eventually leads to left ventricular hypertrophy in addition to diastolic and systolic dysfunction. In recent studies, hyperglycemia-induced reactive oxygen species (ROS) in cardiomyocytes have been linked to diabetic cardiomyopathy. GATA binding protein 4 (GATA-4) regulates the expression of many cardio-structural genes including cardiac troponin-I (cTnI).

Methods

Streptozotocin-induced diabetic rats and H9c2 embryonic rat cardiomyocytes treated with a high concentration of glucose (a D-glucose concentration of 30 mM was used and cells were cultured for 24 hr) were used to examine the effect of hyperglycemia on GATA-4 accumulation in the nucleus. cTnI expression was found to be linked to cardiac tonic dysfunction, and we evaluated the expression levels of cTnI and GATA-4 by Western blot analysis.

Results

Cardiac output was lowered in STZ-induced diabetic rats. In addition, higher expressions of cardiac troponin I (cTnI) and phosphorylated GATA-4 were identified in these rats by Western blotting. The changes were reversed by treatment with insulin or phlorizin after correction of the blood sugar level. In H9c2 cells, ROS production owing to the high glucose concentration increased the expression of cTnI and GATA-4 phosphorylation. However, hyperglycemia failed to increase the expression of cTnI when GATA-4 was silenced by small interfering RNA (siRNA) in H9c2 cells. Otherwise, activation of ERK is known to be a signal for phosphorylation of serine105 in GATA-4 to increase the DNA binding ability of this transcription factor. Moreover, GSK3β could directly interact with GATA-4 to cause GATA-4 to be exported from the nucleus. GATA-4 nuclear translocation and GSK3β ser9 phosphorylation were both elevated by a high glucose concentration in H9c2 cells. These changes were reversed by tiron (ROS scavenger), PD98059 (MEK/ERK inhibitor), or siRNA of GATA-4. Cell contractility measurement also indicated that the high glucose concentration decreased the contractility of H9c2 cells, and this was reduced by siRNA of GATA-4.

Conclusions

Hyperglycemia can cause systolic dysfunction and a higher expression of cTnI in cardiomyocytes through ROS, enhancing MEK/ERK-induced GATA-4 phosphorylation and accumulation in the cell nucleus.

Attributes of antiangiogenic factor plasminogen kringle 5 in glomerulonephritis

CONTEXT

Plasminogen kringle domain (K) 5 is known to inhibit endothelial cell growth, but limited data are available investigating the relationship between K5 and glomerulonephritis (GN).

OBJECTIVE

To understand the relationships among K5, GN, and glomerular endothelial cells in GN mice models and human subjects.

DESIGN

Two mice models of GN and 2 categories of human GN biopsy samples were collected to gain insight into the disease mechanism from the laboratory to bedside. In the mechanistic animal study, membranous nephropathy (MN) and focal segmental glomerulosclerosis mice models were used. Kringle domain 5 in the diseased kidney was located by immunofluorescence and quantified by Western blotting. In the kinetic animal study, different MN time points were stained with K5, immunoglobulin G, and C3 by immunofluorescence. CD31 and proliferating cell nuclear antigen were evaluated by immunohistochemical double staining for alterations in the glomerular endothelial cells. Biopsy samples from patients diagnosed with antibody (Ab)-mediated and non-Ab-mediated GN were collected for K5 analysis.

RESULTS

The expression level of K5 was found to be significant in MN, but not in focal segmental glomerulosclerosis, and was markedly elevated in the diseased glomeruli along the capillary walls. Kringle domain 5 levels increased steadily with the evolution of MN, appearing after the deposition of Abs. In altered glomerular endothelial cells, CD31 decreased with the evolution of MN. In human subjects, K5 occurred only in patients with Ab GN.

CONCLUSIONS

Kringle domain 5 might be involved in the progression of Ab-mediated GN and associated with the alteration of MN glomerular endothelial cell growth.

Effects of fungal statins on high-glucose-induced mouse mesangial cell hypocontractility may involve filamentous actin, t-complex polypeptide 1 subunit beta, and glucose regulated protein 78

Glomerular hyperfiltration is associated with mesangial cell hypocontractility. How 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitors (statins) influence mesangial cell contraction is unclear. We investigated the effect of statins on mesangial cell hypocontractility and identified candidate proteins and filamentous/globular (F/G)-actin involved in this process. A high-glucose-induced mouse mesangial cell hypocontractility model was treated with fungal statins, simvastatin (Sim), lovastatin (Lov), and pravastatin (Pra). The optimum statin dose was determined by an 3-(4,5-Dimethylthiazol-2-Yl)-2,5-Diphenyltetrazolium Bromide (MTT) assay and then applied to a cell model. A 2-dimensional gel/matrix-assisted laser desorption/ionization time-of-flight mass spectrometer analysis was used to evaluate protein expression cells incubated in the presence of a normal level of glucose (N), a high level of glucose (H), and a high level of glucose plus Sim (H + S). Candidate proteins were analyzed. Finally, the ratio of F/G actin in groups N, H, and H+S was evaluated. The MTT assay showed that Sim and Lov exerted dose- and time-related inhibition of proliferation of mesangial cells at N, but Pra had no effect. The optimum doses selected for Sim was 1 microM and for Lov was 3 microM, which were 1 increment before significant proliferation inhibition. Both doses reversed cell hypocontractility significantly, but Sim was chosen for further proteomic and F/G actin analyses. Proteomic analysis of groups N, H, and H + S showed that 18 proteins were involved in hypocontractility. These proteins were grouped and analyzed based on their known functions. Two selected proteins, TCP-1beta and GRP78, that were upregulated and downregulated, respectively, were confirmed by Western blot and immunohistochemistry. In regard to the F/G actin, group H had a significantly lower ratio than that of group N, and group H + S returned to a level similar to that of group N. In conclusion, Sim and Lov both seem to reverse mesangial cell hypocontractility. The process of Sim reversal of mesangial cell hypocontractility may involve F-actin, TCP-1beta, and GRP78.

Emodin ameliorates high-glucose induced mesangial p38 over-activation and hypocontractility via activation of PPARgamma

Early stage diabetic nephropathy is characterized by elevated glomerular filtration. Recent studies have identified high-glucose induced p38 MAPK (p38) over-activation in mesangial cells. Mesangial hypocontractility is the major underlying mechanism, however, no ameliorating agents are currently available. We investigated the protective effects of emodin on high-glucose induced mesangial cell hypocontractility. Mesangial cells were cultured under normal (5.6 mM) and high glucose (30 mM) conditions. Emodin was administrated at doses of 50 mg/l and 100 mg/l. Angiotension II stimulated cell surface reductions were measured to evaluate cell contractility. p38 activity was detected using Western blotting. To further explore the possible mechanism of emodin, expression of the peroxisome proliferator- activated receptorgamma (PPARgamma) was measured and its specific inhibitor, gw9662, was administrated. Our results showed: (1) high-glucose resulted in a 280% increase in p38 activity associated with significant impairment of mesangial contractility; (2) emodin treatment dose-dependently inhibited high-glucose induced p38 over-activation (a 40% decrease for 50 mg/l emodin and a 73% decrease for 100 mg/l emodin), and mesangial hypocontractility was ameriolated by emodin; (3) both the PPARgamma mRNA and protein levels were elevated after emodin treatment; (4) inhibition of PPARgamma using gw9662 effectively blocked the ameliorating effects of emodin on high-glucose induced p38 over-activation and mesangial hypocontractility. Emodin effectively ameliorated p38 over-activation and hypocontractility in high-glucose induced mesangial cells, possibly via activation of PPARgamma.

Effects of mannitol alone and mannitol plus furosemide on renal oxygen consumption, blood flow and glomerular filtration after cardiac surgery

OBJECTIVE

Imbalance of the renal medullary oxygen supply/demand relationship can cause hypoxic medullary damage and ischaemic acute renal failure (ARF). The use of mannitol for prophylaxis/treatment of clinical ischaemic ARF is controversial and the effect of mannitol on renal oxygenation in man has not yet been investigated. We evaluated the effects of mannitol on renal oxygen consumption (RVO(2))(,) renal blood flow (RBF) and glomerular filtration rate (GFR) in postoperative patients.

DESIGN

Prospective interventional study.

SETTING

University hospital cardiothoracic ICU.

PATIENTS

Ten uncomplicated mechanically ventilated and sedated postcardiac surgery patients with preoperatively normal renal function.

INTERVENTIONS

Mannitol infusion (225 mg/kg + 75 mg/kg/h) and combined mannitol and furosemide infusion (0.25 mg/kg + 0.25 mg/kg/h).

MEASUREMENTS AND RESULTS

Systemic haemodynamics were evaluated by a pulmonary artery catheter. RBF and GFR were measured by the renal vein thermodilution technique and by renal extraction of (51)Cr-EDTA, respectively. Mannitol increased urine flow (60%), GFR (20%) and filtration fraction (FF) (20%) with no change in RBF. This was accompanied by an increase in renal sodium reabsorption (18%), RVO(2) (19%) and renal oxygen extraction (21%). When combined with mannitol, furosemide normalised sodium reabsorption, RVO(2), renal oxygen extraction with no change in RBF, while GFR and FF were still elevated compared to control.

CONCLUSIONS

In patients with normal renal function, mannitol increases GFR, which increases tubular sodium load, sodium reabsorption and RVO(2) after cardiac surgery. The lack of effect on RBF, indicates that mannitol impairs the renal oxygen supply/demand relationship. Furosemide normalised renal oxygenation when combined with mannitol.

Detailed glomerular ultrastructure in Japanese type 2 diabetic patients by the quick-freezing and deep-etching method

Mesangial expansion and glomerular basement membrane (GBM) thickening did not correlate with urinary albumin excretion (UAE) in type 2 diabetic patients in our previous studies; therefore, it was necessary to elucidate more detailed ultrastructural changes in the early stages of diabetic nephropathy (DN) in type 2 diabetic patients. The quick-freezing and deep-etching (QF-DE) method allows us to examine three-dimensional ultrastructures of human renal glomeruli in vivo at high resolution. The QF-DE method was applied to six type 2 diabetic patients without definable renal diseases other than DN. Four patients were normoalbuminuric (NA) and the other two were microalbuminuria (MA). Three control specimens were the normal parts from nephrectomies due to renal cell carcinomas. Electron microscopic morphometric analyses provided quantitative glomerular structural changes. Replica membranes were prepared by the QF-DE method, and diameters of mesh structures at the GBM and mesangial matrix (MM) were measured on electron micrographs as previously described. By the QF-DE method, both the GBM middle layer and MM were composed of polygonal meshwork structures. The mesh pores of the GBM and MM were more enlarged and irregular in shape in NA diabetic patients than those of the controls, and these ultrastructural changes became more obvious in MA patients. The mesh diameters of the GBM and MM in the diabetic patients were also larger than those of the controls. Such a mesh diameter of the GBM was well correlated with the amount of UAE, while the mesh diameter of MM showed a slight correlation with UAE. Although there were small number of subjects in the present study, the detailed ultrastructural changes in NA and MA type 2 diabetic patients, which had not been disclosed by conventional electron microscopy, were revealed by the QF-DE method. Increased mesh diameters of GBM might be related with the increase of UAE.

Hyperglycemia reduces survival and impairs function of circulating blood-derived progenitor cells

OBJECTIVE

Function and availability of circulating progenitor cells (CPC) have been shown to be impaired in patients with diabetes mellitus (DM). Therefore, the aim of the present study was to analyze possible mechanisms leading to the reduction of CPC amount and function.

METHODS AND RESULTS

Peripheral blood mononuclear cells (MNCs) of healthy donors (n=15) were cultivated under hyperglycemia (HG) conditions (12 mmol/L D-Glucose) or in osmotic control medium (Con) (5 mmol/L D-Glucose plus 7 mmol/L L-Glucose) for 7 days. CPC amount was determined by uptake of acetylated low-density lipoprotein and lectin binding. On the functional level, cell cycle status, nitric oxide (NO) production, and migrational and integrative capacity of CPCs were assessed. HG conditions caused a significant decrease in CPC amount derived from healthy MNCs. Furthermore, HG conditions led to a functional impairment, reflected in a decreased NO production and matrix metalloproteinase (MMP)-9 activity, as well as an impairment of the migrational and integrative capacities.

CONCLUSIONS

HG, a main feature of DM, affects important functional characteristics of CPCs. These results may provide further insight into the pathomechanism of endothelial dysfunction in HG.