Interaction of MAPK and 12-lipoxygenase pathways in growth and matrix protein expression in mesangial cells

Impact of SGLT2 inhibitors on the kidney in people with type 2 diabetes and severely increased albuminuria

INTRODUCTION

Diabetes is the most common cause of end stage kidney disease. Therapies such as sodium-glucose co-transporter-2 inhibitors have been identified over the last decade as effective oral hypoglycemic agents that also confer additional cardio and kidney protection. Knowledge of their mechanism of action and impact on patients with diabetes and albuminuria is vital in galvanizing prescriber confidence and increasing clinical uptake.

AREAS COVERED

This manuscript discusses the pathophysiology of diabetic kidney disease, patho-physiological mechanisms for sodium-glucose co-transporter-2 inhibitors, and their impact on patients with Type 2 diabetes mellitus and albuminuric kidney disease.

EXPERT OPINION

Sodium-glucose co-transporter-2 inhibitors reduce albuminuria with consequent benefits on cardiovascular and kidney outcomes in patients with diabetes and severe albuminuria. Whilst they have been incorporated into guidelines, the uptake of these agents into clinical practice has been slow. Increasing the uptake of these agents into clinical practice is necessary to improve outcomes for the large number of patients with diabetic kidney disease globally.

Increased lipoxygenase and decreased cytochrome P450s metabolites correlated with the incidence of diabetic nephropathy: Potential role of eicosanoids from metabolomics in type 2 diabetic patients

Diabetic nephropathy (DN) is the major cause of chronic kidney disease and end-stage renal disease. Previous studies have demonstrated that long-chain omega-3 polyunsaturated fatty acids (PUFAs) might have therapeutic potential in reducing proteinuria in DN. However, the local level of eicosanoids derived from PUFAs in the plasma of DN patients remains unclear. This work aims to study the eicosanoid profile difference in plasma of DN patients and type 2 diabetes (T2D) without DN. A total of 27 T2D patients with similar diabetic duration were recruited and divided into T2D+DN group and T2D+NDN (non-DN) group based on urinary albumin excretion (UAE) detection. Using LC-MS/MS-based metabolomics, DN patients showed increased level of lipoxygenase (LOX) metabolites (5-HETE and LTB4) and decreased levels of eicosanoids derived according to the cytochrome P450s (CYP450) metabolic pathway (5,6-DHET; 14,15-DHET and 9,10-diHOME). Receiver operating characteristics and logistic regression analysis revealed increased level LOX metabolites and decreased level of CYP450 metabolites were significantly correlated with the incidence of DN in T2D patients. LOX and CYP450 metabolites correlated with DN incidence in T2D patients, which might be treatment targets for DN in T2D patients.

Update on diagnosis, pathophysiology, and management of diabetic kidney disease

Diabetic kidney disease (DKD) is a chronic complication of diabetes mellitus which may eventually lead to end-stage kidney disease (ESKD). Despite improvements in glycaemic control and blood pressure management with renin-angiotensin-aldosterone system (RAAS) blockade, the current therapy cannot completely halt DKD progression to ESKD in some patients. DKD is a heterogeneous disease entity in terms of its clinical manifestations, histopathology and the rate of progression, which makes it difficult to develop effective therapeutics. It was formerly considered that albuminuria preceded kidney function decline in DKD, but recent epidemiological studies revealed that a distinct group of patients presented kidney dysfunction without developing albuminuria. Other comorbidities, such as hypertension, obesity and gout, also affect the clinical course of DKD. The pathophysiology of DKD is complex and multifactorial, involving both metabolic and haemodynamic factors. These induce activation of intracellular signalling pathways, oxidative stress, hypoxia, dysregulated autophagy and epigenetic changes, which result in kidney inflammation and fibrosis. Recently, two groups of antidiabetic drugs, sodium-glucose cotransporter 2 (SGLT2) inhibitors and glucagon-like peptide-1 (GLP-1) receptor agonists, were demonstrated to provide renoprotection on top of their glucose-lowering effects. Several other therapeutic agents are also being developed and evaluated in clinical trials.

Elevated lipoxygenase and cytochrome P450 products predict progression of chronic kidney disease

BACKGROUND

The clinical relevance of arachidonic acid (AA) metabolites in chronic kidney disease (CKD) progression is poorly understood. We aimed to compare the concentrations of 85 enzymatic pathway products of AA metabolism in patients with CKD who progressed to end-stage kidney disease (ESKD) versus patients who did not in a subcohort of Chronic Renal Insufficiency Cohort (CRIC) and to estimate the risk of CKD progression and major cardiovascular events by levels of AA metabolites and their link to enzymatic metabolic pathways.

METHODS

A total 123 patients in the CRIC study who progressed to ESKD were frequency matched with 177 nonprogressors and serum eicosanoids were quantified by mass spectrometry. We applied serum collected at patients' Year 1 visit and outcome of progression to ESKD was ascertained over the next 10 years. We used logistic regression models for risk estimation.

RESULTS

Baseline 15-hydroxyeicosatetraenoate (HETE) and 20-HETE levels were significantly elevated in progressors (false discovery rate Q ≤ 0.026). The median 20-HETE level was 7.6 pmol/mL [interquartile range (IQR) 4.2-14.5] in progressors and 5.4 pmol/mL (IQR 2.8-9.4) in nonprogressors (P < 0.001). In an adjusted model, only 20-HETE independently predicted CKD progression. Each 1 standard deviation increase in 20-HETE was independently associated with 1.45-fold higher odds of progression (95% confidence interval 1.07-1.95; P = 0.017). Principal components of lipoxygenase (LOX) and cytochrome P450 (CYP450) pathways were independently associated with CKD progression.

CONCLUSIONS

We found higher odds of CKD progression associated with higher 20-HETE, LOX and CYP450 metabolic pathways. These alterations precede CKD progression and may serve as targets for interventions aimed at halting progression.

Role of the 12-lipoxygenase pathway in diabetes pathogenesis and complications

12-lipoxygenase (12-LOX) is one of several enzyme isoforms responsible for the metabolism of arachidonic acid and other poly-unsaturated fatty acids to both pro- and anti-inflammatory lipid mediators. Mounting evidence has shown that 12-LOX plays a critical role in the modulation of inflammation at multiple checkpoints during diabetes development. Due to this, interventions to limit pro-inflammatory 12-LOX metabolites either by isoform-specific 12-LOX inhibition, or by providing specific fatty acid substrates via dietary intervention, has the potential to significantly and positively impact health outcomes of patients living with both type 1 and type 2 diabetes. To date, the development of truly specific and efficacious inhibitors has been hampered by homology of LOX family members; however, improvements in high throughput screening have improved the inhibitor landscape. Here, we describe the function and role of human 12-LOX, and mouse 12-LOX and 12/15-LOX, in the development of diabetes and diabetes-related complications, and describe promise in the development of strategies to limit pro-inflammatory metabolites, primarily via new small molecule 12-LOX inhibitors.

7-Ketocholesterol induces ROS-mediated mRNA expression of 12-lipoxygenase, cyclooxygenase-2 and pro-inflammatory cytokines in human mesangial cells: Potential role in diabetic nephropathy

7-Ketocholesterol (7-KCHO) is a highly proinflammatory oxysterol and plays an important role in the pathophysiology of diabetic nephropathy (DN). Lipoxygenases (LOXs) and cyclooxygenases (COXs) are also involved in the development of DN. The aim of this study was to clarify the effects of 7-KCHO on mRNA expression of LOXs and COXs as well as pro-inflammatory cytokines in human mesangial cells (HMC). We evaluated cell viability by WST-8 assay and measured mRNA expression by reverse transcription-polymerase chain reaction. Intracellular reactive oxygen species (ROS) production was evaluated by flow cytometry. Although 7-KCHO did not affect cell viability of HMC, 7-KCHO stimulated significant increases in mRNA expression of 12-LOX, COX-2 and pro-inflammatory cytokines. 7-KCHO also induced an increase in ROS production, while N-acetylcysteine partially suppressed the increase. The 12-LOX and COX-2 inhibitors also suppressed mRNA expression of cytokines. These findings may contribute to the elucidation of the molecular mechanism of the pathophysiology of DN.

Effect of angiotensin II type 1 receptor blocker on 12-lipoxygenase activity and slit diaphragm protein expression in type 2 diabetic rat glomeruli

BACKGROUND

The 12-lipoxygenase (12-LO) and angiotensin II (Ang II) interaction plays an important role in diabetic nephropathy (DN). Proteinuria in DN is associated with decreased slit diaphragm proteins including nephrin and P-cadherin. Therefore, we investigated whether Ang II type 1 receptor (AT1) blocker (ARB) regulates 12-LO activity and slit diaphragm protein expression in diabetic rat glomeruli.

METHOD

Glomeruli were isolated with the sieving method, and classified into small glomeruli (SG; 75-μm sieve) and large glomeruli (LG; 125-μm sieve).

RESULTS

12(S)-HETE, a lipid product of 12-LO, was increased by Ang II in the glomeruli. Infusion of 12(S)-HETE and Ang II significantly decreased nephrin expression in LG, but increased it in SG compared to control. Glomerular P-cadherin expression was reduced after Ang II and 12(S)-HETE treatment without differences between LG and SG. ARB did not influence glycemic levels but completely abolished the increases in 12(S)-HETE, AT1 expression, and proteinuria in diabetic rats. Nephrin expression was significantly reduced in LG but increased in SG in diabetic rats compared to control. P-cadherin expression decreased in both diabetic LG and SG. The abnormalities of nephrin and P-cadherin were partially but significantly reversed by ARB.

CONCLUSION

ARB potentially ameliorates DN via the up-regulation of glomerular nephrin and P-cadherin expression through the inhibition of 12-LO activation in the glomeruli of rats with DN.

Epigenetic Histone Modifications Involved in Profibrotic Gene Regulation by 12/15-Lipoxygenase and Its Oxidized Lipid Products in Diabetic Nephropathy

AIMS

Epigenetic mechanisms, including histone post-translational modifications and DNA methylation, are implicated in the pathogenesis of diabetic nephropathy (DN), but the mediators are not well known. Moreover, although dyslipidemia contributes to DN, epigenetic changes triggered by lipids are unclear. In diabetes, increased expression of 12/15-lipoxygenase (12/15-LO) enhances oxidized lipids such as 12(S)-hydroxyeicosatetraenoic acid [12(S)-HETE], which promote oxidant stress, glomerular and mesangial cell (MC) dysfunction, and fibrosis, and mediate the actions of profibrotic growth factors. We hypothesized that 12/15-LO and its oxidized lipid products can regulate epigenetic mechanisms mediating profibrotic gene expression related to DN.

RESULTS

12(S)-HETE increased profibrotic gene expression and enrichment of permissive histone lysine modifications at their promoters in MCs. 12(S)-HETE also increased protein levels of SET7, a histone H3 lysine 4 methyltransferase, and promoted its nuclear translocation and enrichment at profibrotic gene promoters. Furthermore, SET7 (Setd7) gene silencing inhibited 12(S)-HETE-induced profibrotic gene expression. 12/15-LO (Alox15) gene silencing or genetic knockout inhibited transforming growth factor-β1 (TGF-β1)-induced expression of Setd7 and profibrotic genes and histone modifications in MCs. Furthermore, 12/15-LO knockout in mice ameliorated key features of DN and abrogated increases in renal SET7 and profibrotic genes. Additionally, 12/15-LO siRNAs in vivo blocked increases in renal SET7 and profibrotic genes in diabetic mice.

INNOVATION AND CONCLUSION

These novel results demonstrate for the first time that 12/15-LO-derived oxidized lipids regulate histone modifications associated with profibrotic gene expression in MCs, and 12/15-LO can mediate similar actions of TGF-β1 and diabetes. Targeting 12/15-LO might be a useful strategy to inhibit key epigenetic mechanisms involved in DN.

The effect of kisspeptin on the regulation of vascular tone

Kisspeptin has been implicated in cardiovascular control. Eicosanoids play a crucial role in the activation of platelets and the regulation of vascular tone. In the present study, we investigated the effect of kisspeptins on eicosanoid synthesis in platelets and aorta in vitro. Platelets and aorta were isolated from Wistar–Kyoto rats. After preincubation with different doses of kisspeptin, samples were incubated with [1-14C]arachidonic acid (0.172 pmol/mL) in tissue culture Medium 199. The amount of labeled eicosanoids was measured with liquid scintillation, after separation with overpressure thin-layer chromatography. Kisspeptin-13 stimulated the thromboxane synthesis. The dose–response curve was bell-shaped and the most effective concentration was 2.5 × 10−8 mol/L, inducing a 27% increase. Lipoxygenase products of platelets displayed a dose-dependent elevation up to the dose of 5 × 10−8 mol/L. In the aorta, kisspeptin-13 induced a marked elevation in the production of 6-keto-prostaglandin F1α, the stable metabolite of prostacyclin, and lipoxygenase products. Different effects of kisspeptin on cyclooxygenase and lipoxygenase products indicate that beyond intracellular Ca2+ mobilization, other signaling pathways might also contribute to its actions. Our data suggest that kisspeptin, through the alteration of eicosanoid synthesis in platelets and aorta, may play a physiologic and (or) pathologic role in the regulation of vascular tone.

Pravastatin Therapy and Biomarker Changes in Children and Young Adults with Autosomal Dominant Polycystic Kidney Disease

BACKGROUND AND OBJECTIVES

Disease-specific treatment options for autosomal dominant polycystic kidney disease are limited. Clinical intervention early in life is likely to have the greatest effect. In a 3-year randomized double-blind placebo-controlled phase 3 clinical trial, the authors recently showed that pravastatin decreased height-corrected total kidney volume (HtTKV) progression of structural kidney disease over a 3-year period. However, the underlying mechanisms have not been elucidated.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Participants were recruited nationally from July 2007 through October 2009. Plasma and urine samples collected at baseline, 18 months, and 36 months from 91 pediatric patients enrolled in the above-mentioned clinical trial were subjected to mass spectrometry-based biomarker analysis. Changes in biomarkers over 3 years were compared between placebo and pravastatin-treated groups. Linear regression was used to evaluate the changes in biomarkers with the percent change in HtTKV over 3 years.

RESULTS

Changes in plasma concentrations of proinflammatory and oxidative stress markers (9- hydroxyoctadecadienoic acid, 13-hydroxyoctadecadienoic acid, and 15-hydroxyeicosatetraenoic acid [HETE]) over 3 years were significantly different between the placebo and pravastatin-treated groups, with the pravastatin group showing a lower rate of biomarker increase. Urinary 8-HETE, 9-HETE, and 11-HETE were positively associated with the changes in HtTKV in the pravastatin group.

CONCLUSIONS

Pravastatin therapy diminished the increase of cyclooxygenase- and lipoxygenase-derived plasma lipid mediators. The identified biomarkers and related molecular pathways of inflammation and endothelial dysfunction may present potential targets for monitoring of disease severity and therapeutic intervention of autosomal dominant polycystic kidney disease.

p16ink4a Expression Is Increased through 12-Lipoxygenase in High Glucose-Stimulated Glomerular Mesangial Cells and Type 2 Diabetic Glomeruli

BACKGROUND/AIMS

Arachidonic acid-metabolizing enzyme, 12-lipoxygenase (12-LO), is involved in the glomerular hypertrophy of diabetic nephropathy (DN), in which cyclin-dependent kinase inhibitors (CKIs) play important roles. However, it is unclear whether 12-LO regulates the expression of the CKI p16(ink4a) in DN.

METHODS

Primary glomerular mesangial cells (MCs) and glomeruli isolated from rats were used in this study. The rats were fed a high-fat diet and given low-dose streptozotocin to induce type 2 diabetes. The 12-LO product, 12(S)-hydroxyeicosatetraenoic acid (12(S)-HETE), was infused through an osmotic minipump. Enzyme-linked immunosorbent assay, Western blot, and morphometric analyses were performed.

RESULTS

High glucose (HG) increased the p16(ink4a) protein expression in MCs, but this increase was prevented by the 12-LO inhibitor, cinnamyl-3,​4-dihydroxy-α-cynanocinnamate (CDC). The levels of p-p38MAPK and p16(ink4a) in MCs were significantly elevated after the 12(S)-HETE treatment, whereas the p38MAPK inhibitor SB203580 prevented these increases. Compared with levels in control MCs, marked increases in p38MAPK activation and p16(ink4a) expression were observed in MCs plated on collagen IV, while the CDC treatment prevented these changes. Subcutaneous injection of CDC did not affect glucose levels, but completely attenuated the diabetes-related increases in the 12(S)-HETE content, p16(ink4a) expression, p-p38MAPK levels, glomerular volume, and the kidney/body weight ratio. Compared with levels in controls, p16(ink4a) and p-p38MAPK in the glomeruli derived from 12(S)-HETE-treated rats were significantly higher.

CONCLUSIONS

12-LO-p38MAPK mediates the upregulation of p16(ink4a) in HG-stimulated MCs and type 2-diabetic glomeruli, and new therapies aimed at 12-LO inhibition may prove beneficial in ameliorating diabetes-induced glomerular hypertrophy.

Benzidine induces epithelial-mesenchymal transition in human uroepithelial cells through ERK1/2 pathway

Prolonged benzidine exposure is a known cause of urothelial carcinoma (UC). Benzidine-induced epithelial-to-mesenchymal transition (EMT) is critically involved in cell malignant transformation. The role of ERK1/2 in regulating benzidine-triggered EMT has not been investigated. This study was to investigate the regulatory role of ERK1/2 in benzidine-induced EMT. By using wound healing and transwell chamber migration assays, we found that benzidine could increase SV-HUC-1 cells invasion activity, western blotting and Immunofluorescence showed that the expression levels of Snail, β-catenin, Vimentin, and MMP-2 were significantly increased, while, the expression levels of E-cadherin, ZO-1 were decreased. To further demonstrate the mechanism in this process, we found that the phosphorylation of ERK1/2, p38, JNK and AP-1 proteins were significantly enhanced compared to the control group (*P < 0.05). Afterward, treated with MAPK pathways inhibitors, only ERK inhibitor（U0126）could reduce the expression of EMT markers in SV-HUC-1 cells, but not p38 and JNK inhibitor（SB203580, SP600125）, which indicated that benzidine induces the epithelial-mesenchymal transition in human uroepithelial cells through ERK1/2 pathway. Taken together, findings from this study could provide into the molecular mechanisms by which benzidine exerts its bladder-cancer-promoting effect as well as its target intervention.

Rapid resolution liquid chromatography coupled with quadrupole time-of-flight mass spectrometry-based metabolomics approach to study the effects of jieduquyuziyin prescription on systemic lupus erythematosus

Jieduquyuziyin prescription (JP), a traditional Chinese medicine (TCM) prescription, has been widely used for the clinical treatment of systemic lupus erythematosus (SLE). However, the complex chemical constituents of JP and the multifactorial pathogenesis of SLE make research on the therapeutic mechanism of JP in SLE challenging. In this paper, a serum metabolomics approach based on rapid resolution liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (RRLC-Q-TOF/MS) was employed to acquire the metabolic characteristics of serum samples obtained from mice in the SLE model group, JP-treated group, prednisone acetate (PA)-treated group and control group. The orthogonal partial least squares (OPLS) was applied to recognize metabolic patterns, and an obvious separation of groups was obtained. Thirteen metabolites, namely, phosphatidylethanolamine (PE 20:3), hepoxilin B3, lyso- phosphatidylethanolamine (lyso-PE 22:6), 12S-hydroxypentaenoic acid (12S-HEPE), traumatic acid, serotonin, platelet-activating factor (PAF), phosphatidylcholine (PC 20:5),eicosapentaenoic acid (EPA), 12(S)-hydroxyei- cosatetraenoic acid (12S-HETE), 14-hydroxy docosahexaenoic acid (14-HDOHE), lyso-phosphatidylcholine (lyso-PC 20:4), and indole acetaldehyde, were identified and characterized as differential metabolites involved in the pathogenesis of SLE. After treatment with JP, the relative content of 12(S)-HETE, PAF, 12(S)-HEPE, EPA, PE (20:3), Lyso-PE(22:6), and 14-HDOHE were effectively regulated, which suggested that the therapeutic effects of JP on SLE may involve regulating disturbances to the metabolism of unsaturated fatty acid, tryptophan and phospholipid. This research also demonstrated that metabolomics is a powerful tool for researching complex disease mechanisms and evaluating the mechanism of action of TCM.

Bioactive lipid mediators in polycystic kidney disease

Inflammatory activity is evident in patients with chronic kidney disease with limited data available in autosomal dominant polycystic kidney disease (ADPKD). We hypothesized that inflammation is an upstream event in the pathogenesis of ADPKD and may be a contributing factor in the disease severity and progression. Serum samples from 61 HALT study A group patients were compared with samples from 49 patients from HALT study B group with moderately advanced disease. Targeted MS analysis of bioactive lipid mediators as markers of inflammation was performed and correlated with eGFR and total kidney volume (TKV) normalized to the body surface area (BSAR) to assess if these markers are predictive of ADPKD severity. ADPKD patients with eGFR >60 ml/min/1.73 m(2) showed higher levels of 5- and 12/15-lipoxygenase (LOX) and cyclooxygenase, and generated higher levels of hydroxy-octadecadienoic acids 9-HODE and 13-HODE and HETEs 8-HETE, 11-HETE, 12-HETE, and 15-HETE as compared with healthy subjects. Linear regression of 9-HODE and 13-HODE revealed a significant relationship with eGFR and TKV, while 15-HETE significantly correlated with TKV/BSAR. Production of 20-HETE, a P450-produced metabolite of arachidonic acid, was higher in ADPKD patients as compared with healthy subjects and significantly correlated with eGFR and TKV/BSAR. Perturbation in fatty acid metabolism is evident early in ADPKD patients, even in those with preserved kidney function. The identified LOX pathways may be potential therapeutic targets for slowing down ADPKD progression.

Effects of lovastatin treatment on the metabolic distributions in the Han:SPRD rat model of polycystic kidney disease

BACKGROUND

We previously demonstrated that lovastatin decreases cyst volume and improves kidney function in the Han:SPRD (Cy/+) rat model of ADPKD. Since endothelial dysfunction and inflammatory activity are evident in patients with ADPKD, we investigated whether lovastatin reduces the inflammation and vascular dysfunction and improves kidney cell energy metabolism of Cy/+ rats.

METHODS

Cy/+ and normal littermate control animals (+/+) were treated with either lovastatin (4 mg/kg/day) or vehicle (ethanol) from 3-8 weeks of age. 1H-NMR analysis was performed on water-soluble and lipid kidney fractions following perchloric acid extraction. Targeted liquid chromatography-tandem mass spectrometry (LC-MS/MS) was used to assess endothelial dysfunction, oxidative stress and inflammation markers in plasma and kidney tissue extracts.

RESULTS

Cy/+ rats showed perturbations in fatty acid metabolism and increased synthesis of pro-inflammatory lipoxygenases-produced bioactive lipids was observed. Lovastatin decreased inflammatory markers, specifically 13-HODE, 12-HETE and leukotriene B4. In Cy/+ rats, lovastatin reduced the elevated homocysteine and allantoin plasma levels and increased arginine, that is known to positively affect NO production.

CONCLUSION

As previously described, lovastatin was able to decrease kidney weight and cyst volume density in Cy/+ rats. The decrease in cyst volume was accompanied by a reduction in arachidonic acid-mediated inflammation markers, the normalization of metabolism of NO precursors and the improvement of kidney energy cell metabolism.

Hepatocyte growth factor-induced amelioration in chronic renal failure is associated with reduced expression of α-smooth muscle actin

This study aimed to examine whether hepatocyte growth factor (HGF) can improve renal function in 5/6 nephrectomized rats and investigate whether this function is associated with a decrease in α-smooth muscle actin (α-SMA) expression in rat glomerulus mesangial cells and renal interstitium. Rats were randomly divided into the following groups: control, PCI-neo, sham-operation, 5/6 nephrectomy, and low-dose and high-dose PCI-neo-HGF. Rats were killed in the ninth week after 5/6 nephrectomy, and the kidney specimens were subjected to pathological examination by Hematoxylin-Eosin staining and detection of α-SMA expression by reverse transcriptase-polymerase chain reaction (RT-PCR), Western blot, and immunohistochemistry. The results showed that blood urea nitrogen and serum creatinine levels were increased, renal interstitium was injured, and α-SMA expression was elevated in 5/6 nephrectomized rats compared with that in control. The above changes were ameliorated in the rats injected with PCI-neo-HGF vector. At the molecular level we found that PCI-neo-HGF repressed α-SMA expression in mesangial cells stimulated by lipopolysaccharide. In conclusion, our data suggest that HGF can relieve chronic renal failure, and this protection is associated with the down-regulation of α-SMA expression in mesangial cells and renal interstitium.

Early protective effect of mitofusion 2 overexpression in STZ-induced diabetic rat kidney

Diabetic nephropathy (DN) is a serious complication of diabetes with a poorly defined etiology and limited treatment options. Early intervention is key to preventing the progression of DN. Mitofusin 2 (Mfn2) regulates mitochondrial morphology and signaling, and is involved in the pathogenesis of numerous diseases. Furthermore, Mfn2 is also closely associated with the development of diabetes, but its functional roles in the diabetic kidney remain unknown. This study investigated the effect of Mfn2 at an early stage of DN. Mfn2 was overexpressed by adenovirus-mediated gene transfer in streptozotocin-induced diabetic rats. Clinical parameters (proteinuria, albumin/creatinine ratio), pathological changes, ultra-microstructural changes in nephrons, expression of collagen IV and phosph-p38, ROS production, mitochondrial function, and apoptosis were evaluated and compared with diabetic rats expressing control levels of Mfn2. Endogenous Mfn2 expression decreased with time in DN. Compared to the blank transfection control group, overexpression of Mfn2 decreased kidney weight relative to body weight, reduced proteinuria and ACR, and improved pathological changes typical of the diabetic kidney, like enlargement of glomeruli, accumulation of ECM, and thickening of the basement membrane. In addition, Mfn2 overexpression inhibited activation of p38, and the accumulation of ROS; prevented mitochondrial dysfunction; and reduced the synthesis of collagen IV, but did not affect apoptosis of kidney cells. This study demonstrates that Mfn2 overexpression can attenuate pathological changes in the kidneys of diabetic rats. Further studies are needed to clarify the underlying mechanism of this protective function. Mfn2 might be a potential therapeutic target for the treatment of early stage DN.

Gene expression differences in skin fibroblasts in identical twins discordant for type 1 diabetes

Clinical studies suggest metabolic memory to hyperglycemia. We tested whether diabetes leads to persistent systematic in vitro gene expression alterations in patients with type 1 diabetes (T1D) compared with their monozygotic, nondiabetic twins. Microarray gene expression was determined in skin fibroblasts (SFs) of five twin pairs cultured in high glucose (HG) for ∼6 weeks. The Exploratory Visual Analysis System tested group differences in gene expression levels within KEGG (Kyoto Encyclopedia of Genes and Genomes) pathways. An overabundance of differentially expressed genes was found in eight pathways: arachidonic acid metabolism (P = 0.003849), transforming growth factor-β signaling (P = 0.009167), glutathione metabolism (P = 0.01281), glycosylphosphatidylinositol anchor (P = 0.01949), adherens junction (P = 0.03134), dorsal-ventral axis formation (P = 0.03695), proteasome (P = 0.04327), and complement and coagulation cascade (P = 0.04666). Several genes involved in epigenetic mechanisms were also differentially expressed. All differentially expressed pathways and all the epigenetically relevant differentially expressed genes have previously been related to HG in vitro or to diabetes and its complications in animal and human studies. However, this is the first in vitro study demonstrating diabetes-relevant gene expression differences between T1D-discordant identical twins. These SF gene expression differences, persistent despite the HG in vitro conditions, likely reflect "metabolic memory", and discordant identical twins thus represent an excellent model for studying diabetic epigenetic processes in humans.

12-lipoxygenase: a potential target for novel anti-platelet therapeutics

Platelets play an essential role in the regulation of hemostasis and thrombosis and controlling their level of activation is central to prevention of occlusive clot formation and stroke. Although a number of anti-platelet targets have been identified to address this issue including COX-1, the P2Y(12) receptor, the integrin αIIbβ3, and more recently the protease-activated receptor-1, these targets often result in a significant increased risk of bleeding which may lead to pathologies as serious as the thrombosis they were meant to treat including intracranial hemorrhage and gastrointestinal bleeding. Therefore, alternative approaches to treat uncontrolled platelet activation are warranted. Platelet-type 12-lipoxygenase is an enzyme which oxidizes the free fatty acid in the platelet resulting in the production of the stable metabolite 12-hydroxyeicosatetraenoic acid (12-HETE). The role of 12-HETE in the platelet has been controversial with reports associating its function as being both anti- and pro-thrombotic. In this review, the role of 12-lipoxygenase and its bioactive metabolites in regulation of platelet reactivity, clot formation, and hemostasis is described. Understanding the mechanisms by which 12-lipoxygenase and its metabolites modulate platelet function may lead to the development of a novel class of anti-platelet therapies targeting the enzyme in order to attenuate injury-induced clot formation, vessel occlusion and pathophysiological shifts in hemostasis.

The role of the p38 MAPK signaling pathway in high glucose-induced epithelial-mesenchymal transition of cultured human renal tubular epithelial cells

BACKGROUND

Epithelial-mesenchymal transition of tubular epithelial cells, which is characterized by a loss of epithelial cell characteristics and a gain of ECM-producing myofibroblast characteristics, is an essential mechanism that is involved in tubulointerstitial fibrosis, an important component of the renal injury that is associated with diabetic nephropathy. Under diabetic conditions, p38 MAPK activation has been reported in glomeruli and mesangial cells; however, studies on p38 MAPK in TECs are lacking. In this study, the role of p38 MAPK in AP-1 activation and in the EMT in the human proximal tubular epithelial cell line (HK-2) under high glucose concentration conditions is investigated.

METHODOLOGY/PRINCIPAL FINDINGS

A vector for small interfering RNA that targets p38 MAPK was constructed; the cells were then either transfected with p38 siRNA or pretreated with a chemical inhibitor of AP-1 and incubated with low glucose plus TGF-β1 or high glucose for 48 h. Cells that were not transfected or pretreated and were exposed to low glucose with or without TGF-β1 or high glucose for 48 h were considered to be the controls. We found that high glucose induced an increase in TGF-β1. And high glucose-induced p38 MAPK activation was inhibited by p38 siRNA (P<0.05). A significant decline in E-cadherin and CK expression and a notable increase in vimentin and α-SMA were detected when exposed to low glucose with TGF-β1 or high glucose, and a significant raise of secreted fibronectin were detected when exposed to high glucose; whereas these changes were reversed when the cells were treated with p38 siRNA or AP-1 inhibitor (P<0.05). AP-1 activity levels and Snail expression were up-regulated under high glucose conditions but were markedly down-regulated through knockdown of p38 MAPK with p38 siRNA or pretreatment with AP-1 inhibitor (P<0.05).

CONCLUSION

This study suggests that p38 MAPK may play an important role in the high glucose-induced EMT by activating AP-1 in tubular epithelial cells.

Role of 12-lipoxygenase in decreasing P-cadherin and increasing angiotensin II type 1 receptor expression according to glomerular size in type 2 diabetic rats

12-lipoxygenase (12-LO) was implicated in the development of diabetic nephropathy (DN), in which the proteinuria was thought to be associated with a decreased expression of glomerular P-cadherin. Therefore, we investigated the role of 12-LO in the glomerular P-cadherin expression in type 2 diabetic rats according to the glomerular sizes. Rats fed with high-fat diet for 6 wk were treated with low-dose streptozotocin. Once diabetes onset, diabetic rats were treated with 12-LO inhibitor cinnamyl-3,4-dihydroxy-cyanocinnamate (CDC) for 8 wk. Then glomeruli were isolated from diabetic and control rats with a sieving method. RT-PCR, Western blotting, and immunofluorescent staining were used for mRNA and protein expressions of P-cadherin and angiotensin II (Ang II) type 1 receptor (AT1). We found that CDC did not affect the glucose levels but completely attenuated diabetic increases in glomerular volume and proteinuria. Diabetes significantly decreased the P-cadherin mRNA and protein expressions and increased the AT1 mRNA and protein expressions in the glomeruli. These changes were significantly prevented by CDC and recaptured by direct infusion of 12-LO product [12(S)-HETE] to normal rats for 7 days. The decreased P-cadherin expression was similar between large and small glomeruli, but the increased AT1 expression was significantly higher in the large than in the small glomeruli from diabetic and 12(S)-HETE-treated rats. Direct infusion of normal rats with Ang II for 14 days also significantly decreased the glomerular P-cadherin expression. These results suggest that diabetic proteinuria is mediated by the activation of 12-LO pathway that is partially attributed to the decreased glomerular P-cadherin expression.

Curcumin activates the p38MPAK-HSP25 pathway in vitro but fails to attenuate diabetic nephropathy in DBA2J mice despite urinary clearance documented by HPLC

BACKGROUND

Curcumin has anti-inflammatory, anti-oxidant, and anti-proliferative properties, and depending upon the experimental circumstances, may be pro- or anti-apoptotic. Many of these biological actions could ameliorate diabetic nephropathy.

METHODS/DESIGN

Mouse podocytes, cultured in basal or high glucose conditions, underwent acute exposure to curcumin. Western blots for p38-MAPK, COX-2 and cleaved caspase-3; isoelectric focusing for HSP25 phosphorylation; and DNase I assays for F- to G- actin cleavage were performed for in vitro analyses. In vivo studies examined the effects of dietary curcumin on the development of diabetic nephropathy in streptozotocin (Stz)-induced diabetes in DBA2J mice. Urinary albumin to creatinine ratios were obtained, high performance liquid chromatography was performed for urinary curcuminoid measurements, and Western blots for p38-MAPK and total HSP25 were performed.

RESULTS

Curcumin enhanced the phosphorylation of both p38MAPK and downstream HSP25; inhibited COX-2; induced a trend towards attenuation of F- to G-actin cleavage; and dramatically inhibited the activation of caspase-3 in vitro. In curcumin-treated DBA2J mice with Stz-diabetes, HPLC measurements confirmed the presence of urinary curcuminoid. Nevertheless, dietary provision of curcumin either before or after the induction of diabetes failed to attenuate albuminuria.

CONCLUSIONS

Apart from species, strain, early differences in glycemic control, and/or dosing effects, the failure to modulate albuminuria may have been due to a decrement in renal HSP25 or stimulation of the 12/15 lipoxygenase pathway in DBA2J mice fed curcumin. In addition, these studies suggest that timed urine collections may be useful for monitoring curcumin dosing and renal pharmacodynamic effects.

Amelioration of nephropathy with apoA-1 mimetic peptide in apoE-deficient mice

BACKGROUND

There is mounting evidence that dyslipidaemia may contribute to development and progression of renal disease. For instance, hyperlipidaemia in apolipoprotein E-deficient (apoE(-/-)) mice is associated with glomerular inflammation, mesangial expansion and foam cell formation. ApoA-1 mimetic peptides are potent antioxidant and anti-inflammatory compounds which are highly effective in ameliorating atherosclerosis and inflammation in experimental animals. Given the central role of oxidative stress and inflammation in progression of renal disease, we hypothesized that apoA-1 mimetic peptide, D-4F, may attenuate renal lesions in apoE(-/-) mice.

METHODS

Twenty-five-month-old female apoE(-/-) mice were treated with D-4F (300 µg/mL in drinking water) or placebo for 6 weeks. Kidneys were harvested and examined for histological and biochemical characteristics.

RESULTS

Compared with the control mice, apoE(-/-) mice showed significant proteinuria, tubulo-interstitial inflammation, mesangial expansion, foam cell formation and up-regulation of oxidative [NAD(P)H oxidase subunits] and inflammatory [NF-κB, MCP-1, PAI-1 and COX-2] pathways. D-4F administration lowered proteinuria, improved renal histology and reversed up-regulation of inflammatory and oxidative pathways with only minimal changes in plasma lipid levels.

CONCLUSIONS

The apoE(-/-) mice develop proteinuria and glomerular and tubulo-interstitial injury which are associated with up-regulation of oxidative and inflammatory mediators in the kidney and are ameliorated by the administration of apoA-1 mimetic peptide. These observations point to the role of oxidative stress and inflammation in the pathogenesis of renal disease in hyperlipidaemic animals and perhaps humans.

Emodin suppresses cell proliferation and fibronectin expression via p38MAPK pathway in rat mesangial cells cultured under high glucose

Our previous findings demonstrated that emodin could improve the renal function in rats with diabetic nephropathy, but little is known about its molecular mechanisms. In this study, we investigated the effects of emodin on high glucose (HG)-induced cell proliferation and fibronectin (FN) protein expression in rat mesangial cells, and explored the possible mechanism. Cell proliferation and cell cycle were determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and flow cytometry assay, respectively. The protein levels of FN, p-p38MAPK, t-p38MAPK, p-CREB, PPARgamma, and CTGF in rat mesangial cells were detected by Western blot. Our results demonstrated that emodin significantly suppressed HG-induced cell proliferation and arrested cell cycle progress. Protein expression of FN, phospho-p38MAPK, phospho-CREB and CTGF was markedly reduced, and PPARgamma protein level was significantly increased after emodin treatment. In conclusion, emodin suppressed HG-induced cell proliferation and FN expression in rat mesangial cells through inhibiting the p38MAPK pathway involved CREB, PPAPgamma and CTGF, suggesting a potential role of emodin in the treatment of diabetic nephropathy.

IL-8/CXCL8 Upregulates 12-Lipoxygenase Expression in Vascular Smooth Muscle Cells from Spontaneously Hypertensive Rats

Background

We previously demonstrated remarkable differences in the expression of IL-8/CXCL8 in aortic tissues and vascular smooth muscle cells (VSMC) from spontaneously hypertensive rats (SHR) compared to VSMC from normotensive Wistar-Kyoto rats (WKY). In the present study, we investigated the direct effect of IL-8/CXCL8 on expression of 12-lipoxygenase (LO), a hypertensive modulator, in SHR VSMC.

Methods

Cultured aortic VSMC from SHR and WKY were used. Expression of 12-LO mRNA was determined by real-time polymerase chain reaction. Phosphorlyation of ERK1/2 and production of 12-LO and angiotensin II subtype 1 (AT₁) receptor were assessed by Western blots. IL-8/CXCL8-stimulated DNA synthesis was determined by measuring incorporation of [³H]-thymidine. And effect of IL-8/CXCL8 on vascular tone was determined by phenylephrine-induced contraction of thoracic aortic rings.

Results

Treatment with IL-8/CXCL8 greatly increased 12-LO mRNA expression and protein production compared to treatment with angiotensin II. IL-8/CXCL8 also increased the expression of the AT₁ receptor. The increase in 12-LO induced by IL-8/CXCL8 was inhibited by treatment with an AT₁ receptor antagonist. The induction of 12-LO mRNA production and the proliferation of SHR VSMC by IL-8/CXCL8 was mediated by the ERK pathway. The proliferation of SHR VSMC and the vascular contraction in the thoracic aortic ring, both of which were induced by IL-8/CXCL8, were inhibited by baicalein, a 12-LO inhibitor.

Conclusion

These results suggest that the potential role of IL-8/CXCL8 in hypertensive processes is likely mediated through the 12-LO pathway.

[Molecular bases of diabetic nephropathy]

The determinant of the diabetic nephropathy is hyperglycemia, but hypertension and other genetic factors are also involved. Glomerulus is the focus of the injury, where mesangial cell proliferation and extracellular matrix occur because of the increase of the intra- and extracellular glucose concentration and overexpression of GLUT1. Sequentially, there are increases in the flow by the poliol pathway, oxidative stress, increased intracellular production of advanced glycation end products (AGEs), activation of the PKC pathway, increase of the activity of the hexosamine pathway, and activation of TGF-beta1. High glucose concentrations also increase angiotensin II (AII) levels. Therefore, glucose and AII exert similar effects in inducing extracellular matrix formation in the mesangial cells, using similar transductional signal, which increases TGF-beta1 levels. In this review we focus in the effect of glucose and AII in the mesangial cells in causing the events related to the genesis of diabetic nephropathy. The alterations in the signal pathways discussed in this review give support to the observational studies and clinical assays, where metabolic and antihypertensive controls obtained with angiotensin-converting inhibitors have shown important and additive effect in the prevention of the beginning and progression of diabetic nephropathy. New therapeutic strategies directed to the described intracellular events may give future additional benefits.

Angiotensin II type 1 receptor expression is increased via 12-lipoxygenase in high glucose-stimulated glomerular cells and type 2 diabetic glomeruli

BACKGROUND

Angiotensin II type 1 receptor (AT1) plays an important role in the development of diabetic nephropathy (DN). However, the roles played by 12-lipoxygenase (12-LO) in the AT1 expression in glomerular cells exposed to high glucose (HG) and diabetic glomeruli remain unclear. Our objective in the present study was to investigate the role of 12-LO in the AT1 expression in glomerular cells and glomeruli under diabetic conditions.

METHODS

Mesangial cells (MCs), podocytes and glomeruli isolated from rats were used in this study. The rats fed a high fat diet received low-dose streptozotocin to make type 2 diabetes. The 12-LO product 12(S)-hydroxyeicosatetraenoic acid [12(S)-HETE] was infused to rats by osmotic mini-pump. Morphometric measurement for glomerular volume, competitive reverse transcription polymerase chain reaction for mRNA expression, western blot and immunohistochemistry for protein expression were performed, respectively.

RESULTS

Both the 12(S)-HETE and HG increased AT1 protein expression in MCs and podocytes. Furthermore, the levels of the AT1 were significantly higher in glomeruli derived from 12(S)-HETE-treated rats compared with control rats. In addition, HG-induced AT1 expression was significantly reduced by the 12-LO inhibitor cinnamyl-3,4-dihydroxy-alpha-cynanocinnamate (CDC). Compared with the non-diabetic controls, DN rats showed significant glomerular hypertrophy and albuminuria. This was associated with significant increases in AT1 protein expression. These abnormalities were prevented by treatment of the CDC.

CONCLUSIONS

These results indicate that AT1 expression is enhanced, at least in part, by 12-LO in the type 2 diabetic glomeruli, and 12-LO inhibition can ameliorate DN progression through downregulation of AT1 expression.

Redox control of renal function and hypertension

Loss of redox homeostasis and formation of excessive free radicals play an important role in the pathogenesis of kidney disease and hypertension. Free radicals such as reactive oxygen species (ROS) are necessary in physiologic processes. However, loss of redox homeostasis contributes to proinflammatory and profibrotic pathways in the kidney, which in turn lead to reduced vascular compliance and proteinuria. The kidney is susceptible to the influence of various extracellular and intracellular cues, including the renin-angiotensin-aldosterone system (RAAS), hyperglycemia, lipid peroxidation, inflammatory cytokines, and growth factors. Redox control of kidney function is a dynamic process with reversible pro- and anti-free radical processes. The imbalance of redox homeostasis within the kidney is integral in hypertension and the progression of kidney disease. An emerging paradigm exists for renal redox contribution to hypertension.

Effect of exercise on cardiac tissue oxidative and inflammatory mediators in chronic kidney disease

BACKGROUND

Chronic renal failure (CRF) results in diminished physical activity and increased risk of cardiovascular disease (CVD). CVD risk factors are raised by sedentary life style and ameliorated by physical fitness in the general population. Accordingly, exercise improves hypertension, endothelial dysfunction, insulin resistance, dyslipidemia, inflammation and oxidative stress in high-risk populations. This study was designed to explore the effect of exercise on oxidative and inflammatory mediators in the left ventricle (LV) of CRF rats.

METHODS AND RESULTS

One week after 5/6 nephrectomy female rats were housed in either regular cages or cages equipped with running wheels for 4 weeks. Sham-operated rats housed in regular cages served as controls. Sedentary CRF rats exhibited azotemia, hypertension, anemia, oxidative stress, activation of NF-kappaB and upregulations of reactive oxygen species-generating enzyme, NAD(P)H oxidase, MCP-1, cyclooxygenase-2 (COX-2), and PAI-1 in LV. The CRF rats assigned to the exercise group ran 6.8 +/- 0.7 km/day and 72 +/- 8 min/day. Voluntary exercise reversed NF-kappaB activation and lowered NAD(P)H oxidase, PAI-1, MCP-1 and COX-2 abundance, increased LV mass by raising myofibrillar proteins and ameliorated anemia without affecting renal function or arterial pressure.

CONCLUSIONS

CRF resulted in upregulation of prooxidant/proinflammatory pathways in LV. These changes were ameliorated by exercise, which indicates the potential cardiovascular benefit of exercise in renal insufficiency.

Regulation of renal 12(S)-hydroxyeicosatetraenoic acid in diabetes by angiotensin AT1 and AT2 receptors

Diabetes is associated with increased production of 12(S)-hydroxyeicosatetraenoic acid [12(S)-HETE]. The mechanisms involved in this process remain unclear. We hypothesized that hyperglycemia and angiotensin II (ANG II) regulate renal 12(S)-HETE production via a balance between angiotensin AT(1) and AT(2) receptors activities. Using a microdialysis technique, renal interstitial fluid (RIF) levels of ANG II and 12(S)-HETE were monitored in normal control and streptozotocin-induced diabetic rats at baseline and then weekly thereafter for 12 wk. In a second group of normal and diabetic rats, 3 wk after development of diabetes, we monitored RIF 12(S)-HETE levels in response to acute AT(1) receptor blockade with valsartan or AT(2) receptor blockade with PD123319 individually or combined. Two weeks after induction of diabetes there was a 404% increase in ANG II (P < 0.05), a 149% increase in 12S-HETE (P < 0.05), and a 649% increase in urinary albumin excretion (P < 0.05). These levels remained elevated throughout the study. PD123319 given alone had no effect on 12(S)-HETE. Valsartan decreased 12(S)-HETE by 61.6% (P < 0.0001), a response that was abrogated when PD123319 was given with valsartan. These data demonstrate that hyperglycemia increases renal ANG II and 12(S)-HETE levels. The increase in 12(S)-HETE is mediated via AT(1) receptor. The attenuation of the effects of AT(1) receptor blockade by PD123319 suggests that AT(2) receptor contributes to the downregulation of renal 12(S)-HETE production.

New aspects of the role of hydroxyeicosatetraenoic acids in cell growth and cancer development

Lipoxygenase (LOX) pathway leads to the formation of leukotrienes and also catalyses the conversion of arachidonic acid (AA) to hydroperoxyeicosatetraenoic acids that are then reduced to hydroxyeicosatetraenoic acids (HETE) by glutathione peroxidase. There are four mammalian LOXs that produce 5-, 8-, 12- and 15-HETE, respectively. Cytochrome P-450 isozymes are also capable of metabolising AA to HETEs either by bis-allylic oxidation (lipoxygenase-like reaction) to generate 5-, 8-, 9-, 11-, 12- and 15-HETE; or by varpi/varpi-1 hydroxylation to yield 16-, 17-, 18-, 19- and 20-HETEs. It is now widely recognised that HETEs have important physiological and pathological functions that modulate ion transport, renal and pulmonary functions, vascular tone and reactivity, and inflammatory and growth responses. They can be released during the action of growth factors and cytokines, reaching physiological concentrations higher than that of prostanoids and modulating the functions of these factors. Their effects can occur through receptor or non-receptor mechanisms. Recent reviews have summarised the effects of HETEs in vascular homeostasis or lung and renal physiology. The present review focuses on the emerging effects of HETEs on cell signalling and physiological cell growth. It also discusses current observations regarding the role of HETEs in apoptosis, angiogenesis, the proliferation of cancer cells and metastasis, which constitute a potential area for successful therapeutic intervention.

Effects of cholesterol-tagged small interfering RNAs targeting 12/15-lipoxygenase on parameters of diabetic nephropathy in a mouse model of type 1 diabetes

We previously showed that the 12/15-lipoxygenase (12/15-LO) pathway of arachidonate acid metabolism is involved in multiple events related to diabetic nephropathy (DN), including glomerular hypertrophy and extracellular matrix deposition (Kang SW, Adler SG, Nast CC, LaPage J, Gu JL, Nadler JL, Natarajan R. Kidney Int 59: 1354-1362, 2001; Kang SW, Natarajan R, Shahed A, Nast CC, LaPage J, Mundel P, Kashtan C, Adler SG. J Am Soc Nephrol 14: 3178-3187, 2003; Kim YS, Lanting L, Adler SG, Natarajan R. Kindney Int 64: 1702-1714, 2003; Reddy MA, Adler SG, Kim YS, Lanting L, Rossi JJ, Kang SW, Nadler JL, Shahed A, Natarajan R. Am J Physiol Renal Physiol 283: F985-F994, 2002). In this study, we investigated whether in vivo delivery of small interfering RNAs (siRNAs) targeting 12/15-LO can ameliorate renal injury and DN in a streptozotocin-injected mouse model of type 1 diabetes. To achieve greater in vivo access and siRNA expression in the kidney, we used double-stranded 12/15-LO siRNA oligonucleotides conjugated with cholesterol. Diabetic DBA/2J mice were injected subcutaneously with either cholesterol-tagged 12/15-LO siRNA, mismatched control siRNA, or vehicle alone, twice weekly for 7 wk. Relative to controls, mice that received 12/15-LO siRNA showed significant reduction in albuminuria, kidney-to-body weight ratios, glomerular mesangial matrix expansion, renal structural damage, and monocyte/macrophage infiltration. These effects were associated with lower renal cortical or glomerular levels of profibrotic markers transforming growth factor-beta, connective tissue growth factor, type I and type IV collagens, plasminogen activator inhibitor 1, and fibronectin. The diabetes-induced increase in glomerular cyclin-dependent kinase inhibitors that are associated with hypertrophy was also prevented by siRNA administration. Our results show for the first time that systemic delivery of cholesterol-tagged siRNAs targeting 12/15-LO has renoprotective effects under diabetic conditions and therefore could be a novel therapeutic approach for DN.

Association of arachidonate 12-lipoxygenase genotype variation and glycemic control with albuminuria in type 2 diabetes

BACKGROUND

Glycemic exposure activates 12-lipoxygenase (12LO) expression and formation of arachidonic acid-derived products. These products can induce cell hypertrophy, cell proliferation, and extracellular matrix deposition, potentially leading to diabetic nephropathy.

STUDY DESIGN

Cross-sectional study.

SETTINGS & PARTICIPANTS

955 European-American siblings from 369 Diabetes Heart Study families. Participants were categorized as nondiabetic, diabetic with hemoglobin A(1c) level less than 6.5%, and diabetic with hemoglobin A(1c) level greater than 6.5% (uncontrolled type 2 diabetes mellitus).

PREDICTOR

Four haplotype-tagging variants in the arachidonate 12LO gene (ALOX12), glycemic control, and other covariates.

OUTCOMES & MEASUREMENTS

Albuminuria measured by means of urinary albumin-creatinine ratio (ACR).

RESULTS

Median ACR was 11.9 mg/g (interquartile range, 5.6 to 39.1). The overall test of the Arg261Gln genotypic association with ACR was significant (P = 0.009). Compared with 261Arg allele carriers, adjusted mean ACR was 42% greater in the 189 carriers of two 261Gln alleles (95% confidence interval, 10 to 83; P = 0.007). This association was confined to the group with uncontrolled type 2 diabetes mellitus (N = 623) with the greatest ACRs (P < 0.001). Adjustments for additional determinants of ACR yielded similar results.

LIMITATIONS

Urine ACR was measured in duplicate on only a single occasion. This study was limited to European Americans.

CONCLUSIONS

Consistent with animal and cellular studies, these results provide additional evidence of the importance of the 12LO pathway in the pathogenesis of human diabetic nephropathy.

Products of 12/15-lipoxygenase upregulate the angiotensin II receptor

Angiotensin II and its type 1 receptor (AT1R) play important roles in the pathogenesis of renal disease and diabetic nephropathy. The 12/15-lipoxygenase pathway of arachidonate metabolism and its lipid products have also been implicated in diabetic nephropathy. However, it is unclear whether 12/15-lipoxygenase regulates expression of AT1R. In cultured rat mesangial cells, we found that the 12/15-lipoxygenase product 12(S)-hydroxyeicosatetraenoic acid (12(S)-HETE) increased AT1R mRNA and protein expression, primarily by stabilizing AT1R mRNA. Pretreatment with 12(S)-HETE also amplified the signaling effects of angiotensin II, likely due to the increased AT1R expression. Levels of AT1R protein expression decreased when 12/15-lipoxygenase was knocked down with specific short hairpin RNA (shRNA) compared with control cells. Similarly, levels of the AT1 receptor, but not the AT2 receptor, were significantly lower in mesangial cells and glomeruli derived from 12/15-lipoxygenase knockout mice compared with control mice. Reciprocally, stable overexpression of 12/15-lipoxygenase increased AT1R expression in cultured mesangial cells. In vivo, modified siRNA targeting 12/15-lipoxygenase reduced glomerular AT1R expression in a diabetic mouse model. Interestingly, angiotensin II induced greater levels of 12/15-lipoxygenase, TGF-beta1, and fibronectin (FN) in AT1R-overexpressing mesangial cells compared with control cells. Therefore, oxidized lipids generated by the 12/15-lipoxygenase-mediated metabolism of arachidonic acid can enhance AT1R expression in mesangial cells and augment the profibrotic effects of angiotensin II.

Effects of dietary salt on intrarenal angiotensin system, NAD(P)H oxidase, COX-2, MCP-1 and PAI-1 expressions and NF-kappaB activity in salt-sensitive and -resistant rat kidneys

BACKGROUND

Chronic consumption of a high-salt diet causes hypertension (HTN) and renal injury in Dahl salt-sensitive (SSR) but not salt-resistant rats (SRR). These events are, in part, mediated by oxidative stress and inflammation in the kidney and vascular tissues. Activation of the angiotensin II type 1 (AT(1)) receptor plays an important role in the pathogenesis of oxidative stress and inflammation in many hypertensive disorders. However, the systemic renin-angiotensin system (RAS) is typically suppressed in salt-sensitive HTN. This study was designed to test the hypothesis that differential response to a high-salt diet in SSR versus SRR may be related to upregulation of tissue RAS and pathways involved in inflammation and reactive oxygen species (ROS) production.

METHODS AND RESULTS

SSR and SRR were studied 3 weeks after consumption of high- (8%) or low-salt (0.07%) diets. The SSR consuming a low-salt diet exhibited significant increases in AT(1) receptor, cyclooxygenase (COX) 2, plasminogen activator inhibitor (PAI) and phospho-I kappaB in the kidney as compared to those found in SRR. The high-salt diet resulted in severe HTN and proteinuria (in SSR but not SRR) and marked elevations of renal tissue monocyte chemoattractant protein 1, p22(phox), NADPH oxidase subunit 4, angiotensin-II-positive cell count, infiltrating T cells and macrophages and further increases in AT(1) receptor, COX-2, PAI-1 and phospho-I kappaB in the SSR group. The high-salt diet significantly lowered plasma renin activity (PRA) in SRR but not in the SSR. COX-1 abundance was similar on the low-salt diet and rose equally with the high-salt diet in both groups. Among subgroups of animals fed the low-salt diet, kidney glutathione peroxidase (GPX) abundance was significantly lower in the SSR than SRR. The high-salt diet raised GPX and mitochondrial superoxide dismutase (SOD) abundance in the SRR kidneys but failed to do so in SSR. Cu/Zn-SOD abundance was similar in the subgroups of SSR and SRR fed the low-salt diet. The high-salt diet resulted in downregulation of Cu/Zn-SOD in SSR but not SRR.

CONCLUSIONS

Salt sensitivity in the SSR is associated with upregulations of the intrarenal angiotensin system, ROS-generating and proinflammatory/profibrotic proteins and an inability to raise antioxidant enzymes and maximally suppress PRA in response to high salt intake. These events can contribute to renal injury with high salt intake in SSR.

Specific down-regulation of connective tissue growth factor attenuates progression of nephropathy in mouse models of type 1 and type 2 diabetes

Diabetic nephropathy (DN) remains a major complication in both type 1 and type 2 diabetes. Systemic administration of antitransforming growth factor-beta (TGF-beta) antibody has shown some promise in mouse models of DN. However, chronic blockade of the multifunctional TGB-beta could be problematic. Several downstream effects of TGF-beta are mediated by connective tissue growth factor (CTGF), which is up-regulated in several renal cells and secreted in the urine in the diabetic state. Using murine models of DN (type 1 and type 2) and a CTGF antisense oligonucleotide (ASO) of novel chimeric chemistry, we evaluated the specific role of this target in DN. In the type 1 model of DN, C57BL6 mice were made diabetic using streptozotocin injections and hyperglycemic animals were treated with CTGF ASOs (20 mg/kg/2 qw) for 4 months. ASO, but not mismatch control oligonucleotide, -treated animals showed significant reduction in target CTGF expression in the kidney with a concomitant decrease in proteinuria and albuminuria. Treatment with the CTGF ASO for 8 wk reduced serum creatinine and attenuated urinary albuminuria and proteinuria in diabetic db/db mice, a model of type 2 DN. The ASO also reduced expression of genes involved in matrix expansion such as fibronectin and collagen (I and IV) and an inhibitor of matrix degradation, PAI-1, in the renal cortex, contributing to significant reversal of mesangial expansion in both models of DN. Pathway analyses demonstrated that diabetes-induced phosphorylation of p38 MAPK and its downstream target CREB was also inhibited by the ASO. Our results strongly suggest that blocking CTGF using a chimeric ASO holds substantial promise for the treatment of DN.

Regulation of transforming growth factor beta in diabetic nephropathy: implications for treatment

The recognition that the drivers of matrix accumulation is an appropriate therapeutic target for diabetic nephropathy is now accepted by the nephrology and pharmaceutical communities. Interventions focused around transforming growth factor-beta (TGF-beta) likely will be an important area of clinical investigation in the near future. Understanding the various pathways involved in stimulating TGF-beta in the diabetic kidney is of paramount importance in devising strategies to combat the development and progression of diabetic nephropathy. In this review we highlight the major pathways involved in stimulating TGF-beta production by increased glucose levels and discuss the therapeutic implications thereof.

CREB mediates UTP-directed arterial smooth muscle cell migration and expression of the chemotactic protein osteopontin via its interaction with activator protein-1 sites

The transcription factor cAMP responsive element-binding protein (CREB) has been found to be involved in arterial smooth muscle cell (SMC) migration. We previously demonstrated that osteopontin (OPN) expression is a key step for UTP-mediated migration of arterial SMCs and that activator protein (AP)-1, nuclear factor kappaB, and upstream stimulatory transcription factors are involved in this OPN expression. The present study aims to determine the role of CREB in UTP-induced migration and OPN expression in cultured SMCs. We found that CREB is activated by UTP via extracellular signal-regulated kinase 1/2 and p38 mitogen-activated protein kinase pathways but not by protein kinase A. Both overexpression of a dominant negative CREB and CREB small interfering RNA treatment suppressed UTP-induced OPN expression and SMC migration. Gel-shift and chromatin immunoprecipitation assays revealed that CREB binds 2 AP-1 sites (-1870 and -76) and a cAMP responsive element-like site (-1403) on the OPN promoter. Mutations of these sites showed that only the 2 AP-1 sites were required for UTP-induced OPN expression. Moreover, gel-supershift and sequential chromatin immunoprecipitation assays suggested that CREB was associated with c-Fos on the AP-1 sites of the OPN promoter. These results demonstrate that CREB participates in the induction of UTP-activated OPN expression via its binding to 2 AP-1 sites and is thus involved in UTP-mediated SMC migration.

Arachidonic acid-dependent activation of a p22(phox)-based NAD(P)H oxidase mediates angiotensin II-induced mesangial cell protein synthesis and fibronectin expression via Akt/PKB

Angiotensin II (Ang II) induces protein synthesis and hypertrophy through arachidonic acid (AA)- and redoxdependent activation of the serine-threonine kinase Akt/PKB in mesangial cells (MCs). The role of NAD(P)H oxidase component p22( phox ) was explored in this signaling pathway and in Ang II-induced expression of the extracellular matrix protein fibronectin. Ang II causes activation of Akt/PKB and induces fibronectin protein expression, effects abrogated by phospholipase A(2) inhibition and mimicked by AA. Ang II and AAalso elicited an increase in fibronectin expression that was reduced with a dominant negative mutant of Akt/PKB. Exposure of the cells to hydrogen peroxide stimulates Akt/PKB activity and fibronectin synthesis. The antioxidant N-acetylcysteine abolished Ang II- and AA-induced Akt/PKB activation and fibronectin expression. Western blot analysis revealed high levels of p22( phox ) in MCs. Antisense (AS) but not sense oligonucleotides for p22( phox ) prevented ROS generation in response to Ang II and AA. AS p22( phox ) inhibited Ang II- or AA-induced Akt/PKB as well as protein synthesis and fibronectin expression. These data provide the first evidence, in MCs, of activation by AAof a p22( phox )-based NAD(P)H oxidase and subsequent generation of ROS. Moreover, this pathway mediates the effect of Ang II on Akt/PKB-induced protein synthesis and fibronectin expression.

TGF-β1 induces COX-2 expression and PGE2 synthesis through MAPK and PI3K pathways in human mesangial cells

Transforming growth factor-beta1 (TGF-beta1) plays a fundamental role in the progression of renal diseases. Accumulating evidence has suggested that eicosanoids derived from cyclooxygenase-2 (COX-2) participate in a number of pathological processes in immune-mediated renal diseases. Mesangial cells (MC) play a major role in physiological and pathophysiological renal processes. MC express receptors for TGF-beta1, and COX-2 expression can be induced in MC. However, to date, there are no published data on the possible role of TGF-beta1 in COX-2 expression in human mesangial cells (HMC). We designed studies to determine (1) whether TGF-beta1 stimulates COX-2 expression in primary HMC, (2) whether mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3-kinase (PI3K) cascades are involved in TGF-beta1-induced COX-2 expression, and (3) whether prostaglandin (PG)E2 synthesis is affected by TGF-beta1 and MAP kinases and PI3K activation. Studies were performed in primary cultures of HMC and in an immortalized line of HMC. TGF-beta1 induces COX-2 promoter activity and COX-2 mRNA and protein expression in HMC. COX-2 induction is accompanied by increased PGE2 synthesis. Extracellular signal-regulated kinase (ERK)1/2, p38 MAPK, and PI3K pathway inhibition blunted TGF-beta1-induced COX-2 overexpression. We demonstrate that TGF-beta1 regulates COX-2 expression in HMC through the activation of ERK1/2, p38 MAPK, and PI3K. These results can help to elucidate the molecular mechanisms underlying the regulation of COX-2 and open up specific strategies for the treatment of glomerular disease.

Relationship between 12/15-lipoxygenase and COX-2 in mesangial cells: potential role in diabetic nephropathy

The 12/15-lipoxygenase (12/15-LO) and cyclooxygenase-2 (COX-2) pathways of arachidonate metabolism have been implicated in the pathogenesis of diabetic nephropathy (DN). In this study, we evaluated whether there is an interplay between 12/15-LO and COX-2 pathways in mesangial cells (MC). We utilized MC, microdissected glomeruli and renal cortical tissues. Transfections with cDNAs or short hairpin RNAs (shRNAs) were performed to overexpress or knockdown 12/15-LO and COX-2, respectively. Reverse transcription-polymerase chain reactions and Western blotting were used for evaluating mRNA and protein expression, respectively. We observed that the expression of both 12/15-LO and COX-2 were increased in high glucose stimulated rat MC relative to normal glucose, and also in cortical tissues from diabetic db/db and streptozotocin-injected mice relative to corresponding control mice. Treatment of rat MC with the 12/15-LO product, 12(S)-hydroxyeicosatetraenoic acid (12(S)-HETE), significantly increased COX-2 expression as well as levels of the COX-2 product, prostaglandin E(2) (PGE(2)). Interestingly, treatment of rat MC with PGE(2) led to a reciprocal increase in 12/15-LO expression as well as levels of 12(S)-HETE. The 12/15-LO shRNA could significantly attenuate COX-2 protein expression and vice versa. Furthermore, COX-2 expression levels were lower in MC and glomeruli from 12/15-LO knockout mice relative to control. Conversely, mouse MC stably overexpressing 12/15-LO had greater levels of COX-2 expression relative to mock-transfected cells. These new results indicate for the first time that 12/15-LO and COX-2 pathways can cross-talk and activate each other in MC. These novel interactions may amplify their effects on the progression of DN.

Gene expression of 5-, 12-, and 15-lipoxygenases and leukotriene receptors along the rat nephron

The arachidonate signaling pathways comprise prostanoids formed by cyclooxygenases, EETs, and HETEs formed by cytochrome P-450 (CYP) enzymes and HETEs and leukotrienes generated by lipoxygenases. Whereas the intrarenal localization of cyclooxygenases and of some CYP enzymes along the nephron has already been determined, the localization of lipoxygenases and leukotriene-forming enzymes together with leukotriene receptors in the kidney is less clear. This study therefore aimed to determine the expression of 5-, 12-, and 15-lipoxygenases as well as the leukotriene receptors along the rat nephron. The kidneys were dissected into cortex and outer and inner medulla, and the microdissected nephron segments were collected after a collagenase digestion. mRNA abundance was determined by RT-PCR and real-time PCR. 15-LOX mRNA showed a characteristic expression pattern along the distal nephron. 12-LOX mRNA was only found in the glomerulus. Similarly, 5-LOX mRNAs together with 5-LOX-activating protein mRNAs were expressed in the glomerulus and also in the vasa recta. The leukotriene A4 hydrolase was found in all nephron segments, whereas leukotriene C4 synthase mRNA could not be found in any nephron segment. The leukotriene receptor B4 and the cysteinyl leukotriene receptor type 1 were selectively expressed in the glomerulus, whereas cysteinyl receptor type 2 was not found in any nephron segment. Our data suggest that the glomerulus is a major source and target for 5- and 12-HETE and for leukotrienes. The collecting duct system, on the other hand, appears to be a major source of 15-HETE.

Disparate effects of 12-lipoxygenase and 12-hydroxyeicosatetraenoic acid in vascular endothelial and smooth muscle cells and in cardiomyocytes

The expression and activity of the arachidonic acid-metabolizing enzyme leukocyte-type 12-lipoxygenase (12-LO) are augmented in cultured vascular endothelial and smooth muscle cells exposed to high glucose concentrations and in blood vessels of diabetic animals. The product of this enzyme, 12-hydroxyeicosatetraenoic acid (12-HETE), evokes two types of interactions in these cells: on one hand it acts as a pro-inflammatory factor that contributes to the initiation and progression of atherosclerotic lesions. Yet on the other, it protects the same cells against deleterious effects of high levels of intracellular glucose by downregulating the glucose transport system in the cells. In addition, it has been shown that 12-LO and 12-HETE support insulin-dependent glucose transporter-4 translocation to the plasma membrane by maintaining intact actin fiber network in the cardiomyocytes. Here we focus on the disparate cellular interactions by which 12-LO and 12-HETE affect the glucose transport system in vascular endothelial and smooth muscle cells and in cardiomyocytes.

Role of AT-1 receptor in regulation of vascular MCP-1, IL-6, PAI-1, MAP kinase, and matrix expressions in obesity

BACKGROUND

Metabolic syndrome has emerged as the major cause of atherosclerosis. The associated atherosclerosis is accompanied by and, in part, due to inflammation. In an attempt to explore the molecular sources of vascular inflammation and possible involvement of renin-angiotensin system, we studied obese Zucker rats, which exhibit all features of metabolic syndrome.

METHODS

Seven-week-old male obese Zucker rats were randomized to losartan-treated (100 mg/L drinking H2O) and untreated groups. Lean Zucker rats served as controls. After four months, aortas were obtained and processed for various determinations by reverse transcription-polymerase chain reaction (RT-PCR) and Western blot and immunohistochemical analysis for collagen type IV.

RESULTS

Compared to the lean controls, obese Zucker rats showed significant increases in collagen staining, as well as expressions of collagen, fibronectin, plasminogen activator inhibitor-1, and two major proinflammatory mediators (i.e., interleukin-6 and monocyte chemoattractant protein-1). This was associated with significant increases in p38 and ERK1/2 mitogen activated protein kinase activities, as well as marked up-regulation of angiotensin II type 1 receptor (AT-1R) mRNA expression. These abnormalities were prevented by administration of the AT-1R blocker (ARB).

CONCLUSION

The untreated obese Zucker rats exhibit increased matrix protein accumulation in the aorta and marked up-regulations of proinflammatory and profibrotic pathways. These abnormalities are associated with up-regulation of AT-1R and are prevented by AT-1R blockade pointing to the potential role of AT-1R activation.

Upregulation of angiotensin II type 1 receptor, inflammatory mediators, and enzymes of arachidonate metabolism in obese Zucker rat kidney: reversal by angiotensin II type 1 receptor blockade

BACKGROUND

Severe obesity can result in proteinuria and progressive glomerulosclerosis in humans and experimental animals. The associated renal disease is ameliorated by weight reduction and/or blockade of the renin-angiotensin system. Various growth factors, cytokines, and lipid mediators are implicated in the pathogenesis of renal disease. To explore the possible involvement of these mediators in obesity-induced renal disease, we examined the expression of key enzymes of arachidonate metabolism and inflammatory genes in untreated and losartan-treated obese Zucker rats, a model of obesity, insulin resistance, and renal injury.

METHODS AND RESULTS

Seven-week-old male obese Zucker rats were randomized to losartan-treated (100 mg/L drinking H2O) and untreated groups, with lean Zucker rats as controls. After 4 months, RNA and protein were obtained from renal cortical tissue for relative reverse transcription-polymerase chain reaction, Western blots, and immunohistochemistry. Compared with the lean controls, obese Zucker rats showed significant glomerular matrix expansion and increased mRNA expression of the extracellular matrix protein fibronectin, inflammatory mediators interleukin-6 and monocyte chemoattractant protein-1, and 2 major enzymes of arachidonate metabolism, namely, 12/15-lipoxygenase and cyclooxygenase-2. This was associated with significant increases in p38 and extracellular signal-regulated kinase (ERK) 1/2 mitogen-activated protein kinase activities and marked upregulation of angiotensin II type 1 receptor (AT1R) mRNA and protein expression. These abnormalities and the associated glomerulopathy and proteinuria were prevented by administration of the AT1R blocker losartan.

CONCLUSIONS

These findings indicate that obesity-induced glomerulopathy is associated with upregulation of key inflammatory mediators. These events are associated with and perhaps in part due to upregulation of AT1R, as evidenced by their reversal with AT1R blocker treatment.

Role of 12-lipoxygenase in hypoxia-induced rat pulmonary artery smooth muscle cell proliferation

The 12-lipoxygenase (12-LO) pathway of arachidonic acid metabolism stimulates cell growth and metastasis of various cancer cells and the 12-LO metabolite, 12(S)-hydroxyeicosatetraenoic acid [12(S)-HETE], enhances proliferation of aortic smooth muscle cells (SMCs). However, pulmonary vascular effects of 12-LO have not been previously studied. We sought evidence for a role of 12-LO and 12(S)-HETE in the development of hypoxia-induced pulmonary hypertension. We found that 12-LO gene and protein expression is elevated in lung homogenates of rats exposed to chronic hypoxia. Immunohistochemical staining with a 12-LO antibody revealed intense staining in endothelial cells of large pulmonary arteries, SMCs (and possibly endothelial cells) of medium and small-size pulmonary arteries and in alveolar walls of hypoxic lungs. 12-LO protein expression was increased in hypoxic cultured rat pulmonary artery SMCs. 12(S)-HETE at concentrations as low as 10(-5) microM stimulated proliferation of pulmonary artery SMCs. 12(S)-HETE induced ERK 1/ERK 2 phosphorylation but had no effect on p38 kinase expression as assessed by Western blotting. 12(S)-HETE-stimulated SMC proliferation was blocked by the MEK inhibitor PD-98059, but not by the p38 MAPK inhibitor SB-202190. Hypoxia (3%)-stimulated pulmonary artery SMC proliferation was blocked by both U0126, a MEK inhibitor, and baicalein, an inhibitor of 12-LO. We conclude that 12-LO and its product, 12(S)-HETE, are important intermediates in hypoxia-induced pulmonary artery SMC proliferation and may participate in hypoxia-induced pulmonary hypertension.

Elevated endothelial nitric oxide bioactivity and resistance to angiotensin-dependent hypertension in 12/15-lipoxygenase knockout mice

12/15-Lipoxygenase (12/15-LOX) plays a pathogenic role in atherosclerosis. To characterize whether 12/15-LOX also contributes to endothelial dysfunction and hypertension, regulation of vessel tone and angiotensin II (ang II) responses were characterized in mice deficient in 12/15-LOX. There was a twofold increase in the magnitude of l-nitroarginine-methyl ester-inhibitable, acetylcholine-dependent relaxation or phenylephrine-dependent constriction in aortic rings isolated from 12/15-LOX(-/-) mice. Plasma NO metabolites and aortic endothelial NO synthase (eNOS) expression were also elevated twofold. Angiotensin II failed to vasoconstrict 12/15-LOX(-/-) aortic rings in the absence of L-nitroarginine-methyl ester, and ang II impaired acetylcholine-induced relaxation in wild-type, but not 12/15-LOX(-/-) rings. In vivo, 12/15-LOX(-/-) mice had similar basal systolic blood pressure measurements to wild type, however, blood pressure elevations in response to ang II infusion (1.1 mg/kg/day) were significantly attenuated (maximal pressure, 143.4 +/- 4 mmHg versus 122.1 +/- 5.3 mmHg for wild type and 12/15-LOX(-/-), respectively). In contrast, vascular hypertrophic responses to ang II, and ang II type 1 receptor (AT1-R) expression were similar in both strains. This study shows that 12/15-LOX(-/-) mice have increased NO biosynthesis and impaired ang II-dependent vascular responses in vitro and in vivo, suggesting that 12/15-LOX signaling contributes to impaired NO bioactivity in vascular disease in vivo.