High Levels of Glucose Stimulate Angiotensinogen Gene Expression Via the P38 Mitogen-Activated Protein Kinase Pathway in Rat Kidney Proximal Tubular Cells* *This work was supported by grants from the Medical Research Council of Canada (MT-13420 to J.S.D.C. and J.G.F., and MT-12573 to J.G.F.) and from the NIH (HL-48455 to J.R.I., and D.K-50836 to S.S.T.)

Urinary Angiotensinogen in Patients With Type 1 Diabetes With Microalbuminuria: Gender Differences and Effect of Intensive Insulin Therapy

Introduction

Angiotensinogen (AOG) is the precursor of peptides of the renin angiotensin system (RAS). Because insulin up-regulates transcriptional factors that normally repress kidney AOG synthesis, we evaluated urinary AOG (uAOG) in patients with type 1 diabetes (T1D) and microalbuminuria who are receiving either intensive or conventional insulin therapy.

Methods

Urine samples from participants of the Diabetes Control and Complications Trial (DCCT) were used for the following: (i) uAOG/creatinine measurements in 103 patients with microalbuminuria and 103 patients with normoalbuminuria, matched for age, gender, disease duration, and allocation to insulin therapy; and (ii) uAOG/creatinine measurements from patients with microalbuminuria allocated to intensive insulin therapy (n = 58) or conventional insulin therapy (n = 41) after 3 years on each modality.

Results

uAOG was higher in patients who started with microalbuminuria than in those with normoalbuminuria (6.65 vs. 4.0 ng/mg creatinine, P < 0.01). uAOG was higher in females than in males with microalbuminuria (11.7 vs. 5.4 ng/mg creatinine, P = 0.015). uAOG was lower in patients with microalbuminuria allocated to intensive insulin therapy than in conventional insulin therapy (3.98 vs. 7.42 ng/mg creatinine, P < 0.01). These differences in uAOG were observed though albumin excretion rate (AER) was not significantly different.

Conclusion

In patients with T1D and microalbuminuria, uAOG is increased and varies with gender and the type of insulin therapy independently of AER. This suggests that AOG production is increased in females and it is decreased by intensive insulin therapy. The reduction in uAOG with intensive insulin therapy, by kidney RAS downregulation, may contribute to the known renoprotective action associated with intensive insulin and improved glycemic control.

Inhibition of p38 MAPK decreases hyperglycemia-induced nephrin endocytosis and attenuates albuminuria

Abstract

Chronic hyperglycemia, as in diabetes mellitus, may cause glomerular damage with microalbuminuria as an early sign. Noteworthy, even acute hyperglycemia can increase glomerular permeability before structural damage of the glomerular filter can be detected. Despite intensive research, specific antiproteinuric therapy is not available so far. Thus, a deeper understanding of the molecular mechanisms of albuminuria is desirable. P38 MAPK signaling is involved in the development of hyperglycemia-induced albuminuria. However, the mechanism of increased p38 MAPK activity leading to increased permeability and albuminuria remained unclear. Recently, we demonstrated that acute hyperglycemia triggers endocytosis of nephrin, the key molecule of the slit diaphragm, and induces albuminuria. Here, we identify p38 MAPK as a pivotal regulator of hyperglycemia-induced nephrin endocytosis. Activated p38 MAPK phosphorylates the nephrin c-terminus at serine 1146, facilitating the interaction of PKCα with nephrin. PKCα phosphorylates nephrin at threonine residues 1120 and 1125, mediating the binding of β-arrestin2 to nephrin. β-arrestin2 triggers endocytosis of nephrin by coupling it to the endocytic machinery, leading to increased glomerular permeability. Pharmacological inhibition of p38 MAPK preserves nephrin surface expression and significantly attenuates albuminuria.

Key messages

Acute hyperglycemia triggers endocytosis of nephrin.

Activated p38 MAPK phosphorylates the nephrin c-terminus at serine 1146, facilitating the interaction of PKCα with nephrin.

PKCα phosphorylates nephrin at threonine residues 1120 and 1125, mediating the binding of β-arrestin2 to nephrin.

β-arrestin2 triggers endocytosis of nephrin by coupling it to the endocytic machinery, leading to a leaky glomerular filter.

Pharmacological inhibition of p38 MAPK preserves nephrin surface expression and significantly attenuates albuminuria under hyperglycemic conditions.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00109-022-02184-5.

Renin-Angiotensin System overactivation in polycystic ovary syndrome, a risk for SARS-CoV-2 infection?

Background

The SARS-CoV-2 coronavirus gains entry to target cells via the angiotensin-converting enzyme 2 (ACE2) receptor present on cells in blood vessels, lungs, heart, intestines, and kidneys. Renin-Angiotensin System (RAS) overactivity has also been described in metabolic syndrome, type 2 diabetes (T2D) and obesity, conditions shared by women with polycystic ovary syndrome (PCOS) We hypothesized that RAS overactivity may be present in PCOS.

Methods

We determined plasma levels of RAS-related proteins in a cohort of age matched control women (n = 97) and women with PCOS (n = 146). Plasma levels of RAS-related proteins (ACE2, Renin and Angiotensinogen (AGT)) were determined by Slow Off-rate Modified Aptamer (SOMA)-scan plasma protein measurement.

Results

PCOS women had a higher BMI (p < 0.001), systolic (p < 0.0001) and diastolic (p < 0.05) blood pressure, waist circumference (p < 0.0001), testosterone (p < 0.0001), free androgen index (p < 0.0001) and CRP (p < 0.0001). Renin was elevated in PCOS (p < 0.05) and angiotensinogen was lower in PCOS (p < 0.05), indicating overactivity of the RAS system in PCOS. ACE2 levels were lower in PCOS (p < 0.05), suggesting that PCOS women are at risk for development of hypertension.

Conclusion

RAS proteins levels differed between PCOS and control women, suggesting that the insulin resistance inherent in PCOS may predispose these women to more severe COVID-19 infection.

High glucose promotes breast cancer proliferation and metastasis by impairing angiotensinogen expression

A number of investigations have addressed the importance of high glucose in breast cancer, however, the involvement of angiotensinogen (AGT) in this scenario is yet to be defined. Here we set out to analyze the potential pro-tumor effects of high glucose in breast cancer, and understand the underlying molecular mechanism. We demonstrated that high glucose promoted cell proliferation, viability, and anchorage-independent growth of breast cancer cells. In addition, the migrative and invasive capacities were significantly enhanced by high glucose medium. Mechanistically, AGT expression was inhibited by high glucose at both transcriptional and translational levels. High AGT remarkably suppressed proliferation, inhibited viability, and compromised migration/invasion of breast cancer cells. Most importantly, ectopic introduction of AGT almost completely abrogated pro-tumor effects of high glucose. Our study has characterized the pro-tumor properties of high glucose in breast cancer cells, which is predominantly attributed to the suppression of AGT.

The relationships between markers of tubular injury and intrarenal haemodynamic function in adults with and without type 1 diabetes: Results from the Canadian Study of Longevity in Type 1 Diabetes

OBJECTIVE

Our aim was to define the relationships between plasma biomarkers of kidney injury and intrarenal haemodynamic function (glomerular filtration rate [GFR], effective renal plasma flow [ERPF], renal vascular resistance [RVR]) in adults with type 1 diabetes (T1D).

METHODS

The study sample comprised patients with longstanding T1D (duration ≥50 years), among whom 44 were diabetic kidney disease (DKD) resistors (eGFR >60 mL/min/1.73 m² and <30 mg/d urine albumin excretion) and 22 had DKD, in addition to 73 control participants. GFR_INULIN and ERPF_PAH were measured, RVR was calculated, and afferent (R_A )/efferent (R_E ) areteriolar resistances were derived from Gomez equations. Plasma neutrophil gelatinase-associated lipocalin (NGAL), β2 microglobulin (B2M), osteopontin (OPN) and uromodulin (UMOD) were measured using immunoassay kits from Meso Scale Discovery.

RESULTS

Plasma NGAL, B2M and OPN were higher and UMOD was lower in DKD patients vs DKD resistors and non-diabetic controls. In participants with T1D, plasma NGAL inversely correlated with GFR (r = -0.33; P = 0.006) and ERPF (r = -0.34; P = 0.006), and correlated positively with R_A (r = 0.26; P = 0.03) and RVR (r = 0.31; P = 0.01). In participants without T1D, NGAL and B2M inversely correlated with GFR (NGAL r = -0.18; P = 0.13 and B2M r = -0.49; P < 0.0001) and with ERPF (NGAL r = -0.19; P = 0.1 and B2M r = -0.42; P = 0.0003), and correlated positively with R_A (NGAL r = 0.19; P = 0.10 and B2M r = 0.3; P = 0.01) and with RVR (NGAL r = 0.20; P = 0.09 and B2M r = 0.34; P = 0.003). Differences were significant after adjusting for age, sex, HbA1c, SBP and LDL. There were statistical interactions between T1D status, B2M and intrarenal haemodynamic function (P < 0.05).

CONCLUSIONS

Elevated NGAL relates to intrarenal haemodynamic dysfunction in T1D, whereas elevated NGAL and B2M relate to intrarenal haemodynamic dysfunction in adults without T1D. These data may define a diabetes-specific interplay between tubular injury and intrarenal haemodynamic dysfunction.

Independent regulation of renin-angiotensin-aldosterone system in the kidney

Renin-angiotensin-aldosterone system (RAAS) plays important roles in regulating renal hemodynamics and functions, as well as in the pathophysiology of hypertension and renal disease. In the kidney, angiotensin II (Ang II) production is controlled by independent multiple mechanisms. Ang II is compartmentalized in the renal interstitial fluid with much higher concentrations than those existing in the circulation. Inappropriate activation of the intrarenal RAAS is an important contributor to the pathogenesis of hypertension and renal injury. It has been revealed that intrarenal Ang II levels are predominantly regulated by angiotensinogen and therefore, urinary angiotensinogen could be a biomarker for intrarenal Ang II generation. In addition, recent studies have demonstrated that aldosterone contributes to the progression of renal injury via direct actions on glomerular podocytes, mesangial cells, proximal tubular cells and tubulo-interstitial fibroblasts through the activation of locally expressed mineralocorticoid receptor. Thus, it now appears that intrarenal RAAS is independently regulated and its inappropriate activation contributes to the pathogenesis of the development of hypertension and renal disease. This short review article will focus on the independent regulation of the intrarenal RAAS with an emphasis on the specific role of angiotensinogen.

High glucose augments angiotensinogen in human renal proximal tubular cells through hepatocyte nuclear factor-5

High glucose has been demonstrated to induce angiotensinogen (AGT) synthesis in the renal proximal tubular cells (RPTCs) of rats, which may further activate the intrarenal renin-angiotensin system (RAS) and contribute to diabetic nephropathy. This study aimed to investigate the effects of high glucose on AGT in the RPTCs of human origin and identify the glucose-responsive transcriptional factor(s) that bind(s) to the DNA sequences of AGT promoter in human RPTCs. Human kidney (HK)-2 cells were treated with normal glucose (5.5 mM) and high glucose (15.0 mM), respectively. Levels of AGT mRNA and AGT secretion of HK-2 cells were measured by real-time polymerase chain reaction (PCR) and enzyme-linked immunosorbent assay (ELISA), respectively. Consecutive 5’-end deletion mutant constructs and different site-directed mutagenesis products of human AGT promoter sequences were respectively transfected into HK-2 cells, followed by AGT promoter activity measurement through dual luciferase assay. High glucose significantly augmented the levels of AGT mRNA and AGT secretion of HK-2 cells, compared with normal glucose treatment. High glucose also significantly augmented AGT promoter activity in HK-2 cells transfected with the constructs of human AGT promoter sequences, compared with normal glucose treatment. Hepatocyte nuclear factor (HNF)-5 was found to be one of the glucose-responsive transcriptional factors of AGT in human RPTCs, since the mutation of its binding sites within AGT promoter sequences abolished the above effects of high glucose on AGT promoter activity as well as levels of AGT mRNA and its secretion. The present study has demonstrated, for the first time, that high glucose augments AGT in human RPTCs through HNF-5, which provides a potential therapeutic target for diabetic nephropathy.

Effect of Sodium-Glucose Co-Transporter 2 Inhibitor, Dapagliflozin, on Renal Renin-Angiotensin System in an Animal Model of Type 2 Diabetes

Background

Renal renin-angiotensin system (RAS) activation is one of the important pathogenic mechanisms in the development of diabetic nephropathy in type 2 diabetes. The aim of this study was to investigate the effects of a sodium-glucose co-transporter 2 (SGLT-2) inhibitor, dapagliflozin, on renal RAS in an animal model with type 2 diabetes.

Methods

Dapagliflozin (1.0 mg/kg, OL-DA) or voglibose (0.6 mg/kg, OL-VO, diabetic control) (n = 10 each) was administered to Otsuka Long-Evans Tokushima Fatty (OLETF) rats for 12 weeks. We used voglibose, an alpha-glucosidase inhibitor, as a comparable counterpart to SGLT2 inhibitor because of its postprandial glucose-lowering effect without proven renoprotective effects. Control Long-Evans Tokushima Otsuka (LT) and OLETF (OL-C) rats received saline (n = 10, each). Changes in blood glucose, urine albumin, creatinine clearance, and oxidative stress were measured. Inflammatory cell infiltration, mesangial widening, and interstitial fibrosis in the kidney were evaluated by histological analysis. The effects of dapagliflozin on renal expression of the RAS components were evaluated by quantitative RT-PCR in renal tissue.

Results

After treatment, hyperglycemia and urine microalbumin levels were attenuated in both OL-DA and OL-VO rather than in the OL-C group (P < 0.05). The urine angiotensin II (Ang II) and angiotensinogen levels were significantly decreased following treatment with dapagliflozin or voglibose, but suppression of urine Ang II level was more prominent in the OL-DA than the OL-VO group (P < 0.05). The expressions of angiotensin type 1 receptor and tissue oxidative stress markers were markedly increased in OL-C rats, which were reversed by dapagliflozin or voglibose (P < 0.05, both). Inflammatory cell infiltration, mesangial widening, interstitial fibrosis, and total collagen content were significantly increased in OL-C rats, which were attenuated in OL-DA group (P < 0.05).

Conclusion

Dapagliflozin treatment showed beneficial effects on diabetic nephropathy, which might be via suppression of renal RAS component expression, oxidative stress and interstitial fibrosis in OLETF rats. We suggest that, in addition to control of hyperglycemia, partial suppression of renal RAS with an SGLT2 inhibitor would be a promising strategy for the prevention of treatment of diabetic nephropathy.

Mechanistic insight of diabetic nephropathy and its pharmacotherapeutic targets: An update

Diabetic nephropathy (DN), a chronic complication of diabetes, is charecterized by glomerular hypertrophy, proteinuria, decreased glomerular filtration, and renal fibrosis resulting in the loss of renal function. Although the exact cause of DN remains unclear, several mechanisms have been postulated, such as hyperglycemia-induced renal hyper filtration and renal injury, AGEs-induced increased oxidative stress, activated PKC-induced increased production of cytokines, chemokines, and different inflammatory and apoptotic signals. Among various factors, oxidative stress has been suggested to play a major role underlying the onset and propagation of DN. It triggers several signaling pathways involved in DN, like AGEs, PKC cascade, JAK/STAT signaling, MAPK, mTOR, and SMAD. Oxidative stress-induced activation of both inflammatory and apoptotic signals are two major problems in the pathogenesis of DN. The FDA approved pharmacotherapeutic agents affecting against polyol pathway principally include anti-oxidants, like α-lipoic acid, vitamin E, and vitamin C. Kremezin and benfotiamine are the FDA approved AGEs inhibitors, another therapeutic target against DN. Ruboxistaurin, telmizartan, rapamycin, fenofibrate, aliskiren, and manidipine are some FDA approved pharmacotherapeutics effective against DN via diverse mechanisms. Beside this, some therapeutic agents are still waiting for FDA approval and few drugs without FDA approval are also prescribed in some countries for the management of DN. Despite the medications available in the market to treat DN, the involvement of multiple mechanisms makes it difficult to choose an optimum therapeutic agent. Therefore, much research is required to find out new therapeutic agent/strategies for an adequate pharmacotherapy of DN.

Gallic acid ameliorates renal functions by inhibiting the activation of p38 MAPK in experimentally induced type 2 diabetic rats and cultured rat proximal tubular epithelial cells

Diabetic nephropathy (DN) is one of the leading causes of morbidity and mortality in diabetic patients that accounts for about 40% of deaths in type 2 diabetes. p38 mitogen activated protein kinase (p38 MAPK), a serine-threonine kinase, plays an important role in tissue inflammation and is known to be activated under conditions of oxidative stress and hyperglycemia. The role of p38 MAPK has been demonstrated in DN, and its inhibition has been suggested as an alternative approach in the treatment of DN. In the present study, we investigated the nephroprotective effects of an anti-inflammatory phenolic compound, gallic acid (GA, 3,4,5-trihydroxybenzoic acid), in high fat diet/streptozotocin (HFD/STZ) induce type 2 diabetic wistar albino rats. GA (25 mg/kgbw and 50 mg/kgbw, p.o.) treatment for 16 weeks post induction of diabetes led to a significant reduction in the levels of blood glucose, HbA1c, serum creatinine, blood urea nitrogen and proteinuria as well as a significant reduction in the levels of creatinine clearance. GA significantly inhibited the renal p38 MAPK and nuclear factor kappa B (N-κB) activation as well as significantly reduced the levels of renal transforming growth factor beta (TGF-β) and fibronectin. Treatment with GA resulted in a significant reduction in the serum levels of proinflammatory cytokines viz. interleukin 1 beta (IL-1β), IL-6 and tumor necrosis factor alpha (TNF-α). Moreover, GA significantly lowered renal pathology and attenuated renal oxidative stress. In cultured rat NRK 52E proximal tubular epithelial cells, GA treatment inhibited high glucose induced activation of p38 MAPK and NF-κB as well as suppressed proinflammatory cytokine synthesis. The results of the present study provide in vivo and in vitro evidences that the p38 MAPK pathway plays an important role in the pathogenesis of DN, and GA attenuates the p38 MAPK-mediated renal dysfunction in HFD/STZ induced type 2 diabetic rats.

Catalase overexpression prevents nuclear factor erythroid 2-related factor 2 stimulation of renal angiotensinogen gene expression, hypertension, and kidney injury in diabetic mice

This study investigated the impact of catalase (Cat) overexpression in renal proximal tubule cells (RPTCs) on nuclear factor erythroid 2-related factor 2 (Nrf2) stimulation of angiotensinogen (Agt) gene expression and the development of hypertension and renal injury in diabetic Akita transgenic mice. Additionally, adult male mice were treated with the Nrf2 activator oltipraz with or without the inhibitor trigonelline. Rat RPTCs, stably transfected with plasmid containing either rat Agt or Nrf2 gene promoter, were also studied. Cat overexpression normalized systolic BP, attenuated renal injury, and inhibited RPTC Nrf2, Agt, and heme oxygenase-1 (HO-1) gene expression in Akita Cat transgenic mice compared with Akita mice. In vitro, high glucose level, hydrogen peroxide, and oltipraz stimulated Nrf2 and Agt gene expression; these changes were blocked by trigonelline, small interfering RNAs of Nrf2, antioxidants, or pharmacological inhibitors of nuclear factor-κB and p38 mitogen-activated protein kinase. The deletion of Nrf2-responsive elements in the rat Agt gene promoter abolished the stimulatory effect of oltipraz. Oltipraz administration also augmented Agt, HO-1, and Nrf2 gene expression in mouse RPTCs and was reversed by trigonelline. These data identify a novel mechanism, Nrf2-mediated stimulation of intrarenal Agt gene expression and activation of the renin-angiotensin system, by which hyperglycemia induces hypertension and renal injury in diabetic mice.

Novel mechanism of blood pressure regulation by forkhead box class O1-mediated transcriptional control of hepatic angiotensinogen

The renin-angiotensin system is a major determinant of blood pressure regulation. It consists of a cascade of enzymatic reactions involving 3 components: angiotensinogen, renin, and angiotensin-converting enzyme, which generate angiotensin II as a biologically active product. Angiotensinogen is largely produced in the liver, acting as a major determinant of the circulating renin-angiotensin system, which exerts acute hemodynamic effects on blood pressure regulation. How the expression of angiotensinogen is regulated is not completely understood. Here, we hypothesize that angiotensinogen is regulated by forkhead transcription factor forkhead box class O1 (Foxo1), an insulin-suppressed transcription factor, and thereby controls blood pressure in mice. We generated liver-specific Foxo1 knockout mice, which exhibited a reduction in plasma angiotensinogen and angiotensin II levels and a significant decrease in blood pressure. Using hepatocyte cultures, we demonstrated that overexpression of Foxo1 increased angiotensinogen expression, whereas hepatocytes lacking Foxo1 demonstrated a reduction of angiotensinogen gene expression and partially impaired insulin inhibition on angiotensinogen gene expression. Furthermore, mouse angiotensinogen prompter analysis demonstrated that the angiotensinogen promoter region contains a functional Foxo1-binding site, which is responsible for both Foxo1 stimulation and insulin suppression on the promoter activity. Together, these data demonstrate that Foxo1 regulates hepatic angiotensinogen gene expression and controls plasma angiotensinogen and angiotensin II levels, modulating blood pressure control in mice.

Detailed localization of augmented angiotensinogen mRNA and protein in proximal tubule segments of diabetic kidneys in rats and humans

In the intrarenal renin-angiotensin system, angiotensinogen levels are well known to be increased in diabetes, and these enhanced intrarenal angiotensinogen levels may initiate the development and accelerate the progression of diabetic nephropathy. However, the specific localization of the augmented angiotensinogen in proximal tubule segments in diabetes is still unknown. We investigated the detailed localization of angiotensinogen in 3 proximal tubule segments in the diabetic Otsuka Long-Evans Tokushima fatty (OLETF) rats and the control Long-Evans Tokushima Otsuka (LETO) rats. We also prepared OLETF rats treated with angiotensin II type 1 receptor blocker, olmesartan or with a combination of vasodilator agents. Moreover, biopsied samples of human kidney cortex were used to confirm the results of animal studies. We examined the co-localization of angiotensinogen with segment-specific markers by double staining using fluorescence in situ hybridization and/or immunofluorescence. Angiotensinogen mRNA expression was barely detectable in segment 1. In segment 3, the area of angiotensinogen mRNA expression was augmented in the OLETF rats compared with the LETO rats. Angiotensinogen protein expression areas in segments 1 and 3 were also increased in the OLETF rats compared with the LETO rats. Chronic treatment with olmesartan ameliorated these areas of augmented angiotensinogen expression. Biopsied human kidney samples showed similar results. These data suggest that the augmented angiotensinogen mRNA levels in segment 3 and angiotensinogen protein levels in segments 1 and 3 may contribute to the progression of diabetic nephropathy.

Tissue Renin-Angiotensin systems: a unifying hypothesis of metabolic disease

The actions of angiotensin peptides are diverse and locally acting tissue renin-angiotensin systems (RAS) are present in almost all tissues of the body. An activated RAS strongly correlates to metabolic disease (e.g., diabetes) and its complications and blockers of RAS have been demonstrated to prevent diabetes in humans. Hyperglycemia, obesity, hypertension, and cortisol are well-known risk factors of metabolic disease and all stimulate tissue RAS whereas glucagon-like peptide-1, vitamin D, and aerobic exercise are inhibitors of tissue RAS and to some extent can prevent metabolic disease. Furthermore, an activated tissue RAS deteriorates the same risk factors creating a system with several positive feedback pathways. The primary effector hormone of the RAS, angiotensin II, stimulates reactive oxygen species, induces tissue damage, and can be associated to most diabetic complications. Based on these observations, we hypothesize that an activated tissue RAS is the principle cause of metabolic syndrome and type 2 diabetes, and additionally is mediating the majority of the metabolic complications. The involvement of positive feedback pathways may create a self-reinforcing state and explain why metabolic disease initiate and progress. The hypothesis plausibly unifies the major predictors of metabolic disease and places tissue RAS regulation in the center of metabolic control.

Heterogeneous nuclear ribonucleoprotein F suppresses angiotensinogen gene expression and attenuates hypertension and kidney injury in diabetic mice

We investigated the impact of heterogeneous nuclear ribonucleoprotein F (hnRNP F) overexpression on angiotensinogen (Agt) gene expression, hypertension, and renal proximal tubular cell (RPTC) injury in high-glucose milieu both in vivo and in vitro. Diabetic Akita transgenic (Tg) mice specifically overexpressing hnRNP F in their RPTCs were created, and the effects on systemic hypertension, Agt gene expression, renal hypertrophy, and interstitial fibrosis were studied. We also examined immortalized rat RPTCs stably transfected with control plasmid or plasmid containing hnRNP F cDNA in vitro. The results showed that hnRNP F overexpression attenuated systemic hypertension, suppressed Agt and transforming growth factor-β1 (TGF-β1) gene expression, and reduced urinary Agt and angiotensin II levels, renal hypertrophy, and glomerulotubular fibrosis in Akita hnRNP F-Tg mice. In vitro, hnRNP F overexpression prevented the high-glucose stimulation of Agt and TGF-β1 mRNA expression and cellular hypertrophy in RPTCs. These data suggest that hnRNP F plays a modulatory role and can ameliorate hypertension, renal hypertrophy, and interstitial fibrosis in diabetes. The underlying mechanism is mediated, at least in part, via the suppression of intrarenal Agt gene expression in vivo. hnRNP F may be a potential target in the treatment of hypertension and kidney injury in diabetes.

Inflammation in diabetic nephropathy

Diabetic nephropathy is the leading cause of end-stage kidney disease worldwide but current treatments remain suboptimal. This review examines the evidence for inflammation in the development and progression of diabetic nephropathy in both experimental and human diabetes, and provides an update on recent novel experimental approaches targeting inflammation and the lessons we have learned from these approaches. We highlight the important role of inflammatory cells in the kidney, particularly infiltrating macrophages, T-lymphocytes and the subpopulation of regulatory T cells. The possible link between immune deposition and diabetic nephropathy is explored, along with the recently described immune complexes of anti-oxidized low-density lipoproteins. We also briefly discuss some of the major inflammatory cytokines involved in the pathogenesis of diabetic nephropathy, including the role of adipokines. Lastly, we present the latest data on the pathogenic role of the stress-activated protein kinases in diabetic nephropathy, from studies on the p38 mitogen activated protein kinase and the c-Jun amino terminal kinase cell signalling pathways. The genetic and pharmacological approaches which reduce inflammation in diabetic nephropathy have not only enhanced our understanding of the pathophysiology of the disease but shown promise as potential therapeutic strategies.

Urinary angiotensinogen as a novel early biomarker of intrarenal renin-angiotensin system activation in experimental type 1 diabetes

Urinary excretion of albumin (UAlb) is used clinically as a marker of diabetic nephropathy (DN). Although DN was thought to be a unidirectional process, recent studies demonstrated that a large proportion of patients diagnosed with DN reverted to normoalbuminuria. Moreover, despite the normoalbuminuria, one-third of them exhibited reduced renal function even during the microalbuminuric stage. This study was performed to investigate whether urinary angiotensinogen (UAGT) level may serve as a useful marker of the early stage of experimental type 1 diabetes (T1DM). T1DM was induced by a single intraperitoneal injection of streptozotocin. Control mice were injected with citrate buffer. Two days after streptozotocin injection, half of the mice received continuous insulin treatment. Our data showed that UAlb excretion was increased 6 days after streptozotocin injection compared to controls, whereas UAGT excretion was increased at an earlier time point. These increases were reversed by insulin treatment. The UAGT to UAlb ratio was increased in diabetic mice compared to control mice. Furthermore, the increased AGT expression in the kidneys was observed in diabetic mice. These data suggest that UAGT might be useful as a novel early biomarker of activation of the renin-angiotensin system in experimental type 1 diabetes.

High glucose up-regulates angiotensin II subtype 2 receptors via interferon regulatory factor-1 in proximal tubule epithelial cells

Earlier studies have reported an increase in the proximal tubule AT(2) receptor (AT(2)R) expression in diabetes, with a beneficial role in kidney function and blood pressure regulation. Here, we demonstrate that the increase in AT(2)R protein expression is associated with an increased expression of transcription factor IRF-1 in hyperglycemic rat and in high glucose-treated HK2 cells. Knock-down of IRF-1 by siRNA in HK2 cells prevented high glucose-induced AT(2)R up-regulation. The data suggest that IRF-1 is a transcriptional regulator of AT(2)R expression in hyperglycemia, and warrant further studies to understand the physiological role of IRF-1 along with AT(2)R in diabetic kidney.

Angiotensin II Type 1 Receptor Blockers Reduce Urinary Angiotensinogen Excretion and the Levels of Urinary Markers of Oxidative Stress and Inflammation in Patients with Type 2 Diabetic Nephropathy

Objective

To demonstrate that the administration of an angiotensin (Ang) II type 1 receptor (AT1R) blocker (ARB) inhibits the vicious cycle of high glucose (HG)-reactive oxygen species (ROS)-angiotensinogen (AGT)-Ang II-AT1R-ROS by suppressing ROSs and inflammation, thus ameliorating diabetic nephropathy (DN).

Research Design and Methods

Thirteen hypertensive DN patients were administered ARBs, and the following parameters were evaluated before and 16 weeks after the treatment: urinary AGT (UAGT), albumin (albumin-creatinine ratio: ACR), 8-hydroxyde-oxyguanosine (8-OHdG), 8-epi-prostaglandin F2α(8-epi-PGF2α), monocyte chemoattractant protein (MCP)-1, interleukin (IL)-6, and IL-10.

Results

ARB treatment reduced the blood pressure and urinary levels of AGT, ACR, 8-OHdG, 8-epi-PGF2α, MCP-1, and IL-6 but increased the urinary levels of IL-10. The reduction rate of UAGT correlated with the reduction rate of blood pressure; the reduction rates of the urinary ACR, 8-OHdG, 8-epi-PGF2α, MCP-1, and IL-6 levels; and the increase rate of the urinary IL-10 levels. Moreover, subjects who had high UAGT values at baseline exhibited higher reduction rates of urinary albumin excretion.

Conclusions

ARB-induced blockade of the abovementioned vicious cycle contributes to the renoprotective effects of ARBs in DN. The urinary levels of AGT could represent a predictive factor for reduced ACR in patients receiving ARB treatment.

Role of MKK3-p38 MAPK signalling in the development of type 2 diabetes and renal injury in obese db/db mice

AIMS/HYPOTHESIS

Obesity and diabetes are associated with increased intracellular p38 mitogen-activated protein kinase (MAPK) signalling, which may promote tissue inflammation and injury. Activation of p38 MAPK can be induced by either of the immediate upstream kinases, MAP kinase kinase (MKK)3 or MKK6, and recent evidence suggests that MKK3 has non-redundant roles in the pathology attributed to p38 MAPK activation. Therefore, this study examined whether MKK3 signalling influences the development of obesity, type 2 diabetes and diabetic nephropathy.

METHODS

Wild-type and Mkk3 (also known as Map2k3) gene-deficient db/db mice were assessed for the development of obesity, type 2 diabetes and renal injury from 8 to 32 weeks of age.

RESULTS

Mkk3 (+/+) db/db and Mkk3 (-/-) db/db mice developed comparable obesity and were similar in terms of incidence and severity of type 2 diabetes. At 32 weeks, diabetic Mkk3 (+/+) db/db mice had increased kidney levels of phospho-p38 and MKK3 protein. In comparison, kidney levels of phospho-p38 in diabetic Mkk3 ( -/- ) db/db mice remained normal, despite a fourfold compensatory increase in MKK6 protein levels. The reduced levels of p38 MAPK signalling in the diabetic kidneys of Mkk3 ( -/- ) db/db mice was associated with protection against the following: declining renal function, increasing albuminuria, renal hypertrophy, podocyte loss, mesangial cell activation and glomerular fibrosis. Diabetic Mkk3 ( -/- ) db/db mice were also significantly protected from tubular injury and interstitial fibrosis, which was associated with reduced Ccl2 mRNA expression and interstitial macrophage accumulation.

CONCLUSIONS/INTERPRETATION

MKK3-p38 MAPK signalling is not required for the development of obesity or type 2 diabetes, but plays a distinct pathogenic role in the progression of diabetic nephropathy in db/db mice.

Atrial natriuretic peptide attenuates high glucose-activated transforming growth factor-beta, Smad and collagen synthesis in renal proximal tubular cells

Atrial natriuretic peptide, besides its role in the regulation of volume homeostasis, has been noted to exert cytoprotective effects in several cell types from hypoxia. The present study was performed to explore the effect of ANP on high glucose-activated transforming growth factor-beta1 (TGF-beta1), Smad and collagen synthesis in renal proximal epithelial cells. Cultured NRK-52E cells were divided into five groups: (1) normal glucose (5.5 mM), (2) high glucose (35 mM), (3) D-mannitol (29.5 mM), (4) high glucose plus ANP (10(-6)-10(-9) M), and (5) high glucose plus ANP (10(-6) M) and guanylate cyclase inhibitor LY83583 (10(-7) M) groups. Messenger RNA levels of TGF-beta1, Smad2, and collagens were measured by RT-PCR. ELISA, immunocytochemistry and Western blotting were used to detect protein levels of TGF-beta1, Smad2, phospho-Smad 2/3 and collagen type 1. We found high glucose to significantly increase mRNA levels of TGF-beta1, Smad 2, collagen types I and III and protein levels of TGF-beta1, phospho-Smad 2/3 and collagen type 1, but mannitol did not affect their expression. The addition of ANP significantly attenuated high glucose-enhanced mRNA and protein levels of TGF-beta1, Smad and collagens. LY83583 blocked the influence of ANP on high glucose-activated TGF-beta1, Smad and collagen synthesis. This is the first study to demonstrate that activation of TGF-beta1, Smad and collagen synthesis stimulated by high glucose can also be inhibited by exogenous ANP in renal tubular epithelial cells.

Renal p38 MAP kinase activity in experimental diabetes

Renal cell activity of p38 mitogen-activated protein kinase (p38) is increased in the diabetic milieu. p38 mediates signals relevant for the development of diabetic nephropathy (DN). However, renal p38 in Type 1 diabetes in vivo, particularly in conditions reflecting the differences in metabolic control, and its activity in advanced stages of DN, has received less attention. We examined the p38 pathway in renal cortex of rats with streptozotocin diabetes (4 weeks) with poor (DS), moderate (DM), and intensive (DII) metabolic control, achieved by varying doses of insulin therapy. Renal p38 was also studied in 12-month diabetic rats with established nephropathy (DM12) and compared with age-matched controls. p38 activity (in vitro kinase assay and expression of phosphorylated (active) p38 (P-p38)) was increased in DM and DS rats, as compared with non-diabetic controls, and attenuated by intensive insulin treatment. In all groups, P-p38 was predominantly localized in macula densa cells. Diabetic rats also demonstrated P-p38 immunoreactivity in the distal tubule and glomeruli. Enhanced p38 activity in DS and DM rats was not associated with increases in expression of active mitogen-activated protein kinase 3/6, an activator of p38, but paralleled with increased expression of scaffolding protein transforming growth factor-beta-activated protein kinase 1-binding protein 1. Expression of mitogen-activated protein phosphatase-1 (MKP-1), one of the phosphatases involved in inactivation of mitogen-activated protein kinase signaling, was increased in all diabetic groups, irrespective of metabolic control. Renal p38 activation was also detectable in D12 rats with established albuminuria and glomerulosclerosis. In summary, renal cortical p38 activity was increased in diabetic rats at early and advanced stages of nephropathy, as compared with non-diabetic animals, and attenuated by improved metabolic control. p38 activation in diabetes is likely to occur via multiple pathways and cannot be explained by downregulation of MKP-1.

Enhanced intrarenal oxidative stress and angiotensinogen in IgA nephropathy patients

This study was performed to determine whether immunoreactivity of intrarenal hemeoxygenase-1 and angiotensinogen are increased in IgA nephropathy (IgAN) patients. Hemeoxygenase-1 and angiotensinogen immunoreactivity were determined by immunohistochemistry robot system in renal specimens from 39 patients with IgAN. Normal portions of surgically resected kidney served as controls. IgAN patients showed moderate proteinuria (1.1+/-0.2 g/day); however, the control group did not show any proteinuria. Immunoreactivity of intrarenal hemeoxygenase-1 and angiotensinogen in IgAN were significantly increased compared to normal kidneys (2.42+/-0.42 vs 1.00+/-0.26 for hemeoxygenase-1 and 4.05+/-0.40 vs 1.00+/-0.21 for angiotensinogen, arbitrary unit). Even though these IgAN patients did not show massive renal damage, hemeoxygenase-1 and angiotensinogen immunoreactivity were increased in these patients at this time point. These data suggest that activated intrarenal reactive oxygen species-angiotensinogen axis plays some roles in development of IgAN at the early stage and will provide supportive foundation of effectiveness of the renin-angiotensin system blockade in IgAN.

Heterogeneous Nuclear Ribonucleoprotein K Modulates Angiotensinogen Gene Expression in Kidney Cells

The present studies aimed to identify the 70-kDa nuclear protein that binds to an insulin-responsive element in the rat angiotensinogen gene promoter and to define its action on angiotensinogen gene expression. Nuclear proteins were isolated from rat kidney proximal tubular cells and subjected to two-dimensional electrophoresis. The 70-kDa nuclear protein was detected by Southwestern blotting and subsequently identified by mass spectrometry, which revealed that it was identical to 65-kDa heterogeneous nuclear ribonucleoprotein K (hnRNP K). hnRNP K bound to the insulin-responsive element of the rat angiotensinogen gene was revealed by a gel mobility shift assay and chromatin immunoprecipitation assay. hnRNP K inhibited angiotensinogen mRNA expression and promoter activity. In contrast, hnRNP K down-expression by small interference RNA enhanced angiotensinogen mRNA expression. Moreover, hnRNP K interacted with hnRNP F in pulldown and co-immunoprecipitation assays. Co-transfection of hnRNP K and hnRNP F further suppressed angiotensinogen mRNA expression. Finally, in vitro and in vivo studies demonstrated that high glucose increases and insulin inhibits hnRNP K expression in rat kidney proximal tubular cells. In conclusion, our experiments revealed that hnRNP K is a nuclear protein that binds to the insulin-responsive element of the rat angiotensinogen gene promoter and modulates angiotensinogen gene transcription in the kidney.

Young Scholars Award Lecture: Intratubular angiotensinogen in hypertension and kidney diseases

Recent findings related to the renin-angiotensin system have provided a more elaborated understanding of the pathophysiology of hypertension and kidney diseases. These findings have led to unique concepts and issues regarding the intrarenal renin-angiotensin system. Angiotensinogen is the only known substrate for renin that is the rate-limiting enzyme of the renin-angiotensin system. Because the level of angiotensinogen in human beings is close to the Michaelis-Menten constant value for renin, changes in angiotensinogen levels can control the activity of the renin-angiotensin system, and its upregulation may lead to elevated angiotensin peptide levels and increases in blood pressure. Enhanced intrarenal angiotensinogen mRNA or protein levels or both have been observed in multiple models of hypertension including angiotensin II-dependent hypertensive rats, Dahl salt-sensitive hypertensive rats, and spontaneously hypertensive rats, as well as in kidney diseases including diabetic nephropathy, immunoglobulin A (IgA) nephropathy, and radiation nephropathy. Renal angiotensinogen is formed primarily in proximal tubular cells and is secreted into the tubular fluid. Urinary angiotensinogen excretion rates show a clear relationship to kidney angiotensin II contents and kidney angiotensinogen levels, suggesting that urinary angiotensinogen may serve as an index of the intrarenal renin-angiotensin system status. Establishment of concise and accurate methods to measure human angiotensinogen may allow clinical studies that would provide important information regarding the roles of intrarenal angiotensinogen in the development and progression of hypertension and kidney diseases.

Agents in development for the treatment of diabetic nephropathy

Diabetic nephropathy is a leading cause of end-stage renal disease, and accounts for significant morbidity and mortality in patients with diabetes. Diabetic nephropathy seems to occur as a result of an interaction between metabolic and haemodynamic factors, which activate common pathways that lead to renal damage. In the past, the treatment of diabetic nephropathy has focused on the control of hyperglycaemia. Newer targets, some of which are linked to glucose-dependent pathways, appear to be a major focus of new treatments directed against the development and progression of renal damage as a result of diabetes. It is anticipated that additional therapeutic approaches that inhibit both metabolic and haemodynamic pathways will include strategies that target growth factors, cytokines and intracellular second messengers. Such an approach is expected to lead to improved therapies for the treatment of diabetic nephropathy.

ERK and p38 mediate high-glucose-induced hypertrophy and TGF-beta expression in renal tubular cells

We investigated the expression of ERK, p38 mitogen-activated protein kinase (p38), and JNK in renal tubules of diabetic rats following 3 wk after streptozotocin injection (DM). Although the expression of ERK was not different between controls and DM, phosphorylated ERK was expressed more intensely in DM. p38 And phosphorylated p38 were detected only in the diabetic kidney and were localized in all tubular segments. JNK and phosphorylated JNK were expressed similarly in controls and DM. Transforming growth factor (TGF)-beta was expressed in all tubular segments of DM, coinciding with the localization of p38. In LLC-PK1 cells, phosphorylation of ERK and p38 increased after 24- to 72-h exposure to high glucose (HG). Coincubation with a p38 inhibitor SB-203580 or a MEK inhibitor, PD-98059, suppressed the HG-induced increases in protein content, [3H]leucine incorporation, and the protein-to-DNA ratio. SB-203580 or PD-98059 also abolished the HG-stimulated expression of TGF-beta protein. These results demonstrate that ERK and p38 are activated in renal tubular cells of DM and may mediate HG-induced cellular hypertrophy and TGF-beta expression.

Activation and cellular localization of the p38 and JNK MAPK pathways in rat crescentic glomerulonephritis

BACKGROUND

The p38 and c-Jun N-terminal kinase (JNK) mitogen-activated protein kinase (MAPK) are intracellular signal transduction pathways involved in the production of inflammatory mediators. Little, however, is known about the contribution of these pathways to renal inflammation, nor the cell types in which these pathways are activated within normal and inflamed kidneys. The aim of this study was therefore to delineate the pattern and cellular localization of p38 and JNK activation in normal rat kidney and rat acute and chronic inflammatory renal disease.

METHODS

Normal male Sprague-Dawley rats and groups of rats given accelerated anti-glomerular basement membrane (GBM) disease were killed at 3 hours, day 1, day 7, or day 28 and examined for p38 and JNK pathway activation by Western blotting and immunolocalization of the phosphorylated p38 (p-p38) and JNK (p-JNK) kinases.

RESULTS

In terms of glomerular MAPK activation, Western blotting identified the presence of both p-p38 and p-JNK in normal glomeruli, localized by immunohistochemistry to podocytes and epithelial cells of Bowman's capsule. In anti-GBM disease, Western blotting showed that p38 activation peaked at 3 hours and remained elevated above normal throughout the disease time course. JNK activation (via the 54 kD isoform) likewise increased at 3 hours of anti-GBM disease and remained elevated throughout disease. At 3 hours, p-p38, but not p-JNK, was localized to neutrophils and glomerular endothelial cells. p-JNK was localized to glomerular endothelial cells at day 7. Macrophages, lymphocytes, activated podocytes, and myofibroblasts were positive for both p-p38 and p-JNK. In terms of tubular MAPK activation, Western blotting identified p38 and JNK activation in tubules of normal kidney. Immunostaining showed that most cortical tubules contained some p-p38 and p-JNK stained cells. There was a significant increase in tubular p38 activation at 3 hours of anti-GBM disease, followed by increased JNK activation of the 54 kD isoform from day 7 onward, and the 46 kD isoform at day 28. Immunostaining of diseased tissue localized p-p38 and p-JNK to virtually all cortical tubular cells.

CONCLUSION

The p38 and JNK MAPK pathways are activated in glomeruli and tubules of normal kidney. In acute anti-GBM disease, there was an increase in p38 activation within glomerular endothelial cells and within infiltrating neutrophils, suggesting an important role for p38 MAPK in acute inflammation. In progressive anti-GBM disease, p38 and JNK activation in podocytes, glomerular endothelial cells, infiltrating macrophages, T cells, and myofibroblasts suggests that both the p38 and JNK MAPK pathways are important in chronic inflammation and fibrosis. Blockade of these pathways may therefore be potentially therapeutic in the treatment of acute and chronic renal inflammation.

High glucose stimulates angiotensinogen gene expression and cell hypertrophy via activation of the hexosamine biosynthesis pathway in rat kidney proximal tubular cells

The present study investigated whether activation of the hexosamine biosynthesis pathway might mediate at least in part the high glucose effect on angiotensinogen (ANG) gene expression and immortalized renal proximal tubular cell (IRPTC) hypertrophy. IRPTC were cultured in monolayer. ANG, renin, and beta-actin mRNA expression were determined by specific RT-PCR assays. Phosphorylation of p38 MAPK, activating transcription factor-2 (ATF-2), and cAMP-responsive element-binding protein (CREB) was determined by Western blot analysis. Cell hypertrophy was assessed by flow cytometry, intracellular p27kip1 protein levels, and [3H]leucine incorporation into proteins. Glucosamine stimulated ANG and renin mRNA expression and enhanced p38 MAPK, ATF-2, and CREB phosphorylation in normal glucose (5 mm) medium. Azaserine and 6-diazo-5-oxo-l-norleucine (inhibitors of glutamine: fructose-6-phosphate amino transferase enzyme) blocked the stimulatory effect of high glucose, but not that of glucosamine, on ANG gene expression in IRPTCs. SB 203580 (a specific p38 MAPK inhibitor) attenuated glucosamine action on ANG gene expression as well as p38 MAPK and ATF-2 phosphorylation, but not that of CREB. GF 109203X and calphostin C (inhibitors of protein kinase C) blocked the effect of glucosamine on ANG gene expression and CREB phosphorylation, but had no impact on p38 MAPK and ATF-2 phosphorylation. Finally, both glucosamine and high glucose induced IRPTC hypertrophy. The hypertrophic effect of glucosamine was blocked in the presence of GF 109203X, but not azaserine and SB 203580. In contrast, the hypertrophic effect of high glucose was blocked in the presence of azaserine and GF 109203X, but not SB203580. Our studies demonstrate that the stimulatory effect of high glucose on ANG gene expression and IRPTC hypertrophy may be mediated at least in part via activation of hexosamine biosynthesis pathway signaling.

Role of MAPK pathways in light chain-induced cytokine production in human proximal tubule cells

We previously demonstrated that light chain (LC) endocytosis by human proximal tubule cells (PTCs) leads to production of cytokines through activation of NF-kappaB. Here, we examined the role of MAPK pathways in these responses using four species of myeloma LCs (kappa(1), kappa(2), kappa(3), and lambda(1)) previously shown to induce cytokine production by PTCs. Among these, kappa(1)-LC, which yielded the strongest cytokine responses, was selected for detailed studies. Activation of MAPKs was probed by Western blot analysis for the active kinases, ERK 1/2, JNK 1/2, and p38 in kappa(1)-LC-exposed human PTCs. To evaluate the functional role of MAPKs in LC-induced cytokine responses, we tested the effects of U-0126, an ERK inhibitor; SP-600125, an inhibitor of JNK; SB-203580, a p38 inhibitor; and curcumin, a JNK-AP-1 inhibitor, all added to media before 4-h exposure to 1.5 mg/ml kappa(1)-LC. IL-6 and monocyte chemotactic protein-1 (MCP-1) were determined by ELISA. Both LC and human serum albumin (HSA) activated ERK, although the HSA effect was weaker. kappa(1)-LC stimulated all three MAPKs, although phosphorylation of ERK was more pronounced and sustained than others. Inhibitors of ERK, JNK, and p38 reduced LC-induced IL-6 and MCP-1 production. These findings suggest that activation of MAPKs plays a role in LC-induced cytokine responses in PTCs. Activation of MAPKs may be involved in cytokine responses induced by other proteins as well as LCs and may be pivotal in the pathophysiology of tubulointerstitial injury in proteinuric diseases.

Insulin inhibits dexamethasone effect on angiotensinogen gene expression and induction of hypertrophy in rat kidney proximal tubular cells in high glucose

The present studies investigated whether insulin inhibits the stimulatory effect of dexamethasone (DEX) on angiotensinogen (ANG) gene expression and induction of hypertrophy in rat immortalized renal proximal tubular cells (IRPTCs) in a high-glucose milieu. Rat IRPTCs were cultured in monolayer. ANG and ANG mRNA expression in IRPTCs were quantified by a specific RIA for rat ANG and by RT-PCR assay, respectively. A fusion gene containing the full length of the 5'-flanking region of the rat ANG gene linked to a chloramphenicol acetyl transferase reporter gene was introduced into IRPTCs. The level of fusion gene expression was determined by cellular chloramphenicol acetyl transferase enzymatic activity. Cellular hypertrophy was assessed by flow cytometry, cellular p27(Kip1) protein expression, and protein assay. Our results showed that high glucose (i.e. 25 mM) and DEX (10(-7) M) additively stimulated ANG gene expression and induced IRPTC hypertrophy. Insulin inhibited the effect of high glucose and DEX on these parameters. The inhibitory effect of insulin was reversed by PD 98059 (a MAPK inhibitor) but not by wortmannin (a phosphatidylinositol-3-kinase inhibitor). These results demonstrate that insulin is effective in blocking the stimulatory action of high glucose and DEX on ANG gene expression and induction of IRPTC hypertrophy, suggesting its important role in preventing local intrarenal renin-angiotensin system activation and renal proximal tubular cell hypertrophy induced by hyperglycemia and glucocorticoids in vivo.

High glucose stimulates angiotensinogen gene expression via reactive oxygen species generation in rat kidney proximal tubular cells

The present studies investigated whether the effect of high glucose levels on angiotensinogen (ANG) gene expression in kidney proximal tubular cells is mediated via reactive oxygen species (ROS) generation and p38 MAPK activation. Rat immortalized renal proximal tubular cells (IRPTCs) were cultured in monolayer. Cellular ROS generation and p38 MAPK phosphorylation were assessed by lucigenin assay and Western blot analysis, respectively. The levels of immunoreactive rat ANG secreted into the media and cellular ANG mRNA were determined by a specific RIA and RT-PCR, respectively. High glucose (25 mM) evoked ROS generation and p38 MAPK phosphorylation as well as stimulated immunoreactive rat ANG secretion and ANG mRNA expression in IRPTCs. These effects of high glucose were blocked by antioxidants (taurine and tiron), inhibitors of mitochondrial electron transport chain complex I (rotenone) and II (thenoyltrifluoroacetone), an inhibitor of glycolysis-derived pyruvate transport into mitochondria (alpha-cyano-4-hydroxycinnamic acid), an uncoupler of oxidative phosphorylation (carbonyl cyanide m-chlorophenylhydrazone), a manganese superoxide dismutase mimetic, catalase, and a specific inhibitor of p38 MAPK (SB 203580), but were not affected by an inhibitor of the malate-aspartate shuttle (aminooxyacetate acid). Hydrogen peroxide (>/=10(-5) M) also stimulated p38 MAPK phosphorylation, ANG secretion, and ANG mRNA gene expression, but its stimulatory effect was blocked by catalase and SB 203580. These studies demonstrate that the stimulatory action of high glucose on ANG gene expression in IRPTCs is mediated at least in part via ROS generation and subsequent p38 MAPK activation.