Glomerular renin angiotensin system in streptozotocin diabetic and Zucker diabetic fatty rats

The angiotensin II/type 1 angiotensin II receptor pathway is implicated in the dysfunction of albumin endocytosis in renal proximal tubule epithelial cells induced by high glucose levels

It is well-established that dysfunction of megalin-mediated albumin endocytosis by proximal tubule epithelial cells (PTECs) and the activation of the Renin-Angiotensin System (RAS) play significant roles in the development of Diabetic Kidney Disease (DKD). However, the precise correlation between these factors still requires further investigation. In this study, we aimed to elucidate the potential role of angiotensin II (Ang II), a known effector of RAS, as the mediator of albumin endocytosis dysfunction induced by high glucose (HG) in PTECs. To achieve this, we utilized LLC-PK1 and HK-2 cells, which are well-established in vitro models of PTECs. Using albumin-FITC or DQ-albumin as tracers, we observed that incubation of LLC-PK1 and HK-2 cells with HG (25 mM for 48 h) significantly reduced canonical receptor-mediated albumin endocytosis, primarily due to the decrease in megalin expression. HG increased the concentration of Ang II in the LLC-PK1 cell supernatant, a phenomenon associated with an increase in angiotensin-converting enzyme (ACE) expression and a decrease in prolyl carboxypeptidase (PRCP) expression. ACE type 2 (ACE2) expression remained unchanged. To investigate the potential impact of Ang II on HG effects, the cells were co-incubated with angiotensin receptor inhibitors. Only co-incubation with 10-7 M losartan (an antagonist for type 1 angiotensin receptor, AT1R) attenuated the inhibitory effect of HG on albumin endocytosis, as well as megalin expression. Our findings contribute to understanding the genesis of tubular albuminuria observed in the early stages of DKD, which involves the activation of the Ang II/AT1R axis by HG.

Aerobic training increases renal antioxidant defence and reduces angiotensin II levels, mitigating the high mortality in SHR-STZ model

OBJECTVE

The purpose of the research was to investigate the effects of aerobic training on renal function, oxidative stress, intrarenal renin-angiotensin system, and mortality of hypertensive and diabetic (SHR-STZ) rats.

MATERIALS AND METHODS

Blood pressure, creatinine, urea levels, urinary glucose, urine volume, and protein excretion were reduced in trained SHR-STZ rats.

RESULTS

Aerobic training not only attenuated oxidative stress but also elevated the activity of antioxidant enzymes in the kid'ney of SHR-STZ rats. Training increased intrarenal levels of angiotensin-converting enzymes (ACE and ACE2) as well as the neprilysin (NEP) activity, along with decreased intrarenal angiotensin II (Ang II) levels. Aerobic training significantly improved the survival of STZ-SHR rats.

CONCLUSION

The protective role of aerobic training was associated with improvements in the renal antioxidative capacity, reduced urinary protein excretion along with reduced intrarenal Ang II and increased NEP activity. These findings might reflect a better survival under the combined pathological conditions, hypertension, and diabetes.

ACE2 in chronic disease and COVID-19: gene regulation and post-translational modification

Angiotensin-converting enzyme 2 (ACE2), a counter regulator of the renin-angiotensin system, provides protection against several chronic diseases. Besides chronic diseases, ACE2 is the host receptor for SARS-CoV or SARS-CoV-2 virus, mediating the first step of virus infection. ACE2 levels are regulated by transcriptional, post-transcriptional, and post-translational regulation or modification. ACE2 transcription is enhanced by transcription factors including Ikaros, HNFs, GATA6, STAT3 or SIRT1, whereas ACE2 transcription is reduced by the transcription factor Brg1-FoxM1 complex or ERRα. ACE2 levels are also regulated by histone modification or miRNA-induced destabilization. The protein kinase AMPK, CK1α, or MAP4K3 phosphorylates ACE2 protein and induces ACE2 protein levels by decreasing its ubiquitination. The ubiquitination of ACE2 is induced by the E3 ubiquitin ligase MDM2 or UBR4 and decreased by the deubiquitinase UCHL1 or USP50. ACE2 protein levels are also increased by the E3 ligase PIAS4-mediated SUMOylation or the methyltransferase PRMT5-mediated ACE2 methylation, whereas ACE2 protein levels are decreased by AP2-mediated lysosomal degradation. ACE2 is downregulated in several human chronic diseases like diabetes, hypertension, or lung injury. In contrast, SARS-CoV-2 upregulates ACE2 levels, enhancing host cell susceptibility to virus infection. Moreover, soluble ACE2 protein and exosomal ACE2 protein facilitate SARS-CoV-2 infection into host cells. In this review, we summarize the gene regulation and post-translational modification of ACE2 in chronic disease and COVID-19. Understanding the regulation and modification of ACE2 may help to develop prevention or treatment strategies for ACE2-mediated diseases.

Kidney Angiotensin in Cardiovascular Disease: Formation and Drug Targeting

The concept of local formation of angiotensin II in the kidney has changed over the last 10-15 years. Local synthesis of angiotensinogen in the proximal tubule has been proposed, combined with prorenin synthesis in the collecting duct. Binding of prorenin via the so-called (pro)renin receptor has been introduced, as well as megalin-mediated uptake of filtered plasma-derived renin-angiotensin system (RAS) components. Moreover, angiotensin metabolites other than angiotensin II [notably angiotensin-(1-7)] exist, and angiotensins exert their effects via three different receptors, of which angiotensin II type 2 and Mas receptors are considered renoprotective, possibly in a sex-specific manner, whereas angiotensin II type 1 (AT1) receptors are believed to be deleterious. Additionally, internalized angiotensin II may stimulate intracellular receptors. Angiotensin-converting enzyme 2 (ACE2) not only generates angiotensin-(1-7) but also acts as coronavirus receptor. Multiple, if not all, cardiovascular diseases involve the kidney RAS, with renal AT1 receptors often being claimed to exert a crucial role. Urinary RAS component levels, depending on filtration, reabsorption, and local release, are believed to reflect renal RAS activity. Finally, both existing drugs (RAS inhibitors, cyclooxygenase inhibitors) and novel drugs (angiotensin receptor/neprilysin inhibitors, sodium-glucose cotransporter-2 inhibitors, soluble ACE2) affect renal angiotensin formation, thereby displaying cardiovascular efficacy. Particular in the case of the latter three, an important question is to what degree they induce renoprotection (e.g., in a renal RAS-dependent manner). This review provides a unifying view, explaining not only how kidney angiotensin formation occurs and how it is affected by drugs but also why drugs are renoprotective when altering the renal RAS. SIGNIFICANCE STATEMENT: Angiotensin formation in the kidney is widely accepted but little understood, and multiple, often contrasting concepts have been put forward over the last two decades. This paper offers a unifying view, simultaneously explaining how existing and novel drugs exert renoprotection by interfering with kidney angiotensin formation.

Resistance exercise shifts the balance of renin-angiotensin system toward ACE2/Ang 1-7 axis and reduces inflammation in the kidney of diabetic rats

AIMS

We aimed to determine whether resistance training (RT) regulates renal renin-angiotensin system (RAS) components and inflammatory mediators in diabetic rats.

MAIN METHODS

Male Wistar rats (3 months old) were randomly assigned into four groups: non-trained (NT), trained (T), non-trained + diabetes (NTD) and trained +diabetes (TD). Diabetes was induced by streptozotocin (50 mg/kg, Sigma Chemical Co., St. Louis, MO, USA), before RT protocol. Trained rats performed RT protocol on a 110-cm ladder (8 ladder climbs, once/day, 5 days/week, 8 weeks), carrying a load corresponding to 50-80% of maximum carrying capacity. Blood glucose, albuminuria and urinary volume were measured. Renal levels of angiotensin peptides (angiotensin I, II and 1-7), inflammatory markers, and also the activities of angiotensin-converting enzyme (ACE) and ACE2 were determined.

KEY FINDINGS

Blood glucose and urinary volume were elevated in diabetic animals, and RT decreased albuminuria, renal Ang I and Ang II levels in diabetic rats. RT shifted the balance of renal RAS toward ACE2/Ang 1-7 axis in TD group, and mitigated the high levels of interleukin (IL)-10, IL-1β and cytokine-induced neutrophil chemoattractant 1 (CINC) in the context of diabetes. Strong positive correlations were found between albuminuria and Ang II, IL-10 and IL-1β. On the other hand, intrarenal Ang 1-7 levels were negatively correlated with IL-10 and IL-1β levels.

SIGNIFICANCE

RT improved kidney function by modulating intrarenal RAS toward ACE2/Ang 1-7 axis and inflammatory cytokines. RT represents a reasonable strategy to improve the renal complications induced by diabetes, counteracting nephropathy-associated maladaptive responses.

d-Ribose as a Contributor to Glycated Haemoglobin

Glycated haemoglobin (HbA1c) is the most important marker of hyperglycaemia in diabetes mellitus. We show that d-ribose reacts with haemoglobin, thus yielding HbA1c. Using mass spectrometry, we detected glycation of haemoglobin with d-ribose produces 10 carboxylmethyllysines (CMLs). The first-order rate constant of fructosamine formation for d-ribose was approximately 60 times higher than that for d-glucose at the initial stage. Zucker Diabetic Fatty (ZDF) rat, a common model for type 2 diabetes mellitus (T2DM), had high levels of d-ribose and HbA1c, accompanied by a decrease of transketolase (TK) in the liver. The administration of benfotiamine, an activator of TK, significantly decreased d-ribose followed by a decline in HbA1c. In clinical investigation, T2DM patients with high HbA1c had a high level of urine d-ribose, though the level of their urine d-glucose was low. That is, d-ribose contributes to HbA1c, which prompts future studies to further explore whether d-ribose plays a role in the pathophysiological mechanism of T2DM.

Eprosartan mesylate loaded bilosomes as potential nano-carriers against diabetic nephropathy in streptozotocin-induced diabetic rats

The objective of the present study was to formulate eprosartan mesylate loaded nano-bilosomes and investigates its potential for controlling streptozotocin induced diabetes nephropathy in Wistar rats. The eprosartan mesylate loaded nano-bilosomes comprising of various ratios of soybean phosphatidylcholine/sodium deoxycholate were prepared by thin film hydration technique. The prepared formulations were evaluated for vesicles size, polydispersity index, zeta potential and entrapment efficiency. Further the optimized formulation was characterized for vesicles morphology, and its efficacy for the management of diabetic nephropathy in Wistar rats. The optimized eprosartan mesylate loaded nano-bilosomes exhibited vesicles size, polydispersity index, zeta potential and entrapment efficiency of 63.88±3.46nm, 0.172±0.026, -30.40±2.75mV and 61.19±0.88% respectively. In vivo activity demonstrated that the prepared eprosartan mesylate loaded nano-bilosomes formulation demonstrated a nephro-protecting outcome as shown by the substantial decrease in serum creatinine, urea, lactate dehydrogenase, total albumin, and malondialdehyde. Additionally, an oral administration of eprosartan mesylate loaded nano-bilosomes decreases the raised expressions of Angiotensin II type 1 receptor, inducible nitric oxide synthase, and transforming growth factor-β1 in Wistar rats. Further, histopathological examination established the nephro-protective effect of prepared formulation. In conclusion, the research work in the paper suggests that the prepared eprosartan mesylate loaded nano-bilosomes could serve as a practical oral formulation for diabetic nephropathy in future therapy and may offer potential benefits in cases with hypertension and renal disease.

Diminazene aceturate prevents nephropathy by increasing glomerular ACE2 and AT2 receptor expression in a rat model of type1 diabetes

BACKGROUND AND PURPOSE

One of the protective actions of angiotensin converting enzyme-2 (ACE2) is the inactivation of angiotensin II. Expression and activity of ACE2 was reduced in glomeruli of diabetic patients and in animal models of diabetes. Recently the potential role of recombinant ACE2 administration in preventing diabetic nephropathy (DN) has been shown. Here we have tested the effects of the ACE2 activator, diminazene aceturate (DIZE), in a model of DN.

EXPERIMENTAL APPROACH

Male Wistar rats were rendered diabetic using a single dose of streptozotocin (55 mg·kg^-1 , i.p.). After 4 weeks, diabetic animals were divided into experimental groups and treated with DIZE, at a low dose (5 mg·kg^-1 ·day^-1 ), a high dose (15 mg·kg^-1 ·day^-1 ) and the high dose with of the AT₂ receptor antagonist PD123319 (10 mg·kg^-1 ·day^-1 ). At the end of the treatment , kidneys from all the groups were collected and processed separately for glomerular isolation, protein isolation, mRNA extraction and for immunohistochemical studies.

KEY RESULTS

Treatment with DIZE restored ACE2 expression in glomeruli and increased expression of AT₂ receptors in whole kidney and isolated glomeruli of diabetic animals. DIZE administration reduced angiotensin II levels and increased angiotensin-(1-7) levels in diabetic kidney. However, PD123319 treatment reversed all these actions of DIZE.

CONCLUSIONS AND IMPLICATIONS

DIZE treatment reduced diabetes-induced renal damage as shown by reduction of fibrosis and apoptosis. These protective actions of DIZE were blocked by the AT₂ receptor antagonist. Taken together, these results suggest that DIZE protected against DN through the ACE2/angiotensin-(1-7)/ AT₂ receptor axis.

Urine RAS components in mice and people with type 1 diabetes and chronic kidney disease

The pathways implicated in diabetic kidney disease (DKD) are largely derived from animal models. To examine if alterations in renin-angiotensin system (RAS) in humans are concordant with those in rodent models, we measured concentration of angiotensinogen (AOG), cathepsin D (CTSD), angiotensin-converting enzyme (ACE), and ACE2 and enzymatic activities of ACE, ACE2, and aminopeptidase-A in FVB mice 13-20 wk after treatment with streptozotocin (n = 9) or vehicle (n = 15) and people with long-standing type 1 diabetes, with (n = 37) or without (n = 81) DKD. In streptozotocin-treated mice, urine AOG and CTSD were 10.4- and 3.0-fold higher than in controls, respectively (P < 0.001). Enzymatic activities of ACE, ACE2, and APA were 6.2-, 3.2-, and 18.8-fold higher, respectively, in diabetic animals (P < 0.001). Angiotensin II was 2.4-fold higher in diabetic animals (P = 0.017). Compared with people without DKD, those with DKD had higher urine AOG (170 vs. 15 μg/g) and CTSD (147 vs. 31 μg/g). In people with DKD, urine ACE concentration was 1.8-fold higher (1.4 vs. 0.8 μg/g in those without DKD), while its enzymatic activity was 0.6-fold lower (1.0 vs. 1.6 × 10⁹ RFU/g in those without DKD). Lower ACE activity, but not ACE protein concentration, was associated with ACE inhibitor (ACEI) treatment. After adjustment for clinical covariates, AOG, CTSD, ACE concentration, and ACE activity remained associated with DKD. In conclusion, in mice with streptozotocin-induced diabetes and in humans with DKD, urine concentrations and enzymatic activities of several RAS components are concordantly increased, consistent with enhanced RAS activity and greater angiotensin II formation. ACEI use was associated with a specific reduction in urine ACE activity, not ACE protein concentration, suggesting that it may be a marker of exposure to this widely-used therapy.

Overexpression of heterogeneous nuclear ribonucleoprotein F stimulates renal Ace-2 gene expression and prevents TGF-β1-induced kidney injury in a mouse model of diabetes

AIMS/HYPOTHESIS

We investigated whether heterogeneous nuclear ribonucleoprotein F (hnRNP F) stimulates renal ACE-2 expression and prevents TGF-β1 signalling, TGF-β1 inhibition of Ace-2 gene expression and induction of tubulo-fibrosis in an Akita mouse model of type 1 diabetes.

METHODS

Adult male Akita transgenic (Tg) mice overexpressing specifically hnRNP F in their renal proximal tubular cells (RPTCs) were studied. Non-Akita littermates and Akita mice served as controls. Immortalised rat RPTCs stably transfected with plasmid containing either rat Hnrnpf cDNA or rat Ace-2 gene promoter were also studied.

RESULTS

Overexpression of hnRNP F attenuated systemic hypertension, glomerular filtration rate, albumin/creatinine ratio, urinary angiotensinogen (AGT) and angiotensin (Ang) II levels, renal fibrosis and profibrotic gene (Agt, Tgf-β1, TGF-β receptor II [Tgf-βrII]) expression, stimulated anti-profibrotic gene (Ace-2 and Ang 1-7 receptor [MasR]) expression, and normalised urinary Ang 1-7 level in Akita Hnrnpf-Tg mice as compared with Akita mice. In vitro, hnRNP F overexpression stimulated Ace-2 gene promoter activity, mRNA and protein expression, and attenuated Agt, Tgf-β1 and Tgf-βrII gene expression. Furthermore, hnRNP F overexpression prevented TGF-β1 signalling and TGF-β1 inhibition of Ace-2 gene expression.

CONCLUSIONS/INTERPRETATION

These data demonstrate that hnRNP F stimulates Ace-2 gene transcription, prevents TGF-β1 inhibition of Ace-2 gene transcription and induction of kidney injury in diabetes. HnRNP F may be a potential target for treating hypertension and renal fibrosis in diabetes.

Role of upstream stimulatory factor 2 in diabetic nephropathy

Diabetic nephropathy (DN) is the most common cause of end-stage renal disease (ESRD). About 20%-30% of people with type 1 and type 2 diabetes develop DN. DN is characterized by both glomerulosclerosis with thickening of the glomerular basement membrane and mesangial matrix expansion, and tubulointerstitial fibrosis. Hyperglycemia and the activation of the intra-renal renin-angiotensin system (RAS) in diabetes have been suggested to play a critical role in the pathogenesis of DN. However, the mechanisms are not well known. Studies from our laboratory demonstrated that the transcription factor-upstream stimulatory factor 2 (USF2) is an important regulator of DN. Moreover, the renin gene is a downstream target of USF2. Importantly, USF2 transgenic (Tg) mice demonstrate a specific increase in renal renin expression and angiotensin II (AngII) levels in kidney and exhibit increased urinary albumin excretion and extracellular matrix deposition in glomeruli, supporting a role for USF2 in the development of diabetic nephropathy. In this review, we summarize our findings of the mechanisms by which diabetes regulates USF2 in kidney cells and its role in regulation of renal renin-angiotensin system and the development of diabetic nephropathy.

Functional and molecular evidence for expression of the renin angiotensin system and ADAM17-mediated ACE2 shedding in COS7 cells

The renin angiotensin system (RAS) plays a vital role in the regulation of the cardiovascular and renal functions. COS7 is a robust and easily transfectable cell line derived from the kidney of the African green monkey, Cercopithecus aethiops. The aims of this study were to 1) demonstrate the presence of an endogenous and functional RAS in COS7, and 2) investigate the role of a disintegrin and metalloproteinase-17 (ADAM17) in the ectodomain shedding of angiotensin converting enzyme-2 (ACE2). Reverse transcription coupled to gene-specific polymerase chain reaction demonstrated expression of ACE, ACE2, angiotensin II type 1 receptor (AT1R), and renin at the transcript levels in total RNA cell extracts. Western blot and immunohistochemistry identified ACE (60 kDa), ACE2 (75 kDa), AT1R (43 kDa), renin (41 kDa), and ADAM17 (130 kDa) in COS7. At the functional level, a sensitive and selective mass spectrometric approach detected endogenous renin, ACE, and ACE2 activities. ANG-(1-7) formation (m/z 899) from the natural substrate ANG II (m/z 1,046) was detected in lysates and media. COS7 cells stably expressing shRNA constructs directed against endogenous ADAM17 showed reduced ACE2 shedding into the media. This is the first study demonstrating endogenous expression of the RAS and ADAM17 in the widely used COS7 cell line and its utility to study ectodomain shedding of ACE2 mediated by ADAM17 in vitro. The transfectable nature of this cell line makes it an attractive cell model for studying the molecular, functional, and pharmacological properties of the renal RAS.

Experimental protection of diabetic mice against Lethal P. aeruginosa infection by bacteriophage

The emergence of antibiotic-resistant bacterial strains has become a global crisis and is vulnerable for the exploration of alternative antibacterial therapies. The present study emphasizes the use of bacteriophage for the treatment of multidrug resistant P. aeruginosa. P. aeruginosa was used to induce septicemia in streptozotocin (STZ) induced diabetic and nondiabetic mice by intraperitoneal (i.p.) injection of 3 × 10⁸ CFU, resulting in a fatal bacteremia within 48 hrs. A single i.p. injection of 3 × 10⁹ PFU phage GNCP showed efficient protection in both diabetic (90%) and nondiabetic (100%) bacteremic mice. It was further noted that the protection rate was reduced in diabetic mice when phage GNCP was administered after 4 h and 6 h of lethal bacterial challenge. In contrast, nondiabetic bacteremic mice were rescued even when treatment was delayed up to 20 h after lethal bacterial challenge. Evaluation of results confirmed that a single intraperitoneal injection of the phage dose (3 × 10⁹ PFU/mL) was more effective than the multiple doses of imipenem. These results uphold the efficacy of phage therapy against pernicious P. aeruginosa infections, especially in cases of immunocompromised host.

Insulin treatment attenuates renal ADAM17 and ACE2 shedding in diabetic Akita mice

Angiotensin-converting enzyme 2 (ACE2) is located in several tissues and is highly expressed in renal proximal tubules, where it degrades the vasoconstrictor angiotensin II (ANG II) to ANG-(1-7). Accumulating evidence supports protective roles of ACE2 in several disease states, including diabetic nephropathy. A disintegrin and metalloprotease (ADAM) 17 is involved in the shedding of several transmembrane proteins, including ACE2. Our previous studies showed increased renal ACE2, ADAM17 expression, and urinary ACE2 in type 2 diabetic mice (Chodavarapu H, Grobe N, Somineni HK, Salem ES, Madhu M, Elased KM. PLoS One 8: e62833, 2013). The aim of the present study was to determine the effect of insulin on ACE2 shedding and ADAM17 in type 1 diabetic Akita mice. Results demonstrate increased renal ACE2 and ADAM17 expression and increased urinary ACE2 fragments (≈70 kDa) and albumin excretion in diabetic Akita mice. Immunostaining revealed colocalization of ACE2 with ADAM17 in renal tubules. Renal proximal tubular cells treated with ADAM17 inhibitor showed reduced ACE2 shedding into the media, confirming ADAM17-mediated shedding of ACE2. Treatment of Akita mice with insulin implants for 20 wk normalized hyperglycemia and decreased urinary ACE2 and albumin excretion. Insulin also normalized renal ACE2 and ADAM17 but had no effect on tissue inhibitor of metalloproteinase 3 (TIMP3) protein expression. There was a positive linear correlation between urinary ACE2 and albuminuria, blood glucose, plasma creatinine, glucagon, and triglycerides. This is the first report showing an association between hyperglycemia, cardiovascular risk factors, and increased shedding of urinary ACE2 in diabetic Akita mice. Urinary ACE2 could be used as a biomarker for diabetic nephropathy and as an index of intrarenal ACE2 status.

Insulin treatment attenuates renal ADAM17 and ACE2 shedding in diabetic Akita mice

Angiotensin-converting enzyme 2 (ACE2) is located in several tissues and is highly expressed in renal proximal tubules, where it degrades the vasoconstrictor angiotensin II (ANG II) to ANG-(1-7). Accumulating evidence supports protective roles of ACE2 in several disease states, including diabetic nephropathy. A disintegrin and metalloprotease (ADAM) 17 is involved in the shedding of several transmembrane proteins, including ACE2. Our previous studies showed increased renal ACE2, ADAM17 expression, and urinary ACE2 in type 2 diabetic mice (Chodavarapu H, Grobe N, Somineni HK, Salem ES, Madhu M, Elased KM. PLoS One 8: e62833, 2013). The aim of the present study was to determine the effect of insulin on ACE2 shedding and ADAM17 in type 1 diabetic Akita mice. Results demonstrate increased renal ACE2 and ADAM17 expression and increased urinary ACE2 fragments (≈70 kDa) and albumin excretion in diabetic Akita mice. Immunostaining revealed colocalization of ACE2 with ADAM17 in renal tubules. Renal proximal tubular cells treated with ADAM17 inhibitor showed reduced ACE2 shedding into the media, confirming ADAM17-mediated shedding of ACE2. Treatment of Akita mice with insulin implants for 20 wk normalized hyperglycemia and decreased urinary ACE2 and albumin excretion. Insulin also normalized renal ACE2 and ADAM17 but had no effect on tissue inhibitor of metalloproteinase 3 (TIMP3) protein expression. There was a positive linear correlation between urinary ACE2 and albuminuria, blood glucose, plasma creatinine, glucagon, and triglycerides. This is the first report showing an association between hyperglycemia, cardiovascular risk factors, and increased shedding of urinary ACE2 in diabetic Akita mice. Urinary ACE2 could be used as a biomarker for diabetic nephropathy and as an index of intrarenal ACE2 status.

Cardinal role of the intrarenal renin-angiotensin system in the pathogenesis of diabetic nephropathy

Diabetes mellitus is one of the most prevalent diseases and is associated with increased incidence of structural and functional derangements in the kidneys, eventually leading to end-stage renal disease in a significant fraction of afflicted individuals. The renoprotective effects of renin-angiotensin system (RAS) blockade have been established; however, the mechanistic pathways have not been fully elucidated. In this review article, the cardinal role of an activated RAS in the pathogenesis of diabetic nephropathy (DN) is discussed with a focus on 4 themes: (1) introduction to RAS cascade, (2) intrarenal RAS in diabetes, (3) clinical outcomes of RAS blockade in DN, and (4) potential of urinary angiotensinogen as an early biomarker of intrarenal RAS status in DN. This review article provides a mechanistic rational supporting the hypothesis that an activated intrarenal RAS contributes to the pathogenesis of DN and that urinary angiotensinogen levels provide an index of intrarenal RAS activity.

ACE2 alterations in kidney disease

Angiotensin-converting enzyme 2 (ACE2) is a monocarboxypeptidase that degrades angiotensin (Ang) II to Ang-(1-7). ACE2 is highly expressed within the kidneys, it is largely localized in tubular epithelial cells and less prominently in glomerular epithelial cells and in the renal vasculature. ACE2 activity has been shown to be altered in diabetic kidney disease, hypertensive renal disease and in different models of kidney injury. There is often a dissociation between tubular and glomerular ACE2 expression, particularly in diabetic kidney disease where ACE2 expression is increased at the tubular level but decreased at the glomerular level. In this review, we will discuss alterations in circulating and renal ACE2 recently described in different renal pathologies and disease models as well as their possible significance.

Cardinal Role of the Intrarenal Renin-Angiotensin System in the Pathogenesis of Diabetic Nephropathy

Diabetes mellitus is one of the most prevalent diseases and is associated with increased incidence of structural and functional derangements in the kidneys, eventually leading to end-stage renal disease in a significant fraction of afflicted individuals. The renoprotective effects of renin-angiotensin system (RAS) blockade have been established; however, the mechanistic pathways have not been fully elucidated. In this review article, the cardinal role of an activated RAS in the pathogenesis of diabetic nephropathy (DN) is discussed with a focus on 4 themes: (1) introduction to RAS cascade, (2) intrarenal RAS in diabetes, (3) clinical outcomes of RAS blockade in DN, and (4) potential of urinary angiotensinogen as an early biomarker of intrarenal RAS status in DN. This review article provides a mechanistic rational supporting the hypothesis that an activated intrarenal RAS contributes to the pathogenesis of DN and that urinary angiotensinogen levels provide an index of intrarenal RAS activity.

Elevated transcriptional co-activator p102 mediates angiotensin II type 1 receptor up-regulation and extracellular matrix overproduction in the high glucose-treated rat glomerular mesangial cells and isolated glomeruli

P102 is a multifunctional transcriptional co-activator. This experiment is designed to investigate the role of p102 in the activation of renin-angiotensin system (RAS) and sequentially extracellular matrix (ECM) over synthesis in diabetic nephropathy. Rat glomerular mesangial cells (MCs) or isolated glomeruli were cultured in normal glucose (NG, 5.5mM) or high glucose (HG, 25 mM) DMEM. The generation of reactive oxygen species was measured by 2',7'-dichlorodihydrofluorescein diacetate (DCFH-DA) fluorescent probe assay. The protein levels were analyzed by Western blot and the mRNA levels were evaluated by real-time PCR. HG treatment induced an increase in reactive oxygen species production. Culturing the cells in HG for 48 h, p102 mRNA and protein, angiotensin II type 1 receptor (AT1 receptor) mRNA, transforming growth factor-β1 (TGF-β1) and fibronectin proteins were significantly increased. NADPH oxidase inhibitor DPI blocked the HG-induced p102, TGF-β1 and fibronetcin elevations. Knockdown on p102 expression by siRNA depressed the HG-induced AT1 receptor up-regulation as well as the increases in TGF-β1 and fibronectin. In contrast, AT1 receptor antagonist candesartan did not influence p102 levels under either NG or HG condition, but blocked the HG-induced TGF-β1 and fibronectin increases. The results from isolated glomeruli were consistent with that of MCs, which showed that HG exposure stimulated the expression of p102. These results suggest that the overproduction of reactive oxygen species at the early stage of HG incubation stimulates p102 synthesis, which in turn up-regulates AT1 receptor expression. The activation of RAS stimulates TGF-β1 and fibronectin production, which further results in ECM accumulation.

Association of all-trans retinoic acid treatment with the renin-angiotensin aldosterone system expression in glomerulosclerosis rats

BACKGROUND AND OBJECTIVE

All-trans retinoic acid (ATRA), a promising therapeutic agent, has been confirmed in animal experiments as playing a protective role against renal diseases. The renin-angiotensin aldosterone system (RAAS) plays a key role in the pathogenesis of renal diseases, and RAAS inhibitors can prevent the progression of kidney diseases. In our previous study, we found that ATRA could play a protective role against glomerulosclerosis (GS) lesions in rats, and its effect was similar to RAAS inhibitors. However, whether ATRA treatment was associated with RAAS expression was not clear.

METHODS

Six-week-old male Wistar rats were divided into three groups: sham operation group (SHO), glomerulosclerosis model group without treatment (GS) and GS model group treated with ATRA (GA). At the end of 13 weeks, the relevant samples were collected and analyzed.

RESULTS

The mRNA and protein expression of angiotensin-converting enzyme 1 (ACE1) in the GS group was notably higher when compared with the SHO group. However, mRNA and protein expression of ACE1 in the ATRA treatment group was markedly down-regulated when compared with the GS group. Angiotensin-converting enzyme 2 (ACE2) expression (mRNA or protein) in the GS group was reduced compared with that in the SHO group, and ATRA markedly increased the mRNA and protein expression of ACE2 compared with the GS group. The levels of protein expression of angiotensin I and angiotensin II were significantly up-regulated in the GS group compared with those in the SHO group, and ATRA reduced their expression in the GA group when compared with the GS group.

CONCLUSION

ATRA is associated with RAAS expression in GS rats, but its detailed mechanism needs to be elucidated by further research.

Augmented intrarenal and urinary angiotensinogen in hypertension and chronic kidney disease

Activated intrarenal renin-angiotensin system plays a cardinal role in the pathogenesis of hypertension and chronic kidney disease. Angiotensinogen is the only known substrate for renin, which is the rate-limiting enzyme of the renin-angiotensin system. Because the levels of angiotensinogen are close to the Michaelis-Menten constant values for renin, angiotensinogen levels as well as renin levels can control the renin-angiotensin system activity, and thus, upregulation of angiotensinogen leads to an increase in the angiotensin II levels and ultimately increases blood pressure. Recent studies using experimental animal models have documented the involvement of angiotensinogen in the intrarenal renin-angiotensin system activation and development of hypertension. Enhanced intrarenal angiotensinogen mRNA and/or protein levels were observed in experimental models of hypertension and chronic kidney disease, supporting the important roles of angiotensinogen in the development and the progression of hypertension and chronic kidney disease. Urinary excretion rates of angiotensinogen provide a specific index of the intrarenal renin-angiotensin system status in angiotensin II-infused rats. Also, a direct quantitative method has been developed recently to measure urinary angiotensinogen using human angiotensinogen enzyme-linked immunosorbent assay. These data prompted us to measure urinary angiotensinogen in patients with hypertension and chronic kidney disease, and investigate correlations with clinical parameters. This short article will focus on the role of the augmented intrarenal angiotensinogen in the pathophysiology of hypertension and chronic kidney disease. In addition, the potential of urinary angiotensinogen as a novel biomarker of the intrarenal renin-angiotensin system status in hypertension and chronic kidney disease will be also discussed.

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.

Angiotensin-(1–7) attenuates diabetic nephropathy in Zucker diabetic fatty rats

Angiotensin (ANG)-(1–7) is known to attenuate diabetic nephropathy; however, its role in the modulation of renal inflammation and oxidative stress in type 2 diabetes is poorly understood. Thus in the present study we evaluated the renal effects of a chronic ANG-(1–7) treatment in Zucker diabetic fatty rats (ZDF), an animal model of type 2 diabetes and nephropathy. Sixteen-week-old male ZDF and their respective controls [lean Zucker rats (LZR)] were used for this study. The protocol involved three groups: 1) LZR + saline, 2) ZDF + saline, and 3) ZDF + ANG-(1–7). For 2 wk, animals were implanted with subcutaneous osmotic pumps that delivered either saline or ANG-(1–7) (100 ng·kg−1·min−1) ( n = 4). Renal fibrosis and tissue parameters of oxidative stress were determined. Also, renal levels of interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), ED-1, hypoxia-inducible factor-1α (HIF-1α), and neutrophil gelatinase-associated lipocalin (NGAL) were determined by immunohistochemistry and immunoblotting. ANG-(1–7) induced a reduction in triglyceridemia, proteinuria, and systolic blood pressure (SBP) together with a restoration of creatinine clearance in ZDF. Additionally, ANG-(1–7) reduced renal fibrosis, decreased thiobarbituric acid-reactive substances, and restored the activity of both renal superoxide dismutase and catalase in ZDF. This attenuation of renal oxidative stress proceeded with decreased renal immunostaining of IL-6, TNF-α, ED-1, HIF-1α, and NGAL to values similar to those displayed by LZR. Angiotensin-converting enzyme type 2 (ACE2) and ANG II levels remained unchanged after treatment with ANG-(1–7). Chronic ANG-(1–7) treatment exerts a renoprotective effect in ZDF associated with a reduction of SBP, oxidative stress, and inflammatory markers. Thus ANG-(1–7) emerges as a novel target for treatment of diabetic nephropathy.

Increased urinary angiotensin-converting enzyme 2 in renal transplant patients with diabetes

Angiotensin-converting enzyme 2 (ACE2) is expressed in the kidney and may be a renoprotective enzyme, since it converts angiotensin (Ang) II to Ang-(1-7). ACE2 has been detected in urine from patients with chronic kidney disease. We measured urinary ACE2 activity and protein levels in renal transplant patients (age 54 yrs, 65% male, 38% diabetes, n = 100) and healthy controls (age 45 yrs, 26% male, n = 50), and determined factors associated with elevated urinary ACE2 in the patients. Urine from transplant subjects was also assayed for ACE mRNA and protein. No subjects were taking inhibitors of the renin-angiotensin system. Urinary ACE2 levels were significantly higher in transplant patients compared to controls (p = 0.003 for ACE2 activity, and p≤0.001 for ACE2 protein by ELISA or western analysis). Transplant patients with diabetes mellitus had significantly increased urinary ACE2 activity and protein levels compared to non-diabetics (p<0.001), while ACE2 mRNA levels did not differ. Urinary ACE activity and protein were significantly increased in diabetic transplant subjects, while ACE mRNA levels did not differ from non-diabetic subjects. After adjusting for confounding variables, diabetes was significantly associated with urinary ACE2 activity (p = 0.003) and protein levels (p<0.001), while female gender was associated with urinary mRNA levels for both ACE2 and ACE. These data indicate that urinary ACE2 is increased in renal transplant recipients with diabetes, possibly due to increased shedding from tubular cells. Urinary ACE2 could be a marker of renal renin-angiotensin system activation in these patients.

Differential regulation of circulating and renal ACE2 and ACE in hypertensive mRen2.Lewis rats with early-onset diabetes

We examined the impact of early diabetes on the circulating and kidney renin-angiotensin system (RAS) in male and female mRen2.Lewis (mRen2) hypertensive rats. Diabetes (DB) was induced by streptozotocin (STZ; 65 mg/kg) at 11 wk of age for 4 wk without insulin replacement. Systolic blood pressures were not increased in DB males or females compared with controls (CON). Circulating angiotensin-converting enzyme 2 (ACE2) increased ninefold (P < 0.05) in DB females and threefold (P < 0.05) in DB males, but circulating ACE and ANG II were higher in the DB groups. Serum C-reactive protein was elevated in DB females but not DB males, and the vascular responses to acetylcholine and estradiol were attenuated in the DB females. Proteinuria, albuminuria, and angiotensinogen excretion increased to a similar extent in both DB females and males. Glomerular VEGF expression also increased to a similar extent in both DB groups. Renal inflammation (CD68(+)cells) increased only in DB females although males exhibited greater inflammation that was not different with DB. Cortical ACE2 did not change in DB females but was reduced (30%) in DB males. Renal neprilysin activity (>75%, P < 0.05) was markedly reduced in the DB females to that in the DB and CON males. ACE activity was significantly lower in both female (75%, P < 0.05) and male (50%; P < 0.05) DB groups, while cortical ANG II and Ang-(1-7) levels were unchanged. In conclusion, female mRen2 rats are not protected from vascular damage, renal inflammation, and kidney injury in early STZ-induced diabetes despite a marked increase in circulating ACE2 and significantly reduced ACE within the kidney.

Angiotensin-converting enzyme 2: enhancing the degradation of angiotensin II as a potential therapy for diabetic nephropathy

Angiotensin-converting enzyme 2 (ACE2) is a monocarboxypeptidase that degrades angiotensin II with high efficiency leading to the formation of angiotensin-(1-7). ACE2 within the kidneys is largely localized in tubular epithelial cells and in glomerular epithelial cells. Decreased glomerular expression of this enzyme coupled with increased expression of ACE has been described in diabetic kidney disease, both in mice and humans with type 2 diabetes. Moreover, both ACE2 genetic ablation and pharmacological ACE2 inhibition have been shown to increase albuminuria and promote glomerular injury. Studies using recombinant ACE2 have shown the ability of ACE2 to rapidly metabolize Ang II in vivo and form the basis for future studies to examine the potential of ACE2 amplification in the therapy of diabetic kidney disease and cardiovascular disease.

Angiotensin II type I receptor blockade suppresses glomerular renin-angiotensin system activation, oxidative stress, and progressive glomerular injury in rat anti-glomerular basement membrane glomerulonephritis

Excessive renin-angiotensin system (RAS) activation within the kidney induces not only renal oxidative stress but also renal scarring and dysfunction. This study examined the effects of an angiotensin II (Ang II) type I receptor (AT1R) blocker (ARB) on the progression of renal injury in rat anti-glomerular basement membrane glomerulonephritis (GN), with a particular focus on the participation of glomerular RAS activation in glomerular structural alterations, inflammation, and oxidative stress. Nephritic rats were divided into 2 groups and treated with vehicle or ARB until day 28. Treatment with ARB improved proteinuria significantly in nephritic rats. Vehicle-treated nephritic rats developed crescentic GN accompanied by marked macrophage infiltration and the enhanced expression of glomerular α-smooth muscle actin (α-SMA), angiotensinogen (AGT), Ang II, AT1R, and NADPH oxidase (Nox2) on days 7 and 28 of GN. ARB improved pathologic alterations such as crescent formation and glomerulosclerosis, and it had a significant inhibitory effect on the levels of these parameters on day 28 of GN. Enhanced superoxide production in nephritic glomeruli was decreased also by ARB. Moreover, Ang II and transforming growth factor beta (TGF-β) in the supernatant of cultured glomeruli was increased significantly in vehicle-treated nephritic rats whereas ARB inhibited the production of these compounds significantly on day 28. These results indicate that increased glomerular RAS activity and the resulting Ang II play important roles in progressive glomerular injury-the induction of oxidative stress and TGF-β expression, and they suggest that AT1R blockade attenuates proteinuria and progressive glomerular remodeling via the suppression of glomerular RAS activation in GN.

Urinary angiotensinogen as a biomarker of nephropathy in childhood

While most circulating angiotensinogen (AGT) is synthesized in the liver, the kidneys also produce AGT. Recently, we reported that urinary AGT is mainly originated from AGT. Using newly developed human AGT ELISA, we measured urinary AGT levels in chronic glomerulonephritis (GN) patients and patients with type 1 diabetes in childhood. Urinary AGT level was positively correlated with diastolic blood pressure, urinary albumin, urinary protein levels, and urinary occult blood in chronic GN patients. Furthermore, urinary AGT level was significantly increased in chronic GN patients not treated with renin-angiotensin system (RAS) blockers compared with control subjects. Importantly, patients treated with RAS blockers had a marked attenuation of this increase. Also, urinary AGT level was significantly higher in patients with diabetic nephropathy in the premicroalbuminuric phase than in control subjects. These results suggest that urinary AGT reflects intrarenal RAS status in chronic GN and may be an early marker of diabetic nephropathy.

Role of the USF1 transcription factor in diabetic kidney disease

The predominant transcription factors regulating key genes in diabetic kidney disease have not been established. The transcription factor upstream stimulatory factor 1 (USF1) is an important regulator of glucose-mediated transforming growth factor (TGF)-β1 expression in mesangial cells; however, its role in the development of diabetic kidney disease has not been evaluated. In the present study, wild-type (WT; USF1 +/+), heterozygous (USF1 +/-), and homozygous (USF1 -/-) knockout mice were intercrossed with Akita mice (Ins2/Akita) to induce type 1 diabetes. Mice were studied up to 36 wk of age. The degree of hyperglycemia and kidney hypertrophy were similar in all groups of diabetic mice; however, the USF1 -/- diabetic mice had significantly less albuminuria and mesangial matrix expansion than the WT diabetic mice. TGF-β1 and renin gene expression and protein were substantially increased in the WT diabetic mice but not in USF1 -/- diabetic mice. The underlying pathway by which USF1 is regulated by high glucose was investigated in mesangial cell culture. High glucose inhibited AMP-activated protein kinase (AMPK) activity and increased USF1 nuclear translocation. Activation of AMPK with AICAR stimulated AMPK activity and reduced nuclear accumulation of USF1. We thus conclude that USF1 is a critical transcription factor regulating diabetic kidney disease and plays a critical role in albuminuria, mesangial matrix accumulation, and TGF-β1 and renin stimulation in diabetic kidney disease. AMPK activity may play a key role in high glucose-induced regulation of USF1.

Beneficial effects of angiotensin (1-7) in diabetic rats with cardiomyopathy

OBJECTIVE

This study was designed to investigate the effect of angiotensin (1-7), a Mas receptor agonist, and A-779, a Mas receptor antagonist, in rats with diabetic cardiomyopathy (DC).

METHODS

Rats treated with a single injection of streptozotocin (50 mg/kg, intraperitoneal), developed DC after 8 weeks. The extent of DC was assessed by measuring the left ventricular weight/body weight (LVW/BW) ratio, absolute LVW, left ventricular developed pressure (LVDP), maximum change in left ventricular pressure over time (dp/dtmax), minimum change in left ventricular pressure over time (dp/dtmin), left ventricular (LV) protein content, LV collagen content, lipid profile, and serum nitrite/nitrate concentration. Test drug treatment was given from week 4 to week 8.

RESULTS

Angiotensin (1-7) treatment attenuated DC by significantly increasing LVDP, dp/dtmax, dp/dtmin, serum nitrite/nitrate concentration and significantly decreasing the LVW/BW ratio and LV collagen content. For the first time, this study has documented that endogenous angiotensin (1-7) regulates lipid profile in rats, and that treatment with angiotensin (1-7) significantly attenuates diabetes-induced changes in lipid profile. However, LV protein content and absolute LVW remain unaffected after treatment.

CONCLUSION

Angiotensin (1-7) significantly attenuates DC in rats because of vasodilatory, antiproliferative and anifibrotic properties but also because of a significant decrease in dyslipidemia, the major culprit for cardiac dysfunctions in diabetes.

Angiotensinogen Expression Is Enhanced in the Progression of Glomerular Disease

Intrarenal renin-angiotensin system (RAS) activation plays a critical role in the development and progression of renal injury. In the kidney, all of the RAS components are present and intrarenal angiotensin II (Ang II) is formed by multiple independent mechanisms. Angiotensinogen (AGT) is the only known substrate for renin that is a rate-limiting enzyme of the RAS. Recently, enhanced intrarenal AGT levels have been shown to reflect the intrarenal RAS status in hypertension, chronic glomerular disease and diabetic nephropathy. In this review, we focus on AGT expression of the diseased glomeruli in the progression of glomerular disease. An anti-glomerular basement membrane nephritis rat model developed progressive proteinuria and glomerular crescent formation, accompanied by increased macrophage infiltration and glomerular expression of AGT and Ang II. The addition of Ang II type 1 receptor blocker to CC-chemokine recaptor 2 antagonist markedly attenuated the induction of macrophage infiltration, AGT and Ang II, and reduced glomerular crescent formation. Next, the levels of glomerular AGT expression and marker of reactive oxygen species in Zucker diabetic fatty (ZDF) obese rats were higher than those in ZDF lean rats. Hydrogen peroxide (H(2)O(2)) induced an increase in the AGT expression in primary rat mesangial cells. Furthermore, the H(2)O(2)-induced upregulation of AGT was inhibited by a mitogen-activated protein kinase kinase and a c-Jun N-terminal kinase inhibitor. These data suggest the potential contribution of enhanced AGT expression in glomeruli to the intrarenal RAS activation for the development of glomerular disease.

Angiotensin (1-7)/Mas receptor axis activation ameliorates the changes in fatty acid composition in diabetic rats with nephropathy

Diabetes mellitus is often associated with altered fatty acids composition. This study was designed to investigate the role of angiotensin (Ang) (1-7)/Mas receptor in improving fatty acids composition in streptozotocin (STZ)-induced diabetic nephropathy (DN) in rats. Rats treated with STZ (50 mg/kg, i.p. once) developed DN after 8 weeks. Fatty acid composition was estimated in renal cortical tissue by gas chromatography. Treatment with Ang (1-7), A-779, and Ang (1-7) plus A-779 was given from week 4 to week 8. Diabetic rats exhibited a significant increase in levels of saturated fatty acids and a significant decrease in levels of polyunsaturated fatty acids (PUFAs). Treatment with Ang (1-7) significantly attenuated these diabetes-induced changes. In diabetic rats, prior administration of A-779 significantly attenuated the increase in PUFAs produced by Ang (1-7); however, for saturated fatty acids, A-779 significantly blocked the decrease in palmitic acid only. Our study, for the first time, documented that endogenous Ang (1-7) modulates fatty acid composition in rats. Further, treatment with Ang (1-7) significantly attenuated diabetes-induced changes in fatty acids composition. This may be an additional mechanism implying the renoprotective role of Ang (1-7) in diabetic rats.

Sex differences in renal angiotensin converting enzyme 2 (ACE2) activity are 17β-oestradiol-dependent and sex chromosome-independent

Background

Angotensin converting enzyme 2 (ACE2) is a newly discovered monocarboxypeptidase that counteracts the vasoconstrictor effects of angiotensin II (Ang II) by converting Ang II to Ang-(1-7) in the kidney and other tissues.

Methods

ACE2 activity from renal homogenates was investigated by using the fluorogenic peptide substrate Mca-YVADAPK(Dnp)-OH, where Mca is (7-methoxycoumarin-4-yl)-acetyl and Dnp is 2,4-dinitrophenyl.

Results

We found that ACE2 activity expressed in relative fluorescence units (RFU) in the MF1 mouse is higher in the male (M) compared to the female (F) kidney [ACE2 (RFU/min/μg protein): M 18.1 ± 1.0 versus F 11.1 ± 0.39; P < 0.0001; n = 6]. Substrate concentration curves revealed that the higher ACE2 activity in the male was due to increased ACE2 enzyme velocity (V_max) rather than increased substrate affinity (K_m). We used the four core genotypes mouse model in which gonadal sex (ovaries versus testes) is separated from the sex chromosome complement enabling comparisons among XX and XY gonadal females and XX and XY gonadal males. Renal ACE2 activity was greater in the male than the female kidney, regardless of the sex chromosome complement [ACE2 (RFU/min/μg protein): intact-XX-F, 7.59 ± 0.37; intact-XY-F, 7.43 ± 0.53; intact-XX-M, 12.1 ± 0.62; intact-XY-M, 12.7 ± 1.5; n = 4-6/group; P < 0.0001, F versus M, by two-way ANOVA]. Enzyme activity was increased in gonadectomized (GDX) female mice regardless of the sex chromosome complement whereas no effect of gonadectomy was observed in the males [ACE2 (RFU/min/μg protein): GDX-XX-F, 12.4 ± 1.2; GDX-XY-F, 11.1 ± 0.76; GDX-XX-M, 13.2 ± 0.97; GDX-XY-M, 11.6 ± 0.81; n = 6/group]. 17β-oestradiol (E₂) treatment of GDX mice resulted in ACE2 activity that was only 40% of the activity found in the GDX mice, regardless of their being male or female, and was independent of the sex chromosome complement [ACE2 (RFU/min/μg protein): GDX+E₂-XX-F, 5.56 ± 1.0; GDX+E₂-XY-F, 4.60 ± 0.52; GDX+E₂-XX-M, 5.35 ± 0.70; GDX+E₂-XY-M, 5.12 ± 0.47; n = 6/group].

Conclusions

Our findings suggest sex differences in renal ACE2 activity in intact mice are due, at least in part, to the presence of E₂ in the ovarian hormone milieu and not to the testicular milieu or to differences in sex chromosome dosage (2X versus 1X; 0Y versus 1Y). E₂ regulation of renal ACE2 has particular implications for women across their life span since this hormone changes radically during puberty, pregnancy and menopause.

High glucose upregulates upstream stimulatory factor 2 in human renal proximal tubular cells through angiotensin II-dependent activation of CREB

BACKGROUND/AIMS

We have previously demonstrated that a transcription factor, upstream stimulatory factor 2 (USF2), regulates glucose-induced thrombospondin 1 expression and transforming growth factor-β activity in mesangial cells, and plays an important role in diabetic glomerulopathy. In this study, we determined whether USF2 expression in renal proximal tubular cells is regulated by glucose and contributes to diabetic tubulointerstitial fibrosis.

METHODS

Human renal proximal tubular cells (HK-2 cells) were treated with normal- or high-glucose medium for 24 h. After treatment, real-time PCR or immunoblotting was used to determine the expression of USF2 and other components of the renin-angiotensin system in HK-2 cells.

RESULTS

High glucose upregulated USF2 expression and increased extracellular matrix accumulation in HK-2 cells; both were inhibited by siRNA-mediated USF2 knockdown. In addition, high glucose stimulated angiotensinogen and renin expression, increased renin activity, and resulted in increased angiotensin II formation. Treatment of HK-2 cells with an angiotensin II receptor 1 (AT1) blocker--losartan--prevented high-glucose-induced USF2 expression and high-glucose-enhanced phosphorylation of CREB (cAMP response element-binding protein).

CONCLUSION

Our data established that high glucose stimulated USF2 expression in HK-2 cells, at least in part, through angiotensin II-AT1-dependent activation of CREB, which can contribute to diabetic tubulointerstitial fibrosis.

The ANG-(1-7)/ACE2/mas axis in the regulation of nephron function

The study of experimental hypertension and the development of drugs with selective inhibitory effects on the enzymes and receptors constituting the components of the circulating and tissue renin-angiotensin systems have led to newer concepts of how this system participates in both physiology and pathology. Over the last decade, a renewed emphasis on understanding the role of angiotensin-(1-7) and angiotensin-converting enzyme 2 in the regulation of blood pressure and renal function has shed new light on the complexity of the mechanisms by which these components of the renin angiotensin system act in the heart and in the kidneys to exert a negative regulatory influence on angiotensin converting enzyme and angiotensin II. The vasodepressor axis composed of angiotensin-(1-7)/angiotensin-converting enzyme 2/mas receptor emerges as a site for therapeutic interventions within the renin-angiotensin system. This review summarizes the evolving knowledge of the counterregulatory arm of the renin-angiotensin system in the control of nephron function and renal disease.

Urinary angiotensinogen accurately reflects intrarenal Renin-Angiotensin system activity

BACKGROUND

We recently reported that immunoreactivity of intrarenal angiotensinogen (AGT) is significantly increased in IgA nephropathy patients. Meanwhile, we have developed direct enzyme-linked immunosorbent assays to measure plasma and urinary AGT (UAGT) in humans. This study was performed to test the hypothesis that UAGT levels are increased in chronic glomerulonephritis patients.

METHODS

We analyzed 100 urine samples from 70 chronic glomerulonephritis patients (26 from IgA nephropathy, 24 from purpura nephritis, 8 from lupus nephritis, 7 from focal segmental glomerulosclerosis, and 5 from non-IgA mesangial proliferative glomerulonephritis) and 30 normal control subjects.

RESULTS

UAGT-creatinine ratio (UAGT/UCre) was correlated positively with diastolic blood pressure (p = 0.0326), urinary albumin-creatinine ratio (p < 0.0001), urinary protein-creatinine ratio (p < 0.0001) and urinary occult blood (p = 0.0094). UAGT/UCre was significantly increased in chronic glomerulonephritis patients not treated with renin-angiotensin system (RAS) blockers compared with control subjects (p < 0.0001). Importantly, glomerulonephritis patients treated with RAS blockers had a marked attenuation of this augmentation (p = 0.0021).

CONCLUSION

These data indicate that UAGT are increased in chronic glomerulonephritis patients and treatment with RAS blockers suppressed UAGT. The efficacy of RAS blockade to reduce the intrarenal RAS activity can be confirmed by measurement of UAGT in chronic glomerulonephritis patients.

Inhibition of intracellular angiotensin II formation blocks high glucose effect on mesangial matrix

High glucose causes increased matrix synthesis by glomerular mesangial cells and angiotensin II (Ang II) has been shown to mediate this effect of glucose. These studies investigate whether inhibition of Ang II formation can block high glucose-induced increase in mesangial matrix. Human mesangial cells were incubated with 25 mM glucose (HG) along with captopril, an ACE inhibitor, to block Ang II formation. In other experiments, cells were nucleofected with siRNA to knockdown angiotensinogen (Agt), the precursor of Ang II, and then exposed to high glucose. Captopril blocked high glucose-induced increase in Ang II levels in the cell media (extracellular) but failed to inhibit it in the cell lysate (intracellular). Moreover, captopril treatment did not block the stimulatory effect of high glucose on TGF-beta1 and fibronectin. In contrast, knockdown of the Agt gene prevented high glucose-induced increase in both extracellular and intracellular Ang II levels, and was accompanied by normalization of TGF-beta1 and fibronectin. These data suggest that intracellular Ang II may play an important role in the mediation of the high glucose effect on matrix and that ACE inhibitors may not be effective in blocking intracellular Ang II formation in mesangial cells.

Pharmacologic modulation of ACE2 expression

Angiotensin-converting enzyme 2 (ACE2) is an enzymatically active homologue of angiotensin-converting enzyme that degrades angiotensin I, angiotensin II, and other peptides. Recent studies have shown that under pathologic conditions, ACE2 expression in the kidney is altered. In this review, we briefly summarize recent studies dealing with pharmacologic interventions that modulate ACE2 expression. ACE2 amplification may have a potential therapeutic role for kidney disease and hypertension.

Activation of renal renin-angiotensin system in upstream stimulatory factor 2 transgenic mice

Previously we demonstrated that upstream stimulatory factor 2 (USF2) transgenic (Tg) mice developed nephropathy including albuminuria and glomerular hypertrophy, accompanied by increased transforming growth factor (TGF)-beta and fibronectin accumulation in the glomeruli. However, the mechanisms by which overexpression of USF2 induces kidney injury are unknown. USF has been shown to regulate renin expression. Moreover, the renin-angiotensin system (RAS) plays important roles in renal diseases. Therefore, in the present studies the effects of USF2 on the regulation of RAS in the kidney as well as in mesangial cells from USF2 (Tg) mice were examined. The role of USF2-mediated regulation of RAS in TGF-beta production in mesangial cells was also determined. Our data demonstrate that USF2 (Tg) mice exhibit increased renin and angiotensin (ANG) II levels in the kidney. In contrast, renal expression of other components of RAS such as renin receptor, angiotensinogen, angiotensin-converting enzyme (ACE), ACE2, angiotensin type 1a (AT(1a)) receptor, and AT(2) receptor was not altered in USF2 (Tg) mice. Similarly, mesangial cells isolated from USF2 (Tg) mice had increased renin and ANG II levels. Mesangial cells overexpressing USF2 also had increased TGF-beta production, which was blocked by small interfering RNA-mediated renin gene knockdown or RAS blockade (enalapril or losartan). Collectively, these results suggest that USF2 promotes renal renin expression and stimulates ANG II generation, leading to activation of the intrarenal RAS. In addition, renin-dependent ANG II generation mediates the effect of USF2 on TGF-beta production in mesangial cells, which may contribute to the development of nephropathy in USF2 (Tg) mice.