Amelioration of long-term renal changes in obese type 2 diabetic mice by a neutralizing vascular endothelial growth factor antibody

Alteration of glomerulogenesis- and podocyte structure-related gene expression in early diabetic nephropathy

Diabetic nephropathy is a leading cause of end-stage renal disease. Several pathways, including the renin-angiotensin system, have been postulated as potential mechanisms of diabetic nephropathy. In addition, glomerulogenesis-related molecules are involved in the pathogenesis of diabetic nephropathy, especially at the early stage. They can be divided into three groups by function, that is, fibrosis-related, podocyte differentiation-related and angiogenesis-related molecules. Most of the molecules are expressed in the podocyte and upregulated, even during the normoalbuminuric stage. Expression of several podocyte structure-related molecules are also altered at the normoalbuminuric stage. They can contribute to the structural alteration of the podocyte in diabetic nephropathy. Thus, normalization of the expression of glomerulogenesis-related molecules could be a new target for preventing the initiation and progression of diabetic nephropathy.

Role of VEGF in maintaining renal structure and function under normotensive and hypertensive conditions

Inhibiting the actions of VEGF is a new therapeutic paradigm in cancer management with antiangiogenic therapy also under intensive investigation in a range of nonmalignant diseases characterized by pathological angiogenesis. However, the effects of VEGF inhibition on organs that constitutively express it in adulthood, such as the kidney, are mostly unknown. Accordingly, we examined the effect of VEGF inhibition on renal structure and function under physiological conditions and in the setting of the common renal stressors: hypertension and activation of the renin-angiotensin system. When compared with normotensive Sprague-Dawley (SD) rats, glomerular VEGF mRNA was increased 2-fold in transgenic (mRen-2)27 rats that overexpress renin with spontaneously hypertensive rat (SHR) kidneys showing VEGF expression levels that were intermediate between them. Administration of either an orally active inhibitor of the type 2 VEGF receptor (VEGFR-2) tyrosine kinase or a VEGF neutralizing antibody to TGR(mRen-2)27 rats resulted in loss of glomerular endothelial cells and transformation to a malignant hypertensive phenotype with severe glomerulosclerosis. VEGFR-2 kinase inhibition treatment was well tolerated in SDs and SHRs; although even in these animals there was detectable endothelial cell loss and rise in albuminuria. Mild mesangial expansion was also noted in hypertensive SHR, but not in SD rats. These studies illustrate: (i) VEGF has a role in the maintenance of glomerular endothelial integrity under physiological circumstances, (ii) glomerular VEGF is increased in response to hypertension and activation of the renin-angiotensin system, and (iii) VEGF signaling plays a protective role in the setting of these renal stressors.

Effects on protein kinase C-β inhibition on glomerular vascular endothelial growth factor expression and endothelial cells in advanced experimental diabetic nephropathy

Ruboxistaurin is an inhibitor of the β isoform of protein kinase C (PKC-β) that reduces the actions of vascular endothelial growth factor (VEGF) and attenuates the progression of diabetic retinopathy. In the glomerulus VEGF is constitutively expressed where it likely has a role in maintaining endothelial cell integrity, particularly in disease states. Given its potential use in diabetic nephropathy, we sought to determine the effects of PKC-β inhibition on VEGF and glomerular endothelial cells in experimental diabetic nephropathy. Studies were conducted in (mRen-2)27 rat, a transgenic rodent with hypertension and an enhanced renin-angiotensin system that following induction of diabetes with streptozotocin develops many of the features of diabetic nephropathy. Moreover, to mimic the clinical context, the effects of PKC-β inhibition were examined both with and without concomitant angiotensin-converting enzyme (ACE) inhibitor therapy. Diabetic Ren-2 rats were randomized to receive either vehicle, the ACE inhibitor, perindopril (0.2 mg/l in drinking water), ruboxistaurin (10 mg·kg−1·day−1, admixed in chow), or their combination and studied for 12 wk. Diabetic Ren-2 rats displayed glomerular endothelial cell loss in association with overexpression of VEGF mRNA. Both cell loss and VEGF overexpression were attenuated by the administration of either perindopril or ruboxistaurin, as single agent treatments with their combination providing additional, incremental improvements, reducing these manifestations of injury down to levels seen in nondiabetic, normotensive, nontransgenic animals. Combination therapy was also associated with additional improvements in albuminuria and glomerulosclerosis.

Heterogeneous nuclear ribonucleoprotein K contributes to angiotensin II stimulation of vascular endothelial growth factor mRNA translation

ANG II rapidly increases VEGF synthesis in proximal tubular epithelial cells through mRNA translation. The role of heterogeneous nuclear ribonucleoprotein K (hnRNP K) in ANG II regulation of VEGF mRNA translation initiation was examined. ANG II activated hnRNP K as judged by binding to poly(C)- and poly(U)-agarose. ANG II increased hnRNP K binding to VEGF mRNA at the same time as it stimulated its translation, suggesting that hnRNP K contributes to VEGF mRNA translation. Inhibition of hnRNP K expression by RNA interference significantly reduced ANG II stimulation of VEGF synthesis. ANG II increased hnRNP K phosphorylation on both tyrosine and serine residues with distinct time courses; only Ser302 phosphorylation paralleled binding to VEGF mRNA. Src inhibition using PP2 or RNA interference inhibited PKCδ activity and prevented hnRNP K phosphorylation on both tyrosine and serine residues and its binding to VEGF mRNA. Under these conditions, ANG II-induced VEGF synthesis was inhibited. ANG II treatment induced redistribution of both VEGF mRNA and hnRNP K protein from light to heavy polysomal fractions, suggesting increased binding of hnRNP K to VEGF mRNA that is targeted for increased translation. This study shows that hnRNP K augments efficiency of VEGF mRNA translation stimulated by ANG II.

Uncoupling of the VEGF-endothelial nitric oxide axis in diabetic nephropathy: an explanation for the paradoxical effects of VEGF in renal disease

In many forms of experimental kidney diseases, renal VEGF is low, and administering VEGF can be shown to be protective. A paradox occurs in diabetes, in which renal VEGF levels are high and a deleterious effect of VEGF on kidney disease has been shown. We have hypothesized that endothelial dysfunction induced by hyperglycemia or other factors may underlie the pathogenic mechanisms of a high VEGF state. VEGF normally stimulates endothelial nitric oxide (NO) release and acts in concert with elevated NO levels as a trophic factor for vascular endothelium. The increased NO derived from the endothelial cell acts as an inhibitory factor that prevents excess endothelial cell proliferation, vascular smooth muscle cell proliferation, and macrophage infiltration. In the setting where NO bioavailability is reduced in diabetes, high levels of VEGF lead to excessive endothelial cell proliferation, stimulation of macrophage chemotaxis, and vascular smooth muscle cell activation. Consistent with this hypothesis is our recent observation that diabetes induced in endothelial NO-deficient mice results in clinical and histological features identical to human diabetic nephropathy. The discovery of the key role for impaired endothelial NO bioavailability in the stimulation of VEGF and VEGF-dependent disease may provide key insights into not only the pathogenesis of diabetic nephropathy but also the utility and hazard of administering VEGF as a treatment for kidney disease.

Increased Expression of Vascular Endothelial Growth Factor in Kidney Leads to Progressive Impairment of Glomerular Functions

Vascular endothelial growth factor (VEGF) is an important mediator in maintaining normal kidney functions. In addition, several lines of evidence suggest that upregulation of VEGF in glomeruli may be associated with or cause renal dysfunction such as diabetic nephropathy. For elucidation of the pathologic consequences of high levels of VEGF in glomeruli, transgenic (Tg) rabbits that express human VEGF(165) isoform in both kidney and liver under the control of the human alpha-1-antitrypsin promoter were generated and characterized. With the use of heterozygous Tg rabbits and their littermates aged 8 to 55 wk, renal functions and structures were investigated. Compared with control rabbits, Tg rabbits exhibited progressive proteinuria with increased GFR at the early stage and decreased GFR at the later stage. Histologic examinations revealed that Tg rabbit kidneys were characterized by considerable glomerular hypertrophy as a result of increased proliferation of both glomerular capillaries and mesangial cells accompanied by prominent podocyte hypertrophy. With increasing age starting from 20 wk, Tg rabbit kidneys showed prominent formation of microaneurysms and capillary proliferation at the vascular pole area. At a later stage (55 wk), many glomeruli showed sclerosis and tuft collapse with the formation of glomerular cysts on a background of tubular atrophy and interstitial fibrosis. This study provides the first evidence that increased expression of VEGF in glomeruli directly causes the glomerular hypertrophy that is associated with proteinuria, suggesting that VEGF exerts multiple effects on the glomerular pathophysiologic processes.

The continuous erythropoietin receptor activator affects different pathways of diabetic renal injury

This study explored the tissue-protective properties of the continuous erythropoietin receptor activator (CERA) in an experimental model of (nonischemic) diabetic kidney injury (i.e., the db/db mouse). Mice were randomly treated with placebo (n = 25), low-dosage CERA (n = 25), and high-dosage CERA (n = 25). Also studied were 25 nondiabetic db/m mice. Hematocrit was comparable in placebo and low-dosage CERA-treated mice but increased significantly with high-dosage CERA (P < 0.01 versus both). Significantly reduced expression of TGF-beta, vascular endothelial growth factor, and collagen IV was found in glomeruli and the tubulointerstitial area with CERA treatment, and these beneficial molecular effects were clearly dosage dependent (both P < 0.05 versus placebo). Similarly, CERA treatment caused a dosage-dependent increase in p-Akt, nephrin, and perlecan tissue expression (all P < 0.05 versus placebo). However, the accelerated mesangial expansion that was observed in placebo-treated db/db mice (versus db/m controls) was significantly reduced only in low-dosage CERA-treated mice (P < 0.01). Moreover, albuminuria was significantly reduced in low- but not high-dosage CERA-treated mice compared with placebo treatment (P < 0.05). In an ancillary study, phlebotomy was performed in high-dosage CERA-treated db/db mice to keep hematocrit within normal (baseline) levels. This procedure resulted in significantly (P < 0.05) less albuminuria as compared with high-dosage CERA-treated mice without phlebotomy, thus preserving the tissue-protective potential of CERA. Long-term CERA treatment has beneficial dosage-dependent effects on molecular pathways of diabetic kidney damage. Low-dosage CERA does not affect hematocrit and therefore may be a feasible method of tissue protection in this setting.

Effect of telmisartan on expression of protein kinase C-alpha in kidneys of diabetic mice

AIM

To investigate the effects of angiotensin receptor blocker (ARB) telmisartan on the expression and distribution of protein kinase C (PKC)-alpha in the kidneys of diabetic mice.

METHODS

Diabetic mice were induced with streptozotocin and a group of them were randomly selected for treatment with telmisartan. After 6 weeks, the expression and localization of PKC-alpha in the renal cortex, and the outer and inner medulla were assessed by immunohistochemistry and semiquantitative Western blotting. In addition, expressions of PKC-alpha, transforming growth factor-beta1 (TGF-beta1), and vascular endothelial growth factor (VEGF) in glomeruli were measured by semiquantitative immunohistochemistry.

RESULTS

Diabetic and normal mice showed similar distributions of PKC-alpha in the kidneys. The expression of PKC-alpha was found in glomeruli, epithelial cells of proximal tubules, and medullary-collecting duct, while not in the medullary and cortical thick ascending limb, and was different in the epithelial cells of proximal tubules of diabetic nephropathy (DN) mice, PKC-alpha was mostly translocated from the basement membrane to the apical membrane, whereas it was largely translocated from the apical membrane to the basement membrane in epithelial cells of the inner medullary-collecting duct. Western blotting detected increased expression of PKC-alpha in the renal cortex and outer medulla, but not in the inner medulla of DN mice. Enhanced expressions of PKC-alpha, TGF-beta1, and VEGF were shown in the glomeruli of DN mice, where PKC-alpha exhibited a correlation to VEGF, but no correlation to TGF-beta1. ARB telmisartan attenuated alterations of PKC-alpha as mentioned earlier in the DN mice.

CONCLUSION

Our findings suggest that PKC-alpha may play a role in the pathogenesis of DN, and that the nephroprotective effects of ARB telmisartan may be partly associated with its influence on PKC-alpha.

Angiogenesis in diabetic nephropathy

Angiogenesis, the formation of new blood vessels from pre-existing vasculature, plays a key role in both physiologic and pathologic events, including wound healing, cancer, and diabetes. Neovascularization has been implicated in the genesis of diverse diabetic complications such as retinopathy, impaired wound healing, neuropathy, and, most recently, diabetic nephropathy. Diabetic nephropathy is one of the major microvascular-associated complications in diabetes and is the leading cause of end-stage renal disease worldwide. In this review we describe the major factors involved in the pathologic glomerular microvascular alterations in response to hyperglycemia and the possible use of anti-angiogenic therapies for the treatment of diabetic nephropathy.

Diabetes-induced changes in the renal cortical proteome assessed with two-dimensional gel electrophoresis and mass spectrometry

To understand the spectrum of proteins affected by diabetes and to characterize molecular functions and biological processes they control, we analyzed the renal cortical proteome of db/db mice using 2-DE combined with MALDI-TOF, MALDI-TOF/TOF, and LC-MS/MS. This approach yielded 278 high confidence identifications whose expression levels were significantly increased or decreased >two-fold by diabetes, of which 170 mapped to gene identifiers representing 147 nonredundant proteins. Gene Ontology classification demonstrated that 80% of these proteins modulated physiological functions, 55% involved metabolism, approximately 25% involved carboxylic and organic acid metabolism, 14% involved biosynthesis or catabolism, and 12% involved fatty acid metabolism. Predominant molecular functions were catalytic (61%), oxidoreductase (20%), and transferase (17%) activities, and nucleotide and ATP binding (11-15%). Twenty eight percent of the proteins identified as significantly altered by diabetes were mitochondrial proteins. The top-ranked network described by Ingenuity Pathway Analysis indicated PPARalpha was the most common node of interaction for the numerous enzymes whose expression levels were influenced by diabetes. These differentially regulated proteins create a foundation for a systems biology exploration of molecular mechanisms underlying the pathophysiology of diabetic nephropathy.

Beneficial effects of thiazolidinediones on diabetic nephropathy in OLETF rats

PURPOSE

Diabetic nephropathy is the most serious of complications in diabetes mellitus. Thiazolidinedione (TZD) is thought to ameliorate diabetic nephropathy; however, the mechanism underlying this effect has not been elucidated. We hypothesized that the vascular endothelial growth factor (VEGF) participates in the pathogenesis of diabetic nephropathy and that TZD may be beneficial for the treatment of diabetic nephropathy because of the effect it has on VEGF.

MATERIALS AND METHODS

23 Otsuka- Long-Evans-Tokushima-Fatty (OLETF) rats and eight control Long-Evans-Tokushima-Otsuka (LETO) rats were divided into the following four groups: LETO group, control OLETF group, pioglitazone treated group (10mg/ kg/day), and rosiglitazone treated group (3mg/kg/day).

RESULTS

A progressive increase in urinary protein excretion was observed in the diabetic rats. Glomerular VEGF expression in the control OLETF rats was significantly higher than in the control LETO rats. However, there was a significant reduction in both the glomerular VEGF expression and the VEGF mRNA levels after treatment with pioglitazone and rosiglitazone. The twenty-four hour urine protein levels were significantly decreased in both groups of the treated OLETF rats.

CONCLUSION

These results suggest that TZD may have beneficial effects on diabetic nephropathy by reducing the VEGF expression.

Kidney growth, hypertrophy and the unifying mechanism of diabetic complications

Michael Brownlee has proposed a 'Unifying Mechanism' of hyperglycemia-induced damage in diabetes mellitus. At the crux of this hypothesis is the generation of reactive oxygen species (ROS), and their impact on glycolytic pathways. Diabetes is the leading cause of chronic kidney failure. In the early phase of diabetes, prior to establishment of proteinuria or fibrosis, comes kidney growth and hyperfiltration. This early growth phase consists of an early period of hyperplasia followed by hypertrophy. Hypertrophy also contributes to cellular oxidative stress, and may precede the ROS perturbation of glycolytic pathways described in the Brownlee proposal. This increase in growth promotes hyperfiltration, and along with the hypertrophic phenotype appears required for hyperglycemia-induced cell damage and the progression of downstream diabetic complications. Here we will evaluate this growth phenomenon in the context of diabetes mellitus.

Phenotypic heterogeneity of the endothelium: II. Representative vascular beds

Endothelial cells, which form the inner cellular lining of blood vessels and lymphatics, display remarkable heterogeneity in structure and function. This is the second of a 2-part review on the phenotypic heterogeneity of blood vessel endothelial cells. The first part discusses the scope, the underlying mechanisms, and the diagnostic and therapeutic implications of phenotypic heterogeneity. Here, these principles are applied to an understanding of organ-specific phenotypes in representative vascular beds including arteries and veins, heart, lung, liver, and kidney. The goal is to underscore the importance of site-specific properties of the endothelium in mediating homeostasis and focal vascular pathology, while at the same time emphasizing the value of approaching the endothelium as an integrated system.

Nephrotic Syndrome After Bevacizumab: Case Report and Literature Review

Bevacizumab, or avastin, is a monoclonal hybrid antibody that binds to and neutralizes vascular endothelial growth factor. It has shown promising efficacy in the adjunctive treatment of patients with several cancers. Recent reports indicated that bevacizumab therapy often was associated with the development of proteinuria, but rarely nephrotic syndrome. In this report, we describe a patient who developed new-onset hypertension and nephrotic syndrome in association with bevacizumab treatment for metastatic pancreatic cancer. Renal biopsy showed an immune-complex-mediated focal proliferative glomerulonephritis. Nephrotic syndrome and hypertension resolved after discontinuation of bevacizumab therapy. The mechanism of bevacizumab-induced glomerulonephritis and nephrotic syndrome is unknown and requires additional investigation. Clinicians should be aware of the potential reversible nephrotoxicity of bevacizumab and should monitor blood pressure and urine protein excretion closely during therapy with this agent.

Deletion of protein kinase C-beta isoform in vivo reduces renal hypertrophy but not albuminuria in the streptozotocin-induced diabetic mouse model

The protein kinase C (PKC)-beta isoform has been implicated to play a pivotal role in the development of diabetic kidney disease. We tested this hypothesis by inducing diabetic nephropathy in PKC-beta-deficient (PKC-beta(-/-)) mice. We studied nondiabetic and streptozotocin-induced diabetic PKC-beta(-/-) mice compared with appropriate 129/SV wild-type mice. After 8 weeks of diabetes, the high-glucose-induced renal and glomerular hypertrophy, as well as the increased expression of extracellular matrix proteins such as collagen and fibronectin, was reduced in PKC-beta(-/-) mice. Furthermore, the high-glucose-induced expression of the profibrotic cytokine transforming growth factor (TGF)-beta1 and connective tissue growth factor were significantly diminished in the diabetic PKC-beta(-/-) mice compared with diabetic wild-type mice, suggesting a role of the PKC-beta isoform in the regulation of renal hypertrophy. Notably, increased urinary albumin-to-creatinine ratio persisted in the diabetic PKC-beta(-/-) mice. The loss of the basement membrane proteoglycan perlecan and the podocyte protein nephrin in the diabetic state was not prevented in the PKC-beta(-/-) mice as previously demonstrated in the nonalbuminuric diabetic PKC-alpha(-/-) mice. In summary, the differential effects of PKC-beta deficiency on diabetes-induced renal hypertrophy and albuminuria suggest that PKC-beta contributes to high-glucose-induced TGF-beta1 expression and renal fibrosis, whereas perlecan, as well as nephrin, expression and albuminuria is regulated by other signaling pathways.

Inhibiting albumin glycation attenuates dysregulation of VEGFR-1 and collagen IV subchain production and the development of renal insufficiency

Glomerular cells in culture respond to albumin containing Amadori glucose adducts (the principal serum glycated protein), with activation of protein kinase C-β1, increased expression of transforming growth factor (TGF)-β1, the TGF-β type II signaling receptor, and the extracellular matrix proteins α1(IV) collagen and fibronectin and with decreased production of the podocyte protein nephrin. Decreasing the burden of glycated albumin in diabetic db/db mice significantly reduces glomerular overexpression of TGF-β1 mRNA, restores glomerular nephrin immunofluorescence, and lessens proteinuria, mesangial expansion, renal extracellular matrix protein production, and increased glomerular vascular endothelial growth factor (VEGF) immunostaining. In the present study, db/db mice were treated with a small molecule, designated 23CPPA, that inhibits the nonenzymatic condensation of glucose with the albumin protein to evaluate whether increased glycated albumin influences the production of VEGF receptors (VEGFRs) and type IV collagen subchains and ameliorates the development of renal insufficiency. Renal levels of VEGF and VEGFR-1 proteins and serum creatinine concentrations were significantly higher and renal levels of α3(IV) collagen and nephrin proteins and endogenous creatinine clearance values were significantly lower in control diabetic than in age-matched nondiabetic ( db/m) mice. These changes were significantly attenuated in db/db littermate mice treated from 9 to 18 wk of age with 23CPPA. The findings indicate that inhibiting excess nonenzymatic glycation of serum albumin improves renal molecular biology abnormalities and protects against the development of renal insufficiency in the db/db mouse.

Diabetic endothelial nitric oxide synthase knockout mice develop advanced diabetic nephropathy

The pathogenesis of diabetic nephropathy remains poorly defined, and animal models that represent the human disease have been lacking. It was demonstrated recently that the severe endothelial dysfunction that accompanies a diabetic state may cause an uncoupling of the vascular endothelial growth factor (VEGF)-endothelial nitric oxide (eNO) axis, resulting in increased levels of VEGF and excessive endothelial cell proliferation. It was hypothesized further that VEGF-NO uncoupling could be a major contributory mechanism that leads to diabetic vasculopathy. For testing of this hypothesis, diabetes was induced in eNO synthase knockout mice (eNOS KO) and C57BL6 controls. Diabetic eNOS KO mice developed hypertension, albuminuria, and renal insufficiency with arteriolar hyalinosis, mesangial matrix expansion, mesangiolysis with microaneurysms, and Kimmelstiel-Wilson nodules. Glomerular and peritubular capillaries were increased with endothelial proliferation and VEGF expression. Diabetic eNOS KO mice showed increased mortality at 5 mo. All of the functional and histologic changes were improved with insulin therapy. Inhibition of eNO predisposes mice to classic diabetic nephropathy. The mechanism likely is due to VEGF-NO uncoupling with excessive endothelial cell proliferation coupled with altered autoregulation consequent to the development of preglomerular arteriolar disease. Endothelial dysfunction in human diabetes is common, secondary to effects of glucose, advanced glycation end products, C-reactive protein, uric acid, and oxidants. It was postulated that endothelial dysfunction should predict nephropathy and that correction of the dysfunction may prevent these important complications.

2-Methoxyestradiol and 2-Ethoxyestradiol Retard the Progression of Renal Disease in Aged, Obese, Diabetic ZSF1 Rats

The metabolic syndrome is a main cause for cardiovascular disease and for the accelerating epidemic of chronic renal failure. Previous studies show that 2-hydroxyestradiol (2-HE), an estradiol metabolite with little estrogenic activity, decreases obesity and arterial blood pressure and attenuates the development of renal disease in young, obese, diabetic ZSF1 rats. In humans, however, diabetic renal disease is more frequent and severe in older patients. In vivo, 2-HE is readily converted to 2-methoxyestradiol (2-ME), an estradiol metabolite with no estrogenic activity. Accordingly, one purpose of this study was to determine whether 2-ME would provide benefit in aged rats with a very severe form of diabetic renal disease. Another objective was to determine whether synthetic analogs of estradiol metabolites might be beneficial in diabetic renal disease. To achieve these objectives we examined the effects of 2-ME and its analog 2-ethoxyestradiol (2-EE) in aged (35-week-old), obese ZSF1 rats. Animals were treated for 9 weeks with vehicle (PEG-400, 0.5 microL per hour), 2-ME or 2-EE (18 microg/kg per hour). Metabolic and renal function were measured at weeks 0, 3, 6, and 9, and renal hemodynamics and excretory function were assessed at week 9. Aged ZSF1 rats had elevated levels of glycosylated hemoglobin; increased renal cortical expression of proliferating cell nuclear antigen (PCNA), nuclear factor kappa B (NF-kappaB), and vascular endothelial growth factor (VEGF); glycosuria, hypertension; and proteinuria. 2-ME and 2-EE did not affect obesity or hypertension and had variable effects on glucose homeostasis, yet they attenuated proteinuria; increased renal blood flow and glomerular filtration; and reduced renal cortical expression of PCNA, NFkappaB, and VEGF. We conclude that 2ME and 2EE are strikingly renoprotective even in aged animals with severe diabetic renal disease. The present study warrants further investigation of 2-ME and analogs of estradiol metabolites for treatment of kidney disease associated with the metabolic syndrome.

Vascular endothelial growth factor administration does not improve microvascular disease in the salt-dependent phase of post-angiotensin II hypertension

Renal microvascular injury and tubulointerstitial inflammation may provide a potential mechanism for the development of salt-sensitive hypertension. Therefore, we hypothesized that vascular endothelial growth factor (VEGF) administration would prevent the development of salt-sensitive hypertension induced by ANG II. Infusion of ANG II in rats for 2 wk led to an elevation in blood pressure and an increase in blood urea nitrogen. Prominent tubular injury, focal areas of peritubular capillary loss accompanied by a decrease in urinary nitrites, thickening of the afferent arteriole, and an elevation in systemic and renal VEGF protein levels also occurred. In separate studies, animals were infused with ANG II and then placed on a low-salt diet for 1 wk. At this point, the animals were paired on the basis of weight and blood pressure and treated with either VEGF121or vehicle subcutaneously for 8 wk while being fed a high-salt diet. During the treatment period, a spontaneous improvement in many parameters, including both renal function and healing of the peritubular capillaries, occurred to the same degree in both vehicle- and VEGF121-treated rats. VEGF121significantly reduced blood pressure and accelerated the recovery of tubular injury. In contrast, vehicle-treated rats demonstrated a persistent increase in afferent arteriolar media-to-lumen ratio, which was further enhanced in rats treated with VEGF121. Therefore, VEGF therapy has only limited benefits on the healing of renal lesions in the salt-dependent phase of post-ANG II-mediated hypertension.

Analysis of glomerular VEGF mRNA and protein expression in murine mesangioproliferative glomerulonephritis

Capillary repair is crucial in the healing of glomerulonephritis (GN). The vascular endothelial growth factor (VEGF) has pro-angiogenic properties and plays an important role in glomerular capillary regeneration. Habu Snake Venom (HSV) GN, a murine model for mesangioproliferative GN, was induced in uninephrectomized C57/BL6 mice. Glomerular damage and capillary repair were assessed using morphometry, stereology, and confocal laser scanning microscopy. Mesangiolytic glomeruli were microdissected (days 1,3,7,14) using laser capture microdissection technique. VEGF mRNA expression was analyzed by real-time polymerase chain reaction and compared to intact glomeruli of healthy controls. Spatiotemporal VEGF gene and protein expression was determined using nonradioactive in situ hybridization and immunohistochemistry. On day 1, diseased animals developed focal mesangiolysis paralleled by a significant decrease in length density of glomerular capillaries that gradually returned to baseline levels thereafter, indicating capillary growth in response to initial injury. Glomerular VEGF mRNA expression increased on day 3 and returned back to baseline and beyond at day 14 when the glomerular recovery process was completed. Similarly, glomerular VEGF protein expression tended to be higher on day 3. The present study documents temporarily increased glomerular VEGF gene and protein expression during the healing of HSV GN, suggesting a potential role of VEGF in the repair of mesangiolytic glomerular damage.

HMG-CoA reductase inhibitor simvastatin mitigates VEGF-induced “inside-out” signaling to extracellular matrix by preventing RhoA activation

The 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors exert modulatory effects on a number of cell signaling cascades by preventing the synthesis of various isoprenoids derived from the mevalonate pathway. In the present study, we describe a novel pleiotropic effect of HMG-CoA reductase inhibitors, also commonly known as statins, on vascular endothelial growth factor (VEGF)-induced type IV collagen accumulation. VEGF is an angiogenic polypeptide that is also known to play a central role in endothelial cell permeability and differentiation. Recently, VEGF has also been implicated in promoting extracellular matrix (ECM) accumulation, although the precise signaling mechanism that mediates VEGF-induced ECM expansion remains poorly characterized. Elucidation of the mechanisms through which VEGF exerts its effect on ECM is clearly a prerequisite for both understanding the complex biology of this molecule as well as targeting VEGF in several pathological processes. To this end, this study explored the underlying molecular mechanisms mediating VEGF-induced ECM expansion in mesangial cells. Our findings show that VEGF stimulation elicits a robust increase in ECM accumulation that involves RhoA activation, an intact actin cytoskeleton, and β1- integrin activation. Our data also indicate that simvastatin, via mevalonate depletion, reverses VEGF-induced ECM accumulation by preventing RhoA activation.

Blockade of vascular endothelial growth factor signaling ameliorates diabetic albuminuria in mice

For investigation of how the vascular endothelial growth factor (VEGF) system participates in the pathogenesis of diabetic kidney disease, type 2 diabetic db/db and control db/m mice were treated intraperitoneally with vehicle or 2 mg/kg of a pan-VEGF receptor tyrosine kinase inhibitor, SU5416, twice a week for 8 wk. Efficacy of SU5416 treatment in the kidney was verified by the inhibition of VEGF receptor-1 phosphorylation. Glomerular VEGF immunostaining, normally increased in diabetes, was unaffected by SU5416. Plasma creatinine did not change with diabetes or SU5416 treatment. The primary end point of albuminuria increased approximately four-fold in the diabetic db/db mice but was significantly ameliorated by SU5416. Correlates of albuminuria were investigated. Diabetic glomerular basement membrane thickening was prevented in the SU5416-treated db/db mice, whereas mesangial matrix expansion remained unchanged by treatment. The density of open slit pores between podocyte foot processes was decreased in db/db diabetes but was partly increased toward normal by SU5416. Finally, nephrin protein by immunofluorescence was decreased in the db/db mice but was significantly restored by SU5416. Paradoxically, total nephrin protein by immunoblotting was increased in diabetes, pointing toward a possible dysregulation of nephrin trafficking. Diabetic albuminuria is partially a function of VEGF receptor signaling overactivity. VEGF signaling was found to affect a number of podocyte-driven manifestations such as GBM thickening, slit pore density, and nephrin quantity, all of which are associated with the extent of diabetic albuminuria. By impeding these pathophysiologic processes, VEGF receptor inhibition by SU5416 might become a useful adjunct to anti-albuminuria therapy in diabetic nephropathy.

mRNA translation: unexplored territory in renal science

Ambient protein levels are under coordinated control of transcription, mRNA translation, and degradation. Whereas transcription and degradation mechanisms have been studied in depth in renal science, the role of mRNA translation, the process by which peptide synthesis occurs according to the genetic code that is present in the mRNA, has not received much attention. mRNA translation occurs in three phases: Initiation, elongation, and termination. Each phase is controlled by unique eukaryotic factors. In the initiation phase, mRNA and ribosomal subunits are brought together. During the elongation phase, amino acids are added to the nascent peptide chain in accordance with codon sequences in the mRNA. During the termination phase, the fully synthesized peptide is released from the ribosome for posttranslational processing. Signaling pathways figure prominently in regulation of mRNA translation, particularly the phosphatidylinositol 3 kinase-Akt-mammalian target of rapamycin pathway, the AMP-activated protein kinase-tuberous sclerosis complex protein 1/tuberous sclerosis complex protein 2-Rheb pathway, and the extracellular signal-regulated kinase 1/2 type mitogen-activated protein kinase signaling pathway; there is significant cross-talk among these pathways. Regulation by mRNA translation is suggested when changes in mRNA and protein levels do not correlate and in the setting of rapid protein synthesis. Ongoing work suggests an important role for mRNA translation in compensatory renal growth, hypertrophy and extracellular matrix synthesis in diabetic nephropathy, growth factor synthesis by kidney cells, and glomerulonephritis. Considering that mRNA translation plays an important role in cell growth, development, malignancy, apoptosis, and response to stress, its study should provide novel insights in renal physiology and pathology.

Local VEGF activity but not VEGF expression is tightly regulated during diabetic nephropathy in man

Several studies have implicated the angiogenic cytokine vascular endothelial growth factor (VEGF) in the development of diabetic nephropathy, but no data are available about its local activity during human disease. Glomeruli from 52 archival biopsies from type II diabetics were evaluated and compared to 10 renal biopsies without kidney disease (controls). Glomerulosclerosis, capillary rarefaction, glomerular and endothelial cell proliferation, apoptosis, VEGF expression, as well as receptor-bound VEGF indicating local VEGF activity, and phosphorylation of the signal transduction molecule Akt were investigated. Owing to substantial heterogeneity of glomerular lesions in individual biopsies, these parameters were correlated with the degree of injury in individual glomeruli rather than biopsies. Severe glomerular capillary rarefaction was linked to the degree of glomerulosclerosis. While cellular apoptosis was detected independent of the stage of injury, endothelial cell proliferation indicating capillary repair was markedly increased only in mildly/moderately injured glomeruli. In controls, VEGF was predominantly expressed in podocytes, whereas receptor-bound VEGF was confined to the glomerular endothelium. VEGF expression was increased in all diabetic glomeruli by many different cell types. In contrast, VEGF receptor activation was increased predominantly in the endothelium of only mildly injured glomeruli, but significantly decreased in more severely injured glomeruli. Diabetic nephropathy is associated with glomerular capillary rarefaction. Despite overall increased glomerular VEGF, the decreased receptor-bound VEGF on the endothelium may be an indicator of an insufficient capillary repair reaction.

Renal vascular endothelial growth factor in neonatal obstructive nephropathy. II. Exogenous VEGF

Chronic unilateral ureteral obstruction (UUO) in the neonatal rat causes delayed renal maturation, tubular apoptosis, and interstitial inflammation. Vascular endothelial growth factor (VEGF) acts as a survival factor for tubular cells and reduces renal injury in several models of renal disease. To determine whether exogenous VEGF attenuates renal injury from UUO, rats were subjected within the first 48 h of life to sham operation, partial UUO, or complete UUO. Saline vehicle or VEGF(121) (50 mg/kg) was injected twice daily for 7 days, after which kidneys were harvested for histological study. The density of peritubular capillaries was measured with platelet-endothelial cell adhesion molecule-1 immunostaining, proliferating nuclei were detected by proliferating-cell nuclear antigen staining, apoptosis by the transferase-mediated dUTP nick end-labeling technique, macrophages by ED-1 immunostaining, and collagen by Sirius red staining. Glomerular number and maturation index were also determined in each group. Following chronic complete UUO in the neonatal rat, peritubular capillary density was significantly decreased. Cortical capillary density was further reduced by exogenous VEGF in the partially obstructed kidney. While UUO also decreased glomerular number and delayed glomerular maturation, exogenous VEGF exerted no additional effects. Cellular proliferation and tubular apoptosis increased in proportion to the severity of obstruction, but exogenous VEGF had no additional effects on proliferation, tubular apoptosis, or macrophage infiltration. However, VEGF reduced interstitial apoptosis in the kidney with partial UUO. We conclude that VEGF does not have salutary effects on the renal lesions caused by chronic UUO in the neonatal rat and may actually worsen obstructive nephropathy by aggravating the interstitial lesions.

Primary kidney growth and its consequences at the onset of diabetes mellitus

Diabetes mellitus is a primary contributor to progressive kidney dysfunction leading to end-stage renal disease (ESRD). In the early phase of diabetes, prior to the onset of further complications, both kidney size and glomerular filtration rate (GFR) increase. Glomerular hyperfiltration is considered a risk factor for downstream complications and progression to ESRD. Abnormalities in vascular control have been purported to account for the glomerular hyperfiltration in early diabetes. In this review we discuss a tubulo-centric concept in which tubular growth and subsequent hyper-reabsorption contribute to the onset of glomerular hyperfiltration that demarks the early stage of diabetes. Kidney growth, in this concept, is no longer relegated to a compensatory response to hyperfiltration, but rather plays a primary and active role in its genesis and progression. As such, components of kidney growth, such as the polyamines, may provide a means of early detection of diabetic kidney dysfunction and more effective therapeutic intervention.

A stereological study of the renal glomerular vasculature in the db/db mouse model of diabetic nephropathy

In diabetic nephropathy, glomerular hypertrophy is evident early in response to hyperglycaemia. Alterations of capillary length and vascular remodelling that may contribute to glomerular hypertrophy and the subsequent development of glomerulosclerosis remain unclear. The present study used the db/db mouse model of Type 2 diabetes to examine the glomerular microvascular changes apparent with long-term diabetic complications. Unbiased stereological methods and high-resolution light microscopy were used to estimate glomerular volume, and glomerular capillary dimensions including length and surface area in 7-month-old db/db diabetic mice and age-matched db/m control mice. The db/db diabetic mice showed significant glomerular hypertrophy, corresponding with elevated blood glucose levels, and increased body weight and kidney weight, compared with db/m control mice. Glomerular enlargement in db/db mice was associated with increases in the surface area (5.387 +/- 0.466 x 10(4) microm2 vs. 2.610 +/- 0.287 x 10(4) microm2; P < 0.0005) and length (0.3343 +/- 0.022 x 10(4) microm vs. 0.1549 +/- 0.017 x 10(4) microm; P < 0.0001) of capillaries per glomerulus, compared with non-diabetic mice. Stereological assessment at the electron microscopic level revealed increased glomerular volume density of mesangial cells and mesangial matrix, and thickening of the glomerular basement membrane in db/db mice. These results demonstrate that glomerular hypertrophy evident in advanced diabetic nephropathy in this model is associated with increased length and surface area of glomerular capillaries. The contribution of angiogenesis and vasculogenesis to the glomerular microvascular alterations in response to hyperglycaemia remain to be determined.

Vascular endothelial growth factor receptor-2 and low affinity VEGF binding sites on human glomerular endothelial cells: Biological effects and advanced glycosilation end products modulation

Vascular Endothelial Growth Factor (VEGF), binding to its receptor in endothelial cells, seems to modulate the increased blood flow in the early phase of diabetic renal disease. The aim of the study was to evaluate, in a diabetic milieu, the expression, biological function and modulation of VEGF binding sites in human glomerular endothelial cells (GENC). We demonstrated the presence of VEGF binding sites with high (VEGFR-2) and low (heparan sulfate proteoglycans, HSPG) affinity. VEGF165 and VEGF121 working through VEGFR-2 stimulated nitric oxide (NO) production at low doses (0.1-1 nM), whereas only VEGF165 at high doses (10-100 nM) increased thymidine incorporation. 1 nM VEGF165 and VEGF121 induced in GENC a significant peak of inducible NO synthase (iNOS) production and, at a lower level, of endothelial NOS (eNOS). The copresence of VEGF165 with aminoguanidine (iNOS inhibitor) determined an increase of eNOS and a significant increase in thymidine incorporation. Advanced glycation end products (AGEs) working through specific receptors (RAGE) up-regulated the expression of VEGFR-2, decreased the expression of HSPG sites and reduced GENC growth. These results identify in GENC VEGFR-2 as a mediator of iNOS and eNOS release under control of VEGF, whereas HSPG binding sites seem to mediate the weak growth effect. The presence of AGEs, up-regulating the VEGFR-2 and decreasing HSPG sites might participate to the block of glomerular angiogenesis addressing the VEGF effects on glomerular permeability.

Aldose reductase inhibition counteracts nitrosative stress and poly(ADP-ribose) polymerase activation in diabetic rat kidney and high-glucose-exposed human mesangial cells

Both increased aldose reductase (AR) activity and oxidative/nitrosative stress have been implicated in the pathogenesis of diabetic nephropathy, but the relation between the two factors remains a subject of debate. This study evaluated the effects of AR inhibition on nitrosative stress and poly(ADP-ribose) polymerase (PARP) activation in diabetic rat kidney and high-glucose-exposed human mesangial cells. In animal experiments, control (C) and streptozotocin-diabetic (D) rats were treated with/without the AR inhibitor fidarestat (F, 16 mg kg(-1) day(-1)) for 6 weeks starting from induction of diabetes. Glucose, sorbitol, and fructose concentrations were significantly increased in the renal cortex of D vs C (p < 0.01 for all three comparisons), and sorbitol pathway intermediate, but not glucose, accumulation, was completely prevented in D + F. F at least partially prevented diabetes-induced increase in kidney weight as well as nitrotyrosine (NT, a marker of peroxynitrite-induced injury and nitrosative stress), and poly(ADP-ribose) (a marker of PARP activation) accumulation, assessed by both immunohistochemistry and Western blot analysis, in glomerular and tubular compartments of the renal cortex. In vitro studies revealed the presence of both AR and PARP-1 in human mesangial cells, and none of these two variables were affected by high glucose or F treatment. Nitrosylated and poly(ADP-ribosyl)ated proteins (Western blot analysis) accumulated in cells cultured in 30 mM D-glucose (vs 5.55 mM glucose, p < 0.01), but not in cells cultured in 30 mM L-glucose or 30 mM D-glucose plus 10 microM F. AR inhibition counteracts nitrosative stress and PARP activation in the diabetic renal cortex and high-glucose-exposed human mesangial cells. These findings reveal new beneficial properties of the AR inhibitor F and provide the rationale for detailed studies of F on diabetic nephropathy.

High Glucose Blunts Vascular Endothelial Growth Factor Response to Hypoxiaviathe Oxidative Stress-Regulated Hypoxia-Inducible Factor/Hypoxia-Responsible Element Pathway

Vascular endothelial growth factor (VEGF) is an important survival factor for endothelial cells in hypoxic environments. High glucose regulates certain aspects of VEGF expression in various cell types, including proximal tubular cells. Thus, ambient glucose levels may modulate the progression of chronic kidney disease, especially diabetic nephropathy. Immortalized rat proximal tubular cells (IRPTC) were cultured for 24 h under hypoxic conditions (1% O(2)), with or without high d-glucose (25 mM), or with or without high l-glucose (25 mM). Controls included culture in normoxic conditions and normal d-glucose (5.5 mM). VEGF mRNA expression was assessed by real-time quantitative PCR, and VEGF protein in the supernatant was assessed by ELISA. Hypoxia increased VEGF expression. This response was significantly blunted by high d-glucose (1.98 +/- 0.11- versus 2.65 +/- 0.27-fold increase for VEGF mRNA expression, 252.8 +/- 14.7 versus 324.0 +/- 11.5 pg/10(5) cells for VEGF protein; P < 0.05 both) but not by high l-glucose. It is interesting that hydrogen peroxide also blunted this response, whereas alpha-tocopherol restored the VEGF response to hypoxia in the presence of high d-glucose. For determination of involvement of the hypoxia-inducible factor (HIF)/hypoxia-responsible element (HRE) pathway, IRPTC that were stably transfected with HRE-luciferase were cultured under the previous conditions. High d-glucose also reduced luciferase activity under hypoxia, whereas alpha-tocopherol restored activity. In vivo experiments using streptozotocin-induced diabetic rats confirmed that hyperglycemia blunted HIF-HRE pathway activation. Insulin treatment restored activation of the HIF-HRE pathway in streptozotocin-induced diabetic rats. In conclusion, high glucose blunts VEGF response to hypoxia in IRPTC. This effect is mediated by the oxidative stress-regulated HIF-HRE pathway.

Inhibition and reversibility of renal changes: lessons from diabetic kidney disease

This review describes the clinical characteristics of kidney disease in patients with diabetes in terms of functional and morphological changes, and summarizes the risk factors for progression of disease and the knowledge available today on various treatment modalities. New insights into the pathogenesis of kidney disease in diabetic patients are also reviewed in the context of the nephropathy of Fabry disease. Newly recognized pathways that play a role in the development/progression of kidney disease in patients with diabetes include metabolic factors, (e.g. advanced glycation end products), intracellular signalling proteins (e.g. protein kinase C) and growth factors/cytokines (e.g. growth hormone, insulin-like growth factors, transforming growth factor beta and vascular endothelial growth factor). As classic examples of progress in our understanding of the pathogenesis of kidney disease in patients with diabetes, the relationship between two growth factor/cytokine-systems and the development of diabetic kidney disease is reviewed, including a description of well-known or potential therapeutic strategies targeting the two systems.

CONCLUSION

It is hoped that the new pathogenetic insights into diabetic kidney disease may facilitate the development of new drugs for the treatment of this and related kidney diseases.

Angiotensin II stimulation of VEGF mRNA translation requires production of reactive oxygen species

ANG II, a mediator of renal injury in diabetic renal disease, promotes vascular endothelial growth factor (VEGF) mRNA translation in proximal tubular epithelial (MCT) cells (Feliers D, Duraisamy S, Barnes JL, Ghosh-Choudhury G, and Kasimath BS. Am J Physiol Renal Physiol 288: F521–F529, 2005). The mechanism by which ANG II elicits this effect is not known. ANG II is known to induce oxidative stress and the rapidity of the effect suggested a role for reactive oxygen species (ROS). The aim of this study is to test the hypothesis that ANG II regulates VEGF mRNA translation in MCT cells through ROS production. In MCT cells exposed to 1 nM ANG II, ROS production was increased in a time-dependent manner. Inhibition of ROS production by N-acetylcysteine (NAC), a precursor of glutathione, and diphenyleneiodonium (DPI), an inhibitor of flavoproteins that include NAD(P)H oxidase, prevented ANG II-stimulated VEGF protein expression. NAC and DPI also inhibited phosphorylation of 4E-BP1 on Thr46 and association of eIF4E with eIF4G, steps that are important in the initiation phase of mRNA translation. NAC and DPI also blocked Akt activation which is required for 4E-BP1 phosphorylation. LY-294002, a selective phosphatidylinositol (PI 3-kinase) inhibitor, did not prevent ROS accumulation in response to ANG II, whereas DPI blocked ANG II activation of PI 3-kinase, demonstrating that ROS production is upstream of the PI 3-kinase signaling pathway. Preincubation with catalase abolished ANG II stimulation of VEGF expression and mRNA translation, suggesting involvement of hydrogen peroxide (H2O2). H2O2reproduced the effects of ANG II on VEGF expression and aforementioned parameters of mRNA translation. Finally, neither preincubation of MCT cells with specific inhibitors of the mitochondrial respiratory chain nor inactivation of the mitochondrial respiratory chain in MCT cells prevented ANG II stimulation of VEGF expression. Inhibition of nitric oxide synthase by l-NAME had no effect on ANG II stimulation of VEGF expression. These data show that ROS, generated probably through activation of an NAD(P)H oxidase, mediate ANG II stimulation of VEGF mRNA translation.

SMP-534 ameliorates progression of glomerular fibrosis and urinary albumin in diabeticdb/dbmice

Diabetic nephropathy is currently the most common cause of end-stage renal disease. Diabetic nephropathy patients, whether insulin dependent or not, develop fibrotic changes in glomeruli that manifest as overt nephropathy. Previously, we demonstrated that 5-chloro-2-{(1E)-3-[2-(4-methoxybenzoyl)-4-methyl-1H-pyrrol-1-yl]prop-1-en-1-yl}- N-(methylsulfonyl)benzamide (SMP-534) reduces extracellular matrix (ECM) production induced by transforming growth factor-β (TGF-β) in vitro and prevents the accumulation of ECM in glomeruli in rat Thy-1 nephritis models. In this study, we examined the long-term effects of SMP-534 on renal insufficiency and glomerulosclerosis in db/db mice, which are models of type 2 diabetes. A diet containing SMP-534 was given to the mice from the age of 9 to 25 wk, and blood and urine analysis were performed at 8, 17, and 25 wk. At the end of study, kidney tissues were analyzed histologically. Treatment with SMP-534 dose dependently suppressed the increase of urinary albumin and type IV collagen excretion in db/db mice. The renal histological analysis showed that SMP-534 dose dependently suppressed the increase of mesangial expansion in the kidney. In the immunohistological analysis, fibronectin and type IV collagen expression were lower in SMP-534-treated db/db mice compared with vehicle-treated db/db mice. This study suggested that SMP-534 ameliorated the increase of ECM production in kidney of db/db mice, possibly through the inhibition of TGF-β action. Hence, antifibrotic agents such as SMP-534 might be a new therapeutic option for the treatment of diabetic nephropathy.

Uncoupling of vascular endothelial growth factor with nitric oxide as a mechanism for diabetic vasculopathy

The role of VEGF in vascular disease is complicated. Vascular endothelial growth factor (VEGF) expression can be deleterious in diabetic vasculopathy, especially in kidney and retina. In contrast, VEGF seems to be renoprotective in nondiabetic renal disease. VEGF exerts it biologic effects in association with nitric oxide (NO), yet it is known that NO bioavailability is reduced in diabetes. Thus, it was hypothesized that this diverse biologic effect of VEGF on diabetic vasculopathy is due to uncoupling of VEGF with NO. VEGF stimulated NO production in a dose-dependent manner in bovine aortic endothelial cells (BAEC), and this was inhibited by either high glucose or Nomega-nitro-l-arginine methyl ester (L-NAME) treatment. Endothelial NO synthase phosphorylation by VEGF was also inhibited by high glucose. It is interesting that both high glucose and L-NAME enhanced the proliferative response of endothelial cells, which was prevented by an NO donor. Furthermore, high glucose as well as L-NAME stimulated VEGF and kinase-insert domain receptor (KDR) (VEGF receptor 2) mRNA expression in BAEC. These data suggest that the uncoupling of VEGF with NO enhances endothelial cell proliferation via the KDR pathway. Compatible with these findings, a KDR antagonist blocked this response. In addition, a VEGF mutant, which binds only KDR, induced extracellular signal-regulated kinase (ERK) activation, and inhibition of ERK completely blocked endothelial cell proliferation under this condition, suggesting a role of the KDR-ERK1/2 pathway on endothelial cell proliferation. In conclusion, high glucose causes an uncoupling of VEGF with NO, which enhances endothelial cell proliferation via activation of the KDR-ERK1/2 pathway. These results may provide new insights into the understanding of the mechanism of diabetic vascular disease.

Therapeutic potential of angiostatin in diabetic nephropathy

Angiostatin is a proteolytic fragment of plasminogen and a potent angiogenic inhibitor. Previous studies have shown that angiostatin inhibits retinal neovascularization and reduces retinal vascular permeability in diabetic retinopathy. Here, it is reported for the first time that angiostatin is also implicated in diabetic nephropathy (DN). Angiostatin levels are dramatically decreased in the kidney of streptozotocin-induced diabetic rats. Consistently, diabetic kidneys also showed decreased expression and proteolytic activities of matrix metalloproteinase-2, an enzyme that releases angiostatin from plasminogen. Adenovirus-mediated delivery of angiostatin significantly alleviated albuminuria and attenuated the glomerular hypertrophy in diabetic rats. Moreover, angiostatin treatment downregulated the expression of vascular endothelial growth factor and TGF-beta1, two major pathogenic factors of DN, in diabetic kidneys. In cultured human mesangial cells, angiostatin blocked the overexpression of vascular endothelial growth factor and TGF-beta1 that were induced by high glucose while increasing the levels of pigment epithelium-derived factor, an endogenous inhibitor of DN. Moreover, angiostatin effectively inhibited the high-glucose-and TGF-beta1-induced overproduction of proinflammatory factors and extracellular matrix proteins via blockade of the Smad signaling pathway. These findings suggest that the decrease of angiostatin levels in diabetic kidney may contribute to the pathologic changes such as inflammation and fibrosis in DN. Therefore, angiostatin has therapeutic potential in DN as a result of its anti-inflammatory and antifibrosis activities.

VEGF regulation of endothelial nitric oxide synthase in glomerular endothelial cells

BACKGROUND

Vascular endothelial growth factor (VEGF) regulation of endothelial nitric oxide synthase (eNOS) and signaling pathways involved have not been well studied in glomerular endothelial cells (GENCs).

METHODS

GENCs grown from tsA58 Immortomice were used. Immunoblotting and in-cell Western blot analysis were employed to assess changes in VEGF receptor signaling pathway and eNOS phosphorylation of ser1177. Immunokinase assay and immunoblotting with phosphospecific antibodies were performed to assess activity of kinases.

RESULTS

VEGF rapidly induced tyrosine phosphorylation of type 1 and type 2 VEGF receptors. Physical association between VEGF-receptor 2 (VEGF-R2) and insulin receptor substrate (IRS-1) and phosphatidylinositol 3'-kinase (PI3K) was induced by VEGF, which augmented PI3K activity in VEGF-R2 immunoprecipitates. VEGF stimulated Akt phosphorylation in a PI3K-dependent manner. VEGF increased eNOS phosphorylation on Ser1177. Activation of eNOS was associated with nitric oxide generation as measured by medium nitrite content. Signaling mechanisms involved in VEGF stimulation of eNOS were explored. VEGF-induced eNOS phosphorylation was abolished by SU1498, a VEGF-R2 inhibitor, LY294002, a PI3K inhibitor, and infection of cells with an adenovirus carrying a dominant negative-mutant of Akt, demonstrating the requirement of the VEGF-R2/IRS-1/PI3K/Akt axis for activation of eNOS. VEGF also activated extracellular signal-regulated protein kinase (ERK) in a time-dependent manner; and VEGF-stimulated eNOS phosphorylation on Ser1177 was prevented by PD098059, an upstream inhibitor of ERK, demonstrating that ERK was involved in VEGF regulation of eNOS. ERK phosphorylation was abolished by LY294002, suggesting ERK was downstream of PI3K in VEGF-treated GENC.

CONCLUSIONS

Our data demonstrate that in GENC, VEGF stimulates VEGF-R2/IRS-1/PI3K/Akt axis to regulate eNOS phosphorylation on Ser1177 in conjunction with the ERK signaling pathway.

Temporal expression profile and distribution pattern indicate a role of connective tissue growth factor (CTGF/CCN-2) in diabetic nephropathy in mice

Connective tissue growth factor (CTGF) is overexpressed in diabetic nephropathy (DN) and has therefore been implicated in its pathogenesis. The objective of the present study was to determine the tissue distribution of increased CTGF expression and the relationship of plasma, urinary, and renal CTGF levels to the development and severity of DN. We studied the relationship between CTGF and renal pathology in streptozotocin (STZ)-induced diabetes in C57BL/6J mice. Diabetic and age-matched control mice were killed after 1, 2, 4, and 9 wk of diabetes. In addition, key parameters of diabetes and DN were analyzed in 10-mo-old diabetic ob/ob mice and their ob/+ littermates. STZ-induced diabetic mice showed a significantly increased urinary albumin excretion after 1 wk and increased mesangial matrix score after 2 wk. Increased renal fibronectin, fibronectin ED-A, and collagen IValpha1 expression, as well as elevated plasma creatinine levels, were observed after 9 wk. After 2 wk, CTGF mRNA was upregulated threefold in the renal cortex. By 9 wk, CTGF mRNA was also increased in the heart and liver. In contrast, transforming growth factor-beta1 mRNA content was significantly increased only in the kidney by 9 wk. Renal CTGF expression was mainly localized in podocytes and parietal glomerular epithelial cells, and less prominent in mesangial cells. In addition, plasma CTGF levels and urinary CTGF excretion were increased in diabetic mice. Moreover, albuminuria strongly correlated with urinary CTGF excretion (R = 0.83, P < 0.0001). Increased CTGF expression was also demonstrated in type 2 diabetic ob/ob mice, which points to a causal relationship between diabetes and CTGF and thus argues against a role of STZ in this process. The observed relationship of podocyte and urinary CTGF to markers of DN suggests a pathogenic role of CTGF in the development of DN.

A neutralizing VEGF antibody prevents glomerular hypertrophy in a model of obese type 2 diabetes, the Zucker diabetic fatty rat

BACKGROUND

Antagonism of vascular endothelial growth factor (VEGF) has improved the outcome in experimental nephropathies of various origins, including diabetic nephropathy in a type 1 diabetic rat model and a type 2 diabetic mouse model. Neutralizing VEGF antibodies prevented glomerular hypertrophy in these models. We examined the renal effects of VEGF blockade in an obese rat model of type 2 diabetic nephropathy and investigated the mechanism underlying the inhibition of glomerular hypertrophy.

METHODS

Twenty female Zucker diabetic fatty (ZDF) rats, fed a high-fat diet and aged 10 weeks, were treated with VEGF antibodies or an irrelevant isotype-matched IgG. Ten heterozygous (fa/+) littermates served as additional non-diabetic, lean controls. Urinary albumin excretion (UAE) and creatinine clearance (CrCl) were assessed at baseline, and at 3 and 5 weeks. Kidney weight and glomerular volume were determined at the end of the study. Glomerular apoptosis was examined with anti-active caspase-3 immunohistochemistry.

RESULTS

All obese animals had established diabetes, hyperlipidaemia and normal blood pressure, which were not influenced by VEGF antibody treatment. ZDF control rats had increased UAE, CrCl, kidney weights and glomerular volumes compared with non-diabetic, lean control rats. VEGF antibody treatment prevented the glomerular hypertrophy, but did not affect UAE, CrCl and kidney weight. Glomerular anti-active caspase-3 immunostaining was not different between the groups.

CONCLUSIONS

Inhibition of VEGF prevented early glomerular hypertrophy in ZDF rats with established diabetes. Increased apoptosis of glomerular endothelial cells does not appear to underly the inhibition of glomerular growth.

Evidence linking glycated albumin to altered glomerular nephrin and VEGF expression, proteinuria, and diabetic nephropathy

BACKGROUND

Albumin modified by Amadori-glucose adducts has been linked to the development of diabetic nephropathy through its ability, independent of hyperglycemia, to activate protein kinase C-beta (PKC-beta), up-regulate the transforming growth factor-beta (TGF-beta) system, and stimulate expression of extracellular matrix proteins in glomerular cells, and by the demonstration that reducing the burden of glycated albumin ameliorates renal structural and functional abnormalities in the db/db mouse.

METHODS

To probe whether the salutary effects consequent to lowering glycated albumin, which include reduction of albuminuria, relate to an influence of the Amadori-modified protein on nephrin, the podocyte protein critical to regulation of protein excretion, and on the angiogenic vascular endothelial growth factor (VEGF), which induces microvascular permeability, diabetic db/db mice were treated with a small molecule that inhibits the nonenzymatic glycation of albumin.

RESULTS

Compared to nondiabetic db/m mice, diabetic controls exhibited increased urinary excretion of albumin and type IV collagen, elevated renal TGF-beta1 protein levels, reduced glomerular nephrin immunofluorescence and nephrin protein by immunoblotting, and increased glomerular VEGF immunostaining and renal VEGF protein content. Diabetic animals receiving test compound showed significant lowering of proteinuria, normalization of renal TGF-beta1 protein, and significant restoration of altered glomerular nephrin and VEGF expression.

CONCLUSION

The findings causally implicate the increased glycated albumin associated with the diabetic state in the abnormal renal nephrin and VEGF expression found in diabetes, thereby promoting proteinuria and glomerulosclerosis.

Antiangiogenic endostatin peptide ameliorates renal alterations in the early stage of a type 1 diabetic nephropathy model

Diabetic nephropathy is one of the major microvascular complications in diabetes and is the leading cause of end-stage renal disease worldwide. Among various factors, angiogenesis-associated factors such as vascular endothelial growth factor (VEGF)-A and angiopoietin (Ang)-2 are involved in the development of diabetic nephropathy. We previously reported the therapeutic efficacy of antiangiogenic tumstatin peptide in the early diabetic nephropathy model. Here, we examine the effect of endostatin peptide, a potent inhibitor of angiogenesis derived from type XVIII collagen, in preventing progression in the type 1 diabetic nephropathy mouse model. Endostatin peptide did not affect hyperglycemia induced by streptozotocin (STZ). Glomerular hypertrophy, hyperfiltration, and albuminuria were significantly suppressed by endostatin peptide (5 mg/kg) in STZ-induced diabetic mice. Glomerular mesangial matrix expansion, the increase of glomerular type IV collagen, endothelial area (CD31(+)), and F4/80(+) monocyte/macrophage accumulation were significantly inhibited by endostatin peptide. Increase in the renal expression of VEGF-A, flk-1, Ang-2, an antagonist of angiopoietin-1, transforming growth factor-beta1, interleukin-6, and monocyte chemoattractant protein-1 was inhibited by endostatin peptide in diabetic mice. Decrease of nephrin mRNA and protein in diabetic mice was suppressed by treatment with endostatin peptide. The level of endostatin in the renal cortex and sera was increased in diabetic mice. Endogenous renal levels of endostatin were decreased in endostatin peptide-treated groups in parallel with VEGF-A. Although serum levels of endostatin were decreased in the low-dose endostatin-peptide group, high-dose administration resulted in elevated serum levels of endostatin. These results demonstrate the potential use of antiangiogenic endostatin peptide as a novel therapeutic agent in diabetic nephropathy.

HMG CoA reductase inhibition modulates VEGF-induced endothelial cell hyperpermeability by preventing RhoA activation and myosin regulatory light chain phosphorylation

The beneficial effects of statins are usually assumed to stem from their ability to reduce cholesterol biosynthesis. However, because statins are potent inhibitors of the mevalonate, which governs diverse cell signaling pathways, inhibition of 3-hydroxy-3-methylglutaryl-coenzyme-A reductase may also result in pleiotropic effects. The present study describes a novel pleiotropic effect of statins on vascular endothelial growth factor (VEGF)-induced glomerular endothelial cell (GEnC) hyperpermeability. Using live cell imaging with green fluorescent protein-tagged myosin regulatory light chain (MLC) and correlative biochemical analyses, we investigated 1) VEGF signaling pathway leading to GEnC hyperpermeability and 2) the modulatory effects of statins on VEGF signaling. Our findings indicate that VEGF stimulation elicits a robust increase in GEnC permeability. The signaling pathway that mediates VEGF-induced GEnC hyperpermeability involves RhoA activation leading to actin cytoskeletal remodeling, MLC diphosphorylation, and enhanced paracellular gap formation. Remarkably, cotreatment of endothelial cells with simvastatin, a hydrophobic statin, reversed VEGF-induced GEnC hyperpermeability by preventing MLC diphosphorylation, and cytoskeletal remodeling. In summary, this study identifies RhoA and MLC phosphorylation as key mediators of VEGF-induced endothelial cell hyperpermeability and demonstrates the modulatory effects of statins on VEGF signaling pathway.

Phospholipase Cγ-Erk Axis in Vascular Endothelial Growth Factor-induced Eukaryotic Initiation Factor 4E Phosphorylation and Protein Synthesis in Renal Epithelial Cells

Vascular endothelial growth factor (VEGF) increases protein synthesis and induces hypertrophy in renal tubular epithelial cells (Senthil, D., Choudhury, G. G., McLaurin, C., and Kasinath, B. S. (2003) Kidney Int. 64, 468-479). We examined the role of Erk1/2 MAP kinase in protein synthesis induced by VEGF. VEGF stimulated Erk phosphorylation that was required for induction of protein synthesis. VEGF-induced Erk activation was not dependent on phosphoinositide (PI) 3-kinase activation but required sequential phosphorylation of type 2 VEGF receptor, PLCgamma and c-Src, as demonstrated by inhibitors SU1498, U73122, and PP1, respectively. c-Src phosphorylation was inhibited by U73122, indicating it was downstream of phospholipase (PL)Cgamma. Studies with PP1/2 showed that phosphorylation of c-Src was required for tyrosine phosphorylation of Raf-1, an upstream regulator of Erk. VEGF also stimulated phosphorylation of Pyk-2; VEGF-induced phosphorylation of Pyk2, c-Src and Raf-1 could be abolished by BAPTA/AM, demonstrating requirement for induction of intracellular calcium currents. We examined the downstream events following the phosphorylation of Erk. VEGF stimulated phosphorylation of Mnk1 and eIF4E and induced Mnk1 to shift from the cytoplasm to the nucleus upon phosphorylation. VEGF-induced phosphorylation of Mnk1 and eIF4E required phosphorylation of PLCgamma, c-Src, and Erk. Expression of dominant negative Mnk1 abrogated eIF4E phosphorylation and protein synthesis induced by VEGF. VEGF-stimulated protein synthesis could be blocked by inhibition of PLCgamma by a chemical inhibitor or expression of a dominant negative construct. Our data demonstrate that VEGF-stimulated protein synthesis is Erk-dependent and requires the activation of VEGF receptor 2, PLCgamma, c-Src, Raf, and Erk pathway. VEGF also stimulates Erk-dependent phosphorylation of Mnk1 and eIF4E, crucial events in the initiation phase of protein translation.

PPARγ agonists diminish serum VEGF elevation in diet-induced insulin resistant SD rats and ZDF rats

We investigated the effect of peroxisome proliferator-activated receptor gamma (PPARgamma) agonists on serum vascular endothelial growth factor (VEGF) in diet-induced insulin resistant SD rats and ZDF rats. SD rats fed a high fat/sucrose diet showed increases in serum insulin and VEGF (both p < 0.01). Treatment with a PPARgamma agonist GI262570 normalized the diet-elevated insulin and VEGF (both p < 0.01). There was a positive correlation between serum insulin and VEGF (p < 0.05) in SD rats. ZDF rats had higher serum glucose, insulin, and VEGF than Zucker lean rats (all p < 0.01). Treatment of ZDF rats with PPARgamma agonist pioglitazone decreased serum glucose and VEGF (both p <0.01). There was a positive correlation between glucose and VEGF in ZDF rats (p < 0.05). In 3T3-L1 adipocytes, GI262570 did not affect insulin-stimulated VEGF secretion. These studies demonstrated that hyperinsulinemia in SD rats and hyperglycemia in ZDF rats were associated with increased serum VEGF; PPARgamma agonists normalized serum insulin, glucose, and VEGF, but did not affect VEGF secretion in vitro.

Regulation of renal lipid metabolism, lipid accumulation, and glomerulosclerosis in FVBdb/db mice with type 2 diabetes

Diabetic kidney disease has been associated with the presence of lipid deposits, but the mechanisms for the lipid accumulation have not been fully determined. In the present study, we found that db/db mice on the FVB genetic background with loss-of-function mutation of the leptin receptor (FVB-Lepr(db) mice or FVBdb/db) develop severe diabetic nephropathy, including glomerulosclerosis, tubulointerstitial fibrosis, increased expression of type IV collagen and fibronectin, and proteinuria, which is associated with increased renal mRNA abundance of transforming growth factor-beta, plasminogen activator inhibitor-1, and vascular endothelial growth factor. Electron microscopy demonstrates increases in glomerular basement membrane thickness and foot process (podocyte) length. We found that there is a marked increase in neutral lipid deposits in glomeruli and tubules by oil red O staining and biochemical analysis for cholesterol and triglycerides. We also detected a significant increase in the renal expression of adipocyte differentiation-related protein (adipophilin), a marker of cytoplasmic lipid droplets. We examined the expression of sterol regulatory element-binding protein (SREBP)-1 and -2, transcriptional factors that play an important role in the regulation of fatty acid, triglyceride, and cholesterol synthesis. We found significant increases in SREBP-1 and -2 protein levels in nuclear extracts from the kidneys of FVBdb/db mice, with increases in the mRNA abundance of acetyl-CoA carboxylase, fatty acid synthase, and 3-hydroxy-3-methylglutaryl-CoA reductase, which mediates the increase in renal triglyceride and cholesterol content. Our results indicate that in FVBdb/db mice, renal triglyceride and cholesterol accumulation is mediated by increased activity of SREBP-1 and -2. Based on our previous results with transgenic mice overexpressing SREBP-1 in the kidney, we propose that increased expression of SREBPs plays an important role in causing renal lipid accumulation, glomerulosclerosis, tubulointerstitial fibrosis, and proteinuria in mice with type 2 diabetes.

Impaired vascular function during short-term poor glycaemic control in Type 1 diabetic patients

AIM

To study the effects of short-term poor glycaemic control on vascular function in Type 1 diabetic patients.

METHODS

Ten Type 1 diabetic patients, with diabetes duration of less than 10 years and normal urinary albumin excretion and ophthalmoscopy, were studied. All patients were examined after 48 h of good vs. poor glycaemic control within a 3-week period. Blood glucose was measured seven times daily for 2 days before each examination. External ultrasound was used to measure the dilatory response of the brachial artery to post-ischaemic increased blood flow (endothelium-dependent dilation) and to nitroglycerin (endothelium-independent dilation). Plasma concentration of von Willebrand factor antigen, adhesion molecules, vascular endothelial growth factor, homocystein and cholesterol were also measured.

RESULTS

The median blood glucose levels in the 48 h before the examinations were [median (range), good vs. poor control]: 6.3 (5.0-7.6) vs. 15.9 (11.3-17.8) (mmol/l). The flow-associated vasodilation (% of baseline) was reduced during poor control: 102.7 (94.7-110.8) vs. 104.0 (99.6-118.5) (P < 0.05) as were the nitroglycerin-induced dilation (% of baseline): 114.5 (103.3-127.9) vs. 120.2 (106.8-148.0) (P < 0.05). P-von Willebrand factor antigen was high during poor control (kIU/l): 1.14 (0.73-1.84) vs. 0.86 (0.72-1.39) (P < 0.05) and so was P-vascular endothelial growth factor (ng/l): 288 (133-773) vs. 254 (90-383) (P < 0.05).

CONCLUSIONS

Short-term (48 h) hyperglycaemia in Type 1 diabetic patients may disturb vascular function, possibly mediated through smooth muscle cell dysfunction as well as endothelial dysfunction. We suggest that prolonged and repeated episodes of hyperglycaemia could possibly lead to permanent vascular dysfunction and thereby development and progression of vascular complications in diabetes.

Vascular endothelial growth factor (VEGF) and soluble VEGF receptor FLT-1 in diabetic nephropathy

BACKGROUND

Vascular endothelial growth factor (VEGF) and its receptors have been implicated in the pathogenesis of diabetic nephropathy. The objective of this study was to determine whether alterations of the plasma and urinary VEGF and sFLT-1 levels were related to the stages and risk factors of diabetic nephropathy. In addition, we also examined the regulation of the VEGF/sFLT-1 expression by various stimuli in cultured human proximal tubule cells (HPTC).

METHODS

A total of 107 type 2 diabetic patients and 47 healthy control subjects were studied. The expression and protein levels of VEGF and sFLT-1 were measured by semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) and enzyme-linked immunosorbent assay (ELISA).

RESULTS

The urinary VEGF and sFLT-1 excretions were significantly increased in the microalbuminuric and proteinuric diabetic patients. The urinary VEGF levels were positively correlated with the urinary albumin to creatinine ratio (ACR), urinary sFLT-1 levels, and negatively correlated with creatinine clearance. The urinary sFLT-1 levels also showed a positive relationship with the urinary ACR. In cultured HPTC, high glucose stimuli rapidly up-regulated VEGF synthesis without having any effect on sFLT-1 synthesis. Interestingly, angiotensin II (Ang II) induced a dose-dependent increase in the synthesis of both VEGF and sFLT-1, which was significantly blocked by losartan.

CONCLUSION

The urinary excretion of VEGF and sFLT-1 increased at a relatively early stage in diabetic nephropathy associated with urinary albumin excretion. A marked increase in both VEGF/sFLT-1 synthesis in response to Ang II was observed in HPTC, which was different from the response to glucose stimuli. These findings may imply that VEGF and sFLT-1 can actively take part in the pathogenesis of diabetic nephropathy.

From the periphery of the glomerular capillary wall toward the center of disease: podocyte injury comes of age in diabetic nephropathy

Nephropathy is a major complication of diabetes. Alterations of mesangial cells have traditionally been the focus of research in deciphering molecular mechanisms of diabetic nephropathy. Injury of podocytes, if recognized at all, has been considered a late consequence caused by increasing proteinuria rather than an event inciting diabetic nephropathy. However, recent biopsy studies in humans have provided evidence that podocytes are functionally and structurally injured very early in the natural history of diabetic nephropathy. The diabetic milieu, represented by hyperglycemia, nonenzymatically glycated proteins, and mechanical stress associated with hypertension, causes downregulation of nephrin, an important protein of the slit diaphragm with antiapoptotic signaling properties. The loss of nephrin leads to foot process effacement of podocytes and increased proteinuria. A key mediator of nephrin suppression is angiotensin II (ANG II), which can activate other cytokine pathways such as transforming growth factor-beta (TGF-beta) and vascular endothelial growth factor (VEGF) systems. TGF-beta1 causes an increase in mesangial matrix deposition and glomerular basement membrane (GBM) thickening and may promote podocyte apoptosis or detachment. As a result, the denuded GBM adheres to Bowman's capsule, initiating the development of glomerulosclerosis. VEGF is both produced by and acts upon the podocyte in an autocrine manner to modulate podocyte function, including the synthesis of GBM components. Through its effects on podocyte biology, glomerular hemodynamics, and capillary endothelial permeability, VEGF likely plays an important role in diabetic albuminuria. The mainstays of therapy, glycemic control and inhibition of ANG II, are key measures to prevent early podocyte injury and the subsequent development of diabetic nephropathy.