Human podocytes express angiopoietin 1, a potential regulator of glomerular vascular endothelial growth factor

Adenovirus-mediated gene transfer of TGF-β1 to the renal glomeruli leads to proteinuria

The mechanism of proteinuria in many common kidney diseases involves glomerular hemodynamic effects and local expression of angiogenic, fibrogenic, and vasoactive factors. Transforming growth factor (TGF)-β has been associated with many diseases involving proteinuria and renal fibrosis. TGF-β has been shown to induce podocyte dedifferentiation in vitro, but its in vivo effects on the glomerular filtration barrier are not well described. In this study, we used an adenovirus vector to transfer active TGF-β1 to the glomeruli of rat kidneys. Transient TGF-β1 overexpression induced significant proteinuria, podocyte foot process effacement, nephrin down-regulation, and nephrinuria. The expression of synaptopodin was also significantly down-regulated by TGF-β1. Increased glomerular expression of Snail, suggestive of an in vivo dedifferentiation process, was associated with a loss of podocyte epithelial markers. The expression of angiopoietin-1 and angiopoietin-2 was significantly increased in TGF-β1-transfected glomeruli, and TGF-β1 increased the expression of the angiopoietin receptor, Tie2, in podocyte cell culture. TGF-β1 down-regulated nephrin and synaptopodin expression in podocytes in cell culture; this effect was reversed by the blockade of both angiopoietin and Tie2 activities. These findings suggest that locally produced TGF-β1 can cause podocyte dedifferentiation marked by a loss of synaptopodin, nephrin, and foot process effacement, partly regulated by angiopoietins. This process represents a novel pathway that may explain proteinuria in a variety of common renal diseases.

Immunohistochemical detection of the angiopoietins during porcine metanephric kidney development

Angiopoietins are growth factors involved in vascular development. They also play an important role in the development of the kidney vasculature. The localization of these growth factors was immunohistochemically investigated in developing porcine metanephric kidneys. Angiopoietin 1 was predominantly present in the maturing glomeruli, while angiopoietin 2 was observed in the early developing glomeruli as well as in maturing glomeruli. Furthermore, angiopoietin 2 was observed in the muscle layer of renal arteries, in the convoluted tubules and in the loops of Henle. In contrast to the situation in the mouse in which angiopoietin 2 has been reported to be mainly expressed in mesangial cells near the glomerular hilus, expression of angiopoietin 2 in the porcine metanephric kidney was observed in the podocytes of early developing glomeruli, but not in the cells near the glomerular hilus. The results of this study support the hypothesis that the angiopoietins play an important role during mammalian metanephric development and during glomerulogenesis in particular, but indicate that species specific characteristics must be taken into account when evaluating their involvement in glomerulogenesis.

Angiopoietin-1 is essential in mouse vasculature during development and in response to injury

Angiopoietin-1/Tek signaling is a critical regulator of blood vessel development, with conventional knockout of angiopoietin-1 or Tek in mice being embryonically lethal due to vascular defects. In addition, angiopoietin-1 is thought to be required for the stability of mature vessels. Using a Cre-Lox conditional gene targeting approach, we have studied the role of angiopoietin-1 in embryonic and adult vasculature. We report here that angiopoietin-1 is critical for regulating both the number and diameter of developing vessels but is not required for pericyte recruitment. Cardiac-specific knockout of angiopoietin-1 reproduced the phenotype of the conventional knockout, demonstrating that the early vascular abnormalities arise from flow-dependent defects. Strikingly, deletion in the entire embryo after day E13.5 produced no immediate vascular phenotype. However, when combined with injury or microvascular stress, angiopoietin-1 deficiency resulted in profound organ damage, accelerated angiogenesis, and fibrosis. These findings redefine our understanding of the biological roles of angiopoietin-1: it is dispensable in quiescent vessels but has a powerful ability to modulate the vascular response after injury.

Expression profiles of podocytes exposed to high glucose reveal new insights into early diabetic glomerulopathy

Podocyte injury has been suggested to have a pivotal role in the pathogenesis of diabetic glomerulopathy. To glean insights into molecular mechanisms underlying diabetic podocyte injury, we generated temporal global gene transcript profiles of podocytes exposed to high glucose for a time interval of 1 or 2 weeks using microarrays. A number of genes were altered at both 1 and 2 weeks of glucose exposure compared with controls grown under normal glucose. These included extracellular matrix modulators, cell cycle regulators, extracellular transduction signals and membrane transport proteins. Novel genes that were altered at both 1 and 2 weeks of high-glucose exposure included neutrophil gelatinase-associated lipocalin (LCN2 or NGAL, decreased by 3.2-fold at 1 week and by 7.2-fold at 2 weeks), endothelial lipase (EL, increased by 3.6-fold at 1 week and 3.9-fold at 2 week) and UDP-glucuronosyltransferase 8 (UGT8, increased by 3.9-fold at 1 week and 5.0-fold at 2 weeks). To further validate these results, we used real-time PCR from independent podocyte cultures, immunohistochemistry in renal biopsies and immunoblotting on urine specimens from diabetic patients. A more detailed time course revealed changes in LCN2 and EL mRNA levels as early as 6 hours and in UGT8 mRNA level at 12 hours post high-glucose exposure. EL immunohistochemistry on human tissues showed markedly increased expression in glomeruli, and immunoblotting readily detected EL in a subset of urine samples from diabetic nephropathy patients. In addition to previously implicated roles of these genes in ischemic or oxidative stress, our results further support their importance in hyperglycemic podocyte stress and possibly diabetic glomerulopathy pathogenesis and diagnosis in humans.

Angiogenesis and chronic kidney disease

The number of patients requiring renal replacement therapy due to end-stage renal disease (ESRD) is increasing worldwide. The prevalence of chronic kidney disease (CKD), and the importance of CKD as a risk factor in development of ESRD and in complicating cardiovascular disease (CVD) have been confirmed. In recent years, the involvement of angiogenesis-related factors in the progression of CKD has been studied, and the potential therapeutic effects on CKD of modulating these factors have been identified. Vascular endothelial growth factor (VEGF)-A, a potent pro-angiogenic factor, is involved in the development of the kidney, in maintenance of the glomerular capillary structure and filtration barrier, and in the renal repair process after injury. VEGF-A is also involved in the development of early diabetic nephropathy, demonstrated by the therapeutic effects of anti-VEGF-A antibody. Angiopoietin (Ang)-1 induces the maturation of newly formed blood vessels, and the therapeutic effects of Ang-1 in diabetic nephropathy have been described. In experimental models of diabetic nephropathy, the therapeutic effects of angiogenesis inhibitors, including angiostatin, endostatin and tumstatin peptides, the isocoumarin NM-3, and vasohibin-1, have been reported.

Further analysis of the involvement of angiogenesis-related factors in the development of CKD is required. Determining the disease stage at which therapy is most effective and developing an effective drug delivery system targeting the kidney will be essential for pro-or anti-angiogenic strategies for patients with CKD.

Angiopoietin-like protein 3 regulates the motility and permeability of podocytes by altering nephrin expression in vitro

It is well known that podocyte injury plays a vital role in massive proteinuria. The increase of podocyte motility results in podocyte foot process (FP) effacement, a typical form of podocyte injury. Our previous studies demonstrated that glomerular podocytes can express angiopoietin-like protein 3 (ANGPTL3) and that the increase of ANGPTL3 in dysfunctional glomerulus is correlated with podocyte FP effacement. Little is known, however, about the role of ANGPTL3 in podocyte injury. In this study, we investigated ANGPTL3's effect on the motility and permeability of podocytes and on the expression of nephrin, a key molecule in podocytes. By scrape-wound and transwell migration assay, we found that ANGPTL3 over-expression significantly increased podocyte motility, whereas after ANGPTL3 knockdown by RNA interference, motility remained the same as that of the control group. Adriamycin (ADR) treatment significantly promoted podocyte motility. However, the same dose of ADR treatment could not promote motility after the knockdown of ANGPTL3. In addition, we assayed the diffusion of FITC-BSA across the podocytes' monolayer to investigate whether ANGPTL3 could promote protein loss by means of an increase in podocyte motility. The results showed that the changes in the FITC-BSA permeability of the podocytes corresponded to changes in motility. Furthermore, we found that ANGPTL3 over-expression dramatically increased the expression of nephrin but that the up-regulation of nephrin induced by ADR was significantly inhibited when ANGPTL3 was diminished by RNAi. In conclusion, we found ANGPTL3 to be capable of regulating the motility and permeability of podocytes and that the mechanism of ANGPTL3's regulation could be associated with the altered expression of nephrin.

Clinical and genetic correlates of circulating angiopoietin-2 and soluble Tie-2 in the community

BACKGROUND

Experimental studies suggest that endothelial growth factors play an important role in angiogenesis and vascular remodeling. The clinical and genetic correlates of circulating angiopoietin-2 (Ang-2) and its soluble receptor/regulator Tie-2 (sTie-2) have not been determined in a community-based sample.

METHODS AND RESULTS

Serum Ang-2 and sTie-2 were assayed in 3778 third-generation cohort participants of the Framingham Heart Study (mean age, 40+/-9 years; 53% women). Clinical correlates and heritability of both biomarkers were assessed using generalized estimating equations and variance-component analyses. Ang-2 levels were higher and sTie-2 levels were lower in women than in men. Ang-2 was positively related to age, smoking, systolic blood pressure, hypertension treatment, and diabetes (P<0.05 for all) but was inversely associated with total cholesterol and diastolic blood pressure (P<0.0001 for both), and sTie-2 was positively associated with body mass index, diabetes, and triglycerides but was inversely related to age, alcohol consumption, and glomerular filtration rate (P<0.05 for all). Both Ang-2 and sTie-2 were higher in participants with metabolic syndrome (P<0.005), with stronger associations of Ang-2 with blood pressure traits and of sTie-2 with obesity-dyslipidemia components. Heritability estimates for Ang-2 and sTie-2 were 27% and 56%, respectively (P<0.0001). A region on chromosome 9 was significantly linked to circulating sTie-2 levels (logarithm of the odds score, 8.31).

CONCLUSION

Circulating levels of Ang-2 and sTie-2 are heritable traits associated with cardiovascular disease risk factors, including the metabolic syndrome. These observations are consistent with the notion that angiogenesis and vascular remodeling are determined in part by genetic influences and associated with metabolic risk factors.

Analysis of circulating hem-endothelial marker RNA levels in preterm infants

Background

Circulating endothelial cells may serve as novel markers of angiogenesis. These include a subset of hem-endothelial progenitor cells that play a vital role in vascular growth and repair. The presence and clinical implications of circulating RNA levels as an expression for hematopoietic and endothelial-specific markers have not been previously evaluated in preterm infants. This study aims to determine circulating RNA levels of hem-endothelial marker genes in peripheral blood of preterm infants and begin to correlate these findings with prenatal complications.

Methods

Peripheral blood samples from seventeen preterm neonates were analyzed at three consecutive post-delivery time points (day 3–5, 10–15 and 30). Using quantitative reverse transcription-polymerase chain reaction we studied the expression patterns of previously established hem-endothelial-specific progenitor-associated genes (AC133, Tie-2, Flk-1 (VEGFR2) and Scl/Tal1) in association with characteristics of prematurity and preterm morbidity.

Results

Circulating Tie-2 and SCL/Tal1 RNA levels displayed an inverse correlation to gestational age (GA). We observed significantly elevated Tie-2 levels in preterm infants born to mothers with amnionitis, and in infants with sustained brain echogenicity on brain sonography. Other markers showed similar expression patterns yet we could not demonstrate statistically significant correlations.

Conclusion

These preliminary findings suggest that circulating RNA levels especially Tie2 and SCL decline with maturation and might relate to some preterm complication. Further prospective follow up of larger cohorts are required to establish this association.

Safety, pharmacokinetics, and antitumor activity of AMG 386, a selective angiopoietin inhibitor, in adult patients with advanced solid tumors

PURPOSE AMG 386 is an investigational peptide-Fc fusion protein (ie, peptibody) that inhibits angiogenesis by preventing the interaction of angiopoietin-1 and angiopoietin-2 with their receptor, Tie2. This first-in-human study evaluated the safety, pharmacokinetics (PK), pharmacodynamics, and antitumor activity of AMG 386 in adults with advanced solid tumors. PATIENTS AND METHODS Patients in sequential cohorts received weekly intravenous AMG 386 doses of 0.3, 1, 3, 10, or 30 mg/kg. Results Thirty-two patients were enrolled on the study and received AMG 386. One occurrence of dose-limiting toxicity was seen at 30 mg/kg: respiratory arrest, which likely was caused by tumor burden that was possibly related to AMG 386. The most common toxicities were fatigue and peripheral edema. Proteinuria (n = 11) was observed without clinical sequelae. Only four patients (12%) experienced treatment-related toxicities greater than grade 1. A maximum-tolerated dose was not reached. PK was dose-linear and the mean terminal-phase elimination half-life values ranged from 3.1 to 6.3 days. Serum AMG 386 levels appeared to reach steady-state after four weekly doses, and there was minimal accumulation. No anti-AMG 386 neutralizing antibodies were detected. Reductions in volume transfer constant (K(trans); measured by dynamic contrast-enhanced magnetic resonance imaging) were observed in 10 patients (13 lesions) 48 hours to 8 weeks after treatment. One patient with refractory ovarian cancer achieved a confirmed partial response (ie, 32.5% reduction by Response Evaluation Criteria in Solid Tumors) and withdrew from the study with a partial response after 156 weeks of treatment; four patients experienced stable disease for at least 16 weeks. CONCLUSION Weekly AMG 386 appeared well tolerated, and its safety profile appeared distinct from that of vascular endothelial growth factor-axis inhibitors. AMG 386 also appeared to impact tumor vascularity and showed antitumor activity in this patient population.

Microalbuminuria--a biomarker of renal microvascular disease

Microalbuminuria (amount greater than 30-300 mg/day) reflects an abnormal glomerular capillary permeability to protein. It is usually dependent upon three mechanisms. First, loss of negatively charged surface of the glomerular capillary wall secondary to circulating toxic substances injury-namely, oxidative stress and proinflammatory cytokines-allows the albumin with negatively charged surface to freely escape into the urine. Second, intraglomerular hypertension and hemodynamic maladjustment secondary to glomerular endothelial dysfunction increases filtration pressure and enhances sized selective proteinuria leakage. Third, podocyte injury leads to a vicious cycle of hemodynamic maladjustment and endothelial and podocyte injuries. All three of these mechanisms induce glomerular endothelial injury and microalbuminuria, which reflects renal microvascular disease.

Cerebral arteriovenous malformations. Part 1: cellular and molecular biology

Object

The scientific understanding of the nature of arteriovenous malformations (AVMs) in the brain is evolving. It is clear from current work that AVMs can undergo a variety of phenomena, including growth, remodeling, and/or regression—and the responsible processes are both molecular and physiological. A review of these complex processes is critical to directing future therapeutic approaches. The authors performed a comprehensive review of the literature to evaluate current information regarding the genetics, pathophysiology, and behavior of AVMs.

Methods

A comprehensive literature review was conducted using PubMed to reveal the molecular biology of AVMs as it relates to their complex growth and behavior patterns.

Results

Growth factors involved in AVMs include vascular endothelial growth factor, fibroblast growth factor, transforming growth factor β, angiopoietins, fibronectin, laminin, integrin, and matrix metalloproteinases.

Conclusions

Understanding the complicated molecular milieu of developing AVMs is essential for defining their natural history. Growth factors, extracellular matrix proteins, and other molecular markers will be the key to unlocking novel targeted drug treatments for these brain malformations.

Glomerular endothelial cell fenestrations: an integral component of the glomerular filtration barrier

Glomerular endothelial cell (GEnC) fenestrations are analogous to podocyte filtration slits, but their important contribution to the glomerular filtration barrier has not received corresponding attention. GEnC fenestrations are transcytoplasmic holes, specialized for their unique role as a prerequisite for filtration across the glomerular capillary wall. Glomerular filtration rate is dependent on the fractional area of the fenestrations and, through the glycocalyx they contain, GEnC fenestrations are important in restriction of protein passage. Hence, dysregulation of GEnC fenestrations may be associated with both renal failure and proteinuria, and the pathophysiological importance of GEnC fenestrations is well characterized in conditions such as preeclampsia. Recent evidence suggests a wider significance in repair of glomerular injury and in common, yet serious, conditions, including diabetic nephropathy. Study of endothelial cell fenestrations is challenging because of limited availability of suitable in vitro models and by the requirement for electron microscopy to image these sub-100-nm structures. However, extensive evidence, from glomerular development in rodents to in vitro studies in human GEnC, points to vascular endothelial growth factor (VEGF) as a key inducer of fenestrations. In systemic endothelial fenestrations, the intracellular pathways through which VEGF acts to induce fenestrations include a key role for the fenestral diaphragm protein plasmalemmal vesicle-associated protein-1 (PV-1). The role of PV-1 in GEnC is less clear, not least because of controversy over existence of GEnC fenestral diaphragms. In this article, the structure-function relationships of GEnC fenestrations will be evaluated in depth, their role in health and disease explored, and the outlook for future study and therapeutic implications of these peculiar structures will be approached.

Roles of angiopoietins in kidney development and disease

Angiopoietins are a family of growth factors, the best studied being angiopoietin 1 (Ang-1), which binds to and tyrosine-phosphorylates endothelial Tie-2, causing enhanced survival and cell-cell stabilization. Ang-2 and Tie-1 downregulate Ang-1-induced Tie-2 signaling, and angiopoietin actions are further modified by vascular endothelial growth factor A and integrins. Metanephric capillaries express Tie genes, whereas metanephric mesenchyme, maturing tubules, and mature podocytes express Ang-1. Ang-1 null embryos begin to form blood vessels, but subsequent vascular remodeling fails, and analyses of chimeric wild-type/Tie null mutant embryos show that Tie genes are needed for renal endothelial survival. Ang-2 is transiently expressed in renal arterial smooth muscle and mesangial cells, and tubules around adult vasa rectae express Ang-2. Ang-2 null mice have increased pericytes around kidney cortical peritubular capillaries, perhaps an indirect consequence of upregulated Tie-2 signaling. Ang-1 therapies attenuate peritubular capillary loss in adult models of tubulointerstitial disease, although, in one study, this was accompanied by enhanced inflammation and fibrosis. Podocyte-directed Ang-2 transgenic overexpression causes glomerular endothelial apoptosis, downregulated nephrin expression, and increased albuminuria, and glomerular Ang-2 is upregulated in hyperglycemic and immune-mediated glomerulopathies. Thus, angiopoietins affect podocyte as well as glomerular endothelial biology, and imbalanced angiopoietin signaling contributes to glomerular pathobiology.

Vascular endothelial growth factor-C, a potential paracrine regulator of glomerular permeability, increases glomerular endothelial cell monolayer integrity and intracellular calcium

We have previously reported expression of vascular endothelial growth factor (VEGF)-A and -C in glomerular podocytes and actions of VEGF-A on glomerular endothelial cells (GEnC) that express VEGF receptor-2 (VEGFR-2). Here we define VEGFR-3 expression in GEnC and investigate the effects of the ligand VEGF-C. Renal cortex and cultured GEnC were examined by microscopy, and both cell and glomerular lysates were assessed by Western blotting. VEGF-C effects on trans-endothelial electrical resistance and albumin flux across GEnC monolayers were measured. The effects of VEGF-C156S, a VEGFR-3-specific agonist, and VEGF-A were also studied. VEGF-C effects on intracellular calcium ([Ca2+]i) were measured using a fluorescence technique, receptor phosphorylation was examined by immunoprecipitation assays, and phosphorylation of myosin light chain-2 and VE-cadherin was assessed by blotting with phospho-specific antibodies. GEnC expressed VEGFR-3 in tissue sections and culture, and VEGF-C increased trans-endothelial electrical resistance in a dose-dependent manner with a maximal effect at 120 minutes of 6.8 Omega whereas VEGF-C156S had no effect. VEGF-C reduced labeled albumin flux by 32.8%. VEGF-C and VEGF-A increased [Ca2+]i by 15% and 39%, respectively. VEGF-C phosphorylated VEGFR-2 but not VEGFR-3, myosin light chain-2, or VE-cadherin. VEGF-C increased GEnC monolayer integrity and increased [Ca2+]i, which may be related to VEGF-C-S particular receptor binding and phosphorylation induction characteristics. These observations suggest that podocytes direct GEnC behavior through both VEGF-C and VEGF-A.

The role of angiopoietin-1 in kidney disease

Injury to the renal microvasculature and inflammatory process may be major factors in the progression of renal disease, therefore, protection of the renal endothelial cell and regulation of inflammatory process may be an important therapeutic target of renal disease. Thus, we evaluated the protective effect of cartilage oligomeric matrix protein-angiopoietin-1 (COMP-Ang1) in unilateral ureteral obstruction (UUO)-induced renal fibrosis, cyclosporine A (CsA)-induced renal injury, and the diabetic nephropathy model. In the UUO model, morphologic examination indicated less tubular injury and tubulointerstitial fibrosis in mice that received COMP-Ang1 compared to vehicle-treated mice. Interstitial type I collagen, myofibroblast accumulation, renal surface microvasculature and renal blood flow were higher after treatment with COMP-Ang1 compared to vehicle-treated mice. COMP-Ang1 treatment decreased monocyte/macrophage infiltration, tissue levels of transforming growth factor β1, and Smad 2/3 phosphorylation and increased Smad 7 in the obstructed kidney. In CsA-induced renal injury, histologic examination showed significantly decreased CsA-induced tubular damage and tubulointerstitial fibrosis in COMP-Ang1 treated mice. COMP-Ang1 administration also decreased increased macrophage infiltration, adhesion molecule expression, TGF-β1, and Smad 2/3 levels in CsA-treated kidneys, while increasing Smad 7 levels. Laser-Doppler sonographic findings and endothelial factor VIII staining revealed that COMP-Ang1 had a preservative effect on peritubular vasculature. In the diabetic nephropathy model, COMP-Ang1 reduced albuminuria and decreased mesangial expansion, thickening of the glomerular basement membrane and podocyte foot process broadening and effacement. COMP-Ang1 may delay the fibrotic changes in the kidney of diabetic db/db mice through its anti-inflammatory or metabolic effects. In conclusion, COMP-Ang1 may be an endothelium-specific and anti-inflammatory therapeutic modality in fibrotic renal disease.

Angiopoietin-like protein 3 modulates barrier properties of human glomerular endothelial cells through a possible signaling pathway involving phosphatidylinositol-3 kinase/protein kinase B and integrin alphaVbeta3

Podocytes can influence glomerular endothelial cell (GEnC) barrier properties and take part in the development of proteinuria by some molecules. Angiopoietin-like protein 3 (Angptl3), secreted by podocytes, is a member of the angiopoietin-like protein family that has important biological functions in endothelial cells. In our previous studies, we showed that mRNA expression of Angptl3 increased significantly in kidneys of children with minimal change nephrotic syndrome. And the mRNA level of Angptl3 was increased in the glomerulus of adriamycin rats with the development of proteinuria. It was also found that Angptl3 was expressed in the cytoplasm of cultured podocytes. Thus, Angptl3 might influence the biological functions of GEnCs in a paracrine manner. In this study, we found that Angptl3 could increase the permeability of GEnCs and increase the level of protein kinase B phosphorylation in cultured GEnCs in vitro. LY294002, a phosphatidylinositol-3 kinase inhibitor, could prevent the increase of permeability of GEnCs induced by Angptl3. Our results also indicated that the integrin alphaVbeta3 antibody (LM609) could block the Angptl3-induced protein kinase B phosphorylation.

Angiopoietin-1 therapy enhances fibrosis and inflammation following folic acid-induced acute renal injury

The loss of interstitial capillaries is a feature of several experimental models of renal disease and this contributes to secondary kidney injury. Angiopoietin-1 is a secreted growth factor which binds to Tie-2 present on endothelia to enhance cell survival thereby stabilizing capillary architecture in-vitro. Previous studies showed that angiopoietin-1 prevented renal capillary and interstitial lesions following experimental ureteric obstruction. We tested here the effect of angiopoietin-1 treatment on capillary loss and associated tubulointerstitial damage known to follow recovery from folic acid-induced tubular necrosis and acute renal injury. We found that delivery of angiopoietin-1 by adenoviral vectors stabilized peritubular capillaries in folic acid nephropathy but this was accompanied by profibrotic and inflammatory effects. These results suggest that the use of endothelial growth factor therapy for kidney disease may have varying outcomes that depend on the disease model tested.

Angiopoietin 1 and 2 gene and protein expression is differentially regulated in acute anti-Thy1.1 glomerulonephritis

Capillary neoformation is important in repair of glomerular injury of various origins. VEGF was shown to be crucial for glomerular capillary repair in glomerulonephritis (GN). We reasoned that other angiogenic factors are likewise involved in glomerular capillary remodeling and found angiopoietin 1 and -2 (ANG1 and ANG2) mRNA to be upregulated in cDNA microarrays of microdissected glomeruli of anti-Thy1.1 GN of the rat. We then studied glomerular in situ gene and protein expression of ANG1 and ANG2 and their receptor Tie-2 in the course of anti-Thy1.1 GN, which was induced by injection of OX-7 antibody. Animals were perfusion fixed at days 6 and 12 after GN induction and compared with nonnephritic controls receiving PBS. Capillary damage and repair were quantitatively analyzed using stereological techniques. Gene and protein expression of ANG1 and ANG2 and their receptor Tie-2 was analyzed using real-time quantitative PCR from microdissected glomeruli, nonradioactive in situ hybridization, double immunofluorescence, and Western blot analysis. Glomerular capillarization assessed as length density was significantly lower at day 6 of anti-Thy1.1 GN than in controls; it was back to normal values at day 12. ANG1 and ANG2 gene expression was markedly upregulated at day 6 of the disease compared with controls. Protein expression of ANG1 and ANG2 was confined to podocytes and that of Tie-2 to endothelial cells. At day 12 of anti-Thy1.1 GN when capillary restoration was nearly completed, ANG1 and ANG2 gene expression returned to basal levels, whereas Tie-2 expression was still high. With the use of a combined molecular and in situ approach, the spatial and temporal gene and protein expression of the angiopoietins and their receptor was analyzed in anti-Thy1.1 GN. The results indicate that glomerular expression of ANG1 and ANG2 and Tie-2 is differentially regulated and may contribute to healing and endothelial cell stabilization in experimental GN.

Hantaviruses direct endothelial cell permeability by sensitizing cells to the vascular permeability factor VEGF, while angiopoietin 1 and sphingosine 1-phosphate inhibit hantavirus-directed permeability

Hantaviruses infect human endothelial cells and cause two vascular permeability-based diseases: hemorrhagic fever with renal syndrome and hantavirus pulmonary syndrome. Hantavirus infection alone does not permeabilize endothelial cell monolayers. However, pathogenic hantaviruses inhibit the function of alphav beta3 integrins on endothelial cells, and hemorrhagic disease and vascular permeability deficits are consequences of dysfunctional beta3 integrins that normally regulate permeabilizing vascular endothelial growth factor (VEGF) responses. Here we show that pathogenic Hantaan, Andes, and New York-1 hantaviruses dramatically enhance the permeability of endothelial cells in response to VEGF, while the nonpathogenic hantaviruses Prospect Hill and Tula have no effect on endothelial cell permeability. Pathogenic hantaviruses directed endothelial cell permeability 2 to 3 days postinfection, coincident with pathogenic hantavirus inhibition of alphav beta3 integrin functions, and hantavirus-directed permeability was inhibited by antibodies to VEGF receptor 2 (VEGFR2). These studies demonstrate that pathogenic hantaviruses, similar to alphav beta3 integrin-deficient cells, specifically enhance VEGF-directed permeabilizing responses. Using the hantavirus permeability assay we further demonstrate that the endothelial-cell-specific growth factor angiopoietin 1 (Ang-1) and the platelet-derived lipid mediator sphingosine 1-phosphate (S1P) inhibit hantavirus directed endothelial cell permeability at physiologic concentrations. These results demonstrate the utility of a hantavirus permeability assay and rationalize the testing of Ang-1, S1P, and antibodies to VEGFR2 as potential hantavirus therapeutics. The central importance of beta3 integrins and VEGF responses in vascular leak and hemorrhagic disease further suggest that altering beta3 or VEGF responses may be a common feature of additional viral hemorrhagic diseases. As a result, our findings provide a potential mechanism for vascular leakage after infection by pathogenic hantaviruses and the means to inhibit hantavirus-directed endothelial cell permeability that may be applicable to additional vascular leak syndromes.

Development of the renal glomerulus: good neighbors and good fences

The glomerulus of the mammalian kidney is an intricate structure that contains an unusual filtration barrier that retains higher molecular weight proteins and blood cells in the circulation. Recent studies have changed our conception of the glomerulus from a relatively static structure to a dynamic one, whose integrity depends on signaling between the three major cell lineages: podocytes, endothelial and mesangial cells. Research into the signaling pathways that control glomerular development and then maintain glomerular integrity and function has recently identified several genes, such as the nephrin and Wilms' tumor 1 genes, that are mutated in human kidney disease.

Effects of podocyte injury on glomerular development

To study the effects of podocyte injury on glomerular maturation and underlying mechanisms of such effects, puromycin aminonucleoside (PAN) was given to neonatal mice at 1 d post partum (1 dpp). Mice with PAN injection had smaller kidney weight (KW) and body weight (BW) at all times and smaller KW/BW at 4, 8, and 12 dpp versus normal saline (NS) controls. Electron microscopy (EM) revealed nearly complete podocyte foot process effacement and segmental microvillous transformation as early as 2 dpp, preceding proteinuria. PAN-injected kidneys showed significantly fewer glomerular capillary loops and decreased glomerular maturation index, as well as less CD31+ endothelium in cortical glomeruli at 12 dpp versus NS controls. Glomerular mesangial injury and glomerulosclerosis along with proteinuria were noted in PAN-injected kidneys starting from 30 dpp. Systolic blood pressure was increased significantly by 60 dpp in PAN mice. PAN mice also had significantly decreased Flk-1 and Tie2 mRNA expression and increased angiopoitein-1 (Ang-1) expression, without change in vascular endothelial growth factor (VEGF) at 2 dpp versus NS. Our study shows that podocyte injury in neonatal mice kidneys alters the expression of key capillary growth modulators in glomeruli, leading to abnormal development of glomerular capillaries, with subsequent development of proteinuria, hypertension, and glomerulosclerosis.

Podocyte-specific expression of angiopoietin-2 causes proteinuria and apoptosis of glomerular endothelia

Angiopoietin-2 (Ang-2) modulates embryonic vascular differentiation primarily by inhibiting the antiapoptotic effects of Ang-1 on endothelia that express the Tie-2 receptor. Ang-2 is transiently expressed by developing glomeruli but is downregulated with normal maturation. Glomerular Ang-2 expression is, however, markedly upregulated in animal models of diabetic nephropathy and glomerulonephritis, both leading causes of human chronic renal disease, affecting 10% of the world population. It was hypothesized that Ang-2 might have significant roles in the pathobiology of glomerular disease. Mice with inducible podocyte-specific Ang-2 overexpression were generated. When the transgene was induced in adults for up to 10 wk, mice had significant increases in both albuminuria and glomerular endothelial apoptosis, with significant decreases of both vascular endothelial growth factor-A and nephrin proteins, critical for maintenance of glomerular endothelia and filtration barrier functional integrity, respectively. There was, however, no significant change of systemic BP, creatinine clearance, or markers of renal fibrosis, and podocytes appeared structurally intact. In kidneys of young animals in which Ang-2 had been upregulated during organogenesis, increased apoptosis occurred in just-formed glomeruli. In vitro, short-term exposure of isolated wild-type murine glomeruli to exogenous Ang-2 led to decreased levels of vascular endothelial growth factor-A protein. These novel results provide insight into molecular mechanisms underlying proteinuric disorders, highlight potentially complex interactions between subsets of glomerular cells, and emphasize how a vascular growth factor that has critical roles in normal development may be harmful when re-expressed in the context of adult disease.

Vascular endothelial growth factor as a survival factor for human islets: effect of immunosuppressive drugs

AIMS/HYPOTHESIS

Rapamycin, part of the immunosuppressive regimen of the Edmonton protocol, has been shown to inhibit vascular endothelial growth factor (VEGF) production and VEGF-mediated survival signalling in tumour cell lines. This study investigates the survival-promoting activities of VEGF in human islets and the effects of rapamycin on islet viability.

MATERIALS AND METHODS

Levels of VEGF and its receptors in isolated human islets and whole pancreas was determined by western blotting and immunostaining. Islet viability following VEGF or immunosuppressive drug treatment was determined using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Islet VEGF release was measured by ELISA. Mouse islets infected with an adenovirus expressing the gene for VEGF were transplanted syngeneically into streptozotocin-induced diabetic mice, with blood glucose levels measured three times per week.

RESULTS

Isolated human islets produced multiple isoforms of VEGF and VEGF receptors 1, 2 and 3 and the coreceptor neuropilin 1. Exogenous VEGF (10 ng/ml) prevented human islet death induced by serum starvation, which suggests that VEGF can act as a survival factor for human islets. Transplantation of mouse islets infected with a VEGF-expressing adenovirus in a syngeneic model, improved glycaemic control at day 1 post-transplantation (p < 0.05). Rapamycin at 10 and 100 ng/ml significantly reduced islet VEGF release (by 37 +/- 4% and 43 +/- 6%, respectively; p < 0.05) and at 100 ng/ml reduced islet viability (by 36 +/- 9%) and insulin release (by 47 +/- 7%, all vs vehicle-treated controls; p < 0.05). Tacrolimus had no effect on islet VEGF release or viability.

CONCLUSIONS/INTERPRETATION

Our data suggest that rapamycin may have deleterious effects on islet survival post-transplantation, both through a direct effect on islet viability and indirectly through blockade of VEGF-mediated revascularisation.

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.

Enhanced Expression of ANGPTL2 in the Microvascular Lesions of Diabetic Glomerulopathy

BACKGROUND

Diabetic nephropathy (DN) is one of the most important microvascular complications of diabetes mellitus. However, the underlying mechanisms remain unclear. We studied the expression characteristics of angiopoietin-like 2 (ANGPTL2), a novel DN-associated growth factor identified in our previous gene chip screening.

METHODS

Glomeruli were microdissected from renal biopsies from 24 patients with DN and 8 donor controls. The expression of ANGPTL2 was assessed by RT-PCR and immunohistochemistry, and then correlated with clinical and pathological indices of glomerular injury.

RESULTS

Consistent with the results of the gene chip experiment, abundant expression of ANGPTL2 was found more frequently in diabetic glomeruli as compared to donor controls (95 vs. 38%, chi(2) = 15.9, p < 0.01). ANGPTL2 mRNA upregulation was more prominent in glomeruli with less microaneurysm (22 vs. 66%, p < 0.05), inflammatory influx (6 vs. 50%, p < 0.05) or endothelial foam cell formation (11 vs. 53%, p < 0.05). Immunostaining revealed an upregulation of ANGPTL2 protein in hypertrophied diabetic glomeruli, mainly distributed in podocytes, which were supposed to be the origin of ANGPTL2.

CONCLUSION

The upregulation of ANGPTL2 in diabetic glomerulopathy shows a close relationship to abnormal microvasculature and endothelial inflammation. ANGPTL2 may play an important role in the pathogenesis of diabetic glomerulopathy.

Conditionally immortalized human glomerular endothelial cells expressing fenestrations in response to VEGF

Glomerular endothelial cells (GEnC) are specialized cells with important roles in physiological filtration and glomerular disease. Despite their unique features, GEnC have been little studied because of difficulty in maintaining them in cell culture. We have addressed this problem by generation of conditionally immortalized (ci) human GEnC using technology with which we have previously produced ci podocytes. Primary culture GEnC were transduced with temperature-sensitive simian virus 40 large tumour antigen and telomerase using retroviral vectors. Cells were selected, cloned, and then characterized by light and electron microscopy (EM), response to vascular endothelial growth factor (VEGF), and tumour necrosis factor (TNF)alpha, expression of endothelial markers by focused gene array, immunofluorescence and Western blotting, and formation and behaviour of monolayers. CiGEnC proliferated at the permissive temperature (33 degrees C) and became growth arrested at the non-permissive temperature (37 degrees C). CiGEnC retained morphological features of early-passage primary culture GEnC up to at least p41, confirming successful immortalization. EM demonstrated fenestrations, increased in number by VEGF. mRNA analysis confirmed expression of the endothelial markers platelet endothelial cell adhesion molecule 1, intercellular adhesion molecule 2, VEGF receptor 2, and von Willebrand factor, validated by immunofluorescence and Western blotting. CiGEnC also expressed Tie2, and TNFalpha upregulated E-selectin. CiGEnC formed monolayers with barrier properties responsive to cyclic adenosine 3',5' monophosphate (cAMP) and thrombin. CiGEnC retain the markers and behaviour of primary culture GEnC. They express fenestrations which are upregulated in response to VEGF. These cells are a unique resource for further study of GEnC and their roles in glomerular filtration, glomerular disease, and response to glomerular injury.

Angiotensin Type 1 Receptor Blocker Restores Podocyte Potential to Promote Glomerular Endothelial Cell Growth

Both podocytes and glomerular endothelial cells (GEN) are postulated to play important roles in the progression and potential regression of glomerulosclerosis. Inhibition of angiotensin is crucial in treatment of chronic kidney disease, presumably via effects on BP and extracellular matrix. This study aimed to investigate how angiotensin inhibition altered the interactions between podocytes and GEN. The effects of supernatants from primary cultured mouse podocytes, before or after sublethal injury by puromycin aminonucleoside, in the presence or absence of angiotensin type 1 receptor blocker (ARB), on GEN sprouting and growth were assessed. Supernatant from normal podocytes significantly increased GEN sprouting, whereas puromycin aminonucleoside-injured podocyte supernatant decreased these GEN responses. These effects were linked to decreased vascular endothelial growth factor A (VEGF-A) and angiopoietin-1 (Ang-1) protein from injured podocytes. This downregulation of VEGF-A and Ang-1 protein was reversed when injured podocytes were treated with ARB. Inhibition of VEGF-A or Ang-1 prevented this restored response by ARB. Activation of intracellular kinases (p38, extracellular signal-regulated kinase, and AKT) was suppressed in GEN that were treated with medium from injured podocytes but restored by medium from ARB-treated injured podocytes. Therefore, injured podocytes are ineffective in promoting GEN sprouting, and this effect is reversed by ARB treatment of the injured podocyte. These data support the idea that ARB effects on podocytes may mediate capillary remodeling in vivo.

The bioactivity of plasma factors in focal segmental glomerulosclerosis

Focal segmental glomerulosclerosis (FSGS) is a devastating form of nephrotic syndrome, often leading to end-stage renal failure after the failure of a succession of highly toxic therapies. It has long been thought to be caused by a circulating factor(s) that may be produced by cells of the immune system. Much research has focused on identifying such factor(s), including the development of a promising in vitro assay, which estimates glomerular permeability based on the swelling of isolated glomeruli in response to patients' plasma. This assay has also been used as the basis of testing plasma fractions for permeability activity, with no specific factor yet identified. Other studies have attempted to replicate proteinuria in whole animals, by injecting plasma or plasma fractions from focal segmental glomerulosclerosis patients, with inconsistent results. More recently there has been evidence that there may be either inhibitory or missing factor(s) in plasma, with respect to permeability. An additional major biological advance is a growing appreciation of the podocyte as the target cell in this disease, and an understanding of the key molecules involved. Putting together this knowledge, with the latest technological advances in protein identification, provides promising avenues towards finally solving the basis of this enigmatic disease.

Detection of bile salt-dependent lipase, a 110 kDa pancreatic protein, in urines of healthy subjects

Bile salt-dependent lipase (BSDL), a 110 kDa glycoprotein secreted by the pancreatic acinar cells, participates in the duodenal hydrolysis of dietary lipid esters. Recent in vitro and in vivo studies demonstrated that the BSDL reaches the blood via a transcytosis motion through enterocytes, suggesting that this enzyme may play a role in vascular biology. Once in the blood, BSDL should be eliminated. We address the hypothesis that BSDL may be filtered by the glomerulus and eliminated in urines. Immunological methods and proteomic were used to detect and to characterize BSDL in urine. The immunoreactive form of BSDL was detected in urines of 36 male subjects devoid of renal failure. Proteomic demonstrated that the immunoreactive protein is BSDL. Experiments using a monoclonal antibody to the oncofetal glycoform of pancreatic BSDL suggested that the protein is not expressed by renal cells but originates from the pancreas via circulation. We demonstrate that under normal physiological conditions, BSDL, a high-molecular weight blood glycoprotein, can be filtered by the renal glomerulus to be eliminated in urines.

Podocyte biology in human disease

The podocyte is a highly specialized cell that plays a key role in regulating the glomerular filtration barrier. A number of advances have been made in recent years, linked to the discovery of single-gene defects in hereditary glomerular disease, which highlight the role of this cell in preventing proteinuria. This article reviews the molecular biology of the podocyte, focusing on known genetic abnormalities.

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.

Infusion of angiotensin II reduces loss of glomerular capillary area in the early phase of anti-Thy-1.1 nephritis possibly via regulating angiogenesis-associated factors

Hyperphosphatemia in patients with chronic kidney disease leads to secondary hyperparathyroidism and renal osteodystrophy, and it is independently associated with mortality risk. The exact mechanism by which hyperphosphatemia increases mortality risk is unknown, but it may relate to enhanced cardiovascular calcification. The National Kidney Foundation Kidney Disease Outcomes Quality Initiative (K/DOQI) Clinical Practice Guidelines for Bone Metabolism and Disease in Chronic Kidney Disease recommends maintenance of serum phosphorus below 5.5 mg/dL, calcium-phosphorus (Ca x P) product less than 55 mg(2)/dL(2), intact parathyroid hormone (iPTH) 150 pg/mL to 300 pg/mL, and bicarbonate (HCO(3)) greater than 22 mEq/L. Although calcium-based phosphate binders (CBPB) are cost effective, there are long-term safety concerns pertaining to their postulated role in the progression of cardiovascular calcification. Sevelamer hydrochloride has been recommended as an alternative noncalcium phosphate binder. Results from the Calcium Acetate Renagel Evaluation (CARE) study indicate that calcium acetate is more effective than sevelamer hydrochloride in controlling serum phosphorous, Ca x P product, and HCO(3) in hemodialysis patients. In the Treat-to-Goal study, dialysis patients treated with sevelamer hydrochloride had slower progression of coronary and aortic calcification than patients treated with CBPB. The mechanism underlying the beneficial effect of sevelamer hydrochloride is unknown but may relate to decreased calcium loading, or to dramatic reductions in low-density lipoprotein (LDL) cholesterol in sevelamer hydrochloride-treated patients. At present, evidence incriminating CBPB in the progression of cardiovascular calcification in end-stage renal disease (ESRD) remains largely circumstantial. As calcium acetate is more efficacious and cost effective than sevelamer hydrochloride, it remains an accepted first-line phosphate binder. This review examines these issues and provides rational guidelines for the use of CBPB in patients on maintenance hemodialysis.

Dysmorphogenesis of kidney cortical peritubular capillaries in angiopoietin-2-deficient mice

Angiopoietin-2 (Ang-2) modulates Tie-2 receptor activation. In mouse kidney maturation, Ang-2 is expressed in arteries, with lower levels in tubules, whereas Tie-2 is expressed by endothelia. We hypothesized that Ang-2 deficiency disrupts kidney vessel patterning. The normal renal cortical peritubular space contains fenestrated capillaries, which have few pericytes; they receive water and solutes which proximal tubules reclaim from the glomerular filtrate. In wild-type neonates, alpha smooth muscle actin (alpha SMA), platelet-derived growth factor receptor beta (PDGFR beta), and desmin-expressing cells were not prominent in this compartment. In Ang-2 null mutants, alpha SMA, desmin, and PDGFR beta prominently immunolocalized in cortical peritubular locations. Some alpha SMA-positive cells were closely associated with CD31- and Tie-2-positive peritubular capillary endothelia, and some of the alpha SMA-positive cells expressed PDGFR beta, desmin, and neural/glial cell 2 (NG2), consistent with a pericyte-like identity. Immunoblotting suggested an increase of total and tyrosine-phosphorylated Tie-2 proteins in null mutant versus wild-type kidneys, and electron microscopy confirmed disorganized capillaries and adjacent cells in cortical peritubular spaces in mutant neonate kidneys. Hence, Ang-2 deficiency causes dysmorphogenesis of cortical peritubular capillaries, with adjacent cells expressing pericyte-like markers; we speculate the latter effect is caused by disturbed paracrine signaling between endothelial and surrounding mesenchymal precursor cells.

Renal glomerular permselectivity and vascular endothelium

The glomerular barrier is the kidney's physical block to the unrestricted flow of molecules from the plasma into the urinary space. Its exquisite selectivity allows solutes and water in the glomerular capillaries to pass through but it prevents the bulk of plasma proteins, most notably albumin, from crossing. Classically the barrier consists of three components: glomerular endothelium, glomerular basement membrane and glomerular epithelium (podocytes) with slit diaphragm. A lot of investigations are experimental but they are sufficient to show the pivotal role of endothelium in glomerular proteinuria. In this study the author discuss glomerular endothelium with particular emphasis on the barrier presumed to be imparted by endothelium-glomerular basement membrane-podocyte interactions. By specialized glomerular endothelial structure (caveolae, tight junctions, endothelium glycocalyx) and by circulating permeability factors (albumin, orosomucoid, apolipoproteins, Amadori's products). Concluding remarks underline the significance to study the glomerular vascular endothelial dysfunction.

The role of vascular endothelial growth factor (VEGF) in renal pathophysiology

Vascular endothelial growth factor (VEGF) is an endothelial-specific growth factor that promotes endothelial cell proliferation, differentiation and survival, mediates endothelium-dependent vasodilatation, induces microvascular hyperpermeability and participates in interstitial matrix remodeling. In the kidney, VEGF expression is most prominent in glomerular podocytes and in tubular epithelial cells, while VEGF receptors are mainly found on preglomerular, glomerular, and peritubular endothelial cells. The role of VEGF in normal renal physiology is essentially unknown. The absence of prominent effects of VEGF blockade in normal experimental animals suggests a limited function during homeostasis, although a role in the formation and maintenance of glomerular capillary endothelial fenestrations has been suggested. VEGF and its receptors are up-regulated in experimental animals and humans with type 1 and type 2 diabetes. Inhibition of VEGF has beneficial effects on diabetes-induced functional and structural alterations, suggesting a deleterious role for VEGF in the pathophysiology of diabetic nephropathy. VEGF is required for glomerular and tubular hypertrophy and proliferation in response to nephron reduction, and loss of VEGF is associated with the development of glomerulosclerosis and tubulointerstitial fibrosis in the remnant kidney. No firm conclusions on the role of VEGF in minimal change or membranous glomerulonephritis can be drawn. VEGF may be an essential mediator of glomerular recovery in proliferative glomerulonephritis. Glomerular and tubulointerstitial repair in thrombotic microangiopathy and cyclosporin nephrotoxicity may also be VEGF-dependent. In conclusion, VEGF is required for growth and proliferation of glomerular and peritubular endothelial cells. While deleterious in some, it may contribute to recovery in other forms of renal diseases.

The role of VEGF-A in glomerular development and function

PURPOSE OF REVIEW

Vascular endothelial growth factor is a major regulator of blood vessel biology and is highly expressed in presumptive and mature podocytes within the glomerulus. It has long been recognized that dysregulation of this factor occurs in a number of glomerular diseases; however, definitive proof that it plays a pathogenic or developmental role in glomerular biology has remained elusive. This review will summarize some of the recent advances in our understanding of the role(s) of VEGF in these processes.

RECENT FINDINGS

Gene targeting in the mouse has shown that tight regulation of vascular endothelial growth factor is required for development and maintenance of the glomerular filtration barrier. Podocyte-specific deletion of both alleles leads to congenital nephropathy and perinatal lethality. The glomeruli of mice that lack the 164 and 184 isoforms but express the 120 isoform, are smaller and have fewer capillary loops, whereas mice with podocyte-specific haploinsufficiency for all isoforms develop glomerular endotheliosis, the renal lesion seen in preeclampsia. Elevated levels of the soluble vascular endothelial growth factor receptor 1, which binds and inhibits circulating forms of VEGF were identified in patients with preeclampsia; rats injected with this soluble receptor develop hypertension, endotheliosis and proteinuria, similar to the lesion seen in podocyte-specific haploinsufficient VEGF mice. Conversely, podocyte-specific overexpression of the 164 isoform leads to collapsing glomerulopathy, the classic lesion seen in HIV-associated nephropathy.

SUMMARY

These results demonstrate that vascular endothelial growth factor plays a critical role in glomerular development and function, and provides the foundation to develop novel diagnostic or therapeutic tools for patients with glomerular disease.

Increased renal vascular endothelial growth factor and angiopoietins by angiotensin II infusion is mediated by both AT1 and AT2 receptors

A link between angiotensin II and cell proliferation has previously been reported. However, there remains controversy as to the role of the individual angiotensin II receptor subtypes in mediating these effects and their link to angiogenic cytokines and their receptors. Male Sprague-Dawley rats were infused with either angiotensin II or vehicle for 14 d at a dose of 58.3 ng/min. Angiotensin II-infused rats received no treatment, an AT(1) receptor antagonist valsartan (30 mg/kg per d), or an AT(2) receptor antagonist PD123319 (830 ng/min). Gene expression of vascular endothelial growth factor (VEGF) and receptor VEGF-R2, as well as Tie-2 and its ligands angiopoietin-1 (Ang-1) and angiopoietin-2 (Ang-2) were assessed by reverse transcription-PCR. Protein expression was assessed by Western blotting and immunohistochemistry. Gene and protein expression of VEGF, Ang-1, and Ang-2 were increased by angiotensin II infusion. Valsartan and PD123319 attenuated angiotensin II-associated increases in VEGF gene and protein expression. Ang-1 and Ang-2 gene but not protein expression were reduced by both treatments. These changes occurred in the context of attenuation of angiotensin II-induced glomerular cell proliferation by both valsartan and PD123319. In situ hybridization and immunohistochemical studies localized VEGF, Ang-1, and Ang-2 expression to the epithelial cells of the glomerulus, and VEGF-R2 and Tie-2 receptors to the endothelial cells of the kidney. These findings extend the increasing evidence that the AT(2) receptor, in addition to the AT(1) receptor subtype, plays an important role in mediating the proliferative actions of angiotensin II in the kidney.

Tumstatin peptide, an inhibitor of angiogenesis, prevents glomerular hypertrophy in the early stage of diabetic nephropathy

In the early stage of diabetic nephropathy (one of the major microvascular complications of diabetes) glomerular hyperfiltration and hypertrophy are observed. It is clinically important to regulate glomerular hypertrophy for preventing glomerulosclerosis. The number of glomerular endothelial cells is known to be increased in diabetic nephropathy associated with enlarged glomerular tufts, suggesting that the mechanism is similar to that of angiogenesis. Tumstatin peptide is an angiogenesis inhibitor derived from type IV collagen and inhibits in vivo neovascularization induced by vascular endothelial growth factor (VEGF), one of the mediators of glomerular hypertrophy in diabetic nephropathy. Here, we show the effect of tumstatin peptide in inhibiting alterations in early diabetic nephropathy. Glomerular hypertrophy, hyperfiltration, and albuminuria were suppressed by tumstatin peptide (1 mg/kg) in streptozotocin-induced diabetic mice. Glomerular matrix expansion, the increase of total glomerular cell number and glomerular endothelial cells (CD31 positive), and monocyte/macrophage accumulation was inhibited by tumstatin peptide. Increase in renal expression of VEGF, flk-1, and angiopoietin-2, an antagonist of angiopoietin-1, was inhibited by tumstatin treatment in diabetic mice. Alteration of glomerular nephrin expression, a podocyte protein crucial for maintaining glomerular filtration barrier, was recovered by tumstatin in diabetic mice. Taken together, these results demonstrate the potential use of antiangiogenic tumstatin peptide as a novel therapeutic agent in early diabetic nephropathy.

Vascular factors altered in glucose-treated mesangial cells and diabetic glomeruli. Changes in vascular factors impair endothelial cell growth and matrix

We studied the effect of a high glucose (HG) environment on the vascular factors that are secreted by mesangial cells, and regulate endothelial growth and mesangial matrix deposition. To this effect, we measured the vascular factors in the glomeruli of streptozotocin-induced diabetic kidneys and in mesangial cells exposed to a HG concentration. We then transferred the media of mesangial cells previously exposed to high glucose to cultured endothelial cells to study the effects on endothelial growth, matrix formation, and in vitro capillary proliferation. In 1-week diabetic kidneys, glomerular vascular endothelial growth factor (VEGF) and angiopoietin-1 were inhibited by 38 and 57%, respectively, but angiopoietin-2 was increased by 318%. We found similar results in mesangial cells exposed to HG. There was a decrease of VEGF (50% by enzyme immunoassay, 27% by mRNA), decrease of angiopoietin-1 (65% by mRNA), and a much greater increase of angiopoietin-2 (280% by immunoassay, 523% by mRNA). Compared to controls, the media of mesangial cells previously exposed to HG impaired endothelial cell growth by 61%, increased extracellular matrix by 100%, and decreased capillary formation by 90%. We conclude that high ambient glucose alters the secretion of vascular factors elaborated by mesangial cells, resulting in an expansion of the endothelial cell matrix and disruption of capillary structure.

Decreased expression of vascular endothelial growth factor in idiopathic membranous glomerulonephritis: relationships to clinical course

BACKGROUND

Membranous glomerulonephritis (MGN) has a variable clinical course, and factors that determine the prognosis are unknown. Our previous study suggested that urinary excretion of vascular endothelial growth factor (VEGF) is decreased in active MGN, but normalizes in remission. In the present study, VEGF protein and messenger RNA (mRNA) expression were investigated in this disease.

METHODS

Twelve patients with clinically active and/or progressive MGN were studied by using urinary assays for VEGF and soluble VEGF receptor-1 (sVEGF-R1), semiquantitative scoring of serial renal biopsy specimens by using immunohistochemical staining for VEGF protein, and in situ hybridization for VEGF mRNA. Results were compared with healthy controls and normal parts of nephrectomized kidneys.

RESULTS

Urinary VEGF excretion was decreased significantly (P < 0.001 versus controls) in MGN, but there was no difference in sVEGF-R1 excretion compared with healthy subjects. VEGF protein expression was diminished significantly in glomerular podocytes (P = 0.008), as well as in extraglomerular small arteries (P = 0.03) and arterioles (P = 0.008) in MGN. Total kidney VEGF score (the sum of scores of individual kidney compartments) also was decreased in MGN (P < 0.05) and remained low in repeated biopsies. Expression of VEGF mRNA localized predominantly to podocytes in normal kidneys was greatly reduced in MGN.

CONCLUSION

Clinically active MGN is associated with diminished expression of VEGF protein and mRNA, mainly in podocytes, and expression remains depressed in persistently active and/or progressive disease. This is reflected by decreased urinary VEGF excretion. These findings point to potentially reversible podocyte injury and, together with our previous study, suggest that VEGF may have a protective role during the evolution of MGN.

Immunolocalization of angiopoietin 1 in human peritoneal endometriotic lesions

OBJECTIVE

To analyze the expression of angiopoietin 1 (ANGPT1) in pigmented and nonpigmented endometriosis implants and specify its role in the interaction of angiogenic factors.

DESIGN

Experimental retrospective study.

SETTING

University hospital.

PATIENT(S)

Eighty-two sections from 201 laparoscopic tissue samples of 43 female patients.

INTERVENTION(S)

Biopsies of peritoneal endometriotic lesions of macroscopically different forms.

MAIN OUTCOME MEASURE(S)

Angiopoietin 1 expression and location pattern in endothelial cells, periendothelial cells, glandular epithelium, and stromal structures.

RESULT(S)

Angiopoietin 1 is immunohistochemically detectable in endothelial cells, periendothelial cells, in the glandular epithelium, and in the stroma. Differences in the expression of pigmented and nonpigmented lesions are not statistically significant.

CONCLUSION(S)

Pigmented and nonpigmented endometriotic lesions differ according to their clinical activity and angiogenic potential. Angiopoietin 1 is an important representative of the angiogenic factors and is involved in the angiogenic processes of these lesions. There were no significant differences in the expression and location within different lesion types for ANGPT1. Thus, it is not a direct activity marker of a lesion.

Differentiated human podocytes endogenously express an inhibitory isoform of vascular endothelial growth factor (VEGF165b) mRNA and protein

Despite production by podocytes of the proangiogenic molecule vascular endothelial growth factor-A (VEGF), the glomeruli are not sites of angiogenesis. We recently described mRNA expression of an inhibitory splice variant of VEGF (VEGF165b) in normal kidney (Bates DO, Cui TG, Doughty JM, Winkler M, Sugiono M, Shields JD, Peat D, Gillatt D, and Harper SJ. Cancer Res 62: 4123-4131, 2002). Available anti-VEGF antibodies do not distinguish stimulatory from inhibitory VEGF families. To assess the production of VEGF165 (stimulatory) and VEGF165b (inhibitory) isoforms by human podocytes, we examined both primary cultured and conditionally immortalized human podocytes using family- and isoform-specific RT-PCR. In addition, VEGF protein production was analyzed in podocytes, using isoform-specific double-strand small-interference RNAs (siRNA). RT-PCR demonstrated the production of VEGF189 mRNA by podocytes of both phenotypes. In contrast, on differentiation there was a splicing change from VEGF165 to VEGF165b mRNA. In addition, VEGF protein in the supernatant of conditionally immortalized, differentiated podocytes was reduced by VEGF165b siRNA to 20+/-11% of the level of mock-transfected cells (P < 0.01). No reduction was seen with mismatch siRNA. Moreover, there was no reduction in VEGF protein concentration in the supernatant of primary cultured, dedifferentiated human podocytes (109+/-8% of mismatch siRNA, P > 0.1). In conclusion, differentiated but not dedifferentiated human podocytes secrete significant amounts of VEGF165b protein. It is possible that this may explain the paradox of high VEGF production in the glomerulus but no angiogenesis. Furthermore, the existence of this splicing switch in relation to podocyte phenotype suggests that alternative splicing of the VEGF pre-RNA is a regulated process that is open to manipulation and therefore could be a target for novel cancer therapies.

Functional evidence that vascular endothelial growth factor may act as an autocrine factor on human podocytes

Vascular endothelial growth factor (VEGF) is expressed by renal glomerular epithelial cells (podocytes) and is thought to be protective against nephrotoxic agents. VEGF has been shown to be an autocrine survival factor in neuropilin-1-positive, VEGF receptor-negative breast carcinoma cells. Normal human podocytes are also known to express neuropilin-1, VEGF, and are VEGF-R2 negative. Here, we investigated whether a similar VEGF autocrine loop may exist in podocytes. Podocyte cytosolic calcium concentration ([Ca(2+)](i)) was analyzed in primary cultured and conditionally immortalized podocytes using ratiometric fluorescence measurement. Cytotoxicity was determined by lactate dehydrogenase assay, proliferation by [(3)H]-thymidine incorporation, and cell counts by hemocytometric assay. VEGF decreased [Ca(2+)](i) in primary podocytes (from 179 +/- 36 to 121 +/- 25 nM, P < 0.05) and conditionally immortalized podocytes (from 95 +/- 10 to 66 +/- 8 nM, P < 0.02) in the absence of extracellular calcium. The type III receptor tyrosine-kinase inhibitor PTK787/ZK222584 abolished this reduction. VEGF increased podocyte [(3)H]-thymidine incorporation (3,349 +/- 283 cpm, control 2,364 +/- 301 cpm, P < 0.05) and cell number (4.5 +/- 0.7 x 10(4)/ml, control 2.6 +/- 0.5 x 10(4)/ml, P < 0.05) and decreased cytotoxicity (5.9 +/- 0.7%, control 12 +/- 3%, P < 0.05), whereas a monoclonal antibody to VEGF increased cytotoxicity. Electron microscopy of normal human glomeruli demonstrated that the glomerular VEGF is mostly podocyte cell membrane associated. These results indicate that one of the functions of VEGF secreted from podocytes may be to act as an autocrine factor on calcium homeostasis and cell survival.