The Role of Vascular Endothelial Growth Factor in the Kidney in Health and Disease

Prognostic and Diagnostic Value of Endocan in Kidney Diseases

Endocan, previously called endothelial cell-specific molecule-1, is a soluble proteoglycan that is predominantly expressed in vascular endothelial cells of the lungs and kidneys. It is upregulated by proinflammatory cytokines and plays a critical role in inflammatory, proliferative, and neovascularization processes. The utility of endocan as a biomarker in a wide spectrum of diseases is being increasingly acknowledged. In this review, we summarize the current evidence concerning the role of endocan in kidney diseases, with emphasis on its prognostic and diagnostic value. It seems that the determination of plasma endocan levels may provide useful prognostic information in many types of renal failure such as chronic kidney disease, IgA nephropathy, and diabetic nephropathy. Endocan could additionally improve the early diagnostic evaluation of acute kidney disease, chronic renal allograft injury, and acute rejection after kidney transplantation, thus contributing to endothelial cell injury monitoring in a timely manner.

MicroRNAs are differentially expressed in the serum and renal tissues of cats with experimentally induced chronic kidney disease: a preliminary study

OBJECTIVE

To identify differentially expressed microRNA in the serum and renal tissues of cats with experimentally induced chronic kidney disease (CKD).

SAMPLE

Banked renal tissues and serum from 4 cats.

PROCEDURES

Cats previously underwent 90-minute unilateral ischemia with delayed contralateral nephrectomy 3 months after ischemia. Tissues were collected from the contralateral kidney at the time of nephrectomy and from the ischemic kidney 6 months after nephrectomy (study end). Serum was collected prior to ischemia (baseline serum) and at study end (end point serum). Total RNA was isolated from tissues and serum, and microRNA sequencing was performed with differential expression analysis between the contralateral and ischemic kidney and baseline and end point serum.

RESULTS

20 microRNAs were differentially expressed between ischemic and contralateral kidneys, and 52 microRNAs were differentially expressed between end point and baseline serum. Five microRNAs were mutually differentially expressed between ischemic and contralateral kidneys and baseline and end point serum, with 4 (mir-21, mir-146, mir-199, and mir-235) having increased expression in both the ischemic kidney and end point serum and 1 (mir-382) having increased expression in the ischemic kidney and decreased expression in end point serum. Predicted target search for these microRNA revealed multiple genes previously shown to be involved in the pathogenesis of feline CKD, including hypoxia-inducible factor-1α, transforming growth factor-β, hepatocyte growth factor, fibronectin, and vascular endothelial growth factor A.

CLINICAL RELEVANCE

MicroRNAs were differentially expressed after CKD induction in this preliminary study. Regulation of renal fibrosis in feline CKD may occur through microRNA regulation of mRNAs of pro- and anti-fibrotic genes.

The Role of Endocan in Selected Kidney Diseases

Endocan, previously referred to as an endothelial-cell-specific molecule-1 (ESM-1) is a member of a proteoglycan family that is secreted by vascular endothelial cells of different organs, mainly lungs and kidneys. It is assumed to participate in endothelial activation and the triggering of inflammatory reactions, especially in microvasculatures. Thanks to its solubility in human fluids, i.e., urine and blood plasma, its stability and its low concentrations in physiological conditions, endocan has been proposed as an easily available, non-invasive biomarker for identifying and predicting the course of many diseases. Recently, endocan has been studied in relation to kidney diseases. In general, endocan levels have been linked to worse clinical outcomes of renal dysfunction; however, results are conflicting and require further evaluation. In this review, authors summarize available knowledge regarding the role of endocan in pathogenesis and progression of selected kidney diseases.

Weight-gain induced changes in renal perfusion assessed by contrast-enhanced ultrasound precede increases in urinary protein excretion suggestive of glomerular and tubular injury and normalize after weight-loss in dogs

Early detection of obesity-related glomerulopathy in humans is challenging as it might not be detected by routine biomarkers of kidney function. This study's aim was to use novel kidney biomarkers and contrast-enhanced ultrasound (CEUS) to evaluate the effect of obesity development and weight-loss on kidney function, perfusion, and injury in dogs. Sixteen healthy lean adult beagles were assigned randomly but age-matched to a control group (CG) (n = 8) fed to maintain a lean body weight (BW) for 83 weeks; or to a weight-change group (WCG) (n = 8) fed the same diet to induce obesity (week 0-47), to maintain stable obese weight (week 47-56) and to lose BW (week 56-83). At 8 time points, values of systolic blood pressure (sBP); serum creatinine (sCr); blood urea nitrogen (BUN); serum cystatin C (sCysC); urine protein-to-creatinine ratio (UPC); and urinary biomarkers of glomerular and tubular injury were measured. Glomerular filtration rate (GFR) and renal perfusion using CEUS were assayed (except for week 68). For CEUS, intensity- and time-related parameters representing blood volume and velocity were derived from imaging data, respectively. At 12-22% weight-gain, cortical time-to-peak, representing blood velocity, was shorter in the WCG vs. the CG. After 37% weight-gain, sCysC, UPC, glomerular and tubular biomarkers of injury, urinary immunoglobulin G and urinary neutrophil gelatinase-associated lipocalin, respectively, were higher in the WCG. sBP, sCr, BUN and GFR were not significantly different. After 23% weight-loss, all alterations were attenuated. Early weight-gain in dogs induced renal perfusion changes measured with CEUS, without hyperfiltration, preceding increased urinary protein excretion with potential glomerular and tubular injury. The combined use of routine biomarkers of kidney function, CEUS and site-specific urinary biomarkers might be valuable in assessing kidney health of individuals at risk for obesity-related glomerulopathy in a non-invasive manner.

Stereological and immunogold studies on TIE1 and TIE2 localization in glomeruli indicate angiopoietin signaling in podocytes

Angiopoietins and their TIE receptors are important regulators of vascular stability and remodeling. These molecules are involved not only in the normal development of kidney glomeruli, but also in disease, thus making them promising targets for therapies. Although TIE receptors are mainly found in endothelial cells, some reports observed TIE2 expression in glomerular podocytes as well. This suggests a role of angiopoietins in the regulation of podocytes. In the present study, we aimed to map the subcellular localization of TIE receptors in metanephric glomeruli of fetal pigs using high-resolution immunogold electron microscopy and the relative labeling index stereological approach. TIE1 and TIE2 antibody labeling was detected on the abluminal side of endothelial cell membranes. In endothelial cells, 4.5% of TIE2 was observed close to cell-cell contacts and 11.9% of TIE2 was found in closely associated pairs, which suggests the presence of homodimers. Interestingly, both receptors were also expressed in podocyte foot processes indicating that TIE1 and TIE2 may play a similar role in podocytes as in endothelial cells.

Therapeutic angiogenesis by vascular endothelial growth factor supplementation for treatment of renal disease

PURPOSE OF REVIEW

Vascular endothelial growth factors (VEGFs) influence renal function through angiogenesis, with VEGF-A being the most potent inducer of vascular formation. In the normal glomerulus, tight homeostatic balance is maintained between the levels of VEGF-A isoforms produced by podocyte cells, and the VEGF receptors (VEGFRs) expressed by glomerular endothelial, mesangial, and podocyte cells. Renal disease occurs when this homeostatic balance is lost, manifesting in the abnormal autocrine and paracrine VEGF-A/VEGFR signaling, ultrastructural glomerular and tubular damage, and impaired filtration.

RECENT FINDINGS

Preclinical disease models of ischemic renal injury, including acute ischemia/reperfusion, thrombotic microangiopathy, and chronic renovascular disease, treated with exogenous VEGF supplementation demonstrated therapeutic efficacy. These results suggest a therapeutic VEGF-A paracrine effect on endothelial cells in the context of acute or chronic obstructive ischemia. Conversely, renal dysfunction in diabetic nephropathy appears to occur through an upregulated VEGF autocrine effect on podocyte cells, which is exacerbated by hyperglycemia. Therefore, VEGF supplementation therapy may be contraindicated for treatment of diabetic nephropathy, but specific results will depend on dose and on the specific site of VEGF delivery. A drug delivery system that demonstrates cell specificity for glomerular or peritubular capillaries could be employed to restore balance to VEGF-A/VEGFR2 signaling, and by doing so, prevent the progression to end-stage renal disease.

SUMMARY

The review discusses the preclinical data available for VEGF supplementation therapy in models of renal disease.

Renal inflammatory changes in acute hepatic failure-associated acute kidney injury

BACKGROUND/AIMS

Acute kidney injury (AKI) is a common complication in advanced liver dysfunction. Our aim is to clarify the mechanisms of acute hepatic failure (AHF)-associated AKI.

METHODS

We examined the mechanisms of AHF-associated AKI, which is characterized by AKI in AHF and hyperbilirubinemia, following DA-to-Lewis rat liver transplantation.

RESULTS

During the progression of AHF and hyperbilirubinemia in liver graft rejection, AHF-associated AKI gradually developed by day 11. Degeneration and apoptotic cells were apparent in tubular epithelial cells with bile pigment accumulation and mitochondrial degeneration. Injury of peritubular capillaries (PTCs) was also noted with apoptotic endothelial cells, decreased expression of endothelial nitric oxide synthase, accumulation of α-smooth muscle actin+ pericytes and/or myofibroblasts, and inflammation. Angiogenic factors including vascular endothelial growth factor, angiopoietin-1, and angiopoietin-2 in the cortex were decreased on day 11. In addition, a marked reduction in the velocity of red blood cells in PTCs was evident in vivo.

CONCLUSIONS

AHF-associated AKI seems to be mediated by renal tubular epithelial cell injury with bile pigment accumulation, impaired microcirculation caused by PTC endothelial cell injury with depletion of endothelial nitric oxide synthase and angiogenic factors, and by a decrease in RBC velocity and renal inflammation. Multiple mechanisms including tubular and PTC injuries and renal inflammation may be involved in the development of AHF-associated AKI.

A potential role for caveolin-1 in VEGF-induced fibronectin upregulation in mesangial cells: involvement of VEGFR2 and Src

VEGF is known to be an endothelial cell mitogen that stimulates angiogenesis by promoting endothelial cell survival, proliferation, migration, and differentiation. Recent studies have suggested that VEGF may play a pivotal role in glomerular sclerosis through extracellular matrix protein (ECM) accumulation, although the signaling mechanism is still unclear. The GTPase RhoA has been implicated in VEGF-induced type IV collagen accumulation in some settings. Here we study the role of different VEGF receptors and membrane microdomain caveolae in VEGF-induced RhoA activation and fibronectin upregulation in mesangial cells (MCs). In primary rat MC, VEGF time and dose dependently increased fibronectin production. Rho pathway inhibition blocked VEGF-induced fibronectin upregulation. VEGF-induced RhoA activation was prevented by disrupting caveolae with cholesterol depletion and rescued by cholesterol repletion. VEGF stimulation led to a markedly increased VEGFR2/caveolin-1 but failed to increase VEGFR1/caveolin-1 association. VEGF also increased caveolin-1/Src association and activated Src, and Src inhibitor blocked RhoA activation and fibronectin upregulation. Src-mediated phosphorylation of caveolin-1 on Y14 has also been implicated in signaling responses. Overexpression of nonphosphorylatable caveolin-1 Y14A prevented VEGF-induced RhoA activation and fibronectin upregulation. In vivo, although VEGFR1 and VEGFR2 protein levels were both increased in the kidney cortices of diabetic rats, VEGFR2/caveolin-1 association but not VEGFR1/caveolin-1 association was significantly increased. In conclusion, VEGF-induced RhoA activation and fibronectin upregulation require caveolae and caveolin-1 interaction with VEGFR2 and Src. Interference with caveolin/-ae signaling may provide new avenues for the treatment of fibrotic renal disease.

Assessment of levels of vascular endothelial growth factor in patients with ESRD and its possible role in cardiovascular morbidity and mortality

Patients with end-stage renal disease (ESRD) are known to have an elevation of a variety of abnormal thrombotic and inflammatory markers associated with high cardiovascular mortality. Vascular endothelial growth factor (VEGF) is also dysregulated in ESRD but not much is known about the serum levels of VEGF in patients with ESRD. Published reports suggest that elevated levels of VEGF may be protective to the kidney during periods of acute injury and may maintain local glomerular function. Impaired production of VEGF may lead to proteinuria, hypertension, and thrombotic microangiopathy. However, its role in chronic kidney disease or ESRD remains undefined. In our study, we analyzed blood samples of 52 patients with ESRD on stable hemodialysis regimen and measured predialysis serum levels of VEGF and compared these with blood samples obtained from 50 healthy volunteers in order to study differences between baseline levels of VEGF and also attempted to determine its role in ESRD-related cardiovascular mortality.

Upregulation of sFlt-1 by trophoblasts induces the barrier dysfunction of glomerular endothelial cells

This study examined the effect of over-expression of sFlt-1 by trophoblasts on the barrier function of glomerular endothelial cells and the role of VEGF in this process in order to explore the pathogenesis of glomerular disease in preeclampsia. SFlt-1 expression in the human trophoblasts (TEV-1 cells) was enhanced by transfecting sFlt-1 plasmid DNA into TEV-1 cells. The monolayer barrier function of glomerular endothelial cells (ciGEnCs) was determined by measuring the fluorescence intensity of bovine serum albumin (BSA) that crossed the monolayer of glomerular endothelial cells. The results showed that the over-expression of sFlt-1 by TEV-1 cells led to the barrier dysfunction of ciGEnCs, and the exogenous VEGF could alleviate the ciGEnCs dysfunction resulting from the over-expression of sFlt-1 to a certain extent. It was concluded that the dysregulation of sFlt-1 and VEGF in preeclamptic pregnancy may contribute to the barrier dysfunction of glomerular endothelial cells, and VEGF may play an important role in maintaining the barrier function of glomerular endothelial cells, but it may not be the sole factor.

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.

Thrombospondin-1 short hairpin RNA suppresses tubulointerstitial fibrosis in the kidney of ureteral obstruction by ameliorating peritubular capillary injury

BACKGROUND/AIMS

Thrombospondin-1 (TSP-1), a naturally occurring inhibitor of angiogenesis, is an important mediator of renal fibrosis in clinical and experimental kidney disease. Increasing evidence shows that the microvasculature plays a critical role in progressive renal disease. The present study was undertaken to investigate whether interstitial fibrosis could be prevented by abolishing TSP-1 function in unilateral ureteral obstruction (UUO)-induced renal fibrosis.

METHODS AND RESULTS

A short hairpin RNA vector, designated Thbs-1, significantly suppressed TSP-1 in both transcriptional and translational levels in in vitro-cultured cells and in vivo fibrosis-induced mouse kidney. Furthermore, TSP-1 RNA interference increased the protein level of vascular endothelial growth factor (VEGF) and the density of peritubular capillaries (PTCs), reduced the expression of hypoxia-inducible factor-1α in tubulointerstitial cells, and collagen III and the connective tissue growth factor expression were markedly reduced from day 7 after UUO-induced fibrosis, but un- or vector-treated mice maintained their expression. TSP-1 shRNA suppressed the protein level of TSP-1, increased VEGF expression and PTC density and alleviated the development of renal interstitial fibrosis in UUO mice.

CONCLUSION

These data suggest that inhibition of TSP-1 expression prevented tubulointerstitial fibrosis through ameliorating PTC injury.

Spironolactone and enalapril differentially up-regulate the expression of VEGF and heme oxygenase-1 in the neonatal rat kidney

Both the renin-angiotensin-aldosterone system (RAAS) and hypoxia are vital physiological factors involved in the control of nephrogenesis and vascularization. We investigated the relationship between RAAS and hypoxia in the developing kidney. The expression of VEGF and heme oxygenase (HO)-1 related with the oxygen was analyzed in the enalapril- or spironolactone-treated neonatal rat kidneys. Enalapril (30 mg/kg/d) or spironolactone (200 mg/kg/d) was administered to newborn rat pups for 7 d. The newborn rats were injected i.p. with pimonidazole (200 mg/kg), a marker of severe tissue hypoxia, 1 h before killing. VEGF and HO-1 protein expression was significantly increased by immunoblots and immunohistochemistry in both the enalapril- and spironolactone-treated kidneys, compared with the controls (p < 0.05). HO-1 mRNA expression was increased in the spironolactone-treated group (p < 0.05). The immunoactivity of pimonidazole was not different from that of the controls in the enalapril-treated group, whereas it was increased in the spironolactone-treated group. The results of this study indicate that aldosterone blockade or angiotensin II inhibition in the developing rat kidney up-regulated renal VEGF and HO-1 expression regardless of the hypoxic conditions and may differentially modulate VEGF and HO-1 production.

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.

Aldosterone upregulates vascular endothelial growth factor expression in mouse cortical collecting duct epithelial cells through classic mineralocorticoid receptor

Accumulating evidence shows that aldosterone plays an important role in the pathogenesis of renal fibrosis but its mechanism has not been completely defined. Recently, exogenous administration of aldosterone significantly alleviated ischemic states in a model of femoral artery ligated rats, accompanied by an obvious enhancement of VEGF upregulation. We hypothesized that aldosterone may also regulate the expression of VEGF in the kidney. To confirm this, cultured cortical collecting duct epithelial cells (M-1 cell line) were incubated with aldosterone and control media, respectively. The pathway by which aldosterone regulates VEGF expression was tested by the administration of spironolactone, a specific mineralocorticoid receptor (MR) antagonist. VEGF expression was detected by immunofluorescence staining, ELISA, Western blot and RT-PCR. Aldosterone induced an elevation of VEGF excretion in a time- and dose-dependent manner. Western blotting showed a 1.4-fold elevation in cytosolic VEGF expression following aldosterone (10(-8) M) incubation for 48 h (p<0.01). After aldosterone (10(-7) M) incubation for 48 h, the mRNA level of VEGF164 and VEGF120 showed 1.8- and 1.7-fold increases, respectively (p<0.01). This upregulation was almost completely blocked by spironolactone as shown both by mRNA levels and cytosolic protein levels. In addition, the mRNA of aldosterone receptor was detected in M-1 cells. We demonstrated for the first time that aldosterone induced VEGF expression in M-1 cells, an effect mediated by classic mineralocorticoid receptor. This finding provides experimental evidence for the local non-hemodynamic action of aldosterone.

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.

Glomerular disease workshop

Recent observations regarding intrinsic glomerular cell biology, particularly in the podocyte, have provided exciting new insights into potential pathogenic mechanisms of human glomerular disease. Although both immune and nonimmune mechanisms of glomerular injury have been studied previously, experimental models of disease and recent techniques that provide tools for molecular profiling show great promise for identifying glomerular disease biomarkers. Despite these recent advances, additional work in both basic and clinical studies of glomerular disease is needed to advance the field. Standardization of animal models of distinct forms of glomerular disease would likely facilitate the search for biomarkers. Several factors limit current efforts to implement clinical trials of glomerular disease. Identification of disease biomarkers, development of disease-specific end points, and organization of collaborative clinical groups are critical for ultimately designing and implementing appropriately powered trials of glomerular disease.