Vascular endothelial growth factor mRNA expression in minimal change, membranous, and diabetic nephropathy demonstrated by non-isotopic in situ hybridisation

Suramin Affects the Renal VEGF-A/VEGFR Axis in Short-Term Streptozotocin-Induced Diabetes

Diabetic nephropathy (DN) accounts for approximately 50% of end-stage renal diseases. Vascular endothelial growth factor A (VEGF-A) is thought to be a critical mediator of vascular dysfunction in DN, but its role is unclear. The lack of pharmacological tools to modify renal concentrations further hinders the understanding of its role in DN. In this study, rats were evaluated after 3 weeks of streptozotocin-induced diabetes and two suramin treatments (10 mg/kg, ip). Vascular endothelial growth factor A expression was evaluated by western blot of glomeruli and immunofluorescence of the renal cortex. RT-PCR for receptors Vegfr1 mRNA and Vegfr2 mRNA quantitation was performed. The soluble adhesive molecules (sICAM-1, sVCAM-1) in blood were measured by ELISA and the vasoreactivity of interlobar arteries to acetylcholine was evaluated using wire myography. Suramin administration reduced the expression and intraglomerular localisation of VEGF-A. Increased VEGFR-2 expression in diabetes was reduced by suramin to non-diabetic levels. Diabetes reduced the sVCAM-1 concentrations. Suramin in diabetes restored acetylcholine relaxation properties to non-diabetic levels. In conclusion, suramin affects the renal VEGF-A/VEGF receptors axis and has a beneficial impact on endothelium-dependent relaxation of renal arteries. Thus, suramin may be used as a pharmacological agent to investigate the potential role of VEGF-A in the pathogenesis of renal vascular complications in short-term diabetes.

An overview of the efficacy and signaling pathways activated by stem cell-derived extracellular vesicles in diabetic kidney disease

Diabetic kidney disease (DKD) is one of complications of diabetes mellitus with severe microvascular lesion and the most common cause of end-stage chronic kidney disease (ESRD). Controlling serum glucose remains the primary approach to preventing and slowing the progression of DKD. Despite considerable efforts to control diabetes, people with diabetes develop not only DKD but also ESRD. The pathogenesis of DKD is very complex, and current studies indicate that mesenchymal stromal cells (MSCs) regulate complex disease processes by promoting pro-regenerative mechanisms and inhibiting multiple pathogenic pathways. Extracellular vesicles (EVs) are products of MSCs. Current data indicate that MSC-EVs-based interventions not only protect renal cells, including renal tubular epithelial cells, podocytes and mesangial cells, but also improve renal function and reduce damage in diabetic animals. As an increasing number of clinical studies have confirmed, MSC-EVs may be an effective way to treat DKD. This review explores the potential efficacy and signaling pathways of MSC-EVs in the treatment of DKD.

Comparison of the Surgical Resection and Infarct 5/6 Nephrectomy Rat Models of Chronic Kidney Disease

The 5/6 nephrectomy rat remnant kidney model is commonly employed to study chronic kidney disease (CKD). This model requires removal of one whole kidney and two-thirds of the other. The two most common ways of producing the remnant kidney are surgical resection of poles, known as the polectomy (Pol) model, or ligation of upper and lower renal arterial branches, resulting in pole infarction (Inf). These models have much in common, but also major phenotypic differences, and thus respectively model unique aspects of human CKD. The purpose of this review is to summarize phenotypic similarities and differences between these two models and their relation to human CKD, while emphasizing their vascular phenotype. In this article we review studies that have evaluated arterial blood pressure, the renin-angiotensin-aldosterone-system (RAAS), autoregulation, nitric oxide, single nephron physiology, angiogenic and anti-angiogenic factors, and capillary rarefaction in these two models. Phenotypic similarities: both models spontaneously develop hallmarks of human CKD including uremia, fibrosis, capillary rarefaction, and progressive renal function decline. They both undergo whole-organ hypertrophy, hyperfiltration of functional nephrons, reduced renal expression of angiogenic factor VEGF, increased renal expression of the anti-angiogenic thrombospondin-1, impaired renal autoregulation, and abnormal vascular nitric oxide physiology. Key phenotypic differences: the Inf model develops rapid-onset, moderate-to-severe systemic hypertension, and the Pol model early normotension followed by mild-to-moderate hypertension. The Inf rat has a markedly more active renin-angiotensin-aldosterone-system. Comparison of these two models facilitates understanding of how they can be utilized for studying CKD pathophysiology (e.g., RAAS dependent or independent pathology).

Molecular Mechanisms of Proteinuria in Minimal Change Disease

Minimal change disease (MCD) is the most common type of idiopathic nephrotic syndrome in childhood and represents about 15% cases in adults. It is characterized by massive proteinuria, edema, hypoalbuminemia, and podocyte foot process effacement on electron microscopy. Clinical and experimental studies have shown an association between MCD and immune dysregulation. Given the lack of inflammatory changes or immunocomplex deposits in the kidney tissue, MCD has been traditionally thought to be mediated by an unknown circulating factor(s), probably released by T cells that directly target podocytes leading to podocyte ultrastructural changes and proteinuria. Not surprisingly, research efforts have focused on the role of T cells and podocytes in the disease process. Nevertheless, the pathogenesis of the disease remains a mystery. More recently, B cells have been postulated as an important player in the disease either by activating T cells or by releasing circulating autoantibodies against podocyte targets. There are also few reports of endothelial injury in MCD, but whether glomerular endothelial cells play a role in the disease remains unexplored. Genome-wide association studies are providing insights into the genetic susceptibility to develop the disease and found a link between MCD and certain human haplotype antigen variants. Altogether, these findings emphasize the complex interplay between the immune system, glomerular cells, and the genome, raising the possibility of distinct underlying triggers and/or mechanisms of proteinuria among patients with MCD. The heterogeneity of the disease and the lack of good animal models of MCD remain major obstacles in the understanding of MCD. In this study, we will review the most relevant candidate mediators and mechanisms of proteinuria involved in MCD and the current models of MCD-like injury.

Lupus podocytopathy superimposed on diabetic glomerulosclerosis: A case report

RATIONALE

Lupus podocytopathy (LP) is an entity that is increasingly being reported in the literature on systemic lupus erythematosus (SLE). LP is characterized by nephrotic syndrome in SLE patients with diffuse glomerular podocyte foot process effacement and no immune complex deposits along the capillary loops. Histologically, LP typically mimics minimal change disease or primary focal segmental glomerulosclerosis (FSGS) on a background of ISN/RPS class I or II lupus nephritis. In situations where there are coexistent glomerular diseases, however, LP may be easily masked by background lesions and overlapping clinical symptoms.

PATIENT CONCERNS

We report the case of a 24-year-old woman with type I diabetes, hypertension, psoriasis/rash, and intermittent arthritis who presented with abrupt onset of severe nephrotic proteinuria and renal insufficiency. Renal biopsy revealed nodular glomerulosclerosis and FSGS. Immune deposits were not identified by immunofluorescence or electron microscopy. Ultrastructurally, there was diffuse glomerular basement membrane thickening and over 90% podocyte foot process effacement. With no prior established diagnosis of SLE, the patient was initially diagnosed with diabetic nephropathy with coexistent FSGS, and the patient was started on angiotensin-converting enzyme inhibitors (ACEI) and diuretics. However, nephrotic proteinuria persisted and renal function deteriorated. The patient concurrently developed hemolytic anemia with pancytopenia.

DIAGNOSES

Subsequent to the biopsy, serologic results showed positive autoantibodies against double strand DNA (dsDNA), Smith antigen, ribonucleoprotein (RNP), and Histone. A renal biopsy was repeated, revealing essentially similar findings to those of the previous biopsy. Integrating serology and clinical presentation, SLE was favored. The pathology findings were re-evaluated and considered to be most consistent with LP and coexistent diabetic nephropathy, with superimposed FSGS either as a component of LP or as a lesion secondary to diabetes or hypertension.

INTERVENTIONS

The patient was started on high-dose prednisone at 60 mg/day, with subsequent addition of mycophenolate mofetil and ACEI, while prednisone was gradually tapered.

OUTCOMES

The patient's proteinuria, serum creatinine, complete blood counts, skin rash, and arthritis were all significantly improved.

CONCLUSION

The diagnosis of LP when confounded by other glomerular diseases that may cause nephrotic syndrome can be challenging. Sufficient awareness of this condition is necessary for the appropriate diagnosis and treatment.

Urinary Markers of Podocyte Dysfunction in Chronic Glomerulonephritis

Chronic glomerulonephritis (CGN) is a disease with a steady progressive course that involves the development of nephrosclerosis, which is especially evident in clinical courses with incidences of high proteinuria (PU). Currently, proteinuria is considered the main laboratory feature (sign) of CGN activity and progression because proteinuria is closely related to the process of tubulointerstitial fibrosis, which is correlated with the grade of renal insufficiency. The injury to podocytes, which are key components of the filtration barrier, plays a central role in proteinuria development. The detachment of podocytes from the glomerular basement membrane leading to podocytopenia is suggested to induce glomerulosclerosis and hyalinosis with obliteration of capillary loops and the progression of chronic kidney disease. Urinary markers of podocyte dysfunction could serve as useful tools while monitoring the activity and prognosis of CGN. In this chapter, the most important mechanisms of podocyte loss and urinary markers of this process are discussed.

Endothelial glycocalyx restoration by growth factors in diabetic nephropathy

The endothelial glycocalyx (eGlx) constitutes the first barrier to protein in all blood vessels. This is particularly noteworthy in the renal glomerulus, an ultrafiltration barrier. Leakage of protein, such as albumin, across glomerular capillaries results in albumin in the urine (albuminuria). This is a hall mark of kidney disease and can reflect loss of blood vessel integrity in microvascular beds elsewhere. We discuss evidence demonstrating that targeted damage to the glomerular eGlx results in increased glomerular albumin permeability. EGlx is lost in diabetes and experimental models demonstrate loss from glomerular endothelial cells. Vascular endothelial growth factor (VEGF)A is upregulated in early diabetes, which is associated with albuminuria. Treatment with paracrine growth factors such as VEGFC, VEGF165b and angiopoietin-1 can modify VEGFA signalling, rescue albumin permeability and restore glomerular eGlx in models of diabetes. Manipulation of VEGF receptor 2 signalling, or a common eGlx biosynthesis pathway by these growth factors, may protect and restore the eGlx layer. This would help to direct future therapeutics in diabetic nephropathy.

Mesenchymal Stromal Cells Induce Podocyte Protection in the Puromycin Injury Model

Podocytes are specialized cells with a limited capacity for cell division that do not regenerate in response to injury and loss. Insults that compromise the integrity of podocytes promote proteinuria and progressive renal disease. The aim of this study was to evaluate the potential renoprotective and regenerative effects of mesenchymal stromal cells (mSC) in a severe form of the podocyte injury model induced by intraperitoneal administration of puromycin, aggravated by unilateral nephrectomy. Bone derived mSC were isolated and characterized according to flow cytometry analyses and to their capacity to differentiate into mesenchymal lineages. Wistar rats were divided into three groups: Control, PAN, and PAN+ mSC, consisting of PAN rats treated with 2 × 10⁵ mSC. PAN rats developed heavy proteinuria, hypertension, glomerulosclerosis and significant effacement of the foot process. After 60 days, PAN rats treated with mSC presented a significant amelioration of all these abnormalities. In addition, mSC treatment recovered WT1 expression, improved nephrin, podocin, synaptopodin, podocalyxin, and VEGF expression, and downregulated proinflammatory Th1 cytokines in the kidney with a shift towards regulatory Th2 cytokines. In conclusion, mSC administration induced protection of podocytes in this experimental PAN model, providing new perspectives for the treatment of renal diseases associated with podocyte damage.

MiR-320a induces diabetic nephropathy via inhibiting MafB

Multiple studies indicate that microRNAs (miRNAs) are involved in diabetes. However, the roles of miRNA in the target organ damages in diabetes remain unclear. This study investigated the functions of miR-320a in diabetic nephropathy (DN). In this study, db/db mice were used to observe the changes in podocytes and their function in vivo, as well as in cultured mouse podocyte cells (MPC5) exposed to high glucose in vitro. To further explore the role of miR-320a in DN, recombinant adeno-associated viral particle was administered intravenously to manipulate the expression of miR-320a in db/db mice. Overexpression of miR-320a markedly promoted podocyte loss and dysfunction in DN, including mesangial expansion and increased levels of proteinuria, serum creatinine and urea nitrogen. Furthermore, MafB was identified as a direct target of miR-320a through AGO2 co-immunoprecipitation, luciferase reporter assay, and Western blotting. Moreover, re-expression of MafB rescued miR-320a-induced podocyte loss and dysfunction by upregulating the expressions of Nephrin and glutathione peroxidase 3 (Gpx3). Our data indicated that miR-320a aggravated renal disfunction in DN by targeting MafB and downregulating Nephrin and Gpx3 in podocytes, which suggested that miR-320a could be a potential therapeutic target of diabetic nephropathy.

VEGFC Reduces Glomerular Albumin Permeability and Protects Against Alterations in VEGF Receptor Expression in Diabetic Nephropathy

Elevated levels of vascular endothelial growth factor (VEGF) A are thought to cause glomerular endothelial cell (GEnC) dysfunction and albuminuria in diabetic nephropathy. We hypothesized that VEGFC could counteract these effects of VEGFA to protect the glomerular filtration barrier and reduce albuminuria. Isolated glomeruli were stimulated ex vivo with VEGFC, which reduced VEGFA- and type 2 diabetes-induced glomerular albumin solute permeability (Ps'alb). VEGFC had no detrimental effect on glomerular function in vivo when overexpression was induced locally in podocytes (podVEGFC) in otherwise healthy mice. Further, these mice had reduced glomerular VEGFA mRNA expression, yet increased glomerular VEGF receptor heterodimerization, indicating differential signaling by VEGFC. In a model of type 1 diabetes, the induction of podVEGFC overexpression reduced the development of hypertrophy, albuminuria, loss of GEnC fenestrations and protected against altered VEGF receptor expression. In addition, VEGFC protected against raised Ps'alb by endothelial glycocalyx disruption in glomeruli. In summary, VEGFC reduced the development of diabetic nephropathy, prevented VEGF receptor alterations in the diabetic glomerulus, and promoted both glomerular protection and endothelial barrier function. These important findings highlight a novel pathway for future investigation in the treatment of diabetic nephropathy.

Amniotic fluid stem cell-derived vesicles protect from VEGF-induced endothelial damage

Injection of amniotic fluid stem cells (AFSC) delays the course of progression of renal fibrosis in animals with Alport Syndrome, enhancing kidney function and improving survival. The mechanisms responsible for these protective outcomes are still largely unknown. Here, we showed that vascular endothelial growth factor (VEGF) signaling within the glomeruli of Alport mice is strongly elevated early on in the disease, causing glomerular endothelial cell damage. Intraventricular injected AFSC that homed within the glomeruli showed strong modulation of the VEGF activity, particularly in glomerular endothelial cells. To investigate this phenomenon we hypothesized that extracellular vesicles (EVs) produced by the AFSC could be responsible for the observed renoprotection. AFSC derived EVs presented exosomal and stem cell markers on their surface membrane, including VEGFR1 and VEGFR2. EVs were able to modulate VEGF in glomerular endothelial cells by effectively trapping the excess VEGF through VEGFR1-binding preventing cellular damage. In contrast, VEGFR1/sVEGFR1 knockout EVs failed to show similar protection, thus indicating that VEGF trapping is a potentially viable mechanism for AFSC-EV mediated renoprotection. Taken together, our findings establish that EVs secreted by AFSC could target a specific signaling pathway within the glomerulus, thus representing a new potential glomerulus-specific targeted intervention.

Renin-angiotensin system transgenic mouse model recapitulates pathophysiology similar to human preeclampsia with renal injury that may be mediated through VEGF

Using a transgenic cross, we evaluated features of preeclampsia, renal injury and the sFlt1/VEGF changes. Transgenic hAGT and hREN, or wild-type (WT) C57Bl/6 mice were cross-bred: female hAGT × male hREN for preeclampsia (PRE) model and female WT × male WT for pregnant controls (WTP). Samples were collected for plasma VEGF, sFlt1, and urine albumin. Blood pressures (BP) were monitored by telemetry. Vascular reactivity was investigated by wire myography. Kidneys and placenta were immunostained for sFlt1 and VEGF. Eleven PRE and 9 WTP mice were compared. PRE more frequently demonstrated albuminuria, glomerular endotheliosis (80% vs. 11%; P = 0.02), and placental necrosis (60% vs. 0%; P < 0.01). PRE group demonstrated declining BPs with advancing gestation. Plasma sFlt1 increased across pregnancy in PRE; VEGF did not vary. IHC demonstrated the presence of sFlt1 in glomeruli, lymphatics, and collecting tubules of PRE kidneys, suggesting excretion. VEGF immunostaining was increased specifically in the glomeruli of PRE kidneys. Placenta in PRE showed marked immunostaining for sFlt1. We conclude that this transgenic model of preeclampsia recapitulates human preeclamptic state with high fidelity, and that, vascular adaptation to pregnancy is suggested by declining BPs and reduced vascular response to PE and increased response to acetylcholine. Placental damage with resultant increased release of sFlt1, proteinuria, deficient spiral artery remodeling, and glomerular endotheliosis were observed in this model of PRE. Increased VEGF binding to glomerular endothelial cells in this model of PRE is similar to human PRE and leads us to hypothesize that renal injury in preeclampsia may be mediated through local VEGF.

Non-invasive Detection of Acute Renal Allograft Rejection by Measurement of Vascular Endothelial Growth Factor in Urine

Urinary vascular endothelial growth factor (VEGF) was determined by enzyme-linked immunosorbent assay in 199 renal allograft recipients and 80 healthy controls. Urinary VEGF level did not change significantly during the first 8 weeks after transplantation in 119 patients with stable renal function and there were no abnormal histological findings (No-AR). In 67 patients with acute rejection, urinary VEGF was significantly higher (28.57 ± 6.21 pg/μmol creatinine) than in the No-AR patients (3.05 ± 0.45 pg/μmol creatinine) and healthy controls (2.87 ± 0.35 pg/μmol creatinine). At a cut-off point of 3.26 pg/μmol creatinine, sensitivity and specificity for diagnosis of acute rejection were 86.6 and 71.4%, respectively. The 13 patients with subclinical rejection excreted urinary VEGF (16.14 ± 4.09 pg/μmol creatinine) at a significantly higher level than No-AR patients (3.05 ± 0.45 pg/μmol creatinine). At a cut-off point of 4.69 pg/μmol creatinine, sensitivity and specificity for diagnosis of subclinical rejection were 84.6 and 79.8%, respectively. In conclusion, monitoring VEGF in urine might offer a new non-invasive way to detect acute and subclinical rejection in renal transplant recipients.

The podocyte as a direct target for treatment of glomerular disease?

The Centers for Disease Control and Prevention estimates more than 10% of adults in the United States, over 20 million Americans, have chronic kidney disease (CKD). A failure to maintain the glomerular filtration barrier directly contributes to the onset of CKD. The visceral epithelial cells, podocytes, are integral to the maintenance of this renal filtration barrier. Direct podocyte injury contributes to the onset and progression of glomerular diseases such as minimal change disease (MCD), focal segmental glomerular sclerosis (FSGS), diabetic nephropathy, and HIV-associated nephropathy (HIVAN). Since podocytes are terminally differentiated with minimal capacity to self-replicate, they are extremely sensitive to cellular injury. In the past two decades, our understanding of the mechanism(s) by which podocyte injury occurs has greatly expanded. With this newfound knowledge, therapeutic strategies have shifted to identifying targets directed specifically at the podocyte. Although the systemic effects of these agents are important, their direct effect on the podocyte proves to be essential in ameliorating glomerular disease. In this review, we highlight the mechanisms by which these agents directly target the podocyte independent of its systemic effects.

Effects of extremely low frequency pulsed magnetic fields on diabetic nephropathy in streptozotocin-treated rats

Background

Extremely low frequency pulsed magnetic fields (ELFPMF) have been shown to induce Faraday currents and measurable effects on biological systems. A kind of very high frequency electromagnetic field was reported that it improved the symptoms of diabetic nephropathy (DN) which is a major complication of diabetes. However, few studies have examined the effects of ELFPMF DN at the present. The present study was designed to investigate the effects of ELFPMF on DN in streptozotocin (STZ)–induced type 1 diabetic rats.

Methods

Adult male SD rats were randomly divided into three weight-matched groups: Control (non-diabetic rats without DN), DN + ELFPMF (diabetic rats with DN exposed to ELFPMF, 8 h/days, 6 weeks) and DN (diabetic rats with DN exposed to sham ELFPMF). Renal morphology was examined by light and electron microscopy, vascular endothelial growth factor (VEGF)-A and connective tissue growth factor (CTGF) were measured by enzyme linked immune sorbent assay.

Results

After 6 weeks’ ELFPMF exposure, alterations of hyperglycemia and weight loss in STZ-treated rats with DN were not found, while both positive and negative effects of ELFPMF on the development of DN in diabetic rats were observed. The positive one was that ELFPMF exposure attenuated the pathological alterations in renal structure observed in STZ-treated rats with DN, which were demonstrated by slighter glomerular and tubule-interstitial lesions examined by light microscopy and slighter damage to glomerular basement membrane and podocyte foot processes examined by electron microscopy. And then, the negative one was that ELFPMF stimulation statistically significantly decreased renal expression of VEGF-A and statistically significantly increased renal expression of CTGF in diabetic rats with DN, which might partially aggravate the symptoms of DN.

Conclusion

Both positive and negative effects of ELFPMF on the development of DN in diabetic rats were observed. The positive effect induced by ELFPMF might play a dominant role in the procession of DN in diabetic rats, and it is suggested that the positive effect should be derived from the correction of pathogenic diabetes-induced mediators.

The Decrement of Hemoglobin Concentration with Angiotensin II Receptor Blocker Treatment Is Correlated with the Reduction of Albuminuria in Non-Diabetic Hypertensive Patients: Post-Hoc Analysis of ESPECIAL Trial

Blockade of the renin-angiotensin-aldosterone system exhibits a renoprotective effect; however, blockade of this system may also decrease hemoglobin (Hb) and erythropoietin (EPO) levels. We evaluated the correlation between reduced albuminuria and decreased hemoglobin concentrations after treatment with an angiotensin II receptor blocker (ARB). Two hundred forty-five non-diabetic hypertensive participants with established albuminuria and relatively preserved renal function were treated with an ARB (40 mg/day olmesartan) for eight weeks. Subsequent changes in various clinical parameters, including Hb, EPO, and albuminuria, were analyzed following treatment. After the 8-week treatment with an ARB, Hb and EPO levels significantly decreased. Patients with a greater decrease in Hb exhibited a greater reduction in 24-hour urinary albumin excretion compared with patients with less of a decrease or no decrease in Hb, whereas no associations with a decline in renal function and EPO levels were noted. Multivariate logistic regression analysis demonstrated a correlation between the reduction of urine albumin excretion and the decrease in Hb levels (after natural logarithm transformation, adjusted odds ratio 1.76, 95% confidence interval 1.21-2.56, P = 0.003). Linear regression analysis also supported this positive correlation (Pearson correlation analysis; R = 0.24, P < 0.001). Decreased Hb concentrations following ARB treatment were positively correlated with reduced albuminuria in non-diabetic hypertensive patients, regardless of decreased blood pressure and EPO levels or renal function decline.

GIV/girdin links vascular endothelial growth factor signaling to Akt survival signaling in podocytes independent of nephrin

Podocytes are critically involved in the maintenance of the glomerular filtration barrier and are key targets of injury in many glomerular diseases. Chronic injury leads to progressive loss of podocytes, glomerulosclerosis, and renal failure. Thus, it is essential to maintain podocyte survival and avoid apoptosis after acute glomerular injury. In normal glomeruli, podocyte survival is mediated via nephrin-dependent Akt signaling. In several glomerular diseases, nephrin expression decreases and podocyte survival correlates with increased vascular endothelial growth factor (VEGF) signaling. How VEGF signaling contributes to podocyte survival and prevents apoptosis remains unknown. We show here that Gα-interacting, vesicle-associated protein (GIV)/girdin mediates VEGF receptor 2 (VEGFR2) signaling and compensates for nephrin loss. In puromycin aminonucleoside nephrosis (PAN), GIV expression increased, GIV was phosphorylated by VEGFR2, and p-GIV bound and activated Gαi3 and enhanced downstream Akt2, mammalian target of rapamycin complex 1 (mTORC1), and mammalian target of rapamycin complex-2 (mTORC2) signaling. In GIV-depleted podocytes, VEGF-induced Akt activation was abolished, apoptosis was triggered, and cell migration was impaired. These effects were reversed by introducing GIV but not a GIV mutant that cannot activate Gαi3. Our data indicate that after PAN injury, VEGF promotes podocyte survival by triggering assembly of an activated VEGFR2/GIV/Gαi3 signaling complex and enhancing downstream PI3K/Akt survival signaling. Because of its important role in promoting podocyte survival, GIV may represent a novel target for therapeutic intervention in the nephrotic syndrome and other proteinuric diseases.

Advanced diabetic nephropathy with nephrotic range proteinuria: a pilot study of the long-term efficacy of subcutaneous ACTH gel on proteinuria, progression of CKD, and urinary levels of VEGF and MCP-1

BACKGROUND AND OBJECTIVE

Adrenocorticotropic hormone (ACTH) is able to reduce proteinuria in nondiabetic glomerulopathies through activation of melanocortin receptors (MCR) expressed in the podocyte. To determine the efficacy of ACTH, we conducted a randomized, open-label pilot trial of ACTH gel in patients with advanced diabetic nephropathy.

STUDY DESIGN

Twenty-three (23) patients with diabetic nephropathy were randomized to daily subcutaneous (SQ) injections of 16 or 32 units of ACTH gel for six months. Outcome. The primary endpoint was the percentage of patients achieving a complete remission (<300 mg/24 hours) within 6 months. Exploratory endpoints included the percentage of partial (50% reduction) remissions, changes in Cr, and urinary cytokine markers.

RESULTS

After 6 months of ACTH gel therapy, 8 of 14 (57%) patients achieved a complete (n = 1) or partial (n = 7) remission. In the low-dose ACTH gel group (16 units), urinary protein fell from 6709 + 953 to 2224 + 489 mg/24 hrs (P < 0.001). In contrast, 2 of 6 patients in the 32-unit group achieved partial remission, but aggregate proteinuria (5324 + 751 to 5154 + 853 mg/24 hours) did not change. Urinary VEGF increased from 388 to 1346 pg/mg urinary creatinine (P < 0.02) in the low-dose group but remained unchanged in the high-dose group.

CONCLUSION

ACTH gel stabilizes renal function and reduces urinary protein for up to 6 months after treatment. The ClinTrials.gov identifier is NCT01028287.

Dasatinib-induced nephrotic-range proteinuria

Since the introduction of imatinib, tyrosine kinase inhibition has been a mainstay in the treatment of many malignancies. The number of these medications is growing, as are the number of targeted tyrosine kinases. Off-target effects of these medications can have beneficial or adverse effects on the kidney. The onus of knowing the implications of these medications on kidney function, and appropriate treatment when such adverse effects occur, is on the nephrologist. We present a patient with chronic myelogenous leukemia who developed nephrotic-range proteinuria after initiation on dasatinib therapy that resolved after changing therapy to imatinib. The mechanism of kidney injury caused by dasatinib has not been described previously in the literature. We provide a review of vascular endothelial growth factor and its pharmacologic inhibition as it pertains to kidney pathology and propose possible mechanisms by which dasatinib induces kidney injury.

Aberrant production of extracellular matrix proteins and dysfunction in kidney endothelial cells with a short duration of diabetes

Diabetic nephropathy is the most common cause of end-stage renal disease and is a major risk factor for cardiovascular disease. In the United States, microvascular complications during diabetic nephropathy contribute to high morbidity and mortality rates. However, the cell-autonomous impact of diabetes on kidney endothelial cell function requires further investigation. Male Akita/+ [autosomal dominant mutation in the insulin II gene (Ins2)] mice reproducibly develop diabetes by 4 wk of age. Here, we examined the impact a short duration of diabetes had on kidney endothelial cell function. Kidney endothelial cells were prepared from nondiabetic and diabetic mice (4 wk of diabetes) to delineate the early changes in endothelial cell function. Kidney endothelial cells from Akita/+ mice following 4 wk of diabetes demonstrated aberrant expression of extracellular matrix proteins including decreased osteopontin and increased fibronectin expression which correlated with increased α5-integrin expression. These changes were associated with the attenuation of migration and capillary morphogenesis. Kidney endothelial cells from Akita/+ mice had decreased VEGF levels but increased levels of endothelial nitric oxide synthase(eNOS) and NO, suggesting uncoupling of VEGF-mediated NO production. Knocking down eNOS expression in Akita/+ kidney endothelial cells increased VEGF expression, endothelial cell migration, and capillary morphogenesis. Furthermore, attenuation of sprouting angiogenesis of aortas from Akita/+ mice with 8 wk of diabetes was restored in the presence of the antioxidant N-acetylcysteine. These studies demonstrate that aberrant endothelial cell function with a short duration of diabetes may set the stage for vascular dysfunction and rarefaction at later stages of diabetes.

Understanding the mechanisms of proteinuria: therapeutic implications

A large body of evidence indicates that proteinuria is a strong predictor of morbidity, a cause of inflammation, oxidative stress and progression of chronic kidney disease, and development of cardiovascular disease. The processes that lead to proteinuria are complex and involve factors such as glomerular hemodynamic, tubular absorption, and diffusion gradients. Alterations in various different molecular pathways and interactions may lead to the identical clinical end points of proteinuria and chronic kidney disease. Glomerular diseases include a wide range of immune and nonimmune insults that may target and thus damage some components of the glomerular filtration barrier. In many of these conditions, the renal visceral epithelial cell (podocyte) responds to injury along defined pathways, which may explain the resultant clinical and histological changes. The recent discovery of the molecular components of the slit diaphragm, specialized structure of podocyte-podocyte interaction, has been a major breakthrough in understanding the crucial role of the epithelial layer of the glomerular barrier and the pathogenesis of proteinuria. This paper provides an overview and update on the structure and function of the glomerular filtration barrier and the pathogenesis of proteinuria, highlighting the role of the podocyte in this setting. In addition, current antiproteinuric therapeutic approaches are briefly commented.

Relevance of VEGF and nephrin expression in glomerular diseases

The glomerular filtration barrier is affected in a large number of acquired and inherited diseases resulting in extensive leakage of plasma albumin and larger proteins, leading to nephrotic syndrome and end-stage renal disease. Unfortunately, the molecular mechanisms governing the development of the nephrotic syndrome remain poorly understood. Here, I give an overview of recent investigations that have focused on characterizing the interrelationships between the slit diaphragm components and podocytes-secreted VEGF, which have a significant role for maintaining the normal podocyte structure and the integrity of the filtering barrier.

Mechanisms and consequences of TGF-ß overexpression by podocytes in progressive podocyte disease

In patients with progressive podocyte disease, such as focal segmental glomerulosclerosis (FSGS) and membranous nephropathy, upregulation of transforming growth factor-ß (TGF-ß) is observed in podocytes. Mechanical pressure or biomechanical strain in podocytopathies may cause overexpression of TGF-ß and angiotensin II (Ang II). Oxidative stress induced by Ang II may activate the latent TGF-ß, which then activates Smads and Ras/extracellular signal-regulated kinase (ERK) signaling pathways in podocytes. Enhanced TGF-ß activity in podocytes may lead to thickening of the glomerular basement membrane (GBM) by overproduction of GBM proteins and impaired GBM degradation in podocyte disease. It may also lead to podocyte apoptosis and detachment from the GBM, and epithelial-mesenchymal transition (EMT) of podocytes, initiating the development of glomerulosclerosis. Furthermore, activated TGF-ß/Smad signaling by podocytes may induce connective tissue growth factor and vascular endothelial growth factor overexpression, which could act as a paracrine effector mechanism on mesangial cells to stimulate mesangial matrix synthesis. In proliferative podocytopathies, such as cellular or collapsing FSGS, TGF-ß-induced ERK activation may play a role in podocyte proliferation, possibly via TGF-ß-induced EMT of podocytes. Collectively, these data bring new mechanistic insights into our understanding of the TGF-ß overexpression by podocytes in progressive podocyte disease.

Podocyte vascular endothelial growth factor (Vegf₁₆₄) overexpression causes severe nodular glomerulosclerosis in a mouse model of type 1 diabetes

AIMS/HYPOTHESIS

The pathogenic role of excessive vascular endothelial growth factor (VEGF)-A in diabetic nephropathy has not been defined. We sought to test whether increased podocyte VEGF-A signalling determines the severity of diabetic glomerulopathy.

METHODS

Podocyte-specific, doxycycline-inducible Vegf₁₆₄ (the most abundant Vegfa isoform) overexpressing adult transgenic mice were made diabetic with low doses of streptozotocin and examined 12 weeks after onset of diabetes. We studied diabetic and non-diabetic transgenic mice fed a standard or doxycycline-containing diet. VEGF-A and albuminuria were measured by ELISA, creatinine was measured by HPLC, renal morphology was examined by light and electron microscopy, and gene expression was assessed by quantitative PCR, immunoblotting and immunohistochemistry.

RESULTS

Podocyte Vegf₁₆₄ overexpression in our mouse model of diabetes resulted in advanced diabetic glomerulopathy, characterised by Kimmelstiel-Wilson-like nodular glomerulosclerosis, microaneurysms, mesangiolysis, glomerular basement membrane thickening, podocyte effacement and massive proteinuria associated with hyperfiltration. It also led to increased VEGF receptor 2 and semaphorin3a levels, as well as nephrin and matrix metalloproteinase-2 downregulation, whereas circulating VEGF-A levels were similar to those in control diabetic mice.

CONCLUSIONS/INTERPRETATION

Collectively, these data demonstrate that increased podocyte Vegf₁₆₄ signalling dramatically worsens diabetic nephropathy in a streptozotocin-induced mouse model of diabetes, resulting in nodular glomerulosclerosis and massive proteinuria. This suggests that local rather than systemic VEGF-A levels determine the severity of diabetic nephropathy and that semaphorin3a signalling and matrix metalloproteinase-2 dysregulation are mechanistically involved in severe diabetic glomerulopathy.

The podocyte as a direct target of immunosuppressive agents

Podocytes play a key role in maintaining the blood-urine barrier for high-molecular-weight proteins. They are considered to be terminally differentiated, and podocyte loss cannot be compensated by regenerative proliferation. Various diseases leading to podocyte damage and loss result in proteinuria and cause nephrotic syndrome. Therefore, direct therapeutical strategies to protect podocytes in disease situations are a logical concept to prevent disease or to delay disease progression. Acquired podocytopathies like idiopathic focal segmental glomerulosclerosis and minimal change disease are historically considered as immunological diseases. Therefore, immunosuppressive agents such as steroids and calcineurin inhibitors are the commonly used treatment strategies. However, the causative disease mechanisms behind these treatment strategies remain elusive. Recent evidence shows that immunosuppressive agents, in addition to the effect on the immune system, directly influence the unique structure and function of podocytes. In this context, the actin cytoskeleton of the podocyte and cytokines such as vascular endothelial growth factor play a pivotal role. In this review, we summarize the direct effects on podocytes obtained in vivo and in vitro after treatment with calcineurin inhibitors, mTOR inhibitors and glucocorticoids. These direct effects could play a key role in the treatment concepts of podocytopathies with an important impact on the long-term renal function in patients with pharmacological immunosuppression.

Autocrine VEGF-VEGF-R loop on podocytes during glomerulonephritis in humans

BACKGROUND

Vascular endothelial growth factor (VEGF) is the most important and tightly regulated angiogenic cytokine in the kidney. Its activity is critical for capillary/glomerular preservation and repair, and recent studies have also demonstrated its relevance for the preservation of podocytes.

METHODS

The present study investigated a large number (n = 153) of renal biopsies from patients with glomerulonephritis (GN) and evaluated the expression and activity of the glomerular VEGF system [VEGF, VEGF-R1, VEGF-R2 and biologically active VEGF as identified by VEGF-VEGF receptor complexes (VEGF-VEGF-R)] in parallel with markers of renal function, injury and repair.

RESULTS

Whereas glomerular VEGF expression was clearly elevated, VEGF-R expression levels were widely unchanged. In parallel to the overall VEGF expression, the biological activity of VEGF on its receptors was uniformly significantly enhanced. Interestingly, the expression pattern of VEGF-R1 and VEGF-R2 significantly changed during GN where a very prominent podocytic pattern appeared, which was also detected for receptor-bound VEGF. VEGF expression and activity could be linked with indicators of renal injury such as glomerular proliferation and creatinine, respectively.

CONCLUSIONS

This study shows, for the first time, increased podocytic VEGF-VEGF-R binding during human GN, suggesting not only the existence of a glomerular paracrine proangiogenic, but also an autocrine role of the VEGF-VEGF-R system in diseased podocytes.

New aspects of glomerular filtration barrier structure and function: five layers (at least) not three

PURPOSE OF REVIEW

Three structures (glomerular endothelial fenestrae, glomerular basement membrane and podocyte interfoot process/slit diaphragms) have traditionally been considered as the major determinants of glomerular permeability. We review recent work demonstrating the functional importance of two additional layers: the endothelial surface layer (ESL) and the subpodocyte space (SPS).

RECENT FINDINGS

Removing glomerular endothelial cell monolayer ESL in vitro significantly alters monolayer permeability, supporting previous in-vivo demonstrations of the importance of the ESL in determining glomerular permeability. Whether fenestral diaphragms are present to support the ESL in healthy adult glomeruli has been examined in a recent report. On the downstream side of the glomerular filtration barrier, the SPS is a recently described structure that covers approximately two-thirds of the barrier, has highly restrictive dimensions and contributes to the hydraulic resistance and ultrafiltration characteristics of the glomerulus. Different layers of the barrier have also been shown to influence the permeability characteristics of one another, either through biophysical interactions, or through the activities of ligand-receptor axes that cross the various layers of the barrier.

SUMMARY

The structure and function of the glomerular filtration barrier remains an area of significant new discovery, and recent work continues to highlight the complexity of this dynamic multilayered watershed.

Vascular endothelial growth factor and diabetic nephropathy

The field of vascular endothelial growth factor (VEGF) has recently witnessed a surge of research into its role in diabetic kidney disease. Based on its credentials as a potent inducer of vasopermeability and angiogenesis, podocyte-derived VEGF is believed to participate in the glomerular capillary hyperpermeability of macromolecules that potentially underlies the pathogenesis of diabetic albuminuria. The evidence for VEGF's role is relatively straightforward in animal models of diabetes, establishing that VEGF is upregulated in the diabetic kidney, that VEGF alone reproduces some aspects of diabetic glomerulopathy, and that antagonism of VEGF attenuates diabetic albuminuria and other associated features of the podocytopathy. However, the promise shown in the animal studies has not carried over as convincingly into the realm of human studies, as some investigators find a negative or no relationship between VEGF and diabetic nephropathy, whereas others find a positive correlation between the two. If VEGF does play a role in diabetic renal disease, its observed effects and known mechanisms seem to point squarely at the podocyte as a central target of the maladaptive VEGF overactivity.

The alternatively spliced anti-angiogenic family of VEGF isoforms VEGFxxxb in human kidney development

BACKGROUND/AIM

Vascular endothelial growth factor (VEGF), required for renal development, is generated by alternative splicing of 8 exons to produce two families, pro-angiogenic VEGF(xxx), formed by proximal splicing in exon 8 (exon 8a), and anti-angiogenic VEGF(xxx)b, generated by distal splicing in exon 8 (exon 8b). VEGF(165)b, the first described exon 8b-containing isoform, antagonises VEGF(165) and is anti-angiogenic in vivo.

METHODS

Using VEGF(xxx)b-specific antibodies, we investigated its expression quantitatively and qualitatively in developing kidney, and measured the effect of VEGF(165)b on renal endothelial and epithelial cells.

RESULTS

VEGF(xxx)b formed 45% of total VEGF protein in adult renal cortex, and VEGF(165)b does not increase glomerular endothelial cell permeability, it inhibits migration, and is cytoprotective for podocytes. During renal development, VEGF(xxx)b was expressed in the condensed vesicles of the metanephros, epithelial cells of the comma-shaped bodies, invading endothelial cells and epithelial cells of the S-shaped body, and in the immature podocytes. Expression reduced as the glomerulus matured.

CONCLUSION

These results show that the anti-angiogenic VEGF(xxx)b isoforms are highly expressed in adult and developing renal cortex, and suggest that the VEGF(xxx)b family plays a role in glomerular maturation and podocyte protection by regulating the pro-angiogenic pro-permeability properties of VEGF(xxx) isoforms.

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

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

Increased glucose uptake and metabolism in mesangial cells overexpressing glucose transporter 1 increases interleukin-6 and vascular endothelial growth factor production: role of AP-1 and HIF-1alpha

Previous results indicate that enhanced glucose transporter (GLUT)1 expression mediates the deleterious effects of metabolic and hemodynamic perturbations leading to diabetic kidney disease. First screening for altered gene expression in GLUT1 overexpressing cells (GT1) by Affymetrix microarray analysis revealed upregulation of interleukin-6 (IL-6) and vascular endothelial growth factor (VEGF) expression, which was verified by RT-PCR. Subsequently, IL-6 and VEGF protein production was more than 3-fold increased in the GT1 cells. This upregulation was independent from each other. Studies on the underlying transcriptional mechanisms by gelshift assays and siRNA approach implicated activation of AP-1 in the increased expression of both, IL-6 and VEGF. We found also increased nuclear protein levels of hypoxia-inducible factor (HIF)-1alpha and enhanced DNA binding activity to a hypoxia responsible element located in the VEGF promoter. Knock-down of HIF-1alpha reduced the VEGF expression to 50% with an additive effect of AP-1 gene silencing down to 24%. The IL-6 expression was not affected by reducing HIF-1alpha. In conclusion our results link increased GLUT1 levels leading to excess glucose metabolism under normoglycemic conditions and altered gene expression of pathogenetic factors involved in diabetic kidney disease.

Reduction of VEGF-A and CTGF expression in diabetic nephropathy is associated with podocyte loss

Micro-vascular and renal complications in diabetic patients are a considerable clinical challenge. In a previous study, we found a significant decrease in vascular endothelial growth factor A (VEGF-A) mRNA levels in glomeruli from patients with diabetic nephropathy (DN). We now set out to investigate the relationship between reduced VEGF-A and connective tissue growth factor (CTGF) expression levels, the number of podocytes, and the extent of interstitial fibrosis. Laser capture microdissection was applied to obtain glomerular RNA from 28 patients with DN and 22 controls. mRNA levels of VEGF-A, CTGF, nephrin, podocin, and Wilms tumor1 (WT1) were measured using real-time polymerase chain reaction. Protein expression was evaluated using immuno-stainings for VEGF-A and CTGF, as well as markers for podocytes (WT1) and endothelial cells (CD31). We found a significant decrease in glomerular mRNA levels for VEGF-A (2.5 times), CTGF (1.6), nephrin (2.8), podocin (3.3), and WT1 (1.7) in patients with DN. There was a significant correlation between expression of podocyte markers and VEGF-A mRNA levels, and an inverse correlation between podocin message and the extent of interstitial fibrosis. CD31-positive area was significantly decreased (3.2 times) in patients with DN. Reduction of angiogenic factors correlated with the extent of interstitial fibrosis. This downregulation was related to a reduction of podocytes in DN. The results may suggest that downregulation of VEGF-A and CTGF in DN is a result of podocyte loss.

Direct effects of dexamethasone on human podocytes

Glucocorticoids are widely used in the treatment of human glomerular diseases, but their mode of action is poorly understood particularly in steroid-sensitive nephrotic syndrome, which is most common in childhood and is characterized by a lack of inflammation in the kidney. The podocyte is a key cell in the glomerulus in health and disease: until recently, human podocytes have been difficult to study in vitro. We have developed a conditionally immortalized human podocyte cell line transfected with a temperature-sensitive simian virus 40 transgene: when the transgene is inactivated in vitro, these cells adopt the phenotype of differentiated podocytes. We have used these cells to evaluate, using immunocytochemistry, reverse transcriptase-polymerase chain reaction, and Western blotting, direct effects of the glucocorticoid dexamethasone at concentrations designed to mimic in vivo therapeutic corticosteroid levels. Dexamethasone upregulated expression of nephrin and tubulin-alpha, and downregulated vascular endothelial growth factor. Effects on cell cycle were complex with downregulation of cyclin kinase inhibitor p21 and augmentation of podocyte survival, without any effect on apoptosis. We report cytokine production by human podocytes, especially interleukin (IL)-6 and -8; IL-6 expression was suppressed by dexamethasone. These potent direct effects on podocytes illustrate a novel mode of action of glucocorticoids and suggest potential new therapeutic strategies for glomerular disease.

VEGF-C promotes survival in podocytes

Vascular endothelial growth factor (VEGF)-A is an autocrine survival factor for podocytes, which express two VEGF receptors, VEGF-R1 and VEGF-R3. As VEGF-A is not a known ligand for VEGF-R3, the aim of this investigation was to examine whether VEGF-C, a known ligand for VEGF-R3, served a function in podocyte biology and whether this was VEGF-R3 dependent. VEGF-C protein expression was localized to podocytes in contrast to VEGF-D, which was expressed in parietal epithelial cells. Intracellular calcium ([Ca2+]i) experiments demonstrated that VEGF-C induced a 0.74 ± 0.09-fold reduction in [Ca2+]icompared with baseline in human conditionally immortalized podocytes (hCIPs; P < 0.05, one sample t-test, n = 8). Cytotoxicity experiments revealed that in hCIPs VEGF-C reduced cytotoxicity to 81.4 ± 1.9% of serum-starved conditions ( P < 0.001, paired t-test, n = 16), similar to VEGF-A (82.8 ± 4.5% of serum-starved conditions, P < 0.05, paired t-test). MAZ51 (a VEGF-R3 kinase inhibitor) inhibited the VEGF-C-induced reduction in cytotoxicity (106.2 ± 2.1% of serum-starved conditions), whereas MAZ51 by itself had no cytotoxic effects on hCIPs. VEGF-C was also shown to induce a 0.5 ± 0.13-fold reduction in levels of MAPK phosphorylation compared with VEGF-A and VEGF-A-Mab treatment ( P < 0.05, ANOVA, n = 4), yet had no effect on Akt phosphorylation. Surprisingly, immunoprecipitation studies detected no VEGF-C-induced autophosphorylation of VEGF-R3 in hCIPs but did so in HMVECs. Moreover, SU-5416, a tyrosine kinase inhibitor, blocked the VEGF-C-induced reduction in cytotoxicity (106 ± 2.8% of serum-starved conditions) at concentrations specific for VEGF-R1. Together, these results suggest for the first time that VEGF-C acts in an autocrine manner in cultured podocytes to promote survival, although the receptor or receptor complex activated has yet to be elucidated.

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

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

Glucocorticoid receptor and vascular endothelial growth factor in nephrotic syndrome

AIM

The aim of the study was to assess plasma and urine concentrations of vascular endothelial growth factor (VEGF) in nephrotic syndrome children (NS) depending on the total dose of glucocorticoids (GC) and the percentage of lymphocytes with glucocorticoid receptor expression (CD3/GCR).

METHODS

We examined 51 children (2-15 years), allocated to three groups: group I: 13 children with the first NS onset, group II: 13 children with NS relapse, group C: 25 healthy children. The NS patients were examined: (A) before treatment and (B) 4-5 weeks after prednisone administration at a dose of 60 mg/m2/24 h. Plasma and urinary VEGF levels were determined using the immunoenzymatic ELISA method. Flow cytometry was applied to assess CD3/GCR expression.

RESULTS

Higher plasma and urinary VEGF concentrations were noted in NS children before treatment (A), as compared to control subjects (C). Following prednisone therapy (B), VEGF level was reduced but it was still higher than in the control group. Positive correlation was observed between VEGF and protein in the urine (group I r = 0.660, P < 0.05, group II r = 0.818, P<0.01) and a weak positive correlation between VEGF in plasma and urine (group I r = 0.531, P<0.05, group II - r = 0.581, P<0.05). CD3/GCR expression was lower in group II. In both groups, the correlation between plasma VEGF and CD3/GCR was positive (P<0.05).

CONCLUSIONS

1. Plasma and urinary VEGF levels increase during nephrotic syndrome onset. 2. Glucocorticoid treatment reduces plasma and urinary VEGF levels in NS children.

Vascular endothelial growth factor in children with nephrotic syndrome treated with cyclosporine A

AIM

To assess the effect of cyclosporine A (CyA) on the level of vascular endothelial growth factor (VEGF) in the plasma and urine of nephrotic syndrome children.

METHODS

The study material consisted of 15 children (F 6, M 9; group I) who were subjected to the following examinations: A) at the time of proteinuria relapse, before treatment with CyA, B) after 3 mo, C) after 6 mo, and D) after 12 mo of CyA administration with prednisone and convertase inhibitor. The control group (II) contained 20 healthy children. The immunoenzymatic ELISA method (R&D Quantikine) was used to determine plasma and urinary VEGF levels, while the immunofluorescence method was applied to assess CyA concentration in the plasma. The statistical program Statistica 6.0 was used for statistical analysis of the results.

RESULTS

In the present study, plasma VEGF level in examination A was higher than in the control group (p<0.01). After proteinuria regression (B), it did not differ from the level observed in healthy children (p>0.05). After 6 and 12 mo of CyA administration, VEGF concentration increased and was higher than in the control group (p<0.05). In all the examinations, urinary excretion of VEGF was higher than in the control group, increasing proportionally with the duration of treatment and plasma CyA level. A positive correlation was observed between plasma and urinary VEGF levels and between VEGF and CyA concentrations in the plasma.

CONCLUSION

Long-term CyA treatment of nephrotic syndrome children leads to an increase in plasma and urinary VEGF.

Effect of tumor necrosis factor alpha and vascular permeability growth factor on albuminuria in rats

The purposes of this study were to measure the serum levels of vascular permeability growth factor (VPGF) and tumor necrosis factor alpha (TNFalpha) in minimal lesion nephrotic syndrome (MLNS) patients and to assess their effect on albuminuria in rats. Serum for VPGF and TNFalpha was obtained during relapse and remission from 18 MLNS patients. Tumor necrosis factor alpha was infused at the rate of 10 and 20 ng/h and VPGF at the rate of 20 and 40 ng/h for 5 days into the left renal artery of rats. Urinary albumin (24-h collection) was measured prior to infusion and on days 2, 4 and 5. Rats infused with 1% bovine serum albumin served as controls. Serum VPGF and TNFalpha levels in MLNS patients in relapse were not different from those seen during remission. A significant increase in albuminuria was observed on day 4 and 5 only when rats were infused with TNFalpha at the rate of 20 ng/h as compared to the excretion seen in same animals prior to the infusion of cytokine and on days 4 and 5 of normal controls. Neither VPGF nor TNFalpha seems to be the circulating pathogenic cytokine for proteinuria in MLNS. However, TNFalpha may contribute to the increased albuminuria via a paracrine effect at the glomerulus.

Implication of Peritubular Capillary Loss and Altered Expression of Vascular Endothelial Growth Factor in IgA Nephropathy

BACKGROUND/AIMS

To determine the roles of peritubular capillary (PTC) loss and expression of vascular endothelial growth factor (VEGF) and its transcription factor, hypoxia-inducible factor-1 (HIF-1), in the progression of IgA nephropathy (IgAN), we analyzed the expression of VEGF and HIF-1, and the number of PTCs in patients with variable severity of IgAN.

METHODS

Renal biopsy specimens from patients with IgAN (n = 23) were classified according to interstitial injury score: grade 0 (0%), grade 1 (1-25%), grade 2 (25-50%) and grade 3 (50-100%). We examined the immunohistochemical expression of CD34, VEGF and HIF-1alpha.

RESULTS

VEGF was expressed in the cytoplasm of tubular epithelia, and VEGF-positive area significantly expanded in grades 1 (35.5 +/- 5.9%, mean +/- SD) and 2 (32.5 +/- 5.9%) compared with grade 0 (23.4 +/- 4.5%). The numbers of PTCs were significantly lower in grades 2 (559 +/- 49/mm2) and 3 (510 +/- 56/mm2) than grade 0 (708 +/- 49/mm2). HIF-1alpha was weakly expressed in tubular epithelia in grade 0, increased with progression to grade 2, and markedly decreased in grade 3. It was also increased in pericapsular interstitial area in grade 1. The expression pattern of HIF-1alpha did not parallel that of VEGF. In renal biopsies of 5 control patients with minor glomerular abnormality, glomerular expression levels of VEGF and HIF-1alpha were similar to those of IgAN grade 0 kidneys.

CONCLUSION

VEGF production was accelerated in the early stage of IgAN but it did not protect against PTC injury/loss. The lack of correlation between VEGF and HIF-1alpha expression suggests HIF-independent VEGF production in IgAN.

Significance of vascular endothelial growth factor expression in renal tissue of patients with preeclamptic nephropathy

OBJECTIVE

It was the aim of this study to evaluate the distribution and expression of vascular endothelial growth factor (VEGF) in kidneys of patients with preeclamptic nephropathy and their relationship with clinical and pathological manifestations.

METHODS

From May 1993 to August 2004, 19 patients with a mean age of 28.1 +/- 4.53 years (range 23-40), diagnosed with preeclamptic nephropathy by renal biopsy, were enrolled in this study. Fifteen were nulliparous and 4 multipara. Their renal tissues were subjected to immunohistochemical staining by a four-layer peroxidase-antiperoxidase method using monoclonal anti-VEGF. Residual normal renal tissue obtained at nephrectomy served as control. The relationship between the expression pattern of VEGF and clinicopathological features was also investigated.

RESULTS

The expression of VEGF markedly increased in renal tissues of patients with preeclamptic nephropathy at the early stage of gestation termination in comparison with normal controls. However, over time, it gradually decreased and reached the level of normal controls (100 vs. 71.43 vs. 20%, p < 0.05). The degree of endothelial proliferation in the glomeruli was closely related to the expression of VEGF, which was stronger in patients with diffuse endothelial proliferation than in those with segment proliferation (p < 0.05). In addition, there was a proportional relationship between the expression of VEGF and the level of urinary protein excretion (p < 0.05).

CONCLUSION

The patients with preeclamptic nephropathy showed strong expressions of VEGF in glomeruli, which were closely associated with glomerular endothelial lesions and proteinuria, and over time, gradually weakened to normal level after gestation termination.

Vascular endothelial growth factor increases the ultrafiltration coefficient in isolated intact Wistar rat glomeruli

Vascular endothelial growth factor (VEGF) is expressed by the podocytes of renal glomeruli, and has profound influences on systemic microvascular permeability and haemodynamics. We describe an extensive refinement of a model that permits evaluation of the ultrafiltration coefficient (LpA) of isolated mammalian glomeruli, in the absence of circulating and haemodynamic influences, and tested the hypothesis that VEGF influences glomerular LpA via an effect on endothelial cells. Glomeruli were isolated by sieving Wistar rat renal cortical tissue, and individually loaded onto a suction micropipette. Flowing perifusate containing 1% bovine serum albumin (BSA) was rapidly switched to an oncopressive perifusate containing 8% BSA, eliciting transglomerular fluid efflux. The rate of the resultant reduction in glomerular volume was used to calculate glomerular LpA (1.07 +/- 0.53 nl min(-1) mmHg(-1) (mean +/-s.d.), n= 51), which compares favourably with those reported in the same rat strain using different techniques. A significant relationship between LpA and initial glomerular volume (Vi) (r= 0.72, n= 41, P < 0.0001) necessitated correction of LpA for Vi. The initial rate of change of glomerular volume, normalized for Vi, showed a strong positive correlation with applied oncotic gradient (Pearson r= 0.59, n= 28, P < 0.001), as predicted by Starling's law of filtration. A 60 min exposure of glomeruli to 1 nm VEGF increased glomerular LpA/Vi (1.19 +/- 0.19 (n= 10) to 2.23 +/- 0.33 (n= 9) min(-1) mmHg(-1) (mean +/-s.e.m.); P < 0.02). Time- and concentration-dependent relations between VEGF and LpA/Vi were observed. The VEGF-induced elevation of LpA/Vi was blocked by the selective VEGF-R2 inhibitor ZM323881. We suggest that glomerular VEGF contributes to the high physiological permeability of mammalian glomeruli to water through an action on endothelial cells.

Ruboxistaurin, a protein kinase C beta inhibitor, as an emerging treatment for diabetes microvascular complications

OBJECTIVE

To review current clinical data regarding the pharmacologic actions of ruboxistaurin (LY333531) mesylate, an inhibitor of protein kinase C (PKC) beta, and its role to potentially reduce the development and/or the progression of diabetic microvascular complications.

DATA SOURCES

Primary literature was obtained via a MEDLINE search (1966-August 2004) and through review of pertinent abstracts and presentations at major medical meetings.

STUDY SELECTION AND DATA EXTRACTION

Literature relevant to PKC physiology, the pharmacokinetics of ruboxistaurin, and data evaluating the use of ruboxistaurin in treating diabetic microvascular complications in human and relevant animal models was reviewed.

DATA SYNTHESIS

PKC is part of a group of intracellular signaling molecules activated in response to various specific hormonal, neuronal, and growth factor stimuli. Hyperglycemia leads to PKC beta 1 and 2 isoform activation, which experimentally has been shown to contribute to the development and progression of diabetic microvascular complications (retinopathy, nephropathy, neuropathy) through various biochemical mechanisms. Animal and/or human studies using ruboxistaurin mesylate, a novel, highly selective inhibitor of PKC beta, have shown delay in the progression and, in some cases, reversal of diabetic retinopathy, nephropathy, and neuropathy.

CONCLUSIONS

Ruboxistaurin mesylate, by inhibiting excessive activation of certain PKC isoforms, has the potential to reduce the burden of microvascular complications for patients with diabetes.

Therapeutic potential of inhibitory VEGF splice variants

Antiangiogenesis by inhibition of vascular endothelial growth factor (VEGF) has recently been demonstrated to be an effective therapeutic mode in human cancer alongside surgery, radiotherapy and chemotherapy. The authors have recently discovered a family of inhibitory VEGF splice variants, which has led to the possibility of using these isoforms as antiangiogenic agents. The discovery, mechanism of action, preclinical evaluation, and the potential uses of these isoforms in future cancer therapy will be discussed herein.

Vascular endothelial growth factor expression and cyclosporine toxicity in renal allograft rejection

The aim of this study was to evaluate the influence of vascular endothelial growth factor (VEGF) on renal function and on development of interstitial fibrosis (IF) in renal allografts. Tubular and interstitial expressions of VEGF and TNF-alpha, and density of macrophages in the interstitium were examined in 92 patients with nonrejected kidneys, acute rejection (AR), chronic allograft nephropathy (CAN), borderline changes (BC) and acute cyclosporin A (CsA) toxicity. Follow-up biopsy specimens from patients with AR and BC were evaluated for development of IF. A significant difference in tubular and interstitial VEGF expressions was found between patients with AR, BC, CAN and CsA toxicity (p < 0.001). Macrophage infiltration was positively correlated with VEGF and TNF-alpha expressions (p < 0.001). VEGF expression increased with increasing expression of TNF-alpha (p < 0.001). Renal function in first 6 months after initial biopsy was better in patients with marked tubular VEGF expression (p < 0.01); however, in follow-up, development of IF and graft loss was found earlier in these patients (p < 0.01 and p < 0.05, respectively). Increased renal VEGF expression has protective properties immediately following renal allograft but allows for increased risk of early IF, and therefore poor graft outcome in the long term.

Antagonism of vascular endothelial growth factor results in microvessel attrition and disorganization of wound tissue

Vascular endothelial growth factor (VEGF) is a potent growth factor that is indispensable for the development of blood vessels in the fetus and for wound healing in adults. VEGF likely plays a role in maintaining the blood vessels once they have been formed. It is not clear, however, whether a low tissue VEGF (caused either by disease or by systemic administration of VEGF antagonists) can cause abnormalities in preexisting blood vessels, especially of wound tissue that requires high local levels of VEGF for healing. The present study investigated the effect of VEGF antagonism on blood vessels of foreign-body granulomas (a model of wound-healing tissue). Granulomas were induced by implanting perforated polyvinyl tubes into the subcutaneous tissue of rats and allowed to develop for 14 days, at which time the implanted tubes were completely encapsulated by the subcutaneous tissue. The encapsulated granulomas consisted of 3 distinct histological layers, of which the middle layer was well perfused by a rich supply of microvessels. Morphologically, the granuloma remained "stable" after developing for 14 days. At 1 week, VEGF levels in the granuloma fluid, which is in equilibrium with the interstitial fluid, were 25 times higher than in the plasma. VEGF levels in the granuloma fluid continued to increase for up to 3 weeks, reflecting the high dependence of the wound tissue on ambient VEGF levels. After injection of the VEGF receptor antagonist in the fully formed granuloma, the preexisting blood vessels in the middle layer regressed and underwent apoptosis, accompanied by expansion of the extracellular matrix (predominately collagen I) into areas normally devoid of matrix. We conclude that wound tissue is sensitive to ambient VEGF levels, and that a low VEGF condition resulting from VEGF receptor antagonism can disrupt the healing of wound tissue.

Vascular endothelial growth factor and nephrin interact and reduce apoptosis in human podocytes

Vascular endothelial growth factor (VEGF) is anti-cytotoxic in podocytes. Moreover, it has been suggested that nephrin, a cell adhesion molecule of the podocyte slit diaphragm, can contribute to antiapoptotic mechanisms in these cells. We therefore investigated whether VEGF signals to reduce apoptosis and the role of nephrin in this survival mechanism. Flow cytometry showed that podocytes with nephrin mutations had a significantly greater proportion of apoptosis. Although VEGF reduced apoptosis in human conditionally immortalized podocytes [wild-type (WT)] by 18.1% of control ( P < 0.001), it was unable to do so in nephrin-deficient human conditionally immortalized podocytes. Moreover, Western blotting and immunodetection with an anti-nephrin antibody showed that the phosphorylation of nephrin, compared with serum-starved WTs, was significantly increased (ratio of 3.36 ± 1.2 to control, P < 0.05) by VEGF treatment and significantly reduced by treatment with a neutralizing VEGF monoclonal antibody (mAb) (ratio of 0.2 ± 0.09 to control, P < 0.05). The AKT signaling pathway has been implicated in nephrin-mediated inhibition of apoptosis in transfected cells, but the role of this pathway has not previously been shown in podocytes. Surprisingly, exogenous VEGF decreased AKT/PKB phosphorylation in normal podocytes but increased it in nephrin-deficient podocytes. We suggest therefore that both exogenous and endogenous (podocyte derived) VEGF can stimulate the phosphorylation of nephrin and through this action may prevent podocyte apoptosis. However, the involvement of AKT in this survival response in normal human podocytes is not clear.