Inducible overexpression of sFlt-1 in podocytes ameliorates glomerulopathy in diabetic mice

Crosstalk mechanisms between glomerular endothelial cells and podocytes in renal diseases and kidney transplantation

The glomerular filtration barrier (GFB), composed of endothelial cells, glomerular basement membrane, and podocytes, is a unique structure for filtering blood while detaining plasma proteins according to size and charge selectivity. Structurally, the fenestrated endothelial cells, which align the capillary loops, are in close proximity to mesangial cells. Podocytes are connected by specialized intercellular junctions known as slit diaphragms and are separated from the endothelial compartment by the glomerular basement membrane. Podocyte-endothelial cell communication or crosstalk is required for the development and maintenance of an efficient filtration process in physiological conditions. In pathological situations, communication also has an essential role in promoting or delaying disease progression. Podocytes and endothelial cells can secrete signaling molecules, which act as crosstalk effectors and, through binding to their target receptors, can trigger bidirectional paracrine or autocrine signal transduction. Moreover, the emerging evidence of extracellular vesicles derived from various cell types engaging in cell communication has also been reported. In this review, we summarize the principal pathways involved in the development and maintenance of the GFB and the progression of kidney disease, particularly in kidney transplantation.

Inducing Angiogenesis in the Nucleus Pulposus

Bone morphogenetic protein (BMP) gene delivery to Lewis rat lumbar intervertebral discs (IVDs) drives bone formation anterior and external to the IVD, suggesting the IVD is inhospitable to osteogenesis. This study was designed to determine if IVD destruction with a proteoglycanase, and/or generating an IVD blood supply by gene delivery of an angiogenic growth factor, could render the IVD permissive to intra-discal BMP-driven osteogenesis and fusion. Surgical intra-discal delivery of naïve or gene-programmed cells (BMP2/BMP7 co-expressing or VEGF165 expressing) +/- purified chondroitinase-ABC (chABC) in all permutations was performed between lumbar 4/5 and L5/6 vertebrae, and radiographic, histology, and biomechanics endpoints were collected. Follow-up anti-sFlt Western blotting was performed. BMP and VEGF/BMP treatments had the highest stiffness, bone production and fusion. Bone was induced anterior to the IVD, and was not intra-discal from any treatment. chABC impaired BMP-driven osteogenesis, decreased histological staining for IVD proteoglycans, and made the IVD permissive to angiogenesis. A soluble fragment of VEGF Receptor-1 (sFlt) was liberated from the IVD matrix by incubation with chABC, suggesting dysregulation of the sFlt matrix attachment is a possible mechanism for the chABC-mediated IVD angiogenesis we observed. Based on these results, the IVD can be manipulated to foster vascular invasion, and by extension, possibly osteogenesis.

Role of insulin signaling and its associated signaling in glomerulus for diabetic kidney disease

The number of patients with diabetic kidney disease (DKD) has been rising significantly over the last several decades and is one of the most frequent causes of chronic kidney disease (CKD) in the United States. Hyperglycemia accelerates development of DKD, a direct result of increased intracellular glucose availability. Two large clinical studies, the Diabetes Control and Complications Trial in type 1 diabetes and the United Kingdom Prospective Diabetes Study in type 2 diabetes showed that intensive glycemic control delayed the onset and the progression of DKD. On the other hand, it is reported that glycemic control alone is not sufficient to control DKD progression. Recent data support that insulin signaling and its associated signaling contribute significantly to preserve glomerular function. However, little is known about the key regulators of insulin signaling in glomerular component cells. In this review, we summarize the novel knowledge regarding the reno-protective effects of insulin signaling or its associated signaling in glomerular constituent cells on DKD.

Enarodustat Treatment for Renal Anemia in Patients With Non-dialysis Chronic Kidney Disease

BACKGROUND/AIM

Renal anemia is a major complication in patients with chronic kidney disease (CKD), leading to morbidity and mortality. Hypoxia-inducible factor (HIF) prolyl hydroxylase inhibitors (PHI), also called HIF stabilizers, increase endogenous erythropoietin production and are expected to be novel orally administrated agents for renal anemia in CKD. Enarodustat is being developed as an oral HIF-PHI. It was recently approved in Japan and clinical development is ongoing in the USA and South Korea. Therefore, there are only a few real-world data regarding treatment of renal anemia using enarodustat. This study evaluated the efficacy of enarodustat in patients with non-dialysis CKD.

PATIENTS AND METHODS

Nine patients (78±11 years old, male=6, female=3) were enrolled in this study. Patients received enarodustat as first-line therapy or changed from erythropoiesis stimulating agents (2-6 mg). The observation period was 4.8±2.0 months.

RESULTS

Levels of hemoglobin were effectively increased and maintained with enarodustat administration. C-reactive protein and serum ferritin were significantly decreased, but no change in renal function was observed. Furthermore, no serious adverse effects were recognized in all patients during the study.

CONCLUSION

Enarodustat is an effective and relatively well-tolerated agent for the treatment of renal anemia in patients with non-dialysis CKD.

Multicentric IL-5-positive Castleman Disease With Nephrotic Syndrome Relapsed After Rituximab Treatment

BACKGROUND/AIM

To date, no reports of interleukin (IL)-5-producing Castleman disease with nephrotic syndrome and moreover no reports of relapse after remission with rituximab treatment, have been published.

CASE REPORT

A 67-year-old male presented to the Osaka Medical and Pharmaceutical University Hospital with a history of low-grade fever, papules, and nephrotic syndrome. Lymph nodes were palpated in the inguinal region. The patient showed anemia, eosinophilia, polyclonal hypergammaglobulinemia, and elevated interleukin (IL)-6 levels. Patient's serum IL-5 and IL-6 levels were measured using ELISA and immunohistochemical staining of lymph nodes was performed with antibodies specific to CD134. Histological examination confirmed diagnosis of a plasma cell variant of Castleman disease. After a total of four weekly doses of rituximab, urinary protein disappeared, and skin symptoms improved. However, one month after rituximab treatment, the skin rash worsened again, and eosinophils and IL-5 were elevated significantly.

CONCLUSION

This is the first report of recurrent Castleman disease with direct evidence of increased serum IL-5. It may be reasonable to use rituximab, an anti-CD20 antibody for treating the disease, however, for IL-5-producing cases the effect of rituximab may be partial.

Paeoniflorin binds to VEGFR2 to restore autophagy and inhibit apoptosis for podocyte protection in diabetic kidney disease through PI3K-AKT signaling pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Paeoniflorin (PF) was found to exhibit renal protection from diabetic kidney disease (DKD) in previous trials, but its specific mechanism remains to be elucidated.

AIM OF THE STUDY

This study furtherly explored the specific mechanism of PF in protect podocyte injury in DKD.

MATERIALS AND METHODS

We observed the effects of PF on renal tissue and podocytes in DKD by constructing the vitro and vivo models after measuring the pharmacokinetic characteristics of PF. Target proteins of PF were found through target prediction, and verified by molecular docking, CESTA, and SPR, and then furtherly explored the downstream regulation mechanism related to podocyte autophagy and apoptosis by network prediction and co-immunoprecipitation. Finally, by using the target protein inhibitor in vivo and knocking down the target protein gene in vitro, it was verified that PF played a role in regulating autophagy and apoptosis through the target protein in diabetic nephropathy.

RESULTS

This study found that in STZ-induced mice model, PF could improve the renal biochemical and pathological damage and podocyte injure (p < 0.05), upregulate autophagy activity (p < 0.05), but inhibit apoptosis (p < 0.01). Vascular endothelial growth factor receptor 2 (VEGFR2), predicted as the target of PF, directly bind with PF reflected by molecular docking and surface plasmon resonance detection. Animal studies demonstrated that VEGFR2 inhibitors have a protective effect similar to that of PF on DKD. Network prediction and co-immunoprecipitation further confirmed that VEGFR2 was able to bind PIK3CA to regulate PI3K-AKT signaling pathway. Furthermore, PF downregulated the phosphorylation of PI3K and AKT (p < 0.05). In vitro, similarly to autophagy inhibitors, PF was also found to improve podocyte markers (p < 0.05) and autophagy activity (p < 0.05), decrease caspase 3 protein (p < 0.05) and further inhibited VEGFR2-PI3K-AKT activity (p < 0.05). Finally, the results of VEGFR2 knockdown were similar to the effect of PF in HG-stimulated podocytes.

CONCLUSION

In conclusion, PF restores autophagy and inhibits apoptosis by targeting the VEGFR2-mediated PI3K-AKT pathway to improve renal injury in DKD, that provided a theoretical basis for PF treatment in DKD.

Hypoxia-inducible factor-prolyl hydroxylase inhibitors for renal anemia in chronic kidney disease: Advantages and disadvantages

Anemia is a common feature and complication of chronic kidney disease (CKD). Erythropoiesis-stimulating agents (ESAs) and recombinant human erythropoietin have been used widely in renal anemia treatment. Recently, hypoxia-inducible factor-prolyl hydroxylase domain inhibitors (HIF-PHIs) that may improve the treatment of renal anemia patients were launched. Previous studies indicated that HIF-PHIs may decrease hepcidin levels and modulate iron metabolism, thereby increasing total iron-binding capacity and reducing the need for iron supplementation. Furthermore, HIF-PHIs can reduce inflammation and oxidative stress in CKD. Recombinant erythropoietin has become a routine treatment for patients with CKD and end-stage renal disease with relatively few adverse effects. However, higher doses of recombinant erythropoietin have been demonstrated to be an independent predictor of mortality in patients under hemodialysis. Phase III clinical trials of HIF-PHIs in patients with anemia and dialysis-dependent CKD have shown their efficacy and safety in both non-dialysis and dialysis CKD patients. However, HIFα binds to specific hypoxia-response elements in the vascular endothelial growth factor or retinoic acid-related orphan receptor gamma t (RORγt) promoter, which may be involved in the progression of cancer, psoriasis, and rheumatoid arthritis. In this paper, we have summarized the mechanism, clinical application, and clinical trials of HIF-PHIs in the treatment of renal anemia and aimed to provide an overview of the new drugs in clinical practice, as well as reconsider the advantages and disadvantages of HIF-PHIs and ESAs. Presently, there are not enough clinical studies examining the effects of long-term administration of HIF-PHIs. Therefore, further studies will be needed.

Kidney disease in diabetes: From mechanisms to clinical presentation and treatment strategies

Metabolic and haemodynamic perturbations and their interaction drive the development of diabetic kidney disease (DKD) and its progression towards end stage renal disease (ESRD). Increased mitochondrial oxidative stress has been proposed as the central mechanism in the pathophysiology of DKD, but other mechanisms have been implicated. In parallel to increased oxidative stress, inflammation, cell apoptosis and tissue fibrosis drive the relentless progressive loss of kidney function affecting both the glomerular filtration barrier and the renal tubulointerstitium. Alteration of glomerular capillary autoregulation is at the basis of glomerular hypertension, an important pathogenetic mechanism for DKD. Clinical presentation of DKD can vary. Its classical presentation, often seen in patients with type 1 diabetes (T1DM), features hyperfiltration and albuminuria followed by progressive fall in renal function. Patients can often also present with atypical features characterised by progressive reduction in renal function without albuminuria, others in conjunction with non-diabetes related pathologies making the diagnosis, at times, challenging. Metabolic, lipid and blood pressure control with lifestyle interventions are crucial in reducing the progressive renal function decline seen in DKD. The prevention and management of DKD (and parallel cardiovascular disease) is a huge global challenge and therapies that target haemodynamic perturbations, such as inhibitors of the renin-angiotensin-aldosterone system (RAAS) and SGLT2 inhibitors, have been most successful.

Circulating Soluble Fms-like Tyrosine Kinase in Renal Diseases Other than Preeclampsia

Soluble Fms-like tyrosine kinase (sFlt-1/sVEGFR1) is a naturally occurring antagonist of vascular endothelial growth factor (VEGF). Despite being a secreted, soluble protein lacking cytoplasmic and transmembrane domains, sFlt-1 can act locally and be protective against excessive microenvironmental VEGF concentration or exert autocrine functions independently of VEGF. Circulating sFlt-1 may indiscriminately affect endothelial function and the microvasculature of distant target organs. The clinical significance of excess sFlt-1 in kidney disease was first shown in preeclampsia, a major renal complication of pregnancy. However, circulating sFlt-1 levels appear to be increased in various diseases with varying degrees of renal impairment. Relevant clinical associations between circulating sFlt-1 and severe outcomes (e.g., endothelial dysfunction, renal impairment, cardiovascular disease, and all-cause mortality) have been observed in patients with CKD and after kidney transplantation. However, sFlt-1 appears to be protective against renal dysfunction-associated aggravation of atherosclerosis and diabetic nephropathy. Therefore, in this study, we provide an update on sFlt-1 in several kidney diseases other than preeclampsia, discuss clinical findings and experimental studies, and briefly consider its use in clinical practice.

Nephrotoxicity of Anti-Angiogenic Therapies

The use of inhibitors of vascular endothelial growth factor (VEGF)/vascular endothelial growth factor receptor 2 (VEGFR2) signaling for the treatment of cancer has increased over the last decade. This signaling pathway plays a fundamental role in angiogenesis and also in kidney physiology. The emergence of anti-angiogenic therapies has led to adverse nephrotoxic effects, despite improving the outcomes of patients. In this review, we will present the different anti-angiogenic therapies targeting the VEGFR pathway in association with the incidence of renal manifestations during their use. In addition, we will discuss, in detail, the pathophysiological mechanisms of frequent renal diseases such as hypertension, proteinuria, renal dysfunction, and electrolyte disorders. Finally, we will outline the cellular damage described following these therapies.

Antiangiogenic therapy in diabetic nephropathy: A double‑edged sword (Review)

Diabetes and the associated complications are becoming a serious global threat and an increasing burden to human health and the healthcare systems. Diabetic nephropathy (DN) is the primary cause of end-stage kidney disease. Abnormal angiogenesis is well established to be implicated in the morphology and pathophysiology of DN. Factors that promote or inhibit angiogenesis serve an important role in DN. In the present review, the current issues associated with the vascular disease in DN are highlighted, and the challenges in the development of treatments are discussed.

Placental and maternal sFlt1/PlGF expression in gestational diabetes mellitus

Gestational diabetes mellitus (GDM) and preeclampsia (PE) are both characterized by endothelial dysfunction and GDM women have higher incidence of PE. The placenta plays a key role in PE pathogenesis but its contribution to PE during GDM remains unclear. Herein, we compared placental and maternal blood anti-angiogenic soluble fms-like tyrosine kinase-1 (sFlt1) and pro-angiogenic Placental Growth Factor (PlGF) expressions in GDM and GDM-PE pregnancies compared to controls (CTRL) and PE cases. Electrochemiluminescence immunoassays showed a significantly higher maternal blood sFlt1/PlGF values in GDM-PE relative to CTRL and GDM pregnancies. We reported that placental PlGF gene expression was significantly decreased in GDM, PE and GDM-PE relative to CTRL. However, PlGF protein levels were significantly increased in GDM and GDM-PE relative to CTRL and PE placentae. Finally, sFlt1 gene expression was significantly increased in PE relative to CTRL, GDM and GDM-PE placentae. In contrast, sFlt1 protein expression was significantly decreased in GDM-PE relative to CTRL, GDM and PE placentae. Finally, higher sFlt1/PlGF ratio in GDM-PE maternal blood suggest that sFlt1 overproduction is related to PE onset also in GDM pregnancies even though characterized by a less severe endothelial dysfunction in terms of angiogenic biomarkers.

Overexpression of Circulating Soluble Nogo-B Improves Diabetic Kidney Disease by Protecting the Vasculature

Damage to the vasculature is the primary mechanism driving chronic diabetic microvascular complications such as diabetic nephropathy, which manifests as albuminuria. Therefore, treatments that protect the diabetic vasculature have significant therapeutic potential. Soluble neurite outgrowth inhibitor-B (sNogo-B) is a circulating N-terminus isoform of full-length Nogo-B, which plays a key role in vascular remodeling following injury. However, there is currently no information on the role of sNogo-B in the context of diabetic nephropathy. We demonstrate that overexpression of sNogo-B in the circulation ameliorates diabetic kidney disease by reducing albuminuria, hyperfiltration, and abnormal angiogenesis and protecting glomerular capillary structure. Systemic sNogo-B overexpression in diabetic mice also associates with dampening vascular endothelial growth factor-A signaling and reducing endothelial nitric oxide synthase, AKT, and GSK3β phosphorylation. Furthermore, sNogo-B prevented the impairment of tube formation, which occurred when human endothelial cells were exposed to sera from patients with diabetic kidney disease. Collectively, these studies provide the first evidence that sNogo-B protects the vasculature in diabetes and may represent a novel therapeutic target for diabetic vascular complications.

Assessment of the SFlt-1 and sFlt-1/25(OH)D Ratio as a Diagnostic Tool in Gestational Hypertension (GH), Preeclampsia (PE), and Gestational Diabetes Mellitus (GDM)

Background

Placental soluble fms-like tyrosine kinase-1 (sFlt-1), an antagonist of vascular endothelial growth factor, is considered an etiological factor of endothelial damage in pregnancy pathologies. An increase in the sFlt-1 level is associated with alterations of endothelial integrity. In contrast, vitamin D exerts a protective effect and low concentrations of 25(OH)D may have an adverse effect on common complications of pregnancy, such as gestational hypertension (GH), preeclampsia (PE), and gestational diabetes mellitus (GDM). The aim of this study was to analyze the levels of sFlt-1 in Polish women with physiological pregnancies and pregnancies complicated by GH, PE, and GDM. Moreover, we analyzed relationships between the maternal serum sFlt-1 level and the sFlt-1 to 25(OH)D ratio and the risk of GH and PE.

Material and Methods

The study included 171 women with complicated pregnancies; among them are 45 with GH, 23 with PE, and 103 with GDM. The control group was comprised of 36 women with physiological pregnancies. Concentrations of sFl-1 and 25(OH)D were measured before delivery, with commercially available immunoassays.

Results

Women with GH differed significantly from the controls in terms of their serum sFlt-1 levels (5797 pg/ml vs. 3531 pg/ml, p = 0.0014). Moreover, a significant difference in sFlt-1 concentrations was found between women with PE and those with physiological pregnancies (6074 pg/ml vs. 3531 pg/ml, p < 0.0001). GDM did not exert a statistically significant effect on serum sFlt-1 levels. Both logistic regression and ROC analysis demonstrated that elevated concentration of sFlt-1 was associated with greater risk of GH (AUC = 0.70, p = 0.0001) and PE (AUC = 0.82, p < 0.0001). Also, the sFlt-1 to 25(OH)D ratio, with the cutoff values of 652 (AUC = 0.74, p < 0.0001) and 653 (AUC = 0.88, p < 0.0001), respectively, was identified as a significant predictor of GH and PE.

Conclusions

Determination of the sFlt-1/25(OH)D ratio might provide additional important information and, thus, be helpful in the identification of patients with PE and GH, facilitating their qualification for intensive treatment and improving the neonatal outcomes.

Modulation of Receptor Tyrosine Kinase Activity through Alternative Splicing of Ligands and Receptors in the VEGF-A/VEGFR Axis

Vascular endothelial growth factor A (VEGF-A) signaling is essential for physiological and pathological angiogenesis. Alternative splicing of the VEGF-A pre-mRNA gives rise to a pro-angiogenic family of isoforms with a differing number of amino acids (VEGF-A_xxxa), as well as a family of isoforms with anti-angiogenic properties (VEGF-A_xxxb). The biological functions of VEGF-A proteins are mediated by a family of cognate protein tyrosine kinase receptors, known as the VEGF receptors (VEGFRs). VEGF-A binds to both VEGFR-1, largely suggested to function as a decoy receptor, and VEGFR-2, the predominant signaling receptor. Both VEGFR-1 and VEGFR-2 can also be alternatively spliced to generate soluble isoforms (sVEGFR-1/sVEGFR-2). The disruption of the splicing of just one of these genes can result in changes to the entire VEGF-A/VEGFR signaling axis, such as the increase in VEGF-A₁₆₅a relative to VEGF-A₁₆₅b resulting in increased VEGFR-2 signaling and aberrant angiogenesis in cancer. Research into this signaling axis has recently focused on manipulating the splicing of these genes as a potential therapeutic avenue in disease. Therefore, further research into understanding the mechanisms by which the splicing of VEGF-A/VEGFR-1/VEGFR-2 is regulated will help in the development of drugs aimed at manipulating splicing or inhibiting specific splice isoforms in a therapeutic manner.

Increased soluble fms-like tyrosine kinase 1 after ischemia reperfusion contributes to adverse clinical outcomes following kidney transplantation

Renal ischemia reperfusion injury (IRI) adversely affects clinical outcomes following kidney transplantation. Understanding the cellular mechanisms and the changes in gene/protein expression following IRI may help to improve these outcomes. Serum soluble fms-like tyrosine kinase 1 (sFlt-1), a circulating antiangiogenic protein, is increased in the first week following kidney transplantation. We evaluated the casual relationship of elevated sFlt-1 levels with renal microvascular dysfunction following IRI in a longitudinal study of 93 kidney transplant recipients and in several animal models. Transplant recipients with higher sFlt-1 levels had higher odds of delayed graft function, graft rejection, impaired graft function, and death. In a subgroup of 25 participants who underwent kidney biopsy within 4 months of kidney transplantation, peritubular capillary area was lower in those with elevated serum sFtl-1 levels. The administration of recombinant sFlt-1 into rodents resulted in significant structural and functional changes of the renal microvasculature, including reduced peritubular capillary density and intracapillary blood volume, and lead to increased expression of inflammatory genes and increased fibrosis. In a murine model of IRI, the kidney was a site of sFlt-1 production, and systemic neutralization of sFlt-1 preserved peritubular capillary density and alleviated renal fibrosis. Our data indicate that high sFlt-1 levels after IRI play an important role in the pathogenesis of microvascular dysfunction, thereby contributing to adverse clinical outcomes following kidney transplantation.

Inflammatory Mediators and Renal Fibrosis

Renal inflammation is the initial, healthy response to renal injury. However, prolonged inflammation promotes the fibrosis process, which leads to chronic pathology and eventually end-stage kidney disease. There are two major sources of inflammatory cells: first, bone marrow-derived leukocytes that include neutrophils, macrophages, fibrocytes and mast cells, and second, locally activated kidney cells such as mesangial cells, podocytes, tubular epithelial cells, endothelial cells and fibroblasts. These activated cells produce many profibrotic cytokines and growth factors that cause accumulation and activation of myofibroblasts, and enhance the production of the extracellular matrix. In particular, activated macrophages are key mediators that drive acute inflammation into chronic kidney disease. They produce large amounts of profibrotic factors and modify the microenvironment via a paracrine effect, and they also transdifferentiate to myofibroblasts directly, although the origin of myofibroblasts in the fibrosing kidney remains controversial. Collectively, understanding inflammatory cell functions and mechanisms during renal fibrosis is paramount to improving diagnosis and treatment of chronic kidney disease.

Endogenous Antiangiogenic Factors in Chronic Kidney Disease: Potential Biomarkers of Progression

Chronic kidney disease (CKD) is a major global health problem. Unless intensive intervention is initiated, some patients can rapidly progress to end-stage kidney disease. However, it is often difficult to predict renal outcomes using conventional laboratory tests in individuals with CKD. Therefore, many researchers have been searching for novel biomarkers to predict the progression of CKD. Angiogenesis is involved in physiological and pathological processes in the kidney and is regulated by the balance between a proangiogenic factor, vascular endothelial growth factor (VEGF)-A, and various endogenous antiangiogenic factors. In recent reports using genetically engineered mice, the roles of these antiangiogenic factors in the pathogenesis of kidney disease have become increasingly clear. In addition, recent clinical studies have demonstrated associations between circulating levels of antiangiogenic factors and renal dysfunction in CKD patients. In this review, we summarize recent advances in the study of representative endogenous antiangiogenic factors, including soluble fms-related tyrosine kinase 1, soluble endoglin, pigment epithelium-derived factor, VEGF-A₁₆₅b, endostatin, and vasohibin-1, in associations with kidney diseases and discuss their predictive potentials as biomarkers of progression of CKD.

Plasma Leucine-Rich α-2-Glycoprotein 1 Predicts Rapid eGFR Decline and Albuminuria Progression in Type 2 Diabetes Mellitus

CONTEXT

Abnormal angiogenesis plays an important role in pathogenesis of diabetic kidney disease (DKD). Leucine-rich α-2 glycoprotein 1 (LRG1) is a newly identified angiogenic factor.

OBJECTIVE

To study whether plasma LRG1 may independently predict progression of DKD in individuals with type 2 diabetes mellitus (T2DM).

DESIGN AND SETTING

Prospective cohort study in a regional hospital.

PATIENTS

In total, 1226 T2DM participants were followed for a mean ± standard deviation (SD) of 3.1 ± 0.4 years.

MAIN OUTCOMES

Albuminuria progression was defined as elevation in albuminuria level to a higher category. Chronic kidney disease (CKD) progression [rapid estimated glomerular filtration rate (eGFR) decline] was defined as a 40% or greater deterioration in eGFR in 3 years.

RESULTS

Both participants with albuminuria progression and those with CKD progression had higher plasma LRG1 levels at baseline. LRG1 independently predicted albuminuria progression above traditional risk factors, including baseline eGFR and urine albumin to creatinine ratio. A 1-SD increment in LRG1 was associated with a 1.26-fold [95% confidence interval (CI), 1.04 to 1.53, P = 0.018] higher adjusted risk for albuminuria progression. The association of LRG1 with microalbuminuria to macroalbuminuria progression was stronger than its association with normoalbuminuria to microalbuminuria progression [odds ratio (OR), 1.51; 95% CI, 1.04 to 2.18, P = 0.029 vs OR, 1.09; 95% CI, 0.86 to 1.37, P = 0.486, per 1-SD LRG1 increment]. Also, LRG1 independently predicted CKD progression above traditional risk factors. A 1-SD increment in LRG1 was associated with a 1.48-fold (95% CI, 1.04 to 2.11, P = 0.032) higher adjusted risk for CKD progression.

CONCLUSIONS

Plasma LRG1 predicts both albuminuria and CKD progression beyond traditional risk factors. It may play a role in the pathologic pathway leading to progression of DKD in T2DM.

The VEGF-A inhibitor sFLT-1 improves renal function by reducing endothelial activation and inflammation in a mouse model of type 1 diabetes

AIMS/HYPOTHESIS

Animal models of diabetic nephropathy show increased levels of glomerular vascular endothelial growth factor (VEGF)-A, and several studies have shown that inhibiting VEGF-A in animal models of diabetes can prevent albuminuria and glomerular hypertrophy. However, in those studies, treatment was initiated before the onset of kidney damage. Therefore, the aim of this study was to investigate whether transfecting mice with the VEGF-A inhibitor sFlt-1 (encoding soluble fms-related tyrosine kinase 1) can reverse pre-existing kidney damage in a mouse model of type 1 diabetes. In addition, we investigated whether transfection with sFlt-1 can reduce endothelial activation and inflammation in these mice.

METHODS

Subgroups of untreated 8-week-old female C57BL/6J control (n = 5) and diabetic mice (n = 7) were euthanised 5 weeks after the start of the experiment in order to determine the degree of kidney damage prior to treatment with sFLT-1. Diabetes was induced with three i.p. injections of streptozotocin (75 mg/kg) administered at 2 day intervals. Diabetic nephropathy was then investigated in diabetic mice transfected with sFlt-1 (n = 6); non-diabetic, non-transfected control mice (n = 5); non-diabetic control mice transfected with sFlt-1(n = 10); and non-transfected diabetic mice (n = 6). These mice were euthanised at the end of week 15. Transfection with sFlt-1 was performed in week 6.

RESULTS

We found that transfection with sFlt-1 significantly reduced kidney damage by normalising albuminuria, glomerular hypertrophy and mesangial matrix content (i.e. glomerular collagen type IV protein levels) (p < 0.001). We also found that transfection with sFlt-1 reduced endothelial activation (p < 0.001), glomerular macrophage infiltration (p < 0.001) and glomerular TNF-α protein levels (p < 0.001). Finally, sFLT-1 decreased VEGF-A-induced endothelial activation in vitro (p < 0.001).

CONCLUSIONS/INTERPRETATION

These results suggest that sFLT-1 might be beneficial in treating diabetic nephropathy by inhibiting VEGF-A, thereby reducing endothelial activation and glomerular inflammation, and ultimately reversing kidney damage.

Antiangiogenic Therapy for Diabetic Nephropathy

Angiogenesis has been shown to be a potential therapeutic target for early stages of diabetic nephropathy in a number of animal experiments. Vascular endothelial growth factor (VEGF) is the main mediator for abnormal angiogenesis in diabetic glomeruli. Although beneficial effects of anti-VEGF antibodies have previously been demonstrated in diabetic animal experiments, recent basic and clinical evidence has revealed that the blockade of VEGF signaling resulted in proteinuria and renal thrombotic microangiopathy, suggesting the importance of maintaining normal levels of VEGF in the kidneys. Therefore, antiangiogenic therapy for diabetic nephropathy should eliminate excessive glomerular angiogenic response without accelerating endothelial injury. Some endogenous antiangiogenic factors such as endostatin and tumstatin inhibit overactivation of endothelial cells but do not specifically block VEGF signaling. In addition, the novel endothelium-derived antiangiogenic factor vasohibin-1 enhances stress tolerance and survival of the endothelial cells, while inhibiting excess angiogenesis. These factors have been demonstrated to suppress albuminuria and glomerular alterations in a diabetic mouse model. Thus, antiangiogenic therapy with promising candidates will possibly improve renal prognosis in patients with early stages of diabetic nephropathy.

PACSIN2 accelerates nephrin trafficking and is up-regulated in diabetic kidney disease

Nephrin is a core component of podocyte (glomerular epithelial cell) slit diaphragm and is required for kidney ultrafiltration. Down-regulation or mislocalization of nephrin has been observed in diabetic kidney disease (DKD), characterized by albuminuria. Here, we investigate the role of protein kinase C and casein kinase 2 substrate in neurons 2 (PACSIN2), a regulator of endocytosis and recycling, in the trafficking of nephrin and development of DKD. We observe that PACSIN2 is up-regulated and nephrin mislocalized in podocytes of obese Zucker diabetic fatty (ZDF) rats that have altered renal function. In cultured podocytes, PACSIN2 and nephrin colocalize and interact. We show that nephrin is endocytosed in PACSIN2-positive membrane regions and that PACSIN2 overexpression increases both nephrin endocytosis and recycling. We identify rabenosyn-5, which is involved in early endosome maturation and endosomal sorting, as a novel interaction partner of PACSIN2. Interestingly, rabenosyn-5 expression is increased in podocytes in obese ZDF rats, and, in vitro, its overexpression enhances the association of PACSIN2 and nephrin. We also show that palmitate, which is elevated in diabetes, enhances this association. Collectively, PACSIN2 is up-regulated and nephrin is abnormally localized in podocytes of diabetic ZDF rats. In vitro, PACSIN2 enhances nephrin turnover apparently via a mechanism involving rabenosyn-5. The data suggest that elevated PACSIN2 expression accelerates nephrin trafficking and associates with albuminuria.—Dumont, V., Tolvanen, T. A., Kuusela, S., Wang, H., Nyman, T. A., Lindfors, S., Tienari, J., Nisen, H., Suetsugu, S., Plomann, M., Kawachi, H., Lehtonen, S. PACSIN2 accelerates nephrin trafficking and is up-regulated in diabetic kidney disease.

Diabetes-Induced Reactive Oxygen Species: Mechanism of Their Generation and Role in Renal Injury

Diabetes induces the onset and progression of renal injury through causing hemodynamic dysregulation along with abnormal morphological and functional nephron changes. The most important event that precedes renal injury is an increase in permeability of plasma proteins such as albumin through a damaged glomerular filtration barrier resulting in excessive urinary albumin excretion (UAE). Moreover, once enhanced UAE begins, it may advance renal injury from progression of abnormal renal hemodynamics, increased glomerular basement membrane (GBM) thickness, mesangial expansion, extracellular matrix accumulation, and glomerulosclerosis to eventual end-stage renal damage. Interestingly, all these pathological changes are predominantly driven by diabetes-induced reactive oxygen species (ROS) and abnormal downstream signaling molecules. In diabetic kidney, NADPH oxidase (enzymatic) and mitochondrial electron transport chain (nonenzymatic) are the prominent sources of ROS, which are believed to cause the onset of albuminuria followed by progression to renal damage through podocyte depletion. Chronic hyperglycemia and consequent ROS production can trigger abnormal signaling pathways involving diverse signaling mediators such as transcription factors, inflammatory cytokines, chemokines, and vasoactive substances. Persistently, increased expression and activation of these signaling molecules contribute to the irreversible functional and structural changes in the kidney resulting in critically decreased glomerular filtration rate leading to eventual renal failure.

VEGF and the diabetic kidney: More than too much of a good thing

Over a decade and a half has passed since the publication of early reports hinting at a pathogenetic role for vascular endothelial growth factor ("VEGF") in the development of diabetic kidney disease. In diabetic rats, renal mRNA levels of the VEGF-A isoform were upregulated and administration of a VEGF-A neutralizing antibody attenuated albuminuria: VEGF was "bad" in diabetic nephropathy. Since that time, our understanding of the complexity of the renal VEGF system has advanced. Unlike its experimental counterpart, human diabetic nephropathy is associated with diminished VEGF-A levels and experience in the oncological setting has taught us that VEGF blocking therapy can cause adverse renal effects in patients. Correspondingly, investigational studies in cultured cells and rodent models have demonstrated that the biological effects of the VEGF system are dependent not only on the amount of VEGF, but also the type of VEGF, its sites of action and the prevailing milieu. Here we reflect back on the discoveries that have been made since those initial reports that shone the spotlight on the importance of the VEGF system in the diabetic kidney and we consider that the role of VEGF in diabetic nephropathy extends well beyond being "too much of a good thing".

Vascular Growth Factors and Glomerular Disease

The glomerulus is a highly specialized microvascular bed that filters blood to form primary urinary filtrate. It contains four cell types: fenestrated endothelial cells, specialized vascular support cells termed podocytes, perivascular mesangial cells, and parietal epithelial cells. Glomerular cell-cell communication is critical for the development and maintenance of the glomerular filtration barrier. VEGF, ANGPT, EGF, SEMA3A, TGF-β, and CXCL12 signal in paracrine fashions between the podocytes, endothelium, and mesangium associated with the glomerular capillary bed to maintain filtration barrier function. In this review, we summarize the current understanding of these signaling pathways in the development and maintenance of the glomerulus and the progression of disease.

Crosstalk in glomerular injury and repair

PURPOSE OF REVIEW

The glomerulus is a unique structure required for filtration of blood, while retaining plasma proteins based on size and charge selectivity. Distinct cell types form the structural unit that creates the filtration barrier. Structurally, fenestrated endothelial cells line the capillary loops and lie in close contact with mesangial cells. Podocytes are connected by specialized intercellular junctions known as slit diaphragms and separated from the endothelial compartment by the glomerular basement membrane. In order for this highly specialized structure to function, cross-communication between these cells must occur.

RECENT FINDINGS

Although classical studies have established key roles for vascular endothelial and platelet-derived growth factors in glomerular cross-communication, novel paracrine signaling pathways within the glomerulus have recently been identified. In addition, unique cellular pathways of established signaling cascades have been identified that are important for maintaining glomerular barrier function in health and disease.

SUMMARY

Here, we will review our current understanding of the processes of cross-communication between the unique cellular constituents forming the glomerular filtration unit. We will highlight recent findings of cellular crosstalk via signaling pathways that regulate glomerular barrier function in pathophysiological conditions.

Impaired Albumin Uptake and Processing Promote Albuminuria in OVE26 Diabetic Mice

The importance of proximal tubules dysfunction to diabetic albuminuria is uncertain. OVE26 mice have the most severe albuminuria of all diabetic mouse models but it is not known if impaired tubule uptake and processing are contributing factors. In the current study fluorescent albumin was used to follow the fate of albumin in OVE26 and normal mice. Compared to normal urine, OVE26 urine contained at least 23 times more intact fluorescent albumin but only 3-fold more 70 kD fluorescent dextran. This indicated that a function other than size selective glomerular sieving contributed to OVE26 albuminuria. Imaging of albumin was similar in normal and diabetic tubules for 3 hrs after injection. However 3 days after injection a subset of OVE26 tubules retained strong albumin fluorescence, which was never observed in normal mice. OVE26 tubules with prolonged retention of injected albumin lost the capacity to take up albumin and there was a significant correlation between tubules unable to eliminate fluorescent albumin and total albuminuria. TUNEL staining revealed a 76-fold increase in cell death in OVE26 tubules that retained fluorescent albumin. These results indicate that failure to process and dispose of internalized albumin leads to impaired albumin uptake, increased albuminuria, and tubule cell apoptosis.

Vascular growth factors play critical roles in kidney glomeruli

Kidney glomeruli ultrafilter blood to generate urine and they are dysfunctional in a variety of kidney diseases. There are two key vascular growth factor families implicated in glomerular biology and function, namely the vascular endothelial growth factors (VEGFs) and the angiopoietins (Angpt). We present examples showing not only how these molecules help generate and maintain healthy glomeruli but also how they drive disease when their expression is dysregulated. Finally, we review how manipulating VEGF and Angpt signalling may be used to treat glomerular disease.

Twenty years after ACEIs and ARBs: emerging treatment strategies for diabetic nephropathy

Diabetic nephropathy (DN) is a serious complication of both type 1 and type 2 diabetes mellitus. The disease is now the most common cause of end-stage kidney disease (ESKD) in developed countries, and both the incidence and prevalence of diabetes mellitus is increasing worldwide. Current treatments are directed at controlling hyperglycemia and hypertension, as well as blockade of the renin angiotensin system with angiotensin-converting enzyme inhibitors (ACEIs), and angiotensin receptor blockers. Despite these therapies, DN progresses to ESKD in many patients. As a result, much interest is focused on developing new therapies. It has been over two decades since ACEIs were shown to have beneficial effects in DN independent of their blood pressure-lowering actions. Since that time, our understanding of disease mechanisms in DN has evolved. In this review, we summarize major cell signaling pathways implicated in the pathogenesis of diabetic kidney disease, as well as emerging treatment strategies. The goal is to identify promising targets that might be translated into therapies for the treatment of patients with diabetic kidney disease.

Gremlin regulates renal inflammation via the vascular endothelial growth factor receptor 2 pathway

Inflammation is a main feature of progressive kidney disease. Gremlin binds to bone morphogenetic proteins (BMPs), acting as an antagonist and regulating nephrogenesis and fibrosis among other processes. Gremlin also binds to vascular endothelial growth factor receptor-2 (VEGFR2) in endothelial cells to induce angiogenesis. In renal cells, gremlin regulates proliferation and fibrosis, but there are no data about inflammatory-related events. We have investigated the direct effects of gremlin in the kidney, evaluating whether VEGFR2 is a functional gremlin receptor. Administration of recombinant gremlin to murine kidneys induced rapid and sustained activation of VEGFR2 signalling, located in proximal tubular epithelial cells. Gremlin bound to VEGFR2 in these cells in vitro, activating this signalling pathway independently of its action as an antagonist of BMPs. In vivo, gremlin caused early renal damage, characterized by activation of the nuclear factor (NF)-κB pathway linked to up-regulation of pro-inflammatory factors and infiltration of immune inflammatory cells. VEGFR2 blockade diminished gremlin-induced renal inflammatory responses. The link between gremlin/VEGFR2 and NF-κB/inflammation was confirmed in vitro. Gremlin overexpression was associated with VEGFR2 activation in human renal disease and in the unilateral ureteral obstruction experimental model, where VEGFR2 kinase inhibition diminished renal inflammation. Our data show that a gremlin/VEGFR2 axis participates in renal inflammation and could be a novel target for kidney disease.

Renal endothelial dysfunction in diabetic nephropathy

Endothelial dysfunction has been posited to play an important role in the pathogenesis of diabetic nephropathy (DN). Due to the heterogeneity of endothelial cells (ECs), it is difficult to generalize about endothelial responses to diabetic stimuli. At present, there are limited techniques fordirectly measuring EC function in vivo, so diagnosis of endothelial disorders still largely depends on indirect assessment of mediators arising from EC injury. In the kidney microcirculation, both afferent and efferent arteries, arterioles and glomerular endothelial cells (GEnC) have all been implicated as targets of diabetic injury. Both hyperglycemia per se, as well as the metabolic consequences of glucose dysregulation, are thought to lead to endothelial cell dysfunction. In this regard, endothelial nitric oxide synthase (eNOS) plays a central role in EC dysfunction. Impaired eNOS activity can occur at numerous levels, including enzyme uncoupling, post-translational modifications, internalization and decreased expression. Reduced nitric oxide (NO) bioavailability exacerbates oxidative stress, further promoting endothelial dysfunction and injury. The injured ECs may then function as active signal transducers of metabolic, hemodynamic and inflammatory factors that modify the function and morphology of the vessel wall and interact with adjacent cells, which may activate a cascade of inflammatory and proliferative and profibrotic responses in progressive DN. Both pharmacological approaches and potential regenerative therapies hold promise for restoration of impaired endothelial cells in diabetic nephropathy.

VEGF-A inhibition ameliorates podocyte apoptosis via repression of activating protein 1 in diabetes

BACKGROUND/AIMS

Vascular endothelial growth factor-A (VEGF-A) upregulation and podocyte apoptosis have been documented in diabetes. This study was designed to investigate whether inhibiting VEGF-A could ameliorate podocyte apoptosis in diabetes and the underlying mechanisms.

METHODS

In vitro, small interfering RNAs (siRNAs) of VEGF-A and activator protein 1 (AP-1, c-fos and c-jun), bevacizumab (VEGF-A inhibitor) and SP600125 (AP-1 inhibitor) were added to high glucose (30 mM) induced podocytes. Luciferase reporter assay was used to investigate whether AP-1 was a direct target of VEGF-A. In vivo, bevacizumab and SP600125 were administered to 12-week-old streptozotocin-induced male Sprague Dawley rats. The level of VEGF-A, c-fos, c-jun and bcl-2 were examined using immunostaining and Western blot analysis. Podocyte apoptosis was detected using the terminal deoxynucleotidyl transferase-mediated uridine 5'-triphosphate-biotin nick end labeling (TUNEL) assay, electron microscopy and flow cytometry.

RESULTS

Silencing VEGF-A or AP-1 upregulated bcl-2 and ameliorated podocyte apoptosis. Silencing VEGF-A decreased the level of c-fos and c-jun and bevacizumab and SP600125 treatment attenuated podocyte apoptosis. Luciferase reporter activity of VEGF-A-3'-UTR constructs was significantly provoked when stimulated with TGF-β1. In diabetic rat kidneys, VEGF-A co-localized with bcl-2 in podocytes. With bevacizumab and SP600125 treatment, the level of VEGF-A and AP-1 decreased while bcl-2 increased. Podocyte apoptotic rate was reduced with condensed podocyte nuclei less frequently observed. The urine albumin excretion rate (UAER) and albumin/creatinine were improved.

CONCLUSION

This study demonstrates VEGF-A inhibition ameliorates podocyte apoptosis by regulating AP-1 and bcl-2 signaling. AP-1 is a direct target of VEGF-A and a novel player in podocyte apoptosis.

Mechanism of kidney injury caused by bevacizumab in rats

OBJECTIVE

We investigate kidney injury caused by high dose bevacizumab to uncover the possible mechanisms involving in this process.

METHODS

Forty rats were divided into four groups: cisplation group (treated with 1 mg/kg cisplation), Bev-high group (treated with 5 mg/kg bevacizumab); Bev-low group (treated with 2.5 mg/kg bevacizumab) and control group (treated with saline). The urine microalbumin, serum cystatin C, blood urea nitrogen and serum creatinine were detected in the four group rats, respectively. The immunoglobulin of IgG, IgA and IgM and protein of VEGF (vascular endothelial growth factor) and nephrin were detected by immunohistochemical methods.

RESULTS

All the levels of microalbumin, cystatin C, serum creatinine and blood urea nitrogen in Bev-high group were significantly higher than those in normal control group (P < 0.05). The cystatin C was much more increased in kidney Bev-high group than cisplatin and Bev-low groups (P < 0.05). The light microscope showed a normal glomerular morphology in the four groups, while the electronic microscopy showed the podocytes were extensively fused in cisplatin group and Bev-high group. The two groups were found IgG and IgM deposition as well. The VEGF in kidney amples were down regulated in high dose bevacizumab group, whereas the nephrin and IgA showed no significant expression changes at all.

CONCLUSION

Bevacizumab increases the risk of injury in glomerular filtration barrier in a dose dependent model. The injury may not only associate with the rising level of proteinuria but also with podocyte-dependent membrane structures.

Glomerular endothelial cell injury and cross talk in diabetic kidney disease

Diabetic kidney disease (DKD) remains a leading cause of new-onset end-stage renal disease (ESRD), and yet, at present, the treatment is still very limited. A better understanding of the pathogenesis of DKD is therefore necessary to develop more effective therapies. Increasing evidence suggests that glomerular endothelial cell (GEC) injury plays a major role in the development and progression of DKD. Alteration of the glomerular endothelial cell surface layer, including its major component, glycocalyx, is a leading cause of microalbuminuria observed in early DKD. Many studies suggest a presence of cross talk between glomerular cells, such as between GEC and mesangial cells or GEC and podocytes. PDGFB/PDGFRβ is a major mediator for GEC and mesangial cell cross talk, while vascular endothelial growth factor (VEGF), angiopoietins, and endothelin-1 are the major mediators for GEC and podocyte communication. In DKD, GEC injury may lead to podocyte damage, while podocyte loss further exacerbates GEC injury, forming a vicious cycle. Therefore, GEC injury may predispose to albuminuria in diabetes either directly or indirectly by communication with neighboring podocytes and mesangial cells via secreted mediators. Identification of novel mediators of glomerular cell cross talk, such as microRNAs, will lead to a better understanding of the pathogenesis of DKD. Targeting these mediators may be a novel approach to develop more effective therapy for DKD.

Vascular endothelial growth factor and the kidney: something of the marvellous

PURPOSE OF REVIEW

The vascular endothelial growth factor (VEGF) system is a multifarious network and an exemplar of an intraglomerular signalling pathway. Here, we review recent advances that highlight the subtle nature of the renal VEGF system and its influencers.

RECENT FINDINGS

The VEGF system is no longer considered as a simple paracrine, ligand-receptor interaction under the regulatory control of a soluble 'decoy', soluble fms-like tyrosine kinase-1 (sFLT1). Rather, the abundantly expressed, podocyte-derived VEGF isoform, VEGF-A, is now recognized to mediate both paracrine effects across the filtration barrier and autocrine actions, functioning to preserve the integrity of the cells from which it arises. Autocrine actions of the podocyte VEGF system extend beyond those of the VEGF-A isoform, however, with sFLT1 itself now appreciated as regulating podocyte morphology by binding to lipid microdomains. These and other functions of the VEGF system are profoundly affected by the presence, nature and abundance of influencers both intrinsic and extrinsic to the pathway, the latter most readily exemplified by the role of the cytokine in the diabetic kidney.

SUMMARY

The glomerular VEGF system plays a delicate, yet critical, role in preserving renal homeostasis. It may be intricate, but 'in all things of nature there is something of the marvellous'.

Cell biology of diabetic nephropathy: Roles of endothelial cells, tubulointerstitial cells and podocytes

Diabetic nephropathy is the major cause of end-stage renal failure throughout the world in both developed and developing countries. Diabetes affects all cell types of the kidney, including endothelial cells, tubulointerstitial cells, podocytes and mesangial cells. During the past decade, the importance of podocyte injury in the formation and progression of diabetic nephropathy has been established and emphasized. However, recent findings provide additional perspectives on pathogenesis of diabetic nephropathy. Glomerular endothelial damage is already present in the normoalbuminuric stage of the disease when podocyte injury starts. Genetic targeting of mice that cause endothelial injury leads to accelerated diabetic nephropathy. Tubulointerstitial damage, previously considered to be a secondary effect of glomerular protein leakage, was shown to have a primary significance in the progression of diabetic nephropathy. Emerging evidence suggests that the glomerular filtration barrier and tubulointerstitial compartment is a composite, dynamic entity where any injury of one cell type spreads to other cell types, and leads to the dysfunction of the whole apparatus. Accumulation of novel knowledge would provide a better understanding of the pathogenesis of diabetic nephropathy, and might lead to a development of a new therapeutic strategy for the disease.

Clinicopathological spectrum of kidney diseases in cancer patients treated with vascular endothelial growth factor inhibitors: a report of 5 cases and review of literature

Recently, cancer therapies have been supplemented by vascular endothelial growth factor (VEGF) inhibitors as anti-angiogenic agents. However, kidney-related adverse reactions associated with these agents clinically manifest as hypertension and proteinuria, the most severe form being thrombotic microangiopathy (TMA). We present the spectrum of pathological features in VEGF inhibitor-associated kidney disease. Clinicopathological findings of kidney disease were retrospectively studied in 5 cancer patients treated with anti-VEGF agents. Although 4 cases received bevacizumab (anti-VEGF-A), one was given sorafenib (small molecule tyrosine kinase inhibitor affecting VEGF-R2). All patients presented with acute kidney injury, hypertension, and/or proteinuria. All kidney biopsies showed recent and chronic endothelial injury of varying severity and vascular sclerosis, including 2 with typical active features of TMA. Furthermore, acute tubular injury with focal necrosis was seen in all cases. While administration of VEGF inhibitor was discontinued in 4 cases, it was resumed for 5 more doses, following steroid therapy in 1 case. Cessation of VEGF inhibitor therapy was successful in reversing anemia and led to improvement of hypertension and proteinuria in 4 of the 5 cases. One case with TMA progressed to end-stage renal disease. A range of renal pathologic lesions secondary to endothelial injury are noted often accompanied by acute tubular damage following anti-VEGF therapy, the most severe being TMA. While most of the clinical manifestations are reversible with discontinuation of therapy, the role of other nephrotoxic chemotherapeutic agents in enhancing renal injury including severe TMA and other host factors with possible poor outcome should be considered.

Signal transduction in podocytes--spotlight on receptor tyrosine kinases

The mammalian kidney filtration barrier is a complex multicellular, multicomponent structure that maintains homeostasis by regulating electrolytes, acid-base balance, and blood pressure (via maintenance of salt and water balance). To perform these multiple functions, podocytes--an important component of the filtration apparatus--must process a series of intercellular signals. Integrating these signals with diverse cellular responses enables a coordinated response to various conditions. Although mature podocytes are terminally differentiated and cannot proliferate, they are able to respond to growth factors. It is possible that the initial response of podocytes to growth factors is beneficial and protective, and might include the induction of hypertrophic cell growth. However, extended and/or uncontrolled growth factor signalling might be maladaptive and could result in the induction of apoptosis and podocyte loss. Growth factors signal via the activation of receptor tyrosine kinases (RTKs) on their target cells and around a quarter of the 58 RTK family members that are encoded in the human genome have been identified in podocytes. Pharmacological inhibitors of many RTKs exist and are currently used in experimental and clinical cancer therapy. The identification of pathological RTK-mediated signal transduction pathways in podocytes could provide a starting point for the development of novel therapies for glomerular disorders.

Pathophysiology of the diabetic kidney

Diabetes mellitus contributes greatly to morbidity, mortality, and overall health care costs. In major part, these outcomes derive from the high incidence of progressive kidney dysfunction in patients with diabetes making diabetic nephropathy a leading cause of end-stage renal disease. A better understanding of the molecular mechanism involved and of the early dysfunctions observed in the diabetic kidney may permit the development of new strategies to prevent diabetic nephropathy. Here we review the pathophysiological changes that occur in the kidney in response to hyperglycemia, including the cellular responses to high glucose and the responses in vascular, glomerular, podocyte, and tubular function. The molecular basis, characteristics, and consequences of the unique growth phenotypes observed in the diabetic kidney, including glomerular structures and tubular segments, are outlined. We delineate mechanisms of early diabetic glomerular hyperfiltration including primary vascular events as well as the primary role of tubular growth, hyperreabsorption, and tubuloglomerular communication as part of a "tubulocentric" concept of early diabetic kidney function. The latter also explains the "salt paradox" of the early diabetic kidney, that is, a unique and inverse relationship between glomerular filtration rate and dietary salt intake. The mechanisms and consequences of the intrarenal activation of the renin-angiotensin system and of diabetes-induced tubular glycogen accumulation are discussed. Moreover, we aim to link the changes that occur early in the diabetic kidney including the growth phenotype, oxidative stress, hypoxia, and formation of advanced glycation end products to mechanisms involved in progressive kidney disease.

Endothelial-podocyte crosstalk: the missing link between endothelial dysfunction and albuminuria in diabetes

Although diabetes is the most common cause of end-stage renal disease (ESRD) worldwide, most people with diabetic nephropathy will never develop ESRD but will instead die of cardiovascular (CV) disease (CVD). The first evidence of kidney injury in diabetes is often microalbuminuria, itself also an independent risk marker for CVD. Although the two processes are closely associated, the recent failure of antialbuminuric therapies to affect CV outcomes has encouraged a reconsideration of how albuminuria may occur in diabetes and how increased urinary albumin excretion may be indicative of CV risk. The relationship between CVD and urinary albumin content (even within the normal range) is widely considered to reflect the common underlying pathology of endothelial dysfunction. At the same time, recent years have witnessed a growing appreciation that diabetic albuminuria commonly arises from damage to glomerular podocytes, specialized epithelial cells acting as the final barrier to macromolecular flow into the urinary filtrate. These superficially discordant paradigms can be assimilated by the emerging concept of endothelial-podocyte crosstalk across the glomerular filtration barrier, whereby the actions of one type of cell may profoundly influence the function of the other. The bidirectional nature of this paracrine network is illustrated by the actions of the vascular endothelial growth factor-A (VEGF-A)/VEGF receptor-2 and activated protein C systems, among others. Identification of novel mediators of endothelial-podocyte crosstalk may lead to the development of more effective treatments for diabetic nephropathy and its sequelae.

Targeted glomerular angiopoietin-1 therapy for early diabetic kidney disease

Vascular growth factors play an important role in maintaining the structure and integrity of the glomerular filtration barrier. In healthy adult glomeruli, the proendothelial survival factors vascular endothelial growth factor-A (VEGF-A) and angiopoietin-1 are constitutively expressed in glomerular podocyte epithelia. We demonstrate that this milieu of vascular growth factors is altered in streptozotocin-induced type 1 diabetic mice, with decreased angiopoietin-1 levels, VEGF-A upregulation, decreased soluble VEGF receptor-1 (VEGFR1), and increased VEGFR2 phosphorylation. This was accompanied by marked albuminuria, nephromegaly, hyperfiltration, glomerular ultrastructural alterations, and aberrant angiogenesis. We subsequently hypothesized that restoration of angiopoietin-1 expression within glomeruli might ameliorate manifestations of early diabetic glomerulopathy. Podocyte-specific inducible repletion of angiopoietin-1 in diabetic mice caused a 70% reduction of albuminuria and prevented diabetes-induced glomerular endothelial cell proliferation; hyperfiltration and renal morphology were unchanged. Furthermore, angiopoietin-1 repletion in diabetic mice increased Tie-2 phosphorylation, elevated soluble VEGFR1, and was paralleled by a decrease in VEGFR2 phosphorylation and increased endothelial nitric oxide synthase Ser(1177) phosphorylation. Diabetes-induced nephrin phosphorylation was also reduced in mice with angiopoietin-1 repletion. In conclusion, targeted angiopoietin-1 therapy shows promise as a renoprotective tool in the early stages of diabetic kidney disease.

Diabetic nephropathy: protective factors and a new therapeutic paradigm

Diabetic nephropathy (DN) is the most common cause of chronic kidney disease (CKD) and its number has been increasing. CKD is a worldwide threat to health but the precise mechanism of this problem is not fully appreciated. It is believed that hyperglycemia is one of the most important metabolic factors in the development of DN. Multiple molecular mechanisms have been proposed to mediate hyperglycemia's adverse effects on kidney. To identify targets for therapeutic intervention, most studies have focused on understanding how abnormal levels of such metabolities cause DN. However, there have been few reports regarding endogenous renal protective factors. Thus, recognition of the importance of this could be providing a new perspective for understanding the development of DN and a new therapeutic paradigm to combat DN.

Role of the eNOS-NO system in regulating the antiproteinuric effects of VEGF receptor 2 inhibition in diabetes

Subtle perturbations in intraglomerular VEGF/VEGFR-2 signaling or in the influencing microenvironment can profoundly affect renal function, resulting in the apparently paradoxical observation that VEGF blockade attenuates proteinuria development in experimental diabetes despite exerting the opposite effect under other circumstances. In the present study, we sought to explore the role of eNOS-NO activity in regulating the differential response to VEGF blockade in the diabetic and nondiabetic settings. In a rodent model of accelerated renal injury, the transgenic (mRen-2)27 (Ren-2) rat, VEGFR-2 inhibition with the small molecule vandetanib resulted in an increase in urine protein excretion preceding a subsequent rise in systolic blood pressure. When compared to their normoglycaemic counterparts, diabetic Ren-2 rats exhibited an increase in the renal expression of eNOS and in urinary excretion of nitric oxide (NO) metabolites. In contrast to the heavy proteinuria observed with vandetanib in nondiabetic TGR(mRen-2)27 rats, VEGFR-2 inhibition reduced urine protein excretion in diabetic animals, despite a comparable magnitude of histological injury. However, proteinuria was markedly increased by concomitant treatment of diabetic Ren-2 rats with vandetanib and the nitric oxide synthase inhibitor L-NAME. These observations highlight the pivotal role that the eNOS-NO system plays in regulating the biologic response to VEGF within the glomerulus.

Albuminuria is associated with too few glomeruli and too much testosterone

Normally, the glomerular filtration barrier almost completely excludes circulating albumin from entering the urine. Genetic variation and both pre- and postnatal environmental factors may affect albuminuria in humans. Here we determine whether glomerular gene expression in mouse strains with naturally occurring variations in albuminuria would allow identification of proteins deregulated in relatively 'leaky' glomeruli. Albuminuria increased in female B6 to male B6 to female FVB/N to male FVB/N mice, whereas the number of glomeruli/kidney was the exact opposite. Testosterone administration led to increased albuminuria in female B6 but not female FVB/N mice. A common set of 39 genes, many expressed in podocytes, were significantly differentially expressed in each of the four comparisons: male versus female B6 mice, male versus female FVB/N mice, male FVB/N versus male B6 mice, and female FVB/N versus female B6 mice. The transcripts encoded proteins involved in oxidation/reduction reactions, ion transport, and enzymes involved in detoxification. These proteins may represent novel biomarkers and even therapeutic targets for early kidney and cardiovascular disease.

VEGF and podocytes in diabetic nephropathy

Vascular endothelial growth factor-A (VEGF-A) is a protein secreted by podocytes that is necessary for survival of endothelial cells, podocytes, and mesangial cells. VEGF-A regulates slit-diaphragm signaling and podocyte shape via VEGF-receptor 2-nephrin-nck-actin interactions. Chronic hyperglycemia-induced excess podocyte VEGF-A and low endothelial nitric oxide drive the development and the progression of diabetic nephropathy. The abnormal cross-talk between VEGF-A and nitric oxide pathways is fueled by the diabetic milieu, resulting in increased oxidative stress. Recent findings on these pathogenic molecular mechanisms provide new potential targets for therapy for diabetic renal disease.

The renal endothelium in diabetic nephropathy

Diabetic nephropathy is the leading cause of end-stage renal disease. Diabetes mellitus is characterized by generalized endothelial dysfunction. However, recent data also emphasizes the role of local renal endothelium dysfunction in the pathogenesis of diabetic nephropathy. Hyperglycemia triggers a complex network of signal-transduction molecules, transcription factors, and mediators that culminate in endothelial dysfunction. In the glomerulus, vascular endothelial growth factor-A (VEGF)-induced neoangiogenesis may contribute to the initial hyperfiltration and microalbuminuria due to increased filtration area and immaturity of the neovessels, respectively. However, subsequent decrease in podocytes number decreases VEGF production resulting in capillary rarefaction and decreased glomerular filtration rate (GFR). Decreased nitric oxide availability also plays a significant role in the development of advanced lesions of diabetic nephropathy through disruption of glomerular autoregulation, uncontrolled VEGF action, release of prothrombotic substances by endothelial cells and angiotensin-II-independent aldosterone production. In addition, disturbances in endothelial glycocalyx contribute to decreased permselectivity and microalbuminuria; whereas there are recent evidences that reduced glomerular fenestral endothelium leads to decreased GFR levels. Endothelial repair mechanisms are also impaired in diabetes, since circulating endothelial progenitor cells number is decreased in diabetic patients with microalbuminuria. Finally, in the context of elevated profibrotic cytokine transforming growth factor-β levels, endothelial cells also confer to the deteriorating process of fibrosis in advanced diabetic nephropathy through endothelial to mesenchymal transition.

Angiogenesis and hypoxia in the kidney

Loss of glomerular function associated with the presence of tubulointerstitial lesions, which are characterized by peritubular capillary loss, is a common finding in progressive renal disorders. Dysregulated expression of angiogenic factors (such as vascular endothelial growth factor [VEGF] and angiopoietins) and endogenous angiogenic inhibitors (such as thrombospondin-1, angiostatin and endostatin) underlie these conditions and negatively influence the balance between capillary formation and regression, resulting in capillary rarefaction. Recent studies have provided unequivocal evidence for a pathogenic role of tubulointerstitial hypoxia and the involvement of hypoxia-inducible transcription factors in the advanced stages of chronic kidney disease. The mainstay of potential angiogenic therapies is the application of angiogenic factors with the primary aim of ameliorating reduced oxygenation in the ischaemic tubulointerstitium. However, this strategy is strongly associated with inflammation and changes in vascular permeability. For example, supraphysiological expression of VEGF results in glomerular expansion and proteinuria, whereas VEGF blockade using neutralizing antibodies can cause hypertension and thrombotic microangiopathy. These effects highlight the importance of tight regulation of angiogenic factors and inhibitors. Novel therapeutic approaches that target vascular maturation and normalization are now being developed to protect kidneys from capillary rarefaction and hypoxic injury.