Secretion of chemokines and cytokines by human tubular epithelial cells in response to proteins

Independent Prognostic and Predictive Role of Interstitial Macrophages in Kidney Biopsies of IgA Nephropathy Patients

A relevant percentage of IgAN patients experience a progressive decline in kidney function. According to the KDIGO guidelines, proteinuria and eGFR are the only validated prognostic markers. The role of interstitial macrophages in kidney biopsies of IgAN patients and the outcome of patients treated with renin-angiotensin system inhibitors (RASBs) alone or combined with glucocorticoids were evaluated. Clinical and laboratory records (age, gender, hypertension, hematuria, proteinuria, eGFR, serum creatinine, and therapy), MEST-C parameters of the Oxford classification, C4d deposition, peritubular capillaries, and glomerular and interstitial macrophages in 47 IgAN patients undergoing kidney biopsy consecutively between 2003 and 2016 were examined. A high number of interstitial macrophages significantly correlated with peritubular capillary rarefaction and impairment of kidney function. Cox's multivariable regression analysis revealed that a value > 19.5 macrophages/HPF behaved as an independent marker of an unfavorable outcome. Patients exhibiting > 19.5 macrophages/HPF treated at the time of diagnosis with RASBs combined with methylprednisolone had an estimated probability of a favorable outcome higher than patients treated with RASBs alone. Thus, a value > 19.5 macrophages/HPF in IgAN biopsies can predict an unfavorable outcome and endorse a well-timed administration of glucocorticoids. Studies evaluating urine biomarkers associated with peritubular capillary rarefaction in patients with marked macrophage infiltration may help personalized treatment decisions.

Role of Mesangial-Podocytic-Tubular Cross-Talk in IgA Nephropathy

IgA nephropathy (IgAN), a common primary glomerulonephritis worldwide, is associated with a substantial risk of progression to end-stage renal failure. The disease runs a highly variable clinical course with frequent involvement of tubulointerstitial damage. A subgroup of IgAN with proximal tubular epithelial cells (PTECs) and tubulointerstitial damage often is associated with rapid progression to end-stage renal failure. Human mesangial cell-derived mediators lead to podocyte and tubulointerstitial injury via mesangial-podocytic-tubular cross-talk. Although mesangial-podocytic communication plays a pathogenic role in podocytic injury, the implication of a podocyte-PTEC cross-talk pathway in the progression of tubulointerstitial injury in IgAN should not be underscored. We review the role of mesangial-podocytic-tubular cross-talk in the progression of IgAN. We discuss how podocytopathy in IgAN promotes subsequent PTEC dysfunction and whether tubulointerstitial injury affects the propagation of podocytic injury in IgAN. A thorough understanding of the cross-talk mechanisms among mesangial cells, podocytes, and PTECs may lead to better design of potential therapeutic options for IgAN.

Acute kidney injury in children with nephrotic syndrome: a single-center study

Background

Children with nephrotic syndrome (NS) are at risk for the development of acute kidney injury (AKI) through a variety of mechanisms.The frequency of NS hospitalizations complicated by AKI has almost doubled in the last decade. Children with AKI have longer hospital length of stay and increased need for intensive care unit admission. The main objectives of this study were to determine the incidence, clinical characteristics, risk factors and short-term outcome of AKI in children hospitalized with NS.

Methods

In this retrospective study, 355 children ≤18 years of age with a clinical diagnosis of NS admitted in the Department of Nephrology, Gauhati Medical College and Hospital from January 2012 to December 2015 were reviewed.

Results

The incidence of AKI in children with NS was found to be 23.66%, 11.24%, 7.95% and 4.48% of children entered Pediatric Risk, Injury, Failure, Loss, End-Stage Renal Disease (pRIFLE) Stages R, I and F, respectively. Infection {odds ratio [OR] 2.53 [95% confidence interval (CI) 1.52–4.22]} and nephrotoxic medication exposure [OR 7.8 (95% CI 4.06–15.01)] were common factors associated with AKI. Children with steroid-dependent NS (SDNS) and steroid-resistant NS (SRNS) were more likely to develop AKI compared with children with steroid-sensitive NS (SSNS). The mean time to recovery for groups pRIFLE Stages R, I and F were 15 ± 2 , 22 ± 3 and 28 ± 5 days, respectively. Children with NS who were hypertensive, had higher urinary protein excretion and low serum albumin were more prone to develop AKI.

Conclusions

AKI is not uncommon in children with NS. Infection and exposure to nephrotoxic drugs are common factors associated with AKI. AKI is more frequent in SDNS and SRNS compared with SSNS. The mean time to recovery is prolonged with more severe AKI.

Nephrogenic acute respiratory distress syndrome: A narrative review on pathophysiology and treatment

The kidneys have a close functional relationship with other organs especially the lungs. This connection makes the kidney and the lungs as the most organs involved in the multi-organ failure syndrome. The combination of acute lung injury (ALI) and renal failure results a great clinical significance of 80% mortality rate. Acute kidney injury (AKI) leads to an increase in circulating cytokines, chemokines, activated innate immune cells and diffuse of these agents to other organs such as the lungs. These factors initiate pathological cascade that ultimately leads to ALI and acute respiratory distress syndrome (ARDS). We comprehensively searched the English medical literature focusing on AKI, ALI, organs cross talk, renal failure, multi organ failure and ARDS using the databases of PubMed, Embase, Scopus and directory of open access journals. In this narrative review, we summarized the pathophysiology and treatment of respiratory distress syndrome following AKI. This review promotes knowledge of the link between kidney and lung with mechanisms, diagnostic biomarkers, and treatment involved ARDS induced by AKI.

MCP1 2518 A/G polymorphism affects progression of childhood focal segmental glomerulosclerosis

Monocyte chemoattractant protein-1 (MCP-1) is a highly specific chemokine for monocytes and plays roles in pathogenesis of various renal diseases. The aim of this study is to investigate the effect of MCP1 2518 A/G polymorphism on the incidence and clinical course of focal segmental glomerulosclerosis (FSGS) in children. MCP1 2518 A/G genotype was identified by PCR-RFLP in 60 biopsy-proven FSGS patients, 76 steroid sensitive nephrotic syndrome (SSNS) patients, and 96 healthy children. MCP-1 levels in urine and serum were measured by ELISA in all patients and the correlations of genotype with MCP-1 levels and clinical outcome were evaluated. The genotype frequencies for MCP1 were similar in all groups. The percentage of patients who develop chronic renal failure was higher in patients with AA allele compared to GA or GG alleles (46% vs. 35% respectively, p < 0.01, Odds ratio: 1.59). Serum MCP-1 levels were similar in all groups, whereas urinary MCP-1 levels of the patients with FSGS (1680 pg/mg creatinine) were significantly higher than that of patients with SSNS (365 pg/mg creatinine, p < 0.05) and healthy controls (348 pg/mg creatinine; p < 0.05). Urinary MCP-1 levels were correlated with the degree of proteinuria in FSGS group (r = 0.529, p = 0.016). Our results suggest that the AA genotype might be a risk factor for the progression of renal disease in FSGS and MCP1 genotyping may help the physicians to predict prognosis in these patients.

Mesenchymal stem/stromal cells as a delivery platform in cell and gene therapies

Regenerative medicine relying on cell and gene therapies is one of the most promising approaches to repair tissues. Multipotent mesenchymal stem/stromal cells (MSC), a population of progenitors committing into mesoderm lineages, are progressively demonstrating therapeutic capabilities far beyond their differentiation capacities. The mechanisms by which MSC exert these actions include the release of biomolecules with anti-inflammatory, immunomodulating, anti-fibrogenic, and trophic functions. While we expect the spectra of these molecules with a therapeutic profile to progressively expand, several human pathological conditions have begun to benefit from these biomolecule-delivering properties. In addition, MSC have also been proposed to vehicle genes capable of further empowering these functions. This review deals with the therapeutic properties of MSC, focusing on their ability to secrete naturally produced or gene-induced factors that can be used in the treatment of kidney, lung, heart, liver, pancreas, nervous system, and skeletal diseases. We specifically focus on the different modalities by which MSC can exert these functions. We aim to provide an updated understanding of these paracrine mechanisms as a prerequisite to broadening the therapeutic potential and clinical impact of MSC.

Hypothesis: Pentoxifylline explores new horizons in treatment of preeclampsia

Preeclampsia, the leading cause of maternal morbidity and perinatal mortality, initiates as inappropriate immune response to trophoblastic invasion impairs placentation and placental circulation. A poorly perfused placenta generates superoxide anions as well as anti-angiogenic factors and this series of events result in impairment of endothelial function, followed by maternal morbidities such as hypertension, kidney injury and proteinuria. Renal loss of anti-coagulant proteins and subsequent hyper-coagulable state along with endothelial dysfunction accelerates progression of the disease toward eclampsia. Since Pentoxifylline, a methyl-xanthine derivative known for enhancement of vascular endothelial function, down-regulation of many inflammatory cytokines increased during preeclampsia, improvement of placental circulation, reduction of ischemia-reperfusion injury, enhancement of vasodilatation and endothelial function, ameliorating proteinuria, inhibition of platelet aggregation and decreasing risk of preterm labor, which are all amongst morbidities of preeclampsia, here it is hypothesized that Pentoxifylline prevents development of preeclampsia and/or decelerate progression of the disease.

Role of Toll-like receptors in diabetic nephropathy

Diabetic nephropathy is the leading cause of kidney failure and its increasing prevalence and incidence has imposed global socio-economic stress on healthcare systems worldwide. Although historically considered a metabolic disorder, recent studies have established that inflammatory responses are central to the pathogenesis of diabetic nephropathy. TLRs (Toll-like receptors) are a family of pattern recognition receptors responsible for the initiation of inflammatory and immune responses. The regulation of TLR2 and TLR4 have been implicated in the pathogenesis of various kidney diseases, and emerging evidence shows their involvement in the perpetuation of inflammation in the diabetic kidney. The present review focuses on the relative contributions of TLR2 and TLR4 in recognizing endogenous ligands relevant to diabetic nephropathy and their subsequent activation of NF-κB (nuclear factor κB), which results in the synthesis and secretion of pro-inflammatory cytokines and chemokines. Moreover, we discuss the pro-inflammatory signalling pathways of TLR2 and TLR4, in which their interruption or blockade may prove to be important therapeutic targets, potentially translated into clinical treatments for diabetic nephropathy. Currently, inhibitors to TLR2 and TLR4 are undergoing clinical trials in various inflammatory models of disease, but none in patients with diabetic nephropathy. Given the existing literature, there is a fundamental necessity to undertake trials in patients with diabetic nephropathy with a focus on renal end points.

Kidney injury molecule-1 expression in IgA nephropathy and its correlation with hypoxia and tubulointerstitial inflammation

Tubulointerstitial injury plays an important role in the development and progression of chronic kidney disease (CKD). Kidney injury molecule (KIM)-1 is induced in damaged proximal tubules in both acute renal injury and CKD. However, the dynamics of KIM-1 in CKD and effects of KIM-1 expression on disease progression are unknown. Here, we aimed to determine the associations between tubular KIM-1 expression levels, renal function, and inflammation in CKD. The relationships between levels of KIM-1 and clinicopathological parameters were analyzed in patients with progressive and nonprogressive IgA nephropathy. KIM-1 expression was increased in patients with IgA nephropathy, and its expression was significantly correlated with the decrease of renal function. KIM-1 was particularly evident at the site with reduced capillary density, and KIM-1-positive tubules were surrounded by infiltrates of inflammatory cells. Using in vitro cell models, we showed that cellular stressors, including hypoxia, induced KIM-1 expression. KIM-1-expressing cells produced more chemokines/cytokines when cultured under hypoxic conditions. Furthermore, we showed that tubular cells with KIM-1 expression can regulate the immune response of inflammatory cells through the secretion of chemotactic factors. These data suggest that KIM-1-expressing epithelial cells may play a role in the pathogenesis of tubulointerstitial inflammation during chronic renal injury through the secretion of chemokines/cytokines.

Urinary immunoglobulin G to albumin ratio and N-Acetyl-Beta-D-Glucosaminidase as early predictors of therapeutic response in ANCA-associated glomerulonephritis

Background

The aim of our study was to evaluate the prognostic value of glomerular and tubular proteinuria and tubular enzymuria as early indicators of therapeutic response to induction therapy with i.v. pulse cyclophosphamide (CyC) and methylprednisolone (MP) in patients with antineutrophil cytoplasmic antibody (ANCA) associated glomerulonephritis.

Methods and Findings

An observational single-center study was conducted in 30 patients with ANCA-associated glomerulonephritis. Patients were divided into subgroups with good or poor response to CyC therapy according to clinical and laboratory parameters. The diagnosis of ANCA-associated glomerulonephritis was based on the Chapel-Hill disease definitions. Good response to induction therapy was significantly associated with higher absolute values of urine N-acetyl-beta-D-glucosaminidase (NAG) to creatinine ratio (above 14.83 microcat/mol) and urine immunoglobulin G (IgG) to albumin ratio (above 0.09) at the time of diagnosis, while albuminuria or proteinuria did not have any early predictive value. The remission of renal disease was anticipated as early as 3 months after introduction of induction therapy in patients with reduction of urine NAG to creatinine ratio below the baseline value and in patients with at least 24% rise in eGFR.

Conclusions

Urine IgG to albumin and urine NAG to creatinine ratio are better early predictors of treatment response in patients with ANCA-associated glomerulonephritis than proteinuria or albuminuria.

Tumor necrosis factor receptor 2: its contribution to acute cellular rejection and clear cell renal carcinoma

Tumor necrosis factor receptor 2 (TNFR2) is a type I transmembrane glycoprotein and one of the two receptors that orchestrate the complex biological functions of tumor necrosis factor (TNF, also designed TNF-α). Accumulating experimental evidence suggests that TNFR2 plays an important role in renal disorders associated with acute cellular rejection and clear cell renal carcinoma but its exact role in these settings is still not completely understood. This papers reviews the factors that may mediate TNFR2 induction in acute cellular rejection and clear cell renal carcinoma and its contribution to these conditions and discusses its therapeutic implications. A greater understanding of the function of TNFR2 may lead to the development of new anti-TNF drugs.

Transplantation of bone marrow-derived MSCs improves cisplatinum-induced renal injury through paracrine mechanisms

Mesenchymal stem cells (MSCs) have been reported to preserve renal function in various models of acute kidney injury (AKI). Different routes were used to transplant MSCs but the role of cell transplantation routes in directing outcomes has been unknown. In the present study, we evaluated organ bio-distributions of transplanted MSCs, and correlated survival of transplanted cells with outcomes in mice with cisplatinum-induced AKI. We found that after intravenous administration, MSCs were largely localized in pulmonary capillaries and only a minute fraction of MSCs entered kidneys and the cells survived only transiently. Therefore, we also transplanted MSCs via intraperitoneal and renal subcapsular routes. Transplanted MSCs survived longer in peritoneal cavity and renal subcapsular space. Interestingly, when MSC transplantation was followed by cisplatinum-induced AKI, renal morphology and renal functions were better preserved, irrespective of the cell transplantation route. As transplanted MSCs did not migrate to kidneys from either peritoneal cavity or renal subcapsular space, this finding suggested that migration of cells was not required for the beneficial response. The possibility of indirect mechanisms was confirmed when administration of the conditioned medium from MSCs also protected renal tubular cells from cisplatinum-induced cytotoxicity. We identified presence of over forty regulatory cytokines in the conditioned medium obtained from MSCs. Since paracrine factors released by transplanted cells accounted for improvements, it appears that the route of cell transplantation is not critical for realizing benefits of cell therapy with MSCs in AKI. Studies of specific cytokines secreted by MSCs will help to obtain new therapeutic mechanisms for renal protection.

Long-term nephrotoxicity in adult survivors of childhood cancer

BACKGROUND AND OBJECTIVES

Because little is known about long-term treatment-related nephrotoxicity, the aim was to determine risk factors for renal impairment long after childhood cancer treatment.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Data from 763 adult childhood cancer survivors (414 men) were obtained during regular visits at the late-effects clinic between 2003 and 2009. Median follow-up time was 18.3 years (range=5.0-58.2). Glomerular function was assessed by estimated GFR (using the Modification of Diet in Renal Disease formula), urinary albumin creatinine ratio, and tubular function by urinary β2-microglobulin creatinine ratio. The association with treatment factors was analyzed with covariance analysis for estimated GFR and logistic regression for urinary albumin and urinary β2-microglobulin creatinine ratios.

RESULTS

Survivors treated with nephrectomy and abdominal irradiation had significantly lower estimated GFR than survivors not treated with nephrectomy/abdominal irradiation (estimated mean=90 ml/min per 1.73 m(2) versus 106, P<0.001). Estimated GFR was significantly lower in survivors after treatment with high-dose ifosfamide (88 versus 98, P=0.02) and high-dose cisplatin (83 versus 101, P=0.004) compared with survivors not treated with these regimen. Nephrectomy combined with abdominal radiotherapy (odds ratio=3.14, 95% confidence interval=1.02; 9.69) and high-dose cisplatin (odds ratio=5.19, 95% confidence interval=1.21; 22.21) was associated with albuminuria. High-dose ifosfamide (odds ratio=6.19, 95% confidence interval=2.45; 15.67) was associated with increased urinary β2-microglobulin creatinine ratio. Hypertension was present in 23.4% of survivors and 31.4% of renal tumor survivors.

CONCLUSIONS

Treatment with unilateral nephrectomy, abdominal radiotherapy, cisplatin, and ifosfamide was associated with lower estimated GFR. Persisting tubular damage was related to ifosfamide treatment.

Inhibition of calcium(2+)/calmodulin-dependent protein kinase type IV ameliorates experimental nephrotic syndrome

OBJECTIVE

Evidence has demonstrated that Ca(2+)/calmodulin-dependent protein kinase type IV (CaMKIV) contributes to altered cytokine production by promoting the production of inflammatory cytokines. This study aimed to explore the protective role and underlying mechanisms of CaMKIV inhibition in experimental nephrotic syndrome.

METHODS

BALB/c mice received single intravenous injections of adriamycin (10 mg/kg) then were sacrificed at two, four and six weeks. In the second study, treatment with KN-93, a CaMKIV inhibitor, or vehicle administered via intraperitoneal injection was started five days after adriamycin injection. Functional and pathologic parameters, the presence of inflammatory infiltration and the expressions of pro-inflammatory cytokines were assessed.

RESULTS

The CaMKIV protein expression levels were upregulated in the mice with adriamycin nephropathy, which was significantly inhibited by KN-93 (p<0.01). As compared with the vehicle-treated controls, KN-93 treatment resulted in marked suppression of proteinuria and serum creatinine at week 6 (p<0.01), but not at two weeks after induction of the disease. KN-93 inhibited glomerulosclerosis and the development of tubulointerstitial lesions. The renal alpha-smooth muscle actin (α-SMA) expression was also significantly suppressed by KN-93 treatment at week 6 (p<0.01). Moreover, KN-93 inhibited the renal monocyte chemoattractant protein-1 (MCP-1) expression, paralleled by a reduction in the interstitial infiltration of macrophages and T-cells (p<0.01).

CONCLUSION

Our findings suggest that activation of CaMKIV signaling is involved in the progression of glomerular diseases with a proteinuric state. Our data therefore justify the development of small molecule CaMKIV inhibitors for the treatment of clinical nephrotic syndrome.

Paracrine interaction between bone marrow-derived stem cells and renal epithelial cells

BACKGROUND/AIMS

Renal tubular cells are the main target of ischemic insult associated with acute renal injury. Low oxygen and nutrient supplies result in ATP depletion, leading to cell death and loss of renal function. A possible mechanism by which bone marrow-derived cells support renal tissue regeneration relies on the capacity of mononuclear cells (BMMC), particularly mesenchymal stem cells (MSC), to secrete paracrine factors that mediate support for kidney regeneration.

METHODS

BMMC/MSC and renal cells (LLC-PK(1) from pig and IRPTC from rat) were co-cultured under stressful conditions (ATP depletion and/or serum free starvation), physically separated by a microporous membrane (0.4 μm), was used to determine whether bone marrow-derived cells can interact with renal cells in a paracrine manner.

RESULTS

This interaction resulted in stimulation of renal cell proliferation and the arrest of cell death. MSC elicit effective responses in renal cells in terms of stimulating proliferation and protection. Such effects are observed in renal cells co-cultured with rat BMMC/MSC, an indication that paracrine mechanisms are not entirely species-specific.

CONCLUSION

The paracrine action of BMMC/MSC was influenced by a renal cell stimulus released during stress, indicating that cross-talk with injured cells is required for renal regeneration supported by bone marrow-derived cells.

Renal fibrosis and proteomics: current knowledge and still key open questions for proteomic investigation

Renal tubulo-interstitial fibrosis is a non-specific process, representing the final common pathway for all kidney diseases, irrespective of their initial cause, histological injury, or etiology, leading to gradual expansion of the fibrotic mass which destroys the normal structure of the tissue and results in organ dysfunction and, ultimately, in end-stage organ failure. Proteomic studies of the fibrotic pathophysiological mechanisms have been performed in cell cultures, animal models and human tissues, addressing some of the key issues. This article will review proteomic contribution to the raising current knowledge on renal fibrosis biology and also mention seminal open questions to which proteomic techniques and proteomists could fruitfully contribute.

Albumin-induced epithelial-mesenchymal transition and ER stress are regulated through a common ROS-c-Src kinase-mTOR pathway: effect of imatinib mesylate

The epithelial-mesenchymal transition (EMT) and endoplasmic reticulum (ER) stress induced by urinary protein, particularly albumin, play an important role in tubulointerstitial injury. However, signaling pathways regulating both albumin-induced EMT and ER stress are not precisely known. We postulated that reactive oxygen species (ROS), c-Src kinase, and mammalian target of rapamysin (mTOR) would act as upstream signaling molecules. We further examined the effect of imatinib mesylate on these processes. All experiments were performed using HK-2 cells, a human proximal tubular cell line. Protein and mRNA expression were measured by Western blot analysis and real-time PCR, respectively. Exposure of tubular cells to albumin (5 mg/ml) for up to 5 days induced EMT in a time-dependent manner, as shown by conversion to the spindle-like morphology, loss of E-cadherin protein, and upregulation of α-smooth muscle actin mRNA and protein. Albumin also induced ER stress as evidenced by phosphorylation of eukaryotic translation initiation factor-2α and increased expression of GRP78 mRNA and protein. Albumin induced ROS, c-Src kinase, and mTOR as well. Antioxidants, c-Src kinase inhibitor (PP2), and mTOR inhibitor (rapamycin) suppressed the albumin-induced EMT and ER stress. Antioxidants and PP2 inhibited the albumin-induced c-Src kinase and mTOR, respectively. Imatinib suppressed the albumin-induced EMT and ER stress via inhibition of ROS and c-Src kinase. Imatinib also inhibited the albumin-induced mRNA expression of MCP-1, VCAM-1, transforming growth factor (TGF)-β1, and collagen I (α1). In conclusion, the ROS-c-Src kinase-mTOR pathway played a central role in the signaling pathway that linked albumin to EMT and ER stress. Imatinib might be beneficial in attenuating the albumin-induced tubular injury.

Multipotent mesenchymal stromal cell therapy in renal disease and kidney transplantation

Cell therapies aim at differentiation of stem cells into the specific cell type required to repair damaged or destroyed cells or tissues. Over recent years, cell therapy has been introduced in a variety of application areas, including cardiovascular repair, diabetes, musculoskeletal disorders and renal repair. Multipotent mesenchymal stromal cells (MSCs), often referred to as mesenchymal stem cells, are of particular interest as a cell therapy model, as this is one of the few cell types that are on the brink of entering the clinical arena in different areas of application. MSCs can be differentiated in vitro and in vivo into various cell types of mesenchymal origin such as bone, fat and cartilage. They have important effects on the innate and adaptive immune system and possess striking anti-inflammatory properties that make them attractive for potential use in diseases characterized by autoimmunity and inflammation. In addition, MSCs have been shown to migrate to sites of tissue injury and to enhance repair by secreting anti-fibrotic and pro-angiogenic factors. In this review, evidence for the renoprotective mechanisms of MSCs as well as their therapeutic possibilities and potential hazards in acute and chronic renal disease and allograft rejection is summarized.

Upregulation of TNF receptor type 2 in human and experimental renal allograft rejection

An important role of TNF interacting with TNFR2 has been shown in different models of ischemic, nephrotoxic and immune-mediated renal injury. To systematically evaluate the expression of TNFR2 in renal allograft rejection, we investigated human renal allograft biopsies and, in addition, established an experimental transplantation model in rats to verify the human data under standardized conditions. The expression of TNFR2 was analyzed in 96 human renal allograft biopsies with different disease entities. In a 6-day and a 28-day experimental protocol, TNFR2 was examined in kidney specimens and in the urine of control, uni-nephrectomized and transplanted rats +/- cyclosporine treatment (n = 114). In human biopsies and in rat allografts on day 6 with acute allograft rejection, significantly elevated expression of TNFR2 was observed in tubular epithelial cells, podocytes, B cells and monocytes/macrophages. The expression level was associated with renal function. The TNFR2 expression level at day 28 was significantly lower compared to day 6. TNFR2 is markedly upregulated both in human and experimental acute renal allograft rejection. Our data are robust and consistent between different species, suggesting a role for TNFR2 in the early course of rejection.

Mesenchymal stem cells in acute kidney injury

The potential role of mesenchymal stem cells (MSCs, also called mesenchymal stromal cells) in endogenous repair and cell-based therapies for acute kidney injury (AKI) is under intensive investigation. Preclinical studies indicate that administered MSCs both ameliorate renal injury and accelerate repair. These versatile cells home to sites of injury, where they modulate the repair process. The mechanisms responsible for their protective and regenerative effects are incompletely understood. Some have reported that MSCs are capable of direct engraftment into injured nephrons under certain circumstances. This is highly controversial, however, and even those who argue there is engraftment acknowledge that the primary means of repair by these cells most likely involves paracrine and endocrine effects, including mitogenic, antiapoptotic, anti-inflammatory, and angiogenic influences. There is a good deal of interest in MSC-based approaches for the treatment of human kidney injury, thanks to positive preclinical results, the strong clinical need for novel therapies to treat AKI, the ease of isolation and expansion of MSCs, and encouraging preliminary clinical trial results in other fields. This review summarizes current knowledge and identifies gaps in our understanding of MSC biology that will need to be filled in order to translate recent discoveries into therapies for AKI in humans.

Early epithelial phenotypic changes predict graft fibrosis

Chronic allograft nephropathy accounts for the loss of approximately 40% of allografts at 10 yr. Currently, no biomarker is available to detect interstitial fibrosis and tubular atrophy in the renal graft at an early stage, when intervention may be beneficial. Because tubular epithelial cells have been shown to exhibit phenotypic changes suggestive of epithelial-to-mesenchymal transition, we studied whether these changes predict the progression of fibrosis in the allograft. Eighty-three kidney transplant recipients who had undergone a protocol graft biopsy at both 3 and 12 mo after transplantation were enrolled. De novo vimentin expression and translocation of beta-catenin into the cytoplasm of tubular cells were detected on the first biopsy by immunohistochemistry. Patients with expression of these markers in >or=10% of tubules at 3 mo had a higher interstitial fibrosis score at 1 yr and a greater progression of this score between 3 and 12 mo. The intensity of these phenotypic changes positively and significantly correlated with the progression of fibrosis, and multivariate analysis showed that their presence was an independent risk factor for this progression. In addition, the presence of early phenotypic changes was associated with poorer graft function 18 mo after transplantation. In conclusion, early phenotypic changes indicative of epithelial-to-mesenchymal transition predict the progression toward interstitial fibrosis in human renal allografts.

Inhibition of Jak/STAT signaling ameliorates mice experimental nephrotic syndrome

BACKGROUND/AIMS

This study investigated the role of JAK/STAT, an important pathway for cytokine signal transduction, in the progression of chronic glomerular diseases.

METHODS

BALB/c mice received a single intravenous injection of adriamycin (10 mg/kg) were sacrificed 2, 4 and 6 weeks later. In the second study, treatment with the selective JAK2 inhibitor AG490 (15 mg/kg, q.d., i.p.) or vehicle was started 5 days after adriamycin injection. Functional and pathologic markers, inflammatory infiltration, expression of pro-inflammatory cytokines and phosphorylation of JAK2/STATs were assessed.

RESULTS

JAK/STAT signaling was activated in adriamycin nephropathy. Phosphorylation of JAK2, STAT1 and STAT3 was significantly inhibited by AG490 (p <0.01). Compared to the vehicle-treated controls, AG490 treatment did not reduce proteinuria 2 weeks after induction of the disease, but resulted in significant decrease in proteinuria and serum creatinine at week 6 (p <0.05). Glomerulosclerosis, tubulointerstitial lesions and renal alpha-SMA expression were also significantly suppressed by AG490 treatment at week 6 (p < 0.01). In addition, AG490 inhibited the expression of MCP-1 mRNA, accompanied by reduced interstitial infiltration of macrophages and T cells (p <0.05).

CONCLUSIONS

This study suggests that activation of JAK/STAT signaling is involved in the progression of glomerular diseases with proteinuric state.

Urinary excretion of monocyte chemoattractant protein-1: a biomarker of active tubulointerstitial damage in patients with glomerulopathies

BACKGROUND/AIMS

The urinary concentration of the monocyte chemoattractant protein-1 (uMCP-1) chemokine is increased in several proteinuric and/or inflammatory renal diseases. In the present study, we evaluated the association between uMCP-1 and renal function, proteinuria, glomerular and interstitial macrophage infiltration, and renal fibrosis in patients with primary and secondary glomerulopathies diagnosed by renal biopsy.

METHODS

Thirty-seven patients aged 32.6 +/- 7.7 years were studied. uMCP-1 was determined by ELISA. Renal macrophage expression (CD68 positive cells) is reported as number of macrophages/10(4) microm2 of the cortical tubulointerstitial (TI) area or of glomerular capillary tuft area. Cortical interstitial fibrosis was quantitated by PicroSirius red staining under polarized light by a computerized manner.

RESULTS

The uMCP-1 ratio (pg/ml/urinary creatinine mg/ml) was positively correlated (Spearman coefficient) with proteinuria (r = 0.4629; p < 0.005) and number of macrophages in the cortical TI area (r = 0.64; p = 0.0005), and negatively correlated with creatinine clearance (r = -0.4877; p < 0.001). The uMCP-1 ratio was not significantly correlated with number of macrophages/glomerular capillary tuft area (r = 0.27; p = 0.19) or with percent cortical interstitial fibrosis (r = 0.08; p = 0.62).

CONCLUSIONS

The uMCP-1 excretion is a biomarker of the inflammatory activity of the TI area, and does not reflect chronic interstitial damage.

CD36 is a novel and potential anti-fibrogenic target in albumin-induced renal proximal tubule fibrosis

Albumin is not only a risk factor for diabetic nephropathy (DN), but also a therapeutic target. Hence, scientists have long sought ways to elucidate the interactions between albumin and diabetic renal tubule fibrosis. CD36, a surface receptor for thrombospondin-1, has been reported to interact with latent transforming growth factor-beta1 (TGF-beta1) and activate its fibrogenic bioactivity. This study elucidates the interactions between CD36 and renal tubule fibrosis. LLC-PK1 cells were applied to represent renal proximal tubule cells. The expression of CD36 was evaluated by flow cytometry. Fibronectin was assayed by Western blot and enzyme-linked immunosorbent assay (ELISA). Bioactive TGF-beta1 was assayed by ELISA. We demonstrated that albumin was shown significantly to inhibit cell growth without affecting hypertrophy status since protein content and cell size remained unaffected under albumin treatment. Moreover, albumin dose-dependently (0, 1, or 10 mg/ml) enhanced the secretion of bioactive TGF-beta1 and fibronectin with the upregulation of CD36. Intriguingly, CD36 siRNA, a potent silencer for CD36 effectively suppressed the albumin-induced increase in CD36, TGF-beta1, and even fibronectin level. Accordingly, albumin is a pro-fibrogenic factor for proximal tubule cells since albumin per se markedly upregulated the expression of TGF-beta1 and fibronectin. Most importantly, CD36 may mediate albumin-induced cellular fibrosis since CD36 siRNA appeared to have anti-fibrosis effects. This work suggests that CD36 is a novel and potential therapeutic target for diabetic renal tubule fibrosis.

Adult minimal-change disease: clinical characteristics, treatment, and outcomes

Minimal-change disease (MCD) counts for 10 to 15% of cases of primary nephrotic syndrome in adults. Few series have examined this disease in adults. A retrospective review was performed of 95 adults who had MCD and were seen at a single referral center. Examined were presenting features, response to daily versus alternate-day steroids, response to second-line agents, relapse patterns, complications of the disease and therapy, presence of acute renal failure (ARF), and outcome data. Sixty-five patients received daily and 23 received alternate-day steroids initially. There were no differences in remissions, time to remission, relapse rate, or time to relapse between daily- and alternate-day-treated patients. More than one quarter of patients were steroid resistant. At least one relapse occurred in 73% of patients; 28% were frequently relapsing. A significant proportion of frequently relapsing patients became steroid dependent. Second-line agents were used for steroid dependence, steroid resistance, or frequent relapses. No single agent proved superior. There were more remissions with second-line agents in steroid-dependent patients compared with steroid-resistant patients, and remissions were more likely to be complete in steroid-dependent patients. ARF occurred in 24 patients; they tended to be older and hypertensive with lower serum albumin and more proteinuria than those without ARF. At follow up, patients with an episode of ARF had higher serum creatinine than those without ARF. Four patients progressed to ESRD. These patients were less likely to have responded to steroids and more likely to have FSGS on repeat renal biopsy. In this referral MCD population, response to daily and alternate-day steroids is similar. Second-line agents give greater response in patients who are steroid dependent. ARF occurs in a significant number of adult MCD patients and may leave residual renal dysfunction. Few patients progress to ESRD.

Resident dendritic cells are the predominant TNF-secreting cell in early renal ischemia-reperfusion injury

Renal ischemia-reperfusion injury (IRI) rapidly induces production of inflammatory mediators including, and in particular, tumor necrosis factor (TNF). Possible sources include resident parenchymal and bone marrow-derived cells as well as recruited leukocytes. Cell suspensions from kidneys subjected to IRI were examined by cell separation followed by in vitro culture and enzyme-linked immunosorbent assay (ELISA), immunoperoxidase and immunofluorescence microscopy, and multicolor flow cytometry to determine the contribution of dendritic cells (DCs) to early production of TNF and other inflammatory mediators. Secretion of TNF, interleukin (IL-6), monocyte chemoattractant protein-1 (MCP-1), and regulated on activation normal T cell expressed and secreted (RANTES) was increased in cell suspensions from IRI compared with control kidneys and was higher in DC-enriched preparations. Immunostaining identified TNF(+ve) cells that coexpressed the DC marker CD11c. Flow cytometry of bone marrow-derived (CD45(+ve)) cell populations at 24 h post-IRI demonstrated that F4/80(+ve)/CD11c(+ve) DCs remained proportionately stable and exhibit higher levels of DC maturation markers, whereas the proportion of F4/80(-ve) DCs, monocytes, neutrophils, and T cells increased. Intracellular staining for TNF confirmed that F4/80(+ve) DCs were the predominant TNF(+ve) cell and expressed higher levels than other TNF(+ve) cells. In vivo depletion of DCs from the kidney substantially attenuated TNF secretion by total and CD45(+ve) cells following IRI. The results uncover a role for resident F4/80(+ve) DCs as the predominant secretors of TNF within 24 h of IRI.

How does proteinuria cause progressive renal damage?

The possibility that proteinuria may accelerate kidney disease progression to end-stage renal failure has received support from the results of increasing numbers of experimental and clinical studies. Evidence indicating that this process occurs through multiple pathways, including induction of tubular chemokine expression and complement activation that lead to inflammatory cell infiltration in the interstitium and sustained fibrogenesis, is reviewed. Macrophages are prominent in the interstitial inflammatory infiltrate. This cell type mediates progression of renal injury to the extent that macrophage numbers in renal biopsy predict renal survival in patients with chronic renal disease. Chemoattractants and adhesive molecules for inflammatory cells are upregulated by excess ultrafiltered protein load of proximal tubular cells via activation of NF-kappaB-dependent and NF-kappaB-independent pathways. This mechanism is a potential target for therapeutic approaches, as shown by beneficial effects of manipulations with inhibitory molecules of NF-kappaB activation or of chemokine receptors in experimental studies. Targeting complement synthesis or activation in proximal tubule might offer novel therapeutic opportunities. Finally, proximal tubular cell receptors for uptake of plasma proteins that are under investigation may provide activation signals on excess tubular protein handling.

Albumin induces endoplasmic reticulum stress and apoptosis in renal proximal tubular cells

Chronic proteinuria appears to be a key factor in tubulointerstitial damage. Recent studies have emphasized a pathogenic role of endoplasmic reticulum (ER) stress which is induced by the accumulation of misfolded proteins in ER, extracellular stress, etc. In the present study, we investigated ER stress and ER stress-induced apoptosis in proximal tubular cells (PTCs). Immortalized rat PTCs (IRPTCs) were cultured with bovine serum albumin (BSA). The viability of IRPTCs decreased proportionately with BSA overload in a time-dependent manner. Quantitative real-time polymerase chain reaction analysis revealed that 40 mg/ml BSA increases mRNA of ER stress markers by 7.7- and 4.6-fold (glucose-regulated protein 78 (GRP78) and oxygen-regulated protein 150 (ORP150), respectively) as compared to control. The increased expression of ORP150 and GRP78 in IRPTCs with albumin overload was detected by Western blot and immunofluorescence study. These in vitro observations were supported by in vivo studies, which demonstrated that ER stress proteins were upregulated at PTCs in experimental proteinuric rats. Furthermore, increased ER stress-induced apoptosis and activation of caspase-12 were observed in IRPTCs with albumin overload and kidneys of experimental proteinuric rats. We confirmed that apoptotic cell death was attenuated by co-incubation with caspase-3 inhibitor or calpain inhibitors. These results indicate that the ER stress-induced apoptosis pathway contributed to the insult of tubular cells by proteinuria. In conclusion, renal tubular cells exposed to high protein load suffer from ER stress. ER stress may subsequently lead to tubular damage by activation of caspase-12.

Albumin induces cellular fibrosis by upregulating transforming growth factor-beta ligand and its receptors in renal distal tubule cells

Albuminuria is indicative of nephropathy. However, little literature has focused on the role of albumin in renal distal tubule fibrosis. We used a well-defined distal tubule cell, Madin-Darby Canine Kidney (MDCK). Proliferation and cytotoxicity were examined. The conditioned supernatant was collected and subjected to ELISA assay for detection of fibronectin and TGF-beta1. Reverse transcription-PCR and Western blot assay were performed to evaluate the expression of mRNA and protein of two types of TGF-beta receptors (TbetaR). Flow cytometry assay and phosphotyrosine (pY)-specific antibodies were used to assay the phosphorylation status of TbetaR. We showed that albumin dose dependently (0, 0.1, 1, or 10 mg/ml) inhibited cellular growth in MDCK cells without inducing cellular cytotoxicity. In addition, albumin significantly upregulated the secretion of both fibronectin and TGF-beta1 at dose over 1 mg/ml. Moreover, 24 h pretreatment of albumin significantly enhanced exogenous TGF-beta1-induced secretion of fibronectin. These observations were reminiscent of the implications of TbetaR since TbetaR appears to correlate with the susceptibility of cellular fibrosis. We found that albumin significantly increased protein levels of type I TbetaR (TbetaRI) instead of type II receptors (TbetaRII). In addition, phosphorylation level of TbetaRII of both pY259 and pY424 was significantly enhanced instead of pY336. The novel observation indicates that extreme dose of albumin upregulates TGF-beta autocrine loop by upregulating TGF-beta1, TbetaRI, and the receptor kinase activity of TbetaRII by inducing tyrosine phosphorylation on key amino residue of TbetaRII in renal distal tubule cells. These combinational effects might contribute to the pathogenesis of renal fibrosis.

Intracellular Delivery of the p38 Mitogen-Activated Protein Kinase Inhibitor SB202190 [4-(4-Fluorophenyl)-2-(4-hydroxyphenyl)-5-(4-pyridyl)1H-imidazole] in Renal Tubular Cells: A Novel Strategy to Treat Renal Fibrosis

During renal injury, activation of p38 mitogen-activated protein kinase (MAPK) in proximal tubular cells plays an important role in the inflammatory events that eventually lead to renal fibrosis. We hypothesized that local inhibition of p38 within these cells may be an interesting approach for the treatment of renal fibrosis. To effectuate this, we developed a renal-specific conjugate of the p38 inhibitor SB202190 [4-(4-fluorophenyl)-2-(4-hydroxyphenyl)-5-(4-pyridyl)1H-imidazole] and the carrier lysozyme. First, we demonstrated that SB202190 inhibited the expression of albumin-induced proinflammatory (monocyte chemoattractant protein-1) and transforming growth factor (TGF)-beta1-induced profibrotic (procollagen-Ialpha1) genes over 50% in renal tubular cells (normal rat kidney-52E). Next, we conjugated SB202190 via a carbamate linkage to lysozyme. However, this conjugate rapidly released the drug upon incubation in serum. Therefore, we applied a new platinum(II)-based linker approach, the so-called universal linkage system (ULS), which forms a coordinative bond with SB202190. The SB202190-ULS-lysozyme remained stable in serum but released the drug in kidney homogenates. SB202190-ULS-lysozyme accumulated efficiently in renal tubular cells and provided a local drug reservoir during a period of 3 days after a single intravenous injection. Treatment with SB202190-ULS-lysozyme inhibited TGF-beta1-induced gene expression for procollagen-Ialpha1 by 64% in HK-2 cells. Lastly, we evaluated the efficacy of a single dose of the conjugate in the unilateral renal ischemia-reperfusion rat model. A reduction of intrarenal p38 phosphorylation and alpha-smooth muscle actin protein expression was observed 4 days after the ischemia-reperfusion injury. In conclusion, we have developed a novel strategy for local delivery of the p38 MAPK inhibitor SB202190, which may be of use in the treatment of renal fibrosis.

Pentoxifylline ameliorates proteinuria through suppression of renal monocyte chemoattractant protein-1 in patients with proteinuric primary glomerular diseases

Proteinuria (albuminuria) reflects dysfunction of the glomerular permeability barrier in which inflammatory cytokines play a key role. Pentoxifylline (PTX) is a phosphodiesterase inhibitor that possesses potent anti-inflammatory and immunomudulatory effects. This study evaluated the effectiveness of PTX to reduce proteinuria and inflammatory mediators in patients with proteinuric primary glomerular diseases. Seventeen patients with primary glomerular diseases, a persistent spot proteinuria exceeding 1.5 g/g creatinine (Cr) and a glomerular filtration rate between 24 and 115 ml/min/1.73 m(2) were treated with PTX 400 mg twice daily for 6 months. Before and after the treatment, serum Cr, plasma renin activity and aldosterone concentrations, plasma and urinary tumor necrosis factor (TNF)-alpha, interleukin-1beta and monocyte chemoattractant protein (MCP)-1, as well as urinary protein and Cr were measured. PTX significantly reduced urinary protein excretion, along with an increase of serum albumin. A significant correlation existed between the basal urinary protein/Cr and the basal urinary MCP-1/Cr ratios. PTX lowered the urinary MCP-1/Cr ratio, and the percent reduction of urinary protein/Cr ratio correlated directly with the precent decrease of urinary MCP-1/Cr ratio after PTX treatment. There was no significant change in blood pressure, renal function, biochemical parameters, plasma renin activity and aldosterone concentrations, or plasma TNF-alpha and MCP-1 levels during the study. In conclusion, administration of PTX 800 mg per day is safe and effective for reducing proteinuria in patients with proteinuric primary glomerular diseases. This beneficial effect occurs in close association with a reduction of urinary MCP-1 excretion.

The relationship between albuminuria, MCP-1/CCL2, and interstitial macrophages in chronic kidney disease

Glomerular-derived proteins may activate tubular cells to express the macrophage-directed chemokine monocyte chemoattractant protein-1 (MCP-1/CCL2). Macrophages at interstitial sites have a central role in directing renal scarring. We have prospectively assessed the relationship between albuminuria, urinary MCP-1/CCL2, interstitial macrophage infiltration, in situ damage, and clinical outcomes in a large group of patients with chronic kidney disease. We studied 215 patients and quantified albumin-creatinine ratio (ACR), urinary MCP-1/CCL2, interstitial macrophage numbers, and in situ damage. ACR correlated with urinary MCP-1/CCL2 (correlation 0.499; P<0.001), interstitial macrophage numbers (correlation 0.481; P<0.001), and index of chronic damage (correlation 0.363; P<0.001). Macrophage numbers closely correlated with in situ damage (correlation 0.755; P<0.001). By multivariate analysis ACR, urinary MCP-1/CCL2, and interstitial macrophage numbers were interdependent. By Kaplan-Meier survival analysis albuminuria, urinary MCP-1/CCL2, interstitial macrophages, and chronic damage predict the outcome. ACR, macrophage numbers, chronic damage, and creatinine independently predicted renal survival. The association of ACR with other variables was strongest in patients with less advanced disease states. There is a close association between albuminuria, urinary MCP-1/CCL2, and interstitial macrophage infiltration with in situ damage and clinical outcomes. These findings support the hypothesis that albuminuria triggers tubular MCP-1/CCL2 expression with subsequent macrophage infiltration. These processes may represent the dominant pathway for the progression of renal injury before the establishment of advanced renal scarring.

Renal albumin absorption in physiology and pathology

Albumin is the most abundant plasmaprotein serving multiple functions as a carrier of metabolites, hormones, vitamins, and drugs, as an acid/base buffer, as antioxidant and by supporting the oncotic pressure and volume of the blood. The presence of albumin in urine is considered to be the result of the balance between glomerular filtration and tubular reabsorption. Albuminuria has been accepted as an independent risk factor and a marker for renal as well as cardiovascular disease, and during the past decade, evidence has suggested that albumin itself may cause progression of renal disease. Thus, the reduction of proteinuria and, in particular, albuminuria has become a target in itself to prevent deterioration of renal function. Studies have shown albumin and its ligands to induce expression of inflammatory and fibrogenic mediators, and it has been hypothesized that increased filtration of albumin causes excessive tubular reabsorption, resulting in inflammation and fibrosis, resulting in the loss of renal function. In addition, it is known that tubular dysfunction in itself may cause albuminuria owing to decreased reabsorption of filtered albumin, and, recently, it has been suggested that significant amounts of albumin fragments are excreted in the urine as a result of tubular degradation. Thus, although both tubular and glomerular dysfunction influences renal handling of albumin, it appears that tubular reabsorption plays a central role in mediating the effects of albumin on renal function. The present paper will review the mechanisms for tubular albumin uptake and the possible implications for the development of renal disease.

Macrophages and progressive tubulointerstitial disease

Macrophages and progressive tubulointerstitial disease. In chronic renal disease, tubulointerstitial inflammation and injury is associated with infiltrating macrophages. As a consequence of primary injury, proteinuria, chronic hypoxia, and glomerular-derived cytokines may all differentially modulate the expression of factors that promote macrophage recruitment. In addition to adhesion molecules and chemokines, products of complement system and renin-angiotensin system activation may direct this process. Once present at interstitial sites, macrophages interact with resident cells and extracellular matrix to generate a proinflammatory microenvironment that amplifies tissues injury and promotes scarring. There is now increasing evidence for the efficacy of interventions directed against factors that recruit, activate, or are produced by macrophages. A detailed understanding of the biology of this area may lead to the further development of therapies that will improve the outcome of renal disease.

Molecular pathogenetic mechanisms of nephrotic edema: progress in understanding

Molecular and pathogenetic mechanisms in sodium retention and water reabsorption of nephrotic edema are discussed. Are reported and analyzed molecular mechanisms about sodium retention in collecting duct cells regarding activation and surface expression of epithelial sodium channels (ENaC) and sodium-potassium-ATPase (Na,K-ATPase) by aldosterone, vasopressin, natriuretic peptide system (underfill theory): is necessary a better understanding about the dysregulation of ENaC and Na,K-ATPase surface expression and the resistance to natriuretic peptide system. Are also reported and analyzed molecular mechanisms of sodium retention in proximal tubule cells regarding intrinsic albumin toxicity upon type 3 sodium-hydrogen exchanger ionic pump and the activity of sodium-hydrogen exchanger regulatory factor protein (overfill theory): a better knowledge about the link between albumin, sodium-hydrogen exchanger type 3 (NHE3) ionic pump, sodium-hydrogen exchanger regulatory factor protein is necessary. Then molecular mechanisms of vasopressin free water retention through acquaporin water channels in collecting duct cells are discussed: further studies are necessary to understand vasopressin release pathway (osmotic/nonosmotic) and V2 receptor activation with cell surface expression of renal acquaporins water channel.

Proteinuria and growth factors in the development of tubulointerstitial injury and scarring in kidney disease

PURPOSE OF REVIEW

There are ongoing debates as to the role and mechanisms of proteinuria in tubulointerstitial fibrogenesis. Moreover, recent experimental findings have allowed for further insights into mediators and interactions between cells in the renal interstitium during fibrogenesis.

RECENT FINDINGS

Proteinuria or albuminuria are likely just markers for the glomerular ultrafiltration and tubular actions of ultrafiltered, biologically active growth factors which 'activate' tubular cells causing basolateral secretion of chemokines and cytokines. Chemokines attract and activate macrophages. Tubular cell-derived platelet-derived growth factor (PDGF) and macrophage-derived transforming growth factor-beta cause fibroblast proliferation. Several growth factors contribute to their transition into extracellular matrix-producing myofibroblasts. This cascade of events provides targets for some currently available and several novel therapies.

SUMMARY

Albuminuria or glomerular proteinuria appear to be markers but ultrafiltered, bioactive growth factors are culprits in proteinuria-associated interstitial fibrosis. Interactions of tubular cells with macrophages and fibroblasts in the interstitium via defined growth factor/cytokines provide opportunities for therapeutic interventions.

Early proinflammatory activation of renal tubular cells by normal and pathologic IgG

BACKGROUND/AIMS

To verify whether human IgG induces proinflammatory activation of human proximal tubular epithelial cells (PTEC) independent of the metabolic overload of protein reabsorption.

METHODS

Cultured PTEC were incubated with normal IgG, IgG from systemic lupus erythematosus (SLE) patients, albumin or transferrin. IL-6 secretion and extracellular regulated kinase (ERK) activation (dual-phosphorylated ERK) were measured by ELISA and by Western blotting of PTEC extracts, respectively; renal biopsy specimens from patients with IgG and non-IgG proteinuria were analyzed by immunohistochemistry and in situ hybridization to detect ERK-P and IL-6.

RESULTS

Normal and SLE IgG, but not albumin or transferrin, induced an early significant increase in IL-6 secretion by PTECs. Also ERK activation was found after 1-hour incubation of PTEC with IgG, but not with control medium and albumin-treated PTEC. Activated ERK and IL-6 were found to colocalize in tubular cells in the kidney specimens of patients with IgG proteinuria only.

CONCLUSION

IgG-dependent early activation of ERK and increased IL-6 secretion in PTEC suggest that IgG filtered during nonselective proteinuria may play a specific role in tubulointerstitial disease. Such a role could be particularly relevant in diseases associated with abnormal IgG pool compositions, such as SLE. Preliminary results on human renal biopsy specimens suggest that our in vitro observations may also be relevant in vivo.

Albumin up-regulates the type II transforming growth factor-beta receptor in cultured proximal tubular cells1

BACKGROUND

Clinical and experimental observations suggest that proteinuria is not merely a marker of chronic nephropathies, but may also be involved in the progression to end-stage renal failure. Filtered proteins are taken up by tubular cells, and overwhelming this system may lead to tubular synthesis of various proinflammatory and profibrogenic cytokines, including transforming growth factor-beta (TGF-beta). TGF-beta acts by first binding to specific receptors. We studied in an in vitro system using a well-defined mouse proximal tubular cell line (MCT cells) whether fatty acid-free bovine albumin modulates expression of specific receptors for TGF-beta.

METHODS

MCT (and LLC-PK1) cells were challenged in serum-free medium with different concentrations of albumin. Activation of a local renin-angiotensin system was tested by real-time polymerase chain reaction (PCR) for renin and angiotensinogen transcripts and determination of secreted angiotensin II (Ang II) by enzyme-linked immunosorbent assay (ELISA). Some cells were also treated with the AT1 receptor antagonist losartan. TGF-beta receptor types I and II mRNA levels were determined by Northern analysis whereas protein abundance was measured by Western blots. To test for a functional consequence of up-regulated TGF-beta receptors, MCT cells were preincubated with albumin and subsequently treated with low-dose TGF-beta that normally does not induce collagen type IV expression by itself. Downstream signaling events were detected by Western blots for phosphorylated Smad2. Scatchard assays with [125I]TGF-beta1 were performed to estimate affinity and number of specific binding sites. Different length TGF-beta type II promoter constructs linked to CAT reporter were transiently transected into MCT cells to determine transcriptional activity.

RESULTS

Incubation of MCT cells with 0.5 to 10 mg/mL albumin leads to an increase in type II TGF-beta receptor mRNA and protein expression without influencing type I receptors. An increase in type II TGF-beta receptor protein expression was detected after 12 hours of albumin incubation and was still detectable after 48 hours. The albumin-mediated increase in type II TGF-beta receptor mRNA was attenuated in the presence of 1 micromol/L losartan, suggesting involvement of a local renin-angiotensin system. MCT cells treated with albumin significantly increased expression of angiotensinogen and renin transcripts and also secreted more Ang II into the culture supernatant. Analysis of transcriptional activity showed that promoter segments containing activating protein (AP-1)-binding sites are necessary for albumin-induced transcription of the TGF-beta type II receptor. Binding assays revealed that albumin treatment significantly increased the overall binding sites as well as the affinity for TGF-beta. This effect had functional consequences because MCT cells pretreated with albumin reacted with a stronger TGF-beta-mediated phosphorylation of down-stream Smad2 and also increased collagen IV expression compared with control cells.

CONCLUSION

Our findings indicate that albumin up-regulates ligand-binding TGF-beta receptors on cultured proximal tubular cells. Albumin-induced activation of local Ang II production appears to be responsible for this effect. This may amplify the matrix-stimulatory actions of TGF-beta on tubular cells and could be a novel mechanism for how proteinuria exhibits pathophysiologic effects on tubular cells ultimately leading to tubulointerstitial fibrosis.

Urinary excretion of monocyte chemoattractant protein-1 in autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) progresses to renal insufficiency in >50% of patients and is characterized by interstitial inflammation and fibrosis in the end stage. In a rat model of ADPKD, monocytes accumulate within the renal interstitium in association with increased levels of monocyte chemoattractant protein-1 (MCP-1) in cyst mural cells and increased excretion of this chemokine into the urine. For determining the extent to which this chemokine is abnormally expressed in patients with ADPKD, a cross-section study was performed of MCP-1 in urine, serum, and cyst fluid and MCP-1 production by mural epithelial cells cultured from the cysts of human patients with ADPKD. Upper boundaries for urinary MCP-1 excretion (>263 pg/mg creatinine) and serum creatinine concentration (>1.5 mg/dl) determined in 19 normal individuals were used to sort 55 ADPKD patients into three groups. In group 1 (n = 13), urine MCP-1 excretion (136 +/- 14 pg/mg creatinine) was not different from normal volunteers (152 +/- 16 pg/mg); serum creatinine levels and urine total protein excretion were normal as well. In group 2 (n = 27), urine MCP-1 excretion was increased (525 +/- 39 pg/mg creatinine), but serum creatinine levels and urine protein excretion were not different from normal. In group 3 (n = 15), urine MCP-1 excretion increased further (1221 +/- 171 pg/mg), serum creatinine levels increased to 4.3 +/- 0.8 mg/dl, and urine protein excretion rose to 0.64 +/- 0.28 mg/mg creatinine. Serum MCP-1 levels of ADPKD patients (84 +/- 9.9 pg/ml; n = 15) did not differ from normal. Levels of MCP-1 much higher than in serum or urine were found in cyst fluids obtained from nephrectomy specimens (range, 767 to 40,860 pg/ml; mean, 6434 +/- 841 pg/ml; n = 73). Polarized, confluent cultures of ADPKD cyst epithelial cells secreted MCP-1 into the apical fluid to levels eightfold greater than in the basolateral medium. Similar results were obtained with tubule epithelial cells cultured from normal human renal cortex. On the basis of these results, it is concluded that urinary excretion of MCP-1 is increased in the majority of adult patients with ADPKD and that the source of some of this chemokine may be the mural epithelium of cysts. Furthermore, it seemed that urinary MCP-1 excretion may have increased in these ADPKD patients before appreciable increases in serum creatinine concentration or urine protein excretion were detected. It is reasonable to include urine MCP-1 excretion among candidate surrogate markers in controlled, longitudinal studies of ADPKD.

Interstitial inflammation, sodium retention, and the pathogenesis of nephrotic edema: a unifying hypothesis

BACKGROUND

The pathophysiology of edema in the nephrotic syndrome is controversial. Some investigators believe that sodium retention may result from a primary renal defect that causes an "overfilled" blood volume. In contrast, other authors believe that fluid escapes the vascular compartment due a low oncotic pressure, and sodium retention is a compensatory physiological response to an "underfilled" blood volume. The patients that best fit the "underfilled" hypothesis are children with minimal-change nephrotic syndrome (MCNS).

METHODS

We analyzed critically the available evidence for and against each proposed pathogenic mechanism in the light of recent evidence indicating that the inflammatory infiltrate may play a role in primary renal sodium retention.

RESULTS

Inflammatory infiltrate in the kidney is a constant characteristic in nephrotic syndrome associated with primary sodium retention and it is absent in most cases of MCNS in children

CONCLUSIONS

We propose that primary sodium retention in the nephrotic syndrome depends on the existence and the intensity of renal inflammatory infiltrate, conspicuously absent in most cases of MCNS in children and present in other conditions associated with massive proteinuria. The tubulointerstitial inflammatory infiltrate is associated with increased vasoconstrictive mediators that result in increased tubular sodium reabsorption and with glomerular hemodynamic changes that reduce filtered sodium load.

Elevated Akt phosphorylation as an indicator of renal tubular epithelial cell stress

Characterization of the phosphoinositide 3-kinase-signaling pathway in a human renal tubular epithelial cell (TEC) line HKC-8 revealed high levels of Akt phosphorylation in serum-starved cultures. In contrast to Erk1/2, little additional phosphorylation of Akt was observed after cytokine or serum stimulation. Replacement of the conditioned medium attenuated Akt phosphorylation such that 90 min after the addition of warmed serum-free media, Akt phosphorylation had fallen sufficiently to allow an epidermal growth factor-stimulated increase to be detected readily. Although the mechanism by which the phosphoinositide 3-kinase/Akt pathway is activated in serum-starved TEC is unknown, the mediator responsible is secreted from these cells. Thus, conditioned media removed from a dish of quiescent TECs stimulated Akt phosphorylation in washed TEC cultures within 10 min. Biochemical characterization of the bioactive agent identified a heat labile factor of small apparent molecular mass. The basal level of Akt phosphorylation observed in serum-starved cultures was inhibited by wortmannin at concentrations that demonstrated its dependence on 3-phosphoinositide synthesis (IC(50) = 8 nm). Regular removal of conditioned media from TEC cultures and its replacement with serum free media resulted in a sustained attenuation of Akt phosphorylation. Interestingly, after 5 days of this treatment, washed TEC cultures contained a greater number of viable cells than cultures maintained in conditioned media throughout. This observation was not explained by a difference in the rate of DNA synthesis. Instead, the number of cells undergoing apoptosis increased markedly in the unwashed cultures. Consequently, we propose that in HKC-8 cells Akt phosphorylation is up-regulated in an effort to minimize cell death. This stress-activated response is initiated by a factor secreted into the conditioned medium that stimulates the phosphoinositide 3-kinase signaling pathway.

Urine excretion of protein HC in proteinuric glomerular diseases correlates to urine IgG but not to albuminuria

BACKGROUND

Proteinuric glomerular diseases often are associated with tubulointerstitial injury, which imposes on the progression of renal failure. Tubular damage is partly referable to toxic effects on the tubular epithelial cells induced by filtered plasma proteins. Patients with nonselective proteinuria, that is, increased urine excretion of high-molecular-weight plasma proteins such as IgG in comparison to albumin, often have poor renal outcome. The present observational study examined correlations between the degree of tubular damage, measured by urine concentration of protein HC, and the levels of urine IgG and albuminuria.

METHODS

Measurements of urine concentrations of IgG, albumin, and protein HC were performed in 56 proteinuric patients (33 males and 23 females) with nondiabetic glomerular diseases at the time of the diagnostic renal biopsy and at a mean of 49 follow-up months.

RESULTS

A highly significant correlation between the urine IgG excretion and the urine protein HC concentration was found both at the start and at the end of the observational time (r = 0.74 and 0.65, respectively, P < 0.001). Furthermore, alterations in the urinary excretion of the two proteins in single patients correlated significantly to each other (r = 0.84, P < 0.001). The correlation between the degree of albuminuria and the protein HC excretion was significant at the time of kidney biopsy, but ceased to exist during the follow-up time. Stepwise linear regression analysis showed that in comparison with the creatinine clearance and albuminuria, only the changes in urinary IgG excretion were related to the corresponding changes in urinary protein HC excretion (r = 0.84 and r2 = 0.7, P < 0.001).

CONCLUSION

The findings of the study suggest that the urinary protein HC concentration correlates to the degree of IgG-uria but not to the degree of albuminuria during the course of proteinuric glomerular disease. Whether this correlation is to be explained by an intrinsic toxic effect on tubular cells executed by IgG or perhaps by some other high molecular weight proteins, needs to be investigated further. However, the results contribute to the understanding of the poor renal survival in patients with glomerular diseases and nonselective proteinuria.