G Protein-Coupled Bile Acid Receptor TGR5 Activation Inhibits Kidney Disease in Obesity and Diabetes

Obesity and diabetes mellitus are the leading causes of renal disease. In this study, we determined the regulation and role of the G protein-coupled bile acid receptor TGR5, previously shown to be regulated by high glucose and/or fatty acids, in obesity-related glomerulopathy (ORG) and diabetic nephropathy (DN). Treatment of diabetic db/db mice with the selective TGR5 agonist INT-777 decreased proteinuria, podocyte injury, mesangial expansion, fibrosis, and CD68 macrophage infiltration in the kidney. INT-777 also induced renal expression of master regulators of mitochondrial biogenesis, inhibitors of oxidative stress, and inducers of fatty acid β-oxidation, including sirtuin 1 (SIRT1), sirtuin 3 (SIRT3), and Nrf-1. Increased activity of SIRT3 was evidenced by normalization of the increased acetylation of mitochondrial superoxide dismutase 2 (SOD2) and isocitrate dehydrogenase 2 (IDH2) observed in untreated db/db mice. Accordingly, INT-777 decreased mitochondrial H2O2 generation and increased the activity of SOD2, which associated with decreased urinary levels of H2O2 and thiobarbituric acid reactive substances. Furthermore, INT-777 decreased renal lipid accumulation. INT-777 also prevented kidney disease in mice with diet-induced obesity. In human podocytes cultured with high glucose, INT-777 induced mitochondrial biogenesis, decreased oxidative stress, and increased fatty acid β-oxidation. Compared with normal kidney biopsy specimens, kidney specimens from patients with established ORG or DN expressed significantly less TGR5 mRNA, and levels inversely correlated with disease progression. Our results indicate that TGR5 activation induces mitochondrial biogenesis and prevents renal oxidative stress and lipid accumulation, establishing a role for TGR5 in inhibiting kidney disease in obesity and diabetes.

Inhibition of TRPC6 by protein kinase C isoforms in cultured human podocytes

Transient receptor potential canonical‐6 (TRPC6) ion channels, expressed at high levels in podocytes of the filtration barrier, are recently implicated in the pathogenesis of various forms of proteinuric kidney diseases. Indeed, inherited or acquired up‐regulation of TRPC6 activities are suggested to play a role in podocytopathies. Yet, we possess limited information about the regulation of TRPC6 in human podocytes. Therefore, in this study, we aimed at defining how the protein kinase C (PKC) system, one of the key intracellular signalling pathways, regulates TRPC6 function and expression. On human differentiated podocytes, we identified the molecular expressions of both TRPC6 and several PKC isoforms. We also showed that TRPC6 channels are functional since the TRPC6 activator 1‐oleoyl‐2‐acetyl‐sn‐glycerol (OAG) induced Ca²⁺‐influx to the cells. By assessing the regulatory roles of the PKCs, we found that inhibitors of the endogenous activities of classical and novel PKC isoforms markedly augmented TRPC6 activities. In contrast, activation of the PKC system by phorbol 12‐myristate 13‐acetate (PMA) exerted inhibitory actions on TRPC6 and suppressed its expression. Importantly, PMA treatment markedly down‐regulated the expression levels of PKCα, PKCβ, and PKCη reflecting their activation. Taken together, these results indicate that the PKC system exhibits a ‘tonic’ inhibition on TRPC6 activity in human podocytes suggesting that pathological conditions altering the expression and/or activation patterns of podocyte‐expressed PKCs may influence TRPC6 activity and hence podocyte functions. Therefore, it is proposed that targeted manipulation of certain PKC isoforms might be beneficial in certain proteinuric kidney diseases with altered TRPC6 functions.

MicroRNA-26a inhibits TGF-β-induced extracellular matrix protein expression in podocytes by targeting CTGF and is downregulated in diabetic nephropathy

AIMS/HYPOTHESIS

The accumulation of extracellular matrix (ECM) is a characteristic of diabetic nephropathy, and is partially caused by profibrotic proteins TGF-β and connective tissue growth factor (CTGF). We aimed to identify microRNAs (miRNAs) targeting CTGF on podocytes in diabetic nephropathy.

METHODS

We investigated miRNAs targeting CTGF on podocytes with miRNA array analysis and identified a candidate miRNA, miR-26a. Using overexpression and silencing of miR-26a in cultured podocytes, we examined changes of ECM and its host genes. We further investigated glomerular miR-26a expression in humans and in mouse models of diabetic nephropathy.

RESULTS

miR-26a, which was downregulated by TGF-β1, was expressed in glomerular cells including podocytes and in tubules by in situ hybridisation. Glomerular miR-26a expression was downregulated by 70% in streptozotocin-induced diabetic mice. Transfection of miR-26a mimics in cultured human podocytes decreased the CTGF protein level by 50%, and directly inhibited CTGF expression in podocytes, as demonstrated by a reporter assay with the 3'-untranslated region of the CTGF gene. This effect was abolished by a mutant plasmid. miR-26a mimics also inhibited TGF-β1-induced collagen expression, SMAD-binding activity and expression of its host genes CTDSP2 and CTDSPL. Knockdown of CTDSP2 and CTDSPL increased collagen expression in TGF-β-stimulated podocytes, suggesting that host genes also regulate TGF-β/SMAD signalling. Finally, we observed a positive correlation between microdissected glomerular miR-26a expression levels and estimated GFR in patients with diabetic nephropathy.

CONCLUSIONS/INTERPRETATION

The downregulation of miR-26a is involved in the progression of diabetic nephropathy both in humans and in mice through enhanced TGF-β/CTGF signalling.

Abstract B17: Tumor-associated stellate cells promote an invasive phenotype of pancreatic cancer cells

At the time of diagnosis, almost 80% of pancreatic cancer patients present with either new-onset type 2 diabetes or impaired glucose tolerance. Pancreatic cancer is associated with a highly abundant stroma, which is believed to influence the pathogenesis of the disease. In the local tumor microenvironment, both elevated glucose levels and the presence of tumor-associated stellate cells are hypothesized to promote the tumor progression and invasion by tumor cells. In this study, the influence by the microenvironment on pancreatic cancer cell invasion was investigated in vitro. Epithelial-to-mesenchymal transition (EMT) of human pancreatic cancer cells co-cultured in normal (5mM) or high (25 mM) glucose conditions with tumor-associated pancreatic stellate cells (TPSCs) was monitored by Western immunoblotting. In addition, a three-dimensional organotypic model was established to study and visualize the pancreatic cancer cell invasion. After co-culture, the expression of several EMT-markers was altered. The levels of E-cadherin were reduced by more than 95% (P<0.001) while vimentin was increased by 45% (P<0.05). In addition, high glucose conditions reduced the levels of ZO-1 and β-catenin compared to normal glucose. TGF-β stimulation, a known inducer of EMT, resulted in a similar modulation of EMT markers. The organotypic model showed differences in the extent of invasion between the cell lines investigated, of which PANC-1 human pancreatic cells were shown to be the most invasive and also formed a highly proliferative epithelium. In high glucose conditions, the invasion of PANC-1 cells appeared to increase both in number and distance covered by the cells. Immunofluorescent staining of EMT-markers in organotypic sections displayed a lack of E-cadherin and extensive expression of vimentin in the tumor epithelium. In conclusion, this study show TPSCs to induce changes in pancreatic cancer cells associated with enhanced invasiveness. In addition, a three-dimensional model visualized the invasive potential of the pancreatic cancer cells, which was further enhanced by high glucose conditions. This study contributes to further elucidate the interplay between, and influence of, the cell types present in the local tumor microenvironment, which promotes the tumor cell invasion as an important step in the pancreatic tumor progression.

Citation Format: Emelie Karnevi, Ann H. Rosendahl, Moin A. Saleem, Roland Andersson. Tumor-associated stellate cells promote an invasive phenotype of pancreatic cancer cells. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Innovations in Research and Treatment; May 18-21, 2014; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2015;75(13 Suppl):Abstract nr B17.

AT1R blockade in adverse milieus: role of SMRT and corepressor complexes

ANG II type 1 receptor blockade (AT1R-BLK) is used extensively to slow down the progression of proteinuric kidney diseases. We hypothesized that AT1R-BLK provides podocyte protection through regulation of silencing mediator of retinoic acid and thyroid hormone receptor (SMRT) and vitamin D receptor (VDR) expression under adverse milieus such as high glucose and human immunodeficiency virus infection. Both AT1R-BLK and VDR agonists (VDAs) stimulated VDR complex formation that differed not only in their composition but also in their functionality. AT1R-BLK-induced VDR complexes contained predominantly unliganded VDR, SMRT, and phosphorylated histone deacetylase 3, whereas VDA-VDR complexes were constituted by liganded VDR and CREB-binding protein/p300. AT1R-BLK-induced complexes attenuated podocyte acetyl-histone 3 levels as well as cytochrome P-450 family 24A1 expression, thus indicating their deacetylating and repressive properties. On the other hand, VDA-VDR complexes not only increased podocyte acetyl-histone 3 levels but also enhanced cytochrome P-450 family 24A1 expression, thus suggesting their acetylating and gene activation properties. AT1R-BLK- induced podocyte SMRT inhibited expression of the proapoptotic gene BAX through downregulation of Wip1 and phosphorylation of checkpoint kinase 2 in high-glucose milieu. Since SMRT-depleted podocytes lacked AT1R-BLK-mediated protection against DNA damage, it appears that SMRT is necessary for DNA repairs during AT1R-BLK. We conclude that AT1R-BLK provides podocyte protection in adverse milieus predominantly through SMRT expression and partly through unliganded VDR expression in 1,25(OH)2D-deficient states; on the other hand, AT1R-BLK contributes to liganded VDR expression in 1,25(OH)2D-sufficient states.

Podocyte apoptosis is prevented by blocking the Toll-like receptor pathway

High serum lipopolysaccharide (LPS) activity in normoalbuminuric patients with type 1 diabetes (T1D) predicts the progression of diabetic nephropathy (DN), but the mechanisms behind this remain unclear. We observed that treatment of cultured human podocytes with sera from normoalbuminuric T1D patients with high LPS activity downregulated 3-phosphoinositide-dependent kinase-1 (PDK1), an activator of the Akt cell survival pathway, and induced apoptosis. Knockdown of PDK1 in cultured human podocytes inhibited antiapoptotic Akt pathway, stimulated proapoptotic p38 MAPK pathway, and increased apoptosis demonstrating an antiapoptotic role for PDK1 in podocytes. Interestingly, PDK1 was downregulated in the glomeruli of diabetic rats and patients with type 2 diabetes before the onset of proteinuria, further suggesting that reduced expression of PDK1 associates with podocyte injury and development of DN. Treatment of podocytes in vitro and mice in vivo with LPS reduced PDK1 expression and induced apoptosis, which were prevented by inhibiting the Toll-like receptor (TLR) signaling pathway with the immunomodulatory agent GIT27. Our data show that LPS downregulates the cell survival factor PDK1 and induces podocyte apoptosis, and that blocking the TLR pathway with GIT27 may provide a non-nephrotoxic means to prevent the progression of DN.

Vascular smooth muscle cells contribute to APOL1-induced podocyte injury in HIV milieu

Clinical reports have demonstrated that higher rates of non-diabetic glomerulosclerosis in African Americans can be attributed to two coding sequence variants (G1 and G2) in the APOL1 gene; however, the underlying mechanism is still unknown. Kidney biopsy data suggest enhanced expression of APOL1/APOL1 variants (Vs) in smooth muscle cells (SMCs) of renal vasculature. Since APOL1 is a secretory protein of relatively low molecular weight (41kDa), SMCs may be a contributory endocrine/paracrine source of APOL1 wild type (WT)/APOL1Vs in the glomerular capillary perfusate percolating podocytes. In the present study, we tested the hypothesis that an HIV milieu stimulated secretion of APOL1 and its risk variants by arterial SMCs contributes to podocyte injury. Human umbilical artery smooth muscle cells (HSMCs)-treated with conditioned media (CM) of HIV-infected peripheral mononuclear cells (PBMC/HIV-CM), CM of HIV-infected U939 cells, or recombinant IFN-γ displayed enhanced expression of APOL1. Podocytes co-cultured in trans-wells with HSMCs-over expressing APOL1WT showed induction of injury; however, podocytes co-cultured with HSMC-over expressing either APOL1G1 or APOL1G2 showed several folds greater injury when compared to HSMC-over expressing APOL1WT. Conditioned media collected from HSMC-over-expressing APOL1G1/APOL1G2 (HSMC/APOL1G1-CM or HSMC/APOL1G2-CM) also displayed higher percentages of injured podocytes in the form of swollen cells, leaky lysosomes, loss of viability, and enhanced sensitivity to adverse host factors when compared to HSMC/APOL1WT-CM. Notably, HSMC/APOL1WT-CM promoted podocyte injury only at a significantly higher concentrations compared to HSMC/APOL1G1/G2-CM. We conclude that HSMCs could serve as an endocrine/paracrine source of APOL1Vs, which mediate accelerated podocyte injury in HIV milieu.

Effects of interleukin-13 and montelukast on the expression of zonula occludens-1 in human podocytes

PURPOSE

The aim of this study was to investigate whether pathologic changes in zonula occludens-1 (ZO-1) are induced by interleukin-13 (IL-13) in the experimental minimal-change nephrotic syndrome (MCNS) model and to determine whether montelukast, a leukotriene receptor antagonist, has an effect on ZO-1 restoration in cultured human podocytes.

MATERIALS AND METHODS

Human podocytes cultured on bovine serum albumin-coated plates were treated with different doses of IL-13 and montelukast and then examined for distribution using confocal microscopy and for ZO-1 protein levels using Western blotting.

RESULTS

ZO-1 was internalized and shown to accumulate in the cytoplasm of human podocytes in an IL-13 dose-dependent manner. High doses (50 and 100 ng/mL) of IL-13 decreased the levels of ZO-1 protein at 12 and 24 h (both p<0.01; n=3), which were significantly reversed by a high dose (0.5 μM) montelukast treatment (p<0.01; n=3).

CONCLUSION

Our results suggest that IL-13 alters the expression of ZO-1, and such alterations in the content and distribution of ZO-1 may be relevant in the pathogenesis of proteinuria in the MCNS model.

One hundred ways to kill a podocyte

The podocyte is a highly specialized cell, forming within the developing glomerulus from a mesenchymal origin, acquiring some but not complete features of an epithelial cell as it matures. Once mature, this cell has the potential to receive signals from several different directions and sits within a dynamic microenvironment. By taking an overview of many lines of evidence, it is clear that we already know many signals that are tightly controlled in keeping the podocyte healthy. For example, vascular endothelial growth factor, insulin and integrins are all known to have bidirectional effects on podocyte functionality, depending on whether there is too much or too little. It is of little surprise therefore that disrupting this delicate balance can result in a dramatic loss of function, and manifestation of glomerular disease originating from many different primary insults. The cues directing podocyte phenotype and functionality for the purpose of this review will be divided into four main sources: (i) genetic, (ii) paracrine signals from endothelial and mesangial cells, (iii) direct contact signals to/from the glomerular basement membrane and (iv) signals from circulating plasma. Of course there are other influences, which we still know little about, such as flow and shear stresses, signals from the urinary space that should all be considered in the overall healthy environment.

Coinheritance of COL4A5 and MYO1E mutations accentuate the severity of kidney disease

BACKGROUND

Mutations in podocyte and basement membrane genes are associated with a growing spectrum of glomerular disease affecting adults and children. Investigation of familial cases has helped to build understanding of both normal physiology and disease.

METHODS

We investigated a consanguineous family with a wide clinical phenotype of glomerular disease using clinical, histological, and new genetic studies.

RESULTS

We report striking variability in severity of nephropathy within an X-linked Alport syndrome (XLAS) family. Four siblings each carried a mutant COL4A5 allele, p.(Gly953Val) and p.(Gly1033Arg). Two boys had signs limited to hematuria and mild/moderate proteinuria. In striking contrast, a sister presented with end-stage renal disease (ESRD) at 8 years of age and an infant brother presented with nephrotic syndrome, progressing to ESRD by 3 years of age. Both were subsequently found to have homozygous variants in MYO1E, p.(Lys118Glu) and p.(Thr876Arg). MYO1E is a gene implicated in focal segmental glomerulosclerosis and it encodes a podocyte-expressed non-muscle myosin. Bioinformatic modeling demonstrated that the collagen IV-alpha3,4,5 extracellular network connected via known protein-protein interactions to intracellular myosin 1E.

CONCLUSIONS

COL4A5 and MYO1E mutations may summate to perturb common signaling pathways, resulting in more severe disease than anticipated independently. We suggest screening for MYO1E and other non-COL4 'podocyte gene' mutations in XLAS when clinical nephropathy is more severe than expected for an individual's age and sex.

Antiproliferative effects of curcumin analog L49H37 in pancreatic stellate cells: a comparative study

BACKGROUND

Pancreatic cancer is a devastating disease with poor prognosis. It is characterized by a pronounced stromal reaction, which resists chemotherapeutics and effective tumor treatment. Pancreatic stellate cells (PSCs) are mainly responsible for this stromal reaction. Moreover, the cancer and stromal interaction seems to promote tumor proliferation. In this study, L49H37, a newly synthesized curcumin analog, was used as intervention to target the stromal compartment of pancreatic cancer.

METHODS

In vitro cultures of human PSCs were exposed to curcumin and L49H37. Cell viability as well as growth promoting and survival signaling pathways were monitored by MTT, flow cytometry and western blotting.

RESULTS

Curcumin and L49H37 effectively inhibited proliferation and induced apoptosis in PSCs. L49H37 was found to be more potent at a lower concentration than curcumin in the induction of apoptosis, as evidenced by cleaved poly (ADP-ribose) polymerase (PARP). The cells were retained in the G0/G1 phase of the cell cycle through the downregulation of p21^WAF1/Cip1. L49H37 significantly decreased the phosphorylation of extracellular signal regulated kinase ½ (ERK½).

CONCLUSION

The results indicate that curcumin analog L49H37 exhibits more potent inhibitory effects than curcumin itself at a lower concentration, which suggests that it may have a potential for further evaluation of its use against pancreatic adenocarcinoma, either as a single agent but, more probable, as part of a combination regimen.

Hyperglycemia enhances kidney cell injury in HIVAN through down-regulation of vitamin D receptors

In the present study, we evaluated the effect of short term hyperglycemia on renal lesions in a mouse model (Tg26) of HIV-associated nephropathy (HIVAN). Control and Tg26 mice in groups (n=6) were administered either normal saline (FVBN or Tg) or streptozotocin (FVBN+STZ or Tg26+STZ). After two weeks, biomarkers were collected and kidneys were harvested. FVBN+ STZ and Tg26+STZ displayed elevated serum glucose levels when compared to FVBN and Tg26 respectively. Tg26+STZ displayed elevated (P<0.05) blood urea nitrogen (BUN) levels (P<0.05) and enhanced (P<0.01) proteinuria when compared to Tg26. Tg26+STZ displayed enhanced (P<0.001) number of sclerotic glomeruli and microcysts vs. Tg26. Renal tissues of Tg26 displayed down regulation of vitamin D receptor (VDR) expression and enhanced Ang II production when compared to FVBN mice. Hyperglycemia exacerbated down regulation of VDR and production of Ang II in FVBN and Tg mice. Hyperglycemia increased kidney cell reactive oxygen species (ROS) production and oxidative DNA damage in both FVBN and Tg26 mice. In in vitro studies, HIV down regulated podocyte VDR expression and also enhanced renin angiotensin system activation. In addition, both glucose and HIV stimulated kidney cell ROS generation and DNA damage and compromised DNA repair; however, tempol (superoxide dismutase mimetic), losartan (Ang II blocker) and EB1089 (VDR agonist) provided protection against DNA damaging effects of glucose and HIV. These findings indicated that glucose activated the RAS and inflicted oxidative stress-mediated DNA damage via down regulation of kidney cell VDR expression in HIV milieu both in vivo and in vitro.

Current evidence for the role of complement in the pathogenesis of Shiga toxin haemolytic uraemic syndrome

Shiga toxin-associated haemolytic uraemic syndrome (Stx HUS) is the leading cause of paediatric acute kidney injury. This toxin-mediated disease carries a significant morbidity and mortality but has no direct treatments. Rare familial atypical HUS (aHUS) is now understood to result from over-activation of the alternative complement pathway causing glomerular endothelial damage. By understanding the pathogenic mechanisms of this disease, the monoclonal antibody eculizumab, which blocks the final common pathway of complement, is now being used to treat aHUS. For this reason, clinicians and scientists are studying the role of the alternative complement pathway in Stx HUS with the aim of targeting treatment in a similar way. There is some evidence suggesting that complement plays a role in the pathogenesis of Stx HUS, but other mechanisms may also be important. Clinically, modulating the complement system using plasma exchange provides no proven benefit in Stx HUS, and the use of eculizumab has provided conflicting results. Understanding the local effect of Stx on the glomerulus, in particular regulation of the complement and coagulation systems, may lead to advances in defining the precise pathogenesis of this disease. Then, targeted treatment strategies could be devised and clinical trials undertaken.

MicroRNA-193a Regulates the Transdifferentiation of Human Parietal Epithelial Cells toward a Podocyte Phenotype

Parietal epithelial cells have been identified as potential progenitor cells in glomerular regeneration, but the molecular mechanisms underlying this process are not fully defined. Here, we established an immortalized polyclonal human parietal epithelial cell (hPEC) line from naive human Bowman's capsule cells isolated by mechanical microdissection. These hPECs expressed high levels of PEC-specific proteins and microRNA-193a (miR-193a), a suppressor of podocyte differentiation through downregulation of Wilms' tumor 1 in mice. We then investigated the function of miR-193a in the establishment of podocyte and PEC identity and determined whether inhibition of miR-193a influences the behavior of PECs in glomerular disease. After stable knockdown of miR-193a, hPECs adopted a podocyte-like morphology and marker expression, with decreased expression levels of PEC markers. In mice, inhibition of miR-193a by complementary locked nucleic acids resulted in an upregulation of the podocyte proteins synaptopodin and Wilms' tumor 1. Conversely, overexpression of miR-193a in vivo resulted in the upregulation of PEC markers and the loss of podocyte markers in isolated glomeruli. Inhibition of miR-193a in a mouse model of nephrotoxic nephritis resulted in reduced crescent formation and decreased proteinuria. Together, these results show the establishment of a human PEC line and suggest that miR-193a functions as a master switch, such that glomerular epithelial cells with high levels of miR-193a adopt a PEC phenotype and cells with low levels of miR-193a adopt a podocyte phenotype. miR-193a-mediated maintenance of PECs in an undifferentiated reactive state might be a prerequisite for PEC proliferation and migration in crescent formation.

Proteinuria in preeclampsia from a podocyte injury perspective

Preeclampsia is a frequent cause of maternal and fetal morbidity and mortality worldwide. The underlying causes of this hypertensive complication have remained elusive. The placenta seems to be at the origin of the disease, as its removal appears to be the only effective treatment available. Many organs can potentially be affected. Nonetheless, kidney alterations are always present: proteinuria is one of the hallmarks for a preeclampsia diagnosis. VEGF is pivotal for maintaining glomerular filtration barrier function; hence, the elevated concentrations of placental-derived VEGF inhibitors, such as sFlt-1, may largely explain the renal alterations observed. Classically, glomerular endothelial injury was considered responsible for the renal impairment present in preeclampsia. Recent findings, however, have shown that podocytes are crucial in explaining the loss of filtration capacity of the preeclamptic kidney. The aims of this manuscript are to detail the main findings that associate podocyte injury with proteinuria in preeclampsia, and discuss the eventual applications of podocyte damage biomarkers in clinical practice.

Localization of APOL1 protein and mRNA in the human kidney: nondiseased tissue, primary cells, and immortalized cell lines

Although APOL1 gene variants are associated with nephropathy in African Americans, little is known about APOL1 protein synthesis, uptake, and localization in kidney cells. To address these questions, we examined APOL1 protein and mRNA localization in human kidney and human kidney-derived cell lines. Indirect immunofluorescence microscopy performed on nondiseased nephrectomy cryosections from persons with normal kidney function revealed that APOL1 protein was markedly enriched in podocytes (colocalized with synaptopodin and Wilms' tumor suppressor) and present in lower abundance in renal tubule cells. Fluorescence in situ hybridization detected APOL1 mRNA in glomeruli (podocytes and endothelial cells) and tubules, consistent with endogenous synthesis in these cell types. When these analyses were extended to renal-derived cell lines, quantitative RT-PCR did not detect APOL1 mRNA in human mesangial cells; however, abundant levels of APOL1 mRNA were observed in proximal tubule cells and glomerular endothelial cells, with lower expression in podocytes. Western blot analysis revealed corresponding levels of APOL1 protein in these cell lines. To explain the apparent discrepancy between the marked abundance of APOL1 protein in kidney podocytes observed in cryosections versus the lesser abundance in podocyte cell lines, we explored APOL1 cellular uptake. APOL1 protein was taken up readily by human podocytes in vitro but was not taken up efficiently by mesangial cells, glomerular endothelial cells, or proximal tubule cells. We hypothesize that the higher levels of APOL1 protein in human cryosectioned podocytes may reflect both endogenous protein synthesis and APOL1 uptake from the circulation or glomerular filtrate.

APOL1 risk variants enhance podocyte necrosis through compromising lysosomal membrane permeability

Development of higher rates of nondiabetic glomerulosclerosis (GS) in African Americans has been attributed to two coding sequence variants (G1 and G2) in the APOL1 gene. To date, the cellular function and the role of APOL1 variants (Vs) in GS are still unknown. In this study, we examined the effects of overexpressing wild-type (G0) and kidney disease risk variants (G1 and G2) of APOL1 in human podocytes using a lentivirus expression system. Interestingly, G0 inflicted podocyte injury only at a higher concentration; however, G1 and G2 promoted moderate podocyte injury at lower and higher concentrations. APOL1Vs expressing podocytes displayed diffuse distribution of both Lucifer yellow dye and cathepsin L as manifestations of enhanced lysosomal membrane permeability (LMP). Chloroquine attenuated the APOL1Vs-induced increase in podocyte injury, consistent with targeting lysosomes. The chloride channel blocker DIDS prevented APOL1Vs- induced injury, indicating a role for chloride influx in osmotic swelling of lysosomes. Direct exposure of noninfected podocytes with conditioned media from G1- and G2-expressing podocytes also induced injury, suggesting a contributory role of the secreted component of G1 and G2 as well. Adverse host factors (AHFs) such as hydrogen peroxide, hypoxia, TNF-α, and puromycin aminonucleoside augmented APOL1- and APOL1Vs-induced podocyte injury, while the effect of human immunodeficiency virus (HIV) on podocyte injury was overwhelming under conditions of APOLVs expression. We conclude that G0 and G1 and G2 APOL1 variants have the potential to induce podocyte injury in a manner which is further augmented by AHFs, with HIV infection being especially prominent.

Podocytes regulate neutrophil recruitment by glomerular endothelial cells via IL-6-mediated crosstalk

Stromal cells actively modulate the inflammatory process, in part by influencing the ability of neighboring endothelial cells to support the recruitment of circulating leukocytes. We hypothesized that podocytes influence the ability of glomerular endothelial cells (GEnCs) to recruit neutrophils during inflammation. To address this, human podocytes and human GEnCs were cultured on opposite sides of porous inserts and then treated with or without increasing concentrations of TNF-α prior to addition of neutrophils. The presence of podocytes significantly reduced neutrophil recruitment to GEnCs by up to 50% when cultures were treated with high-dose TNF-α (100 U/ml), when compared with GEnC monocultures. Importantly, this phenomenon was dependent on paracrine actions of soluble IL-6, predominantly released by podocytes. A similar response was absent when HUVECs were cocultured with podocytes, indicating a tissue-specific phenomenon. Suppressor of cytokine signaling 3 elicited the immunosuppressive actions of IL-6 in a process that disrupted the presentation of chemokines on GEnCs by altering the expression of the duffy Ag receptor for chemokines. Interestingly, suppressor of cytokine signaling 3 knockdown in GEnCs upregulated duffy Ag receptor for chemokines and CXCL5 expression, thereby restoring the neutrophil recruitment. In summary, these studies reveal that podocytes can negatively regulate neutrophil recruitment to inflamed GEnCs by modulating IL-6 signaling, identifying a potential novel anti-inflammatory role of IL-6 in renal glomeruli.

Unilateral hypoplastic kidney - a novel highly penetrant feature of familial juvenile hyperuricaemic nephropathy

BACKGROUND

Familial juvenile hyperuricaemic nephropathy is a rare inherited nephropathy with genetic heterogeneity. Categorised by genetic defect, mutations in uromodulin (UMOD), renin (REN) and hepatocyte nuclear factor-1β (HNF-1β) genes as well as linkage to chromosome 2p22.1-21 have previously been identified. Knowledge of the genetics of this phenotype has provided important clues to developmental pathways in the kidney.

CASE PRESENTATION

We report a novel phenotype, with the typical features of hyperuricemia and renal deterioration, but with the additional unexpected feature of unilateral renal hypoplasia. Mutation analyses of the existing known genes and genetic loci were negative indicating a new monogenic cause. Interestingly two cousins of the index case did not share the latter feature, suggesting a modifier gene effect.

CONCLUSION

Unilateral renal hypo/aplasia is usually sporadic and relatively common, with no genetic cause to date identified. This reported pedigree reveals the possibility that a new, unknown renal developmental gene may be implicated in the FJHN phenotype.

The effect of albumin on podocytes: the role of the fatty acid moiety and the potential role of CD36 scavenger receptor

Evidence is emerging that podocytes are able to endocytose proteins such as albumin using kinetics consistent with a receptor-mediated process. To date the role of the fatty acid moiety on albumin uptake kinetics has not been delineated and the receptor responsible for uptake is yet to be identified. Albumin uptake studies were carried out on cultured human podocytes exposed to FITC-labelled human serum albumin either carrying fatty acids (HSA+FA) or depleted of them (HSA-FA). Receptor-mediated endocytosis of FITC-HSA+FA over 60 min was 5 times greater than that of FITC-HSA-FA. 24h exposure of podocytes to albumin up-regulated nephrin expression and induced the activation of caspase-3. These effects were more pronounced in response to HSA-FA. Individually, anti-CD36 antibodies had no effect upon endocytosis of FITC-HSA. However, a cocktail of 2 antibodies reduced uptake by nearly 50%. Albumin endocytosis was enhanced in the presence of the CD36 specific inhibitor sulfo-N-succinimidyl oleate (SSO) while knock-down of CD36 using CD36siRNA had no effect on uptake. These data suggest that receptor-mediated endocytosis of albumin by podocytes is regulated by the fatty acid moiety, although, some of the detrimental effects are induced independently of it. CD36 does not play a direct role in the uptake of albumin.

Short course daily prednisolone therapy during an upper respiratory tract infection in children with relapsing steroid-sensitive nephrotic syndrome (PREDNOS 2): protocol for a randomised controlled trial

BACKGROUND

Relapses of childhood steroid-sensitive nephrotic syndrome (SSNS) are treated with a 4- to 8-week course of high-dose oral prednisolone, which may be associated with significant adverse effects. There is a clear association between upper respiratory tract infection (URTI) and relapse development. Previous studies in developing nations have suggested that introducing a 5- to 7-day course of daily prednisolone during an URTI may prevent a relapse developing and the need for a treatment course of high-dose prednisolone. The aim of PREDNOS 2 is to evaluate the effectiveness of a 6-day course of daily prednisolone therapy during an URTI in reducing the development of a subsequent relapse in a developed nation.

METHODS/DESIGN

The subjects will be 300 children with relapsing SSNS (≥2 relapses in preceding year), who will be randomised to receive either a 6-day course of daily prednisolone or no change to their current therapy (with the use of placebo to double blind) each time they develop an URTI over 12 months. A strict definition for URTI will be used. Subjects will be reviewed at 3, 6, 9 and 12 months to capture data regarding relapse history, ongoing therapy and adverse effect profile, including behavioural problems and quality of life. A formal health economic analysis will also be performed. The primary end point of the study will be the incidence of URTI-related relapse (3 days of Albustix +++) following the first infection during the 12-month follow-up period. DNA and RNA samples will be collected to identify a potential genetic cause for the disease. Subjects will be recruited from over 100 UK centres with the assistance of the Medicines for Children Research Network.PREDNOS 2 is funded by the National Institute for Health Research Health Technology Assessment Programme (11/129/261).

DISCUSSION

We propose that PREDNOS 2 will be a pivotal study that will inform the future standard of care for children with SSNS. If it is possible to reduce the disease relapse rate effectively and safely, this will reduce the morbidity and cost associated with drug treatment, notwithstanding hospital admission and parental absence from employment.

TRIAL REGISTRATION

Current Controlled Trials (ISRCTN10900733).

Initial steroid sensitivity in children with steroid-resistant nephrotic syndrome predicts post-transplant recurrence

Of children with idiopathic nephrotic syndrome, 10%-20% fail to respond to steroids or develop secondary steroid resistance (termed initial steroid sensitivity) and the majority progress to transplantation. Although 30%-50% of these patients suffer disease recurrence after transplantation, with poor long-term outcome, no reliable indicator of recurrence has yet been identified. Notably, the incidence of recurrence after transplantation appears reduced in patients with steroid-resistant nephrotic syndrome (SRNS) due to monogenic disorders. We reviewed 150 transplanted patients with SRNS to identify biomarkers that consistently predict outcome of SRNS after transplantation. In all, 25 children had genetic or familial SRNS and did not experience post-transplant recurrence. We reviewed phenotypic factors, including initial steroid sensitivity, donor type, age, ethnicity, time to ESRD, and time on dialysis, in the remaining 125 children. Of these patients, 57 (45.6%) developed post-transplant recurrence; 26 of 28 (92.9%) patients with initial steroid sensitivity recurred after transplantation, whereas only 26 of 86 (30.2%) patients resistant from the outset recurred (odds ratio, 30; 95% confidence interval, 6.62 to 135.86; P<0.001). We were unable to determine recurrence in two patients (one with initial steroid sensitivity), and nine patients did not receive initial steroids. Our data show that initial steroid sensitivity is highly predictive of post-transplant disease recurrence in this pediatric patient population. Because a pathogenic circulating permeability factor in nephrotic syndrome remains to be confirmed, we propose initial steroid sensitivity as a surrogate marker for post-transplant recurrence.