Renal glomerular and tubular responses to glutaraldehyde- polymerized human hemoglobin

Hemoglobin-based oxygen carriers (HBOCs) are being developed as oxygen and volume replacement therapeutics, however, their molecular and cellular effects on the vasculature and different organ systems are not fully defined. Using a guinea pig transfusion model, we examined the renal glomerular and tubular responses to PolyHeme, a highly characterized glutaraldehyde-polymerized human hemoglobin with low tetrameric hemoglobin content. PolyHeme-infused animals showed no major changes in glomerular histology or loss of specific markers of glomerular podocytes (Wilms tumor 1 protein, podocin, and podocalyxin) or endothelial cells (ETS-related gene and claudin-5) after 4, 24, and 72 h. Relative to sham controls, PolyHeme-infused animals also showed similar expression and subcellular distribution of N-cadherin and E-cadherin, two key epithelial junctional proteins of proximal and distal tubules, respectively. In terms of heme catabolism and iron-handling responses, PolyHeme induced a moderate but transient expression of heme oxygenase-1 in proximal tubular epithelium and tubulointerstitial macrophages that was accompanied by increased iron deposition in tubular epithelium. Contrary to previous findings with other modified or acellular hemoglobins, the present data show that PolyHeme does not disrupt the junctional integrity of the renal glomerulus and tubular epithelium, and triggers moderate activation of heme catabolic and iron sequestration systems likely as part of a renal adaptive response.

Cytoplasmic WT1 in IgA nephropathy, an indicator of poor prognosis associated with mesangial/peri-mesangial C4d

BACKGROUND

We aimed to investigate the immuno-histochemical expression of C4d, ADAM10 and WT1 in kidney biopsies of immunoglobulin A nephropathy (IgAN) patients and correlate the findings with clinical, laboratory and histopathologic features in the hope of defining new parameters to better understand the pathogenesis of the disease, and predict prognosis.

MATERIALS AND METHODS

Paraffin-embedded kidney biopsy samples of 128 IgAN patients were immuno-histochemically treated with C4d and ADAM10/WT1 dual stain. Results were evaluated according to Oxford classification parameters, epidemiologic features, laboratory findings at presentation and clinical follow-up.

RESULTS

We observed C4d positivity in 40.6% of our patients, 25% of which was mesangial/peri-mesangial (m/pm) staining. Only m/pmC4d positivity statistically correlated with progression to end-stage renal disease (ESRD). M/pmC4d positive patients had statistically significantly higher baseline proteinuria levels, presence of crescents and > 25% segmental sclerosis of glomeruli. There was cytoplasmic staining of WT1 in 11.2% of cases. Presence of cWT1 correlated with m/pmC4d positivity and progression to ESRD. There was no glomerular ADAM10 detected and tubular expression of this protein did not relate to amount of tubular damage or other parameters.

CONCLUSION

This study is the first to show that cWT1is involved in IgAN and appears as an independent variable for worse prognosis.

Association between proteinuria trajectories and outcomes in critically ill patients with sepsis or shock

Background

Proteinuria results from kidney damage and can be a predictor of illness severity and mortality in the intensive care unit (ICU). However, the optimal timing of proteinuria measurements and the reference values remain undetermined. Our objective was to identify the patterns of proteinuria change associated with mortality in ICU patients with sepsis or shock.

Methods

This monocentric retrospective cohort study performed from April 2010 to April 2018 involved all ICU patients with sepsis or shock and at least two measurements of proteinuria from a 24h-urine collection during the first 10 days of ICU stay, the first of which was made within 48h after ICU admission. We identified proteinuria trajectories by a semi-parametric mixture model and analysed the association between the trajectories and the mortality at day 28 by Cox proportional-hazards model.

Results

A total of 3,344 measurements of proteinuria from 659 patients were analysed. Four proteinuria trajectories were identified. Trajectories 1, 2, 3 and 4 comprised 127, 421, 60 and 51 patients, and were characterized by a first proteinuria of 1.14 [0.66–1.55], 0.52 [0.26–0.91], 2.92 [2.38–3.84] and 2.58 [1.75–3.32] g/24h (p<0.001) and a mortality of 24.4%, 38%, 20% and 43% (p = 0.002), respectively. Trajectories 3 and 4 had a high first proteinuria (>2g/24h). Only, the proteinuria of trajectory 4 increased within 3 days following the first measurement and was associated with increased mortality at day 28 (hazard ratio: 2.36 95%CI [1.07–5.19], p = 0.03), regardless of acute renal failure. The factors associated with trajectory 4 were cancer (relative risk: 8.91 95%CI [2.09–38.02], p = 0.003) and use of inotropic drugs (relative risk: 0.17 95%CI [0.04–0.69], p = 0.01).

Conclusion

This exploratory study of ICU patients with sepsis or shock identified four proteinuria trajectories with distinct patterns of proteinuria change over time and mortality rates. These results provide novel insights into renal pathophysiology and may be helpful to investigate subphenotypes of kidney injury among ICU patients in future studies.

Angiotensin II type-2-receptor stimulation ameliorates focal and segmental glomerulosclerosis in mice

Podocyte damage and loss are the early event in the development of focal segmental glomerulosclerosis (FSGS). Podocytes express angiotensin II type-2-receptor (AT2R), which may play a key role in maintaining kidney integrity and function. Here, we examined the effects of AT2R deletion and AT2R agonist compound 21 (C21) on the evolution of FSGS. FSGS was induced by adriamycin (ADR) injection in both male wild-type (WT) and AT2R knockout (KO) mice. C21 was administered to WT-FSGS mice either one day before or 7 days after ADR (Pre-C21 or Post-C21), using two doses of C21 at either 0.3 (low dose, LD) or 1.0 (high dose, HD) mg/kg/day. ADR-induced FSGS was more severe in AT2RKO mice compared with WT-FSGS mice, and included profound podocyte loss, glomerular fibrosis, and albuminuria. Glomerular cathepsin L expression increased more in AT2RKO-FSGS than in WT-FSGS mice. C21 treatment ameliorated podocyte injury, most significantly in the Pre C21-HD group, and inhibited glomerular cathepsin L expression. In vitro, Agtr2 knock-down in mouse podocyte cell line given ADR confirmed the in vivo data. Mechanistically, C21 inhibited cathepsin L expression, which protected synaptopodin from destruction and stabilized actin cytoskeleton. C21 also prevented podocyte apoptosis. In conclusion, AT2R activation by C21 ameliorated ADR-induced podocyte injury in mice by the inhibition of glomerular cathepsin L leading to the maintenance of podocyte integrity and prevention of podocyte apoptosis.

[Effect and molecular mechanism of interferon-α on podocyte apoptosis induced by hepatitis B virus X protein]

OBJECTIVE

To investigate the effect and molecular mechanism of interferon-α (INF-α) on the apoptosis of the mouse podocyte cell line MPC5 induced by hepatitis B virus X (HBx) protein.

METHODS

MPC5 cells were transfected with the pEX plasmid carrying the HBx gene. RT-PCR was used to measure the mRNA expression of HBx at different time points. MPC5 cells were divided into 4 groups: control group (MPC5 cells cultured under normal conditions), INF-α group (MPC5 cells cultured with INF-α), HBx group (MPC5 cells induced by HBx), and HBx+INF-α group (MPC5 cells induced by HBx and cultured with INF-α). After 48 hours of intervention under different experimental conditions, flow cytometry was used to measure the apoptosis of MPC5 cells, and quantitative real-time PCR and Western blot were used to measure the mRNA and protein expression of slit diaphragm-related proteins (nephrin, CD2AP, and synaptopodin) and the cytoskeleton-related protein transient receptor potential cation channel 6 (TRPC6).

RESULTS

MPC5 cells transfected by pEX-HBx had the highest expression of HBx mRNA at 48 hours after transfection (P<0.05). Compared with the control, INF-α and HBx+INF-α groups, the HBx group had a significant increase in the apoptosis rate of MPC5 cells (P<0.05). Compared with the control and INF-α groups, the HBx group had significant reductions in the mRNA and protein expression of nephrin, synaptopodin, and CD2AP and significant increases in the mRNA and protein expression of TRPC6 (P<0.05). Compared with the HBx group, the HBx+INF-α group had significant increases in the mRNA and protein expression of nephrin, synaptopodin, and CD2AP and significant reductions in the mRNA and protein expression of TRPC6 (P<0.05).

CONCLUSIONS

INF-α can inhibit the apoptosis of podocytes induced by HBx, possibly through improving the abnormal expression of slit diaphragm-related proteins (CD2AP, nephrin, and synaptopodin) and cytoskeleton-related protein (TRPC6) induced by HBx.

miR-124a enhances therapeutic effects of bone marrow stromal cells transplant on diabetic nephropathy-related epithelial-to-mesenchymal transition and fibrosis

BACKGROUND

Epithelial-to-mesenchymal transition (EMT) has been gradually considered as one of the major pathways that causes the production of interstitial myofibroblasts in diseased kidneys.

MATERIALS AND METHODS

The study was done to investigate the effect of a bone marrow stromal cell (BMSCs) transplant on rat podocytes and diabetic nephropathy (DN) rats in high-glucose concentration, and to explore the effect of miR-124a on BMSC therapy. High glucose-injured podocytes and streptozotocin-induced DN rats have been respectively used as injury models in in vitro and in vivo studies. Podocyte viability was measured using the Cell Counting Kit-8 assay. Renal pathological examination was observed by HE staining and Masson staining. The messenger RNA and protein levels were determined via real-time polymerase chain reaction and Western blotting, respectively.

RESULTS

By mediating the activation of caveolin-1 (cav-1) and β-catenin and affecting the expression levels of EMT biomarkers including p-cadherin, synaptopodin, fibroblast-specific protein-1, α-smooth muscle actin and snail, our in vitro study confirmed that miR-124a played a significant role in the treatment of high glucose-induced podocyte injury by BMSCs. The therapeutic effects of the BMSC transplant on DN rats were also proved to be further enhanced by miR-124a overexpression in BMSCs, and such a phenomenon was accompanied by the improvement of renal fibrosis and mitigation of DN-related kidney impairment. Regulation of fibronectin, collagen1, and EMT-related proteins was closely implicated with the mechanism, and the activation of cav-1 and β-catenin was also possibly involved.

CONCLUSION

The study demonstrated the pivotal effect of miR-124a on BMSC therapy for DN rats via mitigating EMT and fibrosis. Our results provide a novel insight into how therapeutic effects of BMSCs can be improved at the posttranscriptional level.

Hepatitis B virus X protein decreases nephrin expression and induces podocyte apoptosis via activating STAT3

The gene for hepatitis B virus X protein (HBx) comprises the smallest open reading frame in the HBV genome, and the protein product can activate various cell signaling pathways and regulate apoptosis, among other effects. However, in different cell types and under different external conditions, its mechanism of action differs. In the present study, the effect of HBx on the viability and apoptosis of mouse podocyte clone 5 (MPC5) cells was investigated. The cells were transfected with the HBx gene using pEX plasmid, and real-time quantitative PCR and western blot analysis were used to test the transfection efficiency and assess related protein expression. The highest expression of HBx occurred at 48 h after MPC5 cells were transfected with HBx. The expression of nephrin protein in the HBx transfection group was lower than that in blank and negative control groups. Following transfection of the HBx gene, podocyte viability was suppressed, while the rate of cell apoptosis was increased; moreover, the expression of signal transducer and activator of transcription 3 (STAT3) and phospho-STAT3 was increased compared with in the control groups. The present study suggests that STAT3 activation may be involved in the pathogenic mechanism of renal injuries caused by HBV injection. Thus STAT3 is a potential molecular target in the treatment of HBV-GN.

LPS removal reduces CD80-mediated albuminuria in critically ill patients with Gram-negative sepsis

LPS-induced sepsis is a leading cause of acute kidney injury (AKI) in critically ill patients. LPS may induce CD80 expression in podocytes with subsequent onset of proteinuria, a risk factor for progressive chronic kidney disease (CKD) frequently observed after AKI. This study aimed to investigate the therapeutic efficacy of LPS removal in decreasing albuminuria through the reduction of podocyte CD80 expression. Between January 2015 and December 2017, 70 consecutive patients with Gram-negative sepsis-induced AKI were randomized to either have coupled plasma filtration and adsorption (CPFA) added to the standard care ( n = 35) or not ( n = 35). To elucidate the possible relationship between LPS-induced renal damage, proteinuria, and CD80 expression in Gram sepsis, a swine model of LPS-induced AKI was set up. Three hours after LPS infusion, animals were treated or not with CPFA for 6 h. Treatment with CPFA significantly reduced serum cytokines, C-reactive protein, procalcitonin, and endotoxin levels in patients with Gram-negative sepsis-induced AKI. CPFA significantly lowered also proteinuria and CD80 urinary excretion. In the swine model of LPS-induced AKI, CD80 glomerular expression, which was undetectable in control pigs, was markedly increased at the podocyte level in LPS-exposed animals. CPFA significantly reduced LPS-induced proteinuria and podocyte CD80 expression in septic pigs. Our data indicate that LPS induces albuminuria via podocyte expression of CD80 and suggest a possible role of timely LPS removal in preventing the maladaptive repair of the podocytes and the consequent increased risk of CKD in sepsis-induced AKI.

Podocyte-specific soluble epoxide hydrolase deficiency in mice attenuates acute kidney injury

Podocytes play an important role in maintaining glomerular function, and podocyte injury is a significant component in the pathogenesis of proteinuria. Soluble epoxide hydrolase (sEH) is a cytosolic enzyme whose genetic deficiency and pharmacological inhibition have beneficial effects on renal function, but its role in podocytes remains unexplored. The objective of this study was to investigate the contribution of sEH in podocytes to lipopolysaccharide (LPS)-induced kidney injury. We report increased sEH transcript and protein expression in murine podocytes upon LPS challenge. To determine the function of sEH in podocytes in vivo we generated podocyte-specific sEH-deficient (pod-sEHKO) mice. Following LPS challenge, podocyte sEH-deficient mice exhibited lower kidney injury, proteinuria, and blood urea nitrogen concentrations than controls suggestive of preserved renal function. Also, renal mRNA and serum concentrations of inflammatory cytokines IL-6, IL-1β, and TNFα were significantly lower in LPS-treated pod-sEHKO than control mice. Moreover, podocyte sEH deficiency was associated with decreased LPS-induced NF-κB and MAPK activation and attenuated endoplasmic reticulum stress. Furthermore, the protective effects of podocyte sEH deficiency in vivo were recapitulated in E11 murine podocytes treated with a selective sEH pharmacological inhibitor. Altogether, these findings identify sEH in podocytes as a contributor to signaling events in acute renal injury and suggest that sEH inhibition may be of therapeutic value in proteinuria.

ENZYMES

Soluble epoxide hydrolase: EC 3.3.2.10.

Cytoplasmic Localization of WT1 and Decrease of miRNA-16-1 in Nephrotic Syndrome

Nephrotic syndrome (NS) is a glomerular disease that is defined by the leakage of protein into the urine and is associated with hypoalbuminemia, hyperlipidemia, and edema. Steroid-resistant NS (SRNS) patients do not respond to treatment with corticosteroids and show decreased Wilms tumor 1 (WT1) expression in podocytes. Downregulation of WT1 has been shown to be affected by certain microRNAs (miRNAs). Twenty-one patients with idiopathic NS (68.75% were SSNS and 31.25% SRNS) and 10 healthy controls were enrolled in the study. Podocyte number and WT1 location were determined by immunofluorescence, and the serum levels of miR-15a, miR-16-1, and miR-193a were quantified by RT-qPCR. Low expression and delocalization of WT1 protein from the nucleus to the cytoplasm were found in kidney biopsies of patients with SRNS and both nuclear and cytoplasmic localization were found in steroid-sensitive NS (SSNS) patients. In sera from NS patients, low expression levels of miR-15a and miR-16-1 were found compared with healthy controls, but only the miR-16-1 expression levels showed statistically significant decrease (p = 0.019). The miR-193a expression levels only slightly increased in NS patients. We concluded that low expression and delocalization from the WT1 protein in NS patients contribute to loss of podocytes while modulation from WT1 protein is not associated with the miRNAs analyzed in sera from the patients.

Nephron, Wilms' tumor-1 (WT1), and synaptopodin expression in developing podocytes of mice

Newborn mouse glomeruli are still immature with a morphological feature of an early capillary loop stage, but infant mice do not manifest proteinuria. Little is known about the molecular mechanism whereby infant mice are resistant to proteinuria. Nephrin and synaptopodin are crucial for slit diaphragm and foot process (FP) formation for avoiding proteinuria. Nephrin tyrosine phosphorylation means a transient biological signaling required for FP repair or extension during nephrotic disease. Using an immunohistochemical technique, we examined the natural course of nephrin, Wilms’ tumor-1 (WT1) and synaptopodin at 16.5 days of embryonic age (E16.5d) and E19.5d, 7 days of post-neonatal age (P7d) and P42d during renal development of mice. As a result, nephrin and synaptopodin were detected at E19.5d in S-shaped bodies. WT1, a transcriptional factor for nephrin, was detected in nucleus in podocyte-like cells in all stages. Nephrin tyrosine phosphorylation was evident in glomeruli at P7d, and this was associated with an early-stage of FP extension. Inversely, nephrin phosphorylation became faint at P42d, along with maturated FP. Based on the present results, we suggest the sequential molecular mechanism to protect growing mice from proteinuria: (i) WT1-induced nephrin production by podocytes in S-shaped bodies at E19.5d; (ii) Synchronized induction of synaptopodin at the same period; and (iii) FP extension is initiated at a milk-suckling stage under a nephrin tyrosine-phosphorylated condition, while it is arrested at an adult stage, associated with a loss of nephrin-based signaling.

Deficiency of fibroblast growth factor-inducible 14 (Fn14) preserves the filtration barrier and ameliorates lupus nephritis

TNF ligand superfamily member 12, also known as TNF-related weak inducer of apoptosis (TWEAK), acts through its receptor, fibroblast growth factor-inducible 14 (Fn14), to mediate several key pathologic processes involved in tissue injury relating to lupus nephritis. To explore the potential for renal protection in lupus nephritis by targeting this pathway, we introduced the Fn14 null allele into the MRL-lpr/lpr lupus mouse strain. At 26-38 weeks of age, female Fn14-knockout MRL-lpr/lpr mice had significantly lower levels of proteinuria compared with female wild-type MRL-lpr/lpr mice. Furthermore, Fn14-knockout mice had significantly improved renal histopathology accompanied by attenuated glomerular and tubulointerstitial inflammation. There was a significant reduction in glomerular Ig deposition in Fn14-knockout mice, despite no detectable differences in either serum levels of antibodies or splenic immune cell subsets. Notably, we found that the Fn14-knockout mice displayed substantial preservation of podocytes in glomeruli and that TWEAK signaling directly damaged barrier function and increased filtration through podocyte and glomerular endothelial cell monolayers. Our results show that deficiency of the Fn14 receptor significantly improves renal disease in a spontaneous lupus nephritis model through prevention of the direct injurious effects of TWEAK on the filtration barrier and/or modulation of cytokine production by resident kidney cells. Thus, blocking the TWEAK/Fn14 axis may be a novel therapeutic intervention in immune-mediated proliferative GN.

IV injection of polystyrene beads for mouse model of sepsis causes severe glomerular injury

Background

Infusion fluids may be contaminated with different types of particulates that are a potential health hazard. Particulates larger than microvessels may cause an embolism by mechanical blockage and inflammation; however, it has been reported that particulates smaller than capillary diameter are relatively safe. Against such a background, one report showed that polystyrene beads smaller than capillary diameter decreased tissue perfusion in ischemia–reperfusion injury. This report suggested that polystyrene beads from 1.5- to 6-μm diameter (dia.) may have unfavorable effects after pretreatment.

Here, we investigated whether injection of polystyrene beads (3- and 6-μm dia.) as an artificial contaminant of intravenous fluid after lipopolysaccharide (LPS) injection affected mortality and organ damage in mice.

Methods

Mice were divided into four groups and injected: polystyrene beads only, LPS only, polystyrene beads 30 min after LPS, or saline. A survival study, histology, blood examination, and urine examination were performed.

Results

The survival rate after LPS and polystyrene bead (6-μm dia.) injection was significantly lower than that of the other three groups. In the kidney sections, injured glomeruli were significantly higher with LPS and polystyrene bead injection than that of the other three groups. LPS and polystyrene bead injection decreased the glomerular filtration rate and led to renal failure. Inflammatory reactions induced with LPS were not significantly different between with or without polystyrene beads. Polystyrene beads were found in urine after LPS and polystyrene bead injection.

Conclusions

Injection of polystyrene beads after LPS injection enhanced glomerular structural injury and caused renal function injury in a mouse sepsis model.

The regulation of the UCH-L1 gene by transcription factor NF-κB in podocytes

In kidney, the ubiquitin carboxy-terminal hydrolase 1 (UCH-L1) is involved in podocyte injury and proteinuria but details of the mechanism underlying its regulation are not known. Activation of NF-κB is thought to be the predominant risk factor for kidney disease; therefore, it is postulated that UCH-L1 may be one of the NF-κB target genes. In this study, we investigated the involvement of NF-κB activation in the regulation of UCH-L1 expression and the function of murine podocytes. Stimulation of podocytes with the cytokines TNF-α and IL-1β up-regulated UCH-L1 expression rapidly at the mRNA and protein levels and the NF-κB-specific inhibitor pyrrolidine dithiocarbamate resulted in down-regulation. NF-κB up-regulates UCH-L1 via binding the --300 bp and --109 bp sites of its promoter, which was confirmed by the electrophoretic mobility shift assay of DNA-nuclear protein binding. In the renal biopsy from lupus nephritis patients, the expressions of NF-κB and UCH-L1 increased in immunohistochestry staining and were positively correlated. Activation of NF-κB up-regulates UCH-L1 expression following changing of other podocytes molecules, such as nephrin and snail. These results suggest that activation of the NF-κB signaling pathway could be the major pathogenesis to up-regulate UCH-L1 in podocyte injury, followed by the turnover of other molecules, which might result in morphological changes and dysfunction of podocytes. This work help us to understand the effect of NF-κB on specific target molecules of podocytes, and suggest that targeting the NF-κB-UCH-L1 interaction could be a novel therapeutic strategy for the treatment of podocyte lesions and proteinuria.

Irreversible renal damage after transient renin-angiotensin system stimulation: involvement of an AT1-receptor mediated immune response

Transient activation of the renin-angiotensin system (RAS) induces irreversible renal damage causing sustained elevation in blood pressure (BP) in Cyp1a1-Ren2 transgenic rats. In our current study we hypothesized that activation of the AT₁-receptor (AT₁R) leads to a T-cell response causing irreversible impairment of renal function and hypertension. Cyp1a1-Ren2 rats harbor a construct for activation of the RAS by indole-3-carbinol (I3C). Rats were fed a I3C diet between 4–8 weeks of age to induce hypertension. Next, I3C was withdrawn and rats were followed-up for another 12 weeks. Additional groups received losartan (20 mg/kg/day) or hydralazine (100 mg/kg/day) treatment between 4–8 weeks. Rats were placed for 24h in metabolic cages before determining BP at week 8, 12 and 20. At these ages, subsets of animals were sacrificed and the presence of kidney T-cell subpopulations was investigated by immunohistochemistry and molecular marker analysis. The development of sustained hypertension was completely prevented by losartan, whereas hydralazine only caused a partial decrease in BP. Markers of renal damage: KIM-1 and osteopontin were highly expressed in urine and kidney samples of I3C-treated rats, even until 20 weeks of age. Additionally, renal expression of regulatory-T cells (Tregs) was highly increased in I3C-treated rats, whereas the expression of T-helper 1 (Th1) cells demonstrated a strong decrease. Losartan prevented these effects completely, whereas hydralazine was unable to affect these changes. In young Cyp1a1-Ren2 rats AT₁R activation leads to induction of an immune response, causing a shift from Th1-cells to Tregs, contributing to the development of irreversible renal damage and hypertension.

Acute endotoxemia in mice induces downregulation of megalin and cubilin in the kidney

Severe sepsis is often accompanied by acute renal failure with renal tubular dysfunction. Albuminuria is a common finding in septic patients and we studied whether it was due to an impairment of proximal tubular endocytosis of filtered albumin. We studied the regulation of megalin and cubilin, the two critical multiligand receptors responsible for albumin absorption, during severe experimental endotoxemia. Lipopolysaccharide (LPS) caused a time- and dose-dependent suppression of megalin and cubilin expression that was paralleled by a decrease in plasma albumin levels and an increase in the urine concentration of albumin in mice. Incubation of rat renal cortical slices with LPS also reduced the mRNA expression of megalin and cubilin. Further, LPS suppressed megalin and cubilin mRNA expression in murine primary proximal tubule cells and decreased the uptake of FITC albumin in these cells. In addition, the increase in urine levels of albumin in response to ischemia/reperfusion-induced acute renal failure was paralleled by a decrease in the expression of megalin and cubilin. Thus, our data indicate that the expression of megalin and cubilin is decreased during experimental endotoxemia and in response to renal ischemia/reperfusion injury. This downregulation may contribute, in part, to an increase in urine levels of albumin during acute renal failure.

Sepsis induces albuminuria and alterations in the glomerular filtration barrier: a morphofunctional study in the rat

Introduction

Increased vascular permeability represents one of the hallmarks of sepsis. In the kidney, vascular permeability is strictly regulated by the 'glomerular filtration barrier' (GFB), which is comprised of glomerular endothelium, podocytes, their interposed basement membranes and the associated glycocalyx. Although it is likely that the GFB and its glycocalyx are altered during sepsis, no study has specifically addressed this issue. The aim of this study was to evaluate whether albuminuria -- the hallmark of GFB perm-selectivity -- occurs in the initial stage of sepsis and whether it is associated with morphological and biochemical changes of the GFB.

Methods

Cecal ligation and puncture (CLP) was used to induce sepsis in the rat. Tumor necrosis factor (TNF)-alpha levels in plasma and growth of microorganisms in the peritoneal fluid were evaluated at 0, 3 and 7 hours after CLP or sham-operation. At the same times, kidney specimens were collected and structural and ultrastructural alterations in the GFB were assessed. In addition, several components of GFB-associated glycocalyx, syndecan-1, hyluronan (HA) and sialic acids were evaluated by immunofluorescence, immunohistochemistry and lectin histochemistry techniques. Serum creatinine and creatinine clearance were measured to assess kidney function and albuminuria for changes in GFB permeability. Analysis of variance followed by Tukey's multiple comparison test was used.

Results

Septic rats showed increased TNF-alpha levels and growth of microorganisms in the peritoneal fluid. Only a few renal corpuscles had major ultrastructural and structural alterations and no change in serum creatinine or creatinine clearance was observed. Contrarily, urinary albumin significantly increased after CLP and was associated with diffuse alteration in the glycocalyx of the GFB, which consisted in a decrease in syndecan-1 expression and in HA and sialic acids contents. Sialic acids were also changed in their structure, exhibiting a higher degree of acetylation.

Conclusions

In its initial phase, sepsis is associated with a significant alteration in the composition of the GFB-associated glycocalyx, with loss of GFB perm-selectivity as documented by albumin leakage into urine.

Decreases in podocin, CD2-associated protein (CD2AP) and tensin2 may be involved in albuminuria during septic acute renal failure

Podocytes have a peculiar structure constituting slit diaphragm (SD) and foot process (FP), and play essential roles in the glomerular filtration barrier. There is now ample evidence that SD- and FP-associated molecules, such as podocin and CD2-associated protein (CD2AP), are down-regulated during albuminuria of chronic kidney disease. However, it is still unclear whether these molecules are altered during acute renal failure (ARF) with albuminuria. Using lipopolysaccharide (LPS)-treated mice as a model of septic ARF, we provide evidence that the expression of SD- and FP-associated molecules becomes faint, along with albuminuria. In the LPS-treated mice, urinary albumin levels gradually increased, associated with the elevation of blood urea nitrogen levels, indicating the successful induction of albuminuria during septic ARF. In this pathological process, glomerular podocin expression became faint, especially at 36 hr post-LPS challenge (i.e., a peak of albuminuria). Likewise, LPS treatment led to a significant decrease in CD2AP, an anchorage between podocin and F-actin. With regard to this, tensin2 is a novel molecule that stabilizes F-actin extension. Interestingly, glomerular tensin2 expression levels were also decreased during the albuminuric phase, associated with losses of glomerular F-actin and synaptopodin under septic states. As a result, there were some lesions of podocytic FP effacement, as shown by electron microscopy. Based on these data, we emphasize the importance of concomitant decreases in podocin, CD2AP and tensin2 during septic ARF-associated proteinuria.