nephrin and Nephritis

Proteinuria results from the disruption of the glomerular filter that is composed of the fenestrated endothelium, glomerular basement membrane, and podocytes with their slit diaphragms. The delicate structure of the glomerular filter, especially the slit diaphragm, relies on the interplay of diverse cell surface proteins. Studying these cell surface proteins has so far been limited to in vitro studies or histologic analysis. Here, we present a murine in vivo biotinylation labeling method, which enables the study of glomerular cell surface proteins under physiologic and pathophysiologic conditions. This protocol contains information on how to perfuse mouse kidneys, isolate glomeruli, and perform endogenous immunoprecipitation of a protein of interest. Semi-quantitation of glomerular cell surface abundance is readily available with this novel method, and all proteins accessible to biotin perfusion and immunoprecipitation can be studied. In addition, isolation of glomeruli with or without biotinylation enables further analysis of glomerular RNA and protein as well as primary glomerular cell culture (i.e., primary podocyte cell culture).

Topics: Animals; Biotin; Kidney Glomerulus; Membrane Proteins; Mice, Inbred C57BL; Nephritis; Perfusion; Podocytes; Staining and Labeling

Injury of the glomerular filter causes proteinuria by disrupting the sensitive interplay of the glomerular protein network. To date, studies of the expression and trafficking of glomerular proteins have been mostly limited to in vitro or histologic studies. Here, we report a novel in vivo biotinylation assay that allows the quantification of surface expression of glomerular proteins in mice. Kidneys were perfused in situ with biotin before harvest. Afterwards glomeruli were isolated and lyzed. The protein of interest was separated by immunoprecipitation and the amount of surface-expressed protein was quantified by Western blot analysis with streptavidin staining. As proof-of-concept, we examined the presence of nephrin in the slit diaphragm in two well-established murine models of proteinuric kidney disease: nephrotoxic nephritis and adriamycin nephropathy. In proteinuric animals, significantly less nephrin was detected in the slit diaphragm. When proteinuria decreased once again during the course of disease, the amount of surface nephrin returned to the baseline. Our present results suggest that our assay is a valuable tool to study the glomerular filter in proteinuric kidney diseases. Note that the assay is not limited to proteins expressed in the slit diaphragm, and all surface proteins that are accessible to biotin perfusion and immunoprecipitation qualify for this analysis.

Topics: Albuminuria; Animals; Disease Models, Animal; Gene Expression; Kidney Diseases; Kidney Glomerulus; Male; Membrane Proteins; Mice; Nephritis; Proteinuria; Time Factors

ADP-ribosylation factor 6 (ARF6) is a small GTPase necessary for regulating cellular structure, motility, and vesicle trafficking. In several cellular systems, ARF6 was shown to regulate actin dynamics in coordination with Rac1, a Rho small GTPase. We examined the function of ARF6 in the kidney podocyte because Rac1 was implicated in kidney diseases involving this cell. We found that ARF6 expression was enriched in human podocytes and that it modulated podocyte cytoskeletal dynamics through a functional interaction with nephrin, an intercellular junction protein necessary for podocyte injury-induced signaling requiring activation by tyrosine phosphorylation of its cytoplasmic domain. ARF6 was necessary for nephrin activation-induced ruffling and focal adhesion turnover, possibly by altering Rac1 activity. In podocyte-specific Arf6 (ARF6_PodKO) knockout mice, ARF6 deficiency did not result in a spontaneous kidney developmental phenotype or proteinuria after aging. However, ARF6_PodKO mice exhibited distinct phenotypes in two in vivo glomerular injury models. In the protamine sulfate perfusion model, which induced acute podocyte effacement, ARF6_PodKO mice were protected from podocyte effacement. In the nephrotoxic serum nephritis model, which induced immune-complex mediated injury, ARF6_PodKO mice exhibited aggravated proteinuria. Together, these observations suggest that while ARF6 is necessary for nephrin tyrosine phosphorylation-induced cytoskeletal dynamics in cultured podocytes, ARF6 has pleotropic podocyte roles in vivo, where glomerular injury-specific mechanisms might activate distinct signaling pathways that dictate whether ARF6 activity is beneficial or deleterious for maintaining the integrity of the glomerular filtration barrier.

Topics: ADP-Ribosylation Factor 6; ADP-Ribosylation Factors; Animals; Female; Humans; Kidney; Membrane Proteins; Mice; Mice, Inbred C57BL; Mice, Knockout; Nephritis; Podocytes; Receptors, IgG; Signal Transduction

In most forms of glomerular diseases, loss of size selectivity by the kidney filtration barrier is associated with changes in the morphology of podocytes. The kidney filtration barrier is comprised of the endothelial lining, the glomerular basement membrane, and the podocyte intercellular junction, or slit diaphragm. The cell adhesion proteins nephrin and neph1 localize to the slit diaphragm and transduce signals in a Src family kinase Fyn-mediated tyrosine phosphorylation-dependent manner. Studies in cell culture suggest nephrin phosphorylation-dependent signaling events are primarily involved in regulation of actin dynamics and lamellipodium formation. Nephrin phosphorylation is a proximal event that occurs both during development and following podocyte injury. We hypothesized that abrogation of nephrin phosphorylation following injury would prevent nephrin-dependent actin remodeling and foot process morphological changes. Utilizing a biased screening approach, we found nonreceptor Src homology 2 (sh2) domain-containing phosphatase Shp2 to be associated with phosphorylated nephrin. We observed an increase in nephrin tyrosine phosphorylation in the presence of Shp2 in cell culture studies. In the human glomerulopathies minimal-change nephrosis and membranous nephropathy, there is an increase in Shp2 phosphorylation, a marker of increased Shp2 activity. Mouse podocytes lacking Shp2 do not develop foot process spreading when subjected to podocyte injury in vivo using protamine sulfate or nephrotoxic serum (NTS). In the NTS model, we observed a lack of foot process spreading in mouse podocytes with Shp2 deleted and smaller amounts of proteinuria. Taken together, these results suggest that Shp2-dependent signaling events are necessary for changes in foot process structure and function following injury.

Topics: Amino Acid Sequence; Animals; Disease Models, Animal; Gene Deletion; Humans; Kidney; Membrane Proteins; Mice, Inbred C57BL; Molecular Sequence Data; Nephritis; Phosphorylation; Podocytes; Protamines; Protein Interaction Maps; Protein Tyrosine Phosphatase, Non-Receptor Type 11; Tyrosine

The aim of the present study was to investigate the mechanisms underlying the effects of prednisone on adriamycin-induced nephritic rat kidney damage via the focal adhesion kinase (FAK)/receptor activator of nuclear factor-κB ligand (RANKL)/mitogen‑activated protein kinase (MAPK) signaling pathway. An adriamycin‑induced nephritic rat model was established to investigate these mechanisms. A total of 30 healthy male Sprague‑Dawley rats were randomly assigned to the normal, model or prednisone group. Samples of urine were collected over the course of 24 h at days 7, 14, and 28, and renal cortex tissue samples were harvested at days 14, and 28 following nephritic rat model establishment. The total urinary protein content was measured by biuret colorimetry. Pathological changes in the kidney tissue samples were observed using an electron microscope. The mRNA expressions levels of FAK, RANKL, p38, extracellular signal‑regulated kinase (ERK), c‑Jun N‑terminal kinase (JNK), and nephrin were then quantified by reverse transcription‑quantitative polymerase chain reaction. In addition, the protein expressions levels of FAK, RANKL, p38, ERK, JNK, phosphorylated (p)‑FAK, p‑ERK, and p‑JNK were quantified by western blotting. As compared with the normal group, the protein expression levels of FAK, RANKL, p-FAK, p38 and p-ERK in the model group were increased. In the prednisone group, the protein expression levels of p-ERK decreased, as compared with the normal group. In the prednisone group, the urinary protein levels, the protein expression levels of FAK, RANKL, p38, p-FAK, p-p38 and the mRNA expression levels of FAK, p38, RANKL, ERK, JNK decreased, as compared with the model group. In the prednisone group, the mRNA and protein expression levels of nephrin and the serum expression levels of RANKL increased, the serum expression levels of osteoprotegerin (OPG) were decreased, as compared with the model group. No significant changes in the protein expression levels of JNK were observed among the groups. These results suggested that prednisone is able to protect podocytes from apoptosis, and reduce urinary protein levels by inhibiting the FAK/RANKL/MAPK signaling pathway in kidney tissue samples. Serum prednisone may induce osteoporosis via the OPG/RANK/RANKL signaling pathway.

Topics: Animals; Antibiotics, Antineoplastic; Doxorubicin; Drug Evaluation, Preclinical; Focal Adhesion Kinase 1; Gene Expression; Kidney; Male; MAP Kinase Signaling System; Membrane Proteins; Mitogen-Activated Protein Kinases; Nephritis; Osteoprotegerin; Prednisone; Proteinuria; RANK Ligand; Rats, Sprague-Dawley

To investigate the effects of prednisone on the expressions of FAK and Pyk2 in the kidneys of rats with adriamycin-induced nephritis.. Thirty SD rats were randomized into normal control group, adriamycin-induced nephritic model group, and prednisone treatment group (n=10). Prednisone was administered at 10 mg/kg once daily in nephritic rats starting since the 7th day after adriamycin injection. Twenty-four-hour proteinuria was measured in the rats at different time points, and renal tissue histology was examined using transmission electron microscope. The expression levels of Pyk2, FAK and nephrin mRNA in the renal tissue were detected tested by RT-PCR, and the protein expressions of FAK, Pyk2, phosphorylated Pyk2 and phosphorylated FAK-Tyr397 were detected by Western blotting; immunohistochemistry was used for detecting nephrin protein expression in the kidney.. Compared with the normal control group, the rats with adriamycin-induced nephritis showed significantly increased proteinuria (P<0.01), which was obviously lowered by prednisone treatment (P<0.01). Transmission electron microscopy revealed extensive fusion of the foot processes of the podocytes in the model group. Prednisone treatment promoted nephrin expression in the kidney (P<0.05). Compared with the control group, the model and prednisone treated groups showed significantly lowered nephrin mRNA expression (P<0.01) but increased FAK mRNA expression (P<0.01), but prednisone-treated group had a higher nephrin mRNA expression than the model group (P<0.05). The model group exhibited significantly increased expressions of FAK total and phosphorylated proteins, P-FAK/FAK, and P-Pyk2/Pyk2 (P<0.01), which were all lowered in the treatment group (P<0.01). Correlation analysis suggested that the expressions of FAK mRNA, FAK, pFAK, Pyk2 mRNA and pPyk2/Pyk2 were positively correlated with proteinuria (r=0.819, 0.750, 0.838, 0.762, 0.934, respectively, P<0.01).. Adriamycin increases phosphorylated FAK and Pyk2 expressions to mediate kidney injury in rats. Prednisone inhibits Pyk2 and FAK activation, decreases proteinuria, and alleviates podocyte lesions to protect the glomerular filtration barrier.

Topics: Animals; Doxorubicin; Focal Adhesion Kinase 2; Kidney; Kidney Glomerulus; Membrane Proteins; Nephritis; Podocytes; Prednisone; Proteinuria; Rats; Rats, Sprague-Dawley; RNA, Messenger

An increasing number of clinical and animal model studies indicate that activation of the innate immune system and inflammatory mechanisms are important in the pathogenesis of diabetic nephropathy. Nucleotide-binding oligomerization domain containing 2 (NOD2), a member of the NOD-like receptor family, plays an important role in innate immune response. Here we explore the contribution of NOD2 to the pathogenesis of diabetic nephropathy and found that it was upregulated in kidney biopsies from diabetic patients and high-fat diet/streptozotocin-induced diabetic mice. Further, NOD2 deficiency ameliorated renal injury in diabetic mice. In vitro, NOD2 induced proinflammatory response and impaired insulin signaling and insulin-induced glucose uptake in podocytes. Moreover, podocytes treated with high glucose, advanced glycation end-products, tumor necrosis factor-α, or transforming growth factor-β (common detrimental factors in diabetic nephropathy) significantly increased NOD2 expression. NOD2 knockout diabetic mice were protected from the hyperglycemia-induced reduction in nephrin expression. Further, knockdown of NOD2 expression attenuated high glucose-induced nephrin downregulation in vitro, supporting an essential role of NOD2 in mediating hyperglycemia-induced podocyte dysfunction. Thus, NOD2 is one of the critical components of a signal transduction pathway that links renal injury to inflammation and podocyte insulin resistance in diabetic nephropathy.

Topics: Adult; Aged; Aged, 80 and over; Animals; Biomarkers; Blood Glucose; Cells, Cultured; Creatinine; Diabetes Mellitus, Experimental; Diabetic Nephropathies; Diet, High-Fat; Female; Glucose Transporter Type 4; Humans; Inflammation Mediators; Insulin; Insulin Resistance; Lipids; Male; MAP Kinase Signaling System; Membrane Proteins; Mice; Mice, Knockout; Middle Aged; Nephritis; Nod2 Signaling Adaptor Protein; Podocytes; Time Factors; Up-Regulation

Rapamycin (Rapa) is an immunosuppressant used to prevent rejection in recipients of renal transplants. Its clinical use is limited by de novo onset or exacerbation of preexisting proteinuria. In the present study, Rapa administration was started 14 days after induction of murine nephrotoxic serum nephritis (NTS) to study glomerular effects of this mammalian target of rapamycin (mTOR) inhibitor. Glomeruli were laser-microdissected, and real-time PCR was performed to assess effects on glomerular cells and the expression of inflammatory cytokines. Immunohistochemical stainings were performed to confirm mRNA data on the protein level. Compared with nephritic control animals, Rapa-treated mice developed significantly increased albuminuria. This was accompanied by a more prominent glomerular infiltration by CD4(+) T cells and macrophages. Glomerular mRNA expression profiling revealed increased levels of the proinflammatory cytokines interleukin-6 and tumor necrosis factor-α, and the chemokines monocyte chemoattractant protein-1 and macrophage inflammatory protein-1β and their cognate macrophage-associated receptors CCR2 and CCR5 in the Rapa-treated animals. Furthermore, there were elevated glomerular transcription levels of the regulatory T cell phenotype transcription factor Foxp3. No differences in the glomerular expression of the podocyte marker nephrin or the endothelial cell marker CD31 were observed on the mRNA or protein level. In conclusion, our data indicate that Rapa-induced proteinuria in NTS is a result of the activation of the innate immune system rather than a direct toxicity to podocytes or glomerular endothelial cells.

Topics: Animals; Gene Expression Regulation; Immunity, Innate; Inflammation Mediators; Male; Membrane Proteins; Mice; Mice, Inbred C57BL; Nephritis; Platelet Endothelial Cell Adhesion Molecule-1; Proteinuria; RNA, Messenger; Sirolimus; TOR Serine-Threonine Kinases; Vascular Endothelial Growth Factor A

Studies suggest that soluble epoxide hydrolase (sEH) inhibition reduces end-organ damage in cardiovascular diseases. We hypothesize that sEH gene (Ephx2) knockout (KO) improves endothelial function and reduces renal injury in streptozotocin-induced diabetes. After 6 wk of diabetes, afferent arteriolar relaxation to acetylcholine was impaired in diabetic wild-type (WT) mice, as the maximum relaxation was 72% of baseline diameter in the WT but only 31% in the diabetic mice. Ephx2 KO improved afferent arteriolar relaxation to acetylcholine in diabetes as maximum relaxation was 58%. Urinary monocyte chemoattractant protein-1 (MCP-1) excretion significantly increased in diabetic WT mice compared with control (868 ± 195 vs. 31.5 ± 7 pg/day), and this increase was attenuated in diabetic Ephx2 KO mice (420 ± 98 pg/day). The renal phospho-IKK-to-IKK ratio and nuclear factor-κB were significantly decreased, and hemeoxygenase-1 (HO-1) expression increased in diabetic Ephx2 KO compared with diabetic WT mice. Renal NADPH oxidase and urinary thiobarbituric acid reactive substances excretion were reduced in diabetic Ephx2 KO compared with diabetic WT mice. Albuminuria was also elevated in diabetic WT mice compared with control (170 ± 43 vs. 37 ± 13 μg/day), and Ephx2 KO reduced this elevation (50 ± 15 μg/day). Inhibition of sEH using trans-4-[4-(3-adamantan-1-yl-ureido)-cyclohexyloxy]-benzoic acid (tAUCB) also reduced renal inflammation and injury in diabetic WT mice. Furthermore, inhibition of HO with stannous mesoporphyrin negated the reno-protective effects of tAUCB or Ephx2 KO during diabetes. These data demonstrate that Ephx2 KO improves endothelial function and reduces renal injury during diabetes. Additionally, our data also suggest that activation of HO-1 contributes to improved renal injury in diabetic Ephx2 KO mice.

Topics: Albuminuria; Animals; Chemokine CCL2; Collagen; Diabetes Mellitus, Experimental; Diabetes Mellitus, Type 1; Diabetic Nephropathies; Dose-Response Relationship, Drug; Endothelium, Vascular; Epoxide Hydrolases; Heme Oxygenase-1; I-kappa B Kinase; Inflammation Mediators; Kidney; Male; Membrane Proteins; Mice; Mice, Inbred C57BL; Mice, Knockout; NADPH Oxidases; Nephritis; Oxidative Stress; Phosphorylation; Thiobarbituric Acid Reactive Substances; Time Factors; Transcription Factor RelA; Vasodilation; Vasodilator Agents

Inhibition of soluble epoxide hydrolase (sEH) has been shown to be renal protective in rat models of salt-sensitive hypertension. Here, we hypothesize that targeted disruption of the sEH gene (Ephx2) prevents both renal inflammation and injury in deoxycorticosterone acetate plus high salt (DOCA-salt) hypertensive mice. Mean arterial blood pressure (MAP) increased significantly in the DOCA-salt groups, and MAP was lower in Ephx2-/- DOCA-salt (129 +/- 3 mmHg) compared with wild-type (WT) DOCA-salt (145 +/- 2 mmHg) mice. Following 21 days of treatment, WT DOCA-salt urinary MCP-1 excretion increased from control and was attenuated in the Ephx2-/- DOCA-salt group. Macrophage infiltration was reduced in Ephx2-/- DOCA-salt compared with WT DOCA-salt mice. Albuminuria increased in WT DOCA-salt (278 +/- 55 microg/day) compared with control (17 +/- 1 microg/day) and was blunted in the Ephx2-/- DOCA-salt mice (97 +/- 23 microg/day). Glomerular nephrin expression demonstrated an inverse relationship with albuminuria. Nephrin immunofluorescence was greater in the Ephx2-/- DOCA-salt group (3.4 +/- 0.3 RFU) compared with WT DOCA-salt group (1.1 +/- 0.07 RFU). Reduction in renal inflammation and injury was also seen in WT DOCA-salt mice treated with a sEH inhibitor {trans-4-[4-(3-adamantan-1-yl-ureido)-cyclohexyloxy]-benzoic acid; tAUCB}, demonstrating that the C-terminal hydrolase domain of the sEH enzyme is responsible for renal protection with DOCA-salt hypertension. These data demonstrate that Ephx2 gene deletion decreases blood pressure, attenuates renal inflammation, and ameliorates glomerular injury in DOCA-salt hypertension.

Topics: Albuminuria; Animals; Benzoates; Blood Pressure; Chemokine CCL2; Desoxycorticosterone; Disease Models, Animal; Enzyme Inhibitors; Epoxide Hydrolases; Gene Deletion; Hypertension; Kidney Glomerulus; Macrophages; Male; Membrane Proteins; Mice; Mice, Inbred C57BL; Mice, Knockout; Nephritis; Protein Structure, Tertiary; Sodium Chloride, Dietary; Time Factors; Urea

Sustained proteinuria is a major factor leading to kidney fibrosis and end-stage renal failure. Tubular epithelial cells are believed to play a crucial role in this process by producing mediators leading to fibrosis and inflammation. Congenital nephrotic syndrome of the Finnish type (NPHS1) is a genetic disease caused by mutations in a podocyte protein nephrin, which leads to constant heavy proteinuria from birth. In this work we studied the tubulointerstitial changes that occur in NPHS1 kidneys during infancy.. The pathologic lesions and expression of profibrotic and proinflammatory factors in nephrectomized NPHS1 kidneys were studied by immunohistochemistry, Western blotting, and cytokine antibody array. Oxidative stress in kidneys was assessed by measurement of gluthatione redox state.. The results indicated that (1) severe tubulointerstitial lesions developed in NPHS1 kidneys during infancy; (2) tubular epithelial cells did not show transition into myofibroblasts as studied by the expression of vimentin, alpha-smooth muscle actin (alpha-SMA), collagen, and matrix metalloproteinases 2 and 9 (MMP-2 and -9); (3) the most abundant chemokines in NPHS1 tissue were neutrophil activating protein-2 (NAP-2), macrophage inhibiting factor (MIF), and monocyte chemoattractant protein-1 (MCP-1); (4) monocyte/macrophage cells expressing CD14 antigen were the major inflammatory cells invading the interstitium; (5) the arteries and arterioles showed intimal hypertrophy, but the microvasculature in NPHS1 kidneys remained quite normal; and (6) excessive oxidative stress was evident in NPHS1 kidneys.. Heavy proteinuria in NPHS1 kidneys was associated with interstitial fibrosis, inflammation, and oxidative stress. The tubular epithelial cells, however, were resistant to proteinuria and did not show epithelial-mesenchymal transition.

Topics: Capillaries; Chemokines; Child, Preschool; Cytokines; Fibrosis; Humans; Infant; Kidney Tubules; Macrophages; Membrane Proteins; Monocytes; Nephritis; Nephrotic Syndrome; Oxidative Stress; Phenotype; Proteinuria