A new view of macula densa cell microanatomy.

Although macula densa (MD) cells are chief regulatory cells in the nephron with unique microanatomical features, they have been difficult to study in full detail due to their inaccessibility and limitations in earlier microscopy techniques. The present study used a new mouse model with a comprehensive imaging approach to visualize so far unexplored microanatomical features of MD cells, their regulation, and functional relevance. MD-GFP mice with conditional and partial induction of green fluorescent protein (GFP) expression, which specifically and intensely illuminated only single MD cells, were used with fluorescence microscopy of fixed tissue and live MD cells in vitro and in vivo with complementary electron microscopy of the rat, rabbit, and human kidney. An elaborate network of major and minor cell processes, here named maculapodia, were found at the cell base, projecting toward other MD cells and the glomerular vascular pole. The extent of maculapodia showed upregulation by low dietary salt intake and the female sex. Time-lapse imaging of maculapodia revealed highly dynamic features including rapid outgrowth and an extensive vesicular transport system. Electron microscopy of rat, rabbit, and human kidneys and three-dimensional volume reconstruction in optically cleared whole-mount MD-GFP mouse kidneys further confirmed the presence and projections of maculapodia into the extraglomerular mesangium and afferent and efferent arterioles. The newly identified dynamic and secretory features of MD cells suggest the presence of novel functional and molecular pathways of cell-to-cell communication in the juxtaglomerular apparatus between MD cells and between MD and other target cells.NEW & NOTEWORTHY This study illuminated a physiologically regulated dense network of basal cell major and minor processes (maculapodia) in macula densa (MD) cells. The newly identified dynamic and secretory features of these microanatomical structures suggest the presence of novel functional and molecular pathways of cell-to-cell communication in the juxtaglomerular apparatus between MD and other target cells. Detailed characterization of the function and molecular details of MD cell intercellular communications and their role in physiology and disease warrant further studies.

Modulation of Macrophage Polarization by Human Glomerular Mesangial Cells in Response to the Stimuli in Renal Microenvironment.

Mesangial cell (MC) activation and macrophage infiltration are 2 major events closely related with each other in mesangial proliferative glomerulonephritis. In the anti-Thy 1 nephritis model, macrophages mediate the damage and also the expansion of mesangium through secreting various inflammatory factors; however, in glomerular microenvironment how MCs affect macrophage activity in the presence of various stimuli have not yet been understood. In the present study, we found that resting human MCs (HMCs) constitutively expressed chemokine [C-C motif] ligand 2 (CCL-2) and interleukin (IL)-6 and induced M2 polarization of macrophages in the coculture system. HMC proliferation and migration and expression of IL-6, CCL-2, and macrophage colony-stimulating factor in HMCs were enhanced after platelet-derived growth factor (PDGF)-BB stimulation, among which CCL-2 was responsible for inducing the M2 polarization of macrophages. Furthermore, PDGF-BB-stimulated HMCs alleviated the classical activation of macrophages and drove more intensified M2 polarization of macrophages than resting HMCs did. However, lipopolysaccharide and interferon-γ (IFN-γ) stimulated HMCs maintained the M1 phenotype of cocultured macrophages. In conclusion, MCs actively participated in glomerular inflammation through influencing macrophage polarization. The interplay between MCs and infiltrated macrophages is finely modulated by secretory factors such as PDGF-BB and IFN-γ in response to the renal inflammatory microenvironment.

Nephronectin Regulates Mesangial Cell Adhesion and Behavior in Glomeruli.

A critical aspect of kidney function occurs at the glomerulus, the capillary network that filters the blood. The glomerular basement membrane (GBM) is a key component of filtration, yet our understanding of GBM interactions with mesangial cells, specialized pericytes that provide structural stability to glomeruli, is limited. We investigated the role of nephronectin (Npnt), a GBM component and known ligand of α8ß1 integrin. Immunolocalization and in situ hybridization studies in kidneys of adult mice revealed that nephronectin is produced by podocytes and deposited into the GBM. Conditional deletion of Npnt from nephron progenitors caused a pronounced increase in mesangial cell number and mesangial sclerosis. Nephronectin colocalized with α8ß1 integrin to novel, specialized adhesion structures that occurred at sites of mesangial cell protrusion at the base of the capillary loops. Absence of nephronectin disrupted these adhesion structures, leading to mislocalization of α8ß1. Podocyte-specific deletion of Npnt also led to mesangial sclerosis in mice. These results demonstrate a novel role for nephronectin and α8ß1 integrin in a newly described adhesion complex and begin to uncover the molecular interactions between the GBM and mesangial cells, which govern mesangial cell behavior and may have a role in pathologic states.

Persistent and inducible neogenesis repopulates progenitor renin lineage cells in the kidney.

Renin lineage cells (RLCs) serve as a progenitor cell reservoir during nephrogenesis and after renal injury. The maintenance mechanisms of the RLC pool are still poorly understood. Since RLCs were also identified as a progenitor cell population in bone marrow we first considered that these may be their source in the kidney. However, transplantation experiments in adult mice demonstrated that bone marrow-derived cells do not give rise to RLCs in the kidney indicating their non-hematopoietic origin. Therefore we tested whether RLCs develop in the kidney through neogenesis (de novo differentiation) from cells that have never expressed renin before. We used a murine model to track neogenesis of RLCs by flow cytometry, histochemistry, and intravital kidney imaging. During nephrogenesis RLCs first appear at e14, form a distinct population at e16, and expand to reach a steady state level of 8-10% of all kidney cells in adulthood. De novo differentiated RLCs persist as a clearly detectable population through embryogenesis until at least eight months after birth. Pharmacologic stimulation of renin production with enalapril or glomerular injury induced the rate of RLC neogenesis in the adult mouse kidney by 14% or more than three-fold, respectively. Thus, the renal RLC niche is constantly filled by local de novo differentiation. This process could be stimulated consequently representing a new potential target to beneficially influence repair and regeneration after kidney injury.

Phosphoinositide 3-kinase/protein kinase B/periostin mediated platelet-derived growth factor-induced cell proliferation and extracellular matrix production in lupus nephritis.

In the present study, the effect and mechanism of periostin on renal proliferation and extracellular matrix accumulation of lupus mice were investigated. MRL /lpr mice, known as lupus mice, were revealed to show enhanced periostin, proliferating cell nuclear antigen (PCNA), and extracellular matrix accumulation in the kidney accompanied by increased serum platelet-derived growth factor (PDGF). Again, cultured mouse mesangial cells (MMCs) were treated with PDGF, then periostin, and PCNA and secreted fibronectin were detected. The results showed that intracellular periostin and PCNA were respectively enhanced by 2.691 and 2.308 times in PDGF-treated MMC cells at 6 h after stimulation. In addition, secreted fibronectin was increased by 1.442 times. Next, the transfection of periostin shRNA vector in PDGF-stimulated MMC cells effectively suppressed periostin, PCNA and secreted fibronectin by 45.27%, 47.75%, and 39.95%, compared with PDGF-stimulated cells transfected with control vector. Furthermore, it was found that PDGF increased the expression of phospho-Akt (Ser 473) from 30 min to 6 h in MMCs. LY294002 effectively inhibited phospho-Akt (Ser 473) expression caused by PDGF stimulation. Then, periostin, PCNA, and fibronectin were respectively decreased by 69.61%, 46.00%, and 46.20%. In the end, phosphoinositide 3-kinase/protein kinase B/periostin was suggested to mediate PDGF-induced cell proliferation and extracellular matrix production in lupus nephritis.

Lipoprotein X Causes Renal Disease in LCAT Deficiency.

Human familial lecithin:cholesterol acyltransferase (LCAT) deficiency (FLD) is characterized by low HDL, accumulation of an abnormal cholesterol-rich multilamellar particle called lipoprotein-X (LpX) in plasma, and renal disease. The aim of our study was to determine if LpX is nephrotoxic and to gain insight into the pathogenesis of FLD renal disease. We administered a synthetic LpX, nearly identical to endogenous LpX in its physical, chemical and biologic characteristics, to wild-type and Lcat-/- mice. Our in vitro and in vivo studies demonstrated an apoA-I and LCAT-dependent pathway for LpX conversion to HDL-like particles, which likely mediates normal plasma clearance of LpX. Plasma clearance of exogenous LpX was markedly delayed in Lcat-/- mice, which have low HDL, but only minimal amounts of endogenous LpX and do not spontaneously develop renal disease. Chronically administered exogenous LpX deposited in all renal glomerular cellular and matrical compartments of Lcat-/- mice, and induced proteinuria and nephrotoxic gene changes, as well as all of the hallmarks of FLD renal disease as assessed by histological, TEM, and SEM analyses. Extensive in vivo EM studies revealed LpX uptake by macropinocytosis into mouse glomerular endothelial cells, podocytes, and mesangial cells and delivery to lysosomes where it was degraded. Endocytosed LpX appeared to be degraded by both human podocyte and mesangial cell lysosomal PLA2 and induced podocyte secretion of pro-inflammatory IL-6 in vitro and renal Cxl10 expression in Lcat-/- mice. In conclusion, LpX is a nephrotoxic particle that in the absence of Lcat induces all of the histological and functional hallmarks of FLD and hence may serve as a biomarker for monitoring recombinant LCAT therapy. In addition, our studies suggest that LpX-induced loss of endothelial barrier function and release of cytokines by renal glomerular cells likely plays a role in the initiation and progression of FLD nephrosis.

CagA promotes proliferation and secretion of extracellular matrix by inhibiting signaling pathway of apoptosis in rat glomerular mesangial cells.

Cytotoxin-associated antigen A (CagA), a major virulence factor of Helicobacter pylori (Hp), is associated with the pathogenesis of peptic ulcer and gastric cancer. Recent researches demonstrated that Hp exists in palatine tonsil in all studied IgA nephropathy (IgAN) patients, most of which were CagA-positive, suggesting that CagA may be a causative pathogenic factor of IgAN. However, the underlying molecular mechanisms and signaling pathway are still largely unclear. In the present study, CCK8 assay, enzyme-linked immunosorbent assay, and immunohistochemistry were performed to investigate the effect of CagA on cell proliferation and extracellular matrix secretion in rat glomerular mesangial cells. RT-PCR and western blotting were used to reveal the potential signaling pathway. Rat glomerular mesangial cells were treated with recombinant CagA protein for 72 h, in a dose- and time-dependent manner. We found that CagA promoted cell proliferation and extracellular matrix secretion by inhibiting signaling pathway of apoptosis. Taken together, these findings suggested that CagA induced cellular injury in glomerular mesangium by proliferation and secretion of extracellular matrix, and may play an important role in pathogenesis of IgAN.

Proliferation and Cytokine Production of Human Mesangial Cells Stimulated by Secretory IgA Isolated from Patients with IgA Nephropathy.

BACKGROUND/AIMS: IgA nephropathy (IgAN) is the most common form of primary glomerulonephritis, and often aggravates by mucosal infection. Secretory IgA (SIgA) is the dominant immunoglobulin in mucosal immunity, and is deposited in the mesangium in IgAN. The biological effects of SIgA on mesangial cells are poorly understood. METHODS: Deposition of SIgA in frozen renal sections from IgAN patients was detected and the association between deposition of SIgA and patients characteristics was analyzed. The biological effects of SIgA and polymeric IgA (pIgA) on human renal mesangial cells were compared. We also studied the molecular mechanism of microRNA regulating the inflammatory effects of SIgA on mesangial cells. RESULTS: Fifty-five of 176 patients had SIgA deposition with higher incidence of infection history and hematuria, lower serum cystatin C, ß2 microglobulin, blood urea nitrogen and T-grade in the Oxford classification, compared with patients without SIgA deposition. SIgA stimulated mesangial cells at a higher ratio of proliferation and higher production of interleukin (IL)-6, IL-8, monocyte chemotactic protein 1, transforming growth factor-ß1 and fibronectin, compared with SIgA from healthy volunteers. The proliferation and cytokines production in mesangial cells stimulated by SIgA were significantly lower than that stimulated by pIgA. miR- 16 targeted the 3'-untranslated region of IL-6 and suppressed its translation in mesangial cells induced by SIgA. CONCLUSIONS: The biological effects of SIgA on mesangial cells differ from those of pIgA. SIgA stimulates mesangial cell proliferation and production of proinflammatory cytokines. IL-6 production is regulated by miR-16 in mesangial cells.

Avances en el tratamiento de cáncer de próstata resistente a la castración: énfasis en nuevas terapias hormonales / Advances in the treatment of castration-resistant prostate cancer: emphasis in new hormonal therapies

Prostate cancer represents the second cancer-related cause of death in North American and Chilean men. The main treatment for incurable stages of disease is surgical or pharmacological castration. However, with time and despite the addition of anti-androgens, the disease progresses to a clinical state that has been commonly referred to as “hormone refractory”. In recent years, the concept of hormone refractoriness has been challenged and replaced by “castration resistance”, acknowledging that further and optimal hormonal manipulation can be attained, beyond achieving testosterone levels at castration range. The purpose of this review is to summarize the recent therapeutic breakthroughs in the management of metastatic castrate resistant prostate cancer (mCRPC), with greater emphasis in the newer hormonal therapy agents such as Abiraterone and Enzalutamide. Future combination and sequential treatment strategies are contextualized in the current era of personalized cancer medicine and genomic characterization of prostate cancer.

Metformin inhibits nuclear factor-κB activation and inflammatory cytokines expression induced by high glucose via adenosine monophosphate-activated protein kinase activation in rat glomerular mesangial cells in vitro.

BACKGROUND: The renoprotective mechanisms of adenosine monophosphate (AMP)-activated protein kinase (AMPK) agonist - metformin have not been stated clearly. We hypothesized that metformin may ameliorate inflammation via AMPK interaction with critical inflammatory cytokines. The aim of this study was to observe the effects of metformin on expression of nuclear factor-κB (NF-κB), monocyte chemoattractant protein-1 (MCP-1), intercellular adhesion molecule-1 (ICAM-1) and transforming growth factor-beta 1 (TGF-ß1) induced by high glucose (HG) in cultured rat glomerular mesangial cells (MCs). METHODS: MCs were cultured in the medium with normal concentration glucose (group NG, 5.6 mmol/L), high concentration glucose (group HG, 25 mmol/L) and different concentrations of metformin (group M1, M2, M3). After 48-hour exposure, the supernatants and MCs were collected. The expression of NF-κB, MCP-1, ICAM-1, and TGF-ß1 mRNA was analyzed by real time polymerase chain reaction. Western blotting was used to detect the expression of AMPK, phospho-Thr-172 AMPK (p-AMPK), NF-κB p65, MCP-1, ICAM-1, and TGF-ß1 protein. RESULTS: After stimulated by HG, the expression of NF-κB, MCP-1, ICAM-1, TGF-ß1 mRNA and protein of MCs in group HG increased significantly compared with group NG (P < 0.05). Both genes and protein expression of NF-κB, MCP-1, ICAM-1, TGF-ß1 of MCs induced by high glucose were markedly reduced after metformin treatment in a dose-dependent manner (P < 0.05). The expression of p-AMPK increased with the rising of metformin concentration, presenting the opposite trend, while the level of total-AMPK protein was unchanged with exposure to HG or metformin. Conlusion Metformin can suppress the expression of NF-κB, MCP-1, ICAM-1 and TGF-ß1 of glomerular MCs induced by high glucose via AMPK activation, which may partly contribute to its reno-protection.

Downregulation of connective tissue growth factor by LPS/IFN-γ-induced nitric oxide is reversed by aristolochic acid treatment in glomerular mesangial cells via STAT-1α and NF-κB signaling.

Aristolochic acid (AA) is a common cause of Chinese herb nephropathy. The mechanisms involved in the pathogenesis of AA nephropathy (AAN) are intricate. One well-documented effect of AA in the kidney is its pro-fibrotic activity. Nitric oxide (NO), a messenger gas generated from l-arginine, is the product of nitric oxide synthase (NOS). NO is involved in renal hemodynamics and exerts cytoprotective effects against renal injury. In the present study, the role of NO in AAN was investigated in MES-13 cells, a glomerular mesangial cell line. NO endogenously generated by the induction of inducible nitric oxide synthase (iNOS) with lipopolysaccharide (LPS)/interferon-γ (IFN-γ) significantly downregulated connective tissue growth factor (CTGF) protein expression in MES-13 cells. AA significantly suppressed LPS/IFN-γ-induced NO production and reversed CTGF expression that was downregulated by LPS/IFN-γ. AA decreased iNOS gene and protein expressions in a concentration-dependent manner. AA caused declines in LPS/IFN-γ-induced signal transducer and activator of transcription-1α (STAT-1α) phosphorylation and interferon response factor-1 (IRF-1) mRNA expression. Furthermore, AA attenuated IκB phosphorylation and reduced NF-κB translocation to the nuclear fraction. Taken together, our data indicate that AA reversed the CTGF expression inhibited by LPS/IFN-γ treatment via suppression of NO and iNOS expressions in MES-13 cells through inhibition of the JAK/STAT-1α and NF-κB signaling pathways. NO potentially exerts antifibrotic activity by down regulation of CTGF in MES-13 cells and inhibition of the iNOS gene by AA might partially account for the fibrotic effects of AA in nephropathy.

Sublytic C5b-9 induces IL-6 and TGF-ß1 production by glomerular mesangial cells in rat Thy-1 nephritis through p300-mediated C/EBPß acetylation.

CCAAT/enhancer-binding protein (C/EBPß)-enhanced IL-6 and TGF-ß1 promoter activity and p300-mediated C/EBPß acetylation were involved in up-regulation of IL-6 and TGF-ß1 expression in GMCs attacked by sublytic C5b-9. In detail, the elements of C/EBPß binding to rat IL-6 and TGF-ß1 promoter and 3 acetylated sites of rat C/EBPß protein were first revealed. Furthermore, silencing the p300 or C/EBPß gene in rat kidney significantly reduced the production of IL-6 and TGF-ß1 and renal lesions in Thy-1N rats. Together, these data indicate that the mechanism of IL-6 and TGF-ß1 production in renal tissue of Thy-1N rats is associated with sublytic C5b-9 up-regulated p300 and p300-mediated C/EBPß acetylation as well as C/EBPß-activated IL-6 and TGF-ß1 genes.

[Effect of exendin-4 on monocyte chemoattractant protein-1 expression in cultured rat glomerular mesangial cells induced by tumor necrosis factor-α in vitro].

OBJECTIVE: To investigate the effect of exendin-4 on the expression of monocyte chemoattractant protein-1 (MCP-1) and fibronectin (FN) in rat glomerular mesangial cells in vitro. METHODS: Rat glomerular mesangial cells were divided into 5 groups, namely control group, tumor necrosis factor-α (TNF-α) group (10 ng/ml), TNF-α (10 ng/ml)+E1 (1 nmol/L exendin-4) group, TNF-α (10 ng/ml)+E5 (5 nmol/L exendin-4) group, and TNF-α (10 ng/ml)+E10 (10 nmol/L exendin-4) group. After cultured 24 h or 48 h, RNA were extracted to determine the expression of MCP-1 with real-time PCR, the supernatant were collected to determine the expression of MCP-1 and FN with ELISA. RESULTS: Compared with control group, the cells treated with TNF-α for 24 h showed significantly increase the expression of MCP-1 and FN (P<0.01), exendin-4 significantly reduced the expression of MCP-1 and FN in TNF-α+E5 group and TNF-α+E10 group (P<0.05). After 48h incubation, the expression of MCP-1 and FN increased significantly in TNF-α group (P<0.01), which was lowered by exendin-4 in TNF-α+E1,TNF-α+E5 and TNF-α+E10 groups (P<0.05). CONCLUSION: Exendin-4 has an intrinsic capability to concentration- and time-dependently inhibit TNF-α-induced expression of MCP-1 and FN in rat mesangial cells, suggesting the beneficial effect of exendin-4 in preventing and treating diabetic nephropathy.

Amadori products promote cellular senescence activating insulin-like growth factor-1 receptor and down-regulating the antioxidant enzyme catalase.

Activation of the insulin growth factor receptor-1 signaling pathways has been largely related to the aging process. Amadori products are produced in pathological conditions such as diabetes and aging, and are potentially involved in diabetic nephropathy or age-associated decline of renal function. We hypothesize that Amadori products induce senescence in primary human mesangial cells through the activation of IGF-1 receptor and investigate, in the present work, the intracellular mechanism involved after this activation. We treated cultured human mesangial cells with glycated albumin, one of the most abundant Amadori product, and senescence was assessed by determining the senescence associated ß-galactosidase activity and the expression of the cell cycle regulators p53 and p21. We demonstrated that prolonged exposition (more than 24h) to glycated albumin induced senescence and, in parallel, incremented the release of IGF-1 and the activation of the IGF-1 receptor. Inhibition of the IGF-1 activation prevented the GA induced senescence. Activation of IGF-1R, after GA addition, promoted a reduction in the catalase content through the constitutive activation of Ras and erk1/2 proteins which were, in turn, responsible of the observed GA-induced senescence. In conclusion, we propose that the Amadori product, glycated albumin, promotes premature cell senescence in mesangial cells through the activation of the IGF-1 receptor and the subsequent reduction in the antioxidant enzyme catalase.

Cadmium affects focal adhesion kinase (FAK) in mesangial cells: involvement of CaMK-II and the actin cytoskeleton.

The toxic metal ion cadmium (Cd(2+)) induces pleiotropic effects on cell death and survival, in part through effects on cell signaling mechanisms and cytoskeletal dynamics. Linking these phenomena appears to be calmodulin-dependent activation of the Ca(2+)/calmodulin-dependent protein kinase II (CaMK-II). Here we show that interference with the dynamics of the filamentous actin cytoskeleton, either by stabilization or destabilization, results in disruption of focal adhesions at the ends of organized actin structures, and in particular the loss of vinculin and focal adhesion kinase (FAK) from the contacts is a result. Low-level exposure of renal mesangial cells to CdCl2 disrupts the actin cytoskeleton and recapitulates the effects of manipulation of cytoskeletal dynamics with biological agents. Specifically, Cd(2+) treatment causes loss of vinculin and FAK from focal contacts, concomitant with cytoskeletal disruption, and preservation of cytoskeletal integrity with either a calmodulin antagonist or a CaMK-II inhibitor abrogates these effects of Cd(2+). Notably, inhibition of CaMK-II decreases the migration of FAK-phosphoTyr925 to a membrane-associated compartment where it is otherwise sequestered from focal adhesions in a Cd(2+)-dependent manner. These results add further insight into the mechanism of the CaMK-II-dependent effects of Cd(2+) on cellular function.

Dipeptidyl peptidase IV regulates proliferation of preglomerular vascular smooth muscle and mesangial cells.

The purpose of this study was to investigate the role of dipeptidyl peptidase IV in regulating the effects of 2 of its substrates, neuropeptide Y(1-36) and peptide YY(1-36), on proliferation of and collagen production by preglomerular vascular smooth muscle and glomerular mesangial cells from spontaneously hypertensive and normotensive rats. In cells from hypertensive rats, neuropeptide Y(1-36) and peptide YY(1-36) stimulated [(3)H]-thymidine incorporation (cell proliferation index), cell number, and [(3)H]-proline incorporation (index of collagen synthesis); and sitagliptin (dipeptidyl peptidase IV inhibitor) significantly enhanced most of these effects. Neuropeptide Y(3-36) and peptide YY(3-36) (products of dipeptidyl peptidase IV) had little effect on [(3)H]-thymidine incorporation, and sitagliptin did not enhance the effects of either peptide. BIBP3226 (Y(1) receptor antagonist) blocked the effects of neuropeptide Y(1-36) and peptide YY(1-36) on [(3)H]-thymidine incorporation in the absence and presence of sitagliptin. Neuropeptide Y(1-36) and peptide YY(1-36) stimulated [(3)H]-thymidine and [(3)H]-proline incorporation and cell number in cells from normotensive rats; however, the effects were weak and mostly not affected by sitagliptin. Real-time PCR and Western blotting showed similar dipeptidyl peptidase IV mRNA and protein levels in cells from hypertensive versus normotensive rats, with greater levels in smooth muscle versus mesangial cells. Both cell types converted peptide YY(1-36) to peptide YY(3-36) in a concentration-dependent manner that was attenuated by sitagliptin, and dipeptidyl peptidase IV activity was greater in smooth muscle versus mesangial cells. In conclusion, dipeptidyl peptidase IV inhibitors might entail a risk of renal dysfunction because of abnormal proliferation of cells in the preglomerular microcirculation and glomeruli.

Guanylyl cyclase/natriuretic peptide receptor-A signaling antagonizes the vascular endothelial growth factor-stimulated MAPKs and downstream effectors AP-1 and CREB in mouse mesangial cells.

Along with its natriuretic, diuretic, and vasodilatory properties, atrial natriuretic peptide (ANP), and its guanylyl cyclase/natriuretic peptide receptor-A (GC-A/NPRA) exhibit an inhibitory effect on cell growth and proliferation. However, the signaling pathways mediating this inhibition are not well understood. The objective of this study was to determine the effect of ANP-NPRA system on mitogen-activated protein kinases (MAPKs) and the downstream proliferative transcription factors involving activating protein-1 (AP-1) and cAMP-response element binding protein (CREB) in agonist-stimulated mouse mesangial cells (MMCs). We found that ANP inhibited vascular endothelial growth factor (VEGF)-stimulated phosphorylation of MAPKs (Erk1, Erk2, JNK, and p38), to a greater extent in NPRA-transfected cells (50-60 %) relative to vector-transfected cells (25-30 %). The analyses of the phosphorylated transcription factors revealed that ANP inhibited VEGF-stimulated activation of CREB, and the AP-1 subunits (c-jun and c-fos). Gel shift assays demonstrated that ANP inhibited VEGF-stimulated AP-1 and CREB DNA-binding ability by 67 and 62 %, respectively. The addition of the protein kinase G (PKG) inhibitor, KT-5823, restored the VEGF-stimulated activation of MAPKs, AP-1, and CREB, demonstrating the integral role of cGMP/PKG signaling in NPRA-mediated effects. Our results delineate the underlying mechanisms through which ANP-NPRA system exerts an inhibitory effect on MAPKs and down-stream effector molecules, AP-1, and CREB, critical for cell growth and proliferation.

Suppression of adiponectin by aberrantly glycosylated IgA1 in glomerular mesangial cells in vitro and in vivo.

The pathogenesis of IgA nephropathy (IgAN) may be associated with the mesangial deposition of aberrantly glycosylated IgA1. To identify mediators affected by aberrantly glycosylated IgA1 in cultured human mesangial cells (HMCs), we generated enzymatically modified desialylated and degalactosylated (deSial/deGal) IgA1. The state of deglycosylated IgA1 was confirmed by lectin binding to Helix aspersa (HAA) and Sambucus nigra (SNA). In the cytokine array analysis, 52 proteins were upregulated and 34 were downregulated in HMCs after stimulation with deSial/deGal IgA1. Among them, the secretion of adiponectin was suppressed in HMCs after stimulation with deSial/deGal IgA1. HMCs expressed mRNAs for adiponectin and its type 1 receptor, but not the type 2 receptor. Moreover, we revealed a downregulation of adiponectin expression in the glomeruli of renal biopsy specimens from patients with IgAN compared to those with lupus nephritis. We also demonstrated that aberrantly glycosylated IgA1 was deposited in the mesangium of patients with IgAN by dual staining of HAA and IgA. Moreover, the urinary HAA/SNA ratio of lectin binding was significantly higher in IgAN compared to other kidney diseases. Since adiponectin has anti-inflammatory effects, including the inhibition of adhesion molecules and cytokines, these data suggest that the local suppression of this adipokine by aberrantly glycosylated IgA1 could be involved in the regulation of glomerular inflammation and sclerosis in IgAN.

The transcription factor ETS-1 regulates angiotensin II-stimulated fibronectin production in mesangial cells.

Angiotensin II (ANG II) produced as result of activation of the renin-angiotensin system (RAS) plays a critical role in the pathogenesis of chronic kidney disease via its hemodynamic effects on the renal microcirculation as well as by its nonhemodynamic actions including the production of extracellular matrix proteins such as fibronectin, a multifunctional extracellular matrix protein that plays a major role in cell adhesion and migration as well as in the development of glomerulosclerosis. ETS-1 is an important transcription factor essential for normal kidney development and glomerular integrity. We previously showed that ANG II increases ETS-1 expression and is required for fibronectin production in mesangial cells. In these studies, we determined that ANG II induces phosphorylation of ETS-1 via activation of the type 1 ANG II receptor and that Erk1/2 and Akt/PKB phosphorylation are required for these effects. In addition, we characterized the role of ETS-1 on the transcriptional activation of fibronectin production in mesangial cells. We determined that ETS-1 directly activates the fibronectin promoter and by utilizing gel shift assays and chromatin immunoprecipitation assays identified two different ETS-1 binding sites that promote the transcriptional activation of fibronectin in response to ANG II. In addition, we identified the essential role of CREB and its coactivator p300 on the transcriptional activation of fibronectin by ETS-1. These studies unveil novel mechanisms involved in RAS-induced production of the extracellular matrix protein fibronectin in mesangial cells and establish the role of the transcription factor ETS-1 as a direct mediator of these effects.

IgA1 immune complexes from pediatric patients with IgA nephropathy activate cultured human mesangial cells.

BACKGROUND: Circulating immune complexes (CIC) containing galactose (Gal)-deficient IgA1 from adults with IgA nephropathy (IgAN) induce proliferation of cultured mesangial cells, but activities of CIC from pediatric patients with the disease have not been studied. METHODS: CIC of different sizes were isolated from sera of pediatric and adult IgAN patients and their effects on cultured human mesangial cells (MC) were assessed by measuring cellular proliferation, expression of IL-6 and IL-8 and laminin and phosphotyrosine signaling. RESULTS: Large CIC from pediatric IgAN patients (>800 kDa) containing Gal-deficient IgA1 stimulated cellular proliferation, whereas in some patients, smaller CIC were inhibitory. Addition of stimulatory and inhibitory CIC to MC differentially altered phosphorylation patterns of three major tyrosine-phosphorylated proteins of molecular mass 37, 60 and 115 kDa. The stimulatory CIC transiently increased tyrosine-phosphorylation of the 37-kDa protein and decreased phosphorylation of the other two proteins, whereas the inhibitory CIC increased phosphorylation of all three proteins. Furthermore, we investigated the influence of IgA1-containing CIC from sera of children with IgAN with clinically active disease (i.e., abnormal urinalysis and/or serum creatinine concentration) or inactive disease (i.e., normal urinalysis and serum creatinine concentration) on the expression of IL-6 and IL-8 genes by mesangial cells. Real-time reverse transcription-polymerase chain reaction results showed that the CIC from a patient with active disease stimulated MC to express the two cytokine genes at higher levels than did the CIC from a patient with inactive disease. Moreover, stimulatory CIC increased production of the extracellular matrix protein laminin. CONCLUSION: These data indicate that sera of pediatric IgAN patients contain biologically active CIC with Gal-deficient IgA1.