The mesangial cell: a tissue culture view

Physiological Replication of the Human Glomerulus Using a Triple Culture Microphysiological System

The function of the glomerulus depends on the complex cell-cell/matrix interactions and replication of this in vitro would aid biological understanding in both health and disease. Previous models do not fully reflect all cell types and interactions present as they overlook mesangial cells within their 3D matrix. Herein, the development of a microphysiological system that contains all resident renal cell types in an anatomically relevant manner is presented. A detailed transcriptomic analysis of the contributing biology of each cell type, as well as functionally appropriate albumin retention in the system, is demonstrated. The important role of mesangial cells is shown in promoting the health and maturity of the other cell types. Additionally, a comparison of the incremental advances that each individual cell type brings to the phenotype of the others demonstrates that glomerular cells in simple 2D culture exhibit a state more reflective of the dysfunction observed in human disease than previously recognized. This in vitro model will expand the capability to investigate glomerular biology in a more translatable manner by the inclusion of the important mesangial cell compartment.

Pathophysiology of mesangial expansion in diabetic nephropathy: mesangial structure, glomerular biomechanics, and biochemical signaling and regulation

Diabetic nephropathy, a kidney complication arising from diabetes, is the leading cause of death in diabetic patients. Unabated, the growing epidemic of diabetes is increasing instances of diabetic nephropathy. Although the main causes of diabetic nephropathy have been determined, the mechanisms of their combined effects on cellular and tissue function are not fully established. One of many damages of diabetic nephropathy is the development of fibrosis within the kidneys, termed mesangial expansion. Mesangial expansion is an important structural lesion that is characterized by the aberrant proliferation of mesangial cells and excess production of matrix proteins. Mesangial expansion is involved in the progression of kidney failure in diabetic nephropathy, yet its causes and mechanism of impact on kidney function are not well defined. Here, we review the literature on the causes of mesangial expansion and its impacts on cell and tissue function. We highlight the gaps that still remain and the potential areas where bioengineering studies can bring insight to mesangial expansion in diabetic nephropathy.

[Reinterpretation of the Malpighian body in light of the existence of a single glomerular arteriole (Trabucco and Marquez)]

INTRODUCTION

In 1842 William Bowman described the microvascular system of the Malpighian body. Electron microscopic studies definitively revealed the spatial structure of its mesangial-capillary-epithelial component. In 1952-54 Trabucco and Marquez challenged the ideas of Bowman, demonstrating the existence of a single glomerular arteriole. Our study supports the finding of a single glomerular arteriole, leading to a definitive interpretation of the Malpighian body structure.

MATERIALS AND METHODS

Serial histological studies were carried out of the vascular pole in a case of oligomeganephrotic renal hypoplasia and the immunohistochemical study of embryonal glomerular development (15 embryos aged between 7 and 11weeks), with alpha-actin (smooth muscle marker), CD31 and CD34 (endothelial markers) and CD10 (podocyte marker).

RESULTS

The study of the glomerular vascular pole in the case of oligomeganephrotic renal hypoplasia supports the existence of a single glomerular arteriole. Our immunohistochemical study confirmed this finding and provided data on the morphogenesis of the mesangial-capillary-epithelial component of the Malpighian body.

CONCLUSIONS

There exist a single glomerular arteriole. Mesangial and endothelial cells originating from a single glomerular arteriole interact with an epithelial component derived from the nephrogenic vesicle which then generate the lobular glomerular tuft, providing the basis for a definitive interpretation of the structure of the Malpighian body. There is no scientific base to the interpretation of the glomerular microvascular system as having two glomerular arterioles with an intercalated capillary network.

The Influence of a Nanopatterned Scaffold that Mimics Abnormal Renal Mesangial Matrix on Mesangial Cell Behavior

The alteration of mesangial matrix (MM) components in mesangium, such as type IV collagen (COL4) and type I collagen (COL1), is commonly found in progressive glomerular disease. Mesangial cells (MCs) responding to altered MM, show critical changes in cell function. This suggests that the diseased MM structure could play an important role in MC behavior. To investigate how MC behavior is influenced by the diseased MM 3D nanostructure, we fabricated the titanium dioxide (TiO2)-based nanopatterns that mimic diseased MM nanostructures. Immortalized mouse MCs were used to assess the influence of disease-mimic nanopatterns on cell functions, and were compared with a normal-mimic nanopattern. The results showed that the disease-mimic nanopattern induced disease-like behavior, including increased proliferation, excessive production of abnormal MM components (COL1 and fibronectin) and decreased normal MM components (COL4 and laminin α1). In contrast, the normal-mimic nanopattern actually resulted in cells displaying normal proliferation and the production of normal MM components. In addition, increased expressions of α-smooth muscle actin (α-SMA), transforming growth factor β1 (TGF-β1) and integrin α5β1 were detected in cells grown on the disease-mimic nanopattern. These results indicated that the disease-mimic nanopattern induced disease-like cell behavior. These findings will help further establish a disease model that mimics abnormal MM nanostructures and also to elucidate the molecular mechanisms underlying glomerular disease.

All-trans retinoic acid suppresses bone morphogenetic protein 4 in mouse diabetic nephropathy through a unique retinoic acid response element

Diabetic nephropathy (DN) causes mesangial matrix expansion, which results in glomerulosclerosis and renal failure. Collagen IV (COL4) is a major component of the mesangial matrix that is positively regulated by bone morphogenetic protein 4 (BMP4)/suppressor of mothers against decapentaplegic (Smad1) signaling. Because previous studies showed that retinoids treatment had a beneficial effect on kidney disease, we investigated the therapeutic potential of retinoids in DN, focusing especially on the regulatory mechanism of BMP4. Diabetes was induced with streptozotocin in 12-wk-old male Crl:CD1(ICR) mice, and, 1 mo later, we initiated intraperitoneal injection of all-trans retinoic acid (ATRA) three times weekly. Glomerular matrix expansion, which was associated with increased BMP4, phosphorylated Smad1, and COL4 expression, worsened in diabetic mice at 24 wk of age. ATRA administration alleviated DN and downregulated BMP4, phosopho-Smad1, and COL4. In cultured mouse mesangial cells, treatment with ATRA or a retinoic acid receptor-α (RARα) agonist significantly decreased BMP4 and COL4 expression. Genomic analysis suggested two putative retinoic acid response elements (RAREs) for the mouse Bmp4 gene. Chromatin immunoprecipitation analysis and reporter assays indicated a putative RARE of the Bmp4 gene, located 11,488-11,501 bp upstream of exon 1A and bound to RARα and retinoid X receptor (RXR), which suppressed BMP4 expression after ATRA addition. ATRA suppressed BMP4 via binding of a RARα/RXR heterodimer to a unique RARE, alleviating glomerular matrix expansion in diabetic mice. These findings provide a novel regulatory mechanism for treatment of DN.

Novel Interplay Between Smad1 and Smad3 Phosphorylation via AGE Regulates the Progression of Diabetic Nephropathy

Diabetic nephropathy (DN) is the major cause of end-stage renal failure and is associated with increased morbidity and mortality compared with other causes of renal diseases. We previously found that Smad1 plays a critical role in the development of DN both in vitro and in vivo. However, functional interaction between Smad1 and Smad3 signaling in DN is unclear. Here, we addressed the molecular interplay between Smad1 and Smad3 signaling under a diabetic condition by using Smad3-knockout diabetic mice. Extracellular matrix (ECM) protein overexpression and Smad1 activation were observed in the glomeruli of db/db mice but were suppressed in the glomeruli of Smad3^+/-; db/db mice. Smad3 activation enhanced the phosphorylation of Smad1 C-terminal domain but decreased the phosphorylation of linker domain, thus regulating Smad1 activation in advanced glycation end product-treated mesangial cells (MCs). However, forced phosphorylation of the Smad1 linker domain did not affect Smad3 activation in MCs. Phosphorylation of the Smad1 linker domain increased in Smad3^+/-; db/db mice and probucol-treated db/db mice, which was consistent with the attenuation of ECM overproduction. These results indicate that Smad3 expression and activation or probucol treatment alters Smad1 phosphorylation, thus suggesting new molecular mechanisms underlying DN development and progression.

Transcriptomic profiling in human mesangial cells using patient-derived lupus autoantibodies identified miR-10a as a potential regulator of IL8

Autoantibody-mediated inflammation directed at resident kidney cells mediates lupus nephritis (LN) pathogenesis. This study investigated the role of miRNA in human mesangial cells (HMCs) stimulated with auto anti-dsDNA immunoglobulin (Ig)G antibodies. HMCs were treated with antibodies purified from active LN patients or non-specific IgG controls in the presence of normal serum. Aberrant miRNA was screened using high throughput sequencing. Anti-dsDNA IgG up-regulated 103 miRNAs and down-regulated 30 miRNAs. The miRNAs regulated genes in the cell cycle, catabolic processes, regulation of transcription and apoptosis signalling. miR-10a was highly abundant in HMCs but was specifically downregulated upon anti-dsDNA IgG induction. Interestingly, the expression of miR-10a in kidney biopsies from class III and IV LN patients (n = 26) was downregulated compared with cadaveric donor kidneys (n = 6). Functional studies highlighted the downstream regulator of miR-10a in the chemokine signalling and cell proliferation or apoptosis pathways. Luciferase assay confirmed for the first time that IL8 was a direct target of miR-10a in HMCs. In conclusion, anti-dsDNA IgG Ab down-regulated miR-10a expression in HMCs resulting in the induction of various target genes involved in HMC proliferation and chemokine expression.

Conditional Deletion of Smad1 Ameliorates Glomerular Injury in Progressive Glomerulonephritis

Matrix expansion and cell proliferation are concomitantly observed in various glomerular injuries. However, the molecular mechanisms responsible for these changes have not been fully elucidated. We have reported that Smad1 is a key signalling molecule that regulates the transcription of type IV collagen (Col4) in mesangial matrix expansion and is thereby involved in glomerular injury in an acute model of glomerulonephritis. In this study, we addressed the role of Smad1 signalling in accelerated nephrotoxic nephritis (NTN), a model of progressive glomerulonephritis, using conditional deletion of Smad1 in Rosa26CreERT2 mice (Smad1-CKO). Mesangial matrix expansion in the Smad1-CKO mice with NTN was significantly inhibited compared with that in wild type mice with NTN, which was consistent with the decrease in Col4 expression level. On the other hand, STAT3 activation and cell proliferation were not influenced by Smad1 deletion in the NTN model. Therefore, we investigated another factor that activates cell proliferation in the absence of Smad1. Id2 induced VEGF secretion and subsequent STAT3 activation, independently of Smad1 expression in mouse mesangial cells. Here we show that Smad1 plays an important role in the development of glomerular injury without affecting cell proliferation, in progressive glomerulonephritis.

A Novel Interaction between FLICE-Associated Huge Protein (FLASH) and E2A Regulates Cell Proliferation and Cellular Senescence via Tumor Necrosis Factor (TNF)-Alpha-p21WAF1/CIP1 Axis

Dysregulation of the cell proliferation has been implicated in the pathophysiology of a number of diseases. Cellular senescence limits proliferation of cancer cells, preventing tumorigenesis and restricting tissue damage. However, the role of cellular senescence in proliferative nephritis has not been determined. The proliferative peak in experimental rat nephritis coincided with a peak in E2A expression in the glomeruli. Meanwhile, E12 (an E2A-encoded transcription factor) did not promote proliferation of Mesangial cells (MCs) by itself. We identified caspase-8-binding protein FLICE-associated huge protein (FLASH) as a novel E2A-binding partner by using a yeast two-hybrid screening. Knockdown of FLASH suppressed proliferation of MCs. This inhibitory effect was partially reversed by the knockdown of E2A. In addition, the knockdown of FLASH induced cyclin-dependent kinase inhibitor p21WAF1/CIP1 (p21) expression, but did not affect p53 expression. Furthermore, overexpression of E12 and E47 induced p21, but not p53 in MCs, in the absence of FLASH. We also demonstrated that E2A and p21 expression at the peak of proliferation was followed by significant induction of FLASH in mesangial areas in rat proliferative glomerulonephritis. Moreover, we revealed that FLASH negatively regulates cellular senescence via the interaction with E12. We also demonstrated that FLASH is involved in the TNF-α-induced p21 expressions. These results suggest that the functional interaction of E2A and FLASH play an important role in cell proliferation and cellular senescence via regulation of p21 expression in experimental glomerulonephritis.

IgM exacerbates glomerular disease progression in complement-induced glomerulopathy

While glomerular IgM deposition occurs in a variety of glomerular diseases the mechanism of deposition and its clinical significance remain controversial. Some have theorized IgM becomes passively trapped in areas of glomerulosclerosis. However, recent studies found that IgM specifically binds damaged glomeruli. Therefore, we tested whether natural IgM binds to neo-epitopes exposed after insults to the glomerulus and exacerbate disease in mice deficient in the complement regulatory protein factor H; a model of non-sclerotic and nonimmune-complex glomerular disease. Immunofluorescence microscopy demonstrated mesangial and capillary loop deposition of IgM while ultrastructural analysis found IgM deposition on endothelial cells and subendothelial areas. Factor H deficient mice lacking B cells were protected from renal damage, as evidenced by milder histologic lesions on light and electron microscopy. IgM, but not IgG, from wild-type mice bound to cultured murine mesangial cells. Furthermore, injection of purified IgM into mice lacking B cells bound within the glomeruli and induced proteinuria. A monoclonal natural IgM recognizing phospholipids also bound to glomeruli in vivo and induced albuminuria. Thus, our results indicate specific IgM antibodies bind to glomerular epitopes and that IgM contributes to the progression of glomerular damage in this mouse model of non-sclerotic glomerular disease.

A new saikogenin from the roots of Bupleurum bicaule

AIM

To study the chemical constituents from the roots of Buleurum bicaule Helm (Apiaceae).

METHOD

Silica gel, Sephadex LH-20, MPLC Rp-C18 column chromatography, and HPLC were used for isolation of compounds. The structures were elucidated on the basis of 1D- and 2D-NMR technology and HRESI-MS. Compounds were evaluated in vitro for their inhibitory ability against the proliferation of rat mesangial cells by the MTT method.

RESULTS

Twelve compounds were isolated, and their structures were identified on the basis of their spectroscopic and physico-chemical properties as 13, 28-epoxy-olean-11-en-3-one (1), saikogenin E (2), saikogenin G (3), 11α-methoxy-3β, 16β, 23, 28-tetrahydroxyolean-12-ene (4), saikogenin D (5), prosaikogenin F (6), prosaikogenin A (7), prosaikogenin G (8), prosaikogenin D (9), laccaic acid (10b), methyl gallate (11), and ethyl gallate (12). Compounds 1, 2, 7, 8, and 10 were observed to have inhibitory activity against mesangial cell proliferationin to different degrees.

CONCLUSION

Compound 1, 8, and 10 exhibit significant inhibitory effects on rat mesangial cell proliferation induced by Ang II.

Tumor necrosis factor-α regulates matrix metalloproteinase-2 expression and cell migration via ERK pathway in rat glomerular mesangial cells

Mesangial cells (MCs), vascular smooth muscle-derived cells, contribute to glomerular injury by generating a number of cytokines such as tumor necrosis factor-α (TNF-α). Matrix metalloproteinases (MMPs), regulated by various stimuli, are important in remodeling of glomerular ECM, which leads to a number of renal diseases. We investigated whether TNF-α participated in the regulation of MMPs and explored signal pathways involved in TNF-α-induced MMPs expression in rat glomerular MCs. Western blot and RT-qPCR results showed that treatment with TNF-α significantly increased the expression of MMP-2, but not MMP-9 at both protein and mRNA levels in rat glomerular MCs. The extracellular signal-regulated kinase (ERK) and nuclear factor-kappaB (NF-κB) signal pathways were activated by TNF-α. Moreover, the activation of NF-κB pathway in rat MCs was effectively inhibited by PD98059, specific inhibitor of ERK, suggesting a role for ERK in regulating NF-κB function. PD98059 or NF-κB signal pathway selective inhibitor Bay 11-7082 effectively blocked TNF-α-induced expression of MMP-2 in rat MCs, as determined by gene and protein expression. C-jun N-terminal kinase (JNK) signal pathway had no effect on TNF-α-induced expression of MMP-2, even though it was also activated by TNF-α in rat MCs. Furthermore, TNF-α could induce the cell migration of rat MCs, whereas ERK signal pathway specific inhibitor PD98059 compromised the cell migration triggered by TNF-α. Thus, TNF-α upregulates the expression of MMP-2 via activation of ERK-dependent NF-κB pathway in rat MCs, which may contribute to the cell migration of rat MCs.

Dimeric and polymeric IgA, but not monomeric IgA, enhance the production of IL-6 by human renal mesangial cells

Depositions of IgA in the renal glomerular mesangial area are a hallmark of IgA nephropathy, and are thought to be crucial for the onset of inflammation processes in IgA nephropathy. In this report we show that human mesangial cells (MC) in vitro bind IgA and that binding of IgA enhances the production of IL-6 by MC. Furthermore we show that the size of IgA is crucial in its capability to enhance IL-6 production. Monomeric IgA does not affect basic IL-6 production, whereas dimeric and polymeric IgA enhance IL-6 production up to 3- to 9-fold respectively. Additional studies demonstrate that enhanced IL-6 production by MC is not accompanied by increased proliferation of human mesangial cells, a finding which is distinct from that found with rat mesangial cells. Taken together, these fmdings suggest that deposition of dimeric and polymeric IgA in the mesangial area of human kidneys in IgA nephropathy may amplify local inflammation.

Protein inhibitor of activated STAT, PIASy regulates α-smooth muscle actin expression by interacting with E12 in mesangial cells

Phenotypic transformation of mesangial cells (MCs) is implicated in the development of glomerular disease; however, the mechanisms underlying their altered genetic program is still unclear. α-smooth muscle actin (α-SMA) is known to be a crucial marker for phenotypic transformation of MCs. Recently, E-boxes and the class I basic helix-loop-helix proteins, such as E12 have been shown to regulateα-SMA expression. Therefore, we tried to identify a novel E12 binding protein in MCs and to examine its role in glomerulonephritis. We found that PIASy, one of the protein inhibitors of activated STAT family protein, interacted with E12 by yeast two-hybrid screens and coimmunopreciptation assays. Overexpression of E12 significantly enhanced theα-SMA promoter activity, and the increase was blocked by co-transfection of PIASy, but not by a PIASy RING mutant. In vivo sumoylation assays revealed that PIASy was a SUMO E3 ligase for E12. Furthermore, transforming growth factor-β (TGF-β) treatment induced expression of both PIASy and E12, consistent with α-SMA expression. Moreover, reduced expression of PIASy protein by siRNA specific for PIASy resulted in increased TGF-β-mediated α-SMA expression. In vivo, PIASy and E12 were dramatically upregulated along with α-SMA and TGF-β in the proliferative phase of Thy1 glomerulonephritis. Furthermore, an association between PIASy and E12 proteins was observed at day 6 by IP-western blotting, but not at day 0. These results suggest that TGF-β up-regulates PIASy expression in MCs to down-regulateα-SMA gene transcription by the interaction with E12.

Scleraxis modulates bone morphogenetic protein 4 (BMP4)-Smad1 protein-smooth muscle α-actin (SMA) signal transduction in diabetic nephropathy

Activation of mesangial cells (MCs), which is characterized by induction of smooth muscle α-actin (SMA) expression, contributes to a key event in various renal diseases; however, the mechanisms controlling MC differentiation are still largely undefined. Activated Smad1 induced SMA in a dose-dependent manner in MCs. As a direct regulating molecule for SMA, we identified and characterized scleraxis (Scx) as a new phenotype modulator in advanced glycation end product (AGE)-exposed MCs. Scx physically associated with E12 and bound the E-box in the promoter of SMA and negatively regulated the AGE-induced SMA expression. Scx induced expression and secretion of bone morphogenetic protein 4 (BMP4), thereby controlling the Smad1 activation in AGE-treated MCs. In diabetic mice, Scx was concomitantly expressed with SMA in the glomeruli. Inhibitor of differentiation 1 (Id1) was further induced by extended treatment with AGE, thereby dislodging Scx from the SMA promoter. These data suggest that Scx and Id1 are involved in the BMP4-Smad1-SMA signal transduction pathway besides the TGFβ1-Smad1-SMA signaling pathway and modulate phenotypic changes in MCs in diabetic nephropathy.

SOX9 protein induces a chondrogenic phenotype of mesangial cells and contributes to advanced diabetic nephropathy

Diabetic nephropathy (DN) is the most important chronic kidney disease. We previously reported that Smad1 transcriptionally regulates the expression of extracellular matrix in DN. Phenotypic change in mesangial cells (MCs) is a key pathologic event in the progression of DN. The aim of this study is to investigate a novel mechanism underlying chondrogenic phenotypic change in MCs that results in the development of DN. MCs showed chondrogenic potential in a micromass culture, and BMP4 induced the expression of chondrocyte markers (SRY-related HMG Box 9 (SOX9) and type II collagen (COL2)). Advanced glycation end products induced the expression of chondrocyte marker proteins downstream from the BMP4-Smad1 signaling pathway in MCs. In addition, hypoxia also induced the expression of BMP4, hypoxia-inducible factor-1α (HIF-1α), and chondrocyte markers. Overexpression of SOX9 caused ectopic expression of proteoglycans and COL2 in MCs. Furthermore, forced expression of Smad1 induced chondrocyte markers as well. Dorsomorphin inhibited these inductions. Glomerular expressions of HIF-1α, BMP4, and chondrocyte markers were observed in diabetic nephropathy mice. These positive stainings were observed in mesangial sclerotic lesions. SOX9 was partially colocalized with HIF-1α and BMP4 in diabetic glomeruli. BMP4 knock-in transgenic mice showed not only similar pathological lesions to DN, but also the induction of chondrocyte markers in the sclerotic lesions. Here we demonstrate that HIF-1α and BMP4 induce SOX9 expression and subsequent chondrogenic phenotype change in DN. The results suggested that the transdifferentiation of MCs into chondrocyte-like cells in chronic hypoxic stress may result in irreversible structural change in DN.

Activation of bone morphogenetic protein 4 signaling leads to glomerulosclerosis that mimics diabetic nephropathy

Diabetic nephropathy (DN) is the most common cause of chronic kidney disease. We have previously reported that Smad1 transcriptionally regulates the expression of extracellular matrix (ECM) proteins in DN. However, little is known about the regulatory mechanisms that induce and activate Smad1. Here, bone morphogenetic protein 4 (Bmp4) was found to up-regulate the expression of Smad1 in mesangial cells and subsequently to phosphorylate Smad1 downstream of the advanced glycation end product-receptor for advanced glycation end product signaling pathway. Moreover, Bmp4 utilized Alk3 and affected the activation of Smad1 and Col4 expressions in mesangial cells. In the diabetic mouse, Bmp4 was remarkably activated in the glomeruli, and the mesangial area was expanded. To elucidate the direct function of Bmp4 action in the kidneys, we generated transgenic mice inducible for the expression of Bmp4. Tamoxifen treatment dramatically induced the expression of Bmp4, especially in the glomeruli of the mice. Notably, in the nondiabetic condition, the mice exhibited not only an expansion of the mesangial area and thickening of the basement membrane but also remarkable albuminuria, which are consistent with the distinct glomerular injuries in DN. ECM protein overexpression and activation of Smad1 in the glomeruli were also observed in the mice. The mesangial expansion in the mice was significantly correlated with albuminuria. Furthermore, the heterozygous Bmp4 knock-out mice inhibited the glomerular injuries compared with wild type mice in diabetic conditions. Here, we show that BMP4 may act as an upstream regulatory molecule for the process of ECM accumulation in DN and thereby reveals a new aspect of the molecular mechanisms involved in DN.

Henoch-Schonlein purpura nephritis: pathophysiology, treatment, and future strategy

Henoch-Schönlein purpura nephritis is a rare kidney disease leading to chronic kidney disease in a non-negligible percentage of patients. Although retrospective studies suggest beneficial effects of some therapies, prospective randomized clinical trials proving treatment efficacy are still lacking. The dilemma of spontaneous recovery even in patients with severe clinical and histologic presentation and of late evolution to chronic kidney disease in patients with mild initial symptoms renders it difficult for clinicians to expose patients to treatment protocols that are not evidence-based. A better understanding of the pathophysiology of progression to chronic kidney disease in Henoch-Schönlein purpura patients could be achieved by designing prospective international multicenter studies looking at determinants of clinical and histopathological evolution as well as possible circulating and urinary markers of progression. Such studies should be supported by a database available on the web and a new histologic classification of kidney lesions. This paper reports clinical, pathologic, and experimental data to be used for this strategy and to assist clinicians and clinical trial designers to reach therapeutic decisions.

Transcription factor 7-like 2 (TCF7L2) regulates activin receptor-like kinase 1 (ALK1)/Smad1 pathway for development of diabetic nephropathy

Smad1 has previously been shown to play a key role in the development of diabetic nephropathy (DN), by increasing synthesis of extracellular matrix. However, the regulatory mechanism of Smad1 in DN is still unclear. This study aims to elucidate molecular interactions between activin receptor-like kinase 1 (ALK1)/Smad1 signaling pathway and transcription factor 7-like 2 (TCF7L2) in the progression of DN in vitro and in vivo. The expressions of TCF7L2 and ALK1 were induced by advanced glycation end products (AGEs) in parallel with Smad1, phosphorylated Smad1 (pSmad1), and alpha-smooth muscle actin (α-SMA) through TGF-β1 in cultured mesangial cells. Constitutively active ALK1 increased pSmad1 and α-SMA expressions. The binding of TCF7L2 to ALK1 promoter was confirmed by chromatin immunoprecipitation assay. Furthermore, TCF7L2 induced promoter activity of ALK1. AGEs and TGF-β1 induced a marked increase in TCF7L2 expression in parallel with ALK1. Overexpression of TCF7L2 increased the expressions of ALK1 and Smad1. Inversely, TCF7L2 knockdown by siRNA suppressed α-SMA expression as well as ALK1 and Smad1. The iNOS transgenic mice (iNOS-Tgm), which developed diabetic glomerulosclerosis resembling human diabetic nephropathy, exhibited markedly increased expressions of ALK1, TCF7L2, Smad1, pSmad1, and α-SMA in glomeruli in association with mesangial matrix expansion. These results provide a new evidence that the TCF7L2/ALK1/Smad1 pathway plays a key role in the development of DN.

Isolation and propagation of glomerular mesangial cells

Cultures of glomerular mesangial cells (MC) of rodent or human origin have been extensively employed in renal research laboratories since the early 1980s. Cultured MC retain extensive analogies with the fairly undifferentiated in vivo phenotype of an intercapillary mesenchymal cell population, i.e., a myofibroblast. MC proliferating in response to mitogens and growth factors can be growth-arrested by withdrawal of serum or 3D culture in collagen gels. They synthesize an extracellular matrix that includes interstitial collagens and has analogies with the glomerular basement membrane; a prominent cytoskeleton acts as a functional contractile apparatus. Cultured MC have been extensively employed as a tool for studying pathophysiological events such as mesangial expansion, scarring, and glomerulosclerosis. Current technology for MC isolation and culture is reviewed, with emphasis on methodological issues relevant to characterization, propagation, and long-term maintenance of homogeneous clones.

TNF-alpha and IL-1 beta-mediated regulation of MMP-9 and TIMP-1 in human glomerular mesangial cells

BACKGROUND

Renal cells such as mesangial cells are known to secrete metalloproteinases that are capable of degrading the constituents of the glomerular basement membrane (GBM). Disruption of the GBM via cytokine-induced alterations in matrixmetalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) may be an important mechanism in the renal disease process. In renal disease, both resident renal cells and infiltrating immune cells are capable of secreting pro-inflammatory cytokines including tumour necrosing factor-alpha (TNFalpha) and interleukin-1 beta (IL-1 beta). In this study, we examine the potential of these cytokines to alter levels of MMPs and TIMPs in human mesangial cells.

METHODS

The T-HMC human mesangial cell line was cultured in RPMI 1640 containing 5% serum. Cells at confluency were serum starved for 24 h prior to exposure to TNF-alpha (0.1-100 ng/ml) or IL-1 beta (0.1-100 ng/ml) or a combination of both for 48 h. Activity of MMP-9 was examined by gelatin zymography and TIMP-1 expression was analysed by Western blotting.

RESULTS

TNF-alpha but not IL-1 beta resulted in a dose-dependent increase in the latent form of MMP-9 and a decrease in TIMP-1 production. Co-treatment with IL-1 beta had no effect on the induction of MMP-9 but increased the inhibition of TIMP-1 in the presence of TNF-alpha. Inhibition of PKC provided evidence of the importance of this pathway in mediating the TNF-alpha-induced suppression of TIMP-1. Activation of the ERK 1/2 MAPK mediated both the upregulation of MMP-9 and the inhibition of TIMP-1 following TNF-alpha treatment. p38 MAPK activation was also found to be involved in the TNF-alpha-stimulated MMP-9.

CONCLUSION

The cytokine TNF-alpha causes different effects on human mesangial MMP-9 and TIMP-1 expression which are mediated through the TNF-RI, and the different signalling pathways of PKC, ERK 1/2 and p38 MAPK. This suggests an important role for pro-inflammatory cytokines in renal disease progression.

SRY-related HMG box 9 regulates the expression of Col4a2 through transactivating its enhancer element in mesangial cells

Accumulation of alpha1(IV) and alpha2(IV) collagen is one of the characteristic pathological changes in glomerulosclerosis. Although the Col4a2 gene is known to have a 0.3-kb critical enhancer element with the GAACAAT motif, which transcription factor binds and transactivates this motif has not been identified. In this study, we found that SRY-related HMG box 9 (SOX9) was bound to the GAACAAT motif in the Col4a2 enhancer in vitro and in vivo in mesangial cells. SOX9 strongly activated this enhancer when cotransfected with Col4a2 enhancer-promoter construct in mesangial cells and Swiss/3T3 cells. Mutation in the GAACAAT motif eliminated the activation by SOX9. Furthermore, transforming growth factor-beta (TGF-beta) treatment induced the expression of SOX9 and Col4a2, and a small interfering RNA against SOX9 reduced Col4a2 expression induced by TGF-beta treatment in mesangial cells. In vivo, we found that the expression of SOX9 was dramatically increased along with the expression of TGF-beta and Col4a2 in mouse nephrotoxic nephritis. These results indicate that SOX9 is essential for Col4a2 expression in mesangial cells and might be involved in the accumulation of alpha2(IV) collagen in experimental nephritis.

Ex vivo transfer of the decorin gene into rat glomerulus via a mesangial cell vector suppressed extracellular matrix accumulation in experimental glomerulonephritis

The activation of transforming growth factor-beta (TGF-beta) is known to be one of the major causes of glomerulosclerosis. Decorin (DCN) is a natural inhibitor of TGF. The purpose of this study was to assess the feasibility of transferring the DCN gene to antithymocyte serum (ATS) glomerulonephritis glomeruli via a mesangial cell vector to treat glomerulonephritis fibrosis. For this process, the recombinant eukaryotic expression plasmid pcDNA3.1A-DCN was constructed and transfected into mesangial cell. The DCN-positive cloned cells were transferred to rat antithymocyte serum glomeruli by a left renal artery injection. Using immunohistochemical staining, approximately 37-60% (48.6% +/- 11.34%; mean +/- SE, n = 8) of the glomeruli were BrdU-positive in the injected-side kidney. DCN proteins were observed in the cytoplast beginning 12 h after injection. TGF-beta1 expression in the injected side glomeruli decreased significantly at day 4 (P < 0.05), compared with that in the uninjected-side kidney. The expression leaves of fibronectin and collagen IV decreased significantly at days 1-2 (P < 0.01) and day 4 (fibronectin, P < 0.01; collagen IV, P < 0.05). These results suggest that the use of DCN can decrease antithymocyte serum glomerulonephritis extracellular matrix (ECM) ingredients and that such use offers a favorable experimental basis for gene therapy for kidney disease.

Crosstalk Between Mesangial and Endothelial Cells: Angiotensin II Down-Regulates Endothelin-Converting Enzyme 1

OBJECTIVE

Since mesangial and endothelial cells interact in the kidney, the present experiments were designed to analyze the ability of human mesangial cells (HMC) to modulate endothelin-1 (ET-1) synthesis by human umbilical vein endothelial cells (HuVEC).

METHODS AND RESULTS

The supernatants of HuVEC/HMC contained significantly lower amounts of ET-1 than those of HuVEC alone. This effect was not due to a decreased prepro-ET-1 mRNA expression and was only partially the consequence of HMC-dependent ET-1 degradation. Therefore, we tested the influence of the coculture on endothelin-converting enzyme-1 (ECE-1), and found a significant reduction of its mRNA and protein levels as well as a decreased activity in HuVEC/HMC as compared to HuVEC alone. Using a pharmacological blockade approach (sulotrobam, BN52021, losartan or catalase), losartan was shown to completely abolish down-regulation of ECE-1 observed in HuVEC/HMC. Angiotensin II (AII) induced a dose and time-dependent inhibition of ECE-1 expression in HuVEC.

CONCLUSIONS

These results support the importance of cross-talk among different cell types in the regulation of vascular or renal function. ET-1, and particularly ECE-1, might constitute a target in this regulation. In addition, locally synthesized AII could be one of the mediators involved in the down-regulation of ECE-1.

Activation of STAT3/Smad1 is a key signaling pathway for progression to glomerulosclerosis in experimental glomerulonephritis

Mesangial cell proliferation is a significant event in the development of progressive glomerular injuries. However, the issue of how cell proliferation is involved in the development of glomerulosclerosis is unclear. Recently, we showed that the overexpression of type IV collagen (Col IV), a major component of mesangial extracellular matrix, is transcriptionally regulated by Smad1 in diabetic glomerulosclerosis. In this study, we have demonstrated the effect of the administration of an anti-platelet-derived growth factor (PDGF) beta-receptor antibody (APB5) blocking activation by the PDGF-B chain on rat glomerulonephritis and have examined the signaling pathways that regulate both glomerular cell proliferation and glomerulosclerosis in vivo and in vitro. Experimental mesangial proliferative glomerulonephritis (Thy1 GN) was induced by a single intravenous injection of anti-rat Thy-1.1 monoclonal antibody. In Thy1 GN, mesangial cell proliferation and the expression of Col IV peaked at day 6. Immunohistochemical staining for the expression of Smad1, phospho-Smad1 (pSmad1), and phospho-STAT3 (pSTAT3) revealed that the peak for glomerular Smad1 expression occurred at day 6, consistent with the peak for mesangial proliferation. The expression of pSmad1 was up-regulated at day 1, and the peak for glomerular pSmad1 expression occurred at day 4 of the disease. When treated with APB5, both mesangial proliferation and sclerosis were reduced significantly. The expression of Smad1, pSmad1, and pSTAT3 was also significantly reduced by the administration of APB5. PDGF induced both mesangial cell replication and Col IV synthesis in association with an increased expression of pSTAT3 and pSmad1 on cultured mesangial cells. In addition, APB5 reduced mesangial cell proliferation in association with decreased pSmad1, pSTAT3, and Col IV protein expressions in vitro. The introduction of dominant negative STAT3 significantly decreased the expression of Col IV in cultured mesangial cells. These data suggest that the activation of STAT3 and Smad1 participates in the developing process of glomerulosclerosis in experimental glomerulonephritis.

AL-amyloidosis and light-chain deposition disease light chains induce divergent phenotypic transformations of human mesangial cells

Human mesangial cells (HMCs) are injured by either excessive amounts or abnormal light chains (LCs), or a combination of both in patients with plasma cell dyscrasias. Consequently, these HMCs undergo phenotypic transformations. HMCs were incubated with eight different light-chains (LCs) for 96 h. These cells, in addition to 51 patient samples from patients with AL-amyloidosis (AL-Am), light-chain deposition disease (LCDD), myeloma cast nephropathy (MCN) and controls were analyzed by immunohistochemistry for CD68, muscle-specific actin (MSA), smooth muscle actin (SMA), CD14, and Ham56 protein expressions. All samples were also studied using electron microscopy. Greater staining (four- and three-fold) expressions of CD68 and Ham56, respectively, were observed in the HMCs incubated with AL-Am-LCs compared to those with LCDD-LCs and control. SMA expression levels were five-fold higher in LCDD-LC-treated cells compared to the other categories of LC-treated and control cells. Similar results were obtained in the renal specimens, however, CD68 levels were 12-fold higher in the AL-Am cases compared to the LCDD cases, respectively. Conversely, MSA and SMA levels were three fold higher in the LCDD cases than in the AL-Am ones. No CD14 expression was noted in any of the samples and CD-34 staining of HMCs treated with the various LCs only showed rare positive cells. Dynamic real-time studies to visualize the rough endoplasmic reticulum (RER) and lysosomal compartments in HMCs incubated with LCDD and AL-Am-LCs showed striking expansion of each of the above-mentioned compartments, respectively. This indicates the presence of more RER in the LCDD-LC-treated HMCs and a striking increase in lysosomes noticeable in the AL-Am-LC-treated cells. Data obtained in this study highlighted that HMCs incubated with LCDD-LCs undergo a myofibroblastic phenotypic transformation, while AL-Am-LCs induce a macrophage-like phenotype in these cells.

Type IV collagen is transcriptionally regulated by Smad1 under advanced glycation end product (AGE) stimulation

Prolonged exposure to hyperglycemia is now recognized as the most significant causal factor of diabetic complications. Excessive advanced glycation end products (AGEs) as a result of hyperglycemia in tissues or in the circulation may critically affect the progression of diabetic nephropathy. In diabetic nephropathy, glomerulosclerosis is a typical pathologic feature characterized by the increase of the extracellular matrix (ECM). We have reported previously that alpha1 type IV collagen (Col4) is one of the major components of ECM, which is up-regulated by AGEs, and that the overexpression of Col4 is transcriptionally regulated by an unknown transcription factor binding to the promoter. Here we identified this protein as Smad1 by yeast one-hybrid screening. Using chromatin immunoprecipitation and reporter assay, we observed that Smad1 directly regulated transcription for Col4 through the binding of Smad1 to the promoter of Col4. Smad1 was significantly induced along with Col4 in AGE-treated mesangial cells. Moreover, suppression of Smad1 by antisense morpholino resulted in a decrease of AGE-induced Col4 overproduction. To elucidate the interaction between transforming growth factor-beta and Smad1, we investigated whether activin receptor-liked kinase1 (ALK1) was involved in this regulation. AGE stimulation significantly increased the expression of the ALK1 mRNA in mesangial cells. We also demonstrated that Smad1 and ALK1 were highly expressed in human diabetic nephropathy. These results suggest that the modulation of Smad1 expression is responsible for the initiation and progression of diabetic nephropathy and that blocking Smad1 signaling may be beneficial in preventing diabetic nephropathy and other various diabetic complications.

Cyclooxygenase-2 inhibits tumor necrosis factor alpha-mediated apoptosis in renal glomerular mesangial cells

Renal mesangial cell apoptosis is a crucial repair mechanism in glomerular nephritis (GN). These cells express receptors to tumor necrosis factor alpha (TNFalpha), a cytokine with proapoptotic properties implicated in the resolution of GN. Progression to proliferative GN is accompanied by cyclooxygenase-mediated formation of prostaglandins and inefficient apoptosis of mesangial cells. The aims of this study were to quantify TNFalpha-mediated apoptosis in renal mesangial cells and to determine whether expression of the inducible form of cyclooxygenase, cylooxygenase-2 (COX-2), inhibits this apoptosis. By 24 h significant levels of apoptosis were induced by TNFalpha (100 ng/ml) or etoposide control (100 microm), as shown by phosphatidylserine externalization, caspase-3 activation, development of a sub-G(0)/G(1) region, and distinct chromatin condensation. Using adenoviral-mediated delivery of the COX-2 gene (AdCOX-2) apoptotic features were prevented from appearing in AdCOX-2 cells treated with TNFalpha, whereas etoposide-treated AdCOX-2 cells were not protected. Furthermore, COX-2 expression, induced by the vasoconstrictor peptide ET-1 or the cytokine interleukin-1beta also inhibited TNFalpha-mediated but not etoposide-mediated apoptosis, to an extent, similar to adenoviral COX-2 infection. Selective COX-2 inhibition by NS-398 restored TNFalpha-mediated apoptosis. Prostaglandin (PG) E(2) and PGI(2) were shown to be the major prostaglandin metabolites in AdCOX-2 cells. The addition of PGE(2) and PGI(2) protected against TNFalpha-mediated apoptosis. These results demonstrate COX-2 anti-apoptotic activity via a death receptor route and suggest that selective COX-2 inhibition may augment TNFalpha apoptosis in chronic inflammatory conditions.

Surface antigens of human mesangial cells: impact of growth surface or IL-1alpha

The interactions of mesangial cells (MC) with their environment are important events in glomerular physiology and pathology, yet a detailed characterization of the MC-surface antigens mediating these interactions is still lacking. In this study, a comparative phenotype analysis of primary human MC in culture using 191 monoclonal antibodies directed against 108 antigens was performed by flow-cytometry. The MC were grown on three different surfaces (human matrix, fibronectin, polystyrene) and cultured in the presence or absence of IL-1alpha. Seventy-one antibodies recognizing 35 different antigens (integrins: CD29, 49b, 49c, 49e, 51, 61; immunoglobulin gene family: CD54, 58, 90, 106, 146, 147, 166; growth factor receptors: CD105, 140b; apoptosis related: CD95; hemostatis related: CD141, 142; miscellaneous: CD44, 109, 138, 151, 157, 165, and 11 nonclustered antigens) reacted with mesangial cells. CD58, 109, 146, 147, 151, 157, 165, and 166 are reported for the first time to be present on human mesangial cells. In comparison to growth on polystyrene, CD44, 54, 95, 105, 109, 140b, 146, 147, 157, 165 and 166, were up-regulated on fibronectin, and CD44, 54, 90, 95, 105, 106, 109, 138, 140b, 141, 142, 146, 147, 151, 157, 165 and 166 were up-regulated on human matrix. The stimulation by IL-1alpha up-regulated CD44, 49e, 51, 54, 61, 106 on MC on polystyrene; CD49e, 51, 61, 106, 146, 165 on MC on fibronectin, and CD49e, 51, 54 on MC grown on human matrix. This analysis of surface antigen expression provides new information to enable a better understanding of the role of mesangial cells in glomerular pathophysiology.

Interactions of human mesangial cells with IgA and IgA-containing immune complexes

BACKGROUND

IgA nephropathy (IgAN) is characterized by IgA1-containing immune complexes in mesangial deposits and in the circulation. The circulating immune complexes (CIC) are composed of galactose- (Gal) deficient IgA1 and IgG or IgA1 antibodies specific for the Gal-deficient IgA1; interactions of these CIC with mesangial cells (MC) were studied.

METHODS

Binding, internalization, and catabolic degradation of myeloma IgA1 protein as a standard control and the isolated CIC were studied using human MC, hepatoma cell line HepG2 expressing the asialoglycoprotein receptor (ASGP-R), and monocyte-like cell line U937 expressing the Fc(alpha)-R (CD89). Biochemical and molecular approaches were used to assess expression of CD89 and ASGP-R by MC.

RESULTS

At 4 degrees C, radiolabeled IgA1 bound to MC and HepG2 cells in a dose-dependent and saturable manner. The binding was inhibited by IgA-containing CIC or excess IgA1 or its Fc fragment but not by the Fab fragment of IgA1. At 37 degrees C, the cell-bound IgA1 was internalized and catabolized. In addition to IgA1, HepG2 cells also bound (in a Ca2+-dependent manner), internalized, and catabolized asialoorosomucoid (ASOR), other asialo-(AS)-glycoproteins, and secretory component (SC). The binding by MC appeared to be restricted to IgA1 or AS-IgA1 and was not Ca2+-dependent. Furthermore, MC and HepG2 cells internalized and catabolized IgA1-containing CIC. Using RT-PCR with ASGP-R- or CD89-specific primers, mRNAs of the two respective genes were not detected in MC.

CONCLUSIONS

The data showed that the ability of MC to bind IgA1 and IgA1-containing CIC in vitro was mediated by an IgA receptor that was different from CD89 or ASGP-R and had a higher affinity for IgA-CIC than for uncomplexed IgA.

Novel regulation of adrenomedullin receptor by PDGF: role of receptor activity modifying protein-3

Receptor activity modifying protein-3 (RAMP-3) has been shown to complex with the calcitonin receptor-like receptor, establishing a functional receptor for adrenomedullin (AM). AM exhibits potent antiproliferative and antimigratory effects on rat mesangial cells (RMCs). In this study we investigated the effect of platelet-derived growth factor (PDGF) on RAMP-3 expression in RMCs. We show here that PDGF-BB stimulates RAMP-3 mRNA expression in a concentration-dependent manner. Pretreatment with actinomycin-D and alpha-amanitin demonstrates that this effect is independent of new RNA synthesis. Furthermore, PDGF increased the half-life of RAMP-3 mRNA from 66.5 to 331.6 min. Using selective inhibitors, our results also indicate that the increase in RAMP-3 mRNA is mitogen-activated protein kinase (MAPK) kinase (MEK)/MAPK and p38 MAPK dependent. PDGF also caused a corresponding elevation in membrane-associated RAMP-3 protein. Associated with this increase, PDGF pretreatment led to a significantly higher AM-mediated adenylate cyclase activity, suggesting a functional consequence for the PDGF-induced increase in RAMP-3 expression. Taken together, these data identify PDGF-dependent regulation of RAMP-3 expression as a possible mechanism for modulating the responsiveness of the mesangial cell to AM.

Extracellular superoxide dismutase and glomerular mesangial cells: its production and regulation

Extracellular superoxide dismutase (EC-SOD) is synthesized in mesenchymally derived cells and prevents the oxygen radical-induced injury. We studied whether kidney mesangial cells (MCs) produce EC-SOD and how its production is associated with chemokine secretion. Under unstimulated condition, MCs produced EC-SOD, and its production was correlated positively with cyclic adenosine monophosphate (cAMP), but negatively with interleukin (IL)-6 or IL-8 production. By prednisolone or phorbol myristate acetate treatment, EC-SOD levels were correlated negatively with levels of IL-6 and IL-8. The presence of adenylate cyclase inhibitor 2',3'-dideoxyadenosine lost the prednisolone effect. The stimulation of EC-SOD production might be one of the important effects of prednisolone via cAMP pathway in MCs.

Bone marrow is a reservoir of repopulating mesangial cells during glomerular remodeling

The renal glomerulus, whose cellular components are developmentally derived from the mesenchyme, plays a pivotal role in filtratating plasma. Irretrievable changes of glomerular components are responsible for the initiation and progression of impaired renal function. Recently, it has been shown that functional stem cells exist in the bone marrow of adult bodies and that they can reconstitute damaged tissues of the mesenchymal origin. To examine whether the bone marrow provides stem cells to damaged glomeruli, transgenic rats carrying enhanced green fluorescence protein (EGFP rat) were established in a systemic and constitutive manner. After transplanting the bone marrow of EGFP rats into wild-type rats, the progeny of the transplanted marrow cells were tracked with a tag of EGFP. Recruitment of bone marrow-derived cells into glomeruli was dramatically facilitated in response to mesangiolysis evoked in anti-Thy1 antibody-mediated glomerulonephritis. In the restored glomeruli, 11% to 12% of glomerular cells were derived from the transplanted bone marrow. The number of bone marrow-derived CD45(+) cells transiently increased during the disease process, and CD45-negative cells constantly accounted for more than half of the bone marrow-derived population in glomeruli. Bone marrow-derived Thy1(+) cells kept increasing in number until the remodeling ceased and finally made up 7% to 8% of glomerular cells. Laser scanning microscopy displayed that the bone marrow-derived Thy1(+) cells provide structural support for glomerular capillaries, which indicates that they are mesangial cells. Although CD45(-)Thy1(-) bone marrow-derived cells exist during the remodeling of glomeruli, none of them expressed endothelial markers such as Factor VIII and RECA1 as long as they were tested. The results indicate that the bone marrow can give rise to mesangial cells in vivo.

What is the difference between IgA nephropathy and Henoch-Schönlein purpura nephritis?

Henoch-Schönlein purpura nephritis (HSPN) and IgA nephropathy (IgAN) are considered to be related diseases since both can be encountered consecutively in the same patient, they have been described in twins, and bear identical pathological and biological abnormalities. Apart from the presence of extrarenal clinical signs found only in HSPN, other differences are noticed between the two diseases. The peak age ranges between 15 and 30 years for a diagnosis of IgAN, whereas HSPN is mainly seen in childhood. Nephritic and/or nephrotic syndromes are more often seen at presentation in HSPN. In contrast to IgAN, HSPN has been described in association with hypersensitivity. Endocapillary and extracapillary inflammations as well as fibrin deposits in the glomerulus are more frequent in HSPN. No major biological differences have been found between the two illnesses, except for a larger size of circulating IgA-containing complexes (IgA-CC) and a greater incidence of increased plasma IgE levels in HSPN. As tissue infiltration by leukocytes is a major feature of HSPN vasculitis, a possible role of a more potent activation of the latter cells by IgA-CC and/or circulating chemokines in HSPN should be considered. Further studies are required to elucidate this possible mechanism as well as the role of hypersensitivity in HSPN.

Involvement of prostaglandin E2 in clearance of aggregated protein via protein kinase A in glomeruli

Recently we immunohistochemically demonstrated that prostaglandin E2 (PGE2) promoted the clearance of aggregated bovine serum albumin (a-BSA) deposited in glomeruli. Herein, we investigated the role of PGE2 and its signal transduction in the disposal of macromolecules in glomeruli. EP2 and EP4 receptor mRNA was detected in glomeruli by RT-PCR analysis. A-BSA was injected twice into mice. Glomeruli were then isolated and incubated. A-BSA gradually disappeared from isolated glomeruli. PGE2 increased the intracellular cyclic AMP and decreased a-BSA level in glomeruli. Additionally, 8-bromocyclic AMP evoked a loss of a-BSA in isolated glomeruli. The effect of 8-bromo-cyclic AMP on the clearance of a-BSA was abolished by KT 5720 in glomeruli. PGE2 and 8-bromo-cyclic AMP also prompted disposal of a-BSA in cultured mesangial cells. These findings indicate that PGE2 positively regulates the removal of macromolecules via cyclic AMP and protein kinase A in glomeruli, and they provide insight into how to prevent the development of glomerulonephritis and glomerulosclerosis.

Caveolae in mesangial cells and caveolin expression in mesangial proliferative glomerulonephritis

BACKGROUND

Caveolae are plasma membrane invaginations that have a diameter of 40 to 60 nm. Recent evidences have demonstrated that caveolae contain a variety of signal transduction molecules. Caveolin is a marker protein of caveolae and has been proposed to play a negative regulatory role in signal transduction. The aim of this study was to investigate the behavior of caveolae and caveolin in experimental glomerulonephritis, the localization of both platelet-derived growth factor (PDGF) and transforming growth factor-beta (TGF-beta) receptors in the caveolae membrane, and the regulation of caveolin expression in cultured mesangial cells.

METHODS

The expression of caveolin-1 was examined by immunoblotting and immunohistology using anti-caveolin antibody in anti-Thy-1 nephritis. The caveolae membrane fraction of mesangial cells was isolated by sucrose gradient method and expression of PDGF receptor and TGF-beta receptor were detected by immunoblotting. The effects of mitogens such as phorbol 12-myristate 13-acetate (PMA) and PDGF on the expression of caveolin-1 protein and mRNA were also examined in cultured mesangial cells.

RESULTS

Caveolin-1 was mainly expressed in glomeruli and was significantly up-regulated in anti-Thy-1 nephritis rat kidney. In cultured mesangial cells, the membrane invaginations of caveolae were revealed by electron microscopy. PDGF receptors abounded in the caveolae membrane and rapidly changed their subcellular distribution after ligand stimulation. In contrast, TGF-beta receptors abounded in the non-caveolae membrane and did not change after ligand stimulation. Decreases in caveolin-1 protein, which were associated with increases in mRNA expression after the exposure of PMA or PDGF-BB, suggested an increased turnover of caveolin-1 in mesangial cells stimulated by mitogens.

CONCLUSION

To our knowledge, this electron microscopical study is the first to demonstrate the presence of caveolae in cultured mesangial cells. Caveolae integrate PDGF receptors, and caveolin-1 may play a role in the pathogenesis of the mesangial proliferative glomerular diseases through PDGF signaling.

Cyclooxygenase 2 promotes cell survival by stimulation of dynein light chain expression and inhibition of neuronal nitric oxide synthase activity

Cyclooxygenase 2 (COX-2) inhibits nerve growth factor (NGF) withdrawal apoptosis in differentiated PC12 cells. The inhibition of apoptosis by COX-2 was concomitant with prevention of caspase 3 activation. To understand how COX-2 prevents apoptosis, we used cDNA expression arrays to determine whether COX-2 regulates differential expression of apoptosis-related genes. The expression of dynein light chain (DLC) (also known as protein inhibitor of neuronal nitric oxide synthase [PIN]) was significantly stimulated in PC12 cells overexpressing COX-2. The COX-2-dependent stimulation of DLC expression was, at least in part, mediated by prostaglandin E(2). Overexpression of DLC also inhibited NGF withdrawal apoptosis in differentiated PC12 cells. Stimulation of DLC expression resulted in an increased association of DLC/PIN with neuronal nitric oxide synthase (nNOS), thereby reducing nNOS activity. Furthermore, nNOS expression and activity were significantly increased in differentiated PC12 cells after NGF withdrawal. This increased nNOS activity as well as increased nNOS dimer after NGF withdrawal were inhibited by COX-2 or DLC/PIN overexpression. An nNOS inhibitor or a membrane-permeable superoxide dismutase (SOD) mimetic protected differentiated PC12 cells from NGF withdrawal apoptosis. In contrast, NO donors induced apoptosis in differentiated PC12 cells and potentiated apoptosis induced by NGF withdrawal. The protective effects of COX-2 on apoptosis induced by NGF withdrawal were also overcome by NO donors. These findings suggest that COX-2 promotes cell survival by a mechanism linking increased expression of prosurvival genes coupled to inhibition of NO- and superoxide-mediated apoptosis.

Stretch-induced mesangial cell ERK1/ERK2 activation is enhanced in high glucose by decreased dephosphorylation

Glomerular hypertension and hyperglycemia are major determinants of diabetic nephropathy. We sought to identify the mechanisms whereby stretch-induced activation of mesangial cell extracellular signal-regulated kinase 1 and 2 (ERK1/ERK2) is enhanced in high glucose (HG). Mesangial cells cultured on fibronectin Flex I plates in normal glucose (NG; 5.6 mM) or HG (30 mM), were stretched by 15% elongation at 60 cycles/min for up to 60 min. In HG, a 5-min stretch increased ERK1/ERK2 phosphorylation by 6.4 +/- 0.4/4.3 +/- 0.3-fold (P < 0.05 vs. NG stretch). In contrast, p38 phosphorylation was increased identically by stretch in NG and HG. Unlike many effects of HG, augmentation of ERK activity by HG was not dependent on protein kinase C (PKC) as indicated by downregulation of PKC with 24-h phorbol ester or inhibition with bisindolylmaleimide IV. In both NG and HG, pretreatment with arginine-glycine-aspartic acid peptide (0.5 mg/ml) to inhibit integrin binding or with cytochalasin D (100 ng/ml) to disassemble filamentous (F) actin, significantly reduced phosphorylation of ERK1/ERK2 and p38. To determine whether the rate of mitogen-activated protein kinase dephosphorylation is affected by HG, cellular kinase activity was inhibited by depleting ATP. Post-ATP depletion, phosphorylation of ERK1/ERK2 was reduced to 36 +/- 9/51 +/- 14% vs. 9 +/- 5/7 +/- 6% in NG (P < 0.05, n = 5). Thus stretch-induced ERK1/ERK2 and p38 activation in both NG and HG is beta(1)-integrin and F-actin dependent. Stretch-induced ERK1/ERK2 is enhanced in high glucose by diminished dephosphorylation, suggesting reduced phosphatase activity in the diabetic milieu. Enhanced mesangial cell ERK1/ERK2 signaling in response to the combined effects of mechanical stretch and HG may contribute to the pathogenesis of diabetic nephropathy.

Phenotypic profiles of cultured glomerular cells following repeated cycles of hydrocarbon injury

BACKGROUND

The glomerulus has been implicated as a target of hydrocarbon injury in vitro and in vivo. In the present studies, the phenotypic profiles of cultured rat glomerular cells (GCs) following repeated cycles of hydrocarbon injury were evaluated. Cultured GCs were incubated for 24 hours with benzo[a]pyrene (BaP; 3 micromol/L), a prototypical polycyclic aromatic hydrocarbon, and were allowed to recover overnight before two additional cycles of chemical challenge during serial propagation in vitro. At the end of this regimen, control cultures were characterized by predominance of fusiform cells that grew in "hills and valleys," while GCs subjected to hydrocarbon injury displayed an epithelial morphology characterized by a rounded, polygonal shape clearly distinct from that normally exhibited by glomerular mesangial cells (GMCs) in culture.

METHODS

Indirect immunofluorescent detection of cell markers was conducted to identify cells of mesenchymal or epithelial origin. Measurements of DNA synthesis and cell number were performed to determine proliferative capacities of the different cell types in response to hydrocarbon challenge.

RESULTS

Immunofluorescence studies revealed that control GC cultures contained mostly alpha-smooth muscle (SM) actin-positive cells, with a few (5.1% +/- 2.6) E-cadherin-positive cells occasionally identified. In contrast, BaP-treated cultures exhibited a mixed cell population in which E-cadherin-positive cells were predominant (66.6% +/- 4.1). Single-cell cloning of naive cultures of GCs yielded four clones, three of which exhibited a fusiform morphology and were alpha-SM actin positive (SCC 1 through SCC 3) and one (SCC 4E) that exhibited epithelial characteristics similar to those found in hydrocarbon-treated cultures. Immunofluorescence studies showed that epithelial cells in hydrocarbon-treated cultures, as well as SCC 4E-derived clones, were vimentin positive and cytokeratin negative, characteristics similar to glomerular visceral epithelial cells (GVECs). DNA synthesis and cell proliferation in clone SCC 1 were decreased following acute BaP challenge, while growth rates in SCC 4E-derived clones were unaffected by hydrocarbon injury. Repeated cycles of hydrocarbon challenge in clonal populations yielded different profiles of DNA synthesis, with significant decreases in SCC 1 and no changes in SCC 4E.

CONCLUSIONS

These observations suggest that hydrocarbon injury induces differential responses in cells of the glomerulus, resulting in inhibition of GMCs and selective growth advantage of GVECs. These alterations are reminiscent of critical events described in the pathogenesis of focal segmental glomerulosclerosis and raise important questions about the pathogenesis of hydrocarbon-induced nephropathies.

A vitamin D analog regulates mesangial cell smooth muscle phenotypes in a transforming growth factor-beta type II receptor-mediated manner

Mesangial cells share features with contractile smooth muscle cells and mechanically support the capillary wall. The role of vitamin D compounds and the transforming growth factor-beta (TGF-beta) type II receptor in modulating the smooth muscle phenotype of cultured mesangial cells was examined. Cell proliferation was significantly inhibited by the vitamin D analog 22-oxa-1,25-dihydroxyvitamin D(3) (22-oxacalcitriol; OCT) rather than by 1,25-dihydroxyvitamin D(3) (1, 25(OH)(2)D(3)) in a dose-dependent manner. OCT-treated early passage mesangial cells (MC-E cells) had increased expression levels of type IV collagen and smooth muscle alpha actin mRNA, but 1, 25(OH)(2)D(3)-treated MC-E cells did not. The addition of a TGF-beta(1)-neutralizing antibody to the OCT-treated MC-E cells blocked this inhibitory effect for cell proliferation and attenuated the up-regulated mRNA levels. However, after exposure to 1, 25(OH)(2)D(3) or OCT, there was no significant difference in the secretion of active TGF-beta. We next investigated whether TGF-beta type II receptor (RII) was involved in this regulation. OCT treatment significantly increased the expression of the RII mRNA in MC-E cells. These results suggest that the vitamin D analog OCT induces smooth muscle phenotypic alterations and that this phenomenon was mediated through the induction of RII in cultured mesangial cells.

Angiotensin II stimulates the synthesis and secretion of vascular permeability factor/vascular endothelial growth factor in human mesangial cells

The aim of the present study was to evaluate the role of angiotensin II (AngII) in regulating both the gene expression and secretion of vascular permeability factor/vascular endothelial growth factor (VPF/VEGF) in human mesangial cells (HMC) in culture. Densitometric analysis of Northern blot experiments demonstrated that AngII increases VPF/VEGF mRNA in a dose-dependent manner. The levels of VPF/VEGF mRNA in HMC exposed for 3 h to 10 nM, 100 nM, and 1 microM AngII were, respectively, 1.5-, 2.3-, and 1.6-fold higher than control cells (P < 0.05, P < 0.0001, and P < 0.05, respectively). This effect was blocked by the pretreatment with losartan (1 microM) (P < 0.005), a selective antagonist of the AngII AT1 receptor. Reverse transcription-PCR performed in HMC using oligonucleotide primers specific for all VPF/VEGF mRNA splicing variants detected three bands corresponding to VEGF 189, 165, and 121. Exposure of the cells to 100 nM AngII resulted in an increase of all the mRNA transcripts. Furthermore, in situ hybridization experiments showed that the levels of hybridization signals for VPF/VEGF mRNA resulted consistently higher in HMC exposed for 3 h to AngII (100 nM) than in control cells. The effects of AngII on the secretion of VPF/VEGF peptide in the culture medium of HMC were assessed using an enzyme-linked immunosorbent assay method. When different concentrations of AngII were tested in 3-h stimulation periods, the percentage of increase in the levels of released VPF/VEGF was significantly higher than control cells for AngII concentrations of 100 nM (62 +/- 11% mean +/- SD, P < 0.0001) and 1 microM (17.3 +/- 10.9%, P < 0.01). The pretreatment of HMC with losartan (1 microM) prevented the increase of VPF/VEGF secretion induced by AngII (100 nM) (AngII 54.7 +/- 3.9 pg/microg DNA versus AngII + losartan 37.8 +/- 3.6 pg/microg DNA, mean +/- SD, P < 0.005). VPF/VEGF protein was time dependently released in the culture medium under basal, steady-state conditions. Compared with control cells, AngII (100 nM) caused a significant increase in the levels of released VPF/VEGF after 3 and 6 h (control 33.8 +/- 1.7 pg/microg DNA at 3 h, 42.1 +/- 1.1 at 6 h, and 117.7 +/- 10 at 24 h; AngII 54.7 +/- 3.9 at 3 h, P < 0.0001, 61.6 +/- 8.7 at 6 h, P < 0.05, and 144.7 +/- 22.7 at 24 h, NS; mean +/- SD). According to the results obtained from enzyme-linked immunosorbent assay experiments, Western blot analysis showed that the intensity of the 19-kD band corresponding to VPF/VEGF was 1.5-fold higher in AngII (100 nM)-treated HMC than in control cells. Similarly, immunocytochemistry on HMC demonstrated an increase in intracellular VPF/VEGF immunostaining in response to AngII treatment (100 nM) compared with control cells. This study demonstrated that in HMC, AngII augmented the levels of VPF/VEGF gene expression and stimulated the synthesis and secretion of its peptide by activating AT1 receptors. Through these mechanisms, AngII may affect the functions of endothelial cells during the development of renal diseases involving the glomerulus.

Endothelin-1-induced mesangial cell contraction involves activation of protein kinase C-alpha, -delta, and -epsilon

In endothelin-1 (ET-1)-stimulated mesangial cells, to identify the independent roles of calcium and protein kinase C (PKC) causing contraction, the changes in planar surface area in response to ET-1, ionomycin, or phorbol 12-myristate 13-acetate (PMA) were compared. ET-1, PMA, and ionomycin reduced planar area to 49 +/- 3%, 56 +/- 3%, and 78 +/- 2% of basal (means +/- SE, n = 40-50 cells), respectively. ET-1 or ionomycin increased cytosolic calcium from 80 +/- 7 to 220 +/- 30 nM or 97 +/- 10 to 192 +/- 10 nM, respectively. The myosin light chain kinase inhibitor, ML-7, blunted ET-1- but not PMA-stimulated contraction (82 +/- 3% and 48 +/- 6% of time 0, respectively). Cells pretreated with 10 microM chelerythrine for 1 h or PMA for 24 h failed to contract to either ET-1 or PMA. To identify the specific PKC isoform response to ET-1, cytosolic, membrane, and particulate fractions of mesangial cell lysates were immunoblotted with PKC isoform-specific polyclonal antibodies. ET-1 increased membrane PKC-alpha, -delta, and -epsilon to 173 +/- 30%, 162 +/- 26%, and 166 +/- 11% of basal (P < 0.05 vs. basal), respectively, and decreased PKC-delta and PKC-epsilon in the cytosol to 56 +/- 11% and 37 +/- 6% of basal, respectively (P < 0.05). ET-1 increased particulate PKC-delta and PKC-epsilon to 172 +/- 15% and 187 +/- 33% of basal (P < 0.05), respectively. PKC-alpha in the cytosol and particulate fractions was not altered by ET-1, but translocation to the nucleus and cell periphery was observed by confocal immunofluorescence imaging. Ionomycin did not change PKC isoform distribution. PKC-zeta was expressed but unaltered by ET-1. Therefore, mesangial cell ET-1-stimulated contraction not only involves a calcium-dependent pathway but also includes the activation of one or more PKC-alpha, -delta, and -epsilon, but not PKC-zeta.

Inhibition of mesangial cell proliferation by E2F decoy oligodeoxynucleotide in vitro and in vivo

The transcription factor E2F coordinately activates several cell cycle-regulatory genes. We attempted to inhibit the proliferation of mesangial cells in vitro and in vivo by inhibiting E2F activity using a 25-bp decoy oligodeoxynucleotide that contained consensus E2F binding site sequence (E2F-decoy) as a competitive inhibitor. The decoy's effect on human mesangial cell proliferation was evaluated by [3H]thymidine incorporation. The E2F decoy inhibited proliferation in a concentration-dependent manner, whereas a mismatch control oligodeoxynucleotide had little effect. Electrophoretic mobility shift assays demonstrated that the decoy's inhibitory effect was due to the binding of the decoy oligodeoxynucleotide to E2F. The effect of the E2F decoy was then tested in a rat anti-Thy 1.1 glomerulonephritis model. The E2F decoy oligodeoxynucleotide was introduced into the left kidney 36 h after the induction of glomerulonephritis. The administration of E2F decoy suppressed the proliferation of mesangial cells by 71%. Furthermore, treatment with the E2F decoy inhibited the glomerular expression of proliferating cell nuclear antigen at the protein level as well as the mRNA level. These findings indicate that decoy oligonucleotides can suppress the activity of the transcription factor E2F, and may thus have a potential in treating glomerulonephritis.

Correlation between sustained c-Jun N-terminal protein kinase activation and apoptosis induced by tumor necrosis factor-alpha in rat mesangial cells

Rat mesangial cells are normally resistant to tumor necrosis factor-alpha (TNF-alpha)-induced apoptosis. In this report we show that the cells can be made susceptible to the apoptotic effect of TNF-alpha when pretreated with actinomycin D, cycloheximide, or vanadate. c-Jun N-terminal protein kinase (JNK) has been thought to mediate apoptotic processes elicited by some stimuli, but its involvement in TNF-alpha-induced apoptosis has been controversial. JNK activation was investigated under conditions where the mesangial cells were either resistant or susceptible to TNF-alpha-induced apoptosis. TNF-alpha alone stimulated a single transient JNK activity peak. However, when the cells were pretreated with actinomycin D or cycloheximide, TNF-alpha stimulated a second sustained JNK activity peak. When the cells were pretreated with the phosphatase inhibitor vanadate, TNF-alpha-induced JNK activation was greatly prolonged. In all three cases, a sustained JNK activation was associated with the initiation of apoptosis. Our data suggest that a sustained activation of JNK induced by these reagents may be associated with blocking the expression of a phosphatase that inactivates JNK. Further studies reveal that the expression of mitogen-activated protein kinase phosphatase-1 (MKP-1) was induced by TNF-alpha, indicating that MKP-1 may be involved in protecting the cells from apoptosis by preventing a prolonged activation of JNK under normal conditions. Additional studies showed that extracellular signal-regulated protein kinase activation stimulated by TNF-alpha was unlikely to contribute to the resistance of mesangial cells to TNF-alpha cytotoxicity.

Distinct pathogenic effects of group B coxsackieviruses on human glomerular and tubular kidney cells

The six group B coxsackieviruses (CVBs) are highly prevalent human pathogens that cause viremia followed by involvement of different organs. Clinical and experimental evidence suggests that CVBs can induce kidney injury, but the susceptibility of human renal cells to these viruses is unknown. By using pure cultures of human glomerular and tubular cells, we demonstrated that all CVBs are capable of productively infecting renal cells of three different histotypes. Distinct pathogenic effects were observed. Proximal tubular epithelial cells and, to a lesser extent, glomerular podocytes were highly susceptible to CVBs; in both cases, infection led to cytolysis. In contrast, glomerular mesangial cells supported the replication of the six CVBs but failed to develop overt cytopathologic changes. Mesangial cells continued to produce infectious progeny for numerous serial subcultures (i.e., more than 50 days), especially with type 1, 3, 4, and 5 viruses. In the above cells, persistent infection induced the de novo synthesis of platelet-derived growth factor A/B and enhanced the release of transforming growth factor beta1/2. These two factors are important mediators of progression from glomerular inflammation to glomerulosclerosis. CVB replication appeared also to impair the phagocytic and contractile activity of mesangial cells. Loss of these properties--which are important in glomerular physiopathology--may contribute to the development of progressive nephropathy. The results show that CVBs induce distinct effects in different types of cultured renal cells and suggest that CVB infections may be associated with both acute and progressive renal injury.

Inhibition of glomerular mesangial cell proliferation and extracellular matrix deposition by halofuginone

Mesangial cell proliferation, increased deposition of collagen, and expansion of the mesangial extracellular matrix (ECM) are key features in the development of mesangioproliferative diseases. Halofuginone, a low molecular weight anti-coccidial quinoazolinone derivative, inhibits collagen type alpha 1(I) gene expression and synthesis. We investigated the effect of halofuginone on both normal and SV40 transformed mesangial cell proliferation, collagen synthesis, and ECM deposition. Proliferation of both cell types was almost completely inhibited in the presence of 50 ng/ml halofuginone. The cells were arrested in the late G1 phase of the cell cycle and resumed their normal growth rate following removal of the compound from the culture medium. The antiproliferative effect of halofuginone was associated with inhibition of tyrosine phosphorylation of cellular proteins. Similar results were obtained whether the mesangial cells were seeded on regular tissue culture plastic or in close contact with a naturally produced ECM resembling their local environment in vivo. Halofuginone also inhibited synthesis and deposition of ECM by mesangial cells as indicated by a substantial reduction in 14C-glycine and Na2(35)SO4 incorporation into the ECM, and by the inhibition of collagen type I synthesis and gene expression. It is proposed that by inhibiting collagen type I synthesis and matrix deposition, halofuginone exerts a potent antiproliferative effect that may be applied to inhibit mesangial cell proliferation and matrix expansion in a variety of chronic progressive glomerular diseases.