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Biomedical subjects

Matthias Kretzler

Publications and source records attributed to Matthias Kretzler.

At least 37 records · Page 2Linked to original sources

Novel role of toll-like receptor 3 in hepatitis C-associated glomerulonephritis.

Hepatitis C virus (HCV) infection is frequently complicated by glomerulonephritis with immune complexes containing viral RNA. We examined the potential influence of Toll-like receptors (TLRs), specifically TLR3 recognition of viral dsRNA exemplified by polyriboinosinic:polyribocytidylic acid [poly(I:C) RNA]. Normal human kidney stained positive for TLR3 on mesangial cells (MCs), vascular smooth muscle cells, and collecting duct epithelium. Cultured MCs have low TLR3 mRNA levels with predominant intracellular protein localization, which was increased by tumor necrosis factor-alpha, interleukin (IL)-1beta, interferon (IFN)-gamma, and the TLR3 ligand poly(I:C) RNA. Poly(I:C) RNA stimulation of MCs increased mRNA and protein synthesis of IL-6, IL-1beta, M-CSF, IL-8/CXCL8, RANTES/CCL5, MCP-1/CCL2, and ICAM-I; it also increased anti-proliferative and proapoptotic effects, the latter of which was decreased by inhibiting caspase-8. In microdissected glomeruli of normal and non-HCV membranoproliferative glomerulonephritis biopsies, TLR3 mRNA expression was low. In contrast TLR3 mRNA expression was significantly increased in hepatitis C-positive glomerulonephritis and was associated with enhanced mRNA for RANTES/CCL5 and MCP-1/CCL2. We hypothesize that immune complexes containing viral RNA activate mesangial TLR3 during HCV infection, thereby contributing to chemokine/cytokine release and effecting proliferation and apoptosis. Thus, TLR3 expression on renal cells, and especially MCs, may establish a link between viral infections and glomerular diseases.

Apoptosis↗

Toll-like receptor-7 modulates immune complex glomerulonephritis.

Viral infections may trigger immune complex glomerulonephritis via Toll-like receptors (TLR), as certain TLR trigger immunity upon recognition of viral nucleic acids. On the basis of previous findings regarding viral double-stranded RNA and TLR3 in experimental lupus erythematosus, a similar role for TLR7 that recognizes viral single-stranded RNA was hypothesized. Immunostaining of kidney sections of nephritic MRLlpr/lpr mice revealed TLR7 expression in infiltrating ER-HR3-positive macrophages and few CD11c-positive dendritic cells but not in glomerular mesangial cells as observed for TLR3. This finding was consistent with the distribution pattern of intravenously injected single-stranded RNA in nephritic MRLlpr/lpr mice. TLR7 ligation activated monocytes and dendritic cells, both isolated from MRLlpr/lpr mice, to secrete IFN-alpha, IL-12p70, IL-6, and CCL2. In vivo, a single injection of the TLR7 ligand imiquimod increased serum levels of IL-12p70, IFN-alpha, and IL-6. A course of 25 microg of imiquimod given every other day from week 16 to 18 of age aggravated lupus nephritis in MRLlpr/lpr mice. This was associated with increased glomerular immune complex deposits as well as interstitial expression of CCL2 in imiquimod-treated MRLlpr/lpr mice. Different types of viral nucleic acids seem to modulate systemic autoimmunity through specific interactions with their respective TLR. Different TLR expression profiles on immune cell subsets and nonimmune parenchymal cell types determine the molecular mechanisms involved in viral infection-associated exacerbation of lupus nephritis and possibly other types of immune complex glomerulonephritis.

Aminoquinolines↗

Polyomavirus DNA and RNA detection in renal allograft biopsies: results from a European multicenter study.

Polyomavirus mediated nephropathy is an increasingly recognized complication in renal transplant recipients. In all, 362 renal biopsies collected from 15 European transplant centers were analyzed for presence of Polyomavirus nucleic acid (BK virus [BKV] and JC virus [JCV]). We evaluated 302 biopsies of patients with renal allograft dysfunction, including three with known BKV allograft nephropathy (BKVAN), and 60 native kidney biopsies. BKV DNA was detected in 8 of the 302 (2.6 %) biopsies obtained for transplant dysfunction, but in none of the controls. BKV RNA, indicating active viral replication, was found in all BKV DNA positive biopsies available for mRNA expression studies. Retrospective immunohistochemical staining was positive for SV40 large T antigen in all seven evaluated biopsies. BKV DNA and RNA were detected in biopsy tissues from patients with inconspicuous light microscopy for BKVAN. Further studies will evaluate the potential of intrarenal viral BKV RNA as an early predictor for BKVAN.

Adult↗

Sam68-like mammalian protein 2, identified by digital differential display as expressed by podocytes, is induced in proteinuria and involved in splice site selection of vascular endothelial growth factor.

Podocytes, the glomerular epithelial cells of the kidney, share important features with neuronal cells. In addition to phenotypical and functional similarities, a number of gene products have been found to be expressed exclusively or predominantly by both cell types. With the hypothesis of a common transcriptome shared by podocytes and neurons, digital differential display was used to identify novel podocyte-expressed gene products. Comparison of brain and kidney cDNA libraries with those of other organs identified Sam68-like mammalian protein 2 (SLM-2), a member of the STAR family of RNA processing proteins, as expressed by podocytes. SLM-2 expression was found to be restricted in the kidney to podocytes. In proteinuric diseases, SLM-2, a known regulator of neuronal mRNA splice site selection, was found significantly upregulated on mRNA and protein levels. Knockdown of SLM-2 by short interfering RNA in podocytes was performed to evaluate its biologic role. RNA splicing of vascular endothelial growth factor (VEGF), a key regulator of the filtration barrier and expressed as functionally distinct splice isoforms, was evaluated. VEGF(165) expression was found to be reduced by 25% after SLM-2 knockdown. In vivo, the glomerular expression of SLM-2 correlated with the mRNA levels of VEGF(165). This study demonstrates the power of digital differential display to predict cell type-specific gene expression by hypothesis-driven analysis of tissue cDNA libraries. SLM-2-dependent VEGF splicing indicates the importance of mRNA splice site selection for glomerular filtration barrier function.

Animals↗

Formation and phosphorylation of the PINCH-1-integrin linked kinase-alpha-parvin complex are important for regulation of renal glomerular podocyte adhesion, architecture, and survival.

Alterations in the cellular architecture, adhesion, and/or loss of glomerular podocytes are causal factors in the development of proteinuria and the progression to end-stage renal failure. With the use of an inducible podocyte differentiation system, it was found that the cellular levels of PINCH-1, integrin linked kinase (ILK), and alpha-parvin, cytoplasmic components of cell-extracellular matrix adhesions, were significantly increased during podocyte differentiation. Concomitantly, an increased amount of the PINCH-1-ILK-alpha-parvin complex was detected in the differentiated, foot process-containing podocytes. Overexpression of the PINCH-1-binding ankyrin repeat domain of ILK but not that of a PINCH-1-binding defective mutant form of the ankyrin domain effectively inhibited the formation of the PINCH-1-ILK-alpha-parvin complex. Disruption of the PINCH-1-ILK-alpha-parvin complex significantly reduced the podocyte-matrix adhesion and foot process formation. Furthermore, a marked increase of apoptosis in the podocytes in which the assembly of the PINCH-1-ILK-alpha-parvin complex was compromised was detected. Inhibition of ILK with a small compound inhibitor also altered podocyte cytoskeleton and increased apoptosis. Finally, it is shown that alpha-parvin is phosphorylated in podocytes. Mutations at the alpha-parvin N-terminal proline-directed serine phosphorylation sites reduced its complex formation with ILK and resulted in defects in podocyte adhesion, architecture, and survival. These results provide important evidence for a crucial role of the PINCH-1-ILK-alpha-parvin complex in the control of podocyte adhesion, morphology, and survival.

Actinin↗

Viral double-stranded RNA aggravates lupus nephritis through Toll-like receptor 3 on glomerular mesangial cells and antigen-presenting cells.

How viral infections trigger autoimmunity is poorly understood. A role for Toll-like receptor 3 (TLR3) was hypothesized in this context as viral double-stranded RNA (dsRNA) activates dendritic cells to secrete type I interferons and cytokines that are known to be associated with the disease activity in systemic lupus erythematosus (SLE). Immunostaining of nephritic kidney sections of autoimmune MRL(lpr/lpr) mice revealed TLR3 expression in infiltrating antigen-presenting cells as well as in glomerular mesangial cells. TLR3-positive cultured mesangial cells that were exposed to synthetic polyinosinic-cytidylic acid (pI:C) RNA in vitro produced CCL2 and IL-6. pI:C RNA activated macrophages and dendritic cells, both isolated from MRL(lpr/lpr) mice, to secrete multiple proinflammatory factors. In vivo, a single injection of pI:C RNA increased serum IL-12p70, IL-6, and IFN-alpha levels. A course of 50 microg of pI:C RNA given every other day from weeks 16 to 18 of age aggravated lupus nephritis in pI:C-treated MRL(lpr/lpr) mice. Serum DNA autoantibody levels were unaltered upon systemic exposure to pI:C RNA in MRL(lpr/lpr) mice, as pI:C RNA, in contrast to CpG-DNA, failed to induce B cell activation. It therefore was concluded that viral dsRNA triggers disease activity of lupus nephritis by mechanisms that are different from those of bacterial DNA. In contrast to CpG-DNA/TLR9 interaction, pI:C RNA/TLR3-mediated disease activity is B cell independent, but activated intrinsic renal cells, e.g., glomerular mesangial cells, to produce cytokines and chemokines, factors that can aggravate autoimmune tissue injury, e.g., lupus nephritis.

Animals↗

Delayed chemokine receptor 1 blockade prolongs survival in collagen 4A3-deficient mice with Alport disease.

Human Alport disease is caused by a lack of the alpha3-, 4-, or 5-chain of type IV collagen (COL4A). Affected humans and COL4A3-deficient mice develop glomerulosclerosis and progressive renal fibrosis in the presence of interstitial macrophages, but their contribution to disease progression is under debate. This question was addressed by treating COL4A3-deficient mice with BX471, an antagonist of chemokine receptor 1 (CCR1) that is known to block interstitial leukocyte recruitment. Treatment with BX471 from weeks 6 to 10 of life improved survival of COL4A3-deficient mice, associated with less interstitial macrophages, apoptotic tubular epithelial cells, tubular atrophy, interstitial fibrosis, and less globally sclerotic glomeruli. BX471 reduced total renal Cll5 mRNA expression by reducing the number of interstitial CCL5-positive cells in inflammatory cell infiltrates. Intravital microscopy of the cremaster muscle in male mice identified that BX471 or lack of CCR1 impaired leukocyte adhesion to activated vascular endothelium and transendothelial leukocyte migration, whereas leukocyte rolling and interstitial migration were not affected. Furthermore, in activated murine macrophages, BX471 completely blocked CCL3-induced CCL5 production. Thus, CCR1-mediated recruitment and local activation of macrophages contribute to disease progression in COL4A3-deficient mice. These data identify CCR1 as a potential therapeutic target for Alport disease or other progressive nephropathies associated with interstitial macrophage infiltrates.

Animals↗

Expression of gremlin, a bone morphogenetic protein antagonist, in human diabetic nephropathy.

BACKGROUND: We report the induction of gremlin, a bone morphogenetic protein antagonist, in cultured human mesangial cells exposed to high glucose and transforming growth factor beta (TGF-beta) levels in vitro and kidneys from diabetic rats in vivo. METHODS: Gremlin expression was assessed in human diabetic nephropathy by means of in situ hybridization, immunohistochemistry, and real-time polymerase chain reaction and correlated with clinical and pathological indices of disease. RESULTS: Gremlin was not expressed in normal human adult kidneys. Conversely, abundant gremlin expression was observed in human diabetic nephropathy. Although some gremlin expression was observed in occasional glomeruli, gremlin expression was most prominent in areas of tubulointerstitial fibrosis, where it colocalized with TGF-beta expression. Gremlin messenger RNA levels correlated directly with renal dysfunction, determined by means of serum creatinine level, but not with proteinuria level. There was a strong correlation between gremlin expression and tubulointerstitial fibrosis score. CONCLUSION: In aggregate, these results indicate that the developmental gene gremlin reemerges in the context of tubulointerstitial fibrosis in diabetic nephropathy and suggests a role for TFG-beta as an inducer of gremlin expression in this context.

Bone Morphogenetic Proteins↗

Integrin-linked kinase in renal disease: connecting cell-matrix interaction to the cytoskeleton.

PURPOSE OF REVIEW: Cellular functions like proliferation, differentiation, migration, morphogenesis and apoptosis are modulated by the extracellular matrix. Integrins are the prototypic heterodimeric transmembrane matrix receptors with competing affinities for individual extracellular matrix ligands. The intracellular integrin domain clusters cytoplasmic proteins into focal adhesion plaques for bidirectional (outside-in and inside-out) signalling. Integrin-linked kinase organizes the connections of the extracellular matrix via integrins to the cytoskeleton and is involved in adhesion plaque signalling. In this review, an introduction of integrin-linked kinase structure and function is followed by a summary of our current understanding of integrin-linked kinase in renal disease with special focus on glomerular cell-matrix interaction. RECENT FINDINGS: Differential regulation of integrin-linked kinase has been observed during the pathogenesis of glomerular disease and tubulo-interstitial fibrosis. In outside-in signalling integrin-linked kinase mediates the response of renal cells to alterations in matrix and growth factor environments. Inside-out signalling transduces inflammatory and oxidative stress responses into decreased matrix attachment. Downstream signalling of integrin-linked kinase activates the Wnt pathway with a switch towards a proliferative, mesenchymal phenotype. In concert with interacting molecules integrin-linked kinase influences the actin cytoskeleton, resulting in shape change and focal adhesion dysfunction observed in podocyte failure and tubulo-interstitial fibrosis. SUMMARY: Integrin-linked kinase has emerged as a key player at the interface between extracellular matrix, integrins, actin-based cytoskeleton and cellular phenotype in kidney diseases. Future studies focusing on interacting molecules and modification of integrin-linked kinase function in vivo will better define the role of cell matrix signalling in progressive renal failure.

Animals↗

Toll-like receptor-4: renal cells and bone marrow cells signal for neutrophil recruitment during pyelonephritis.

BACKGROUND: The molecular mechanisms of pathogen recognition that initiate infective pyelonephritis are poorly understood. Toll-like receptor-4 (TLR4) mutant mice infected with uropathogenic Escherichia coli lack renal CXCL2 mRNA expression, subsequent neutrophil recruitment, and renal abscess formation. METHODS: We used a bone marrow transplant approach in order to investigate the contribution of TLR4 in intrinsic renal cells or bone-marrow-derived immune cells to neutrophil recruitment during infective pyelonephritis. RESULTS: Both chimera either expressing mutant tlr4 in intrinsic renal cells and wild-type tlr4 in bone marrow-derived cells or vice versa showed an impaired response to uropathogenic E. coli infection in terms of leukocyturia and renal abscess formation when compared to tlr4 wild-type mice with congenic bone marrow transplants. CONCLUSION: These data suggest that TLR4 is required on both intrinsic renal cells (e.g., tubular epithelial cells) and bone marrow-derived immune cells for the control of ascending uropathogenic E. coli infection by initiating chemokine-driven renal neutrophil recruitment.

Animals↗

Functional consequences of integrin-linked kinase activation in podocyte damage.

BACKGROUND: The delicate foot process architecture of glomerular podocytes critically depends on integrin mediated cell-glomerular basement membrane (GBM) interaction. Integrin signaling via the integrin-linked kinase (ILK) is activated in podocyte damage and associated with considerable podocyte phenotype alterations. ILK has been shown to regulate cell fate via nuclear interaction of beta-catenin with lymphoid enhancer factor (LEF-1) transcription factors. The aim of this study was to elucidate the molecular mechanisms of ILK dependant phenotype regulation in podocytes. METHODS: ILK function was evaluated in conditionally immortalized murine glomerular epithelial cells using overexpression of ILK and a small molecule ILK inhibitor in puromycin/adriamycin-induced podocyte damage in vitro and in vivo. RESULTS: Kinase active, but not mutant ILK induced translocation of beta-catenin to the cell nucleus, de novo expression of LEF-1, and nuclear colocalization of beta-catenin and LEF-1. The role of ILK signaling in podocyte damage was evaluated using puromycin, an agent known to cause selective proteinuria and to increase ILK activity. The small molecular ILK inhibitor MC-5 blocked puromycin-induced nuclear translocation of beta-catenin, podocyte detachment, cell proliferation, and repression of the slit membrane molecules P-cadherin and CD2ap. In vivo activation of the beta-catenin pathway could be shown by nuclear colocalization of beta-catenin with WT-1 in adriamycin nephropathy. CONCLUSION: ILK regulates podocyte cell matrix interaction, proliferation, and slit membrane gene expression in podocyte damage. As this pathway is amendable to pharmacologic intervention, further detailed studies of in vivo ILK function in glomerular disease appear justified.

Active Transport, Cell Nucleus↗

BK virus associated nephropathy in native kidneys of a heart allograft recipient.

Polyomavirus-mediated nephropathy is an increasingly recognized complication in renal transplant recipients, but data on the status of viral activity in the native kidneys of non-renal solid organ recipients are limited. Thirteen native kidney biopsies of heart transplant recipients with significant renal impairment were evaluated for the evidence of polyomavirus reactivation by immunohistochemistry and PCR. One case of BK virus-mediated nephropathy in a cardiac transplant recipient exposed to high levels of immunosuppressive drugs was identified. Clinical and histopathological findings of this patient progressing to terminal renal failure are discussed in detail. In conclusion, polyomavirus reactivation in native kidneys of heart transplant recipients can cause significant renal impairment and should be considered in the differential diagnosis in this patient cohort.

Adult↗

Role of podocytes for reversal of glomerulosclerosis and proteinuria in the aging kidney after endothelin inhibition.

The cause of focal-segmental glomerulosclerosis as a consequence of physiological aging, which is believed to be inexorable, is unknown. This study investigated whether inhibition of endothelin-1, a growth-promoting peptide contributing to renal injury in hypertension and diabetes, affects established glomerulosclerosis and proteinuria in the aged kidney. We also determined the role of endothelin receptors for podocyte injury in vivo and in vitro. Aged Wistar rats, a model of spontaneous age-dependent glomerulosclerosis, were treated with the orally active endothelin subtype A (ET(A)) receptor antagonist darusentan, and evaluation of renal histology, renal function studies, and expression analyses were performed. In vitro experiments using puromycin aminonucleoside to induce podocyte injury investigated the role of ET(A) receptor signaling for apoptosis, cytoskeletal injury, and DNA synthesis. In aged Wistar rats, established glomerulosclerosis and proteinuria were reduced by >50% after 4 weeks of darusentan treatment, whereas blood pressure, glomerular filtration rate, or tubulo-interstitial renal injury remained unaffected. Improvement of structural injury in glomeruli and podocytes was accompanied by a reduction of the expression of matrix metalloproteinase-9 and p21Cip1/WAF1. In vitro experiments blocking ET(A) receptors using specific antagonists or RNA interference prevented apoptosis and structural damage to podocytes induced by puromycin aminonucleoside. In conclusion, these results support the hypothesis that endogenous endothelin contributes to glomerulosclerosis and proteinuria in the aging kidney. The results further suggest that age-dependent glomerulosclerosis is not merely a "degenerative" but a reversible process locally confined to the glomerulus involving recovery of podocytes from previous injury.

Aging↗

Activation of toll-like receptor-9 induces progression of renal disease in MRL-Fas(lpr) mice.

How bacterial or viral infections trigger flares of autoimmunity is poorly understood. As toll-like receptor (TLR)-9 activation by exogenous or endogenous CpG-DNA may contribute to disease activity of systemic lupus erythematosus, we examined the effects of CpG-oligodeoxynucleotides (ODN) or DNA derived from Escherichia coli (E. coli) on the course of nephritis in MRL(lpr/lpr) mice. In kidneys of these mice, TLR9 localized to glomerular, tubulointerstitial, and perivascular infiltrates. After intraperitoneal injection labeled CpG-ODN localized to glomerular and interstitial macrophages and dendritic cells in nephritic kidneys of MRL(lpr/lpr) mice but not in healthy MRL controls. Furthermore, murine J774 macrophages and splenocytes from MRL(lpr/lpr) mice, but not tubular epithelial cells, renal fibroblasts, or mesangial cells, expressed TLR9 and up-regulated CCL5/RANTES mRNA upon stimulation with CpG-ODN in vitro. In vivo both E. coli DNA and CpG-ODN increased serum DNA autoantibodies of the IgG2a isotype in MRL(lpr/lpr) mice. This was associated with progression of mild to crescentic glomerulonephritis, interstitial fibrosis, and heavy proteinuria. CpG-ODN increased renal CCL2/MCP-1 and CCL5/RANTES expression associated with increased glomerular and interstitial leukocyte recruitment. In contrast control GpC-ODN had no effect. We conclude that TLR9 activation triggers disease activity of systemic autoimmunity, for example, lupus nephritis, and that adaptive and innate immune mechanisms contribute to the CpG-DNA-induced progression of lupus nephritis.

Animals↗

Reduced intragraft mRNA expression of matrix metalloproteinases Mmp3, Mmp12, Mmp13 and Adam8, and diminished transplant arteriosclerosis in Ccr5-deficient mice.

Experimental and human organ transplant studies suggest an important role for chemokine (C-C-motif) receptor-5 (CCR5) in the development of acute and chronic allograft rejection. Because early transplant damage can predispose allografts to chronic dysfunction, we sought to identify potential pathophysiologic mechanisms leading to allograft damage by using wild-type and Ccr5-deficient mice as recipients of fully MHC-mismatched heart and carotid-artery allografts. Gene expression in rejecting heart allografts was analyzed 2 and 6 days after transplantation using Affymetrix GeneChips. Microarray analysis led to identification of four metalloproteinase genes [matrix metalloproteinase (Mmp)3, Mmp12, Mmp13 and a disintegrin and metalloprotease domain (Adam)8] with significantly diminished intragraft mRNA expression in Ccr5-deficient mice at day 6. Accordingly, allografts from Ccr5-deficient mice showed less tissue remodeling and hence better preservation of the myocardial architecture compared with allografts from wild-type recipients. Moreover, survival of cardiac allografts was significantly increased in Ccr5-deficient mice. Carotid artery allografts from Ccr5-deficient recipients showed better tissue preservation, and significant reduction of neointima formation and CD3+ T cell infiltration. Ccr5 appears to play an important role in transplant-associated arteriosclerosis that may involve metalloproteinase-mediated vessel wall remodeling. We conclude that early tissue remodeling may be a critical feature in the predisposition of allografts to the development of chronic dysfunction.

ADAM Proteins↗

CXCR3 is involved in tubulointerstitial injury in human glomerulonephritis.

Chemokines play pivotal roles in the recruitment of inflammatory cells into the kidney. The chemokine receptors CXCR3 and CCR5 are expressed on activated T lymphocytes, and expression of CXCR3 by mesangial cells has been suggested. Detailed description of CXCR3 expression might form a rational basis for use as a diagnostic marker and for therapeutic CXCR3 targeting in human glomerulonephritis. We studied the expression of CXCR3 in renal biopsies by immunohistochemistry (n = 45), and real time RT-PCR (n = 78). Biopsies were from patients with IgA nephropathy, lupus nephritis, and membranoproliferative glomerulonephritis. Furthermore, cultured human mesangial cells (HMC) were studied for CXCR3 expression, and for functional responses to the ligands CXCL10/IP-10 and CXCL9/Mig. CXCR3-positive cells were rarely found in glomerular tufts, but formed a major part of the tubulointerstitial infiltrates. Consistently, CXCR3 mRNA expression was too low to be quantified in glomerular compartments, and was not detectable in HMC. The published staining for CXCR3 of mesangial cells could be traced to cross-reactivity of an antibody for CXCR3 with a potentially related chemokine receptor as revealed by FACS analysis. Despite an absence of CXCR3 expression, mesangial cells reacted to CXCR3 ligands by proliferation and migration, which was blocked by pertussis toxin but not by an anti-CXCR3 antibody. These results indicate that HMC do not express the classical CXCR3, but may potentially express a related receptor with shared ligand specificity. By immunohistochemistry the number of CXCR3-positive cells, mainly interstitial T cells, correlated with renal function, proteinuria, and percentage of globally sclerosed glomeruli. A significant morphological and numerical correlation between CD3, CXCR3, and CCR5-positive cells indicated a CXCR3/CCR5 double-positive T cell population. No apparent difference in the CXCR3 expression pattern was found between disease entities. CXCR3 expression was localized to interstitial T cells, and these cells correlated strongly with important prognostic markers. Therefore interstitial CXCR3, as well as CCR5-positive T cells might play an important role during progressive loss of renal function, and are potential therapeutic targets in human glomerular diseases.

Adolescent↗