BMP-7 protects mesangial cells from injury by polymeric IgA
2008; Elsevier BV; Volume: 74; Issue: 8 Linguagem: Inglês
10.1038/ki.2008.209
ISSN1523-1755
AutoresWai Long Chan, Joseph C.K. Leung, Loretta Y.Y. Chan, Ka Ying Tam, Sydney C.W. Tang, Kar Neng Lai,
Tópico(s)Renal Diseases and Glomerulopathies
ResumoBone morphogenetic protein-7 (BMP-7) is a potential therapeutic agent for acute and chronic renal diseases. Here we found that addition of polymeric IgA, isolated from patients with IgA nephropathy, increased the synthesis of tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), transforming growth factor-β (TGF-β) and fibronectin in cultured human mesangial cells, effects blunted by BMP-7. When mesangial cells were cultured with both polymeric IgA and BMP-7 there was an increase in the expression of peroxisome proliferator-activated receptor-γ (PPAR-γ). The activation of NFκB and TNF-α synthesis induced by polymeric IgA or TNF-α were downregulated by BMP-7 or rosiglitazone. BMP-7 inhibited TNF-α release from polymeric IgA-stimulated mesangial cells by activation of PPAR-γ but suppressed TGF-β release by mechanisms independent of PPAR-γ. The expression of inhibitory Smad6 and 7 was increased whereas the expression of active Smad2 and 3 was reduced in these mesangial cells by BMP-7. Our study shows that BMP-7 ameliorates IgA nephropathy-derived polymeric IgA-induced TNF-α and TGF-β synthesis in human mesangial cells through multiple mechanisms involving inhibitory Smads and PPAR-γ. Bone morphogenetic protein-7 (BMP-7) is a potential therapeutic agent for acute and chronic renal diseases. Here we found that addition of polymeric IgA, isolated from patients with IgA nephropathy, increased the synthesis of tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), transforming growth factor-β (TGF-β) and fibronectin in cultured human mesangial cells, effects blunted by BMP-7. When mesangial cells were cultured with both polymeric IgA and BMP-7 there was an increase in the expression of peroxisome proliferator-activated receptor-γ (PPAR-γ). The activation of NFκB and TNF-α synthesis induced by polymeric IgA or TNF-α were downregulated by BMP-7 or rosiglitazone. BMP-7 inhibited TNF-α release from polymeric IgA-stimulated mesangial cells by activation of PPAR-γ but suppressed TGF-β release by mechanisms independent of PPAR-γ. The expression of inhibitory Smad6 and 7 was increased whereas the expression of active Smad2 and 3 was reduced in these mesangial cells by BMP-7. Our study shows that BMP-7 ameliorates IgA nephropathy-derived polymeric IgA-induced TNF-α and TGF-β synthesis in human mesangial cells through multiple mechanisms involving inhibitory Smads and PPAR-γ. IgA nephropathy (IgAN) is the most common chronic glomerulonephritis worldwide.1.D'Amico G. The commonest glomerulonephritis in the world: IgA nephropathy.Q J Med. 1987; 64: 709-727PubMed Google Scholar A prominent pathological feature of the disease is the deposition of polymeric IgA (pIgA) in the mesangium, followed by proliferation of the mesangial cells and/or mesangial matrix.2.Julian B.A. Tomana M. Novak J. et al.Progress in the pathogenesis of IgA nephropathy.Adv Nephrol Necker Hosp. 1999; 29: 53-72PubMed Google Scholar Polymeric IgA from patient with IgAN causes glomerular damage by inducing release of proinflammatory and profibrotic cytokines, including tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and transforming growth factor-β (TGF-β), in mesangial cells.3.Lai K.N. Tang S.C. Guh J.Y. et al.Polymeric IgA1 from patients with IgA nephropathy upregulates transforming growth factor-beta synthesis and signal transduction in human mesangial cells via the rennin–angiotensin system.J Am Soc Nephrol. 2003; 14: 3127-3137Crossref PubMed Scopus (70) Google Scholar,4.Leung J.C. Tang S.C. Chan L.Y. et al.Polymeric IgA increases the synthesis of macrophage migration inhibitory factor by human mesangial cells in IgA nephropathy.Nephrol Dial Transplant. 2003; 18: 36-45Crossref PubMed Scopus (49) Google Scholar Bone morphogenetic protein-7 (BMP-7), a member of the TGF-β superfamily, is crucial in nephrogenesis during development.5.Helder M.N. Ozkaynak E. Sampath K.T. et al.Expression pattern of osteogenic protein-1 (bone morphogenetic protein-7) in human and mouse development.J Histochem Cytochem. 1995; 43: 1035-1044Crossref PubMed Scopus (153) Google Scholar BMPs exert their effects via two sets of serine–threonine kinase receptors: a type-II receptor, which binds ligand and a type-I receptor, which is recruited to the complex and transduces the signal.6.Kopp J.B. BMP receptors in kidney.Kidney Int. 2000; 58: 2237-2238Abstract Full Text Full Text PDF PubMed Google Scholar BMP receptors (BMPRs) identified to date include type-I receptors, activin receptor-like kinase-2 (ALK2), BMPR-IA (or ALK3), BMPR-IB (or ALK6), and type-II receptors, BMPR-II, activin receptor-II (ActRII) and activin receptor-IIB (ActRIIB). Complex formation between BMP-7 or TGF-β1 with type-II and ALK type-I receptors leads to the intracellular signaling pathway mediated by Smad proteins.7.Ebara S. Nakayama K. Mechanism for the action of bone morphogenetic proteins and regulation of their activity.Spine. 2002; 27: S10-S15Crossref PubMed Scopus (122) Google Scholar Smad1, Smad5, and Smad8 transduce the action of BMP-7, whereas Smad2 and Smad3 mediate the action of TGF-β1 in epithelial cells. Smad4 is common to both pathways. Membrane-bound, highly specific BMP-7 receptors have been recently localized in the glomerulus, convoluted tubules, and collecting tubules of the rat kidney, suggesting the autocrine and paracrine role for BMP-7. BMP-7 has potential as a therapeutic agent for treatment of acute and chronic renal failure. Recent studies reveal BMP-7 can reduce the severity of glomerulonephritis and tubulointerstitial fibrosis in various experimental models of acute or chronic renal injury, including unilateral ureteral obstruction,8.Klahr S. Morrissey J. Obstructive nephropathy and renal fibrosis: the role of bone morphogenic protein-7 and hepatocyte growth factor.Kidney Int Suppl. 2003; 64: S105-S112Abstract Full Text Full Text PDF Scopus (81) Google Scholar acute ischemic renal injury,9.Vukicevic S. Basic V. Rogic D. et al.Osteogenic protein-1 (bone morphogenetic protein-7) reduces severity of injury after ischemic acute renal failure in rat.J Clin Invest. 1998; 102: 202-214Crossref PubMed Scopus (266) Google Scholar diabetic nephropathy,10.Wang S.N. Lapage J. Hirschberg R. Loss of tubular bone morphogenetic protein-7 in diabetic nephropathy.J Am Soc Nephrol. 2001; 12: 2392-2399Crossref PubMed Google Scholar and lupus nephritis.11.Zeisberg M. Bottiglio C. Kumar N. et al.Bone morphogenic protein-7 inhibits progression of chronic renal fibrosis associated with two genetic mouse models.Am J Physiol Renal Physiol. 2003; 285: F1060-F1067Crossref PubMed Scopus (241) Google Scholar BMP-7 exerts its antifibrotic effect in the kidney through counteracting the profibrotic effects of TGF-β in human mesangial cells (HMCs)12.Wang S. Hirschberg R. BMP7 antagonizes TGF-beta -dependent fibrogenesis in mesangial cells.Am J Physiol Renal Physiol. 2003; 284: F1006-F1013Crossref PubMed Scopus (33) Google Scholar and proximal tubular epithelial cells.13.Gould S.E. Day M. Jones S.S. et al.BMP-7 regulates chemokine, cytokine, and hemodynamic gene expression in proximal tubule cells.Kidney Int. 2002; 61: 51-60Abstract Full Text Full Text PDF PubMed Scopus (187) Google Scholar BMP-7 represses basal and TNF-α-induced expression of proinflammatory cytokines (IL-6 and IL-1β) and chemokines in proximal tubular epithelial cells.13.Gould S.E. Day M. Jones S.S. et al.BMP-7 regulates chemokine, cytokine, and hemodynamic gene expression in proximal tubule cells.Kidney Int. 2002; 61: 51-60Abstract Full Text Full Text PDF PubMed Scopus (187) Google Scholar Previously, we demonstrated that pIgA from patients with IgAN is capable of inducing macrophage migration-inhibitory factor and TNF-α production in HMCs.4.Leung J.C. Tang S.C. Chan L.Y. et al.Polymeric IgA increases the synthesis of macrophage migration inhibitory factor by human mesangial cells in IgA nephropathy.Nephrol Dial Transplant. 2003; 18: 36-45Crossref PubMed Scopus (49) Google Scholar The finding that the neutralizing antibody to TNF-α partially blocked this mesangial synthesis of macrophage migration-inhibitory factor suggests the possibility of upregulatory macrophage migration-inhibitory factor synthesis in HMCs being mediated via an amplifying proinflammatory loop involving TNF-α. pIgA1 in IgAN also upregulates the intrarenal rennin–angiotensin system and TGF-β, leading to chronic renal failure with renal fibrosis.3.Lai K.N. Tang S.C. Guh J.Y. et al.Polymeric IgA1 from patients with IgA nephropathy upregulates transforming growth factor-beta synthesis and signal transduction in human mesangial cells via the rennin–angiotensin system.J Am Soc Nephrol. 2003; 14: 3127-3137Crossref PubMed Scopus (70) Google Scholar Based on the counteracting effect of BMP-7 on biological actions of TGF-β and TNF-α, it is logical to hypothesize that BMP-7 could also counteract the action of these profibrotic and proinflammatory cytokines in IgAN and ameliorate the pIgA-induced renal injury. Despite increasing evidence of the reno-protective role of BMP-7, its role in IgAN has yet been explored. In this study, we hypothesized that BMP-7 counteracts the action of these profibrotic and proinflammatory cytokines in IgAN, and hence reduces the pIgA-induced renal injury. We determined the effect of BMP-7 on the action of TNF-α, IL-6, and TGF-β in pIgA-stimulated HMCs, and analyzed the involved signal transduction pathways. Immunoreactive BMP-7 was found in podocytes in glomeruli from normal subjects, but was weakly detectable in glomeruli from IgAN patients (Figure 1). Localization of BMP-7 in epithelial cells was demonstrated by double staining with nephrin (Figure 1g and i). Glomerular BMP-7 score was significantly lower in patients with IgAN (mean score 0.4667 versus 2.125 in control subjects, P=0.0003) (Figure 1k). Constitutive gene expression of the five BMP receptors, including ALK2, ALK3, ALK6, ActRII, and BMPR-II, was documented in cultured HMCs (Figure 2a). The protein expression of these receptors was further confirmed by immunohistochemical staining (Figure 2b). Compared with pIgA isolated from healthy subjects, pIgA from patients with IgAN had significantly decreased receptor expression of ALK2, ALK6, and BMPR-II (P<0.01) when cultured with HMCs (Figure 2c). We then performed in vitro studies to determine whether BMP-7 may exert any reno-protective effect in IgAN. Figure 3 depicts the metabolic activity and cell viability of HMCs following incubation with pIgA preparations in the presence or absence of BMP-7 for 48 h. Polymeric IgA from patients with IgAN significantly increased the metabolic activity in HMCs (P<0.05) when compared with pIgA from healthy subjects (Figure 3a). Proliferation of HMCs induced by pIgA was significantly reduced by BMP-7 (P<0.05). HMCs remained viable when exposed to various IgA preparations at a concentration of 0.5 mg/ml with or without BMP-7 (Figure 3b). Similar findings were obtained for HMC proliferation as determined by bromodeoxyuridine incorporation assay (Figure 3c) and direct cell counting (Figure 3e). The increased cell proliferation was blunted by preincubating HMCs with BMP-7 (P<0.001). There was no increase in apoptosis in HMCs exposed to pIgA in the presence or absence of BMP-7, as shown by the caspase-3 activity (Figure 3d) or TdT-mediated X-dUTP nick-end labeling assay (Figure 3f). The concentration of BMP-7 used in this study (up to 1000 ng/ml) neither induced apoptosis nor affected the cell viability, metabolic activity, and HMC proliferation (data not shown). As depicted in Figures 4, 5, 6 and 7, gene expression and protein release of TNF-α, IL-6, TGF-β, and fibronectin were significantly increased in HMCs cultured with pIgA from patients with IgAN when compared with pIgA from healthy subjects at equivalent concentration of 0.5 mg/ml (P<0.001). These upregulations were reduced when HMCs were preincubated with BMP-7 (P<0.01). BMP-7 at concentrations greater than 125 ng/ml reduced protein release of TNF-α, IL-6, and TGF-β in a dose-dependent manner.Figure 5Gene expression and protein synthesis of IL-6 in HMCs cultured with different pIgA preparations with or without BMP-7. Both gene expression (a) and protein synthesis (b) of IL-6 increase in HMCs cultured with pIgA from patients with IgAN or pIgA from healthy controls (0.5 mg/ml). BMP-7 (250 ng/ml) reduces gene expression and protein synthesis of IL-6 induced by pIgA from IgAN patients. All results represent mean±s.d. of 32 patients and 32 healthy controls. *P<0.001 versus medium control; ΩP<0.05 versus medium control; #P<0.001 versus HMCs cultured with pIgA preparation from controls; φP<0.05 versus HMCs cultured with pIgA preparation from controls in the presence of BMP-7; @P<0.001 versus HMCs cultured with pIgA preparation from patients in the presence of BMP-7. (c). BMP-7 dose dependently decreases the protein synthesis of IL-6 induced by pIgA from IgAN patients. ΘP<0.01 or σP<0.05 versus HMCs cultured with pIgA in the absence of BMP-7. Data are expressed as means±s.d. of five separate experiments.View Large Image Figure ViewerDownload (PPT)Figure 6Gene expression and protein synthesis of TGF-β in HMCs cultured with different pIgA preparations with or without BMP-7. (a) The gene expression and (b) protein synthesis of TGF-β increase in HMCs cultured with pIgA from patients with IgAN (0.5 mg/ml). BMP-7 (250 ng/ml) reduces gene expression and protein synthesis of TGF-β induced by pIgA from patients. All results represent mean±s.d. of 32 patients and 32 healthy controls. *P<0.001 versus medium control; ΩP<0.05 versus medium control; #P<0.001 versus HMCs cultured with pIgA preparation from control; δP<0.05 versus HMCs cultured with pIgA preparation from controls; @P<0.001 versus HMCs cultured with pIgA preparation from patients in the presence of BMP-7. (c) BMP-7 dose dependently decreases the protein synthesis of TGF-β induced by pIgA from IgAN patients. ΘP<0.01 versus HMCs cultured with pIgA in the absence of BMP-7. Data are expressed as means±s.d. of five separate experiments.View Large Image Figure ViewerDownload (PPT)Figure 7Gene expression and protein synthesis of fibronectin in HMCs cultured with different pIgA preparations with or without BMP-7. (a) The gene expression and (b) protein synthesis of fibronectin increase in HMCs cultured with pIgA from patients with IgAN (0.5 mg/ml). BMP-7 (250 ng/ml) reduces the gene expression and protein synthesis of fibronectin induced by pIgA from patients. Gene expression results represent mean±s.d. of 32 patients and 32 healthy controls. Immunoblot data represent mean±s.d. of 10 patients and 10 healthy controls. *P<0.001 versus medium control; ΩP<0.05 versus medium control; #P<0.001 versus HMCs cultured with pIgA preparation from control; @P 0.1 ng/ml significantly increased TNF-α (Figure 8a) and IL-6 (Figure 8b) production by HMCs (P<0.001), but the upregulation was blocked by BMP-7 at a concentration of 250 ng/ml (P<0.01). However, TNF-α exerted no effect on the synthesis of TGF-β (Figure 8c). Incubation of HMCs with pIgA from patients or controls did not alter gene expression of peroxisome proliferator-activated receptor-γ (PPAR-γ). However, gene expression of PPAR-γ increased significantly (P<0.001) when BMP-7 (250 ng/ml) was added (Figure 9a). BMP-7 increased the expression of PPAR-γ at both transcriptional and post-transcriptional levels in a dose-dependent manner (Figure 9b and c). HMCs were cultured with pIgA or TNF-α in the presence or absence of PPAR-γ agonist (rosiglitazone). Rosiglitazone significantly reduced TNF-α and IL-6 release by HMCs induced by TNF-α (Figure 10a) or pIgA from IgAN patients (Figure 10b). PIgA, but not TNF-α, increased TGF-β release by HMCs (Figure 10a and b). This upregulation of TGF-β release by pIgA was not affected by rosiglitazone (Figure 10b). The role nuclear factor-κB (NF-κB) in the induction of QJ;TNF-α and IL-6 by HMCs cultured with TNF-α or pIgA was examined by electrophoretic mobility-shift assay (EMSA) and immunofluorescence staining. As depicted in Figure 10c and d, translocation of NF-κB into the nucleus of HMCs occurred after exposure to pIgA or TNF-α. Furthermore, both BMP-7 and rosiglitazone attenuated nuclear translocation of NF-κB activated by pIgA or TNF-α. There was no change in gene expression of Smad6 (Figure 11a) or Smad7 (Figure 11b) when HMCs were incubated with pIgA from patients or controls. However, addition of BMP-7 (250 ng/ml) significantly increased gene expression of Smad6 and Smad7 (P 125 ng/ml increased the expression of Smad6 (Figure 11c) and Smad7 (Figure 11d) in HMCs in a dose-dependent manner (P<0.01). Activation of Smad2/3 and expression of Smad6 and Smad7 protein was also examined by western blotting (Figure 11e). Upregulation of phosphorylated Smad2/3 (pSmad2/3) was induced by pIgA but not TNF-α. The pIgA-induced activation of Smad2/3 was blunted by BMP-7. There was no induction of Smad6 or Smad7 protein when HMCs were incubated with pIgA or TNF-α alone without BMP-7. The addition of BMP-7 induced protein synthesis of Smad6 and Smad7 by HMCs preincubated with pIgA or TNF-α. BMP-7 is the most abundant BMP in fetal and adult mammalian kidney.5.Helder M.N. Ozkaynak E. Sampath K.T. et al.Expression pattern of osteogenic protein-1 (bone morphogenetic protein-7) in human and mouse development.J Histochem Cytochem. 1995; 43: 1035-1044Crossref PubMed Scopus (153) Google Scholar Cortical and medullary BMP-7 mRNA expression decreased markedly in rats with ischemia–reperfusion injury. Intravenous administration of recombinant BMP-7 reduces histological and functional injuries in a rat model of ischemic acute renal failure.9.Vukicevic S. Basic V. Rogic D. et al.Osteogenic protein-1 (bone morphogenetic protein-7) reduces severity of injury after ischemic acute renal failure in rat.J Clin Invest. 1998; 102: 202-214Crossref PubMed Scopus (266) Google Scholar In murine model of unilateral ureteral obstruction, BMP-7 effectively prevented interstitial inflammation and tubulointerstitial fibrosis, leading to preservation of renal function.8.Klahr S. Morrissey J. Obstructive nephropathy and renal fibrosis: the role of bone morphogenic protein-7 and hepatocyte growth factor.Kidney Int Suppl. 2003; 64: S105-S112Abstract Full Text Full Text PDF Scopus (81) Google Scholar In addition, BMP-7 treatment significantly reduced interstitial macrophage infiltration, raising the possibility of regulation of chemokine expression in renal cells by BMP-7. In murine streptozocin-induced diabetic nephropathy, tubular BMP-7 expression was reduced and the reduction was associated with transdifferentiation of tubular cells.10.Wang S.N. Lapage J. Hirschberg R. Loss of tubular bone morphogenetic protein-7 in diabetic nephropathy.J Am Soc Nephrol. 2001; 12: 2392-2399Crossref PubMed Google Scholar Exogenous BMP-7 therapy partially reversed renal hypertrophy and restored glomerular filtration rate in a dose-dependent manner.14.Wang S. Chen Q. Simon T.C. et al.Bone morphogenic protein-7 (BMP-7), a novel therapy for diabetic nephropathy.Kidney Int. 2003; 63: 2037-2049Abstract Full Text Full Text PDF PubMed Scopus (199) Google Scholar In MRL lpr/lpr murine lupus nephritis, BMP-7 administration for 10 weeks reduced glomerular abnormality and tubulointerstitial fibrosis.11.Zeisberg M. Bottiglio C. Kumar N. et al.Bone morphogenic protein-7 inhibits progression of chronic renal fibrosis associated with two genetic mouse models.Am J Physiol Renal Physiol. 2003; 285: F1060-F1067Crossref PubMed Scopus (241) Google Scholar Nonetheless, research on BMP-7 in IgAN is not available. BMP-7 circulates in the blood at a concentration range of 100 to 300 pg/ml.15.Vukicevic S. Latin V. Chen P. et al.Localization of osteogenic protein-1 (bone morphogenetic protein-7) during human embryonic development: high affinity binding to basement membranes.Biochem Biophys Res Commun. 1994; 198: 693-700Crossref PubMed Scopus (178) Google Scholar The optimal therapeutic dose of BMP-7 used in various animal models of chronic kidney disease is about 300 μg/kg.16.Zeisberg M. Bone morphogenic protein-7 and the kidney: current concepts and open questions.Nephrol Dial Transplant. 2006; 21: 568-573Crossref PubMed Scopus (68) Google Scholar Despite the absence of sufficiently high levels of BMP-7 in the circulating blood to stimulate cells, HMC has BMP-7 receptors and is responsive to BMP-7.17.Miyazaki Y. Ueda H. Yokoo T. et al.Inhibition of endogenous BMP in the glomerulus leads to mesangial matrix expansion.Biochem Biophys Res Commun. 2006; 340: 681-688Crossref PubMed Scopus (19) Google Scholar The concentration of BMP-7 used in this study is 250 ng/ml and is comparable to the dose that was reported in various in vitro models.11.Zeisberg M. Bottiglio C. Kumar N. et al.Bone morphogenic protein-7 inhibits progression of chronic renal fibrosis associated with two genetic mouse models.Am J Physiol Renal Physiol. 2003; 285: F1060-F1067Crossref PubMed Scopus (241) Google Scholar,18.Sugimoto H. Grahovac G. Zeisberg M. et al.Renal fibrosis and glomerulosclerosis in a new mouse model of diabetic nephropathy and its regression by bone morphogenic protein-7 and advanced glycation end product inhibitors.Diabetes. 2007; 56: 1825-1833Crossref PubMed Scopus (171) Google Scholar It is speculated that mesangial damage by the pathogenic pIgA molecules could be ameliorated if specific delivery of this amount of exogenous BMP-7 into the glomerulus or mesangium in vivo. The present data confirmed our previous finding that pIgA from patients with IgAN increased HMC proliferation with upregulatory synthesis of TNF-α, TGF-β, and IL-6.3.Lai K.N. Tang S.C. Guh J.Y. et al.Polymeric IgA1 from patients with IgA nephropathy upregulates transforming growth factor-beta synthesis and signal transduction in human mesangial cells via the rennin–angiotensin system.J Am Soc Nephrol. 2003; 14: 3127-3137Crossref PubMed Scopus (70) Google Scholar,4.Leung J.C. Tang S.C. Chan L.Y. et al.Polymeric IgA increases the synthesis of macrophage migration inhibitory factor by human mesangial cells in IgA nephropathy.Nephrol Dial Transplant. 2003; 18: 36-45Crossref PubMed Scopus (49) Google Scholar,19.Chan L.Y. Leung J.C. Tsang A.W. et al.Activation of tubular epithelial cells by mesangial-derived TNF-alpha: glomerulotubular communication in IgA nephropathy.Kidney Int. 2005; 67: 602-612Abstract Full Text Full Text PDF PubMed Scopus (87) Google Scholar We found that glomerular expression of BMP-7 was markedly diminished in IgAN. Furthermore, expression of ALK2, ALK6, and BMPR-II was significantly reduced in HMCs cultured with pIgA from IgAN patients. In vitro studies showed BMP-7 significantly reduced pIgA-induced HMC proliferation, fibronectin synthesis, and immune injury. These in vivo and in vitro data provide new evidences that BMP-7 could counteract the actions of the profibrotic TGF-β and proinflammatory TNF-α in IgAN, and hence ameliorating the pIgA-induced injury in mesangial cells. TNF-α is an important mediator in the pathogenesis of IgAN. TNF-α is produced early in the inflammatory process and induces the expression of major histocompatibility complex class-I and class-II molecules.20.Vassalli P. The pathophysiology of tumor necrosis factors.Annu Rev Immunol. 1992; 10: 411-452Crossref PubMed Scopus (1762) Google Scholar,21.Feldmann M. Brennan F.M. Maini R. Cytokines in autoimmune disorders.Int Rev Immunol. 1998; 17: 217-228Crossref PubMed Scopus (107) Google Scholar Overexpression of TNF-α leads to release of other mediators, upregulation of endothelial adhesion molecules and other proinflammatory growth factors, including IL-6, IL-8, and TNF-α itself.22.Ruddle N.H. Tumor necrosis factor (TNF-alpha) and lymphotoxin (TNF-beta).Curr Opin Immunol. 1992; 4: 327-332Crossref PubMed Scopus (138) Google Scholar We showed that BMP-7 not only reduced the upregulation of IL-6 and TNF-α induced by pIgA, but, most interestingly, also blocked the autocrine loops of amplification of immune injury to mesangial cells initiated by TNF-α and TGF-β. These data lend support to the notion that exogenous BMP-7 delivery to the kidney is a promising therapeutic in IgAN, especially BMP-7 is an endogenous molecule with minimal potential of self-toxicity. Although a reno-protective role of BMP-7 in acute and chronic kidney diseases is increasingly convincing, the mechanisms of these protective effects are not well defined. In murine mesangial cell culture, BMP-7 antagonized the fibrotic effect of TGF-β by suppressing the plasminogen activator inhibitor-1 through maintaining the level of matrix metalloprotease-2.12.Wang S. Hirschberg R. BMP7 antagonizes TGF-beta -dependent fibrogenesis in mesangial cells.Am J Physiol Renal Physiol. 2003; 284: F1006-F1013Crossref PubMed Scopus (33) Google Scholar In HMC culture, BMP-7 inhibited basal and IL-1β-induced release of MCP-1 through activity of c-Jun N-terminal kinase and AP-1 activation.23.Lee M.J. Yang C.W. Jin D.C. et al.Bone morphogenetic protein-7 inhibits constitutive and interleukin-1 beta-induced monocyte chemoattractant protein-1 expression in human mesangial cells: role for JNK/AP-1 pathway.J Immunol. 2003; 170: 2557-2563Crossref PubMed Scopus (41) Google Scholar In this study, we provided novel evidence that BMP-7 suppressed immune injury in HMCs induced by pIgA through two distinct signaling pathways, namely, the PPAR-γ and inhibitory Smads. PPARs are a family of ligand-activated nuclear hormone receptors that belong to the steroid-receptor superfamily.24.Evans R.M. 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Peroxisome proliferator-activated receptor alpha activation modulates cellular redox status, represses nuclear factor-kappaB signaling, and reduces inflammatory cytokine production in aging.J Biol Chem. 1998; 273: 32833-32841Crossref PubMed Scopus (476) Google Scholar Rosiglitazone (a thiazolidinediones) reduces the serum level of TNF-α and IL-1β during sepsis in a murine sepsis model.27.Lee S. Kim W. Kang K.P. et al.Agonist of peroxisome proliferator-activated receptor-gamma, rosiglitazone, reduces renal injury and dysfunction in a murine sepsis model.Nephrol Dial Transplant. 2005; 20: 1057-1065Crossref PubMed Scopus (50) Google Scholar PPAR-γ agonists also abrogate ischemia–reperfusion kidney injury28.Sivarajah A. Chatterjee P.K. Patel N.S. et al.Agonists of peroxisome-proliferator activated receptor-gamma reduce renal ischemia/reperfusion injury.Am J Nephrol. 2003; 23: 267-276Crossref PubMed Scopus (129) Google Scholar and proliferative mesangial diseases,29.Ghosh S.S. Gehr T.W. Ghosh S. et al.PPARgamma ligand attenuates PDGF-induced mesangial cell proliferation: role of MAP kinase.Kidney Int. 2003; 64: 52-62Abstract Full Text Full Text PDF PubMed Scopus (52) Google Scholar and block mesangial expansion in diabetic glomerulosclerosis.30.McCarthy K.J. Routh R.E. Shaw W. et al.Troglitazone halts diabetic glomerulosclerosis by blockade of mesangial expansion.Kidney Int. 2000; 58: 2341-2350Abstract Full Text Full Text PDF PubMed Scopus (98) Google Scholar The observed anti-inflammatory effect of rosiglitazone in proximal tubular epithelial cells is suggested to be due to inhibition of NF-κB activation.27.Lee S. Kim W. Kang K.P. et al.Agonist of peroxisome proliferator-activated receptor-gamma, rosiglitazone, reduces renal injury and dysfunction in a murine sepsis model.Nephrol Dial Transplant. 2005; 20: 1057-1065Crossref PubMed Scopus (50) Google Scholar We demonstrated that BMP-7 increased PPAR-γ expression by HMCs cultured with pIgA. The enhanced release of TNF-α in HMCs induced by pIgA or exogenous TNF-α was reduced by the PPAR-γ agonist, rosiglitazone. Both BMP-7 and rosiglitazone attenuated nuclear translocation of NF-κB activated by pIgA or TNF-α. These observations suggest the anti-inflammatory effect of BMP-7 to be associated with PPAR-γ activation. In contrast to TNF-α, we found that upregulation of TGF-β induced by pIgA was independent of PPAR-γ activation and was not attenuated by rosiglitazone. Previously, we reported that pIgA upregulated TGF-β synthesis in cultured HMCs associated with increased Smad activities (Smad2 and Smad3).3.Lai K.N. Tang S.C. Guh J.Y. et al.Polymeric IgA1 from patients with IgA nephropathy upregulates transforming growth factor-beta synthesis and signal transduction in human mesangial cells via the rennin–angiotensin system.J Am Soc Nephrol. 2003; 14: 3127-3137Crossref PubMed Scopus (70) Google Scholar BMP-7 and TGF-β belong to the same family of pleiotropic cytokines. The action of TGF-β is mediated through pathway analogous to that of BMP-7.31.Miyazono K. Maeda S. Imamura T. BMP receptor signaling: transcriptional targets, regulation of signals, and signaling cross-talk.
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