Fibronectin In Mesangial Cells Research Articles

ALK7 Knockdown Plays a Protective Role on HG-Stimulated MCs through Activation of the Nrf2/HO-1 Pathway.

Objective Activin receptor-like kinase 7 (ALK7) is a member of the ALK family that has a key role in diabetes. However, the role of ALK7 in diabetic nephropathy (DN) remains unclear. Methods Herein, we evaluated the effects of ALK7 on mesangial cells (MCs). MCs were transfected with si-ALK7 or pcDNA3.0-ALK7, and then stimulated with 40 mM glucose for 24 h. Cell proliferation was detected by MTT assay. Relative ROS level was detected using DCFH-DA staining. The contents of inflammatory cytokines were determined by ELISA. Western blot analysis was used to determine the expression levels of FN, Col IV, Nrf2, and HO-1 in MCs. Results Our results showed that ALK7 expression was induced by HG in MCs. Knockdown of ALK7 inhibited HG-induced cell proliferation. The HG-induced ROS was mitigated by si-ALK7 with decreased ROS level and NOX activity. In addition, ALK7 knockdown exhibited anti-inflammatory activity in HG-stimulated MCs. Moreover, ALK7 knockdown attenuated fibronectin (FN) and collagen IV (Col IV) expression in MCs. Knockdown of ALK7 enhanced Nrf2/HO-1 pathway in MCs. Inhibition of Nrf2 reversed the protective effects of ALK7 knockdown on HG-stimulated MCs. Conclusion ALK7 knockdown exerted protective effects on HG-stimulated MCs through activation of the Nrf2/HO-1 pathway. Thus, targeting ALK7 might be a therapeutic approach for the treatment of DN.

The Polysaccharide of Ligustrum Lucidum Ait. Protected from Renal Fibrosis by Interfering with Angiotensin II Signaling

BackgroundA number of preclinical advances have indicated the cellular and molecular mechanisms underlying renal fibrosis, such as the signaling of angiotensin II (Ang II), which is a bioactive peptide in renin‐angiotensin system. As one of kidney‐tonifying herbs, Fructus Ligustri Lucidi (FLL), the fruit of Ligustrum lucidum Ait. (Oleaceae) recorded as a tonic and dietary supplement, is a commonly prescribed component in traditional kidney‐tonifying herbal formula. This study aimed to clarify the polysaccharide component in FLL and investigate its potential role in preservation against renal fibrosis.MethodsThe crude polysaccharide of FLL was prepared and deproteinized by Sevag reagent. After lyophilization, the DEAE‐cellulose DE52 column and the Sephacryl S‐200 HR column were used for further isolation and purification of homogenous polysaccharide. The mice with unilateral ureteral obstruction (UUO) underwent daily intraperitoneal injection with FLL polysaccharide starting 7 days before UUO surgery until day 7 after surgery. The murine mesangial SV40‐MES13 cells were treated with vehicle, Ang II (10‐7 M) either with the absence and presence of angiotensin type I receptor blocker (ARB) (10‐6M), or with low dose (50 μg/mL, Poly‐L) and high dose (200 μg/mL, Poly‐H) of FLL polysaccharide.ResultsThe purified homogenous polysaccharide (Poly) was explored from FLL and the carbohydrate content was 97.45%. A hypothetical structure for Poly was proposed considering the comprehensive data of methylation, monosaccharides, and NMR analyses. Treatment of UUO mice with Poly decreased kidney index and ameliorated glomerular sclerosis and interstitial fibrosis, as well as down‐regulated the expression of profibrogenic factor VEGF and matrix fibrotic protein fibronectin (FN). Furthermore, as the same effect to ARB, the pre‐incubation with Poly alleviated the Ang II‐induced up‐regulation of FN in mesangial cells by immunofluoresence staining. The protein expressions of FN and proinflammatory factors like MCP‐1 and Rantes were significantly lower in Poly‐treated cell group than those in Ang II treatment group.ConclusionThe polysaccharide of Ligustrum lucidum Ait. was accurately explored with structure clarification. This polysaccharide component repressed angiotensin II‐induced fibrotic phenotype of renal mesangial cells and exerted beneficial effects on kidney of UUO mice.

MO014DANHONG INJECTION INHIBITS LIPOPOLYSACCHARIDE-ENHANCED CELL PROLIFERATION OF RAT RENAL MESANGIAL CELLS VIA NF-ΚB SIGNALING PATHWAY

Abstract Background and Aims Mesangioproliferative glomerulonephritis (MsPGN) is well known as one of the leading causes of end-stage renal failure (ESRD), especially in the Asian population. The principal characteristic of MsPGN is the over proliferation of glomerular mesangial cells (MCs) accompanied by expansion of the extracellular matrix (ECM). Our previous studies demonstrated that Danhong injection (DHI), is a traditional Chinese medicine injection, could improve the renal function and inhibit the MCs proliferation and ECM expansion in rats with MsPGN. However, the molecular mechanisms have not been fully elucidated. To explore the potential mechanisms of DHI in the treatment of MsPGN, we investigated the effects of DHI on lipopolysaccharide (LPS)-induced nuclear factor-kappa B (NF-κB) activation and its downstream inflammatory mediators, such as intercellular adhesion molecule-1 (ICAM-1), transforming growth factor-beta 1 (TGF-β1), inducible nitric oxide synthase (iNOS) and fibronectin (FN) protein expression in rat MCs. Method The rat MCs treated with different concentrations of DHI (0, 50, 100, 200, 500, 1000, and 2000 uL/L) for 12 h, then incubated with or without 100 ng/ml LPS for another 24 h. Subsequently, cell proliferation was determined by Cell Counting Kit-8 (CCK8). Furthermore, the rat MCs treated with low-dose DHI (250 uL/L), median-dose DHI (500 uL/L) and high-dose DHI (1000 uL/L) for 12 h or Ammonium pyrrolidine dithiocarbamate (PDTC) for 30 min before 24h treatment of LPS. Then the activation of NF-κB was detected by Western blot and immunofluorescence. The protein levels of ICAM-1, TGF-β1, iNOS and FN in rat MCs were detected by Western blot. Results The results of CCK-8 revealed that DHI significantly suppressed LPS-induced cell proliferation (shown in Fig.1). LPS stimulation resulted in a significant increment of p65 contents in nucleus and a decrement of p65 contents in cytoplasm in rat MCs compared with NC. PDTC and DHI exerted potent inhibitory effect on increasing expression of p65 in nucleus and decreasing in cytoplasm compared with LPS treatment group. The inhibitory effect on NF-κB nuclear translocation of DHI was in a dose- dependent manner (shown in Fig.2). The Western blot assay showed that the protein level of IκB-α in cytoplasm treated by LPS decreased significantly compared with that in control (shown in Fig. 3) and this decrement was significantly reversed by PDTC and DHI. In addition, the protein expression of ICAM-1, TGF-β1, iNOS and FN was also inhibited by PDTC and DHI (shown in Fig. 4). Conclusion DHI significantly repressed LPS-induced cell proliferation and FN expression in rat MCs through inhibiting the activation of NF-κB signaling pathway and protein expression of its downstream inflammatory mediators. The ameliorative effects of DHI on MsPGN might be associated with this inhibition effect on NF-B signaling pathway.

Circular RNA HIPK3 exacerbates diabetic nephropathy and promotes proliferation by sponging miR-185.

The aim of the present study was to investigate expression levels of circular RNA HIPK3 (circHIPK3) in mice with diabetic nephropathy (DN) and the role of circHIPK3 in rat mesangial cells (MCs). Quantitative real-time polymerase chain reaction was performed to detect expression levels of circHIPK3, miR-185, cyclin D1, proliferating cell nuclear antigen (PCNA), transforming growth factor-β1 (TGF-β1), collagen Ⅰ (Col. Ⅰ), and fibronectin (FN) in mice with DN and rat mesangial cells. Luciferase assay was performed to investigate the binding sites of circHIPK3 and miR-185. Silencing cells of circHIPK3 and miR-185 were constructed using cell transfection assay. Our results revealed that the levels of 24-hour urinary albumin and urinary 8-hydroxy-2'-deoxyguanosine (8-OH-dG) from diabetic mice increased considerably. Up-regulation of circHIPK3 was observed in the renal tissues of mice with DN. Similarly, circHIPK3 expression in rat mesangial cells increased significantly in a microenvironment of high glucose. A loss-of-function experiment indicated that down-regulation of circHIPK3 inhibited cell proliferation and significantly decreased mRNA abundance of cyclin D1, PCNA, TGF-β1, Col. I, and FN in MCs. Luciferase assay demonstrated that circHIPK3 can specifically sponge miR-185, and silencing of miR-185 can reverse the effects of knocking down circHIPK3 on cell proliferation and mRNA abundance of cyclin D1, PCNA, TGF-β1, Col. I, and FN in MCs. Overall, circHIPK3 exhibits a promotive function in DN by sponging miR-185 and this evidence suggests that circHIPK3 might be a biomarker or therapeutic target for DN.

Inhibitor of MyoD family A increased fibronectin production by mesangial cells

Overproduction of extracellular matrix proteins, including fibronectin by glomerular mesangial cells (MCs) contributes to the development of diabetic nephropathy. Inhibitor of myogenic differentiation family isoform a (I‐mfa) is a multifunctional cytosolic protein, functioning as a transcription modulator or plasma membrane channel protein regulator. However, its renal effects are unknown. The aim of the present study was to determine if I‐mfa regulated fibronectin production by MCs and the mechanisms involved. In cultured human MCs, I‐mfa expression levels were upregulated and downregulated by transiently transfecting I‐mfa expression plasmids and siRNA against I‐mfa, respectively. Western blot analysis was conducted to determine the abundance of fibronectin protein in human MCs with different treatments and in kidney tissues from rats with and without diabetic nephropathy. RT‐PCR analysis was performed to assess mRNA levels of I‐mfa and fibronectin in human MCs with various treatments and in glomeruli from mice with and without diabetic nephropathy, respectively. We found that overexpression of I‐mfa significantly increased fibronectin protein abundance in human MCs. Silencing I‐mfa significantly reduced the expression level of fibronectin mRNA and blunted TGF‐β1‐stimulated production of fibronectin protein. We further found that high glucose, a central pathogenic stimulus in diabetes increased I‐mfa protein content in a time (≥ 48 h) and concentration (≥ 25 mM) dependent manner. Although high glucose exposure increased fibronectin at the protein level, it did not significantly elevate transcript levels of fibronectin in MCs. In agreement with the data from cultured cells, the abundance of I‐mfa protein was significantly greater in the renal cortex of rats with diabetic nephropathy compared to non‐diabetic rats. However, there was no significant difference in the level of glomerular I‐mfa mRNA between the mice with and without diabetic nephropathy. Moreover, hydrogen peroxide significantly increased I‐mfa protein abundance in a dose‐dependent manner (≥ 100 μM) in cultured human MCs. Antioxidants polyethylene glycol‐catalase, ammonium pyrrolidithiocarbamate and N‐acetyl cysteine significantly blunted high glucose‐induced increase of I‐mfa protein abundance. Taken together, our study suggests that an increased level of I‐mfa induced by high glucose/diabetes through the production of reactive oxygen species stimulates fibronectin production by MCs.Support or Funding InformationNIH/NIDDK (1RO1 DK115424); AHA Southwest Affiliate (16GRNT27780043); Harry S. Moss Heart Trust Award

Antilipotoxicity Activity of Osmanthus fragrans and Chrysanthemum morifolium Flower Extracts in Hepatocytes and Renal Glomerular Mesangial Cells

The excess influx of free fatty acids (FFAs) into nonadipose tissues, such as those of liver and kidney, induces lipotoxicity leading to hepatic steatosis and renal dysfunction. The aim of this study was to investigate the protective effects of methanolic flower extracts of Osmanthus fragrans (OF) and Chrysanthemum morifolium (CM) against FFA-induced lipotoxicity in hepatocytes (human HepG2 cells) and renal glomerular mesangial cells (mouse SV40-Mes13 cells). The results showed that OF and CM significantly suppressed FFA-induced intracellular triacylglycerol accumulation via partially inhibiting the gene expression of sterol regulatory element-binding protein-1c (SREBP-1c) and glycerol-3-phosphate acyltransferase (GPAT) in HepG2 cells. Both extracts inhibited reactive oxygen species (ROS) generation by FFA-stimulated HepG2 cells. OF and CM also suppressed the mRNA expression of interleukin- (IL-) 1β, IL-6, IL-8, tumor necrosis factor- (TNF-) α, and transforming growth factor- (TGF-) β by HepG2 cells treated with conditioned medium derived from lipopolysaccharide-treated THP-1 monocytes. Furthermore, OF and CM effectively inhibited oleate-induced cellular lipid accumulation, TGF-β secretion, and overexpression of fibronectin in mesangial cells. In conclusion, OF and CM possess hepatoprotective activity by inhibiting hepatic fat load and inflammation and renal protection by preventing FFA-induced mesangial extracellular matrix formation.

Effect of Moutan Cortex on AGEs-induced mesangial cell proliferation and basement membrane thickening

To investigate the effect of Moutan Cortex on mesangial proliferation and basement membrane thickening induced by advanced glycation end products (AGEs). The glomerular mesangial cells (MC) injury model was established by inducing by AGEs. The cell were divided into 6 groups: the blank group ( BSA, 200 mg L-1) , the model group (AGEs, 200 mg L-1), the positive control group (AG, 10 mmol L L-1), and drug administration groups, namely the Moutan Cortex-treated high-dose group (2 x 10(-4) g mL(- 1)), the Moutan Cortex-treated medium-dose group (1 x 10(-4) g mL-1 ), and the Moutan Cortex-treated low-dose group (0. 5 x 10(-4) g . mL(-1)). The MTT method was performed to observe the effect of Moutan Cortex on the proliferation of MC. The content of fibronectin (FN) and collagen secretion 1V (Col IV) in cell supernatant were detected by ELISA kits. The western blot analysis was carried out to observe the FN expression. The Real-time PCR analysis was applied to examine the Col IV mRNA expression. AGEs significantly increased AGEs-induced MC proliferation and FN and Col 1V secretion. The western blot analysis showed that MC could down-regulate the FN expression of MC secretion. According to the results of the real-time PCR assay, MC could down-regulate AGEs-induced MC secretion Col IV mRNA expression. MC had a certain protective effect on MC cultured under AGEs conditions. MC could remarkably inhibit the composition and secretion of Col IV and FN in matrix and the basement membrane thickening, and provide an experimental basis for the treatment of diabetic nephropathy.

Abstract 245: Synergistic Effects of Nicotine and Angiotensin II: Implications for Progression of Chronic Kidney Disease in Smokers

Increased generation of Angiotensin II (ANG II) plays a key role in the progression of chronic kidney disease (CKD). Cigarette smoking accelerates the progression of CKD of different etiologies including hypertension and diabetes. We have shown that nicotine (NIC), a biologically active compound present in large amounts in tobacco, worsens the severity of injury in experimental models of CKD. The aim of this study is to determine whether NIC and ANG II have synergistic effects on fibronectin production and proliferation in mesangial cells (MC). Rat MC were exposed to different concentrations of NIC (10 -4 M to 10 -10 M) and/or ANG II (10 -6 M to 10 -10 M) for 24 hours. Fibronectin production was measured by western blot and proliferation by EdU incorporation. As shown in Table 1, NIC and ANG II have synergistic effects on the production of fibronectin in MC. Shown in Table 2, NIC and ANG II have additive effects on MC proliferation. These synergistic effects of NIC and ANG II may explain the deleterious effects of smoking in conditions associated with increased activation of the renin angiotensin system.

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

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

Berberine attenuates lipopolysaccharide-induced extracelluar matrix accumulation and inflammation in rat mesangial cells: Involvement of NF-κB signaling pathway

Background Our previous studies demonstrated that berberine could improve the renal function in rats and mice with diabetic nephropathy (DN) and inhibit extracellular matrix (ECM) component, fibronectin (FN) expression in rat mesangial cells (MCs) cultured under high glucose. However, the molecular mechanisms have not been fully elucidated. Objective To explore the potential mechanisms of berberine in the treatment of DN, we investigated the effects of berberine on lipopolysaccharide (LPS)-induced nuclear factor-kappa B (NF-κB) activation and its downstream inflammatory mediators, such as intercellular adhesion molecule-1 (ICAM-1), transforming growth factor-beta 1 (TGF-β1), inducible nitric oxide synthase (iNOS) and fibronectin (FN) protein expression in rat MCs. Method Cell proliferation was determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT). The activation of NF-κB was detected by Western blot and confocal microscopy. The protein levels of ICAM-1, TGF-β1, iNOS and FN in rat MCs were detected by Western blot. Results Our results revealed that berberine significantly suppressed LPS-induced cell proliferation and inhibited LPS-induced NF-κB nuclear translocation in MCs, as well as protein expression of ICAM-1, TGF-β1, iNOS and FN. Conclusion Berberine significantly repressed LPS-induced cell proliferation and FN expression in rat MCs through inhibiting the activation of NF-κB signaling pathway and protein expression of its downstream inflammatory mediators. The ameliorative effects of berberine on DN might be associated with this inhibition effect on NF-κB signaling pathway which was independent of its hypoglycemic effect.

Dickkopf-1 Promotes Hyperglycemia–Induced Accumulation of Mesangial Matrix and Renal Dysfunction

Wnt/beta-catenin signaling mediates renal fibrosis in several model systems including diabetic nephropathy. Dickkopf-1 (DKK-1) is an endogenous inhibitor of Wnt/beta-catenin signaling, but whether DKK-1 modulates diabetic nephropathy is unknown. Here, we studied whether DKK-1 participates in high glucose (HG)-induced expression of profibrotic factors and renal damage. In vitro, HG increased expression of DKK1, receptor Kremen-2, TGF-beta1, and fibronectin in mesangial cells. Loss and gain of DKK1 function modulated HG-mediated c-Jun, TGF-beta1, and fibronectin expression. DKK1 mediated HG-induced phosphorylation of Ser45-beta-catenin and reduction of nuclear beta-catenin levels, but not phosphorylation of ERK kinase. Wnt3a protein and the beta-catenin (Delta45) mutation increased nuclear beta-catenin but abrogated HG-induced DKK1 and fibronectin expression. Exogenous DKK1 antisense oligonucleotide attenuated the increase in both serum DKK1 and urinary protein excretion in streptozotocin-induced diabetic rats. Knocking down DKK1 inhibited mesangial expression of TGF-beta1 and fibronectin and reduced both the glomerular volume and deposition of mesangial matrix in diabetic kidneys. Taken together, DKK1 mediates HG-induced destabilization of beta-catenin and matrix accumulation in mesangial cells. Knocking down DKK1 prevents diabetes-induced renal dysfunction and microstructure deterioration, suggesting that inhibition of DKK1offers therapeutic potential for diabetic nephropathy.

Effects of α-lipoic acid on transforming growth factor β1–p38 mitogen-activated protein kinase–fibronectin pathway in diabetic nephropathy

In diabetic nephropathy, transforming growth factor β1 (TGF β1) is related to p38 mitogen-activated protein kinase (MAPK) that induces production of fibronectin in mesangial cells. We investigated the effects of α-lipoic acid (ALA), a potent antioxidant, on proteinuria and TGF β1–p38 MAPK–fibronectin pathway in diabetic Otsuka Long-Evans Tokushima Fatty (OLETF) rats. After ALA treatment for 5 weeks in OLETF rats at 30 weeks of age, plasma malondialdehyde, urinary protein excretion, renal cortical TGF β1, and fibronectin protein levels were decreased; and urinary protein excretion was positively correlated with renal cortical TGF β1 and fibronectin protein levels. Phospho-form but not total-form levels as well as fold activations of each protein consisting of p38 MAPK pathway were also attenuated. These results suggest that ALA ameliorates proteinuria by attenuating expressions of TGF β1 and fibronectin proteins, and these favorable effects are related to inhibition of phosphorylating activation of p38 MAPK pathway in renal cortex of OLETF rats.

The role of bradykinin in the antifibrotic actions of perindoprilat on human mesangial cells

Angiotensin-converting enzyme inhibitors (ACE-I) protect against the development of glomerulosclerosis using mechanisms partly dissociated from their systemic antihypertensive action. The aim of the current study was to delineate the mechanism of action underlying the antifibrotic effects of the ACE-I perindoprilat in the context of macrophage-mediated scarring in human mesangial cells. Mesangial cells were treated with macrophage-conditioned medium (MPCM) in the presence or absence of the ACE-I perindoprilat. Forty micromol/L perindoprilat reduced MPCM-induced mesangial cell fibronectin levels by 19.4 +/- 0.6% (P < 0.001). Immunoprecipitation of 35S-methionine biosynthetically labeled fibronectin and Northern analysis suggested that the decrease in fibronectin levels was not caused by reduced synthesis. MPCM stimulated the production of matrix metalloproteinases (MMP) 2, 3, and 9 in mesangial cells; however, these were not significantly altered by ACE-I treatment, and neither was production of their tissue inhibitor of metalloproteinases (TIMP-1). Addition of exogenous bradykinin to MPCM-treated mesangial cells resulted in a 22.5 +/- 1.4% (P < 0.02) reduction in secreted fibronectin levels, while semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) and Southern blotting demonstrated that bradykinin B2 receptor expression was up regulated by 71 +/- 30% in MPCM-stimulated mesangial cells in response to ACE-I treatment (P= 0.032). Moreover, the bradykinin B2 receptor antagonist HOE 140 attenuated the beneficial effects of perindoprilat. MPCM-stimulated mesangial cell protein expression levels of plasminogen activator system components tissue plasminogen activator (tPA) and plasminogen activator inhibitor-1 (PAI-1) were altered after treatment with ACE-I. These results suggest that ACE-I-induced renoprotection, in the context of macrophage-stimulated mesangial cell scarring, is mediated, at least in part, via the actions of bradykinin.

Smad pathway is activated in the diabetic mouse kidney and Smad3 mediates TGF-β-induced fibronectin in mesangial cells

Activation of the transforming growth factor-β (TGF-β) system has been implicated in the pathological changes of diabetic nephropathy such as renal hypertrophy and accumulation of extracellular matrix. Streptozotocin-induced diabetic mice were used to examine whether the Smad pathway, which transduces the TGF-β signal, is activated in the diabetic kidney, employing Southwestern histochemistry with labeled Smad-binding element (SBE) oligonucleotides and immunoblotting of nuclear protein extracts for Smad3. Mouse mesangial cells were used to study the role of Smads in mediating the effects of high glucose and TGF-β on fibronectin expression, using transient transfections of Smad expression vectors and TGF-β-responsive reporter assays. By Southwestern histochemistry, the binding of nuclear proteins to labeled SBE increased in both glomeruli and tubules at 1, 3, and 6 weeks of diabetes. Likewise, immunoblotting demonstrated that nuclear accumulation of Smad3 was increased in the kidney of diabetic mice. Both increases were prevented by insulin treatment. In mesangial cells, high glucose potentiated the effect of low-dose TGF-β1 (0.2 ng/ml) on the following TGF-β-responsive constructs: 3TP-Lux (containing AP-1 sites and PAI-1 promoter), SBE4-Luc (containing four tandem repeats of SBE sequence), and the fibronectin promoter. Additionally, Smad3 overexpression increased fibronectin promoter activity, an effect that was enhanced by high ambient glucose or treatment with TGF-β1 (2 ng/ml). The TGF-β-stimulated activity of the fibronectin promoter was prevented by transfection with either a dominant-negative Smad3 or the inhibitory Smad7. We conclude that hyperglycemia activates the intrarenal TGF-β/Smad signaling pathway, which then promotes mesangial matrix gene expression in diabetic nephropathy.

Transforming growth factor-β suppresses macrophage-induced mesangial cell fibronectin expression

We have previously shown that macrophages are able to promote prosclerotic responses in rat mesangial cells. Th2-type cytokines, including interleukin-10 (IL-10), IL-13, and IL-4 as well as transforming growth factor-beta (TGF-beta), are known to have suppressive effects on various aspects of macrophage function. In the current study, we investigated the effect of TGF-beta pretreatment on the ability of macrophages to induce fibronectin expression. Conditioned medium from TGF-beta pretreated macrophages (MPCM(TGF)) induced lower fibronectin levels in mesangial cells in both the secreted and cell-associated forms, compared with conditioned medium from standard macrophages (MPCM) (5.5 +/- 0.2 vs. 3.4 +/- 0.3 and 4.05 +/- 0.45 vs. 2.3 +/- 0.2-fold increase over medium alone for MPCM versus MPCM(TGF) in supernatants and cell lysates, respectively). Northern blot analysis demonstrated that fibronectin message was marginally reduced to 0.88 +/- 0.04 (P < 0.03 vs. MPCM, N = 3) of MPCM-induced levels. However, mesangial cell transin mRNA levels induced in response to MPCM(TGF) were 2.29 +/- 0.47-fold greater than those induced by standard MPCM (P = 0.03 vs. MPCM, N = 4). TIMP-1 mRNA levels were also increased in response to MPCM(TGF), but only by 1.43 +/- 0.1-fold (P = 0.02 vs. MPCM, N = 5). Casein-FITC digestion studies confirmed that MPCM(TGF) stimulated more mesangial cell caseinolytic activity than did MPCM. In addition, MPCM-mediated up-regulation of mesangial cell TGF-beta mRNA and protein expression was significantly reduced in response to conditioned medium from macrophages pretreated with TGF-beta. This study suggests that TGF-beta is able to regulate negatively the profibrotic effects of macrophages on mesangial cells by both enhancing matrix degradation and reducing synthesis.

Cholesterol feeding activates macrophages to upregulate rat mesangial cell fibronectin production.

Cholesterol feeding has been shown to accelerate the development of glomerulosclerosis in many experimental renal diseases, possibly by promoting the infiltration of macrophages into the glomerulus. In order to assess whether hyperlipidaemia could directly modulate macrophage function to promote glomerulosclerosis, confluent quiescent mesangial cells were exposed to resident (r) or elicited (e) macrophages, from either control (C) or cholesterol-fed (HC) rats or the conditioned media derived from the various macrophage preparations. All macrophage preparations stimulated mesangial cell fibronectin accumulation over medium alone, but eHC macrophages stimulated significantly greater fibronectin levels. Similarly, all macrophage conditioned media (MPCM) stimulated mesangial cell fibronectin production over medium alone and again the effect was greatest with MPCM derived from eHC macrophages. Proliferation studies using [(3)H]thymidine incorporation demonstrated that all conditioned media, with the exception of rC, stimulated significant mesangial cell proliferation over control levels. TGF-beta and PDGF, pro-fibrogenic growth factors known to be associated with macrophage infiltration, could not be detected in the MPCMs per se. However, they were detected in the culture supernatants of mesangial cells exposed to MPCMs and again secretion was greatest from mesangial cells exposed to eHC-MCPM. Monocytes are systemically activated by high serum cholesterol levels so that following maturation to macrophages they elaborate soluble factors that can stimulate mesangial cell fibronectin production, cell proliferation, and growth factor secretion. Hypercholesterolaemia may therefore accelerate glomerulosclerosis not only by increasing macrophage number, but also by upregulating the ability of macrophages to induce pro-sclerotic responses in glomerular mesangial cells.

ATHEROSCLEROSIS-INDUCED CHRONIC ISCHEMIA CAUSES BLADDER FIBROSIS AND NON-COMPLIANCE IN THE RABBIT

The overall goal was to determine whether chronic ischemia and hypercholesterolemia interfere with bladder function and structure. The roles of atherosclerosis-induced chronic ischemia and hypercholesterolemia in bladder fibrosis and non-compliance were studied in the rabbit. The relationship between ischemia-induced changes in the expression of transforming growth factor-beta1 (TGF-beta1) and basic fibroblast growth factor (bFGF) and the severity of bladder fibrosis was also investigated. Male New Zealand White rabbits were divided into chronic bladder ischemia (CBI, n = 11), hypercholesterolemia (Hch, n = 8) and control (n = 8) groups. The CBI group underwent balloon endothelial injury of the iliac arteries and received a 0.5% cholesterol diet. The Hch group received a 0.5% cholesterol diet alone. The control group was placed on a regular diet. After 16 weeks, iliac artery and bladder wall blood flow measurements, cystometrograms (CMG) and aorto-iliac arteriograms were obtained in all animals. Iliac arteries and bladder tissues were processed for histological staining and computer-assisted histomorphometric image analysis. The expressions of TGF-beta1 and bFGF in bladder tissue were determined by immunohistochemical staining utilizing monoclonal antibodies. At 16 weeks, arteriography and histology showed significant diffuse atherosclerotic occlusive disease of the aorto-iliac arteries in the CBI group. Iliac artery and bladder wall blood flows were significantly decreased in the CBI group compared with the Hch and control groups. Atherosclerosis-induced CBI shifted the volume-pressure curve to the left and caused severe bladder fibrosis. Hypercholesterolemia also caused fibrosis and non-compliance but to a much lesser extent compared with those caused by CBI. In histomorphometry, the percentage of detrusor smooth muscle was moderately decreased in the Hch group and severely decreased in the CBI group compared with the control group. In immunohistochemical stains of bladder tissues, bFGF expression was similar in the three groups of animals. TGF-beta1 expression was significantly greater in bladder tissues from the CBI group compared with the Hch and control groups. Our studies show that atherosclerosis-induced chronic ischemia increases TGF-beta1 expression in the bladder leading to fibrosis, smooth muscle atrophy and non-compliance. Hypercholesterolemia also interferes with bladder structure and compliance but to a significantly lesser extent compared with CBI. Our studies suggest that arterial insufficiency and hypercholesterolemia, common aging-associated disorders, may play important roles in the pathophysiology of voiding dysfunction in the elderly.

Stretch-induced overproduction of fibronectin in mesangial cells is mediated by the activation of mitogen-activated protein kinase.

An excessive production of extracellular matrix (ECM) proteins in glomerular mesangial cells is considered to be responsible for the development of mesangial expansion seen in diabetic nephropathy. Mechanical stretch due to glomerular hypertension has been proposed as one of the factors leading to an increase in the production of ECM proteins in mesangial cells, but the precise mechanism of stretch-induced overproduction of ECM proteins has not been elucidated. Herein, we provide the evidence that mitogen-activated protein kinase (MAPK) may play a key role in the overproduction of fibronectin (FN) in mesangial cells exposed to mechanical stretch. MAPK, also termed extracellular signal-regulated kinase (ERK) and c-Jun NH2-terminal kinase (JNK), was activated by mechanical stretch in time- and intensity-dependent manners. Stretch-induced activation of ERK was inhibited by herbimycin A, a tyrosine kinase inhibitor, but not by GF109203X or calphostin C, the inhibitors of protein kinase C. Mechanical stretch also enhanced DNA-binding activity of AP-1, and this enhancement was inhibited by PD98059, an inhibitor of MAPK or ERK kinase (MEK). Furthermore, mechanical stretch stimulated the expression of FN mRNA followed by a significant increase in its protein accumulation. PD98059 could prevent stretch-induced increase in the expression of FN mRNA and protein. These results indicate that the activation of ERK may mediate the overproduction of ECM proteins in mesangial cells exposed to mechanical stretch, an in vitro model for glomerular hypertension seen in diabetes.

Cytokine interactions promote synergistic fibronectin accumulation by mesangial cells

The development of glomerulosclerosis has been associated with the presence of the cytokines transforming growth factor-beta 1 (TGF-beta 1), tumor necrosis factor-alpha (TNF-alpha) and/or interleukin-1 beta (IL-1 beta), at some stage in the glomerulus. To better understand the role of these cytokines in the scarring process their effect on rat mesangial cell fibronectin production was investigated.Mesangial cells were exposed to 10 ng/ml of either TGF-beta 1, TNF-alpha, or IL-1 beta or to TGF-beta 1 in combination with TNF-alpha or IL-1 beta. Tissue culture supernatants and cell lysates were assayed for fibronectin. Supernatants were also assayed for TGF-beta 1. Northern blot analyses probing for fibronectin, transin, TIMP-1 and TGF-beta 1 were carried out on RNA extracted from mesangial cells exposed to individual and combinations of cytokines.Individually these cytokines were only able to induce modest increases in fibronectin protein levels. However, when mesangial cells were exposed to TGF-beta 1 in combination with either TNF-alpha or IL-1 beta then fibronectin levels were synergistically up-regulated approximately fivefold over unstimulated levels. Northern analysis demonstrated that fibronectin mRNA levels in the combination were also synergistically increased. In contrast, rat transin gene expression in the combinations was reduced to well below levels induced by TNF-alpha and IL-1 beta individually. In addition, synergistic up-regulation of both TGF-beta 1 protein and message by the cytokine combinations was also observed. TGF-beta 1: TNF-alpha and TGF-beta 1: IL-1 beta induced additive increases in TIMP-1 (tissue inhibitor of metalloproteinases-1) mRNA levels.These data illustrate that complex interactions can occur between cytokines within the glomerulus modulating both matrix synthetic and degradation pathways. These could initiate the scarring process and the development of glomerulosclerosis.

Macrophages promote prosclerotic responses in cultured rat mesangial cells: a mechanism for the initiation of glomerulosclerosis.

Glomerulosclerosis is the final outcome of a number of different causes of glomerular injury, during which the structures of the glomerulus are obliterated by extracellular matrix. Accumulating evidence suggests that infiltrating macrophages play a pivotal role in the progression to glomerulosclerosis. The present study defines the role played by macrophages at both cellular and molecular levels in the initiation of the sclerotic process in cultured rat mesangial cells. Macrophage-conditioned medium (MPCM) generated from thioglycollate-elicited, lipopolysaccharide-stimulated macrophages upregulated mesangial cell fibronectin production in a dose- and time-dependent manner, independently of cell proliferation. Immunoprecipitation of metabolically labeled 35S-fibronectin confirmed that the matrix protein was synthesized de novo. The genes for fibronectin and the matrix proteins laminin and collagen IV were also found to be upregulated 2.86 +/- 0.24-, 4.94 +/- 0.17-, and 3.03 +/- 0.31-fold over controls, respectively (P < 0.001). Macrophage modulation of matrix turnover was suggested by an upregulation of both transin and tissue inhibitor of metalloproteinase-1 gene transcription. Transforming growth factor (TGF) beta1, platelet-derived growth factor, tumor necrosis factor (TNF) alpha, or interleukin (IL)-1beta could not be detected in the MPCM per se; however, TGFbeta1 and platelet-derived growth factor AB were found to be secreted into mesangial cell culture supernatants. Secretion was augmented 1.69 +/- 0.16- and 2.28 +/- 0.28-fold, respectively (both P < 0.001), in response to MPCM. Northern blot analysis demonstrated that protein secretion had been preceded by upregulation of the genes for these cytokines (2.2 +/- 0.4-fold [P < 0.001] and 5.7 +/- 1.2-fold [P < 0.004], respectively). Incubation of MPCM with either neutralizing antibody or the growth factor receptor antagonist suramin demonstrated that TGFbeta1 played a significant, although minor, role in MPCM-stimulated fibronectin production. In conclusion, this study provides compelling evidence for a direct role of macrophages in the progression to glomerulosclerosis.