Cell to cell interaction between mesangial cells and macrophages induces the expression of monocyte chemoattractant protein-1 through nuclear factor-kappaB activation

Efficacy of antisense monocyte chemoattractant protein-1 (MCP-1) in a rat model of mesangial proliferative glomerulonephritis

OBJECTIVE

The effects of inhibition of monocyte chemoattractant protein-1 (MCP-1) on a rat model of mesangial proliferative glomerulonephritis (MsPGN) were evaluated.

METHODS

The anti-Thy-1 MsPGN model was developed by intravenously injecting anti-Thy-1 monoclonal antibodies into rats, followed by an injection of mesangial cells transfected with antisense MCP-1 into the renal artery. Exogenous cells were detected by in situ hybridization. Rats (40 total) were randomly divided into five groups: SO (sham operation), TG (Thy-1 glomerulonephritis model), MC (non-transfected normal rat mesangial cell), BC (pLXSN empty vector or blank control), and AM (antisense MCP-1 transfection) groups. Effects of exogenous MCP-1 on urinary protein excretion rate, biochemical parameters, and pathological changes were evaluated. Expression of MCP-1 and transforming growth factor-β1 (TGF-β1) were detected by immunohistochemistry. mRNA expression of MCP-1, TGF-β1, and CC chemokine receptor 2 (CCR2) were detected by RT-PCR.

RESULTS

Exogenous MCP-1 cDNA was successfully transfected into mesangial cells. Exogenous mesangial cells were detected in glomeruli by in situ hybridization. Glomerular mesangial cell proliferation, 24-h urinary protein excretion rate, mRNA expression of MCP-1, TGF-β1, and CCR2, and protein expression of MCP-1 all decreased in the AM group as compared to the control group (p < 0.05), but there was no significant difference in the expression level of TGF-β1 protein.

CONCLUSIONS

(1) Mesangial cells can be used as a vector to transfect exogenous genes into kidneys; (2) antisense MCP-1 decreases mesangial cell proliferation and pathological injury in MsPGN model rats by decreasing expression of MCP-1 and CCR2; and (3) antisense MCP-1 suppressed mesangial cell proliferation and matrix accumulation in anti-Thy-1 MsPGN model rats, which did not entirely depend on TGF-β1.

Potential antifibrotic effects of AT1 receptor antagonist, losartan, and/or praziquantel on acute and chronic experimental liver fibrosis induced by Schistosoma mansoni

1. This study investigates the potential antifibrotic effect of losartan, AT-1 receptor antagonist, and/or praziquantel (PZQ) on acute and chronic hepatic fibrosis induced by Schistosoma mansoni (S. mansoni). 2. Schistosoma mansoni-infected mice were in two batches (I & II), each in four groups: (i) Infected untreated; (ii) treated with losartan, starting from the 4th or 12th weeks post-infection (PI); (iii) treated with PZQ in the 7th week PI; and (iv) treated with losartan, as group (ii) plus PZQ as group (iii). Comparable groups of uninfected mice were run in parallel with infected groups. Mice of batches I and II were killed 10 and 18 weeks PI, respectively. Hepatic content of hydroxyproline (HYP), serum levels and tissue expression of matrix metalloproteinase-2 (MMP-2), and transforming growth factor-β1 (TGF-β1) were determined. Parasitological, biochemical and histological parameters, which reflect disease severity and morbidity, were examined. 3. Losartan alone caused a considerable decrease in worm burden, hepatic tissue egg load with an increase in percentage of dead eggs, modulation of granuloma size and regression of inflammatory reactions, which was less obvious in the chronic stage. The best results were obtained when losartan was co-administered with PZQ, especially in the acute stage. This was revealed by a remarkable reduction in serum levels and tissue expression of MMP-2, TGF-β1 and HYP content, accompanied by conservation of hepatic reduced glutathione (GSH) versus the PZQ-treated group. 4. In conclusion, losartan has a promising antifibrotic action and could be introduced as a therapeutic tool with PZQ especially in acute schistosomal hepatic fibrosis.

The MCP-1/CCR2 system has direct proinflammatory effects in human mesangial cells

Both inflammatory and haemodynamic factors have been implicated in the pathogenesis of diabetic and other progressive glomerulopathies. Mesangial cell exposure to mechanical stretch induces both intercellular adhesion molecule 1 (ICAM-1) and monocyte chemoattractant protein-1 (MCP-1) expression. CC Chemokine receptor 2 (CCR2), the cognate MCP-1 receptor, has been recently demonstrated in human mesangial cells (HMCs). We tested whether MCP-1 binding to CCR2 affects ICAM-1 expression in HMCs and, secondly, if stretch-induced ICAM-1 is mediated by MCP-1 via an autocrine mechanism. Serum-deprived HMCs were exposed to either rh-MCP-1 (0.1-1-10-50-100 ng/ml) or mechanical stretch in the presence and in the absence of RS102895, a specific CCR2 inhibitor. ICAM-1 expression was assessed both by immunofluorescence and cytofluorimetry. Monocyte-HMC interaction was tested by adhesion assay. CCR2 expression was studied by reverse transcriptase-polymerase chain reaction, immunoblotting, and flow cytometry. HMCs exposure to rh-MCP-1 induced a significant twofold increase in ICAM-1 expression at 24 h, leading to enhanced monocyte adhesion. This effect occurred via the CCR2 receptor as CCR2 was expressed in HMCs and CCR2 blockade prevented ICAM-1 upregulation. Stretch-induced ICAM-1 expression was not altered by CCR2 blockade and stretch significantly reduced CCR2 mRNA and protein expression via an MCP-1-independent mechanism. In conclusion, stretch and MCP-1 independently induce ICAM-1 expression in HMCs. Stretch-induced CCR2 downregulation may favour MCP-1 paracrine activity.

Priming of glomerular mesangial cells by activated macrophages causes blunted responses to proinflammatory stimuli

Macrophage-mesangial cell interaction plays a crucial role in the pathogenesis of glomerulonephritis. Activated macrophages trigger mesangial cells to express an array of inflammation-associated genes via activation of NF-kappaB and AP-1. However, this inflammatory response is often transient and subsides spontaneously. We found that mesangial cells activated by bystander macrophages showed blunted responses of NF-kappaB to subsequent macrophage exposure. It was associated with sustained levels of IkappaBbeta, but not IkappaBalpha. The tolerance observed was reversible and reproduced by conditioned media from activated macrophages (macrophage-conditioned medium (MphiCM)). In vivo priming of mesangial cells by activated glomerular macrophages also caused the tolerance of mesangial cells. The macrophage-derived tolerance inducers were heat-labile, and multiple molecules were involved. Among inflammatory cytokines produced by macrophages, TNF-alpha and IL-1beta were able to induce mesangial cell tolerance dose-dependently. The mesangial cell tolerance was also observed in activation of the MAPK-AP-1 pathway; i.e., phosphorylation of ERK, JNK, and p38 MAPK by macrophages was blunted when the cells were pre-exposed to MphiCM. Induction of c-fos and c-jun was also abrogated in mesangial cells pre-exposed to MphiCM, and the suppression was attenuated by blockade of MAPK activation during the first exposure to MphiCM. These data elucidated that mesangial cells, once exposed to macrophages, become insensitive to subsequent activation by macrophages and proinflammatory stimuli. This self defense of glomerular cells may play a role in the resolution of macrophage-mediated, acute glomerulonephritis.

Reactive oxygen species-mediated signaling pathways in angiotensin II-induced MCP-1 expression of proximal tubular cells

Angiotensin II (AngII) has pleiotropic effects, the most well known of which is the generation of reactive oxygen species (ROS) and chemokines in inflammatory lesions. Monocyte chemoattractant protein-1 (MCP-1) is considered a major chemokine in the pathogenesis of kidney diseases. We examined signaling pathways of AngII-induced MCP-1 expression and the role of ROS in the murine proximal tubular cells (mProx) using various inhibitors. Furthermore, we compared the signaling pathways between mProx and mesangial cells (MC). AngII-induced MCP-1 protein expression in mProx at 6 h was largely blocked by ROS (N-acetylcysteine; 82 +/- 14%), Ras (N-acetyl-S-trans,trans-farnesyl-L-cysteine; 82 +/- 13%), and nuclear factor-kappaB (NF-kappaB) (parthenolide; 89 +/- 7.9%) inhibitors. Both AT1 receptor (AT1R) (Olmesartan; 41 +/- 12%) and the AT2R (PD123319; 24 +/- 11%) antagonists partially blocked the MCP-1 expression. Furthermore, mitogen-activated protein kinase (MAPK) pathways were also implicated in this protein expression, but it is less dependent on ROS/Ras pathways. In MC, protein kinase (calphostin C; 84 +/- 2.8%) and NF-kappaB (89 +/- 1.4%) inhibitors attenuated acute AngII-induced MCP-1 expression stronger than ROS/Ras inhibitors (1.0 +/- 0.9/29 +/- 9.5%). MAPK pathways, especially p38 MAPK, were involved in MC more than in mProx. AT1R (69 +/- 8.6%) and AT2R (57 +/- 21%) antagonists also were blocked. We suggested that, although NF-kappaB activation has a critical role, signaling pathways are different between mProx and MC. ROS-mediated signaling in mProx may have more contribution to AngII-induced inflammatory responses than to those in MC.

Cooperative Expression of Monocyte Chemoattractant Protein 1 Within the Bovine Corpus Luteum: Evidence of Immune Cell-Endothelial Cell Interactions in a Coculture System1

Endothelial cells (EC) of the bovine corpus luteum (CL) are a known source of proinflammatory mediators, including monocyte chemoattractant protein 1 (CCL2) and endothelin 1 (EDN1). Here, a coculture system was devised to determine if immune cells and PGF 2alpha together affect CCL2 and EDN1 secretion by EC. Luteal EC were cultured either alone or together with peripheral blood mononuclear cells (PBMC), and treated without or with PGF 2alpha for 48 h (n = 6 experiments). Coculture of EC with PBMC increased CCL2 secretion an average of 5-fold higher compared with either cell type alone (P < 0.05). Basal secretion of EDN1 by EC was substantial (approximately 2 ng/ml), but was not affected by coculture with PBMC (P > 0.05). EC cocultured with concanavalin A-activated PBMC (ActPBMC) increased CCL2 secretion an average of 12-fold higher compared with controls (P < 0.05), but again, EDN1 secretion was unchanged (P > 0.05). Interestingly, PGF 2alpha did not alter either CCL2 or EDN1 secretion, regardless of culture conditions (P > 0.05). In a second series of experiments (n = 3 experiments), mixed luteal cells (MLC) were cultured alone or with PBMC as described above. Secretion of CCL2 and EDN1 was not affected by coculture or by PGF 2alpha (P > 0.05), but MLC produced less progesterone in the presence of ActPBMC (P < 0.05). Collectively, these results suggest that immune cells and EC can interact cooperatively to increase CCL2 secretion in the CL, but this interaction does not affect EDN1 secretion nor is it influenced by PGF 2alpha. Additionally, activated immune cells appear to produce a factor that impairs progesterone production by luteal steroidogenic cells.

The -2518 Promotor Polymorphism in the MCP-1 Gene Is Associated with Systemic Sclerosis

Factors influencing the initiation or progression of sclerosis in patients with systemic sclerosis (SSc) are poorly understood. Monocyte chemotactic protein-1 (MCP-1) is a potent chemokine, which is upregulated in fibroblasts during development of sclerosis. In this study, we investigated the frequency of the functional -2518G MCP-1 promoter polymorphism in 18 patients with SSc and 139 healthy controls. In the lesional skin of the same SSc patients, expression of MCP-1 protein was examined by immunohistochemistry. To investigate a genotype/phenotype correlation, basal as well as tumor necrosis factor (TNF)-induced MCP-1 expression was analyzed in fibroblasts isolated from the skin of SSc patients with different MCP-1 genotypes by quantitative RT-PCR and ELISA. Genotyping for the -2518 (A/G) MCP-1 promotor polymorphism showed that GG homozygotes were significantly more frequent in patients with SSc than in controls (28%vs 6%). Results of immunohistochemistry revealed that MCP-1 was expressed in keratinocytes, infiltrating inflammatory cells, fibroblasts, and endothelial cells in scleroderma skin, whereas normal control skin showed no MCP-1 expression. MCP-1 expression in fibroblasts from GG-homozygote individuals tended to be stronger as compared to AG or AA genotypes. Furthermore, basal as well as TNF-induced MCP-1 expression of fibroblasts isolated from a GG-homozygote SSc patient was significantly higher than MCP-1 expression of fibroblasts isolated from heterozygote or AA-homozygote donors. The A -2518G polymorphism of the MCP-1 gene appears to affect MCP-1 expression of skin fibroblasts of patients with SSc. In accordance, the G/G genotype may predispose patients to SSc.

Involvement of p300 in TGF-β/Smad-Pathway-Mediated α2(I) Collagen Expression in Mouse Mesangial Cells

BACKGROUND

Transforming growth factor beta 1 (TGF-beta1) induces alpha2(I) collagen gene (COL1A2) expression in mesangial cells through physical and functional cooperation of Smad proteins and Sp1. A transcriptional coactivator, p300, is also suggested to play an important role in TGF-beta1/Smad signal transduction. However, the role of p300 in TGF-beta1/Smad-pathway-mediated transcriptional activation of the COL1A2 gene in mesangial cells is still obscure.

METHODS

Endogenous p300 expression and its modulation by TGF-beta1 were evaluated by Western blotting and immunofluorescence. The physical interaction of p300 with Smad2/3 was examined by immunoprecipitation followed by Western blotting. The functional role of p300 in TGF-beta1/Smad-pathway-mediated COL1A2 transcription was investigated in cotransfection experiments using a COL1A2 promoter-luciferase reporter gene construct and p300 expression plasmids.

RESULTS

TGF-beta1 induced COL1A2 gene expression in cultured mouse mesangial cells which was blocked by overexpression of inhibitory Smad7. In addition, TGF-beta1-induced nuclear export of endogenous Smad7 was observed in mouse mesangial cells. Endogenous p300 was expressed in the nucleus of the cells. TGF-beta1 induced interaction of endogenous p300 with Smad2/3, and a dominant negative construct of p300 inhibited the TGF-beta1-induced COL1A2 expression in cultured mouse mesangial cells.

CONCLUSIONS

p300 may be involved in TGF-beta1/Smad-pathway-mediated type I collagen gene transcription in mouse mesangial cells. Our findings would reveal a molecular basis of TGF-beta1-induced type I collagen gene transcription in mouse mesangial cells.

Advanced glycation endproduct (AGE) receptor 1 is a negative regulator of the inflammatory response to AGE in mesangial cells

Advanced glycation endproducts (AGE) contribute to kidney disease due to diabetes or aging by means of mesangial cell (MC) receptors, such as the receptor for AGE (RAGE), which promote oxidant-stress-dependent NF-kappaB activation and inflammatory gene expression. MC also express scavenger receptors SR-I and SR-II and AGE receptors 1, 2, and 3 (AGE-R1, -R2, and -R3), some of which are linked to AGE turnover. Because AGE-R1 expression is found suppressed in severe diabetic kidney disease, as other receptors increase, we investigated whether his molecule has a protective role against AGE-induced MC injury. A stable murine MC line overexpressing AGE-R1 (R1-MC) was generated, exhibiting a 1.8- to 2.7-fold increase in (125)I-AGE-specific binding, uptake, and degradation, compared with mock-MC. However, AGE-stimulated NF-kappaB activity and mitogen-activated protein kinase (MAPK) (p44/42) phosphorylation were found markedly suppressed in R1-MC. Additionally, AGE-stimulated macrophage chemotaxis protein 1 and RAGE overexpression were abolished in R1-MC. The effect of R1 on RAGE signaling was investigated after overexpressing RAGE in Chinese hamster ovary cells, which lack RAGE. AGE stimulation elicited NF-kappaB and MAPK activities in RAGE-Chinese hamster ovary cells; however, after cotransfection with R1, these responses were suppressed. Also, after silencing endogenous R1 in wild-type MC by R1 small interfering RNA, AGE-mediated MAPK/p44/42 activation exceeded by >2-fold that of mock-MC, consistent with loss of the activation-inhibitory properties of native AGE-R1. AGE-R1, although enhancing AGE removal, is also a distinct receptor in that it suppresses AGE-mediated MC inflammatory injury through negative regulation of RAGE, a previously uncharacterized pathway that may protect renal and other tissue injury due to diabetes and aging.

Direct contact between human peripheral blood mononuclear cells and renal fibroblasts facilitates the expression of monocyte chemoattractant protein-1

BACKGROUND

Cell-to-cell interaction is thought to be an important feature of a variety of biological processes. As far as the proinflammatory process is concerned, the interaction between mesangial cells and monocytes/macrophages induces the expression of monocyte chemoattractant protein-1 (MCP-1), and this may play a role in glomerulonephritis. In this study, we investigated whether the cell-to-cell interaction between immune cells and renal fibroblasts induces MCP-1 gene expression, which may be involved in interstitial inflammation in the kidney.

METHODS

Human renal fibroblast cell lines, tNKF (from a normal kidney) and tFKIF (from a kidney with fibrosis), and peripheral blood mononuclear cells (PBMC) were used to assess the effect of cell-to-cell contact on the expression of MCP-1 mRNA in the fibroblasts. The expression of the MCP-1 gene in the fibroblasts was also examined after stimulation with tumor necrosis factor-alpha (TNF-alpha) and the culture supernatant from PBMC. RT-PCR was used to detect MCP-1 mRNA expression. Neutralizing antibodies to intercellular adhesion molecule-1 (ICAM-1) and vascular endothelial adhesion molecule-1 (VCAM-1) were used to block the cell-to-cell contact between the fibroblasts and PBMC.

RESULTS

TNF-alpha and the culture supernatant from PBMC increased MCP-1 gene expression in tNKF cells. Contact culture with PBMC also significantly increased MCP-1 gene expression in tNKF cells. Although the basal level of MCP-1 mRNA was higher in tFKIF than tNKF cells, tFKIF cells did not respond significantly to any stimulation in this study. Following pretreatment with anti-ICAM-1 antibody, MCP-1 gene expression in tNKF cells was significantly suppressed in contact culture with PBMC. Anti-VCAM-1 antibody treatment had no effects.

CONCLUSION

It is suggested that the interaction between renal fibroblasts and PBMC was mediated through direct contact and by secreted humoral factors. ICAM-1 on renal fibroblasts may be involved in the direct cell-to-cell interaction inducing MCP-1 gene expression, which seems to be involved in renal interstitial inflammation.

Human RPE-monocyte co-culture induces chemokine gene expression through activation of MAPK and NIK cascade

Cell-cell contact between human retinal pigment epithelium (hRPE) cells and monocytes occurs in many retinal diseases involving blood-retinal barrier breakdown. This study investigates chemokine secretion induced by co-culture of hRPE cells and monocytes and illustrates the roles of p38 kinase, ERK, JNK/SAPK and NF-kappaB-inducing kinase signaling pathways for hRPE IL-8 and MCP-1 secretion induced in hRPE by co-culture with monocytes. Co-culture of hRPE cells with monocytes increased steady-state IL-8 and MCP-1 mRNA and protein secretion. Stimulation of hRPE cells by monocytes resulted in prominent increases in p38, ERK1/2 and JNK/SAPK phosphorolation, IkappaBalpha degradation, and NF-kappaB nuclear translocation. The induced IL-8 and MCP-1 proteins were almost completely supporessed by U0126, a specific mitogen-activated protein kinase kinase (MEK) inhibitor, or by SB203580, a selective p38 inhibitor. Chemokine secretion was completely blocked by simultaneous administration of U0126 and SB203580. Induction of IL-8 and MCP-1 was abrogated by Ro318220, an inhibitor of PKC, as well as by genistein or herbimycin A, inhibitors of PTK. In addition, anti-inflammatory drugs dexamethasone (DEX) and cyclosporin A (CSA) both blocked activation of JNKS/SAPK and the cell-cell contact induced production of hRPE IL-8 and MCP-1, while activation of p38 and ERK was only inhibited by DEX, but not by CSA. These results suggest that activation of DEX-sensitive, CSA-resistant MEK/ERK and p38 pathways, and activation of NF-kappaB, PKC, and PTK are essential for IL-8 and MCP-1 expression by hRPE cells.

Expression of the chemokines MCP-1/CCL2 and RANTES/CCL5 is differentially regulated by infiltrating inflammatory cells

BACKGROUND

Chemokines are involved in the regulation of the cellular renal infiltrate in glomerulonephritis; however, it is unclear to which degree resident glomerular cells or infiltrating leukocytes contribute to the formation of chemokines in glomerular inflammatory lesions. We therefore examined whether monocytes/macrophages play a role in the expression of the C-C chemokines MCP-1/CCL2 and RANTES/CCL5 in renal tissue in a lipopolysaccharide (LPS)-induced model of inflammation, where previously we have shown increased glomerular RANTES expression and glomerular infiltration of ED-1-positive cells.

METHODS

Inflammatory lesions were induced by an intraperitoneal injection of LPS. The infiltration of monocytes into the glomerulus was reduced by two experimental approaches. First, rats were depleted of monocytes by the use of specific monocyte-antisera or by cytotoxic drugs. Second, the infiltration of monocytes into the kidney was reduced by using intercellular adhesion molecule-1 (ICAM-1) knockout mice.

RESULTS

Both experimental approaches demonstrated a significant reduction in the number of infiltrating monocytes/macrophages after lipopolysaccharide injection. This reduction in the infiltration of inflammatory cells was associated with significantly reduced RANTES/CCL5 mRNA expression. However, MCP-1/CCL2 mRNA expression was not inhibited after the LPS injection by monocyte/macrophage depletion. Also, the increase in nuclear factor-kappaB (NF-kappaB) binding activity after the LPS injection was not reduced in pretreated animals. The experiments therefore demonstrate that infiltrating monocytes/macrophages contribute to increased RANTES/CCL5 mRNA expression in inflammatory renal lesions, whereas MCP-1/CCL2 mRNA expression and NF-kappaB activation were not reduced by monocyte/macrophage depletion.

CONCLUSION

MCP-1/CCL2 released from renal tissue upon stimulation plays a major role in the regulation of monocyte/macrophage infiltration, which contributes significantly to increased renal RANTES/CCL5 expression. This cross-talk between resident renal cells and monocytes/macrophages is therefore likely to boost the number of infiltrating inflammatory cells.

Regulation of chemokine expression in atherosclerosis

(1) Chemokines play a central role in the pathogenesis of atherosclerosis, contributing to leukocyte recruitment, angiogenesis and also proliferation and migration of smooth muscle cells into atherosclerotic plaques. (2) Leukocytes and endothelial cells are an important source of chemokines, and many of the risk factors associated with atherosclerosis increase chemokine expression. There is now a body of evidence to suggest that interactions between cells such as leukocytes and endothelial cells amplify chemokine release, and this may contribute to sustained chemokine generation in inflammatory conditions. (3) This article summarises, briefly, what is currently known about chemokines release. A number of important pharmacological strategies used in the treatment of atherosclerosis inhibit chemokine release and the extent to which this may contribute to their therapeutic effect will be discussed. Understanding the mechanisms controlling chemokine expression is essential for the design of specific therapeutic interventions in atherosclerosis.

Evaluation of E-cadherin/catenin complex in primary and secondary glomerulonephritis

Catenins (alpha-, beta-, gamma-catenin, p120(ctn)) are cytoplasmic proteins initially identified in a complex with E-cadherin (ECD). The latter belongs to a superfamily of transmembrane glycoproteins important for cell adhesion in normal and disease states. Catenins and p120(ctn), in particular, are substrates for growth factor receptor tyrosine kinases. Cell adhesive mechanisms have an impact on cell migration and proliferation and thus are potentially involved in the pathogenesis of glomerulonephritides (GNs). Using appropriate monoclonal antibodies, we investigated the immunohistochemical expression of ECD, alpha-catenin, beta-catenin, gamma-catenin, and p120(ctn) in renal biopsy specimens from 95 patients with primary GN (n = 51) and secondary lupus-associated GN (n = 44). Examined cases were divided into two groups (proliferative [n = 35] and nonproliferative [n = 60] GNs). Among examined molecules, p120(ctn), beta-catenin, and gamma-catenin were expressed more frequently in glomerular epithelial cells, mainly in parietal epithelium (76%, 48%, and 40%, respectively). p120(ctn) and gamma-catenin epithelial expression appeared to be linked closely with proliferative lupus-associated GNs (P = 0.050 and P = 0.029, respectively). Mainly in lupus GNs, with regard to cellular crescents and epithelial cells around microadhesions to Bowman's capsule, p120(ctn) (63% and 73%, respectively), beta-catenin (72% and 75%), and gamma-catenin (75% and 64%) showed the greatest frequencies of positive detection. Mesangial cells were positive only occasionally for the examined molecules. In proliferative lupus GNs, expression of beta-catenin in mesangial cells tended to be prominent (P = 0.066). ECD and alpha-catenin were not expressed in cellular crescents or microadhesions, whereas only ECD was barely detectable in glomerular epithelial cells. In conclusion, expression of beta-catenin, gamma-catenin, and p120(ctn) is focused on glomerular epithelium, as well as on such lesions deriving from it as cellular crescents. This expression probably is linked with epithelial cells' responses to various mitogens, such as growth factors.

Unexpected transcriptional induction of monocyte chemoattractant protein 1 by proteasome inhibition: involvement of the c-Jun N-terminal kinase-activator protein 1 pathway

Proteasome inhibitors, the well-known inhibitors of NF-kappaB, are recently considered therapeutic agents for inflammation. However, the anti-inflammatory properties of these agents have not been fully evaluated. In this report we describe a novel effect of proteasome inhibitors on the expression of monocyte chemoattractant protein 1 (MCP-1) in mesangial cells. We found that proteasome inhibitor MG132 dose-dependently induced expression of MCP-1 at the transcriptional level. The stimulatory effect was similarly observed with other proteasome inhibitors (proteasome inhibitor 1 and lactacystin) and in other cell types (NRK fibroblasts). The 5'-flanking region of the MCP-1 gene contains multiple AP-1 sites. To explore the mechanisms involved, we examined the effects of proteasome inhibition on the AP-1 pathway. Northern blot analysis showed that MG132 rapidly induced the expression of c-jun, but not c-fos. Immunoblot analysis showed that MG132 prevented degradation of c-Jun protein. Kinase assay revealed that c-Jun N-terminal kinase (JNK) was rapidly activated by MG132. Consistent with these results, a reporter assay showed that AP-1 activity was up-regulated after treatment with MG132. Curcumin, a pharmacological inhibitor of the JNK-AP-1 pathway, abrogated the induction of MCP-1 by MG132. Similarly, stable transfection with a dominant-negative mutant of c-Jun attenuated both MG132-induced activation of AP-1 and expression of MCP-1. The transcriptional activation by proteasome inhibitors was observed not only in MCP-1, but also in other AP-1-dependent genes, including stromelysin and mitogen-activated protein kinase phosphatase 1. These data revealed that proteasome inhibition triggered the expression of MCP-1 and other genes via the multistep induction of the JNK-c-Jun/AP-1 pathway.

The regulatory role of AT1 receptor on activated HSCs in hepatic fibrogenesis: Effects of RAS inhibitors on hepatic fibrosis induced by CCl4

AIM: To assess the effect of ACE inhibitor and AngII type 1 (AT1) receptor antagonist in preventing hepatic fibrosis caused by CCl₄ administration in rats; to investigate whether or not there are expression of AT1 receptors on hepatic stellate cells; and to observe the effect of AngII on proliferation and ECM synthesis of cultured HSCs.

METHODS: Studies were conducted in male Sprague-Dawley rats. Except for the hepatofibrotic model group and the control group, in three treated groups, either enalapril (5 mg/kg), or losartan (10 mg/kg), or enalapril + losartan were given to the fibrotic rats by daily gavage, and saline vehicle was given to model and normal control rats. After 6 wk, liver fibrosis was assessed directly by hepatic morphometric analysis, which has been considered the gold standard for the quantification of fibrosis. The expressions of AT1 receptors and (α-mooth muscle actin, α-SMA) in liver tissue or isolated hepatic stellate cells (HSCs) were detected by immunohistochemical techniques. The effect of AngII on HSC proliferation was determined by MTT method. Effect of AngII on collagen synthesis of HSCs was de termined by ³H-proline incorporation.

RESULTS: Contrasted to the fibrosis in rats of the model group, groups of rats treated with either enalapril or losartan, or a combination of two drugs showed a limited expansion of the interstitium (4.23 ± 3.70 vs 11.22 ± 4.79, P < 0.05), but no difference was observed among three treated groups (5.38 ± 3.43, 4. 96 ± 2.96, 4.23 ± 2.70, P > 0.05). Expression of AT1 receptors was found in fibrotic interstitium of fibrotic rats, whereas in normal control rats they were limited to vasculature only to a very slight degree. AT1 receptors were also expressed on activated HSCs in the culture. At concentrations from 10^-9 to 10^-5 mol/L, AngII stimulated HSC proliferation in culture in a dose-dependent manner. Increasing AngII concentrations produced corresponding increases in ³H-proline incorporation. Differences among groups were significant.

CONCLUSION: Angiotensin-converting enzyme inhibitors and AT 1 blocker may slow the progression of hepatic fibrosis; activated HSCs express AT1 receptors, and AngII can stimulate the proliferation and collagen synthesis of HSCs in a dose-dependent manner; and activation of RAS may be related to hepatic fibrogenesis induced by CCl₄.