Fibronectin mRNA in the developing glomerular crescent in rabbit antiglomerular basement membrane disease

The Small Tellurium Compound AS101 Ameliorates Rat Crescentic Glomerulonephritis: Association with Inhibition of Macrophage Caspase-1 Activity via Very Late Antigen-4 Inactivation

Crescentic glomerulonephritis (CGN) is the most aggressive form of GN and, if untreated, patients can progress to end-stage renal failure within weeks of presentation. The α4β1 integrin very late antigen-4 (VLA-4) is an adhesion molecule of fundamental importance to the recruitment of leukocytes in inflammation. We addressed the role of VLA-4 in mediating progressive renal injury in a rat model of CGN using a small tellurium compound. AS101 [ammonium trichloro(dioxoethylene-o,o')tellurate]. This compound has been previously shown to uniquely inhibit VLA-4 activity by redox inactivation of adjacent thiols in the exofacial domain of VLA-4. The study shows that administration of AS101 either before or after glomerular basement membrane anti-serum injection ameliorates crescent formation or preserves renal function. This was associated with profound inhibition of critical inflammatory mediators, accompanied by decreased glomerular infiltration of macrophages. Mechanistic studies demonstrated vla-4 inactivation on glomerular macrophages both in vitro and in vivo as well as inhibition of caspase-1 activity. Importantly, this cysteine protease activity modification was dependent on VLA-4 inactivation and was associated with the anti-inflammatory activity of AS101. We propose that inactivation of macrophage VLA-4 by AS101 in vivo results in a decrease of inflammatory cytokines and chemokines produced in the glomeruli of diseased rats, resulting in decreased further macrophage recruitment and decreased extracellular matrix expansion. Thus, AS101, which is currently in clinical trials for other indications, might be beneficial for treatment of CGN.

Identification of a pre-mRNA splicing factor, arginine/serine-rich 3 (Sfrs3), and its co-expression with fibronectin in fetal and postnatal rabbit airway mucosal and skin wounds

Fibronectin (FN) is a multi-functional, adhesion protein and involved in multi-steps of the wound healing process. Strong evidence suggests that FN protein diversity is controlled by alternative RNA splicing; a coordinated transcription and RNA processing that is development-, age-, and tissue/cell type-regulated. We previously demonstrated that fetal rabbit airway mucosal healing is regenerative and scarless. Expression, regulation, and biological function of the FN gene and various spliced forms in this model are unknown. Airway and skin incisional wounds were made in fetal (gestation days 21-23), weanling (4-6 weeks) and adult (>6 months) rabbits. Non-wounded and wounded tissues were collected at 12 h (all age groups), 24 h and 48 h (weanling only) post-wounding. Expression profiles were obtained using mRNA differential display and cDNAs of interest were cloned, sequenced and validated by real-time PCR. Here, we report two rabbit cDNAs that showed similar expression patterns after wounding. One encodes a rabbit fibronectin gene, Fn1, and another shares a high sequence homology to a human pre-mRNA splicing factor, arginine/serine-rich 3 (Sfrs3), coding for a RNA binding protein, SRp20. Both Fn1 and Sfrs3 mRNAs were suppressed in fetal wounds but induced in postnatal wounds 12 h post-wounding. The increased levels of both Fn1 and Sfrs3 transcripts were sustained up to 48 h in weanling airway mucosal wounds. The augmentations of the two genes in postnatal airway mucosal wounds were more prominent than that in skin wounds, indicating that the involvement of Sfrs3 and Fn1 genes in postnatal airway mucosal wounds is tissue-specific. Literature provides evidence that SRp20 is indeed involved in the alternative splicing of FN and that the embryonic FN variants reappear during adult wound healing. A connection between the enhanced molecular activity of Sfrs3 and the regulation of the FN gene expression through alternative splicing during the early events of postnatal airway mucosal wound repair was proposed.

Macrophage-derived MT1-MMP and increased MMP-2 activity are associated with glomerular damage in crescentic glomerulonephritis

Membrane-type matrix metalloproteinases (MT-MMPs) have been shown to activate pro-MMP-2 on the cell surface and are suggested to be key enzymes in tissue remodelling under various physiological and pathological conditions. To investigate the role of MT-MMP in progressive renal injury, the gene expression and enzymatic activity of MT-MMP were examined in crescentic glomerulonephritis induced by anti-glomerular basement membrane (GBM) antibody in WKY rats. Isolated glomeruli were subjected to RNA and protein extraction 0, 1, 3, 7, 14, and 28 days after intravenous injection of rabbit anti-GBM antibody. Semiquantitative RT-PCR analysis revealed that among the three members of the MT-MMP family, mRNA expression of MT2-MMP remained unchanged and that of MT3-MMP was not observed in glomeruli during the development of nephritis. However, MT1-MMP gene expression increased from day 3 and reached maximum levels at day 7 (5.5+/-0.7-fold increase over day 0), closely associated with macrophage accumulation, crescent formation, and increased proteinuria. Gelatin zymography showed that the active from of MMP-2 emerged from day 7 and remained during the experimental period accompanied by increased proMMP-2, while no active form of MMP-2 was found in control rats. Using an antisense cRNA probe, intense signals of MT1-MMP mRNA were observed mostly in cells within the crescent and in some cells in the mesangial areas. Most of these cells were ED-1-positive macrophages, based on immunostaining of sequential sections. These results suggested that in the MT-MMP family, MT1-MMP was induced in infiltrating macrophages during the development of crescentic glomerulonephritis and possibly contributed to pathological degradation of glomerular extracellular matrices through the activation of proMMP-2.

Initial evidence for the involvement of bone morphogenetic protein-2 early during periosteal chondrogenesis

The potential of periosteum to form cartilage makes periosteal transplantation a viable approach to repairing defects in articular cartilage, which has a limited potential for repair. However, cartilage repair, including that by periosteal chondrogenesis, is poorly understood. Consequently, a thorough understanding of its molecular mechanisms will help to achieve the quality of neocartilage required for its clinical application in damaged joints. An in vitro model was used to study the early molecular events of periosteal chondrogenesis. During the search for the expression of transforming growth factor-beta-related mRNAs in this model system, bone morphogenetic protein-2 mRNA expression was found to be upregulated 20-fold within the first 12 hours of culture. This stimulation was dependent on the explants being suspended in agarose and did not occur with explants cultured in liquid medium. The upregulation of bone morphogenetic protein-2 mRNA expression was also enhanced by exogenously added transforming growth factor-beta1 in the presence of fetal calf serum. The upregulation, however, was not transient; rather, it persisted over a prolonged period in both transforming growth factor-beta1-treated and untreated explants. Further data indicate that this stimulation of bone morphogenetic protein-2 mRNA expression was regulated at the transcriptional level and that no new protein synthesis was required for this. Bone morphogenetic protein-2 is known to influence developmental chondrogenesis; therefore, these observations direct our attention toward an important potential role of it as a regulator of the early events in cartilage repair. Furthermore, because periosteum produces fracture (cartilage) callus, these findings may be important in defining the molecular mechanisms of fracture healing.

Angiotensin II type I receptor antagonist suppresses proteinuria and glomerular lesions in experimental nephritis

Angiotensin-converting enzyme inhibitors exert a beneficial effect on nephritis. We investigated the effects of KD3-671, an angiotensin AT1 receptor antagonist (2-propyl-8-oxo-1-[(2'-(H-tetrazole-5-yl)biphenyl-4-yl)methyl]-4,5,6,7-t etrahydro-cycloheptimidazole), on anti-glomerular basement membrane antibody-associated nephritis in rats. Untreated nephritic rats had massive proteinuria, glomerular lesions including crescent formation, a significant augmentation of proliferating cell nuclear antigen-positive cells, alpha-smooth muscle actin-positive cells, and the increase in deposition of proteoglycan, fibronectin and desmin in the glomeruli. Administration of KD3-671 to nephritic rats prevented the development of intense proteinuria, glomerular alterations and the increase in plasma urea nitrogen. KD3-671 suppressed the deposition of matrix protein and the expression of alpha-smooth muscle actin and desmin in the nephritic glomeruli. Captopril, an angiotensin-converting enzyme inhibitor, suppressed urinary protein excretion and the expression of desmin in the nephritic glomeruli, but not other parameters. These results suggest that KD3-671 may be a useful medicine against glomerulonephritis and glomerulosclerosis.

Changes of glomerular basement membrane components in Vacor-induced diabetic nephropathy

OBJECTIVES

The thickening of the glomerular basement membrane in rats after Vacor ingestion was examined by electron microscopy. This study was performed to elucidate which biochemical components changed in the glomerular basement membrane after Vacor-induced diabetic glomerulopathy.

METHODS

Immunohistochemical analyses of type IV collagen, laminin, fibronectin and chondroitin sulfate proteoglycan were performed. A single dose of Vacor (molecular weight 272), 80 mg/kg, was administered to adult male Wistar rats by orogastric canule, and the animals were sacrificed at 0.5, 1, 3, 7, 14, 28 and 56 days after administration.

RESULTS

Mild thickening of the glomerular basement membrane was evident 7 days after Vacor administration, and the width of the glomerular basement membrane was more than twice that of normal controls at 28 and 56 days. Significantly increased expressions of type IV collagen, laminin, fibronectin and neutral polysaccharide in the thickened glomerular basement membrane were noted 14 to 56 days after administration, and a mildly increased expression of chondroitin sulfate proteoglycan appeared between 3 to 7 days.

CONCLUSION

These abnormally increased glomerular basement membrane components might be part of what causes diabetic nephropathy after Vacor administration.

Fibronectin synthesis by human tubular epithelial cells in culture: effects of PDGF and TGF-beta on synthesis and splicing

BACKGROUND

Enhanced synthesis of extracellular matrix proteins including fibronectin (FN) is associated with the development of sclerosis. In this context we studied FN synthesis by tubular epithelial cells in response to transforming growth factor-beta (TGF-beta) and platelet-derived growth factor (PDGF).

METHODS

FN protein synthesis by human tubular epithelial cells in culture (TEC) was measured by biosynthetic labeling and ELISA. Splicing of FN was assessed by RT-PCR and by Northern blotting.

RESULTS

Cultivated TEC synthesized and released FN, the majority of which was deposited as an unsoluble protein and a minor portion (10 to 15%) was released into the supernatant. TGF-beta and, to a lesser degree, PDGF, up-regulated FN synthesis. All three FN splice variants (EDA, EDB, and IIICS) were produced. PDGF did not influence the splicing. TGF-beta preferentially up-regulated the EDA splice variant, but had no effect on the splicing of the other domains.

CONCLUSIONS

PDGF and TGF-beta both up-regulate FN synthesis of TEC. TGF-beta, but not PDGF, also changed the quality of the de novo synthesized FN, and thus has a different role in the development of sclerosis.

Renal biopsy collagen I mRNA predicts scarring in rabbit anti-GBM disease: comparison with conventional measures

Progressive loss of normal structure associated with scarring is the hallmark of chronic diseases of most organs. To test the hypothesis that measurement of interstitial collagen mRNA levels would be a useful index to predict future scarring, we developed an assay to quantitate alpha 1(I) procollagen mRNA factored for GAPDH mRNA using RT-PCR (the "CI:G ratio"). We first defined conditions under which the assay could be used for analysis of renal biopsy samples. The CI:G ratio was then used to determine whether mRNA measurements performed at an early stage of inflammation (day 7) in a model of anti-GBM disease in the rabbit would predict outcome at day 30 as measured by interstitial and glomerular scarring and renal cortical hydroxyproline accumulation. The predictive value of this assay was compared to functional (serum creatinine and urine protein:creatinine ratio) and histologic (glomerular and interstitial scoring) parameters also measured at day 7. We found that the CI:G ratio alone provided a sensitive and discriminating assay over a wide range of renal injury that predicted various parameters of scarring with an average coefficient of determination (r2) of 0.69. This predictive power was higher than that found for conventional measures, which tended to have good discriminatory capacity over limited ranges of renal injury. The CI:G ratio provided significant additional predictive power over and above that available from combinations of conventional functional or histologic parameters. We conclude that measurement of the CI:G ratio in biopsy samples deserves further assessment as a potentially useful quantitative predictor of outcome that could lead to improved clinical decision-making.

Matrix and adhesion molecules in kidney pathology: recent observations

The purpose of this article is to review a set of recently obtained data concerning matrix and matrix adhesion molecules in renal disease. Our goal is not to cover the entire topic, but rather to focus on findings obtained with an experimental model for chronic lupus nephritis, evoked in mice by inducing graft-versus-host disease (GVHD). The overall aim of these studies was to investigate the role of adhesion molecules as targets for autoantibodies, in the recruitment of inflammatory cells, and in the accumulation of matrix in kidney disorders. In addition, we set out to discover how matrix proteins in renal diseases differ from normal matrix molecules both quantitatively, in their increased frequency, and qualitatively, in their intramolecular structure. The advances in understanding and methodology described in this review imply a substantial capability for greater insight into the pathogenesis of kidney disease; for making better use of renal biopsies, such as in applying competitive reverse-transcriptase-polymerase chain reaction (RT-PCR) in RNA analysis for matrix; and in developing more effective treatment strategies for patients with kidney disease.

Glomerular up-regulation of EIIIA and V120 fibronectin isoforms in proliferative immune complex nephritis

Fibronectin: (FNs) comprise a family of adhesive glycoproteins that are prominent components of mesangial extracellular matrix and accumulate during glomerular injury. By alternative splicing of an unique mRNA precursor, various FN isoforms can be originated. In rat, three regions of the molecule are involved: EIIIA, EIIIB and V. Because specific FN isoforms are expressed in embryogenesis and wound healing, conditions characterized by cell migration and adhesion, we examined the pattern of FN isoforms in the mild and severe phases of a progressive immune complex proliferative nephritis in rats. We constructed specific probes to analyze the splicing pattern of FN pre-mRNAs by ribonuclease protection assays. FN mRNAs containing EIIIA, EIIIB and V regions increased along, the progression of nephritis, though the increment of EIIIB-FN mRNA was modest. However, different regulation of all these isoforms was observed. The percentage of FN mRNA containing the EIIIA exon versus total FN increased with the severity of the disease, while the percentage of FN mRNA containing the EIIIB exon decreased. Relative V-FN mRNA expression versus total FN mRNA increased only in the severe phase. By means of specific antibodies we also studied the presence of EIIIA, EIIIB and V-FN proteins in the kidney. In the normal glomerutus, EIIIA-FN protein was barely detectable in the mesangium, increasing in the mild phase of nephritis. In the severe phase of nephritis, increased EIIIA-FN was localized in the mesangium, in Bowman's capsule and in crescents. By contrast, EIIIB-FN protein in the glomerulus was absent even in the severe phase. V120-FN protein, an isoform that mediates the attachment of leukocytes through the VLA-4 integrin, was present in the mesangium and glomerular capillary loops in control animals, and increased in the severe phase of nephritis, coinciding with a strong leukocyte infiltration. In conclusion, our results show that during immune glomerular injury there were marked changes in the pattern of FN isoforms expression. Since those isoforms, particularly V120 isoform, are important in cell adhesion and migration, their up-regulation may facilitate the recruitment of cells into the injured glomeruli. The blockade of the interaction between V120-FN and infiltrating leukocytes may represent a new approach to the treatment of nephritis.