Amino acid sequence of the non-collagenous globular domain (NC1) of the alpha 1(IV) chain of basement membrane collagen as derived from complementary DNA

Blockade of Smad signaling by 3'-deoxyadenosine: a mechanism for its anti-fibrotic potential

Cordyceps militaris has been used in Eastern countries for the treatment of various diseases including chronic kidney diseases. However, there are no reports that identified its active entities and molecular mechanisms underlying its therapeutic effectiveness. 3'-Deoxyadenosine is a major nucleoside derivative isolated from C. militaris. Some reports suggested that both C. militaris and 3'-deoxyadenosine have anti-inflammatory and anti-fibrotic effects. In the present report, we investigated whether and how 3'-deoxyadenosine interferes with fibrogenic processes in the kidney. For this purpose, we examined effects of 3'-deoxyadenosine on the expression of collagens triggered by transforming growth factor-β (TGF-β1) and bone morphogenetic protein-4 (BMP-4), especially focusing on the regulation of Smad signaling in vitro and in vivo. We found that 3'-deoxyadenosine suppressed expression of collagens induced by TGF-β1 and BMP-4 dose dependently. This suppression occurred at the transcriptional level and was correlated with blunted activation of the CAGA box and the BMP-responsive element. The suppressive effect on the TGF-β/BMP signaling was mediated mainly by adenosine transporter and partially by the A3 adenosine receptor, but not A1/A2 adenosine receptors. 3'-Deoxyadenosine reduced levels of both phosphorylated and total Smad proteins (Smad1, 2 and 3) dose dependently. It was mainly ascribed to transcriptional suppression, but not to enhanced protein degradation and eIF2α-mediated translational suppression. Consistent with the in vitro results, in vivo administration with 3'-deoxyadenosine reduced the levels of phosphorylated and total Smad proteins, as well as the levels of Smad mRNAs, in the kidney subjected to unilateral ureteral obstruction. It was associated with blunted induction of type I collagen and α-smooth muscle actin, a decrease in the number of interstitial myofibroblasts and reduced fibrotic area. These results suggest that 3'-deoxyadenosine interferes with the TGF-β and BMP signaling via downregulation of Smads, which may underlie the anti-fibrotic effect of this agent. 3'-Deoxyadenosine may be useful for therapeutic intervention in various TGF-β-related fibrotic disorders.

Unfolded protein response causes a phenotypic shift of inflamed glomerular cells toward redifferentiation through dual blockade of Akt and Smad signaling pathways

During recovery from acute glomerulonephritis, cell proliferation, matrix expansion, and expression of the dedifferentiation marker α-smooth muscle actin (α-SMA) subside spontaneously. However, the molecular mechanisms underlying this recovery process remain elusive. In mesangioproliferative glomerulonephritis, the unfolded protein response (UPR) is induced in activated, dedifferentiated mesangial cells. We investigated the role of the UPR in mesangial cell deactivation and redifferentiation and found that, during experimental glomerulonephritis in rats, reinforcement of the UPR significantly attenuated mesangial cell proliferation, matrix expansion, and expression of α-SMA. Consistent with this in vivo result, induction of the UPR suppressed cell proliferation and transcriptional expression of type IV collagen (ColIV) and α-SMA in activated mesangial cells. The UPR reduced phosphorylation of Akt in vitro and in vivo, and it was responsible for attenuation of cell proliferation. The UPR also preferentially depressed levels of total and phosphorylated Smads without affecting transcriptional levels, and it was responsible for suppression of ColIV and α-SMA. Translational suppression via the eIF2α pathway, but not proteasome-mediated protein degradation, was responsible for the down-regulation of Smads. These results suggest the novel potential of the UPR to facilitate a phenotypic shift of activated glomerular cells toward deactivation and redifferentiation. The UPR may serve as endogenous machinery that supports recovery of glomeruli from acute inflammation.

A critical function of the pial basement membrane in cortical histogenesis

Mice with a targeted deletion of the nidogen-binding site of laminin gamma1 were used to study the function of the pial basement membrane in cortical histogenesis. The pial basement membrane in the mutant embryos assembled but was unstable and disintegrated at random segments. In segments with a disrupted basement membrane, radial glia cells were retracted from the pial surface, and radially migrating neurons, including Cajal-Retzius cells and cortical plate neurons, passed the meninges or terminated their migration prematurely. By correlating the disruptions in the pial basal lamina with changes in the morphology of radial glia cells, the aberrant migration of Cajal-Retzius cells, and subsequent dysplasia of cortical plate neurons, the present data establish a causal relationship of proper cortical histogenesis with the presence of an intact pial basement membrane.

Role of hypomagnesemia in chronic cyclosporine nephropathy

BACKGROUND

Hypomagnesemia is a common finding of cyclosporine (CsA)-treated patients and has been proposed as both a cause and a consequence of CsA-induced nephrotoxicity. This experiment was conducted to elucidate the role of hypomagnesemia in the pathogenesis of chronic CsA nephropathy.

METHODS

CsA (15 mg/kg/day subcutaneously) was administered to rats maintained on a low-sodium diet for 1, 2, and 4 weeks, and the effects of magnesium (Mg) supplementation on renal function, renal histology, and renal gene expression profile of fibrogenic molecules and vasoconstrictors was examined.

RESULTS

CsA elicited hypomagnesemia and induced a progressive decline in glomerular filtration. At 28 day, renal tubular atrophy and cortical striped interstitial fibrosis were evident with CsA treatment. Dietary supplementation of Mg ameliorated CsA-induced hypomagnesemia and almost completely abolished CsA-induced chronic fibrotic lesions. Neither CsA nor Mg supplementation affected blood pressure. Renal cortical mRNA of transforming growth factor beta, plasminogen activator inhibitor (PAI)-1, and extracellular matrix started to increase at 14 days and elevated further at 28 days. In contrast, the increase in mRNA of tissue inhibitor of matrix metalloproteinase-1 and renin was evident early at 7 days and reached peak at 14 days. These mRNA increases, except that of renin, were almost abolished when hypomagnesemia was corrected. Magnesium supplementation also improved glomerular dysfunction, at least in part, through inhibition of up-regulated mRNA of endothelin-1.

CONCLUSION

CsA-induced hypomagnesemia contributes to chronic renal fibrotic lesions seen during CsA treatment through up-regulation of fibrogenic molecules, most notably early activation of tissue inhibitor of matrix metalloproteinase-1 expression.

Characterization of hydra type IV collagen. Type IV collagen is essential for head regeneration and its expression is up-regulated upon exposure to glucose

Hydra vulgaris mesoglea is a primitive basement membrane that also exhibits some features of an interstitial matrix. We have characterized cDNAs that encode the full-length hydra alpha1(IV) chain. The 5169-base pair transcript encodes a protein of 1723 amino acids, including an interrupted 1455-residue collagenous domain and a 228-residue C-terminal noncollagenous domain. N-terminal sequence analyses of collagen IV peptides suggest the molecule is homotrimeric. Denatured hydra type IV collagen protein occurs as dimers and higher order aggregates held together by nonreducible cross-links. Hydra collagen IV exhibits no functional evidence for the presence of a 7 S domain. Type IV collagen is expressed by the ectoderm along the entire longitudinal axis of the animal but is most intense at the base of the tentacles at the site of battery cell transdifferentiation. Antisense studies show that inhibition of collagen IV translation causes a blockage in head regeneration, indicating its importance in normal hydra development. Exposure of adult hydra to 15 mm glucose resulted in up-regulation of type IV collagen mRNA levels within 48 h and significant thickening of the mesoglea within 14 days, suggesting that basement membrane thickening seen in diabetes may be, in evolutionary terms, an ancient glucose-mediated response.

Degradation of type IV collagen by matrix metalloproteinases is an important step in the epithelial-mesenchymal transformation of the endocardial cushions

Morphogenesis of some tissues and organs in the developing embryo requires the transformation of epithelial cells into mesenchyme followed by cell motility and invasion of surrounding connective tissues. Details of the mechanisms involved in this important process are beginning to be elucidated. The epithelial-mesenchymal transformation (EMT) process involves many steps, one of which is the upregulation and activation of specific extracellular proteinases including members of the matrix metalloproteinase (MMP) family. Here we analyze the role of MMPs in the initiation of the mesenchymal cell phenotype in the developing heart, and find that they are necessary for the invasion of mesenchymal cells into the extracellular matrix of the endocardial cushion tissues. An important requirement in the formation of this mesenchyme is the turnover of type IV collagen along the basal surface of endocardial cells. In vitro experiments suggest that type IV collagen does not provide a suitable migratory substrate for endocardial cushion cells unless MMP-2 and MT-MMP are active. Relevant MMPs were found to be upregulated by factors known to be involved in the induction of the EMT such as TGFbeta3. These results provide evidence of an important role for MMPs during a specific stage of the epithelial mesenchymal transformation in the embryonic heart, and suggest that specific cell-matrix interactions which facilitate cell migration only occur when the composition of the surrounding extracellular matrix is proteolytically altered.

Cyclic expression of mRNA transcripts for connective tissue components in the mouse ovary

In the ovary, differentiation of germinal cells into primordial follicles, functional ovulatory follicles and corpus luteum, all take place in a connective tissue matrix. We postulated that extracellular matrix (ECM) of the ovary participates actively in ovarian functions. To test this, the mRNA levels for several ECM components were determined in the mouse ovary at six distinct stages of the 4-day oestrous cycle. Northern analysis revealed statistically significant cyclic expression patterns for the mRNAs coding for type III, IV and VI collagens as well as for the small proteoglycan, biglycan, and for syndecan-1 and osteonectin. The cyclic changes observed in the mRNAs for these structural components exceeded those for matrix metalloproteinases (MMP)-2, -9 and -13, and for tissue inhibitors of matrix metalloproteinases (TIMP)-1, -2 and -3, where the changes were not statistically significant, despite their apparent role in ECM remodelling in the ovary. These observations support the hypothesis that cyclic changes in the production and degradation of ECM are part of normal ovarian function connected with follicular maturation, rupture and corpus luteum formation.

A vitamin D analog regulates mesangial cell smooth muscle phenotypes in a transforming growth factor-beta type II receptor-mediated manner

Mesangial cells share features with contractile smooth muscle cells and mechanically support the capillary wall. The role of vitamin D compounds and the transforming growth factor-beta (TGF-beta) type II receptor in modulating the smooth muscle phenotype of cultured mesangial cells was examined. Cell proliferation was significantly inhibited by the vitamin D analog 22-oxa-1,25-dihydroxyvitamin D(3) (22-oxacalcitriol; OCT) rather than by 1,25-dihydroxyvitamin D(3) (1, 25(OH)(2)D(3)) in a dose-dependent manner. OCT-treated early passage mesangial cells (MC-E cells) had increased expression levels of type IV collagen and smooth muscle alpha actin mRNA, but 1, 25(OH)(2)D(3)-treated MC-E cells did not. The addition of a TGF-beta(1)-neutralizing antibody to the OCT-treated MC-E cells blocked this inhibitory effect for cell proliferation and attenuated the up-regulated mRNA levels. However, after exposure to 1, 25(OH)(2)D(3) or OCT, there was no significant difference in the secretion of active TGF-beta. We next investigated whether TGF-beta type II receptor (RII) was involved in this regulation. OCT treatment significantly increased the expression of the RII mRNA in MC-E cells. These results suggest that the vitamin D analog OCT induces smooth muscle phenotypic alterations and that this phenomenon was mediated through the induction of RII in cultured mesangial cells.

Experimental AA amyloidogenesis is associated with differential expression of extracellular matrix genes

An abnormality in basement membrane metabolism has been postulated to play an important role in the pathogenesis of experimental murine AA amyloidosis. The potential contribution of the structural basement membrane proteins laminin, type IV collagen and entactin to amyloidogenesis in this model was investigated with a kinetic analysis of the expression of the corresponding genes during amyloid formation. Splenic AA amyloid deposition was stimulated by the concomitant administration of subcutaneous silver nitrate, as an inflammatory stimulus, and intravenous amyloid enhancing factor. Using a reverse transcription-polymerase chain reaction assay, a differential pattern of expression of these genes was observed at the mRNA level. Whereas laminin B1 mRNA levels did not change at any time during amyloidogenesis, a 2.2 to 3 fold induction of laminin B2, entactin and alpha 1-type IV collagen mRNAs coincided with the initial detection of splenic amyloid deposits at 48 hours post-stimulation, as detected by immunohistochemistry. Temporal and spatial codeposition of laminin and type IV collagen with amyloid was demonstrated by immunohistochemistry. A 1.4, 2.3 and 2.2-fold increase in laminin B2, entactin and alpha 1-type IV collagen mRNA levels, respectively, was detected at 24 hours post-stimulation, a point at which amyloid deposits could not be detected. Neither inflammation nor amyloid enhancing factor alone influenced laminin, entactin or type IV collagen expression at the protein or mRNA level. These observations suggest that the laminin B2 chain and alpha 1-type IV collagen chain account, at least in part, for the observed laminin and collagen IV immunoreactivity in AA amyloid deposits and that entactin may also be a component of the amyloid deposit. The onset of the induction of laminin B2, entactin and alpha 1-type IV collagen gene expression prior to the appearance of amyloid deposits, and our previous data with the heparan sulfate proteoglycan, perlecan, suggests these basement membrane proteins may play a role in the initial stages of AA fibrillogenesis.

Up-regulation of glomerular extracellular matrix and transforming growth factor-beta expression in RF/J mice

BACKGROUND

RF/J mice were first reported as a murine model of spontaneous glomerulosclerosis by Gude and Lupton in 1960, but the precise histologic characteristics and immunopathological background of this mouse have not been investigated further.

METHODS

Measurements of serum levels of immunoglobulins, anti-single strand DNA (anti-ss-DNA) antibody, complement (C3), and circulating immune complex (IC) were performed. Analyses of glomerular histological and immunopathological lesions in association with the detection of mRNA expression of collagen IV, TGF-beta, matrix protein turnover related enzymes, matrix metalloproteinase-2 (MMP-2), tissue inhibitor of metalloproteinase-2 (TIMP-2) and platelet-derived growth factor (PDGF) were also performed in young (10-week-old) and elderly (60-week-old) RF/J mice with age-matched BALB/C mice as the controls.

RESULTS

High levels of serum IgA and IgG from as early as 20 weeks of age were noted in the RF/J mice. Serum anti-ss-DNA antibody of aged RF/J mice increased up to 23% of that of aged MRL-lpr/lpr mice, and serum C3 concentration significantly decreased with age, reaching lower levels than that of BALB/c mice. IgA-IC levels were significantly high compared to BALB/C mice both in the early and late stages of life, whereas IgG-IC levels were high only in mice younger than 20 weeks. Semiquantitative and quantitative analyzes of renal histopathological findings revealed significantly marked and age-related mesangial matrix expansion in RF/J mice, with increasing frequency of global glomerular sclerosis and tubulointerstitial damage. On the other hand, although precise measurements of glomerular cell numbers also showed an apparent augmentation in both young and old RF/J mice compared to BALB/C mice, glomerular cellularity decreased with age in RF/J mice. Immunohistochemical study revealed massive immunoglobulin deposition from a young age in association with significantly higher accumulation of matrix proteins, such as types I and IV collagen and laminin from the early stage of life. In addition, in these glomeruli, transforming growth factor-beta1 (TGF-beta1) was highly expressed both in young and old mice. The mRNA expression of MMP-2 was up-regulated only in the early stage of life. Although PDGF mRNA of RF/J mice was significantly up-regulated in the early stage of life, the differences between the mice disappeared in the late stage of life.

CONCLUSIONS

These findings suggest that in RF/J mice, an immunopathological background inducing high serum immunoglobulin and IC levels from the early stage of life is closely related to mesangioproliferative glomerular lesions mediated by PDGF, and that development of massive extracellular matrix accumulation in glomeruli was induced by up-regulated expression of TGF-beta with inappropriate regulation of protein turnover-related enzyme production.

Vitamin C deficiency in guinea pigs differentially affects the expression of type IV collagen, laminin, and elastin in blood vessels

Vitamin C deficiency causes morphologic changes in the endothelial and smooth muscle compartments of guinea pig blood vessels. Endothelial cells synthesize the basement membrane components, type IV collagen and laminin, and smooth muscle cells synthesize elastin in blood vessels. Therefore, we examined the possibility that vitamin C deficiency affects the expression of these proteins. Decreased expression of types I and II collagens in other tissues of vitamin C-deficient guinea pigs is associated with weight loss and the consequent induction of insulin-like growth factor binding proteins; thus we also used food deprivation to induce weight loss. Female guinea pigs received a vitamin C-free diet, supplemented orally with ascorbate. Vitamin C-deficient guinea pigs received the same diet but no ascorbate, and the food-deprived group received no food, but were supplemented with vitamin C. Concentrations of mRNAs for basement membrane components and elastin in blood vessels were measured by Northern blotting; overall basement membrane metabolism was assessed by measuring immunoreactive laminin and type IV 7S collagen in serum. Laminin mRNA in blood vessels and serum laminin concentrations were unaffected by vitamin C deficiency. Concentrations of type IV collagen and elastin mRNAs in blood vessels were not significantly affected in moderately scorbutic guinea pigs (0-7% weight loss), but with increased weight loss, type IV collagen mRNA was 57% (P < 0.05) and elastin mRNA was 3% (P < 0. 01) of normal values. In food-deprived guinea pigs, type IV collagen mRNA was 51% (P < 0.05) and elastin mRNA was 35% (P < 0.05) of normal. Serum type IV 7S collagen concentrations were 25% of normal in scorbutic guinea pigs with extensive weight loss. The lower expression of type IV collagen and elastin mRNAs in blood vessels may contribute to defects observed in blood vessels during scurvy.

A multifunctional transcription factor (A1p145) regulates the smooth muscle phenotype in mesangial cells

A1p145, a novel DNA binding protein for type IV collagen gene (COL4), has multiple functions including DNA replication factor C and DNA binding for several other genes. To elucidate the mechanisms underlying the differentiation process of mesangial cells (MCs), we investigated the effects of A1p145 on rat MCs. Cells in the early passages showed a smooth muscle-like phenotype such as low cell turnover, high levels of expression for COL4, and smooth muscle alpha-actin (SMA). Cells in the late passages lost their phenotype. The amount of binding activity to COL4 promoter was inversely correlated with the level of COL4 mRNA. Introduction of antisense for A1p145 into late passage cells enhanced the levels of mRNA for COL4 and SMA. The levels of proliferating cell nuclear antigen mRNA were also suppressed. These results suggest that A1p145 is a negative transcription factor for COL4 and may be a phenotypic modulator.

Expression of heat shock protein 47 is increased in remnant kidney and correlates with disease progression

Glomerulosclerosis is characterized by accumulation of the mesangial extracellular matrix, including type I and V collagen. The processing for the collagens in the glomeruli may play a critical role for development of glomerulosclerosis. We examined the expression of heat shock protein 47 (HSP47), a collagen-binding molecular chaperone in the progressive glomerulosclerosis model. Subtotally nephrectomized rats, unlike sham-operated rats, developed focal and segmental glomerulosclerosis. Immunological staining demonstrated an increased expression of HSP47 which paralleled the expression of type I and IV collagen in the glomeruli of the nephrectomized rats as the glomerulosclerosis developed. The mRNA levels encoding type I and type IV collagen and HSP47 were increased 3.4 fold, 3.6 fold and 2.8 fold, respectively, at week 7 after nephrectomy. By in situ hybridization, the expression of HSP47 mRNA was determined to be localized to the glomeruli with segmental sclerosis. These results suggest that HSP47 may play a central role in the process of extracellular matrix accumulation during the development of glomerulosclerosis.

Comparative analysis of the noncollagenous NC1 domain of type IV collagen: identification of structural features important for assembly, function, and pathogenesis

Type IV collagen alpha1-alpha6 chains have important roles in the assembly of basement membranes and are implicated in the pathogenesis of Goodpasture syndrome, an autoimmune disorder, and Alport syndrome, a hereditary renal disease. We report comparative sequence analyses and structural predictions of the noncollagenous C-terminal globular NC1 domain (28 sequences). The inferred tree verified that type IV collagen sequences fall into two groups, alpha1-like and alpha2-like, and suggested that vertebrate alpha3/alpha4 sequences evolved before alpha1/alpha2 and alpha5/alpha6. About one fifth of NC1 residues were identified to confer either the alpha1 or alpha2 group-specificity. These residues accumulate opposite charge in subdomain B of alpha1 (positive) and alpha2 (negative) sequences and may play a role in the stoichiometric chain selection upon type IV collagen assembly. Neural network secondary structure prediction on multiple aligned sequences revealed a subdomain core structure consisting of six hydrophobic beta-strands and one short alpha-helix with a significant hydrophobic moment. The existence of opposite charges in the alpha-helices may carry implications for intersubdomain interactions. The results provide a rationale for defining the epitope that binds Goodpasture autoantibodies and a framework for understanding how certain NC1 mutations may lead to Alport syndrome. A search algorithm, based entirely on amino acid properties, yielded a possible similarity of NC1 to tissue inhibitor of metalloproteinases (TIMP) and prompted an investigation of a possible functional relationship. The results indicate that NC1 preparations decrease the activity of matrix metalloproteinases 2 and 3 (MMP-2, MMP-3) toward a peptide substrate, though not to [14C]-gelatin. We suggest that an ancestral NC1 may have been incorporated into type IV collagen as an evolutionarily mobile domain carrying proteinase inhibitor function.

Ribozyme targeting of receptor for advanced glycation end products in mouse mesangial cells

Accumulation of extracellular matrix is a characteristic of diabetic nephropathy, and advanced glycation end products (AGEs) are considered to play an important role in the mechanism. To investigate the involvement of the receptor for AGE (RAGE) in upregulation of type IV collagen by AGEs, we applied the hammerhead ribozyme for targeting RAGE. We established a stable mouse mesangial cell line that produces the RAGE-specific ribozyme (Rz-RAGE). Both the RAGE mRNA and protein were decreased in the cell line. The amount of type IV collagen mRNA increased by AGEs' treatment in control cells. In contrast, the increase of type IV collagen induced by AGEs was not observed in the Rz-RAGE-producing cells. We conclude that the induction of type IV collagen by AGEs is mediated by RAGE and this mechanism could be involved in diabetic nephropathy. This study also suggested the experimental/therapeutic potential of hammerhead ribozymes.

Effect of manidipine hydrochloride, a calcium antagonist, on isoproterenol-induced left ventricular hypertrophy

We examined the effect of a calcium antagonist, manidipine hydrochloride, on cardiac hypertrophy and the expression of the atrial natriuretic peptide (ANP), transforming growth factor beta 1 (TGF-beta 1), and extracellular matrix protein genes in rats with isoproterenol-induced cardiac hypertrophy. Rats were continuously infused with saline or isoproterenol (0.5 mg/kg per day) for 7 days using an osmotic minipump. Treatment with manidipine hydrochloride (once a day at 3 mg/kg) began 1 day before minipump implantation and continued until the end of the experiments (each group; n = 6). After treatment, left ventricular weight was measured and mRNA was extracted and analyzed by Northern blot hybridization. Isoproterenol increased left ventricular weight (2.40 +/- 0.04 g/kg; p < 0.01) without increasing blood pressure. ANP, collagen type I and type III, and fibronectin mRNAs were increased 1.5-(p < 0.01), 1.9- (p < 0.01), 2.7- (p < 0.01), and 3.2-fold (p < 0.01), respectively, by isoproterenol infusion. However, TGF-beta 1, collagen type IV, and laminin B1 and B2 mRNA levels were unchanged by isoproterenol. Manidipine hydrochloride prevented isoproterenol-induced left ventricular hypertrophy (2.26 +/- 0.02 g/kg; p < 0.01) and expression of mRNA of ANP (0.9-fold of the control value; p < 0.01), collagen types I (1.1-fold; p < 0.01) and type III (1.6-fold; p < 0.01), and fibronectin (1.1-fold; p < 0.01). Thus, manidipine hydrochloride prevented cardiac hypertrophy and changes in the expression of genes for ANP and interstitial components of extracellular matrix induced by isoproterenol.

Modulation of collagen gene expression by cytokines: stimulatory effect of transforming growth factor-beta1, with divergent effects of epidermal growth factor and tumor necrosis factor-alpha on collagen type I and collagen type IV

Transforming growth factor-beta1 (TGF-beta1) is well recognized as a potent mediator of both fibrillar (collagen type I) and basement membrane (collagen type IV) production. However, tissue injury is characterized by the concomitant expression of many cytokines and/or growth factors in addition to TGF-beta1, and the ultimate extent of extracellular-matrix (ECM) deposition may reflect the interacting effects of TGF-beta1 and these other cytokines and/or growth factors. We, therefore, sought to determine whether other cytokines and/or growth factors, known to be produced after tissue injury, are capable either alone or in combination with TGF-beta1 of modulating collagen gene expression. Collagen type I and collagen type IV gene expression was assessed in NIH-3T3 cells, a murine fibroblast-like cell line that responds to TGF-beta1, with increases in both collagen type I and collagen type IV production. TGF-beta1 coordinately induced production of collagen type IV messenger ribonucleic acid (mRNA) to a level 3.8-fold above its baseline value (p < 0.001) and collagen type I mRNA to a level 2.6-fold above its baseline value (p < 0.001). Of the other cytokines and/or growth factors tested, only epidermal growth factor (EGF) had significant effects on collagen mRNA expression. We report the novel observation that EGF significantly induced collagen type IV mRNA (3.0-fold; p < 0.001) but did not alter collagen type I mRNA expression. Platelet-derived growth factor (PDGF), basic fibroblast growth factor (bFGF), tumor necrosis factor-alpha (TNF-alpha), interleukin-1 (IL-1), and insulin-like growth factor-1 (IGF-1) did not alter the expression of mRNA for collagen type IV or collagen type I. Addition of TGF-beta1 to cytokine- and/or growth factor-treated cells increased both collagen type IV and collagen type I mRNA levels. However, collagen type IV mRNA levels were similar in cultures given TGF-beta1 alone and cultures given TGF-beta1 with other cytokines and/or growth factors; there were no additive, synergistic, or antagonistic effects after coadministration of TGF-beta1 and other cytokines and/or growth factors. With regard to collagen type I mRNA expression, all cytokines and/or growth factors tested, with the exception of TNF-alpha, had no effect on collagen type I mRNA levels in TGF-beta1-treated cultures. Importantly, TNF-alpha antagonized the stimulatory effect of TGF-beta1 on collagen type I mRNA levels. These observations support a dominant role for TGF-beta1 in stimulating coordinate expression of collagen type I and collagen type IV mRNAs by NIH-3T3 cells; EGF and TNF-alpha are capable of inducing divergent expression of the genes for these two types of collagen.

viking: identification and characterization of a second type IV collagen in Drosophila

We have taken an enhancer trap approach to identify genes that are expressed in hematopoietic cells and tissues of Drosophila. We conducted a molecular analysis of two P-element insertion strains that have reporter gene expression in embryonic hemocytes, strain 197 and vikingICO. This analysis has determined that viking encodes a collagen type IV gene, alpha2(IV). The viking locus is located adjacent to the previously described DCg1, which encodes collagen alpha1(IV), and in the opposite orientation. The alpha2(IV) and alpha1(IV) collagens are structurally very similar to one another, and to vertebrate type IV collagens. In early development, viking and DCg1 are transcribed in the same tissue-specific pattern, primarily in the hemocytes and fat body cells. Our results suggest that both the alpha1 and alpha2 collagen IV chains may contribute to basement membranes in Drosophila. This work also provides the foundation for a more complete genetic dissection of collagen type IV molecules and their developmental function in Drosophila.

A novel transcription factor is correlated with both glomerular proliferation and sclerosis in the rat renal ablation model

Glomerular accumulation of the extracellular matrix (ECM) with subsequent sclerosis is a common finding in most progressive renal diseases. Recently MSW (Mouse South Western) protein was cloned by its ability to bind the bidirectional promoter of the collagen IV genes. This protein was also reported as the large subunit of the DNA replication complex A1, as well as the promoter binding protein of corticotropin-releasing hormone and the angiotensinogen gene. To investigate the mechanism of accumulation of the ECM as it relates to glomerular cellular events, the expression of MSW protein was studied in the remnant kidney model. Progressive expression of MSW protein was found in the glomerular sclerotic lesion at week 4 and at later time points after renal ablation. The expression of proliferating cell nuclear antigen (PCNA) and type IV collagen was also correlated with the expression of MSW protein by immunofluorescence. RNA dot blot analysis also showed that the expression of MSW mRNA was increased at week 7 in association with the augmented expression of type IV collagen. These results, taken together, suggest that MSW protein plays an important role in the regulation of type IV collagen gene expression in vivo and may contribute to glomerular cell proliferation and the development of glomerulosclerosis.

Imidapril inhibits increased transforming growth factor-beta1 expression in remnant kidney model

To elucidate the effect of imidapril, an angiotensin-converting enzyme inhibitor, on molecular events in progressive glomerulosclerosis, we administered imidapril to 5/6 nephrectomized rats and measured the glomerular expression of genes for transforming growth factor (TGF)-beta1, fibronectin and collagen IV. Glomerular TGF-beta1, fibronectin and collagen IV mRNAs in nephrectomized rats were significantly higher than those in sham-operated rats. Treatment with imidapril for 10 weeks significantly reduced the enhanced glomerular expression of TGF-beta1 and collagen IV mRNA in nephrectomized rats, and prevented the associated proteinuria and glomerulosclerosis. Thus, imidapril may arrest progressive glomerulosclerosis by inhibiting the expression of TGF-beta1 and collagen IV.

Inhibition of nitric oxide synthase causes cardiac phenotypic modulation in rat

Cardiac gene expressions of collagen and contractile proteins were examined in rats treated with a nitric oxide (NO) synthase inhibitor, NG-nitro-L-arginine methyl ester (L-NAME), for 3 weeks. The rats became hypertensive, which caused left ventricular hypertrophy. Among the mRNAs examined, beta-myosin heavy chain was increased and alpha-myosin heavy chain was decreased in both left and right ventricles, whereas skeletal alpha-actin and atrial natriuretic polypeptide were increased in the left ventricle only. Furthermore, coadministration of losartan with L-NAME lowered blood pressure and caused regression of left ventricular hypertrophy, but did not affect beta- and alpha-myosin heavy chain mRNA levels, indicating that L-NAME directly regulates beta- and alpha-myosin heavy chain mRNA.

Characteristics of diabetes, blood pressure, and cardiac and renal complications in Otsuka Long-Evans Tokushima Fatty rats

To characterize the molecular mechanism of cardiac and renal complications in non-insulin-dependent diabetes mellitus (NIDDM), we examined the gene expression of Otsuka Long-Evans Tokushima Fatty (OLETF) rats, a new animal model for human NIDDM, at the ages of 14 weeks (prediabetic stage), 30 weeks (NIDDM stage), and 54 weeks (IDDM stage). Tissue mRNA levels were measured by Northern blot analysis. In 14-week-old OLETF rats, cardiac mRNAs for transforming growth factor-beta1 (TGF-beta1) and extracellular matrix, including collagen types I, III, and IV and laminin, were significantly increased compared with control rats (Long-Evans Tokushima Otsuka rats). Cardiac beta-myosin heavy chain (MHC) mRNA of OLETF was increased at 30 and 54 weeks of age, whereas alpha-MHC mRNA of OLETF was inversely decreased at 54 weeks. Marked perivascular fibrosis was seen in the hearts of OLETF rats from 30 weeks of age. In the kidney of OLETF rats, glomerular TGF-beta1 expression was temporally increased at 30 weeks of age, followed by glomerulosclerosis characterized by mesangial proliferation, thickening of the basement membrane, and nodular lesions. Blood pressure of OLETF rats remained higher than that of control rats from the prediabetic stage to the IDDM stage. Thus, in OLETF rats, cardiac fibrosis-related gene expressions were already enhanced at the prediabetic stage, which supports the involvement of these gene expressions in cardiac perivascular fibrosis. The antithetical change in beta- and alpha-MHC expressions seems to participate in the decreased cardiac contractility seen in diabetes. Furthermore, TGF-beta1 may also contribute to glomerulosclerosis of OLETF rats. OLETF rats seem to be a useful model to study the mechanism of hypertension and cardiac and renal complications in NIDDM.

Formation of recombinant triple-helical [alpha 1(IV)]2 alpha 2(IV) collagen molecules in CHO cells

Collagen IV molecules represent a major structural component of basement membranes providing a network of support for the supramolecular structure. Like other collagens, collagen IV forms a triple-helical molecule composed of three alpha chains. Six different alpha chains exist for collagen IV, although the most common isoform consists of two alpha 1(IV) and one alpha 2(IV) chain. To understand the molecular mechanism of triple-helical formation of collagen IV, we expressed recombinant alpha 1(IV) and alpha 2(IV) mouse collagen chains in Chinese hamster ovary (CHO) cells. An expression vector containing the full length cDNA for the mouse alpha 1(IV) chain was stably transfected into CHO cells and a cell line, A222, which expressed recombinant alpha 1(IV) chains was selected. These A222 cells were then infected with a retroviral expression vector containing the mouse alpha 2(IV) chain and a cell line, A222-A2, stably expressing both recombinant alpha 1(IV) and alpha 2(IV) chains was obtained. Immunoprecipitation of A222 cell lysates revealed a high level of alpha 1(IV) chain monomer, which was unable to form a homotrimer. Analysis of A222-A2 cell lysates revealed the presence of both monomeric alpha 2(IV) and alpha 1(IV) chains as well as a higher molecular weight collagen IV species. Second dimensional SDS-PAGE analysis demonstrated that the high molecular weight species was a heterotrimer consisting of two alpha 1(IV) and one alpha 2(IV) chain. This heterotrimer collagen IV species was pepsin-resistant indicating the formation of a stable triple-helical structure. Pulse-chase experiments showed that the monomer alpha 1(IV) chain was secreted, but at a much slower rate than the heterotrimer. Together these results demonstrate that the alpha 1(IV) chain is not capable of forming homotrimers and suggest that the coexpression with the alpha 2(IV) chain is necessary to form a triple-helical structure.

Enhanced production of glomerular extracellular matrix in a new mouse strain of high serum IgA ddY mice

To investigate the relationship between high serum levels of IgA and glomerular lesions, selective mating was performed in high serum IgA ddY mice, a murine model of spontaneously developing mesangioproliferative glomerulonephritis mimicking human IgA nephropathy. The selection and mating of high IgA ddY mice were accomplished when the mice were three to four months old. In the 12th generation of high IgA ddY (HIGA) mice, significantly higher levels of serum IgA from 10 age weeks to 60 weeks (P < 0.0002 to 0.0001) were observed in comparison with BALB/c mice. Relatively high proteinuria was observed at 40 weeks of age, although hematuria was consistently negative. Microscopic observations of renal tissue disclosed a marked glomerular mesangial matrix increase and a reduction of cell proliferation with age by both semiquantitative and morphometric analyses with moderate tubulointerstitial damage. These mesangial matrices were stained markedly by antisera for collagen type IV and by fibronectin, but not by collagen type I. Localization of TGF-beta protein was also detected in the mesangium of the HIGA mice. The positive mesangial IgA deposition was maintained consistently by this mating procedure and became more marked with age. Size analysis of IgA from ten pooled HIGA mice aged 50 to 60 weeks revealed dominant polymeric IgA in sera and dimeric IgA in glomerular eluates. Clonal analysis of serum IgA disclosed heterogeneous spectrotypes in a wide pH range (4.5 to 6.5), in contrast to very limited spectrotypes in the acidic pH range (4.5 to 5.2) of IgA in the glomerular eluates from these mice. The analyses of retroviral gp70 antigen involvement in the HIGA mice disclosed a significant increase of serum levels of gp70 anti-gp70 immune complexes with age, with no relationship to the severity of glomerular gp70 deposition. Northern blot analysis of renal tissue revealed markedly high mRNA expression of collagen type I, IV, fibronectin and TGF-beta even in 10-week-old HIGA mice in comparison with BALB/c mice. The expression became more significant in 60-week-old animals. The genetic background required to induce the expansion of IgA-producing B-cell clones is suggested to be closely related to the increased gene expression of TGF-beta, which induces enhanced glomerular extracellular matrix (especially fibronectin) accumulation in HIGA mice, being possibly mediated by the mesangial deposition of dimeric and highly acidic IgA. This newly established strain may provide a model for investigating the relationship between progressive glomerular sclerotic lesions and the induction of pathogenic IgA in human IgA nephropathy.

Analysis of connexin43 gene expression induced by retinoic acid in F9 teratocarcinoma cells

All-trans retinoic acid (10(-7) M) induces cell-cell communication and expression of the gap junction protein connexin43 in mouse F9 teratocarcinoma cells. Northern blot analysis revealed an increase of connexin43 mRNA after treatment with retinoic acid, accompanied by an increase of the mRNA of collagen IV, a differentiation marker. To address the question at what level gene expression is enhanced by retinoic acid, nuclear run-on experiments were carried out. There was no detectable change in the level of newly transcribed connexin43 mRNA. Therefore, we postulate a post-transcriptional mechanism responsible for the regulation of connexin43 mRNA levels by retinoic acid.

Role of angiotensin-converting enzyme, adrenergic receptors, and blood pressure in cardiac gene expression of spontaneously hypertensive rats during development

We undertook this study to investigate the regulatory mechanism of cardiac gene expression in spontaneously hypertensive rats (SHR) during development. We measured cardiac mRNAs by Northern blot analysis. In 9-week-old SHR at the very early stage of cardiac hypertrophy, the expression of various cardiac genes related to the regulation of cardiac contraction and relaxation was already significantly changed compared with control Wistar-Kyoto rats, indicating that cardiac molecular changes are responsible for cardiac remodeling or the modulation of cardiac performance in SHR. We gave various types of antihypertensive drugs, at oral doses causing a mild and comparable hypotensive effect, to 27-week-old SHR to examine the effects on the altered cardiac gene expression. Imidapril, an angiotensin-converting enzyme inhibitor, normalized the increased gene expression of atrial natriuretic polypeptide and collagen types I and III and the decreased expression of alpha-myosin heavy chain in SHR heart. Atenolol (a beta 1-blocker) combined with doxazosin did not affect cardiac ANP and alpha-myosin heavy chain expression of SHR but normalized the increased collagen expression. In contrast, despite a hypotensive effect comparable to these two drug treatments, doxazosin (an alpha 1-blocker) alone or manidipine (a calcium antagonist) did not normalize these altered gene expressions of SHR. These results show that the cardiac renin-angiotensin system is involved in the altered cardiac gene expression in SHR. The beta 1- but not alpha 1-adrenergic receptor is also responsible for the increased cardiac collagen expression in SHR.

Advanced glycation end products modulate transcriptional regulation in mesangial cells

Advanced glycation end products (AGEs) stimulate synthesis of extracellular matrix (ECM) in a receptor-mediated manner on mesangial cells. In the present study, we examined the transcriptional regulation of the gene for type IV collagen [(IV)collagen], which is one of the major components of mesangial sclerosis, after stimulation of AGEs on mesangial cells. The methylation pattern of the promoter/enhancer region of (IV)collagen gene was similar in AGE-treated and control cells. AGEs significantly increased the transcriptional activity of the (IV)collagen gene, as measured by transient transfection assays using the reporter gene construct containing (IV)collagen promoter/enhancer and the chloramphenicol acetyltransferase gene. AGEs also increased smooth muscle alpha-actin mRNA levels as well as its transcriptional activity. Nuclear factor binding of the promoter of (IV)collagen gene was stimulated by AGEs. Furthermore, AGEs dramatically decreased the mRNA levels of (IV)collagen promoter binding protein (MSW), a larger subunit of DNA replication complex, AP1. These results suggest that AGEs increase expression of (IV)collagen gene by modulating the levels of promoter binding proteins. These transcriptional events may play a critical role in ECM accumulation in response to AGEs.

Contribution of local renin-angiotensin system to cardiac hypertrophy, phenotypic modulation, and remodeling in TGR (mRen2)27 transgenic rats

BACKGROUND

The transgenic rat TGR(mRen2)27, carrying the mouse Ren-2 gene, is a new model to elucidate the role of the local renin-angiotensin system in vivo. However, the role of the local renin-angiotensin system in the heart remains to be determined in TGR(mRen2)27.

METHODS AND RESULTS

TGR(mRen2)27 were treated with various antihypertensive drugs for 6 weeks to examine the effects on cardiac hypertrophy and gene expression. Cardiac mRNAs were examined by Northern blot analysis. In TGR(mRen2)27, left ventricular hypertrophy was associated with a decrease in alpha-myosin heavy chain expression of 31% and an increase in skeletal alpha-actin and atrial natriuretic polypeptide expression by 2.6- and 21-fold, respectively (P < .05), thereby showing the shift of myocardium to a fetal phenotype. Furthermore, cardiac collagen and laminin expressions were increased in TGR(mRen2)27 (P < .05), suggesting the occurrence of cardiac remodeling. Although treatment of TGR(mRen2)27 with a high dose of TCV-116 (angiotensin AT1 receptor antagonist) or manidipine (calcium antagonist) combined with atenolol (beta 1-adrenergic receptor blocker) completely normalized blood pressure, TCV-116 regressed cardiac hypertrophy and suppressed the changes in cardiac mRNA levels of TGR(mRen2)27 much more potently than manidipine with atenolol. Furthermore, the inhibitory effects of a low dose of TCV-116 on cardiac hypertrophy and altered gene expressions of TGR(mRen2)27 were greater than those of doxazosin (alpha 1-adrenergic receptor blocker) combined with atenolol, despite their similar hypotensive effects.

CONCLUSIONS

Our present observations provide evidence that the cardiac renin-angiotensin system in TGR(mRen2)27 is responsible for cardiac hypertrophy, phenotypic modulation, and remodeling.

Coordinate gene expression of the alpha3, alpha4, and alpha5 chains of collagen type IV. Evidence from a canine model of X-linked nephritis with a COL4A5 gene mutation

Canine X-linked hereditary nephritis is an animal model for human X-linked hereditary nephritis with a premature stop codon in the alpha5(IV) gene of collagen type IV. We used this model to examine the other alpha(IV) chains at the mRNA and protein level in the kidney, since in human X-linked hereditary nephritis, the alpha3(IV) and alpha4(IV) chains are often absent from the glomerular basement membrane, although both are encoded by autosomal genes. cDNA probes for the alpha1(IV)-alpha6(IV) chains were generated from normal dog kidney using the polymerase chain reaction. Sequences were >/=88% identical at the DNA level and >/=92% identical at the protein level to the respective human alpha(IV) chains. By Northern analysis, transcripts for the alpha1(IV), alpha2(IV), and alpha6(IV) chains were detected at comparable levels in both normal and affected male dog kidney RNA. As previously shown, the transcript for the alpha5(IV) chain was reduced to approximately 10% of normal. Unexpectedly, the alpha3(IV) and alpha4(IV) transcripts were both decreased >/=77% in affected male dog kidney, suggesting a mechanism coordinating the expression of these three basement membrane components. The NC1 domain of collagen type IV isolated from normal dog glomeruli was positive for the alpha3(IV), alpha4(IV), and alpha5(IV) chains by Western blotting. In contrast, in the NC1 domain isolated from affected dog glomeruli, these three chains were not detectable, except for a trace of alpha3(IV) dimer. In X-linked hereditary nephritis, the absence of the alpha3(IV) and alpha4(IV) chains from glomerular basement membrane may reflect factors acting at the transcriptional and/or translational level in addition to the protein assembly level.

Effects of an AT1 receptor antagonist, an ACE inhibitor and a calcium channel antagonist on cardiac gene expressions in hypertensive rats

1. This study was undertaken to determine whether the AT1 receptor directly contributes to hypertension-induced cardiac hypertrophy and gene expressions. 2. Stroke-prone spontaneously hypertensive rats (SHRSP) were given orally an AT1, receptor antagonist (losartan, 30 mg kg-1 day-1), an angiotensin converting enzyme inhibitor (enalapril 10 mg kg-1 day-1), a dihydropyridine calcium channel antagonist (amlodipine, 5 mg kg-1 day-1), or vehicle (control), for 8 weeks (from 16 to 24 weeks of age). The effects of each drug were compared on ventricular weight and mRNA levels for myocardial phenotype- and fibrosis-related genes. 3. Left ventricular hypertrophy of SHRSP was accompanied by the increase in mRNA levels for two foetal phenotypes of contractile proteins (skeletal alpha-actin and beta-myosin heavy chain (beta-MHC)), atrial natriuretic polypeptide (ANP), transforming growth factor-beta-1 (TGF-beta 1) and collagen, and a decrease in mRNA levels for an adult phenotype of contractile protein (alpha-MHC). Thus, the left ventricle of SHRSP was characterized by myocardial transition from an adult to a foetal phenotype and interstitial fibrosis at the molecular level. 4. Although losartan, enalapril and amlodipine lowered blood pressure of SHRSP to a comparable degree throughout the treatment, losartan caused regression of left ventricular hypertrophy of SHRSP to a greater extent than amlodipine (P < 0.01). 5. Losartan significantly decreased mRNA levels for skeletal alpha-actin, ANP, TGF-beta 1 and collagen types I, III and IV and increased alpha-MHC mRNA in the left ventricle of SHRSP. Amlodipine did not alter left ventricular ANP, alpha-MHC and collagen types I and IV mRNA levels of SHRSP. 6. The effects of enalapril on left ventricular hypertrophy and gene expressions of SHRSP were similar to those of losartan, except for the lack of inhibition of collagen type I expression by enalapril. 7. Unlike the hypertrophied left ventricle, there was no significant difference between losartan and amlodipine in the effects on non-hypertrophied right ventricular gene expressions of SHRSP. 8. Our results show that hypertension causes not only left ventricular hypertrophy but also molecular transition of myocardium to a foetal phenotype and interstitial fibrosis-related molecular changes. These hypertension-induced left ventricular molecular changes may be at least in part mediated by the direct action of local angiotensin II via the AT1, receptor.

Differentiation of smooth muscle phenotypes in mouse mesangial cells

Smooth muscle alpha-actin (SMA) mRNA, a marker of vascular smooth muscle cells, was identified in the normal glomerular mesangium both in vivo and in vitro. Several populations of mesangial cells were studied to determine if SMA and basement membrane collagen were regulated together. The levels of SMA expression, which could be linked to the stage of differentiation, were different for the differing cell populations. One cell population had high SMA and type IV collagen levels at its early passages. The others expressed both interstitial and basement membrane collagens. The first population developed these phenotypic features at later passages. The levels of SMA and alpha 1(IV) collagen expression were regulated together in concert, whereas the alpha 2(I) collagen levels were expressed inversely to SMA and alpha 1(IV) collagen. Both SMA and type IV collagen were controlled by the methylation states of the cis-regulators; however, type I collagen was mainly regulated by the trans-acting regulators. Treatment with 5-azacytidine converted the cells of a fibroblast-phenotype to a smooth muscle cell-like phenotype. These cell lines may be useful for studying the differentiation process in vitro.

Regulation of DNA methyltransferase during differentiation of F9 mouse embryonal carcinoma cells

DNA becomes demethylated when F9 mouse embryonal carcinoma cells differentiate into parietal endoderm. DNA methyltransferase (DNA-MTase) activity decreased by 50% during 1 week of differentiation. The level of DNA-MTase mRNA was also diminished accordingly, but the transcription rate of the DNA-MTase gene measured by run-on transcription was essentially unchanged, indicating regulation of DNA-MTase expression at a posttranscriptional step. The decline of DNA-MTase mRNA paralleled that of histone H3 mRNA in accord with the notion that DNA-MTase is preferentially expressed in the S phase of the cell cycle. Since DNA-MTase expression decreases in parallel with DNA synthesis, DNA demethylation during differentiation of F9 cells appears not to be due to limited expression of DNA-MTase. However, the plasmid pAFP7000CAT, alpha-fetoprotein (AFP), which is strongly de novo methylated when transfected into F9 stem cells became only weakly methylated after transfection into the F9 parietal endoderm derivative P1, indicating that the activity of DNA-MTase within parietal endoderm cells is more strongly diminished than is apparent from measurements of mRNA amounts and of overall DNA-MTase activity in vitro. The discrepancy between DNA-MTase expression and its actual activity within the cell indicates the existence of a novel mechanism controlling the activity of DNA-MTase.

Angiotensin II type 1 receptor blockade inhibits the expression of immediate-early genes and fibronectin in rat injured artery

BACKGROUND

Vascular injury activates various kinds of genes, including proto-oncogenes, growth factors, and extracellular matrix proteins. However, the significance of activation of these genes in neointimal formation is poorly understood. Angiotensin II type 1 (AT1) receptor antagonist is shown to prevent neointimal formation after vascular injury, although the mechanism is unclear. To understand the molecular mechanism of vascular thickening, we examined the effects of AT1 receptor blockade on the gene expression of proto-oncogenes, transforming growth factor-beta 1 (TGF-beta 1), and extracellular matrix proteins after vascular injury.

METHODS AND RESULTS

Endothelial denudation of the left common carotid artery in Sprague-Dawley rats was performed with a Fogarty 2F balloon catheter. TCV-116 (10 mg.kg-1.d-1), a selective nonpeptide AT1 receptor antagonist, or vehicle was administered orally to rats from 1 day before to 14 days after balloon injury. Injured left and uninjured right common carotid arteries were removed from rats at 1, 6, and 24 hours and 3, 7, and 14 days after balloon injury. Tissue mRNA levels were measured with Northern blot analysis using specific cDNA probes and corrected for 18S ribosomal RNA value. Arterial mRNAs for c-fos, c-jun, jun B, jun D, and Egr-1 increased significantly at 1 hour after balloon injury and decreased rapidly. At 6 hours, ornithine decarboxylase (ODC) mRNA expression reached the maximal levels. TGF-beta 1 and fibronectin mRNA levels started to increase at 6 hours after injury and remained enhanced until 7 days after injury. On the other hand, collagen types I, III, and IV and laminin mRNA levels were not significantly increased over 7 days. Treatment with TCV-116 significantly inhibited the induction of mRNAs for c-fos, c-jun, Egr-1, ODC, and fibronectin in injured artery, whereas the increase in TGF-beta 1 gene expression after injury was not prevented by TCV-116. Immunohistological studies indicated that TCV-116 decreased not only the intimal thickening but also the amount of these extracellular matrix proteins in the intima.

CONCLUSIONS

The results indicate that AT1 receptor blockade inhibits the induction of immediate-early genes, ODC, and fibronectin in rat injured artery. Thus, inhibition of intimal thickening by AT1 receptor blockade may be mediated at least in part by suppression of multiple genes related to cell growth and migration in the very early phase after vascular injury.

Transforming growth factor-beta 1 expression and phenotypic modulation in the kidney of hypertensive rats

We have previously reported that renal mRNA levels for transforming growth factor-beta 1, fibronectin, and collagens were increased in 32-week-old stroke-prone spontaneously hypertensive rats (SHRSP) with severe nephrosclerosis. To elucidate the mechanism of hypertension-induced nephrosclerosis, we examined gene expression and localization of transforming growth factor-beta 1 and cellular phenotype in the kidney of 25-week-old SHRSP with moderate renal damage. Renal mRNA was measured by Northern blot analysis. The localization of transforming growth factor-beta 1 and cellular phenotype was determined by immunohistochemistry. In the kidney of 25-week-old SHRSP, renal transforming growth factor-beta 1 mRNA was elevated compared with Wistar-Kyoto rats (WKY), whereas renal collagen mRNAs of SHRSP were not increased. Immunoreactive transforming growth factor-beta 1 in SHRSP was mainly localized in glomerular cells. Furthermore, alpha-smooth muscle actin and desmin were significantly expressed in SHRSP glomerular cells, in contrast to negligible expression of these proteins in WKY. alpha-Smooth muscle actin staining was also observed in interstitial cells, and vimentin, another phenotypic marker, was expressed in atrophic tubular cells of SHRSP, despite no staining of these proteins in WKY. Furthermore, all these phenotypic changes in SHRSP were associated with increased cell proliferation, as shown by the increased number of proliferating cell nuclear antigen-positive cells. Treatment of SHRSP with cilazapril and nifedipine (from the age of 13 to 25 weeks) prevented the increase in transforming growth factor-beta 1 expression and the cellular phenotypic modulation and was accompanied by a reduction of urinary albumin excretion and inhibition of cell proliferation.(ABSTRACT TRUNCATED AT 250 WORDS)

Hepatocyte growth factor stimulates extensive development of branching duct-like structures by cloned mammary gland epithelial cells

Although epithelial-mesenchymal (stromal) interactions are thought to play an important role in embryonic and postnatal development of the mammary gland, the underlying mechanisms are still poorly understood. To address this issue, we assessed the effect of fibroblast-derived diffusible factors on the growth and morphogenetic properties of a clonally derived subpopulation (clone TAC-2) of normal murine mammary gland (NMuMG) epithelial cells embedded in collagen gels. Under control conditions, TAC-2 mammary gland epithelial cells suspended within collagen gels formed either irregularly shaped cell aggregates or short branching cord-like structures. Addition of conditioned medium from Swiss 3T3 or MRC-5 fibroblasts dramatically stimulated cord formation by TAC-2 cells, resulting in the development of an extensive, highly arborized system of duct-like structures, which in appropriate sections were seen to contain a central lumen. The effect of fibroblast conditioned medium was completely abrogated by antibodies against hepatocyte growth factor (also known as scatter factor), a fibroblast-derived polypeptide that we have previously shown induces tubulogenesis by Madin-Darby canine kidney epithelial cells. Addition of exogenous recombinant human hepatocyte growth factor to collagen gel cultures of TAC-2 cells mimicked the tubulogenic activity of fibroblast conditioned medium by stimulating formation of branching duct-like structures in a dose-dependent manner, with a maximal 77-fold increase in cord length at 20 ng/ml. The effect of either fibroblast conditioned medium or hepatocyte growth factor was markedly potentiated by the simultaneous addition of hydrocortisone (1 microgram/ml), which also enhanced lumen formation. These results demonstrate that hepatocyte growth factor promotes the formation of branching duct-like structures by mammary gland epithelial cells in vitro, and suggest that it may act as a mediator of the inducing effect of mesenchyme (or stroma) on mammary gland development.

Evidence for involvement of activin A and bone morphogenetic protein 4 in mammalian mesoderm and hematopoietic development

Xenopus in vitro studies have implicated both transforming growth factor beta (TGF-beta) and fibroblast growth factor (FGF) families in mesoderm induction. Although members of both families are present during mouse mesoderm formation, there is little evidence for their functional role in mesoderm induction. We show that mouse embryonic stem cells, which resemble primitive ectoderm, can differentiate to mesoderm in vitro in a chemically defined medium (CDM) in the absence of fetal bovine serum. In CDM, this differentiation is responsive to TGF-beta family members in a concentration-dependent manner, with activin A mediating the formation of dorsoanterior-like mesoderm and bone morphogenetic protein 4 mediating the formation of ventral mesoderm, including hematopoietic precursors. These effects are not observed in CDM alone or when TGF-beta 1, -beta 2, or -beta 3, acid FGF, or basic FGF is added individually to CDM. In vivo, at day 6.5 of mouse development, activin beta A RNA is detectable in the decidua and bone morphogenetic protein 4 RNA is detectable in the egg cylinder. Together, our data strongly implicate the TGF-beta family in mammalian mesoderm development and hematopoietic cell formation.

Contribution of renal angiotensin II type I receptor to gene expressions in hypertension-induced renal injury

Recent evidence indicates that transforming growth factor-beta 1 (TGF-beta 1) plays an important role in renal fibrosis via stimulation of extracellular matrix synthesis. The present study was undertaken to investigate the role of angiotensin II type I receptor (AT1 receptor) in hypertension-induced renal injury. Twenty-two-week-old stroke-prone spontaneously hypertensive rats (SHRSP), which had established hypertension and moderate renal damage, were orally given TCV-116, a selective non-peptide AT1 receptor antagonist (0.1, 1 or 10 mg/kg/day), enalapril (10 mg/kg/day) or vehicle once a day for 10 weeks. At the end point of the treatment, we examined renal function, the gene expressions of TGF-beta 1 and extracellular matrix components in the interstitium [collagen types I (COI) and III (COIII), fibronectin (FN)] and the basement membrane (COIV and laminin), and renal microscopic morphology in rats aged 32 weeks. In vehicle-treated 32 week-old SHRSP with renal dysfunction and nephrosclerosis, renal mRNA levels for TGF-beta 1, COI, COIII, FN, COIV were all several-fold higher than in WKY. Thus, renal TGF-beta 1 gene expression was enhanced in SHRSP, which may contribute to the increased renal expressions of COI, COIII, FN, COIV in SHRSP. Treatment with TCV-116 (0.1 mg/kg/day) in SHRSP, in spite of no reduction of blood pressure, decreased renal mRNA levels for TGF-beta 1, COI, COIII, FN, COIV, being accompanied by the significant decrease in urinary protein and albumin excretion, blood urea nitrogen and plasma creatinine. Treatment with TCV-116 (10 mg/kg/day) in SHRSP decreased mRNAs for TGF-beta 1, COI, COIII, FN and COIV to almost the same levels as WKY, being associated with normalization of urinary protein and albumin excretion and the prevention of nephrosclerosis, as judged by microscopic histological observations. On the other hand, the effects of enalapril (10 mg/kg/day) on the above mentioned mRNA levels, renal function and renal morphology were weaker than those of TCV-116 (10 mg/kg/day) and were as much as TCV-116 (1 mg/kg/day). These results suggest that independently of hypotensive action, AT1 receptor antagonist has a potent renal protective effect by inhibiting the gene expression of renal TGF-beta 1 and extracellular matrix components.

Expression of the alpha-5(IV) collagen chain in the fetal human small intestine

BACKGROUND/AIMS

The basement membrane type IV collagen is a family composed of at least five genetically distinct but structurally similar polypeptide chains, alpha 1-alpha 5. The alpha 1(IV) and alpha 2(IV) chains are ubiquitous components of basement membranes, whereas the alpha 3(IV), alpha 4(IV), and alpha 5(IV) chains have a restricted tissue distribution. The aim of this study was to analyze the presence of these minor type IV collagen chains in the small intestinal mucosa.

METHODS

The expression of type IV collagen chains in the developing and adult human small intestine was determined by indirect immunofluorescence with monoclonal and polyclonal antibodies. Western blotting and Northern hybridization analysis were also used to additionally investigate the expression of the alpha 1(IV) and alpha 5(IV) chains.

RESULTS

The alpha 3-alpha 5(IV) chains were absent from the adult epithelium, but, surprisingly, the alpha 5(IV) chain was consistently detected in the fetal mucosa. Its expression was confirmed by Western blotting, complementary DNA polymerase chain-reaction amplification, and Northern hybridization analysis.

CONCLUSIONS

The alpha 5(IV) chain of collagen is expressed in the fetal but not adult human intestinal epithelium. Its position at the basolateral domain of epithelial cells suggests a potential role for this molecule during development.

Role of angiotensin II in extracellular matrix and transforming growth factor-beta 1 expression in hypertensive rats

The in vivo effects of alacepril (1-[(S)-3-acetylthio-2-methylpropanoyl]- L-prolyl-L-phenylalanine), an angiotensin converting enzyme inhibitor, and SC-52458 (5-[(3,5-dibutyl-1H-1,2,4-triazol-1- yl)methyl]-2-[2-(1H-tetrazol-5-ylphenyl)]pyridine), an angiotensin AT1 receptor antagonist, were examined on the cardiac and aortic gene expressions of extracellular matrices and TGF-beta 1 in young spontaneously hypertensive rats (SHR). In SHR, types I and III collagen mRNAs were increased in the left ventricle, and in contrast, fibronectin, collagen IV, and transforming growth factor-beta 1 (TGF-beta 1) mRNAs were increased in aorta, compared with those in Wistar-Kyoto rats. All the enhanced mRNAs in both organs in SHR were significantly inhibited by the short-term treatment with the above two drugs. Thus, angiotensin AT1 receptor may play an important role in the regulation of extracellular matrices and TGF-beta 1 expressions in SHR.

Intracellular glutathione influences collagen generation by mesangial cells

The cellular redox state is altered in a number of pathological conditions, including various forms of glomerular injury and diabetes. For example, glucose, via the pentose phosphate pathway generates NADPH, which maintains glutathione (GSH) (part of a major intracellular reducing system) in its reduced state. GSH in turn influences the activity of transcription factors on gene expression. We therefore examined whether changes in cellular GSH influence total collagen synthesis and mRNA levels for collagen I, collagen IV and TGF-beta in SV-40 transformed mouse mesangial cells (MC) maintained in either 5 or 25 mM glucose media. Total intracellular GSH was increased by N-acetylcysteine (NAC; 10 mM) or decreased with the GSH synthesis inhibitor buthionine sulfoximine (BSO; 0.2 mM) in MC. NAC increased 3H-proline incorporation into collagenase-sensitive protein while BSO decreased it under both glucose conditions. The presence of BSO did not reverse the increased collagen synthesis seen in the NAC stimulated cells. Northern blot analysis showed increased mRNA levels for collagen I, collagen IV and TGF-beta in cells grown in high glucose (25 mM). NAC increased the mRNA for all three compounds while BSO alone had no effect on these mRNA levels. However, BSO reversed the increased mRNA levels for collagen I, IV and TGF-beta seen in the presence of NAC. These findings suggest that the cellular redox state may influence gene transcription in MC, and may have implications in explaining injury-associated alterations of mesangial matrix generation.

Role of angiotensin II in renal injury of deoxycorticosterone acetate-salt hypertensive rats

To investigate the role of angiotensin II (Ang II) in hypertension-induced tissue injury, we gave TCV-116 (1 mg/kg per day PO), a nonpeptide Ang II type I receptor antagonist, or enalapril (10 mg/kg per day PO) to deoxycorticosterone acetate (DOCA)-salt hypertensive rats for 3 weeks and examined the effects on tissue mRNA levels for transforming growth factor-beta 1 (TGF-beta 1) and extracellular matrix components. Tissue mRNA levels were measured by Northern blot analysis. Renal mRNA levels for TGF-beta 1; types I, III, and IV collagen; and fibronectin in DOCA-salt hypertensive rats were increased by severalfold (P < .01) compared with sham-operated rats. In the aorta of DOCA-salt hypertensive rats, TGF-beta 1 and fibronectin mRNA levels were increased, but types I, III, and IV collagen mRNAs did not increase. In the heart, increased mRNA was found only for fibronectin. Thus, these gene expressions are regulated in a tissue-specific manner. TCV-116 or enalapril did not lower blood pressure in DOCA-salt hypertensive rats. However, the increase in renal mRNAs for TGF-beta 1 and extracellular matrix components in DOCA-salt hypertensive rats was significantly inhibited by treatment with TCV-116 or enalapril, which was associated with a significant decrease in urinary protein and albumin excretions and histological improvement of renal lesions. In contrast, in the aorta and heart these gene expressions were not affected by TCV-116 or enalapril. Thus, local Ang II may contribute to renal injury of DOCA-salt hypertension by stimulating the gene expression of TGF-beta 1 and extracellular matrix components.

Characterization of the Han:SPRD rat model for hereditary polycystic kidney disease

The Han:SPRD rat model for inherited polycystic kidney disease (PKD) was characterized (clinical parameters, morphology, immunohistochemistry and in situ hybridization). Homozygous animals died of uremia after three to four weeks with severe cystic transformation of virtually all nephrons and collecting ducts (serum urea: 616 +/- 195 mg/dl; kidney-to-body weight ratio: > 20%). In heterozygotes, slow progression of the disease led to death between the 12th and 21st month (median: 17 months; serum urea levels above 200 mg/dl). Kidney enlargement was moderate, and cysts were restricted to the cortex and outer medulla. Immunohistochemical markers showed that approximately 75% of the cysts were derived from the proximal tubule. Cystic transformation started in the proximal tubule with a sharp onset of basement membrane alteration and a loss of epithelial differentiation restricted to small focal areas. In these areas, alpha 1(IV) collagen and laminin B1 mRNA were enhanced as revealed by isotopic and non-isotopic in situ hybridization. Fibroblasts underlying the affected tubular portions were involved in matrix overexpression resulting in subepithelial accumulation of immunoreactive collagen IV and laminin. In later stages of cystic transformation distal nephron segments were affected as well. A reversal in epithelial polarity as judged from Na,K-ATPase-immunoreactivity was not observed. Renal immunoreactive renin-status was significantly decreased. Hematocrit was lowered in heterozygotes (40.4 +/- 5.8 vol% compared to 46.7 +/- 1.99 vol% in controls; P < 0.05) and total renal EPO mRNA was reduced to 36 +/- 14% of the mean value of control animals, whereas serum EPO levels were not significantly altered. We conclude that the Han:SPRD rat is a useful model for the study of human ADPKD since both diseases are similar in several aspects. The model is particularly suitable for the study of epithelial-mesenchymal interactions at the beginning of tubular cystic transformation.

Neoplastic progression of human and rat intestinal cell lines after transfer of the ras and polyoma middle T oncogenes

BACKGROUND

Activation of the p21ras and pp60c-src oncoproteins occurred at high incidence in the early stage of human colorectal carcinogenesis. Our study aimed to investigate the role of these signal-transduction pathways in the process of initiation and promotion of the malignant phenotype in intestinal cells.

METHODS

The human Ha-ras and the polyoma middle T (Py-MT) viral oncogenes were transferred into large T oncogene of simian virus 40 immortalized rat intestinal epithelial SLC-44 cells and human colonic adenocarcinoma Caco-2 cells.

RESULTS

These transfers conferred the tumorigenic and invasive phenotypes on immortalized SLC-44 cells and potentiated the tumorigenicity of Caco-2 cells and markedly repressed the terminal differentiation of this cell line. In SLC-44T cells, induction of the invasive phenotype by the activated Ha-ras oncogene correlated with weak expression of E-cadherin and reduced accumulation of the transcripts encoding the basement membrane components alpha 1 (IV) collagen, nidogen, and BM40, which might result partly from the inactivation of the transforming growth factor beta signaling pathway. The down-regulation of the alpha 1 (IV) collagen messenger RNA in SLC-44T cells was not due to the protein kinase C-dependent pathways or the secretion of autocrine factor(s).

CONCLUSIONS

These results suggest that the activation of the p21ras and Py-MT/pp60c-src oncogenic pathways are critical effectors at different stages of colorectal carcinogenesis and in Caco-2 cells interferes with the program of enterocyte differentiation.

Interstitial fibrosis in obstructive nephropathy

Interstitial fibrosis and tubular basement membrane (TBM) thickening are evident within 16 days of unilateral ureteral obstruction (UUO) in the rabbit, and resemble the changes previously reported in hydronephrotic human kidneys. The cortical interstitial volume fraction in this rabbit model at 16 days is 43.3 +/- 6.1% (+/- 1 SD) in UUO kidneys, 4.9 +/- 3.1% in contralateral kidneys (CLK), and 2.8 +/- 0.8% in kidneys from sham-operated animals (ANOVA, P < 0.0001). Immunohistochemically, UUO is associated with increased interstitial collagens I and III, fibronectin, heparan sulfate proteoglycan and tubulointerstitial nephritis antigen. Aberrant collagen expression is also evident as interstitial collagen IV becomes prominent. Focal, peritubular accumulation of collagens I and II also appear to encircle the TBM. These changes are accompanied by an early, transient increase in renal cortical mRNA encoding the alpha 1 monomers of collagens I, III and IV, implicating increased matrix synthesis in the pathogenesis of obstructive nephropathy. In situ hybridization localized increased expression of alpha 1 (I) and alpha 1 (IV) mRNA to cells in the interstitial space, with clusters of alpha 1(I) positive cells associated with dilated tubules, muscular arteries and the periglomerular interstitium.

Interaction of type IV collagen with the isolated integrins alpha 1 beta 1 and alpha 2 beta 1

The triple-helical cyanogen-bromide-derived fragment CB3[IV] of collagen IV, located 100 nm from the N-terminus of the molecule, contains the binding sites for the integrins alpha 1 beta 1 and alpha 2 beta 1. To investigate the interaction of these integrins and collagen IV, we performed solid-phase and inhibition assays using as receptor isolated alpha 1 beta 1 and alpha 2 beta 1. The ligands used were the binding-site-bearing trimeric peptide CB3[IV] and its shorter tryptic fragments F1-F4. Using titration curves, in which the binding of soluble receptors to coated ligands and the binding of soluble ligands to coated receptors were analyzed, the binding sites for alpha 1 beta 1 and alpha 2 beta 1 were in different but adjacent areas of CB3[IV]. Triple-helical conformation and distinct primary structures were required for the interaction. Dissociation constants (Kd), for the affinity of integrins for collagen IV, were determined in the 1-nM range in the presence of Mn2+ and Mg2+. In the absence of Mn2+, the Kd values indicated a 30-60-fold decrease in the affinities, which for alpha 2 beta 1 was further reduced by adding Ca2+. In the presence of Ca2+ and Mg2+ the affinity of collagen IV for alpha 1 beta 1 was four-times higher than for alpha 2 beta 1.

Thromboxane and prostacyclin differentially regulate murine extracellular matrix gene expression

Alterations in the arachidonic acid metabolites thromboxane and prostacyclin are known to contribute to hemodynamic changes observed in certain models of acute and chronic renal failure. We have previously shown that thromboxane may have an important role in mediating glomerulosclerosis by stimulating the expression of certain extracellular matrix proteins. In the present study, we compared the effects of thromboxane and prostacyclin on the expression of genes encoding basement membrane proteins using a murine teratocarcinoma cell line, that when differentiated to an endodermal phenotype synthesizes abundant extracellular matrix. Incubation of these cells with stable analogs of thromboxane and prostacyclin for four hours resulted in changes in basement membrane gene expression. Thromboxane increased steady-state mRNA levels for all three laminin chains, type IV collagen, and fibronectin, but decreased the level of mRNA for heparan sulfate proteoglycan. In contrast, incubation with carbo-prostacyclin, a stable analog of prostacyclin, decreased the steady-state mRNA level for the laminin A and B1 chains, type IV collagen and fibronectin, and increased the mRNA level for heparan sulfate proteoglycan and laminin B2. Carbo-prostacyclin did not affect cellular proliferation or thymidine incorporation. These results indicate that eicosanoids directly modulate matrix gene expression independently of hemodynamic influence, and independently of effects mediated by platelets, or mitogenesis. Furthermore, these findings suggest that the alterations in renal eicosanoid metabolism may directly participate in the pathogenesis of glomerulosclerosis and thus provide a rationale for therapy directed toward the specific inhibition of thromboxane in the treatment of progressive glomerular sclerosis.

Type IV collagen production by rat pulmonary alveolar epithelial cells

Maintenance and repair of the pulmonary alveolar basement membrane are critical processes for preserving normal alveolar structure and function. To elucidate the mechanisms that control type IV collagen production by pulmonary alveolar epithelial cells, type II pneumocytes from rat lungs were isolated and maintained in tissue culture as monolayers. Using Northern blot analysis and metabolic labeling, we found that the cultured epithelial cells express type IV collagen mRNA and incorporate [3H]proline into type IV collagen. To determine the effects of phenotype on control of type IV collagen synthesis, we took advantage of the well-described observation that isolated type II cells lose their distinctive type II features when cultured on plastic in serum-containing medium for 7 days and assume an appearance more like that of type I epithelial cells. We found that [3H]proline incorporation into type IV collagen increased from day 1 to day 2 and thereafter decreased gradually up to day 7. Despite this decrease in [3H]proline incorporation, type IV collagen mRNA increased over the same period. If the loss of type II cell characteristics was prevented by culturing the cells in EHS matrix, a basement membrane-like extracellular matrix, there was little increase in relative abundance of type IV collagen mRNA as compared with cells cultured on plastic. We therefore conclude that type IV collagen production by isolated pulmonary alveolar epithelial cells is controlled, at least in part, by translational or post-translational mechanisms. Furthermore, the full type II cell phenotype is not required for expression of type IV collagen genes.(ABSTRACT TRUNCATED AT 250 WORDS)

Synthesis of digoxigenin-labeled cRNA probes for nonisotopic in situ hybridization using reverse transcription polymerase chain reaction

Nonisotopic methods of mRNA in situ hybridization have distinct advantages over isotopic techniques. Nonisotopically labeled probes are stable and nontoxic, have short detection times, demonstrate excellent spatial resolution of their signals and have sensitivities comparable to radiolabeled probes. We developed a simple method of generating nonisotopically labeled cRNA probes which is based on the reverse transcription polymerase chain reaction (RT-PCR) and used it to synthesize a panel of probes for various murine extracellular matrix genes. Engelbreth-Holm-Swarm (EHS) tumor RNA was reverse transcribed and PCR was used to amplify defined regions of multiple extracellular matrix protein genes from the resulting first strand cDNAs. Bacteriophage promoters which had been incorporated into the PCR products were then used to generate digoxigenin-conjugated antisense and sense cRNAs. The antisense probes were employed to detect the specific extracellular matrix protein mRNAs in the EHS tumor by in situ hybridization. This technique provides a rapid and efficient alternative to conventional transcription systems which use plasmid vectors for the synthesis of digoxigenin-labeled cRNA probes.

Nonenzymatic glycation of mesangial matrix and prolonged exposure of mesangial matrix to elevated glucose reduces collagen synthesis and proteoglycan charge

Expansion of the mesangial matrix in diabetes occurs after prolonged exposure to the diabetic milieu. To mimic the long-term hyperglycemia of diabetes mellitus we developed tissue culture systems that might approximate the chronic state. This was accomplished in two ways: (1) by growing mesangial cells on extracellular matrix glycated and crosslinked in vitro and (2) by continuously growing cells on their own matrix on filters in elevated glucose medium (500 mg/dl) for up to eight weeks without passage. Synthesis of collagen and proteoglycans was evaluated in cells grown under these conditions. In both these situations, 3H-proline incorporation into collagenase sensitive protein and 35S incorporation into sulfated proteins were reduced compared to control cultures. Despite reduction in 35S incorporation into proteoglycans in the high glucose cultures, total glycosaminoglycan content was unchanged. However, proteoglycans generated by mesangial cells grown in elevated glucose media were of a lower negative charge than controls. In mesangial cells continuously grown on filters, the levels of messenger RNA for collagen types I and IV, biglycan and TGF-beta were not different in cells grown at elevated or standard glucose concentrations for two and four weeks. We conclude that crosslinking of mesangial matrix or continuous culture of cells for prolonged periods of time in high glucose medium, which may also crosslink matrix, suppresses collagen synthesis and reduces the negative charges on matrix proteoglycans without altering mRNA levels.