Inhibition of glomerular mesangial cell proliferation and extracellular matrix deposition by halofuginone

Mesangial cell proliferation, increased deposition of collagen, and expansion of the mesangial extracellular matrix (ECM) are key features in the development of mesangioproliferative diseases. Halofuginone, a low molecular weight anti-coccidial quinoazolinone derivative, inhibits collagen type alpha 1(I) gene expression and synthesis. We investigated the effect of halofuginone on both normal and SV40 transformed mesangial cell proliferation, collagen synthesis, and ECM deposition. Proliferation of both cell types was almost completely inhibited in the presence of 50 ng/ml halofuginone. The cells were arrested in the late G1 phase of the cell cycle and resumed their normal growth rate following removal of the compound from the culture medium. The antiproliferative effect of halofuginone was associated with inhibition of tyrosine phosphorylation of cellular proteins. Similar results were obtained whether the mesangial cells were seeded on regular tissue culture plastic or in close contact with a naturally produced ECM resembling their local environment in vivo. Halofuginone also inhibited synthesis and deposition of ECM by mesangial cells as indicated by a substantial reduction in 14C-glycine and Na2(35)SO4 incorporation into the ECM, and by the inhibition of collagen type I synthesis and gene expression. It is proposed that by inhibiting collagen type I synthesis and matrix deposition, halofuginone exerts a potent antiproliferative effect that may be applied to inhibit mesangial cell proliferation and matrix expansion in a variety of chronic progressive glomerular diseases.     

Nitric oxide modulates the synthesis of extracellular matrix proteins in cultured rat mesangial cells

Nitric oxide (NO) is an important effector molecule of the inflammatory response. It is synthesized by mesangial cells and has been proposed to contribute to glomerular injury in various disease states. We studied whether NO modulates extracellular matrix production in cultured rat mesangial cells. Stimulation of rat mesangial cell NO release with gamma-interferon and lipopolysaccharide resulted in reduced production of collagen (by 35%) fibronectin (by 48%) (P < 0.05). In contrast, laminin synthesis was enhanced two-fold by the same maneuver (P < 0.05). These changes were reversed by the addition of L-NAME, a selective inhibitor of inducible nitric oxide synthase. This is the first demonstration that NO regulates the synthesis of extracellular matrix by mesangial cells. The results indicate that increased renal production of NO in glomerular diseases may attenuate the production and accumulation of matrix proteins and limit the severity of glomerulosclerosis.     

Exogenous nitric oxide inhibits mesangial cell adhesion to extracellular matrix components

Interactions of mesangial cells (MCs) with components of the extracellular matrix (ECM) profoundly influence the MC phenotype, such as attachment, contraction, migration, survival and proliferation. Here, we investigated the effects of exogenous nitric oxide (NO) on the process of MC adhesion to ECM molecules. Incubation of rat MCs with the NO donor S-nitroso-N-acetylpenicillamine (SNAP) dose- and time-dependently inhibited MC adhesion and spreading on various ECM substrata, being more pronounced on collagen type I than on collagen type IV, laminin or fibronectin. In contrast, SNAP did not inhibit MC adhesion to L-polylysine-coated plates. The inhibitory effects of SNAP were reduced by hemoglobin and enhanced by superoxide dismutase. The anti-adhesive action of SNAP was mimicked not only by other NO donors but also by 8-bromo-cGMP, and significantly reversed by the soluble guanylate cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3,-alpha]quinoxalin-1-one (ODQ). Moreover, SNAP and 8-bromo-cGMP decreased the adhesion-induced phosphorylation of focal adhesion kinase (pp125FAK). In the presence of SNAP or 8-bromo-cGMP, adherent MCs exhibited disturbed organization of alpha-actin filaments and reduced numbers of focal adhesions, as shown by immunocytochemistry. In additional experiments with adherent MCs, it was found that exposure to SNAP or 8-bromo-cGMP for 12 and 24 hours induced detachment of MCs. The results indicate that exogenous NO interferes with the establishment and maintenance of MC adhesion to ECM components. This inhibitory NO effect is mediated predominantly by cGMP-signaling. Disturbance of MC attachment to ECM molecules could represent an important mechanism by which NO affects MC behavior in vitro and in vivo.     

Regulation of filtration rate by glomerular mesangial cells in health and diabetic renal disease

The rate of renal filtration is in large part responsible for volume and electrolyte balance in an organism. Integral components of the renal glomerulus are the mesangial cells (MCs), excitable renal pericytes that regulate the glomerular filtration rate by modulating the surface area of the capillaries. Similar to vascular smooth muscle, the signal transduction pathways and ion selective channels regulating isotonic and isometric contraction of MCs are dependent on the voltage-gated Ca influx. During the response to contractile agonists, both Cl and nonselective cation channels play critical roles to depolarize the membrane potential and activate Ca channels. The relaxation pathways involve a negative-feedback mechanism that counteracts mesangial contraction by regulating voltage-dependent Ca signaling. Part of the feedback response involves the activation of plasmalemmal K channels, which hyperpolarize the membrane potential and inhibit voltage-gated Ca entry. This calcium- and voltage-activated feedback K (BKCa) channel shares biophysical, pharmacologic, and molecular properties with the BKCa channels identified in brain and muscle, and with the sio gene product as expressed in Xenopus laevis oocytes. Systemic hormones, such as atrial natriuretic peptide, and paracrine factors, such as nitric oxide (NO), use guanosine 3',5'-cyclic monophosphate (GMP) as a second messenger and enhance the gain in this feedback system by decreasing the voltage and Ca activation thresholds for BKCa. Diabetes mellitus is often associated with high rates of glomerular filtration, mesangial expansion, and secretory abnormalities of the basement membrane. NO-mediated increases in negative-feedback regulation of mesangial tone may attribute, in part, to the pathology of hyperfiltration. Stimulation of inducible nitric oxide synthetase in glomerular MCs by inflammatory cytokines is a possible positive-feedback pathway that contributes to further glomerular destruction. In addition, high ambient glucose, through modulation of BKCa activity, facilitates MC relaxation and thus propagates hyperfiltration. Since cellular arachidonic acid is metabolically linked to extracellular glucose, this fatty acid is a possible mediator of the pathologic actions of hyperglycemia. Clarification of the signal transduction pathways and ionic mechanisms regulating the normal and dysfunctional tones of MCs is essential for rational clinical management of glomerular disease and critical to understanding fluid and electrolyte homeostasis.     

Regulation of eosinophil apoptosis: transduction of survival and death signals

To analyze the effects of supraphysiological dosages of growth hormone (GH) on carbohydrate (CH) and lipid metabolism, we investigated 87 girls with Turner syndrome (TS) in two studies: (1) a 4-year GH dose-response (DR) study comparing three groups with stepwise GH dosage increases up to 8 IU/m2/d in girls aged 2 to 11 years, and (2) a 2-year GH administration frequency-response (FR) study in girls aged 11 to 17 years, comparing once-daily (OD) and twice-daily (BID) injections of a total GH dose of 6 IU/m2/d in combination with low-dose ethinyl estradiol (50 ng/kg/d orally). At baseline, impaired glucose tolerance (IGT) was present in 6% of the girls, and at the end of the studies, in 5%. In the DR study, the area under the curve for time-concentration (AUCab) for glucose after an oral glucose tolerance test (OGTT) showed no change over time and no significant difference between any of the study groups. However, in all three DR groups, the AUCab for insulin, fasting glucose, the insulinogenic index, hemoglobin A1c (HbA1c), and urinary C-peptide (uCp) were all significantly higher after 4 years compared with pretreatment (P<.05). In the FR study, group differences were not observed. Compared with healthy Dutch control subjects, the median baseline levels in relatively young girls in the DR study were similar for total cholesterol (TC) and lower for high-density lipoprotein (HDL) cholesterol. In contrast, the median TC levels of relatively older girls in the FR study were higher and HDL levels were similar. With increasing GH dosage in the DR study, median TC and low-density lipoprotein (LDL) levels decreased, whereas median HDL levels increased. The changes after 4 years were significant, including a decrease in the atherogenic index. GH treatment at the supraphysiological dosages used in this study did not increase the frequency of IGT or clinical diabetes. However, we observed an increased insulinogenic index indicative of insulin resistance. Therefore, long-term follow-up study is warranted in these otherwise healthy subjects. OD injection regimens changed the lipid profile toward a more cardioprotective direction with a significant reduction of the TC/HDL cholesterol ratio.     

Regulation of smooth muscle alpha-actin expression and hypertrophy in cultured mesangial cells

BACKGROUND: Mesangial cells during embryonic development and glomerular disease express smooth muscle alpha-actin (alpha-SMA). We were therefore surprised when cultured mesangial cells deprived of serum markedly increased expression of alpha-SMA. Serum-deprived mesangial cells appeared larger than serum-fed mesangial cells. We hypothesized that alpha-SMA expression may be more reflective of mesangial cell hypertrophy than hyperplasia. METHODS: Human mesangial cells were cultured in medium alone or with fetal bovine serum, thrombin, platelet-derived growth factor-BB (PDGF-BB) and/or transforming growth factor-beta1 (TGF-beta1). Alpha-SMA expression was examined by immunofluorescence, Western blot, and Northern blot analysis. Cell size was analyzed by forward light scatter flow cytometry. RESULTS: Alpha-SMA mRNA was at least tenfold more abundant after three to five days in human mesangial cells plated without serum, but beta-actin mRNA was unchanged. Serum-deprived cells contained 5.3-fold more alpha-SMA after three days and 56-fold more after five days by Western blot. Serum deprivation also increased alpha-SMA in rat and mouse mesangial cells. The effects of serum deprivation on alpha-SMA expression were reversible. Mesangial cell mitogens, thrombin or PDGF-BB, decreased alpha-SMA, but TGF-beta1 increased alpha-SMA expression and slowed mesangial cell proliferation in serum-plus medium. Flow cytometry showed that serum deprivation or TGF-beta1 treatment caused mesangial cell hypertrophy. PDGF-BB, thrombin, or thrombin receptor-activating peptide blocked hypertrophy in response to serum deprivation. CONCLUSIONS: We conclude that increased alpha-SMA expression in mesangial cells reflects cellular hypertrophy rather than hyperplasia.     

Contraction of extracellular matrix by transdifferentiated retinal pigment epithelial cells, inducers and inhibitors

Adhesion molecules relate to cell invasion of autoimmune thyroid disease. We studied plasma soluble P-Selectin (platelet activation-dependent granule-external membrane protein), E-Selectin (endothelial leukocyte adhesion molecule) and L-Selectin (leukocyte endothelial cell adhesion molecule-1) levels in patients with Graves' disease before and during methimazole treatment. Plasma P-, E- and L-Selectin levels in patients with untreated Graves' disease were significantly higher than those in normal subjects. Plasma P-Selectin levels decreased when their thyroid functions were normal for more than 6 months after the start of methimazole treatment. No significant change in plasma E- and L-Selectin levels in patients with Graves' disease was found between hyperthyroid state and euthyroid state after the start of methimazole treatment, but plasma L-Selectin levels in patients with untreated Graves' disease were significantly lower than those in the patients in the first euthyroid state. There was no significant correlation between plasma P-Selectin levels and serum FT4 levels, nor between plasma P-Selectin levels and serum FT3 levels. These results suggested that thyroid hormones might reflect expression of P-, L- and E-Selectin from endothelial cells, or lymphocytes, or platelets in patients with Graves' disease.     

Stimulation of extracellular matrix components in the normal brain by invading glioma cells

Malignant gliomas are characterized by an extensive invasion of tumor cells into the normal brain parenchyma. A substantial amount of data indicates that cell movement in general is regulated by specific interactions between extracellular matrix components and specific cell-surface receptors. In the present work, multicellular spheroids from 4 human glioma cell lines (U-373Mg, A-172Mg, U-251Mg and HF-66) were confronted with normal rat brain cell aggregates in vitro, which resulted in a progressive invasion of tumor cells into the brain aggregates. The co-cultures were then sectioned and immuno-stained for specific extracellular matrix components (laminin, fibronectin and collagen type IV) and for specific cell-surface receptors which bind to these components (integrins beta1, beta4, alpha3, alpha6). In addition, flow-cytometric measurements and Northern blot analyses showed expression of several different integrins within the cell lines. The alpha3 subunit was expressed strongly in all cell lines. Whereas the beta1 subunit was expressed weakly in exponentially growing monolayer cultures, it showed a pronounced expression in multicellular spheroids, indicating that the integrin expression may vary depending on the micro-environment within a tumor. Furthermore, normal brain tissue was able to produce laminin when confronted with the glioma cells, which also was observed for fibronectin and collagen type IV. The relevance of our observations to the in vivo situation was investigated further by immuno-staining 5 human glioma biopsy samples for laminin. In some areas of the tumors, specific deposits of laminin were observed. In conclusion, we have shown that normal brain tissue has the ability to produce extracellular matrix components, such as laminin, collagen type IV and fibronectin, when confronted with invading glioma cells. Our results show that the glioma cells express specific integrins which can interact with these extracellular matrix components. Such interactions may facilitate tumor cell migration and invasion.     

Metabolism of the extracellular matrix formed by intervertebral disc cells cultured in alginate

STUDY DESIGN: Cells from normal rabbit nucleus pulposus (NP) and anulus fibrosus (AF) were cultured in alginate beads for as long as 14 days to allow them to reform a matrix made up of two compartments: the cell-associated matrix (CM) and further removed matrix (FRM). At different time points, the CM and FRM made by each cell population were analyzed using histologic, biochemical, and immunologic assays. OBJECTIVES: To study the metabolism of normal rabbit NP and AF cells in alginate by characterizing the CM and FRM formed by each cell population, and to identify metabolic properties that may shed light on mechanisms at play in disc degeneration. SUMMARY OF BACKGROUND DATA: Little is known about the metabolism of intervertebral disc cells, in part because of the lack of microculture systems appropriate for the study of these cells in vitro. In recent studies from our laboratories, it was suggested that articular chondrocytes cultured in alginate beads remain phenotypically stable and reform a matrix similar to the one they populate in vivo. This culture system appears ideally suited for the study of intervertebral cells available only in limited numbers. METHODS: Rabbit NP and AF cells released from the matrix by sequential enzyme digestion were encapsulated in alginate beads (20,000 cells/bead) and cultured for as long as 14 days. At selected time points, beads were solubilized with calcium chelating agents, and the CM and FRM were isolated. The rate of 35S-sulfate incorporation into proteoglycans, and the contents of various extracellular matrix molecules (total sulfated proteoglycans, antigenic keratan sulfate, hyaluronan, collagen, and pyridinium crosslinks) were measured. RESULTS: Both NP and AF cells remained phenotypically stable in the alginate gel throughout the culture period and reestablished a matrix composed of CM and FRM compartments. The two cell populations exhibited numerous differences in their metabolic activities in vitro. Nucleus pulposus cells synthesized fewer proteoglycan and collagen molecules and were less effective in incorporating these into the CM than AF cells. CONCLUSIONS: Intervertebral disc cells, especially NP cells, are extremely sluggish in reforming a CM, a protective shell rich in proteoglycans and collagen molecules. This may help explain why damage to the NP often is accompanied by progressive degeneration of the disc in vivo.     

Enhanced proliferation, apoptosis, and matrix accumulation by mesangial cells derived from HIV-1 transgenic mice

BACKGROUND: Mice, transgenic for HIV-1 genes, have been demonstrated to develop renal lesions mimicking HIV-associated nephropathy. Focal glomerulosclerosis (FGS) has been reported to be the predominant glomerular lesion in these animals. In the other models of FGS, the accumulation of mesangial matrix and mesangial cell proliferation have been shown to be the preceding abnormalities. We evaluated the proliferation, apoptosis, and matrix accumulation by mesangial cells derived from mice transgenic for HIV-1 genes as well as from nontransgenic mice. METHODS: Mesangial cells were cultured from mice transgenic for HIV-1 genes (HTrMC) and nontransgenic mice (NTrMC) of the same age and sex. The growth rate of HTrMC and NTrMC was determined under identical conditions. Morphologic evaluation of apoptosis was performed by staining cells with Hoechst (H)-33342 and propidium iodide. Accumulation of mesangial cell collagen type IV, laminin, and fibronectin was measured by the dot blot assay. Total RNA was extracted from HTrMC and NTrMC and Northern blots were generated. These blots were probed with specific probes for TGF-beta, proteoglycan (P16), and GAPDH. RESULTS: Mesangial cells (HTrMC) derived from transgenic mice had greater (P < 0.004) proliferation when compared to mesangial cells (NTrMCs) from nontransgenic mice (HTrMCs, 4.2 +/- 0.3 vs NTrMCs, 3.0 +/- 0.2 x 10(4) cells/well). HTrMCs also showed enhanced (P < 0.0001) apoptosis compared to NTrMCs (HTrMCs, 13.2 +/- 1.5% vs NTrMCs, 3.1 +/- 0.5% apoptotic cells/field). HTrMCs accumulated an increased (P < 0.02) amount of collagen type IV (HTrMCs, 5659.7 +/- 472.8 vs NTrMCs, 3882.2 +/- 339.7 ng/well); whereas NTrMCs accumulated a greater amount of laminin when compared to HTrMCs (HTrMCs, 12.8 vs NTrMCs, 29.6 +/- 2.9 ng/well). HTrMCs also showed an enhanced mRNA expression of TGF-beta and an attenuated expression of proteoglycan (P16). CONCLUSIONS: These results suggest that mesangial cells derived from mice transgenic for HIV-1 genes have enhanced proliferation and collagen accumulation. The enhanced expression of TGF-beta may have contributed to enhanced HTrMC proliferation and the accumulation of collagen. The present study provides the basis for a hypothesis that mesangial cells may be contributing to the development of focal glomerulosclerosis in mice transgenic for HIV-1 genes.     

Regulation of tissue plasminogen activator production in cultured human fetal mesangial cells

This study was designed to determine the persistence of culturable bacteria versus DNA in the presence of a middle ear effusion in a chinchilla model of otitis media. Cohorts of animals were either infected with an ampicillin-resistant Haemophilus influenzae strain or injected with a tripartite inoculum consisting of freeze-thawed Streptococcus pneumoniae; pasteurized Moraxella catarrhalis; and DNA from H influenzae. The H influenzae-infected animals displayed culture positivity and polymerase chain reaction positivity through day 35. In the chinchillas infected with the low-copy number inocula of S pneumoniae, DNA was not detectable after day 1 from the co-inoculated pasteurized M catarrhalis bacteria or the purified H influenzae DNA; however, amplifiable DNA from the live low-copy number bacteria persisted through day 21 even though they were not culture-positive past day 3. These results demonstrate that DNA, and DNA from intact but nonviable bacteria, does not persist in an amplifiable form for more than a day in the presence of an effusion; however, live bacteria, while not culturable, persist in a viable state for weeks.     

Radiation-induced alteration of rat mesangial cell transforming growth factor-beta and expression of the genes associated with the extracellular matrix

We hypothesized that the altered mesangial cell phenotype observed in radiation nephropathy reflects, at least partly, radiation-induced changes in expression of the genes associated with transforming growth factor-beta (TGF-beta) and extracellular matrix (ECM). To test this hypothesis, rat mesangial cells were used between passages 7 and 11 after primary isolation from glomeruli. Cells were placed in serum-free medium 24 h prior to irradiation and irradiated with single doses of 5-20 Gy 137Cs gamma rays; control cells received sham irradiation. After irradiation, the cells were maintained in serum-free medium for up to 48 h postirradiation. Total RNA was isolated, and Northern analysis was performed using cDNA probes for TGF-beta 1, beta 2 and beta 3 and several ECM genes. Irradiation resulted in isoform-specific alterations in TGF-beta mRNA; TGF-beta 1 levels showed a dose-independent increase 24-48 h postirradiation; TGF-beta 3 mRNA levels showed a progressive dose-independent decrease over the same period, decreasing to levels approximately 25% of those seen in controls. These changes were associated with a concomitant increase in levels of mRNA expressed by genes for the components of the ECM; no changes were observed in TGF-beta 2, collagen I, collagen III or decorin. Thus radiation can alter mesangial cell TGF-beta and the expression of the genes involved in ECM, although the nature of this alteration varies for the TGF-beta isoforms and specific ECM genes.     

SPARC is expressed by mesangial cells in experimental mesangial proliferative nephritis and inhibits platelet-derived-growth-factor-medicated mesangial cell proliferation in vitro

Mesangial cell proliferation is a characteristic feature of many glomerular diseases and often precedes extracellular matrix expansion and glomerulosclerosis. This study provides the first evidence that SPARC (secreted protein acidic and rich in cysteine) could be an endogenous factor mediating resolution of experimental mesangial proliferative nephritis in the rat. SPARC is a platelet-derived-growth-factor-binding glycoprotein that inhibits proliferation of endothelial cells and fibroblasts. We now show that SPARC is synthesized by mesangial cells in culture and that SPARC mRNA levels are increased by platelet-derived growth factor and basic fibroblast growth factor. Recombinant SPARC or the synthetic SPARC peptide 2.1 inhibited platelet-derived-growth-factor-induced mesangial cell DNA synthesis in vitro. In a model of experimental mesangioproliferative glomerulonephritis, SPARC mRNA was increased 5-fold by day 7 and was identified in the mesangium by in situ hybridization. Similarly, SPARC was increased in glomerular mesangial cells and visceral epithelial cells by day 5 and reached maximal expression levels by day 7. Mesangial cell proliferation increased by 36-fold on day 5 and decreased abruptly on day 7. Maximal expression of SPARC was correlated with the resolution of mesangial cell proliferation. We propose that SPARC functions in part as an endogenous inhibitor of platelet-derived-growth-factor-mediated mesangial cell proliferation in glomerulonephritis and that it could account for the resolution of cellular proliferation in this disease.     

Binding to human extracellular matrix by Neisseria meningitidis

Adhesion of Neisseria meningitidis strains to extracellular matrix (ECM) and purified matrix components was examined. Most strains bound to subendothelial ECM as well as to immobilized fibronectin and types I, III, and V collagen. Strains from healthy carriers adhered significantly better than isolates from patients. The binding site was localized to the central 75-kDa cell-binding domain of the fibronectin molecule. This domain has not been described previously to interact with bacterial structures.