The impact of gender on the progression of chronic renal disease

Observations in experimental animals and in humans have shown that the rate of progression of renal disease is influenced by gender. Deterioration of renal function in patients with chronic renal disease is more rapid in men than in women, independent of differences in blood pressure or serum cholesterol levels. In addition to genetically determined differences between the sexes in renal structure and function, sex hormones may directly influence many of the processes implicated in the pathogenesis of renal disease progression. Potential mechanisms include receptor-mediated effects of sex hormones on glomerular hemodynamics and mesangial cell proliferation and matrix accumulation as well as effects on the synthesis and release of cytokines, vasoactive agents, and growth factors. In addition, estrogens may exert potent antioxidant actions in the mesangial microenvironment, which may contribute to the protective effect of female gender.

Thrombospondin sequence motif (CSVTCG) is responsible for CD36 binding

To clarify the role of CD36 as a TSP receptor and to investigate the mechanisms of the TSP-CD36 interaction, transfection studies were performed using CD36-cDNA in a CDM8 plasmid. Jurkat cells transfected with CD36 cDNA express an 88kD membrane surface protein and acquire the ability to bind thrombospondin. The TSP amino acid sequence, CSVTCG, mediates the interaction of thrombospondin with CD36. CD36 transfectants but not control transfectants bind radiolabeled tyrosinated peptide (YCSVTCG). The hexapeptide inhibits thrombospondin expression on activated human platelets and results in diminished platelet aggregation. CSVTCG-albumin conjugates support CD36-dependent adhesion of tumor cells. We conclude that the CSVTCG repeat sequence is a crucial determinant of CD36 thrombospondin binding.

Effects of sex hormones on mesangial cell proliferation and collagen synthesis

In a variety of renal diseases, males progress at a more rapid rate and have a more fulminant course than females. This gender difference may be related to the direct effects of sex hormones on the cells of the kidney. To evaluate this hypothesis, we studied the effects of estrogens and testosterone on mesangial cell proliferation and collagen synthesis. At 48 hours, estradiol at 10 nM and 100 nM had a modest proliferative effect on cultured mesangial cells, as measured by 3H thymidine incorporation into DNA and direct cell counting. This estradiol effect was fully reversed by Tamoxifen (1 microM). Estradiol had no effect on cellular proliferation at 1 microM concentrations, but suppressed proliferation at 10 microM doses. Testosterone had a modest but statistically insignificant effect on proliferation at 10 nM and 100 nM concentrations but no effect at 1 microM or 10 microM. Neither estradiol nor testosterone at 10 microM affected total cellular protein accumulation. Estradiol at 1 microM and 10 microM, markedly suppressed total collagen synthesis as measured by 3H proline incorporation, and specifically suppressed the synthesis of collagen types I and IV, as measured by immunoprecipitation and gel electrophoresis. Testosterone did not affect collagen synthesis. Estradiol also reduced the steady state message for the alpha 2 chain of type I collagen, while testosterone had no effect. Neither estradiol nor testosterone affected the steady state message for TGF beta or EGF. The direct effects of estradiol on mesangial cell collagen generation may help explain the slower development of glomerulosclerosis in women and therefore the "protective" effect of female gender on the progression of renal disease.

Sex hormones and renal nitric oxide synthases

The present study was undertaken to determine whether sex hormones influence nitric oxide synthase levels in the kidney. Five groups of rats were studied: males, castrated males, females, oophorectomized females, and oophorectomized females receiving estradiol replacement therapy. Endothelial nitric oxide synthase (eNOS) levels in the kidney were measured by Western blotting. eNOS levels were significantly greater in the renal medulla of female rats compared with male rats (3545 +/- 473 versus 2418 +/- 205 densitometry units (DU), P < 0.05). Oophorectomy reduced renal medullary eNOS levels to that of intact male rats (2566 +/- 304 DU, P = NS). Estrogen replacement therapy significantly increased medullary eNOS levels in oophorectomized animals (3249 +/- 377 versus 2302 +/- 213 DU, P < 0.05). Renal inducible nitric oxide synthase (iNOS) levels were measured after induction with lipopolysaccharide. iNOS levels were significantly greater in the renal medulla of female rats compared with male rats (677 +/- 253 versus 252 +/- 12 DU, P < 0.05). Oophorectomy reduced renal medullary iNOS levels to that of intact male rats (295 +/- 57 DU, P = NS). In contrast, estrogen replacement therapy significantly increased medullary iNOS levels in oophorectomized animals (682 +/- 356 versus 160 +/- 92 DU, P < 0.05). Steady-state levels of mRNA for iNOS were found to be higher in the inner medulla of female rats compared with male rats (1519 +/- 211 versus 899 +/- 105 DU, P < 0.05). In contrast to these findings, sex hormones failed to influence nitric oxide production or iNOS levels in lipopolysaccharide-stimulated mesangial cells in culture. These results suggest that gender may influence renal medullary synthesis of nitric oxide.

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.

Selective estrogen receptor modulators suppress mesangial cell collagen synthesis

Estrogen receptor modulators (SERMs) are "designer drugs" that exert estrogen-like actions in some cells but not in others. We examined the effects of the SERMs LY-117018 (an analog of raloxifene) and tamoxifen on mesangial cells synthesis of type I and type IV collagen. We found that LY-117018 and tamoxifen suppressed mesangial cell type IV collagen gene transcription and type IV collagen protein synthesis in a dose-dependent manner, with a potency identical to that of estradiol. Type I collagen synthesis was also suppressed by LY-117018 in a dose-dependent manner with a potency identical to that of estradiol but greater than that of tamoxifen. Genistein, which selectively binds to estrogen receptor-beta in nanomolar concentrations, suppressed type I and type IV collagen synthesis, suggesting that estrogen receptor-beta mediates the effects of estrogen on collagen synthesis. Because matrix accumulation is central to the development of glomerulosclerosis, second-generation SERMs may prove clinically useful in ameliorating progressive renal disease without the adverse effects of estrogen on reproductive tissues.

Protein kinase CK2 mediates TGF-beta1-stimulated type IV collagen gene transcription and its reversal by estradiol

BACKGROUND

We have previously shown that the transcription factor Sp1 mediates the stimulatory effects of transforming growth factor-beta1 (TGF-beta1) on type IV collagen gene transcription and protein synthesis, and that estradiol reverses these effects by down-regulating Sp1 activity. Protein kinase casein kinase II (CK2) phosphorylates Egr-1 and prevents its binding to Sp1. We hypothesized that TGF-beta1 stimulates CK2 activity, which in turn activates type IV collagen gene transcription via increased availability of free Sp1.

METHODS

The effects of TGF-beta1 and of estradiol on murine mesangial cell type IV collagen gene transcription were measured using a reporter mini gene construct and on collagen IV protein synthesis by Western blotting. Nuclear Egr-1, phosphorylated Egr-1, Sp1, Egr-1/Sp1 complexes and unbound Sp1 were measured using co-immunoprecipitation and Western blotting techniques.

RESULTS

TGF-beta1 stimulated CK2 activity in murine mesangial cells. Although TGF-beta1 failed to alter total Egr-1 protein, it increased phosphorylated Egr-1. This led to decreased Egr-1/Sp1 complex formation, increased unbound Sp1, increased binding of nuclear extracts to the collagen IV promoter, and increased type IV collagen gene transcription and protein synthesis. Physiologic concentrations of estradiol reversed these effects.

CONCLUSIONS

These studies suggest that activation of CK2 mediates the stimulatory effect of TGF-beta1 on type IV collagen gene transcription. Moreover, the ability of estradiol to reverse TGF-beta1-stimulated type IV collagen synthesis is mediated by down-regulating CK2 activity, which ultimately limits the availability of unbound Sp1 to activate gene transcription.

Glomerulosclerosis in aging humans is not influenced by gender

Aging male rats develop progressive glomerulosclerosis, proteinuria, and loss of renal function, whereas females are remarkably resistant to the development of these abnormalities. Although sex hormones appear to contribute to gender-related differences in the development of glomerulosclerosis in aging rats, it is not clear that sexual dimorphism characterizes glomerular obsolescence in aging humans. To study this question further, the glomerular histology of males and females ranging in age from infancy to 90 years was compared in 250 autopsy specimens. We found no differences between the sexes in the development of glomerulosclerosis in aging humans. These data disprove the hypothesis that testosterone is an important factor contributing to progressive glomerulosclerosis in aging men. Conversely, any renoprotective effects of estrogen would be limited by the onset of menopause because significant glomerulosclerosis did not develop until after the age of 50 years.

Estradiol suppresses type I collagen synthesis in mesangial cells via activation of activator protein-1

BACKGROUND

Estradiol suppresses the synthesis of type I collagen by murine mesangial cells. However, neither the alpha 1(I) nor the alpha 2(I) collagen gene contains an estrogen-response element. Because estradiol modulates the transcription of several genes that lack an estrogen-response element but contain a regulatory activator protein-1 (AP-1) binding motif, we hypothesized that AP-1 may mediate estradiol-induced suppression of type I collagen synthesis.

METHODS

We measured type I collagen synthesis in murine mesangial cells exposed to estradiol, phorbol 12-myristate 13-acetate (an activator of AP-1), or curcumin (an inhibitor of AP-1). We also assessed the effects of estradiol on the steady-state level of c-fos and c-jun mRNA and on the binding of mesangial cell nuclear extracts to an AP-1 consensus binding site oligonucleotide.

RESULTS

Estradiol (10(-10) M to 10(-7) M) suppressed type I collagen synthesis by murine mesangial cells in a dose-dependent manner (10(-7) M, 43.7 +/- 8.2% of control values, P < 0.001). Phorbol 12-myristate 13-acetate (10 microM, four-hr exposure) also decreased type I collagen in the media. In contrast, curcumin (1 microM) increased type I collagen. Estradiol increased the steady-state level of c-fos mRNA twofold at 30 minutes, with a return to basal levels at one hour. This was associated with a greater than threefold increase in the binding of nuclear extracts from estradiol-treated mesangial cells to an AP-1 consensus binding site oligonucleotide. Estradiol-enhanced binding of nuclear extracts to the AP-1 oligonucleotide was reversed by cycloheximide.

CONCLUSIONS

These data suggest that estradiol suppresses collagen I synthesis by murine mesangial cells via enhanced AP-1 activity.

Effects of sex hormones on mesangial cells

Male gender is associated with a more rapid progression of chronic renal disease. In various experimental models of renal injury, manipulation of the hormonal milieu can replicate the effects of gender on the course of renal disease. These observations suggest that sex hormones per se may be important determinants of the greater susceptibility of the male kidney to progressive renal injury. Sex hormones may influence many of the processes implicated in the pathogenesis of renal disease progression, including cell proliferation and the synthesis and degradation of collagen and proteoglycans. In addition, sex hormones may indirectly influence these processes by modulating the synthesis and release of vasoactive agents, cytokines, and other growth factors, which in turn are capable of altering mesangial cell function. Finally, estrogens also exert potent antioxidant effects that may contribute to the protective effect of female gender on the course of renal disease.

Estradiol suppresses mesangial cell type I collagen synthesis via activation of the MAP kinase cascade

We have previously shown that estradiol suppresses the synthesis of type I collagen by murine mesangial cells grown in the presence of serum via activation of the transcription factor activator protein-1 (AP-1). We hypothesized that estradiol upregulates AP-1 via activation of the mitogen-activated protein (MAP) kinase cascade, a signal transduction pathway that regulates AP-1 activity. Estradiol (10(-10) to 10(-7) M) upregulated the MAP kinase pathway in murine mesangial cells grown in the presence of serum in a dose-dependent manner. Activation was evident by 1 min, peaked at 10 min, and was completely dissipated by 2 h. In contrast, estradiol had no significant effect on total (phosphorylated + unphosphorylated) p44 extracellular signal-related protein kinase (ERK) or p42 ERK. Nuclear extracts isolated from mesangial cells treated with estradiol showed increased binding to a consensus sequence AP-1 binding oligonucleotide in gel shift assays. In contrast, nuclear extracts from cells exposed to PD-98059, a highly selective inhibitor of MAP kinase-ERK kinase 1 (MEK1) and MEK2, showed reduced binding. In addition, PD-98059 antagonizes the enhanced binding induced by estradiol. Estradiol (10(-9) M) suppressed mesangial cell type I collagen synthesis (37.8 +/- 2.4%, expressed as a percentage of control values, P < 0.001 vs. control). In contrast, PD-98059 increased type I collagen synthesis (344.6 +/- 98.8, P < 0.01) and reversed the suppression of type I collagen synthesis induced by estradiol. The effects of estradiol, PD-98059, and PD-98059 plus estradiol on type I collagen protein synthesis were closely paralleled by their effects on steady-state levels of mRNA for the alpha(1) chain of type I collagen. These data suggest that estradiol suppresses type I collagen synthesis via upregulation of the MAP kinase cascade, leading to stimulation of AP-1 activity.

The effect of donor gender on renal allograft survival

Donor gender plays a role in the outcome of renal transplantation, but the mechanisms responsible for this effect are unclear. In this study, actuarial graft survival in 1049 recipients transplanted at Montefiore Medical Center between 1979 and 1994 was examined. It was found that donor gender had no influence on graft survival in recipients treated with precyclosporine immunosuppressive agents. In contrast, graft survival time was greater in cyclosporine-treated recipients of male donor kidneys compared with female kidneys (p < 0.05). This survival time difference was evident in the early post-transplant period and was entirely accounted for by the survival advantage of kidneys from white male donors. There was no gender-related difference in graft survival time among recipients of African-American donor kidneys. Recent attention has focused on the hypothesis that a mismatch between female donor kidney nephron supply and male recipient functional demand results in hyperfiltration-mediated glomerular injury and that this is responsible for reduced survival time of female allografts. Any hypothesis purporting to explain gender-related differences in graft survival time must take into account this study's observations that the donor-gender effect was observed only in cyclosporine-treated recipients, was not seen in African-American donors, appeared soon after renal transplantation, and did not increase progressively with time. These observations are most consistent with the hypothesis that gender-related differences in graft survival time may reflect differences in susceptibility to cyclosporine nephrotoxicity or differences in the therapeutic response to cyclosporine.

Estradiol reverses TGF-beta1-stimulated type IV collagen gene transcription in murine mesangial cells

We have previously shown that estradiol suppresses types I and IV collagen synthesis by mesangial cells grown in the presence of serum. In the present study, we examined the interaction between estradiol and transforming growth factor-beta (TGF-beta) on collagen IV synthesis. In a luciferase reporter gene construct containing the type IV collagen promoter and 1-chain regulatory sequences, we found that TGF-beta1 (2 ng/ml) stimulated alpha1-collagen IV gene transcription in serum-free media (140.5 +/- 6.2 relative luciferase units, expressed as a percent of control untreated cells, P < 0.001). Estradiol reversed the stimulatory effects of TGF-beta1 on reporter gene transcription in a dose-dependent manner [for 2.5 x 10(-9) M, 114.2 +/- 0.2, P < 0.002 vs. TGF-beta1; for 10(-7) M, 89.5 +/- 4.0, P < 0.001 vs. TGF-beta1 and P = not significant (NS) vs. control]. Using immunoprecipitation techniques, we found that estradiol (10(-7) M) reversed TGF-beta1-stimulated type IV collagen synthesis (175.3 +/- 14.7 vs. 111.6 +/- 7.1, expressed as a percent of control untreated cells, P < 0.001) but did not affect TGF-beta1-stimulated type I collagen synthesis (166.9 +/- 18.8 vs. 162.2 +/- 16.2, P = NS). These results were confirmed with Western blotting. Nuclear extracts from mesangial cells treated with TGF-beta1 showed increased binding to a Sp1 consensus binding sequence oligonucleotide and to an Sp1 binding site in the collagen IV promoter. Estradiol reversed this enhanced binding. These data suggest that estradiol antagonizes TGF-beta1-stimulated type IV collagen synthesis at a transcriptional level and that this effect may be mediated by interactions with the transcription factor Sp1.

Hypervitaminosis A in two hemodialysis patients

We present two cases of hemodialysis patients developing vitamin A toxicity related to excessive consumption of nutritional supplements containing large quantities of vitamin A. In one patient, severe hypercalcemia was the lone presenting sign; in the other, hypercalcemia was associated with unusual neurologic manifestations. We will discuss the reason why hemodialysis patients are at special risk for the development of hypervitaminosis A and review the mechanism leading to the associated hypercalcemia.

Serum-stimulated alpha 1 type IV collagen gene transcription is mediated by TGF-beta and inhibited by estradiol

We examined the hypothesis that fetal calf serum (FCS) stimulates murine mesangial cell alpha 1 type IV collagen (COL4A1) gene transcription by increasing autocrine production of transforming growth factor-beta (TGF-beta) through a platelet-derived growth factor (PDGF)-dependent mechanisms. PDGF-stimulated COL4A1 gene transcription was inhibited by neutralizing antibody to TGF-beta (119.3 +/- 3.6 vs. 106.0 +/- 6.2 relative luciferase units, expressed as a percentage of control untreated cells, P < 0.003). FCS-stimulated gene transcription was inhibited by neutralizing antibody to PDGF (148.3 +/- 4.1 vs. 136.7 +/- 0.3 relative luciferase units, P < 0.002) and by neutralizing antibody to TGF-beta (148.3 +/- 4.1 vs. 127.1 +/- 3.4 relative luciferase units, P < 0.036). The inhibitory effect of combined treatment with anti-PDGF and anti-TGF-beta antibody on gene transcription was no greater than that of anti-TGF-beta antibody alone [129.5 +/- 0.53 vs. 127.1 +/- 3.4 relative luciferase units, P = not significant (NS)]. FCS-stimulated gene transcription was also inhibited by estradiol (10(-7) M) (148.4 +/- 3.1 vs. 119.4 +/- 8.1 relative luciferase units, P < 0.019). In the presence of estradiol, anti-TGF-beta antibody failed to further reduce serum-stimulated gene transcription (119.4 +/- 8.1 vs. 115.6 +/- 9.8, P = NS), suggesting that estradiol reverses FCS-stimulated COL4A1 gene transcription by antagonizing the actions of TGF-beta. Measurement of type IV collagen synthesis by Western blotting confirmed that the intact gene responded in a manner analogous to the promoter construct.

The effect of glucose on proteoglycans produced by cultured mesangial cells

Altered proteoglycan metabolism may play a role in the development of diabetic glomerulopathy. This study was conducted to examine the effects of glucose on the production and physical characteristics of proteoglycans generated by rat mesangial cells in culture. Rat mesangial cells were exposed to elevated glucose media (500 mg/dl) or standard glucose media (200 mg/dl) for 8-10 days, and proteoglycan synthesis was determined using 35S-labeling in conjunction with anion exchange and sizing chromatography. Rat mesangial cells generated predominantly chondroitin/dermatan sulfate proteoglycans, with small amounts of heparan sulfate proteoglycans. High glucose did not alter the number of rat mesangial cells after 24 h or after 8-10 days, compared with cells grown under standard glucose conditions. The total amount of glycosaminoglycan generated and the sizes of the major proteoglycans were not different between cultures grown in standard and elevated glucose medium. Levels of mRNA for the proteoglycan, biglycan (as assessed by Northern blot analysis), also were comparable between the standard and elevated glucose conditions. Exposure to media high in glucose did not change the rate of secretion of proteoglycans from the cell layer to the medium, but did result in a greater quantity of radiolabeled proteoglycan deposited in the extracellular matrix. The cell, extracellular matrix and medium proteoglycans isolated from the elevated glucose cultures, consistently eluted from the anion exchange column at a lower [NaCl] compared with those generated under standard glucose conditions, indicating a loss of anionic charges.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of sex hormones on fluid and solute transport in Madin-Darby canine kidney cells

Polycystic kidney disease progresses more rapidly in men than in women. To investigate the basis for this sexual dimorphism, we exposed Madin-Darby canine kidney (MDCK) cells grown on collagen-coated cell culture inserts to control media, or to estradiol or testosterone (1 nM-1 microM). Compared to control and estradiol-treated cells, testosterone stimulated fluid secretion in a dose-dependent manner, enhancing fluid secretion 4.8-fold at 1 nM and 19.7-fold at 1 microM (0.59 +/- 0.18 vs. 0.03 +/- 0.01 microliter/cm2/hr, P < 0.001). Chloride transport paralleled fluid secretion. Testosterone increased cellular cyclic AMP levels 3.2-fold at 1 nM and 12.3-fold at 1 microM (81.3 +/- 30.7 vs. 6.6 +/- 3.3 pmol/mg protein, P < 0.001). GDP beta S (500 microM), an inhibitor of Gs, and 2',3'-dideoxyadenosine (10 microM), an inhibitor of the catalytic subunit of adenylate cyclase, suppressed testosterone-induced fluid and solute secretion. Neither testosterone nor estradiol had any effect on microsomal Na,K-ATPase activity, cellular proliferation or cellular total protein content. Our studies show that testosterone stimulates fluid secretion and solute transport by MDCK cells by increasing cAMP generation. In vivo, testosterone may contribute to cyst expansion by enhancing fluid secretion. This observation may help explain the worse prognosis of polycystic kidney disease observed in men.

Combined antihypertensive and lipid-lowering therapy in experimental glomerulonephritis

We examined the interrelation between systemic hypertension, hyperlipidemia, and progressive renal injury in experimental glomerulonephritis. Induction of nephrotoxic serum nephritis in Sprague-Dawley rats led to systemic hypertension and hyperlipidemia. Four groups of rats were studied over a 16-week period: (1) untreated nephritic rats; (2) nephritic rats treated with hydralazine, reserpine, and lasix (AH); (3) nephritic rats treated with lovastatin (4 mg/kg) (Lova); and (4) nephritic rats treated with combined antihypertensive/lipid-lowering therapy (AH/Lova). Systolic blood pressure rose progressively in untreated rats (152 +/- 4 mm Hg at 16 weeks). Blood pressure was reduced by antihypertensive therapy (P < .001) (108 +/- 2 mm Hg in the AH group and 111 +/- 3 mm Hg in the AH/Lova group) but remained elevated in animals treated with lovastatin alone (P > .05) (156 +/- 3 mm Hg in the Lova group). Serum cholesterol rose progressively in untreated rats (3.70 +/- 0.85 mmol/L [143 +/- 33 mg/dL] at 16 weeks). The rise in serum cholesterol was prevented by lovastatin therapy (P < .001) (2.22 +/- 0.41 mmol/L [86 +/- 16 mg/dL] in the Lova group and 2.09 +/- 0.52 mmol/L [81 +/- 2 mg/dL] in the AH/Lova group) but not antihypertensive therapy (P > .05) (2.92 +/- 0.65 mmol/L [113 +/- 25 mg/dL] in the AH group). Proteinuria was reduced by antihypertensive therapy (P < .001) and lipid-lowering therapy (P < .05) (16-week values: 1.069 +/- 0.167 g/d in untreated rats, 0.663 +/- 0.164 g/d in the Lova group, 0.392 +/- 0.051 g/d in the AH group, and 0.176 +/- 0.035 g/d in the AH/Lova group).(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Glomerular macrophages in nephrotoxic serum nephritis are activated to oxidize low-density lipoprotein

Studies were undertaken to investigate the hypothesis that infiltrating glomerular macrophages in experimental glomerulonephritis are activated to produce oxygen-free radicals that are capable of enhancing oxidation of low-density lipoprotein (LDL). Low-density lipoprotein oxidation was assessed by increased electrophoretic mobility on agarose gel electrophoresis and by the generation of thiobarbituric acid-reactive substances. Lipoprotein uptake, degradation, and re-esterification by macrophages were assessed by measuring 14C-oleic acid incorporation into cholesteryl oleate. Both peritoneal and glomerular macrophages have the ability to oxidize LDL to a form showing increased mobility on agarose gel electrophoresis. However, LDL incubated with glomerular macrophages underwent greater oxidation, resulting in increased generation of thiobarbituric acid-reactive substances (15.1 +/- 1.2 nmol malondialdehyde/mg LDL protein v 7.2 +/- 2.1 nmol malondialdehyde/mg LDL protein; P < 0.01). In addition, glomerular macrophages modified LDL to a form that greatly enhanced cellular synthesis of cholesteryl oleate compared with peritoneal macrophage-modified LDL (30 +/- 11 pmol/10(6) cells/hr v 10 +/- 4 pmol/10(6) cells/hr; P < 0.01). Superoxide dismutase, a scavenger of superoxide anion, inhibited macrophage-mediated oxidation of LDL. These results suggest that glomerular macrophages from nephritic rats are activated to modify LDL to a form avidly taken up by macrophage scavenger receptors. Thus, enhanced formation of oxidized LDL by infiltrating glomerular macrophages may contribute to glomerular injury in nephrotoxic serum nephritis.

Defective glomerular beta-adrenergic signal transmission in spontaneously diabetic rats

Previous studies in experimental diabetes have demonstrated cardiovascular abnormalities of the beta-adrenergic system and reduced adrenergically stimulated renal renin secretion. To examine the defect in the beta-adrenergic signal, glomerular cyclic adenosine monophosphate (cAMP) levels were measured in response to isoproterenol and other humoral agonists (coincubated with the phosphodiesterase inhibitor isomethylxanthine) in nondiabetic and diabetic BB/Wor rats. Basal (unstimulated) levels of glomerular cAMP did not differ between control and diabetic BB/Wor rats, nor did cAMP accumulation differ on incubation with the humoral agonists PGE2 and histamine. However, on incubation with varied concentrations of the nonselective beta-adrenergic agonist isoproterenol, control glomeruli demonstrated a twofold increase in cAMP while a negligible response was observed in diabetic glomeruli. Peak levels of cAMP were higher in control (192 +/- 24 pmol/mg protein) than in diabetic (141 +/- 8 pmol/mg protein) glomeruli (p < 0.01). No differences were observed on incubation with the adenylate cyclase stimulator forskolin. Measurement of glomerular beta-adrenoreceptors by coincubation with iodine 125-labeled cyanopindolol demonstrated no differences in either receptor number (Bmax) or affinity (KD). These data indicate that a specific defect in beta-adrenergic signalling exists in glomerular tissue from spontaneously diabetic rats. Because no decrease in forskolin-stimulated adenylate cyclase was observed, defective coupling of the receptor to its effector, perhaps through the guanine nucleotide stimulatory protein, may account for these observations.

Estradiol inhibits mesangial cell-mediated oxidation of low-density lipoprotein

It has been suggested that hyperlipidemia may contribute to the progression of renal disease via the deleterious effects of oxidized low-density lipoprotein (LDL) on the glomerular mesangium. Because estrogens possess potent antioxidant activity, we sought to determine whether sex hormones influence the oxidation of LDL by mesangial cells. Rat mesangial cells were incubated with LDL (200 micrograms/ml), and the extent of lipid oxidation was assessed by the generation of thiobarbituric acid reactive substances (TBARS), by increased electrophoretic mobility, and by enhanced uptake of mesangial cell-modified LDL by macrophages. A progressive rise in TBARS and an increase in electrophoretic mobility was observed on incubation of LDL with mesangial cells. Coincubation with estradiol (10 mumol/L) reduced TBARS generation by 46% at 36 hours (p < 0.01) and reversed the increase in relative electrophoretic mobility (1.25 +/- 0.07 vs 1.01 +/- 0.03, p < 0.05). LDL that had been oxidized by mesangial cells in the presence of estradiol (10 mumol/L) showed reduced uptake by macrophages when compared with LDL that had been oxidized by mesangial cells in the absence of estradiol (14 +/- 2 pmol/10(6) cells per hour vs 22 +/- 3 pmol/10(6) cells per hour, p < 0.05). In contrast, neither testosterone nor estrone had any effect on these parameters. We conclude that estradiol, by virtue of its antioxidant properties, inhibits mesangial cell-mediated oxidation of LDL and reduces the uptake of mesangial cell-modified LDL by macrophages.

Cellular attachment to thrombospondin. Cooperative interactions between receptor systems

Tumor cell attachment to thrombospondin (TSP) in the extracellular matrix may be of critical importance in the processes of invasion and hematogenous dissemination. To determine the specific receptor systems that mediate the interaction of tumor cells with insoluble TSP, the attachment of HT1080 fibrosarcoma and C32 and G361 melanoma cells to TSP-coated discs was studied in the presence of heparin, Arg-Gly-Asp-Ser, or antibodies to glycoprotein (GP) IV (CD36, GPIIIb), a TSP receptor. HT1080 and C32 cell attachment to TSP was inhibited by the combination of heparin and a monoclonal (or polyclonal) antibody to GPIV but not by either alone. Heparin alone inhibited cell spreading. Neither control monoclonal antibodies nor the cell attachment peptide Arg-Gly-Asp-Ser inhibited tumor cell attachment to TSP, alone or in the presence of heparin. HT1080 cells attached equally as well to a 140-kDa proteolytic TSP fragment lacking the heparin-binding domain as to intact TSP. A monoclonal antibody to GPIV alone inhibited tumor cell attachment to the heparin-domainless 140-kDa TSP fragment. No attachment to the heparin-binding fragment was observed, but the addition of the heparin fragment to 140-kDa heparin-domainless TSP restored the heparin sensitivity of binding. G361 cells that lack GPIV attached well to TSP but were not inhibited by heparin or anti-GPIV alone or in combination. The combination of heparin and Arg-Gly-Asp-Ser inhibited G361 attachment to TSP. These studies suggest that tumor cells may utilize separate receptor systems in a cooperative manner to adhere to TSP. HT1080 fibrosarcoma and C32 melanoma cells utilize GPIV in concert with a heparin-modulated binding systems to attach and spread on TSP. G361 cells, which lack GPIV expression, attach and spread on TSP using an integrin system as well as a heparin-modulated system.