Lysophosphatidylcholine activates mesangial cell PKC and MAP kinase by PLCgamma-1 and tyrosine kinase-Ras pathways.

Although lysophosphatidylcholine (LPC)-mediated cellular responses are attributed to the activation of protein kinase C (PKC), relatively little is known about the upstream signaling mechanisms that regulate the activation of PKC and downstream mitogen-activated protein (MAP) kinase. LPC activated p42 MAP kinase and PKC in mesangial cells. LPC-mediated MAP kinase activation was inhibited (but not completely) by PKC inhibition, suggesting additional signaling events. LPC stimulated protein tyrosine kinase (PTK) activity and induced Ras-GTP binding. LPC-induced MAP kinase activity was blocked by the PTK inhibitor genistein. Because LPC increased PTK activity, we examined the involvement of phospholipase Cgamma-1 (PLCgamma-1) as a key participant in LPC-induced PKC activation. LPC stimulated the phosphorylation of PLCgamma-1. PTK inhibitors suppressed LPC-induced PKC activity, whereas the same had no effect on phorbol 12-myristate 13-acetate-mediated PKC activity. Other lysophospholipids [e.g., lysophosphatidylinositol and lysophosphatidic acid (LPA)] also induced MAP kinase activity, and only LPA-induced MAP kinase activation was sensitive to pertussis toxin. These results indicate that LPC-mediated PKC activation may be regulated by PTK-dependent activation of PLCgamma-1, and both PKC and PTK-Ras pathways are involved in LPC-mediated downstream MAP kinase activation.

Oxidized low-density lipoprotein stimulates monocyte adhesion to glomerular endothelial cells.

BACKGROUND: Abnormalities in lipid and lipoprotein metabolism have been implicated in the pathogenesis of glomerulosclerosis. Atherogenic lipoproteins [for example, low-density lipoprotein (LDL) and oxidized LDL (ox-LDL)] have been shown to stimulate glomerular monocyte chemoattractants involved in monocyte infiltration. However, the role of LDL and ox-LDL in the early monocyte adhesion to glomerular endothelial cells (ECs) and associated intracellular signaling mechanisms are not clearly understood. METHODS: In this study, we examined the effect of LDL and ox-LDL on intracellular signaling mechanisms associated with monocyte adhesion to glomerular ECs and intercellular adhesion molecule-1 (ICAM-1) expression. RESULTS: Ox-LDL, but not LDL, stimulated EC ICAM-1 expression and monocyte adhesion. Ox-LDL elevated protein tyrosine kinase (PTK) activity, and the preincubation of ECs with specific PTK inhibitors blocked ox-LDL-induced ICAM-1 message and monocyte adhesion. Whereas experimental maneuvers that inhibit either protein kinase C activation (by PKC depletion or with inhibitors) or Gi-protein-mediated pathways (pertussis toxin sensitive) had no effect on ox-LDL-induced monocyte adhesion and ICAM-1 expression. cAMP-elevating compounds did not induce ICAM-1 or monocyte adhesion. CONCLUSIONS: The data indicate that ox-LDL, by stimulating monocyte adhesion to the glomerular endothelium, may regulate monocyte infiltration within the glomerulus, supporting an early pathobiological role for atherogenic lipoproteins in glomerular injury. The results suggest that the activation of specific PTK and associated signaling may, at least in part, play a critical role in ox-LDL-mediated endothelial-monocyte interaction-related events. The data suggest that the interventions aimed at modifying associated intracellular signaling events within the glomerulus may provide potential therapeutic modalities in monocyte/macrophage-mediated glomerular disease.

Effect of inhibition of cholesterol synthetic pathway on the activation of Ras and MAP kinase in mesangial cells.

Intermediary metabolites of cholesterol synthetic pathway are involved in cell proliferation. Lovastatin, an inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase, blocks mevalonate synthesis, and has been shown to inhibit mesangial cell proliferation associated with diverse glomerular diseases. Since inhibition of farnesylation and plasma membrane anchorage of the Ras proteins is one suggested mechanism by which lovastatin prevents cellular proliferation, we investigated the effect of lovastatin and key mevalonate metabolites on the activation of mitogen-activated protein kinase (MAP kinase) and Ras in murine glomerular mesangial cells. The preincubation of mesangial cells with lovastatin inhibited the activation of MAP kinase stimulated by either FBS, PDGF, or EGF. Mevalonic acid and farnesyl-pyrophosphate, but not cholesterol or LDL, significantly prevented lovastatin-induced inhibition of agonist-stimulated MAP kinase. Lovastatin inhibited agonist-induced activation of Ras, and mevalonic acid and farnesylpyrophosphate antagonized this effect. Parallel to the MAP kinase and Ras data, lovastatin suppressed cell growth stimulated by serum, and mevalonic acid and farnesylpyrophosphate prevented lovastatin-mediated inhibition of cellular growth. These results suggest that lovastatin, by inhibiting the synthesis of farnesol, a key isoprenoid metabolite of mevalonate, modulates Ras-mediated cell signaling events associated with mesangial cell proliferation.

Oxidative modification of low-density lipoprotein enhances mesangial cell protein synthesis and gene expression of extracellular matrix proteins.

The proliferation of intrinsic glomerular cells and the accumulation of extracellular matrix proteins are principal histopathological features seen in glomerular injury. Because of the marked similarity between the cellular and molecular events that occur in both atherosclerosis and glomerulosclerosis and the commonly accepted hypothesis that lipoproteins are implicated in the pathogenesis of glomerulosclerosis, we examined the effect of three atherogenic lipoproteins, low-density lipoprotein (LDL), oxidized (ox)-LDL, and minimally modified (mm)-LDL on the synthesis and secretion of extracellular matrix (ECM) proteins by mesangial cells. The incubation of SV-40 transformed murine mesangial cells with LDL (25-100 microg/ml) increased the synthesis and secretion of both fibronectin and laminin in a dose-dependent manner. Similarly, oxidized forms of LDL (25-100 micro/ml) increased fibronectin and laminin synthesis and secretion dose dependently. However, both oxidatively modified forms of LDL had a greater effect on increasing ECM protein synthesis than their native counterpart. Northern blot analysis showed a dose-dependent increase in mRNA transcripts for fibronectin and laminin in response to the incubation of mesangial cells with LDL, ox-LDL, and mm-LDL. Similar to the ECM protein expression data, the oxidatively modified forms of LDL had more pronounced effects on the gene expression of both fibronectin and laminin. These data show that both LDL and, perhaps more importantly, its oxidatively modified forms stimulate mesangial cells to upregulate both the gene expression and synthesis and secretion of ECM proteins, supporting a role for atherogenic lipoproteins in the pathobiology of glomerular injury.

Atherogenic lipoproteins enhance mesangial cell expression of platelet-derived growth factor: role of protein tyrosine kinase and cyclic AMP-dependent protein kinase A.

Mesangial cell proliferation and extracellular matrix accumulation are fundamental in the pathogenesis of glomerulosclerosis. Platelet-derived growth factor (PDGF) is a major cytokine involved in mesangial cell proliferation, and its increased expression is seen in glomerular injury. Atherogenic lipoproteins stimulate mesangial cell proliferation and induce glomerular injury in experimental animals. We examined the effect of low-density lipoprotein (LDL) and its more atherogenic oxidized forms, minimally modified LDL (mm-LDL) and oxidized LDL (ox-LDL) on mesangial cell PDGF mRNA expression. Incubation with 2.5 to 25 microg/ml LDL or mm-LDL for 1 to 4 hours stimulated mesangial cell PDGF mRNA expression (mm-LDL 2 to 3 times greater than LDL); ox-LDL had no effect. Similarly, both LDL and mm-LDL induced mesangial cell DNA synthesis (mm-LDL 1.5 to 2 times greater). In further studies evaluating key associated intracellular signal transduction mechanisms, the protein tyrosine kinase (PTK) inhibitors herbimycin and genistein markedly decreased basal and lipoprotein-induced PDGF mRNA expression. Both pertussis toxin and isoproterenol, cyclic AMP-generating substances, stimulated PDGF mRNA expression. Preincubation with H-8 or H-89, cyclic AMP-dependent protein kinase A (PKA) inhibitors, blocked the lipoprotein-induced PDGF message, whereas preincubation with calphostin C, a protein kinase C inhibitor, did not alter LDL- or mm-LDL-mediated PDGF mRNA expression. These data suggest that the accumulation of atherogenic lipoproteins and their endogenous oxidized forms within the glomerulus may regulate mesangial cell PDGF expression and related cellular responses. These events appear to be modulated by signal transduction pathways involving PTK and PKA.

Atherogenic lipoproteins stimulate mesangial cell p42 mitogen-activated protein kinase.

Previously, it has been shown that atherogenic lipoproteins, through the activation of glomerular cells, stimulate pathobiological processes involved in monocyte infiltration into the mesangium. This study examined the role of LDL and its oxidatively modified variants (mildly oxidatively modified LDL [mm-LDL] and oxidatively modified LDL [ox-LDL]) on the activation of mesangial cell p42 mitogen-activated protein kinase (MAP kinase), a key intracellular signaling mechanism associated with cell proliferation. The incubation of mesangial cells with either LDL, mm-LDL, or ox-LDL induced the activation of MAP kinase dose dependently. The activation of MAP kinase by these lipoproteins in mesangial cells occurred biphasically: initially at 15 min of incubation period and at later time points of 8 to 24 h. No activation of MAP kinase was noted between 30 min (except in LDL) and 6 h. The induction of MAP kinase by both mm-LDL and ox-LDL was greater by 1.5- to 2-fold when compared with LDL. Similarly, these atherogenic lipoproteins stimulated mesangial cell proliferation. Lysophosphatidylcholine, a component of both oxidatively modified variants of LDL, markedly stimulated mesangial cell MAP kinase activity at early incubation times (5 to 30 min) but not at later time points (3 to 24 h), suggesting that lysophosphatidylcholine may, at least in part but not solely, act as an active component of ox-LDL-mediated effects. These data define putative key signal transduction events associated with lipoprotein-mediated induction of mesangial cell proliferation.

Atherogenic lipoproteins enhance murine cortical epithelial cell fibronectin protein synthesis and gene expression.

Tubulointerstitial changes, characterized by the accumulation of extracellular matrix proteins (ECM) and fibrosis, are often associated with primary glomerular injury. Furthermore, these changes may be better prognostic indicators for decline in renal function than the anatomical changes seen within the glomerulus itself. Although hyperlipidemia and the increased renal accumulation of atherogenic lipoproteins are commonly seen in both human and experimental models of renal disease, the possible role that atherogenic lipoproteins may play in the cellular and molecular events associated with the development of tubulointerstitial injury remains unclear. Since atherogenic lipoproteins have been shown to be mediators of renal injury, we examined the effects of native LDL and oxidatively-modified LDL (ox-LDL, a more atherogenic form of LDL) on fibronectin protein synthesis and gene expression in proximal tubular epithelial cells (TEC). Human LDL was freshly isolated and ox-LDL prepared by incubation of LDL with 100 microM CuS04. Incubation of TEC with LDL or ox-LDL (25-50 micrograms/ml) for 24 h increased the steady-state mRNA expression of fibronectin by 16-135% over control as measured by Northern blot analysis and the effect was greater with ox-LDL than native LDL. Additional studies were done to examine whether the increased fibronectin message in response to lipoprotein activation was translated into TEC protein synthesis. The activation of TEC by LDL or ox-LDL stimulated the synthesis and secretion of fibronectin (52-150%, over control) as measured by Western blot analysis. The data show that LDL and ox-LDL stimulate TEC fibronectin gene message and protein synthesis supporting a pathobiological role for these atherogenic lipoproteins in tubulointerstitial fibrosis.

Hyperlipidemia and kidney disease: concepts derived from histopathology and cell biology of the glomerulus.

The association between hyperlipidemia and renal disease was noted by Virchow as early as the 19th century. Subsequently, similar histopathological lipid depositions were confirmed-in diverse human and experimental renal disease. Although, no studies have been established in man to suggest a causal relationship between lipids and the pathogenesis of renal disease, compelling evidence accumulated in experimental animals suggests a direct role of lipids in the initiation and progression of glomerular disease. These studies showed that cholesterol-feeding to various experimental animals induced the development of glomerular injury. Furthermore, the treatment of hyperlipidemic animals with lipid lowering drugs prevented the development of glomerulosclerosis. In this article, we will review recent advances made in understanding various aspects of lipid-mediated renal injury including biochemical mechanisms of hyperlipidemia, a possible direct role of hyperlipidemia in the pathogenesis of renal disease, pathobiological accumulation of lipids and lipoproteins, biochemical and histological similarities between systemic atherosclerosis and glomerulosclerosis, and cellular processes involved in the development of glomerular disease. Furthermore, we will define cellular and molecular hypotheses that provide putative mechanisms by which hyperlipidemia and atherogenic lipoproteins induce series of cytoregulatory peptide-mediated events involved in the development of glomerular disease.

Effect of serum subfractions from peritoneal dialysis patients on Hep-G2 cell apolipoprotein A-I and B metabolism.

We previously showed that uremic serum subfractions isolated from hemodialysis (HD) patients inhibited the production of apolipoprotein (apo) A-I by human hepatoblastoma cells, Hep-G2. Because of the reported differences in atherogenic cardiovascular mortality between HD and peritoneal dialysis (PD) patients, we examined the effect of similar subfractions from PD patients on apo A-I and apo B synthesis. After obtaining informed consent, serum samples from five normal subjects and nine stable PD patients were applied to Sephadex G-25 columns to obtain the serum subfractions used in the various experiments. Sephadex G-25 chromatograms of PD sera showed a broad peak from fractions 30 through 60 (molecular wt 500 to 2000 Da). Control serum showed no peak in this region. PD serum subfractions decreased apo A-I synthesis, secretion, and apo A-I mRNA expression by Hep-G2 cells when compared to subfractions from control subjects. Cholesterol efflux studies showed that conditioned media obtained from Hep-G2 cells incubated with PD serum subfractions inhibited cholesterol efflux from fibroblasts, suggesting a biologically-significant decrease in apo A-I synthesis. PD serum subfractions increased protein synthesis and mRNA expressions of apo B by Hep-G2 cells. Therefore, serum subfractions obtained from PD patients decreased apo A-I and increased apo B synthesis, findings consistent with their serum lipoprotein profiles suggesting that a biologically-active component in these subfractions could contribute to the risk of atherogenic cardiovascular disease in PD.

Activation of mesangial cells with TNF-alpha stimulates M-CSF gene expression and monocyte proliferation: evidence for involvement of protein kinase C and protein tyrosine kinase.

In this study, we examined the effect of TNF-alpha on mesangial cell gene expression of M-CSF, a colony-stimulating factor associated with monocyte differentiation into macrophages and proliferation. Incubation of mesangial cells with TNF-alpha-stimulated mRNA expression and protein synthesis of M-CSF. Mesangial cell activation with PMA, a PKC activator, stimulated M-CSF mRNA expression while PKC depletion decreased M-CSF mRNA expression to control levels. Stimulation of PKC-depleted mesangial cells with either PMA or TNF-alpha inhibited M-CSF mRNA transcripts. Preincubation of mesangial cells with calphostin C, a PKC inhibitor, reduced both PMA- and TNF-alpha-induced M-CSF mRNA transcripts. Specific protein tyrosine kinase inhibitors blocked TNF-alpha-induced mesangial cell M-CSF mRNA expression. Additional studies showed that pertussis toxin, isoproterenol, and dibutyryl (db)cAMP did not induce mesangial cell M-CSF gene expression. However, coincubation of mesangial cells with TNF-alpha and either dbcAMP, forskolin, or pertussis toxin inhibited TNF-alpha-induced M-CSF gene expression. Finally, TNF-alpha-activated mesangial cell conditioned media stimulated monocyte/macrophage proliferation dose-dependently and was prevented by using anti-M-CSF. These data suggested that M-CSF can regulate monocyte differentiation into macrophages and proliferation within the mesangium induced by proinflammatory cytokines such as TNF-alpha. These cellular events appeared to be modulated by signal transduction pathways mediated by PKC and PTK.

Oxidative modification of low-density lipoprotein enhances the murine mesangial cell cytokines associated with monocyte migration, differentiation, and proliferation.

The oxidative modification of atherogenic lipoproteins has been proposed to induce critical interactions between the monocytes and glomerular cells that are mediated by the expression of adhesion molecules and monocyte chemoattractants. Because increased localization of atherogenic lipoproteins, including oxidatively modified low-density lipoprotein (ox-LDL) and monocytes, has been seen in experimental glomerulosclerotic lesions, we examined the ability of ox-LDL to activate mesangial cells to express macrophage-colony stimulating factor (M-CSF) and the murine homologue of human monocyte chemotactic protein-1 (JE/MCP-1) and to induce monocyte migration and proliferation. Incubation of mesangial cells with ox-LDL markedly increased M-CSF and JE/MCP-1 gene expression dose-dependently when compared with native LDL. The biologic activity of lipoprotein-induced M-CSF secretion by mesangial cells was examined by adding aliquots of native or ox-LDL-activated mesangial cell-conditioned media to bone marrow cells in a methylcellulose semisolid culture dish. Conditioned media from ox-LDL-activated mesangial cells enhanced the growth of bone marrow progenitor colonies when compared with either control or native LDL-activated cell media. The increase in progenitor colony formation in response to either LDL or ox-LDL could be attenuated by the addition of anti-M-CSF. The conditioned media obtained from lipoprotein-activated mesangial cells increased the incorporation of 3H-thymidine into monocyte DNA that could be attenuated by the addition of anti-M-CSF. Finally, the supernatant that was obtained from mesangial cells activated with ox-LDL-stimulated monocyte migration dose-dependently when compared with media that were obtained from cells incubated with native LDL. Increased monocyte migration could also be blocked by the addition of anti-JE/MCP-1. The results of these studies indicate that oxidative modification of LDL further enhances its potency to induce renal injury by stimulating M-CSF and JE/MCP-1 expression. Thus, the data suggest that ox-LDL may play a critical role similar to that of systemic vascular cells in the pathobiologic cellular events associated with glomerulosclerosis by increasing monocyte recruitment, retention, and proliferation within the mesangium.

Role of tumor necrosis factor-alpha on mesangial cell MCP-1 expression and monocyte migration: mechanisms mediated by signal transduction.

Monocyte chemotactic protein-1 (MCP-1), a specific chemoattractant for monocytes, has been thought to play an important role in the recruitment and accumulation of monocytes within the glomerulus seen in glomerular diseases. This study examined the role of tumor necrosis factor (TNF)-alpha-mediated cellular signal transduction pathways on mesangial cell MCP-1 gene expression and monocyte migration. Incubation of mesangial cells with TNF-alpha stimulated MCP-1 mRNA expression in a dose- and time-dependent manner. Phorbol myristate acetate (PMA), a protein kinase C (PKC) activator, increased MCP-1 message by mesangial cells while depleting PKC decreased MCP-1 gene expression to control levels. Activation of PKC-depleted mesangial cells with PMA but not with TNF-alpha inhibited MCP-1 mRNA expression. Similarly, calphostin C, a PKC inhibitor, failed to inhibit TNF-alpha-induced MCP-1 expression. The incubation of mesangial cells with various protein tyrosine kinase inhibitors (PTK, e.g., herbimycin, tyrphostin, genistein) blocked TNF-alpha-induced MCP-1 mRNA message. Additional experiments examining the role of cAMP on MCP-1 expression indicated that the preincubation of mesangial cells with various cAMP generating substances (pertussis toxin, isoproterenol, dbcAMP) did not induce mesangial cell MCP-1 mRNA transcripts. However, the coincubation of mesangial cells with TNF-alpha and dbcAMP completely inhibited TNF-alpha-induced MCP-1 gene expression. Finally, TNF-alpha-activated mesangial cell media increased monocyte transmigration that could be blocked by neutralizing anti-MCP-1. These studies indicate that TNF-alpha facilitates monocyte transmigration into the glomerulus mediated by the increased expression of MCP-1 by mesangial cells. TNF-alpha-induced mesangial cell MCP-1 expression is regulated by signal transduction pathways involving PTK but not those dependent on PKC or cAMP.

TNF-alpha stimulates monocyte adhesion to glomerular mesangial cells. The role of intercellular adhesion molecule-1 gene expression and protein kinases.

TNF-alpha has been implicated in glomerular cell activation to produce adhesion molecules and monocyte chemoattractants associated with glomerular monocyte infiltration. This study examined the regulatory role of protein kinases and cAMP on TNF-alpha-induced intercellular adhesion molecules-1 (ICAM-1) expression and monocyte adhesion to mesangial cells. Activation of mesangial cells with TNF-alpha induced ICAM-1 mRNA and protein expression. Mesangial cells preincubated with phorbol 12-myristate 13-acetate (PMA), a protein kinase C (PKC) activator, stimulated both the gene and protein expression of ICAM-1. Mesangial cell PKC depletion abolished ICAM-1 mRNA message, while activation with TNF-alpha did not inhibit ICAM-1 transcripts. Preincubation of mesangial cells with calphostin C did not affect TNF-alpha-induced mesangial cell ICAM-1 message, while it blocked PMA-induced ICAM-1 mRNA expression. Protein tyrosine kinase (PTK) inhibitors blocked TNF-alpha-mediated mesangial cell ICAM-1 transcripts. cAMP-generating substances (e.g., pertussis toxin, isoproterenol, or dibutyryl cAMP) did not induce mesangial cell ICAM-1 gene expression. However, incubation of mesangial cells with TNF-alpha and dibutyrl cAMP blocked TNF-alpha-induced ICAM-1 message. Finally, preincubation of mesangial cells with TNF-alpha increased monocyte adhesion that could be blocked by anti-ICAM-1. Parallel to ICAM-1 gene expression data, TNF-alpha-induced monocyte-mesangial cell adhesion was inhibited by PTK inhibitors, but was not regulated through either PKC or intracellular cAMP-associated pathways. These results suggest that increased ICAM-1 expression by TNF-alpha activation of mesangial cells is one of the major pathways involved in monocyte adhesion to the mesangium, a phenomenon presumably regulated by signal-transduction pathways dependent on PTK, but not PKC or cAMP.

Role of atherogenic lipoproteins in cytokine-mediated renovascular injury.

Recent advances have clarified many basic cellular and molecular mechanisms associated with glomerular injury. We propose that atherogenic lipoproteins (e.g., native LDL and its more atherogenic oxidized variants) play a central role as biological modifiers in monocyte- and cytoregulatory peptide-induced glomerulosclerosis. Following lipoprotein activation of mesangial and other intrinsic glomerular cells, monocytes adhere, transmigrate, differentiate, and proliferate within the glomerular mesangium. These events are mediated by increased expression of adhesion molecules (ICAM-1, VCAM-1, etc.) and specific monocyte chemoattractants (M-CSF, MCP-1, etc.). Furthermore, atherogenic lipoprotein can activate mesangial cells to express additional proinflammatory cytokines (TNF-alpha, TGF-beta, etc.) that culminate in the elaborated expression of extracellular matrix proteins and irreversible injury. These results support a distinct pathobiological role for atherogenic lipoproteins in the initiation and progression of cytokine-mediated renal injury.

Low-density lipoprotein stimulates the expression of macrophage colony-stimulating factor in glomerular mesangial cells.

Disordered lipoprotein metabolism and the enhanced influx and accumulation of circulating mononuclear leukocytes into vascular tissue are common pathobiological phenomena associated with both atherosclerosis and glomerulosclerosis. Since atherogenic lipoproteins (such as low density lipoprotein, LDL) have been implicated in monocyte migration and proliferation into the glomerular mesangium, we examined the effect of LDL on mesangial cell expression of macrophage colony-stimulating factor (M-CSF), a cytoregulatory peptide associated with monocyte chemoattraction, differentiation and proliferation. Mesangial cell M-CSF gene expression, protein synthesis and secretion, and its biological activity to induce progenitor colony formation and monocyte proliferation were studied in murine mesangial cells. Incubation of either primary cultures or SV-40 transformed murine mesangial cells with LDL (0 to 200 micrograms/ml) induced M-CSF steady-state mRNA expression, in a dose-dependent manner (52 to 183% of control) when Northern blots were analyzed quantitatively by densitometric scanning. Similarly, Western blot analysis showed that LDL-activated SV-40 transformed mesangial cells increased M-CSF protein synthesis and secretion in a dose-dependent manner. The conditioned media obtained by incubating mesangial cells with LDL induced bone marrow progenitor colony formation that could be inhibited by specific neutralizing antibodies against murine M-CSF. Finally, the biological activity of M-CSF secreted by LDL-activated mesangial cells was further confirmed by its enhanced ability to induce monocyte proliferation. These data indicate that LDL, by activating mesangial cells to induce M-CSF and possibly other monocyte chemoattractants, may regulate the migration and proliferation of cells of mononuclear leukocytic origin into the mesangium supporting a pathobiological role for LDL in glomerular injury.

Hematopoietic colony stimulatory factor formation by murine mesangial cells: gene expression and biological activity.

This study examined the ability of mesangial cells to synthesize colony-stimulating factors (CSF), cytoregulatory peptides associated with the differentiation and proliferation of hematopoietic cells. Conditioned media obtained from SV-40 transformed murine mesangial cells stimulated the growth of murine bone marrow progenitor cells of the myeloid series. Differential analysis of these cells showed the presence of both macrophages and granulocytes. Cellular identification of bone marrow colonies stimulated in response to mesangial cell conditioned media was examined by flow cytometric analysis and revealed the presence of F4/80 antigen positive macrophages (67%) and Gran-1 antigen positive granulocytes (21%). Neutralizing antibodies to macrophage colony-stimulating factor (M-CSF) and granulocyte-macrophage colony-stimulating factor (GM-CSF) but not antibody to interleukin-3 (IL-3), or stem cell factor (SCF) significantly inhibited the growth of the progenitor cells induced by mesangial cell conditioned media. Utilizing Northern blot analysis, murine mesangial cells expressed mRNA transcripts for M-CSF, GM-CSF, and granulocyte colony-stimulating factor (G-CSF). Further studies were performed to determine optimal incubation conditions for mesangial cell CSF gene expression. These studies revealed that both GM-CSF and G-CSF mRNA were maximally expressed at early time points (4 and 8 h of incubation), while M-CSF mRNA expression remained unchanged during the incubation of mesangial cells from 4-48 h. Incubation of mesangial cells with various concentrations of fetal bovine serum (FBS, 0.5-15%) markedly increased the mRNA expression of M-CSF, GM-CSF and G-CSF in a dose-dependent manner. These studies indicated that transformed murine mesangial cells are able to synthesize and secrete biologically active CSF that are associated with the migration and proliferation of circulating mononuclear cells in the glomerulus. Furthermore, observations regarding the role of duration of incubation and the media concentration of FBS on mesangial cell CSF mRNA expression may provide useful data to understand the optimal conditions for studies that examine the gene expression of basal or inducible CSF in mesangial cells.

Uremic serum subfraction inhibits apolipoprotein A-I production by a human hepatoma cell line.

Abnormalities in lipoprotein metabolism are common in uremic patients and may represent an additional risk factor for the development of atherosclerosis. Despite the frequent occurrence of lipoprotein abnormalities, the role of various serum toxins and subfractions that accumulate in uremic patients on lipoprotein metabolism is not clearly understood. This study addressed the role of uremic toxins on lipoprotein metabolism by examining the effect of a 500 to 2,000-d subfraction obtained from the serum of uremic and control subjects on the synthesis of apolipoprotein (apo) A-I in a human hepatoma cell line (Hep-G2). Serum subfractions obtained from uremic patients inhibited apo A-I synthesis and secretion by Hep-G2 cells in a dose-dependent manner as measured by (3H)leucine incorporation into apo A-I, immunoprecipitation, and ELISA. The uremic serum subfraction decreased the mRNA expression for apo A-I in Hep-G2 cells when compared with controls. These observations suggest that a component of uremic serum can have the potential to inhibit hepatic apo A-I synthesis and may adversely influence high-density lipoprotein metabolism, thus increasing the risk for the development of atherosclerotic vascular complications in uremic patients.