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R B Sterzel

Publications and source records attributed to R B Sterzel.

At least 55 records · Page 3Linked to original sources
PubMed1994

Serum response elements mediate protein kinase C dependent transcriptional induction of early growth response gene-1 by arginine vasopressin in rat mesangial cells.

Arginine vasopressin (AVP) regulates glomerular hemodynamics, alters extracellular matrix production, and induces proliferation of glomerular mesangial cells (MCs). Therefore, AVP may play a role in glomerular sclerosis and the progression of chronic renal failure. To investigate changes in early gene expression which may link intracellular biochemical events with changes in MC phenotype following AVP stimulation, we studied expression of the Early growth response gene-1 (Egr-1). Nuclear run off assays demonstrate that AVP induces Egr-1 at the transcriptional level. Transcriptional induction was, like induction of mitogenesis, dependent upon activation of protein kinase C (PK C). Promoter deletion analysis revealed that the region critical for Egr-1 inducibility by AVP contained several serum response element (SRE) consensus sequences. Sequential deletion of these SREs led to a drop in AVP-stimulated promoter activity. AVP was also able to stimulate transcription from a construct containing an Egr-1 SRE upstream of a heterologous promoter and this effect required activation of PK C. Electrophoretic mobility shift assays, using an Egr-1 SRE as probe, demonstrate up to four protein-SRE complexes of differing size that undergo modest quantitative changes following AVP stimulation. These data in MCs suggest that upstream SREs mediate transcriptional induction of Egr-1 by AVP in a PK C-dependent fashion and that changes in DNA-protein interaction involving the SREs may be in part responsible for this effect.

Animals↗
PubMed1994

Cytokine-induced expression of leukemia inhibitory factor in renal mesangial cells.

Leukemia inhibitory factor (LIF) is a pleiotropic cytokine, which shares many characteristics with interleukin-6 (IL-6). Recent observations indicate a role for LIF in inflammatory processes. To examine the potential involvement of LIF in the regulation of mesangial cell behavior, we studied LIF expression in early primary cultures of rat and human mesangial cells, as well as the response of mesangial cells to exogenous LIF. Growing or growth-arrested rat mesangial cells constitutively expressed very low levels of LIF mRNA, barely detectable by Northern blot analysis. Strong induction of LIF mRNA expression was caused by cytokines, such as interleukin-1 beta (5 ng/ml), tumor necrosis factor alpha (100 ng/ml) and PDGF (100 ng/ml), as well as LPS (200 ng/ml). The induction was transient with a peak after three to five hours. Dexamethasone (0.1 microM) almost completely inhibited the induction of LIF. Weak induction of LIF mRNA was observed after stimulation with basic fibroblast growth factor, endothelin and transforming growth factor beta. In combination with IL-1 beta, TGF beta showed synergistic effects on LIF induction. LIF itself or IL-6 had no effect on LIF mRNA expression. A similar induction pattern was observed for the expression of IL-6 mRNA. LIF protein was detected by specific ELISA in the supernatants of human mesangial cells stimulated by LPS or IL-1 beta. In addition, we found that mesangial cells not only express LIF but they are also target cells for LIF. Recombinant LIF effectively induced transient expression of the immediate early genes, c-fos, jun-B and Egr-1 in rat mesangial cells, with a maximum at 30 to 60 minutes. LIF was not mitogenic for mesangial cells. Our findings indicate that glomerular mesangial cells produce and react to LIF. As a cytokine with autocrine potential, LIF may play a physiological and/or pathophysiological role in the glomerulus, the exact nature and relevance of which remain to be explored.

Animals↗
PubMed1994

Altered nitric oxide production and exogenous nitric oxide do not affect the proliferation of rat mesangial cells.

OBJECTIVE: To examine the hypothesis that nitric oxide (NO) acts as an autocrine, antiproliferative regulator and that exogenous NO donor inhibitors the proliferation of cultured rat mesangial cells. DESIGN AND METHODS: The cellular effects of endogenous and exogenous NO were studied in rat mesangial cells in a two-dimensional culture of early mesangial cell passages. The proliferation of mesangial cells was determined by cell-counting and uptake of [3H]-thymidine. NO generation was induced by incubation with interleukin-1 beta (5 u/ml) or bacterial lipopolysaccharide (10 micrograms/ml) for 24 h. NO release by mesangial cells was assessed by measuring the accumulation of nitrite, the major stable end-product of NO, in mesangial cell supernates. In addition, cyclic GMP (cGMP) formation was measured by radioimmunoassay as an indicator for NO generation. RESULTS: The formation of nitrite and cGMP was significantly increased after incubation of mesangial cells with interleukin-1 beta or lipopolysaccharide. This effect was greatly reduced by an inhibitor of NO synthesis. NG-monomethyl-L-arginine (L-NMMA; 0.1 mmol/l). The NO donor 3-morpholino-sydnonimine-HCl also increased the cGMP concentrations in the mesangial cells. The proliferation of mesangial cells was analysed in growth-arrested and mitogen-stimulated (platelet-derived growth factor, platelet-derived growth factor plus ATP and fetal calf serum) mesangial cells in the presence and absence of L-NMMA and the NO synthase substrate L-arginine (1 mmol/l). At 48 h platelet-derived growth factor (50 ng/ml), and platelet-derived growth factor (50 ng/ml) plus ATP (0.1 mmol/l) and fetal calf serum 5% each significantly increased the uptake of [3H]-thymidine in mesangial cells. These effects were not altered in the presence of L-NMMA or L-arginine. Pretreatment with interleukin-1 beta or with lipopolysaccharide also failed to affect the uptake of [3H]-thymidine in resting or proliferating mesangial cells. 3-Morpholino-sydnonimine-HCl (10(-3) to 10(-6) mol/l) did not suppress the mitogen-induced proliferation of mesangial cells, even when it was administered three times a day. CONCLUSIONS: The present findings support recent observations that interleukin-1 beta and lipopolysaccharide strongly induce NO production in mesangial cells, as is shown indirectly by the greatly increased formation of nitrite and cGMP. However, these effects were not associated with antiproliferative action on mitogen-stimulated mesangial cells. Similarly, the exogenous NO donor 3-morpholino-sydnonimine-HCl induced cGMP formation but failed to inhibit proliferation of mesangial cells when used at a non-toxic dose. Our observations do not support the contention that the formation of NO and cGMP constitutes an autocrine downregulating mechanism in the control of the growth of mesangial cells. It remains to be seen what pathophysiological role the induction of NO release plays in the regulation of the behaviour of mesangial cells, e.g. during an inflammatory response to glomerular injury.

Animals↗
PubMed1993

Polymerase chain reaction and focal contact formation indicate integrin expression in mesangial cells.

Cultured kidney glomerular mesangial cells (MCs) allow the role of extracellular matrix (ECM) and growth factors in glomerular inflammatory disease to be studied. To investigate the potential of MCs to interact with matrix components, the expression of integrin mRNA in cultured MCs was examined by polymerase chain reaction (PCR), by Northern blotting and by immunofluorescence. In addition, the effect of matrix substrates on mRNA expression was assessed by PCR. Northern blots with cDNA probes to integrin alpha-chains revealed that MCs expressed alpha 1, alpha 3 and alpha 5 integrin mRNA. alpha 1 and alpha 3 were the major messages. No alpha 2, alpha 4 or alpha 6 were detectable. RT-PCR revealed that alpha 2 and alpha 6 were also expressed at low levels. The control cells, HT1080, expressed alpha 2, alpha 3, alpha 4, alpha 5 and alpha 6 mRNA, and Rugli expressed alpha 1, alpha 3 and alpha 5, supporting previous studies. Immunocytochemistry confirmed that alpha 1 beta 1, alpha 2 beta 1, and alpha 5 beta 1 integrins were expressed and that they were concentrated into focal adhesions (alpha 1 beta 1 on type I collagen and laminin; alpha 2 beta 1 on type I collagen; alpha 3 beta 1 on type I collagen, laminin and fibronectin; alpha 5 beta 1 on fibronectin). alpha 6 beta 1 was not detected in focal contacts. Attachment, spreading, and formation of talin and integrin containing focal contacts still occurred when endogenous protein synthesis was blocked with 30 micrograms.ml-1 cycloheximide.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Divergent effects of arginine vasopressin and angiotensin II on proliferation and expression of the immediate early genes c-fos, c-jun and Egr-1 in cultured rat glomerular mesangial cells.

OBJECTIVE: The vasoactive peptides arginine vasopressin (AVP) and angiotensin II (Ang II) induce similar second messengers in cultured glomerular mesangial cells, as shown by the rise in intracellular calcium and the activation of phospholipases C and A2. In contrast, AVP is a strong mitogen for cultured rat mesangial cells while Ang II is not. To elucidate the level of signal divergence, we examined the effects of AVP and Ang II on the expression of the immediate early genes c-fos, c-jun and Egr-1, which have been associated with cell growth. We also tested the effect of AVP and Ang II on the induction of the ornithine decarboxylase gene and enzyme in order to examine a process that is induced in cell activation, e.g. it has been associated with the G1 phase after mitogen-receptor binding. DESIGN AND METHODS: Cellular effects of Ang II and AVP were studied in rat mesangial cells in conventional two-dimensional culture. Proliferation of the mesangial cells was measured by cell-counting and by [3H]-thymidine uptake. The presence of receptors for Ang II and AVP was assessed by measurement of prostaglandin E2 by a radioimmunoassay following stimulation with vasoactive peptides and a receptor-binding assay for Ang II. Messenger (m)RNA levels of c-fos, c-jun Egr-1 and ornithine decarboxylase were determined by Northern blot analysis. Ornithine decarboxylase activity was measured by an enzyme substrate assay. RESULTS: AVP (10(-7) mol/l) stimulated [3H]-thymidine uptake by 3.7-fold after 48 h and increased mesangial cell counts by 42% (P < 0.05), while Ang II was not mitogenic. Stimulation of resting mesangial cells with AVP (10(-9) to 10(-6) mol/l) caused maximal expression of the immediate early genes after 0.5-1 h, which disappeared after 2-4 h. The relative increases were: c-fos, 15-fold; c-jun, 12-fold; Egr-1, sixfold. Ang II (10(-9) to 10(-6) mol/l) did not induce these genes at any time. In contrast, ornithine decarboxylase mRNA and enzyme activity were induced by both AVP and Ang II. CONCLUSIONS: The results demonstrate that AVP, but not Ang II, is a strong inducer of the immediate early genes c-fos, c-jun and Egr-1 in cultured mesangial cells. We conclude that signalling pathways activated by AVP and Ang II in mesangial cells diverge within 30 min after ligand-receptor binding and proximal to the transient expression of immediate early genes. While mitogenesis of cultured mesangial cells, as effected by AVP, involves the expression of immediate early genes, Ang II-induced non-mitogenic changes in the mesangial cell phenotype do not. The increase in ornithine decarboxylase mRNA and enzyme activity following stimulation with both AVP and Ang II indicates that its induction can occur independently of the immediate early gene expression and mitogenesis.

Angiotensin II↗
PubMed1993

Renal matrix and adhesion in injury and inflammation.

Over the past year, there have been major advances in the descriptive analysis of the extracellular matrix in the kidney. Several aspects of the interaction of matrix molecules with renal and, in particular with glomerular cells via specific integrin receptors, have also been studied. Most results on cell-matrix interactions have been obtained by in vitro investigations of glomerular mesangial cells in two-dimensional culture. The regulation of matrix formation and degradation has been shown to involve the concerted action of several soluble factors, notably transforming growth factor-beta, as well as the effects of nonsoluble matrix components themselves, such as collagens and proteoglycans. The mediation of such complex interactions between cells, matrix, and cytokines is facilitated by the tightly regulated expression of cell surface receptors, eg, cytokine receptors and integrins of the beta 1 series, which bind specific matrix molecules. New results have yielded more insight into the regulation not only of matrix formation but also of the specific interactions between cells and matrix and of the modulation of cytokine activity by matrix molecules. Using experimental rat models and transgenic mouse models of kidney disease, the first in vivo findings using immunohistochemistry and mRNA analysis have confirmed that major changes occur in the expression of matrix molecules, integrins, and cytokines in the process of glomerular inflammation. With the advent of specific modulators of the bioactivity of ligands and receptors, it is hoped that more information will be forthcoming on the functional relevance of various components of the cell-matrix-cytokine crosstalk in the normal and injured kidney.

Animals↗
PubMed1993

PDGF-induced Egr-1 expression in rat mesangial cells is mediated through upstream serum response elements.

Platelet-derived growth factor (PDGF) has been implicated in the process of mesangial cell (MC) proliferation in vitro and in vivo. To investigate early changes in gene expression that couple biochemical events with changes in phenotype in PDGF-stimulated cultured MC, we studied expression of the early growth response gene 1 (Egr-1), a member of the family of immediate early genes. Our findings show that protein tyrosine phosphorylation is required for induction of Egr-1 mRNA and proliferation by PDGF in MC. Nuclear run-off assays show that Egr-1 induction occurs at the transcriptional level. An 11.3-fold increase in Egr-1 transcription rate was observed as early as 5 min after PDGF stimulation of MC. Promoter deletion analysis revealed that the region critical for Egr-1 inducibility by PDGF contains serum response element (SRE) consensus sequences. Sequential deletion of the Egr-1 SREs led to a stepwise drop in promoter activity, suggesting that PDGF induces Egr-1 transcription through SREs in the Egr-1 promoter region. Interestingly, electrophoretic mobility shift assays, with an Egr-1 SRE as probe, demonstrate that protein-SRE complexes of differing size undergo modest quantitative changes following PDGF stimulation. These data in MC suggest that the upstream SREs mediate the transcriptional induction of Egr-1 by PDGF.

Animals↗
PubMed1993

Effect of transforming growth factor-beta on extracellular matrix production by cultured rat mesangial cells.

The effects of transforming growth factor-beta (TGF-beta) on the protein synthesis and gene expression of collagen I (CI), III (CIII), IV (CIV) and laminin (LM) in cultured rat mesangial cells (MCs) were examined to determine whether or not TGF-beta could modulate the formation of extracellular matrix (ECM) constituents, employing immunocytochemistry, enzyme-linked immunoadsorbent assay (ELISA) and Northern blotting. Although TGF-beta did not modulate MC proliferation, it induced slight enhancement of immunoperoxidase staining for CIV in the cytoplasm. ELISA demonstrated a significant increase in the amounts of CIV and LM, a tendency for CIII to increase, and a significantly lower amount of CI at 4 days after TGF-beta administration. Northern blotting showed that the mRNA expression displayed different patterns among the 4 matrix components during a 24-hr period. These findings suggest that a single growth factor, TGF-beta, in vitro modulates the synthesis of individual ECM constituents in MCs differently at the level of both genetic expression and protein production. The specific effects of TGF-beta on the increase in amounts of CIV and LM indicate that TGF-beta may contribute to glomerular remodeling and ECM accumulation in various kinds of glomerular injuries.

Animals↗
PubMed1993

Cytokines and mesangial cells.

Hyperplasia of mesangial cells (MCs) precedes or accompanies progressive glomerular scarring, as is seen in chronic glomerulonephritis and diabetic glomerulosclerosis. The mechanisms causing in vivo MC proliferation and production of extracellular matrix (ECM) are incompletely understood. Cell culture studies have demonstrated that MCs produce as well as react to various polypeptide cytokines. Thus, MCs have the potential to generate soluble mediators which can, in a paracrine fashion, attract and activate inflammatory cells (platelets, monocyte-macrophages, granulocytes), for example by IL-6, IL-8, MCP-1 and GM-CSF, and exert autocrine effects on MCs themselves, such as by promoting MC proliferation (by PDGF, IL-1, IL-6) or ECM production (by TGF-beta, IL-1). Recent in vitro results have revealed that specific non-soluble ECM components (collagen III, IV; laminin) also affect MC behavior with regard to adhesion, cell replication, ECM production as well as their response to cytokines. The latter effect appears to be mediated by alterations of cytokine receptor expression on MCs in the presence of the ECM components. "Cross-talk" between MCs, cytokines, ECM and inflammatory cells is likely to be of great importance in the regulation of the MC phenotype and may play a prominent role in the initiation and progression of glomerular inflammation. First in vivo findings in rats with experimental glomerular disease and in kidney biopsies from patients with glomerulonephritis have supported this concept by demonstrating abnormal MC expression of cytokines, their receptors and ECM proteins. These MC products may promote the recruitment and activation of inflammatory cells and perpetuate MC proliferation as well as ECM build-up.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Extracellular ATP stimulates proliferation of cultured mesangial cells via P2-purinergic receptors.

We examined the role of the platelet product ATP in regulating replication and secretory activity of cultured rat mesangial cells (MCs). Extracellular ATP (25-100 microM) significantly increased [3H]thymidine uptake of growth-arrested MCs 2.1-fold; cell counts increased by 35.1%. Addition of ATP to MCs in combination with other platelet products, such as platelet-derived growth factor, isoform BB (100 ng/ml), and serotonin (1 microM), resulted in strong synergistic mitogenicity (up to 45.6-fold over control). As immediate signaling events following stimulation with ATP, we found increased production of inositol phosphates (3.2-fold increase for inositol bisphosphate and 1.6-fold increase for inositol trisphosphate by 30 s) and release of prostaglandin E2 (PGE2, 9.2-fold increase by 5 min). When we studied the rank order of potency of various ATP analogues for the production of inositol phosphates and PGE2, ATP, UTP, and adenosine 5'-O-(3-thio)triphosphate (ATP gamma S) were the most potent agonists. Although ATP and ATP gamma S were also strong mitogens, UTP was not. Additional inhibitor studies indicated that protein kinase C or cyclooxygenase products were not involved in the mitogenic effects of ATP. In summary, the major platelet product ATP is a potent comitogen for cultured MCs and strongly synergizes with other growth factors. The experiments with ATP analogues point to different receptors mediating mitogenesis, generation of inositol phosphates, and PGE2 production. The precise mechanism of the mitogenic action of ATP on MCs remains to be characterized.

Adenosine Triphosphate↗
PubMed1992

Effect of vasoactive agents on induction of Egr-1 in rat mesangial cells: correlation with mitogenicity.

The early growth response gene 1 (Egr-1) is a member of the family of immediate early response genes. Egr-1 encodes a nuclear phosphoprotein that binds a specific nonameric DNA sequence through three zinc-finger domains and functions as a transcriptional activator. We tested whether the vasoactive agents platelet-derived growth factor (PDGF), arginine vasopressin (AVP), serotonin (5-HT), and angiotensin II (ANG II) induced Egr-1 mRNA in cultured rat mesangial cells (MCs) and investigated the role of protein kinase C (PKC) in mediating the induction process. PDGF, AVP, and 5-HT induced Egr-1 mRNA within 15 min, reaching peak levels at 45-60 min. After PDGF and 5-HT stimulation, Egr-1 mRNA levels returned to baseline within 4 h, whereas AVP induced a sustained increase for up to 8 h. There was a very close correlation between doses required for Egr-1 induction and induction of MC proliferation. ANG II was a very weak MC mitogen and induced only a small increase in Egr-1 mRNA. Comparison of control cells with cells depleted of PKC by 48 h of PMA treatment revealed that induction of Egr-1 by PDGF and 5-HT is independent of PKC. In contrast, however, the Egr-1 response to AVP was diminished in PKC-depleted cells. AVP induced Egr-1 mRNA 10.9-fold in control cells, compared with 7.8-fold in PKC-depleted cells. Egr-1 mRNA after AVP stimulation remained elevated in control cells for up to 8 h but returned to baseline after 120 min in PKC-depleted cells. Similar results were obtained using the PKC-inhibitor H-7. Using immunocytochemistry, PDGF and AVP were found to induce Egr-1 protein within 30 min localized to the nucleus. We conclude that there is a strong correlation between induction of Egr-1 after stimulation with PDGF, AVP, 5-HT, and ANG II and the proliferative response elicited by these agents in MCs. AVP induces Egr-1 by both PKC-dependent and PKC-independent pathways, whereas the effects of PDGF and 5-HT are independent of PKC.

Angiotensin II↗
PubMed1992

Interactions between glomerular mesangial cells, cytokines, and extracellular matrix.

This brief overview summarizes recent information on the interactions of glomerular mesangial cells (MC) with soluble cytokines and nonsoluble extracellular matrix (ECM). The presently available knowledge stems largely from glomerular cell culture studies and from experimental work with laboratory animals. ECM production by MC appears to be regulated primarily by the paracrine or autocrine effects of cytokines, such as interleukin 1, platelet-derived growth factor, and transforming growth factor beta. However, ECM itself also affects the behavior of cultured MC, e.g., with regard to cell replication and the production of ECM components and other proteins. At present, little is known about the recognition of ECM and cytokines by MC that allows these interactions to take place. First results indicate that MC, like other cell types, possess surface proteins belonging to the beta 1 integrin family, which serve as specific receptors for ECM molecules. Receptors for the cytokines platelet-derived growth factor, insulin-like growth factor 1, epidermal growth factor, and transforming growth factor beta have also been demonstrated on MC. The expression of various receptors on MC appears to be affected by the ECM substratum. Thus, it is becoming apparent that mesangial ECM is not only important as a mechanical scaffold of the glomerular capillary tuft but that it also contains and conveys information relevant for the regulation of the MC phenotype, e.g., by modulating the MC response to cytokines. The available evidence suggests that alterations of ECM composition in glomerular disease can directly or indirectly affect MC behavior, e.g., by promoting cell replication and further accumulation of ECM, eventually resulting in progressive mesangial and glomerular sclerosis.

Animals↗
PubMed1992

Extracellular matrix protein: gene expression and synthesis in cultured rat mesangial cells.

Production of extracellular matrix (ECM) by mesangial cells (MCs) contributes to progressive glomerulosclerosis. Our previous immunocytochemical studies on ECM production by MCs [1] were extended by examining the gene expression and protein synthesis using Northern blotting and ELISA. ELISA demonstrated that fetal calf serum (FCS) stimulated the synthesis of collagen I (CI), III (CIII) and IV (CIV), and laminin (LM). At and after confluence, the amounts of CIII, CIV and LM per DNA amount began to decrease, whereas that of CI did not. Northern blotting indicated that the mRNA expressions for CIV and LM were transiently increased by FCS. The mRNA expressions for CI and CIII decreased until confluence and then returned to the initial levels. These results suggest that FCS and cellular confluence affected the synthesis of ECM at both the level of gene expression and protein synthesis. The mRNA expressions for CIV and LM paralleled the protein synthesis and appeared tightly regulated. CI and CIII synthesis and mRNA expression were not coordinate and were not regulated in the same manner as the basement membrane matrix components.

Animals↗
PubMed1991

Atrial natriuretic peptide in the locus coeruleus and its possible role in the regulation of arterial blood pressure, fluid and electrolyte homeostasis.

Atrial natriuretic factor (ANP) is present in neuronal cells of the locus coeruleus and its vicinity in the pontine tegmentum and moderate amount of ANP is detectable in this area by radioimmunoassay. The ANP (both peripheral and brain-born) is known as a neuropeptide which may influence the body salt and water homeostasis and blood pressure by targeting both central and peripheral regulatory mechanisms. Whether this pontine ANP cell group is involved in any of these regulatory mechanisms, the effect of various types of hypertension and experimental alterations in the salt and water balance on ANP levels was measured by radioimmunoassay in the locus coeruleus of rats. Adrenalectomy, as well as aldosterone and dexamethasone treatments failed to alter ANP levels in the locus coeruleus. Reduced ANP levels were measured in spontaneously hypertensive (both young and adult) rats, and in diabetes insipidus (Brattleboro) rats with vasopressin replacement. In contrast to these situations, elevated ANP levels were found in rats with DOCA-salt or 1-kidney-1-clip hypertension. These data suggest a link between ANP levels in the locus coeruleus and fluid volume homeostasis. Whether this link is causal and connected with the major activity of locus coeruleus neurons (noradrenergic influence on brain regulatory activities) needs further informations.

Adrenalectomy↗
PubMed1991

Role of ornithine decarboxylase for proliferation of mesangial cells in culture.

To elucidate the role of polyamine metabolism in the regulation of mesangial cell growth, we examined the involvement of ornithine decarboxylase (ODC), the rate limiting enzyme for polyamine synthesis, in the mitogenesis of cultured rat mesangial cells (MCs). Resting MCs, stimulated with fetal calf serum (FCS 10%), showed an induction of ODC activity from undetectable values in resting cells to mean = 5035 nmol CO2/10(10) cells.hr (range 3157 to 7154, N = 5), which is 25-fold above the detection limit. We found a single peak of ODC activity eight to ten hours after stimulation, declining to 22 to 34% of peak levels after 24 hours. 3H-thymidine (TdR) uptake, an S-phase marker of MC replication, peaked at 24 hours, reaching 10.7-fold values of resting MCs. ODC mRNA levels were low in resting cells. After serum stimulation there was a two- to 10-fold increase in ODC mRNA with a maximum after six hours. ODC activity with similar kinetics but lower peak levels was also induced by incubating MCs with mitogens, such as platelet-derived growth factor (PDGF-AB 20 ng/ml), arginine vasopressin (AVP 10(-7) M), phorbol myristate acetate (PMA 10(-7) M), interleukin 1 alpha and beta (IL-1 alpha 10 U/ml, IL-1 beta 10 U/ml). In the presence of alpha-difluoromethylornithine (DFMO), an enzyme-activated irreversible inhibitor of ODC, the growth rate of MCs, assessed by cell counts and by 3H-TdR uptake, was markedly reduced by 62 to 100%. This antiproliferative effect of DFMO could be reversed by addition of putrescine, the reaction product of ODC.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Interleukin 6 is an autocrine growth factor for mesangial cells.

Interleukin 6 (IL-6) induces the acute phase response, differentiation of B cells, proliferation of T cells, thymocytes, hematopoietic progenitors, hybridoma and plasmacytoma cells. Monocytes, T cells, fibroblasts, epithelial and endothelial cells secrete IL-6. Since IL-6 responsive cell-types may participate in the pathogenesis of glomerular inflammation, we studied the secretion of IL-6 by rat MCs, using the IL-6 dependent hybridoma cell line B9. The results of our studies indicate that MCs secrete IL-6 with a molecular weight of 17-42 kDa and isoelectric point of 4.0 to 5.3 MC-IL-6 activity could be blocked by a polyclonal antimurine-IL-6 antibody. MC express IL-6 mRNA as determined by Northern blot. Furthermore, our data demonstrate that IL-6 acts as an autocrine growth factor for MC. Incubation of subconfluent MC with recombinant IL-6 results in a dose-dependent increase of 3H-thymidine incorporation and number of MCs. Moreover, reverse phase HPLC fractions of MC-CM containing IL-6 activity increase 3H-thymidine incorporation by MC. In addition to its possible paracrine role in mediating the immune response in the glomerulus, MC-IL-6 may also be one of the autocrine signals leading to mesangial cell proliferation in vivo.

Animals↗