Effect of platelet-activating factor and serum-treated zymosan on prostaglandin E2 synthesis, arachidonic acid release, and contraction of cultured rat mesangial cells

Polysaccharide-rich extract of Genipa americana leaves exerts anti-inflammatory effects modulated by platelet mediators

ETHNOPHARMACOLOGICAL RELEVANCE

Genipa americana L. (Rubiaceae) leaves are traditionally used to treat fever, pharyngitis, healing, luxation and bruises.

AIM OF THE STUDY

This study aimed to investigate the anti-inflammatory effect of the polysaccharide-rich extract of G. americana leaves (PE-Ga) in acute inflammation models and underlying mechanisms associated with platelet activity.

MATERIALS AND METHODS

Rats received PE-Ga (0.3-3.0 mg/kg; IV) 30 min before injection (IP or SC) of zymosan, serotonin, PGE2, PLA2, PAF or L-arginine, and evaluated in the models of paw edema and acute peritonits. The blockage of plasma serotonin reuptake into platelets was performed with fluoxetine (40 mg/kg; IP).

RESULTS

In vitro, PE-Ga inhibited ADP-induced platelet aggregation up to 49%. In the edema model, PE-Ga reduced (41%) the time-course of the edema induced by zymosan, mainly the last phase (62%), as well as that induced by PLA2 (32%), PAF (35%), L-arginine (36%), PGE2 (49%) or serotonin (54% AUC); and reversed paw hypernociception induced by PGE2 or serotonin. In the peritonitis model, PE-Ga reversed abdominal hypernociception and reduced leukocyte migration induced by zymosan to blood (38%) and peritoneal cavity (55%), mainly neutrophils (70%). PE-GA also decreased leukocyte rolling (32%) and adhesion (47%), and increased the rolling velocity 2.2-fold. In the peritoneal fluid, PE-Ga reversed P-selectin and reduced total proteins (17%), MDA (40%), NO2-/NO3- (27%), and MPO activity (43%) but increased catalase activity 3.3-fold compared to zymosan. In addition, fluoxetine reversed PE-Ga anti-inflammatory effect on leukocyte migration and adhesion.

CONCLUSIONS

PE-Ga exerts antiplatelet and anti-inflammatory effects in acute inflammation induced by zymosan, being modulated by P-selectin and platelet serotonin, among other inflammatory mediators.

The role of platelet-activating factor in mesangial pathophysiology

Platelet-activating factor (PAF) is a powerful proinflammatory mediator that displays an exceedingly diverse spectrum of biological effects. Importantly, PAF is shown to participate in a broad range of pathologic conditions. This review focuses on the role that PAF plays specifically in the pathophysiology of the kidney, the organ that is both a source and a target of PAF. Renal mesangial cells are responsible for glomerular PAF generation and, ultimately, are the victims of its excessive production. Mesangial pathology is widely acknowledged to reflect glomerular damage, which culminates in glomerulosclerosis and proteinuria. Therefore, modulation of mesangial cell responses would offer a pathophysiology-based therapeutic approach to prevent glomerular injury. However, the currently available therapeutic modalities do not allow for targeted intervention into these processes. A more profound understanding of the mechanisms that govern PAF metabolism and signaling in mesangial cells is important, because it could facilitate the quest for improved therapies for renal patients on the basis of PAF as a drug target.

The long pentraxin PTX3 is synthesized in IgA glomerulonephritis and activates mesangial cells

The long pentraxin PTX3 has been recently involved in amplification of the inflammatory reactions and regulation of innate immunity. In the present study we evaluated the expression and role of PTX3 in glomerular inflammation. PTX3 expression was investigated in the IgA, type I membranoproliferative, and diffuse proliferative lupus glomerulonephritis, which are characterized by inflammatory and proliferative lesions mainly driven by resident mesangial cells, and in the membranous glomerulonephritis and the focal segmental glomerular sclerosis, where signs of glomerular inflammation are usually absent. We found an intense staining for PTX3 in the expanded mesangial areas of renal biopsies obtained from patients with IgA glomerulonephritis. The pattern of staining was on glomerular mesangial and endothelial cells. Scattered PTX3-positive cells were also detected in glomeruli of type I membranoproliferative glomerulonephritis. The concomitant expression of CD14 suggests an inflammatory origin of these cells. Normal renal tissue and biopsies from patients with the other glomerular nephropathies studied were mainly negative for PTX3 expression in glomeruli. However, PTX3-positive cells were detected in the interstitium of nephropathies showing inflammatory interstitial injury. In vitro, cultured human mesangial cells synthesized PTX3 when stimulated with TNF-alpha and IgA and exhibited specific binding for recombinant PTX3. Moreover, stimulation with exogenous PTX3 promoted mesangial cell contraction and synthesis of the proinflammatory lipid mediator platelet-activating factor. In conclusion, we provide the first evidence that mesangial cells may both produce and be a target for PTX3. The detection of this long pentraxin in the renal tissue of patients with glomerulonephritis suggests its potential role in the modulation of glomerular and tubular injury.

Nitric oxide/platelet activating factor cross-talk in mesangial cells modulates the interaction with leukocytes

BACKGROUND

Platelet activating factor (PAF) and nitric oxide (NO) exert opposite effects on adherence and activation of circulating leukocytes to endothelium. Several studies have implicated the production of PAF and NO by mesangial cells in the regulation of glomerular filtration, permeability and inflammation. However, the reciprocal interaction between PAF and NO in mesangial cells and their role in leukocyte adhesion has not been investigated.

METHODS

We evaluated whether blockade of constitutive production of NO by two different NO synthase (NOS) inhibitors (L-NAME and L-NMMA) could modulate PAF synthesis, and conversely whether exogenous PAF could influence the production of NO by mesangial cells. We evaluated whether modulation of PAF synthesis by NOS inhibitors could affect leukocyte adhesion to mesangial cells. The effect of PAF-receptor antagonist WEB2170, of anti-beta(2) integrins and intracellular adhesion molecule-1 (ICAM-1) blocking antibodies and of soluble Sialyl-Lewis-a also was evaluated.

RESULTS

Blockade of NO synthesis by NOS inhibitors induced a spontaneous synthesis of PAF that was conversely inhibited by NO generation. On the other hand, PAF inhibited both the basal and l-arginine induced synthesis of NO by mesangial cells. Moreover, NOS inhibition promoted the adhesion of polymorphonuclear cells and monocytes to mesangial cells by a mechanism dependent on the synthesis of PAF and on the interaction of beta(2) integrins and ICAM-1.

CONCLUSIONS

These data indicate that PAF and NO exhibit a bi-directional effect on their respective synthesis in human mesangial cells, and suggest that their reciprocal regulation may be relevant for leukocyte adhesion to glomerular mesangial cells.

Potential role of platelet activating factor in acute renal failure

The clinical condition of acute renal failure (ARF) can be caused by a diverse number of renal injuries, but it is generally characterized by a sharp reduction in the glomerular filtration rate (GFR). A lipid mediator, platelet activating factor (PAF), may be one of the entities responsible for causing the hemodynamic changes in the ARF kidney because it can act as a vasodilator or vasoconstrictor, depending upon its concentration. This review examines the action and mechanisms of PAF in experimental animal models of ischemia and nephrotoxicity, as well as renal failure associated with extrarenal disease. While further research is necessary before extrapolating our current knowledge of PAF into the prevention of renal failure of therapeutic intervention using PAF antagonists in human ARF, there is reasonable evidence to support its role as a mediator of the decrease in GFR characteristic of ARF.

Mechanisms involved in the contraction of endothelial cells by hydrogen peroxide

The importance of endothelial contraction in the genesis of inflammatory edema has been reported. ROS are metabolites synthesized in pathological conditions in that a significant intravascular fluid leak occurs, such as ischemia-reperfusion. Present experiments were designed to test the hypothesis that ROS, particularly H2O2, may elicit the contraction of endothelial cells, and to explore the mechanisms involved. Bovine aortic endothelial cells incubated with H2O2 showed a significant reduction in planar cell surface area (PCSA), and a significant increase in myosin light chain phosphorylation (MLCP), with a time- and dose-dependent pattern, without any significant toxicity. This effect of H2O2 was not blocked by sulotroban (TxA2 antagonist) or BN 52021 (PAF antagonist). Lanthanum chloride (calcium channel blocker) and EGTA partially inhibited the increase in MLCP induced by H2O2. H7 and staurosporine, PKC inhibitors, and PKC down-regulation (phorbol myristate acetate treatment, 24 h) also blocked H2O2-dependent endothelial contraction, measured as PCSA or MLCP. H2O2 increased the intracellular calcium concentration, an effect blunted by EGTA and lanthanum chloride. H2O2 also increased the phosphorylation of an 80 kD polypeptide, probably MARCKS, a PKC substrate. In summary, the present results demonstrate the ROS-dependent contraction of endothelial cells, an effect that could explain the intravascular fluid leak observed in some pathophysiological situations. Calcium and PKC may be involved in the development of this contraction.

Interleukin-12 is synthesized by mesangial cells and stimulates platelet-activating factor synthesis, cytoskeletal reorganization, and cell shape change

Preliminary studies indicate the involvement of interleukin (IL)-12 in experimental renal pathology. In the present study, we evaluated whether cultured glomerular mesangial cells are able to produce IL-12 and whether IL-12 may regulate some of their functions, including the cytoskeletal reorganization, the change in cell shape, and the production of platelet-activating factor (PAF). The results obtained indicate that pro-inflammatory stimuli, such as tumor necrosis factor-alpha and bacterial polysaccharides, induce the expression of IL-12 mRNA and the synthesis of the protein by cultured mesangial cells. Moreover, cultured mesangial cells were shown to bind IL-12 and to express the human low-affinity IL-12 beta1-chain receptor. When challenged with IL-12, mesangial cells produced PAF in a dose- and time-dependent manner and superoxide anions. No production of tumor necrosis factor-alpha and IL-8 was observed. Moreover, we demonstrate that IL-12 induced a delayed and sustained shape change of mesangial cells that reached its maximum between 90 and 120 minutes of incubation. The changes in cell shape occurred concomitantly with cytoskeletal rearrangements and may be consistent with cell contraction. As IL-12-dependent shape change of mesangial cells was concomitant with the synthesis of PAF, which is known to promote mesangial cell contraction, we investigated the role of PAF using two chemically different PAF receptor antagonists. Both antagonists inhibited almost completely the cell shape change induced by IL-12, whereas they were ineffective on angiotensin-II-induced cell shape change. In conclusion, our results suggest that mesangial cells can either produce IL-12 or be stimulated by this cytokine to synthesize PAF and to undergo shape changes compatible with cell contraction.

Sarcomeric gene expression and contractility in myofibroblasts

Myofibroblasts are unusual cells that share morphological and functional features of muscle and nonmuscle cells. Such cells are thought to control liver blood flow and kidney glomerular filtration rate by having unique contractile properties. To determine how these cells achieve their contractile properties and their resemblance to muscle cells, we have characterized two myofibroblast cell lines. Here, we demonstrate that myofibroblast cell lines from kidney mesangial cells (BHK) and liver stellate cells activate extensive programs of muscle gene expression including a wide variety of muscle structural proteins. In BHK cells, six different striated myosin heavy chain isoforms and many thin filament proteins, including troponin T and tropomyosin are expressed. Liver stellate cells express a limited subset of the muscle thick filament proteins expressed in BHK cells. Although these cells are mitotically active and do not morphologically differentiate into myotubes, we show that MyoD and myogenin are expressed and functional in both cell types. Finally, these cells contract in response to endothelin-1 (ET-1); and we show that ET-1 treatment increases the expression of sarcomeric myosin.

Ligation of the alpha 2-macroglobulin signaling receptor on macrophages induces synthesis of platelet activating factor

The binding of receptor-recognized forms of alpha 2-macroglobulin (alpha 2M) to macrophage alpha 2M signaling receptors increases inositol-1,4,5-triphosphate synthesis and induces Ca2+ mobilization. In this report, we demonstrate that ligation of the macrophage alpha 2M signaling receptor is also associated with synthesis of platelet activating factor (PAF) by both the de novo and remodeling pathways. Both alpha 2M-methylamine and a cloned and expressed 20-kDa receptor binding fragment (RBF) from rat alpha 1M+, stimulated macrophage synthesis of PAF from [3H]acetate, [3H]methylcholine, and 1-O-[3H]alkyl lyso-PAF by two- to threefold. PAF levels reached a peak in 20 min after the cells were exposed to alpha 2M-methylamine or RBF; they remained elevated for about 1 h after ligand addition to the cells. When [3H]methylcholine was the substrate, pertussis toxin did not block PAF synthesis, but the protein kinase C inhibitor staurosporin reduced synthesis by 65-70%. Cycloheximide completely abolished the increase in synthesis of PAF by macrophages exposed to alpha 2M-methylamine. By contrast, when [3H]acetate was employed as a precursor, staurosporin or cycloheximide did not abolish the increase in PAF synthesis. These studies suggest that protein kinase C is necessary for the induction of the de novo pathway by alpha 2M-methylamine. Both alpha 2M-methylamine and RBF stimulated the activity of lyso-PAF acetyltransferase by about fourfold. Both ligands also stimulated the activity of PAF acetylhydrolase by about six- to sevenfold, indicating that ligation of the alpha 2M signaling receptor also regulates the degradation of PAF. The ability of receptor-recognized forms of alpha 2M to regulate levels of PAF suggests that alpha 2M-proteinase complexes not only regulate macrophage function by activating intracellular signaling but also may indirectly regulate the function of other cells that cannot bind alpha 2M-proteinase complexes.

Protective effect of a platelet-activating factor antagonist (WEB-2086) in postischemic renal failure

The purpose of this study was to evaluate the renoprotective effect of a specific platelet-activating factor antagonist (WEB-2086) in an experimental model of normothermic renal ischemia. Twenty New Zealand white rabbits were studied for 2 days before and 24 hours after a 60-minute period of renal ischemia induced by bilateral clamping of the renal arteries. The animals were divided into two groups: a control group (group A; n = 10) and a treated group (group B; n = 10). In group A the urinary flow rate decreased significantly (from 0.098 +/- 0.008 ml/min to 0.029 +/- 0.005 ml/min) (p < 0.001) and there was a significant reduction in creatinine clearance (from 11.4 +/- 1.2 ml/min to 3.4 +/- 1.1 ml/min) (p < 0.001). In group B no significant changes were observed, although the urinary flow rate increased even in the postischemic period (from 0.09 +/- 0.008 ml/min to 0.11 +/- 0.02 ml/min). Microcirculatory cortical flow showed a postischemic reduction in both groups, although it was most significant in the control group (group A = 43.7%, group B = 71.5%; p < 0.001). Histologic study showed mild damage with patchy tubular necrosis in both groups, although this injury was less severe in the treated group. The results suggest that the preoperative administration of WEB-2086 produces a potent diuretic effect with significant attenuation of postischemic acute renal failure.

Gentamicin activates rat mesangial cells. A role for platelet activating factor

Gentamicin-induced decreases in glomerular filtration rate have been associated with a marked decline in the glomerular capillary ultrafiltration coefficient which could be mediated by mesangial cell contraction or release of vasoactive hormones. We studied the effect of gentamicin on mesangial cells proliferation, contraction and Ca2+ mobilization. Moreover, we attempted to assess a possible role of platelet activating factor (PAF) as a mediator of the observed effects of gentamicin on mesangial cells. Gentamicin induced a reduction of planar surface area of cultured rat mesangial cells that was blunted by the PAF-antagonist, BN-52021. Gentamicin induced an increase in [Ca2+]i that was inhibited by BN-52021. Gentamicin also stimulated [3H]thymidine incorporation into DNA, an effect that was also reduced by BN-52021, and by other two structurally different PAF receptor antagonists: alprazolam and BB-823. Gentamicin induced c-fos mRNA expression in quiescent mesangial cells. Gentamicin stimulated the synthesis and release of PAF in cultured rat mesangial cells. The present studies demonstrate that gentamicin activates mesangial cell function. These actions seem to be mediated, at least in part, by PAF synthesis and release.

Insulin nonattenuation of vasoactive agent-induced responses in mesangial cells from spontaneously hypertensive rats

We recently found that insulin attenuates intracellular calcium transients and cell contraction caused by vasoactive agents in cultured rat mesangial cells. Because altered glomerular function may be causally related to the evolution of hypertension, we examined in the present study the effects of insulin on the functions of mesangial cells derived from spontaneously hypertensive rats (SHR) of 4- and 8-weeks of age. Age-matched Wistar Kyoto rats (WKY) were used as controls. Intracellular calcium concentration ([Ca2+]i) was measured with Fura-2 method in suspended mesangial cells. Pretreatment of mesangial cells with 5 micrograms/ml insulin for 120 minutes did not affect basal [Ca2+]i in either WKY or SHR mesangial cells. However, insulin pretreatment significantly attenuated [Ca2+]i transients to vasoactive agents in WKY mesangial cells. In contrast, [Ca2+]i transients to these agents were not attenuated by insulin in SHR mesangial cells. Additionally, SHR mesangial cell contraction in response to angiotensin II (Ang II) was not altered by insulin, while WKY mesangial cell contraction to Ang II was, as in normal Wistar rats, significantly reduced by insulin. Since we previously showed the possibility that the attenuation of calcium signal by insulin is via insulin-like growth factor I (IGF-I) receptor, we also examined the effect of IGF-I. In contrast to WKY mesangial cells, IGF-I-induced attenuation of [Ca2+]i responses to platelet activating factor was absent in SHR mesangial cells. [125I]-IGF-I binding in SHR mesangial cells was not significantly different from that in WKY mesangial cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Pathogenesis of IgA nephropathy: in vitro activation of human mesangial cells by IgA immune complex leads to cytokine secretion

IgA immune complex (IC) plays a crucial role in the pathogenesis of IgA nephropathy (IgAN). As IgA-IC is not itself cytotoxic, other mediators may be involved in the pathogenesis. In order to elucidate the mechanisms by which IgA-IC mediates renal injury in IgAN, the ability of IgA-IC to 'activate' cultured human mesangial cells (HMC) was studied. HMC were incubated with nephritogenic IgA-IC, containing a MOPC-315 plasmacytoma-derived IgA anti-dinitrophenyl (DNP) and DNP-conjugated bovine serum albumin. The cells showed morphological changes, an accelerated rate of proliferation, and increased production of interleukin-1 (IL-1), interleukin-6 (IL-6), platelet activating factor (PAF) and generation of superoxide anion. The enhancement of IL-1 and IL-6 mRNA expression in HMC incubated with IgA-IC was identified by dot blot analysis. Northern blot hybridization also demonstrated an augmented IL-6 mRNA expression in HMC treated with IgA-IC. These results suggest that nephritogenic IgA-IC may amplify the proliferation of HMC and the production of immune/chemical mediators and superoxide anion thereby resulting in the renal lesions of IgAN.

Insulin attenuates intracellular calcium responses and cell contraction caused by vasoactive agents

In the present study, we examined the effects of insulin and insulin-like growth factor I (IGF-I) on cultured rat mesangial cell responses to vasoactive agents. Intracellular calcium concentration ([Ca2+]i) was measured with the Fura-2 method in suspended mesangial cells. Pretreatment of mesangial cells with insulin (from 0.05 to 5 micrograms/ml) attenuated Ca2+ transients by platelet activating factor (PAF) in a dose dependent and a time dependent manner. Insulin also attenuated sustained elevation of [Ca2+]i elicited by PAF. Basal [Ca2+]i was not affected by insulin pretreatment. Since the effective dose of insulin (0.5 microgram/ml or higher) is much higher than the physiological concentration, the effects of insulin may be via IGF-I receptor. Indeed, IGF-I (50 ng/ml) similarly attenuated [Ca2+]i responses to PAF. Moreover, insulin pretreatment attenuated [Ca2+]i responses evoked by angiotensin II (Ang II) and endothelin-1. In addition, the pretreatment with insulin or IGF-I inhibited mesangial cell contraction in response to Ang II. The suppression of [Ca2+]i responses to vasoactive agents by insulin was abolished when extracellular Ca2+ was removed. These data suggest that insulin, probably via IGF-I receptor, attenuates [Ca2+]i responses and cell contraction of mesangial cells induced by vasoactive agents. It is likely that the change in Ca2+ influx from outside to inside the cell underlie the effect of insulin. The modification of mesangial cell function through IGF-I receptor may play a role in the regulation of glomerular hemodynamics.

A role for platelet-activating factor in endothelin-1-induced rat mesangial cell proliferation

Endothelin-1 stimulated the release of bioassayable platelet-activating factor-like material and the incorporation of acetate to PAF in rat mesangial cells, in a dose-dependent manner, with an EC50 of about 10(-9) M. Endothelin-1 also stimulated dose dependently [3H]thymidine incorporation into DNA, protein synthesis and cell growth. The platelet-activating factor antagonists BN-52021 (10(-5) M), and alprazolam (10(-5) M), reduced significantly endothelin-1-stimulated thymidine incorporation into DNA, protein synthesis and cell growth. Platelet-activating factor also stimulated significantly thymidine incorporation into DNA, cell proliferation and protein synthesis. In conclusion, the present results suggest that endothelin-1 induces mesangial cell proliferation through a mechanism involving among others, synthesis and release of platelet-activating factor by these cells.

Effect of extracellular ATP on contraction, cytosolic calcium activity, membrane voltage and ion currents of rat mesangial cells in primary culture

1. The effects of extracellular ATP on contraction, membrane voltage (Vm), ion currents and intracellular calcium activity [Ca2+]i were studied in rat mesangial cells (MC) in primary culture. 2. Addition of extracellular ATP (10(-5) and 10(-4) M) to MC led to a cell contraction which was independent of extracellular calcium. 3. Membrane voltage (Vm) and ion currents were measured with the nystatin patch clamp technique. ATP induced a concentration-dependent transient depolarization of Vm (ED50: 2 x 10(-6) M). During the transient depolarization ion currents were monitored simultaneously and showed an increase of the inward- and outward current. 4. In a buffer with a reduced extracellular chloride concentration (from 145 to 30 mM) ATP induced a depolarization augmented to -4 +/- 4 mV. 5. ATP-gamma-S and 2-methylthio-ATP depolarized Vm to the same extent as ATP, whereas alpha,beta-methylene-ATP (all 10(-5) M) had no effect on Vm. 6. The Ca2+ ionophore, A23187, depolarized Vm transiently from -51 +/- 2 to -28 +/- 4 mV and caused an increase of the inward current. 7. The intracellular calcium activity [Ca2+]i was measured with the fura-2 technique. ATP stimulated a concentration-dependent increase of [Ca2+]i (ED50: 5 x 10(-6) M). The increase of [Ca2+]i was biphasic with an initial peak followed by a sustained plateau. 8. The [Ca2+]i peak was still present in an extracellular Ca(2+)-free buffer, whereas the plateau was abolished. Verapamil (10(-4) M) did not inhibit the [Ca2+]i increase induced by ATP. 9. The data indicate that extracellular ATP contracts MC and is able to increase [Ca2+]i by the release of Ca2+ from intracellular stores and recruitment from the extracellular space. In addition ATP depolarizes Vm of MC by activating a Cl- conductance. The ATP-induced depolarization is mediated by a P2y receptor.

Platelet-activating factor stimulates phosphatidic acid formation in cultured rat mesangial cells: roles of phospholipase D, diglyceride kinase, and de novo phospholipid synthesis

Platelet-activating factor (PAF) stimulates phospholipase C (PLC)-induced hydrolysis of phosphatidylinositol-4,5-bisphosphate (PtdIns-4,5-P2). Yet, PAF-stimulated diglycerides (DG) are still elevated at time points where inositol polyphosphates have returned to basal levels. Thus, other signal transduction pathways that hydrolyze phosphatidylcholine (PtdCho) or phosphatidylethanolamine (PtdEth) and form DG and phosphatidic acids (PA) through either PLC or phospholipase D (PLD) may also mediate PAF-stimulated cellular responses. Initially the effects of PAF upon 32P-PA generation in mesangial cells (MC) were assessed. PA formation may be indicative of several metabolic pathways including PLD and DG kinase activities as well as de novo phospholipid synthesis. PAF (10(-7) M) increased 32P-PA formation as early as 5 seconds and this elevation persisted up to 15 minutes. When MC were pretreated with the DG kinase inhibitor-R59022, PAF-induced 32P-PA formation was diminished at early but not late time points, demonstrating that the initial component of PA formation may be due, in part, to PLC activation and subsequent phosphorylation of DG. The reciprocal reaction, PA phosphohydrolase, which dephosphorylates PA to from DG was not stimulated by PAF, suggesting that the sustained elevation of DG induced by PAF is primarily a reflection of PLC. 3H-glycerol pulse-labeling experiments suggest that PAF also stimulates de novo phospholipid synthesis which also contributes to PA formation. Conclusive proof for PLD in the generation of PA was obtained by assessing the formation of 3H-phosphatidyl-ethanol (PEt) from 3H-alkyl-lyso-glycero phosphocholine (GPC) and exogenous ethanol. PAF stimulated alkyl-PEt generation in the presence but not the absence of 0.5% ethanol. Also, PAF induced a concomitant elevation of alkyl-PA at 15 minutes and this elevation of alkyl-PA was reduced when the cells were exposed to exogenous ethanol, reflecting the formation of PEt. Corroborating evidence suggests that PAF stimulates 3H-choline and 3H-ethanolamine release, suggesting that PtdCho and PtdEth are substrates for PLD. Thus, these data demonstrate that MC respond to PAF with elevated PLD and DG kinase activities as well as with an increased rate of de novo lipid synthesis which increases PA, a potential intracellular signal.

Platelet-activating factor: receptors and signal transduction

During the past two decades, studies describing the chemistry and biology of PAF have been extensive. This potent phosphoacylglycerol exhibits a wide variety of physiological and pathophysiological effects in various cells and tissues. PAF acts, through specific receptors and a variety of signal transduction systems, to elicit diverse biochemical responses. Several important future directions can be enumerated for the characterization of PAF receptors and their attendant signalling mechanisms. The recent cloning and sequence analysis of the gene for the PAF receptor will allow a number of important experimental approaches for characterizing the structure and analysing the function of the various domains of the receptor. Using molecular genetic and immunological technologies, questions relating to whether there is receptor heterogeneity, the precise mechanism(s) for the regulation of the PAF receptor, and the molecular details of the signalling mechanisms in which the PAF receptor is involved can be explored. Another area of major significance is the examination of the relationship between the signalling response(s) evoked by PAF binding to its receptor and signalling mechanisms activated by a myriad of other mediators, cytokines and growth factors. A very exciting recent development in which PAF receptors undoubtedly play a role is in the regulation of the function of various cellular adhesion molecules. Finally, there remain many incompletely characterized physiological and pathophysiological situations in which PAF and its receptor play a crucial signalling role. Our laboratory has been active in the elucidation of several tissue responses in which PAF exhibits major autocoid signalling responses, e.g. hepatic injury and inflammation, acute and chronic pancreatitis, and cerebral stimulation and/or trauma. As new experimental strategies are developed for characterizing the fine structure of the molecular mechanisms involved in tissue injury and inflammation, the essential role of PAF as a primary signalling molecule will be affirmed. Doubtless the next 20 years of experimental activity will be even more interesting and productive than the past two decades.

Cultured rat mesangial cells contain smooth muscle alpha-actin not found in vivo

A monoclonal antibody against smooth muscle alpha-actin (SM alpha-actin) was used to study the expression of SM alpha-actin in kidney sections and mesangial cell (MC) cultures. In the tissue sections, indirect immunofluorescence revealed intense labeling of vascular smooth muscle cells and precapillary pericytes for SM alpha-actin. Glomerular cells including MC were negative, with the exception of scattered smooth muscle cells in the wall of the intraglomerular segment of the efferent arteriole. In contrast, in MC cultures 50 to 95% of the cells displayed bright fluorescence. Immunoreactivity for SM alpha-actin first appeared 3 days after explanation of glomeruli and increased until the primary culture reached subconfluence. In each subculture (1 to 10) expression of SM alpha-actin was weak on day 1 and pronounced at subconfluence. Growth arrest of subconfluent cultures for 1 to 7 days in serum-free medium did not alter the percentage of cells positive for SM alpha-actin. However, exposure of MC to serum-free medium beginning on the first day of subculture curtailed expression of SM alpha-actin. Double-labeling with antibodies against proliferating cell nuclear antigen and SM alpha-actin revealed SM alpha-actin-positive filaments in both replicating and resting cells. In summary, our results demonstrate that some process or processes associated with cell proliferation and cell growth of MC are accompanied by de novo expression of SM alpha-actin. The relevance to the contractile behavior of the difference in SM alpha-actin expression under in vitro and in vivo conditions is unknown.

Porins and lipopolysaccharide stimulate platelet activating factor synthesis by human mesangial cells

Porins, a family of hydrophobic proteins located in the outer membrane of the cell wall of gram-negative bacteria and lipopolysaccharide (LPS), were shown to stimulate the synthesis of platelet activating factor (PAF), a phospholipid mediator of inflammation and endotoxic shock, by cultured human glomerular mesangial cells (MC). The synthesis of PAF induced by porins was rapid (peak at 20 min) and independent either from contamination by LPS or from generation of an endotoxin-induced cytokine such as tumor necrosis factor (TNF) since it was not prevented by cycloheximide, an inhibitor of protein synthesis or anti-TNF blocking antibodies. LPS also stimulated PAF synthesis by MC. However, the kinetic of PAF synthesis induced by LPS was biphasic with an early and transient peak at 10 minutes and a second and sustained peak at three to six hours. This second peak required an intact protein synthesis and was prevented by anti-TNF antibodies, suggesting the dependency on LPS-induced synthesis of TNF. Experiments with labeled precursors demonstrated that in MC, either after stimulation with porins or LPS, PAF was synthesized via the remodeling pathway that involves acetylation of 1-0-alkyl-sn-glyceryl-3-phosphorylcholine (2-lyso-PAF) generated from 1-0-alkyl-2-acyl-sn-glyceryl-3-phosphorylcholine by phospholipase A2 (PLA2) activity. Porins and LPS, indeed, induced PLA2-dependent mobilization of [14C]-arachidonic acid that was inhibited by p-bromodiphenacylbromide (PBDB). PBDB, an inhibitor of PLA2, also blocked PAF synthesis by preventing the mobilization of 2-lyso-PAF, the substrate for PAF-specific acetyltransferase.(ABSTRACT TRUNCATED AT 250 WORDS)

Mesangial deposition of type I collagen in human glomerulosclerosis

The presence of type I collagen in both diffuse and nodular diabetic glomerular lesions has been examined using immunohistochemical and electron microscopic techniques. At the ultrastructural level, banded collagen fibrils were observed in the mesangium in all cases of nodular (Kimmelstiel-Wilson) sclerosis and in 60% of the diffuse sclerotic lesions. Antibodies against type I collagen were localized in the fibrotic interstitium and the mesangium in all cases examined. Staining with type I collagen antibodies occurred in glomeruli with intact Bowman's capsules, and was predominantly localized to areas immediately adjacent to mesangial cells. In cases of focal sclerosis of nondiabetic origin, banded collagen fibrils and staining with anti-type I collagen antibody were observed in all cases in which the segmental lesion was presented in the specimen. The pattern of antibody localization in both the diabetic lesions and focal sclerosis differed from that obtained using anti-type IV (basement membrane) collagen antibodies. These results demonstrate that type I collagen is among the extracellular matrix components that comprise the sclerotic glomerular lesions of both diabetic and nondiabetic origin. Furthermore, the spatial localization of this collagen type suggests mesangial cell origin.

Platelet-activating factor stimulates multiple signaling pathways in cultured rat mesangial cells

We have previously reported that platelet-activating factor (PAF) elevates cytosolic free calcium concentration ([Ca2+]i) in fura-2-loaded glomerular mesangial cells. To confirm that this increase in [Ca2+]i is a result of receptor-mediated activation of phospholipase C, we investigated hydrolysis of phosphatidylinositol-4,5-bisphosphate (PtdIns-4,5-P2) in PAF-treated mesangial cells. PAF (10(-7) M) stimulated a rapid and transient formation of inositol trisphosphate. In concomitant experiments, PAF stimulated a biphasic accumulation of 3H-arachidonate-labeled 1,2-diacylglycerol (DAG). The secondary elevation in DAG was coincident with a rise in 3H-phosphorylcholine (PC) and 3H-phosphorylethanolamine (PE) suggesting that PAF stimulates delayed phospholipase activities which hydrolyze alternate phospholipids besides the polyphosphoinositides. This PAF-stimulated elevation in 3H-water soluble phosphorylbases was seen at 5 min but not at 15 sec suggesting that the initial rise in DAG as well as the initial elevation in [Ca2+]i are due primarily to PtdIns-4,5-P2 hydrolysis. PAF also stimulated PGE2 as well as 3H-arachidonic acid and 3H-lyso phosphatidylcholine (PtdCho) formation. We suggest that arachidonate released specifically from PtdCho via phospholipase A2 is a source of this PAF-elevated PGE2. It has been postulated that anti-inflammatory prostaglandins may antagonize the contractile and proinflammatory effects of PAF via activation of adenylate cyclase. Surprisingly, exogenous PAF reduced basal and receptor-mediated cAMP concentration indicating that PAF-stimulated transmembrane signaling pathways may oppose receptor-mediated activation of adenylyl cyclase. We have taken advantage of the different sensitivities of phospholipases A2 and C(s) to PMA, EGTA, and pertussis toxin to dissociate phospholipase A2 and C activities. Acute PMA-treatment enhanced PAF-stimulated PGE2 formation, reduced PAF-induced elevations in [Ca2+]i and had no effect upon PAF-stimulated 3H-PE. We have also demonstrated that phospholipase A2, but not PtdIns-specific phospholipase C, was sensitive to external calcium concentration. The role of a GTP-binding protein to couple PAF-receptors to the PtdIns-specific phospholipase C was confirmed as GTP gamma S synergistically elevated PAF-stimulated inositol phosphate formation. We also demonstrated that pertussis toxin ADP-ribosylates a single protein of an apparent 42 kD mass and that PAF pretreatment reduced subsequent ADP-ribosylation in a time-dependent manner. However, pertussis toxin had no effect upon phospholipase C-generated water soluble phosphorylbases or inositol phosphates. In contrast, PAF-stimulated phospholipase A2 and PAF-inhibited adenylyl cyclase activities were sensitive to pertussis toxin.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of anti-interleukin-1 administration to rats with adriamycin-induced nephrosis

Rats receiving a single dose of adriamycin (7.5 mg/kg) develop heavy proteinuria and histologic lesions similar to those found in minimal change nephrotic syndrome in humans. We found that whole isolated glomeruli from rats injected with adriamycin secreted an IL-1-like cytokine which closely resembled macrophage IL-1. Maximal IL-1-like activity was detected on day 14 of the experiment when rats were heavily proteinuric. Administration of anti-IL-1 antiserum to rats with adriamycin-induced nephrosis provoked a transient but marked reduction in the urinary protein excretion. Our results indicate that IL-1-could be an important mediator implicated in the development of proteinuria in this experimental nephropathy.

Effects of platelet-activating factor on prostaglandin E2 production by intact fetal membranes

OBJECTIVE

The hypothesis tested in this study is that platelet-activating factor increases prostaglandin E2 synthesis from fetal membranes.

STUDY DESIGN

Fetal membrane disks obtained before or after labor were incubated with or without platelet-activating factor for time periods of up to 24 hours. The production of prostaglandin E2 and its inactive metabolites was determined by specific radioimmunoassays.

RESULTS

Platelet-activating factor (1 to 10 mumol/L) stimulated the production of prostaglandin E2 and its metabolites by intact fetal membranes and chorion-decidua threefold to fourfold after 24 hours of incubation. Platelet-activating factor had far greater effects on the production of prostaglandin E2 by intact fetal membranes obtained after the onset of labor, such that prostaglandin E2 production was increased by tenfold to 100-fold.

CONCLUSION

These results suggest that platelet-activating factor mainly stimulates prostaglandin E2 production by the chorion-decidua before labor and that it may act in synergism with other stimulatory factors present in the fetal membranes during labor.

Platelet activating factor inhibits Cl and K transport in the medullary thick ascending limb

Since the kidney medulla was reported to generate platelet activating factor (PAF), we investigated a possible effect of this agent on the reabsorptive function of in vitro microperfused medullary thick ascending limbs from mouse kidney (mTAL). PAF, 10(-7) M in the bath, significantly decreased the net chloride flux (JCl) from 48.8 +/- 7.1 to 27.4 +/- 5.7 pmol/min. This effect was reversible, blocked by the antagonist BN 50730, and not reproduced by the inactive metabolite lyso-PAF. PAF inhibited the transepithelial potential difference with a threshold at 10(-9) M. In the presence of isoproterenol, the PAF-induced decrease of JCl was not significantly different from that observed in basal conditions; moreover, PAF did not modify the adenylate cyclase activity in isolated mTALs, either in basal condition or under stimulation by isoproterenol. The effect of PAF on JCl was not prevented by mepacrine, NDGA associated with proadifen, or adenosine desaminase. When the apical Na-K-2Cl cotransport was blocked by furosemide or bumetanide, a net K secretion occurred (-1.1 +/- 0.2 pmol/min), which was significantly decreased by PAF (-0.06 +/- 0.3 pmol/min). Moreover, it was verified on isolated mTALs that PAF did not modify the Na,K-ATPase activity. It is concluded that PAF inhibits the reabsorptive function of the mTAL, as indicated by the decrease of Cl reabsorption and K secretion. This effect could not be accounted for by adenosine or arachidonic acid metabolite action, and was not mediated by an inhibition of the adenylate cyclase activity.

Role of platelet-activating factor in hemodynamic derangements in an acute rodent pancreatic model

Systemic hemodynamics were assessed in a model of experimental pancreatitis induced in rats by the retrograde injection of sodium deoxycholate, 40%, 1 mL/kg, in the pancreatic duct, using the radioactive microsphere technique before and 25 minutes after pancreatitis induction while blood pressure was stable (n = 10). A 55% decrease in cardiac out-put, a 14% decrease in heart rate, and a 3.3-fold increase in total peripheral resistances, without significant changes in blood pressure, were observed. Renal blood flow decreased by 68%. When rats were given BN-52021, a blocker of platelet-activating factor receptors (5 mg/h, IV; n = 13) coinciding with pancreatitis induction, no significant hemodynamic changes were observed. Animals treated with BN-52021 survived 89 +/- 10 minutes, whereas death occurred 67 +/- 5 minutes after pancreatitis induction in untreated rats (P less than 0.001). A different group of rats with pancreatitis showed higher blood levels of platelet-activating factor (0.28 +/- 0.06 ng/mL; n = 11) than control rats (0.16 +/- 0.03; n = 15; P less than 0.05). Very high levels of platelet-activating factor were found in peritoneal exudate from rats with pancreatitis. These data show an effective protective effect of BN-52021 on the hemodynamic impairment that follows pancreatitis induction, as well as a role of platelet-activating factor in these alterations.

Complement activation retards resolution of acute ischemic renal failure in the rat

We investigated the role of complement activation on the resolution of acute ischemic renal failure in the rat. Acute renal failure was induced by clamping of the renal arteries of Sprague-Dawley rats for 45 minutes (Day 0). On subsequent days, groups of rats with acute renal failure were exposed to daily zymosan infusion (an activator of the complement system), or to blood incubated with cuprophane (CUP) or polyacrylonitrile (PAN) dialysis membranes. We serially measured the change in BUN daily, glomerular filtration rate and 24-hour proteinuria on Day 3 and Day 5 following ischemia. On Day 6, the animals were sacrificed and their kidneys examined histologically. Zymosan and cuprophane exposed rats had a significant delay in the recovery of renal failure, reduced glomerular filtration rate, and histologically had more neutrophil infiltration than control or PAN exposed animals. To investigate the potential pathophysiology of these observations, we assessed the response of zymosan-exposed rats to infusion of deferoxamine (DFO), a potent inhibitor of hydroxyl radical formation (OH.). Infusion of DFO prior to zymosan significantly improved recovery of renal function. We also measured urinary thromboxane B2 levels in these groups of rats. While the groups of rats exposed to zymosan had the highest levels of thromboxane B2, these levels were not different between the groups exposed to zymosan alone, or to zymosan and DFO. These observations suggest a role for hydroxyl radicals in the prolongation of renal failure in this model. Taken together, these findings may have implications for the dialytic intervention in patients with acute renal failure.

Nephrotoxicity of cyclosporine: the role of platelet-activating factor and thromboxane

Cyclosporine (CsA), an immunosuppressive agent, is potentially nephrotoxic. We had previously observed that acute administration of CsA to Munich-Wistar rats induced a decrease in single nephron glomerular filtration rate, due to a decline in glomerular plasma flow, and in the glomerular ultrafiltration coefficient. Moreover, these alterations were prevented when an antagonist of platelet-activating factor (PAF) was administered. In the present study we examined whether the protective effect of the PAF blocker in CsA nephrotoxicity could have been mediated by thromboxane (TxA2). Our data show that the PAF effects were not mediated by TxA2, since administration of dazmegrel, a thromboxane synthetase inhibitor, did not ameliorate the acute renal failure caused by CsA. Thus, PAF appears to be a direct mediator of acute CsA nephrotoxicity, while TxA2 is not significantly involved in this process.

Role of platelet activating factor in gentamicin and cisplatin nephrotoxicity

The present study was undertaken to evaluate the effects of platelet activating factor (PAF) antagonists on nephrotoxicity induced by gentamicin (GENTA) and cisplatin (DDP) in rats. PAF infusion provoked a 56% decline in single nephron (SN) GFR due to a decrease in glomerular plasma flow (QA, 55%), glomerular transcapillary hydraulic pressure (delta P, 13%), and glomerular ultrafiltration coefficient (Kf, 37%). Four days after a single dose of DDP (6 mg/kg, i.p.) we observed non-oliguric acute renal failure (ARF) with reduced SNGFR (45%), QA (46%) and delta P (10%) and unchanged Kf. GENTA administration for 10 days (40 mg/kg, i.p. daily) induced a decline in SNGFR (40%), QA (41%) and Kf (41%). Chronic treatment with a GENTA + PAF antagonist (BN 52021) partially prevented the decline in SNGFR (22%) by an amelioration in QA (25%) and Kf (13%). However, simultaneous treatment with DDP and BN 52063 completely prevented the ARF induced by DDP, normalizing all parameters of renal function. Thus, PAF may be a potential mediator involved in the nephrotoxicity induced by GENTA and DDP.

Effect of platelet activating factor on prostaglandin release from ovine endometrial cells in culture

Platelet activating factor (PAF) added in vitro to ovine endometrial cells in primary culture caused a dose-dependent increase in the release of prostaglandin (PG) E into the medium compared with release from untreated cells. At a concentration of 1000 ng/ml of PAF, PGE levels in treatment dishes were significantly higher (P less than 0.05) than those in control dishes [130 +/- 8% vs 100% (mean +/- SEM, N = 5 ewes)]. PAF did not alter the release of PGF2 alpha by the same cells. By contrast, the ovine trophoblast interferon, ovine trophoblast protein-1 (oTP-1, 1 ng/ml) attenuated the release of both PGE and PGF2 alpha and this was not overcome by the presence of PAF (100 ng/ml). Thus does not appear that PAF contributes to the antiluteolytic signal in sheep by a direct action on release of PGF2 alpha although it could influence implantation via stimulation of PGE.

Effects of YM264, a novel PAF antagonist, on puromycin aminonucleoside-induced nephropathy in the rat

We investigated the effects of YM264, WEB2086, methylprednisolone and ticlopidine on puromycin-induced nephropathy in the rat. Puromycin produces marked proteinuria, hypercholesterolemia, and hypoalbuminemia. The structurally differing PAF antagonists YM264 and WEB2086 inhibited proteinuria and improved hypercholesterolemia and hypoalbuminemia. Methylprednisolone also exhibited a beneficial effect on these variables. However, ticlopidine, a platelet inhibitor, showed no inhibitory effect on nephropathy. These results indicate that PAF may play a major role in puromycin-induced nephropathy in the rat, and that PAF antagonists may prove of therapeutic value in the treatment of nephropathy in humans.

Renal effects and mesangial cell contraction induced by endothelin are mediated by PAF

The recently discovered vasoactive peptide endothelin and platelet activating factor (PAF) share similar renal effects. The purpose of the present series of experiments has been to analyze the functional relations between the effect of endothelin on renal function and glomerular and mesangial cell contraction and the production and actions of PAF in kidney. Endothelin 1 nmol/kg body wt induced a transient decrease of glomerular filtration rate (from 1.99 +/- 0.17 to 0.56 +/- 0.18 ml/min) and renal blood flow (from 10.8 +/- 1.3 to 2.7 +/- 0.3 ml/min). Endothelin also induced a marked reduction of planar cell surface area of cultured mesangial cells (30 +/- 5%) and of cross sectional area of isolated glomeruli (from 1.51 +/- 0.02 to 1.31 +/- 0.02 m2 x 10(-8]. BN-52021 or WEB-2170, two potent specific inhibitors of PAF receptor binding, blocked the effects of endothelin on renal function and on the contraction of isolated glomeruli and mesangial cells. In addition, endothelin induced a significant increase in the production of PAF by isolated glomeruli (Basal, 81 +/- 10 pg/mg protein; endothelin, 10(-7) M, 140 +/- 18 pg/mg protein). Endothelin also stimulated the incorporation of [3H]acetate into PAF, both in glomeruli (264.27 +/- 27.7%) and mesangial cells (251 +/- 41%). These effects were blocked by EGTA and by verapamil. Our results suggest that PAF may be a mediator of the effects of endothelin on renal function and glomerular and mesangial cell contraction.

Regulation of Fc receptors for IgG on cultured rat mesangial cells

Localization of immune complexes (IC) to the mesangium may contribute to glomerular disease. Recently, we and others characterized Fc receptors (Fc gamma R) for IgG-IC on mesangial cells (MC). This study examines regulation of Fc gamma R by cAMP, interferon gamma (IFN-gamma) and by macrophage colony stimulating factor (CSF-1), an agent controlling Fc gamma R in leukocytes and generated by MC. Preincubation of MC (3rd to 6th subculture) with CSF-1, db-cAMP or IFN-gamma for two to 48 hours resulted in a time dependent (maximal 24 to 48 hrs) two- to threefold increase of specific [125I] IgG-IC binding to MC at 4 degrees C. The increase of Fc receptors induced by CSF-1, db-cAMP or IFN-gamma was confirmed by enhanced binding of the monoclonal anti-Fc receptor antibody 2.4G2 to MC. Uptake of IgG-IC at 37 degrees C was also enhanced in MC pretreated with CSF-1, db-cAMP or IFN-gamma. This indicates that the increase in binding for IgG-IC is associated with functional receptors. Immunoprecipitation of extracts of [125I] surface labeled MC with polyclonal anti-Fc gamma R-Ab followed by SDS-PAGE also showed increased amounts of [125I] Fc gamma R protein after pretreatment with CSF-1, db-cAMP or IFN-gamma. The pretreatment also enhanced staining of MC with anti-Fc gamma R-Ab by immunogold-silver enhancement technique. We conclude that MC express Fc gamma R for IgG-IC that can be regulated by CSF-1, cAMP and IFN-gamma, factors that may be important in glomerular immune injury.

Insulin-dependent contractility of glomerular mesangial cells in response to angiotensin II, platelet-activating factor and endothelin is attenuated by prostaglandin E2

Culture of glomerular mesangial cells in the absence of insulin decreased the degree of contraction of individual cells in response to vasoconstrictive agonists, angiotensin II, platelet-activating factor and endothelin 1, as compared with cells cultured in the presence of insulin (0.7 nM). This change was associated with a decreased sensitivity of the intracellular Ca2+ response to vasoactive agents in fura-2-loaded cells and with an increase in the basal level of prostanoid [prostaglandins (PG) E1 and E2] production estimated by radioimmunoassay. Addition of exogenous PGE2 to insulin-exposed cells decreased the contractile response to that observed in insulin-deficient cells. Inclusion of 8-bromo cyclic AMP had a similar effect. In 45Ca2(+)-release studies it was shown that, in saponin-permeabilized insulin-exposed cells, preincubation with exogenous PGE2 or 8-bromo cyclic AMP decreased the sensitivity of 45Ca2+ release in response to Ins(1,4,5)P3, as demonstrated by an increase in the EC50 (concn. giving half-maximal effect) to 0.182 +/- 0.024 microM and 0.457 +/- 0.031 microM respectively, as compared with untreated permeabilized cells (EC50 0.091 +/- 0.021 microM). A similar decrease in Ins(1,4,5)P3-sensitive 45Ca2+ release was seen in permeabilized cells from insulin-free conditions of culture (EC50 0.20 +/- 0.061 microM). As altered glomerular haemodynamics are found in insulinopaenic diabetic conditions, it is proposed that a decrease in intracellular Ca2+ availability in response to vasoactive agonists and consequent decrease in mesangial-cell contractility contributes to the hyperfiltration seen in this condition.

Platelet activating factor receptor blockade ameliorates murine systemic lupus erythematosus

Untreated 16-week-old MRL/MpJ-lpr/lpr (lpr) mice, when compared to congenic MRL/MpJ-+/+ (+/+) mice, are characterized by a systemic lupus erythematosus syndrome, including severe glomerulonephritis, proteinuria and reduction of renal function. We hypothesized that platelet activating factor (PAF), a potent chemotactic and proinflammatory phospholipid mediator synthesized and released by circulating cells, glomerular mesangial and renal medullary interstitial cells, may play a role in the development of renal injury in lupus mice. We assessed renal PAF synthesis in lpr as well as +/+ mice and the effect of treatment with a PAF receptor blocking agent. Treatment with the PAF receptor antagonist L659,989 for four weeks, starting at 12 weeks of age, significantly reduced acute glomerular infiltration and proliferation, and prevented chronic glomerular histological changes; proteinuria and serum creatinine levels were also significantly reduced in treated mice. Renal PAF production was increased in lpr when compared to +/+ mice, and treatment with L659,989 restored renal PAF synthesis to the control levels. Our results support the hypothesis that PAF can be one of the mediators of glomerular injury characteristic of murine lupus nephritis, and indicate the possible therapeutic utility of PAF receptor antagonists in immunologic renal diseases.

Contributions of mesangial cells to glomerular immune functions

Mesangial cells play an important role in the maintenance of the structure and function of the glomerulus. In addition mesangial cells are capable of macromolecular uptake, and generation of autocoids and cytokines. Our studies have explored the mechanism of IgG uptake by cultured rat mesangial cells. Mesangial cells were found to express Fc receptors for IgG as demonstrated by specific binding studies, indirect immunofluorescence microscopy, immunoblotting and Northern blot analysis. The number of Fc receptors for IgG on mesangial cells was upregulated by interferon gamma, cyclic AMP and monocyte-macrophage specific colony stimulating factor--CSF-1. In addition uptake of IgG complexes was acutely increased by angiotensin II and inhibited by cAMP. These latter effects are independent of receptor number, but are mediated by changes in the cytoskeleton. These observations may be of significance for hemodynamically independent effects of vasoactive agents on mesangial function. Finally we examined the potential of mesangial cells for generation of CSF-1. Cultured mesangial cells produced radioimmunoassayable CSF-1 and expressed mRNA for CSF-1. Interferon gamma stimulated, whereas cAMP and agents increasing cAMP, such as forskolin and PGE2, inhibited CSF-1 production. This was due to decreased transcription resulting in lower levels of mRNA for CSF-1. The interactions of CSF-1, other cytokines, prostaglandins and cAMP may be important in regulating immune-like functions of mesangial cells, and especially their response to immunecomplexes.

Tumor necrosis factor induces contraction of mesangial cells and alters their cytoskeletons

Cultures of human mesangial cells (MC) were established from the renal cortex of surgical specimen. The characteristic spindle-shaped or stellate appearance of MC was altered after treatment with tumor necrosis factor (TNF). After two hours, the MC retracted and lost reciprocal contacts. Furthermore, this treatment altered the cytoskeletal organization of MC, since a peripheral band of actin and stress fibers disappeared while the streaks of vinculin at focal contacts decreased. These changes were reversible when the MC were cultured in fresh medium. After five minutes of treatment with platelet activating factor (PAF), changes similar to those induced by TNF were observed. Inhibitors of PAF synthesis, such as plasma alpha 1-proteinase inhibitor and an anti-inflammatory peptide, blocked changes induced by TNF, PAF receptor antagonists inhibited changes induced by PAF and also by TNF. These results and the finding that MC are stimulated to produce PAF by TNF suggest that PAF is a secondary mediator of the changes in cell shape and cytoskeletal organization induced by this cytokine.

Regulation of human mesangial cell growth in culture by thromboxane A2 and prostacyclin

Elevated eicosanoid biosynthesis characterizes certain forms of human and experimental glomerular proliferative disease. Thromboxane A2 (TxA2) and other prostaglandins (PG) act through specific receptors and mechanisms of intracellular signal transduction in human mesangial cells. We studied the actions of U-46619, a TxA2 mimetic which stimulates mesangial phospholipase C, and of the PGI2 analogue, Iloprost, a potent activator of adenylate cyclase, on proliferation of cultured human mesangial cells. When applied alone to quiescent cells, U-46619 had only weak mitogenic activity, as assessed by [3H]thymidine [( 3H]-TdR) incorporation and cell counts. On the other hand, addition of U-46619 10 minutes prior to stimulation of the cells with 1 to 17% fetal bovine serum (FBS) for 24 hours, potently and dose-dependently inhibited FBS-stimulated [3H]-TdR incorporation. Similarly, U-46619 inhibited the effects of 10 ng/ml platelet-derived growth factor (PDGF), epidermal growth factor or basic fibroblast growth factor on [3H]-TdR incorporation, by 55, 79 and 88%, respectively. The effects of U-46619 were not mimicked by another stimulus of phospholipase C, angiotensin II. Iloprost also inhibited FBS-activated proliferation. Neither eicosanoid inhibited the rise of cytosolic Ca2+ induced by FBS or PDGF. The actions of TxA2 and Iloprost in cultured cells point to multiple functional interactions between eicosanoids and growth factors in the control of mesangial cell proliferation.

Interleukin-6 production by tumor necrosis factor and lipopolysaccharide-stimulated rat renal cells

Interleukin-6 (IL-6) is produced by various cell types, including monocytes, fibroblasts, and endothelial cells. IL-6 has also been detected in the urine of normal and renal transplant patients. Thus, the possible production of this cytokine by glomeruli and mesangial cells was investigated. Rat glomeruli were obtained by serial sieving of cortical homogenates of blood-free kidneys. Mesangial cells were obtained from the glomeruli and cultured under standard methods in RPMI 1640 medium containing 15% fetal calf serum. Glomeruli or confluent monolayers cells were then incubated in RPMI 1640 for 18 hr, in the presence or not of tumor necrosis factor-alpha (TNF alpha), lipopolysaccharide (LPS), or platelet-activating factor (PAF). IL-6 activity was measured using the IL-6-dependent cell line subclone (B 9-9) and expressed with respect to a standard curve established with recombinant IL-6. Glomeruli generate IL-6 upon TNF alpha (100 ng/ml) and LPS (1 microgram/ml), 11,500 +/- 3000 and 22,000 +/- 7500 U/ml, respectively. Nonstimulated mesangial cells produced 50 +/- 5 U/ml (mean +/- SEM, n = 4) of IL-6. TNF alpha (1 ng/ml) and LPS (1 microgram/ml) induced the production of 800 +/- 90 and 40,000 +/- 5000 U/ml, respectively (n = 4). In contrast, PAF (0.1 nM-1 microM) did not increase IL-6 production from glomeruli or mesangial cells. These results demonstrate that renal cells spontaneously generate minimal amounts of IL-6 and that this production is significantly increased by TNF alpha or LPS. A synergy between LPS and TNF alpha was induced in glomerular cells with 10 ng/ml of TNF alpha and graded concentrations of LPS. Thus, the production of IL-6 by glomerular cells and its modulation by other cytokines or endotoxins may play a role in the local immunological processes leading to immune glomerular diseases.

Platelet-activating factor alters the dynamics of prostaglandin and protein synthesis by endometrial explants from pregnant and cyclic cows at Day 17 following estrus

Factors produced by bovine conceptuses alter prostaglandin (PG) and protein secretion by endometrial explants from cyclic cows and induce an intracellular inhibitor of PG synthesis. Endometrial explants from cyclic (n = 4) and pregnant (n = 3) cows at Day 17 following estrus were incubated for 24 h with 0, 0.1, 0.5, 1 and 5 microg platelet-activating factor (PAF)/ml. Cotyledonary microsomes from parturient cows were utilized to determine levels of an intracellular/cytosolic inhibitor of PG synthesis. Endometrial explants from additional cyclic cows (n = 4) were incubated for 24 h with 0 or 5 microg PAF/ml with and without 50 microCi [(3)H]leucine. Endometrial explants (cyclic cows, n = 3) were also incubated for 12 h with each of the following treatments: 1) Control; 2) PAF (1 microg/ml); 3) lyso-PAF (2 to 10 microg/ml); 4) PAF-receptor antagonist (2 to 10 microg/ml); 5) PAF (1 microg/ml) + antagonist (2 to 10 microg/ml); 6) bovine conceptus secretory proteins (bCSP; 25 microg/ml); and 7) bCSP (25 microg/ml) + antagonist (5 microg/ml). Platelet-activating factor had distinct negative and positive dose effects on PGF and PGE-2 secretion, respectively, by explants from cyclic cows, whereas PG secretion was not altered by PAF in the endometrium of pregnant cows. Platelet-activating factor did not alter the level of an intracellular inhibitor of prostaglandin synthesis, whereas, bCSP increased the level of this inhibitor. Platelet-activating factor decreased the incorporation of [(3)H]leucine into tissue and secreted proteins for explants from cyclic cows. Lyso-PAF did not alter endometrial prostaglandin secretion. The effects of PAF but not of bCSP were blocked by the PAF-receptor antagonist. Platelet-activating factor altered PG and protein secretion by the endometrium from cyclic cows, and it may be a potential regulatory factor during early pregnancy if secreted by the bovine conceptus.

Prostaglandins and rat glomerular mesangial cell proliferation

Arachidonate metabolites modulate glomerular mesangial cell contractility through specific receptors coupled to phospholipase C or adenylate cyclase. The resulting intracellular signals, including changes of cytosolic Ca2+, pH, and cyclic adenosine 3'5'-monophosphate (cAMP) are known to also regulate the growth of many cell types. Since eicosanoids have been shown to interfere with cell proliferation in culture, we studied DNA synthesis and cell number in rat mesangial cell cultures exposed to a selective phospholipase C activator, prostaglandin F2 alpha (PGF2 alpha), or to the cAMP-stimulating PGI2 analogue, Iloprost. PGF2 alpha dose-dependently enhanced DNA synthesis and cell proliferation in the presence of insulin, with an EC50 of 0.1 microM. This eicosanoid potentiated the effects of platelet-derived growth factor (PDGF) or low concentrations of serum. Maximum stimulatory potency was about one-third that of PDGF. Removal of PGF2 alpha after short-term stimulation (30 min) did not reverse its mitogenic effect. Iloprost had no effect on DNA synthesis of quiescent cells, but potently inhibited growth stimulated by various concentrations of fetal serum. PG released within the glomerular microcirculation may play a regulatory role in both normal and deranged mesangial cell growth.

Monokines and platelet-derived growth factor modulate prostanoid production in growth arrested, human mesangial cells

Previous studies have demonstrated considerable prostanoid production by cultured proliferating rat mesangial cells (MC). In this study, human mesangial cells (HMC) were examined during serum-free culture in which the cells were reversibly growth arrested and did not suffer obvious irreversible functional changes. Non-stimulated cells released 2 to 10 pg/24 hr/micrograms cellular protein of PGE2, PGF2 alpha, 6-keto-PGF1 alpha, while TXB2 was not detectable. Stimulation with interleukin-1 beta (IL-1 beta) or tumor necrosis factor alpha (TNF alpha) induced up to 18-fold (IL-1 beta) or up to fourfold (TNF alpha) increases of prostanoid release. Combinations of the two monokines resulted in significant synergistic induction of PGE2 and 6-keto-PGF1 alpha up to 38 times that of control cells. Interleukin-6 (IL-6) and the HMC-mitogen, platelet-derived growth factor-BB (PDGF-BB) only induced marginal increases in HMC prostanoid generation. However, when PDGF-BB or -AB was combined with IL-1 beta or IL-6, prostanoid generation by HMC was synergistically increased up to 222-fold (IL-1 beta) or 12-fold (IL-6) above the control values, with the induction of PGE2 greater than 6-keto-PGF1 alpha greater than PGF2 alpha much greater than TXB2. In the case of IL-1 beta + PDGF-BB the induction of PGE2 release was at least partly due to the synergistic induction of cyclooxygenase activity. These findings demonstrate that both proliferating and reversibly growth arrested HMCs release prostaglandins in response to various inflammatory stimulators and combinations thereof. The findings support the important role of HMC in the regulation of glomerular hemodynamics during inflammatory processes.