Prostaglandin synthesis by rat glomerular mesangial cells in culture. Effects of angiotensin II and arginine vasopressin

Aldose reductase expression and prostaglandin E2 production are coordinately regulated in cultured rat mesangial cells

There is increasing evidence that a link between the polyol pathway and prostaglandins is important in the pathogenesis of diabetic nephropathy. The presence of the polyol pathway in the kidneys of normal animals, the galactose-fed rat, and animals with experimental diabetes has been established. While aldose reductase (AR) immunoreactive protein (AR-IRP) and AR mRNA are expressed at high levels in renal medulla, the sites of AR synthesis and regulation and metabolic consequences of AR activity in renal cortex are uncertain. The present study was conducted to test the hypothesis that AR expression and PGE2 production are coordinately regulated in glomerular mesangial cells. To test this hypothesis, we measured AR-IRP, AR mRNA, and PGE2 production in mesangial cells isolated from rats maintained on diets containing normal chow (MC-N), 50% galactose (MC-G), and 50% dextrin (MC-D). The rank order for each parameter studied (AR-IRP, AR mRNA, PGE2) was MC-N > MC-G > MC-D. Western blot analysis demonstrated that MC-N (optical density [OD] 1.0), MC-G (OD 0.59), and MC-D (OD 0.25) express AR-IRP. Slot-blot analyses demonstrated that levels of AR mRNA were greatest in MC-N (1.0), intermediate in MC-G (0.49), and lowest in MC-D (0.31). Ribonuclease (RNase) protection analyses demonstrated a similar pattern of AR mRNA expression, with MC-N at 1.0, MC-G at 0.60, and MC-D at 0.33. PGE2 production (pg/5 x 10(4) cells/30 min) was highest in MC-N (278 +/- 29), intermediate in MC-G (110 +/- 9), and lowest in MC-D (37 +/- 4).(ABSTRACT TRUNCATED AT 250 WORDS)

Oxidant stress and glomerular prostanoid production: influence of angiotensin converting enzyme inhibition

1. The effect of H2O2 (4.7 x 10(-9) -4.7 x 10(-3) M) on prostanoid production by isolated glomeruli from normotensive (WKY) and, spontaneously hypertensive rats (SHR) has been studied. 2. Oxidant stress significantly increased synthesis of prostaglandin E2 (PGE2), I2 (PGI2) and thromboxane A2 (TxA2) by glomeruli from both strains whereas the ratio (PGE2 + PGI2)/TxA2 increased in only SHR. 3. Pre-incubation of glomeruli with the angiotensin converting enzyme inhibitors captopril or lisinopril, had virtually no effect on H2O2-induced synthesis of individual prostanoids nor on the ratio (PGE2 + PGI2)/TxA2 by glomeruli from either WKY or SHR. 4. The findings suggest that H2O2-induced changes in glomerular function may be mediated, in part, by PGs but fail to support the suggestion that the ability of ACEI to protect glomeruli from H2O2-induced damage is determined by PGs.

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)

Acute renal failure following binge drinking and nonsteroidal antiinflammatory drugs

Two college students who developed reversible acute deterioration in renal function following binge drinking of beer and the use of nonsteroidal antiinflammatory drugs (NSAIDs) are reported. Both patients presented with back and flank pain with muscle tenderness, but showed no evidence of overt rhabdomyolysis. The first case had marked renal failure, with a peak serum creatinine reaching 575 mumol/L (6.5 mg/dL), and acute tubular necrosis was documented by renal biopsy. The second case had only modest elevation in serum creatinine, and renal function rapidly improved on rehydration. The contribution of the potential muscle damage associated with alcohol ingestion to the changes in renal function in these two cases is not clear. However, the major mechanism for the acute renal failure was thought to be related to inhibition of renal prostaglandin synthesis in the face of compromised renal hemodynamics secondary to alcohol-induced volume depletion.

Characterization of rat glomerular thromboxane A2 receptors: comparison to rat platelets

This study was designed to characterize rat glomerular thromboxane A2 (TxA2) receptors and compare them to rat platelet TxA2 receptors. The radioligand binding characteristics of the receptors were characterized using [125I][1S-(1 alpha,2 beta(5Z),3 alpha-(1E,3R*),4 alpha]-7-[3-(3-hydroxy-4-(4'-iodophenoxy)-1-butenyl)-7-oxabicyclo- [2.2.1]heptan-2yl]-5-heptenoic acid ([125I]BOP), a TxA2 agonist. Equilibrium binding with [125I]BOP, as well as competitive binding assays between [125I]BOP and 13-azapinane TxA2 receptors antagonists, were performed in rat glomerular membranes (RGM) and washed rat platelets (WRP). [125I]BOP identified a single class of TxA2 receptor sites in glomerular membranes with a Kd of 318 +/- 55 pM and a Bmax of 260 +/- 62 fmol/mg protein (n = 14). [125I]BOP was displaced by the TxA2 agonist 15S-hydroxy-11 alpha,9 alpha(epoxymethano)-prosta-5Z,13E-dienoic acid (U-46,619) (IC50 = 22 +/- 6 nM, n = 3), the antagonist SQ-29,548 (IC50 = 41 +/- 7 nM, n = 4), and stereoselectively by the antagonists (-)-9-chlorobenzyl-6-fluoro-1,2,3,4-tetrahydrocarbazol-1-yl acetic acid (L-657,925) (IC50 = 0.27 +/- 0.04 nM, n = 3) and (+)-9-chlorobenzyl-6-fluoro-1,2,3,4-tetrahydrocarbazol-1-yl acetic acid (L-657,926) (IC50 = 124 +/- 0 nM, n = 2). The ability of six 13-azapinane TxA2 antagonists to compete with [125I]BOP was evaluated. The rank orders for the 13-azapinanes showed no significant correlation between RGM and WRP.(ABSTRACT TRUNCATED AT 250 WORDS)

Production of interleukin-1-like cytokine by cultured rat glomerular macrophages

Resident glomerular macrophages from normal rats were isolated and grown through long-term cultures in order to obtain confluent cell monolayers. These cells have a secretory function as revealed by the production of a cytokine with a molecular weight similar to interleukin-1 (IL-1). The demonstration that rat glomerular macrophages secrete an IL-1-like cytokine emphasizes the role of these cells in a number of glomerular secretory functions, including some which have been commonly attributed only to mesangial contractile cells.

Thromboxane synthesis and action within the kidney

PGH2 and TxA2 exert their actions via tissue specific, receptor isoforms. PGH2/TxA2-dependent platelet aggregation and contraction of vascular and bronchial smooth muscle and of glomerular mesangial cells occur via receptors linked to activation of phospholipase C. Although PGH2/TxA2 appear to be of little importance in the maintenance of renal function under physiological circumstances, increased renal TxA2 biosynthesis has been documented in a variety of animal models of renal disease and in some clinical disorders (Table 2). The effects of this eicosanoid on renal tissues in vitro and of pharmacological manipulation of TxA2 synthesis and action in vivo suggest that such interventions will provide new drugs for the treatment of human kidney disease.

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.

Upregulation of D-myo-inositol transport in diabetic rat glomerular cells

In the streptozotocin (STZ)-treated diabetic rat, reduced glomerular arteriolar resistance leads to raised intraglomerular pressure. Because vasoconstrictor hormones, such as angiotensin II, stimulate arteriolar smooth muscle and mesangial cell contraction via the D-myo-inositol (MI)-dependent transmembrane signaling pathway, in diabetes extracellular D-glucose may inhibit MI transport causing MI depletion, reduced signaling, and hypocontractility. Therefore we studied the regulation of Na-dependent MI transport in the intact cells (mesangial and endothelial) of isolated glomeruli from STZ rats after 2 wk of diabetes, with and without insulin, compared with controls. Specific [3H]MI uptake per milligram glomerular protein (10-150 min, 37 degrees C) was observed in the presence of 0, 5.5, and 30 mM D-glucose using L-[14C]glucose as a marker of nonspecific uptake. D-Glucose competitively inhibited Na-dependent MI transport (maximum velocity) into diabetic and normal glomerular cells. At 5.5 mM D-glucose, MI uptake by diabetic non-insulin-treated glomeruli was increased to 191 +/- 14% (SE) above normal glomeruli. Insulin treatment resulted in less upregulation (116 +/- 11%) of normal MI transport. High glucose concentration did not alter the rate of [3H]MI efflux from preloaded glomerular cells. To determine whether diabetes alters available substrate for transmembrane signaling, after incubation for 120 min, the incorporation of [3H]MI into cellular membrane phosphoinositides and soluble D-myo-inositol phosphates of isolated diabetic and control glomerular cells was compared. Diabetic glomerular cells displayed a significant increase (P less than 0.005) in [3H]MI incorporation into these fractions compared with controls.

IL-1-like production in adriamycin-induced nephrotic syndrome in the rat

Rats receiving a single dose of adriamycin (7.5 mg/kg) develop heavy proteinuria and morphological abnormalities similar to those observed in minimal change nephrotic syndrome in humans. A concomitance between enhanced I-a display by resident glomerular macrophages, IL-1-like cytokine secreted by whole isolated rat glomeruli and proteinuria was observed in adriamycin-injected rats during the experimental protocol. In addition, in vitro studies have shown that after stimulation with adriamycin or lipopolysaccharide (LPS) this cytokine is mainly produced by resident glomerular macrophages in culture. Although the precise mechanism of proteinuria in this model needs to be further studied, our results indicate that IL-1-like cytokine could be an important mediator implicated in the structural and functional disturbances occurring at the glomerular capillary wall level in adriamycin nephrosis.

Effects of arginine vasopressin and extracellular osmolarity on atrial natriuretic peptide release by superfused rat atria

This study investigated the characteristics of atrial natriuretic peptide (ANP) release from superfused sliced atria and ventricles of rats. Right atria spontaneously released more immunoreactive ANP (Ir-ANP: pg/min per mg tissue) (32 +/- 3) than did left atria (11 +/- 2) or right ventricles (1.5 +/- 0.5). Addition of 10(-9) to 10(-5) M of arginine vasopressin (AVP) to the superfusing fluid or increasing its osmolarity (290 to 490 mOsM) resulted in a significant increase of the Ir-ANP outflow from right atria. The effect of AVP was prevented by a specific V1 receptor antagonist, ([d(ch2)5Tyr(Me)]AVP). Superfusion with indomethacin (10(-5) M) did not alter spontaneous release but inhibited the peak levels of Ir-ANP induced by AVP (10(-5) M). Moreover, DDAVP, a specific V2 receptor agonist, did not induce Ir-ANP release. Ca(2+)-free medium alone or plus 1 mM EGTA induced a significant increase in basal Ir-ANP outflow. The Ir-ANP released chromatographed similarly to the standard alpha-rANP. These results suggest a specific stimulatory effect of AVP and osmolarity and a negative influence of extracellular Ca2+ on atrial spontaneous Ir-ANP release. It appears that the effect of AVP could be mediated by prostaglandin synthesis.

Calcium channel blockade inhibits platelet activating factor production by human umbilical vein endothelial cells

An increase in intracellular calcium level is an important signal in the regulation of cellular responses under normal and pathological conditions. Because two key enzymes in the synthetic pathway of platelet activating factor (PAF), phospholipase A2 and acetyltransferase, are calcium dependent, we hypothesized that calcium channel blockade may inhibit agonist-induced PAF synthesis. Primary cultures of human umbilical vein endothelial cells (EC), pre-incubated with [3H]acetate, were exposed to thrombin (5 U/mL) and PAF production was quantitated by incorporation of radiolabel into the EC lipid fraction co-migrating with exogenous PAF in thin-layer chromatography. The effect of pre-incubation with calcium channel blockers (verapamil, diltiazem, 10(-4) M) or buffer was determined. Results (triplicate experiments, * P less than 0.05 vs buffer, P less than 0.05 vs thrombin) demonstrate that pre-incubation with calcium channel blocker markedly inhibits thrombin-induced PAF production (verapamil:buffer 273 +/- 122, thrombin 10,735 +/- 1524*, thrombin + verapamil 178 +/- 91 cpm/plate; diltiazem:buffer 1097 +/- 581, thrombin 15,283 +/- 2661*, thrombin + diltiazem 280 +/- 56 cpm/plate). The effect of diltiazem was dose-dependent (% inhibition: 10(-7) M, 46%; 10(-5) M, 60%; 10(-4) M, 98%). Diltiazem also inhibited bradykinin (10(-8) M) induced PAF synthesis. In calcium-free medium or in the presence of LaCl3 (10(-3) M), the PAF response of EC to thrombin was blunted (buffer 582 +/- 360, thrombin 5394 +/- 1069, thrombin + calcium free medium 1055 +/- 571, thrombin + LaCl3 1271 +/- 58 cpm/plate). We conclude that calcium channel blockers prevent agonist-induced PAF synthesis, possibly by preventing cellular calcium influx and activation of PAF synthetic enzymes. We speculate that this mechanism may underlie, at least in part, the beneficial effect of calcium channel blockade under various pathological conditions.

Effects of ozone on lung mechanics and cyclooxygenase metabolites in dogs

To determine if acute exposure to ozone can cause changes in the production of cyclooxygenase metabolites of arachidonic acid (AA) in the lung which are associated with changes in lung mechanics, we exposed mongrel dogs to 0.5 ppm ozone for two hours. We measured pulmonary resistance (RL) and dynamic compliance (Cdyn) and obtained methacholine dose response curves and bronchoalveolar lavagate (BAL) before and after the exposures. We calculated the provocative dose of methacholine necessary to increase RL 50% (PD50) and analyzed the BAL for four cyclooxygenase metabolites of AA: a stable hydrolysis product of prostacyclin, 6-keto-prostaglandin F1 alpha (6-keto-PgF1 alpha); prostaglandin E2 (PgE2); a stable hydrolysis product of thromboxane A2, thromboxane B2 (TxB2); and prostaglandin F2 alpha (PgF2 alpha). Following ozone exposure, RL increased from 4.75 +/- 1.06 to 6.08 +/- 1.3 cm H2O/L/sec (SEM) (p less than 0.05), Cdyn decreased from 0.0348 +/- 0.0109 TO .0217 +/- .0101 L/cm H2O (p less than 0.05), and PD50 decreased from 4.32 +/- 2.41 to 0.81 +/- 0.49 mg/cc (p less than 0.05). The baseline metabolite levels were as follows: 6-keto PgF1 alpha: 96.1 +/- 28.8 pg/ml; PgE2: 395.8 +/- 67.1 pg/ml; TxB2: 48.5 +/- 11.1 pg/ml; PgF2 alpha: 101.5 +/- 22.6 pg/ml. Ozone had no effect on any of these prostanoids. These studies quantify the magnitude of cyclooxygenase products of AA metabolism in BAL from dog lungs and demonstrate that changes in their levels are not prerequisites for ozone-induced changes in lung mechanics or airway reactivity.

Mesangial cell immune injury. Synthesis, origin, and role of eicosanoids

The synthesis, cell origin, and physiologic role of eicosanoids were investigated in a model of mesangial cell immune injury induced by a monoclonal antibody against the rat thymocyte antigen Thy 1.1 also expressed in rat mesangial cells. A single intravenous injection of the antibody resulted in enhanced glomerular synthesis of thromboxane (Tx)B2, leukotriene (LT)B4, and 12-hydroxyeicosatetraenoic acid (HETE), whereas that of PGE2 and PGF2 alpha was either unaltered or impaired. The enhanced eicosanoid synthesis was associated with decrements in glomerular filtration rate (GFR) and renal blood flow (RBF). Complement activation mediated both the increments in TxB2, LTB4, and 12-HETE and the decrements in GFR and RBF. The decrements in GFR were abolished by the TxA2 receptor antagonist SQ-29,548. Although both neutrophiles and Ia (+) leukocytes infiltrated glomeruli, glomerular LTB4 originated mainly from the latter. Platelets entirely accounted for the enhanced 12-HETE synthesis in isolated glomeruli and to a lesser extent for that of LTB4 and TxB2. Glomerular PGE2 and PGF2 alpha originated from mesangial cells as their impaired synthesis coincided with extensive mesangial cell lysis. The observations indicate that in mesangial cell immune injury vasoactive and proinflammatory eicosanoids originate from recruited or activated Ia (+) leukocytes and platelets and may exert paracrine effects on mesangial cells.

Characterization of a B2-bradykinin receptor in rat renal mesangial cells

The specific binding of bradykinin (BK) was investigated using membrane fractions from mesangial cells in primary culture, a cloned cell line, and in intact adherent cells with three different radiolabelled BK analogues: 125I-[Tyr0]BK, 125I-[Tyr5]BK and 125I-[Tyr8]BK. The best radioligand was 125I-[Tyr0]BK, and assay conditions were determined to ensure maximal stable binding. Binding appeared to be reversible and not to be inhibited by a wide variety of protease inhibitors including converting enzyme inhibitor and phosphoramidon. The maximum density of binding sites (Bmax) was about 88 +/- 18 fmol/mg protein, which is equivalent to about 6000 sites/cell, and the dissociation constant averaged 2 nM. No significant difference in Bmax was observed between membranes from cells in primary culture and those from cloned cells. Of the BK analogues tested, unmodified BK exhibited the highest inhibition constant (close to 10(-10) M). No displacement of 125I-[Tyr0]BK was observed in the presence of the B1 agonist des-Arg9-BK or several unrelated peptides, including atrial natriuretic factor and angiotensin I and II, whereas 50% inhibition of binding was achieved with the B2 antagonist [D-Arg,Hyp3,D-Phe7]BK (10(-9)M). Addition of BK for 3 min to the incubation medium of cloned mesangial cells induced a dose- and time-dependent increase in PGE2 unlike des-Arg9-BK, which showed no such effect. The secretion was strongly inhibited by prior incubation with the B2 antagonist [D-Arg,Hyp3,D-Phe7]BK. The pharmacological profile of the binding site determined with various BK agonists and antagonists, and the stimulating effect of binding site activation on prostaglandin release strongly suggest that B2-kinin-like receptors are present in rat mesangial cells.

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.

Prostaglandin E2 binding sites in human renal tissue: characterization and localization by radioligand binding and autoradiography

The prostaglandin E2 (PGE2) binding site in human kidney was characterized in membrane preparations from cortex, outer medulla and inner medulla using radioligand binding techniques. The localization of the binding sites for [3H]PGE2 was visualized autoradiographically. In the membrane suspensions, the highest level of specific [3H]PGE2 binding was detected in the outer medulla (Bmax = 335 +/- 28 fmol mg-1 protein) followed by the inner medulla (Bmax = 258 +/- 21 fmol mg-1 protein) and the cortex (Bmax = 143 +/- 22 fmol mg-1 protein). The binding was of high affinity with KD values between 3.7 and 6.2 nM in the various regions. Unlabelled prostaglandins competed for the [3H]PGE2 binding sites in the following rank order of potency: PGE2 approximately PGE1 greater than PGF2 alpha approximately PGA2 greater than PGB2 greater than PGI2 approximately PGD2. Autoradiographs revealed that a high density of [3H]PGE2 (2 nM) binding sites were located on the distal tubule, particularly on the thick ascending limbs of Henle. Lower densities of [3H]PGE2 binding sites were found on the medullary collecting ducts and possibly on the thin loops of Henle. In contrast, no specific [3H]PGE2 binding could be found on the proximal tubule, glomeruli or on blood vessels. This distribution is in accordance with the assumed site of action for the salt and water regulatory function of PGE2.

Production of endothelin-1 by rat cultured mesangial cells

We investigated whether ET-1 is synthesized by and released from mesangial cells. ET-1-like immunoreactivity (LI) released into medium increased time-dependently under a serum-free condition. The amounts of ET-1-LI released into the medium was augmented in the presence of fetal calf serum. Reverse-phase HPLC profile of the conditioned media revealed a major component coeluting with standard ET-1. Northern blot analysis of poly(A) +RNA extracted from mesangial cells showed a single major band corresponding to the size of preproET-1 mRNA (2.3 kb). These findings demonstrate that ET-1 is synthesized by and released from rat mesangial cells and suggest a possibility that it acts on their own cells as an autocrine factor.

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.

Endothelin and eicosanoid synthesis in cultured mesangial cells

We investigated the effect of endothelin on the generation of eicosanoids, which are known to regulate basal and stimulated mesangial cell tone. The results showed that endothelin is a potent stimulus of prostaglandin E2 (PGE2), prostacyclin (PGI2), and thromboxane A2 (TxA2) synthesis by bovine mesangial cells. Percentage increases in eicosanoid synthesis induced by endothelin (10(-10) to 10(-6) M), were 50 to 275% for PGE2, 28 to 168% for PGI2 and 42 to 111% for TxA2, respectively. Endothelin-induced eicosanoid synthesis in mesangial cells was concentration, but not time dependent. Aspirin (500 microM) completely prevented endothelin-induced eicosanoid synthesis. The calcium entry blocker nitrendipine (10(-8) M) failed to inhibit endothelin-induced eicosanoid synthesis. These data suggest that endothelin-induced changes in renal circulation and glomerular function in normal and disease conditions may be modulated by the concomitant stimulation of mesangial eicosanoid synthesis.

Recovery of prostaglandin synthesis in rat glomerular mesangial cells after aspirin inhibition: induction of cyclooxygenase activity by serum and epidermal growth factor

We assessed cyclooxygenase activity in cultured rat mesangial cells by measuring prostaglandin production with reverse phase HPLC upon addition of exogenous 14C arachidonic acid. The profile of prostaglandins produced was PGE2 greater than PGF2a much greater than 6-keto PGF1a much greater than thromboxane and PGD2. In quiescent mesangial cells, exposure to 300 microM aspirin for 30 minutes irreversibly inhibited cyclooxygenase activity; after 5 hours, cyclooxygenase activity was only 19 +/- 3% of control. Addition of 10% fetal bovine serum after aspirin inactivation stimulated time-dependent recovery of cyclooxygenase activity to 118 +/- 30% of control by 5 hours. Serum induced-recovery was significantly inhibited by the simultaneous administration of the protein kinase C inhibitor, staurosporine. Phorbol myristate acetate also induced recovery of cyclooxygenase activity, suggesting that protein kinase C may be involved in the signaling process. In addition to serum, epidermal growth factor was also found to lead to partial recovery of cyclooxygenase activity. The serum and EGF-induced recoveries were inhibitable by cycloheximide and actinomycin D. These results suggest that recovery of cyclooxygenase activity in mesangial cells is stimulated by EGF and other components of serum, is dependent upon new protein synthesis and appears to be transcriptionally regulated.

The role of mesangial cells in glomerular pathology

The glomerular mesangial cell has become increasingly recognized as a multifunctional cell capable of mediating glomerular disease. This article reviews recent findings regarding the biology of these cells, and the relevance that these findings may have for our understanding of glomerular pathology.

Atrial natriuretic factor alters phospholipid metabolism in mesangial cells

The mechanism for the vasorelaxant effect of atrial natriuretic factor (ANF) remains to be clarified. Recent evidence suggests that this agent can antagonize the action of angiotensin II (ANG II) by affecting intracellular calcium metabolism. The biochemical basis for this phenomenon was investigated in cultured rat mesangial cells (MCs), a preparation which exhibits the contractile properties of smooth muscle cells and is responsive to ANG II and ANF. Preincubation of MCs with ANF significantly inhibited ANG II-induced release of inositol trisphosphate (IP3) resulting from hydrolysis of phosphatidylinositol 4, 5-bisphosphate. Similarly, ANG II-stimulated increases in cytosolic free Ca2+ [( Ca2+]i), 45Ca efflux, as well as 45Ca influx were diminished by ANF. In addition, these alterations in Ca2+ kinetics were associated with ANF-mediated antagonism of ANG II-induced phospholipid turnover and prostaglandin (PG) E2 release. Sodium nitroprusside (SNP), which augmented guanosine 3',5'-cyclic monophosphate (cGMP) accumulation to a degree comparable to ANF, likewise inhibited ANG II action on the phosphoinositide (PI) pathway, Ca2+ regulation, and PGE2 production. Collectively our results indicate that the effects of ANF on [Ca2+]i in MCs relate to cGMP-induced alterations of PI metabolism. In this fashion cGMP-elevating agents may influence a variety of calcium-dependent biochemical pathways including prostaglandin synthesis.

Ambient C1- ions modify rat mesangial cell contraction by modulating cell inositol trisphosphate and Ca2+ via enhanced prostaglandin E2

Our recent observation showed that angiotensin II (AII) and arginine vasopressin (AVP) stimulate Ca2+-activated Cl- conductance in mesangial cells. These data raise the possibility that mesangial cell function may be modulated by extracellular chloride concentration [( Cl-]o). The present study was undertaken to test this possibility using cultured rat mesangial cells. When the [Cl-]o was reduced to zero, the percentage of mesangial cells showing contraction responding to AII and AVP was decreased from 72 +/- 9 to 33 +/- 10% and from 60 +/- 4 to 24 +/- 11%, respectively. Ca2+ transients induced by AII and AVP, measured in mesangial cells loaded with Ca2+-sensitive photoprotein aequorin, were attenuated as [Cl-]o decreased. Also, when [Cl-]o decreased, inositol trisphosphate (IP3) levels of mesangial cells were suppressed, both in the presence and absence of AII or AVP. PGE2 production by mesangial cells increased when [Cl-]o decreased and the effects of ambient Cl- deprivation could be restored by addition of indomethacin to the Cl- -free medium. Moreover, PGE2 decreased mesangial cell contractility, Ca2+ transients, and IP3 production in response to AII and AVP. These data suggest that the decrease in [Cl-]o attenuates mesangial cell contraction by suppressing IP3 production and thus Ca2+ transients in response to AII and AVP through enhanced PGE2 production.

Aspirin lowers blood pressure in patients with renovascular hypertension

To clarify the role of renal prostanoid in hyperreninemia and high blood pressure in human renovascular hypertension, we measured prostaglandin E2 and renin activity in renal venous and abdominal aortic plasma before and after the intravenous administration of the cyclooxygenase inhibitor, aspirin DL-lysine. Subjects were six patients with unilateral renovascular hypertension and six with essential hypertension. In patients with renovascular hypertension, prostaglandin E2 concentration in renal venous plasma from the stenotic kidney was 9.25 +/- 1.48 pg/ml, which was significantly higher (p less than 0.01) than the concentration in the renal venous plasma from the normal kidney (4.97 +/- 1.02 pg/ml) or in the aortic plasma (2.59 +/- 0.15 pg/ml). Plasma renin activity was also higher in the renal vein of the stenotic kidney than in the other two sites. The stenotic side/normal side ratio of the renal venous prostaglandin E2 correlated significantly with a renin ratio greater than 1.5 (r = 0.8211, p less than 0.05). Intravenous injection of aspirin DL-lysine (18 mg/kg) 30 minutes later markedly suppressed prostaglandin E2 and renin levels at all sites and clearly lowered arterial blood pressure (mean: from 120 +/- 6 to 110 +/- 5 mm Hg, p less than 0.01). The reduction in blood pressure correlated significantly with the suppression of plasma renin activity in the aorta (p less than 0.05) and in the renal vein of the stenotic kidney (p less than 0.01). Conversely, in patients with essential hypertension, aspirin had little effect on renin levels and increased mean blood pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Respiratory syncytial virus infection of human cord and adult blood monocytes and alveolar macrophages

We studied the permissiveness of human leukocytes, blood monocytes, alveolar macrophages, and cord blood monocytes to infection with respiratory syncytial virus (RSV). Specific immunofluorescence was used to determine the percentage of infected leukocytes. The results indicated that monocytes were the most susceptible human leukocyte to in vitro infection with RSV. Polymorphonuclear leukocytes demonstrated no specific fluorescent staining after 24 h of exposure to RSV, whereas peripheral blood nonadherent mononuclear cells demonstrated a low percentage of positive cells, with a mean of 6 +/- 1% SE. In contrast, 37 +/- 5% of monocytes expressed RSV antigen after viral exposure. Exposure of monocytes to lipopolysaccharide (LPS) for 1 h prior to RSV increased the percentage of infected cells to 48 +/- 6% and stimulated their secretion of prostaglandin E2 (PGE2) and alpha tumor necrosis factor (TNF). Intrinsic mononuclear phagocytic factors influencing the permissiveness to RSV were studied by determining infection of adult and cord blood and alveolar mononuclear phagocytes (MP). Alveolar and blood MP simultaneously isolated from adult donors were similarly infected by RSV, which varied with the viral dose. Cord blood MP were more susceptible to RSV infection than were adult MP, 58 +/- 9% infected versus 37 +/- 5%, respectively (p less than 0.05). Treatment with LPS for 1 h prior to RSV exposure did not increase infection of cord blood MP as seen with adult blood MP. However, LPS can induce human monocytes to secrete cytokines with antiviral activity, and our results indicate that both gamma interferon and TNF, independently or in combination, prevented infection of monocytes in a dose-dependent manner.

Inhibition of prostaglandin E2 synthesis by a blocker of epithelial chloride channels

Arginine-vasopressin (AVP) elicits a variety of responses in cultured rat mesangial cells, among them stimulation of prostaglandin biosynthesis and activation of Cl- channels. AVP produced an 11-fold increase over basal levels in prostaglandin E2 release from cultured mesangial cells. This response was completely inhibited by 25 microM indomethacin and 82 +/- 5% inhibited by 25 microM 5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB) which is a potent blocker of epithelial Cl- channels. The IC50 for NPPB inhibition of prostaglandin E2 release was 8 microM. Indomethacin and NPPB at 25 microM also inhibited AVP-stimulated cellular accumulation of prostaglandin E2 by 98% and 79 +/- 7% respectively. The inhibitory effect of NPPB was not due to interference with the cellular response to AVP since at 50 microM it did not block AVP-stimulated release of arachidonate metabolites from cells metabolically labeled with [3H]-arachidonic acid. It is suggested that NPPB inhibition of prostaglandin E2 synthesis is at the cyclooxygenase level on the basis of its structural similarity to the fenamic acid type of cyclooxygenase inhibitors.

Transformation of leukotriene A4 to lipoxins by rat kidney mesangial cell

Incubation of rat mesangial cells with leukotriene A4 in the presence of calcium ionophore A23187 led to a substrate dependent formation of lipoxin and its isomers. The major metabolite coeluted with authentic lipoxin A4 (LXA4) and lipoxin B4 (LXB4) in RP-HPLC system, and possessed a characteristic U.V. spectrum and C-value which were identical to authentic standards. GC/MS analysis on LXA4 further demonstrates that the mesangial cell derived LXA4 was identical to that reported by Serhan et al. (1) as LXA4 [5(S), 6,(R), 15(S)-trihydroxy7,9,13-trans-11-cis-eicosatetraenoic acid]. The formation of LXA4 was linear with substrate (LTA4) concentration. No similar products occurred in boiled controls. Incubation of mesangial cell with 15-HPETE failed to produce any lipoxin-like material. The absence of LX-like substance following incubation of 15-HPETE with mesangial cells suggested that 5-lipoxygenase activity is not expressed in mesangial cells under these conditions. The generation of LXA4 from LTA4 in mesangial cells suggested that there is an active 15- or 12- lipoxygenase activity in the kidney. The production of LX may play an important role in the regulation of renal function and the response to inflammatory stimuli.

Eicosanoids in renal function

The major role of renal eicosanoid synthesis appears to be a protective one. In the cortex, prostaglandin synthesis minimises potential anoxic and ischaemic damage by vasodilatation. In the medulla, prostaglandin synthesis appears to stabilise the corticomedullary solute gradient and may play a role in cell volume regulation. Mono-oxygenase production at this site, by modifying blood flow and cellular active transport processes could again serve a protective function against anoxia and ischaemia. The release of erythropoietin also appears to be prostaglandin dependent. It is likely that leukotrienes released from inflammatory cells within the kidney will affect renal haemodynamics and capillary permeability as in other tissues.

Morphologic demonstration of adrenergic influences on the glomerulus

Previous micropuncture studies found that increasing the adrenergic nerve activity to the kidneys elevates the pre- and postglomerular arteriolar resistances and decreases the glomerular capillary ultrafiltration coefficient (product of the filtration surface area and the hydraulic conductivity to water). To define the morphologic expression of this adrenergic effect on the glomerular capillaries the authors compared the microscopic vascular casts of entire glomeruli from right and left kidneys that were simultaneously perfusion-fixed during selective stimulation of only the left renal nerves. The maximum cross-sectional diameter of ten randomly chosen glomeruli from each stimulated and contralateral kidneys of eight rats averaged 123.7 +/- 4.1 mu in stimulated kidneys compared with a maximum diameter of 136.3 +/- 6.4 in the contralateral kidneys (P less than 0.001). The average perpendicular diameter of 100.4 +/- 1.5 mu in the stimulated kidneys was also significantly smaller than the average diameter of 110.7 +/- 1.9 mu in the contralateral kidneys (P less than 0.005). To examine if morphologic changes analogous to those found in whole glomeruli can be demonstrated at the single cell level, the authors assessed the size of mesangial cells in vitro before, during, and after exposure to the adrenergic neurotransmitter, norepinephrine. First passage mesangial cells approximately 4 weeks after explantation were studied by phase-contrast microscopy and recorded on time-lapse video recorder. The planar surface area of individual mesangial cells was measured by electronic planimeter from photographs of the video images. In response to norepinephrine (1 microM), the surface area decreased significantly on average, from 3.58 +/- 0.28 X 10(-6) sq mm to 3.38 +/- 0.27 (P less than 0.005). Washout of norepinephrine and replacement with hormone-free media in other cells led an increase in the surface area (from 2.47 +/- 0.43 X 10(-6) sq mm to 2.61 +/- 0.40, P less than 0.005). No changes were observed in cells initially bathed in hormone-free media. Thus, the morphologic equivalent of the adrenergic nerve-induced reduction in the ultrafiltration coefficient is a contraction of the glomerular corpuscle. By regulating the configuration of mesangial cells that anchor the glomerular capillary network to the vascular pole, the adrenergic nerve may concurrently determine the number of capillary channels available for filtration as well as the glomerular corpuscular volume.

Cyclosporin A inhibits protein kinase C activity: a contributing mechanism in the development of nephrotoxicity?

Cyclosporin A modifies many intracellular functions in a variety of different cells. This study investigated the potential interaction between cyclosporin A and protein kinase C, as a possible mechanism for the development of nephrotoxicity. The activity of protein kinase C, in the cytosol of renal epithelial cells, was shown to be significantly inhibited in a dose-dependent manner by CSA. Activation of protein kinase C by 12-O-tetradecanoylphorbol-13-acetate (phorbol ester) in rat mesangial cells in culture leads to an increase in PGE2 release. Phorbol ester stimulated PGE2 release was significantly inhibited by cyclosporin A. These results would suggest that intracellular site of action of cyclosporin A, in producing alterations in intracellular function and toxicity, may be at the level of protein kinase C.

Dietary eicosapentaenoic acid does not modify cyclosporin-induced inhibition of angiotensin II-stimulated prostaglandin synthesis in mesangial cells

Clinical and experimental cyclosporin A (CSA) nephrotoxicity is characterized by alterations in renal hemodynamics and a reduction in glomerular filtration rate (GFR). The mesangial cell may be a target for the actions of CSA. CSA has been shown to activate the renin angiotensin system and to increase the excretion of TXB2 (the stable metabolite of TXA2). This study investigated the role of CSA and mesangial cell prostaglandin release in mediating some of the alterations in renal hemodynamics. Primary rat mesangial cell cultures (first passage) were exposed to CSA followed by stimulation with angiotensin II (AII) 10(-7) M. PGE2 and TXB2 release was measured after 5 and 15 minutes incubation. Experimental CSA nephrotoxicity in rats has been shown to be reduced by the use of MaxEPA fish oil (containing eicosapentaenoic acid) as the vehicle for CSA. Therefore, the experiments were repeated using mesangial cells obtained from rats fed an enriched eicosapentaenoic acid (MaxEPA) diet for 3 weeks. CSA significantly inhibited AII stimulated PGE2 release in both experiments. There was no increase in TXB2 release. Alterations in membrane fatty acid composition, available for prostaglandin synthesis, did not alter the results. This study demonstrated that CSA significantly inhibits AII-stimulated prostaglandin release. The increased excretion of TXB2, seen with CSA treatment, does not arise from the mesangial cells, and the protective effect of MaxEPA, as a vehicle for CSA, is not due to its effects on mesangial cell prostaglandin release.

Effect of thromboxane synthesis inhibition in a model of membranous nephropathy

The effect of the thromboxane synthesis inhibitor UK 38485 on glomerular filtration rate (GFR) and proteinuria was evaluated in a rat model of unilateral membranous nephropathy. Two and 24 hours following perfusion of kidneys with cationized human IgG and i.v. administration of anti-human IgG-antiserum (in situ ICGN), glomerular thromboxane B2 (TxB2) formation was significantly higher (2 hr: 448 +/- 116 pg/mg protein/min; 24 hr: 173 +/- 21 pg/mg protein/min) compared to control (C) kidneys (2 hr: 173 +/- 21 pg/mg protein/min, P less than 0.005; 24 hr: 154 +/- 17 pg/mg protein/min, P less than 0.025). Two and seven days after induction of ICGN these differences were no longer present. Pretreatment with the thromboxane synthesis inhibitor UK 38485 prevented the decrease in GFR, which occurred two hours after induction of the glomerular disease (without UK: 161 +/- 31; with UK 325 +/- 21 microliters/100 g body wt/min). This UK 38485 effect on GFR was no longer detectable at 24 hours, two days and seven days. Initiation of glomerular immune injury was followed by significant proteinuria which averaged 250 +/- 85 mg/24 hr at day two. UK 38485 treatment, which reduced TxB2 formation in isolated glomeruli by 90% did not influence proteinuria. These data demonstrate that induction of heterologous, in situ immune complex glomerulonephritis stimulates glomerular thromboxane B2 formation, an effect which partially modulates the decrease in GFR at two hours. Thromboxane, however, does not seem to play a role in the mediation of proteinuria in this animal model.

Eicosapentaenoic and dihomo gamma linolenic acid metabolism by cultured rat mesangial cells

To better understand the effects of dietary fatty acid manipulations on glomerular function, we compared mesangial incorporation, release, and metabolism of arachidonic (AA), eicosapentaenoic (EPA), and dihomo gamma linolenic (DHG) acids. We found marked differences in mesangial handling of these fatty acids. AA was incorporated into lipids of mesangial cells much more rapidly than EPA or DHG. Ionophore-induced stimulation of fatty acid release from mesangial cells prelabeled with [14C]AA, [14C]EPA, or [14C]DHG caused a release of labeled AA greater than DHG much less than EPA, respectively. Preloading mesangial cells with DHG or EPA for 24 h reduced subsequent basal, ionophore-, and hormone-stimulated prostaglandin E2 (PGE2) synthesis. Finally, unlike AA, neither EPA nor DHG was converted to a significant extent by mesangial cyclooxygenase or lipoxygenase. Thus the mesangial metabolism of DHG and EPA differs both quantitatively and qualitatively from that of AA. Furthermore, EPA and DHG inhibit metabolism of AA at the level of mesangial cyclooxygenase.

Vasopressin V1 receptors on the principal cells of the rabbit cortical collecting tubule. Stimulation of cytosolic free calcium and inositol phosphate production via coupling to a pertussis toxin substrate

The effects of arginine vasopressin (AVP) on the cytosolic free calcium concentration ([Ca2+]f) were examined in freshly immunodissected rabbit cortical collecting tubule cells using fluorescent Ca2+ indicators fura-2 and indo-1. The addition of AVP to a cell suspension resulted in a rapid and transient increase in the [Ca2+]f. The 1-deamino-8-D-AVP (dDVP), a V2 receptor agonist of AVP that stimulated adenosine 3',5' cAMP production in these cells, had no effect on [Ca2+]f and did not affect AVP-induced increase in [Ca2+]f. The AVP-induced increase in [Ca2+]f but not cAMP production was blocked by the V1 receptor antagonist, [1-(beta-mercapto-beta-beta-cyclopentamethylene propionic acid), 2-(O-methyl)tyrosine] Arg8-vasopressin. The AVP-stimulated increase in [Ca2+]f appeared to be largely due to Ca2+ release from intracellular stores as reduction of extracellular Ca2+ with EGTA had little if any effect on the AVP-induced increase in [Ca2+]f. This AVP-induced increase in [Ca2+]f was associated with an increase in inositol-1,4,5-trisphosphate production and appeared to involve a guanine nucleotide-binding protein (G), since the pretreatment of cells with pertussis toxin for 4-6 h inhibited this effect. Finally, measurements of [Ca2+]f in single cells suggest that only the principal cells of the collecting tubules respond to AVP with an increase in [Ca2+]f. In summary, these results demonstrate that the principal cells of the cortical collecting tubule possess two distinct receptor systems for vasopressin, the well-known V2 receptor coupled to adenylate cyclase, and a V1 receptor system that leads to the mobilization of cytosolic calcium, coupled through a pertussis toxin substrate (G protein) to a production of inositol phosphates.

Vasoconstrictor hormones depolarize renal glomerular mesangial cells by activating chloride channels

Mesangial cells are smooth muscle-like cells of the renal glomerulus which contract and produce prostaglandins in response to vasopressin and angiotensin. These responses serve to regulate the glomerular capillary filtering surface area. We have used the membrane potential-sensitive fluorescent dye bis-oxonol and the intracellular fluorescent calcium-sensitive probe Indo-1 to study the changes in membrane potential (Em) and intracellular free calcium concentration ([Ca2+]i) in cultured rat mesangial cells in response to vasoconstrictor hormones. Basal [Ca2+]i was 227 +/- 4 nM, and stimulation by maximal concentrations of either vasopressin or angiotensin resulted in a transient 4-6-fold rise. Resting membrane potential was 45.8 +/- 0.9 mV and vasoconstrictor hormones caused a depolarization of 14-18 mV. The following extracellular ion substitutions indicated that chloride efflux was the predominant ion flux responsible for depolarization: 1) depolarization persisted when sodium in the medium was substituted with N-methylglucamine; 2) substitution of medium sodium chloride with sodium gluconate, which enhances the gradient for chloride efflux, augmented vasoconstrictor-stimulated depolarization; 3) suspension of cells in potassium chloride medium resulted in depolarization, following which, stimulation by either vasopressin or angiotensin resulted in hyperpolarization; and 4) this hyperpolarization did not occur when potassium gluconate medium was used to depolarize the cells. The calcium ionophore ionomycin also resulted in membrane depolarization. However, prevention of the rise in [Ca2+]i by prior exposure to ionomycin in calcium-free medium or by loading mesangial cells with the intracellular calcium buffer BAPTA did not abrogate the depolarization response to vasoconstrictor hormones. This indicates that a rise in intracellular calcium is not necessary for depolarization. In contrast, prior depolarization of the cells using varying concentrations of KCl in the external medium, which dissipated the electrochemical gradient for chloride efflux, resulted in a corresponding prolongation of the transient calcium response to vasopressin and angiotensin. These findings indicate that angiotensin and vasopressin depolarize mesangial cells by activating chloride channels and that this activation can occur by both calcium-dependent and -independent mechanisms. In addition, activation of chloride channels with resulting depolarization may serve to modulate the calcium signal.

Involvement of a pertussis toxin-sensitive G-protein-coupled phospholipase A2 in lipopolysaccharide-stimulated prostaglandin E2 synthesis in cultured rat mesangial cells

E. coli lipopolysaccharide (LPS) stimulated a dose- and time-dependent release of prostaglandin E2 (PGE2) in cultured rat glomerular mesangial cells. Pertussis toxin, an inhibitor of several GTP-binding proteins (G proteins), blocked nearly 80% of the LPS-stimulated PGE2 formation, while having virtually no effect on calcium ionophore-stimulated PGE2 production. We tested the possibility that a G protein-coupled activation of phospholipase A2 mediated the LPS-stimulated PGE2 production. Evidence for LPS activation of phospholipase A2 included a time-dependent LPS-induced generation of [32P]lysophosphatidylcholine and the inhibitory effects of a phospholipase A2 inhibitor, mepacrine, on LPS-induced PGE2 formation. Possible roles for phospholipase C-dependent activation of PGE2 synthesis by LPS seemed unlikely, as LPS did not elevate the cytosolic free calcium concentration or augment the appearance of water-soluble inositol phosphates. We conclude that LPS-induced PGE2 synthesis in rat glomerular mesangial cells is mediated through a G-protein-coupled phospholipase A2 activation. The activation of phospholipase A2 releases arachidonic acid and stimulates PGE2 synthesis preferentially, thereby improving glomerular hemodynamic events in endotoxemia.

The glomerular mesangium

The mesangium is more than simply a support structure for glomerular capillary circulation. Mesangial cells respond to various vasoactive mediators and probably contribute to the regulation of mesangial cell contractility and, consequently, glomerular perfusion. The surrounding extracellular matrix contains several glycoproteins and collagens that may affect the immune interactions of antigens and antibodies and may possibly influence the disposition of immune complexes. These properties may modulate the consequences of deposition of IgA-containing immune complexes in the mesangium in patients with IgA nephropathy and the consequent expression of clinical disease.

Prostaglandin E2 and atriopeptin III oppose the contractile effect of angiotensin II in rat kidney mesangial cell cultures

Effects of vasoconstrictory and of dilatory hormones were studied on the contractile activity of cultured rat kidney mesangial cells. By phase contrast microscopy, a rapid contraction was seen of most cells treated with angiotensin II (10(-6) - 10(-10) mol/L), which was sometimes followed by autonomous relaxation after 10 to 20 min. Prostaglandin E2 and atriopeptin III prevented the contractile effect of angiotensin II in a dose-dependent manner. Angiotensin II, but not atriopeptin III, stimulated prostaglandin E2 synthesis in mesangial cell cultures.