Cell culture approaches to the analysis of glomerular inflammation

Extracellular matrix-induced Hic-5 expression in glomerular mesangial cells leads to a prosclerotic phenotype independent of TGF-β

Chronic fibroproliferative diseases account for approximately 45% of all deaths in the developed world. In the kidney, glomerulosclerosis is the underlying pathology in approximately half of patients with renal failure receiving dialysis. Mesangial cell expression of the LIM protein hydrogen peroxide-induced clone-5 (Hic-5) is important in its pathogenesis. Hic-5 expression increases following mesangial cell attachment to collagen I, associated with increased collagen I expression and increased susceptibility to apoptosis both in vitro and in experimental glomerulosclerosis. TGF-β has an established role in many fibrotic diseases, including glomerulosclerosis, where it increases collagen I deposition in vivo and promotes mesangial cell apoptosis in vitro. In other cell types, TGF-β induces Hic-5 expression. We investigated whether Hic-5-induced changes in mesangial cell phenotype were TGF-β-dependent. Adding exogenous TGF-β to mesangial cell cultures failed to increase Hic-5 expression; blocking TGF-β signaling did not reduce Hic-5 expression. However, inducing Hic-5 expression in mesangial cells by adhesion to collagen I led to TGF-β expression, which was abolished by small interfering RNA (siRNA) Hic-5 knockdown. Mesangial cells expressing Hic-5 showed altered latent TGF-β-binding protein expression and Smad signaling, with enhanced susceptibility to TGF-β-induced apoptosis. Mesangial cell attachment to collagen I led to increased Hic-5 expression within 2-4 h and increased procollagen I transcription within 12 h, whereas adding TGF-β to siRNA Hic-5 knockdown mesangial cells increased procollagen I transcription to a lesser degree after 48 h. Mesangial cell Hic-5 expression was associated with increased α-smooth muscle actin and plasminogen activator inhibitor-1 expression. Taken together, these data indicate that there is a prosclerotic feedback loop in mesangial cells dependent on matrix-derived signals in which Hic-5 is a pivotal signaling protein. This feedback loop is TGF-β-independent. The role of TGF-β-dependent and -independent sclerotic pathways merit further investigation.

Inhibition of collagen I accumulation reduces glomerulosclerosis by a Hic-5-dependent mechanism in experimental diabetic nephropathy

Glomerulosclerosis of any cause is characterized by loss of functional glomerular cells and deposition of excessive amounts of interstitial collagens including collagen I. We have previously reported that mesangial cell attachment to collagen I leads to upregulation of Hic-5 in vitro, which mediates mesangial cell apoptosis. Furthermore, glomerular Hic-5 expression was increased during the progression of experimental glomerulosclerosis. We hypothesized that reducing collagen I accumulation in glomerulosclerosis would in turn lower Hic-5 expression, reducing mesangial cell apoptosis, and thus maintaining glomerular integrity. We examined archive renal tissue from rats undergoing experimental diabetic glomerulosclerosis, treated with the transglutaminase-2 inhibitor NTU281. Untreated animals exhibited increased glomerular collagen I accumulation, associated with increased glomerular Hic-5 expression, apoptosis, and mesangial myofibroblast transdifferentiation characterized by α-smooth muscle actin (α-SMA) expression. NTU281 treatment reduced glomerular collagen I accumulation, Hic-5 and α-SMA expression, and apoptosis. Proteinurea and serum creatinine levels were significantly reduced in animals with reduced Hic-5 expression. In vitro studies of Hic-5 knockdown or overexpression show that mesangial cell apoptosis and expression of both α-SMA and collagen I are Hic-5 dependent. Together, these data suggest that there exists, in vitro and in vivo, a positive feedback loop whereby increased levels of collagen I lead to increased mesangial Hic-5 expression favoring not only increased apoptosis, but also mesangial myofibroblast transdifferentiation and increased collagen I expression. Prevention of collagen I accumulation interrupts this Hic-5-dependent positive feedback loop, preserving glomerular architecture, cellular phenotype, and function.

A potential therapeutic role for P2X7 receptor (P2X7R) antagonists in the treatment of inflammatory diseases

INTRODUCTION

The P2X7 receptor (P2X7R) has an important role in inflammation and immunity, but until recently, clinical application has been limited by a lack of specific antagonists. Recent studies using P2X7R knockout mice and specific receptor antagonists have shown that the P2X7R is an important therapeutic target in inflammatory diseases.

AREAS COVERED

We have reviewed the current literature on the role of the P2X7R in inflammatory diseases, focusing on potential therapeutic applications of selective P2X7R antagonists as anti-inflammatory agents. Particular emphasis has been placed on the potential role of P2X7R in common inflammatory diseases. The latest developments in Phase I and II clinical trials of P2X7R antagonists are covered.

EXPERT OPINION

Recent studies using gene knockout mice and selective P2X7R antagonists suggest that P2X7R is a viable therapeutic target for inflammatory diseases. However, efficacious P2X7R antagonists for use in clinical studies are still at an early stage of development. Future challenges include: identifying potential toxicity and side effects of treatment, timing of treatment initiation and its duration in chronic inflammatory conditions, optimum dosage and development of a functional assay for P2X7R that would help to guide treatment.

Upregulation of Hic-5 in glomerulosclerosis and its regulation of mesangial cell apoptosis

Glomerulosclerosis is characterized by the loss of glomerular cells by apoptosis and deposition of collagen type I into the normal collagen IV-containing mesangial matrix. We sought to determine the alterations that might contribute to these changes by performing proteomic analysis of rat mesangial cell lysates comparing cells cultured on normal collagen type IV to those grown on abnormal collagen type I surfaces. Subculture on collagen type I was associated with changed expression of several proteins, including a significant upregulation of the paxillin-like LIM protein, hydrogen-peroxide-induced clone 5 (Hic-5), and increased the susceptibility of the cells to apoptosis in response to physiological triggers. When we knocked down Hic-5 (using siRNA), we found mesangial cells grown on collagen type I were protected from apoptosis to the same degree as untreated cells grown on collagen type IV. Further we found that the level of Hic-5 in vivo was almost undetectable in control rats but increased dramatically in the glomerular mesangium of remnant kidneys 90 and 120 days after subtotal nephrectomy. This induction of Hic-5 paralleled the upregulation of mesangial collagen type I expression and glomerular cell apoptosis. Our results suggest that Hic-5 is pivotal in mediating the response of mesangial cells to attachment on abnormal extracellular matrix during glomerular scarring.

PPAR{alpha} attenuates the proinflammatory response in activated mesangial cells

The activated mesangial cell is an important therapeutic target for the control of glomerulonephritis. The peroxisome proliferator-activated receptor alpha (PPARalpha) has attracted considerable attention for its anti-inflammatory effects; however, its roles in the mesangial cells remain unknown. To determine the anti-inflammatory function of PPARalpha in mesangial cells, wild-type and Ppara-null cultured mesangial cells were exposed to lipopolysaccharide (LPS). LPS treatment caused enhanced proinflammatory responses in the Ppara-null cells compared with wild-type cells, as revealed by the induction of interleukin-6, enhanced cell proliferation, and the activation of the nuclear factor (NF)-kappaB signaling pathway. In wild-type cells resistant to inflammation, constitutive expression of PPARalpha was undetectable. However, LPS treatment induced the significant appearance and substantial activation of PPARalpha, which would attenuate the proinflammatory responses through its antagonizing effects on the NF-kappaB signaling pathway. The induction of PPARalpha was coincident with the appearance of alpha-smooth muscle actin, which might be associated with the phenotypic changes of mesangial cells. Moreover, another examination using LPS-injected wild-type mice demonstrated the appearance of PPARalpha-positive cells in glomeruli, suggesting in vivo correlation with PPARalpha induction. These results suggest that PPARalpha plays crucial roles in the attenuation of inflammatory response in activated mesangial cells. PPARalpha might be a novel therapeutic target against glomerular diseases.

Initiation of caspase-independent death in mouse mesangial cells by Cd2+: involvement of p38 kinase and CaMK-II

Cadmium (Cd) is a toxic metal with multiple effects on cell signaling and cell death. We studied the effects of Cd(2+) on quiescent mouse mesangial cells in serum-free conditions. Cadmium induces cell death over 6 h through annexin V+ states without or with causing uptake of propidium iodide, termed apoptotic and apoptosis-like death, respectively. Little or no necrosis is observed, and cell death is caspase-independent and associated with nuclear translocation of the apoptosis-inducing factor, AIF. We previously showed that Cd(2+) increased phosphorylation of Erk and CaMK-II, and CaMK-II activation increased cell death in an Erk-independent manner. Here we demonstrate that Cd(2+) increases Jnk and p38 kinase phosphorylation, and inhibition of p38-but not of Jnk-increases cell viability by suppressing apoptosis in preference to apoptosis-like death. Neither p38 kinase nor CaMK-II inhibition protects against a decrease in mitochondrial membrane potential, psi, indicating that kinase-mediated death is either independent of, or involves events downstream of a mitochondrial pathway. However, both the antioxidant N-acetyl cysteine (NAC) and the mitochondrial membrane-stabilizing agent cyclosporine A (CsA) partially preserve psi, suppress activation of p38 kinase, and partially protect the cells from Cd(2+)-induced death. Whereas the effect of CsA is on apoptosis, NAC acts on apoptosis-like death. Inhibition of glutathione synthesis exacerbates a Cd(2+)-dependent increase in cellular peroxides and favors apoptosis-like death over apoptosis. The caspase-independence of these modes of cell death is not due to an absence of this machinery in the mesangial cells: when they are exposed to Cd(2+) for longer periods in the presence of serum, procaspase-3 and PARP are cleaved and caspase inhibition is protective. We conclude that Cd(2+) can kill mesangial cells by multiple pathways, including caspase-dependent and -independent apoptotic and apoptosis-like death. Necrosis is not prominent. Activation of p38 kinase and of CaMK-II by Cd(2+) are associated with caspase-independent apoptosis that is not dependent on mitochondrial destabilization.

Recombinant tissue factor pathway inhibitor induces apoptosis in cultured rat mesangial cells via its Kunitz-3 domain and C-terminal through inhibiting PI3-kinase/Akt pathway

Tissue factor pathway inhibitor (TFPI) is an endogenous inhibitor of tissue factor (TF) induced coagulation. In addition to its anticoagulation activity, TFPI has other functions such as antiproliferation and inducing apoptosis. In the present study, we investigated whether or not TFPI induced apoptosis in cultured rat mesangial cells (MsCs) and the possible signal pathway that involved in the apoptotic process. We demonstrated that recombinant TFPI (rTFPI) induced apoptosis in cultured MsCs via its Kunitz-3 domain and C-terminal in a dose- and time-dependent manner by Hoechst 33258 assay, flow cytometry, nucleosomal laddering of DNA, caspase 3 assay. Because the serine/threonine protein kinase Akt has attracted attention as a mediator of survival (anti-apoptotic) signal in MsCs, we investigated the expression of phosphospecific-Akt and its downstream signal phospho-IkappaB-alpha and some other signal molecules like Fas and bcl-2. The results indicated that the process of apoptosis triggered by rTFPI is, at least in part, actively conducted by rat MsCs possibly through PI3-Kinase-Akt signal pathway not by binding to tissue factor. Our findings suggest that rTFPI has the potential usefulness in inducing apoptosis of MsCs under inflammatory conditions.

Cadmium inhibits both intrinsic and extrinsic apoptotic pathways in renal mesangial cells

Cadmium is a potent nephrotoxin that has been shown to induce apoptosis in some cells but also to prevent it under certain circumstances. In several clinical situations and experimental models of injury to the renal glomerulus, pathological proliferation of mesangial cells is followed by resolution involving mesangial cell apoptosis. We investigated the effects of Cd(2+) on rat mesangial cells induced to undergo apoptosis through either the extrinsic receptor-mediated pathway or the intrinsic mitochondrial-dependent pathway. Camptothecin initiated the intrinsic pathway with activation of caspase-9 and caspase-dependent cleavage of procaspase-3. Tumor necrosis factor-alpha (TNF-alpha) initiated caspase-8 activity and cleavage of pro-caspase-3 at the convergence point of the two pathways. However, pro-caspase-8 levels were low, and caspase-9 was also activated in response to TNF-alpha, characteristic of what have been termed type II cells. With both TNF-alpha and camptothecin, concurrent exposure to 10 microM CdCl(2) suppressed DNA laddering, nuclear condensation, and pro-caspase-3 cleavage. It also decreased activity of both caspase-8 and caspase-9, prevented caspase-8-dependent cleavage of the proapoptotic factor Bid, and suppressed release of cytochrome c from mitochondria. At this 10-microM concentration, Cd(2+) was unique among a number of metal ions in preventing DNA fragmentation. We conclude that Cd(2+) is anti-apoptotic in rat mesangial cells, acting by a mechanism that may involve general caspase inhibition. This may have consequences for the resolution of nephritis in situations of mesangial cell hyperproliferation.

Methylglyoxal induces apoptosis through activation of p38 mitogen-activated protein kinase in rat mesangial cells

BACKGROUND

The formation of methylglyoxal (MG), a highly reactive dicarbonyl compound, is accelerated through several pathways, including the glycation reaction under diabetic conditions, presumably contributing to tissue injury in diabetes. On the other hand, apoptotic cell death of glomerular cells has been suggested to play a role in the development of glomerulosclerosis in various types of glomerular injuries. We therefore examined whether MG was capable of inducing apoptosis in rat mesangial cells to address the possible mechanism by which hyperglycemia-related products accelerated pathologic changes in diabetic glomerulosclerosis.

METHODS

Rat mesangial cells were incubated with 0 to 400 micromol/L MG, followed by the detection of apoptosis by both TUNEL method and electrophoretic analysis for DNA fragmentation. In addition, we investigated intracellular mechanisms mediating MG-induced apoptosis, focusing especially on the p38 mitogen-activated protein kinase (MAPK) pathway.

RESULTS

MG induced apoptosis in rat mesangial cells in a dose-dependent manner and was accompanied by the activation of p38alpha isoform. Aminoguanidine and N-acetyl-l-cysteine inhibited the MG-induced p38 MAPK activation, as well as apoptosis in rat mesangial cells, suggesting the involvement of oxidative stress in these phenomena. SB203580, a specific inhibitor of p38 MAPK also suppressed the MG-induced apoptosis in rat mesangial cells.

CONCLUSIONS

These results suggest a potential role for MG in glomerular injury through p38 MAPK activation under diabetic conditions and may serve as a novel insight into the therapeutic strategies for diabetic nephropathy.

Monocarboxylate transporter mediates uptake of lovastatin acid in rat cultured mesangial cells

To clarify the uptake mechanism(s) for statins, we examined whether monocarboxylate transporter (MCT) contributed to the uptake of lovastatin acid by rat cultured mesangial cells. Expression of mRNAs for MCT1, 2, and 4 was confirmed in mesangial cells. The uptake of lovastatin acid by mesangial cells increased with decreasing extracellular pH. There was clear overshooting in lovastatin acid uptake by the ATP-depleted cells in the presence, but not in the absence, of an inwardly directed H(+)-gradient. The representative MCT substrates/inhibitors inhibited the lovastatin acid uptake. In particular, the inhibition of lovastatin acid uptake by L-lactic acid at the concentration of 80 mM reached 70%, and L-lactic acid and valproic acid inhibited the uptake competitively. On preloading of mesangial cells with L-lactic acid or valproic acid, the lovastatin acid uptake was significantly stimulated. The inhibition constant of L-lactic acid for the lovastatin acid uptake was 32 mM, and this value is comparable to the Michaelis constant (>20 mM) of L-lactic acid for MCT4 described elsewhere. These results demonstrate that lovastatin acid was largely taken up by mesangial cells via MCT, and suggest that MCT4 might contribute to lovastatin acid uptake in the cells.

15-Deoxy-Delta12,14-prostaglandin J2 inhibits IL-1beta-induced cyclooxygenase-2 expression in mesangial cells

BACKGROUND

Cyclooxygenase-2 (COX-2), a key enzyme in the synthesis of prostaglandins, is induced in mesangial cells in response to proinflammatory cytokines. Recently, 15-deoxy-Delta12,14-prostaglandin J2 (15d-PGJ2), one of the natural ligands of peroxisome proliferator-activated receptor gamma (PPARgamma), has been reported to have an anti-inflammatory effect. Therefore, we examined the effect of 15d-PGJ2 on COX-2 expression in cultured rat mesangial cells.

METHODS

Mesangial cells were incubated with 15d-PGJ2 for 30 minutes and then exposed to interleukin-1beta (IL-1beta). The expression of COX-2 mRNA and proteins was determined by Northern blot and immunoblot analyses, respectively. Accumulation of prostaglandin E2 (PGE2) was measured by an enzyme-linked immunosorbent assay (ELISA). Activities of mitogen-activated protein kinases (MAPKs) were evaluated by an immunoblot analysis. DNA binding activities of activator protein-1 (AP-1) or nuclear factor-kappaB (NF-kappaB) were examined by an electrophoretic mobility shift assay (EMSA). The activities of PPAR responsive elements (PPRE) and COX-2 promoter were measured by a luciferase reporter assay.

RESULTS

15D-PGJ2 significantly suppressed IL-1beta-induced COX-2 expression and PGE2 production, but thiazolidinediones, synthetic PPARgamma ligands, did not affect COX-2 expression. Moreover, the cells transfected with a PPRE luciferase reporter did not respond to 15d-PGJ2. IL-1beta rapidly activated extracellular signal-regulated kinase (ERK) and c-Jun NH2-terminal kinase (JNK), which were involved in the up-regulation of COX-2 induction, but 15d-PGJ2 inhibited the activation of these kinases. 15d-PGJ2 inhibited the IL-1beta-induced increase in binding activities of nuclear proteins to consensus AP-1 site and AP-1-like site of COX-2 promoter but not of NF-kappaB. IL-1beta was unable to activate the COX-2 promoter when the AP-1-like site was mutated.

CONCLUSIONS

These data suggest that 15d-PGJ2 inhibits IL-1beta-induced COX-2 expression, independent of PPARgamma activation, by suppression of ERK and JNK pathways and AP-1 activation in mesangial cells. Thus, 15d-PGJ2 may play an important role in the negative feedback mechanism of COX-2 expression in renal inflammation and may be useful as an anti-inflammatory agent.

Induction of proliferation and apoptotic cell death via P2Y and P2X receptors, respectively, in rat glomerular mesangial cells

BACKGROUND

Cell surface receptors for adenosine 5'-triphosphate (ATP; P2 receptors) have been subdivided into two families: ligand-gated ion channels (P2X1-7) and G-protein-coupled (P2Y1-8) receptors. We investigated the potential role of P2 receptors on rat glomerular mesangial cells.

METHODS

To investigate cell proliferation, DNA synthesis was assayed by measuring [3H]thymidine incorporation into DNA. For detecting apoptosis, morphological features, DNA fragmentation, and exposure of phosphatidylserine on the outside surface of the cell membrane were investigated. Expression of mRNA and distribution of receptors were detected by reverse transcription-polymerase chain reaction and immunohistochemistry, respectively.

RESULTS

ATP triggered a dose-dependent increase in DNA synthesis. This response was also induced by uridine triphosphate (UTP), an agonist equipotent with ATP at P2Y2 and P2Y4 receptors; both P2Y2 and P2Y4 mRNA are expressed in glomerular mesangial cells and isolated glomeruli. In contrast, the P2X7 receptor agonist 2'-83'-O-(4-benzoyl benzoyl) ATP (BzATP) caused a decrease in cell number. BzATP produced DNA cleavage and exposure of phosphatidylserine on the outside of the cell membrane. P2X7 receptors were distributed heterogeneously in unstimulated cells. The expression of P2X7 mRNA was maintained at a low level, but was induced by tumor necrosis factor-alpha.

CONCLUSIONS

Stimulation of glomerular mesangial cells via P2Y2 and/or P2Y4 and via P2X7 receptors can induce proliferation and apoptotic cell death, respectively. The balance between proliferation and apoptosis will depend on the relative stimulation and expression of these P2 receptor subtypes, and could play an important role in normal and abnormal glomerular function.

c-Rel and p65 trans-activate the monocyte chemoattractant protein-1 gene in interleukin-1 stimulated mesangial cells

BACKGROUND

The chemokine monocyte chemoattractant protein-1 (MCP-1) is secreted by human glomerular mesangial cells in response to interleukin-1 (IL-1) and has a central role in amplifying the inflammatory response during glomerulonephritis. However, the mechanism by which IL-1 regulates its transcription is not understood. Specific members of the nuclear factor kappaB/rel (NF-kappaB) proteins may regulate MCP-1 expression in a stimulus- and tissue-specific manner.

METHODS

Electrophoretic mobility shift assays and Western blot analysis characterized the members of the NF-kappaB family that bound the two NF-kappaB sites of the MCP-1 enhancer (A1 and A2) in vitro. Trans-activation of the MCP-1 gene was investigated by transfer of the MCP-1 enhancer DNA to mesangial cells.

RESULTS

Primary human mesangial cells contained in addition to p50 (NF-kappaB1) and p65 (Rel A) NF-kappaB proteins, the oncoprotein c-rel, and Rel B, but not p52 (NF-kappaB2). IL-1 induced c-rel to form a complex with p65, which bound the MCP-1 A2 site but not the A1 or IL-6 NF-kappaB sites in vitro. IL-1 up-regulated transfected MCP-1 enhancer activity. Cotransfer of the MCP-1 enhancer together with individual members of the NF-kappaB family showed that the heterodimer c-relp65 or (p65)2 can selectively trans-activate the MCP-1 gene via its A1 and A2 sites in mesangial cells.

CONCLUSIONS

This study demonstrates for the first time that the c-rel oncoprotein can enhance MCP-1 transcription in mesangial cells and suggests that it may have an important role in amplifying gene expression in the inflamed glomerulus.

Type IV collagen and laminin regulate glomerular mesangial cell susceptibility to apoptosis via beta(1) integrin-mediated survival signals

Postinflammatory scarring is characterized by changes in extracellular matrix (ECM) composition and progressive loss of normal resident cells. In glomerular inflammation there is now evidence that unscheduled apoptosis (programmed cell death) of mesangial and other resident cells may mediate progression to irreversible glomerulosclerosis. In the current study we examined the hypothesis that ECM components may differ in their capacity to support mesangial cell survival by suppression of apoptosis. Using a well-established in vitro model of mesangial cell apoptosis, we found that collagen IV and laminin, components of normal mesangial ECM, protected rat mesangial cells from apoptosis induced by serum starvation and DNA damage, by a beta(1) integrin-mediated, but arg-gly-asp (RGD)-independent mechanism. In contrast, collagen I, fibronectin, and osteonectin/SPARC, which are overexpressed in diseased glomeruli, failed to promote rat mesangial cell survival. However, the survival-promoting effect of collagen IV and laminin was not associated with changes in cellular levels of apoptosis regulatory proteins of the Bcl-2 family. These experiments demonstrate that glomerular mesangial cell survival is dependent on interactions with ECM and provide insights into potential mechanisms by which resident cell loss may occur during acute inflammation and postinflammatory scarring of the kidney and other organs.

Angiotensin II Participates in Mononuclear Cell Recruitment in Experimental Immune Complex Nephritis Through Nuclear Factor-κB Activation and Monocyte Chemoattractant Protein-1 Synthesis

Angiotensin-converting enzyme (ACE) inhibitors reduce macrophage infiltration in several models of renal injury. We approached the hypothesis that angiotensin II (AngII) could be involved in inflammatory cell recruitment during renal damage through the synthesis of monocyte chemoattractant protein-1 (MCP-1). In a model of immune complex nephritis, we observed an up-regulation of renal MCP-1 (mRNA and protein) coincidentally with mononuclear cell infiltration that were markedly reduced by treatment with the ACE inhibitor quinapril. Exposure of cultured rat mesangial cells to AngII increased MCP-1 mRNA expression (2.7-fold) and synthesis (3-fold), similar to that observed with TNF-α. Since NF-κB is involved in the regulation of MCP-1 gene, we explored whether the effects of AngII were mediated through NF-κB activation. Untreated nephritic rats showed increased renal NF-κB activity (3.5-fold) that decreased in response to ACE inhibition. In mesangial cells, AngII activated NF-κB (4.3-fold), and the NF-κB inhibitor pyrrolidine dithiocarbamate abolished the AngII-induced NF-κB activation and MCP-1 gene expression. Our results suggest that AngII could participate in the recruitment of mononuclear cells through NF-κB activation and MCP-1 expression by renal cells. This could be a novel mechanism that might further explain the beneficial effects of ACE inhibitors in progressive renal diseases.

Mesangial cell hypertrophy induced by NH4Cl: role of depressed activities of cathepsins due to elevated lysosomal pH

Enhanced ammoniagenesis is currently thought to play an important role in renal hypertrophy and subsequent tubulointerstitial fibrosis. Under certain conditions glomeruli also may be affected by ammonia toxicity. Exposure of glomeruli to augmented ammonia levels may occur: (i) in advanced liver diseases due to elevated blood ammonia concentrations; (ii) in conditions of enhanced tubular ammoniagenesis following cortical "trapping;" and (iii) due to increased ammonia formation in the glomeruli in the presence of impaired renal function. To elucidate the potential role of ammonia in glomerular injury, we investigated the effect of NH4Cl on protein turnover as well as on activities of various cathepsins in cultured rat mesangial cells. The results show that NH4Cl (20 mM) induced cell hypertrophy as defined by an increase in both cell protein content and cell volume (+38% and +10.1%, respectively, after 48 hr). This hypertrophy was associated with suppression of the activities of cathepsins B and L + B (-56.8% and -51.3% after 48 hr) and reduction of protein degradation rate (-61% after 48 hr), but without enhanced protein synthesis. Inhibition of Na+/H+ antiport by amiloride (1 mM) neither prevented the reduction of cathepsin activities nor the hypertrophy of the mesangial cells. Upon NH4Cl application lysosomal pH was elevated. This alkalinization may be causatively involved in the impairment of cathepsin B and L + B due to shifting the lysosomal pH above the optimum of their activities. In conclusion, NH4Cl induces hypertrophy but not hyperplasia in mesangial cells. This hypertrophy is caused by the reduction of protein degradation, mainly due to depressed activities of cathepsin B and L + B in the absence of enhanced protein synthesis. A shift of lysosomal pH above the optimum of the acidic cathepsins seems to be a key factor in their impaired activities in mesangial cells.

Lysophosphatidic acid-mediated signal-transduction pathways involved in the induction of the early-response genes prostaglandin G/H synthase-2 and Egr-1: a critical role for the mitogen-activated protein kinase p38 and for Rho proteins

During inflammatory processes of the kidney, lesions of the glomerulus lead to aggregation of thrombocytes and infiltration of macrophages, which can release bioactive mediators. One of these important signalling molecules is lysophosphatidic acid (LPA). Incubation of rat mesangial cells with LPA induced mRNA and protein expression of the early-response genes pghs-2 (for prostaglandin G/H synthase-2/cyclo-oxygenase-2) and egr-1. As shown by antisense experiments, induction of egr-1 was related to the strong mitogenic effect of LPA. LPA-mediated gene expression was inhibited by pertussis toxin, indicating coupling to G-proteins of the Gi family. Specific inhibition of proteins of the small G-protein subfamily Rho with toxin B from Clostridium difficile led to changes in mesangial cell morphology without induction of apoptosis. LPA-mediated expression of pghs-2 and egr-1 was reduced to base-line levels by toxin B, indicating a role for Rho proteins in LPA-mediated gene induction. Of the two mitogen-activated protein kinase (MAPK) pathways investigated, the MAPK kinase-extracellular signal-regulated kinase pathway was involved in the induction of both pghs-2 and egr-1 mRNA expression, as shown by the inhibitory effect of PD98059. Activation of the MAPK p38, however, was only related to pghs-2 expression, whereas egr-1 expression was not affected by treatment of mesangial cells with the specific inhibitor SB203580. Taken together our data provide evidence that LPA-mediated activation of MAPK kinase and Rho proteins leads to the induction of the functionally distinct early-response genes pghs-2 and egr-1, whereas activation of MAPK p38 revealed considerable differences between the regulation of these two genes.

Development of pH regulatory transport in glomerular mesangial cells

Developmental changes in activity or expression of transporters may account for alterations in cell behavior as the nonpolarized cell matures. We sought to ascertain whether there is a maturational change in each of the major acid-base transporters in the developing mesangial cell (MC), the Na/H exchanger, Na-dependent Cl/HCO3 exchanger, and the Cl/HCO3 exchanger. Intracellular pH (pHi) was determined by the use of the fluorescent pH-sensitive dye, 2',7'-bis(2- carboxyethyl)-5(6)-carboxyfluorescein (BCECF). We assessed transporter activity by studying recovery from an acid load (NH4/NH3) in CO2/HCO3. In adult MCs, Na/H exchanger was responsible for 35.2 +/- 4.3% of steady-state pHi, whereas the Na-dependent Cl/HCO3 exchanger contributed 58.7 +/- 6.1 (n = 14). In term MCs (tMCs), from days 1-3 after birth, the Na/H exchanger contributes 62.9 +/- 7.8% (n = 11, P < 0.001 vs. adult), whereas the Na-dependent Cl/HCO3 exchanger contributes 34.0 +/- 5.7% (n = 12, P < 0.001 vs. adult), to the rate of recovery from an acid load in these cells. However, in tMCs (days 4-6), the Na/H contributes 47.2 +/- 5.9% (n = 8, P < 0.05 vs. adult), whereas the Na-dependent Cl/HCO3 exchanger contributes 48.7 +/- 7.3% (n = 13, P < 0.05 vs. adult), to the rate of recovery. tMCs (days 6-12) yielded transporter activity that was not statistically different than adult MCs (37.8 +/- 4.9 and 54.3 +/- 10.2% for Na/H and Na-dependent Cl/HCO3, respectively). The magnitude of the stimulated response to angiotensin II by Na/H and Na-dependent Cl/HCO3 exchanger in adult and tMCs is unchanged throughout development. The Na/H exchanger appears to play a greater role in pHi homeostasis earlier on in development, and this may reflect developmental needs of the maturing cell.

Modulation of phospholipase D stimulation in c-src transfected mesangial cells

Stimulation of rat mesangial cells with platelet-derived growth factor BB (PDGF-BB) enhanced phospholipase D (PLD) activity in a concentration dependent manner. Mesangial cells overexpressing the tyrosine kinase pp60c-src (c-Src) were used to determine the effect of this non transforming protooncogene on PLD activation. Overexpression of c-Src interfered with PDGF-BB-mediated activation of PLD. This modulation was dependent on the tyrosine kinase activity of c-Src, since overexpression of tyrosine kinase-negative mutants of c-Src did not affect PLD activation. No effect of c-Src overexpression was observed, when PLD was activated by ATP or guanosine 5'-3-O-(thio)triphosphate (GTP gamma S). The results indicate that the tyrosine kinase c-Src specifically interfered with PDGF-mediated but not with ATP- or GTP gamma S-mediated PLD activation.

Posttranscriptional effects of glucose on proteoglycan expression in mesangial cells

Hyperglycemic conditions are known to increase mRNA and protein levels of several extracellular matrix molecules in cultured mesangial cells, but accompanying increases in proteoglycan mRNA have not been found, and there are discrepant reports of normal or decreased proteoglycan synthesis with or without undersulfation in diabetic kidneys and hyperglycemic cultures. We examined the effects in proliferating cells of glucose on [35S]Sulfate incorporation into heparan and dermatan sulfates and on mRNA levels of decorin, biglycan, and basement membrane perlecan. In both mesangial cells and vascular smooth muscle cells, 30 mmol/L glucose caused a decrease of 15% to 25% in the amount of sulfate incorporated into each proteoglycan in cultures confluent for 1 to 4 days, compared with 10 mmol/L glucose. The effect showed no specificity for the class of proteoglycan and was not a consequence of changes in total protein synthesis, which increased, or cell proliferation, which was unaffected. No decrease in charge density of any of the proteoglycan fractions was observed by ion-exchange chromatography. Therefore, the decrease in labeling was due to a decrease in synthesis and not undersulfation. mRNA levels for biglycan and perlecan increased slightly and transiently, and these changes cannot account for the decreased synthesis. Decorin mRNA was detected only in smooth muscle cells, where it and biglycan were differentially affected by glucose, apparently at the transcriptional level; stabilities of the two messages were unaffected by glucose. Although transforming growth factor-beta 1 (TGF-beta 1) mRNA levels increased in response to glucose, the cytokine did not appear to regulate proteoglycan synthesis, because structural changes in proteoglycans elicited by addition of TGF-beta 1 to the culture medium did not occur in the hyperglycemic cultures. On the other hand, inhibition and downregulation of protein kinase C (PKC), while decreasing net sulfate incorporation into mesangial cell proteoglycans, prevented the effect of high glucose. We conclude that a high glucose concentration causes a general decrease in the synthesis of all classes of proteoglycans at a posttranscriptional level, and can do so without affecting the charge density of individual proteoglycan molecules.

Inhibition of mitogenesis and c-fos induction in mesangial cells by heparin and heparan sulfates

When rat renal mesangial cells (RMC) or vascular smooth muscle cells are released from quiescence by serum stimulation they express c-fos mRNA transiently at 30 to 60 minutes and progress in synchrony to S phase. Heparin causes significant suppression of [3H]-thymidine incorporation into DNA in S phase and a decrease and delay of entry of cells into S/G2. Added at the time of serum stimulation, heparin (1 microgram/ml or less) causes a decrease in the subsequent expression of c-fos mRNA in RMC, and a similar effect is observed with heparan sulfate chains isolated from RMC-cultures themselves. Although these cells internalize and degrade heparin, the timing of the maximal effect indicates an extracellular action of heparin. In keeping with this idea, 125I-heparin binds specifically to a single class of high affinity sites on the cell surface. The effect of heparin on c-fos induction may be independent of interaction with cytokines or cytokine receptors; its magnitude is not diminished when heparin-binding substances are removed from serum by heparin-Sepharose. Furthermore, direct activation of protein kinase C (PKC) with a phorbol ester in the absence of serum likewise induces c-fos and 1 microgram/ml heparin inhibits this response by 65%. Phorbol ester caused an increase in the proportion of histone H1-active PKC associated with the cell membrane fraction, from approximately 25% to 70% of total activity. Heparin affected neither the total activity of the kinase nor the proportion associated with the membrane. When PKC was inhibited with staurosporine, only very low levels of c-fos were induced by serum. We conclude that low concentrations of heparin and heparan sulfate suppress the mitogenic response of mesangial cells to serum and inhibit c-fos mRNA induction through an effect of cell surface-bound glycosaminoglycan on a signalling pathway downstream of PKC.

Glomerular antigens in severe hereditary nephrosis

In search of the basic defect and cell type responsible for the massive treatment-resistant proteinuria of congenital nephrotic syndrome of the Finnish type (CNF), we examined tissue samples of CNF kidneys using established antibody and lectin markers of various glomerular cell types. Markers of vascular endothelium (antibodies to factor VIII and a human homologue of podocalyxin (anti-PHM5) and UEA I lectin) showed no qualitative changes in the endothelial cells of glomeruli or peritubular areas in CNF as compared with controls. Markers of glomerular mesangial cells (antibodies to desmin, smooth muscle actin, RCA I lectin) revealed a secondary increase in mesangial reactivity reflecting the sclerosis and expansion of the mesangial areas in CNF. Markers of visceral epithelial cells (antibodies to a human homologue of podocalyxin, C3b receptor, vimentin, common lymphocytic leukemia antigen, gp44, and the WGA, LFA and, after neuraminidase treatment, PNA lectin) failed to show appreciable qualitative changes in CNF kidney samples. Interestingly, the alpha 2 beta 1 integrins appeared greatly reduced in all CNF samples studied, possibly explaining the mechanisms of CNF-associated proteinuria.

Mesangial cell apoptosis: the major mechanism for resolution of glomerular hypercellularity in experimental mesangial proliferative nephritis

Increases in mesangial cell number may herald glomerular scarring, but they are not irreversible. This study sought mechanisms by which surplus glomerular mesangial cells can be cleared. A small proportion of cultured mesangial cells exhibited typical morphological features of apoptosis (programmed cell death), which was increased by growth factor deprivation or exposure to cycloheximide, stimuli known to increase apoptosis in other cell types. Apoptosis was confirmed by typical internucleosomal chromatin cleavage. In vivo, clear morphological evidence of mesangial apoptosis leading to phagocytosis by neighboring mesangial cells was obtained in self-limited mesangial proliferation induced in rats by Thy1.1 antibody, apoptosis occurring approximately 10-fold more frequently than in the healthy rat glomerulus. Indeed, changes in glomerular cell number in Thy1.1 nephritis strongly suggested that apoptosis is the major cell clearance mechanism counterbalancing cell division, thereby mediating resolution of glomerular hypercellularity in experimental mesangial proliferation.

Uptake of nanoparticles by rat glomerular mesangial cells in vivo and in vitro

Glomerular mesangial cells play a major role in the structure of capillary loops, generation of mediators of inflammation, and uptake of macromolecules. We demonstrate here that isobutylcyanoacrylate nanoparticles loaded with actinomycin D (ADNP) concentrate in rat mesangial cells in vitro and in vivo, as compared to the free drug (AD). In normal rats injected with 20 micrograms of 3H-ADNP or 3H-AD, the uptake ratios 3H-ADNP/3H-AD measured in whole kidneys at 30 and 120 min were 2.2 +/- 1.0 and 2.3 +/- 0.9, respectively. The same ratios calculated for isolated rat glomeruli and tubules, were 4.1 +/- 0.5 and 0.8 +/- 0.2 at 30 min, and 2.6 +/- 0.5 and 0.6 +/- 0.3 at 120 min, respectively. In the glomeruli, the absolute uptake of 3H-ADNP corresponded to 7.5 (30 min) and 1.8 (120 min)% I.D./100 mg of protein. In rats with experimental glomerulonephritis, the uptakes of 3H-ADNP and 3H-AD by the glomeruli were 6.9 and 4.0 times higher than in normal rats, respectively. In vitro experiments demonstrated up to 5 times higher uptake by glomerular mesangial cells than by epithelial cells. Uptake was maximum after 60 min, higher at 37 degrees C than at 4 degrees C, dependent on the presence of fresh serum and inhibited by cytochalasin-B. Drug targeting by nanoparticles is thus possible to renal cells involved in inflammatory processes, especially mesangial cells and macrophages. Nanoparticles could also be useful for lowering drug concentration in tubular cells, to reduce any tubular toxicity.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of tumour necrosis factor alpha and interleukin 1 beta on the proliferation of cultured glomerular epithelial cells

Rat glomerular epithelial cells were cultured with human monocyte supernatant or with recombinant cytokines. A primary glomerular culture and a glomerular epithelial cell culture were made; supernatant from monocyte cultures derived from healthy humans, and recombinant tumour necrosis factor alpha (TNF alpha) or recombinant interleukin 1 beta (IL-1 beta) were added. Cell proliferation rates were assayed by the MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) assay. In serum-free media, consistent proliferation of glomerular epithelial cells (GEC) was observed throughout the 3 week culture period. Significant growth-stimulatory effects were induced by lipopolysaccharide-treated monocyte conditioned medium and by 1-50 ng/ml of TNF alpha, growth being up to 400% more than in the control culture. The effect of TNF alpha depended mainly on its interaction with epidermal growth factor (EGF). In contrast to TNF alpha, IL-1 beta inhibited GEC proliferation; this was due to the early appearance and proliferation of mesangial cells, despite the culture being serum-free. This study showed that activated monocytes secrete growth factors for GEC in vitro, and that interaction between both TNF alpha and IL-1 beta and between TNF alpha and EGF can modulate GEC proliferation. These findings suggest that, under pathological conditions, monocytes or macrophages affect GEC proliferation, probably being involved in crescent formation.

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.

Growth modulation and proteoglycan turnover in cultured mesangial cells

Proliferation of mesangial cells is a common feature of renal disease, and conditioned media from glomerular epithelial and endothelial cells have been found to contain heparin-like molecules that suppress proliferation of rat mesangial cells (RMC). We have partially characterized the glycosaminoglycans that are labeled with 35SO4(2-) by RMC in culture at early passage and examined their ability to inhibit mitogenic stimulation of the cells. Four chondroitin/dermatan sulfate proteoglycans (CS/DSPG) were identified, the largest and smallest of which (Kd of 0.04 and 0.26 on Superose 6) were retained in the cell layer while the other two (Kd = 0.17 and 0.22) were secreted into the medium. Heparan sulfate proteoglycans (HSPG) with Kd values of 0.09, 0.13, and 0.39 were minor components of the cell layer, while a single heparan sulfate (Kd = 0.17) was recovered from the medium. After 16 h of labeling in serum-free medium, about 60% of macromolecular 35S was cell-associated and 40% was in the medium. Cell-associated label consisted of 7% CS/DSPG, 9% HSPG, and 84% free glycosaminoglycan chains (mostly CS/DS), whereas the medium contained 52% CS/DSPG, 17% HSPG, and approximately equal amounts of free HS and CS/DS chains. Bovine lung heparin (1 microgram/ml) decreased by 45% the incorporation of [3H]-thymidine into DNA after release of serum-starved RMC from growth arrest. Heparin acted prior to the G1/S interface; arrest of the cells in early S phase with aphidicolin abrogated the heparin response. The endogenous HSPGs had a slight antimitogenic effect on the RMC, but heparan sulfate chains from both the medium and cell layer had a potent effect. On an equivalent mass basis, only the free glycosaminoglycan chains were more potent than heparin in this regard, decreasing thymidine incorporation by over 90% when present at 1 microgram/ml. These results demonstrate that heparan sulfate glycosaminoglycans derived from mesangial proteoglycans are potential negative autocrine growth regulators. Proteoglycan metabolism releases these soluble heparan sulfate chains, determining the level of this activity.

Congenital nephrosis of the Finnish type (CNF): matrix components of the glomerular basement membranes and of cultured mesangial cells

Congenital nephrosis of the Finnish type (CNF) is a hereditary renal disease of unknown aetiology manifested by massive proteinuria of the newborn and unresponsive to any treatment. In this study kidney samples and cultured glomerular mesangial cells from five patients with CNF were studied by indirect immunofluorescence microscopy for the presence and location of major basement membrane matrix (GBM) components. Histological changes of glomeruli ranging from mild thickening of basement membranes to total obliteration and sclerosis were seen. Notably, thickening of the subepithelial layer of Bowman's capsules was regularly seen along with hypercellularity at the juxtaglomerular areas. The matrix components studied (laminin, plasma- and cellular fibronectin, type IV collagen, including the NC-1, alpha-1 and alpha-3 chains, heparan sulphate proteoglycan (HSPG) core protein, thrombospondin) were characteristically seen within the glomeruli. Local thickenings alternating with total loss of epitopes along the GBM were seen, especially with anti-type IV collagen and anti-HSPG antibodies. Sera from CNF patients after transplantation failed to show antibodies against GBM structures in immunofluorescence microscopy, suggesting that no missing epitopes of GBM are introduced with the transplant kidney. Cultured mesangial cells of CNF glomeruli also showed continued in vitro production of the matrix components and their incorporation into the matrix underneath the cell layer.

Glomerular mesangial cells and inflammatory macrophages ingest neutrophils undergoing apoptosis

Apoptosis or programmed cell death of senescent neutrophils leading to their uptake by phagocytes is a general mechanism by which neutrophils may be removed from inflamed sites in vivo, promoting resolution rather than persistence of inflammation. We now report morphological evidence of neutrophil apoptosis leading to uptake by glomerular cells in rats with experimental glomerulonephritis. In addition to confirming that inflammatory macrophages take up apoptotic neutrophils, these studies indicated that glomerular mesangial cells can also participate in this mode of neutrophil clearance. Furthermore, human neutrophils which had been "aged" in vitro so as to undergo apoptosis were ingested by 31.5 +/- 1.3% (mean +/- SE) of cultured human mesangial cells, but there was minimal recognition of freshly isolated neutrophils (2.2 +/- 0.1%). Centrifugal elutriation of aged neutrophil populations yielded fractions with varying degrees of apoptosis (from 11.1 to 79.4%). Uptake of these fractions (by 8.2% to 59.8% of mesangial cells) was closely correlated with apoptosis (r = 0.96, P less than 0.0001). This demonstrated that recognition was dependent upon apoptosis, as in previous reports of macrophage recognition of aged neutrophils. However, by contrast, a partial requirement for serum was observed. These data indicate a hitherto unexpected function for the mesangial cell in clearance of senescent neutrophils from the glomerulus which may supplement inflammatory macrophage uptake of leucocytes undergoing apoptosis.

A monoclonal antibody (1G10) recognizes a novel human mesangial antigen

We have identified a unique mesangial matrix protein of the human glomerulus by using a monoclonal antibody, 1G10, generated against culture human glomerular cells. By immunofluorescence, the antigen recognized by 1G10 (1G10 antigen) is present in mesangium and smooth muscle tissue and cannot be detected in any other tissue examined. Immunoelectron microscopy of glomeruli indicated that 1G10 antigen is present exclusively in the mesangial matrix at the endothelial-mesangial interface. The 1G10 antigen is also expressed by cultured mesangial cells, but not by cultured glomerular epithelial cells, umbilical endothelial cells or fibroblasts. 1G10 did not react with the mesangial matrix proteins [fibronectin (FN), laminin (LAM), collagen types I, III, IV, V, and VI (Col I, III, IV, V, VI), heparin sulfate proteoglycan (HSPG), or thrombospondin (TS)] present under normal and diseased states or smooth muscle antigens (myosin, actin), but did react with a 4 M urea extract of renal cortex and a 0.3% deoxycholate extract of isolated glomeruli. Two dimensional immunoblot analysis using the urea extract demonstrated the binding of 1G10 to an approximately 200 KDa polypeptide with pI 6.0. On one dimensional immunoblot this band did not show cross react with polyclonal antisera to FN, LAM, Col IV, V, VI, HSPG or TS. This mesangial matrix component is trypsin and periodate sensitive, suggesting that it has the character of glycoprotein. In renal biopsy specimens from patients with mesangial proliferative glomerulonephritis (GN) and membranoproliferative GN, the expression of the 1G10 antigen increased along with mesangial hypercellularity or increased accumulation of mesangial matrix, but decreased in completely sclerosed glomeruli. No significant changes in 1G10 antigen expression was observed in membranous GN or minimal change nephrosis compared to normal glomeruli. This study suggests that the 1G10 antigen may not only be a useful marker for the clinical assessment of GN, but may also serve as a potential tool for the study of the pathogenesis of glomerular diseases characterized by cellular proliferation and mesangial matrix expansion.

Effects of CdCl2 and Cd-metallothionein on cultured mesangial cells

Cadmium is a potent nephrotoxin known to cause damage to the proximal tubular epithelium in vivo. The renal glomerulus is less frequently a target and is sensitive to Cd in vitro. We have previously presented evidence that the mesangial cell is a major target for Cd2+ toxicity in the isolated glomerulus (D. M. Templeton and N. Chaitu, Toxicology 61, 119-133, 1990). The present study was undertaken to investigate the sensitivity to Cd of rat mesangial cells grown in homogeneous culture. At a concentration of 1 microM, Cd2+ was a potent inducer of its binding protein metallothionein (MT). Cd2+ inhibited DNA synthesis in these cells with an EC50 of 5.4 +/- 0.4 microM, while preinduction of MT with Zn2+ was protective, raising the EC50 to 17.6 +/- 0.7 microM Cd2+. DNA synthesis in these cells is especially sensitive to Cd2+; only at concentrations of 20 microM Cd2+ and higher were significant effects on cell viability, attachment, and protein synthesis observed. Renal function depends in part on synthesis of specialized matrices by glomerular cells. Synthesis of both matrix and secreted proteoglycans was specifically affected by Cd2+ with an EC50 of about 10 microM for proteoglycan sulfation. We also investigated the effects of Cd-MT on these parameters. Contrary to observations that extracellular Cd-MT is a potent nephrotoxin in vivo, we were unable to demonstrate any effects of Cd-MT on DNA and protein synthesis at Cd concentrations below 60 microM in the cultured cells. Nor did Cd-MT at these concentrations affect DNA or protein synthesis in LLC-PK1 cells, a proximal tubule cell line. This was not due to failure of the cells to take up Cd because they accumulated comparable amounts of Cd whether it was provided as CdCl2 or Cd-MT. We conclude that ionic Cd2+ is the most toxic form of this metal to cultured mesangial cells. While these cells respond to micromolar concentrations of Cd2+ by increasing their content of metallothionein, presumably a protective response, only slightly higher levels may impair the regenerative capacity of mesangial cells, in addition to interfering with the specialized function of matrix synthesis.

Enhanced expression of “muscle-specific” actin in glomerulonephritis

Increased expression of "muscle-specific" actin can be correlated with mesangial cell injury and proliferation in the rat. We performed similar immunohistochemical studies using two monoclonal antibodies (MoAb) to "muscle-specific" actins (HHF-35, a MoAb to pan muscle actin and alpha-SM-1, a MoAb to alpha-smooth muscle actin) on methyl Carnoy's fixed human renal biopsies which demonstrated a wide variety of inflammatory, proliferative, and non-proliferative glomerular diseases. Most glomerular diseases were associated with increased "smooth-muscle" actin expression. Exceptions almost invariably were disease settings without prominent cellular proliferation. As in the rat, there was a correlation of induced actin expression with increased glomerular cell proliferation, as detected by staining with a MoAb to proliferating cell nuclear antigen (PCNA). Double immunolabeling studies with an antibody to the leukocyte common antigen showed the great majority of PCNA+ proliferating cells to be intrinsic glomerular cells rather than infiltrating leukocytes. These studies demonstrate that phenotypic changes of mesangial cells occur in both human and experimental glomerulonephritis, and are identifiable in fixed tissue sections. These studies also suggest that markers of mesangial cell injury or activation and proliferation, such as immunostaining of renal biopsies for "muscle-specific" actins, might be useful diagnostic and/or prognostic indicators in proliferative or sclerosing glomerular diseases.

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.

Proteoglycans in cell regulation

Proteoglycans are a diverse group of proteins carrying one or more glycosaminoglycan side chains linked to the protein as O-glycosides. Our appreciation of these structures has matured from a curiosity about unusual structural glycoproteins, to confer upon them a central role in cell biology. The major classes of glycosaminoglycans are heparan sulfate and heparin, chondroitin and dermatan sulfates, keratan sulfate and hyaluronic acid. The latter is unique in that it does not contain sulfate residues, and appears to be synthesized, at least sometimes, free of a carrier protein. There is now a wealth of information on the ability of these structures to influence the growth and development of cells and tissues. Many direct and specific effects of proteoglycans will undoubtedly be found, and there are likely to be indirect effects of the glycosaminoglycans relating to their polyelectrolyte nature. Convincing arguments that biological activity resides in certain proteoglycan core proteins are also appearing. The following discussion concerns the role of proteoglycans in the regulation and action of autocrine and polypeptide growth factors, direct mitogenic and antimitogenic actions of glycosaminoglycans, the role of these structures in regulating gene expression, and the biological activities of proteoglycan core proteins. The probable role of proteoglycans in normal glomerular cell function, and in progressive renal disease, will be presented as a harbinger of the significant role we can expect them to play in diagnosis and therapy in the near future.

Vasoactive agents affect growth and protein synthesis of cultured rat mesangial cells

Mesangial cell (MC) proliferation and extracellular matrix (ECM) formation are hallmarks of chronic glomerular disease. The present in vitro study examined the effects of the vasoactive agents angiotensin II (Ang II), arginine vasopressin (AVP), and serotonin (5-HT) on growth and protein biosynthesis of cultured rat MCs after 72 hours of incubation. AVP and 5-HT (10(-6) M) significantly increased DNA synthesis and growth of quiescent subconfluent MCs to levels of 25 and 45%, respectively, of the optimal stimulatory effect of 10% fetal calf serum (FCS) (both P less than 0.001). The mitogenic effect of Ang II was 10% of the 10% FCS effect (P less than 0.01). ECM production was studied by ELISA assay for fibronectin (FN) secreted into the culture medium (SeFN) and cell-associated FN, that is, intra- and pericellular FN (CaFN). In all incubations, highly significant negative linear relationships were found between the numbers of MCs per well and quantities of both SeFN and CaFN after normalization of the data by logarithmic transformation (SeFN: r values greater than -0.9705; CaFN: r greater than -0.9620; P less than 0.001). Thus, increasing cell densities progressively suppressed ECM formation by MCs. The ECM production was found to be independent of growth activity. AVP significantly increased SeFN (P less than 0.05) and decreased CaFN (P less than 0.001) in subconfluent cultures; Ang II and 5-HT had no effect. Metabolic labeling with 35S-methionine (18 hr, 200 microCi/ml medium) and 2-D electrophoresis of MC lysates resulted in resolution of greater than 500 different radiolabeled intracellular proteins in molecular weight from 110 to 20 Kd over an isoelectric interval of 5.0 to 7.0.(ABSTRACT TRUNCATED AT 250 WORDS)

Human and rat mesangial cell receptors for glucose-modified proteins: potential role in kidney tissue remodelling and diabetic nephropathy

Advanced glycosylation endproducts (AGEs) are derived from the nonenzymatic addition of glucose to proteins. AGEs have been found to accumulate on tissue proteins in patients with diabetes, and their accumulation is thought to play a role in the development of diabetic complications. The finding that macrophages and endothelial cells contain AGE-specific receptors led us to examine whether mesangial cells (MCs) also possess a mechanism for recognizing and processing AGEs. Membrane extracts isolated from rat and human MCs were found to bind AGE-bovine serum albumin (BSA) in a saturable fashion, with a binding affinity of 2.0 +/- 0.4 x 10(6) M-1 (500 nM). The binding was specific for the AGE adduct, since AGE-modified collagen I and ribonuclease both competitively inhibited 125I-AGE-BSA binding to MC membranes, while the unmodified proteins did not compete. Binding of AGE proteins was followed by slow internalization and degradation of the ligand. Ligand blotting of MC membrane extracts demonstrated three distinct AGE-binding membrane proteins of 50, 40, and 30 kD. Growth of MCs on various AGE-modified matrix proteins resulted in alterations in MC function, as demonstrated by enhanced production of fibronectin and decreased proliferation. These results point to the potential role that the interaction of AGE-modified proteins with MCs may play in vivo in promoting diabetic kidney disease.

Actions of 1,25-dihydroxyvitamin D3 on human mesangial cells

In the present study, we examined specific binding of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] by an effects of 1,25(OH)2D3 on human mesangial cells (hMC), obtained from healthy portions of tumor-bearing kidneys. Receptors for 1,25(OH)2D3 were characterized by (1) sucrose density gradient analysis, (2) Scatchard analysis, and (3) DNA affinity of the receptor molecule. Specific binding occurred by a single class of macromolecules, sedimenting with 3.5 S in sucrose density gradients (5% to 20%). Receptors showed high affinity (Kd, 1.39 x 10(-10)), and specific binding capacity (Nmax) of 821 binding sites per cell. 1,25(OH)2D3 (10(-6) to 10(-10)) reduced both DNA synthesis (by [3H]thymidine incorporation) and cell growth (by cell counting) throughout the log-phase and confluence. Further evidence of functional effects of 1,25(OH)2D3 on hMC is provided by ultrastructural studies, which showed rapid increase of electron-dense lysosomal particles in hMC exposed to 1,25(OH)2D3. The data identify actions of 1,25(OH)2D3, a molecule with recently recognized immunoregulatory roles, on hMC. The results are consistent with a role of 1,25(OH)2D3 in control of mesangial cell function.

Glomerular macrophage proliferation in experimental immune complex nephritis

In immune complex nephritis, glomerular hypercellularity is known to result from the proliferation of intrinsic cells and from the infiltration of mononuclear cells, primarily macrophages. An immunohistochemical double-labeling procedure was used to determine whether macrophages were among the cells which may undergo mitosis within the glomerular tuft. The monoclonal antibody ED1 served as a macrophage marker; cells in the S-phase of mitosis were recognized by uptake of bromodeoxyuridine. Glomerular proliferation was studied in chronic serum sickness of LEW rats, an animal model of immune complex nephritis for which the relationship between immunopathology and pathophysiology has been well described. In normal glomeruli, resident mesangial macrophages accounted for an unexpectedly large proportion (greater than or equal to one-third) of the total mitotic activity. In immune complex glomerulonephritis, the rate of glomerular macrophage proliferation increased rapidly just at the onset of proteinuria and remained high throughout the remaining course of disease. Glomerular macrophages from rats with proliferative nephritis also divided more vigorously than normal in short term culture in vitro, while persistently expressing abnormal surface marker phenotypes. The proliferation of mesangial macrophages appears to be a prominent feature of the normal process of glomerular cell renewal. In hypercellular glomeruli, vigorous local proliferation could greatly amplify the potential of macrophages to cause damage.

Expression of smooth muscle cell phenotype by rat mesangial cells in immune complex nephritis. Alpha-smooth muscle actin is a marker of mesangial cell proliferation

Mesangial cell proliferation is common in glomerulonephritis but it is unclear if proliferation is associated with any in vivo alteration in phenotype. We investigated whether mesangial of mesangial proliferative nephritis induced with antibody to the Thy-1 antigen present on mesangial cells. At day 3 glomeruli displayed de novo immunostaining for alpha-smooth muscle actin in a mesangial pattern, correlating with the onset of proliferation, and persisting until day 14. An increase in desmin and vimentin in mesangial regions was also noted. Immunoelectron microscopy confirmed that the actin-positive cells were mesangial cells, and double immunolabeling demonstrated that the smooth muscle actin-positive cells were actively proliferating. Northern analysis of isolated glomerular RNA confirmed an increase in alpha and beta/gamma actin mRNA at days 3 and 5. Complement depletion or platelet depletion prevented or reduced proliferation, respectively; these maneuvers also prevented smooth muscle actin and actin gene expression. Studies of five other experimental models of nephritis confirmed that smooth muscle actin expression is a marker for mesangial cell injury. Thus, mesangial cell proliferation in glomerulonephritis in the rat is associated with a distinct phenotypic change in which mesangial cell assume smooth muscle cell characteristics.

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.