Interleukin-1 and the mesangial cell

The role of the mesangium in glomerular function

When discussing glomerular function, one cell type is often left out, the mesangial cell (MC), probably since it is not a part of the filtration barrier per se. The MCs are instead found between the glomerular capillaries, embedded in their mesangial matrix. They are in direct contact with the endothelial cells and in close contact with the podocytes and together they form the glomerulus. The MCs can produce and react to a multitude of growth factors, cytokines, and other signaling molecules and are in the perfect position to be a central hub for crosstalk communication between the cells in the glomerulus. In certain glomerular diseases, for example, in diabetic kidney disease or IgA nephropathy, the MCs become activated resulting in mesangial expansion. The expansion is normally due to matrix expansion in combination with either proliferation or hypertrophy. With time, this expansion can lead to fibrosis and decreased glomerular function. In addition, signs of complement activation are often seen in biopsies from patients with glomerular disease affecting the mesangium. This review aims to give a better understanding of the MCs in health and disease and their role in glomerular crosstalk and inflammation.

Transient Receptor Potential Ankyrin-1-expressing vagus nerve fibers mediate IL-1β induced hypothermia and reflex anti-inflammatory responses

BACKGROUND

Inflammation, the physiological response to infection and injury, is coordinated by the immune and nervous systems. Interleukin-1β (IL-1β) and other cytokines produced during inflammatory responses activate sensory neurons (nociceptors) to mediate the onset of pain, sickness behavior, and metabolic responses. Although nociceptors expressing Transient Receptor Potential Ankyrin-1 (TRPA1) can initiate inflammation, comparatively little is known about the role of TRPA1 nociceptors in the physiological responses to specific cytokines.

METHODS

To monitor body temperature in conscious and unrestrained mice, telemetry probes were implanted into peritoneal cavity of mice. Using transgenic and tissue specific knockouts and chemogenetic techniques, we recorded temperature responses to the potent pro-inflammatory cytokine IL-1β. Using calcium imaging, whole cell patch clamping and whole nerve recordings, we investigated the role of TRPA1 during IL-1β-mediated neuronal activation. Mouse models of acute endotoxemia and sepsis were used to elucidate how specific activation, with optogenetics and chemogenetics, or ablation of TRPA1 neurons can affect the outcomes of inflammatory insults. All statistical tests were performed with GraphPad Prism 9 software and for all analyses, P ≤ 0.05 was considered statistically significant.

RESULTS

Here, we describe a previously unrecognized mechanism by which IL-1β activates afferent vagus nerve fibers to trigger hypothermia, a response which is abolished by selective silencing of neuronal TRPA1. Afferent vagus nerve TRPA1 signaling also inhibits endotoxin-stimulated cytokine storm and significantly reduces the lethality of bacterial sepsis.

CONCLUSION

Thus, IL-1β activates TRPA1 vagus nerve signaling in the afferent arm of a reflex anti-inflammatory response which inhibits cytokine release, induces hypothermia, and reduces the mortality of infection. This discovery establishes that TRPA1, an ion channel known previously as a pro-inflammatory detector of cold, pain, itch, and a wide variety of noxious molecules, also plays a specific anti-inflammatory role via activating reflex anti-inflammatory activity.

PPARβ/δ Augments IL-1β-Induced COX-2 Expression and PGE2 Biosynthesis in Human Mesangial Cells via the Activation of SIRT1

Peroxisome proliferator-activated receptor β/δ (PPARβ/δ), a ligand-activated nuclear receptor, regulates lipid and glucose metabolism and inflammation. PPARβ/δ can exert an anti-inflammatory effect by suppressing proinflammatory cytokine production. Cyclooxygenase-2 (COX-2)-triggered inflammation plays a crucial role in the development of many inflammatory diseases, including glomerulonephritis. However, the effect of PPARβ/δ on the expression of COX-2 in the kidney has not been fully elucidated. The present study showed that PPARβ/δ was functionally expressed in human mesangial cells (hMCs), where its expression was increased by interleukin-1β (IL-1β) treatment concomitant with enhanced COX-2 expression and prostaglandin E2 (PGE2) biosynthesis. The treatment of hMCs with GW0742, a selective agonist of PPARβ/δ, or the overexpression of PPARβ/δ via an adenovirus-mediated approach significantly increased COX-2 expression and PGE2 production. PPARβ/δ could further augment the IL-1β-induced COX-2 expression and PGE2 production in hMCs. Moreover, both PPARβ/δ activation and overexpression markedly increased sirtuin 1 (SIRT1) expression. The inhibition or knockdown of SIRT1 significantly attenuated the effects of PPARβ/δ on the IL-1β-induced expression of COX-2 and PGE2 biosynthesis. Taken together, PPARβ/δ could augment the IL-1β-induced COX-2 expression and PGE2 production in hMCs via the SIRT1 pathway. Given the critical role of COX-2 in glomerulonephritis, PPARβ/δ may represent a novel target for the treatment of renal inflammatory diseases.

The Glomerulus According to the Mesangium

The glomerulus is the functional unit for filtration of blood and formation of primary urine. This intricate structure is composed of the endothelium with its glycocalyx facing the blood, the glomerular basement membrane and the podocytes facing the urinary space of Bowman's capsule. The mesangial cells are the central hub connecting and supporting all these structures. The components as a unit ensure a high permselectivity hindering large plasma proteins from passing into the urine while readily filtering water and small solutes. There has been a long-standing interest and discussion regarding the functional contribution of the different cellular components but the mesangial cells have been somewhat overlooked in this context. The mesangium is situated in close proximity to all other cellular components of the glomerulus and should be considered important in pathophysiological events leading to glomerular disease. This review will highlight the role of the mesangium in both glomerular function and intra-glomerular crosstalk. It also aims to explain the role of the mesangium as a central component involved in disease onset and progression as well as signaling to maintain the functions of other glomerular cells to uphold permselectivity and glomerular health.

Does daily fasting shielding kidney on hyperglycemia-related inflammatory cytokine via TNF-α, NLRP3, TGF-β1 and VCAM-1 mRNA expression

This study aimed to investigate the effects of blood glucose control and the kidneys' functions, depending on fasting, in the streptozotocin-induced diabetes model in rats via TNF-α, NLRP-3, TGF-β1 and VCAM-1 mRNA expression in the present study. 32 Wistar albino rats were allocated randomly into four main groups; H (Healthy, n = 6), HF (Healthy fasting, n = 6), D (Diabetes, n = 10), DF (Diabetes and fasting, n = 10). Blood glucose and HbA1c levels significantly increased in the D group compared to the healthy ones (p < 0.05). However, the fasting period significantly improved blood glucose and HbA1c levels 14 days after STZ induced diabetes in rats compared to the D group. Similar findings we obtained for serum (BUN-creatinine) and urine samples (creatinine and urea levels). STZ induced high glucose levels significantly up-regulated TNF-α, NLRP-3, TGF-β1 and VCAM-1 mRNA expression and fasting significantly decreased these parameters when compared to diabetic rats. Histopathological staining also demonstrated the protective effects of fasting on diabetic kidney tissue. In conclusion, intermittent fasting regulated blood glucose level as well as decreasing harmful effects of diabetes on kidney tissue. The fasting period significantly decreased the hyperglycemia-related inflammatory cytokine damage on kidneys and also reduced apoptosis in favor of living organisms.

Interleukin 1 beta-induced calcium signaling via TRPA1 channels promotes mitogen-activated protein kinase-dependent mesangial cell proliferation

Glomerular mesangial cell (GMC)-derived pleiotropic cytokine, interleukin-1 (IL-1), contributes to hypercellularity in human and experimental proliferative glomerulonephritis. IL-1 promotes mesangial proliferation and may stimulate extracellular matrix accumulation, mechanisms of which are unclear. The present study shows that the beta isoform of IL-1 (IL-1β) is a potent inducer of IL-1 type I receptor-dependent Ca²⁺ entry in mouse GMCs. We also demonstrate that the transient receptor potential ankyrin 1 (TRPA1) is an intracellular store-independent diacylglycerol-sensitive Ca²⁺ channel in the cells. IL-1β-induced Ca²⁺ and Ba²⁺ influxes in the cells were negated by pharmacological inhibition and siRNA-mediated knockdown of TRPA1 channels. IL-1β did not stimulate fibronectin production in cultured mouse GMCs and glomerular explants but promoted Ca²⁺ -dependent cell proliferation. IL-1β also stimulated TRPA1-dependent ERK mitogen-activated protein kinase (MAPK) phosphorylation in the cells. Concomitantly, IL-1β-induced GMC proliferation was attenuated by TRPA1 and RAF1/ MEK/ERK inhibitors. These findings suggest that IL-1β-induced Ca²⁺ entry via TRPA1 channels engenders MAPK-dependent mesangial cell proliferation. Hence, TRPA1-mediated Ca²⁺ signaling could be of pathological significance in proliferative glomerulonephritis.

The Renal Safety of L-Carnitine, L-Arginine, and Glutamine in Athletes and Bodybuilders

One of the major concerns about taking amino acid supplements is their potential adverse effects on the kidney as a major organ involved in the metabolism and excretion of exogenous substances. The aim of this study is to review available data about renal safety of the most prominent amino acid supplements including L-arginine, glutamine and also L-carnitine as well as creatine (as amino acid derivatives) in athletes and bodybuilders. The literature was searched by keywords such as "L-carnitine", "L-arginine", "glutamine", and "kidney injury" in databases such as Scopus, Medline, Embase, and ISI Web of Knowledge. Articles published from 1950 to December 2017 were included. Among 3171, 5740, and 1608 records after primary search in the relevant databases, 8, 7, and 5 studies have been finally included, respectively, for L-carnitine, L-arginine, and glutamine in this review. Arginine appears to have both beneficial and detrimental effects on kidney function. However, adverse effects are unlikely to occur with the routine doses (from 3 to >100 g/day). The risks and benefits of L-carnitine on the athletes' and bodybuilders' kidney have not been evaluated yet. However, L-carnitine up to 6000 mg/day is generally considered to be a safe supplement at least in healthy adults. Both short-term (20-30 g within a few hours) and long-term (0.1 g/kg four times daily for 2 weeks) glutamine supplementation in healthy athletes were associated with no significant adverse effects, but it can cause glomerulosclerosis and serum creatinine level elevation in the setting of diabetic nephropathy. Creatine supplementation (ranged from 5 to 30 g/day) also appears to have no detrimental effects on kidney function of individuals without underlying renal diseases. More clinical data are warranted to determine the optimal daily dose and intake duration of common supplemental amino acids associated with the lowest renal adverse effects in sportsmen and sports women.

The emerging role of coagulation proteases in kidney disease

A role of coagulation proteases in kidney disease beyond their function in normal haemostasis and thrombosis has long been suspected, and studies performed in the past 15 years have provided novel insights into the mechanisms involved. The expression of protease-activated receptors (PARs) in renal cells provides a molecular link between coagulation proteases and renal cell function and revitalizes research evaluating the role of haemostasis regulators in renal disease. Renal cell-specific expression and activity of coagulation proteases, their regulators and their receptors are dynamically altered during disease processes. Furthermore, renal inflammation and tissue remodelling are not only associated, but are causally linked with altered coagulation activation and protease-dependent signalling. Intriguingly, coagulation proteases signal through more than one receptor or induce formation of receptor complexes in a cell-specific manner, emphasizing context specificity. Understanding these cell-specific signalosomes and their regulation in kidney disease is crucial to unravelling the pathophysiological relevance of coagulation regulators in renal disease. In addition, the clinical availability of small molecule targeted anticoagulants as well as the development of PAR antagonists increases the need for in-depth knowledge of the mechanisms through which coagulation proteases might regulate renal physiology.

Effects of glutamine supplementation on kidney of diabetic rat

Glutamine is the most important donor of NH(3) in kidney playing an important role in acid-base buffering system. Besides this effect, glutamine presents many other relevant functions in the whole body, such as a precursor of arginine in adult and neonates. In addition to these effects, some studies have shown that glutamine can potentiate renal disease. In the present study, the effect of short-term treatment (15 days) with glutamine on control and diabetic rats was investigated. Using biochemical, histological and molecular biology analysis from control and diabetic rats we verified that glutamine supplementation increase in pro-inflammatory interleukins (IL)-1beta and IL-6 content in renal cortex and induce alteration in glomerular characteristics. This study showed that short-term treatment with glutamine in association with increased glucose levels could cause important alterations in glomerular morphology that may result in fast progression of kidney failure.

Bone morphogenetic protein-7 inhibits constitutive and interleukin-1 beta-induced monocyte chemoattractant protein-1 expression in human mesangial cells: role for JNK/AP-1 pathway

Bone morphogenetic protein-7 (BMP-7), which belongs to the TGF-beta superfamily, has been shown to reduce macrophage infiltration and tissue injury in animal models of inflammatory renal disease. To explore the mechanism involved in the anti-inflammatory effect, we investigated the effect of BMP-7 on monocyte chemoattractant protein-1 (MCP-1) expression in cultured human mesangial cells. BMP- 7 significantly inhibited constitutive and IL-1 beta-induced MCP-1 protein production and MCP-1 mRNA expression by mesangial cells in a time- and concentration-dependent manner. BMP-7 also inhibited IL-1 beta-induced monocyte chemotactic activity released from the mesangial cells. We examined the role of transcription factors NF-kappa B and AP-1 in BMP-7 inhibition of IL-1 beta-induced MCP-1 expression. IL-1 beta increased NF-kappa B and AP-1 activity and both transcription factors mediated IL-1 beta-induced MCP-1 expression in mesangial cells. BMP-7 inhibited IL-1 beta-induced AP-1 activity in a concentration-dependent manner. In contrast, IL-1 beta-induced NF-kappa B activity and I kappa B alpha degradation were not affected by BMP-7. Furthermore, IL-1 beta-induced phosphorylation of c-Jun N-terminal kinase was inhibited by BMP-7. These data suggest that BMP-7 inhibits constitutive and IL-1 beta-induced MCP-1 expression in human mesangial cells partly by inhibiting c-Jun N-terminal kinase activity and subsequent AP-1 activity, and provide new insight into the therapeutic potential of BMP-7 in the inflammatory renal diseases.

H1-A extracted from Cordyceps sinensis suppresses the proliferation of human mesangial cells and promotes apoptosis, probably by inhibiting the tyrosine phosphorylation of Bcl-2 and Bcl-XL

H1-A, a pure compound used in traditional Chinese medicine, is effective in the treatment of autoimmune disorders of MRL lpr/lpr mice. We have previously reported that after 8 weeks of oral therapy with H1-A, 40 microg/kg/day, MRL lpr/lpr mice demonstrated significantly less proteinuria, lower serum creatinine levels, and less renal mesangial proliferation than mice in an untreated group. To clarify the pharmacologic properties of H1-A, we studied its cellular and subcellular effects in cultured human mesangial cells. Our results show that H1-A inhibits cell proliferation and promotes the apoptosis of interleukin (IL)-1- and platelet-derived growth factor (PDGF)-BB-activated human mesangial cells in vitro. Uptake of tritiated thymidine was nearly totally suppressed by the addition of 12.5 micromol/L H1-A (counts per minute decreased from 3905 +/- 70 to 141 +/- 5). The population of S-phase cells decreased from 15.5% +/- 1.7% to 10.0% +/- 0.3%, and G0 + G1 phase cells increased from 68.8% +/- 0.07% to 74.6% +/- 0.05%. This suppression was not a result of cytotoxicity. Apoptosis of human mesangial cells was detectable after treatment with 12.5 or 25 micromol/L H1-A. Using immunoprecipitation and immunoblotting, we found that H1-A inhibits tyrosine phosphorylation of human mesangial proteins and that Bcl-2 and Bcl-XL were probably among these proteins. These findings suggest that H1-A modulates some subcellular signal-transduction pathways and changes the balance between proliferation and apoptosis of mesangial cells in vitro or in vivo. H1-A may be effective in the management of autoimmune disorders, and the modulation of the signal transduction proteins Bcl-2 and Bcl-XL may represent a target for future pharmacologic interventions.

Lupus nephritis: lessons from experimental animal models

Lupus nephritis is a frequent and severe complication of SLE. In the last decades, animal models for SLE have been studied widely to investigate the immunopathology of this autoimmune disease because abnormalities can be studied and manipulated before clinical signs of the disease become apparent. In this review an overview is given of our current knowledge on the development of lupus nephritis, as derived from animal models, and a hypothetical pathway for the development of lupus nephritis is postulated. The relevance of the studies in experimental models in relationship with our knowledge of human SLE is discussed.

Role of platelet-activating factor acetylhydrolase gene mutation in Japanese childhood IgA nephropathy

Platelet-activating factor (PAF) is a potent mediator of inflammatory injury in renal diseases. PAF is degraded to inactive products by PAF acetylhydrolase. Recently, a point mutation (G to T transversion) of the PAF acetylhydrolase gene was observed at position 994, and this mutation was found to contribute to the variability in plasma PAF levels, with undetectable plasma PAF acetylhydrolase activity occurring in homozygous patients (TT genotype) and reduced levels of activity in heterozygous patients (GT genotype). Therefore, we investigated the effect of the PAF acetylhydrolase gene mutation on the pathogenesis and progression of immunoglobulin A (IgA) nephropathy. Genomic DNA was obtained from 89 children with IgA nephropathy and 100 controls. We identified the PAF acetylhydrolase gene mutation (G994T) by polymerase chain reaction. There was no significant difference in genotypic frequency between patients and controls. However, urinary protein excretion at the time of biopsy was significantly greater in patients with the GT/TT genotypes than in those with the GG genotype. The percentage of glomeruli with mesangial cell proliferation was significantly greater in patients with the GT/TT genotypes than in those with the GG genotype. These results indicate the PAF acetylhydrolase gene mutation may influence the degree of proteinuria and the extent of mesangial proliferation in the early stage of childhood IgA nephropathy.

Thrombin stimulates synthesis of type IV collagen and tissue inhibitor of metalloproteinases-1 by cultured human mesangial cells

Glomerular accumulation of extracellular matrix (ECM) is the common pathologic feature following glomerular injury, and the alteration in the synthesis and degradation of ECM may be involved in the glomerular accumulation of ECM. Glomerular fibrin formation occurs in various forms of human and experimental glomerulonephritis, and it may play an important role in progressive glomerular injury. Thrombin, a multifunctional serine proteinase that is generated at the site of vascular injury, has central functions in hemostasis and it also shows various biologic effects. In this study, it is hypothesized that thrombin may alter the production and the degradation of type IV collagen, which is an important component of ECM in the glomeruli. Human mesangial cells (HMC) were cultured, and the levels of type IV collagen, tissue inhibitor of metalloproteinase-1 (TIMP-1), and matrix metalloproteinase-2 (MMP-2) in the culture supernatants were measured by enzyme immunoassay using specific antibodies. MMP-2 activity was also evaluated by zymography using polyacrylamide/ sodium dodecyl sulfate gel-containing gelatin. Thrombin increased the production of type IV collagen and TIMP-1 in a dose-and time-dependent manner, but it did not increase MMP-2. Thrombin also stimulated the gene expressions of the type IV collagen and TIMP-1 in HMC in a dose- and time-dependent manner. Thrombin treated with diisopropylfluorophosphate, a serine proteinase inhibitor, did not show any of these effects. Hirudin, a natural thrombin inhibitor, and anti-transforming growth factor-beta-neutralizing antibody inhibited the stimulating effect of thrombin. These findings suggest that thrombin may contribute to the excessive accumulation of ECM and progression of glomerulosclerosis through an increase of type IV collagen production and a decreased matrix degradation presumably via a transforming growth factor-beta-dependent mechanism.

Blocking of cell proliferation, cytokines production and genes expression following administration of Chinese herbs in the human mesangial cells

In the hope of identifying agents of therapeutic value in immuoglobulin A nephropathy (IgA-N), we tested crude methanol extracts of 15 Chinese herbs for their effect on human mesangial cell proliferation. The results indicated that 4 out of the 15 crude extracts inhibited human cells proliferation activated by IL-1beta and IL-6. The extracts and their median inhibitory concentrations were as follows (in microg/ml): Ludwiga octovalvis (MLS-052), 49.9 +/- 1.8; Rhus semialata (MLS-053), 31.2 +/- 1.6; Tabernaemontana divaricata (MLS-054), 50.0 +/- 2.1; Amepelopsis brevipedunculata (MLS-059), 42.9 +/- 1.1. These findings indicate that human mesangial cells were most sensitive to MLS-053 treatment. These herbs also decreased interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha) production. Moreover, IL- 1beta mRNA expression was inhibited by Rhus semialata (R. semialata; MLS-053). It is unlikely that cytotoxicity was involved, because no cell deaths were observable. We hypothesize that the inhibitory mechanisms of these Chinese herbs may be related to the impairments of gene expression and production of cytokines in human mesangial cells. Plans are underway for the isolation of pure compounds from these Chinese herbs and the elucidation of their mechanisms of action.

The concept of glomerular self-defense

The balance between local offense factors and defense machinery determines the fate of tissue injury: progression or resolution. In glomerular research, the most interest has been on the offensive side, for example, the roles of leukocytes, platelets, complement, cytokines, eicosanoids, and oxygen radical intermediates. There has been little focus on the defensive side, which is responsible for the attenuation and resolution of disease. The aim of this review is to address possible mechanisms of local defense that may be exerted during glomerular injury. Cytokine inhibitors, proteinase inhibitors, complement regulatory proteins, anti-inflammatory cytokines, anti-inflammatory eicosanoids, antithrombotic molecules, and extracellular matrix proteins can participate in the extracellular and/or cell surface defense. Heat shock proteins, antioxidants, protein phosphatases, and cyclin kinase inhibitors may contribute to the intracellular defense. This article outlines how the glomerulus, when faced with injurious cells or exposed to pathogenic mediators, defends itself via the intrinsic machinery that is brought into play in resident glomerular cells.

Chinese herbs as modulators of human mesangial cell proliferation: preliminary studies

In the hope of identifying agents of therapeutic value in immunoglobulin A nephropathy (IgA-N), we tested crude methanol extracts of 15 Chinese herbs for their effect on human mesangial cel proliferation in vitro. The results indicated that 7 out of the 15 crude extracts inhibited human mesangial cell proliferation activated by interleukin-1beta and interleukin-6. The extracts and their median inhibitory concentrations were as follows (in microg/ml): Selaginella tamariscina (MLS-032), 56.0 +/- 2.0; Ixeris chinensis (MLS-033), 62.7 +/- 1.7; Polygonum hypoleucum Ohwi (MLS-034), 25.0 +/- 1.5; Scutellaris rivularis (MLS-036), 39.6 +/- 1.1; Condonacanthus paucifiorus (MLS-042),63.6 +/- 2.6; Xanthium strumarium (MLS-043), 42.8 +/- 1.3; Daemonoropus margaritae (MLS-044), 56.1 +/- 1.9. These findings indicate that human mesangial cells were most sensitive to MLS-034 treatment. These herbs also decreased interleukin-1beta and tumor necrosis factor-alpha production. Moreover, TNF-alpha mRNA expression was inhibited by MLS-034. It is unlikely that cytotoxicity was involved, because no cell deaths were observable. We hypothesize that the inhibitory mechanisms of these Chinese herbs may be related to the impairments of gene expression and production of cytokines in human mesangial cells. Plans are underway for the isolation of pure compounds from these Chinese herbs and the elucidation of their mechanisms of action.

TGF-β1 as an Endogenous Defender Against Macrophage-Triggered Stromelysin Gene Expression in the Glomerulus

Recent investigation has indicated that TGF-β1, the macrophage (Mφ) deactivator, may attenuate Mφ-mediated acute glomerular injury. Using stromelysin as an indicator, this study investigated whether and how endogenous TGF-β1 modulates the glomerular cell activation triggered by Mφ. Rat mesangial cells were stably transfected with a cDNA encoding the active form of TGF-β1 and a cDNA coding for a dominant-negative mutant of the TGF-βR type II. Compared with mock-transfected cells, TGF-β1 transfectants exhibited blunted expression of stromelysin in response to the Mφ-derived, inflammatory cytokine IL-1β. In contrast, mesangial cells expressing the dominant-interfering TGF-βR showed enhanced expression of stromelysin in response to IL-1β, suggesting that endogenous TGF-β functions as an autocrine inhibitor of the IL-1 response. In isolated, normal rat glomeruli, externally added TGF-β1 suppressed the induction of stromelysin by mediators that were elaborated by activated Mφ. Similarly, when isolated, nephritic glomeruli producing the active form of TGF-β1 were stimulated by IL-1β or Mφ-conditioned medium, the induction of stromelysin was dramatically suppressed as compared with normal glomeruli. To investigate whether endogenous TGF-β1 affects the glomerular cell activation triggered by Mφ, a technique for adoptive Mφ transfer was used. LPS-stimulated reporter Mφ were transferred into either normal rat glomeruli or nephritic glomeruli expressing active TGF-β1. In the normal glomeruli, stromelysin expression was markedly induced in resident cells after the transfer of activated Mφ. This induction was substantially repressed in those glomeruli producing active TGF-β1. These results reinforce the idea that TGF-β1 is an endogenous defender that attenuates certain actions of infiltrating Mφ in the glomerulus.

Interleukin-1-induced ether-linked diglycerides inhibit calcium-insensitive protein kinase C isotypes. Implications for growth senescence

It is hypothesized that inflammatory cytokines and vasoactive peptides stimulate distinct species of diglycerides that differentially regulate protein kinase C isotypes. In published data, we demonstrated that interleukin-1, in contrast to endothelin, selectively generates ether-linked diglyceride species (alkyl, acyl- and alkenyl, acylglycerols) in rat mesangial cells, a smooth muscle-like pericyte in the glomerulus. We now demonstrate both in intact cell and in cell-free preparations that these interleukin-1 receptor-generated ether-linked diglycerides inhibit immunoprecipitated protein kinase C delta and epsilon but not zeta activity. Neither interleukin-1 nor endothelin affect de novo protein expression of these protein kinase C isotypes. As down-regulation of calcium-insensitive protein kinase C isotypes has been linked to antimitogenic activity, we investigated growth arrest as a functional correlate for IL-1-generated ether-linked diglycerides. Cell-permeable ether-linked diglycerides mimic the effects of interleukin-1 to induce a growth-arrested state in both G-protein-linked receptor- and tyrosine kinase receptor-stimulated mesangial cells. This signaling mechanism implicates cytokine receptor-induced ether-linked diglycerides as second messengers that inhibit the bioactivity of calcium-insensitive protein kinase C isotypes resulting in growth arrest.

Regulation of vascular type 1 angiotensin receptors by cytokines

Although various cytokines are known to be expressed in atherosclerotic lesions, it is not known how these cytokines affect receptors for the peptide hormone angiotensin II (Ang II). We therefore examined the effects of interleukin-1 alpha (220 U/mL [10 ng/mL]), tumor necrosis factor-alpha (280 U/mL [100 ng/mL]), and interferon gamma (100 U/mL) on Ang II type 1 (AT1) receptors expressed in rat vascular smooth muscle cells. Treatment with interleukin-1 alpha caused a 1.4- to 1.7-fold increase in AT1 binding after 24 hours (P<.01) and a 2.3-fold increase in AT1 mRNA (P<.05). Tumor necrosis factor-alpha and interferon gamma did not cause a significant change in AT1 binding when administered alone but caused a 30% reduction in binding when administered together (P<.05). The maximal decrease in AT1 binding (60%, P<.01) was seen with the combination of interleukin-1 alpha with tumor necrosis factor-alpha and interferon gamma. Although the upregulation of AT1 by interleukin-1 alpha was unaffected by pretreatment of cells with N-monomethyl-L-arginine or indomethacin, downregulation of AT1 by interleukin-1 alpha combined with tumor necrosis factor-alpha/interferon gamma was inhibited by N-monomethyl-L-arginine (P<.01). Interleukin-1 alpha treatment enhanced Ang II-induced [3H]uridine incorporation, whereas treatment with interleukin-1 alpha combined with tumor necrosis factor-alpha/interferon gamma attenuated Ang II-induced [3H]uridine and [3H]leucine incorporation. These results demonstrate that interleukin-1 alpha upregulates AT1 receptors and enhances Ang II-stimulated hypertrophic responses. However, a combination of interleukin-1 alpha with tumor necrosis factor-alpha and interferon gamma downregulates AT1 receptors by a nitric oxide-dependent mechanism and reduces Ang II-stimulated trophic responses in vascular smooth muscle cells.

Interleukin-1beta induction of mitogen-activated protein kinases in human mesangial cells. Role of oxidation

Interleukin-1beta (IL-1beta) significantly influences renal cellular function through the induction of several gene products. The molecular mechanisms involved in gene regulation by IL-1beta are poorly understood; however, the appearance of novel tyrosine phosphoproteins in IL-1beta-treated cells suggests that IL-1beta may function through tyrosine phosphoprotein intermediates. The mitogen-activated protein (MAP) kinases are tyrosine phosphoproteins that could potentially mediate the effects of IL-1beta. Protein tyrosine phosphorylation following IL-1beta treatment may be dependent on redox changes since the IL-1beta receptor is not a protein-tyrosine kinase and oxidation has been shown to induce tyrosine phosphorylation. In this report we demonstrate that conditioning human glomerular mesangial cells with IL-1beta results in the tyrosine phosphorylation and activation of two members of the MAP kinase family, extracellular signal-regulated protein kinase 2 (ERK2) and p54 Jun-NH2-terminal kinase (JNK). This effect of IL-1beta is abrogated by pretreating cells with the antioxidants N-acetyl-L-cysteine or dithiothreitol. Furthermore, the effects of IL-1beta on ERK and JNK activation are reproduced by treating mesangial cells with membrane-permeable oxidants. IL-1beta and oxidants also cause phosphorylation and activation of the upstream ERK regulatory element MAP kinase kinase. Interestingly, IL-1beta, but not exogenous oxidants, causes phosphorylation of the upstream JNK activator, JNK kinase. These data indicate that IL-1beta activates ERK2 through an oxidation-dependent pathway. Exogenous oxidants and IL-1beta activate JNK through different upstream mechanisms; however, antioxidant inhibition of JNK activation indicates that endogenous oxidants may play a role in IL-1beta-induced JNK activation. Thus IL-1beta may affect mesangial cell function by activating MAP kinases, which can then regulate gene transcription. Furthermore, reactive oxygen species released during inflammatory glomerular injury may also affect mesangial function through a MAP kinase signal.

Group II phospholipase A2 as an autocrine growth factor mediating interleukin-1 action on mesangial cells

The proliferation of mesangial cells plays a central role in the progression of glomerulonephritis. We studied the role of group II phospholipase A2 in interleukin-1-stimulated proliferation of mesangial cells. Cultured rat mesangial cells secreted 5.3 units group II phospholipase A2/24 h per 10(5) cells in response to stimulation of 200 U/ml of interleukin-1. Northern hybridization analysis showed that mRNA for group II phospholipase A2 was induced by exogenously added group II phospholipase A2 (15 U/ml) as well as interleukin-1. The pretreatment of quiescent mesangial cells with interleukin-1 augmented [3H]thymidine incorporation caused by platelet derived growth factor. Exogenous group II phospholipase A2 (5-36 U/ml) purified homogeneously from rat spleen also increased [3H]thymidine incorporation by platelet derived growth factor-stimulated mesangial cells in a dose dependent manner (36 U/ml phospholipase A2; 1.9-fold). The stimulatory effect of interleukin-1 on DNA synthesis of mesangial cells was specifically blunted by immunoglobulin raised against group II phospholipase A2. Group II phospholipase A2 (16 U/ml) amplified a platelet derived growth factor-stimulated increase in the mesangial cell number by 1.5-fold. Among the products of the phospholipase A2-catalyzed reaction, lysophospholipids including lysophosphatidylcholine, lysophosphatidylethanolamine and lysophosphatidic acid, but not fatty acids, mimicked the stimulatory effect of interleukin-1 and phospholipase A2. These results suggest that group II phospholipase A2 acts as a signaling molecule that mediates interleukin-1-induced growth of rat mesangial cells through yielding lysophospholipids.

MP84 expression in the urine specimens of acute rejection renal transplant recipients

MP84 is a novel protein synthesized in response to all cytokines. This antigen is expressed only in stimulated mesangial cells and decreased kidney sections, but not in the normal kidney sections (1,2). This study was performed to determine the excretion of MP84 in the urine of renal transplant recipients with acute rejection. Six persons with renal transplant acute rejection and 10 healthy persons were included. Two urine specimens from each person were collected. Dot-blot assay was performed. It was shown that 12 urine specimens from 6 persons with acute rejection revealed MP84 in the matrix dot-blot assay while there was no staining for MP84 in the urine specimens of healthy persons. This could be due to the immunological alteration during the acute rejection which could lead to autocrine and paracrine secretion of growth factors and then the excretion of MP84 in the urine. The mechanism of MP84 secretion is not clear.

Opposite, binary regulatory pathways involved in IL-1-mediated stromelysin gene expression in rat mesangial cells

Glomerular mesangial cells express matrix metalloproteinase sromelysin in response to the proinflammatory cytokine IL-1 beta. The present study was conducted to identify intracellular machinery involved in this IL-1 action, especially focusing on the role of the TPA response element (TRE) located in the 5'-flanking region of the stromelysin gene. Using transient transfection with a pTRE-LacZ reporter plasmid, we detected no obvious up-regulation of TRE activity in rat mesangial cells following the IL-1 stimulation. However, the basal activity of TRE was found to be essential to the stromelysin induction, since (i) mesangial cells stably expressing a transdominant negative mutant of c-Jun, which effectively suppressed both basal and inducible TRE activity, exhibited the blunted expression of stromelysin in response to IL-1 beta, whereas (ii) transfection with a c-fos antisense gene, which suppressed only the inducible TRE activity, did not affect the stromelysin induction. To seek cooperative pathways required for the IL-1 action, we next focused on protein kinases, the potential regulators of the stromelysin gene. Stimulation of mesangial cells with a protein kinase C (PKC) activator, phorbol 12-myristate 13-acetate (PMA), induced the stromelysin transcript without affecting TRE activity. Depletion of intracellular PKC by high-dose PMA or inhibition of PKC activity with calphostin C suppressed the stromelysin induction by IL-1 beta, suggesting the crucial contribution of a PKC-mediated, but TRE-independent pathway. In contrast, either cAMP inducer forskolin or dibutyryl cAMP suppressed the IL-1-mediated stromelysin expression. An inhibitor of cAMP-dependent protein kinase A (PKA), HA1004, enhanced the IL-1 effect in a dose-dependent manner. Unexpectedly, the inhibitory action of PKA was not through cAMP response element (CRE) but through TRE, because (i) activation of CRE was not induced by IL-1 beta, and (ii) cAMP-mediated activation of PKA suppressed the basal TRE activity. These findings elucidated the unique, binary regulation of stromelysin by IL-1 beta; that is, IL-1 up-regulated the transcript via the PKC-dependent pathway under the cooperation with constitutively active TRE, and this stimulatory effect was in part counterbalanced by the IL-1-inducible PKA which down-regulated the basal TRE activity.

Cytokines, growth factors, and other inflammatory mediators in glomerulonephritis

Over the past decade, research has been centered on the identification of factors that mediate glomerular immune injury and the assessment of their roles in this disease process. The spectrum of mediators identified to date encompasses a diverse array of bioactive molecules such as phospholipids, including cytokines and growth factors, and lipid-derived mediators such as eicosanoids. Given the extensive number of potentially important mediators in glomerulonephritis (GN), I focus only on some of them, for which strong in vitro and in vivo data suggest a major role in the pathogenesis of immune-mediated renal injury. So, in the first part, I discuss some cytokines and growth factors; and in the second, some other important mediators, the eicosanoids and especially the lipoxygenase-derived products, leukotrienes and lipoxins.

Interleukin-1 alpha enhances the biosynthesis of complement C3 and factor B by human kidney proximal tubular epithelial cells in vitro

Local production in tubular cells of complement has been shown to occur in several kidney diseases by in situ hybridization, but the regulation at the local site during an inflammation is still unknown. In the present study, we demonstrate that human proximal tubular epithelial cells (PTEC) are able to produce complement components C3 and Factor B under non-stimulated conditions in vitro. The basal production of both was increased by 0.5 ng/ml interleukin-1 alpha (IL-1 alpha) for C3: from 95.5 +/- 4.0 ng/10(6) cells to 416.5 +/- 4.9 ng/10(6), and for Factor B: from 271 +/- 7.0 ng/10(6) cells to 457.5 +/- 7.0 ng/10(6) cells. In contrast cytokines such as TNF-alpha, IFN-gamma, IL-10 and IL-15 had no detectable effect. The upregulation by IL-1 alpha was dose- and time-dependent. The response to IL-1 alpha was shown to be mediated via the IL-1 receptor, as the addition of recombinant interleukin-1 receptor antagonist inhibited the IL-1 alpha induced complement production by more than 80%. IL-1 alpha enhanced mRNA expression of both C3 and Factor B as demonstrated by RT-PCR and dot-blot analysis. This indicated that IL-1 alpha upregulated the expression of the C3 and Factor B at the transcriptional level. We hypothesize that in vivo the production of C3 and Factor B at the local site during an inflammatory response in the kidney may be regulated by IL-1 alpha produced by inflammatory cells.

Nitric oxide amplifies interleukin 1-induced cyclooxygenase-2 expression in rat mesangial cells

Interleukin 1 and nitric oxide (NO) from infiltrating macrophages and activated mesangial cells may act in concert to sustain and promote glomerular damage. To evaluate if such synergy occurs, we evaluated the effect if IL-1 beta and NO on the formation of prostaglandin (PG)E2 and cyclooxygenase (COX) expression. The NO donors, sodium nitroprusside and S-nitroso-N-acetylpenicillamine, alone did not increase basal PGE2 formation. However, these compounds amplified IL-1 beta-induced PGE2 production. Similarly, sodium nitroprusside and S-nitroso-N-acetylpenicillamine by themselves did not induce mRNA and protein for COX-2, the inducible isoform of COX; however, they both potentiated IL-1 beta-induced mRNA and protein expression of COX-2. The stimulatory effect of NO is likely to be mediated by cGMP since (a) an inhibitor of the soluble guanylate cyclase, methylene blue, reversed the stimulatory effect of NO donors on COX-2 mRNA expression; (b) the membrane-permeable cGMP analogue, 8-Br-cGMP, mimicked the stimulatory effect of NO donors on COX-2-mRNA expression; and (c) atrial natriuretic peptide, which increases cellular cGMP by activating the membrane-bound guanylate cyclase, also amplified IL-1 beta-induced COX-2 mRNA expression. These data indicate a novel interaction between NO and COX pathways.

Interleukin-1 beta up-regulates the plasminogen activator/plasmin system in human mesangial cells

The plasminogen activators (PA), which are regulated by their specific inhibitor, PAI-1, convert the zymogen plasminogen to plasmin, a protease involved in fibrinolysis and extracellular matrix turnover. Interleukin 1 beta (IL-1) is a key cytokine released from infiltrating monocytes/macrophages during the initial stages of glomerular injury. We investigated the effects of IL-1 on the production of tissue-type plasminogen activator (t-PA), urokinase (u-PA) and PAI-1 by glomerular cells. IL-1 significantly increased the synthesis of t-PA by mesangial cells and glomerular epithelial cells (P < 0.005 for both cell types), while u-PA production was unaltered. PAI-1 in mesangial cell supernatants was significantly lower when cultured in the presence of IL-1 (p < 0.008), and the synthesis decreased in a time and dose dependent manner. The effects of IL-1 were eliminated by anti-IL-1 neutralizing antibodies. The PAI-1 sequestered in the extracellular matrix of mesangial cells was also decreased. No significant change in PAI-1 synthesis by epithelial cells was observed with exogenous IL-1. Northern blot analysis paralleled the protein results, demonstrating an increase in t-PA and a decrease in PAI-1 mRNA of mesangial cells after 6 and 24 hours stimulation with 10 U/ml IL-1. These studies suggest a role for IL-1 in regulating localized proteolysis by mesangial cells during acute inflammation.

Interleukin-1-induced IL-8 and IL-6 gene expression and production in human mesangial cells is differentially regulated by cAMP

We have previously proposed that activated mesangial cells (MC) have a direct role in the initiation and propagation of inflammatory events within the glomerulus via the generation of the mesangioproliferative cytokine IL-6 and the chemokines IL-8 and MCP-1. The objective of this study was to investigate the role of cAMP in the regulation of IL-6 and IL-8 gene expression and peptide production in IL-1 stimulated human MC. Agents known to elevate cAMP, including dibutyryl cAMP (db-cAMP), forskolin or isobutyl-methylxanthine (IBMX) were alone unable to induce IL-6 or IL-8 expression or production above media control levels, indicating activation of the cAMP pathway could not mimic IL-1 signaling events. In the presence of IL-1, all three agents produced a marked potentiation of IL-6 mRNA expression and dose-dependent increase in IL-6 peptide production (twofold), but had little or no effect on IL-8 mRNA expression or peptide generation. In marked contrast cholera toxin (CT) caused a dose-dependent potentiation of both IL-1-induced IL-6 (approximately fourfold) and IL-8 peptide (approximately twofold) generation. The control agent, the purified binding subunit of cholera toxin (CT-B) which is devoid of ADP-ribosylating activity also enhanced IL-6 and IL-8 (approximately twofold) peptide generation indicating cAMP-independent mechanisms may be involved in the CT up-regulation of these cytokines. Treatment of MC with the cycloxygenase inhibitor indomethacin resulted in partial inhibition (37%) of IL-6 production but had no effect on IL-8 generation. Thus our data show that cAMP can potentiate IL-1 induced IL-6 production, while having no effect on IL-8 induction, and PGE2 may operate via a positive feedback loop to up-regulate IL-1 induced IL-6. Taken together, our results demonstrate that cAMP differentially regulates IL-6 and IL-8 production in IL-1-stimulated human MC.

Endothelin-1 inhibits cytokine-stimulated transcription of inducible nitric oxide synthase in glomerular mesangial cells

Endothelin-1 (ET-1) is a potent vasoconstrictor while nitric oxide (NO) has strong vasodilatory effects. Recent studies have indicated that vasoconstrictors and NO may mutually modulate their production and/or activity, thus regulating each other in the context of microcirculatory maintenance. We examined the question whether ET-1 may affect NO formation by controlling the expression of the inducible isoform of the NO synthase (iNOS) in cultured rat glomerular mesangial cells (MCs), as induced by the inflammatory cytokines, tumor necrosis factor-alpha (TNF-alpha) plus interleukin-1 beta (IL-1 beta). We found that ET-1 in MCs markedly reduced cytokine-induced NO production (measured as stable NO2-) and inhibited the expression of iNOS mRNA (Northern blot analysis) and of iNOS protein (Western blotting). Inhibition of cytokine-stimulated iNOS mRNA expression by ET-1 was almost complete at the level of gene transcription while post-transcriptional effects were not detected. The ETA receptor antagonist BQ-123 blocked the inhibitory effect of ET1. The ETA agonist sarafotoxin 6b (S6b) inhibited, while the ETB agonist-sarafotoxin 6c (S6c) did not inhibit cytokine-initiated iNOS transcription in MCs. The results demonstrate that ET-1 can strongly inhibit cytokine induction of iNOS and formation of NO in cultured MCs, and that this action is mediated via the ETA receptor. While the precise mechanism(s) and biological relevance of this ET-1 effect are presently unclear, it is conceivable that down-regulation of iNOS by the vasopressor ET-1 may serve in vivo to prevent massive NO build-up and subsequent vasomotor collapse in the glomerular capillary tuft. This could help to maintain glomerular ultrafiltration in states of endotoxin excess as well as during glomerular formation and action of TNF-alpha and IL-1 beta causing iNOS induction and subsequent overproduction of NO.

Transfer of a mutated gene encoding active transforming growth factor-beta 1 suppresses mitogenesis and IL-1 response in the glomerulus

Using in vivo gene transfer, we examined the anti-inflammatory potential of transforming growth factor-beta 1 (TGF-beta 1) in the renal glomerulus. TGF-beta 1 cDNA, modified to allow for secretion of the active form of TGF-beta 1, was introduced into cultured rat mesangial cells. The responses of the established transfectants were examined in culture. In vitro, the transduced mesangial cells showed a reduced mitogenic response to fetal calf serum and were insensitive to induction of matrix metalloproteinase-9 (MMP-9) by the proinflammatory cytokine IL-1 beta. To examine whether glomeruli which express active TGF-beta 1 in vivo are insensitive to these same stimuli, TGF-beta transfectants were transferred into normal rat glomeruli via renal artery injection. After 24 hours, isolated glomeruli containing transfectants exhibited TGF-beta bioactivity, a reduced mitogenic response, and repressed expression of MMP-9 in response to IL-1 beta. We further examined the responses of these chimeric glomeruli to an in vivo mitogenic stimulus by transferring TGF-beta transfectants into glomeruli of kidneys one day after the induction of anti-Thy-1 nephritis. The mitogenic activity of isolated glomeruli was examined four days after the cell injection. Compared to unmodified or mock cell-containing glomeruli, the in vivo mitogenic activity of glomeruli containing TGF-beta transfectants was significantly repressed. Furthermore, cellular outgrowth from nephritic glomeruli expressing active TGF-beta 1 was also suppressed ex vivo compared to controls. These data indicate that TGF-beta 1 inhibits mitogenesis and IL-1 response of the glomerulus and may, in part, act as a potential early suppressor of glomerular inflammation.

Modulation of antibody-mediated glomerular injury in vivo by IL-1ra, soluble IL-1 receptor, and soluble TNF receptor

The severity of glomerular injury in the heterologous phase of NTN is dependent on proinflammatory cytokines including TNF alpha and IL-1 beta, and can be enhanced by LPS. We have previously shown that passive immunization against IL-1 beta and TNF partially abrogated the LPS effect in this model. In the present work, we have assessed the effects on glomerular injury of blocking and binding of IL-1 to its receptor by rh IL-1 receptor antagonist (IL-1ra) and by neutralizing IL-1 and TNF with rm soluble IL-1 receptor type1 (sIL-1Rt1) and rh sTNF receptor (sTNFr p55), respectively. Pretreatment with either IL-1ra, sIL-1Rt1, or sTNFr partially abrogated the effects of LPS and reduced albumin excretion from 45 +/- 8, 66 +/- 9, and 101 +/- 17 mg/24 hr at 13 +/- 4 (P < 0.02), 14 +/- 4 (P < 0.001), and 21 +/- 7 mg/24 hr (P < 0.001), respectively. Similarly, these inhibitors reduced the prevalence of glomerular capillary thrombi and the intensity of glomerular neutrophil infiltration. Glomerular thrombosis was reduced from 18 +/- 3%, 28 +/- 5%, and 25 +/- 7% to 3 +/- 2% (P < 0.002), 6 +/- 2% (P < 0.001), and 3 +/- 2 (P < 0.001), respectively, and glomerular neutrophil infiltration was reduced from 46 +/- 3, 54 +/- 2, 59 +/- 8 to 19 +/- 2 (P < 0.001), 25 +/- 2 (P < 0.001), and 28 +/- 2 neutrophils/50 glomeruli in section, respectively. Coadministration of both soluble receptors of IL-1 and TNF caused a further decrease in glomerular injury. The protective effect was also noticed at four hours after induction of nephritis, and even when these inhibitors were administered after the LPS injection and at the same time of induction of nephritis. All three treatments reduced circulating TNF concentration (down to 20%, 34%, and 0%, respectively) but without detectable glomerular TNF gene expression. Glomerular IL-1 beta mRNA levels were also reduced by 41%, 53%, and 67%, respectively, when assessed by densitometric analysis of Northern blots. In contrast, the glomerular expression of IL-1ra was not affected by its exogenous administration but was mildly reduced by sIL-1Rt1 and sTNFr, which demonstrates the potential role for host derived IL-1ra as an endogenous negative feedback mediator in the glomerulus. These results confirm the direct involvement of IL-1 and TNF in LPS-enhanced hNTN and demonstrate the potency of these inhibitors in modulating injury even when administered after LPS and in time of induction of nephritis. They were more specific and effective than passive immunization with polyclonal antibodies, and this demonstrates their potential usefulness in the management of nephritis.

Differential regulation of sphingomyelinase and ceramidase activities by growth factors and cytokines. Implications for cellular proliferation and differentiation

Sphingosine is a product of sphingolipid metabolism that has been linked to a protein kinase C-independent mitogenic response. In previously published data, utilizing an in vitro model system for platelet-derived growth factor (PDGF)-induced vascular smooth muscle proliferation, we have demonstrated that sphingosine is increased at the expense of a concomitant decrease in ceramide formation, implicating an altered ceramidase activity. To explore mechanisms of growth factor-stimulated sphingosine formation, we have developed and investigated a cell-free model system assessing ceramidase activity. We now report that an alkaline, membrane-associated, ceramidase activity in the rat glomerular mesangial cell, a smooth muscle-like pericyte, is up-regulated by growth factors, apparently via a tyrosine kinase phosphorylation mechanism. PDGF also stimulated sphingomyelinase activity which generates sufficient substrate to drive the subsequent ceramidase reaction. Inflammatory cytokines, including interleukin-1, and tumor necrosis factor-alpha, stimulated sphingomyelinase but not ceramidase activity, a result consistent with the cellular accumulation of the ceramide, apoptidic, differentiating second messenger. Mitogenic vasoconstrictor peptides such as endothelin-1 stimulated neither sphingomyelinase nor ceramidase activities. An inhibitor of ceramidase activity, N-oleoylethanolamine, reduced PDGF- but not endothelin-1-stimulated proliferation. Thus, we conclude that, in mesangial cells, growth factors but not vasoconstrictor peptides or cytokines induce mitogenesis, in part, through ceramidase-mediated sphingosine formation.

Interleukin-1 and endothelin stimulate distinct species of diglycerides that differentially regulate protein kinase C in mesangial cells

Diglycerides are phospholipid-derived second messengers that serve as cofactors for protein kinase C activation. We have previously shown that, in rat glomerular mesangial cells, the cytokine, interleukin-1 alpha, and the vasoactive peptide, endothelin, generate diglycerides from unique phospholipid precursors. However, neither the molecular species of these diglycerides nor their biological actions were determined. It is now hypothesized that interleukin-1- and endothelin-treated mesangial cells form distinct molecular species of diglycerides which may serve different roles as intracellular signaling molecules. Diglyceride molecular species were resolved and quantified by TLC and high performance liquid chromatography as diglyceride-[14C]acetate derivatives. Endothelin stimulates predominantly ester-linked species (diacylglycerols) in contrast to interleukin-1 which stimulates only ether-linked species (alkyl, acyl- and alkenyl,acylglycerols). In support of these data, interleukin-1-treated mesangial cells hydrolyze ethanolamine plasmalogens, vinyl ether-linked phospholipids. It has been reported that ether-linked, in contrast to ester-linked, diglyceride species do not activate protein kinase C activity. Thus, we next assessed membrane protein kinase C activity in endothelin- or interleukin-1-treated mesangial cells. Even though interleukin-1 has no effect upon basal protein kinase C activity, this cytokine, through the formation of ether-linked diglyceride second messengers, inhibits endothelin, platelet-activating factor, or arginine vasopressin-stimulated protein kinase C activity. We further demonstrate that ester-linked diacylglycerols but not alkyl,acyl- or alkenyl,acylglycerols substitute for phorbol esters in a cell-free protein kinase C assay. In addition, alkenyl,acylglycerols inhibit diacylglycerol-stimulated immunoprecipitated protein kinase C alpha activity in vitro and total protein kinase C activity in permeabilized mesangial cells ex vivo. Taken together, these data suggest that interleukin-1-induced formation of ether-linked diglycerides may physiologically serve to down-regulate receptor-mediated protein kinase C activity and that individual molecular species of diglycerides may serve different roles as intracellular signaling molecules.

Group II phospholipase A2 activates mitogen-activated protein kinase in cultured rat mesangial cells

Group II phospholipase A2 (PLA2) is a mediator of inflammation in various disease including glomerulonephritis. We recently found that urinary excretion of PLA2 was increased in patients with mesangial proliferative glomerulonephritis and that interleukin-1 (IL-1) enhanced platelet derived growth factor-stimulated mesangial cell proliferation through the action of group II PLA2 secreted in response to IL-1 stimuli. Here we report signal transducing mechanism through group II PLA2 in mesangial cells. Group II PLA2 (1-15 U/ml) rapidly activated mitogen-activated protein (MAP) kinase. IL-1 beta activated MAP kinase in two phases and the slow activation in the late phase, proceeding in parallel with increased group II PLA2 secretion elicited by IL-1 treatment, was inhibited by the specific antibody raised against group II PLA2. This suggests that the late phase activation of IL-1-induced MAP kinase was mediated, at least in part, by secreted group II PLA2.

Cytokines in human renal interstitial fibrosis. II. Intrinsic interleukin (IL)-1 synthesis and IL-1-dependent production of IL-6 and IL-8 by cultured kidney fibroblasts

We compared cytokine production from transformed human fibroblast cell lines derived from either a kidney with interstitial fibrosis or a normal kidney to that from primary human foreskin fibroblasts. Fibrosis-derived as well as normal renal fibroblasts, but not skin fibroblasts, spontaneously produced the chemokine, IL-8, and the growth promoting cytokine, IL-6. Spontaneous IL-8 and IL-6 synthesis by renal fibroblasts was dependent on the intrinsic release of IL-1, since blocking IL-1 receptors with IL-1 receptor antagonist (IL-1Ra) partially inhibited the constitutive production of these cytokines. Both kidney cell lines had detectable mRNA and protein for IL-1 alpha and IL-1 beta. Renal and skin fibroblasts stimulated by picomolar concentrations of exogenous IL-1 or TNF-alpha produced large amounts of IL-6 and IL-8, whereas nanomolar concentrations of basic fibroblast growth factor did not. Fibrosis-derived cells expressed less high affinity IL-1 receptors (600 receptors/cell; KD = 0.6 pM) compared to normal renal fibroblasts (1000 receptors/cell). However, fibrosis-derived renal fibroblasts produce three- to fourfold more IL-8 and IL-6 in response to picomolar concentrations of IL-1 beta compared to cells derived from a normal kidney. As this enhanced production is not due to increased numbers of IL-1 receptors, we speculate that post-receptor responsiveness to either endogenous or exogenous IL-1 is greater in fibrosis-derived renal fibroblasts than in cells from normal kidneys.

In vitro effects of interleukins on human mesangial cells: implications for glomerulonephritis

Intrinsic glomerular cells, especially mesangial cells, are considered to be actively involved in the pathogenesis of glomerulonephritis (GN), but the precise mechanism(s) remains elusive. We have previously demonstrated that nephritogenic IgA immune complex can stimulate human mesangial cells (HMCs) to increase their production of interleukin-1 (IL-1) and interleukin-6 (IL-6). In order to evaluate the roles of cytokines such as IL-1 and/or IL-6 and mesangial cells as mediators of renal injury in GN, we have now examined the changes of HMCs and their secreted products in vitro, after stimulation with various concentrations of IL-1 and IL-6. Cytokine-activated HMCs showed the following changes: (1) increased cell size, with intracytoplasmic vacuoles, dilated endoplasmic reticulum, increased free ribosomes and polysomes, and mitochondrial swelling; (2) increased cell proliferation, reflected in thymidine incorporation and an increased proportion of S and G2/M phase cells by cell cycle analysis; (3) enhancement of IL-6 mRNA expression in HMCs with stimulation of IL-6 alone or IL-1 plus IL-6; and (4) release of large amounts of platelet activating factor (PAF), thromboxane B2 (TxB2), and superoxide anion. Taken together, these results strongly suggest that mesangial cell proliferation and increased production of immune/chemical mediators and superoxide anion can be directly induced by IL-1 plus IL-6. These changes may lead to ongoing renal injury.

Role of protein kinase pathways in IL-1-induced chemoattractant expression by human mesangial cells

Human mesangial cells produce the monocyte-specific chemotactic factor monocyte chemoattractant protein-1 (MCP-1) in response to a variety of stimuli, including the pro-inflammatory cytokine interleukin-1 beta (IL-1). The intracellular signals responsible for mediating the effects of IL-1 on MCP-1 expression in human mesangial cells have not been defined. Evidence from other types of cells suggests that protein kinases are involved in MCP-1 gene regulation. We investigated the role of protein kinase pathways in mediating IL-1-induced MCP-1 expression. Activation of protein kinase C (PKC) by phorbol esters or diacyglycerol up-regulated mesangial MCP-1 message and bioactivity in a fashion similar to IL-1. However, while inhibition of PKC activity completely blocked phorbol-induced MCP-1 up-regulation, induction by IL-1 was not prevented. Inhibitors of cyclic AMP (cAMP)-dependent protein kinase (PKA) also failed to block IL-1-induced MCP-1 expression. Furthermore, increasing intracellular cAMP and activating PKA attenuated basal MCP-1 mRNA levels by 82% and blocked IL-1 induced MCP-1 expression by 88%. Finally, the role of protein tyrosine kinases was studied. The structurally distinct protein tyrosine kinase (PTK) inhibitors genistein, herbimycin A, and tyrphostin each caused a dose-dependent inhibition of the effects of IL-1 on mesangial MCP-1 activity. IL-1 treatment of mesangial cells resulted in the up-regulation of three tyrosine phosphoproteins with apparent molecular masses between 40 and 62 kD. These results suggest that the effects of IL-1 on MCP-1 expression are not mediated through PKC or cAMP-PKA, but may be transduced through PTKs.

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.

Cellular localization of inflammatory cytokines in human glomerulonephritis

We evaluated the expression of inflammatory cytokines in renal tissues obtained from 45 patients with several types of glomerulonephritis. Immunofluorescence studies with specific antibodies to interleukin (IL)-1 alpha, IL-1 beta, IL-6, tumour necrosis factor (TNF)-alpha, and TNF-beta showed intense cytoplasmic staining in the glomeruli and interstitium. Cells positive for these cytokines were found frequently in tissue from patients with lupus nephritis (WHO Class IV) and membranoproliferative glomerulonephritis, and, to a lesser extent, in tissue from patients with mesangial proliferative glomerulonephritis, Henoch-Schönlein purpura nephritis, and minimal change nephrotic syndrome. Most of these cells were dual-stained with a monoclonal antibody to monocytes-macrophages. In situ hybridization for cytokine mRNA, combined with immunoperoxidase staining for monocytes-macrophages, detected IL-1 alpha, IL-6, and TNF-alpha mRNA in monocytes-macrophages infiltrating the glomeruli and interstitium. Occasionally, there was weak or moderate immunostaining for IL-1 alpha, IL-6, and TNF-alpha in the glomerular mesangial and epithelial cells, but in situ hybridization signals were rarely found in these loci. These findings suggest that infiltrating monocytes-macrophages, rather than resident glomerular cells, are the major source of inflammatory cytokines in human glomerulonephritis.

Interleukin 1 alpha causes rapid activation of cytosolic phospholipase A2 by phosphorylation in rat mesangial cells

We have shown previously that interleukin 1 (IL-1) stimulates eicosanoid production in glomerular mesangial cells (MC) by de novo synthesis of a 14-kD, group II phospholipase A2 (PLA2). IL-1-stimulated prostaglandin E2 synthesis precedes expression of this enzyme, suggesting that another PLA2 isoform must be more rapidly activated. In the presence but not absence of calcium inophore, [3H]arachidonate release is increased significantly as early as 5 min after addition of IL-1, and IL-1 concurrently stimulates a Ca(2+)-dependent phospholipase activity, which was characterized as the cytosolic form of PLA2 (cPLA2). IL-1 does not alter either cPLA2 mRNA expression or mass in serum-stimulated MC, suggesting that cPLA2 activity is increased by a posttranslational modification. IL-1 treatment for 30 min doubles 32P incorporation into immunoprecipitable cPLA2 protein, concordant with the increase in enzyme activity. Immunoblot analysis of extracts derived from IL-1-treated (30 min) cells demonstrates a decreased mobility of cPLA2, and treatment of MC lysates with acid phosphatase significantly reduces cytokine-activated cPLA2 activity, further indicating that IL-1 stimulates phosphorylation of the enzyme. IL-1 treatment (24 h) of serum-deprived MC doubled cPLA2 mRNA, protein, and activity. In summary, IL-1 increases cPLA2 activity in a biphasic, time-dependent manner both by posttranslational modification and de novo synthesis. We consider cPLA2 activation a key step in IL-1-stimulated synthesis of pro-inflammatory, lipid mediators, and an integral event in the phenotypic responses induced in target cells by this cytokine.

Cytokine stimulation of prostaglandin production inhibits the proliferation of serum-stimulated mesangial cells

Mesangial cell proliferation contributes to glomerulosclerosis and is associated with the development of end-stage renal disease. We examined the effects of the cytokines interleukin 1 (IL-1 beta) and interleukin 6 (IL-6) on the mitogenesis and proliferation of rat glomerular mesangial cells. Exposure of serum-stimulated cells to IL-1 beta and IL-6 for 48 hours resulted in a dose-dependent inhibition of both mitogenesis, determined by 3H-thymidine incorporation, and proliferation, determined by absolute cell counts. Both IL-1 beta and IL-6 stimulated endogenous PGE2 production in this cell system. Cyclooxygenase inhibition by indomethacin and meclofenamate abrogated the inhibitory effects of both IL-1 beta and IL-6. Furthermore, addition of exogenous PGE2 to cytokine-stimulated cells in which cyclooxygenase activity was blocked resulted in inhibition of mitogenesis, while addition of exogenous aracidonic acid to the cytokine-stimulated cells enhanced the induced inhibition of mitogenesis. These results demonstrate that in serum-stimulated mesangial cells, both IL-1 beta and IL-6 inhibit mitogenesis and proliferation, and that these effects are mediated, in part, by stimulated endogenous prostaglandin production.

Cell-specific regulation of type II phospholipase A2 expression in rat mesangial cells

IL-1 stimulates mesangial cells to synthesize specific proteins, including a non-pancreatic (Type II) phospholipase A2 (PLA2). We have studied the regulation of PLA2 by proinflammatory mediators, implicated in the pathogenesis of glomerulonephritis, and have assessed whether the activation of second messenger systems modulates or mimics PLA2 gene expression by cytokines. IL-1 alpha and beta, TNF alpha, and LPS, but not serum, IL-2, or PDGF, potently induce PLA2 mRNA, and enzyme expression. IL-1-stimulated mesangial cells express a 1.0 kB PLA2 mRNA transcript that is induced in a dose- and time-dependent manner. IL-1-stimulated increases in steady-state PLA2 mRNA abundance result from a moderate increase in PLA2 transcription rate that is amplified by the prolonged persistence of the transcript. Forskolin and dibutyryl cAMP potentiate IL-1-induced PLA2 mRNA and enzyme expression, but have no effect in the absence of cytokine. 12-tetradecanoyl phorbol 13-acetate, sn-1, 2-dioctanoyl glycerol or 1-oleoyl-2-acetyl-sn-glycerol fail to induce PLA2 expression or to alter the effect of IL-1 when coincubated with the cytokine. In contrast, serum deprivation for 24 h specifically enhances IL-1-stimulated PLA2. Genistein potentiates PLA2 mRNA expression in cells exposed to both IL-1 and serum. The inhibitory effect of serum on IL-1-induced PLA2 mRNA abundance is reproduced by PDGF but not dexamethasone. These data demonstrate that the signaling pathways directly engaged by IL-1 to induce PLA2 expression in mesangial cells interact with several second messenger systems in a cell-specific manner. We speculate that IL-1 induces specialized changes in mesangial cell structure and function through direct activation of a transcription factor(s), that result in induction of a specific gene set.

In situ expression of cytokines in IgA nephritis

We studied mRNA and protein expression of interleukins (IL) and tumor necrosis factor (TNF) in renal tissues biopsied from 40 patients with IgA nephritis. Immunofluorescent staining with antibodies to IL-1 alpha, IL-1 beta, IL-6, IL-8, TNF-alpha, and TNF-beta was intense in the cytoplasm of cells in glomeruli, which were dual-stained with an anti-monocyte-macrophage antibody. In addition, moderate immunofluorescence for TNF-alpha, and weak staining for IL-1 alpha and IL-6 were occasionally found in resident glomerular cells. Immunoperoxidase-in situ hybridization dual-labeling revealed that IL-1 alpha, IL-6, and TNF-alpha mRNA signals were present in intraglomerular cells reactive with anti-monocyte-macrophage antibody, which further supported the immunofluorescent findings. Cells expressing IL-1 alpha, IL-1 beta, IL-6, IL-8, TNF-alpha, and TNF-beta were also observed in the interstitium. Most of these cells were also labeled with the anti-monocyte-macrophage antibody. The number of IL-1 alpha, IL-6, and TNF-alpha-positive cells infiltrating the glomerulus significantly correlated with mesangial hypercellularity. IL-8 and TNF-alpha-positive intraglomerular cells were correlated with the magnitude of proteinuria. The population of interstitial cells positive for IL-1 alpha, IL-6, IL-8, and TNF-alpha was associated with the grade of tubulointerstitial changes and proteinuria. There was no correlation between local IL-1 alpha, IL-6, and TNF-alpha expression in glomeruli or interstitium and serum or urinary levels of the respective cytokines.(ABSTRACT TRUNCATED AT 250 WORDS)