Cytokines in renal inflammation

Fell-Muir lecture: Connective tissue growth factor (CCN2) -- a pernicious and pleiotropic player in the development of kidney fibrosis

Connective tissue growth factor (CTGF, CCN2) is a member of the CCN family of matricellular proteins. It interacts with many other proteins, including plasma membrane proteins, modulating cell function. It is expressed at low levels in normal adult kidney cells but is increased in kidney diseases, playing important roles in inflammation and in the development of glomerular and interstitial fibrosis in chronic disease. This review reports the evidence for its expression in human and animal models of chronic kidney disease and summarizes data showing that anti-CTGF therapy can successfully attenuate fibrotic changes in several such models, suggesting that therapies targeting CTGF and events downstream of it in renal cells may be useful for the treatment of human kidney fibrosis. Connective tissue growth factor stimulates the development of fibrosis in the kidney in many ways including activating cells to increase extracellular matrix synthesis, inducing cell cycle arrest and hypertrophy, and prolonging survival of activated cells. The relationship between CTGF and the pro-fibrotic factor TGFβ is examined and mechanisms by which CTGF promotes signalling by the latter are discussed. No specific cellular receptors for CTGF have been discovered but it interacts with and activates several plasma membrane proteins including low-density lipoprotein receptor-related protein (LRP)-1, LRP-6, tropomyosin-related kinase A, integrins and heparan sulphate proteoglycans. Intracellular signalling and downstream events triggered by such interactions are reviewed. Finally, the relationships between CTGF and several anti-fibrotic factors, such as bone morphogenetic factor-4 (BMP4), BMP7, hepatocyte growth factor, CCN3 and Oncostatin M, are discussed. These may determine whether injured tissue heals or progresses to fibrosis.

Cytokine profile and immune status of patients with chronic glomerulonephritis concomitant with chronic opisthorchiasis

Decrease in the absolute count of T lymphocytes in the peripheral blood (mainly CD4+ cells), activation of humoral immunity with accumulation of immune complexes, and suppression of the neutrophil metabolic activity were detected in patients with chronic glomerulonephritis in the presence of opisthorchis invasion. Imbalance in the serum concentrations of cytokines produced by T-helper subpopulations (predominance of Th products) was detected.

Extracellular superoxide dismutase and glomerular mesangial cells: its production and regulation

Extracellular superoxide dismutase (EC-SOD) is synthesized in mesenchymally derived cells and prevents the oxygen radical-induced injury. We studied whether kidney mesangial cells (MCs) produce EC-SOD and how its production is associated with chemokine secretion. Under unstimulated condition, MCs produced EC-SOD, and its production was correlated positively with cyclic adenosine monophosphate (cAMP), but negatively with interleukin (IL)-6 or IL-8 production. By prednisolone or phorbol myristate acetate treatment, EC-SOD levels were correlated negatively with levels of IL-6 and IL-8. The presence of adenylate cyclase inhibitor 2',3'-dideoxyadenosine lost the prednisolone effect. The stimulation of EC-SOD production might be one of the important effects of prednisolone via cAMP pathway in MCs.

HLA-DR modulates autoantibody repertoire, but not mortality, in a humanized mouse model of systemic lupus erythematosus

To evaluate the disease-modulating role of HLA-DR2 and DR3 molecules, which have been associated with systemic lupus erythematosus, a humanized mouse model was examined. HLA-DR2 (DRB1*1502)- and DR3 (DRB1*0301)-transgenic mice were backcrossed to the New Zealand Mixed 2410 (NZM 2410, H2(z)) strain. Seventh generation DR2 and DR3 transgene-positive animals along with their transgene-negative littermates and the parental strain NZM2410 were monitored for proteinuria, azotemia, autoantibody production, development of nephritis, and mortality. The results showed no significant differences in proteinuria, azotemia, or mortality between the backcrosses with and without HLA-DR2 or HLA-DR3. However, the genetic analysis of different backcrosses showed that heterozygosity at the endogenous H2-E locus (E(z)/E(b)) was strongly linked with acceleration of lupus nephritis in both HLA-DR2 and HLA-DR3 transgenics. More importantly, the presence of the HLA-DR2, but not the HLA-DR3, transgene significantly enhanced the production of anti-dsDNA, but not anti-ssDNA, anti-histone-dsDNA complex, or anti-histone, Abs. In contrast, neither HLA-DR2 nor HLA-DR3 influenced the development of glomerulonephritis or the degree of immune complex deposition. Moreover, nephritic kidneys from mice with and without HLA-DR2 or HLA-DR3 transgenes showed similar patterns of cytokine expression. Collectively, these findings provide molecular evidence that the association of HLA-DR2 or HLA-DR3 with lupus susceptibility is related to the type of autoantibody rather than to disease mortality. The use of a humanized mouse model provides a way of dissecting the roles of human MHC genes in systemic lupus erythematosus pathogenesis.

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.

[Pathogenesis of interstitial kidney fibrosis. Studies in the rat model of unilateral ureteral obstruction]

BACKGROUND

The animal model of unilateral ureteral obstruction (UUO) of the rat is suitable to cause a renal interstitial fibrosis within a few weeks. Prior to the 10th day after UUO, no fibrotic changes were detectable in ureter-ligated kidneys, whereas after day 20 fibrosis was developing strongly.

METHOD

Using cell cultures it was examined whether any in vivo changes in proliferation and function of fibroblasts are also detectable in cell cultures and whether, due to their persistency, they are of fundamental importance for the development of renal interstitial fibrosis.

RESULTS

The comparison of the proliferation in cell cultures established 5 and 21 days after UUO showed that the cultures of the two experimental groups behave similarly. Consequently, the action of acute inflammatory processes on fibroblast proliferation without any existing fibrosis is comparable with that of pronounced fibrosis in the animal model. High concentrations of fetal calf serum in the culture medium cause a stimulation of the cell proliferation as well as a selection of mitotically active differentiation stages of fibroblasts.

CONCLUSION

Obviously, the loss of inhibition of the fibroblast proliferation under the conditions of cell culture causes similar changes to those effected by pathogenic mechanisms in the kidneys of rats with UUO. If the behaviour of fibroblasts in organs is to be assessed using results of cell culture experiments, the stimulating action of the culture conditions and the missing influence of other cells present in the tissue should be considered. These factors make the recognition of remaining differences between cells from normal and damaged kidneys more difficult under the conditions of primary cell cultures.

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-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.

Human mesangial cell production of monocyte chemoattractant protein-1: modulation by lovastatin

Macrophages play a critical role in the progression of clinical and experimental glomerular injury. Serum-stimulated human fetal mesangial cells in culture produce a chemotactic factor that is monocyte-selective. This chemotactic factor is most likely monocyte chemoattractant protein-1 (MCP-1) as a monoclonal antibody directed against MCP-1, but not an irrelevant antibody, suppressed the mesangial cell-derived chemotactic activity. Inhibition of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase by lovastatin resulted in a reduction of the mesangial cell-derived chemotactic activity as well as MCP-1 mRNA expression. The inhibitory effects of lovastatin in the presence of exogenous cholesterol were reversed by mevalonate, suggesting a role for isoprenoid intermediates of the mevalonate pathway and/or isoprenylated proteins in mesangial cell MCP-1 regulation. These findings suggest an additional mechanism by which HMG-CoA reductase inhibition in vivo may reduce glomerular injury.

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.