Interferon-gamma regulation of human renal cortical epithelial cell-derived monocyte chemotactic peptide-1

Production and cytokine-mediated regulation of monocyte chemoattractant protein-1 by human proximal tubular epithelial cells

Impairment of renal function in various types of glomerular disease is associated with tubulointerstitial changes. The mechanism of mononuclear cell infiltration in the interstitium is not fully understood. Recently, monocyte chemoattractant protein-1 (MCP-1) has been identified as a monocyte-specific chemotactic factor. We analyzed the presence of MCP-1 in renal biopsies from patients with various forms of glomerular disease and demonstrated that MCP-1 expression is increased in renal tubular epithelial cells during disease. Further analysis showed that various cell lines of human proximal tubular epithelial cells (PTEC) produce MCP-1 in culture under serum-free conditions and that the production is inhibited by cycloheximide. IL-1 alpha and TNF-alpha enhanced the production by each cell line in a dose- and time-dependent manner as measured by radioimmunoassay. Northern blot analysis demonstrated that IL-1 alpha and TNF-alpha markedly enhanced the expression of MCP-1 mRNA. Taken together these observations support the notion that MCP-1 is synthesized de novo by PTEC. MCP-1 produced by PTEC is found to be 13 kD by gel filtration chromatography. It is chemotactically active for monocytes. We conclude that in various types of glomerular disease, MCP-1 expression in tubular epithelial cells is associated with up-regulation of MCP-1 production by PTEC. These findings raise the possibility that macrophages may accumulate in renal interstitium as a consequence of MCP-1 production by PTEC.

Evidence of autocrine modulation of macrophage nitric oxide synthase by alpha-melanocyte-stimulating hormone

alpha-Melanocyte-stimulating hormone (alpha-MSH) is a potent inhibitory agent in all major forms of inflammation. To identify a potential mechanism of antiinflammatory action of alpha-MSH, we tested its effects on production of nitric oxide (NO), believed to be a mediator common to all forms of inflammation. We measured NO and alpha-MSH production in RAW 264.7 cultured murine macrophages stimulated with bacterial lipopolysaccharide and interferon gamma. alpha-MSH inhibited production of NO, as estimated from nitrite production and nitration of endogenous macrophage proteins. This occurred through inhibition of production of NO synthase II protein; steady-state NO synthase II mRNA abundance was also reduced. alpha-MSH increased cAMP accumulation in RAW cells, characteristic of alpha-MSH receptors in other cell types. RAW cells also expressed mRNA for the primary alpha-MSH receptor (melanocortin 1). mRNA for proopiomelanocortin, the precursor molecular of alpha-MSH, was expressed in RAW cells, and tumor necrosis factor alpha increased production and release of alpha-MSH. These results suggest that the proinflammatory cytokine tumor necrosis factor alpha can induce macrophages to increase production of alpha-MSH, which then becomes available to act upon melanocortin receptors on the same cells. Such stimulation of melanocortin receptors could modulate inflammation by inhibiting the production of NO. The results suggest that alpha-MSH is an autocrine factor in macrophages which modulates inflammation by counteracting the effects of proinflammatory cytokines.

Macrophages and progressive renal disease in experimental hydronephrosis

Many recent clinical and experimental studies have clearly demonstrated that one of the initial events taking place in the process of progressive renal injury is monocytic infiltration of the glomerular and tubulointerstitial compartments. In this report, experimental data supporting the role of the infiltrating renal macrophage (M phi) as a mediator of interstitial fibrosis during the course of obstructive nephropathy will be reviewed as it pertains to the unilateral ureteral obstruction model in the rat. The central pathobiologic theme drawn on data from this model is that fibrogenic cytokines, especially transforming growth factor-beta, are, in part, M phi-derived and represent pivotal links between the initial postobstructive renal inflammation and the late development of renal scarring. The tubular epithelium, as a consequence of the mechanical disturbance produced by ureteral obstruction, may elaborate a host of M phi chemoattractant moieties. Many substances can be released by these infiltrating M phi; however, our studies have focused on transforming growth factor-beta 1. Transforming growth factor-beta is an important regulator of extracellular matrix, through its direct effects and modulation of other growth factors to maintain matrix homeostasis. We propose that the markedly increased expression of transforming growth factor-beta 1 following ureteral ligation, as detected by a number of laboratories, induces a profibrogenic state and initiates a cascade of dysregulatory events, including the upregulation of tissue inhibitors of metalloproteinase. Transforming growth factor-beta 1 also may serve as a potent stimulus for the modulation of quiescent interstitial fibroblasts into myofibroblasts. From a therapeutic standpoint, targeting these early cellular and molecular events may be extremely important in interrupting the interstitial fibrotic response to long-term obstructive uropathy.

Renal expression of genes that promote interstitial inflammation and fibrosis in rats with protein-overload proteinuria

Rats with significant proteinuria induced by daily injections of bovine serum albumin develop interstitial inflammation and fibrosis. The present study was designed to investigate the molecular basis of interstitial monocyte (Mø) recruitment and early interstitial fibrosis. Groups of rats were sacrificed after one, two and three weeks. Despite an increase in interstitial Mø at week 1, whole kidney mRNA levels were not elevated for monocyte chemoattractant protein-1 (MCP-1), osteopontin or vascular cell adhesion molecule-1 (VCAM-1). Only osteopontin mRNA levels were significantly elevated in the renal cortex at four days. At two and three weeks, MCP-1 and osteopontin mRNA levels were increased and the proteins showed distinct tubular patterns of distribution. By immunostaining increased expression of VCAM-1 and intercellular adhesion molecule-1 (ICAM-1) was restricted to their presence or the surface of the interstitial inflammatory cells. TGF-beta 1 mRNA levels were increased at weeks 1, 2 and 3 (2.1, 2.9, 3.6x); interstitial and occasional cortical tubular cells expressed TGF-beta 1 mRNA and protein. There was a progressive rise in the number of cortical interstitial fields with increased staining for collagen (col) 1 (18, 29, 44%), col III (39, 61, 63%), col IV (7, 13, 29%), laminin (4, 10, 30%), fibronectin (14, 28, 37%), tenascin (19, 22, 14%) and in total renal col measured biochemically (1.1, 1.4, 2.0x) at weeks 1, 2 and 3, respectively. Renal matrix protein mRNA levels were variable and not always predictive of fibrosis. Only col I and tenascin levels were increased at week 1; all matrix protein mRNA levels except col IV were increased at week 2; but only tenascin, laminin and col IV mRNA levels remained elevated at three weeks. Plasminogen activator inhibitor-1 (PAI-1) and tissue inhibitor of metallo-proteinases (TIMP)-1 mRNA levels were significantly increased at two weeks. During the three weeks there was no change in urokinase, stromelysin or TIMP-3 mRNA levels. These results suggest that both increased matrix protein synthesis and altered matrix remodeling/degradation contribute to the final interstitial fibrogenic process in rats with protein-overload proteinuria. Mø, one of the sources of TGF-beta 1, infiltrate the interstitium by complex recruitment mechanisms which may depend in part on osteopontin, ICAM-1 and VCAM-1 expression.

Podocyte expression of MHC class I and II and intercellular adhesion molecule-1 (ICAM-1) in experimental pauci-immune crescentic glomerulonephritis

We examined immunopathological changes of podocytes in vivo which, based on in vitro studies, are thought to be relevant for the pathogenesis of renal diseases. We investigated the alterations of podocytes in local inflammation in a recently developed model of pauci-immune necrotizing crescentic glomerulonephritis (NCGN) in the rat. Frozen and plastic embedded kidney sections at different time points of the disease were incubated with antibodies directed to MHC class I, MHC class II, ICAM-1 and to relevant cytokines. Strong glomerular expression of MHC class I, II and ICAM-1 was found within 4 days, and plastic embedded sections clearly demonstrated increased cell membrane staining of podocytes. Increased glomerular interferon-gamma (IFN-gamma) was detected within 24 h of induction of NCGN, and IL-1 beta and tumour necrosis factor-alpha (TNF-alpha) were found from day 4. The potency of these cytokines to induce adhesion molecules on podocytes was investigated on rat glomerular epithelial cells in vitro. By using FACS analysis and electron microscopical techniques, we found that the in vivo expression of MHC class I, II and ICAM-1 by podocytes could in vitro be simulated by IFN-gamma. IFN-alpha weakly induced MHC class I, while IL-1 beta and TNF-alpha were ineffective. We hypothesize that podocytes in this in vivo model are important to maintain the local inflammatory process in the glomerulus by expression of relevant adhesion molecules and MHC molecules upon stimulation with specific cytokines.

Tubular-derived growth factors and cytokines in the pathogenesis of tubulointerstitial fibrosis: implications for human renal disease progression

Detailed histomorphometric analysis of human biopsy tissue over the last 30 years has convincingly demonstrated that preservation of the tubulointerstitial compartment of the kidney is the major determinant of renal outcome in a variety of human renal diseases. Nevertheless, the pathophysiology of tubulointerstitial disease remains obscure. In particular, the primary role of tubular injury has not been explored adequately. There is now accumulating evidence that apart from their many transport functions, tubular cells also secrete an array of cytokines, including chemotactic cytokines, polypeptide growth factors, and vasoactive peptides. Three paracrine growth systems acting at different levels in the kidney are described as examples of potential interactions between tubular and interstitial cells in health and disease. We hypothesize that while glomerular injury may precede tubular injury, it is tubular injury that sets into motion the irreversible process of tubulointerstitial fibrosis characteristic of progressive human renal disease, leading to secondary loss of glomerular function.