Fibronectin (FN) decreases glomerular lesions and synthesis of tumour necrosis factor-alpha (TNF-alpha), platelet-activating factor (PAF) and FN in proliferative glomerulonephritis

Functions of TNF and its receptors in renal disease: distinct roles in inflammatory tissue injury and immune regulation

Tumor necrosis factor (TNF) alpha is a potent proinflammatory cytokine and important mediator of inflammatory tissue damage. In addition, it has important immune-regulatory functions. Many experimental studies and clinical observations support a role for TNF in the pathogenesis of acute and chronic renal disease. However, given its dual functions in inflammation and immune regulation, TNF may mediate both proinflammatory as well as immunosuppressive effects, particularly in chronic kidney diseases and systemic autoimmunity. Blockade of TNF in human rheumatoid arthritis or Crohn's disease led to the development of autoantibodies, lupus-like syndrome, and glomerulonephritis in some patients. These data raise concern about using TNF-blocking therapies in renal disease because the kidney may be especially vulnerable to the manifestation of autoimmune processes. Interestingly, recent experimental evidence suggests distinct roles for the 2 TNF receptors in mediating local inflammatory injury in the kidney and systemic immune-regulatory functions. In this review the biologic properties of TNF and its receptors, TNF receptors 1 and 2, relevant to kidney disease are summarized followed by a review of the available experimental and clinical data on the pathogenic role of the TNF system in nonimmune and immune renal diseases. Experimental evidence also is reviewed that supports a rationale for specifically blocking TNF receptor 2 versus anti-TNF therapies in some nephropathies, including immune complex-mediated glomerulonephritis.

From Cell-ECM interactions to tissue engineering

The extracellular matrix (ECM) consists of a complex mixture of structural and functional macromolecules and serves an important role in tissue and organ morphogenesis and in the maintenance of cell and tissue structure and function. The great diversity observed in the morphology and composition of the ECM contributes enormously to the properties and function of each organ and tissue. The ECM is also important during growth, development, and wound repair: its own dynamic composition acts as a reservoir for soluble signaling molecules and mediates signals from other sources to migrating, proliferating, and differentiating cells. Approaches to tissue engineering center on the need to provide signals to cell populations to promote cell proliferation and differentiation. These "external signals" are generated from growth factors, cell-ECM, and cell-cell interactions, as well as from physical-chemical and mechanical stimuli. This review considers recent advances in knowledge about cell-ECM interactions. A description of the main ECM molecules and cellular receptors with particular care to integrins and their role in stimulation of specific types of signal transduction pathways is also explained. The general principles of biomaterial design for tissue engineering are considered, with same examples.

Treatment of experimental nephrosis by culture filtrate of Cryptococcus neoformans var. gattii (CneF)

The therapeutic effect of the culture filtrate of cryptococcus neoformans var. gattii (CneF) was tested in Adriamycin-induced nephropathy. The CneF was administered at different doses (36, 54 and 90 mg/kg based on carbohydrate concentration), one i.p. injection every 72 hours for a total of 10 injections. The treated patient rats showed a significant reduction in proteinuria, plasma cholesterol concentration, BUN and significant increase in urine creatinine levels. Moreover, treatment with CneF significantly reduced number of glomerular leukocytes and decreased the tubular casts. These data suggest that CneF therapy can ameliorate proteinuria, hypercholesterolemia and suppress the progression of glomerular lesions in experimental model of nephrosis.

Proapoptotic Fas ligand is expressed by normal kidney tubular epithelium and injured glomeruli

Fas ligand (FasL) is a cell membrane cytokine that can promote apoptosis through activation of Fas receptors. Fas receptor activation induces glomerular cell apoptosis in vivo and participates in tubular cell death during acute renal failure. However, there is little information on the expression of FasL in the kidney. This study reports that FasL mRNA and protein are present in normal mouse and rat kidney. In situ hybridization and immunohistochemistry showed that proximal tubular epithelium is the main site of FasL expression in the normal kidney. In addition, increased total kidney FasL mRNA and de novo FasL protein expression by glomerular cells were observed in two different models of glomerular injury : rat immune-complex proliferative glumerulonephritis and murine lupus nephritis. Both full-length and soluble FasL were increased in the kidneys of the mice with nephritis. Cultured murine proximal tubular epithelial MCT cells and primary cultures of murine tubular epithelial cells expressed FasL mRNA and protein. Tubular epithelium-derived FasL induced apoptosis in Fassensitive lymphoid cell lines but not in Fas-resistant lymphoid cell lines. By contrast, MCT cells grown in the presence of the survival factors of serum were resistant to FasL, and only became partially sensitive to apoptosis induced by high concentrations (100 ng/ml) of FasL upon serum deprivation. However, MCT cells stimulated with inflammatory mediators (tumor necrosis factor-alpha, interferon-gamma, and lipopolysaccharide) increased cell surface Fas expression and were sensitized to apoptosis induced by FasL (FasL 55 +/- 5% versus control 8.3 +/- 4.1% apoptotic cells at 24 h, P < 0.05). Cytokine-primed primary cultures of tubular epithelial cells also acquired sensitivity to FasL-induced apoptosis. These results suggest that FasL expression by intrinsic renal cells may play a role in cell homeostasis in the normal kidney and during renal injury.

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

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

Agonistic anti-Fas antibodies induce glomerular cell apoptosis in mice in vivo

Recent studies suggest that apoptotic cell death regulates the cell complement in glomerular diseases. However, little is-known about the factors that promote glomerular cell apoptosis. Activation of the Fas receptor by the Fas ligand or agonistic antibodies triggers apoptosis in some cell types that express Fas. Cultured human mesangial cell are among the cells that undergo apoptosis upon Fas activation, but it is unclear whether mesangial cells are sensitive to death induced by Fas in vivo. We have now explored the role of Fas in experimental glomerular injury. Murine mesangial cells in culture express fas and undergo apoptosis when stimulated with the Jo2 agonistic anti-Fas mAb. A fas mRNA transcript is present in normal murine kidney and freshly isolated glomeruli. Balb-c mice developed hematuria and proteinuria within 24 hours of the intraperitoneal injection of 10 micrograms Jo2 anti-Fas mAb. In addition to liver cell apoptosis, glomerular cell apoptosis and mesangial cell depletion were evident in the kidney at three hours and more pronounced at 24 hours. Glomerular and liver injury were not prevented by decomplementation. These data suggest that Fas activation in vivo by specific antibodies induces glomerular and mesangial cell apoptosis in mice.

Glomerular up-regulation of EIIIA and V120 fibronectin isoforms in proliferative immune complex nephritis

Fibronectin: (FNs) comprise a family of adhesive glycoproteins that are prominent components of mesangial extracellular matrix and accumulate during glomerular injury. By alternative splicing of an unique mRNA precursor, various FN isoforms can be originated. In rat, three regions of the molecule are involved: EIIIA, EIIIB and V. Because specific FN isoforms are expressed in embryogenesis and wound healing, conditions characterized by cell migration and adhesion, we examined the pattern of FN isoforms in the mild and severe phases of a progressive immune complex proliferative nephritis in rats. We constructed specific probes to analyze the splicing pattern of FN pre-mRNAs by ribonuclease protection assays. FN mRNAs containing EIIIA, EIIIB and V regions increased along, the progression of nephritis, though the increment of EIIIB-FN mRNA was modest. However, different regulation of all these isoforms was observed. The percentage of FN mRNA containing the EIIIA exon versus total FN increased with the severity of the disease, while the percentage of FN mRNA containing the EIIIB exon decreased. Relative V-FN mRNA expression versus total FN mRNA increased only in the severe phase. By means of specific antibodies we also studied the presence of EIIIA, EIIIB and V-FN proteins in the kidney. In the normal glomerutus, EIIIA-FN protein was barely detectable in the mesangium, increasing in the mild phase of nephritis. In the severe phase of nephritis, increased EIIIA-FN was localized in the mesangium, in Bowman's capsule and in crescents. By contrast, EIIIB-FN protein in the glomerulus was absent even in the severe phase. V120-FN protein, an isoform that mediates the attachment of leukocytes through the VLA-4 integrin, was present in the mesangium and glomerular capillary loops in control animals, and increased in the severe phase of nephritis, coinciding with a strong leukocyte infiltration. In conclusion, our results show that during immune glomerular injury there were marked changes in the pattern of FN isoforms expression. Since those isoforms, particularly V120 isoform, are important in cell adhesion and migration, their up-regulation may facilitate the recruitment of cells into the injured glomeruli. The blockade of the interaction between V120-FN and infiltrating leukocytes may represent a new approach to the treatment of nephritis.

Anti-Fas antibodies induce cytolysis and apoptosis in cultured human mesangial cells

Death of renal cells often occurs during the acute and resolution phases of some forms of glomerulonephritis. The apoptotic Fas protein belongs to a recently described family of cytokine receptors with similarities to tumor necrosis factor (TNF) receptors, and may contribute to the necrobiology of renal cells. Fas transduces a signal for apoptosis in sensitive cells after binding by specific antibodies or following contact with natural Fas ligand. We have studied Fas in cultured human mesangial cells. Cytoflurography demonstrated Fas expression on the surface of human mesangial cells that was increased by stimulation with interferon gamma (IFN gamma). Agonistic anti-human Fas antibodies were cytotoxic to these cells. Cytotoxicity was time- and dose-dependent, and was modulated by pre-stimulation of the mesangial cells with IFN gamma and/or by co-treatment with actinomycin-D. Mesangial cell death following exposure to anti-Fas antibodies has features consistent with apoptosis, such as internucleosomal DNA fragmentation, nuclear shrinkage and condensation, and decreased DNA content. These data suggest that Fas and its ligand could play a mechanistic role in human glomerular cell injury.