Cytokine interactions promote synergistic fibronectin accumulation by mesangial cells

Abstract

Background. The development of glomerulosclerosis has been associated with the presence of the cytokines transforming growth factor-β1 (TGF- β1), tumor necrosis factor-α (TNF-α) and/or interleukin-1β (IL-1β), at some stage in the glomerulus. To better understand the role of these cytokines in the scarring process their effect on rat mesangial cell fibronectin production was investigated. Methods. Mesangial cells were exposed to 10 ng/ml of either TGF-β1, TNF-α, or IL-1β or to TGF-β1 in combination with TNF-α Or IL-1β. Tissue culture supernatants and cell lysates were assayed for fibronectin. Supernatants were also assayed for TGF- β1. Northern blot analyses probing for fibronectin, transin, TIMP-1 and TGF-β1 were carried out on RNA extracted from mesangial cells exposed to individual and combinations of cytokines. Results. Individually these cytokines were only able to induce modest increases in fibronectin protein levels. However, when mesangial cells were exposed to TGF-β1 in combination with either TNF-α or IL-1β then fibronectin levels were synergistically up- regulated approximatelly fivefold over unstimulated levels. Northern analysis demonstrated that fibronectin mRNA levels in the combination were also synergistically increased. In contrast, rat transin gene expression in the combinations was reduced to well below levels induced by TNF-α and IL-1β individually. In addition, synergistic up-regulation of both TGF-β1 protein and message by the cytokine combinations was also observed. TGF-β1: TNF-α and TGF-β1: IL-1β induced additive increases in TIMP-1 (tissue inhibitor of metalloproteinases-1) mRNA levels. Conclusions. These data illustrate that complex interactions can occur between cytokines within the glomerulus modulating both matrix synthetic and degradation pathways. These could initiate the scarring process and the development of glomerulosclerosis.