Normal human lung fibroblasts downregulate the production of tumor necrosis factor (TNF)-alpha by activated monocytes through the production of prostaglandin E(2) (PGE(2)), contributing to the local control of the inflammatory process. In this study, we provide evidence that fibroblasts derived from diseased tissue, such as fibrotic lung fibroblasts, exhibit different functional features compared with normal cells, with particular regard to their modulatory role. Indeed, fibrotic fibroblasts (FF) spontaneously produced less PGE(2) (3,300 +/- 410 pg/ml) compared with normal fibroblasts (NF) (7,500 +/- 270 pg/ml) and, as a consequence, they showed a reduced ability to downregulate the production of TNF-alpha by lipopolysaccharide (LPS)- activated monocytes. The percentage of inhibition induced by normal cells on the production of TNF-alpha by LPS-activated monocytes was 61 +/- 5.9%, whereas the inhibitory effect exerted by fibrotic cells was reduced to 32 +/- 4% (P < 0.01). We have also observed that the ability of TNF-alpha to induce PGE(2) was impaired in FF and was related to a reduced expression of cyclooxygenase 2. This was possibly due to the reduction of the expression of TNF receptors (TNFRs) in fibrotic cell lines compared with normal cell lines. Flow cytometry revealed that the mean fluorescence intensity (MFI) of both isoforms of TNFR was significantly lower in FF compared with NF. The MFI of TNFR1 was 3. 55 +/- 0.12 for NF and 1.78 +/- 0.35 for FF (P < 0.001). The MFI of TNFR2 was 1.95 +/- 0.27 for NF and 0.99 +/- 0.16 for FF (P < 0.01). The analysis of the effect of TNF-alpha on some functions associated with collagen metabolism in NF and FF showed an increase of the expression of the receptor for collagen type I (alpha(2)beta(1) integrin) in NF (42 +/- 10%) and an even larger increase in FF (102 +/- 23%) (P < 0.05). Interestingly, unlike NF, TNF-alpha failed to increase matrix metalloproteinase 1 levels in FF and did not cause any growth inhibition in these cells. The reduced capability of fibrotic cells to produce PGE(2) either spontaneously or after TNF-alpha treatment may lead to an unrestrained release of TNF-alpha from activated monocytes and, as a result of the reduced expression of TNFRs, to a different response of these cells to TNF-alpha. These changes may be important in the evolution of the inflammatory process, potentially contributing to its transformation into a chronic and self-perpetuating process.

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Rationale: Gap junctions are membrane channels formed by an array of connexins which links adjacent cells realizing an electro-metabolic synapse. Connexin-mediated communication is crucial in the regulation of cell growth, differentiation, and development. The activation and proliferation of phenotypically altered fibroblasts are central events in the pathogenesis of idiopathic pulmonary fibrosis. We sought to evaluate the role of connexin-43, the most abundant gap-junction subunit in the human lung, in the pathogenesis of this condition. Methods:We investigated the transcription and protein expression of connexin-43 and the gapjunctional intercellular communication (GJIC) in 5 primary lung fibroblast lines derived from normal subjects (NF) and from 3 histologically proven IPF patients (FF). Results:Here we show that connexin-43 mRNA was significantly reduced in FF as demonstrated by standard and quantitative RT-PCR. GJIC was functionally evaluated by means of flow-cytometry. In order to demonstrate that dye spreading was taking place through gap junctions, we used carbenoxolone as a pharmacological gap-junction blocker. Carbenoxolone specifically blocked GJIC in our system in a concentration dependent manner. FF showed a significantly reduced homologous GJIC compared to NF. Similarly, GJIC was significantly impaired in FF when a heterologous NF line was used as dye donor, suggesting a complete defect in GJIC of FF. Conclusion:These results suggest a novel alteration in primary lung fibroblasts from IPF patients. The reduced Cx43 expression and the associated alteration in cell-to-cell communication may justify some of the known pathological characteristic of this devastating disease that still represents a challenge to the medical practice.

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