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Inhibition of STAT3 decreases OSM induced EDA-FN expression in human lung fibroblasts Tse, Joyce


Fibrosis is excessive deposition of connective tissue components that results in the destruction of normal tissue architecture and compromises organ function. When fibrosis occurs in the major organs such as the lung, for example in idiopathic pulmonary fibrosis (IPF), it inevitably leads to organ failure and premature death of the afflicted individual. The development of fibrosis follows a similar pathway to normal wound healing, although there is chronic progression of the disease without resolution, suggesting the fine control of cellular functions that occur during wound healing is disturbed. Determining where this control is lost is paramount to preventing and treating this condition. Fibroblasts are the main cell type responsible for extracellular matrix (ECM) production. The transcription factor signal-transducer-and-activator-of-transcription-3 (STAT-3) regulates genes involved in cell differentiation and wound healing. It has been shown that fibroblasts isolated from normal and IPF lungs differ in STAT3 dependent interleukin-6 (IL-6)/glycoprotein 130 (gp130) cell signaling and proliferation. Therefore, we aimed to evaluate whether STAT3 inhibition could decrease expression of ECM proteins, including collagen and extra-domain A fibronectin (EDA-FN) in human lung fibroblasts. We also sought to examine the effect of knocking down STAT3 function on fibroblast proliferation. Cells were exposed to Oncostatin-M (OSM) or IL-6, and collagen-1 and EDA-FN protein expression was analyzed by western blotting, while cell proliferation was assessed by bromo-deoxyuridine (BrdU) incorporation. STAT3 function was inhibited in two ways: Firstly, inhibition with a small molecule inhibitor, STA-21, blocks STAT3 dimerization and nuclear translocation and secondly, inhibition of STAT3 gene transcription by short interfering RNA (siRNA). Both methods inhibited OSM induced EDA-FN expression and proliferation in human fetal lung (HFL) fibroblasts. However, STAT3 had negligible effects in adult lung fibroblasts. We attempted to resolve the disparate effects by inhibiting another downstream signaling pathway, the extracellular receptor kinase (ERK)-1/2, which is also activated by gp130. In conclusion, OSM induced EDA-FN expression and cell proliferation in HFL fibroblasts are dependent upon STAT3 activation. In contrast, STAT3 has minimal involvement in adult cells. The mechanisms underlying these disparate effects remain to be elucidated. Interestingly, inhibiting either STAT3 or ERK1/2 inhibited OSM induced proliferation in HFL fibroblasts.

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