KL-6 regulated the expression of HGF, collagen and myofibroblast differentiation

KL-6 is a pulmonary epithelial-derived mucin which is secreted mainly by type II alveolar epithelial cells. The level of KL-6 in serum is closely correlated to the clinical activity of various interstitial lung diseases (ILD) and acts as a prognostic factor for ILD patients. Previous studies have showed that KL-6 promoted chemotaxis, proliferation and inhibited the apoptosis of human lung fibroblasts. However, the underlying mechanism remains unknown. In this study, we investigated the function of KL-6 on the expression of hepatocyte growth factor (HGF), transforming growth factor-β1 (TGF-β1), collagen and α-smooth muscle actin(α-SMA) in human embryonic lung fibroblasts cell line MRC-5.

Human embryonic lung fibroblasts were cultured in Eagle's minimum essential medium. The cells plated in 6-well plates was cultured in serum-free medium at 37°C in 5% CO2 and challenged with recombinant KL-6 at a final concentration of 0, 10, 20, 40 ng/mL. Five micrograms of total RNA template were transcripted to cDNA by using AMV (Avian Myeloblastosis Virus) reverse transcriptase and random 9 mers as the first-strand primer. Synthesized cDNA was used in PCR experiments. The expression of TGF-β1 and HGF in cell culture supernatants was measured using ELISA kit. Cells incubated with KL-6 for 72h were collected for flow-cytometry analysis. The analysis was done using a Beckman counter device.

It was found that KL-6 up-regulated the expression of collagen type I and III in a dose-dependent manner. However, the addition of KL-6 significantly inhibited the production of HGF. As regard to the biological function, KL-6 induced myofibroblast differentiation confirmed by the elevated expression of a-SMA.

KL-6 is one of the key molecules involved in epithelial-mesenchymal interactions and might contribute to the fibrosis in ILD.