Transition of asthmatic bronchial fibroblasts to myofibroblasts is inhibited by cell-cell contacts

Abstract

The role of airway wall remodelling in bronchial asthma is well established. Myofibroblasts, the cells displaying features intermediate between fibroblasts and smooth muscle cells, are involved in this process but the mechanism of myofibroblasts activation in the onset of the disease remains obscure. Myofibroblasts can differentiate from various cell types, including resident fibroblasts, and the fibroblasts to myofibroblasts transition (FMT) can be reproduced in vitro. We aimed to investigate the process of FMT in human bronchial fibroblasts (HBF) derived from non-asthmatic (n = 7) and asthmatic (n = 7) subjects. We also tested whether cell-cell contacts affect FMT by using N-cadherin blocking antibody. HBF plated in low or high cell density were treated with TGF-β(1) up to one week to induce FMT. The percentage of myofibroblsts was counted and expression of α-smooth muscle actin was evaluated by cytoimmunofluorescence, flow cytometry and immunobloting. We demonstrated that the intensity of FMT induced by TGF-β(1)in vitro was strongly enhanced in asthmatic as compared to non-asthmatic HBF populations. This process was facilitated by low cell plating density in both groups of cultures. Furthermore, we proved that neither HBF-conditioned medium nor growth arrest in G(0)/G(1) phase of cell cycle could stop the TGF-β(1)-induced FMT in asthmatic cell populations. However, even in sparse asthmatic HBF, the blocking of N-cadherin resulted in the inhibition of FMT. Our findings show for the first time that the initial absence or an induced loss of cell-cell adhesions in asthmatic HBF populations is important for the completion of FMT.