Bradykinin differentiates human lung fibroblasts to a myofibroblast phenotype via the B2 receptor

Background

The identification of factors mediating the transition of lung fibroblasts into myofibroblasts is considered fundamental in the comprehension of abnormal reparative processes. Bradykinin, a mediator known for its proinflammatory action, is able to induce cytokine production and contractility in fibroblast cultures.

Objectives

In this study the ability of bradykinin to drive fibroblast into a myofibroblast phenotype at the cellular and molecular level was evaluated.

Methods

α-Smooth muscle actin (α-SMA) expression and TGF-β in bradykinin stimulated fibroblasts were tested by means of flow cytometry, Western blot, and RT-PCR. Cell proliferation and collagen production were evaluated by the colorimetric methylthiazol tetrazolium assay and sirius red assay, respectively. Which bradykinin receptor mediates the expression of α-SMA was evaluated using selective B1 and B2 blocking agents. Furthermore, the effect of bradykinin on extracellular signal-regulated kinase 1/2 phosphorylation was explored.

Results

Bradykinin caused in lung fibroblasts a significant increase in α-SMA at the cellular and molecular level. The B2 receptor was held responsible for this effect because a specific receptor antagonist had entirely blocked this effect. Bradykinin was able to induce fibroblast proliferation and collagen production. Bradykinin significantly activated mitogen-activated protein kinase pathway by phosphorylating extracellular signal-regulated kinase 1/2, whereas PD98059, a specific inhibitor, was able to block myofibroblast induction. Although bradykinin induced an increase of TGF-β on fibroblasts, the blockage of this cytokine did not alter α-SMA expression.

Conclusion

The data support the hypothesis that bradykinin may be involved in bronchial remodeling and lung fibrosis beyond its well recognized proinflammatory activity, also suggesting a new potential therapeutic strategy to control altered reparatory processes.

Key words: Remodeling, lung fibrosis, α-SMA, MAPK

Abbreviations used: α-SMA, α-Smooth muscle actin, ERK, Extracellular signal-regulated kinase, MAPK, Mitogen-activated protein kinase, MFI, Mean fluorescence intensity, MTT, Colorimetric methylthiazol tetrazolium assay