Mast Cells and Fibroblasts Work in Concert to Aggravate Pulmonary Fibrosis

Abstract

Mast cell (MC) accumulation has been demonstrated in the lungs of idiopathic pulmonary fibrosis (IPF) patients. Mediators released from MCs may regulate tissue remodeling processes, thereby contributing to IPF pathogenesis. We investigated the role of MC-fibroblast interaction in the progression of lung fibrosis. Increased numbers of activated MCs, in close proximity to fibroblast foci and alveolar type II cells, were observed in IPF lungs. Correspondingly elevated tryptase levels were detected in IPF lung tissue samples. Coculture of human lung MCs with human lung fibroblasts (HLFs) induced MC activation, as evinced by tryptase release, and stimulated HLF proliferation; IPF HLFs exhibited a significantly higher growth rate, compared with control. Tryptase stimulated HLF growth in a PAR-2/PKC-α/Raf-1/p44/42-dependent manner and potentiated extracellular matrix production, but independent of PKC-α, Raf-1, and p44/42 activities. Proproliferative properties of tryptase were attenuated by knockdown or pharmacological inhibition of PAR-2, PKC-α, Raf-1, or p44/42. Expression of transmembrane SCF, but not soluble SCF, was elevated in IPF lung tissue and in fibroblasts isolated from IPF lungs. Coculture of IPF HLFs with MCs enhanced MC survival and proliferation. These effects were cell-contact dependent and could be inhibited by application of anti-SCF antibody or CD117 inhibitor. Thus, fibroblasts and MCs appear to work in concert to perpetuate fibrotic processes and so contribute to lung fibrosis progression.

A Brief Exposure to Tryptase or Thrombin Potentiates Fibrocyte Differentiation in the Presence of Serum or Serum Amyloid P

“…PAR-1 inhibitors SCH 79797 hydrochloride (Axon Medchem, Reston, VA, added to cells at 5 µg/ml (51)) and vorapaxar (Axon Mechem, 25 µg/ml (52)), and PAR-2 inhibitors ENMD-1068 (Enzo Life Sciences, Farmingdale, NY, 50 µg/ml (37)) and FSLLRY (Tocris, 1 µg/ml (47)) were resuspended following the manufacturer’s instructions. After a 1-hour incubation on ice in PFM, PBMC were collected by centrifugation at 300 x g for 10 minutes, resuspended in ice-cold PBS, and washed at 300 x g for 10 minutes, twice.…”

“…Mast cells are found in both internal fibrotic lesions and sites of wound healing (35–37). Mast cells degranulate in response to external stimuli (37) to release, among other things, the protease tryptase (37–39).…”

“…Mast cells degranulate in response to external stimuli (37) to release, among other things, the protease tryptase (37–39). Tryptase is upregulated in areas of increased mast cell degranulation, including wounds and especially in fibrotic lung tissue (35, 36, 38–40).…”

“…Tryptase cleaves at lysine and arginine residues, except when the following amino acid is proline (41). Tryptase activates protease activated receptor-2 (PAR-2) (37, 42). This receptor is found on a variety of cells including monocytes (33), and mediates the ability of tryptase to increase the proliferation of, and collagen production by, fibroblasts (37).…”

“…Tryptase activates protease activated receptor-2 (PAR-2) (37, 42). This receptor is found on a variety of cells including monocytes (33), and mediates the ability of tryptase to increase the proliferation of, and collagen production by, fibroblasts (37). Intratracheal administration of tryptase causes inflammation, and inhibition of tryptase attenuates this inflammation (43–46).…”