Altered response of fibroblasts from human tympanosclerotic membrane to interacting mast cells: Implication for tissue remodeling

Abstract

Several lines of evidence suggest that a tympanosclerotic (TMS) lesion often develops secondary to acute and chronic otitis media. Histological findings indicate that fibroblasts and inflammatory cells, including mast cells, play a key role in the tympanosclerotic plaque formation. However, details on the functional characteristics of tympanosclerotic fibroblasts (FsTMS) are scanty. Therefore the aim of our study was to examine the activity of human fibroblasts from tympanosclerotic lesions and to evaluate the influence of stimulated by crosslinking of IgE receptor mast cells (HMC-1FcɛRI) on fibroblast functional behavior. We observed that fibroblasts from normal tympanic membrane (FsTM) released less TNF-α, TGF-β1 and IL-6 compared to FsTMS. FsTMS but not FsTM upon interaction with HMC-1FcɛRI released increased quantities of TNF-α and TGF-β1. Exposing the fibroblast to HMC-1FcɛRI cells resulted in an increased synthesis of proteins including collagen. We noted that the COL2A1 transcript level increased ∼5- and ∼12-fold in FsTM and FsTMS co-cultured with HMC-1FcɛRI, respectively. Both FsTM and FsTMS upon maintenance in the primary culture released significant quantities of matrix metalloproteinase 9 (MMP-9). However, FsTMS released ∼5-fold more MMP-9 activity compared to the FsTM cultures. The mast cell-induced release of TNF-α, TGF-β1 and MMP-9 sustained for a longer time in FsTMS cultures compared to FsTM.Concluding, our data strongly indicate that increased fibroblast sensitivity to mast cell stimulation greatly contributes to the excessive fibrosis and pathological remodeling of the tympanic membrane. We postulate that the persistency of the FsTMS activated state could be an important factor in the pathogenesis of tympanosclerosis.