Preliminary Investigation of In vitro, Bidirectional Vocal Fold Muscle-Mucosa Interactions

Objective: Oversimplified clinical dogma suggests that laryngeal diseases fall into two broad, mutually exclusive diagnostic categories-mucosal injury or neuromuscular/functional disorders. Extensive investigation in the lower airway as well as other organ systems suggest complex interactions between tissue types underlying both tissue health and pathological states. To date, no such relationship has been described in the vocal folds, likely the most bioactive organ in the body. We hypothesize interactions between the vocal fold muscle and mucosa likely contribute to aberrant phonatory physiology and warrant further investigation to ultimately develop novel therapeutic strategies. Methods: Primary culture of myoblasts from rat thyroarytenoid muscle and fibroblasts from the vocal fold mucosa were established. Co-culture and conditioned media experiments were performed to established bidirectional interactions between cell types. Transforming Growth Factor (TGF)-beta was employed to stimulate a fibrotic phenotype in culture. In addition to quantitative PCR, standard migration and proliferation assays were performed as well as immunocytochemistry. Results: Bidirectional cell-cell interactions were observed. Without TGF-beta stimulation, myoblast conditioned media inhibited fibroblast migration, but enhanced proliferation. Conversely, fibroblast conditioned media increased both myoblast proliferation and migration. Myoblast conditioned media decreased TGF-beta-mediated gene expression and of particular interest, ACTA2 mRNA expression. In both co-culture and in response to fibroblast conditioned media, myosin heavy chain (Myh2) mRNA expression decreased in myoblasts. Conclusions: These data are the first to describe interactions between cell types within the vocal fold. The implications for these interactions in vivo warrant further investigation to develop and refine optimal treatment strategies.