Characterization of the role and fate of nasal mucosal epithelial cell sheets in middle ear regeneration

Rapid and functional regeneration of the middle ear mucosa after surgery is essential for maintaining postoperative aeration and improving long-term outcomes in middle ear diseases such as cholesteatoma. Although nasal mucosal epithelial cell sheet transplantation has shown clinical efficacy, the in vivo behavior, fate of transplanted cells, and the underlying mechanisms remain incompletely understood. A middle ear mucosal removal model was established in immunodeficient rats. EGFP-labeled nasal mucosal epithelial cell sheets were transplanted onto the denuded bone surface of the middle ear cavity. The engraftment, persistence, and fate of transplanted cells were evaluated longitudinally using macroscopic fluorescence imaging, histological and immunohistochemical analyses, and in vivo micro-computed tomography (micro-CT). To identify an optimal cell source for middle ear mucosal regeneration, oral mucosal epithelial cell sheets and adipose-derived mesenchymal stem cell (ASC) sheets were also transplanted and comparatively analyzed. Nasal mucosal epithelial cell sheets rapidly engrafted onto the exposed middle ear bone surface and formed a continuous epithelial covering. Micro-CT analysis demonstrated preservation of middle ear aeration in the nasal cell sheet group, whereas progressive aeration loss and bone overgrowth were observed in the mucosal removal and ASC groups. Histological analyses revealed that most transplanted nasal epithelial cells were gradually replaced by host-derived middle ear mucosa, indicating a transient scaffold-like role rather than permanent epithelial replacement. In contrast, oral mucosal epithelial cell sheets showed epithelial stratification and keratinization, while ASC sheets induced early bone hyperplasia and middle ear cavity narrowing. Nasal mucosal epithelial cell sheets suppress pathological wound healing responses, including reactive bone formation, by temporarily covering the exposed middle ear bone surface and promoting regeneration of host-derived middle ear mucosa. Among the tested cell sources, nasal mucosal epithelium was the most suitable for middle ear mucosal regeneration. These findings provide valuable insights into the behavior of transplanted cells and a scientific basis for clinical approaches aimed at improving postoperative outcomes in middle ear surgery.