Observation of Apoptosis and Bone Lamella Structures in the Human Mastoid

Abstract

To investigate the localization of apoptotic cells and the lamellar bone structure in mastoid bone tissue, focusing on the mechanism of the development of mastoid pneumatization in humans. The biological mechanism of poor development of the mastoid air cells found in patients with otitis media (OM) has not yet been fully clarified, as there have been few immunohistochemical research studies to examine the cell biology involved. We evaluated the localization of apoptotic cells and the lamellar bone structure in 112 human mastoid bones harvested during various ear surgeries from 57 patients with OM and 55 patients without OM. We used the TdT-mediated dUTP nick end-labeling (TUNEL) method and a polarizing microscope for observing the apoptotic cells and lamellar bone structure, respectively. The TUNEL-positive cell ratio in an arbitrary 500 cells in the specimen (apoptotic index: AI) was 13.8 in the healthy group and 1.2 in the OM group (Mann-Whitney U test, p < 0.001). From their localization, these apoptotic cells were considered to be osteocytes. The observation of lamellar structures revealed many eroded surfaces in the circumference of the appositional bone in the healthy group. In contrast, apposition of bone without an eroded surface was evident in the bone circumference in the OM group. Apoptosis of osteocytes was significantly suppressed in the mastoid bone of the OM patients. Apoptotic osteocytes may be one of the signals of bone resorption in the process of development of the mastoid air cells. The lamellar structure of the mastoid bone suggested that poor development of the mastoid air cells was caused by decreased resorption of the appositional bone.