Abstract: BACKGROUND: Autophagy is easily activated under hypoxia and has been demonstrated to regulate bone metabolism. Sleep apnea keeps the body in a state of intermittent hypoxia, and whether sleep apnea-induced hypoxia affects the autophagy levels of mandibular alveolar bone and periodontal ligament has not been reported.
OBJECTIVE: To observe the autophagy level in the rat mandible under hypoxic conditions. 
METHODS: Thirty 1-week-old male Wistar rats were randomly divided into three groups (n=10 per group). In unilateral and bilateral nasal obstruction groups, the left nostril was blocked with high-frequency electrocautery after 30 minutes of anesthesia, and 1 week later, the right nostril in the bilateral nasal obstruction group was blocked using the same method. Rats in control group were with no nostril blocking. Four weeks after the successful modeling of unilateral nasal obstruction, the model rats at the age of 5 weeks were anesthetized and sacrificed, and the mandibles were removed to prepare periodontal bone tissue sections of the mandibular first molar for hematoxylin-eosin staining and LC3 immunohistochemical staining. Localization of the stained sections was quantified using the image-J image analysis system. Western blot assay was used to detect the expression of hypoxia-inducible factor 1α and autophagy-related protein p62 in mandibular alveolar bone, as well as the ratio of autophagy marker protein LC3 isoforms LC3-II/LC3-I.
RESULTS AND CONCLUSION: Hematoxylin-eosin staining results revealed disordered arrangement of trabecules of the mandibular alveolar bone in the unilateral and bilateral nasal obstruction groups. Immunohistochemical results indicated an increased expression of LC3 in the alveolar bone cells and periodontal ligament cells of mandibular first molars in the unilateral and bilateral nasal obstruction groups, suggesting that autophagy mainly occurred in the periodontal ligament and alveolar bone. Western blot results showed that compared with the control group, the expression level of hypoxia-inducible factor 1α protein in the mandibular alveolar bone tissue was significantly increased, the expression level of p62 protein was significantly decreased (P < 0.05), and the ratio of LC3-II/LC3-I was significantly increased in the unilateral and bilateral nasal obstruction groups (P < 0.05). Moreover, the ratio of LC3-II/LC3-I in the bilateral nasal obstruction group was slightly lower than that in the unilateral nasal obstruction group (P > 0.05). All these findings indicate that hypoxia caused by unilateral and bilateral nasal obstruction increases the expression level of hypoxia-inducible factor 1α protein in the mandible and the level of autophagy in the periodontal ligament and alveolar bone of mandibular first molars in rats. However, the increase in autophagy has no positive correlation with the severity of nasal obstruction.

Key words: obstructive sleep apnea hypopnea syndrome, alveolar bone, nasal obstruction, intermittent hypoxia, autophagy, rat