Immunohistochemical Analysis of SQSTM1/p62 and LC3 in Human Gingiva

Objectives: Although has been implicated in inflammation and cancer pathogenesis, the role of autophagy in human periodontitis has not been elucidated. This study aimed at investigating if autophagy may play part in human chronic periodontitis.
Methods: Human gingival biopsies were collected from 24 periodontitis and 11 periodontitis-free individuals. Immunohistochemical analysis was performed to detect the expression of autophagy markers: sequestosome 1 (SQSTM1/p62) and microtubule-associated protein 1 light chain 3 (LC3).
Results: SQSTM1/p62 and LC3 immunoreactivities were found in subepithelial connective tissue cells in gingival sulcus and periodontal pocket biopsies. No labelling could be detected in keratinocytes in any sections investigated. In diseased periodontal subepithelial connective tissue, the proportion of SQSTM1/p62-positive cells were significantly higher than that in corresponding region of healthy gingiva (oral 19.4% ± 11.5% vs 6.8% ± 4.5%, P < 0.05; pocket/sulcus 9.4% ± 8.2% vs 3.7% ± 3.4%, P < 0.05), and so as the expression profile of LC3 in diseased versus healthy gingiva (oral 18.7% ± 10.5% vs 6.0% ± 4.2%, P < 0.05; pocket/sulcus 8.9% ± 7.9% vs 3.4% ± 1.9%, P < 0.05). There were no significant differences regarding SQSTM1/p62 and LC3 positive cells proportion beneath various sites in healthy gingiva: oral epithelium, oral sulcular epithelium or junctional epithelium (7.0%, 7.6%, and 3.7%; 6.0%, 7.8% and 3.4%, respectively). More SQSTM1/p62- and LC3- positively stained cells were observed at subepithelial connective tissue beneath oral epithelium from periodontitis biopsies (P < 0.001).
Conclusions: SQSTM1/p62 and LC3 are positively expressed in subepithelial connective tissue of both periodontitis and periodontitis-free biopsies. Their expression in diseased gingiva appeared stronger in particular beneath oral epithelium, suggesting the association of autophagy with human chronic periodontitis. Further investigations are needed to explain why there is no detectable expression of SQSTM1/p62 or LC3 in oral and pocket epithelium.