Identification of candidate immunity biomarkers associated with age-related variations in osteoclast activity in a mouse model of orthodontic tooth movement.

BACKGROUND: This study provides a comprehensive examination of the influence of age on osteoclast activity during orthodontic tooth movement, analyzed through the lens of osteoimmunology, identifying key immune molecules and cells involved in the regulation. METHODS: C57BL/6 mice of two different age groups were utilized, with each group subjected to an orthodontic tooth movement (OTM) model established between the maxillary first molar and maxillary incisors on the left side for durations of 7 and 14 days. For RNA sequencing, total RNA was extracted from the alveolar bone surrounding the first molar. Bioinformatics analyses were conducted to identify key molecules and cells associated with local osteoclast activity across different age groups. The findings were validated through immunofluorescence examination, quantitative real-time polymerase chain reaction (qRT-PCR) and in vitro cell experiments. RESULTS: In comparison to the control group, 227 up-regulated and 206 down-regulated differently expressed genes (DEGs) were identified on day 7 in the younger group, while 152 up-regulated and 63 down-regulated DEGs were identified on day 14. In the older group, 90 up-regulated and 243 down-regulated DEGs were found on day 7, and 31 up-regulated and 45 down-regulated DEGs on day 14. The up-regulated DEGs were significantly enriched in pathways related to immune response, inflammatory response and osteoclast formation. In adult cohorts, genes were predominantly associated with bone metabolism processes, including osteoclast and osteoblast differentiation. Conversly, in young cohorts, genes were primarily linked to inflammation-related processes, such as inflammatory and immune responses, as well as cellular responses to cytokine stimuli. The top 10 immune-related genes in two age groups were identified. Immunofluorescence staining revealed an increased expression of CCL3, CCL2, CXCL2, and CCR1 which were colocalized with macrophages. CONCLUSIONS: We identified key molecules that play an important role in orthodontic bone reconstruction by analyzing the differences in immune inflammatory differential gene expression across different age groups. These molecules, which facilitate macrophage migration to the local site and their differentiation into osteoclasts, as well as directly enhance osteoclast differentiation and function, are differentially expressed in young groups, but not in adult groups.