ABSTRACT: Background: Temporomandibular joint (TMJ) degenerative diseases are increasingly affecting elderly populations, with aging being a significant risk factor driving the TMJ changes. This study aims to explore the shared characteristics between aging and TMJ degenerative diseases at the tissue level, and to identify aging-related signature genes in TMJ degenerations using bioinformatics approaches. Methods: Young (2 months of age, n=7) and aged (18 months of age, n=6) mice’s condyles were used to construct an aging dataset. Overlapping genes were selected from differentially expressed genes in the TMJOA dataset, aging dataset and mechanical stimulation dataset. Temporomandibular joint osteoarthritis-associated and aging-related differentially expressed genes (TMJOA-ARDEGs) were identified through Weighted gene co-expression network analysis. Functional enrichment analysis and Protein-Protein Interaction networks were employed. Machine learning was applied to select Hub temporomandibular joint osteoarthritis-associated and aging-related differentially expressed genes (Hub TMJOA-ARDEGs). An age-related TMJOA mouse model (18 months of age) was established and grouped based on the micro-CT and the modified Mankin scores. The expression changes of key Hub TMJOA-ARDEGs were verified by immunohistochemical staining. The Mann-Whitney U test was used in non-normally distributed data, presented as [median (interquartile range)]. Results: Fifty-two TMJOA-ARDEGs were identified, with functional enrichment analysis revealed that these genes participate in circadian rhythm and apoptosis. Eight Hub TMJOA-ARDEGs were identified, ANK1, MELTF, FERMT3, MDFI, CXCL14, EPHA3, SMOC2 and NR1D1. Based on the micro-CT, 12 TMJs of aged mice were divided into the TMJOA group (n=6) and the healthy group (n=6). Micro-CT revealed bone resorption in the TMJOA group compared to the healthy group, with a decrease in BV/TV (p<0.05) and an increase in Tb.Sp (p<0.05). The modified Mankin scores showed that the TMJOA group had a score of 5.61 (2.28), higher than the healthy group's score of 0.83 (1.28), p<0.01. These results confirm the validity of the model grouping. Among the Hub TMJOA-ARDEGs, NR1D1 is a key gene involved in regulating circadian rhythm. In immunohistochemical staining, the expression level of NR1D1 showed significantly elevated expression in osteoarthritis mice (p<0.01). Conclusion: NR1D1, a negative feedback regulator in the circadian rhythm loop, is a characteristic gene associated with both aging and TMJ degenerative diseases.
