Circadian Clock Gene Expression in Periodontal Disease

Circadian rhythms are generated through transcriptional-translational feedback loops involving core clock genes such as CLOCK, BMAL1, PER1-3, CRY1-2, ROR-α, and REV-ERB-β. These molecular oscillators regulate immune function, inflammatory signaling, and bone metabolism. Experimental evidence suggests that circadian dysregulation may aggravate periodontal inflammation and alveolar bone loss; however, comprehensive human data under controlled chronotype conditions remain limited. This single-center, observational case-control study includes 60 systemically healthy, non-smoking individuals (30 males, 30 females) aged 22-45 years. Chronotype was determined using the Munich Chronotype Questionnaire, and only individuals with intermediate chronotype and self-reported sleep duration between 6 and 9 hours were included to minimize circadian variability. Participants were classified into three groups (n=20 per group): periodontally healthy, gingivitis, and stage III grade B periodontitis according to the 2017 World Workshop criteria. Comprehensive periodontal examination included plaque index, gingival index, bleeding on probing, probing depth, and clinical attachment loss measurements. Gingival tissue biopsies were obtained during clinically indicated procedures and collected between 09:00 and 11:00 a.m. to standardize circadian timing. Samples were stored at -80°C until molecular analysis. Total RNA was extracted from gingival tissues, and gene expression was quantified using RT-qPCR with normalization to β-actin and analysis via the 2\^-ΔΔCT method. Protein expression of circadian clock components was assessed by Western blot, and inflammatory cytokine levels (IL-1β, IL-6) were quantified by ELISA. Correlation analyses were performed to evaluate associations between circadian gene expression, inflammatory mediators, and clinical periodontal parameters. The primary objective is to determine whether periodontal inflammation is associated with disruption of gingival circadian clock gene and protein expression in individuals with comparable chronotype profiles.