Expression of circadian core clock genes in fibroblasts of human gingiva and periodontal ligament is modulated by L-Mimosine and hypoxia in monolayer and spheroid cultures.

OBJECTIVE: The circadian clock is involved in a plethora of physiological processes including bone formation and tooth development. While expression of circadian core clock genes was observed in various tissues, their role in the periodontium is unclear. We hypothesized that periodontal cells express circadian core clock genes and that their levels are modulated by hypoxia mimetic agents and hypoxia.

MATERIAL AND METHODS: Fibroblasts of human gingiva (GF) and periodontal ligament (PDLF) in monolayer and spheroid cultures were treated with the hypoxia mimetic agent L-Mimosine (L-MIM) or hypoxia. Reverse transcription and quantitative PCR were performed to assess the impact on mRNA levels of the circadian core clock genes Clock, Bmal1, Cry1, Cry2, Per1, Per2, and Per3.

RESULTS: GF and PDLF expressed Clock, Bmal1, Cry1, Cry2, Per1, Per2, and Per3 in monolayer and spheroid cultures. In monolayer cultures, L-MIM significantly reduced Clock, Cry2, and Per3 mRNA expression in GF and Clock, Cry1, Cry2, Per1, and Per3 in PDLF. Hypoxia significantly reduced Clock, Cry2, and Per3 in GF and Cry1, Cry2, and Per3 in PDLF. In spheroid cultures, L-MIM significantly decreased Clock, Cry1, Cry2, and Per3 in GF and PDLF. Hypoxia significantly decreased Cry2 and Per3 in GF and Clock and Per3 in PDLF.

CONCLUSIONS: GF and PDLF express circadian core clock genes. The hypoxia mimetic agent L-MIM and hypoxic conditions can decrease the expression of Clock, Cry1-2 and Per1 and Per3. The specific response depends on cell type and culture model. Future studies will show how this effect contributes to periodontal health and disease.