Peripheral Clock Gene, Npas2 in Oral and Skin Wound Healing

Objectives: It is widely accepted that wound healing in the oral mucosa proceeds faster than in skin. However, the mechanism and accelerating factors for oral wound healing have not been well understood. It has been reported that denervation significantly delays the wound healing and regeneration. The neuronal influence on peripheral tissues is, in part, mediated by circadian clock mechanism. The objective of this study was to characterize the role of peripheral circadian rhythm during oral and skin wound healing.
Methods: Oral and skin fibroblasts were harvested from C57B6/J mice (B6) and the expression of clock-related genes including Npas2 was measured by qPCR. In vitro migration and floating collagen gel contraction assays were performed using oral and skin fibroblasts from wild type B6 mice as well as Npas2+/- and Npas2-/- mice. Dorsal full-thickness skin punched out wounds (5 mm diameter) were created in WT, Npas2+/- and Npas2-/- mice and the time course closure/contraction was measured.
Results: Among the peripheral circadian rhythm genes, Npas2 expression was found substantially different between oral and skin fibroblasts. While in vitro migration rate of oral and skin fibroblasts was equivalent, the floating collagen gel contraction rate of oral fibroblast was significantly faster and greater than that of skin fibroblast. When Npas2+/- and Npas2-/- skin fibroblasts were tested, the floating collagen contraction was significantly accelerated and reached to the level of oral fibroblast. Finally, the dorsal skin wound demonstrated the accelerated closure/contraction in Npas2-/- mice as compared to WT and Npas2+/- mice (p <0.05).
Conclusions: Using a mouse model carrying Npas2 knockout mutation, this study demonstrated the role of peripheral circadian rhythm on oral and skin wound healing. The outcome of this study suggest that peripheral circadian rhythm may provide an important clue in dissecting the differential regulatory mechanism of oral and skin wound healing.