BMAL1 Deficiency Contributes To Mandibular Dysplasia By Upregulating MMP3

Background:Skeletal mandibular hypoplasia?SMH?is one of the most common craniofacial developmental malformations,which not only seriously affects the patient's pronunciation,chewing,appearance,but also induce severe complications such as obstructive sleep apnea syndrome?OSAS?.It was reported that the circadian clock takes part in many behavioral and physiological processes,which have a significant influence on the growth and development of organisms.Objective:Therefore,our study aims to explore the effects and mechanisms of the circadian clock on the growth and development of the mandible.Methods:To further determine if circadian rhythm participates in mandibular bone development specifically,we established a jet-lag mouse model to observe the impact of circadian rhythm disruption on the occurrence and development of SMH.To establish the role of BMAL1 in SMH,we constructed Bmal1^-/-mice.Bone marrow mesenchymal stem cells?mBMSC?from wild-type mice and Bmal1^-/-mice were subjected to perform RNA sequence,and differentially expressed genes related to bone development were screened.Differentially expressed proteins were further verified by protein chip.After screening for target molecule,the molecular mechanism of Bmal1 affecting the growth and development of mandible was studied.Results:The circadian clock genes were rhythmically expressed in the normal mandibular tissue.The Jet-Lag mice had lower mandibular bone mass than wild type mice.It is indicated that the reduction of mandibular bone mass during development is closely related to the destruction of circadian rhythm.Compared with the normal mandibular tissue,the expression of Bmal1 was significantly lower in adolescent mandibular tissue of skeletal mandibular hypoplasia?SMH?.Bmal1^-/-mice have lower levels of mandible development than wild-type mice.To explore the possible regulatory targets of BMAL1,we extracted bone marrow mesenchymal stem cells?mBMSC?from wild-type mice and Bmal1^-/-mice for whole-genome RNA sequencing?RNA-seq?,and results showed that MMP3 expression was significantly increased after BMAL1 knockout.Protein chip verified that Mmp3 was significantly increased in the mandibular tissues of Bmal1^-/-mice.In addition,MMP3expression was higher in the mandibular tissues of adolescents with SMH compared with normal.Therefore,we speculate that MMP3 may be a potential target for mandibular dysplasia caused by BMAL1 deletion.Further mechanism studies revealed that knockdown of BMAL1 promotes phosphorylation of p65,while phosphorylated p65 can enter the nucleus,directly regulate Mmp3 transcription,and increase MMP3 expression.MMP3 can inhibit the osteogenic differentiation of BMSCs and promote the osteoclast differentiation of RAW264.7 cells.Conclusion:The circadian clock affects the growth and development of the mandible.The deletion of BMAL1 up-regulates the expression of MMP3 by affecting the phosphorylation of p65,thereby inhibiting osteogenic differentiation and promoting osteoclast differentiation.This result provides a new idea for the prevention and treatment of adolescent skeletal dysplasia?SMH?.