Bmal1 Deficiency Contributes To Mandibular Dysplasia Through Downregulation Of Osteoprotegerin

Backgrouds and objectives:Mandibular skeletal hypoplasia,presenting with small mandibular deformity,always results in an unfavorable facial profile.In addition to affecting the appearance,chewing and pronunciation,it can cause psychological and social impact.Severe mandibular hypoplasia can lead to Obstructive Sleep Apnea Syndrome,hypertension,cardiovascular disease.Genetic and environmental factors both contribute to the development of the mandibles.However,the environmental factors affecting mandibular growth and development have yet not been clearly clarified.Circadian rhythm(CR)is critical for a living organism to maintain a rhythmic daily life.It plays essential roles in many physiological and behavioral processes.Stay up late,light pollution and irregular diet are the common risk factors of circadian rhythm disorder.It has been reported that circadian rhythm disturbance could lead to cancer,obesity and reduce the bone mass of the intervertebral disc and femur.However,the effect of circadian rhythm disturbance on the adolescent mandibular hypoplasiahas not attracted enough attention.CR is generated and modulated by the core clockgenes.Brain and muscle ARNT-likel(Bmal1)is the core component of the circadian molecular oscillator,which is expressed in the nucleus of the optic chiasm and the peripheral tissues such as bone,hematopoietic stem cells and bone marrow.It plays an important role in the primary mammalian oscillatory mechanism.Bmall deficient or arrhythmic mice can result in pathological phenomena.However,whether the Bmall disturbance could finally resulte in mandibular hypoplasia is still unknown.If we can demonstrate that Bmall rhythm deficiency could cause mandibular dysplasia through destroying the balance between osteogenesis and osteoclast.This study might provide a new perspective for prevention of the mandibular deformity.Materials and Methods(1)The twelve human cases were aquired from pathologically diagnosed mandibular dysplasia patients,and other twelve cases as control were from normally mandibular patients who had undergone alveolar surgery.And RT-PCR and Western-blot were used to detect the expressions of circadian genes.(2)Micro computed tomography was used to observe the mandibles changes in circadian rhythm-disordered mouse and Bmal1 knockout mice.(3)genome-wide RNA sequencing was performed to acquire the transcriptional profile(4)In vitro,Chromatin immunoprecipitation assay(CHIP)and luciferase reporter assay were used to explore the mechanism of how Bmal1 influence the BMSC osteogenesis differentiation and RAW264.7 osteoporosis differentiation.Results(1)Bmal1 and Clock expressions in mandibles were significantly decreased in patients with mandibular skeletal hypoplasia.(2)In circadian rhythm-disordered mouse and Bmall knockout mice,reduced bone formation,decreased bone mineral density,and broadened trabecular space were observed.RNA sequence and protein chips analysis showed Osteoprotegerin(OPG)was the potential target of Bmal1 in regulating mandibular development.(3)Bmal1 deficiency contributes to BMSC and RAW264.7 differentiation through downregulation of OPG.(4)Bmal1 upregulates OPG production by directly binding to the OPG promoterConclusionsDepended on the results,we have confirmed Bmall expressions in mandibles were significantly decreased in patients with mandibular skeletal hypoplasia,and in circadian rhythm-disordered mouse and Bmal1 knockout mice,reduced bone formation,decreased bone mineral density,and broadened trabecular space were observed.Moreover,Bmal1 deficiency contributes to mandibular dysplasia through downregulation of Osteoprotegerin by directly binding to the Opg promoter...