Preliminary Study On The Expression Of HMGB1 During Orthodontic Periodontal Remodeling Induced By Heavy Force

Background"Achieving effective orthodontic tooth movement without compromising periodontal tissue health" has always been a concern for orthodontic clinicians and academics.How to reduce adverse complications such as alveolar bone atrophy and root resorption in orthodontic clinical work is one of the current research hotspots.High mobility group protein box 1(HMGB1),a dual-function alarmins,is active in bone remodeling,which can either promote "inflammatory response and osteoclastogenesis" or "cell differentiation and osteogenesis" .Current research indicates that it participates in orthodontic tooth movement.However,it is not clear about the expression and mechanism during the process of stess overload-induced orthodontic periodontal remodeling and destruction.ObjectiveThis study aims to reveal the changes of HMGB1 under the process of tress overload induced peripdontal remodeling and destruction from vivo and vitro experiment.Methods1 In vivo experiments:Thirty-six Sprague-Dawley(SD)rats(male,180g-200g,5-7w)were randomly divided into three groups,namely,No Force,50 gF and 100 gF.One week later,the tooth movement distance was calculated by overlapping the initial model and finished model and the maxilla was separated for real time fluorescent polymerase chain reaction(Real-time PCR),hematoxylin and eosin(HE)staining,tartrate-resistant acid phosphatase(TRAP)staining and immunofluorescence(IF)analysis.2 In vitro experiments:Human periodontal ligament cells(hPDLCs)were respectively loaded with static pressure by 2 g/cm~2,4 g/cm~2 and 0 g/cm~2 as a control.The changes of HMGB1 and some related molecules were detected by Real-time PCR and IF at 8h,24h and 48h.Results1 Vivo:1.1 The heavy force of 50 g and 100 g can distal the rat's maxillary first molar(M1)and the amount tooth movement distance was significantly different among groups.1.2 Histomorphological changes have induced:coarse and disoriented periodontal ligaments were irregularly arranged around the roots;rough alveolar surfaces and resorption lacunae could be observed and also an increasing number of infiltrating mononuclear inflammatory cells was detected.Notably,increased periodontal destruction took place in the furcation area of M1,the mesial region of M1 and interdental regions between and the second molar(M2)and these three regions were accordingly used as the areas of interest(AOIs).The number of osteoclasts and the total area of root resorption on the first molar were significantly increased and there was a significant difference between 100 gF and the other groups(P<0.05).1.3 At the molecular level,the results of Real-time PCR showed that HMGB1,RANKL,and OPG changed at the mRNA level:HMGB1 decreased significantly in100 gF(P<0.05);the RANKL/OPG ratio increased significantly in force groups(P<0.05)and these results were consistent with changes in protein levels detected by IF.While there was no significant change occurred in the expression of the advanced glycosylation end product receptors(RAGE)at the mRNA level(P>0.05).Besides,HMGB1 widely and strongly distributed in periodontal tissue and is mainly located in the nucleus no stimulation and have a translocation from nuclear to cytoplasm or extracellular in the AOIs of 100 gF.The mean optical density of HMGB1 decreased significantly(P<0.05).2 Vitro:The vitro experiments further verified that the ratio of RANKL/OPG increased under the action of excessive static compressive stress,accompanying the downregulation of HMGB1 and its receptor of toll-like 4(TLR-4)at the mRNA level,as well as the translocation of the HMGB1 protein from the nucleus to the cytoplasm.Conclusions1 During the orthodontic tooth movement,the degree of damage of periodontal tissue is related to the force value.The greater the heavy force,the more obvious the damage to the periodontal tissue,which suggests that in orthodontic clinic,we must apply the force properly to avoid the destruction of periodontal tissue.2 Stress overload induced changes of HMGB1 during periodontal remodeling and destruction in tooth movement,both the location and expression,which hint at a much more complex time-and force-dependent regulation and an"alamin" role of HMGB1expression during orthodontic tooth movement than anticipated.The mechanism may be related to TLR-4,RANKL,OPG,which should prompt further investigations.