The Role Of TLR4/MyD88/NF-?B Pathway In Periodontitis-induced Liver Inflammation Of Rats

Background:Periodontitis is an inflammatory oral disease characterized by destruction of periodontal connective tissue,that is gingiva,periodontal ligament,and alveolar bone resorption.Multiple studies have reported that periodontitis can not only cause injury to the periodontal tissues,but also harm patients' overall health by increasing the risk of diabetes,hepatic diseases,rheumatoid arthritis,cancer,and atherosclerosis NAFLD is one of the most common chronic liver diseases.A large number of studies have shown that periodontitis is associated with NAFLD,but the specific mechanism is still unclear.P.gingivalis is the key pathogen of periodontitis.Some studies have confirmed that LPS,the main toxic factor in the outer membrane of P.gingivalis,can reach to many tissues and organs.TLRs are mainly expressed on the surface of KCs in liver.LPS can be identified by TLR2 and TLR4,then induce the inflammatory response.It is reported that LPS-TLR4 plays an important role in the liver inflammation.TLR4 can be activated by LPS then lead to increased hepatic expression of MyD88 and NF-?B,and rise in inflammatory cytokines.Our previous study has found that the expression of pro-inflammatory cytokines in the liver tissue of mice with periodontitis which is caused by P.gingivalis was significantly increased,but the mechanism is still unclear To clarify this point,a Wistar rat model of ligature-induced periodontitis was used in this studyMethods:1.Twenty-four male Wistar rats,8 weeks old,weighing 200-220g,were randomly divided into two groups:control group(n=12,no ligature)and periodontitis group(n=12,with ligature).Experimental periodontitis was induced by the placement of a ligature which tied around bilateral maxillary first molar.Eight weeks after modeling,the following indicators were tested2.Periodontal disease parameters:Gingival index(GI),Tooth mobility(TM),probing pocket depth(PPD)3.Bone retraction by Micro-CT analysis4.To evaluate hepatic injury,ALT,AST,GGT,AlkP,TC,and TG were measured5.Histological evaluation of the periodontal and the liver tissues1)The periodontal and hepatic tissues of rats were analyzed by HE staining2)Oil Red O was used to detect the hepatic steatosis of the rats3)Immunohistochemical staining was used to detect the protein expressions of TLR4,MyD88,TNF-? and IL-6 in rat liver tissues4)Protein expression of NF-?B in rat liver was detected by immunofluorescence staining6.The mRNA expressions of TLR4,MyD88,NF-?B,TNF-? and IL-6 in rat liver tissues were detected by qRT-PCR7.The protein expression levels of TLR4,MyD88,NF-?B,I?B?,and p-I?B? were determined by Western BlotResults:1.GI,PPD,mobility,and alveolar bone resorption of upper 1st molar were significantly severe in the periodontitis group than the control group2.Serum AST,ALT,AlkP,and GGT presented higher levels in the periodontitis group versus the control group.In addition,hepatic and serum levels of TC and TG were shown to be increased in the periodontitis group,compared to the control group3.HE and Oil Red O staining results showed that no obvious histological changes observed in the liver tissues of the control group.However,inflammation and steatosis were presented in periodontitis group4.The mRNA expression levels of TLR4,MyD88,NF-?B,TNF-?,and IL-6 in the rat liver of the periodontitis group were significantly higher than those in the control group5.Immunohistochemistry,immunofluorescence staining,and Western Blot results showed that the protein expression levels of TLR4,MyD88,NF-?B,and p-I?B?in the periodontitis group were significantly higher than those in the control group,while the protein expression level of I?B? was significantly lower than that in the control groupConclusions:TLR4/MyD88/NF-?B signaling pathway may play a role in periodontitis-induced liver inflammation of rats.