Helicobacter Hepaticus Infection Promotes Nonalcoholic Fatty Liver Disease

In recent years,non-alcoholic fatty liver disease has become the most common chronic liver disease with an increasing incidence year by year,including hepatic steatosis and non-alcoholic steatohepatitis(NASH),etc.In the later stage,it may develop into hepatic cirrhosis and hepatocellular carcinoma(HCC),which has been a threat to human life and health.At present,most of the models of non-alcoholic fatty liver disease are fed with high-oil and high-fat diets,and microorganisms are rarely involved in the model preparation.Helicobacter hepaticus(H.h)is an insecticide known to induce liver injury,including hepatitis and liver fibrosis.BALB/c mice infected with H.h fed a high-fat diet(High fat diet,HFD)to establish a new type of NAFLD animal mode.Helping us to explore the possible mechanism of H.h infection promoting the progression of hepatic steatosis to NASH from immunology,histopathology,molecular biology and so on1.H.h infection promotes the development of NASHH.h infection can cause liver inflammation and fibrosis in sensitive mice,but its role in liver fat metabolism is still unclear.Therefore,the NAFLD model induced by H.h and HFD was established to understand the role of H.h in the occurrence and development of NAFLD.Male SPF mice aged 6 weeks were randomly divided into 4 groups with 20 mice in each group,which were labeled as blank control group,HFD group,H.h group and HFD+H.h group.After H.h infected,mice in each infected group were fed a HFD.At 8,12,16 and 20 weeks after H.h infection,5 mice in each group were randomly selected for euthanasia and samples were collected for serum biochemical and liver histomathological tests.H&E staining and Sirius red staining showed that the degree of liver inflammation and fibrosis in the model increased with the duration of H.h infection and HFD,especially after 16 weeks of liver inflammation and fibrosis.The results of oil red staining showed that the fat deposition in the model group increased with the time during 8-12 weeks,but the fat deposition decreased after 16 weeks.Serum biochemical results showed that the levels of alanine aminotransferase and aspartate aminotransferase in the model group were significantly increased.These data suggest that H.h infection may promote the progression of non-alcoholic fatty liver disease in mice fed a high-fat diet with more severe liver damage and lipid accumulation,with early NASH symptoms at 12 weeks after infection and more typical NASH symptoms at 16 weeks after infection.2.H.h infection aggravates liver inflammation and fibrosis caused by HFDThe results of H&E staining and quantitative PCR showed that the levels of oxidative stress and inflammation in HFD+H.h group were significantly increased compared with those in HFD and H.h groups.The results of liver load test of H.h showed that the amount of H.h colonization was increased in HFD+H.h group compared with H.h group.H&E and PAS staining of the colon showed goblet cell loss and enhanced permeability in the intestine after feeding the HFD,but H.h infection did not significantly alter the colon tissue structure.The results of Sirius red staining of liver tissue sections showed that compared with HFD and H.h groups,the accumulation of liver collagen was increased and the level of fibrosis was up-regulated in HFD+H.h group.The results of fluorescence quantitative PCR and immunohistochemistry showed that the expression levels of TGF-β,Collagen I and α-SMA were increased in HFD+H.h group compared with HFD and H.h group.We speculate that H.h infection may promote the progression of hepatitis during the course of NAFLD by activating the NF-κB pathway.and that we also speculate H.h infection promotes the activation of hepatic stellate cells and the expression of large amounts of TGF-β and other fibrotic effector proteins to promote the progression of NAFLD-associated liver fibrosis.3.H.h infection regulates liver lipid metabolismIn order to investigate the effect of H.h on liver lipid metabolism during the progression of NAFLD,the liver of mice in each group was detected by oil red staining,immunohistochemistry and RT-PCR.The results showed that compared with the HFD group,the liver lipid accumulation in the HFD+H.h group was increased more significantly after 8-16 weeks of HFD,while the lipid accumulation was decreased at 20 weeks.The mRNA expression levels of SREBP-lc,SCD-1 and Fas were increased in liver at 8-16 weeks,while the expression levels of these genes were down-regulated at 20 weeks.Interestingly,at 20 weeks,the expression of FXR protein related to bile acid metabolism and fat metabolism was significantly increased in the liver of the HFD+H.h group,while it was almost not expressed in the control group or the HFD group at this time.These results suggest that H.h infection induces high expression of inflammatory factors such as TNF-α,which ultimately promotes lipid synthesis and accumulation,but FXR was activated to inhibit lipid synthesis at late stage.In this paper,the NAFLD model established by H.h combined with a HFD showed early NASH symptoms at 12 weeks after infection,which could better simulate the progression of NAFLD.In addition,we found that H.h infection caused abnormal activation of NF-κB protein in the liver,which may promote inflammatory progression in this model and ultimately exacerbate TGF-β-mediated liver fibrosis.In terms of lipid metabolism,the proinflammatory effect of H.h in the early stage of infection led to a large expression of TNF-α and stimulated liver cells to transcripte more SREBP-lc to promote lipid accumulation.However,the increased expression of FXR in liver in the late stage may reduce liver lipid accumulation by inhibiting bile acid synthesis.