Inflammatory Stress Exacerbates CCl₄-induced Hepatic Lipid Accumulation And The Molecular Mechanism

PART ONE: LIPID ACCUMULATION ISINDUCED BY CARBON TETRACHLORIDE AND THEMOLECULAR MECHANISMObjective To investigate if carbon tetrachloride disrupte hepaticcholesterol import and lead to cholesterol accumulation in C57BL/6J miceand the molecular mechanism.Methods Male C57BL/6J mice of6~8weeks were randomlydivided into control group (n=6) and CCl4group (n=6).The control groupand CCl4group were respectively given normal saline and CCl4subcutaneous injection for2weeks.After2weeks, The cholesterol levels ofliver tissue were measured by chemical enzymatic assay. Lipidaccumulation in the liver was observed by oil red O staining.The mRNAexpression of LDLr、SCAP and SREBP-2were measured by real-time PCR,and the protein expression of LDLr、SCAP and SREBP-2were analyzedby western blot. Result The hepatic lipid levels in CCl4group were significantlyhigher than those in the control group. Increased lipid accumulation asdemonstrated by Oil red O staining was observed in CCl4group.The mRNAand protein expression of LDLr、SREBP-2and SCAP in CCl4group werehigher than those in control group.Conclusion CCl4may exacerbate lipid accumulation via up-regulating the expressions of LDLr, SREBP-2and SCAP in the fatty liverof C57BL/6J mice. PART TWO:INFLAMMATION EXACERBATES THEHEPATIC LIPID ACCUMULATION AND CHANGES OFCHOLESTEROL ACCUMULATION RELATIVE INDEXObjective To investigate if inflammatory stress promotes the simplesteatosis caused by CCl4to further lipid accumulation and the molecularmechanism.Methods6~8weeks of male C57BL/6J mice were randomlyassigned to control group (n=6) and inflammation group (n=6). Thecontrol group and inflammation group were respectively given normalsaline and casein subcutaneous injection for16weeks after treatment of Carbon tetrachloride for2weeks.After18weeks, serum and liver tissue ofmice were obtained for study.The liver index was measured to study thedamage to the liver,Serum levels of lipid were detected by enzymaticassay.Inflammatory cytokines,such as serum amyloid A(SAA)、interleukin-6(IL-6) and tumor necrosis factor-α(TNF-α) weredetermined by ELISA. Lipid accumulation in the liver was evaluated byhematoxylin-eosin staining and oil red O staining,the lipid levels of livertissue were measured by chemical enzymatic assay. mRNA and proteinexpressions of LDLr, SREBP-2, SCAP, SREBP-1and HMGCR wereanalyzed by real-time PCR,immunohistochemistry staining and Westernblot respectively.Result Liver indexes of mice in inflammation group were significantlyhigher compare with those in control mice.The serum SAA、IL-6andTNF-α levels in inflammation group were significantly higher compare withthose in the control group(P＜0.05).Levels of HDL-C,LDL-C and TC weresignificantly lower in inflammation group than control group(P＜0.05), Thehepatic lipid levels in inflammation group were significantly higher thanthose in the control group,a lot of lipid accumulation were observed in liverof mice in inflammation group by HE and oil red O staining, mRNA andprotein expressions of LDLr, SREBP-2、 SCAP、SREBP-1and HMGCRin inflammation group increased significantly compared with those incontrol mice(P＜0.05). Conclusion Inflammatory stress probably promotes cholesterolaccumulation in fatty liver induced by CCl4via up-regulating theexpressions of LDLr、SREBP-2、SCAP、SREBP-1and HMGCR, and thismay contribute to the abnormal lipid accumulation in liver.