易成石和抗成石小鼠肝脏胆固醇代谢调节酶的基因表达特征

Characteristics of mRNA levels of hepatic cholesterol metabolism regulatory enzymes in genetically gallstone-susceptible and resistant mice

目的通过研究胆囊胆固醇结石易成石小鼠(C57L鼠)和抗成石小鼠(AKR鼠)肝脏胆固醇代谢调节酶的基因表达差异来探讨胆囊胆固醇结石形成的分子机制。方法用致石饲料(含15%脂肪、1.25%胆固醇和0.5%胆酸)喂养C57L和AKR鼠4周,分别在喂养前、后检查其肝脏重量、肝脏胆固醇含量和胆囊内结石形成情况,并用RT PCR法分析参与肝脏胆固醇代谢调节的肝脏3羟基3甲基戊二酰辅酶A还原酶(HMG CoAR)、胆固醇7α羟化酶(C7H)、乙酰基辅酶A胆固醇酰基转移酶(ACAT)和低密度脂蛋白受体(LDLR)的mRNA含量。结果致石饲料喂养前、后AKR鼠肝脏胆固醇含量均明显高于C57L鼠,致石饲料诱导4周后C57L鼠胆囊内有胆固醇结石形成,而AKR鼠则无。致石饲料诱导前AKR鼠肝脏HMG CoAR的mRNA表达水平明显高于C57L鼠,而ACAT、LDLR、C7H的mRNA水平在两组小鼠间差异无统计学意义(P>0.05)。致石饲料诱导后,AKR鼠肝脏HMG CoAR和C7H的mRNA水平分别下降31%和30%,但C57L鼠无明显改变,其中AKR和C57L鼠肝脏LDLR的mRNA表达水平则分别提高14%和41%。结论致石饲料作为一种环境因素能揭示C57L和AKR鼠肝脏胆固醇代谢调节酶的基因表达特征。

Objective To investigate the difference of mRNA levels of hepatic cholesterol ~metabolism regulatory enzymes between genetically gallstone-susceptible (C57L) and resistant (AKR) mice for exploring the molecular mechanism of biliary cholesterol hypersecretion and cholesterol gallstone ~formation. Methods The inbred C57L and AKR mice were fed with a lithogenic diet containing 15% fat, ~1.25% cholesterol and 0.5% cholic acid for four weeks. Before and after the lithogenic diet, their liver weight, hepatic cholesterol content and gallstone formation in gallbladder were examined, and ~mRNA levels of hepatic 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCoAR), cholesterol 7α-hydroxylase ^(C7H) , acyl-CoA: cholesterol acyltransferase (ACAT) and low density lipoprotein receptor (LDLR) were analyzed by RT-PCR. Results Before or after feeding the lithogenic diet, hepatic cholesterol content in AKR mice displayed markedly higher than that in C57L mice. Challenged with the lithogenic diet for four weeks, cholesterol gallstones were formed in C57L mice but not in AKR mice. Basal hepatic HMGCoAR mRNA level was significantly higher in gallstone-resistant AKR mice compared with the C57L gallstone-susceptible strain. Basal mRNA levels of ACAT, LDLR and C7H did not differ significantly among the mouse strains studied. In response to the lithogenic diet, expression levels of HMGCoAR and C7H mRNAs significantly decreased by 31% and 30%, respectively, in AKR mice, but unchanged in C57L mice, the LDLR ~mRNA levels increased slightly (14%) in AKR mice, and a 41% elevation was present in C57L mice. ~Conclusions The lithogenic diet as an environmental challenge unmasked phenotypes of mRNA expression of hepatic cholesterol metabolism regulatory enzymes of C57L and AKR mice. After feeding the lithogenic diet, failure to sufficiently down-regulate HMGCoAR expression and significant increase of LDLR level in C57L mice may play a role in biliary cholesterol hypersecretion and cholesterol gallstone formation.