LXR激活对大鼠原代培养海马神经元胆固醇代谢关键酶基因表达的影响

EFFECTS OF ACTIVATED LIVER X RECEPTOR ON GENE EXPRESSIONS OF KEY ENZYMES IN CHOLESTEROL HOMESTASIS IN PRIMARY HIPPOCAMPAL NEURONAL CULTURE OF RATS

为了探讨肝X受体(LXR)激活对海马神经元胆固醇代谢关键酶基因表达和胆固醇外流的影响,本研究取当天新生大鼠海马神经元行体外培养7d,随机分为TO组(培养液含2.0μmol/L的TO901317)和正常对照组(CON),继续培养48h。用胆固醇氧化酶-比色法检测TO组胆固醇的排出量;应用RT-PCR方法检测两组海马神经元ATP结合盒转运体A1(ABCA1)、HMG-CoA还原酶(HMGR)、胆固醇24-羟化酶(CYP46)、P450侧链裂解酶(P450scc)、固醇生成急性调节蛋白(StAR)和酰基辅酶A-胆固醇酰基转移酶1(ACAT1)等胆固醇代谢关键酶基因的mRNA的表达。结果显示:TO组mRNA表达上调的酶有HMGR、P450scc和StAR(P<0.01);表达下调的酶是ACAT1(P<0.01);表达不受影响的酶是CYP46。上述结果表明LXR激活、促进细胞内胆固醇外流时,海马神经元可能通过协调胆固醇代谢关键酶基因的表达,增加胆固醇的合成和向神经甾体的转化,抑制胆固醇的储备,而不影响胆固醇排出血脑屏障,从而维持细胞内胆固醇的动态平衡,保证神经元的正常生理功能。

To investigate the effect of activated liver X receptor （LXR） on the expression of genes related to cholesterol homestasis and cholesteral efflux, the hippocampal neurons were isolated from new-born rats in the present study. After 7-day-cuhure, the neuronal cells were treated for 48 h in culture media containing 2.0 μmol/L of TO901317 （TO group） or the normal control group. The incubation with TO901317 was detected to cholesterol efflux by enzymatic-colorimetric assay. The mRNA expressions of ATP binding cassette transporter AI （ABCAI）, 3-hydroxy-3-methylglutaryl coenzyme A reductase （HMGR）, cholesterol 24-hydroxylase （CYP46）, P450 side chain cleavage （P450scc）, Steroidogenic acute regulatory protein （STAR） and acyl-CoA： cholesterol acyhransferase 1 （ACATI） were measured by RT-PCR both on TO group and control group. The results showed that TO group significantly increased the mRNA expression of HMGR, P450scc and StAR （P 〈0.01 ） , but reduced ACATI mRNA expression （ P 〈 0.01 ） and caused no change in the expression of CYP46 mRNA. These results indicate that while cholesterol efflux caused by activation of LXR, the hippocampal neurons could modify the expression of a group of genes in cholesterol metabolism to maintain the cholesterol homeostasis by accelerating cholesterol biosynthesis and conversion to neurosteroid, inhibiting cholseterol ester synthesis, but does not influence the cholesterol expulsion from the blood brain barrier, and maintain the intracellular cholesterol balance and ensure the neuronal normal physiological functions.