敲除清道夫受体AⅠ/Ⅱ基因对小鼠氧化型低密度脂蛋白组织分布和清除的影响

The Impact of Scavenger Receptor Class A Type Ⅰ/Ⅱ on Distribution and Clearance of Oxidative Low Density Lipopprotein in Mice

目的应用清道夫受体AⅠ/Ⅱ基因敲除小鼠及其野生对照小鼠,观察在正常饮食和高脂饮食情况下,清道夫受体AⅠ/Ⅱ对小鼠氧化型低密度脂蛋白分布和清除的影响。方法用Southernblot和免疫组织化学法鉴定实验小鼠清道夫受体AⅠ/ⅡDNA和蛋白的表达。将2月龄雄性野生对照小鼠和清道夫受体AⅠ/Ⅱ基因敲除小鼠各50只随机分为4组:清道夫受体AⅠ/Ⅱ基因敲除小鼠和野生对照小鼠各38只,给予高脂饮食(常规饲料加15%油脂和1.25%胆固醇)8周,观察实验前后血清总胆固醇、甘油三酯、高密度脂蛋白、低密度脂蛋白、载脂蛋白A、载脂蛋白B及血肌酐等水平的变化;清道夫受体AⅠ/Ⅱ基因敲除小鼠和野生对照小鼠各12只,高脂饮食3天后从尾静脉注射125I标记的氧化型低密度脂蛋白,于10min、1、3和6h获取血液、心脏、肝脏、脾脏、肺脏、肾脏、胃、肠、脂肪和肌肉等标本,分别称取质量并用γ射线计数仪检测其放射性强度。结果正常饮食下,清道夫受体AⅠ/Ⅱ基因敲除小鼠和野生对照小鼠血脂水平接近;高脂饮食下两组小鼠血脂水平均明显升高,但清道夫受体AⅠ/Ⅱ基因敲除小鼠血浆低密度脂蛋白水平明显高于野生对照小鼠;清道夫受体AⅠ/Ⅱ基因敲除小鼠在注射125I标记的氧化型低密度脂蛋白10min后的清除率明显低于野生对照小鼠,注射125I标记的氧化型低密度脂蛋白6h后其主要分布于肝脏,在心脏和肾脏也有高分布;高脂饮食条件下,敲除清道夫受体AⅠ/Ⅱ基因对经尾静脉注射的125I标记的氧化型低密度脂蛋白在体内的分布不同于野生对照小鼠。结论敲除清道夫受体AⅠ/Ⅱ后,小鼠脂质代谢的调节能力受到损伤,机体对血液中氧化型低密度脂蛋白的清除能力下降,组织细胞对氧化型低密度脂蛋白的摄取减少,血低密度脂蛋白水平升高。

Aim To investigate the impact of scavenger receptor class A type Ⅰ/Ⅱ（SRAⅠ/Ⅱ） on the clearance and distribution of oxidized low density lipoprotein （LDL） of mouse under the condition of normal diet and high lipid diet. Methods Each one of SRAⅠ/Ⅱ geneknockout （SR^-/- ） mice and wild control （SR^＋/＋） micewas randomly picked from each strip to be Mentified by Southern blot and immunohistochemistry. And then, 50 SR^-/- and 50 SR^＋/＋ 2-month-old male, weighting about 25 g mice were divided into 4 groups： 38 SR^-/- mice and 38 SR^＋/＋ mice were fed with high lipid diet （normal food with 15% fatty and 1.25% cholesterol） for 8 weeks. The serum levels of creafinine （Cr）, triglyceride （TG）, total cholesterol （TC）, LDL, high density lipoprotein （HDL）, apolipoprotein A （apo A）, apolipoprotein B （apo B） and body weight （BW） were measured at 8 weeks. 12 SR^-/- mice and 12 SR^＋/＋ mice were intravenous injected ^125 I labeled ox-LDL （^125I-ox-LDL） through their tail veins after 3 days high lipid diet. 10 min and 3 h after injection, blood samples were harvested from 6 mice by cutting the tail, 1 h and 6 h after injection, blood samples were harvested again respectively from eye veins. After humanly killed, the heart, liver, spleen, lung, kidney, stomach, intestines, fat as well as muscle samples were harvested and carefully weighted after circulation was perfused with 5 mL PBS at 4℃. The radiation activity was determined in a multiple-channel gamma counter. Results No significant difference of serum levels of lipid were found between SR^-/- and SR^＋/＋ mice fed withND, however the serum levels of TC, TG, LDL, HDL increased drastically after HD for 8 weeks. Significant higher serum level of LDL was found in SR^-/- mice compared with SR^＋/＋. mice. The clearance rate of T-oxLDL injected through tail vein was significandy delayed in SR^-/- mice compared to that of SR^＋/＋ mice at 10 min after injection, though no significant difference of the distribution of T-oxLDL was found between SR^-/- and SR^＋/＋ mice all the time. More than half amount of injected radioactivity was mainly located in liver, the relative high radioactivity also showed in heart and kidney. Conclusions The results demonstrated that the lipid metabolism is disturbed after SR A Ⅰ/Ⅱ gene was knocked out in mice, manifested by a decreasing of clearance rate of ox-LDL and an accumulation of LDL in circulation.