Li Jing, Li Hang, Wen Yu-bing, Li Xue-wang
Division of Nephrology, Department of Internal Medicine, Peking Union Medical College Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, People's Republic of China.
Nephron Physiol. 2008;110(1):p1-10. doi: 10.1159/000151272. Epub 2008 Aug 13.
Very-low-density lipoprotein (VLDL) in vitro can induce foam cell formation in human mesangial cells. Lipoprotein lipase (LPL) expressed in the arterial wall plays a key role in atherogenesis by actions of enzymolysis and 'molecular bridge', and, thereby, leads to the formation of lipid-loaded foam cells. It is known that LPL is expressed by glomerular mesangial cells. This study was designed to investigate if LPL plays a role in VLDL-induced lipid accumulation in human mesangial cells and its underlying mechanism.
Human wild-type LPL (hLPLwt), catalytically inactive LPL (hLPL194) or control alkaline phosphatase (hAP) were expressed in human mesangial cell line (HMCLs) via adenoviral vectors. Orlistat (tetrahydrolipstatin), a specific inhibitor of the lipoidolytic activity of endogenous LPL, and heparinase, which degrades cell-surface heparan sulfate proteoglycans, were also used to estimate the role of either the enzymolysis or 'molecular bridge' actions of LPL in the uptake of VLDL. Anti-low-density lipoprotein receptor (LDLr) antibody and anti-LDL receptor-related protein antibody were used to evaluate the effect of lipoprotein receptors on VLDL-induced lipid accumulation in HMCLs. Cellular lipid deposition was visualized by Oil Red O staining and analyzed quantitatively by standard enzymatic procedures. LPL protein expression and activity were measured by Western blot and a chemical analysis, respectively.
VLDL induced triglyceride accumulation in HMCLs in a time- and dose-dependent manner. Compared with Ad-hAP transfected HMCLs, cellular triglyceride content increased 4.55-fold (p < 0.05) in Ad-hLPLwt-transfected HMCLs and 1.52-fold (p < 0.05) in Ad-hLPL194-transfected HMCLs. Triglyceride accumulation in response to VLDL was mostly blocked by orlistat. Pretreatment of the cells with heparinase slightly reduced cellular triglyceride accumulation in the present of high concentrations of VLDL. The blockade of some lipoprotein receptors, such as LDLr, did not significantly reduce cellular triglyceride accumulation. LPL expression was upregulated by VLDL.
VLDL-induced triglyceride accumulation in human mesangial cells is mainly mediated by LPL, and the enzymolysis action of LPL could be a major factor in this process. These results suggest that LPL may be an important factor participating in the initiation and progression of VLDL-mediated lipid renal injury.
极低密度脂蛋白（VLDL）在体外可诱导人系膜细胞形成泡沫细胞。动脉壁中表达的脂蛋白脂肪酶（LPL）通过酶解作用和“分子桥”作用在动脉粥样硬化形成中起关键作用，从而导致脂质负载的泡沫细胞形成。已知LPL由肾小球系膜细胞表达。本研究旨在探讨LPL是否在VLDL诱导的人系膜细胞脂质蓄积中起作用及其潜在机制。
通过腺病毒载体在人系膜细胞系（HMCLs）中表达人野生型LPL（hLPLwt）、催化失活的LPL（hLPL194）或对照碱性磷酸酶（hAP）。还使用奥利司他（四氢脂抑素），一种内源性LPL脂解活性的特异性抑制剂，以及肝素酶，其可降解细胞表面硫酸乙酰肝素蛋白聚糖，来评估LPL的酶解作用或“分子桥”作用在VLDL摄取中的作用。抗低密度脂蛋白受体（LDLr）抗体和抗低密度脂蛋白受体相关蛋白抗体用于评估脂蛋白受体对VLDL诱导的HMCLs脂质蓄积的影响。通过油红O染色观察细胞脂质沉积，并通过标准酶法进行定量分析。分别通过蛋白质免疫印迹和化学分析测量LPL蛋白表达和活性。
VLDL以时间和剂量依赖性方式诱导HMCLs中甘油三酯蓄积。与Ad-hAP转染的HMCLs相比，Ad-hLPLwt转染的HMCLs中细胞甘油三酯含量增加4.55倍（p<0.05），Ad-hLPL194转染的HMCLs中增加1.52倍（p<0.05）。奥利司他可大部分阻断VLDL诱导的甘油三酯蓄积。在高浓度VLDL存在下，用肝素酶预处理细胞可轻微降低细胞甘油三酯蓄积。阻断某些脂蛋白受体，如LDLr，并未显著降低细胞甘油三酯蓄积。VLDL可上调LPL表达。
VLDL诱导的人系膜细胞甘油三酯蓄积主要由LPL介导，且LPL的酶解作用可能是此过程中的主要因素。这些结果表明，LPL可能是参与VLDL介导的脂质肾损伤起始和进展的重要因素。
