Institute of Cardiovascular Research, Key Laboratory for Atherosclerology of Hunan Province, Life Science Research Center, University of South China, Hengyang, China.
Acta Biochim Biophys Sin (Shanghai). 2012 Feb;44(2):119-28. doi: 10.1093/abbs/gmr119. Epub 2012 Jan 9.
The Niemann-Pick type C1 (NPC1) is located mainly in the membranes of the late endosome/lysosome and controls the intracellular cholesterol trafficking from the late endosome/lysosome to the plasma membrane. It has been reported that oxidized low-density lipoprotein (oxLDL) can up-regulate NPC1 expression. However, the detailed mechanisms are not fully understood. In this study, we investigated the effect of oxLDL stimulation on NPC1 expression in THP-1 macrophages. Our results showed that oxLDL up-regulated NPC1 expression at both mRNA and protein levels in a dose-dependent and time-dependent manner. In addition, oxLDL also induced the phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2). Treatment with oxLDL significantly increased cyclooxygenase-2 (COX-2) mRNA and protein expression in the macrophages, and these increases were suppressed by the ERK1/2 inhibitor PD98059 or ERK1/2 small interfering RNA (siRNA) treatment. OxLDL up-regulated the expression of peroxisome proliferator-activated receptor α (PPARα) at the mRNA and protein levels, which could be abolished by COX-2 siRNA or COX-2 inhibitor NS398 treatment in these macrophages. OxLDL dramatically elevated cellular cholesterol efflux, which was abrogated by inhibiting ERK1/2 and/or COX-2. In addition, oxLDL-induced NPC1 expression and cellular cholesterol efflux were reversed by PPARα siRNA or GW6471, an antagonist of PPARα. Taken together, these results provide the evidence that oxLDL can up-regulate the expression of the NPC1 through ERK1/2/COX-2/PPARα-signaling pathway in macrophages.
尼曼-匹克 C1 型（NPC1）主要位于晚期内体/溶酶体的膜中，并控制胆固醇从晚期内体/溶酶体向质膜的细胞内转运。据报道，氧化型低密度脂蛋白（oxLDL）可以上调 NPC1 的表达。然而，其详细机制尚不完全清楚。在本研究中，我们研究了 oxLDL 刺激对 THP-1 巨噬细胞中 NPC1 表达的影响。结果表明，oxLDL 以剂量和时间依赖的方式上调 NPC1 在 mRNA 和蛋白水平的表达。此外，oxLDL 还诱导细胞外信号调节激酶 1/2（ERK1/2）磷酸化。oxLDL 处理明显增加巨噬细胞中环氧化酶-2（COX-2）mRNA 和蛋白表达，而 ERK1/2 抑制剂 PD98059 或 ERK1/2 小干扰 RNA（siRNA）处理则抑制了这些增加。oxLDL 上调了过氧化物酶体增殖物激活受体 α（PPARα）在 mRNA 和蛋白水平的表达，而 COX-2 siRNA 或 COX-2 抑制剂 NS398 处理则可以消除这些巨噬细胞中的表达。oxLDL 显著增加了细胞胆固醇流出，而抑制 ERK1/2 和/或 COX-2 则可以阻断该作用。此外，oxLDL 诱导的 NPC1 表达和细胞胆固醇流出可通过 PPARα siRNA 或 PPARα 拮抗剂 GW6471 逆转。综上所述，这些结果提供了证据表明 oxLDL 可以通过 ERK1/2/COX-2/PPARα 信号通路上调巨噬细胞中 NPC1 的表达。
