From the Institut d'Investigacions Biomèdiques Sant Pau, Barcelona, Spain (L.C., D.S., A.G.-L., S.S.-S., N.R., A.R.-U., K.A.M.-L., M.T., J.J., V.P., A.P., J.L.S.-Q., F.B.-V., J.C.E.-G.).
CIBER de Diabetes y Enfermedades Metabólicas Asociadas, CIBERDEM, Madrid, Spain (L.C., D.S., N.P., J.J., A.P., J.L.S.-Q., L.M., F.B.-V., J.C.E.-G.).
Circ Res. 2020 Aug 28;127(6):778-792. doi: 10.1161/CIRCRESAHA.119.316424. Epub 2020 Jun 4.
The HDL (high-density lipoprotein)-mediated stimulation of cellular cholesterol efflux initiates macrophage-specific reverse cholesterol transport (m-RCT), which ends in the fecal excretion of macrophage-derived unesterified cholesterol (UC). Early studies established that LDL (low-density lipoprotein) particles could act as efficient intermediate acceptors of cellular-derived UC, thereby preventing the saturation of HDL particles and facilitating their cholesterol efflux capacity. However, the capacity of LDL to act as a plasma cholesterol reservoir and its potential impact in supporting the m-RCT pathway in vivo both remain unknown.
We investigated LDL contributions to the m-RCT pathway in hypercholesterolemic mice.
Macrophage cholesterol efflux induced in vitro by LDL added to the culture media either alone or together with HDL or ex vivo by plasma derived from subjects with familial hypercholesterolemia was assessed. In vivo, m-RCT was evaluated in mouse models of hypercholesterolemia that were naturally deficient in CETP (cholesteryl ester transfer protein) and fed a Western-type diet. LDL induced the efflux of radiolabeled UC from cultured macrophages, and, in the simultaneous presence of HDL, a rapid transfer of the radiolabeled UC from HDL to LDL occurred. However, LDL did not exert a synergistic effect on HDL cholesterol efflux capacity in the familial hypercholesterolemia plasma. The m-RCT rates of the LDLr (LDL receptor)-KO (knockout), LDLr-KO/APOB100, and PCSK9 (proprotein convertase subtilisin/kexin type 9)-overexpressing mice were all significantly reduced relative to the wild-type mice. In contrast, m-RCT remained unchanged in HAPOB100 Tg (human APOB100 transgenic) mice with fully functional LDLr, despite increased levels of plasma APO (apolipoprotein)-B-containing lipoproteins.
Hepatic LDLr plays a critical role in the flow of macrophage-derived UC to feces, while the plasma increase of APOB-containing lipoproteins is unable to stimulate m-RCT. The results indicate that, besides the major HDL-dependent m-RCT pathway via SR-BI (scavenger receptor class B type 1) to the liver, a CETP-independent m-RCT path exists, in which LDL mediates the transfer of cholesterol from macrophages to feces. Graphical Abstract: A graphical abstract is available for this article.
高密度脂蛋白（HDL）介导的细胞胆固醇外流刺激巨噬细胞特异性胆固醇逆向转运（m-RCT），最终导致巨噬细胞衍生的未酯化胆固醇（UC）从粪便中排出。早期研究表明，LDL（低密度脂蛋白）颗粒可以作为细胞来源的 UC 的有效中间接受体，从而防止 HDL 颗粒饱和并促进其胆固醇外流能力。然而，LDL 作为血浆胆固醇储库的能力及其在体内支持 m-RCT 途径的潜在影响仍然未知。
我们研究了 LDL 在高胆固醇血症小鼠的 m-RCT 途径中的作用。
评估了在体外培养的巨噬细胞中由 LDL 诱导的胆固醇外流，LDL 可单独或与 HDL 一起添加到培养基中，或由家族性高胆固醇血症患者的血浆在体内诱导。在天然缺乏胆固醇酯转移蛋白（CETP）并喂食西方饮食的高胆固醇血症小鼠模型中评估了 m-RCT。LDL 诱导培养的巨噬细胞中放射性标记的 UC 流出，并且在 HDL 同时存在的情况下，放射性标记的 UC 从 HDL 快速转移到 LDL。然而，LDL 并未在家族性高胆固醇血症患者的血浆中对 HDL 胆固醇外流能力产生协同作用。LDLr（LDL 受体）-KO（敲除）、LDLr-KO/APOB100 和 PCSK9（前蛋白转化酶枯草溶菌素/克那酶 9）过表达小鼠的 m-RCT 率均明显低于野生型小鼠。相比之下，尽管载脂蛋白 B 含量增加的脂蛋白水平升高，但在具有完全功能性 LDLr 的 HAPOB100Tg（人 APOB100 转基因）小鼠中，m-RCT 保持不变。
肝脏 LDLr 在巨噬细胞衍生的 UC 流向粪便的过程中起着关键作用，而载脂蛋白 B 含量增加的血浆不能刺激 m-RCT。结果表明，除了主要通过 SR-BI（清道夫受体 B 型 1）到肝脏的 HDL 依赖性 m-RCT 途径外，还存在一种 CETP 独立的 m-RCT 途径，其中 LDL 介导胆固醇从巨噬细胞转移到粪便。
