White Olivia, Aligabi Zahra, Burks Kendall H, Tang Jingrong, Stitziel Nathan O, Goldberg Ira J, Remaley Alan T, Lucero Diego
Lipoprotein Metabolism Laboratory. Translational Vascular Medicine Branch. National Heart, Lung, and Blood Institute. National Institutes of Health. Bethesda, MD, USA.
Center for Cardiovascular Research, Division of Cardiology, Department of Medicine, Washington University School of Medicine, Saint Louis, MO, USA.
bioRxiv. 2025 May 26:2025.03.02.640965. doi: 10.1101/2025.03.02.640965.
Current lipid-lowering drugs are relatively ineffective in reducing low-density lipoprotein (LDL) cholesterol in patients with Familial Hypercholesterolemia (FH) due to a dysfunctional LDL receptor (LDLR). However, LDL cholesterol reductions have been achieved in FH patients using angiopoietin-like 3 (ANGPTL3) inhibitors, which act through an uncharacterized, LDLR-independent pathway that requires endothelial lipase (EL). Here, we aim to investigate EL's direct role in LDLR-independent uptake of LDL in hepatocytes. Control and LDLR-KO HepG2 cells were transfected with an empty plasmid or a plasmid encoding the human LIPG gene, and the cellular uptake of fluorescent human LDL was measured by FACS. To test the contribution of heparan sulfate proteoglycans (HSPG), LDL uptake was assessed with and without the pre-incubation with heparin or a heparinase cocktail. Finally, tetrahydrolipstatin was used to inhibit EL enzymatic activity in uptake studies. Unsurprisingly, LDLR-KO HepG2 cells showed an 80% reduction in LDL uptake compared to controls (p<0.001). Remarkably, EL overexpression almost fully rescued LDL uptake in LDLR-KO cells (p<0.001), without effects in control cells. EL-mediated LDL uptake was completely blocked by heparinases and heparin in LDLR-KO cells, suggesting a crucial role of HSPG in EL-mediated LDL uptake. Notably, treatment with tetrahydrolipstatin reduced LDL uptake in EL-overexpressing LDLR-KO cells (p=0.0015). Our data reveals that EL facilitates the uptake of LDL in hepatocytes through an LDLR-independent, HSPG-dependent pathway that involves EL's enzymatic activity. This pathway provides an additional mechanism to explain the reduction of LDL cholesterol induced by ANGPTL3 inhibitors and represents a potential druggable target to treat FH.
由于低密度脂蛋白受体(LDLR)功能失调,目前的降脂药物在降低家族性高胆固醇血症(FH)患者的低密度脂蛋白(LDL)胆固醇方面相对无效。然而,使用血管生成素样3(ANGPTL3)抑制剂已使FH患者的LDL胆固醇降低,该抑制剂通过一种未知的、不依赖LDLR的途径发挥作用,该途径需要内皮脂肪酶(EL)。在这里,我们旨在研究EL在肝细胞中不依赖LDLR摄取LDL的直接作用。用空质粒或编码人LIPG基因的质粒转染对照和LDLR敲除的HepG2细胞,并通过流式细胞术测量荧光人LDL的细胞摄取。为了测试硫酸乙酰肝素蛋白聚糖(HSPG)的作用,在有或没有与肝素或肝素酶混合物预孵育的情况下评估LDL摄取。最后,在摄取研究中使用四氢脂抑素抑制EL酶活性。不出所料,与对照相比,LDLR敲除的HepG2细胞的LDL摄取减少了80%(p<0.001)。值得注意的是,EL过表达几乎完全挽救了LDLR敲除细胞中的LDL摄取(p<0.001),而对对照细胞没有影响。在LDLR敲除细胞中,肝素酶和肝素完全阻断了EL介导的LDL摄取,表明HSPG在EL介导的LDL摄取中起关键作用。值得注意的是,用四氢脂抑素处理可降低EL过表达的LDLR敲除细胞中的LDL摄取(p=0.0015)。我们的数据表明,EL通过一种不依赖LDLR、依赖HSPG的途径促进肝细胞对LDL的摄取,该途径涉及EL的酶活性。该途径提供了一种额外的机制来解释ANGPTL3抑制剂诱导的LDL胆固醇降低,并代表了治疗FH的潜在可药物化靶点。
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