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Role of angiopoietin-like 3 (ANGPTL3) in regulating plasma level of low-density lipoprotein cholesterol

      Highlights

      • Angptl3 silencing induced combined hypolipidemia in WT and obese mice.
      • Angptl3 silencing reduced plasma TG and LDL-C, but not HDL-C, in hCETP/ApoB-100 transgenic mice.
      • The low LDL-C from Angptl3 silencing is linked to LDLR in Apobec1−/−/ApoB-100 transgenic mice lacking LDLR.
      • ANGPTL3 deficiency in human hepatoma cells reduced nascent ApoB-100 secretion and increased LDL/VLDL uptake.
      • Reduced secretion and increased uptake of ApoB-containing lipoproteins contribute to the low LDL-C caused by ANGPTL3 deficiency.

      Abstract

      Background and aims

      Angiopoietin-like 3 (ANGPTL3) has emerged as a key regulator of lipoprotein metabolism in humans. Homozygous loss of ANGPTL3 function causes familial combined hypolipidemia characterized by low plasma levels of triglycerides (TG), high-density lipoprotein cholesterol (HDL-C), and low-density lipoprotein cholesterol (LDL-C). While known effects of ANGPTL3 in inhibiting lipoprotein lipase and endothelial lipase contribute to the low TG and HDL-C, respectively, the basis of low LDL-C remains unclear. Our aim was to explore the role of ANGPTL3 in modulating plasma LDL-C.

      Methods

      We performed RNAi-mediated gene silencing of ANGPTL3 in five mouse models and in human hepatoma cells. We validated results by deleting ANGPTL3 gene using the CRISPR/Cas9 genome editing system.

      Results

      RNAi-mediated Angptl3 silencing in mouse livers resulted in very low TG, HDL-C and LDL-C, a pattern similar to the human phenotype. The effect was observed in wild-type and obese mice, while in hCETP/apolipoprotein (Apo) B-100 double transgenic mice, the silencing decreased LDL-C and TG, but not HDL-C. In a humanized mouse model (Apobec1−/− carrying human ApoB-100 transgene) deficient in the LDL receptor (LDLR), Angptl3 silencing had minimum effect on LDL-C, suggesting the effect being linked to LDLR. This observation is supported by an additive effect on LDL-C between ANGPTL3 and PCSK9 siRNAs. ANGPTL3 gene deletion induced cellular long-chain TG and ApoB-100 accumulation with elevated LDLR and LDLR-related protein (LRP) 1 expression. Consistent with this, ANGPTL3 deficiency by gene deletion or silencing reduced nascent ApoB-100 secretion and increased LDL/VLDL uptake.

      Conclusions

      Reduced secretion and increased uptake of ApoB-containing lipoproteins may contribute to the low LDL-C observed in mice and humans with genetic ANGPTL3 deficiency.

      Keywords

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