Genome-wide RNAi screen reveals ALK1 mediates LDL uptake and transcytosis in endothelial cells

Nat Commun. 2016 Nov 21;7:13516. doi: 10.1038/ncomms13516.

Abstract

In humans and animals lacking functional LDL receptor (LDLR), LDL from plasma still readily traverses the endothelium. To identify the pathways of LDL uptake, a genome-wide RNAi screen was performed in endothelial cells and cross-referenced with GWAS-data sets. Here we show that the activin-like kinase 1 (ALK1) mediates LDL uptake into endothelial cells. ALK1 binds LDL with lower affinity than LDLR and saturates only at hypercholesterolemic concentrations. ALK1 mediates uptake of LDL into endothelial cells via an unusual endocytic pathway that diverts the ligand from lysosomal degradation and promotes LDL transcytosis. The endothelium-specific genetic ablation of Alk1 in Ldlr-KO animals leads to less LDL uptake into the aortic endothelium, showing its physiological role in endothelial lipoprotein metabolism. In summary, identification of pathways mediating LDLR-independent uptake of LDL may provide unique opportunities to block the initiation of LDL accumulation in the vessel wall or augment hepatic LDLR-dependent clearance of LDL.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Activin Receptors, Type I / genetics
  • Activin Receptors, Type I / metabolism
  • Activin Receptors, Type II / genetics
  • Activin Receptors, Type II / metabolism*
  • Animals
  • Apolipoproteins B / genetics
  • Apolipoproteins B / metabolism
  • Biological Transport
  • Cells, Cultured
  • Cholesterol, LDL / genetics
  • Cholesterol, LDL / metabolism*
  • Cloning, Molecular
  • Endothelial Cells / metabolism*
  • Gene Knockdown Techniques
  • Genome-Wide Association Study
  • Humans
  • Male
  • Mice
  • RNA Interference

Substances

  • Apolipoproteins B
  • Cholesterol, LDL
  • ACVRL1 protein, human
  • Activin Receptors, Type I
  • Activin Receptors, Type II
  • Acvrl1 protein, mouse