title: The lysosomal transfer of LDL/cholesterol from macrophages into vascular smooth muscle cells induces their phenotypic alteration.
abstract: OBJECTIVE
  Macrophages (MPs) and vascular smooth muscle cells (VSMCs) closely interact within the growing atherosclerotic plaque. An in vitro co-culture model was established to study how MPs modulate VSMC behaviour.
  
  
  RESULTS
  MPs were exposed to fluorescence-labelled-acetylated LDL (FL-acLDL) prior to co-culture with VSMCs. Fluorescence microscopy visualized first transport of FL-acLDL within 6 h after co-culture implementation. When MPs had been fed with FL-acLDL in complex with fluorescence-labelled cholesterol (FL-Chol), these complexes were also transferred during co-culture and resulted in cholesterol positive lipid droplet formation in VSMCs. When infected with a virus coding for a fusion protein of Rab5a and fluorescent protein reporter (FP) to mark early endosomes, no co-localization between Rab5a-FP and the transported FL-acLDL within VSMCs was detected implying a mechanism independent of phagocytosis. Next, expression of lysosome-associated membrane glycoprotein 1 (LAMP1)-FP, marking all lysosomes in VSMCs, revealed that the FL-acLDL was located in non-acidic lysosomes. MPs infected with virus encoding for LAMP1-FP prior to co-culture demonstrated that intact fluorescence-marked lysosomes were transported into the VSMC, instead. Xenogenic cell composition (rat VSMC, human MP) and subsequent quantitative RT-PCR with rat-specific primers rendered induction of genes typical for MPs and down-regulation of the cholesterol sensitive HMG-CoA reductase.
  
  
  CONCLUSIONS
  Our results demonstrate that acLDL/cholesterol-loaded lysosomes are transported from MPs into VSMCs in vitro. Lysosomal transfer results in a phenotypic alteration of the VSMC towards a foam cell-like cell. This way VSMCs may lose their plaque stabilizing properties and rather contribute to plaque destabilization and rupture.
authors.affiliation: Internal Medicine/Cardiology, Angiology and Pneumology,  Magdeburg University, Leipziger Straße 44, 39120 Magdeburg,  Germany.
authors.forename: Sönke
authors.initials: S
authors.lastname: Weinert
authors.forename: David M
authors.initials: DM
authors.lastname: Poitz
authors.forename: Susanne
authors.initials: S
authors.lastname: Auffermann-Gretzinger
authors.forename: Lars
authors.initials: L
authors.lastname: Eger
authors.forename: Joerg
authors.initials: J
authors.lastname: Herold
authors.forename: Senad
authors.initials: S
authors.lastname: Medunjanin
authors.forename: Alexander
authors.initials: A
authors.lastname: Schmeisser
authors.forename: Ruth H
authors.initials: RH
authors.lastname: Strasser
authors.forename: Ruediger C
authors.initials: RC
authors.lastname: Braun-Dullaeus
mesh_terms: D000818:Animals; D001012:Aorta, Abdominal / Q000166:cytology / Q000378:metabolism; D002450:Cell Communication / Q000502:physiology; D002478:Cells, Cultured; D002784:Cholesterol / Q000378:metabolism*; D008078:Cholesterol, LDL / Q000378:metabolism; D018920:Coculture Techniques; D006801:Humans; D006903:Hydroxymethylglutaryl CoA Reductases / Q000378:metabolism; D008077:Lipoproteins, LDL / Q000378:metabolism*; D052118:Lysosomal-Associated Membrane Protein 1 / Q000378:metabolism; D008247:Lysosomes / Q000378:metabolism*; D008264:Macrophages / Q000166:cytology / Q000378:metabolism*; D008856:Microscopy, Fluorescence; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000378:metabolism*; D010641:Phenotype; D051381:Rats; D017208:Rats, Wistar
chemical_list: D008078:Cholesterol, LDL; D008077:Lipoproteins, LDL; D052118:Lysosomal-Associated Membrane Protein 1; C032629:acetyl-LDL; D002784:Cholesterol; D006903:Hydroxymethylglutaryl CoA Reductases