title: Concentration-Dependent Diversifcation Effects of Free Cholesterol Loading on Macrophage Viability and Polarization.
abstract: OBJECTIVE
  The accumulation of free cholesterol in atherosclerotic lesions has been well documented in both animals and humans. In studying the relevance of free cholesterol buildup in atherosclerosis, contradictory results have been generated, indicating that free cholesterol produces both pro- and anti-atherosclerosis effects in macrophages. This inconsistency might stem from the examination of only select concentrations of free cholesterol. In the present study, we sought to investigate the implication of excess free cholesterol loading in the pathophysiology of atherosclerosis across a broad concentration range from (in µg/ml) 0 to 60.
  
  
  METHODS
  Macrophage viability was determined by measuring formazan formation and flow cytometry viable cell counting. The polarization of M1 and M2 macrophages was differentiated by FACS (Fluorescence-Activated Cell Sorting) assay. The secretion of IL-1β in macrophage culture medium was measured by ELISA kit. Macrophage apoptosis was detected by flow cytometry using a TUNEL kit.
  
  
  RESULTS
  Macrophage viability was increased at the treatment of lower concentrations of free cholesterol from (in µg/ml) 0 to 20, but gradually decreased at higher concentrations from 20 to 60. Lower free cholesterol loading induced anti-inflammatory M2 macrophage polarization. The activation of the PPARx03B3; (Peroxisome Proliferator-Activated Receptor gamma) nuclear factor underscored the stimulation of this M2 phenotype. Nevertheless, higher levels of free cholesterol resulted in pro-inflammatory M1 activation. Moreover, with the application of higher free cholesterol concentrations, macrophage apoptosis and secretion of the inflammatory cytokine IL-1β increased significantly.
  
  
  CONCLUSIONS
  These results for the first time demonstrate that free cholesterol could render concentration-dependent diversification effects on macrophage viability, polarization, apoptosis and inflammatory cytokine secretions, thereby reconciling the pros and cons of free cholesterol buildup in macrophages to the pathophysiology of atherosclerosis.
authors: Department of Pharmacology & Toxicology, Medical College of Virginia, Virginia Commonwealth University, VA 23298.
authors: Xiaoyang
authors: X
authors: Xu
authors: Department of Pharmacology & Toxicology, Medical College of Virginia, Virginia Commonwealth University, VA 23298.
authors: Aolin
authors: A
authors: Zhang
authors: Department of Pharmacology & Toxicology, Medical College of Virginia, Virginia Commonwealth University, VA 23298.
authors: Ningjun
authors: N
authors: Li
authors: Department of Pharmacology & Toxicology, Medical College of Virginia, Virginia Commonwealth University, VA 23298.
authors: Pin-Lan
authors: PL
authors: Li
authors: Department of Pharmacology & Toxicology, Medical College of Virginia, Virginia Commonwealth University, VA 23298.
authors: Fan
authors: F
authors: Zhang
mesh_terms: D000818:Animals; D017209:Apoptosis; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D002784:Cholesterol / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D053583:Interleukin-1beta / Q000378:metabolism*; D008264:Macrophages / Q000166:cytology* / Q000187:drug effects / Q000276:immunology; D051379:Mice; D047495:PPAR gamma / Q000378:metabolism
chemical_list: C587672:IL1B protein, mouse; D053583:Interleukin-1beta; D047495:PPAR gamma; D002784:Cholesterol