title: Bioactive lysophospholipids generated by hepatic lipase degradation of lipoproteins lead to complement activation via the classical pathway.
abstract: OBJECTIVE
  We determined bioactivity of lysophospholipids generated by degradation of the low-density (LDL), very low-density (VLDL), and high-density (HDL) lipoproteins with hepatic lipase (HL), cholesterol esterase (CE), and lipoprotein-associated phospholipase A2 (Lp-PLA2).
  
  
  METHODS
  The LDL, VLDL, and HDL were treated with HL, CE, and Lp-PLA2 after immobilization on plates, and complement activation studies were performed with diluted human serum. Complement component 3 (C3) fixation, a marker for complement activation, was determined with a monoclonal anti-human C3d antibody. Enzymatic properties of HL and CE were assayed with triglyceride and phosphatidylcholine substrates for triglyceride hydrolase and phospholipase A activities. The ARPE-19 cells were used for viability studies.
  
  
  RESULTS
  The HL degradation of human lipoproteins LDL, VLDL, or HDL results in the formation of modified lipoproteins that can activate the complement pathway. Complement activation is dose- and time-dependent upon HL and occurs via the classical pathway. Enzymatic studies suggest that the phospholipase A1 activity of HL generates complement-activating lysophospholipids. C-reactive protein (CRP), known to simultaneously interact with complement C1 and complement factor H (CFH), further enhances HL-induced complement activation. The lysophospholipids, 1-Palmitoyl-sn-glycero-3-phosphocholine and 1-Oleoyl-sn-glycero-3-phosphocholine, can be directly cytotoxic to ARPE-19 cells.
  
  
  CONCLUSIONS
  The HL degradation of lipoproteins, known to accumulate in the outer retina and in drusen, can lead to the formation of bioactive lysophospholipids that can trigger complement activation and induce RPE cellular dysfunction. Given the known risk associations for age-related macular degeneration (AMD) with HL, CRP, and CFH, this study elucidates a possible damage pathway for age-related macular degeneration (AMD) in genetically predisposed individuals, that HL activity may lead to accumulation of lysophospholipids to initiate complement activation, with CFH dysregulation exacerbating the effects of this process.
authors.affiliation: Department of Ophthalmology, Columbia University, New York, New York, United States.
authors.forename: Wanchao
authors.initials: W
authors.lastname: Ma
authors.affiliation: Department of Ophthalmology, Columbia University, New York, New York, United States.
authors.forename: David C
authors.initials: DC
authors.lastname: Paik
authors.affiliation: Department of Ophthalmology, Columbia University, New York, New York, United States.
authors.forename: Gaetano R
authors.initials: GR
authors.lastname: Barile
mesh_terms: D002470:Cell Survival; D002478:Cells, Cultured; D003167:Complement Activation / Q000502:physiology*; D006801:Humans; D008049:Lipase / Q000378:metabolism*; D008074:Lipoproteins / Q000378:metabolism*; D008246:Lysophospholipids / Q000378:metabolism*; D008268:Macular Degeneration / Q000378:metabolism* / Q000473:pathology; D059748:Proteolysis
chemical_list: C504173:LIPC protein, human; D008074:Lipoproteins; D008246:Lysophospholipids; D008049:Lipase
keywords: C-reactive protein; RPE cytotoxicity; age-related macular degeneration; complement activation; hepatic lipase; lipoproteins; lysophospholipids