title: Impact of genetic deletion of platform apolipoproteins on the size distribution of the murine lipoproteome.
abstract: Given their association with cardiovascular disease protection, there has been intense interest in understanding the biology of high density lipoproteins (HDL). HDL is actually a family of diverse particle types, each made up of discrete - but as yet undetermined - combinations of proteins drawn from up to 95 lipophilic plasma proteins. The abundant apolipoproteins (apo) of the A class (apoA-I, apoA-II and apoA-IV) have been proposed to act as organizing platforms for auxiliary proteins, but this concept has not been systematically evaluated. We assessed the impact of genetic knock down of each platform protein on the particle size distribution of auxiliary HDL proteins. Loss of apoA-I or apoA-II massively reduced HDL lipids and changed the plasma size pattern and/or abundance of several plasma proteins. Surprisingly though, many HDL proteins were not affected, suggesting they assemble on lipid particles in the absence of apoA-I or apoA-II. In contrast, apoA-IV ablation had minor effects on plasma lipids and proteins, suggesting that it forms particles that largely exclude other apolipoproteins. Overall, the data indicate that distinct HDL subpopulations exist that do not contain, nor depend on, apoA-I, apoA-II or apoA-IV and these contribute substantially to the proteomic diversity of HDL.
  
  
  
  Plasma levels of high density lipoproteins (HDL) are inversely correlated with cardiovascular disease. These particles are becoming known as highly heterogeneous entities that have diverse compositions and functions that may impact disease. Unfortunately, we know little about the forces that maintain the composition of each particle in plasma. It has been suggested that certain 'scaffold' proteins, such as apolipoprotein (apo) A-I, apoA-II and apoA-IV, may act as organizing centers for the docking of myriad accessory proteins. To test this hypothesis, we took advantage of the genetic tractability of the mouse model and ablated these three proteins individually. We then tracked the abundance and size profile of the remaining HDL proteins by gel filtration chromatography combined with mass spectrometry. The results clearly show that certain cohorts of proteins depend on each scaffold molecule to assemble normal sized HDL particles under wild-type conditions. This work forms the basis for more detailed studies that will define the specific compositions of HDL subspecies with the possibility of connecting them to specific functions or roles in disease.
authors.affiliation: Center for Lipid and Arteriosclerosis Science, Department of Pathology and Laboratory Medicine, University of Cincinnati, 2120 East Galbraith Road, Cincinnati, OH 45237-0507, USA. Electronic address: Scott.Gordon@nih.gov.
authors.forename: Scott M
authors.initials: SM
authors.lastname: Gordon
authors.affiliation: Division of Biomedical Informatics, Cincinnati Children's Hospital Research Foundation, 3333 Burnet Avenue, MLC 7024, Cincinnati, OH 45229-3039, USA. Electronic address: hailong.li@cchmc.org.
authors.forename: Hailong
authors.initials: H
authors.lastname: Li
authors.affiliation: Division of Biomedical Informatics, Cincinnati Children's Hospital Research Foundation, 3333 Burnet Avenue, MLC 7024, Cincinnati, OH 45229-3039, USA. Electronic address: xiaoting.zhu@cchmc.org.
authors.forename: Xiaoting
authors.initials: X
authors.lastname: Zhu
authors.affiliation: Center for Lipid and Arteriosclerosis Science, Department of Pathology and Laboratory Medicine, University of Cincinnati, 2120 East Galbraith Road, Cincinnati, OH 45237-0507, USA. Electronic address: Patrick.Tso@uc.edu.
authors.forename: Patrick
authors.initials: P
authors.lastname: Tso
authors.affiliation: Department of Pathology, University of Chicago, Chicago, IL 60637, USA. Electronic address: reardon@uchicago.edu.
authors.forename: Catherine A
authors.initials: CA
authors.lastname: Reardon
authors.affiliation: Department of Pediatrics, Cincinnati Children's Hospital Research Foundation, 3333 Burnet Avenue, MLC 7012, Cincinnati, OH 45229-3039, USA. Electronic address: Amy.Shah@cchmc.org.
authors.forename: Amy S
authors.initials: AS
authors.lastname: Shah
authors.affiliation: Division of Biomedical Informatics, Cincinnati Children's Hospital Research Foundation, 3333 Burnet Avenue, MLC 7024, Cincinnati, OH 45229-3039, USA. Electronic address: long.lu@cchmc.org.
authors.forename: L Jason
authors.initials: LJ
authors.lastname: Lu
authors.affiliation: Center for Lipid and Arteriosclerosis Science, Department of Pathology and Laboratory Medicine, University of Cincinnati, 2120 East Galbraith Road, Cincinnati, OH 45237-0507, USA. Electronic address: Sean.Davidson@uc.edu.
authors.forename: W Sean
authors.initials: WS
authors.lastname: Davidson
mesh_terms: D000818:Animals; D016632:Apolipoprotein A-I / Q000737:chemistry / Q000235:genetics; D016633:Apolipoprotein A-II / Q000737:chemistry / Q000235:genetics; D001053:Apolipoproteins / Q000032:analysis / Q000737:chemistry* / Q000235:genetics; D001054:Apolipoproteins A / Q000737:chemistry / Q000235:genetics; D002850:Chromatography, Gel; D017353:Gene Deletion; D008075:Lipoproteins, HDL / Q000737:chemistry*; D013058:Mass Spectrometry; D051379:Mice; D010316:Particle Size; D040901:Proteomics / Q000379:methods
chemical_list: D016632:Apolipoprotein A-I; D016633:Apolipoprotein A-II; D001053:Apolipoproteins; D001054:Apolipoproteins A; D008075:Lipoproteins, HDL; C022205:apolipoprotein A-IV
keywords: Apolipoprotein; High density lipoprotein; Lipoprotein; Mass spectrometry; Mouse model; Proteomics