Collectively, cardiovascular diseases (CVD) are the number one killer in the USA, with the annual mortality reaching nearly one million lives. Coronary artery disease (CAD) is the major CVD which occurs due to the deposition of excess cholesterol and other cellular waste products on inner arterial wall thereby blocking arterial blood flow that can even lead to sudden death. It is now well established that among other beneficial functions, high density lipoproteins (HDLs) play a major role in reducing CAD risk, removing excess deposited cholesterol on the arterial wall, and transporting such cholesterol back to the liver for catabolism. In fact, HDL raising drugs are currently a major focus of CAD therapies.
The main interest of our laboratory is to understand the role of apolipoprotein A-II (apoA-II), the second major protein constituent in HDL. To date, most studies on HDL have been focused on the main protein of HDL, apoA-I, which undoubtedly have confirmed its beneficial roles. However, limited studies on apoA-II have resulted in controversial interpretations with no clear functions attributed to the protein. To get insights into structure-function relationships of apoA-II, we are generating simple-homogeneous HDL in vitro that contain controlled amounts of apoA-I and apoA-II that mimic native HDL. We are using a variety of techniques including mass spectrometry, optical spectroscopy, and chromatography for obtaining fine structural details of these particles. A part of the laboratory’s focus is to develop new techniques on these reconstituted HDLs that can be adapted to analyze native HDL populations. These techniques will be used to understand the apoA-II induced site specific structural changes on different HDL subclasses and to correlate them with any changes in functional properties. Our current interest is to use different plasma factors that involve in HDL maturation and lipid metabolism in the assessment of HDL functional properties.
Our future plans include: How and when does apoA-II gets onto HDL? How does apoA-II remodel the size and inner lipid composition of different HDL particles in the presence or absence of other plasma factors? What types of effects do these changes have on HDL catabolism? Moreover, we are planning to target questions as anti-oxidative properties of apoA-II and whether it plays a role in preventing or delaying other HDL components from oxidation. The long term goal of our laboratory is to understand the role of apoA-II in HDL metabolism which will greatly benefit CVD disease research.
Massey JB, Pownall HJ, Macha S, Morris J, Tubb M, Silva RA. Mass spectrometry determination of apolipoprotein molecular stoichiometry in reconstituted high density lipoprotein particles. J. Lipid Res. 2009 Jun;50(6):1229-36. PMID: 19179308.
Davidson WS, Silva RA, Chantepie S, Lagor WR, Chapman MJ, Kontush A. Proteomicanalysis of defined HDL subpopulations reveals particle-specific proteinclusters: relevance to antioxidative function. Arterioscler Thromb Vasc Biol.2009 Jun;29(6):870-6. Epub 2009 Mar 26. PubMed PMID: 19325143.
Silva RA, Huang R, Morris J, Fang J, Gracheva EO, Ren G, Kontush A, Jerome WG,Rye KA, Davidson WS. Structure of apolipoprotein A-I in spherical high densitylipoproteins of different sizes. Proc Natl Acad Sci U S A. 2008 Aug26;105(34):12176-81. Epub 2008 Aug 21. PubMed PMID: 18719128; PubMed CentralPMCID: PMC2527885
Tubb MR, Silva RA, Fang J, Tso P, Davidson WS. A three-dimensional homologymodel of lipid-free apolipoprotein A-IV using cross-linking and massspectrometry. J Biol Chem. 2008 Jun 20;283(25):17314-23. Epub 2008 Apr 22. PubMedPMID: 18430727; PubMed Central PMCID: PMC2427326.
Tubb MR, Silva RA, Pearson KJ, Tso P, Liu M, Davidson WS. Modulation ofapolipoprotein A-IV lipid binding by an interaction between the N and C termini. J Biol Chem. 2007 Sep 28;282(39):28385-94. Epub 2007 Aug 8. PubMed PMID:17686771.
Silva RA, Schneeweis LA, Krishnan SC, Zhang X, Axelsen PH, Davidson WS. Thestructure of apolipoprotein A-II in discoidal high density lipoproteins. J BiolChem. 2007 Mar 30;282(13):9713-21. Epub 2007 Jan 30. PubMed PMID: 17264082.