The HDL proteome: a marker–and perhaps mediator–of coronary artery disease

Abstract

One important cardioprotective function of HDL is to remove cholesterol from lipid-laden macrophages in the artery wall. HDL also exerts anti-inflammatory effects that might inhibit atherogenesis. However, HDL has been proposed to be dysfunctional in humans with established coronary artery disease (CAD), though the underlying mechanisms are unclear. Therefore, we used mass spectrometry to investigate the roles of HDL proteins in inflammation and cardiovascular disease. Shotgun proteomic analysis identified multiple complement regulatory proteins, protease inhibitors, and acute-phase response proteins in HDL, strongly implicating the lipoprotein in inflammation and the innate immune system. Moreover, mass spectrometry and biochemical analyses demonstrated that HDL 3 from subjects with clinically significant CAD was selectively enriched in apolipoprotein E, suggesting that it carries a distinctive protein cargo in humans with atherosclerosis. HDL from CAD subjects also contained markedly elevated levels of chlorotyrosine and nitrotyrosine, two characteristic products of myeloperoxidase, indicating that oxidative damage might generate dysfunctional HDL. Aggressive lipid therapy with a statin and niacin remodeled the HDL proteome to resemble that of apparently healthy subjects. Collectively, our observations indicate that quantifying the HDL proteome by mass spectrometry should help identify novel anti-inflammatory and cardioprotective actions of HDL and provide insights into lipid therapy.-Heinecke, J. W. The HDL proteome: a marker-and perhaps mediator-of coronary artery disease. J. Lipid Res. 2009. 50: S167-S171.Supplementary key words high density lipoprotein • apolopoprotein E • oxidized high density lipoprotein • C-reactive protein • apolopoprotein A-I • clusterin HDL and LDL are the major carriers of cholesterol in human blood (1-3). Epidemiological, genetic, and clinical studies demonstrate that elevated levels of LDL or low levels of HDL are important risk factors for coronary artery disease (CAD). In striking contrast, high levels of HDL are cardioprotective. LDL promotes heart disease by delivering cholesterol to macrophages, a key early event in atherogenesis (1-3). HDL protects against atherosclerosis by removing cholesterol from artery wall macrophages by a process termed reverse cholesterol transport.HDL exhibits other biological activities that may contribute to its anti-atherogenic properties, such as the ability to inhibit inflammation (4). It has been proposed that its cardioprotective effects depend on the types of particles generated in vivo and that HDL in humans with established CAD is dysfunctional (4). Indeed, animal studies convincingly demonstrate that changes in proteins involved in HDL metabolism can promote atherosclerosis, even when plasma levels of HDL-cholesterol are elevated (5, 6). Moreover, in vitro studies demonstrate that oxidative damage impairs the ability of apolipoprotein A-I (apoA-I), the major HDL protein, to remove cholesterol from macrophages (7).One possible con...

Structure of HDL: Particle Subclasses and Molecular Components

“…HDL proteins can be divided into several major subgroups which include apolipoproteins, enzymes, lipid transfer proteins, acute-phase response proteins, complement components, proteinase inhibitors and other protein components. Whereas apolipoproteins and enzymes are widely recognised as key functional HDL components, the role of minor proteins, primarily those involved in complement regulation, protection from infections and the acute-phase response, has received increasing attention only in recent years, mainly as a result of advances in proteomic technologies (Heinecke 2009;Hoofnagle and Heinecke 2009;Davidsson et al 2010;Shah et al 2013). These studies have allowed reproducible identification of more than 80 proteins in human HDL (Heinecke 2009;Hoofnagle and Heinecke 2009;Davidsson et al 2010;Shah et al 2013) (for more details see the HDL Proteome Watch at http://homepages.uc.edu/~davidswm/HDLproteome.…”

“…Positive acute-phase response proteins, whose plasma concentrations are markedly elevated by acute inflammation, form a large family of HDL-associated proteins (Vaisar et al 2007;Heinecke 2009). Under normal conditions, the content of such proteins in HDL is however much lower as compared to apolipoproteins.…”

“…Vitronectin is largely expressed in the liver but also in visceral tissue and adrenals. The presence of vitronectin in HDL raises the possibility that certain HDL components can be derived from non-cellular sources or cells distinct from those that synthesise apoA-I in the liver and intestine (Heinecke 2009). …”

“…The diversity of molecules which bind to HDL suggests that the lipoprotein can serve as a versatile adsorptive surface for proteins and peptides to form complexes playing roles not only in lipid metabolism but equally in acute-phase response, innate immune response, complement activation, plaque stability and proteolysis inhibition (Heinecke 2009). As the abundance of the most of HDL-associated proteins is below 1 mol/mol HDL (i.e.…”

Quantitative analysis of intact apolipoproteins in human HDL by top-down differential mass spectrometry

“…HDL 3 (d ¼ 1.13-1.21 g∕mL) was isolated by density gradient ultracentrifugation of freshly acquired EDTA plasma, and samples were normalized for total protein concentration prior to LC-MS analysis. The HDL 3 subfraction was chosen because of its atheroprotective potential and has been extensively characterized in many laboratories using proteomics, including stable isotope dilution mass spectrometry and bottom-up techniques (6,(26)(27)(28).…”