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 HDL3 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.
Highlights
One important cardioprotective function of HDL is to remove cholesterol from lipid-laden macrophages in the artery wall
In vitro studies demonstrate that oxidative damage impairs the ability of apolipoprotein A-I, the major HDL protein, to remove cholesterol from macrophages [7]
We identified all of those proteins, as well as many others, suggesting that liquid chromatography tandem mass spectrometry (MS/MS) methods are more sensitive than gel-based proteomic methods for detecting HDL-associated proteins
Summary
We identified 48 proteins in HDL isolated by ultracentrifugation from healthy controls and/or CAD subjects [20] They included 22 of 23 known HDL proteins with well-characterized roles in lipid metabolism, which validates our experimental approach. Given that proteolysis of structural proteins in atherosclerotic lesions is thought to play a critical role in plaque rupture, the major cause of myocardial infarction and sudden death in subjects with CAD [22], it is noteworthy that we found a family of proteins in HDL that contain serine proteinase inhibitor domains. We detected the thiol proteinase inhibitor kininogen-1 and haptoglobin-related protein, which contains a crippled catalytic triad residue that may allow it to act as a decoy substrate to prevent proteolysis These observations suggest that HDL plays a previously unsuspected role in preventing plaque rupture, perhaps by protecting vascular lesions from promiscuous proteolysis. Inhibition of complement deposition by HDL may limit injury to cardiac cells and prevent activation of the coagulant response in endothelium and platelets, two critical events in acute thrombosis
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