Shotgun proteomics implicates protease inhibition and complement activation in the antiinflammatory properties of HDL

TLDR

HDL reduces atherosclerotic cardiovascular disease risk by promoting cholesterol efflux from macrophage foam cells, yet its other antiatherosclerotic functions remain poorly understood. The study aimed to determine whether HDL carries proteins with novel cardioprotective activities by performing shotgun proteomics on HDL from healthy individuals and CAD patients. HDL was isolated from healthy subjects and CAD patients, and shotgun proteomic analysis was used to characterize its protein cargo. Proteomic analysis revealed complement‑regulatory proteins, diverse serpins, and acute‑phase proteins on HDL, with CAD‑derived HDL3 enriched in apoE, indicating HDL’s role in complement regulation, protease inhibition, and antiinflammatory/antiatherogenic protection.

Abstract

HDL lowers the risk for atherosclerotic cardiovascular disease by promoting cholesterol efflux from macrophage foam cells. However, other antiatherosclerotic properties of HDL are poorly understood. To test the hypothesis that the lipoprotein carries proteins that might have novel cardioprotective activities, we used shotgun proteomics to investigate the composition of HDL isolated from healthy subjects and subjects with coronary artery disease (CAD). Unexpectedly, our analytical strategy identified multiple complement-regulatory proteins and a diverse array of distinct serpins with serine-type endopeptidase inhibitor activity. Many acute-phase response proteins were also detected, supporting the proposal that HDL is of central importance in inflammation. Mass spectrometry and biochemical analyses demonstrated that HDL3 from subjects with CAD was selectively enriched in apoE, raising the possibility that HDL carries a unique cargo of proteins in humans with clinically significant cardiovascular disease. Collectively, our observations suggest that HDL plays previously unsuspected roles in regulating the complement system and protecting tissue from proteolysis and that the protein cargo of HDL contributes to its antiinflammatory and antiatherogenic properties.