Abstract 180: Missense Mutations in ABCA1 and CETP Associate with Changes in the HDL Proteome in Primate Half-Sibs Discordant for HDL Cholesterol Levels

Abstract

HDL protein composition and corresponding function may impact cardiovascular disease risk. Identifying genetic variation that influences the HDL proteome may reveal modifiable HDL functions that impact this risk. We studied genetic determinants of the HDL proteome in a cohort of rhesus macaques enriched for extreme HDL cholesterol levels (HDL-c). We selected macaques from 2 distinct paternal half-sibships, each comprising 8 half-sib pairs matched for age-class and sex, but with large differences in HDL-c (N=22 genomes). HDL was isolated by ultracentrifugation and the protein cargo analyzed by mass spectrometry. Identified peptide sequences were compared to a Swiss-Prot canonical human protein database using BLAST to determine ortholog matches. Among the proteins identified, 64 are among the 229 reported in similar human studies, and 45 of these 64 are among the 95 highest-confidence HDL proteins tracked by the HDL Proteome Watch. We performed deep exome sequencing, and assessed predicted function for all genetic variants in macaques, among 23 genes associated with HDL disorders or variation in HDL-c in humans. We focused on the higher-impact variants most likely to have conserved effects between macaques and humans by proximity (i.e., <10 bp) to known human mutations. This produced a set of 3 missense variants in ABCA1 associated with Tangier disease and HDL deficiency, and 4 missense variants in CETP associated with CETP deficiency, reduced CETP activity, and hyper- and hypoalphalipoproteinemias. Using a measured genotype approach, we tested for association of all 7 variants with adjusted spectral counts, while accounting for age and sex, and applied a false discovery rate (FDR) of 20% to all nominally significant results. After controlling for FDR, 3 missense variants in ABCA1 were significantly associated with spectral counts for VCAM1 , ITGA2 , and ITGB1 (nominal P-values 0.0005-0.0026), and 4 missense variants in CETP were significantly associated with spectral counts for APOA2 , APOC3 , C4BPA , and PLTP (nominal P-values 0.0002-0.0038). While our results require replication, these proteins suggest that changes in HDL-c in macaques are associated with changes in HDL that modulate vascular inflammation, immune response, and particle remodeling.