Abstract 198: HDL Function and Genetic Regulation in a Nonhuman Primate Model of HDL Cholesterol Extremes

Recent data indicate that HDL function has effects independent of HDL cholesterol (HDL-C) levels that better predict cardiovascular risk. We aimed to characterize sterol efflux across a wide range of HDL-C, and to identify genetic determinants for both traits in a non-human primate model. To do this, we took advantage of rhesus macaque families that display spontaneous, extreme variation in HDL-C (range 13-106 mg/dL), but have total cholesterol, LDL-C, and triglyceride levels considered normal in humans. We hypothesized that genetic regulation of HDL metabolism is conserved between macaques and humans, and that sterol efflux is independent of HDL-C across the observed range of HDL-C values. We selected 16 macaque half-sib pairs matched for age-class and sex, based on maximum differences in HDL-C characterized in a larger sample (n=193), and conducted deep sequencing of exons and regulatory regions. We assessed predicted function for all variants in macaques found at 23 genes that regulate reverse cholesterol transport or are associated with HDL-C in humans, and that share ~93% identity with the corresponding human proteins. We assessed sterol efflux using J774 macrophages labeled with [ 3 H]cholesterol and stimulated with a cAMP analogue in 16 sequenced macaques, plus 6 macaques selected from the th />95 th percentiles of HDL-C (n=22). We found 27 predicted functional variants located at regulatory or coding regions in macaques that were within 10 bp of known variants in humans associated with HDL-C levels, coded protein deficiencies, or familial alpha-dyslipoproteinemias. Further, we show that 4 of these variants in CETP , LCAT , and ABCA1 are expected to inhibit normal protein function, as indicated by in silico prediction of changes in protein folding. Within these families, correlation between HDL-C and sterol efflux was 0.78 (P=1.65 X 10 -5 ), suggesting that a significant portion of the variation in efflux capacity cannot be accounted for by HDL-C levels. We conclude that functional genetic variation in pathways of HDL metabolism is conserved between humans and macaques, and is likely to influence both HDL-C and efflux capacity. However, a significant proportion of efflux capacity operates independently of HDL-C.