In this study, Duong et al. sought to determine the role of ABCA1 in promoting efflux of phospholipids and cholesterol to preβ1-HDL or lipid-poor apo AI particles. To address this issue, they characterized the nascent HDL particles formed when lipid-free apo AI was incubated with fibroblasts in which expression of ABCA1 was upregulated. The resulting apo AI lipid-poor particles contained one apo A1, three to four phospholipid molecules, and one to two cholesterol molecules. These particles were found to be as effective as apo AI alone in promoting lipid efflux via ABCA1 and the formation of larger discoidal HDL particles. These observations suggest that preβ1-HDL particles are formed through the conversion of lipid-free apo AI particles into lipid-poor apo AI via ABCA1 before eventually becoming nascent HDL particles.
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