Purpose of review: The interest for the human HDL system was recently revived by the identification of the ABCA1 as a critical component in the formation and maintenance of plasma HDL levels. The present review focuses on recent progress in our understanding of the basic mechanisms underlying HDL biogenesis pathways.
Recent findings: Several novel mechanisms governing ABCA1/apoA-I interactions have recently been identified: apolipoprotein A-I activates ABCA1 phosphorylation through the cAMP/protein kinase A-dependent pathway; the majority of ABCA1 exists as a tetramer in human living cell, supporting the concept that the homotetrameric ABCA1 complex constitutes the minimum functional unit for the formation of nascent HDL particles; apolipoprotein A-I has been shown to have a recycling retroendocytic pathway with uptake and resecretion of the lipidated nascent HDL particles by the cell, most likely through the ABCA1 transporter pathway; there is evidence that the speciation of nascent HDL into pre-beta and alpha-HDL is linked to specific cell lines, and occurs by both ABCA1-dependent and independent pathways.
Summary: The fundamental mechanisms underlying the biogenesis, speciation and maturation of HDL remain complex and not well understood. Understanding the mechanisms governing HDL genesis at the cellular level could provide novel insights into the human atheroprotective system in health and disease.