Factors controlling nascent high‐density lipoprotein particle heterogeneity: ATP‐binding cassette transporter A1 activity and cell lipid and apolipoprotein AI availability

Abstract

Nascent high-density lipoprotein (HDL) particles arise in different sizes. We have sought to uncover factors that control this size heterogeneity. Gel filtration, native PAGE, and protein cross-linking were used to analyze the size heterogeneity of nascent HDL produced by BHK-ABCA1, RAW 264.7, J774, and HepG2 cells under different levels of two factors considered as a ratio, the availability of apolipoprotein AI (apoAI) -accessible cell lipid, and concentration of extracellular lipid-free apoAI. Increases in the available cell lipid:apoAI ratio due to either elevated ATP-binding cassette transporter A1 (ABCA1) expression and activity or raised cell density (i.e., increasing numerator) shifted the production of nascent HDL from smaller particles with fewer apoAI molecules per particle and fewer molecules of choline-phospholipid and cholesterol per apoAI molecule to larger particles that contained more apoAI and more lipid per molecule of apoAI. A further shift to larger particles was observed in BHK-ABCA1 cells when the available cell lipid:apoAI ratio was raised still higher by decreasing the apoAI concentration (i.e., the denominator). These changes in nascent HDL biogenesis were reminiscent of the transition that occurs in the size composition of reconstituted HDL in response to an increasing initial lipid:apoAI molar ratio. Thus, the ratio of available cell lipid:apoAI is a fundamental cause of nascent HDL size heterogeneity, and rHDL formation is a good model of nascent HDL biogenesis.—Lyssenko, N. N., Nickel, M., Tang, C., Phillips, M. C. Factors controlling nascent high-density lipoprotein particle heterogeneity: ATP-binding cassette transporter A1 activity and cell lipid and apolipoprotein AI availability.

Is ABCA1 a lipid transfer protein?

“…Because the solubilization of PL bilayers by apoA-I occurs similarly in cell-free systems and at the surface of ABCA1-expressing cells, parallel effects are observed in both cases. For instance, a shift to formation of larger particles containing more PL and apoA-I molecules is seen when the ratio of available PL to apoA-I is increased in both a dimyristoyl PC multilamellar vesicle/apoA-I system (154) and cell systems where ABCA1 is active (155). Variations in apoA-I structure and physical properties also exert similar effects on the sizes of HDL particles created by PL solubilization in cell-free and cellsystems (115).…”

“…b. The relative production of larger and smaller nascent HDL particles is controlled by the ratio of available cellular phospholipid to concentration of apoA-I in the extracellular medium, with a higher ratio favoring production of larger particles (155). c. The number of + and -signs indicates the direction and degree of change relative to either the chosen starting condition or WT human ABCA1 or apoA-I.…”

ApoA1 and ApoA1-specific self-antibodies in cardiovascular disease

“…68 In a case of high phospholipid content, generation of larger HDL particles is enhanced. 69,70 As ApoA1 is directly involved in lipid metabolism, this property is important for considering this apolipoprotein as one of key molecular players in the pathogenesis of cardiometabolic diseases, such as atherosclerosis.…”

Influence of apolipoprotein A-I and apolipoprotein A-II availability on nascent HDL heterogeneity

“…These cells in which ABCA1 activity was upregulated were exposed to 0-40 µg/ml of either human apoA-I, human apoA-II, human [ 14 C]apoA-I [trace labeled to ‫ف‬ 1 µCi/mg as previously described ( 20 )], and/or human [ 3 H]apoA-II in MEM/50 µg/ml gentamicin plus ACAT inhibitor (2 µg/ml) for 2-8 h. ApoA-I and apoA-II were isolated from frozen plasma of normolipidemic donors as described earlier ( 21,22 ). Cell medium containing nascent HDL particles was collected, fi ltered through a 0.45 µm PVDF membrane fi lter unit (EMD Millipore, Billerica, MA), reduced in volume 20× from 30 ml to 1.5 ml using an Amicon Ultracel-10K centrifugal fi lter (EMD Millipore, Billerica, MA) and stored at 4°C for further analysis ( 12,20,23 ).…”

“…HDL heterogeneity originates at the point of biogenesis at which apoA-I and ABCA1 interact to create discoidal nascent particles; the relative available lipid/apoA-I ratio controls the size distribution ( 12 ). The heterogeneity of mature spherical HDL is also affected by remodeling by lipases and lipid transfer proteins in the plasma ( 6 ).…”