High-density lipoprotein subpopulation profiles in lipoprotein lipase and hepatic lipase deficiency

Abstract

Background and aims: Our aim was to gain insight into the role that lipoprotein lipase (LPL) and hepatic lipase (HL) plays in HDL metabolism and to better understand LPL- and HL-deficiency states.

Methods: We examined the apolipoprotein (apo) A-I-, A-II-, A-IV-, C-I-, C-III-, and E-containing HDL subpopulation profiles, assessed by native 2-dimensional gel-electrophoresis and immunoblotting, in 6 homozygous and 11 heterozygous LPL-deficient, 6 homozygous and 4 heterozygous HL-deficient, and 50 control subjects.

Results: LPL-deficient homozygotes had marked hypertriglyceridemia and significant decreases in LDL-C, HDL-C, and apoA-I. Their apoA-I-containing HDL subpopulation profile was shifted toward small HDL particles compared to controls. HL-deficient homozygotes had moderate hypertriglyceridemia, modest increases in LDL-C and HDL-C level, but normal apoA-I concentration. HL-deficient homozygotes had a unique distribution of apoA-I-containing HDL particles. The normally apoA-I:A-II, intermediate-size (α-2 and α-3) particles were significantly decreased, while the normally apoA-I only (very large α-1, small α-4, and very small preβ-1) particles were significantly elevated. In contrast to control subjects, the very large α-1 particles of HL-deficient homozygotes were enriched in apoA-II. Homozygous LPL- and HL-deficient subjects also had abnormal distributions of apo C-I, C-III, and E in HDL particles. Values for all measured parameters in LPL- and HL-deficient heterozygotes were closer to values measured in controls than in homozygotes.

Conclusions: Our data are consistent with the concept that LPL is important for the maturation of small discoidal HDL particles into large spherical HDL particles, while HL is important for HDL remodeling of very large HDL particles into intermediate-size HDL particles.

Keywords: Apolipoproteins; HDL particles; HDL remodeling; Lipoprotein metabolism; Reverse cholesterol transport.

Fig. 1. ApoA-I-containing HDL subpopulations of a representative control (LDL-C=105 mg/dL, TG 87 mg/dL, HDL-C 54 mg/dL, apoA-I 165 mg/dL, and no history of CVD), a heterozygous LPL-deficient (LDL-C=120 mg/dL, TG 137 mg/dL, HDL-C 40 mg/dL, apoA-I 145 mg/dL), a homozygous LPL-deficient (LDL-C=65 mg/dL, TG 2740 mg/dL, HDL-C 14 mg/dL, apoA-I 55 mg/dL), a heterozygous HL-deficient (LDL-C=140 mg/dL, TG 120 mg/dL, HDL-C 74 mg/dL, apoA-I 175 mg/dL), and a homozygous HL-deficient (LDL-C=122 mg/dL, TG 500 mg/dL, HDL-C 64 mg/dL, apoA-I 161 mg/dL) subject

HDL particles were separated from plasma by non-denaturing 2d gel electrophoresis followed by electrotransfer of the gel content to nitrocellulose membrane and immunoprobe for apoA-I. The first panel is a schematic representation of HDL particles: lighter grey indicates LpA-I HDL particles (containing apoA-I without apoA-II) and darker gray indicates LpA-I:A-II HDL particles (containing both apoA-I and apoA-II) in normolipidemic control subjects.

Fig. 2. ApoA-II-, apoC-I-, apoC-III-, and apoE-containing HDL subpopulations of a representative control and a homozygous LPL-deficient subject (LPL^−/−)

HDL particles were separated from plasma by non-denaturing 2d gel electrophoresis followed by electrotransfer of the gel content to nitrocellulose membrane and immunoblot for the apolipoprotein of interest. ApoA-II- (yellow), apoC-I- (blue), apoC-III- (green), and E (red) -containing HDL subpopulations are superimposed on apoA-I-containing HDL subpopulation distribution (grey). Membranes were first immunoprobed for the minor apolipoproteins and after documenting their distribution pattern, the membranes were immunoprobed for apoA-I for documenting co-migration of these apolipoproteins.

Fig. 3. ApoA-II-, apoC-I-, apoC-III-, and apoE-containing HDL subpopulations of a representative control and a homozygous HL-deficient subject (HL^−/−)

HDL particles were separated from plasma by non-denaturing 2d gel electrophoresis followed by electrotransfer of the gel content to nitrocellulose membrane and immunoblot for the apolipoprotein of interest. ApoA-II- (yellow), apoC-I- (blue), apoC-III- (green), and E (red) -containing HDL subpopulations are superimposed on apoA-I-containing HDL subpopulation distribution (grey). Membranes were first immunoprobed for the minor apolipoproteins and after documenting their distribution pattern, the membranes were immunoprobed for apoA-I for documenting co-migration of these apolipoproteins.

Fig. 4. A hypothetical model of the metabolism of apoA-I-containing HDL subpopulations

Green lines represent steps associated with particle maturation from small lipid-poor discs into larger more complex spherical HDL particles. Brown lines represent steps associated with HDL particle remodeling from larger into smaller particles. Blue lines represent steps associated with HDL particle catabolism. ABCA1, ATP-binding cassette transporter A1; apo, apolipoprotein; CE, cholesteryl esther; FC, free cholesterol; HL, hepatic lipase; LCAT, lecithin:cholesterol acyltransferase; LPL, lipoprotein lipase; PL, phospholipid; RLP, remnant-like particle; SR-BI, scavenger receptor BI; TG, triglyceride; TRL. triglyceride-rich lipoproteins.