The distinct metabolism between large and small HDL indicates unique origins of human apolipoprotein A4
Allison B. Andraski, … , Masanori Aikawa, Frank M. Sacks
Allison B. Andraski, … , Masanori Aikawa, Frank M. Sacks
Published April 24, 2023
Citation Information: JCI Insight. 2023;8(8):e162481. https://doi.org/10.1172/jci.insight.162481.
View: Text | PDF
Research Article Metabolism

The distinct metabolism between large and small HDL indicates unique origins of human apolipoprotein A4

Abstract

Apolipoprotein A4’s (APOA4’s) functions on HDL in humans are not well understood. A unique feature of APOA4 is that it is an intestinal apolipoprotein secreted on HDL and chylomicrons. The goal of this study was to gain a better understanding of the origin and function of APOA4 on HDL by studying its metabolism across 6 HDL sizes. Twelve participants completed a metabolic tracer study. HDL was isolated by APOA1 immunopurification and separated by size. Tracer enrichments for APOA4 and APOA1 were determined by targeted mass spectrometry, and metabolic rates were derived by compartmental modeling. APOA4 metabolism on small HDL (alpha3, prebeta, and very small prebeta) was distinct from that of APOA4 on large HDL (alpha0, 1, 2). APOA4 on small HDL appeared in circulation by 30 minutes and was relatively rapidly catabolized. In contrast, APOA4 on large HDL appeared in circulation later (1–2 hours) and had a much slower catabolism. The unique metabolic profiles of APOA4 on small and large HDL likely indicate that each has a distinct origin and function in humans. This evidence supports the notion that APOA4 on small HDL originates directly from the small intestine while APOA4 on large HDL originates from chylomicron transfer.

Authors

Allison B. Andraski, Sasha A. Singh, Hideyuki Higashi, Lang Ho Lee, Masanori Aikawa, Frank M. Sacks

×

Figure 1

Study design overview.

Options: View larger image (or click on image) Download as PowerPoint
Study design overview. (A) A total of 12 participants were recruited and...
(A) A total of 12 participants were recruited and completed a metabolic tracer study. Participants consumed a controlled diet (40% fat, 45% carbohydrate, 15% protein) for 4 weeks prior to the tracer study and a low-leucine diet (38% fat, 56% carbohydrate, 6% protein) for 3 days during the tracer study. During the morning of the tracer infusion, participants consumed breakfast between 6 and 8 am before being admitted to the hospital at 9 am. At 10 am (time 0 hour) each participant was infused with a bolus of tri-deuterated leucine (D3-Leu). D3-Leu circulates throughout the body and incorporates into newly synthesized proteins in the small intestine (i.e., APOA1 and APOA4), liver (i.e., APOA1), and other organ systems. Blood samples were collected for 70 hours postinfusion (blood sample time points are shown as black lines on tracer infusion timeline). Participants consumed lunch, dinner, and a snack immediately following the 2-hour (12 pm), 8-hour (6 pm), and 10-hour (8 pm) blood draws, respectively. Breakfast the following morning was given at 7:15 am, before the 22-hour (8 am) blood draw (meals shown as blue arrows above tracer infusion timeline). (B) APOA1-HDL was isolated by anti-APOA1 immunoaffinity column chromatography for 1 to 14 time points per participant and (C) separated into 6 HDL sizes by nondenaturing polyacrylamide gel electrophoresis (ND-PAGE). Samples were then prepared for analysis by liquid chromatography-tandem mass spectrometry (LC-MS/MS). (D, top) APOA4 and APOA1 enrichments were quantified by targeted mass spectrometry, and absolute quantification of protein pool sizes were determined by stable isotope-labeled peptide standards for participants 1–6. These data were then used for kinetic modeling. (D, bottom) The HDL proteome was determined by global proteomics for the 6 APOA1-HDL sizes for all participants 1–12.