Lipin 2/3 phosphatidic acid phosphatases maintain phospholipid homeostasis to regulate chylomicron synthesis
Peixiang Zhang, … , Stephen G. Young, Karen Reue
Peixiang Zhang, … , Stephen G. Young, Karen Reue
Published December 3, 2018
Citation Information: J Clin Invest. 2019;129(1):281-295. https://doi.org/10.1172/JCI122595.
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Research Article Metabolism

Lipin 2/3 phosphatidic acid phosphatases maintain phospholipid homeostasis to regulate chylomicron synthesis

Abstract

The lipin phosphatidic acid phosphatase (PAP) enzymes are required for triacylglycerol (TAG) synthesis from glycerol 3-phosphate in most mammalian tissues. The 3 lipin proteins (lipin 1, lipin 2, and lipin 3) each have PAP activity, but have distinct tissue distributions, with lipin 1 being the predominant PAP enzyme in many metabolic tissues. One exception is the small intestine, which is unique in expressing exclusively lipin 2 and lipin 3. TAG synthesis in small intestinal enterocytes utilizes 2-monoacylglycerol and does not require the PAP reaction, making the role of lipin proteins in enterocytes unclear. Enterocyte TAGs are stored transiently as cytosolic lipid droplets or incorporated into lipoproteins (chylomicrons) for secretion. We determined that lipin enzymes are critical for chylomicron biogenesis, through regulation of membrane phospholipid composition and association of apolipoprotein B48 with nascent chylomicron particles. Lipin 2/3 deficiency caused phosphatidic acid accumulation and mammalian target of rapamycin complex 1 (mTORC1) activation, which were associated with enhanced protein levels of a key phospholipid biosynthetic enzyme (CTP:phosphocholine cytidylyltransferase α) and altered membrane phospholipid composition. Impaired chylomicron synthesis in lipin 2/3 deficiency could be rescued by normalizing phospholipid synthesis levels. These data implicate lipin 2/3 as a control point for enterocyte phospholipid homeostasis and chylomicron biogenesis.

Authors

Peixiang Zhang, Lauren S. Csaki, Emilio Ronquillo, Lynn J. Baufeld, Jason Y. Lin, Alexis Gutierrez, Jennifer R. Dwyer, David N. Brindley, Loren G. Fong, Peter Tontonoz, Stephen G. Young, Karen Reue

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Figure 3

Increased levels of phospholipids and chylomicron-associated proteins in Lpin2/3-KO intestine.

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Increased levels of phospholipids and chylomicron-associated proteins in...
(A) Immunoblot analysis of intestinal protein levels for apolipoproteins apoB48, apoA-I, and apoA-IV, lipid droplet protein perilipin 2, phospholipid synthetic enzyme CCTα, and ER protein calnexin. Mice were fed a high-fat diet for 6 days. WT, wild-type. All panels are the same protein samples. The top 4 blots were run contemporaneously, with α-tubulin as a normalization control. The lower 4 blots were run contemporaneously with a nonspecific protein band as a normalizing control. Three biological replicates of each genotype are shown, and are representative of 5–8 samples of each genotype. (B–D) Proximal intestinal lipidomics analysis by electrospray ionization–tandem mass spectrometry in mice maintained on chow diet or fed a high-fat diet (HFD) for 6 days. Average ± SD, n = 4–6. (E) Altered PC composition in Lpin2/3-KO intestine, with reduced proportion of arachidonyl-PC species compared with WT. Average ± SD, n = 4–6. (F) CCTα (Pcyt) mRNA levels in intestine from mice indicated. Average ± SD, n = 4–6. (G) Immunoblot analysis of the mTORC1 target, p70S6 kinase, in intestine. Total and phosphorylated p70S6 kinase (Thr 389) were detected by specific antibodies. Blots were run contemporaneously with the same protein samples. *P < 0.05; **P < 0.01 by ANOVA.