Deficiency in Lysophosphatidylcholine Acyltransferase 3 Reduces Plasma Levels of Lipids by Reducing Lipid Absorption in Mice

Abstract

BACKGROUND & AIMS Phosphatidylcholines (PCs) are structural and functional constituents of cell membranes. The activity of acyltransferase (LPCAT) is required for addition of polyunsaturated fatty acids to the sn-2 position of PCs, and is therefore required to maintain cell membrane structure and function. LPCAT3 is the most abundant isoform of LPCAT in the small intestine and liver—are important sites of plasma lipoprotein metabolism. We investigated the effects of Lpcat3 disruption on lipid metabolism in mice. METHODS We disrupted the gene Lpcat3 in C57BL/6J mice to create LPCAT3 knockout (KO) mice. Livers and small intestinal tissues were collected from LPCAT3 KO and C57BL/6J parental strain (controls), and levels of LPCAT mRNAs and protein were measured. Levels of lipids and lipoproteins were measured in plasma samples. We isolated enterocytes from mice and measured levels of RNAs and proteins involved in lipid uptake by real-time PCR and immunoblot assays, respectively. We assessed lipid absorption and PC subspecies in the enterocyte plasma membrane using liquid chromatography with tandem mass spectometry. RESULTS LPCAT3 KO mice survived only 3 weeks after birth. Oil Red O staining showed that the control but not LPCAT3 KO mice accumulated lipids in the small intestine; levels of Niemann-Pick C1-like 1 (NPC1L1) and fatty acid transporter protein 4 (FATP4), which regulate lipid uptake, were greatly reduced in the small intestines of LPCAT3 KO mice. Oral administration of PC and olive oil allowed the LPCAT3 KO mice to survive, with the same body weights as controls, but the KO mice had shorter and wider small-intestinal villi and longer and bigger small intestines. Plasma membranes of enterocytes from LPCAT3 KO mice also had significant reductions in the composition of polyunsaturated PCs and reduced levels of NPC1L1, CD36, and FATP4 proteins. These reductions were associated with reduced intestinal uptake of lipid by the small intestine and reduced plasma levels of cholesterol, phospholipid, and triglyceride. CONCLUSIONS LPCAT3 KO mice have longer and larger small intestines than control mice, with shorter wide villi, reduced lipid absorption, and lower levels NPC1L1, CD36, and FATP4 proteins. Inhibition of LPCAT3 in the small intestine could be developed as an approach to treat hyperlipidemia.

Small Intestine but Not Liver Lysophosphatidylcholine Acyltransferase 3 (Lpcat3) Deficiency Has a Dominant Effect on Plasma Lipid Metabolism

“…One explanation could be due to the compensation of other Lpcats. Indeed, we previously reported that global Lpcat3 deficiency causes about 90% reduction of total Lpcat activity in the small intestine, whereas the deficiency only causes about a 70% reduction of total activity in the liver (11). We confirmed this phenomenon in this study (Fig.…”

“…However, the same group recently reported that Lpcat3 deficiency in the liver does not affect the expression of ER stress markers (9). We also recently reported that global Lpcat3 deficiency has no impact on ER stress (11). In this study, we again measured the expression of ER stress markers in the Lpcat3-deficient small intestine and found that the deficiency attenuated (rather than enhanced) the expression of PERK and IRE-1␣ (Fig.…”

“…We previously reported that the neonatal lethality of global Lpcat3 KO mice could be rescued. However, the KO mice had shorter and wider small intestinal villi and a longer and larger small intestine (11). Thus, the impact of Lpcat3 deficiency on small intestine-related lipoprotein metabolism in adult animals remains unknown.…”

“…Very recently, we found that the neonatal lethality of global Lpcat3 KO mice could be rescued by oral administration of PC plus olive oil. However, the KO mice had shorter and wider small intestinal villi and a longer and larger small intestine (11). Thus, the following remains to be investigated: 1) the impact of small intestine Lpcat3 deficiency in adult mice on lipid metabolism; and 2) the respective contribution of small intestine and liver Lpcat3 to plasma lipid levels.…”

Intestinal CD36 and Other Key Proteins of Lipid Utilization: Role in Absorption and Gut Homeostasis

“…The reacylation step is catalyzed by lysophosphatidylcholine acyltransferase (LPCAT), which adds the PUFA at the sn-2 position of PC. Lpcat3 knockout mice die shortly after birth and when rescued by supplementing their diet with phosphatidylcholine, they display reduced lipid absorption and lower expression levels of Nieman-Pick C1-like 1 (NPC1L1), CD36, and FA transport protein 4 (FATP4) (88). Intestine specific Lpcat3 deficiency leads to a selective defect in the incorporation of the EFAs linoleate and arachidonate into phospholipids changing the biophysical properties of the enterocyte membranes (62,164).…”