Intestinal deletion of fatty acid transport protein 4 in mice increases blood chylomicrons

Polymorphisms of fatty acid transport protein 4 (FATP4) are associated with blood lipoproteins and insulin resistance. As FATP4 is localized in intracellular organelles and highly expressed in mouse small intestine, Fatp4 role in fat absorption in mice is still controversial. As our recent studies have suggested Fatp4 role in triglyceride (TAG) metabolism, we here investigated intestinal fat absorption and blood TAG-chylomicrons (CM) in villin-Cre specific inactivation of the Fatp4 gene with exon 3 deletion (entFatp4KO mice).

Methods:

Blood lipoproteins were measured by using gel-permeation high-performance liquid chromatography. Lipidomics were carried out using ESI/MS-MS and LC/MS-MS.

Results:

Under chow feeding, entFatp4KO showed no difference in villous and crypt architecture but showed a decrease of intestinal very long chain fatty acids, phospholipids (PL), sphingomyelin and ceramides (Cer) concomitant with an increase of cholesterol esters (CE). Following overnight starvation, male entFatp4KO showed an increase of serum total TAG-rich and cholesterol (CHOL)-rich lipoprtoeins (combined CM, VLDL, LDL, HDL) and particle numbers of CM and HDL by 20 – 30%. This was concomitant with an increase trend of serum glycerol and jejunum TAG. Following starvation and an oral gavage with 400 µl 2% intralipids for 4h, female entFatp4KO also showed an increase of total TAG-rich lipoproteins and CM particle numbers by 30%. Following feeding with high-fat/high-CHOL diet (HFHC, 15% fat, 1.25% CHOL) for 16 weeks, female entFatp4KO showed an increase of body, liver, and spleen weights without altering liver enzyme activities. HFHC-fed entFatp4KO also showed marked increase of serum TAG, non-esterified free fatty acids, and PL as well as TAG-rich CM, VLDL, LDL, and glycerol by 60 – 80%. This was concomitant with a decrease of intestinal Cer and an increase of oleate-containing CE. Notably, these mutant mice showed a significant shift of ileal fat-droplet size from 20 – 30 towards 50 – 70 µm. This was concomitant with an increase trend of liver TAG but a significant increase of hepatocyte nucleus/cell diameter ratio.

Conclusions:

Intestinal Fatp4 deletion induced an increase in blood CM by diverting fatty acids from the syntheses of PL and Cer towards neutral lipids TAG and CE resulting in larger fat-droplet sizes after high-fat feeding. Our results implicate hyperchylomicronemia and hepatic abnormalities in patients with FATP4 mutations who consume high dietary fat.