Fatty acid transport protein 4 is dispensable for intestinal lipid absorption in mice - PubMed (original) (raw)

Fatty acid transport protein 4 is dispensable for intestinal lipid absorption in mice

Jien Shim et al. J Lipid Res. 2009 Mar.

Abstract

FA transport protein 4 (FATP4), one member of a multigene family of FA transporters, was proposed as a major FA transporter in intestinal lipid absorption. Due to the fact that Fatp4(-/-) mice die because of a perinatal skin defect, we rescued the skin phenotype using an FATP4 transgene driven by a keratinocyte-specific promoter (Fatp4(-/-);Ivl-Fatp4(tg/+) mice) to elucidate the role of intestinal FATP4 in dietary lipid absorption. Fatp4(-/-);Ivl-Fatp4(tg/+) mice and wild-type littermates displayed indistinguishable food consumption, growth, and weight gain on either low or high fat (Western) diets, with no differences in intestinal triglyceride (TG) absorption or fecal fat losses. Cholesterol absorption and intestinal TG absorption kinetics were indistinguishable between the genotypes, although Western diet fed Fatp4(-/-);Ivl-Fatp4(tg/+) mice showed a significant increase in enterocyte TG and FA content. There was no compensatory upregulation of other FATP family members or any other FA or cholesterol transporters in Fatp4(-/-);Ivl-Fatp4(tg/+) mice. Furthermore, although serum cholesterol levels were lower in Fatp4(-/-);Ivl-Fatp4(tg/+) mice, there was no difference in hepatic VLDL secretion in-vivo or in hepatic lipid content on either a chow or Western diet. Taken together, our studies find no evidence for a physiological role of intestinal FATP4 in dietary lipid absorption in mice.

PubMed Disclaimer

Figures

Fig. 1.

Expression of FA transport protein 4 (FATP4) in control and Fatp4 −/− ;Ivl-Fatp4 tg/+ intestine. FATP4 immunofluorescence in the small intestine of adult control mice (A) and Fatp4 −/− ;Ivl-Fatp4 tg/+ mice (B). Immunofluorescent localization of collagen IV shows comparable appearance of villi in both control (C) and Fatp4 −/− ;Ivl-Fatp4 tg/+ sections (D). E: One hundred micrograms of scraped mucosal proteins from control and Fatp4 −/− ;Ivl-Fatp4 _tg/+_mice were separated by SDS-PAGE and Western-blotted for FATP4 (top) and Hsp40 as a loading control (bottom). F: Control small intestine was divided into six sections. Scraped mucosal proteins from four mice were pooled, separated by SDS-PAGE, and Western-blotted for FATP4. The Western blot was stripped and probed again for α-tubulin.

Fig. 2.

Intestinal lipid absorption in control and Fatp4 −/− ;Ivl-Fatp4 tg/+ mice fed a Western diet. A: Dietary fat absorption in mice fed a low-fat, sucrose polybehenate (SPB)-containing diet (left panel) or a high-fat, Western diet (right panel). n = 6–7 mice/genotype for SPB diet and n = 10–11 mice/genotype for Western diet studies. Body weight (B) and weight gain (C) were measured in control (n = 14, black squares) and Fatp4 −/− ;Ivl-Fatp4 tg/+ (n = 16, open circles) mice fed a Western diet for 10–12 weeks. Data were recorded weekly. The trend toward decreased body weight and weight gain in Western diet-fed Fatp4 −/− ;Ivl-Fatp4 tg/+ mice was primarily due to female mice (n = 8 females in control group, 9 in Fatp4 −/− ;Ivl-Fatp4 tg/+ group), though the differences still did not reach statistical significance. Separate graphs for male and female mice are shown in supplementary Figure I. Data are shown as mean ± SE.

Fig. 3.

Intestinal lipid content in chow and Western diet-fed control and Fatp4 −/− ;Ivl-Fatp4 tg/+ mice. Intracellular triglyceride (TG), cholesterol, and free FA content of scraped mucosa from mice fed a chow (A) (control, n = 6 and Fatp4 −/− ;Ivl-Fatp4 tg/+, n = 5–6) or Western diet (B) (control, n = 5–6 and Fatp4 −/− ;Ivl-Fatp4 tg/+, n = 5–7) were measured. Mice were fasted for 4 h prior to sacrifice. * P < 0.05. Data are shown as mean ± SE.

Fig. 4.

Intestinal lipid trafficking in control and Fatp4 −/− ;Ivl-Fatp4 tg/+ mice. A–C: Control (n = 3, black squares) and Fatp4 −/− ;Ivl-Fatp4 tg/+ (n = 4, open circles) mice were fasted overnight, injected intravenously with Tyloxapol to block serum lipase activity, then gavaged with a long-chain FA lipid bolus containing [3H]triolein. Serum radioactivity (A) and TG (B) were measured every h for 4 h following the gavage. Following the last time point, animals were sacrificed, and intestinal TG content of each third of the intestine was determined (C). D–F: Control (n = 5, black bars) and Fatp4 −/− ;Ivl-Fatp4 tg/+ (n = 6, gray bars) mice were fasted overnight, then gavaged with a VLCFA bolus containing [14C]lignoceric acid in Menhaden oil. Intracellular TG (D) and FFA (E) content of each third of the intestine 5 h after bolus was determined and normalized to protein concentration. Cellular radioactivity (F) was determined by scintillation counting and normalized to protein content. * P < 0.05. Data are shown as mean ± SE.

Fig. 5.

Cholesterol absorption and relative mRNA expression of genes involved in lipid metabolism in control and Fatp4 −/− ;Ivl-Fatp4 tg/+ mice. A: Cholesterol absorption in control and Fatp4 −/− ;Ivl-Fatp4 tg/+ was measured using a fecal dual isotope assay on mice fed a chow diet (control n = 13, Fatp4 −/− ;Ivl-Fatp4 tg/+ n = 10) and on mice fed a chow diet containing ezetimibe to block cholesterol absorption (control n = 7, Fatp4 −/− ;Ivl-Fatp4 tg/+ n = 6). B: Relative mRNA levels of genes involved in lipid metabolism in scraped mucosa from proximal small intestine (control n = 5–6, Fatp4 −/− ;Ivl-Fatp4 tg/+ n = 5–6) were measured using real-time quantitative PCR. Relative expression is expressed as fold change normalized to enterocytes from control mice. * P < 0.007. Data are shown as mean ± SE.

Fig. 6.

Hepatic lipid secretion in control and Fatp4 −/− ;Ivl-Fatp4 tg/+ mice. A, C: Control (n = 3, black squares) and Fatp4 −/− ;Ivl-Fatp4 tg/+ (n = 4, open circles) female mice fed a chow diet (A) and a Western diet (C) were fasted for 4 h and intravenously injected with Tyloxapol. Blood was taken from mice every 30 min for 120 min. Serum TG was measured at each time point. Time zero blood samples were taken prior to Tyloxapol injections. B, D: Hepatic TG, cholesterol, and free FA content in livers of mice fed a chow (B, n = 5) or Western diet (D, n = 9-10) were measured. Data are shown as mean ± SE.

References

1. Chen, Z., and N. O. Davidson. 2006. Genetic regulation of intestinal lipid transport and metabolism. In Physiology of the Gastrointestinal Tract. L. R. Johnson, editor. Elsevier Academic Press, Boston, MA 1711–1734.
1. Mansbach C. M., and F. Gorelick. 2007. Development and physiological regulation of intestinal lipid absorption. II. Dietary lipid absorption, complex lipid synthesis, and the intracellular packaging and secretion of chylomicrons. Am. J. Physiol. 293 G645–G650. - PubMed
1. Drover V. A., M. Ajmal, F. Nassir, N. O. Davidson, A. M. Nauli, D. Sahoo, P. Tso, and N. A. Abumrad. 2005. CD36 deficiency impairs intestinal lipid secretion and clearance of chylomicrons from the blood. J. Clin. Invest. 115 1290–1297. - PMC - PubMed
1. Stremmel W. 1988. Uptake of fatty acids by jejunal mucosal cells is mediated by a fatty acid binding membrane protein. J. Clin. Invest. 82 2001–2010. - PMC - PubMed
1. Pohl J., A. Ring, R. Ehehalt, T. Herrmann, and W. Stremmel. 2004. New concepts of cellular fatty acid uptake: role of fatty acid transport proteins and of caveolae. Proc. Nutr. Soc. 63 259–262. - PubMed

Fatty acid transport protein 4 is dispensable for intestinal lipid absorption in mice - PubMed (original) (raw)