Mice deleted for fatty acid transport protein 5 have defective bile acid conjugation and are protected from obesity.

BACKGROUND & AIMS: Fatty Acid Transport Protein 5 (FATP5) is a liver-specific member of the FATP/Slc27 family, which has been shown to exhibit both fatty acid transport and bile acid-CoA ligase activity in vitro. Here, we investigate its role in bile acid metabolism and body weight homeostasis in vivo by using a novel FATP5 knockout mouse model. METHODS: Bile acid composition was analyzed by mass spectroscopy. Body weight, food intake, energy expenditure, and fat absorption were determined in animals fed either a low- or a high-fat diet. RESULTS: Although total bile acid concentrations were unchanged in bile, liver, urine, and feces of FATP5 knockout mice, the majority of gallbladder bile acids was unconjugated, and only a small percentage was conjugated. Primary, but not secondary, bile acids were detected among the remaining conjugated forms in FATP5 deletion mice, suggesting a specific requirement for FATP5 in reconjugation of bile acids during the enterohepatic recirculation. Fat absorption in FATP5 deletion mice was largely normal, and only a small increase in fecal fat was observed on a high-fat diet. Despite normal fat absorption, FATP5 deletion mice failed to gain weight on a high-fat diet because of both decreased food intake and increased energy expenditure. CONCLUSIONS: Our findings reveal an important role for FATP5 in bile acid conjugation in vivo and an unexpected function in body weight homeostasis, which will require further analysis. FATP5 deletion mice provide a new model to study the intersection of bile acid metabolism, lipid metabolism, and body weight regulation.

Targeted deletion of FATP5 reveals multiple functions in liver metabolism: alterations in hepatic lipid homeostasis.

BACKGROUND & AIMS: Fatty acid transport protein 5 (FATP5/Slc27a5) has been shown to be a multifunctional protein that in vitro increases both uptake of fluorescently labeled long-chain fatty acid (LCFA) analogues and bile acid/coenzyme A ligase activity on overexpression. The aim of this study was to further investigate the diverse roles of FATP5 in vivo. METHODS: We studied FATP5 expression and localization in liver of C57BL/6 mice in detail. Furthermore, we created a FATP5 knockout mouse model and characterized changes in hepatic lipid metabolism (this report) and bile metabolism (the accompanying report by Hubbard et al). RESULTS: FATP5 is exclusively expressed by the liver and localized to the basal plasma membrane of hepatocytes, congruent with a role in LCFA uptake from the circulation. Overexpression of FATP5 in mammalian cells increased the uptake of 14C-oleate. Conversely, FATP5 deletion significantly reduced LCFA uptake by hepatocytes isolated from FATP5 knockout animals. Moreover, FATP5 deletion resulted in lower hepatic triglyceride and free fatty acid content despite increased expression of fatty acid synthetase and also caused a redistribution of lipids from liver to other LCFA-metabolizing tissues. Detailed analysis of the hepatic lipom of FATP5 knockout livers showed quantitative and qualitative alterations in line with a decreased uptake of dietary LCFAs and increased de novo synthesis. CONCLUSIONS: Our findings support the hypothesis that efficient hepatocellular uptake of LCFAs, and thus liver lipid homeostasis in general, is largely a protein-mediated process requiring FATP5. These new insights into the physiological role of FATP5 should lead to an improved understanding of liver function and disease.

Identification and characterization of 4-aryl-3,4-dihydropyrimidin-2(1H)-ones as inhibitors of the fatty acid transporter FATP4.

Several potent, cell permeable 4-aryl-dihydropyrimidinones have been identified as inhibitors of FATP4. Lipophilic ester substituents at the 5-position and substitution at the para-position (optimal groups being -NO(2) and CF(3)) of the 4-aryl group led to active compounds. In two cases racemates were resolved and the S enantiomers shown to have higher potencies.

Inactivation of fatty acid transport protein 1 prevents fat-induced insulin resistance in skeletal muscle.

Insulin resistance in skeletal muscle plays a major role in the development of type 2 diabetes and may be causally associated with increases in intramuscular fatty acid metabolites. Fatty acid transport protein 1 (FATP1) is an acyl-CoA synthetase highly expressed in skeletal muscle and modulates fatty acid uptake and metabolism by converting fatty acids into fatty acyl-CoA. To investigate the role of FATP1 in glucose homeostasis and in the pathogenesis of insulin resistance, we examined the effect of acute lipid infusion or chronic high-fat feeding on insulin action in FATP1 KO mice. Whole-body adiposity, adipose tissue expression of adiponectin, intramuscular fatty acid metabolites, and insulin sensitivity were not altered in FATP1 KO mice fed a regular chow diet. In contrast, FATP1 deletion protected the KO mice from fat-induced insulin resistance and intramuscular accumulation of fatty acyl-CoA without alteration in whole-body adiposity. These findings demonstrate an important role of intramuscular fatty acid metabolites in causing insulin resistance and suggest that FATP1 may be a novel therapeutic target for the treatment of insulin resistance and type 2 diabetes.

Targeted deletion of fatty acid transport protein-4 results in early embryonic lethality.

Fatty acid transport protein-4 (FATP4) is the major FATP in the small intestine. We previously demonstrated, using in vitro antisense experiments, that FATP4 is required for fatty acid uptake into intestinal epithelial cells. To further examine the physiological role of FATP4, mice carrying a targeted deletion of FATP4 were generated. Deletion of one allele of FATP4 resulted in 48% reduction of FATP4 protein levels and a 40% reduction of fatty acid uptake by isolated enterocytes. However, loss of one FATP4 allele did not cause any detectable effects on fat absorption on either a normal or a high fat diet. Deletion of both FATP4 alleles resulted in embryonic lethality as crosses between heterozygous FATP4 parents resulted in no homozygous offspring; furthermore, no homozygous embryos were detected as early as day 9.5 of gestation. Early embryonic lethality has been observed with deletion of other genes involved in lipid absorption in the small intestine, namely microsomal triglyceride transfer protein and apolipoprotein B, and has been attributed to a requirement for fat absorption early in embryonic development across the visceral endoderm. In mice, the extraembryonic endoderm supplies nutrients to the embryo prior to development of a chorioallantoic placenta. In wild-type mice we found that FATP4 protein is highly expressed by the epithelial cells of the visceral endoderm and localized to the brush-border membrane of extraembryonic endodermal cells. This localization is consistent with a role for FATP4 in fat absorption in early embryogenesis and suggests a novel requirement for FATP4 function during development.

Characterization of a heart-specific fatty acid transport protein.

Fatty acids are a major source of energy for cardiac myocytes. Changes in fatty acid metabolism have been implicated as causal in diabetes and cardiac disease. The mechanism by which long chain fatty acids (LCFAs) enter cardiac myocytes is not well understood but appears to occur predominantly by protein-mediated transport. Here we report the cloning, expression pattern, and subcellular localization of a novel member of the fatty acid transport protein (FATP) family termed FATP6. FATP6 is principally expressed in the heart where it is the predominant FATP family member. Similar to other FATPs, transient and stable transfection of FATP6 into 293 cells enhanced uptake of LCFAs. FATP6 mRNA was localized to cardiac myocytes by in situ hybridization. Immunofluorescence microscopy of FATP6 in monkey and murine hearts revealed that the protein is exclusively located on the sarcolemma. FATP6 was restricted in its distribution to areas of the plasma membrane juxtaposed with small blood vessels. In these membrane domains FATP6 also colocalizes with another molecule involved in LCFA uptake, CD36. These findings suggest that FATP6 is involved in heart LCFA uptake, in which it may play a role in the pathogenesis of lipid-related cardiac disorders.