The metabolic regulator fibroblast growth factor 21 (FGF21) has antidiabetic properties in animal models of diabetes and obesity. Using quantitative RT-PCR, we here show that the hepatic gene expression of FGF21 is regulated by the peroxisome proliferator-activated receptor alpha (PPARα). Fasting or treatment of mice with the PPARα agonist Wy-14,643 induced FGF21 mRNA by 10-fold and 8-fold respectively. In contrast, FGF21 mRNA was low in PPARα deficient mice, and fasting or treatment with Wy-14,643 did not induce

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Peroxisomes function in ␤-oxidation of very long and long-chain fatty acids, dicarboxylic fatty acids, bile acid intermediates, prostaglandins, leukotrienes, thromboxanes, pristanic acid, and xenobiotic carboxylic acids. These lipids are mainly chain-shortened for excretion as the carboxylic acids or transported to mitochondria for further metabolism. Several of these carboxylic acids are slowly oxidized and may therefore sequester coenzyme A (CoASH). To prevent CoASH sequestration and to facilitate excretion of chain-shortened carboxylic acids, acyl-CoA thioesterases, which catalyze the hydrolysis of acyl-CoAs to the free acid and CoASH, may play important roles. Here we have cloned and characterized a peroxisomal acyl-CoA thioesterase from mouse, named PTE-2 (peroxisomal acyl-CoA thioesterase 2). PTE-2 is ubiquitously expressed and induced at mRNA level by treatment with the peroxisome proliferator WY-14,643 and fasting. Induction seen by these treatments was dependent on the peroxisome proliferator-activated receptor ␣. Recombinant PTE-2 showed a broad chain length specificity with acyl-CoAs from short-and medium-, to long-chain acyl-CoAs, and other substrates including trihydroxycoprostanoyl-CoA, hydroxymethylglutaryl-CoA, and branched chain acyl-CoAs, all of which are present in peroxisomes. Highest activities were found with the CoA esters of primary bile acids choloyl-CoA and chenodeoxycholoyl-CoA as substrates. PTE-2 activity is inhibited by free CoASH, suggesting that intraperoxisomal free CoASH levels regulate the activity of this enzyme. The acyl-CoA specificity of recombinant PTE-2 closely resembles that of purified mouse liver peroxisomes, suggesting that PTE-2 is the major acyl-CoA thioesterase in peroxisomes. Addition of recombinant PTE-2 to incubations containing isolated mouse liver peroxisomes strongly inhibited bile acidCoA:amino acid N-acyltransferase activity, suggesting that this thioesterase can interfere with CoASH-dependent pathways. We propose that PTE-2 functions as a key regulator of peroxisomal lipid metabolism.Peroxisomes are cellular organelles present in all eukaryotic cells. They play an indispensable role in the metabolism of a variety of lipids including very long-chain fatty acids, dicarboxylic fatty acids, bile acids, prostaglandins, leukotrienes, thromboxanes, pristanic acid, and xenobiotic fatty acids (for review, see Refs. 1 and 2). The peroxisomal ␤-oxidation system contains two sets of enzymes, one of which is involved in the oxidation of branched chain fatty acids and intermediates in the hepatic bile acid biosynthetic pathway and consists of one or two branched-chain acyl-CoA oxidase(s), a D-specific bifunctional protein and the sterol carrier-like protein x (SCPx). The second pathway is involved in the oxidation of very long straight-chain fatty acids, CoA esters of prostaglandins, leukotrienes, and thromboxanes (prostanoids) and dicarboxylic acids. This system is composed of a straight-chain acyl-CoA oxidase, an L-specific bifunctional protein and straight-chain 3-ke...

The cellular uptake of free fatty acids (FFA) is followed by esterification to coenzyme A (CoA), generating fatty acyl-CoAs that are substrates for oxidation or incorporation into complex lipids. Acyl-CoA thioesterases constitute a family of enzymes that hydrolyze fatty acyl-CoAs to form FFA and CoA. Although biochemically and biophysically well characterized, the metabolic functions of these enzymes remain incompletely understood. Existing evidence suggests regulatory roles in controlling rates of peroxisomal and mitochondrial fatty acyl-CoA oxidation, as well as in the subcellular trafficking of fatty acids. Emerging data implicate acyl-CoA thioesterases in the pathogenesis of metabolic diseases, suggesting that better understanding their pathobiology could reveal unique targets in the management of obesity, diabetes and non-alcoholic fatty liver disease.

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The maintenance of cellular levels of free fatty acids and acyl-CoAs, the activated form of free fatty acids, is extremely important as imbalances in lipid metabolism have serious consequences for human health. Acyl-CoA thioesterases (ACOTs) hydrolyze acyl-CoAs to the free fatty acid and CoASH, and thereby have the potential to regulate intracellular levels of these compounds. We have previously identified and characterized a mouse ACOT gene cluster, comprised of six genes that apparently arose by gene duplications, encoding acylCoA thioesterases with localizations in cytosol (ACOT1), mitochondria (ACOT2) and peroxisomes (ACOT3-6). However, the corresponding human gene cluster contains only three genes, ACOT1, ACOT2 and ACOT4 coding for full-length thioesterase proteins, of which only one is peroxisomal (ACOT4). We therefore set out to characterize the human genes, and we here show that the human ACOT4 protein catalyzes the activities of three mouse peroxisomal ACOTs (ACOT3, 4, and 5), being active on succinyl-CoA and mediumto long-chain acyl-CoAs, while ACOT1 and ACOT2 carry out similar functions to the corresponding mouse genes. These data strongly suggest that the human ACOT4 gene has acquired the functions of three mouse genes by a functional convergent evolution that also provides an explanation for the unexpectedly low number of human genes.

Fibrates are a group of hypolipidemic agents that efficiently lower serum triglyceride levels by affecting the expression of many genes involved in lipid metabolism. These effects are exerted via the peroxisome proliferator-activated receptor ␣ (PPAR␣). In addition, fibrates also lower serum cholesterol levels, suggesting a possible link between the PPAR␣ and cholesterol metabolism. Bile acid formation represents an important pathway for elimination of cholesterol, and the sterol 12␣-hydroxylase is a branch-point enzyme in the bile acid biosynthetic pathway, which determines the ratio of cholic acid to chenodeoxycholic acid. Treatment of mice for 1 week with the peroxisome proliferator WY-14,643 or fasting for 24 h both induced the sterol 12␣-hydroxylase mRNA in liver. Using the PPAR␣ knockout mouse model, we show that the induction by both treatments was dependent on the PPAR␣. A reporter plasmid containing a putative peroxisome proliferator-response element (PPRE) identified in the rat sterol 12␣-hydroxylase promoter region was activated by treatment with WY-14,643 in HepG2 cells, being dependent on co-transfection with a PPAR␣ expression plasmid. The rat 12␣-hydroxylase PPRE bound in vitro translated PPAR␣ and retinoid X receptor ␣, albeit weakly, in electrophoretic mobility shift assay. Treatment of wild-type mice with WY-14,643 for 1 week resulted in an increased relative amount of cholic acid, an effect that was abolished in the PPAR␣ null mice, verifying the functionality of the PPRE in vivo.Fibrates and their derivatives constitute a group of hypolipidemic agents that are used in the treatment of hypertriglyceridemia and combined hyperlipidemia. These fibrates belong to a structurally diverse group of compounds known as peroxisome proliferators, which have been shown to cause liver hepatomegaly, proliferation of peroxisomes, and induction of many enzymes involved in peroxisomal and mitochondrial ␤-oxidation and -oxidation of fatty acids (for review, see Ref.