Malonyl-CoA, generated by acetyl-CoA carboxylases ACC1 and ACC2, is a key metabolite in the control of fatty acid synthesis and oxidation in response to dietary changes. ACC2 is associated to the mitochondria, and Acc2 ؊/؊ mice have a normal lifespan and higher fatty acid oxidation rate and accumulate less fat. Mutant mice fed high-fat͞high-carbohydrate diets weighed less than their WT cohorts, accumulated less fat, and maintained normal levels of insulin and glucose, whereas the WT mice became type-2 diabetic with hyperglycemic and hyperinsulinemic status. Fatty acid oxidation rates in the soleus muscle and in hepatocytes of Acc2 ؊/؊ mice were significantly higher than those of WT cohorts and were not affected by the addition of insulin. mRNA levels of uncoupling proteins (UCPs) were significantly higher in adipose, heart (UCP2), and muscle (UCP3) tissues of mutant mice compared with those of the WT. The increase in the UCP levels along with increased fatty acid oxidation may play an essential role in the regulation of energy expenditure. Lowering intracellular fatty acid accumulation in the mutant relative to that of the WT mice may thus impact glucose transport by higher GLUT4 activity and insulin sensitivity. These results suggest that ACC2 plays an essential role in controlling fatty acid oxidation and is a potential target in therapy against obesity and related diseases.I n animals, including humans, there are two major isoforms of acetyl-CoA carboxylase, ACC1 (M r Ϸ 265,000) and ACC2 (M r Ϸ 280,000), which are encoded by separate genes and display distinct tissue and cellular distribution (1-4). The cDNAs encoding the human ACC1 and ACC2 were cloned and sequenced (1, 2, 5), and the predicted amino acid sequences revealed high homologies between the two isoforms except for the extra 114 aa present in the N terminus of ACC2. The first 20 aa of this extra peptide are highly hydrophobic, and they are responsible for guiding the ACC2 to the mitochondrial membrane (6). ACC1, on the other hand, lacks the hydrophobic N-terminal peptide and was shown to be located in the cytosol (6). In the liver and other lipogenic tissues, ACC1 is highly expressed, and the malonylCoA it generates is the source of the C 2 units for the synthesis of fatty acids. In the heart, muscle, and liver, the malonyl-CoA generated by ACC2 is probably the regulator of the carnitine͞ palmitoyl-CoA shuttle system associated with the mitochondrial membrane (7).Increasing evidence suggests that ACC1 and ACC2 play major roles in regulating the rates of fatty acid synthesis and oxidation, respectively, as they relate to energy homeostasis (8). They are under a strict regulation by diet, hormones, and other physiological factors (9). These regulators manifested their actions at the levels of gene expression and by modulating enzyme activities either through allosteric activation by citrate or by covalent modification, phosphorylation͞dephosphorylation of specific serine residues (9-13). Starvation-refeeding, especially with a high-carbohydrate diet,...

In animals, liver and white adipose are the main sites for the de novo fatty acid synthesis. Deletion of fatty acid synthase or acetyl-CoA carboxylase (ACC) 1 in mice resulted in embryonic lethality, indicating that the de novo fatty acid synthesis is essential for embryonic development. To understand the importance of de novo fatty acid synthesis and the role of ACC1-produced malonyl-CoA in adult mouse tissues, we generated liver-specific ACC1 knockout (LACC1KO) mice. LACC1KO mice have no obvious health problem under normal feeding conditions. Total ACC activity and malonyl-CoA levels were Ϸ70 -75% lower in liver of LACC1KO mice compared with that of the WT mice. In addition, the livers of LACC1KO mice accumulated 40 -70% less triglycerides. Unexpectedly, when fed fat-free diet for 10 days, there was significant up-regulation of PPAR␥ and several enzymes in the lipogenic pathway in the liver of LACC1KO mice compared with the WT mice. Despite the significant up-regulation of the lipogenic enzymes, including a >2-fold increase in fatty acid synthase mRNA, protein, and activity, there was significant decrease in the de novo fatty acid synthesis and triglyceride accumulation in the liver. However, there were no significant changes in blood glucose and fasting ketone body levels. Hence, reducing cytosolic malonyl-CoA and, therefore, the de novo fatty acid synthesis in the liver, does not affect fatty acid oxidation and glucose homeostasis under lipogenic conditions.Cre-loxP ͉ fatty acid synthesis ͉ tissue-specific knockout I n eukaryotes, acetyl-CoA carboxylase (ACC) is a biotinylated enzyme that catalyzes the ATP-dependent carboxylation of acetyl-CoA to produce malonyl-CoA. Fatty acid synthase (FAS), the multifunctional enzyme, catalyzes the synthesis of long-chain fatty acid, palmitate, by using acetyl-CoA as a primer, malonylCoA as a two-carbon donor for chain elongation, and NADPH for the reduction reactions. The synthesis of malonyl-CoA is the committed step toward the synthesis of fatty acids (1-5). In addition, malonyl-CoA also plays an important role in the regulation of fatty acid oxidation in the mitochondria as an inhibitor of the carnitine palmitoyl transferase 1, which performs the first step in the transfer of long-chain fatty acyl CoA into mitochondria for their oxidation (6, 7). Hence, malonyl-CoA participates in two opposing pathways, a substrate for fatty acid synthesis and a regulator of fatty acid oxidation. Lately, there are also reports that malonyl-CoA regulates orexigenic responses in hypothalamus (8) and insulin secretion by pancreatic ␤-islets (9, 10). Malonyl-CoA is generated by two isoforms of acetyl-CoA carboxylases, ACC1 and ACC2 of molecular mass 265 kDa and 280 kDa, respectively (11-16). ACC1 is a cytosolic enzyme, and ACC2 is associated with mitochondria (17). Although both isoforms are expressed in various tissues, ACC1 is predominantly expressed in lipogenic tissues such as liver, adipose, and lactating mammary gland, and ACC2 is predominantly expressed in muscle tissues and heart ...

Acetyl-CoA carboxylases (ACC1 and ACC2) catalyze the carboxylation of acetyl-CoA to form malonyl-CoA, an intermediate metabolite that plays a pivotal role in the regulation of fatty acid metabolism. We previously reported that ACC2 null mice are viable, and that ACC2 plays an important role in the regulation of fatty acid oxidation through the inhibition of carnitine palmitoyltransferase I, a mitochondrial component of the fatty-acyl shuttle system. Herein, we used gene targeting to knock out the ACC1 gene. The heterozygous mutant mice (Acc1 ؉/؊ ) had normal fertility and lifespans and maintained a similar body weight to that of their wild-type cohorts. The mRNA level of ACC1 in the tissues of Acc1 ؉/؊ mice was half that of the wild type; however, the protein level of ACC1 and the total malonyl-CoA level were similar. In addition, there was no difference in the acetate incorporation into fatty acids nor in the fatty acid oxidation between the hepatocytes of Acc1 ؉/؊ mice and those of the wild type. In contrast to Acc2 ؊/؊ mice, Acc1 ؊/؊ mice were not detected after mating. Timed pregnancies of heterozygotes revealed that Acc ؊/؊ embryos are already undeveloped at embryonic day (E)7.5, they die by E8.5, and are completely resorbed at E11.5. Our previous results of the ACC2 knockout mice and current studies of ACC1 knockout mice further confirm our hypotheses that malonyl-CoA exists in two independent pools, and that ACC1 and ACC2 have distinct roles in fatty acid metabolism. malonyl-CoAA cetyl-CoA carboxylases (ACCs) are biotin-containing enzymes that catalyze the carboxylation of acetyl-CoA to form malonyl-CoA, an intermediate metabolite that plays a key role in the regulation of fatty acid metabolism. In addition, malonylCoA, as a precursor of the synthesis of long-chain fatty acids, has been implicated as a signal molecule for insulin secretion from the pancreatic ␤-islets (1, 2). The role that ACC plays in energy metabolism in lipogenic tissues (liver and adipose) and in oxidative tissues (liver, heart, and skeletal muscle) have become the focus of many studies (3-8). In lipogenic tissues, malonylCoA is the C 2 -unit donor for de novo synthesis of long-chain fatty acids catalyzed by fatty acid synthase (FAS) and for the chain elongation of fatty acid to very long-chain fatty acids. Moreover, increasing evidence suggests that malonyl-CoA is a regulator of fatty acid oxidation through the inhibition of carnitine palmitoyltransferase I, an enzyme that controls the entry of long-chain fatty acids into the mitochondria for ␤-oxidation (3). In animals, including humans, ACC1 (M r ϭ 265,000) and ACC2 (M r ϭ 280,000) are the two isoforms of acetyl-CoA carboxylase that are encoded by two separate genes, ACC1 and ACC2, respectively, and they display distinct tissue distribution (9-12). ACC1 is abundant in lipogenic tissues, such as liver and adipose tissue, whereas ACC2 is highly expressed in heart, skeletal muscle, and liver (9, 10). Recently, Loftus et al. (13) proposed that malonylCoA plays a role in the central ne...

To test this idea, a new nonpolar mutagenesis method employing a spectinomycin resistance cassette was used to inactivate the sic gene in an M1 GAS strain. The isogenic Sic-negative mutant strain was significantly (P < 0.019) impaired in ability to colonize the mouse mucosal surface after intranasal infection. These results support the hypothesis that the predominance of M1 strains in human infections is related, in part, to a Sic-mediated enhanced colonization ability.

Serotype M1 group A Streptococcus strains cause epidemic waves of human infections long thought to be mono- or pauciclonal. The gene encoding an extracellular group A Streptococcus protein (streptococcal inhibitor of complement) that inhibits human complement was sequenced in 1,132 M1 strains recovered from population-based surveillance of infections in Canada, Finland and the United States. Epidemic waves are composed of strains expressing a remarkably heterogeneous array of variants of streptococcal inhibitor of complement that arise very rapidly by natural selection on mucosal surfaces. Thus, our results enhance the understanding of pathogen population dynamics in epidemic waves and infectious disease reemergence.