aP2-Cre-mediated inactivation of acetyl-CoA carboxylase 1 causes growth retardation and reduced lipid accumulation in adipose tissues

Abstract

Adipose tissue is one of the major sites for fatty acid synthesis and lipid storage. We generated adipose (fat)-specific ACC1 knockout (FACC1KO) mice using the aP2-Cre/loxP system. FACC1KO mice showed prenatal growth retardation; after weaning, however, their weight gain was comparable to that of wild-type (WT) mice on a normal diet. Under lipogenic conditions of fasting/re-feeding a fat-free diet, lipid accumulation in adipose tissues of FACC1KO mice was significantly decreased; this is consistent with a 50 -66% reduction in the ACC activity in these tissues compared with that of WT mice. Surprisingly, FACC1KO mice manifested skeletal growth retardation phenotype accompanied by decreased chondrocyte proliferation in the growth plate and lower trabecular bone density. In addition, there was about a 30% decrease in serum insulin-like growth factor I (IGF1), and while the serum leptin level was decreased by about 50%, it did not counteract the osteopenic effects of IGF1 on the bone. Fatty acid analyses of mutant bone lipids revealed relatively higher levels of C18:2n-6 and C18:3n-3 and lower levels of their elongation C20 homologs than that of WT cohorts, leading to lower levels of C20 homologs and bone development. Moreover, aP2-Cre-mediated ACC1 inactivation in bone tissue led to a decreased number of osteoblasts but not of osteoclasts. The downregulation of ACC1 on osteoblastogenesis may be the cause for the osteopenia phenotype of FACC1KO bone homeostasis.fat-specific ACC1 knockout ͉ osteoblastogenesis A cetyl-CoA carboxylase 1 (ACC1) catalyzes the synthesis of malonyl-CoA, the committed step toward de novo synthesis of long-chain fatty acids from acetyl-CoA (1). Deletion of ACC1 in mice resulted in embryonic lethality, indicating that fatty acid synthesis is essential for embryonic development (2). To understand the importance of de novo fatty acid synthesis and the role of ACC1 in adult mouse tissues, we generated tissue-specific knockout mice using the Cre-loxP system (3). Mice with liverspecific knockout of ACC1 (LACC1KO) fed normal chow did not exhibit any significant physiological differences from wildtype (WT) mice (3). But when fed a fat-free diet, they accumulated significantly less triglyceride (TG) in the liver compared with their WT cohorts. Although inactivation of ACC1 resulted in 70-75% lower ACC activity in the liver, it did not affect either glucose homeostasis or hepatic fatty acid oxidation (3). When the LACC1KO mice were fed a fat-free diet for 10 days, there was an upregulation of PPAR␥ and several lipogenic enzymes in the liver, including a 2-fold increase in fatty acid synthase (FAS) mRNA, protein, and activity. However, syntheses of fatty acid and TG were reduced significantly. Upregulated ACC2 gene expression did not compensate for the loss of ACC1 function, an observation similar to that noted in Acc2 Ϫ/Ϫ mice in which the cytosolic ACC1 did not compensate for the mitochondrialassociated ACC2 and its product malonyl-CoA (4).Adipose tissues are active lipogenic and fat storage tissues,...

Lipid Biosynthesis Coordinates a Mitochondrial-to-Cytosolic Stress Response

“…To test whether induction of cytosolic chaperones may be mediated by fat accumulation, we reduced expression of each of the major enzymes that are essential for fatty acid biosynthesis and evaluated the induction of cytosolic small heat shock protein hsp-16.2 expression. pod-2 RNAi, which targets the homolog of mammalian acetyl-coenzyme A (acetyl-CoA) carboxylase (acc1), is predicted to decrease malonyl-CoA, a substrate for fatty acid synthesis and a regulator of fatty acid β-oxidation, triglycerides (Mao et al, 2006), and lipid accumulation in adipose tissues (Mao et al, 2009). Reduced expression of the fatty acid synthase ( fasn ) fasn-1 is similarly predicted to reduce fatty acid biosynthesis, resulting in the accumulation of malonyl-CoA and inhibition of fatty acid β-oxidation (Fritz et al, 2013) (Figure 4A).…”

Role of Exchange Protein Directly Activated by Cyclic AMP Isoform 1 in Energy Homeostasis: Regulation of Leptin Expression and Secretion in White Adipose Tissue

“…To bridge this gap in our knowledge, we generated conditional adipose tissue-specific Epac1 knockout mice using the transgenic Cre line driven by the adipocyte protein 2 (␣P2) gene promoter (16). Although ␣P2-Cre has been widely used for generating conditional adipose-specific knockout models, it has been reported that expression of ␣P2-driven Cre recombinase can be detected in macrophages (23) and brains (24) in certain instances. Therefore, in addition to confirming the knockdown of Epac1 in WAT, special attention was devoted to monitoring the expression levels of Epac1 in the hypothalamus and macrophages.…”

Genetic Deletion of Catalytic Subunits of AMP-activated Protein Kinase Increases Osteoclasts and Reduces Bone Mass in Young Adult Mice

“…An explanation on AMPK-mediated regulation of osteoblast differentiation can be found in the study by Mao et al (45). They showed that aP2 (adipocyte protein 2)-Cre-mediated conditional KO of ACC1 results in reduced bone formation caused by defective osteoblastogenesis (45). ACC catalyzes a crucial step of the fatty acid synthesis pathway, and phosphorylation of ACC by AMPK inhibits the enzymatic activity of ACC (46).…”