Loss of Muscle MTCH2 Increases Whole-Body Energy Utilization and Protects from Diet-Induced Obesity

SummaryMitochondrial carrier homolog 2 (MTCH2) is a repressor of mitochondrial oxidative phosphorylation (OXPHOS), and its locus is associated with increased BMI in humans. Here, we demonstrate that mice deficient in muscle MTCH2 are protected from diet-induced obesity and hyperinsulinemia and that they demonstrate increased energy expenditure. Deletion of muscle MTCH2 also increases mitochondrial OXPHOS and mass, triggers conversion from glycolytic to oxidative fibers, increases capacity for endurance exercise, and increases heart function. Moreover, metabolic profiling of mice deficient in muscle MTCH2 reveals a preference for carbohydrate utilization and an increase in mitochondria and glycolytic flux in muscles. Thus, MTCH2 is a critical player in muscle biology, modulating metabolism and mitochondria mass as well as impacting whole-body energy homeostasis

Lessons on Conditional Gene Targeting in Mouse Adipose Tissue

Conditional gene targeting has been extensively used for in vivo analysis of gene function in adipocyte cell biology but often with debate over the tissue specificity and the efficacy of inactivation. To directly compare the specificity and efficacy of different Cre lines in mediating adipocyte specific recombination, transgenic Cre lines driven by the adipocyte protein 2 (aP2) and adiponectin (Adipoq) gene promoters, as well as a tamoxifen-inducible Cre driven by the aP2 gene promoter (iaP2), were bred to the Rosa26R (R26R) reporter. All three Cre lines demonstrated recombination in the brown and white fat pads. Using different floxed loci, the individual Cre lines displayed a range of efficacy to Cre-mediated recombination that ranged from no observable recombination to complete recombination within the fat. The Adipoq-Cre exhibited no observable recombination in any other tissues examined, whereas both aP2-Cre lines resulted in recombination in endothelial cells of the heart and nonendothelial, nonmyocyte cells in the skeletal muscle. In addition, the aP2-Cre line can lead to germline recombination of floxed alleles in ∼2% of spermatozoa. Thus, different “adipocyte-specific” Cre lines display different degrees of efficiency and specificity, illustrating important differences that must be taken into account in their use for studying adipose biology

Ablation of TRIP-Br2, a novel regulator of fat lipolysis, thermogenesis and oxidative metabolism, prevents diet-induced obesity and insulin resistance

SUMMARY Obesity develops due to altered energy homeostasis favoring fat storage. Here we describe a novel transcription co-regulator for adiposity and energy metabolism, TRIP-Br2 (also called SERTAD2). TRIP-Br2 null mice are resistant to obesity and obesity-related insulin resistance. Adipocytes of the knockout (KO) mice exhibited greater stimulated lipolysis secondary to enhanced expression of hormone sensitive lipase (HSL) and β3-adrenergic (Adrb3) receptors. The KOs also exhibit higher energy expenditure due to increased adipocyte thermogenesis and oxidative metabolism by up-regulating key enzymes in respective processes. Our data show for the first time that a cell cycle transcriptional co-regulator, TRIP-Br2, modulates fat storage through simultaneous regulation of lipolysis, thermogenesis and oxidative metabolism. These data together with the observation that TRIP-BR2 expression is selectively elevated in visceral fat in obese humans suggests that this transcriptional co-regulator is a novel therapeutic target for counteracting the development of obesity, insulin resistance and hyperlipidemia

TRB3 Blocks Adipocyte Differentiation through the Inhibition of C/EBPβ Transcriptional Activity▿

TRB3 has been implicated in the regulation of several biological processes in mammalian cells through its ability to influence Akt and other signaling pathways. In this study, we investigated the role of TRB3 in regulating adipogenesis and the activity of adipogenic transcription factors. We find that TRB3 is expressed in 3T3-L1 preadipocytes, and this expression is transiently suppressed during the initial days of differentiation concomitant with induction of C/EBPβ. This event appears to be a prerequisite for adipogenesis. Overexpression of TRB3 blocks differentiation of 3T3-L1 cells at a step downstream of C/EBPβ. Ectopic expression of TRB3 in mouse fibroblasts also inhibits the C/EBPβ-dependent induction of PPARγ2 and blocks their differentiation into adipocytes. This inhibition of preadipocyte differentiation by TRB3 appears to be the result of two complementary effects. First, TRB3 inhibits extracellular signal-regulated kinase activity, which prevents the phosphorylation of regulatory sites on C/EBPβ. Second, TRB3 directly interacts with the DR1 domain of C/EBPβ in the nucleus, further inhibiting both its ability to bind its response element and its ability to transactivate the C/EBPα and a-FABP promoters. Thus, TRB3 is an important negative regulator of adipogenesis that acts at an early step in the differentiation cascade to block the C/EBPβ proadipogenic function

Adipocyte differentiation is inhibited by melatonin through the regulation of C/EBP beta transcriptional activity

Considering that melatonin has been implicated in body weight control, this work investigated whether this effect involves the regulation of adipogenesis. 3T3-L1 preadipocytes were induced to differentiate in the absence or presence of melatonin (10(-3) m). Swiss-3T3 cells ectopically and conditionally (Tet-off system) over-expressing the 34 kDa C/EBP beta isoform (Swiss-LAP cells) were employed as a tool to assess the mechanisms of action at the molecular level. Protein markers of the adipogenic phenotype were analyzed by Western blot. At 36 hr of differentiation of 3T3-L1 preadipocytes, a reduction of PPAR gamma expression was detected followed by a further reduction, at day 4, of perilipin, aP2 and adiponectin protein expression in melatonin-treated cells. Real-time PCR analysis also showed a decrease of PPAR gamma (60%), C/EBP alpha (75%), adiponectin (30%) and aP2 (40%) mRNA expression. Finally, we transfected Swiss LAP cells with a C/EBP alpha gene promoter/reporter construct in which luciferase expression is enhanced in response to C/EBP beta activity. Culture of such transfected cells in the absence of tetracycline led to a 2.5-fold activation of the C/EBP alpha promoter. However, when treated with melatonin, the level of C/EBP alpha promoter activation by C/EBP beta was reduced by 50% (P = 0.05, n = 6). In addition, this inhibitory effect of melatonin was also reflected in the phenotype of the cells, since their capacity to accumulate lipids droplets was reduced as confirmed by the poor staining with Oil Red O. In conclusion, melatonin at a concentration of 10(-3) m works as a negative regulator of adipogenesis acting in part by inhibiting the activity of a critical adipogenic transcription factor, C/EBP beta.Sao Paulo State Research Foundation (FAPESP)[04/06767-2]Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Sao Paulo State Research Foundation (FAPESP)[04/14696-8]Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Sao Paulo State Research Foundation (FAPESP)[07/50404-0

Inhibition of Acetyl-CoA Carboxylase 1 (ACC1) and 2 (ACC2) Reduces Proliferation and <i>De Novo</i> Lipogenesis of EGFRvIII Human Glioblastoma Cells

<div><p>Tumor cell proliferation and migration processes are regulated by multiple metabolic pathways including glycolysis and de novo lipogenesis. Since acetyl-CoA carboxylase (ACC) is at the junction of lipids synthesis and oxidative metabolic pathways, we investigated whether use of a dual ACC inhibitor would provide a potential therapy against certain lipogenic cancers. The impact of dual ACC1/ACC2 inhibition was investigated using a dual ACC1/ACC2 inhibitor as well as dual siRNA knock down on the cellular viability and metabolism of two glioblastoma multiform cancer cell lines, U87 and a more aggressive form, U87 EGFRvIII. We first demonstrated that while ACCi inhibited DNL in both cell lines, ACCi preferentially blunted the U87 EGFRvIII cellular proliferation capacity. Metabolically, chronic treatment with ACCi significantly upregulated U87 EGFRvIII cellular respiration and extracellular acidification rate, a marker of glycolytic activity, but impaired mitochondrial health by reducing maximal respiration and decreasing mitochondrial ATP production efficiency. Moreover, ACCi treatment altered the cellular lipids content and increased apoptotic caspase activity in U87 EGFRvIII cells. Collectively these data indicate that ACC inhibition, by reducing DNL and increasing cellular metabolic rate, may have therapeutic utility for the suppression of lipogenic tumor growth and warrants further investigation.</p></div

Inhibition of ACC leads to decreased de novo lipogenesis in both U87 and U87 EGFRvIII but reduced the number of U87 EGFRvIII cells to a greater extent.

<p>(A) mRNA expression of ACC1 (left panel) and ACC2 (right panel) in both U87 and U87 EGFRvIII cells after treatment with a combination of siRNAs targeted to ACC1 and ACC2 (siACC1/2) or scrambled control siRNAs as assessed by qPCR. Data are normalized to housekeeping genes expression. Each data point represents mean +/- sem, n = 3. *p<0.05, **p<0.01, *** p<0.001. (B) U87 and U87 EGFRvIII cells were treated with a combination of siRNAs targeted to ACC1 and ACC2 (siACC1/2) or scrambled control siRNAs for 144 hours. Extracted proteins were assessed by western blot (top panel). ACC1 protein (lower left panel) and ACC2 protein (lower right panel) were quantified by measurement of band intensity volume normalized to α-tubulin loading control. N = 3 experiments with representative blots shown. **** p<0.0001. (C) Inhibition of de novo lipogenesis in both U87 and U87 EGFRvIII cells as assessed by measurement of ¹⁴C-acetate incorporation into neutral lipids after treatment with a dose range of ACCi or DMSO control. Data are expressed as percent (%) of DMSO control. Each data point represents mean +/- sem, n = 3. (D) Total cellular proteins were assessed after 72 hours treatment with either a combination of siRNAs targeted to ACC1 and ACC2 (siACC1/2), scrambled control siRNAs, 30 μM ACCi or DMSO control. Data are represented as fold change from transfection reagent only control (Control) or DMSO control. Each data point represents mean +/- sem, n = 3. *** p<0.001, **** p<0.0001. (E) Total cellular proteins were assessed after 144 hours treatment with either a combination of siRNAs targeted to ACC1 and ACC2 (siACC1/2), scrambled control siRNAs, 30 μM ACCi or DMSO control. Data are represented as fold change from either transfection reagent only control (Control) or DMSO control. Each data point represents mean +/- sem, n = 3. *** p<0.001, **** p<0.0001.</p