746 Diabetes Volume 64, March 2015 Alexandra Chadt,1,2 Anja Immisch,3 Christian de Wendt,1 Christian Springer,1 Zhou Zhou,1 Torben Stermann,1 Geoffrey D. Holman,4 Dominique Loffing-Cueni,5 Johannes Loffing,5 Hans-Georg Joost,2,3 and Hadi Al-Hasani1,2 Deletion of Both Rab-GTPase– Activating Proteins TBC1D1 and TBC1D4 in Mice Eliminates Insulin- and AICAR-Stimulated Glucose Transport Diabetes 2015;64:746–759 | DOI: 10.2337/db14-0368 The Rab-GTPase–activating proteins TBC1D1 and TBC1D4 from intracellular vesicles to the cell surface (1,2). The (AS160) were previously shown to regulate GLUT4 trans- two related Rab-GTPase–activating proteins TBC1D1 and location in response to activation of AKT and AMP- TBC1D4 (AS160) are phosphorylated in response to in- dependent kinase. However, knockout mice lacking sulin, AMPK, and exercise/muscle contraction and have either Tbc1d1 or Tbc1d4 displayed only partially impaired been implicated in important roles in regulating the trans- insulin-stimulated glucose uptake in fat and muscle tis- location of GLUT4 (3–9). By positional cloning, we pre- sue. The aim of this study was to determine the impact of viously identified a naturally occurring loss-of-function Tbc1d1 Tbc1d4 the combined inactivation of and on glu- mutation in Tbc1d1 as an obesity suppressor in the cose metabolism in double-deficient (D1/4KO) mice. METABOLISM lean, diabetes-resistant SJL mouse strain (10). In humans, D1/4KO mice displayed normal fasting glucose concen- mutations in TBC1D4 (R3633) and TBC1D1 (R125W) trations but had reduced tolerance to intraperitoneally have been linked to severe postprandial hyperinsulinemia administered glucose, insulin, and AICAR. D1/4KO mice and obesity, respectively (11–13). TBC1D4 is found showed reduced respiratory quotient, indicating in- mainly in the heart, adipose tissue, and oxidative muscle creased use of lipids as fuel. These mice also consis- fi tently showed elevated fatty acid oxidation in isolated bers, whereas TBC1D1 is predominantly expressed in skeletal muscle, whereas insulin-stimulated glucose up- glycolytic skeletal muscle and is nearly absent from fat take in muscle and adipose cells was almost completely tissue (10,14,15). Both TBC1D1 and TBC1D4 display a abolished. In skeletal muscle and white adipose tissue, similar domain architecture that includes two N-terminal the abundance of GLUT4 protein, but not GLUT4 mRNA, phosphotyrosine-binding domains and a Rab-GTPase- was substantially reduced. Cell surface labeling of GLUTs activating (GAP) domain. The latter is believed to control indicated that RabGAP deficiency impairs retention of the activation state of Rab-GTPases by converting them GLUT4 in intracellular vesicles in the basal state. Our from the active guanosine triphosphate–bound state into results show that TBC1D1 and TBC1D4 together play es- the inactive guanosine diphosphate–bound state. Several sential roles in insulin-stimulated glucose uptake and lines of evidence suggest that the GAP domains in substrate preference in skeletal muscle and adipose cells. TBC1D1 and TBC1D4 directly regulate the activity of an overlapping set of Rab-GTPases, thereby controlling the In skeletal muscle and adipose cells, insulin stimulation subcellular targeting and transport activity of GLUT4 leads to a rapid and reversible redistribution of GLUT4 (7). So far, Rab2, Rab8b, Rab10, and Rab14 have been 1German Diabetes Center, Leibniz Center for Diabetes Research, Heinrich-Heine- Received 3 March 2014 and accepted 16 September 2014. University, Düsseldorf, Germany This article contains Supplementary Data online at http://diabetes 2 German Center for Diabetes Research (DZD), Düsseldorf, Germany .diabetesjournals.org/lookup/suppl/doi:10.2337/db14-0368/-/DC1. 3German Institute for Human Nutrition, Potsdam, Germany © 2015 by the American Diabetes Association. Readers may use this article as 4Department of Biology and Biochemistry, University of Bath, Bath, U.K. long as the work is properly cited, the use is educational and not for profit, and 5Institute of Anatomy, University of Zurich, Zurich, Switzerland the work is not altered. Corresponding author: Hadi Al-Hasani, [email protected]. diabetes.diabetesjournals.org Chadt and Associates 747 identified as substrates for recombinant GAP domains of D4KO mice (.97.5% congenic with C57BL/6J) then were TBC1D1 and TBC1D4 in vitro (4,16), but the significance intercrossed to generate the four experimental genotypes: of these findings for GLUT4 translocation in adipose and wild type (WT), D1KO, D4KO, and Tbc1d1/Tbc1d4 double- muscle cells in vivo remains to be further investigated. deficient D1/4KO. Animals were kept in accordance with Moreover, the phosphotyrosine-binding domains may the National Institutes of Health guidelines for the care also be involved in TBC1D1/TBC1D4 signaling (17–19). and use of laboratory animals, and all experiments were Previous studies of isolated L6 muscle cells and 3L3-L1 approved by the Ethics Committee of the State Ministry of adipocytes demonstrated that ablation of either Tbc1d1 or Agriculture, Nutrition and Forestry (States of Brandenburg Tbc1d4, or overexpression of mutated proteins, resulted and North Rhine-Westphalia, Germany). Three to six mice in reduced insulin-stimulated translocation of GLUT4 per cage (Macrolon type III) were housed at a temperature (20–22). However, knockout mice lacking either Tbc1d1 of 22°C and a 12-h light–dark cycle (lights on at 6 A.M.)with (15,23) or Tbc1d4 (14,24) displayed only tissue-specific ad libitum access to food and water. After weaning at the impairments of insulin-stimulated glucose uptake and age of 19–21 days, animals received a standard chow rather minor alterations in glycemic control, indicating with 19% (wt/wt) protein (23 cal%), 3.3% fat (8 cal%), a substantial level of redundant expression and signaling. and 54.1% carbohydrates (69 cal%) containing 3.06 The aim of this study was to determine the impact of kcal/g energy (V153 3 R/M-H; Ssniff, Soest, Germany). Tbc1d1 Tbc1d4 the combined inactivation of and on glu- Genotyping cose metabolism. Therefore, we characterized energy and DNA was isolated from mouse tail tips using the InViSorb substrate metabolism of Tbc1d1/Tbc1d4 double-deficient Genomic DNA Kit II (Invitek, Berlin, Germany). Mice were mice. Our results demonstrate that both TBC1D1 and genotyped by PCR with three primers for the Tbc1d4 TBC1D4 operate in concert and play essential roles in knockout (Fwd: 59-AGTAGACTCAGAGTGGTCTTGG-39; insulin-stimulated glucose uptake and substrate prefer- Rev-WT: 59-GTCTTCCGACTCCATATTTGC-39;Rev-KO: ence in skeletal muscle. 59-GCAGCGCATCGCCTTCTATC-39)andprimersforD1KO mice, as described elsewhere (10). RESEARCH DESIGN AND METHODS RNA Extraction, cDNA Synthesis, and Quantitative Materials Real-Time PCR Radiochemicals ([9,10(n)-3H]-palmitic acid; 2-[1,2-3H(N)]- 14 14 RNA was extracted and cDNA was synthesized as described deoxy-D-glucose, [1- C]-D-mannitol, and [ C]-D-glucose previously (10). Real-time PCR was performed with a 7500 [U]) were purchased from Hartmann Analytic (Braunschweig, Fast Real-Time PCR System using TaqMan PCR probes Germany). Human recombinant insulin Actrapid HM (Applied Biosystems, Foster City, CA) for Tbc1d1, Tbc1d4, Penfill from Novo Nordisk Pharma GmbH (Mainz, Germany) and Slc2a4, and data were normalized to Actb according to was used throughout the experiments. Collagenase (type the DCt method (26). I) was from Worthington Biochemical Corp. (Lakewood, NJ). AICAR was purchased from Enzo Life Sciences Analysis of Body Weight and Body Composition (Lörrach, Germany). Antibodies against TBC1D1 and Body weight was measured with an electronic scale GLUT4 were described previously (10). Antibodies against (Sartorius, Göttingen, Germany). Body composition AKT, phospho-AKT (Ser473), AMPKa, phospho-AMPK was analyzed with a nuclear magnetic resonance spec- (Thr172), and phosphoenolpyruvate carboxykinase 2 trometer (Echo MRI, Houston, TX). (PCK2), glycogen synthase, and glycogen synthase kinase Indirect Calorimetry a 3 were from Cell Signaling Technology (Danvers, MA). Animals were placed in individual cages and respiratory Antibodies against PCK1 were from Abcam (Cambridge, quotient (RQ) was measured by indirect calorimetry after UK); antibodies against TBC1D4 were from Millipore a 24-h adaption phase, as described previously (23). Rates (Temecula, CA); and GAPDH antibodies were from Ambion V of oxygen consumption ( O2) and carbon dioxide produc- (Austin, TX). Antibodies against insulin-regulated amino- tion (VCO2) were monitored for 23 h at 22°C at a flow rate peptidase (IRAP) and GLUT1 were generous gifts from Dr. of 30 L/min. Animals had free access to water, and food Susanna Keller (University of Virginia, Charlottesville, VA) was removed during the daytime (6 A.M. to 6 P.M.). Whole- and Dr. Annette Schürmann (German Institute of Human body carbohydrate and fat oxidation rates (grams per Nutrition, Potsdam, Germany), respectively. minute) were calculated using the following equations: 3 V 2 Experimental Animals carbohydrate oxidation rate = 4.585 CO2 (L/min) 3.226 3 VO (L/min); fat oxidation rate = 1.695 3 VO Recombinant congenic Tbc1d1-deficient C57BL/6J mice 2 2 (L/min) 2 1.701 3 VCO (L/min) (27). (whole-body D1KO) were described previously (10). 2 Mice with targeted deletion of Tbc1d4 (whole-body Tolerance Tests D4KO) were obtained from Texas A&M Institute for For glucose tolerance tests (GTTs), sterile glucose (2 g/kg Genomic Medicine (Houston, TX) and backcrossed to body weight, 20%