title: Deletion of Rab GAP AS160 modifies glucose uptake and GLUT4 translocation in primary skeletal muscles and adipocytes and impairs glucose homeostasis.
abstract: Tight control of glucose uptake in skeletal muscles and adipocytes is crucial to glucose homeostasis and is mediated by regulating glucose transporter GLUT4 subcellular distribution. In cultured cells, Rab GAP AS160 controls GLUT4 intracellular retention and release to the cell surface and consequently regulates glucose uptake into cells. To determine AS160 function in GLUT4 trafficking in primary skeletal muscles and adipocytes and investigate its role in glucose homeostasis, we characterized AS160 knockout (AS160(-/-)) mice. We observed increased and normal basal glucose uptake in isolated AS160(-/-) adipocytes and soleus, respectively, while insulin-stimulated glucose uptake was impaired and GLUT4 expression decreased in both. No such abnormalities were found in isolated AS160(-/-) extensor digitorum longus muscles. In plasma membranes isolated from AS160(-/-) adipose tissue and gastrocnemius/quadriceps, relative GLUT4 levels were increased under basal conditions and remained the same after insulin treatment. Concomitantly, relative levels of cell surface-exposed GLUT4, determined with a glucose transporter photoaffinity label, were increased in AS160(-/-) adipocytes and normal in AS160(-/-) soleus under basal conditions. Insulin augmented cell surface-exposed GLUT4 in both. These observations suggest that AS160 is essential for GLUT4 intracellular retention and regulation of glucose uptake in adipocytes and skeletal muscles in which it is normally expressed. In vivo studies revealed impaired insulin tolerance in the presence of normal (male) and impaired (female) glucose tolerance. Concurrently, insulin-elicited increases in glucose disposal were abolished in all AS160(-/-) skeletal muscles and liver but not in AS160(-/-) adipose tissues. This suggests AS160 as a target for differential manipulation of glucose homeostasis.
authors.affiliation: Dept. of Medicine/Division of Endocrinology, Univ. of Virginia, Charlottesville, VA 22908, USA. srk4b@virginia.edu
authors.forename: Melissa N
authors.initials: MN
authors.lastname: Lansey
authors.forename: Natalie N
authors.initials: NN
authors.lastname: Walker
authors.forename: Stefan R
authors.initials: SR
authors.lastname: Hargett
authors.forename: Joseph R
authors.initials: JR
authors.lastname: Stevens
authors.forename: Susanna R
authors.initials: SR
authors.lastname: Keller
mesh_terms: D017667:Adipocytes / Q000378:metabolism*; D000818:Animals; D005260:Female; D020690:GTPase-Activating Proteins / Q000172:deficiency* / Q000235:genetics / Q000378:metabolism; D005947:Glucose / Q000378:metabolism*; D005951:Glucose Tolerance Test; D051275:Glucose Transporter Type 4 / Q000378:metabolism*; D006706:Homeostasis; D015151:Immunoblotting; D007328:Insulin / Q000378:metabolism*; D008297:Male; D051379:Mice; D057507:Mice, 129 Strain; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D018482:Muscle, Skeletal / Q000378:metabolism*; D012333:RNA, Messenger / Q000737:chemistry / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: D020690:GTPase-Activating Proteins; D051275:Glucose Transporter Type 4; D007328:Insulin; D012333:RNA, Messenger; C495693:Slc2a4 protein, mouse; C505647:Tbc1d4 protein, mouse; D005947:Glucose