title: The cholesterol-lowering agent methyl-β-cyclodextrin promotes glucose uptake via GLUT4 in adult muscle fibers and reduces insulin resistance in obese mice.
abstract: Insulin stimulates glucose uptake in adult skeletal muscle by promoting the translocation of GLUT4 glucose transporters to the transverse tubule (T-tubule) membranes, which have particularly high cholesterol levels. We investigated whether T-tubule cholesterol content affects insulin-induced glucose transport. Feeding mice a high-fat diet (HFD) for 8 wk increased by 30% the T-tubule cholesterol content of triad-enriched vesicular fractions from muscle tissue compared with triads from control mice. Additionally, isolated muscle fibers (flexor digitorum brevis) from HFD-fed mice showed a 40% decrease in insulin-stimulated glucose uptake rates compared with fibers from control mice. In HFD-fed mice, four subcutaneous injections of MβCD, an agent reported to extract membrane cholesterol, improved their defective glucose tolerance test and normalized their high fasting glucose levels. The preincubation of isolated muscle fibers with relatively low concentrations of MβCD increased both basal and insulin-induced glucose uptake in fibers from controls or HFD-fed mice and decreased Akt phosphorylation without altering AMPK-mediated signaling. In fibers from HFD-fed mice, MβCD improved insulin sensitivity even after Akt or CaMK II inhibition and increased membrane GLUT4 content. Indinavir, a GLUT4 antagonist, prevented the stimulatory effects of MβCD on glucose uptake. Addition of MβCD elicited ryanodine receptor-mediated calcium signals in isolated fibers, which were essential for glucose uptake. Our findings suggest that T-tubule cholesterol content exerts a critical regulatory role on insulin-stimulated GLUT4 translocation and glucose transport and that partial cholesterol removal from muscle fibers may represent a useful strategy to counteract insulin resistance.
authors.affiliation: Center for Molecular Studies of the Cell, Facultad de Medicina, Universidad de Chile, Santiago, Chile; Institute for Research in Dental Sciences, Facultad de Odontología, Universidad de Chile, Santiago, Chile; pllanos@med.uchile.cl.
authors.forename: Paola
authors.initials: P
authors.lastname: Llanos
authors.affiliation: Center for Molecular Studies of the Cell, Facultad de Medicina, Universidad de Chile, Santiago, Chile; Institute for Research in Dental Sciences, Facultad de Odontología, Universidad de Chile, Santiago, Chile;
authors.forename: Ariel
authors.initials: A
authors.lastname: Contreras-Ferrat
authors.affiliation: Medical Biophysics, Institute of Physiology und Pathophysiology, Ruprecht Karls Universität, Heidelberg, Germany;
authors.forename: Tihomir
authors.initials: T
authors.lastname: Georgiev
authors.affiliation: Laboratorio de Bionanotecnología, Universidad Bernardo O'Higgins, Santiago, Chile;
authors.forename: Cesar
authors.initials: C
authors.lastname: Osorio-Fuentealba
authors.affiliation: Center for Molecular Studies of the Cell, Facultad de Medicina, Universidad de Chile, Santiago, Chile;
authors.forename: Alejandra
authors.initials: A
authors.lastname: Espinosa
authors.affiliation: Center for Molecular Studies of the Cell, Facultad de Medicina, Universidad de Chile, Santiago, Chile; Physiology and Biophysics Program, Institute of Biomedical Sciences (ICBM), Facultad de Medicina, Universidad de Chile, Santiago, Chile;
authors.forename: Jorge
authors.initials: J
authors.lastname: Hidalgo
authors.affiliation: Center for Molecular Studies of the Cell, Facultad de Medicina, Universidad de Chile, Santiago, Chile; Physiology and Biophysics Program, Institute of Biomedical Sciences (ICBM), Facultad de Medicina, Universidad de Chile, Santiago, Chile; Biomedical Neuroscience Institute, Facultad de Medicina, Universidad de Chile, Santiago, Chile; and.
authors.forename: Cecilia
authors.initials: C
authors.lastname: Hidalgo
authors.affiliation: Center for Molecular Studies of the Cell, Facultad de Medicina, Universidad de Chile, Santiago, Chile; Cell and Molecular Biology Program, ICBM, Facultad de Medicina, Universidad de Chile, Santiago, Chile.
authors.forename: Enrique
authors.initials: E
authors.lastname: Jaimovich
mesh_terms: D000818:Animals; D000924:Anticholesteremic Agents / Q000494:pharmacology / Q000627:therapeutic use*; D001692:Biological Transport / Q000187:drug effects; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2 / Q000037:antagonists & inhibitors / Q000378:metabolism; D002478:Cells, Cultured; D002784:Cholesterol / Q000378:metabolism; D005947:Glucose / Q000378:metabolism*; D051275:Glucose Transporter Type 4 / Q000819:agonists* / Q000037:antagonists & inhibitors / Q000378:metabolism; D007004:Hypoglycemic Agents / Q000819:agonists / Q000494:pharmacology; D007328:Insulin / Q000819:agonists / Q000494:pharmacology; D007333:Insulin Resistance; D008297:Male; D049990:Membrane Transport Modulators / Q000494:pharmacology; D008810:Mice, Inbred C57BL; D018485:Muscle Fibers, Skeletal / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D009765:Obesity / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D010766:Phosphorylation / Q000187:drug effects; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D051057:Proto-Oncogene Proteins c-akt / Q000037:antagonists & inhibitors / Q000378:metabolism; D019837:Ryanodine Receptor Calcium Release Channel / Q000187:drug effects / Q000378:metabolism; D047392:beta-Cyclodextrins / Q000494:pharmacology / Q000627:therapeutic use*
chemical_list: D000924:Anticholesteremic Agents; D051275:Glucose Transporter Type 4; D007004:Hypoglycemic Agents; D007328:Insulin; D049990:Membrane Transport Modulators; D047428:Protein Kinase Inhibitors; D019837:Ryanodine Receptor Calcium Release Channel; C495693:Slc2a4 protein, mouse; D047392:beta-Cyclodextrins; C108732:methyl-beta-cyclodextrin; D002784:Cholesterol; C514862:Akt1 protein, mouse; D051057:Proto-Oncogene Proteins c-akt; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D005947:Glucose
keywords: calcium; diabetes; glucose transporter 4; high-fat diet; ryanodine receptor; transverse tubules