title: Loss of cortical actin filaments in insulin-resistant skeletal muscle cells impairs GLUT4 vesicle trafficking and glucose transport.
abstract: Study has demonstrated an essential role of cortical filamentous actin (F-actin) in insulin-regulated glucose uptake by skeletal muscle. Here, we tested whether perturbations in F-actin contributed to impaired insulin responsiveness provoked by hyperinsulinemia. In L6 myotubes stably expressing GLUT4 that carries an exofacial myc-epitope tag, acute insulin stimulation (20 min, 100 nM) increased GLUT4myc translocation and glucose uptake by approximately 2-fold. In contrast, a hyperinsulinemic state, induced by inclusion of 5 nM insulin in the medium for 12 h decreased the ability of insulin to stimulate these processes. Defects in insulin signaling did not readily account for the observed disruption. In contrast, hyperinsulinemia reduced cortical F-actin. This occurred concomitant with a loss of plasma membrane phosphatidylinositol 4,5-bisphosphate (PIP(2)), a lipid involved in cytoskeletal regulation. Restoration of plasma membrane PIP(2) in hyperinsulinemic cells restored F-actin and insulin responsiveness. Consistent with these in vitro observations suggesting that the hyperinsulinemic state negatively affects cortical F-actin structure, epitrochlearis skeletal muscle from insulin-resistant hyperinsulinemic Zucker fatty rats displayed a similar loss of F-actin structure compared with that in muscle from lean insulin-sensitive littermates. We propose that a component of insulin-induced insulin resistance in skeletal muscle involves defects in PIP(2)/F-actin structure essential for insulin-regulated glucose transport.
authors.affiliation: Dept. of Cellular and Integrative Physiology, Indiana University School of Medicine, Indianapolis, IN 46202, USA.
authors.forename: Alicia M
authors.initials: AM
authors.lastname: McCarthy
authors.forename: Kristen O
authors.initials: KO
authors.lastname: Spisak
authors.forename: Joseph T
authors.initials: JT
authors.lastname: Brozinick
authors.forename: Jeffrey S
authors.initials: JS
authors.lastname: Elmendorf
mesh_terms: D008841:Actin Cytoskeleton / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002462:Cell Membrane / Q000187:drug effects; D002478:Cells, Cultured; D003599:Cytoskeleton / Q000473:pathology; D005260:Female; D005947:Glucose / Q000378:metabolism*; D051275:Glucose Transporter Type 4 / Q000378:metabolism*; D007328:Insulin / Q000494:pharmacology; D007333:Insulin Resistance / Q000502:physiology*; D018485:Muscle Fibers, Skeletal / Q000166:cytology / Q000187:drug effects; D018482:Muscle, Skeletal / Q000166:cytology* / Q000187:drug effects*; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000378:metabolism; D011236:Prediabetic State / Q000473:pathology; D051381:Rats; D015398:Signal Transduction / Q000187:drug effects; D022161:Transport Vesicles / Q000187:drug effects / Q000378:metabolism*
chemical_list: D051275:Glucose Transporter Type 4; D007328:Insulin; D019269:Phosphatidylinositol 4,5-Diphosphate; C495694:Slc2a4 protein, rat; D005947:Glucose