title: Evidence coupling increased hexosamine biosynthesis pathway activity to membrane cholesterol toxicity and cortical filamentous actin derangement contributing to cellular insulin resistance.
abstract: Hyperinsulinemia is known to promote the progression/worsening of insulin resistance. Evidence reveals a hidden cost of hyperinsulinemia on plasma membrane (PM) phosphatidylinositol 4,5-bisphosphate (PIP(2))-regulated filamentous actin (F-actin) structure, components critical to the normal operation of the insulin-regulated glucose transport system. Here we delineated whether increased glucose flux through the hexosamine biosynthesis pathway (HBP) causes PIP(2)/F-actin dysregulation and subsequent insulin resistance. Increased glycosylation events were detected in 3T3-L1 adipocytes cultured under conditions closely resembling physiological hyperinsulinemia (5 nm insulin; 12 h) and in cells in which HBP activity was amplified by 2 mm glucosamine (GlcN). Both the physiological hyperinsulinemia and experimental GlcN challenge induced comparable losses of PIP(2) and F-actin. In addition to protecting against the insulin-induced membrane/cytoskeletal abnormality and insulin-resistant state, exogenous PIP(2) corrected the GlcN-induced insult on these parameters. Moreover, in accordance with HBP flux directly weakening PIP(2)/F-actin structure, pharmacological inhibition of the rate-limiting HBP enzyme [glutamine-fructose-6-phosphate amidotransferase (GFAT)] restored PIP(2)-regulated F-actin structure and insulin responsiveness. Conversely, overexpression of GFAT was associated with a loss of detectable PM PIP(2) and insulin sensitivity. Even less invasive challenges with glucose, in the absence of insulin, also led to PIP(2)/F-actin dysregulation. Mechanistically we found that increased HBP activity increased PM cholesterol, the removal of which normalized PIP(2)/F-actin levels. Accordingly, these data suggest that glucose transporter-4 functionality, dependent on PIP(2) and/or F-actin status, can be critically compromised by inappropriate HBP activity. Furthermore, these data are consistent with the PM cholesterol accrual/toxicity as a mechanistic basis of the HBP-induced defects in PIP(2)/F-actin structure and impaired glucose transporter-4 regulation.
authors.affiliation: Department of Cellular and Integrative Physiology, Indiana University School of Medicine, Indianapolis, Indiana 46202, USA.
authors.forename: Padma
authors.initials: P
authors.lastname: Bhonagiri
authors.forename: Guruprasad R
authors.initials: GR
authors.lastname: Pattar
authors.forename: Kirk M
authors.initials: KM
authors.lastname: Habegger
authors.forename: Alicia M
authors.initials: AM
authors.lastname: McCarthy
authors.forename: Lixuan
authors.initials: L
authors.lastname: Tackett
authors.forename: Jeffrey S
authors.initials: JS
authors.lastname: Elmendorf
mesh_terms: D041721:3T3-L1 Cells; D000199:Actins / Q000378:metabolism*; D000818:Animals; D002462:Cell Membrane / Q000378:metabolism*; D002784:Cholesterol / Q000378:metabolism*; D003599:Cytoskeleton / Q000378:metabolism; D005947:Glucose / Q000378:metabolism; D005945:Glutamine-Fructose-6-Phosphate Transaminase (Isomerizing); D006595:Hexosamines / Q000378:metabolism*; D007328:Insulin / Q000378:metabolism; D007333:Insulin Resistance / Q000502:physiology*; D051379:Mice; D019884:Nitrogenous Group Transferases / Q000378:metabolism; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology
chemical_list: D000199:Actins; D006595:Hexosamines; D007328:Insulin; D019269:Phosphatidylinositol 4,5-Diphosphate; D002784:Cholesterol; D019884:Nitrogenous Group Transferases; C488523:Gfpt1 protein, mouse; D005945:Glutamine-Fructose-6-Phosphate Transaminase (Isomerizing); D005947:Glucose