Impaired Tethering and Fusion of GLUT4 Vesicles in Insulin-resistant Human Adipose Cells

  1. Karin G. Stenkula2,4
  1. 1Program in Physical Biology, Eunice Kennedy Shriver National Institute of Child Health and Human Development
  2. 2Experimental Diabetes, Metabolism, and Nutrition Section
  3. 3Diabetes, Endocrinology, and Obesity Branch, National Institute of Diabetes and Digestive and Kidney Diseases; National Institutes of Health, Bethesda, MD, U.S.A.
  4. 4Experimental Medical Sciences, Lund University, Lund, Sweden
  1. Corresponding author: Joshua Zimmerberg joshz{at}mail.nih.gov
  • * Present address: Industrial Technology Research Institute, Chutung, Hsinchu, Taiwan, R.O.C.

Abstract

Systemic glucose homeostasis is profoundly influenced by adipose cell function. Here we investigated glucose transporter-4 (GLUT4) dynamics in living adipose cells from human subjects with varying body mass index (BMI) and insulin sensitivity index (SI). Cells were transfected with hemaglutinin (HA)-GLUT4-GFP (green fluorescence)/mCherry (red fluorescence), and imaged live using total internal reflection fluorescence and confocal microscopy. HA-GLUT4-GFP redistribution to the plasma membrane (PM) was quantified by surface-exposed HA-epitope. In the basal state, GLUT4 storage vesicle (GSV) trafficking to and fusion with the PM were invariant with donor subject SI, as was total cell-surface GLUT4. In cells from insulin-sensitive subjects, insulin augmented GSV tethering and fusion ∼3-fold, resulting in a corresponding increase in total PM GLUT4. However, with decreasing SI, these effects diminished progressively. All insulin-induced effects on GLUT4 redistribution and trafficking correlated strongly with SI and only weakly with BMI. Thus, while basal GLUT4 dynamics and total cell-surface GLUT4 are intact in human adipose cells, independent of donor SI, cells from insulin-resistant donors show markedly impaired GLUT4 vesicle tethering and fusion responses to insulin, even after overnight culture. This altered insulin responsiveness is consistent with the hypothesis that adipose cellular dysfunction is a primary contributor to systemic metabolic dysfunction.

Footnotes

    • Received December 12, 2012.
    • Accepted May 20, 2013.

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