Naturally occurring compensated insulin resistance selectively alters glucose transporters in visceral and subcutaneous adipose tissues without change in AS160 activation

Abstract

Although the importance of adipose tissue (AT) glucose transport in regulating whole-body insulin sensitivity is becoming increasingly evident and insulin resistance (IR) has been widely recognized, the underlying mechanisms of IR are still not well understood. The purpose of the present study was to determine the early pathological changes in glucose transport by characterizing the alterations in glucose transporters (GLUT) in multiple visceral and subcutaneous adipose depots in a large animal model of naturally-occurring compensated IR. AT biopsies were collected from horses, which were classified as insulin-sensitive (IS) or compensated IR based on the results of an insulin-modified frequently-sampled intravenous glucose tolerance test. Protein expression of GLUT4 (major isoform) and GLUT12 (one of the most recently discovered isoforms) were measured by Western blotting in multiple AT depots, as well as AS160 (a potential key player in GLUT trafficking pathway). Using a biotinylated bis-mannose photolabeled technique, active cell surface GLUT content was quantified. Omental AT had the highest total GLUT content compared to other sites during the IS state. IR was associated with a significantly reduced total GLUT4 content in omental AT, without a change in content in other visceral or subcutaneous adipose sites. In addition, active cell surface GLUT-4, but not -12, was significantly lower in AT of IR compared to IS horses, without change in AS160 phosphorylation between groups. Our data suggest that GLUT4, but not GLUT12, is a pathogenic factor in AT during naturally-occurring compensated IR, despite normal AS160 activation.

Chronic heart failure selectively induces regional heterogeneity of insulin-responsive glucose transporters

“…Equal amounts of protein were subjected to SDS polyacrylamide gel electrophoresis, electrophoretically transferred to a polyvinylidene fluoride membrane with subsequent immunoblotting. Membrane proteins were incubated with a rabbit polyclonal antibody directed against the last 12 COOHterminal amino acids of GLUT4 (AbD Serotec, Raleigh, NC) or with a rabbit polyclonal antibody directed against the 16 COOH-terminal amino acids of human GLUT12 protein (generated in Dr. Rogers' laboratory and validated for the detection of canine GLUT12 protein) (27), with subsequent appropriate secondary antibodies conjugated to horseradish peroxidase (GE Healthcare, Buckinghamshire, UK) as previously described (10,11,27,36). Protein bands were visualized by enhanced chemiluminescence (KPL, Gaithersburg, MD) and quantified using Gel-Pro Analyzer blot scanning and analysis system (Media Cybernetics, Bethesda, MD).…”

Sarcoplasmic reticulum Ca2+ ATPase pump is a major regulator of glucose transport in the healthy and diabetic heart

“…Furthermore, although the downstream signaling pathways regulating glucose transport are not well defined, the Akt substrate protein of 160 kDa (AS160) is the most distal signaling protein implicated in both insulin and Ca 2+ -mediated GLUT4 translocation in skeletal muscle [8,9]. While there is some evidence that alteration in AS160 activation is one of the mechanisms for the impaired GLUT trafficking in skeletal muscle during insulin resistance and diabetes [10][11][12], some results are controversial [10][11][12]. In addition, a similar pathogenic role in the diabetic heart is unknown.…”

Structure of, and functional insight into the GLUT family of membrane transporters

“…[144][145][146][147][148][149][150][151][152][153][154] GLUT4 trafficking and recycling are also regulated independently from the insulin signal, which is referred to as a general (insulin-independent) pathway and that the movement of GLUT4 is also controlled by muscle contraction. Muscle contraction activates several signaling messengers, including calcium, nitric oxide, and reactive oxygen species within the muscle cells themselves, that regulate glucose homeostasis endogenously.…”