Dysregulated glutathione metabolism links to impaired insulin action in adipocytes.
Oxidative stress plays an important role in obesity-related metabolic diseases. Glutathione peroxidase (GPX) is an antioxidant enzyme downregulated in adipose tissue of obese mice. However, the role of GPX in adipocytes remains elusive. The objective of this study was to clarify the pathophysiological changes in GPX activity and glutathione metabolism and their roles in the pathogenesis of insulin resistance in adipocytes. To achieve this goal, we measured cellular GPX activity, glutathione (GSH) contents, GSH/GSSG ratio, and mRNA expression of gamma-glutamylcysteine synthetase (gamma-GCS), a rate-limiting enzyme for de novo GSH synthesis, in adipose tissue of control and ob/ob mice and in 3T3-L1 adipocytes treated with insulin, H(2)O(2), free fatty acid (FFA), or TNFalpha. Furthermore, we investigated the effects of GPX inhibition with a specific GPX inhibitor or RNA interference against GPX, H(2)O(2), and reduced GSH on insulin signaling in 3T3-L1 adipocytes. ob/ob Mice showed not only a decrease in cellular activity of GPXs (GPX1, -4, and -7) but also an increase in gamma-GCS expression, resulting in increased GSH contents in adipose tissue. These alterations in glutathione metabolism were also observed during differentiation of 3T3-L1 cells and their exposure to insulin, FFA, or H(2)O(2). Inhibition of GPX activity, addition of GSH, and H(2)O(2) resulted in impaired insulin signaling in 3T3-L1 adipocytes. These results suggest that decreased GPX activity and increased gamma-GCS expression lead to overaccumulation of GSH, which might be involved in the pathogenesis of insulin resistance in obesity.
Kobayashi
Hironori
H
Dept. of Metabolic Medicine, Graduate School of Medicine, Osaka University, 2-2 Yamada-oka, Suita-shi, Osaka 565-0871, Japan.
Matsuda
Morihiro
M
Fukuhara
Atsunori
A
Komuro
Ryutaro
R
Shimomura
Iichiro
I
D041721:3T3-L1 Cells; D017667:Adipocytes / Q000201:enzymology*; D000818:Animals; D015536:Down-Regulation / Q000502:physiology; D005721:Glutamate-Cysteine Ligase / Q000235:genetics / Q000378:metabolism; D005978:Glutathione / Q000378:metabolism*; D005979:Glutathione Peroxidase / Q000235:genetics / Q000378:metabolism; D007328:Insulin / Q000378:metabolism*; D007333:Insulin Resistance / Q000502:physiology*; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D008820:Mice, Obese; D009765:Obesity / Q000378:metabolism* / Q000503:physiopathology; D018384:Oxidative Stress / Q000502:physiology; D017382:Reactive Oxygen Species / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000502:physiology
D007328:Insulin; D007527:Isoenzymes; D017382:Reactive Oxygen Species; D005979:Glutathione Peroxidase; D005721:Glutamate-Cysteine Ligase; D005978:Glutathione