Endogenous glucocorticoids and impaired insulin signaling are both required to stimulate muscle wasting under pathophysiological conditions in mice
Zhaoyong Hu, … , Jie Du, William E. Mitch
Zhaoyong Hu, … , Jie Du, William E. Mitch
Published September 14, 2009
Citation Information: J Clin Invest. 2009;119(10):3059-3069. https://doi.org/10.1172/JCI38770.
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Research Article Muscle biology

Endogenous glucocorticoids and impaired insulin signaling are both required to stimulate muscle wasting under pathophysiological conditions in mice

Abstract

Muscle wasting is associated with a number of pathophysiologic conditions, including metabolic acidosis, diabetes, sepsis, and high angiotensin II levels. Under these conditions, activation of muscle protein degradation requires endogenous glucocorticoids. As the mechanism(s) underlying this dependence on glucocorticoids have not been identified, we analyzed the effects of glucocorticoids on muscle wasting in a mouse model of acute diabetes. Adrenalectomized, acutely diabetic mice given a physiologic dose of glucocorticoids exhibited decreased IRS-1–associated PI3K activity in muscle and progressive muscle atrophy. These responses were related to increased association of PI3K with the glucocorticoid receptor (GR). In mice with muscle-specific GR deletion (referred to as MGRKO mice), acute diabetes minimally suppressed IRS-1–associated PI3K activity in muscle and did not cause muscle atrophy. However, when a physiologic dose of glucocorticoids was given to mice with muscle-specific IR deletion, muscle protein degradation was accelerated. Fluorescence resonance energy transfer and an in vitro competition assay revealed that activated GRs competed for PI3K, reducing its association with IRS-1. Reexpression of WT GRs or those with a mutation in the nuclear localization signal in the muscle of MGRKO mice indicated that competition for PI3K was a prominent mechanism underlying reduced IRS-1–associated PI3K activity. This nongenomic influence of the GR contributes to activation of muscle protein degradation. We therefore conclude that stimulation of muscle proteolysis requires 2 events, increased glucocorticoid levels and impaired insulin signaling.

Authors

Zhaoyong Hu, Huiling Wang, In Hee Lee, Jie Du, William E. Mitch

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Figure 7

The activated GR competes with IRS-1 for PI3K.

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The activated GR competes with IRS-1 for PI3K. (A) Dex treatment of COS1...
(A) Dex treatment of COS1 cells transfected with GR-CFP (donor) and p85-YFP (recipient) stimulated a time-dependent interaction between GR and p85, as assessed by FRET analysis (n = 3 separate experiments). The box shows the area where emission ratio was measured. (B) After addition of Dex, a substantial portion of the GR was in the cytosol (Cyto) despite accumulation of the GR in the nucleus (Nu). (C) In an in vitro competition assay, addition of increasing amounts of recombinant GR led to a progressive decrease in the PI3K activity and PI3K subunits associated with IRS-1 (n = 3). (D) C2C12 muscle cells were treated with insulin (INS), insulin plus Dex (I+D), or Dex alone. Dex alone increased GR-associated PI3K as well as PI3K subunit proteins. Cells treated with insulin alone had increased IRS-1–associated PI3K activity and minimal GR-associated PI3K activity. Treatment with insulin largely overcame the Dex-induced depression of IRS-1–associated PI3K activity.