Dexamethasone-Mediated Changes in Adipose Triacylglycerol Metabolism Are Exaggerated, Not Diminished, in the Absence of a Functional GR Dimerization Domain

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Abstract

The glucocorticoid (GC) receptor (GR) has multiple effector mechanisms, including dimerization-mediated transactivation of target genes via DNA binding and transcriptional repression mediated by protein-protein interactions. Much attention has been focused on developing selective GR modulators that would dissociate adverse effects from therapeutic anti-inflammatory effects. The GRdim/dim mouse has a mutation in the dimerization domain of GR and has been shown to have attenuated transactivation with intact repression. To understand the role of GR dimerization-dependent targets in multiple tissues, we measured metabolic fluxes through several disease-relevant GC target pathways using heavy water labeling and mass spectrometry in wild-type and GRdim/dim mice administered the potent GC dexamethasone (DEX). Absolute triglyceride synthesis was increased in both wild-type and GRdim/dim mice by DEX in the inguinal and epididymal fat depots. GRdim/dim mice showed an exaggerated response to DEX in both depots. De novo lipogenesis was also greatly increased in both depots in response to DEX in GRdim/dim, but not wild-type mice. In contrast, the inhibitory effect of DEX on bone and skin collagen synthesis rates was greater in wild-type compared with GRdim/dim mice. Wild-type mice were more sensitive to DEX-dependent decreases in insulin sensitivity than GRdim/dim mice. Wild-type and GRdim/dim mice were equally sensitive to DEX-dependent decreases in muscle protein synthesis. Chronic elevation of GCs in GRdim/dim mice results in severe runting and lethality. In conclusion, some metabolic effects of GC treatment are exaggerated in adipose tissue of GRdim/dim mice, suggesting that selective GR modulators based on dissociating GR transactivation from repression should be evaluated carefully.

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