Abstract
Recent studies demonstrated expression and activity of the intracellular cortisone-cortisol shuttle 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1) in skeletal muscle and inhibition of 11beta-HSD1 in muscle cells improved insulin sensitivity. Glucocorticoids induce muscle atrophy via increased expression of the E3 ubiquitin ligases Atrogin-1 (Muscle Atrophy F-box (MAFbx)) and MuRF-1 (Muscle RING-Finger-1). We hypothesized that 11beta-HSD1 controls glucocorticoid-induced expression of atrophy E3 ubiquitin ligases in skeletal muscle. Primary human myoblasts were generated from healthy volunteers. 11beta-HSD1-dependent protein degradation was analyzed by [3H]-tyrosine release assay. RT-PCR was used to determine mRNA expression of E3 ubiquitin ligases and 11beta-HSD1 activity was measured by conversion of radioactively labeled [3H]-cortisone to [3H]-cortisol separated by thin-layer chromatography. We here demonstrate that 11beta-HSD1 is expressed and biologically active in interconverting cortisone to active cortisol in murine skeletal muscle cells (C2C12) as well as in primary human myotubes. 11beta-HSD1 expression increased during differentiation from myoblasts to mature myotubes (p<0.01), suggesting a role of 11beta-HSD1 in skeletal muscle growth and differentiation. Treatment with cortisone increased protein degradation by about 20% (p<0.001), which was paralleled by an elevation of Atrogin-1 and MuRF-1 mRNA expression (p<0.01, respectively). Notably, pre-treatment with the 11beta-HSD1 inhibitor carbenoxolone (Cbx) completely abolished the effect of cortisone on protein degradation as well as on Atrogin-1 and MuRF-1 expression. In summary, our data suggest that 11beta-HSD1 controls glucocorticoid-induced protein degradation in human and murine skeletal muscle via regulation of the E3 ubiquitin ligases Atrogin-1 and MuRF-1.
Highlights
Glucocorticoid excess is associated with central obesity, insulin resistance, arterial hypertension and skeletal muscle atrophy
We demonstrate that 11beta-HSD1 controls glucocorticoid-induced protein degradation and transcription of the E3 ubiquitin ligases Atrogin-1 and MuRF-1 in the skeletal muscle cell line C2C12 and in primary human myotubes
We show that 11beta-HSD1 mRNA expression increases during differentiation of primary human myoblasts to mature myotubes indicating a role of 11betaHSD1 in differentiation of myocytes
Summary
Glucocorticoid excess is associated with central obesity, insulin resistance, arterial hypertension and skeletal muscle atrophy. 11beta-HSD1 was suggested to be involved in the differentiation of skeletal myoblasts to mature myotubes due to an increasing 11beta-HSD1 expression during the differentiation process, shown in the skeletal muscle C2C12 cell line [10], [11]. Despite those convincing data that 11beta-HSD1 is functionally active in skeletal muscle, the underlying role of this enzyme for muscle atrophy associated pathways is still unclear. We analyzed in the skeletal muscle cell line C2C12 and in primary human myotubes whether 11beta-HSD1 controls glucocorticoid-induced protein degradation and whether this effect is attributed to an increased expression of the E3 ubiquitin ligases Atrogin-1 and MuRF-1
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