Abstract
Our goal was to determine whether in vivo administration of the proteasome inhibitor MG132 can prevent muscle atrophy caused by hindlimb unloading (HU). Twenty-seven NMRI mice were assigned to a weight-bearing control, a 6-day HU, or a HU+MG132 (1 mg/kg/48 h) treatment group. Gastrocnemius wasting was significantly less in HU+MG132 mice (-6.7 ± 2.0%) compared with HU animals (-12.6 ± 1.1%, P = 0.011). HU was also associated with an increased expression of MuRF-1 (P = 0.006), MAFbx (P = 0.001), and USP28 (P = 0.027) mRNA, whereas Nedd4, E3α, USP19, and UBP45 mRNA did not change significantly. Increases in MuRF-1, MAFbx, and USP28 mRNA were largely repressed after MG132 administration. β5 proteasome activity tended to increase in HU (+16.7 ± 6.1%, P = 0.086). Neither β1 and β2 proteasome activities nor ubiquitin-conjugated proteins were changed by HU. Our results indicate that in vivo administration of MG132 partially prevents muscle atrophy associated with disuse and highlight an unexpected regulation of MG132 proteasome inhibitor on ubiquitin-ligases.
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