| Abstract: | Many inflammatory and autoimmune diseases are treated using synthetic glucocorticoids. However, excessive glucocorticoid can often cause unpredictable effects including muscle atrophy. Endogenous glucocorticoid levels robustly fluctuate in a circadian manner and peak just before the onset of the active phase in both humans and nocturnal rodents. The present study determines whether muscle atrophy induced by exogenous glucocorticoid can be avoided by optimizing dosing times. We administered single daily doses of the glucocorticoid analog dexamethasone (Dex) to mice for 10 days at the times of day corresponding to peak (early night) or trough (early morning) endogenous glucocorticoid levels. Administration at the acrophase of endogenous glucocorticoids significantly attenuated Dex-induced wasting of the gastrocnemius (Ga) and tibialis anterior (TA) muscles that comprise mostly fast-twitch muscle fibers. Real-time RT-PCR revealed that the Dex-induced mRNA expression of genes encoding the atrophy-related ubiquitin ligases Muscle Atrophy F-box (Fbxo32, also known as MAFbx/Atrogin-1) and Muscle RING finger 1 (Trim63, also known as MuRF1) in the Ga and TA muscles was significantly attenuated by Dex when administered during the early night. Dex negligibly affected the weight of the soleus (So) muscle that mostly comprises slow-twitch muscle fibers, but significantly and similarly decreased the weight of the spleen at both dosing times. These results suggest that glucocorticoid-induced muscle atrophy can be attenuated by optimizing the dosing schedule. |
