The Effect Of Androgen On Skeletal Muscle Of Glucocorticoid-treated Rats And Its Mechanism

Objective: Glucocorticoids are important mediators to cause muscle wasting. Various stresses including severe burn injury and sepsis induce glucocorticoid release in association with muscle wasting. Muscle wasting results in serious consequences, for example it can lead to immunodepression, significant increases in infection rate and delayed mobilization of patients. These prolong the recovery, and greatly reduce life quality. It is obvious, then, that pharmacological intervention regimen that antagonizes the side effects of glucocorticoids on muscle wasting would have important clinical implications. It has been reported that anabolic steroids androgens potentially reverse glucocorticoid-induced effects on muscle. However, so far, the effects are still not clear and the precise mechanisms by which androgens reverse glucocorticoid-induced muscle wasting are not known. The present study was performed to determine the in vivo effects of androgen treatment on muscle wasting, especially the increase of muscle protein degradation induced by glucocorticoid, and elucidate the anabolic effects of androgen in relation to IGF-1 signal pathways in skeletal muscle of glucocorticoid-treated rat model.Methods: One hundred and sixty female SD rats were randomly divided into four groups as follows: control group that received injections of saline and sesame oil (CON group); the dexamethasone group that received injections of dexamethasone and sesame oil (DEX group); the testosterone group that received injections of saline and testosterone (TES group); the testosterone + dexamethasone group that received injections of dexamethasone and testosterone (TES+DEX group). Animals were anesthetized 1d, 3d, 5d or 10d after dexamethasone or saline injections. Blood, muscles (gastrocnemius muscle,extensor digitorum longus muscle, soleus muscle, tibialis anterior muscle, plantaris muscle) and urine samples were harvested. Rats and muscles were weighed. Muscle fiber cross-sectional area (CSA) was determined by imaging processing system after muscle fiber cross-section underwent HE staining or immunohistochemistry staining. 3-methylhistidine (3-MH) in skeletal muscle and urine, testosterone in serum and IGF-1 in serum were determined by high performance liquid chromatography (HPLC), radioimmunity and ELISA, respectively. The activation of protein kinase B (Akt), glycogen synthase kinase-3β (GSK-3P) and 70-kDa ribosomal protein S6 kinase (p70S6K) was examined by Western blot. mRNA expression of IGF-1, muscle atrophy F-box (MAFbx) and muscle RING finger-1 (MuRF1) was measured by real-time quantitative PCR.Results: 1. Dexamethasone reduced the body weights, muscle weights and muscle fiber CSA of rats. Testosterone in part prevented the loss of the body weights and muscle wights and the reduction of muscle fiber CSA. 2. Testosterone prevented the increase of 3-MH in gastrocnemius muscles and urine of dexamethasone-treated rats partly. 3. Testosterone prevented the decrease of IGF-1 mRNA expression in gastrocnemius muscles of rats induced by dexamethasone, but had no effects on the decrease of IGF-1 protein level in serum of rats induced by dexamethasone. 4. Dexamethasone decreased the activation of Akt, p70S6K in gastrocnemius muscles, while testosterone increased the activation of Akt and p70S6K, and decreased the activation of GSK-3β in gastrocnemius muscles. Testosterone in part prevented the effect of dexamethasone on the activation of Akt, p70S6K. 5. Dexamethasone increased the mRNA expression of MuRF1 and MAFbx in gastrocnemius muscles, and testosterone did not prevent the effect of dexamethasone on mRNA expression of MuRF1 and MAFbx.Conclusions: 1. Androgen can attenuate muscle wasting induced by glucocorticoid. 2. Androgen can prevent the increase of muscle proteindegradation in glucocorticoid-treated rats partly. 3. The anabolic effects of androgen on muscle wasting induced by glucocorticoid involves a mechanism of regulating the activation of signal molecules (Akt; GSK-3β; p70S6K) downstream targets of IGF-1 which are associated with protein synthesis in skeletal muscle. 4. Androgen can prevent the increase of muscle protein degradation induced by glucocorticoid, but the mechanism may be not by regulating the expression of ubiquitin-protein ligases MuRF1 and MAFbx downstream targets of IGF-1 which are associated with muscle protein degradation.