Maintenance of skeletal muscle mass depends on the equilibrium between
protein synthesis and
protein breakdown; diminished functional demand during unloading breaks this balance and leads to
muscle atrophy. The current study analyzed time-course alterations in regulatory genes and
proteins in the unloaded soleus muscle and the effects of
branched-chain amino acid (BCAA) supplementation on
muscle atrophy and abundance of molecules that regulate
protein turnover. Short-term (6 days) hindlimb suspension of rats resulted in significant losses of myofibrillar
proteins, total
RNA, and rRNAs and pronounced
atrophy of the soleus muscle. Muscle disuse induced upregulation and increases in the abundance of the eukaryotic translation
initiation factor 4E-binding
protein 1 (4E-BP1), increases in gene and
protein amounts of two
ubiquitin ligases (muscle RING-finger
protein 1 and
muscle atrophy F-box protein), and decreases in the expression of
cyclin D1, the
ribosomal protein S6 kinase 1, the
mammalian target of rapamycin (mTOR), and ERK1/2. BCAA addition to the diet did not prevent
muscle atrophy and had no apparent effect on regulators of proteasomal protein degradation. However, BCAA supplementation reduced the loss of myofibrillar
proteins and
RNA, attenuated the increases in 4E-BP1, and partially preserved
cyclin D1, mTOR and ERK1
proteins. These results indicate that BCAA supplementation alone does not oppose protein degradation but partly preserves specific signal transduction
proteins that act as regulators of
protein synthesis and cell growth in the non-weight-bearing soleus muscle.