Loading‐associated expression of TRIM72 and caveolin‐3 in antigravitational soleus muscle in mice

Effects of mechanical loading on the expression level of tripartite motif‐containing 72 (TRIM72) and caveolin‐3 (Cav‐3) in mouse soleus muscle were investigated. Mice were subjected to (1) continuous hindlimb suspension (HS) for 2 weeks followed by 1‐week ambulation recovery or (2) functional overloading (FO) on the soleus by cutting the distal tendons of the plantaris and gastrocnemius muscles. Soleus muscle atrophy was induced by 2‐week hindlimb suspension (HS). Reloading‐associated regrowth of atrophied soleus muscle was observed by 1‐week reloading following HS. HS also depressed the expression level of insulin receptor substrate‐1 (IRS‐1) mRNA, TRIM72, Cav‐3, and phosphorylated Akt (p‐Akt)/total Akt (t‐Akt), but increased the phosphorylated level of p38 mitogen‐activated protein kinase (p‐p38MAPK) in soleus muscle. Thereafter, the expression level of MyoD mRNA, TRIM72 (mRNA, and protein), and Cav‐3 was significantly increased and recovered to the basal level during 1‐week reloading after HS. Although IRS‐1 expression was also upregulated by reloading, the expression level was significantly lower than that before HS. Significant increase in p‐Akt and phosphorylated p70 S6 kinase (p‐p70S6K) was observed by 1‐day reloading. On the other hand, 1‐week functional overloading (FO) induced soleus muscle hypertrophy. In FO‐associated hypertrophied soleus muscle, the expression level of IRS‐1 mRNA, MyoD mRNA, TRIM72 mRNA, p‐Akt, and p‐p70S6K was increased, but the expression of Cav‐3 and p‐p38MAPK was decreased. FO had no effect on the protein expression level of TRIM72. These observations suggest that the loading‐associated upregulation of TRIM72 protein in skeletal muscle may depress the regrowth of atrophied muscle via a partial suppression of IRS‐1. In addition, downregulation of Cav‐3 in skeletal muscle may depress overloading‐induced muscle hypertrophy.