Adaptive response of slow and fast skeletal muscle following mechanical hindlimb suspension in Wistar male rats

Mechanical hindlimb suspension of lower extremities leads to prompt atrophy in rats’ skeletal muscles. The present research was designed to study cross-section area (CSA) and the expression level of the genes ATF4, P53, MST1, and atrogin-1 in slow and fast skeletal muscles following mechanical hindlimb suspension. 20 male Wistar rats were assigned randomly in to two groups: control (Con) and hind-limb suspension (HU) (10 rats per each group). In HU group, tail suspension was designed for 14 constitutive days; however, animals in the control group passed a normal life.  The findings indicated that hind-limb suspension could relatively diminish CSA, myonuclei number per fiber and the weight of both soleus and EDL muscles. However, these reductions were not significant for EDL muscle. Furthermore, the expression level of the MST1, atrogin-1, ATF4, and p53 in soleus muscles elevated significantly. Moreover, the expression level of all four genes increased significantly in EDL muscle. Comparison of genes expression level between two soleus and EDL muscles showed that expression of MST1, ATF4, and p53 genes were higher in soleus than EDL, but it was not the case for atrogin-1 as its expression level was more in EDL compared to soleus. Our study provides novel evidence that immobilization of hind-limbs can induce a more powerful atrophic response in slow muscles in comparison to fast ones.