Abstract
We have reported the effectiveness of resistance exercise against skeletal muscle atrophy caused by hindlimb unloading (HU). This study was undertaken to examine an association of ubiquitin proteasome activity with this exercise effect. Adult F344 female rats were placed into either weight-bearing control (n=7) or HU group (n=14). Rats in the HU group had their hindlimbs suspended for 3 weeks. The HU group was subdivided to a group with (n=7) or without (n=7) an intermittent resistance exercise (IRE), in which the rats were put in a cylindrical wire mesh inclined 60 or 80 degree with a weight of 50-70% of body mass hung from the tail. The IRE was performed for 10 min, three times a day (total 30 min/day) throughout the HU. After the HU period, the soleus (SOL) and medial gastrocnemius (MG) muscles were dissected out, weighed, and then homogenated. The protein expression levels of two ubiquitin ligases, MAFbx-1 and MuRF-1 were determined using a western blotting method. The HU resulted in significant atrophy in the SOL (-47%) and MG (-31%). The IRE attenuated the atrophy of the SOL (37%) and MG (54%). The HU resulted in significant increases in the expression levels of MAFbx-1 and MuRF-1. However, IRE attenuated up-regulations of MAFbx-1 and MuRF-1 with HU in both muscles. These results show that down-regulation of ubiquitin ligase protein is account for the inhibitory effect of IRE against muscle atrophy. [J Physiol Sci. 2008;58 Suppl:S160]
