Received October 26, 2007
Revised December 5, 2007
Accepted after revision December 17, 2007

¹ Univ Illinois,
² UCLA

^* To whom correspondence should be addressed. E-mail: khuey{at}uiuc.edu.

	Abstract

The levels of muscle activation and loading may regulate Hsp25 expression and phosphorylation (pHsp25) which may contribute to attenuating caspase-3 proteolytic activity, a critical step in muscle protein breakdown. However, the effects of spinal cord transection (ST) on Hsp25 and pHsp25 have never been determined among muscles having different fiber type compositions and functions. We quantified Hsp25, pHsp25, and caspase-3 activity in rat soleus, adductor longus (AL), plantaris, and tibialis anterior (TA) muscles at 0 (control), 1, 8, or 28 days after a complete ST. Hsp25 levels were unaffected on days 1 and 8 in all muscles, except for a significant reduction on day 8 in plantaris. Hsp25 levels were lower than control in all muscles except TA on day 28. pHsp25 levels were lower than control after 8 and 28 days in plantaris and AL and after 28 days in soleus, but higher than control in TA after 8 and 28 days. Caspase-3 activity was higher in ST than control rats on day 8 in all muscles except TA. Caspase-3 activity was negatively correlated with muscle mass for all muscles. In plantaris, Hsp25 and pHsp25 were negatively correlated with caspase-3 activity and Hsp25 was correlated with muscle mass. These relationships were not observed in other muscles. Thus the effects of ST on Hsp25 and caspase-3 are muscle specific and time dependent, factors that should be considered in developing any intervention to maintain muscle mass after a spinal cord injury.

Key Words: Muscle, Skeletal muscle, Spinal cord injury