C-29 Free Communication/Poster - Muscle 3: MAY 29, 2008 7:30 AM - 12:30 PM ROOM: Hall B
PURPOSE: Previous reports suggest a role for muscle activation and loading in regulating Hsp25 expression and phosphorylation (pHsp25) in skeletal muscles. However, Hsp25 and pHsp25 have never been studied for up to 28 days in a model of spinal cord injury or across muscles having different fiber type compositions and functions. Importantly, Hsp25 may attenuate caspase-3 proteolytic activity, a critical initial step in muscle contractile protein breakdown. Thus, the current study quantified time-dependent changes in Hsp25, pHsp25, and caspase-3 activity in rat soleus, adductor longus (AL), plantaris, and tibialis anterior (TA) muscles, 1, 8, or 28 days after a complete mid-thoracic spinal cord transection (ST).
METHODS: Protein levels of Hsp25 and pHsp25 were quantified with Western blot analysis and caspase-3 activity with the Caspase-Glo Assay System (Promega). Two- way ANOVAs were used to assess the main (days of ST and muscle) and interaction effects. Pearson correlation coefficients were calculated between caspase-3 activity, muscle mass, Hsp25, and pHsp25 within each muscle across all days of ST.
RESULTS: Hsp25 was unchanged on days 1 and 8 in all muscles, with the exception of a decrease on day 8 in plantaris. Hsp25 in ST rats was lower than control in all muscles except TA on day 28. pHsp25 was 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 and remained elevated 28 days after ST only in plantaris. 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 directly correlated with muscle mass. These relationships were not observed in other muscles.
CONCLUSIONS: These results suggest that Hsp25 and pHsp25 may play a role in reducing caspase-3 activity after ST in a predominantly fast anti-gravity muscle, but not predominantly slow anti-gravity or predominantly fast flexor muscles. Thus the effects of ST on Hsp25 and caspase-3 are muscle specific and time dependent, factors that should be considered in developing interventions to maintain muscle mass after a spinal cord injury.
Supported by NIH NS16333 and RO3 AR049855.