Heat shock transcription factor activation and Hsp72 accumulation in aged skeletal muscle

Induction of the protective heat shock proteins (Hsps), and of Hsp72 in par ticular, has been reported to be decreased in certain tissues from aged ani mals. To determine if both fast and slow skeletal muscles from aged animals demonstrate an altered ability to induce and accumulate Hsp72, adult (age, 6 months) and aged (age, 20 months) Fischer 344 rats were subjected to hea t stress. At selected times (0, 1, 3, and 24 hours) after a 10-minute, 41 d egrees C heat stress, fast (white gastrocnemius [WG]) and slow (soleus) ske letal muscles were examined for either heat shock transcription factor (HSF ) activation (trimerization and DNA-binding activity) or Hsp72 content usin g electrophoretic gel mobility shift assays and Western blotting, respectiv ely. Immediately after heat stress, the level of HSF activation between age d and adult animals was similar for both muscles. HSF activation was undete ctable at 1 and 3 hours after heat stress in all cases. Twenty-four hours a fter heat stress, Hsp72 content in the WG muscles from both aged and adult animals was significantly increased compared with unstressed, age-matched c ontrols (P < 0.05). In contrast, perhaps because of their high constitutive Hsp72 levels, soleus muscles from both aged and adult animals did not demo nstrate a significant increase in Hsp72 content after heat shock, but there was a trend toward increased levels. Hsp72 content in both the soleus and WG muscles demonstrated no significant differences between adult and aged a nimals in either the unstressed state (controls) or after heat shock. These results suggest that skeletal muscles from aged animals are capable of ind ucing the heat shock response and accumulating Hsp72.