C-29 Free Communication/Poster - Muscle 3: MAY 29, 2008 7:30 AM - 12:30 PM ROOM: Hall B
Heat Shock Proteins (HSP) serve a protective function in skeletal muscle and may also aid in protein synthesis. A decline in HSPs may contribute to age-related sarcopenia. Discrepancies exist in the literature regarding the activity of HSPs in aging muscle, in particular, following a hypertrophic stimulus.
PURPOSE: The purpose of this research was to investigate (1) if a hypertrophic stimulus would lead to HSP production in aging muscle, and (2) if a change in HSP70 is fiber type specific.
METHODS: Young (17 wk) and older (90 wk) male Fisher 344 rats were subject to one of two conditions: (1) bilateral surgical ablation of the gastrocnemius muscle to promote compensatory hypertrophy in synergist muscles (plantaris and soleus) or (2) non-surgical control. Four weeks post-surgery, animals were sacrificed, and soleus and plantaris muscles were removed. Serial cross-sections were immunohistochemically assayed for myosin heavy chains (MHC) and HSP70. MHC staining properties of individual fibers were compared to discern muscle fiber types. Pixel density was used to assess HSP70 staining intensity. Cross-sectional area (CSA) was measured on at least 50 fibers per fiber type. Group comparisons were made using a two-way ANOVA. Significant interactions were determined with Tukey's post hoc tests.
RESULTS: In young animals, HSP70 expression increased in overloaded soleus and plantaris muscles (P < 0.05 and P < 0.01, respectively). In aged animals, HSP70 increased in fibers of the overloaded plantaris (P < 0.05), but there was no significant increase in the overloaded soleus. Regardless of age, an increase in HSP70 was restricted to type I or IIA fibers. HSP70 expression in IID/B fibers was not significant in the control or surgical groups at any age. In the plantaris, type I and IIA fibers from overloaded muscle had larger CSAs than control muscle, regardless of age (P < 0.05). For young rats, IID/B fibers also had larger CSAs in the overloaded plantaris relative to control. CSA of fibers in the overloaded soleus did not change, regardless of age or fiber type.
CONCLUSION: These data suggest HSP70 is upregulated, but attenuated, during hypertrophy of older muscle fibers, and this upregulation is fiber type specific. This observation is consistent with the hypothesis that HSP70 plays a role in skeletal muscle hypertrophy.