Skeletal muscle HSP60 expression is fiber-type specific and increases after endurance training

Heat shock protein (Hsp) 60 is primarily localized inside mitochondrial, plays a key role in the translocation of proteins and cytoprotection, and its levels increase in skeletal muscle upon exercise. The purpose of this study was to examine muscle fiber specificity of HSP60 at rest and after an endurance training program of 6 weeks. Forth-eight young (7-weeks old) healthy mice (BALB/c) were subdivided into sedentary and trained groups. Training was performed over a period of 6 weeks on a rota-rod, at a gradually increasing duration and speed. Eight mice of each group were sacrificed after 15, 30 and 45 days. Two days after the last exercise session all mice were sacrificed by cervical dislocation and posterior (gastrocnemius, soleus and plantaris) muscles group of hindlimb were dissected, weighed and frozen in liquid nitrogen or embedded into paraffin. Immunohystochemistry and immunofluorescence analysis showed that skeletal muscle type I fiber expressed high levels of Hsp60. The western blotting analyses of the entire posterior muscle group did not show any difference in the protein levels after endurance training, while the analysis of soleus muscle (reach in type I fibers) showed an over expression of Hsp60 after 30 and 45 days of endurance training. These results indicated that Hsp60 is fibre type–specific. This may be due to the differences in mitochondrial content between slow and fast fibres. Anyway Hsp60 may be localized also in the cytoplasm, in the outer membrane, in the interstitium and in the blood stream, hence the role of this protein in endurance training should be elucidated.