Age-related changes in satellite cell proliferation by compensatory activation in rat diaphragm muscles

To investigate the age-related changes in satellite cell (SC) proliferation in vivo, we used a compensatory activation (CAC) model of the hemi-diaphragm muscle. Young (2-month), adult (14-month) and old (24-month) rats were randomly divided into control and CAC groups. In the CAC group, denervation surgery in the left hemi-diaphragm was performed to induce CAC of the right hemi-diaphragm. Six days after the surgery, the CAC diaphragm muscle was removed and separated into two blocks for immunohistochemical staining and real time RT-PCR procedures. The number of SCs in type I and IIa fibers were not affected significantly by the CAC in any age groups, but that in type IIx/b fibers was significantly increased in the young and adult groups. As compared to the age-matched control group, the Pax7 mRNA expression level was significantly higher in the young and adult CAC groups, but not in the old CAC group. These results may suggest that the mechanism of SC proliferation in type IIx/b fibers is impaired in aged diaphragm muscles.