OVERLOAD-INDUCED C-MYC ONCOPROTEIN IS REDUCED IN AGED SKELETAL-MUSCLE

The C-Myc oncoprotein was examined in anterior latissimus dorsi (ALD) muscles of young (6 weeks) and aged (90 weeks) quail after 0.5 hours t o 14 days of stretch. Western analyses of nuclear extracts showed an i ncrease in the C-Myc oncoprotein after 1 h of stretch in young adult b irds, and C-Myc remained elevated for 3 days of stretch. The onset and total accumulation of the C-Myc oncoprotein was less in muscles from aged quail as compared to muscles from young adult birds. Immunocytoch emical analyses showed that C-Myc was localized in nuclei and averaged 0.2 +/- 0.04 nuclei/muscle fiber cross-section (n/f) in control muscl es. C-Myc immunopositive nuclei sere more numerous in muscles from you ng adult birds (1.7 +/- 0.2 n/f) compared to aged birds (1.1 +/- 0.1 n /f) after 2-12 h of stretch. C-Myc positive nuclei declined to 0.7 +/- 0.1 n/f after 3 days of stretch, iii muscles from young adult birds; however this was greater than in muscles from aged birds at the same t ime point (0.3 +/- 0.04 n/f). Many nuclei that were associated with mu scle fibers expressed the C-Myc oncoprotein but did not incorporate br omodeoxyuridine, a marker of DNA synthesis and activated satellite cel ls. These data show a decreased ability of skeletal muscles from aged quads to initiate a program inclusive of early C-Myc oncoprotein accum ulation in response to stretch.