Overload-induced C-Myc oncoprotein is reduced in aged skeletal muscle.

Abstract

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 to 14 days of stretch. Western analyses of nuclear extracts showed an increase in the C-Myc oncoprotein after 1 h of stretch in young adult birds, 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. Immunocytochemical analyses showed that C-Myc was localized in nuclei and averaged 0.2 +/- 0.04 nuclei/muscles fiber cross-section (n/f) in control muscles. C-Myc immunopositive nuclei were more numerous in muscles from young 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, in muscles from young adult birds; however, this was greater than in muscles from aged birds at the same time point (0.3 +/- 0.04 n/f). Many nuclei that were associated with muscle fibers expressed the C-Myc oncoprotein but did not incorporate bromodeoxyuridine, a marker of DNA synthesis and activated satellite cells. These data show a decreased ability of skeletal muscles from aged quails to initiate a program inclusive of early C-Myc oncoprotein accumulation in response to stretch.