Fig. 3

Increased adipose-like tissues, degeneration and regeneration of myofibers were observed in aged muscle. a Histogram of muscle fiber diameter sizing showed smaller fibers in aged mice. b-c Histological observation of rectus femoris obtained from 3-month-old wild-type mice. d-e Mild degeneration and severe lipid infiltration in the rectus femoris of 24-month-old mice. Yellow arrow indicates lipid infiltration. f Significant increase of the adipose-like tissues was found in aged mice. g-j The swelling fibers and severe degenerated fibers were observed in the skeletal muscle of 24-month-old mice. k Significant increase of the degenerated myofibers was observed in aged mice. l-m Myofibers with central nuclei, indicated regenerating myofibers, were found in the aged skeletal muscle. n Significant increase of the regenerated myofibers was found in aged mice. In (f), (k) and (n), there were 6 mice in each group; 6 micrographs (100X) for each mouse were conducted in a blinded fashion. The degenerated myofibers were defined and quantified follow the information on National Toxicology Program of NIH website. The area of adipose tissues was calculated using SPOT software. The results are presented as the mean ± SD. ∗p < 0.05; ∗∗p < 0.005. Tissues of rectus femoris were collected from male mice at 3 (young) and 24 (old) months of age. Black arrow indicates the collagen accumulation; black arrow head indicates the degenerated myofiber; red arrow indicates the regenerated myofiber; asterisk indicates the swollen myofiber