Fig 6.
Daily IL-15 therapy in mice mimics the anti-aging effects of exercise on skin structure and mitochondria. Chow-fed mice were injected once daily via tail vein with PBS, recombinant mouse IL-15 (rmIL-15), or underwent forced exercise training (EX) for 33 consecutive days and were sacrificed at the age indicated. (A) Quadriceps muscle mtDNA copy number and (B) cytochrome c oxidase (COX) activity. n = 6–8 per group. (C) Skin mtDNA copies and (D) COX activity. n = 6–8 per group. (E) Cage activity and (F) oxygen uptake (VO2) over a 24-h period in 23-month-old mice treated with PBS, rmIL-15, or EX. (G) Peak grip strength in each treatment group normalized to body weight. (H) Quantification of dermal collagen content (left) and representative images of trichrome-stained skin cross sections from each treatment group (right). n = 4–8 per group. White asterisk indicates the dermis. (I) Quantification of stratum spinosum thickness and representative images of H&E-stained cross sections of skin from each group. n = 4–8 per group. Arrow indicates the stratum spinosum layer. Scale bar is 100 μm. (J) Plasma IL-6 and (K) MCP-1 drawn at sacrifice from mice in each treatment group. (L) Graphical illustration of the effects of exercise-induced muscle IL-15 signaling to skin tissue. Five-month-old and 23-month-old mice were injected with 500 and 1000 pg of rmIL-15, respectively. All data were compared using a two-way anova. *indicates a significant difference (P < 0.05) from PBS or the indicated group. †indicates an overall effect of age. Data are mean ± SE.