Fig. 4

Metabolism and mitochondrial functions are reduced in rat skeletal muscles, but not in mouse skeletal muscles. Graphic representation of pathways enriched by downregulated age-related genes in diaphragm, gastrocnemius, soleus, and tibialis anterior muscles from male mice and rats across multiple ages (from 6 to 27 months). Pathways enriched by linear-down, early-down and late-down genes in each muscle (from mice and rats respectively) are depicted graphically as circles. Each column of circles, for each muscle, corresponds to the comparison between 6 month and the older age (12, 18, 21, 24, and 27 months for mice and 9, 12, 18, 21, 24, and 27 months for rats). The circle size represents the number of age-related genes enriched to each pathway: small circles denote enrichment of the pathway by 0–5 genes; medium circles, enrichment by 6–15 genes and large circles, enrichment by > 15 genes. The circle color key indicates the average fold-change in the expression levels of these genes versus 6 months, with the deepest blue being a decrease of ≥ four fold. Dark squares on the right-hand side of the graphical heatmap indicate that enrichment for a specific pathway was statistically significant