Metabolic shift in TA muscles of WT, Tg, and Ghrl KO mice. (A) Representative images of succinate dehydrogenase (SDH) staining (scale bars: 200 μm) representing the oxidative capacity of TA muscles of 3-month old (young) and 24-month old (old) mice and quantification of SDH-positive fibers in TA muscle presented as the percentage of SDH-positive area above the total muscle surface. Young mice: WT= 5, Tg= 4, Ghrl KO= 5; old mice: WT= 4, Tg= 3, Ghrl KO= 5. (B) Representative Western blots images and protein densitometry quantification for mitochondrial transcription factor A (TFAM), ATP-synthase β-subunit (β-ATPase), succinate-dehydrogenase complex subunit-A (SDHA), peroxisome proliferator-activated receptor gamma (PPARγ), and PPARγ-coactivator-1-α (PGC1α) protein levels. Protein levels were probed in gastrocnemii of old mice, WT= 4, Tg= 5, Ghrl KO= 5. (C) Representative images of cytochrome c oxidase subunit 4 (COX4) immunofluorescence (scale bars: 200 μm) and quantification. Young mice: WT = 3, Tg = 3, Ghrl KO = 3; old mice: WT = 4, Tg = 4, Ghrl KO = 4. Data are presented as mean ± SEM. *p<0.05 and **p<0.01, old vs. young; $p<0.05 and $$p<0.01, Tg and Ghrl KO vs. WT.