Succinate dehydrogenase (SDH) staining analysis for oxidative capacity in TA muscle of TWEAK-KO mice. Frozen transverse TA muscle sections from 4.5- or 12-month old wild-type and TWEAK-KO mice were used to stain for SDH. (A) Representative SDH-stained images are presented here. TA muscle of TWEAK-KO showed relatively dark staining for SDH compared to wild-type mice. Scale bars: 50 μm. Quantification of SDH-positive fibers in TA muscle of (B) 4.5-month, and (C) 12-month old wild-type and TWEAK-KO mice. Data are presented as mean ± SD. *P <0.05; values vary significantly from wild-type mice. KO, knockout; TA, tibial anterior; TWEAK, TNF-like weak inducer of apoptosis.