Analysis of capillary density in skeletal muscle of wild-type and TWEAK-KO mice. Transverse sections of TA muscle prepared from 4.5-month-old wild-type and TWEAK-KO mice were immunostained for CD31 (red) and counterstained for laminin (green). (A) Representative CD31- and laminin-immunostained and merged images are presented here. Scale bars: 50 μm. (B) Quantification of CD31-postive capillaries per myofiber in TA muscle. N = 8 in each group. (C) Relative mRNA levels of VEGF in TA muscle of wild-type and TWEAK-KO mice (N = 4 in each group) measured by qRT-PCR analysis. (D) Primary myotubes were treated with the indicated concentration of TWEAK for 24 hours followed by measurement of mRNA levels of VEGF by qRT-PCR. Relative mRNA levels of VEGF are shown here. Data are presented as mean ± SD. *P <0.05; values vary significantly from untreated myotubes. KO, knockout; TA, tibial anterior; TWEAK, TNF-like weak inducer of apoptosis; VEGF, vascular endothelial growth factor.