Adiponectin is Expressed in Skeletal Muscle and Influences Muscle Phenotype and Function

Adiponectin (Ad) plays a vital role in various diseases and generally mediates anti‐diabetic and anti‐inflammatory effects. It was originally thought that Ad expression was limited to adipocytes, however, recent evidence has demonstrated its expression in other cells/tissues such as cardiac muscle. We present evidence that Ad is expressed in L6 myotubes and mouse soleus, as assessed by RT‐PCR and Western blot analysis. Furthermore, Ad was detected within the muscle fibers of wild‐type (WT) mouse tibialis anterior sections via IHC. Subsequently, we employed the Ad‐null (KO) mouse to determine the effect of Ad on muscle phenotype and function. Body mass increased significantly in KO mice (+5.5 ± 2.9% relative to WT) with no change in muscle mass. Epidydymal fat mass appeared to increase in KO mice (+35.1 ± 22.8%) vs. WT mice but was not statistically significant ( p =0.16). Intramuscular triglyceride content was significantly greater in KO mice (+75.1 ± 25.1%) than WT. Muscle fiber type composition did not change, though there was a trend for an increase in muscle fiber area in KO mice (type IIA +13.6 ± 3.2%, IIB +25.5 ± 5.7%, IID +12.3 ± 12.7%) vs. WT. Using in situ electrical muscle stimulation, peak tetanic force was lower in KO mice (−47.5 ± 6.0) than WT with no change in muscle fatigue rates. Future studies will assess if muscle‐derived and circulating Ad elicit differential effects on skeletal muscle phenotype and function.