Aims: 

Uncoupling proteins (UCPs) are mitochondrial transport proteins likely involved in thermogenesis by dissipating the proton gradient and releasing stored energy as heat. The physiological function of skeletal muscle-specific UCP3 is, however, contradictory; some studies support a role for UCP3 in energy metabolism, others relate UCP3 expression to fatty acid oxidation or protection of mitochondria against lipid-induced oxidative stress. In an attempt to clarify the role of UCP3 in skeletal muscle, protein levels were measured in different hind leg muscles of control, fasted and wild seasonal raccoon dogs (Nyctereutes procynoides), which have a prolonged fasting-induced winter sleep.

Methods: 

UCP3 protein concentrations were measured by Western blot. In addition, the relationship between selected metabolic and endocrine factors and UCP3 was examined.

Results: 

The expression of UCP3 significantly varies between different hind leg muscles and is most abundant in tibialis anterior (TA) muscle. UCP3 protein expression significantly correlates with type IIA fiber. Fasting decreases UCP3 protein level in TA and extensor digitorum longus (EDL) muscles. In wild dogs the levels are significantly lower compared to farmed controls. UCP3 positively correlates with plasma insulin but negatively with free fatty acids.

Conclusion: 

Our results suggest that UCP3 is not directly involved in fatty acid metabolism in raccoon dog skeletal muscle. In seasonal animal model the changes in UCP3 concentration are different to those previously observed in rodents and humans after fasting.