Mitochondrial Respiration, Oxidative Capacity, and Oxidative Stress in Skeletal Muscle

Abstract

Biologists and physiologists have been interested in the differences between birds and mammals for many years. Part of this is due to the distinct differences observed in fat breakdown in these animals. Importantly, fat breakdown occurs in the mitochondria, which leads investigators to explore the mitochondrial differences between birds and mammals. Interestingly, when comparisons between birds and mammals have been done, overall mitochondrial function only seems to differ with fatty acid, and not carbohydrate oxidation. The purpose of this study was to continue to explore the differences between bird and mammalian mitochondrial biochemistry. We isolated mitochondria from the skeletal muscle of house finches (Haemorhous mexicanus), house mice (Mus musculus), and deer mice (Peromyscus maniculatus). Our results demonstrate higher maximal and basal mitochondrial respiration in house finches as compared to deer mice, but not in house finches compared to house mice. Although some differences were observed in state 3 and state 4 values, overall mitochondrial function was not different across species. Furthermore, when assaying mitochondrial complex activities, house finches present the highest activity of complex II, which supports prior data suggesting the heightened ability for birds to break down fats. Data on the normal oxidative stress of these three species revealed that house finches have significantly less protein oxidation, but similar levels of lipid oxidation compared to the house and deer mice. Moreover, antioxidant protein expression was higher in house mice compared to house finches for superoxide dismutase 2 (SOD2), whereas glutathione peroxidase (GPX1) had highest expression in house finches, and house mice had higher expression compared to deer mice. In conclusion, this study generally finds markers of mitochondrial performance (i.e. respiration and enzyme activity) of house finches and house mice being higher compared to deer mice. Furthermore, oxidative stress measures determined an inconsistent pattern of antioxidants in the three species, with house finches having significantly less protein damaged compared to both mice species. This study continues to highlight the distinct differences between bird and mammalian physiology by highlighting the mitochondrial maximal and basal respiration differences, complex activity differences, oxidative damage differences, and antioxidant expression differences.