Sialylation and Muscle Performance: Sialic Acid Is a Marker of Muscle Ageing

Sialic acids (Sia) are widely expressed as terminal monosaccharides on eukaryotic glycoconjugates. They are involved in many cellular functions, such as cell–cell interaction and signal recognition. The key enzyme of sialic acid biosynthesis is the bifunctional UDP-N-acetylglucosamine-2-epimerase/N-acetylmannosamine kinase (GNE), which catalyses the first two steps of Sia biosynthesis in the cytosol. In this study we analysed sialylation of muscles in wild type (C57Bl/6 GNE+/+) and heterozygous GNE-deficient (C57Bl/6 GNE+/−) mice. We measured a significantly lower performance in the initial weeks of a treadmill exercise in C57Bl/6 GNE+/− mice compared to wild type C57Bl/6 GNE+/+animals. Membrane bound Sia of C57Bl/6 GNE+/− mice were reduced by 33–53% at week 24 and by 12–15% at week 80 in comparison to C57Bl/6 GNE+/+mice. Interestingly, membrane bound Sia concentration increased with age of the mice by 16–46% in C57Bl/6 GNE+/+, but by 87–207% in C57Bl/6 GNE+/−. Furthermore we could identify specific morphological changes in aged muscles. Here we propose that increased Sia concentrations in muscles are a characteristic feature of ageing and could be used as a marker for age-related changes in muscle.