Nitric oxide synthase in skeletal muscle fibres of patients with type 2 diabetes

Muscle-derived nitric oxide (NO) mediates fundamental physiological actions on skeletal muscle including glucose uptake into muscle cells. Recently, we have shown that the altered glucose metabolism in skeletal muscle of patients with type 2 diabetes (T2D) is associated with changes in the metabolic profile of individual muscle fibres, but fibre-type specific changes in NO synthase (NOS) expression in skeletal muscle of T2D patients remain to be elucidated. Here we investigated fibre-type related NOS expression in vastus lateralis muscle of T2D patients compared with healthy individuals with normal glucose tolerance (NGT). Cytophotometrical assay and Western blotting did not reveal any quantitative differences between NOS expression in muscles from NGT and T2D subjects. Positive NOS immunoreactivity in vastus lateralis of T2D patients was found to be associated with fast-oxidative glycolytic (FOG) muscle phenotype. This indicates that NOS expression in T2D patients correlates both with skeletal muscle fibre type distribution and the activity of oxidative and glycolytic enzymes

Skeletal muscle expression of the adhesion-GPCR CD97: CD97 deletion induces an abnormal structure of the sarcoplasmatic reticulum but does not impair skeletal muscle function

CD97 is a widely expressed adhesion class G-protein-coupled receptor (aGPCR). Here, we investigated the presence of CD97 in normal and malignant human skeletal muscle as well as the ultrastructural and functional consequences of CD97 deficiency in mice. In normal human skeletal muscle, CD97 was expressed at the peripheral sarcolemma of all myofibers, as revealed by immunostaining of tissue sections and surface labeling of single myocytes using flow cytometry. In muscle cross-sections, an intracellular polygonal, honeycomb-like CD97-staining pattern, typical for molecules located in the T-tubule or sarcoplasmatic reticulum (SR), was additionally found. CD97 co-localized with SR Ca2+-ATPase (SERCA), a constituent of the longitudinal SR, but not with the receptors for dihydropyridine (DHPR) or ryanodine (RYR), located in the T-tubule and terminal SR, respectively. Intracellular expression of CD97 was higher in slow-twitch compared to most fast-twitch myofibers. In rhabdomyosarcomas, CD97 was strongly upregulated and in part more N-glycosylated compared to normal skeletal muscle. All tumors were strongly CD97-positive, independent of the underlying histological subtype, suggesting high sensitivity of CD97 for this tumor. Ultrastructural analysis of murine skeletal myofibers confirmed the location of CD97 in the SR. CD97 knock-out mice had a dilated SR, resulting in a partial increase in triad diameter yet not affecting the T-tubule, sarcomeric, and mitochondrial structure. Despite these obvious ultrastructural changes, intracellular Ca2+ release from single myofibers, force generation and fatigability of isolated soleus muscles, and wheel-running capacity of mice were not affected by the lack of CD97. We conclude that CD97 is located in the SR and at the peripheral sarcolemma of human and murine skeletal muscle, where its absence affects the structure of the SR without impairing skeletal muscle functio