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The interplay between skeletal muscle and bone is primarily mechanical; however, biochemical crosstalk by secreted mediators has recently gained increased attention. The aim of this study was to investigate metabolic effects of conditioned medium from osteoblasts (OB-CM) on myotubes and vice versa. Human skeletal muscle cells incubated with OB-CM showed increased glucose uptake and oxidation, and mRNA expression of the glucose transporter (GLUT) 1, while fatty acid uptake and oxidation, and mRNA expression of the fatty acid transporter CD36 were decreased. This was supported by proteomic analysis, where expression of proteins involved in glucose uptake, glycolytic pathways, and the TCA cycle were enhanced, and expression of several proteins involved in fatty acid metabolism were reduced. Similar effects on energy metabolism were observed in human bone marrow stromal cells differentiated to osteoblastic cells incubated with conditioned medium from myotubes (SKM-CM), with increased glucose uptake and reduced oleic acid uptake. Proteomic analyses of the two conditioned media revealed many common proteins. Thus, our data may indicate a shift in fuel preference from fatty acid to glucose metabolism in both cell types, induced by conditioned media from the opposite cell type, possibly indicating a more general pattern in communication between these tissues., The interplay between skeletal muscle and bone is primarily mechanical; however, biochemical crosstalk by secreted mediators has recently gained increased attention. The aim of this study was to investigate metabolic effects of conditioned medium from osteoblasts (OB-CM) on myotubes and vice versa. Human skeletal muscle cells incubated with OB-CM showed increased glucose uptake and oxidation, and mRNA expression of the glucose transporter (GLUT) 1, while fatty acid uptake and oxidation, and mRNA expression of the fatty acid transporter CD36 were decreased. This was supported by proteomic analysis, where expression of proteins involved in glucose uptake, glycolytic pathways, and the TCA cycle were enhanced, and expression of several proteins involved in fatty acid metabolism were reduced. Similar effects on energy metabolism were observed in human bone marrow stromal cells differentiated to osteoblastic cells incubated with conditioned medium from myotubes (SKM-CM), with increased glucose uptake and reduced oleic acid uptake. Proteomic analyses of the two conditioned media revealed many common proteins. Thus, our data may indicate a shift in fuel preference from fatty acid to glucose metabolism in both cell types, induced by conditioned media from the opposite cell type, possibly indicating a more general pattern in communication between these tissues.

Regular physical exercise evokes profound physiological responses which are strongly associated with many health benefits. However, the details of cellular networks and mechanisms underlying the adaptive responses to exercise remain to be elucidated. We have previously shown the usefulness of electrical pulse stimulation (EPS) to investigate metabolic effects of exercise in cultured human myotubes. The aim of the present study was to uncover networks of signaling pathways and regulatory molecules responsible for the metabolic effects of exercise in human skeletal muscle cells exposed to chronic EPS. Differentiated myotubes were subjected to two different EPS protocols (protocol 1; 2 ms, 10 V, 0.1 Hz for 24 h or protocol 2; 2 ms, 30 V, and 1 Hz for 48 h). Fuel handling was assessed using radiolabeled substrates. The transcriptome, cell proteome, and secreted proteins from EPS-treated and untreated myotubes were analyzed using a combination of high-throughput RNA sequencing, microarray, and high-resolution liquid chromatography mass spectrometry. Independent validation of selected putative myokines were measured using ELISA or multiplex assay. Oxidative metabolism was enhanced in human myotubes exposed to EPS protocol 1. A total of 81 differentially regulated proteins and 952 differentially expressed genes (DEGs) were observed in the cells after EPS protocol 1. Gene ontology (GO) analysis indicated that significantly regulated proteins and genes were enriched in biological processes related to glycolytic pathways, positive regulation of fatty acid oxidation, and oxidative phosphorylation, as well as muscle contraction, autophagy/mitophagy, and oxidative stress. Moreover, proteomic identification of secreted proteins revealed extracellular levels of 137 proteins were changed in myotubes subjected to EPS protocol 1. We also found some degree of overlap between the DEGs found in myotubes submitted to EPS protocol 1 and protocol 2. Among these DEGs was a myokine, leukemia, Regular physical exercise evokes profound physiological responses which are strongly associated with many health benefits. However, the details of cellular networks and mechanisms underlying the adaptive responses to exercise remain to be elucidated. We have previously shown the usefulness of electrical pulse stimulation (EPS) to investigate metabolic effects of exercise in cultured human myotubes. The aim of the present study was to uncover networks of signaling pathways and regulatory molecules responsible for the metabolic effects of exercise in human skeletal muscle cells exposed to chronic EPS. Differentiated myotubes were subjected to two different EPS protocols (protocol 1; 2 ms, 10 V, 0.1 Hz for 24 h or protocol 2; 2 ms, 30 V, and 1 Hz for 48 h). Fuel handling was assessed using radiolabeled substrates. The transcriptome, cell proteome, and secreted proteins from EPS-treated and untreated myotubes were analyzed using a combination of high-throughput RNA sequencing, microarray, and high-resolution liquid chromatography mass spectrometry. Independent validation of selected putative myokines were measured using ELISA or multiplex assay. Oxidative metabolism was enhanced in human myotubes exposed to EPS protocol 1. A total of 81 differentially regulated proteins and 952 differentially expressed genes (DEGs) were observed in the cells after EPS protocol 1. Gene ontology (GO) analysis indicated that significantly regulated proteins and genes were enriched in biological processes related to glycolytic pathways, positive regulation of fatty acid oxidation, and oxidative phosphorylation, as well as muscle contraction, autophagy/mitophagy, and oxidative stress. Moreover, proteomic identification of secreted proteins revealed extracellular levels of 137 proteins were changed in myotubes subjected to EPS protocol 1. We also found some degree of overlap between the DEGs found in myotubes submitted to EPS protocol 1 and protocol 2. Among these DEGs was a myokine, leukemia