Globular Adiponectin Activates Motility and Regenerative Traits of Muscle Satellite Cells

Regeneration of adult injured skeletal muscle is due to activation of satellite cells, a population of stem cells resident beneath the basal lamina. Thus, information on soluble factors affecting satellite cell activation, as well as migration towards injury and fusion into new myofibers are essential. Here, we show that globular adiponectin (gAd), positively affects several features of muscle satellite cells. gAd activates satellite cells to exit quiescence and increases their recruitment towards myotubes. gAd elicits in satellite cells a specific motility program, involving activation of the small GTPase Rac1, as well as expression of Snail and Twist transcription factors driving a proteolytic motility, useful to reach the site of injury. We show that satellite cells produce autocrine full length adiponectin (fAd), which is converted to gAd by activated macrophages. In turns, gAd concurs to attract to the site of injury both satellite cells and macrophages and induces myogenesis in muscle satellite cells. Thus, these findings add a further role for gAd in skeletal muscle, including the hormone among factors participating in muscle regeneration

Plasticity of the Muscle Stem Cell Microenvironment

Satellite cells (SCs) are adult muscle stem cells capable of repairing damaged and creating new muscle tissue throughout life. Their functionality is tightly controlled by a microenvironment composed of a wide variety of factors, such as numerous secreted molecules and different cell types, including blood vessels, oxygen, hormones, motor neurons, immune cells, cytokines, fibroblasts, growth factors, myofibers, myofiber metabolism, the extracellular matrix and tissue stiffness. This complex niche controls SC biology-quiescence, activation, proliferation, differentiation or renewal and return to quiescence. In this review, we attempt to give a brief overview of the most important players in the niche and their mutual interaction with SCs. We address the importance of the niche to SC behavior under physiological and pathological conditions, and finally survey the significance of an artificial niche both for basic and translational research purposes

Natação e aspectos morfológicos do músculo esquelético em processo de reparo após criolesão Swimming and morphology of skeletal muscle repair process after cryoinjury

O objetivo do estudo foi investigar a influência da natação sobre as alterações morfológicas do músculo esquelético em processo de reparo após criolesão. Foram usados 45 ratos divididos em cinco grupos: controle (n=5); sham (n=5), adaptação (n=5), criolesionados e tratados com natação sacrificados após 7, 14 e 21 dias (n=15); criolesionados e sem tratamento aquático sacrificados após 7, 14 e 21 dias (n=15). As sessões de natação foram realizadas 6 vezes por semana com 90 min de duração cada. Ao término do protocolo os animais foram sacrificados e a análise morfológica da área da lesão foi realizada. A análise morfológica semiquantitativa demonstrou que os músculos do grupo controle apresentaram aspecto histológico normal. O grupo sham apresentou edema, mionecrose e infiltrado inflamatório em grau 1. Nos grupos 7, 14 e 21 dias, não existiram diferenças estatisticamente significativas nas 4 etapas de remodelamento tecidual avaliadas (infiltrado inflamatório, edema, necrose e fibras musculares imaturas) entre os grupos lesionados quando comparados aos grupos com lesão e tratamento aquático. Em conclusão, foi possível verificar que a natação não causou alterações morfológicas durante o reparo do músculo esquelético após criolesão.<br>The aim of study was investigate the influence of swimming on the morphological changes in skeletal muscle repair process following cryoinjury. There were used 45 rats divided into 5 groups: control (n=5), sham (n=5), adaptation (n=5), cryolesioned treated with swimming and sacrificed after 7, 14 and 21 days (n=15), untreated and cryolesioned sacrificed after 7, 14, and 21 days (n=15). Animals swan for 90 min/ each session and 6 times a week. At the end of the protocol, the animals were sacrificed and morphological analysis of the lesion area was performed. The semi-quantitative morphological analysis showed that the muscles in the control group exhibited normal histological aspects while the sham group exhibited edema, myonecrosis and inflammatory infiltrate grade 1. In groups 7, 14, and 21 days, the results indicated that there were no statistically significant differences in four stages of tissue remodeling evaluated (inflammatory infiltration, edema, necrosis, and immature muscle fibers) between the injured groups compared to groups with lesion and treated with swimming. In conclusion, it was verified that swimming did not alter morphological aspects of skeletal muscle during the repair process following cryoinjury

Sox15 and Fhl3 transcriptionally coactivate Foxk1 and regulate myogenic progenitor cells

The regulation of myogenic progenitor cells during muscle regeneration is not clearly understood. We have previously shown that the Foxk1 gene, a member of the forkhead/winged helix family of transcription factors, is expressed in myogenic progenitor cells in adult skeletal muscle. In the present study, we utilize transgenic technology and demonstrate that the 4.6 kb upstream fragment of the Foxk1 gene directs β-galactosidase expression to the myogenic progenitor cell population. We further establish that Sox15 directs Foxk1 expression to the myogenic progenitor cell population, as it binds to an evolutionarily conserved site and recruits Fhl3 to transcriptionally coactivate Foxk1 gene expression. Knockdown of endogenous Sox15 results in perturbed cell cycle kinetics and decreased Foxk1 expression. Furthermore, Sox15 mutant mice display perturbed skeletal muscle regeneration, due in part to decreased numbers of satellite cells and decreased Foxk1 expression. These studies demonstrate that Sox15, Fhl3 and Foxk1 function to coordinately regulate the myogenic progenitor cell population and skeletal muscle regeneration

Nanopore long-read RNAseq reveals widespread transcriptional variation among the surface receptors of individual B cells

Understanding gene regulation and function requires a genome-wide method capable of capturing both gene expression levels and isoform diversity at the single-cell level. Short-read RNAseq is limited in its ability to resolve complex isoforms because it fails to sequence full-length cDNA copies of RNA molecules. Here, we investigate whether RNAseq using the long-read single-molecule Oxford Nanopore MinION sequencer is able to identify and quantify complex isoforms without sacrificing accurate gene expression quantification. After benchmarking our approach, we analyse individual murine B1a cells using a custom multiplexing strategy. We identify thousands of unannotated transcription start and end sites, as well as hundreds of alternative splicing events in these B1a cells. We also identify hundreds of genes expressed across B1a cells that display multiple complex isoforms, including several B cell-specific surface receptors. Our results show that we can identify and quantify complex isoforms at the single cell level