Search

Muscle regeneration depends on muscle stem cell (MuSC) activity. Myogenic regulatory factors, including myoblast determination protein 1 (MyoD), regulate the fate transition of MuSCs. However, the direct target of MYOD in the process is not completely clear. Using previously established MyoD knock-in (MyoD-KI) mice, we revealed that MyoD targets dual-specificity phosphatase (Dusp) 13 and Dusp27. In Dusp13:Dusp27double knock-out mice, the ability for muscle regeneration after injury was reduced. Moreover, single-cell RNA sequencing of MyoD-high expressing MuSCs from MyoD-KI mice revealed that Dusp13and Dusp27are expressed only in specific populations within MyoD-high MuSCs, which also express Myogenin. Overexpressing Dusp13in MuSCs causes premature muscle differentiation. Thus, we propose a model where DUSP13 and DUSP27 contribute to the fate transition of MuSCs from proliferation to differentiation during myogenesis.Graphical Abstract

In patients with chronic kidney disease (CKD), skeletal muscle mass and function are known to occasionally decline. However, the muscle regeneration and differentiation process in uremia has not been extensively studied. In mice with CKD induced by adenine-containing diet, the tibialis anterior muscle injured using a barium chloride injection method recovered poorly as compared to control mice. In the cultured murine skeletal myocytes, stimulation with indoxyl sulfate (IS), a representative uremic toxin, morphologically jeopardized the differentiation, which was counteracted by L-ascorbic acid (L-AsA) treatment. Transcriptome analysis of cultured myocytes identified a set of genes whose expression was down-regulated by IS stimulation but up-regulated by L-AsA treatment. Gene silencing of myomixer, one of the genes in the set, impaired myocyte fusion during differentiation. By contrast, lentiviral overexpression of myomixer compensated for a hypomorphic phenotype caused by IS treatment. The split-luciferase technique demonstrated that IS stimulation negatively affected early myofusion activity that was rescued by L-AsA treatment. Lastly, in mice with CKD compared with control mice, myomixer expression in the muscle tissue in addition to the muscle weight after the injury was reduced, both of which were restored with L-AsA treatment. Collectively, data showed that the uremic milieu impairs the expression of myomixer and impedes the myofusion process. Considering frequent musculoskeletal injuries in uremic patients, defective myocyte fusion followed by delayed muscle damage recovery could underlie their muscle loss and weakness.

In this study, we have revealed that highly fluorescence (FL)-enhancing all-dielectric metasurface biosensors are capable of detecting single-target DNA, which is cell-free DNA (cfDNA) specific to the human practice effect. The ultimately high-precision detection was achieved in a scheme combining the metasurface biosensors with a short-time nucleic acid amplification technique, that is, a reduced-cycle polymerase chain reaction (PCR). In this combined scheme, we obtained a series of FL signals at a single-molecule concentration, reflecting the Poisson distribution, and moreover elucidated that the FL signals exhibit the single-molecule cfDNA detection with more than 84% statistical confidence in an automated FL detection system and with 99.9% statistical confidence in confocal FL microscopy. As a result, we have found a simple and practical test to discriminate the target of 1 copy/test from zero using metasurface biosensors, which has not been realized by other elaborate techniques such as digital PCR.