Dynamics of skeletal muscle-resident stem cells during myogenesis in fibrodysplasia ossificans progressiva

Fibrodysplasia ossificans progressiva (FOP) is a rare genetic disease in which extraskeletal (heterotopic) bone forms within tissues such as skeletal muscles, often in response to injury. Mutations in the BMP type I receptor ACVR1/ALK2 cause FOP by increasing BMP pathway signaling. In contrast to the growing understanding of the inappropriate formation of bone tissue within the muscle in FOP, much is still unknown about the regenerative capacity of adult diseased muscles. Utilizing an inducible ACVR1R206H knock-in mouse, we found that injured Acvr1R206H/+ skeletal muscle tissue regenerates poorly. We demonstrated that while two resident stem cell populations, muscle stem cells (MuSCs) and fibro/adipogenic progenitors (FAPs), have similar proliferation rates after injury, the differentiation potential of mutant MuSCs is compromised. Although MuSC-specific deletion of the ACVR1R206H mutation does not alter the regenerative potential of skeletal muscles in vivo, Acvr1R206H/+ MuSCs form underdeveloped fibers that fail to fuse in vitro. We further determined that FAPs from Acvr1R206H/+ mice repress the MuSC-mediated formation of Acvr1R206H/+ myotubes in vitro. These results identify a previously unrecognized role for ACVR1R206H in myogenesis in FOP, via improper interaction of tissue-resident stem cells during skeletal muscle regeneration.

The Effect of Long-Lasting Swimming on Rats Skeletal Muscles Energy Metabolism after Nine Days of Dexamethasone Treatment

This study investigates the effect of Dexamethasone (Dex) treatment on blood and skeletal muscle metabolites level and skeletal muscle activity of enzymes related to energy metabolism after long-duration swimming. To evaluate whether Dex treatment, swimming, and combining these factors act on analyzed data, rats were randomly divided into four groups: saline treatment non-exercise and exercise and Dex treatment non-exercised and exercised. Animals in both exercised groups underwent long-lasting swimming. The concentration of lipids metabolites, glucose, and lactate were measured in skeletal muscles and blood according to standard colorimetric and fluorimetric methods. Also, activities of enzymes related to aerobic and anaerobic metabolism were measured in skeletal muscles. The results indicated that Dex treatment induced body mass loss and increased lipid metabolites in the rats’ blood but did not alter these changes in skeletal muscles. Interestingly, prolonged swimming applied after 9 days of Dex treatment significantly intensified changes induced by Dex; however, there was no difference in skeletal muscle enzymatic activities. This study shows for the first time the cumulative effect of exercise and Dex on selected elements of lipid metabolism, which seems to be essential for the patient’s health due to the common use of glucocorticoids like Dex.

TMEM8C-mediated fusion is regionalized and regulated by NOTCH signalling during foetal myogenesis

The location and regulation of fusion events within skeletal muscles during development remain unknown. Using the fusion marker myomaker (Mymk), named TMEM8C in chicken, as a readout of fusion, we identified a co-segregation of TMEM8C-positive cells and MYOG-positive cells in single-cell RNA-sequencing datasets of limbs from chicken embryos. We found that TMEM8C transcripts, MYOG transcripts and the fusion-competent MYOG-positive cells were preferentially regionalized in central regions of foetal muscles. We also identified a similar regionalization for the NOTCH ligand JAGGED2 along with an absence of NOTCH activity in TMEM8C+ fusion-competent myocytes. NOTCH function in myoblast fusion had not been addressed so far. We analysed the consequences of NOTCH inhibition for TMEM8C expression and myoblast fusion during foetal myogenesis in chicken embryos. NOTCH inhibition increased myoblast fusion and TMEM8C expression and released the HEYL transcriptional repressor from the TMEM8C regulatory regions. These results identify a regionalization of TMEM8C-dependent fusion and a molecular mechanism underlying the fusion-inhibiting effect of NOTCH in foetal myogenesis. The modulation of NOTCH activity in the fusion zone could regulate the flux of fusion events.

miR-18a-3p and Its Target Protein HuR May Regulate Myogenic Differentiation in Immune-Mediated Necrotizing Myopathy

Immune-mediated necrotizing myopathy (IMNM) is characterized by manifestation of myonecrosis and regeneration of muscle fibers; however, the underlying pathogenesis remains unclear. This study aimed to investigate the role and mechanism of miR-18a-3p and its target RNA-binding protein HuR in IMNM. HuR and miR-18a-3p levels were detected in the skeletal muscles of 18 patients with IMNM using quantitative reverse-transcription real-time polymerase chain reaction (qRT-PCR) and western blotting analysis. Human myoblasts were transfected with small interfering RNA targeting HuR and miR-18a-3p mimic or inhibitor. Myogenic differentiation markers, myogenin and myosin heavy chain, were analyzed by qRT-PCR, western blotting analysis, and immunofluorescence staining. The results showed that miR-18a-3p was upregulated (p=0.0002), whereas HuR was downregulated (p=0.002) in the skeletal muscles of patients with IMNM. The expression of miR-18a-3p in patients with IMNM was negatively correlated with those of HuR (r = -0.512, p = 0.029). We also found that disease activity was positively correlated with HuR expression (r = 0.576, p = 0.012) but muscle activity was negatively correlated with miR-18a-3p expression (r = -0.550, p = 0.017). Besides, bioinformatics analysis and dual-luciferase reporter assays suggested that miR-18a-3p could directly target HuR. Cellular experiments showed that overexpression of miR-18a-3p inhibited myogenic differentiation by targeting HuR, whereas inhibition of miR-18a-3p led to opposite results. Therefore, miR-18a-3p and its target protein HuR may be responsible for modulating the myogenic process in IMNM and can thus be therapeutic targets for the same.

Camrelizumab-Related Myocarditis and Myositis With Myasthenia Gravis: A Case Report and Literature Review

Immune checkpoint inhibitors (ICIs) have substantially changed the treatment of a variety of malignant tumors. With the increasing of their usage, the unique immune-mediated toxicity profile of ICIs has become apparent. We report a case of esophageal squamous cell carcinoma in a patient who received anti-programmed cell death protein 1 (PD-1) (camrelizumab) therapy and the occurrence of sequential immune-related adverse events (irAEs). Although many irAEs have been reported, severe myositis caused by camrelizumab with simultaneous involvement of multiple organs, including the myocardium, respiratory muscles, and skeletal muscles, has rarely been described in literature. This 69-year-old male patient developed a grade 4 camrelizumab-induced adverse reaction according to the Common Terminology Criteria for Adverse Events (CTCAE) and was successfully treated with methylprednisolone and immunoglobulins. The early identification of irAEs, immediate discontinuation of immunotherapy, use of steroids and/or immunosuppressants, and adjuvant supportive treatment are critical to the clinical prognosis of patients. It should be aware that autoimmune complications can occur even when ICI treatment is ceased.

Natural and experimental salinomycin poisoning associated with the use of florfenicol in pigs

ABSTRACT: This study describes the spontaneous and experimental salinomycin poisoning associated with the use of florfenicol and warns about the effects of the administration of antibiotics to animals that receive ionophores in the feed as growth promoters. A batch with 1,200 finishing pigs fed a diet containing 30ppm of salinomycin received florfenicol (60ppm via feed) to control respiratory diseases. Twenty-seven pigs had difficulty walking, tip-toe walking, muscle tremors, and anorexia seven days after the start of treatment. Twenty-two animals died, 10 recovered, and two were sent to the Laboratory of Animal Pathology of CAV-UDESC to be necropsied. The experimental reproduction of the disease was carried out to clarify the possible influence of florfenicol on salinomycin poisoning using 12 pigs divided into four groups with three animals each, treated for 16 days with diets containing no additives (Group 1), 50ppm of salinomycin (Group 2), 40ppm of florfenicol (Group 3), and 50ppm of salinomycin and 40ppm of florfenicol (Group 4). Only animals in Group 4 became ill. The clinical disease was reproduced from the ingestion of 24.67mg/kg/LW of salinomycin and 19.74mg/kg/LW of florfenicol. Both natural and experimental salinomycin poisoning associated with the use of florfenicol caused a condition of myopathy characterized in histology by hyaline degeneration and floccular necrosis of skeletal fibers, with macrophage infiltrate, associated with the figures of regeneration in skeletal muscles and multifocal areas of the proliferation of fibroblasts, being more intense in the longissimus dorsi and semimembranosus muscles. Therefore, florfenicol can cause the accumulation of ionophore salinomycin in the animal organism, resulting in a condition of toxic myopathy.