Extracellular matrix remodelling is associated with muscle force increase in overloaded mouse plantaris muscle.

AIMS: Transforming growth factor-ß (TGF-ß) signalling is thought to contribute to the remodelling of extracellular matrix (ECM) of skeletal muscle and to functional decline in patients with muscular dystrophies. We wanted to determine the role of TGF-ß-induced ECM remodelling in dystrophic muscle. METHODS: We experimentally induced the pathological hallmarks of severe muscular dystrophy by mechanically overloading the plantaris muscle in mice. Furthermore, we determined the role of TGF-ß signalling on dystrophic tissue modulation and on muscle function by (i) overloading myostatin knockout (Mstn-/- ) mice and (ii) by additional pharmacological TGF-ß inhibition via halofuginone. RESULTS: Transcriptome analysis of overloaded muscles revealed upregulation predominantly of genes associated with ECM, inflammation and metalloproteinase activity. Histology revealed in wild-type mice signs of severe muscular dystrophy including myofibres with large variation in size and internalized myonuclei, as well as increased ECM deposition. At the same time, muscle weight had increased by 208% and muscle force by 234%. Myostatin deficiency blunted the effect of overload on muscle mass (59% increase) and force (76% increase), while having no effect on ECM deposition. Concomitant treatment with halofuginone blunted overload-induced muscle hypertrophy and muscle force increase, while reducing ECM deposition and increasing myofibre size. CONCLUSIONS: ECM remodelling is associated with an increase in muscle mass and force in overload-modelled dystrophic muscle. Lack of myostatin is not advantageous and inhibition of ECM deposition by halofuginone is disadvantageous for muscle plasticity in response to stimuli that induce dystrophic muscle.

Live-imaging of revertant and therapeutically restored dystrophin in the DmdEGFP-mdx mouse model for Duchenne muscular dystrophy.

BACKGROUND: Dmdmdx , harbouring the c.2983C>T nonsense mutation in Dmd exon 23, is a mouse model for Duchenne muscular dystrophy (DMD), frequently used to test therapies aimed at dystrophin restoration. Current translational research is methodologically hampered by the lack of a reporter mouse model, which would allow direct visualization of dystrophin expression as well as longitudinal in vivo studies. METHODS: We generated a DmdEGFP-mdx reporter allele carrying in cis the mdx-23 mutation and a C-terminal EGFP-tag. This mouse model allows direct visualization of spontaneously and therapeutically restored dystrophin-EGFP fusion protein either after natural fibre reversion, or for example, after splice modulation using tricyclo-DNA to skip Dmd exon 23, or after gene editing using AAV-encoded CRISPR/Cas9 for Dmd exon 23 excision. RESULTS: Intravital microscopy in anaesthetized mice allowed live-imaging of sarcolemmal dystrophin-EGFP fusion protein of revertant fibres as well as following therapeutic restoration. Dystrophin-EGFP-fluorescence persisted ex vivo, allowing live-imaging of revertant and therapeutically restored dystrophin in isolated fibres ex vivo. Expression of the shorter dystrophin-EGFP isoforms Dp71 in the brain, Dp260 in the retina, and Dp116 in the peripheral nerve remained unabated by the mdx-23 mutation. CONCLUSION: Intravital imaging of DmdEGFP-mdx muscle permits novel experimental approaches such as the study of revertant and therapeutically restored dystrophin in vivo and ex vivo.

A spontaneous missense mutation in the chromodomain helicase DNA-binding protein 8 (CHD8) gene: a novel association with congenital myasthenic syndrome.

AIMS: Congenital myasthenic syndromes (CMS) are characterized by muscle weakness, ptosis and episodic apnoea. Mutations affect integral protein components of the neuromuscular junction (NMJ). Here we searched for the genetic basis of CMS in female monozygotic twins. METHODS: We employed whole-exome sequencing for mutation detection and Sanger sequencing for segregation analysis. Immunohistology was done with antibodies against CHD8, rapsyn, ß-catenin (ßCAT) and golgin on fi-bro-blasts, human and mouse muscle. We recorded superresolution images of the NMJ using 3D-structured illumination microscopy. RESULTS: We discovered a spontaneous missense mutation in CHD8 [chr14:g.21,884,051G>A, GRCh37.p11 | c.1732C>T, NM_00117062 | p.(R578C)], the gene encoding chromodomain helicase DNA-binding protein 8. This is the first missense mutation affecting Duplin, the short 110 kDa isoform of CHD8. It is known that CHD8/Duplin negatively regulates ßCAT signalling in the WNT pathway and plays a role in chromatin remodelling. Inactivating CHD8 mutations are associated with autism spectrum disorder and intellectual disability in combination with facial dysmorphism, overgrowth and macrocephalus. No muscle-specific phenotype has been reported to date. Co-immunostaining with rapsyn on human and mouse muscle revealed a strong presence of CHD8 at the NMJ being located towards the sarcoplasmic side of the rapsyn cluster, where it co-localizes with ßCAT. CONCLUSION: We hypothesize CHD8 to have a role in the maintenance of the structural integrity and function of the NMJ. Both patients benefited from treatment with 3,4-diaminopyridine, a reversible blocker of voltage-gated potassium channels at the nerve terminal that prolongs the action potential and increases acetylcholine release.

[Intense icterus in the course of EBV infectious mononucleosis]. / Intensa ictericia en el curso de una mononucleosis infecciosa por EBV.

Infectious mononucleosis induced by the Epstein Barr Virus (EBV) is a benign illness that is frequently accompanied by a slight hepatic disfunction. On occasion it may be accompanied by autoimmune hemolytic anemia of little clinical importance. Nevertheless, this association can cause a serious set of symptoms that can put the patient's life in danger if it is not treated quickly. We present the case of a 21-year-old male with infectious mononucleosis and severe jaundice (total bilirubin 40 mg/dl) due to the combination of diseased liver and secondary autoimmune hemolytic anemia, caused by the EBV infection.