Urinary titin is not an early biomarker of skeletal muscle atrophy induced by muscle denervation in mice

Early detection of skeletal muscle atrophy is important to prevent further muscle weakness. However, there are few non-invasive biomarkers for skeletal muscle atrophy. Recent studies have reported that the N-terminal fragment (N-titin) of titin, a giant sarcomeric protein, is detected in the urine of patients with muscle damage. In this study, we hypothesized that urinary N-titin would be a potential early biomarker of skeletal muscle atrophy in mice caused by sciatic nerve denervation. Male mice were randomly divided into control and denervation groups, and urinary N-titin levels were assessed daily for 9 days using an enzyme-linked immunosorbent assay system. Despite reduced titin protein levels in atrophic muscles 10 days after denervation, cleaved N-titin fragments were not increased in the urine of mice with denervation-induced muscle atrophy. Furthermore, we found no uptake of Evans blue dye from the extracellular space into the cytoplasm in atrophic muscles, suggesting that the sarcomeric membrane is intact in those muscles. The present results suggest that cleaved N-titin in the urine is not suitable as an early biomarker of skeletal muscle atrophy.

Full-length human dystrophin on human artificial chromosome compensates for mouse dystrophin deficiency in a Duchenne muscular dystrophy mouse model

Dystrophin maintains membrane integrity as a sarcolemmal protein. Dystrophin mutations lead to Duchenne muscular dystrophy, an X-linked recessive disorder. Since dystrophin is one of the largest genes consisting of 79 exons in the human genome, delivering a full-length dystrophin using virus vectors is challenging for gene therapy. Human artificial chromosome is a vector that can load megabase-sized genome without any interference from the host chromosome. Chimeric mice carrying a 2.4-Mb human dystrophin gene-loaded human artificial chromosome (DYS-HAC) was previously generated, and dystrophin expression from DYS-HAC was confirmed in skeletal muscles. Here we investigated whether human dystrophin expression from DYS-HAC rescues the muscle phenotypes seen in dystrophin-deficient mice. Human dystrophin was normally expressed in the sarcolemma of skeletal muscle and heart at expected molecular weights, and it ameliorated histological and functional alterations in dystrophin-deficient mice. These results indicate that the 2.4-Mb gene is enough for dystrophin to be correctly transcribed and translated, improving muscular dystrophy. Therefore, this technique using HAC gives insight into developing new treatments and novel humanized Duchenne muscular dystrophy mouse models with human dystrophin gene mutations.

Involvement of Parkin-mediated mitophagy in the pathogenesis of chronic obstructive pulmonary disease-related sarcopenia

BACKGROUND

Sarcopenia is characterized by the loss of skeletal muscle mass and strength and is associated with poor prognosis in patients with chronic obstructive pulmonary disease (COPD). Cigarette smoke (CS) exposure, a major cause for COPD, induces mitochondrial damage, which has been implicated in sarcopenia pathogenesis. The current study sought to examine the involvement of insufficient Parkin-mediated mitophagy, a mitochondrion-selective autophagy, in the mechanisms by which dysfunctional mitochondria accumulate with excessive reactive oxygen species (ROS) production in the development of COPD-related sarcopenia.

METHODS

The involvement of Parkin-mediated mitophagy was examined using in vitro models of myotube formation, in vivo CS-exposure model using Parkin^-/- mice, and human muscle samples from patients with COPD-related sarcopenia.

RESULTS

Cigarette smoke extract (CSE) induced myotube atrophy with concomitant 30% reduction in Parkin expression levels (P < 0.05). Parkin-mediated mitophagy regulated myotube atrophy by modulating mitochondrial damage and mitochondrial ROS production. Increased mitochondrial ROS was responsible for myotube atrophy by activating Muscle Ring Finger 1 (MuRF-1)-mediated myosin heavy chain (MHC) degradation. Parkin^-/- mice with prolonged CS exposure showed enhanced limb muscle atrophy with a 31.7% reduction in limb muscle weights (P < 0.01) and 2.3 times greater MuRF-1 expression (P < 0.01) compared with wild-type mice with concomitant accumulation of damaged mitochondria and oxidative modifications in 4HNE expression. Patients with COPD-related sarcopenia exhibited significantly reduced Parkin but increased MuRF-1 protein levels (35% lower and 2.5 times greater protein levels compared with control patients, P < 0.01 and P < 0.05, respectively) and damaged mitochondria accumulation demonstrated in muscles. Electric pulse stimulation-induced muscle contraction prevented CSE-induced MHC reduction by maintaining Parkin levels in myotubes.

CONCLUSIONS

Taken together, COPD-related sarcopenia can be attributed to insufficient Parkin-mediated mitophagy and increased mitochondrial ROS causing enhanced muscle atrophy through MuRF-1 activation, which may be at least partly preventable through optimal physical exercise.

Transcriptome analysis of gravitational effects on mouse skeletal muscles under microgravity and artificial 1 g onboard environment

Spaceflight causes a decrease in skeletal muscle mass and strength. We set two murine experimental groups in orbit for 35 days aboard the International Space Station, under artificial earth-gravity (artificial 1 g; AG) and microgravity (μg; MG), to investigate whether artificial 1 g exposure prevents muscle atrophy at the molecular level. Our main findings indicated that AG onboard environment prevented changes under microgravity in soleus muscle not only in muscle mass and fiber type composition but also in the alteration of gene expression profiles. In particular, transcriptome analysis suggested that AG condition could prevent the alterations of some atrophy-related genes. We further screened novel candidate genes to reveal the muscle atrophy mechanism from these gene expression profiles. We suggest the potential role of Cacng1 in the atrophy of myotubes using in vitro and in vivo gene transductions. This critical project may accelerate the elucidation of muscle atrophy mechanisms.

Mutation-independent Proteomic Signatures of Pathological Progression in Murine Models of Duchenne Muscular Dystrophy

The absence of the dystrophin protein in Duchenne muscular dystrophy (DMD) results in myofiber fragility and a plethora of downstream secondary pathologies. Although a variety of experimental therapies are in development, achieving effective treatments for DMD remains exceptionally challenging, not least because the pathological consequences of dystrophin loss are incompletely understood. Here we have performed proteome profiling in tibialis anterior muscles from two murine DMD models (mdx and mdx52) at three ages (8, 16, and 80 weeks of age), all n = 3. High-resolution isoelectric focusing liquid chromatography-tandem MS (HiRIEF-LC-MS/MS) was used to quantify the expression of 4974 proteins across all 27 samples. The two dystrophic models were found to be highly similar, whereas multiple proteins were differentially expressed relative to WT (C57BL/6) controls at each age. Furthermore, 1795 proteins were differentially expressed when samples were pooled across ages and dystrophic strains. These included numerous proteins associated with the extracellular matrix and muscle function that have not been reported previously. Pathway analysis revealed multiple perturbed pathways and predicted upstream regulators, which together are indicative of cross-talk between inflammatory, metabolic, and muscle growth pathways (e.g. TNF, INFγ, NF-κB, SIRT1, AMPK, PGC-1α, PPARs, ILK, and AKT/PI3K). Upregulation of CAV3, MVP and PAK1 protein expression was validated in dystrophic muscle by Western blot. Furthermore, MVP was upregulated during, but not required for, the differentiation of C2C12 myoblasts suggesting that this protein may affect muscle regeneration. This study provides novel insights into mutation-independent proteomic signatures characteristic of the dystrophic phenotype and its progression with aging.

Age-Dependent Echocardiographic and Pathologic Findings in a Rat Model with Duchenne Muscular Dystrophy Generated by CRISPR/Cas9 Genome Editing

Duchenne muscular dystrophy (DMD) is X-linked recessive myopathy caused by mutations in the dystrophin gene. Although conventional treatments have improved their prognosis, inevitable progressive cardiomyopathy is still the leading cause of death in patients with DMD. To explore novel therapeutic options, a suitable animal model with heart involvement has been warranted.We have generated a rat model with an out-of-frame mutation in the dystrophin gene using CRISPR/Cas9 genome editing (DMD rats). The aim of this study was to evaluate their cardiac functions and pathologies to provide baseline data for future experiments developing treatment options for DMD.In comparison with age-matched wild rats, 6-month-old DMD rats showed no significant differences by echocardiographic evaluations. However, 10-month-old DMD rats showed significant deterioration in left ventricular (LV) fractional shortening (P = 0.024), and in tissue Doppler peak systolic velocity (Sa) at the LV lateral wall (P = 0.041) as well as at the right ventricular (RV) free-wall (P = 0.004). These functional findings were consistent with the fibrotic distributions by histological analysis.Although the cardiac phenotype was milder than anticipated, DMD rats showed similar distributions and progression of heart involvement to those of patients with DMD. This animal may be a useful model with which to develop effective drugs and to understand the underlying mechanisms of progressive heart failure in patients with DMD.

Thiamine treatment preserves cardiac function against ischemia injury via maintaining mitochondrial size and ATP levels

Thiamine (vitamin B1) is necessary for energy production, especially in the heart. Recent studies have demonstrated that thiamine supplementation for cardiac diseases is beneficial. However, the detailed mechanisms underlying thiamine-preserved cardiac function have not been elucidated. To this end, we conducted a functional analysis, metabolome analysis, and electron microscopic analysis to unveil the mechanisms of preserved cardiac function through supplementation with thiamine for ischemic cardiac disease. Male Sprague-Dawley rats (around 10 wk old) were used. Following pretreatment with or without thiamine pyrophosphate (TPP; 300 µM), hearts were exposed to ischemia (40 min of global ischemia followed by 60 min of reperfusion). We measured the left ventricle developed pressure (LVDP) throughout the protocol. The LVDP during reperfusion in the TPP-treated heart was significantly higher than that in the untreated heart. Metabolome analysis was performed using capillary electrophoresis-time-of-flight mass spectrometry, and it revealed that the TPP-treated heart retained higher adenosine triphosphate (ATP) levels compared with the untreated heart after ischemia. The metabolic pathway showed that there was a significant increase in fumaric acid and malic acid from the tricarboxylic acid cycle following ischemia. Electron microscope analysis revealed that the mitochondria size in the TPP-treated heart was larger than that in the untreated heart. Mitochondrial fission in the TPP-treated heart was also inhibited, which was confirmed by a decrease in the phosphorylation level of DRP1 (fission related protein). TPP treatment for cardiac ischemia preserved ATP levels probably as a result of maintaining larger mitochondria by inhibiting fission, thereby allowing the TPP-treated heart to preserve contractility performance during reperfusion.NEW & NOTEWORTHY We found that treatment with thiamine can have a protective effect on myocardial ischemia. Thiamine likely mediates mitochondrial fission through the inhibition of DRP1 phosphorylation and the preservation of larger-sized mitochondria and ATP concentration, leading to higher cardiac contractility performance during the subsequent reperfusion state.

iNOS is not responsible for RyR1 S-nitrosylation in mdx mice with truncated dystrophin

Background

Previous research indicated that nitric oxide synthase (NOS) is the key molecule for S-nitrosylation of ryanodine receptor 1 (RyR1) in DMD model mice (mdx mice) and that both neuronal NOS (nNOS) and inducible NOS (iNOS) might contribute to the reaction because nNOS is mislocalized in the cytoplasm and iNOS expression is higher in mdx mice. We investigated the effect of iNOS on RyR1 S-nitrosylation in mdx mice and whether transgenic expression of truncated dystrophin reduced iNOS expression in mdx mice or not.

Methods

Three- to 4-month-old C57BL/6 J, mdx, and transgenic mdx mice expressing exon 45–55-deleted human dystrophin (Tg/mdx mice) were used. We also generated two double mutant mice, mdx iNOS KO and Tg/mdx iNOS KO to reveal the iNOS contribution to RyR1 S-nitrosylation. nNOS and iNOS expression levels in skeletal muscle of these mice were assessed by immunohistochemistry (IHC), qRT-PCR, and Western blotting. Total NOS activity was measured by a citrulline assay. A biotin-switch method was used for detection of RyR1 S-nitrosylation. Statistical differences were assessed by one-way ANOVA with Tukey-Kramer post-hoc analysis.

Results

mdx and mdx iNOS KO mice showed the same level of RyR1 S-nitrosylation. Total NOS activity was not changed in mdx iNOS KO mice compared with mdx mice. iNOS expression was undetectable in Tg/mdx mice expressing exon 45–55-deleted human dystrophin, but the level of RyR1 S-nitrosylation was the same in mdx and Tg/mdx mice.

Conclusion

Similar levels of RyR1 S-nitrosylation and total NOS activity in mdx and mdx iNOS KO demonstrated that the proportion of iNOS in total NOS activity was low, even in mdx mice. Exon 45–55-deleted dystrophin reduced the expression level of iNOS, but it did not correct the RyR1 S-nitrosylation. These results indicate that iNOS was not involved in RyR1 S-nitrosylation in mdx and Tg/mdx mice muscles.

Glycerophospholipid profile alterations are associated with murine muscle-wasting phenotype

INTRODUCTION

Phospholipids are essential components of cellular membranes and are closely associated with cellular functions, but relationships involving skeletal muscle phospholipid profiles and their physiological phenotypes have remained unclear.

METHODS

We carried out comprehensive phospholipid analyses using liquid chromatography-tandem mass spectrometry to determine the phospholipid profiles of skeletal muscles derived from muscle-wasting mouse models, including denervated and Duchenne muscular dystrophy mouse models (mdx) as well as rescued mdx mice expressing truncated dystrophin.

RESULTS

Consistent phosphatidylcholine and phosphatidylethanolamine alterations in skeletal muscles isolated from denervated and mdx mice were observed. Notably, the levels of these phospholipids binding polyunsaturated fatty acids were reduced in denervated and mdx muscles. Moreover, rescuing the mdx pathology by expressing truncated dystrophin led to the restoration of phospholipid profiles.

DISCUSSION

Our findings support the hypothesis that phospholipid profiles of the skeletal muscle may be associated with skeletal muscle function.

Abstract 861: Inner Mitochondrial Collapsing in Response to Acute Overstretch of Rat Ventricular Papillary Muscles

Introduction: The effect of acute ventricular volume overload on organelles such as myofibrils and mitochondria are incompletely understood.

Purpose: We performed acute overstretch on cardiac papillary muscle to investigate the functional and morphological changes.

Methods: We used male SD-rats (10-12 weeks old) and dissected papillary muscles from the right ventricle. A papillary muscle preparation was stretched to Lmax. We overstretched it within 2 seconds up to 110% of Lmax (110%Overstretch; 110%OS) or 120% of Lmax (120%OS), and stimulated it (1Hz, 36°C) with tension measurement, compared with Lmax group. After the measurement of tension, we analyzed the morphological changes in muscle fibers and organelles using a Transmission electron microscopy (TEM).

Results: The active tension after overstretch was immediately decreased to 67.8±3.8% in 110%OS, and to 17.3±4.0% in 120%OS. In TEM study, muscle fibers kept their well-organized structures and the sarcomere length was stretched to 2.4 μm in 110%OS, and to 2.6 μm in 120%OS. In contrast, in 110%OS, inner mitochondrial density was lower than that in Lmax, indicating swelled mitochondria. In 120%OS, inner mitochondrial empty space with vacuolation was found in the large area of myocardium, indicating that inner mitochondria cristae were susceptible to mechanical stress-induced deterioration.

Conclusions: Acute overstretch of rat papillary muscles causes inner mitochondrial collapsing with preserved the sarcomere structure. It could account for the mechanisms of acute volume-overloaded heart failure.

Exons 45-55 Skipping Using Mutation-Tailored Cocktails of Antisense Morpholinos in the DMD Gene

Mutations in the dystrophin (DMD) gene and consequent loss of dystrophin cause Duchenne muscular dystrophy (DMD). A promising therapy for DMD, single-exon skipping using antisense phosphorodiamidate morpholino oligomers (PMOs), currently confronts major issues in that an antisense drug induces the production of functionally undefined dystrophin and may not be similarly efficacious among patients with different mutations. Accordingly, the applicability of this approach is limited to out-of-frame mutations. Here, using an exon-skipping efficiency predictive tool, we designed three different PMO cocktail sets for exons 45-55 skipping aiming to produce a dystrophin variant with preserved functionality as seen in milder or asymptomatic individuals with an in-frame exons 45-55 deletion. Of them, the most effective set was composed of select PMOs that each efficiently skips an assigned exon in cell-based screening. These combinational PMOs fitted to different deletions of immortalized DMD patient muscle cells significantly induced exons 45-55 skipping with removing 3, 8, or 10 exons and dystrophin restoration as represented by western blotting. In vivo skipping of the maximum 11 human DMD exons was confirmed in humanized mice. The finding indicates that our PMO set can be used to create mutation-tailored cocktails for exons 45-55 skipping and treat over 65% of DMD patients carrying out-of-frame or in-frame deletions.

Loss of RNA-Binding Protein Sfpq Causes Long-Gene Transcriptopathy in Skeletal Muscle and Severe Muscle Mass Reduction with Metabolic Myopathy

Growing evidences are suggesting that extra-long genes in mammals are vulnerable for full-gene length transcription and dysregulation of long genes is a mechanism underlying human genetic disorders. How long-distance transcription is achieved is a fundamental question to be elucidated. In previous study, we had discovered that RNA-binding protein SFPQ preferentially binds to long pre-mRNAs and specifically regulates the cluster of neuronal genes >100 kbp. Here we investigated the roles of SFPQ for long gene expression, target specificities, and also physiological functions in skeletal muscle. Loss of Sfpq selectively downregulated genes >100 kbp including Dystrophin, which is 2.26 Mbp in length. Sfpq knockout (KO) mice showed progressive muscle mass reduction and metabolic myopathy characterized by glycogen accumulation and decreased abundance of mitochondrial oxidative phosphorylation complexes. Functional clustering analysis identified energy metabolism pathway genes as SFPQ's targets. These findings indicate target gene specificities and tissue-specific physiological functions of SFPQ in skeletal muscle.

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SFPQ is essential for long gene expression, including Dystrophin, in skeletal muscle

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Disruption of Sfpq caused severe muscle mass reduction and premature death

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SFPQ is required for metabolic pathway gene expression in skeletal muscle

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Loss of Sfpq decreased OXPHOS complexes and caused glycogen accumulation

Urinary Titin Is Increased in Patients After Cardiac Surgery

Background: Few non-invasive biomarkers have been used to detect myocardial injury in patients with heart diseases. Recently, the N-terminal fragment (N-titin) of titin, a giant sarcomeric protein, which is involved in muscular passive tension and viscoelasticity, has been reported to detect muscle damage in patients with cardiomyopathy as well as in patients with skeletal muscle dystrophy and in healthy volunteers with endurance exercise. In the present study, we evaluated whether urinary N-titin is changed during a perioperative period and whether its increase reflects myocardial damage.

Materials and Methods: In 18 patients who underwent cardiac surgery, blood and urine samples were obtained before and after surgery. We measured the urinary levels of N-titin with a highly sensitive ELISA system.

Results: Urinary N-titin to creatinine (N-titin/Cr) was significantly increased in all patients postoperatively (43.3 ± 39.5 pmol/mg/dL on the day of operation) and remained significantly high for at least 4 days postoperatively. Urinary N-titin/Cr was positively correlated with serum cardiac troponin T (r = 0.36, p = 0.0006, n = 90) but not creatine kinase-MB (CK-MB). We also found that urinary N-titin/Cr in patients after a coronary artery bypass grafting operation was higher by day 2 postoperatively than in patients following open cardiac surgeries.

Conclusion: The cleaved N-titin was significantly increased in urine after cardiac surgery. Urinary N-titin may be useful for detecting the risk of latent postoperative cardiac damage.

Characterization of a novel microRNA, miR-188, elevated in serum of muscular dystrophy dog model

MicroRNAs (miRNAs) are non-coding small RNAs that regulate gene expression at the post-transcriptional level. Several miRNAs are exclusively expressed in skeletal muscle and participate in the regulation of muscle differentiation by interacting with myogenic factors. These miRNAs can be found at high levels in the serum of patients and animal models for Duchenne muscular dystrophy, which is expected to be useful as biomarkers for their clinical conditions. By miRNA microarray analysis, we identified miR-188 as a novel miRNA that is elevated in the serum of the muscular dystrophy dog model, CXMDJ. miR-188 was not muscle-specific miRNA, but its expression was up-regulated in skeletal muscles associated with muscle regeneration induced by cardiotoxin-injection in normal dogs and mice. Manipulation of miR-188 expression using antisense oligo and mimic oligo RNAs alters the mRNA expression of the myogenic regulatory factors, MRF4 and MEF2C. Our results suggest that miR-188 is a new player that participates in the gene regulation process of muscle differentiation and that it may serve as a serum biomarker reflecting skeletal muscle regeneration.

Synthesis of 2'-O-(N-methylcarbamoylethyl) 5-methyl-2-thiouridine and its application to splice-switching oligonucleotides

The effect of 2'-O-(N-methylcarbamoyl)ethyl (MCE) modification on splice-switching oligonucleotides (SSO) was systematically evaluated. The incorporation of five MCE nucleotides at the 5'-termini of SSOs effectively improved the splice switching effect. In addition, the incorporation of 2'-O-(N-methylcarbamoylethyl)-5-methyl-2-thiouridine (s²T_MCE), a duplex-stabilizing nucleotide with an MCE modification, into SSOs further improved splice switching. These SSOs may be useful for the treatment of genetic diseases associated with splicing errors.

[Mechanisms of systemic energy metabolism control through gene regulation in skeletal muscle.]

Skeletal muscle is the largest tissue in the human body and plays an important role in the regulation of systemic homeostasis and displays remarkable plasticity in their metabolic responses to caloric availability and physical activity. Skeletal muscle maintains muscle mass suitable for the environment according to its own activity state. Skeletal muscles also affect the energy regulation of the whole body by skeletal muscle itself changing muscle fiber composition due to external and internal factors. This review focuses on the transcriptional regulation mechanism of muscle fiber type, which is responsible for overall energy consumption.

Treatment with the anti-IL-6 receptor antibody attenuates muscular dystrophy via promoting skeletal muscle regeneration in dystrophin-/utrophin-deficient mice

Background

Chronic increases in the levels of the inflammatory cytokine interleukin-6 (IL-6) in serum and skeletal muscle are thought to contribute to the progression of muscular dystrophy. Dystrophin/utrophin double-knockout (dKO) mice develop a more severe and progressive muscular dystrophy than the mdx mice, the most common murine model of Duchenne muscular dystrophy (DMD). In particular, dKO mice have smaller body sizes and muscle diameters, and develop progressive kyphosis and fibrosis in skeletal and cardiac muscles. As mdx mice and DMD patients, we found that IL-6 levels in the skeletal muscle were significantly increased in dKO mice. Thus, in this study, we aimed to analyze the effects of IL-6 receptor (IL-6R) blockade on the muscle pathology of dKO mice.

Methods

Male dKO mice were administered an initial injection (200 mg/kg intraperitoneally (i.p.)) of either the anti-IL-6R antibody MR16-1 or an isotype-matched control rat IgG at the age of 14 days, and were then given weekly injections (25 mg/kg i.p.) until 90 days of age.

Results

Treatment of dKO mice with the MR16-1 antibody successfully inhibited the IL-6 pathway in the skeletal muscle and resulted in a significant reduction in the expression levels of phosphorylated signal transducer and activator of transcription 3 in the skeletal muscle. Pathologically, a significant increase in the area of embryonic myosin heavy chain-positive myofibers and muscle diameter, and reduced fibrosis in the quadriceps muscle were observed. These results demonstrated the therapeutic effects of IL-6R blockade on promoting muscle regeneration. Consistently, serum creatine kinase levels were decreased. Despite these improvements observed in the limb muscles, degeneration of the diaphragm and cardiac muscles was not ameliorated by the treatment of mice with the MR16-1 antibody.

Conclusion

As no adverse effects of treatment with the MR16-1 antibody were observed, our results indicate that the anti-IL-6R antibody is a potential therapy for muscular dystrophy particularly for promoting skeletal muscle regeneration.

Electronic supplementary material

The online version of this article (10.1186/s13395-017-0140-z) contains supplementary material, which is available to authorized users.

Low-Intensity Training and the C5a Complement Antagonist NOX-D21 Rescue the mdx Phenotype through Modulation of Inflammation

Inflammatory events occurring in dystrophic muscles contribute to the progression of Duchenne muscular dystrophy (DMD). Low-intensity training (LIT) attenuates the phenotype of mdx mice, an animal model for DMD. Therefore, we postulated that LIT could have anti-inflammatory properties. We assessed levels of inflammatory cytokines and infiltrated immune cells in gastrocnemius muscle of mdx mice after LIT. We detected high levels of complement component C5a, chemokine ligand (CCL) 2, CD68⁺ monocytes/macrophages, and proinflammatory M1 macrophages in muscles of mdx mice. LIT decreased CCL2 levels, increased CD68⁺ cell numbers, and shifted the macrophage population to the regenerative M2 type. We investigated whether inhibition of C5a or CCL2 with L-aptamers could mimic the effects of LIT. Although no effect of CCL2 inhibition was detected, treatment with the C5a inhibitor, NOX-D21, rescued the phenotype of nonexercised mdx mice, but not of exercised ones. In both cases, the level of CD68⁺ cells increased and macrophage populations leaned toward the inflammatory M1 type. In muscles of nonexercised treated mice, the level of IL-1 receptor antagonist increased, damage decreased, and fibers were switched toward the glycolytic fast type; in muscles of exercised mice, fibers were switched to the oxidative slow type. These results reveal the effects of LIT on the inflammatory status of mdx mice and suggest that NOX-D21 could be an anti-inflammatory drug for DMD.

Characterization and Functional Analysis of Extracellular Vesicles and Muscle-Abundant miRNAs (miR-1, miR-133a, and miR-206) in C2C12 Myocytes and mdx Mice

Duchenne muscular dystrophy (DMD) is a progressive neuromuscular disorder. Here, we show that the CD63 antigen, which is located on the surface of extracellular vesicles (EVs), is associated with increased levels of muscle-abundant miRNAs, namely myomiRs miR-1, miR-133a, and miR-206, in the sera of DMD patients and mdx mice. Furthermore, the release of EVs from the murine myoblast C₂C₁₂ cell line was found to be modulated by intracellular ceramide levels in a Ca²⁺-dependent manner. Next, to investigate the effects of EVs on cell survival, C₂C₁₂ myoblasts and myotubes were cultured with EVs from the sera of mdx mice or C₂C₁₂ cells overexpressing myomiRs in presence of cellular stresses. Both the exposure of C₂C₁₂ myoblasts and myotubes to EVs from the serum of mdx mice, and the overexpression of miR-133a in C₂C₁₂ cells in presence of cellular stress resulted in a significant decrease in cell death. Finally, to assess whether miRNAs regulate skeletal muscle regeneration in vivo, we intraperitoneally injected GW4869 (an inhibitor of exosome secretion) into mdx mice for 5 and 10 days. Levels of miRNAs and creatine kinase in the serum of GW4869-treated mdx mice were significantly downregulated compared with those of controls. The tibialis anterior muscles of the GW4869-treated mdx mice showed a robust decrease in Evans blue dye uptake. Collectively, these results indicate that EVs and myomiRs might protect the skeletal muscle of mdx mice from degeneration.

Endogenous Multiple Exon Skipping and Back-Splicing at the DMD Mutation Hotspot

Duchenne muscular dystrophy (DMD) is a severe muscular disorder. It was reported that multiple exon skipping (MES), targeting exon 45–55 of the DMD gene, might improve patients’ symptoms because patients who have a genomic deletion of all these exons showed very mild symptoms. Thus, exon 45–55 skipping treatments for DMD have been proposed as a potential clinical cure. Herein, we detected the expression of endogenous exons 44–56 connected mRNA transcript of the DMD using total RNAs derived from human normal skeletal muscle by reverse transcription polymerase chain reaction (RT-PCR), and identified a total of eight types of MES products around the hotspot. Surprisingly, the 5′ splice sites of recently reported post-transcriptional introns (remaining introns after co-transcriptional splicing) act as splicing donor sites for MESs. We also tested exon combinations to generate DMD circular RNAs (circRNAs) and determined the preferential splice sites of back-splicing, which are involved not only in circRNA generation, but also in MESs. Our results fit the current circRNA-generation model, suggesting that upstream post-transcriptional introns trigger MES and generate circRNA because its existence is critical for the intra-intronic interaction or for extremely distal splicing.

[Changes in cytosolic Ca2+dynamics associated with muscular dystrophy]

Duchenne muscular dystrophy(DMD)is X-linked genetic disorder caused by a lack of the membrane-associated protein dystrophin. DMD is characterized by progressive muscle wasting secondary to repeated muscle damage and inadequate repair. The mechanisms underlying the functional impairments in dystrophic muscle have not yet been fully determined. However, several recent studies indicate that elevated intracellular Ca²⁺homeostasis is a cause or facilitator of the development of muscle weakness in muscular dystrophy. This review focuses on abnormalities of Ca²⁺homeostasis and the possibilities for treatment by counteracting the Ca²⁺dysregulation.

Low intensity training of mdx mice reduces carbonylation and increases expression levels of proteins involved in energy metabolism and muscle contraction

High intensity training induces muscle damage in dystrophin-deficient mdx mice, an animal model for Duchenne muscular dystrophy. However, low intensity training (LIT) rescues the mdx phenotype and even reduces the level of protein carbonylation, a marker of oxidative damage. Until now, beneficial effects of LIT were mainly assessed at the physiological level. We investigated the effects of LIT at the molecular level on 8-week-old wild-type and mdx muscle using 2D Western blot and protein-protein interaction analysis. We found that the fast isoforms of troponin T and myosin binding protein C as well as glycogen phosphorylase were overcarbonylated and downregulated in mdx muscle. Some of the mitochondrial enzymes of the citric acid cycle were overcarbonylated, whereas some proteins of the respiratory chain were downregulated. Of functional importance, ATP synthase was only partially assembled, as revealed by Blue Native PAGE analysis. LIT decreased the carbonylation level and increased the expression of fast isoforms of troponin T and of myosin binding protein C, and glycogen phosphorylase. In addition, it increased the expression of aconitate hydratase and NADH dehydrogenase, and fully restored the ATP synthase complex. Our study demonstrates that the benefits of LIT are associated with lowered oxidative damage as revealed by carbonylation and higher expression of proteins involved in energy metabolism and muscle contraction. Potentially, these results will help to design therapies for DMD based on exercise mimicking drugs.

Long-term efficacy of systemic multiexon skipping targeting dystrophin exons 45-55 with a cocktail of vivo-morpholinos in mdx52 mice

Antisense-mediated exon skipping, which can restore the reading frame, is a most promising therapeutic approach for Duchenne muscular dystrophy. Remaining challenges include the limited applicability to patients and unclear function of truncated dystrophin proteins. Multiexon skipping targeting exons 45–55 at the mutation hotspot of the dystrophin gene could overcome both of these challenges. Previously, we described the feasibility of exons 45–55 skipping with a cocktail of Vivo-Morpholinos in vivo; however, the long-term efficacy and safety of Vivo-Morpholinos remains to be determined. In this study, we examined the efficacy and toxicity of exons 45–55 skipping by intravenous injections of 6 mg/kg 10-Vivo-Morpholino cocktail (0.6 mg/kg each vPMO) every 2 weeks for 18 weeks to dystrophic exon-52 knockout (mdx52) mice. Systemic skipping of the entire exons 45–55 region was induced, and the Western blot analysis exhibited the restoration of 5–27% of normal levels of dystrophin protein in skeletal muscles, accompanied by improvements in histopathology and muscle strength. No obvious immune response and renal and hepatic toxicity were detected at the end-point of the treatment. We demonstrate our new regimen with the 10-Vivo-Morpholino cocktail is effective and safe for long-term repeated systemic administration in the dystrophic mouse model.

Enhancement of exon skipping in mdx52 mice by 2′-O-methyl-2-thioribothymidine incorporation into phosphorothioate oligonucleotides

Incorporation of 2′-O-methyl-2-thioribothymidine (s²T_m) into antisense oligoribonucleotides significantly enhanced the exon skipping activity in Duchenne muscular dystrophy model mice.

Generation of muscular dystrophy model rats with a CRISPR/Cas system

Duchenne muscular dystrophy (DMD) is an X-linked lethal muscle disorder caused by mutations in the Dmd gene encoding Dystrophin12. DMD model animals, such as mdx mice and canine X-linked muscular dystrophy dogs, have been widely utilized in the development of a treatment for DMD3. Here, we demonstrate the generation of Dmd-mutated rats using a clustered interspaced short palindromic repeats (CRISPR)/Cas system, an RNA-based genome engineering technique that is also adaptive to rats. We simultaneously targeted two exons in the rat Dmd gene, which resulted in the absence of Dystrophin expression in the F0 generation. Dmd-mutated rats exhibited a decline in muscle strength, and the emergence of degenerative/regenerative phenotypes in the skeletal muscle, heart, and diaphragm. These mutations were heritable by the next generation, and F1 male rats exhibited similar phenotypes in their skeletal muscles. These model rats should prove to be useful for developing therapeutic methods to treat DMD.

Mutation types and aging differently affect revertant fiber expansion in dystrophic mdx and mdx52 mice

Duchenne muscular dystrophy (DMD), one of the most common and lethal genetic disorders, and the mdx mouse myopathies are caused by a lack of dystrophin protein. These dystrophic muscles contain sporadic clusters of dystrophin-expressing revertant fibers (RFs), as detected by immunohistochemistry. RFs are known to arise from muscle precursor cells with spontaneous exon skipping (alternative splicing) and clonally expand in size with increasing age through the process of muscle degeneration/regeneration. The expansion of revertant clusters is thought to represent the cumulative history of muscle regeneration and proliferation of such precursor cells. However, the precise mechanisms by which RFs arise and expand are poorly understood. Here, to test the effects of mutation types and aging on RF expansion and muscle regeneration, we examined the number of RFs in mdx mice (containing a nonsense mutation in exon 23) and mdx52 mice (containing deletion mutation of exon 52) with the same C57BL/6 background at 2, 6, 12, and 18months of age. Mdx mice displayed a significantly higher number of RFs compared to mdx52 mice in all age groups, suggesting that revertant fiber expansion largely depends on the type of mutation and/or location in the gene. A significant increase in the expression and clustering levels of RFs was found beginning at 6months of age in mdx mice compared with mdx52 mice. In contrast to the significant expansion of RFs with increasing age, the number of centrally nucleated fibers and embryonic myosin heavy chain-positive fibers (indicative of cumulative and current muscle regeneration, respectively) decreased with age in both mouse strains. These results suggest that mutation types and aging differently affect revertant fiber expansion in mdx and mdx52 mice.

Adaptive effects of the beta2-agonist clenbuterol on expression of beta2-adrenoceptor mRNA in rat fast-twitch fiber-rich muscles

Administration of the beta(2)-agonist clenbuterol has been shown to reduce the expression of beta(2)-adrenoceptor (AR) mRNA in fast-twitch fiber-rich (extensor digitorum longus, EDL) muscle without changing that in slow-twitch fiber-rich (soleus, SOL) muscle in rats. However, the regulatory mechanism for muscle fiber type-dependent down-regulation of the expression of beta(2)-AR mRNA induced by clenbuterol is still unclear. Therefore, mRNA expression of transcriptional and post-transcriptional regulatory factors for beta(2)-AR mRNA levels in fast-twitch fiber-rich (EDL and plantaris, PLA) and slow-twitch fiber-rich (SOL) muscles in clenbuterol-administered (1.0 mg/kg body weight/day for 10 days, subcutaneous) rats was studied by real-time reverse transcription-polymerase chain reaction. Administration of clenbuterol significantly reduced expression of beta(2)-AR mRNA in EDL and PLA muscles without changing that in SOL muscle. Administration of clenbuterol also significantly reduced the mRNA expression of transcriptional regulatory factor (glucocorticoid receptor) and mRNA stabilizing factor (Hu antigen R) in EDL and PLA muscles without changing those in SOL muscle. These results suggest that muscle fiber type-dependent effects of clenbuterol on expression of beta(2)-AR mRNA are closely related to the down-regulation of mRNA expression of transcriptional and post-transcriptional regulatory factors for beta(2)-AR mRNA levels.

Acute effects of dihydrocapsaicin and capsaicin on the distribution of white blood cells in rats

The acute effects of dihydrocapsaicin (DHC) and capsaicin (CAP) on the number of white blood cells (WBCs), neutrophils, eosinophils, basophils, monocytes, lymphocytes, T lymphocytes, B lymphocytes and NK cells, and serum corticosterone levels were studied in rats. Male 7-wk-old SD rats were divided into DHC (3.0 mg/kg BW), CAP (3.0 mg/kg BW) and control (CON) groups. The number of total WBCs was 1.30-1.42 times significantly higher in the DHC group than in the CON group at 6-12 h. The number of neutrophils was 1.62 times significantly higher in the DHC group than in the CON group at 12 h. The number of total WBCs and neutrophils, however, showed no significant changes between the CAP and CON groups. The number of lymphocytes was 0.61 and 0.70 times significantly lower in the DHC and CAP groups than in the CON group at 3 h. The number of T lymphocytes and B lymphocytes was 0.74 and 0.54 times lower in the DHC group than in the CON group, respectively. CAP, however, did not significantly change the number of T lymphocytes or B lymphocytes. No significant changes in the number of NK cells were observed among the three groups. CAP and DHC did not change the number of monocytes, eosinophils or basophils. No significant changes of the serum corticosterone levels were observed among the three groups. In conclusion, capsaicinoids decreased the number of acquired immunity cells, and increased the number of total WBCs and neutrophils without changing the number of monocytes, eosinophils or basophils. The magnitude of these effects was relatively higher in DHC than in CAP.

Effects of dexamethasone on the expression of beta(1)-, beta (2)- and beta (3)-adrenoceptor mRNAs in skeletal and left ventricle muscles in rats

Glucocorticoids are known to increase the density and mRNA levels of beta-adrenoceptors (beta-AR) via the glucocorticoid receptor (GR) in many tissues. However, the effects of these changes in the skeletal and cardiac muscles remain relatively unknown. We have investigated the effects of dexamethasone on the expression of the beta(1)-, beta(2)-, and beta(3)-AR mRNAs and GR mRNA in fast-twitch fiber-rich extensor digitorum longus (EDL), slow-twitch fiber-rich soleus (SOL), and left ventricle (LV) muscles by real-time quantitative RT-PCR. Male rats were divided into a dexamethasone group and control group. The weight, RNA concentration, and total RNA content of EDL muscle were 0.76-, 0.85-, and 0.65-fold lower, respectively, in the dexamethasone group than in the control group. The weight, RNA concentration, and total RNA content of SOL muscle were 0.92-, 0.87-, and 0.81-fold lower, respectively, in the dexamethasone group than in the control group; these differences were significant. However, the weight/body weight and total RNA content/body weight of LV muscle were 1.38- and 1.39-fold higher, respectively, in the dexamethasone group than in the control group, respectively; these differences were also significant. Dexamethasone significantly decreased GR mRNA expression in EDL muscle without changing the expression of the beta(1)-, beta(2)-, and beta(3)-AR mRNAs. However, dexamethasone significantly decreased the expressions of beta(2)-AR and GR mRNAs in SOL muscle and significantly increased beta(1)-AR mRNA expression in LV muscle-without changing GR mRNA expression. These results suggest that the effects of dexamethasone on the expression of beta(1)- and beta(2)-AR mRNAs and muscle mass depend on the muscle contractile and/or constructive types.

Downstream utrophin enhancer is required for expression of utrophin in skeletal muscle

BACKGROUND

Duchenne muscular dystrophy is caused by the absence of the muscle cytoskeletal protein dystrophin. Utrophin is an autosomal homologue of dystrophin, and overexpression of utrophin is expected to compensate for the dystrophin deficit. We previously reported that the 5.4-kb 5'-flanking region of the utrophin gene containing the A-utrophin core promoter did not drive transgene expression in heart and skeletal muscle. To clarify the regulatory mechanism of utrophin expression, we generated a nuclear localization signal-tagged LacZ transgenic (Tg) mouse, in which the LacZ gene was driven by the 129-bp downstream utrophin enhancer (DUE) and the 5.4-kb 5'-flanking region of the utrophin promoter.

METHODS

Two Tg lines were established. The levels of transgene mRNA expression in several tissues were examined by reverse transcriptase-polymerase chain reaction (RT-PCR) and quantitative RT-PCR. Cryosections of several tissues were stained with haematoxylin and eosin and X-gal.

RESULTS

The transgene expression patterns were consistent with endogenous utrophin in several tissues including heart and skeletal muscle. Transgene expression was also up-regulated more in regenerating muscle than in nonregenerating muscle. Moreover, utrophin expression was augmented in the skeletal muscle of DUE Tg/dystrophin-deficient mdx mice through cross-breeding experiments. We finally established cultures of primary myogenic cells from this Tg mouse and found that utrophin up-regulation during muscle differentiation depends on the DUE motif.

CONCLUSIONS

Our results showed that DUE is indispensable for utrophin expression in skeletal muscle and heart, and primary myogenic cells from this Tg mice provide a high through-put screening system for drugs that up-regulate utrophin expression.

Effects of the beta2-agonist clenbuterol on beta1- and beta2-adrenoceptor mRNA expressions of rat skeletal and left ventricle muscles

The beta2-agonist clenbuterol [4-amino-alpha(t-butyl-amino)methyl-3,5-dichlorobenzyl alcohol] is used as a non-steroidal anabolic drug for sports doping. The effects of clenbuterol on the transcriptional process and mRNA stability of beta-adrenoceptor (beta-AR) in skeletal and cardiac muscles are still unknown. Therefore, we investigated the effects of clenbuterol on beta1- and beta2-AR mRNA expressions of fast-twitch fiber-rich extensor digitorum longus (EDL), slow-twitch fiber-rich soleus (SOL), and left ventricle (LV) muscles by real-time RT-PCR. Adult male Sprague Dawley rats were divided into the clenbuterol-administered group and control group. The administration (dose = 1.0 mg/kg body weight/day, s.c.) of clenbuterol was maintained for 10 days. The administration of clenbuterol significantly increased the weight, RNA concentration, and total RNA content of EDL muscle. No effects of clenbuterol on those of SOL and LV muscles, however, were observed. The administration of clenbuterol significantly decreased beta1-AR mRNA expression of LV muscle. Furthermore, the administration of clenbuterol significantly decreased beta2-AR mRNA expression of EDL and LV muscles. No effect of clenbuterol on beta2-AR mRNA expression of SOL muscle, however, was observed. These results suggest that the effects of clenbuterol on beta1- and beta2-AR mRNA expressions and muscle hypertrophy depend on muscle fiber types.

Beta2-agonist clenbuterol induced changes in the distribution of white blood cells in rats

Clenbuterol [CLE: 4-amino-alpha(t-butyl-amino)methyl-3,5-dichlorobenzyl alcohol] is well known as a potent beta2-adrenergic agonist and non-steroidal anabolic drug, and thus it is generally used for sports doping and asthma therapy. Although the functions of immune cells such as white blood cells (WBCs) have shown to be modulated through beta2-adrenoceptors, the effects of CLE on immune-responsive systems have not been elucidated systematically. Therefore, the effects of CLE on the number of WBCs were studied in rats. Male adult rats were divided into CLE-administered group and the control group to compare the number of total WBCs, neutrophils, monocytes, lymphocytes, eosinophils, and basophils. The administration (dose = 1.0 mg . kg(-1) body weight . day(-1), s.c.) of CLE was maintained for 30 days. CLE did not change the number of total WBCs during the experimental period. However, CLE increased significantly the number of neutrophils and monocytes, while CLE decreased drastically the number of lymphocytes and eosinophils. There was no significant change in the number of basophils between both groups. These results suggest that the administration of CLE induces drastic redistribution of WBCs in circulation without changing the number of total WBCs, and these responses of WBCs during the administration of CLE are sustained for at least 30 days.

Effects of two types of inactivity on the number of white blood cells in rats

Prolonged inactivity is known to induce changes in responses of many physiological defense systems such as the hypothalamo-hypophyseal-adrenocortical axis, the sympathetic nervous system, and immuno-responsive systems. However, effects of various types of inactivity on immuno-responsive systems are still unknown. Therefore, the effects of two types of inactivity (immobilization: IMM and whole body suspension: WBS) on the number of white blood cells were studied in rats. Rats were divided into the control group and each inactivity group to compare the number of total white blood cells, lymphocytes, monocyte, neutrophil, eosinophil, and basophil during the experimental periods. Both IMM and WBS were maintained for 11 days. IMM markedly increased the number of total white blood cells, monocyte, neutrophil, and eosinophil in the 1st to 10th day. However, the number of total white blood cells, monocyte, neutrophil, and eosinophil during the experiment of WBS were characterized by the presence of a lag phase followed by the significant increased actions. IMM did not change the number of basophil during the experimental period. However, WBS increased the number of basophil in the 1st to 8th day to 2.8-4.8 times, compared with the values of the control. Both IMM and WBS did not change the number of lymphocytes. From these results, WBS increases the number of natural immunity cells without changing acquired immunity cells, and there are different responses in the number of total white blood cells, monocyte, neutrophil, eosinophil, and basophil between IMM and WBS.