In vivo neutralization of IL-6 receptors ameliorates gastrointestinal dysfunction in dystrophin-deficient mdx mice

Systemic Treatment of Body-Wide Duchenne Muscular Dystrophy Symptoms

Duchenne muscular dystrophy (DMD) is a fatal X-linked disease that leads to premature death due to the loss of dystrophin. Current strategies predominantly focus on the therapeutic treatment of affected skeletal muscle tissue. However, certain results point to the fact that with successful treatment of skeletal muscle, DMD-exposed latent phenotypes in tissues, such as cardiac and smooth muscle, might lead to adverse effects and even death. Likewise, it is now clear that the absence of dystrophin affects the function of the nervous system, and that this phenotype is more pronounced when shorter dystrophins are absent, in addition to the full-length dystrophin that is present predominantly in the muscle. Here, I focus on the systemic aspects of DMD, highlighting the ubiquitous expression of the dystrophin gene in human tissues. Furthermore, I describe therapeutic strategies that have been tested in the clinic and point to unresolved questions regarding the function of distinct dystrophin isoforms, and the possibility of current therapeutic strategies to tackle phenotypes that relate to their absence.

Current and investigational medications for the treatment of sarcopenia

Sarcopenia, defined as the loss of muscle mass and function, is a widely prevalent and severe condition in older adults. Since 2016, it is recognized as a disease. Strength exercise training and nutritional support are the frontline treatment of sarcopenia, with no drug currently approved for this indication. However, new therapeutic options are emerging. In this review, we evidenced that only very few trials have focused on sarcopenia/sarcopenic patients. Most drug trials were performed in different clinical older populations (e.g., men with hypogonadism, post-menopausal women at risk for osteoporosis), and their efficacy were tested separately on the components of sarcopenia (muscle mass, muscle strength and physical performances). Results from trials testing the effects of Testosterone, Selective Androgen Receptor Modulators (SARMs), Estrogen, Dehydroepiandrosterone (DHEA), Insulin-like Growth Factor-1 (IGF-1), Growth Hormone (GH), GH Secretagogue (GHS), drug targeting Myostatin and Activin receptor pathway, Vitamin D, Angiotensin Converting Enzyme inhibitors (ACEi) and Angiotensin Receptor Blockers (ARBs), or β-blockers, were compiled. Although some drugs have been effective in improving muscle mass and/or strength, this was not translated into clinically relevant improvements on physical performance. Finally, some promising molecules investigated in on-going clinical trials and in pre-clinical phase were summarized, including apelin and irisin.

Identification of Novel Gene Regulatory Networks for Dystrophin Protein in Vascular Smooth Muscle Cells by Single-Nuclear Transcriptome Analysis

Duchenne muscular dystrophy is an X-linked recessive disease caused by mutations in dystrophin proteins that lead to heart failure and respiratory failure. Dystrophin (DMD) is not only expressed in cardiomyocytes and skeletal muscle cells, but also in vascular smooth muscle cells (VSMCs). Patients with DMD have been reported to have hypotension. Single nuclear RNA sequencing (snRNA-seq) is a state-of-the-art technology capable of identifying niche-specific gene programs of tissue-specific cell subpopulations. To determine whether DMD mutation alters blood pressure, we compared systolic, diastolic, and mean blood pressure levels in mdx mice (a mouse model of DMD carrying a nonsense mutation in DMD gene) and the wide-type control mice. We found that mdx mice showed significantly lower systolic, diastolic, and mean blood pressure than control mice. To understand how DMD mutation changes gene expression profiles from VSMCs, we analyzed an snRNA-seq dataset from the muscle nucleus of DMD mutant (DMDmut) mice and control (Ctrl) mice. Gene Ontology (GO) enrichment analysis revealed that the most significantly activated pathways in DMDmut-VSMCs are involved in ion channel function (potassium channel activity, cation channel complex, and cation channel activity). Notably, we discovered that the DMDmut-VSMCs showed significantly upregulated expression of KCNQ5 and RYR2, whereas the most suppressed pathways were transmembrane transporter activity (such as anion transmembrane transporter activity, inorganic anion transmembrane transporter activity, import into cell, and import across plasma membrane). Moreover, we analyzed metabolic pathways from the Kyoto Encyclopedia of Genes and Genomes (KEGG) using "scMetabolism" R package. DMDmut-VSMCs exhibited dysregulation of pyruvate metabolism and nuclear acid metabolism. In conclusion, via the application of snRNA-seq, we (for the first time) identify the potential molecular regulation by DMD in the upregulation of the expression of KCNQ5 genes in VSMCs, which helps us to understand the mechanism of hypotension in DMD patients. Our study potentially offers new possibilities for therapeutic interventions in systemic hypotension in DMD patients with pharmacological inhibition of KCNQ5.

Muscle cell-derived cytokines in skeletal muscle regeneration

Regeneration of the mammalian adult skeletal muscle is a well-orchestrated process regulated by multiple proteins and signalling pathways. Cytokines constitute a major class of regulators of skeletal myogenesis. It is well established that infiltrating immune cells at the site of muscle injury secrete cytokines, which play critical roles in the myofibre repair and regeneration process. In the past 10-15 years, skeletal muscle itself has emerged as a prolific producer of cytokines. Much attention in the field has been focused on the endocrine effects of muscle-secreted cytokines (myokines) on metabolic regulation. However, ample evidence suggests that muscle-derived cytokines also regulate myogenic differentiation and muscle regeneration in an autocrine manner. In this review, we survey cytokines that meet two criteria: (a) evidence of expression by muscle cells; (b) evidence demonstrating a myogenic function. Dozens of cytokines representing several major classes make up this group, and together they regulate all steps of the myogenic process. How such a large array of cytokines coordinate their signalling to form a regulatory network is a fascinating, pressing question. Functional studies that can distinguish the source of the cytokines in vivo are also much needed in order to facilitate exploration of their full therapeutic potential.

Investigating the Potential for Sulforaphane to Attenuate Gastrointestinal Dysfunction in mdx Dystrophic Mice

Gastrointestinal (GI) dysfunction is an important, yet understudied condition associated with Duchenne muscular dystrophy (DMD), with patients reporting bloating, diarrhea, and general discomfort, contributing to a reduced quality of life. In the mdx mouse, the most commonly used mouse model of DMD, studies have confirmed GI dysfunction (reported as altered contractility and GI transit through the small and large intestine), associated with increased local and systemic inflammation. Sulforaphane (SFN) is a natural isothiocyanate with anti-inflammatory and anti-oxidative properties via its activation of Nrf2 signalling that has been shown to improve aspects of the skeletal muscle pathology in dystrophic mice. Whether SFN can similarly improve GI function in muscular dystrophy was unknown. Video imaging and spatiotemporal mapping to assess gastrointestinal contractions in isolated colon preparations from mdx and C57BL/10 mice revealed that SFN reduced contraction frequency when administered ex vivo, demonstrating its therapeutic potential to improve GI function in DMD. To confirm this in vivo, four-week-old male C57BL/10 and mdx mice received vehicle (2% DMSO/corn oil) or SFN (2 mg/kg in 2% DMSO/corn oil) via daily oral gavage five days/week for 4 weeks. SFN administration reduced fibrosis in the diaphragm of mdx mice but did not affect other pathological markers. Gene and protein analysis revealed no change in Nrf2 protein expression or activation of Nrf2 signalling after SFN administration and oral SFN supplementation did not improve GI function in mdx mice. Although ex vivo studies demonstrate SFN’s therapeutic potential for reducing colon contractions, in vivo studies should investigate higher doses and/or alternate routes of administration to confirm SFN’s potential to improve GI function in DMD.

Pathological alterations in the gastrointestinal tract of a porcine model of DMD

BACKGROUND

Patients with Duchenne muscular dystrophy (DMD) develop severe skeletal and cardiac muscle pathologies, which result in premature death. Therefore, the current therapeutic efforts are mainly targeted to correct dystrophin expression in skeletal muscle and heart. However, it was reported that DMD patients may also exhibit gastrointestinal and nutritional problems. How the pathological alterations in gastrointestinal tissues contribute to the disease are not fully explored.

RESULTS

Here we employed the CRISPR/Cas9 system combined with somatic nuclear transfer technology (SCNT) to establish a porcine model of DMD and explored their pathological alterations. We found that genetic disruption of dystrophin expression led to morphological gastrointestinal tract alterations, weakened the gastrointestinal tract digestion and absorption capacity, and eventually led to malnutrition and gastric dysfunction in the DMD pigs.

CONCLUSIONS

This work provides important insights into the pathogenesis of DMD and highlights the need to consider the gastrointestinal dysfunction as an additional therapeutic target for DMD patients.

Biological characteristics of IL-6 and related intestinal diseases

The intestine serves as an important digestive and the largest immune organ in the body. Interleukin-6(IL-6), an important mediator of various pathways, participates in the interactions between different kinds of cells and closely correlates with intestinal physiological and pathological condition. In this review we summarize the signaling pathways of IL-6 and its functions in maintaining intestinal homeostasis. We also explored its relation with nervous system and highlight its potential role in Parkinson's disease. Based on its specialty of the double-side influences on intestinal tumors and inflammation, we summarize how they are done through distinctive process.

Spatiotemporal Mapping Reveals Regional Gastrointestinal Dysfunction in mdx Dystrophic Mice Ameliorated by Oral L-arginine Supplementation

Background/Aims

Patients with Duchenne muscular dystrophy exhibit significant, ongoing impairments in gastrointestinal (GI) function likely resulting from dysregulated nitric oxide production. Compounds increasing neuronal nitric oxide synthase expression and/or activity could improve GI dysfunction and enhance quality of life for dystrophic patients. We used video imaging and spatiotemporal mapping to identify GI dysfunction in mdx dystrophic mice and determine whether dietary intervention to enhance nitric oxide could alleviate aberrant colonic activity in muscular dystrophy.

Methods

Four-week-old male C57BL/10 and mdx mice received a specialized diet either with no supplementation (control) or supplemented (1 g/kg/day) with L-alanine, L-arginine, or L-citrulline for 8 weeks. At the conclusion of treatment, mice were sacrificed by cervical dislocation and colon motility examined by spatiotemporal (ST) mapping ex vivo.

Results

ST mapping identified increased contraction number in the mid and distal colon of mdx mice on control and L-alanine supplemented diets relative to C57BL/10 mice (P < 0.05). Administration of either L-arginine or L-citrulline attenuated contraction number in distal colons of mdx mice relative to C57BL/10 mice.

Conclusions

GI dysfunction in Duchenne muscular dystrophy has been sadly neglected as an issue affecting quality of life. ST mapping identified regional GI dysfunction in the mdx dystrophic mouse. Dietary interventions to increase nitric oxide signaling in the GI tract reduced the number of colonic contractions and alleviated colonic constriction at rest. These findings in mdx mice reveal that L-arginine can improve colonic motility and has potential therapeutic relevance for alleviating GI discomfort, improving clinical care, and enhancing quality of life in Duchenne muscular dystrophy.

Recovery of respiratory function in mdx mice co-treated with neutralizing interleukin-6 receptor antibodies and urocortin-2

KEY POINTS

Impaired ventilatory capacity and diaphragm muscle weakness are prominent features of Duchenne muscular dystrophy, with strong evidence of attendant systemic and muscle inflammation. We performed a 2-week intervention in young wild-type and mdx mice, consisting of either injection of saline or co-administration of a neutralizing interleukin-6 receptor antibody (xIL-6R) and urocortin-2 (Ucn2), a corticotrophin releasing factor receptor 2 agonist. We examined breathing and diaphragm muscle form and function. Breathing and diaphragm muscle functional deficits are improved following xIL-6R and Ucn2 co-treatment in mdx mice. The functional improvements were associated with a preservation of mdx diaphragm muscle myosin heavy chain IIx fibre complement. The concentration of the pro-inflammatory cytokine interleukin-1β was reduced and the concentration of the anti-inflammatory cytokine interleukin-10 was increased in mdx diaphragm following drug co-treatment. Our novel findings may have implications for the development of pharmacotherapies for the dystrophinopathies with relevance for respiratory muscle performance and breathing.

ABSTRACT

The mdx mouse model of Duchenne muscular dystrophy shows evidence of hypoventilation and pronounced diaphragm dysfunction. Six-week-old male mdx (n = 32) and wild-type (WT; n = 32) mice received either saline (0.9% w/v) or a co-administration of neutralizing interleukin-6 receptor antibodies (xIL-6R; 0.2 mg kg-1 ) and corticotrophin-releasing factor receptor 2 agonist (urocortin-2; 30 μg kg-1 ) subcutaneously over 2 weeks. Breathing and diaphragm muscle contractile function (ex vivo) were examined. Diaphragm structure was assessed using histology and immunofluorescence. Muscle cytokine concentration was determined using a multiplex assay. Minute ventilation and diaphragm muscle peak force at 100 Hz were significantly depressed in mdx compared with WT. Drug treatment completely restored ventilation in mdx mice during normoxia and significantly increased mdx diaphragm force- and power-generating capacity. The number of centrally nucleated muscle fibres and the areal density of infiltrates and collagen content were significantly increased in mdx diaphragm; all indices were unaffected by drug co-treatment. The abundance of myosin heavy chain (MyHC) type IIx fibres was significantly decreased in mdx diaphragm; drug co-treatment preserved MyHC type IIx complement in mdx muscle. Drug co-treatment increased the cross-sectional area of MyHC type I and IIx fibres in mdx diaphragm. The cytokines IL-1β, IL-6, KC/GRO and TNF-α were significantly increased in mdx diaphragm compared with WT. Drug co-treatment significantly decreased IL-1β and increased IL-10 in mdx diaphragm. Drug co-treatment had no significant effect on WT diaphragm muscle structure, cytokine concentrations or function. Recovery of breathing and diaphragm force in mdx mice was impressive in our studies, with implication for human dystrophinopathies.

Colonic migrating motor complexes are inhibited in acute tri-nitro benzene sulphonic acid colitis

Background

Inflammatory Bowel Disease (IBD) is characterized by overt inflammation of the intestine and is typically accompanied by symptoms of bloody diarrhea, abdominal pain and cramping. The Colonic Migrating Motor Complex (CMMC) directs the movement of colonic luminal contents over long distances. The tri-nitrobenzene sulphonic acid (TNBS) model of colitis causes inflammatory damage to enteric nerves, however it remains to be determined whether these changes translate to functional outcomes in CMMC activity. We aimed to visualize innate immune cell infiltration into the colon using two-photon laser scanning intra-vital microscopy, and to determine whether CMMC activity is altered in the tri-nitro benzene sulphonic (TNBS) model of colitis.

Methods

Epithelial barrier permeability was compared between TNBS treated and healthy control mice in-vitro and in-vivo. Innate immune activation was determined by ELISA, flow cytometry and by 2-photon intravital microscopy. The effects of TNBS treatment and IL-1β on CMMC function were determined using a specialized organ bath.

Results

TNBS colitis increased epithelial barrier permeability in-vitro and in-vivo. Colonic IL-1β concentrations, colonic and systemic CD11b+ cell infiltration, and the number of migrating CD11b+ cells on colonic blood vessels were all increased in TNBS treated mice relative to controls. CMMC frequency and amplitude were inhibited in the distal and mid colon of TNBS treated mice. CMMC activity was not altered by superfusion with IL-1β.

Conclusions

TNBS colitis damages the epithelial barrier and increases innate immune cell activation in the colon and systemically. Innate cell migration into the colon is readily identifiable by two-photon intra-vital microscopy. CMMC are inhibited by inflammation, but this is not due to direct effects of IL-1β.

Combined XIL-6R and urocortin-2 treatment restores MDX diaphragm muscle force

INTRODUCTION

Duchenne muscular dystrophy (DMD) is characterized by progressive muscle degeneration leading to immobility, respiratory failure, and premature death. As chronic inflammation and stress are implicated in DMD pathology, the efficacy of an anti-inflammatory and anti-stress intervention strategy in ameliorating diaphragm dysfunction was investigated.

METHODS

Diaphragm muscle contractile function was compared in wild-type and dystrophin-deficient mdx mice treated with saline, anti-interleukin-6 receptor antibodies (xIL-6R), the corticotrophin-releasing factor receptor 2 (CRFR2) agonist, urocortin 2, or both xIL-6R and urocortin 2.

RESULTS

Combined treatment with xIL-6R and urocortin 2 rescued impaired force in mdx diaphragms. Mechanical work production and muscle shortening was also improved by combined drug treatment.

DISCUSSION

Treatment which neutralizes peripheral IL-6 signaling and stimulates CRFR2 recovers force-generating capacity and the ability to perform mechanical work in mdx diaphragm muscle. These findings may be important in the search for therapeutic targets in DMD. Muscle Nerve 56: E134-E140, 2017.

Restoration of pharyngeal dilator muscle force in dystrophin-deficient (mdx) mice following co-treatment with neutralizing interleukin-6 receptor antibodies and urocortin 2

What is the central question of this study? We previously reported impaired upper airway dilator muscle function in the mdx mouse model of Duchenne muscular dystrophy (DMD). Our aim was to assess the effect of blocking interleukin-6 receptor signalling and stimulating corticotrophin-releasing factor receptor 2 signalling on mdx sternohyoid muscle structure and function. What is the main finding and its importance? The interventional treatment had a positive inotropic effect on sternohyoid muscle force, restoring mechanical work and power to wild-type values, reduced myofibre central nucleation and preserved the myosin heavy chain type IIb fibre complement of mdx sternohyoid muscle. These data might have implications for development of pharmacotherapies for DMD with relevance to respiratory muscle performance. The mdx mouse model of Duchenne muscular dystrophy shows evidence of impaired pharyngeal dilator muscle function. We hypothesized that inflammatory and stress-related factors are implicated in airway dilator muscle dysfunction. Six-week-old mdx (n = 26) and wild-type (WT; n = 26) mice received either saline (0.9% w/v) or a co-administration of neutralizing interleukin-6 receptor antibodies (0.2 mg kg-1 ) and corticotrophin-releasing factor receptor 2 agonist (urocortin 2; 30 μg kg-1 ) over 2 weeks. Sternohyoid muscle isometric and isotonic contractile function was examined ex vivo. Muscle fibre centronucleation and muscle cellular infiltration, collagen content, fibre-type distribution and fibre cross-sectional area were determined by histology and immunofluorescence. Muscle chemokine content was examined by use of a multiplex assay. Sternohyoid peak specific force at 100 Hz was significantly reduced in mdx compared with WT. Drug treatment completely restored force in mdx sternohyoid to WT levels. The percentage of centrally nucleated muscle fibres was significantly increased in mdx, and this was partly ameliorated after drug treatment. The areal density of infiltrates and collagen content were significantly increased in mdx sternohyoid; both indices were unaffected by drug treatment. The abundance of myosin heavy chain type IIb fibres was significantly decreased in mdx sternohyoid; drug treatment preserved myosin heavy chain type IIb complement in mdx muscle. The chemokines macrophage inflammatory protein 2, interferon-γ-induced protein 10 and macrophage inflammatory protein 3α were significantly increased in mdx sternohyoid compared with WT. Drug treatment significantly increased chemokine expression in mdx but not WT sternohyoid. Recovery of contractile function was impressive in our study, with implications for Duchenne muscular dystrophy. The precise molecular mechanisms by which the drug treatment exerts an inotropic effect on mdx sternohyoid muscle remain to be elucidated.

Pharmacological therapeutics targeting the secondary defects and downstream pathology of Duchenne muscular dystrophy

INTRODUCTION

Since the identification of the dystrophin gene in 1986, a cure for Duchenne muscular dystrophy (DMD) has yet to be discovered. Presently, there are a number of genetic-based therapies in development aimed at restoration and/or repair of the primary defect. However, growing understanding of the pathophysiological consequences of dystrophin absence has revealed several promising downstream targets for the development of therapeutics.

AREAS COVERED

In this review, we discuss various strategies for DMD therapy targeting downstream consequences of dystrophin absence including loss of muscle mass, inflammation, fibrosis, calcium overload, oxidative stress, and ischemia. The rationale of each approach and the efficacy of drugs in preclinical and clinical studies are discussed.

EXPERT OPINION

For the last 30 years, effective DMD drug therapy has been limited to corticosteroids, which are associated with a number of negative side effects. Our knowledge of the consequences of dystrophin absence that contribute to DMD pathology has revealed several potential therapeutic targets. Some of these approaches may have potential to improve or slow disease progression independently or in combination with genetic-based approaches. The applicability of these pharmacological therapies to DMD patients irrespective of their genetic mutation, as well as the potential benefits even for advanced stage patients warrants their continued investigation.