Silencing Myostatin Using Cholesterol-conjugated siRNAs Induces Muscle Growth

Short interfering RNAs (siRNAs) are a valuable tool for gene silencing with applications in both target validation and therapeutics. Many advances have recently been made to improve potency and specificity, and reduce toxicity and immunostimulation. However, siRNA delivery to a variety of tissues remains an obstacle for this technology. To date, siRNA delivery to muscle has only been achieved by local administration or by methods with limited potential use in the clinic. We report systemic delivery of a highly chemically modified cholesterol-conjugated siRNA targeting muscle-specific gene myostatin (Mstn) to a full range of muscles in mice. Following a single intravenous injection, we observe 85–95% knockdown of Mstn mRNA in skeletal muscle and >65% reduction in circulating Mstn protein sustained for >21 days. This level of Mstn knockdown is also accompanied by a functional effect on skeletal muscle, with animals showing an increase in muscle mass, size, and strength. The cholesterol-conjugated siRNA platform described here could have major implications for treatment of a variety of muscle disorders, including muscular atrophic diseases, muscular dystrophy, and type II diabetes.

Development of antibody-siRNA conjugate targeted to cardiac and skeletal muscles

Despite considerable efforts to develop efficient carriers, the major target organ of short-interfering RNAs (siRNAs) remains limited to the liver. Expanding the application outside the liver is required to increase the value of siRNAs. Here we report on a novel platform targeted to muscular organs by conjugation of siRNAs with anti-CD71 Fab' fragment. This conjugate showed durable gene-silencing in the heart and skeletal muscle for one month after intravenous administration in normal mice. In particular, 1μg siRNA conjugate showed significant gene-silencing in the gastrocnemius when injected intramuscularly. In a mouse model of peripheral artery disease, the treatment with myostatin-targeting siRNA conjugate by intramuscular injection resulted in significant silencing of myostatin and hypertrophy of the gastrocnemius, which was translated into the recovery of running performance. These data demonstrate the utility of antibody conjugation for siRNA delivery and the therapeutic potential for muscular diseases.

Effectiveness of cationic liposome-mediated local delivery of myostatin-targeting small interfering RNA in vivo

This study evaluated the effectiveness of local administration of cationic liposome-delivered myostatin-targeting siRNA. Myostatin (Mst)-siRNA and scrambled (scr)-siRNA-lipoplexes were injected into the masseter muscles of wild type and dystrophin-deficient mdx mice, which model Duchenne muscular dystrophy. One week after injection, the masseter muscles were dissected for histometric analyses. To evaluate changes in masseter muscle activity, masseter electromyographic (EMG) measurements were performed. One week after local administration of Mst-siRNA-lipoplexes, masseter muscles and myofibrils were significantly larger compared to control masseter muscles treated with scr-siRNA-lipoplexes. Real-time polymerase chain reaction (PCR) analyses revealed significant upregulation of the myogenic regulatory factors MyoD and myogenin and significant downregulation of the adipogenic transcription factors peroxisome proliferator-activated receptor-γ (PPARγ) and CCAAT/enhancer binding protein-α (CEBPα) in masseter muscles treated with Mst-siRNA-lipoplexes. The duty times of masseter muscle activity exceeding 5% showed a slight tendency to increase in both wild type and mdx mice. Therefore, cationic liposome-mediated local administration of Mst-siRNA could increase muscular size and improve muscle activity. Since cationic liposomes delivered siRNA to muscles effectively and are safe and cost-effective, they may represent a therapeutic tool for use in treating muscular diseases.

Limb-girdle muscular dystrophies: where next after six decades from the first proposal (Review)

Limb-girdle muscular dystrophies (LGMD) are a heterogeneous group of disorders, which has led to certain investigators disputing its rationality. The mutual feature of LGMD is limb-girdle affection. Magnetic resonance imaging (MRI), perioral skin biopsies, blood-based assays, reverse-protein arrays, proteomic analyses, gene chips and next generation sequencing are the leading diagnostic techniques for LGMD and gene, cell and pharmaceutical treatments are the mainstay therapies for these genetic disorders. Recently, more highlights have been shed on disease biomarkers to follow up disease progression and to monitor therapeutic responsiveness in future trials. In this study, we review LGMD from a variety of aspects, paying specific attention to newly evolving research, with the purpose of bringing this information into the clinical setting to aid the development of novel therapeutic strategies for this hereditary disease. In conclusion, substantial progress in our ability to diagnose and treat LGMD has been made in recent decades, however enhancing our understanding of the detailed pathophysiology of LGMD may enhance our ability to improve disease outcome in subsequent years.

New aspects of gene-silencing for the treatment of cardiovascular diseases

Coronary heart disease (CHD), mainly caused by atherosclerosis, represents the single leading cause of death in industrialized countries. Besides the classical interventional therapies new applications for treatment of vascular wall pathologies are appearing on the horizon. RNA interference (RNAi) represents a novel therapeutic strategy due to sequence-specific gene-silencing through the use of small interfering RNA (siRNA). The modulation of gene expression by short RNAs provides a powerful tool to theoretically silence any disease-related or disease-promoting gene of interest. In this review we outline the RNAi mechanisms, the currently used delivery systems and their possible applications to the cardiovascular system. Especially, the optimization of the targeting and transfection procedures could enhance the efficiency of siRNA delivery drastically and might open the way to clinical applicability. The new findings of the last years may show the techniques to new innovative therapies and could probably play an important role in treating CHD in the future.

Local applications of myostatin-siRNA with atelocollagen increase skeletal muscle mass and recovery of muscle function

Background

Growing evidence suggests that small-interfering RNA (siRNA) can promote gene silencing in mammalian cells without induction of interferon synthesis or nonspecific gene suppression. Recently, a number of highly specific siRNAs targeted against disease-causing or disease-promoting genes have been developed. In this study, we evaluate the effectiveness of atelocollagen (ATCOL)-mediated application of siRNA targeting myostatin (Mst), a negative regulator of skeletal muscle growth, into skeletal muscles of muscular dystrophy model mice.

Methods and Findings

We injected a nanoparticle complex containing myostatin-siRNA and ATCOL (Mst-siRNA/ATCOL) into the masseter muscles of mutant caveolin-3 transgenic (mCAV-3Tg) mice, an animal model for muscular dystrophy. Scrambled (scr) -siRNA/ATCOL complex was injected into the contralateral muscles as a control. Two weeks after injection, the masseter muscles were dissected for histometric analyses. To investigate changes in masseter muscle activity by local administration of Mst-siRNA/ATCOL complex, mouse masseter electromyography (EMG) was measured throughout the experimental period via telemetry. After local application of the Mst-siRNA/ATCOL complex, masseter muscles were enlarged, while no significant change was observed on the contralateral side. Histological analysis showed that myofibrils of masseter muscles treated with the Mst-siRNA/ATCOL complex were significantly larger than those of the control side. Real-time PCR analysis revealed a significant downregulation of Mst expression in the treated masseters of mCAV-3Tg mice. In addition, expression of myogenic transcription factors was upregulated in the Mst-siRNA-treated masseter muscle, while expression of adipogenic transcription factors was significantly downregulated. EMG results indicate that masseter muscle activity in mCAV-3Tg mice was increased by local administration of the Mst-siRNA/ATCOL complex.

Conclusion

These data suggest local administration of Mst-siRNA/ATCOL complex could lead to skeletal muscle hypertrophy and recovery of motor disability in mCAV-3Tg mice. Therefore, ATCOL-mediated application of siRNA is a potential tool for therapeutic use in muscular atrophy diseases.

Down-regulation of Smad3 Accelerates Palatal Wound Repair

Smad3-deficient mice exhibit accelerated re-epithelialization and tissue remodeling during palatal wound repair. In addition, transforming growth factor beta 1 (TGF-β1) and other inflammatory factors are down-regulated compared with those in wild-type mice. The aim of this study was to examine whether targeting of Smad3 with small interfering RNA (siRNA) accelerates wound-healing and inhibits wound contraction in palatal mucoperiosteal wounds. An initial histological examination of wound closure in mouse palates treated with Smad3-targeted siRNA vs. a scrambled siRNA found that wound-healing was accelerated when levels of Smad3 were decreased. Furthermore, with real-time PCR, mRNA levels of Smad3, TGF-β1, monocyte chemotactic protein-1 ( MCP-1), and macrophage inflammatory protein-1α ( MIP-1α) were found to be significantly down-regulated in palatal tissue treated with Smad3–targeted siRNA vs. a control siRNA. Protein and mRNA levels of α-smooth-muscle actin (α-SMA), type I collagen, and fibronectin were also lower in palates treated with Smad3-targeted siRNA vs. control siRNA. Taken together, these results indicate that down-regulation of Smad3 expression by siRNA can accelerate wound-healing and may inhibit wound contraction. Therefore, siRNA-targeted inhibition of Smad3 may represent a valuable therapeutic tool for palatal mucoperiosteal wound-healing.

Genetic variation in human muscle strength--opportunities for therapeutic interventions?

Inter-individual variation in muscle mass and muscular fitness is broad; being at the upper tail of the distribution not only contributes to improve elite sport performance, but is also associated with longer independent living and higher quality-of-life in the aging population. Heritability estimates of muscle phenotypes are substantial and warrant the search for genetic components underlying this individual variability. The 'kinesiogenomics' field is young, but genetic associations with muscle strength-related phenotypes have been reported already for more than 40 candidate genes, and genome-wide scans revealed several additional regions of interest in the genome. Although genetic findings may reveal attractive targets for novel muscle atrophy therapy, the benefit of exercise as a major stimulus for natural muscle mass enhancement or maintenance cannot be underestimated.

TGF-β signaling in Duchenne muscular dystrophy

The TGF-β protein family consists of secreted multifunctional cytokines that control diverse processes, such as cell growth and differentiation. Aberrant expression and downstream signaling of these growth factors have been associated with multiple diseases, including muscle wasting disorders, such as Duchenne muscular dystrophy. In this review we discuss recent advances in understanding the role of TGF-β family members during normal skeletal muscle biology/regeneration and their role in muscle pathology, with a special focus on Duchenne muscular dystrophy. In addition, we will highlight progress in the development of potential therapeutics for Duchenne muscular dystrophy based on intervention of TGF-β signaling.

[Anti-myostatin antibody therapy for myopathies]

Myostatin, a member of the muscle-specific transforming growth factor (TGF)-β family, negatively regulates skeletal muscle growth. It inhibits muscle stem cell proliferation and differentiation, and attenuates adult muscle fiber protein accretion, resulting in decreased skeletal muscle mass. Thus it has been considered to be a therapeutic target of myopathies including muscular dystrophy. Notably, administration of a blocking antibody against myostatin ameliorated the pathophysiology of dystrophin-deficient mdx mice. Although a clinical trial of an anti-myostatin antibody MYO-029 failed to achieve a significant outcome in patients with muscular dystrophies, various distinct approaches have been taken to establish anti-myostatin therapy including a myostatin decoy receptor ACE-031, a peptide drug derived from myostatin prodomain, small-molecule inhibitors against the myostatin receptor, a follistatin-derived peptibody inhibiting myostatin and myostatin siRNA with collagen-derived carrier particles. Clinical application of the anti-myostatin therapeutics for the treatment of patients with muscular dystrophy needs further evaluation of safety and specification of the target disease types among various muscular dystrophies.