The action of obestatin in skeletal muscle repair: stem cell expansion, muscle growth, and microenvironment remodeling

The development of therapeutic strategies for skeletal muscle diseases, such as physical injuries and myopathies, depends on the knowledge of regulatory signals that control the myogenic process. The obestatin/GPR39 system operates as an autocrine signal in the regulation of skeletal myogenesis. Using a mouse model of skeletal muscle regeneration after injury and several cellular strategies, we explored the potential use of obestatin as a therapeutic agent for the treatment of trauma-induced muscle injuries. Our results evidenced that the overexpression of the preproghrelin, and thus obestatin, and GPR39 in skeletal muscle increased regeneration after muscle injury. More importantly, the intramuscular injection of obestatin significantly enhanced muscle regeneration by simulating satellite stem cell expansion as well as myofiber hypertrophy through a kinase hierarchy. Added to the myogenic action, the obestatin administration resulted in an increased expression of VEGF/VEGFR2 and the consequent microvascularization, with no effect on collagen deposition in skeletal muscle. Furthermore, the potential inhibition of myostatin during obestatin treatment might contribute to its myogenic action improving muscle growth and regeneration. Taken together, our data demonstrate successful improvement of muscle regeneration, indicating obestatin is a potential therapeutic agent for skeletal muscle injury and would benefit other myopathies related to muscle regeneration

HDAC4 regulates skeletal muscle regeneration via soluble factors

Skeletal muscle possesses a high ability to regenerate after an insult or in pathological conditions, relying on satellite cells, the skeletal muscle stem cells. Satellite cell behavior is tightly regulated by the surrounding microenvironment, which provides multiple signals derived from local cells and systemic factors. Among epigenetic mechanisms, histone deacetylation has been proved to affect muscle regeneration. Indeed, pan-histone deacetylase inhibitors were found to improve muscle regeneration, while deletion of histone deacetylase 4 (HDAC4) in satellite cells inhibits their proliferation and differentiation, leading to compromised muscle regeneration. In this study, we delineated the HDAC4 function in adult skeletal muscle, following injury, by using a tissue-specific null mouse line. HDAC4 resulted crucial for skeletal muscle regeneration by mediating soluble factors that influence muscle-derived cell proliferation and differentiation. These findings add new biological functions to HDAC4 in skeletal muscle that need considering when administering histone deacetylase inhibitors

Macrophage-released ADAMTS1 promotes muscle stem cell activation.

Coordinated activation of muscle stem cells (known as satellite cells) is critical for postnatal muscle growth and regeneration. The muscle stem cell niche is central for regulating the activation state of satellite cells, but the specific extracellular signals that coordinate this regulation are poorly understood. Here we show that macrophages at sites of muscle injury induce activation of satellite cells via expression of Adamts1. Overexpression of Adamts1 in macrophages in vivo is sufficient to increase satellite cell activation and improve muscle regeneration in young mice. We demonstrate that NOTCH1 is a target of ADAMTS1 metalloproteinase activity, which reduces Notch signaling, leading to increased satellite cell activation. These results identify Adamts1 as a potent extracellular regulator of satellite cell activation and have significant implications for understanding the regulation of satellite cell activity and regeneration after muscle injury.Satellite cells are crucial for growth and regeneration of skeletal muscle. Here the authors show that in response to muscle injury, macrophages secrete Adamts1, which induces satellite cell activation by modulating Notch1 signaling

Effects of Diet-Induced Obesity on Extracellular Matrix Remodeling During Skeletal Muscle Regeneration

THE EFFECT OF DIET-INDUCED OBESITY ON EXTRACELLULAR MATRIX REMODELING DURING SKELETAL MUSCLE REGENERATION Michelle A. Tedrowe, Lemuel A. Brown, Richard A. Perry Jr., Megan E. Rosa, Jacob L. Brown, David E. Lee, Nicholas P. Greene, Tyrone A. Washington. University of Arkansas, Fayetteville, Arkansas Skeletal muscle has the ability to regenerate from damage; however, recent studies have reported a negative effect of obesity on skeletal muscle regenerative capacity. The extracellular matrix (ECM) contributes to skeletal muscle structure acting as a scaffold for skeletal muscle. Additionally, skeletal muscle serves as a reservoir for proteins and growth factors that promote regeneration. Optimal skeletal muscle regeneration includes inflammation, ECM remodeling, and myofiber growth. Disruption to any of these processes can negatively affect skeletal muscle regeneration. PURPOSE: The purpose of this study was to determine how diet-induced obesity (DIO) affects ECM remodeling during skeletal muscle regeneration. METHODS: Fifty-six male C57BL/6J mice were randomly assigned to two groups; lean diet (10% fat) and high fat diet (HFD) (60% fat). Within those two groups, mice were randomly assigned to either a PBS (uninjured) group or a bupivacaine (injured) group. Bupivacaine is a myotoxin which induces injury to skeletal muscle. Both groups received injections into the tibialis anterior (TA). Three or 28 days post-bupivacaine injection, the TAs were extracted and PCR reaction was done to quantify ECM-related gene expression (i.e. Collagen-I, Collagen-III, Fibronectin, TGF-β, MMP-2, MMP-9, and TIMP-I). RESULTS: There was no difference in Collagen III:I gene expression 3 days post-injection in the lean group (p\u3e0.05). However, there was a 3 fold increase (p0.05). Three and 28 days post injection there was a main effect of injury to increase MMP-2 gene expression (pCONCLUSION: Obesity altered ECM composition during skeletal muscle regeneration. This could negatively impact the ability of obese muscle to recovery form injury. These findings suggest that an altered composition could lead to a change in exercise prescription for this specific population. This work was supported by a grant from the American Biosciences Institute and a Student Undergraduate Research Fellowship Grant

Oxytocin is an age-specific circulating hormone that is necessary for muscle maintenance and regeneration.

The regenerative capacity of skeletal muscle declines with age. Previous studies suggest that this process can be reversed by exposure to young circulation; however, systemic age-specific factors responsible for this phenomenon are largely unknown. Here we report that oxytocin--a hormone best known for its role in lactation, parturition and social behaviours--is required for proper muscle tissue regeneration and homeostasis, and that plasma levels of oxytocin decline with age. Inhibition of oxytocin signalling in young animals reduces muscle regeneration, whereas systemic administration of oxytocin rapidly improves muscle regeneration by enhancing aged muscle stem cell activation/proliferation through activation of the MAPK/ERK signalling pathway. We further show that the genetic lack of oxytocin does not cause a developmental defect in muscle but instead leads to premature sarcopenia. Considering that oxytocin is an FDA-approved drug, this work reveals a potential novel and safe way to combat or prevent skeletal muscle ageing

Highly Coordinated Gene Regulation in Mouse Skeletal Muscle Regeneration

Mammalian skeletal muscles are capable of regeneration after injury. Quiescent satellite cells are activated to reenter the cell cycle and to differentiate for repair, recapitulating features of myogenesis during embryonic development. To understand better the molecular mechanism involved in this process in vivo, we employed high density cDNA microarrays for gene expression profiling in mouse tibialis anterior muscles after a cardiotoxin injection. Among 16,267 gene elements surveyed, 3,532 elements showed at least a 2.5-fold change at one or more time points during a 14-day time course. Hierarchical cluster analysis and semiquantitative reverse transcription-PCR showed induction of genes important for cell cycle control and DNA replication during the early phase of muscle regeneration. Subsequently, genes for myogenic regulatory factors, a group of imprinted genes and genes with functions to inhibit cell cycle progression and promote myogenic differentiation, were induced when myogenic stem cells started to differentiate. Induction of a majority of these genes, including E2f1 and E2f2, was abolished in muscles lacking satellite cell activity after gamma radiation. Regeneration was severely compromised in E2f1 null mice but not affected in E2f2 null mice. This study identifies novel genes potentially important for muscle regeneration and reveals highly coordinated myogenic cell proliferation and differentiation programs in adult skeletal muscle regeneration in vivo

Pharmacological inhibition of PKCθ counteracts muscle disease in a mouse model of duchenne muscular dystrophy

Inflammation plays a considerable role in the progression of Duchenne Muscular Dystrophy (DMD), a severe muscle disease caused by a mutation in the dystrophin gene. We previously showed that genetic ablation of Protein Kinase C θ (PKCθ) in mdx, the mouse model of DMD, improves muscle healing and regeneration, preventing massive inflammation. To establish whether pharmacological targeting of PKCθ in DMD can be proposed as a therapeutic option, in this study we treated young mdx mice with the PKCθ inhibitor Compound 20 (C20). We show that C20 treatment led to a significant reduction in muscle damage associated with reduced immune cells infiltration, reduced inflammatory pathways activation, and maintained muscle regeneration. Importantly, C20 treatment is efficient in recovering muscle performance in mdx mice, by preserving muscle integrity. Together, these results provide proof of principle that pharmacological inhibition of PKCθ in DMD can be considered an attractive strategy to modulate immune response and prevent the progression of the disease

Controlled Delivery of Sdf-1 Alpha and Igf-1: Cxcr4(+) Cell Recruitment and Functional Skeletal Muscle Recovery

Therapeutic delivery of regeneration-promoting biological factors directly to the site of injury has demonstrated its efficacy in various injury models. Several reports describe improved tissue regeneration following local injection of tissue specific growth factors, cytokines and chemokines. Evidence exists that combined cytokine/growth factor treatment is superior for optimizing tissue repair by targeting different aspects of the regeneration response. The purpose of this study was to evaluate the therapeutic potential of the controlled delivery of stromal cell-derived factor-1alpha (SDF-1 alpha) alone or in combination with insulin-like growth factor-I (SDF-1 alpha/IGF-I) for the treatment of tourniquet-induced ischemia/reperfusion injury (TK-I/R) of skeletal muscle. We hypothesized that SDF-1 alpha will promote sustained stem cell recruitment to the site of muscle injury, while IGF-I will induce progenitor cell differentiation to effectively restore muscle contractile function after TK-I/R injury while concurrently reducing apoptosis. Utilizing a novel poly-ethylene glycol PEGylated fibrin gel matrix (PEG-Fib), we incorporated SDF-1 alpha alone (PEG-Fib/SDF-1 alpha) or in combination with IGF-I (PEG-Fib/SDF-1 alpha/IGF-I) for controlled release at the site of acute muscle injury. Despite enhanced cell recruitment and revascularization of the regenerating muscle after SDF-1 alpha treatment, functional analysis showed no benefit from PEG-Fib/SDF-1 alpha therapy, while dual delivery of PEG-Fib/SDF-1 alpha/IGF-I resulted in IGF-I-mediated improvement of maximal force recovery and SDF-1 alpha-driven in vivo neovasculogenesis. Histological data supported functional data, as well as highlighted the important differences in the regeneration process among treatment groups. This study provides evidence that while revascularization may be necessary for maximizing muscle force recovery, without modulation of other effects of inflammation it is insufficient.Kinesiology and Health Educatio

Angiotensin II type 1 receptor antagonists alleviate muscle pathology in the mouse model for laminin-alpha2-deficient congenital muscular dystrophy (MDC1A)

BACKGROUND: Laminin-alpha2-deficient congenital muscular dystrophy (MDC1A) is a severe muscle-wasting disease for which no curative treatment is available. Antagonists of the angiotensin II receptor type 1 (AT1), including the anti-hypertensive drug losartan, have been shown to block also the profibrotic action of transforming growth factor (TGF)-beta and thereby ameliorate disease progression in mouse models of Marfan syndrome. Because fibrosis and failure of muscle regeneration are the main reasons for the severe disease course of MDC1A, we tested whether L-158809, an analog derivative of losartan, could ameliorate the dystrophy in dyW/dyW mice, the best-characterized model of MDC1A. METHODS: L-158809 was given in food to dyW/dyW mice at the age of 3 weeks, and the mice were analyzed at the age of 6 to 7 weeks. We examined the effect of L-158809 on muscle histology and on muscle regeneration after injury as well as the locomotor activity and muscle strength of the mice. RESULTS: We found that TGF-beta signaling in the muscles of the dyW/dyW mice was strongly increased, and that L-158809 treatment suppressed this signaling. Consequently, L-158809 reduced fibrosis and inflammation in skeletal muscle of dyW/dyW mice, and largely restored muscle regeneration after toxin-induced injury. Mice showed improvement in their locomotor activity and grip strength, and their body weight was significantly increased. CONCLUSION: These data provide evidence that AT1 antagonists ameliorate several hallmarks of MDC1A in dyW/dyW mice, the best-characterized mouse model for this disease. Because AT1 antagonists are well tolerated in humans and widely used in clinical practice, these results suggest that losartan may offer a potential future treatment of patients with MDC1A