Myostatin Inhibition Using ActRIIB-mFc Does Not Produce Weight Gain or Strength in the Nebulin Conditional KO Mouse

Tinklenberg, J.; Siebers, Emily M.; Beatka, Margaret; Fickau, Brittany A; Ayres, Samuel; Meng, Hui; Yang, Lin; Simpson, Pippa; Granzier, Henk; Lawlor, Michael W.

doi:10.1093/jnen/nly120

Cited by 11 publications

(10 citation statements)

References 38 publications

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“…Type 1 myosin heavy-chain expression was visualized on the red channel, type 2A myosin heavy-chain expression was visualized on the green channel, and together these fibers were assessed as the oxidative fiber population. 72 Fibers negative for type 1 and type 2A myosin heavy chain were assumed to be glycolytic and categorized separately. The Visiopharm software identified muscle fibers using laminin expression to determine cell edges and fiber size limits of between 5 and 110 μm, which was assessed by manual measurement of the smallest and largest fibers in samples from this dataset.…”

Section: Methodsmentioning

confidence: 99%

Voluntary wheel running complements microdystrophin gene therapy to improve muscle function in mdx mice

Hamm

Fathalikhani

Bukovec

et al. 2021

Molecular Therapy - Methods & Clinical Development

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We tested the hypothesis that voluntary wheel running would complement microdystrophin gene therapy to improve muscle function in young mdx mice, a model of Duchenne muscular dystrophy. mdx mice injected with a single dose of AAV9-CK8-microdystrophin or vehicle at age 7 weeks were assigned to three groups: mdxRGT (run, gene therapy), mdxGT (no run, gene therapy), or mdx (no run, no gene therapy). Wild-type (WT) mice were assigned to WTR (run) and WT (no run) groups. WTR and mdxRGT performed voluntary wheel running for 21 weeks; remaining groups were cage active. Robust expression of microdystrophin occurred in heart and limb muscles of treated mice. mdxRGT versus mdxGT mice showed increased microdystrophin in quadriceps but decreased levels in diaphragm. mdx final treadmill fatigue time was depressed compared to all groups, improved in mdxGT, and highest in mdxRGT. Both weekly running distance (km) and final treadmill fatigue time for mdxRGT and WTR were similar. Remarkably, mdxRGT diaphragm power was only rescued to 60% of WT, suggesting a negative impact of running. However, potential changes in fiber type distribution in mdxRGT diaphragms could indicate an adaptation to trade power for endurance. Post-treatment in vivo maximal plantar flexor torque relative to baseline values was greater for mdxGT and mdxRGT versus all other groups. Mitochondrial respiration rates from red quadriceps fibers were significantly improved in mdxGT animals, but the greatest bioenergetic benefit was observed in the mdxRGT group. Additional assessments revealed partial to full functional restoration in mdxGT and mdxRGT muscles relative to WT. These data demonstrate that voluntary wheel running combined with microdystrophin gene therapy in young mdx mice improved whole-body performance, affected muscle function differentially, mitigated energetic deficits, but also revealed some detrimental effects of exercise. With microdystrophin gene therapy currently in clinical trials, these data may help us understand the potential impact of exercise in treated patients.

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Section: Methodsmentioning

confidence: 99%

Voluntary wheel running complements microdystrophin gene therapy to improve muscle function in mdx mice

Hamm

Fathalikhani

Bukovec

et al. 2021

Molecular Therapy - Methods & Clinical Development

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“…Specifically, we recently reported on the importance of nebulin's Cterminal region in sarcomere stability [31]. In turn, recent attempts at therapies have focused primarily on improving contractility through pharmacological means [42][43][44][45][46]. Very few studies have attempted to restore nebulin expression due to its size, though one cell culture study in chick myocytes reported that introducing a shortened nebulin construct (termed 'mini-nebulin') into nebulin-deficient sarcomeres can be beneficial [72].…”

Section: Discussionmentioning

confidence: 99%

“…Due to nebulin's contributions to thin filament length regulation, force production, and structural maintenance [31][32][33][34][35][36][37][38][39][40][41], several studies have focused on improving these aspects of the sarcomere through therapeutic interventions. Studies targeting troponin activation have reported increases in force production at submaximal stimulation frequencies [42,43], but other attempts to improve muscle weight and function have shown that such therapeutic changes are difficult to achieve [44][45][46]. In this study, we sought to improve sarcomere structure and function by inserting a partial fragment of nebulin into the sarcomeres via an adeno-associated viral vector (AAV).…”

Section: Introductionmentioning

confidence: 99%

Expressing a Z-disk nebulin fragment in nebulin-deficient mouse muscle: effects on muscle structure and function

Kolb

Crudele

et al. 2020

Skeletal Muscle

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Background: Nebulin is a critical thin filament-binding protein that spans from the Z-disk of the skeletal muscle sarcomere to near the pointed end of the thin filament. Its massive size and actin-binding property allows it to provide the thin filaments with structural and regulatory support. When this protein is lost, nemaline myopathy occurs. Nemaline myopathy causes severe muscle weakness as well as structural defects on a sarcomeric level. There is no known cure for this disease. Methods: We studied whether sarcomeric structure and function can be improved by introducing nebulin's Z-disk region into a nebulin-deficient mouse model (Neb cKO) through adeno-associated viral (AAV) vector therapy. Following this treatment, the structural and functional characteristics of both vehicle-treated and AAV-treated Neb cKO and control muscles were studied.Results: Intramuscular injection of this AAV construct resulted in a successful expression of the Z-disk fragment within the target muscles. This expression was significantly higher in Neb cKO mice than control mice. Analysis of protein expression revealed that the nebulin fragment was localized exclusively to the Z-disks and that Neb cKO expressed the nebulin fragment at levels comparable to the level of full-length nebulin in control mice. Additionally, the Z-disk fragment displaced full-length nebulin in control mice, resulting in nemaline rod body formation and a worsening of muscle function. Neb cKO mice experienced a slight functional benefit from the AAV treatment, with a small increase in force and fatigue resistance. Disease progression was also slowed as indicated by improved muscle structure and myosin isoform expression. Conclusions: This study reveals that nebulin fragments are well-received by nebulin-deficient mouse muscles and that limited functional benefits are achievable.

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“…ActRIIB-mFc inhibits the function of myostatin and may thus help ameliorate the myofiber atrophy commonly observed in nemaline myopathy. However, treatment with ActRIIB-mFc from an age of 14 days did result in increased muscle weights in the wild-type mice but not in the Neb cKO mice (comparison of treated vs. untreated of each genotype) (Tinklenberg et al 2019). The study also did not find a significant effect on grip strength, open field, survival or skeletal muscle histology due to myostatin inhibitor treatment on Neb cKO mice (Tinklenberg et al 2019).…”

Section: Myostatin Inhibitor Actriib-mfcmentioning

confidence: 73%

“…However, treatment with ActRIIB-mFc from an age of 14 days did result in increased muscle weights in the wild-type mice but not in the Neb cKO mice (comparison of treated vs. untreated of each genotype) (Tinklenberg et al 2019). The study also did not find a significant effect on grip strength, open field, survival or skeletal muscle histology due to myostatin inhibitor treatment on Neb cKO mice (Tinklenberg et al 2019). The authors hypothesised that the lack of efficacy observed did not relate to myostatin signalling, since no evidence of abnormal hypertrophic signalling was found.…”

Section: Myostatin Inhibitor Actriib-mfcmentioning

confidence: 94%

Nebulin: big protein with big responsibilities

Yuen

Ottenheijm

2020

J Muscle Res Cell Motil

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Nebulin, encoded by NEB, is a giant skeletal muscle protein of about 6669 amino acids which forms an integral part of the sarcomeric thin filament. In recent years, the nebula around this protein has been largely lifted resulting in the discovery that nebulin is critical for a number of tasks in skeletal muscle. In this review, we firstly discussed nebulin's role as a structural component of the thin filament and the Z-disk, regulating the length and the mechanical properties of the thin filament as well as providing stability to myofibrils by interacting with structural proteins within the Z-disk. Secondly, we reviewed nebulin's involvement in the regulation of muscle contraction, cross-bridge cycling kinetics, Ca 2+-homeostasis and excitation contraction (EC) coupling. While its role in Ca 2+-homeostasis and EC coupling is still poorly understood, a large number of studies have helped to improve our knowledge on how nebulin affects skeletal muscle contractile mechanics. These studies suggest that nebulin affects the number of force generating actin-myosin cross-bridges and may also affect the force that each cross-bridge produces. It may exert this effect by interacting directly with actin and myosin and/or indirectly by potentially changing the localisation and function of the regulatory complex (troponin and tropomyosin). Besides unravelling the biology of nebulin, these studies are particularly helpful in understanding the patho-mechanism of myopathies caused by NEB mutations, providing knowledge which constitutes the critical first step towards the development of therapeutic interventions. Currently, effective treatments are not available, although a number of therapeutic strategies are being investigated.

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Myostatin Inhibition Using ActRIIB-mFc Does Not Produce Weight Gain or Strength in the Nebulin Conditional KO Mouse

Cited by 11 publications

References 38 publications

Voluntary wheel running complements microdystrophin gene therapy to improve muscle function in mdx mice

Voluntary wheel running complements microdystrophin gene therapy to improve muscle function in mdx mice

Expressing a Z-disk nebulin fragment in nebulin-deficient mouse muscle: effects on muscle structure and function

Nebulin: big protein with big responsibilities

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