Exons 45-55 Skipping Using Antisense Oligonucleotides in Immortalized Human DMD Muscle Cells

Antisense oligonucleotides (AOs) have demonstrated high potential as a therapy for treating genetic diseases like Duchene muscular dystrophy (DMD). As a synthetic nucleic acid, AOs can bind to a targeted messenger RNA (mRNA) and regulate splicing. AO-mediated exon skipping transforms out-of-frame mutations as seen in DMD into in-frame transcripts. This exon skipping approach results in the production of a shortened but still functional protein product as seen in the milder counterpart, Becker muscular dystrophy (BMD). Many potential AO drugs have advanced from laboratory experimentation to clinical trials with an increasing interest in this area. An accurate and efficient method for testing AO drug candidates in vitro, before implementation in clinical trials, is crucial to ensure proper assessment of efficacy. The type of cell model used to examine AO drugs in vitro establishes the foundation of the screening process and can significantly impact the results. Previous cell models used to screen for potential AO drug candidates, such as primary muscle cell lines, have limited proliferative and differentiation capacity, and express insufficient amounts of dystrophin. Recently developed immortalized DMD muscle cell lines effectively addressed this challenge allowing for the accurate measurement of exon-skipping efficacy and dystrophin protein production. This chapter presents a procedure used to assess DMD exons 45-55 skipping efficiency and dystrophin protein production in immortalized DMD patient-derived muscle cells. Exons 45-55 skipping in the DMD gene is potentially applicable to 47% of patients. In addition, naturally occurring exons 45-55 in-frame deletion mutation is associated with an asymptomatic or remarkably mild phenotype as compared to shorter in-frame deletions within this region. As such, exons 45-55 skipping is a promising therapeutic approach to treat a wider group of DMD patients. The method presented here allows for improved examination of potential AO drugs before implementation in clinical trials for DMD.

ANT1 overexpression models: Some similarities with facioscapulohumeral muscular dystrophy

Facioscapulohumeral muscular dystrophy (FSHD) is an autosomal dominant disorder characterized by progressive muscle weakness. Adenine nucleotide translocator 1 (ANT1), the only 4q35 gene involved in mitochondrial function, is strongly expressed in FSHD skeletal muscle biopsies. However, its role in FSHD is unclear. In this study, we evaluated ANT1 overexpression effects in primary myoblasts from healthy controls and during Xenopus laevis organogenesis. We also compared ANT1 overexpression effects with the phenotype of FSHD muscle cells and biopsies. Here, we report that the ANT1 overexpression-induced phenotype presents some similarities with FSHD muscle cells and biopsies. ANT1-overexpressing muscle cells showed disorganized morphology, altered cytoskeletal arrangement, enhanced mitochondrial respiration/glycolysis, ROS production, oxidative stress, mitochondrial fragmentation and ultrastructure alteration, as observed in FSHD muscle cells. ANT1 overexpression in Xenopus laevis embryos affected skeletal muscle development, impaired skeletal muscle, altered mitochondrial ultrastructure and led to oxidative stress as observed in FSHD muscle biopsies. Moreover, ANT1 overexpression in X. laevis embryos affected heart structure and mitochondrial ultrastructure leading to cardiac arrhythmia, as described in some patients with FSHD. Overall our data suggest that ANT1 could contribute to mitochondria dysfunction and oxidative stress in FSHD muscle cells by modifying their bioenergetic profile associated with ROS production. Such interplay between energy metabolism and ROS production in FSHD will be of significant interest for future prospects.

Exposure to radial extracorporeal shock waves modulates viability and gene expression of human skeletal muscle cells: a controlled in vitro study

BACKGROUND

Recent clinical and animal studies have shown that extracorporeal shock wave therapy has a promoting influence on the healing process of musculoskeletal disorders. However, the underlying biological effects of extracorporeal shock wave therapy on human skeletal muscle cells have not yet been investigated.

METHODS

In this study, we investigated human skeletal muscle cells after exposure to radial extracorporeal shock waves in a standardized in vitro setup. Cells were isolated from muscle specimens taken from adult patients undergoing spine surgery. Primary muscle cells were exposed once or twice to radial extracorporeal shock waves in vitro with different energy flux densities. Cell viability and gene expression of the paired box protein 7 (Pax7), neural cell adhesion molecule (NCAM), and myogenic factor 5 (Myf5) and MyoD as muscle cell markers were compared to non-treated muscle cells that served as controls.

RESULTS

Isolated muscle cells were positive for the hallmark protein of satellite cells, Pax7, as well as for the muscle cell markers NCAM, MyoD, and Myf5. Exposure to radial extracorporeal shock waves at low energy flux densities enhanced cell viability, whereas higher energy flux densities had no further significant impact. Gene expression analyses of muscle specific genes (Pax7, NCAM, Myf5, and MyoD) demonstrated a significant increase after single exposure to the highest EFD (4 bar, 0.19 mJ/mm²) and after double exposure with the medium EFDs (2 and 3 bar; 0.09 and 0.14 mJ/mm², respectively). Double exposure of the highest EFD, however, results in a significant down-regulation when compared to single exposure with this EFD.

CONCLUSIONS

This is the first study demonstrating that radial extracorporal shock wave therapy has the potential to modulate the biological function of human skeletal muscle cells. Based on our experimental findings, we hypothesize that radial extracorporal shock wave therapy could be a promising therapeutic modality to improve the healing process of sports-related structural muscle injuries.

Quantitative Evaluation of Exon Skipping in Immortalized Muscle Cells In Vitro

Exon skipping through the use of antisense oligonucleotides (AOs) is currently one of the most promising approaches for treating Duchenne muscular dystrophy (DMD). While we now have a number of AO drug candidates in clinical trials, we are still faced with issues of poor or controversial efficacy in some of these drugs. This is the case with eteplirsen, an exon 51-skipping AO that is the first and only FDA-approved drug for DMD to date. Effective procedures must, therefore, be set up for the in vitro screening of potential AOs for DMD treatment. Here, we describe one such procedure using immortalized DMD patient-derived muscle cells. Aside from allowing for the quantitative evaluation of candidate AOs based on their exon skipping efficiency and dystrophin protein rescue levels, these immortalized cells are stable, pure, easy to grow, and not subject to confounding by senescence-related issues. This procedure enables a more reliable screening of AOs prior to their entry in clinical trials and greatly facilitates the search for more efficacious candidate exon skipping AOs for DMD treatment.

High concentrations of genistein exhibit pro-oxidant effects in primary muscle cells through mechanisms involving 5-lipoxygenase-mediated production of reactive oxygen species

Genistein, a typical soy isoflavone, is an important antioxidant for improving human health and animal production but the compound possesses some pro-oxidant potential. In order to explore the latter, the dose-response relationship of various concentrations of genistein on both cellular proliferation and the redox system were examined. The proliferation of primary muscle cells was promoted by a low concentration of genistein but was inhibited by high concentrations, which also enhanced lipid oxidation and suppressed membrane fluidity. By selecting a high concentration (200 μM) as a pro-oxidant treatment, the mechanism underlying the pro-oxidant function of genistein was then explored. The generation of intracellular reactive oxygen species (ROS) was stimulated by 200 μM genistein, with inhibited expression of NADPH oxidase 4 and cyclooxygenase 1 and 2 as well as increased activity of the glutathione redox system. The cellular expression of 5-lipoxygenase, however, was up-regulated by 200 μM genistein and the addition of 5-lipoxygenase inhibitor (Zileuton) decreased genistein-induced intracellular ROS level, close to that from the addition of the ROS scavenger, N-acetylcysteine. It is concluded that higher concentrations of genistein exert pro-oxidant potential in the primary muscle cells through enhancing ROS production in a 5-lipoxygenase-dependent manner.