131. Targeted Genome Editing in Spinal Muscular Atrophy

Spinal muscular atrophy (SMA) is an autosomal recessive neuromuscular disorder caused by mutations in the survival-motor-neuron 1 (SMN1) telomeric gene. Deficiencies in the ubiquitous SMN function affect multiple tissues and organs; however neuronal tissue is primarily sensitive, resulting in α-motor neuron degeneration in the ventral horn of the spinal cord with subsequent neuromuscular-junction dysfunction and proximal muscle weakness. The onset of disease and degree of severity are variable in patients and they are determined in part by multiple copies of the centromeric homologue SMN2 that inversely correlate with the phenotypic severity. Indeed, SMN2 gene mainly produces a truncated form SMNΔ7 by aberrant alternative splicing and a small amount (~10%) of the fully active full-length SMN, thus buffering the SMN deficiency. A potential strategy for treating SMA patients is to increase SMN levels in the affected tissues, hence gene therapy and modifiers of SMN2-alternative splicing have proved therapeutic efficacy in SMA animal models.In this study, we explored the possibility of applying targeted genome editing technology to the human SMN locus in order to revert the SMN2 sequence to a SMN1-like sequence that may undergo proper splicing under the the endogenous transcriptional control. The resulting correction would be permanent and lead to longlasting protein production in gene-edited cells. We used the streptococcus pyogenes Cas9-CRISPR system to target the SMN2 gene at different locations. Two main strategies were explored: i) SMN1_exon7 addition/correction by promoting homology-driven DNA repair, ii) SMN2_intron7_ intronic-splicing-silencer (ISS-N1)mutation and correction of SMN2 aberrant splicing, by exploiting the non-homologous end-joining (NHEJ) pathway. Plasmids encoding Cas9-GFP under the control of CMV promoter, and selected gRNAs downstream to the Pol-III U6 promoter (Addgene) were transfected in HEK-293T cell line and in immortalized myoblasts derived from either healthy donors or SMA patients. Transfection efficiency was estimated as percentage of GFP-expressing cells (20-50% and 1-10%, respectively) and nuclease activity detected by Surveyor assay and target site sequencing. In particular, in SMA patient-derived myoblasts we detected mutations (indels) at the level of the induced DNA double-strand break at ~30% frequency. Levels of SMN restoration will be investigated by qPCR of the different species of SMN transcripts and by western blotting of SMN protein. The goal of this study is to provide an in vitro proof of principle of effective gene correction in SMA patient-derived cells. In the context of a multisystemic, complicated disease such as SMA, targeted genome editing strategy could represent an additional therapeutic tool

Constitutive expression of Yes-associated protein (Yap) in adult skeletal muscle fibres induces muscle atrophy and myopathy

Peer reviewedPublisher PD

Changes in communication between muscle stem cells and their environment with aging

Aging is associated with both muscle weakness and a loss of muscle mass, contributing towards overall frailty in the elderly. Aging skeletal muscle is also characterised by a decreasing efficiency in repair and regeneration, together with a decline in the number of adult stem cells. Commensurate with this are general changes in whole body endocrine signalling, in local muscle secretory environment, as well as in intrinsic properties of the stem cells themselves. The present review discusses the various mechanisms that may be implicated in these age-associated changes, focusing on aspects of cell-cell communication and long-distance signalling factors, such as levels of circulating growth hormone, IL-6, IGF1, sex hormones, and inflammatory cytokines. Changes in the local environment are also discussed, implicating IL-6, IL-4, FGF-2, as well as other myokines, and processes that lead to thickening of the extra-cellular matrix. These factors, involved primarily in communication, can also modulate the intrinsic properties of muscle stem cells, including reduced DNA accessibility and repression of specific genes by methylation. Finally we discuss the decrease in the stem cell pool, particularly the failure of elderly myoblasts to re-quiesce after activation, and the consequences of all these changes on general muscle homeostasis

CRISPR/Cas9-induced (CTG⋅CAG)n repeat instability in the myotonic dystrophy type 1 locus: implications for therapeutic genome editing

Myotonic dystrophy type 1 (DM1) is caused by (CTG⋅CAG)n-repeat expansion within the DMPK gene and thought to be mediated by a toxic RNA gain of function. Current attempts to develop therapy for this disease mainly aim at destroying or blocking abnormal properties of mutant DMPK (CUG)n RNA. Here, we explored a DNA-directed strategy and demonstrate that single clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9-cleavage in either its 5′ or 3′ unique flank promotes uncontrollable deletion of large segments from the expanded trinucleotide repeat, rather than formation of short indels usually seen after double-strand break repair. Complete and precise excision of the repeat tract from normal and large expanded DMPK alleles in myoblasts from unaffected individuals, DM1 patients, and a DM1 mouse model could be achieved at high frequency by dual CRISPR/Cas9-cleavage at either side of the (CTG⋅CAG)n sequence. Importantly, removal of the repeat appeared to have no detrimental effects on the expression of genes in the DM1 locus. Moreover, myogenic capacity, nucleocytoplasmic distribution, and abnormal RNP-binding behavior of transcripts from the edited DMPK gene were normalized. Dual sgRNA-guided excision of the (CTG⋅CAG)n tract by CRISPR/Cas9 technology is applicable for developing isogenic cell lines for research and may provide new therapeutic opportunities for patients with DM1

Drug Repurposing for Duchenne Muscular Dystrophy: The Monoamine Oxidase B Inhibitor Safinamide Ameliorates the Pathological Phenotype in mdx Mice and in Myogenic Cultures From DMD Patients

Oxidative stress and mitochondrial dysfunction play a crucial role in the pathophysiology of muscular dystrophies. We previously reported that the mitochondrial enzyme monoamine oxidase (MAO) is a relevant source of reactive oxygen species (ROS) not only in murine models of muscular dystrophy, in which it directly contributes to contractile impairment, but also in muscle cells from Collagen VI-deficient patients. Here we now assessed the efficacy of a novel MAO-B inhibitor, safinamide, using in vivo and in vitro models of Duchenne muscular dystrophy (DMD). Specifically, we found that administration of safinamide in 3-month old mdx mice reduced myofiber damage and oxidative stress, and improved muscle functionality. In vitro studies with myogenic cultures from mdx mice and DMD patients showed that even cultured dystrophic myoblasts were more susceptible to oxidative stress than matching cells from healthy donors. Indeed, upon exposure to the MAO substrate tyramine or to hydrogen peroxide, DMD muscle cells displayed a rise in ROS levels and a consequent mitochondrial depolarization. Remarkably, both phenotypes normalized when cultures were treated with safinamide. Given that safinamide is already in clinical use for neurological disorders, our findings could pave the way towards a promising translation into clinical trials for DMD patients as a classic case of drug repurposing

Multi-Tasking Role of the Mechanosensing Protein Ankrd2 in the Signaling Network of Striated Muscle

Background Ankrd2 (also known as Arpp) together with Ankrd1/CARP and DARP are members of the MARP mechanosensing proteins that form a complex with titin (N2A)/calpain 3 protease/myopalladin. In muscle, Ankrd2 is located in the I-band of the sarcomere and moves to the nucleus of adjacent myofibers on muscle injury. In myoblasts it is predominantly in the nucleus and on differentiation shifts from the nucleus to the cytoplasm. In agreement with its role as a sensor it interacts both with sarcomeric proteins and transcription factors. Methodology/Principal Findings Expression profiling of endogenous Ankrd2 silenced in human myotubes was undertaken to elucidate its role as an intermediary in cell signaling pathways. Silencing Ankrd2 expression altered the expression of genes involved in both intercellular communication (cytokine-cytokine receptor interaction, endocytosis, focal adhesion, tight junction, gap junction and regulation of the actin cytoskeleton) and intracellular communication (calcium, insulin, MAPK, p53, TGF-\u3b2 and Wnt signaling). The significance of Ankrd2 in cell signaling was strengthened by the fact that we were able to show for the first time that Nkx2.5 and p53 are upstream effectors of the Ankrd2 gene and that Ankrd1/CARP, another MARP member, can modulate the transcriptional ability of MyoD on the Ankrd2 promoter. Another novel finding was the interaction between Ankrd2 and proteins with PDZ and SH3 domains, further supporting its role in signaling. It is noteworthy that we demonstrated that transcription factors PAX6, LHX2, NFIL3 and MECP2, were able to bind both the Ankrd2 protein and its promoter indicating the presence of a regulatory feedback loop mechanism. Conclusions/Significance In conclusion we demonstrate that Ankrd2 is a potent regulator in muscle cells affecting a multitude of pathways and processes