Restoration of SMN expression in mesenchymal stem cells derived from gene-targeted patient-specific iPSCs

Enhanced expression of the human Survival motor neuron 1 gene from a codon-optimised cDNA transgene in vitro and in vivo

Spinal muscular atrophy (SMA) is a neuromuscular disease particularly characterised by degeneration of ventral motor neurons. Survival motor neuron (SMN) 1 gene mutations cause SMA, and gene addition strategies to replace the faulty SMN1 copy are a therapeutic option. We have developed a novel, codon-optimised hSMN1 transgene and produced integration-proficient and integration-deficient lentiviral vectors with cytomegalovirus (CMV), human synapsin (hSYN) or human phosphoglycerate kinase (hPGK) promoters to determine the optimal expression cassette configuration. Integrating, CMV-driven and codon-optimised hSMN1 lentiviral vectors resulted in the highest production of functional SMN protein in vitro. Integration-deficient lentiviral vectors also led to significant expression of the optimised transgene and are expected to be safer than integrating vectors. Lentiviral delivery in culture led to activation of the DNA damage response, in particular elevating levels of phosphorylated ataxia telangiectasia mutated (pATM) and γH2AX, but the optimised hSMN1 transgene showed some protective effects. Neonatal delivery of adeno-associated viral vector (AAV9) vector encoding the optimised transgene to the Smn2B/- mouse model of SMA resulted in a significant increase of SMN protein levels in liver and spinal cord. This work shows the potential of a novel codon-optimised hSMN1 transgene as a therapeutic strategy for SMA.

Targeted addition of mini-dystrophin into rDNA locus of Duchenne muscular dystrophy patient-derived iPSCs

Duchenne muscular dystrophy (DMD), the most common lethal muscular disorder, affects 1 in 5000 male births. It is caused by mutations in the X-linked dystrophin gene (DMD), and there is no effective treatment currently. Gene addition is a promising strategy owing to its universality for patients with all gene mutations types. In this study, we describe a site-specific gene addition strategy in induced pluripotent stem cells (iPSCs) derived from a DMD patient with exon 50 deletion. By using transcription activator-like effector nickases (TALENickases), the mini-dystrophin cassette was precisely targeted at the ribosomal RNA gene (rDNA) locus via homologous recombination with high targeting efficiency. The targeted clone retained the main pluripotent properties and was differentiated into cardiomyocytes. Significantly, the dystrophin expression and membrane localization were restored in the genetic corrected iPSCs and their derived cardiomyocytes. More importantly, the enhanced spontaneous contraction was observed in modified cardiomyocytes. These results provide a proof of principle for an efficient targeted gene addition for DMD gene therapy and represents a significant step toward precisely therapeutic for DMD.

Cell-Based Therapy for Spinal Muscular Atrophy

Spinal muscular atrophy (SMA) is a devastating neurodegenerative disease characterized by the degeneration of lower motor neurons in the spinal cord, leading to progressive paralysis and early death in the severe cases. SMA is primarily caused by the mutations in the gene of SMN (survival motor neuron). More research has focused on the development of SMN-targeted replacement therapy for SMA. The first US Food and Drug Administration (FDA)-approved modified antisense oligonucleotide (nusinersen) to treat SMA is to reverse intronic splicing silencer of SMN to produce fully functional SMN2. Recently, stem cell transplantation has shown the potential to repair the injured tissue and differentiate into neurons to rescue the phenotypes of SMA in animal models. In this chapter, we first review the clinical, genetic, and pathogenic mechanisms of SMA. Then, we discuss current pharmacological treatments and point out the therapeutic efficacy of stem cell transplantation and future directions and priorities for SMA.

Spinal Muscular Atrophy Modeling and Treatment Advances by Induced Pluripotent Stem Cells Studies

Spinal Muscular Atrophy (SMA) is a neurodegenerative disease characterized by specific and predominantly lower motor neuron (MN) loss. SMA is the main reason for infant death, while about one in 40 children born is a healthy carrier. SMA is caused by decreased levels of production of a ubiquitously expressed gene: the survival motor neuron (SMN). All SMA patients present mutations of the telomeric SMN1 gene, but many copies of a centromeric, partially functional paralog gene, SMN2, can somewhat compensate for the SMN1 deficiency, scaling inversely with phenotypic harshness. Because the study of neural tissue in and from patients presents too many challenges and is very often not feasible; the use of animal models, such as the mouse, had a pivotal impact in our understanding of SMA pathology but could not portray totally satisfactorily the elaborate regulatory mechanisms that are present in higher animals, particularly in humans. And while recent therapeutic achievements have been substantial, especially for very young infants, some issues should be considered for the treatment of older patients. An alternative way to study SMA, and other neurological pathologies, is the use of induced pluripotent stem cells (iPSCs) derived from patients. In this work, we will present a wide analysis of the uses of iPSCs in SMA pathology, starting from basic science to their possible roles as therapeutic tools.