Nerve sprouting capacity in a pharmacologically induced mouse model of spinal muscular atrophy

Drug Screening and Drug Repositioning as Promising Therapeutic Approaches for Spinal Muscular Atrophy Treatment

Spinal muscular atrophy (SMA) is the most common genetic disease affecting infants and young adults. Due to mutation/deletion of the survival motor neuron (SMN) gene, SMA is characterized by the SMN protein lack, resulting in motor neuron impairment, skeletal muscle atrophy and premature death. Even if the genetic causes of SMA are well known, many aspects of its pathogenesis remain unclear and only three drugs have been recently approved by the Food and Drug Administration (Nusinersen-Spinraza; Onasemnogene abeparvovec or AVXS-101-Zolgensma; Risdiplam-Evrysdi): although assuring remarkable results, the therapies show some important limits including high costs, still unknown long-term effects, side effects and disregarding of SMN-independent targets. Therefore, the research of new therapeutic strategies is still a hot topic in the SMA field and many efforts are spent in drug discovery. In this review, we describe two promising strategies to select effective molecules: drug screening (DS) and drug repositioning (DR). By using compounds libraries of chemical/natural compounds and/or Food and Drug Administration-approved substances, DS aims at identifying new potentially effective compounds, whereas DR at testing drugs originally designed for the treatment of other pathologies. The drastic reduction in risks, costs and time expenditure assured by these strategies make them particularly interesting, especially for those diseases for which the canonical drug discovery process would be long and expensive. Interestingly, among the identified molecules by DS/DR in the context of SMA, besides the modulators of SMN2 transcription, we highlighted a convergence of some targeted molecular cascades contributing to SMA pathology, including cell death related-pathways, mitochondria and cytoskeleton dynamics, neurotransmitter and hormone modulation.

AAV9-DOK7 gene therapy reduces disease severity in Smn2B/- SMA model mice

Spinal Muscular Atrophy (SMA) is an autosomal recessive neuromuscular disease caused by deletions or mutations in the survival motor neuron (SMN1) gene. An important hallmark of disease progression is the pathology of neuromuscular junctions (NMJs). Affected NMJs in the SMA context exhibit delayed maturation, impaired synaptic transmission, and loss of contact between motor neurons and skeletal muscle. Protection and maintenance of NMJs remains a focal point of therapeutic strategies to treat SMA, and the recent implication of the NMJ-organizer Agrin in SMA pathology suggests additional NMJ organizing molecules may contribute. DOK7 is an NMJ organizer that functions downstream of Agrin. The potential of DOK7 as a putative therapeutic target was demonstrated by adeno-associated virus (AAV)-mediated gene therapy delivery of DOK7 in Amyotrophic Lateral Sclerosis (ALS) and Emery Dreyefuss Muscular Dystrophy (EDMD). To assess the potential of DOK7 as a disease modifier of SMA, we administered AAV-DOK7 to an intermediate mouse model of SMA. AAV9-DOK7 treatment conferred improvements in NMJ architecture and reduced muscle fiber atrophy. Additionally, these improvements resulted in a subtle reduction in phenotypic severity, evidenced by improved grip strength and an extension in survival. These findings reveal DOK7 is a novel modifier of SMA.