Brief Report: Phenotypic Rescue of Induced Pluripotent Stem Cell-Derived Motoneurons of a Spinal Muscular Atrophy Patient

Abstract

Spinal muscular atrophy (SMA) is one of the most common autosomal recessive disorders in humans and is a common genetic cause of infant mortality. The disease is caused by loss of the survival of motoneuron (SMN) protein, resulting in the degeneration of alpha motoneurons in spinal cord and muscular atrophy in the limbs and trunk. One function of SMN involves RNA splicing. It is unclear why a deficiency in a housekeeping function such as RNA splicing causes profound effects only on motoneurons but not on other cell types. One difficulty in studying SMA is the scarcity of patient's samples. The discovery that somatic cells can be reprogrammed to become induced pluripotent stem cell (iPSCs) raises the intriguing possibility of modeling human diseases in vitro. We reported the establishment of five iPSC lines from the fibroblasts of a type 1 SMA patient. Neuronal cultures derived from these SMA iPSC lines exhibited a reduced capacity to form motoneurons and an abnormality in neurite outgrowth. Ectopic SMN expression in these iPSC lines restored normal motoneuron differentiation and rescued the phenotype of delayed neurite outgrowth. These results suggest that the observed abnormalities are indeed caused by SMN deficiency and not by iPSC clonal variability. Further characterization of the cellular and functional deficits in motoneurons derived from these iPSCs may accelerate the exploration of the underlying mechanisms of SMA pathogenesis.

How to make spinal motor neurons

“…For example, human MNs have been shown to exhibit selective sensitivity to glia cells expressing a mutant gene linked to ALS (Di Giorgio et al, 2008;Marchetto et al, 2008). Additionally, multiple groups have reported disease-specific phenotypes in differentiated iPSC-derived MNs from patients with SMA (Ebert et al, 2009;Chang et al, 2011;Corti et al, 2012;Wang et al, 2013) or ALS (Bilican et al, 2012;Egawa et al, 2012;Donnelly et al, 2013;Sareen et al, 2013). Building on this, the in vitro generation of MNs via direct conversion of fibroblasts may additionally accelerate disease-modeling studies with patient cells, as it does not require the time-consuming step of iPSC generation and characterization.…”

Induced pluripotent stem cells for modeling neurological disorders

“…SMA is an autosomal recessive neurodegenerative disease caused by mutations in survival of motor neuron gene (SMN-1), characterized by a selective and progressive loss of lower motor neurons resulting in degeneration of motor neurons in the spinal cord and muscular atrophy on limbs and trunk [50][51][52] . In order to uncover what is really happening from an inside perspective of the patient's body, iPSC technology can be used to elucidate this disease mechanism [53] .…”

“…Valproic acid and anti-sense oligo treatment help improve defects in AChR clustering, increasing levels of SMN transcripts [55] . The neuronal differentiation of SMA iPSCs show reduced capacity to produce motor neurons [51] , therefore, applying gene correcting technology may aid in overcoming these methodological shortcomings. The correction of SMN gene, using single-stranded oligonucleotide, was shown to restore the SMN gene profile in neurons derived from SMA-iPSC, converting SMN2 in SMN1 [56] .…”

Fibroblast sources: Where can we get them?

“…In addition, fibroblasts derived from skin are frequently used to produce induced pluripotent stem cells, or iPSCs (Takahashi et al 2007), a powerful tool that allows production of other kinds of desired cells, which is now being widely used for disease modeling in vitro (Freitas et al 2012;Ring et al 2012;Chang et al 2011;Marchetto et al 2010;Dimos et al, 2008;Park et al 2008). The use of iPSC technique for disease modeling is particularly important because it makes possible to generate the cell target of the disease by still keeping the genetic background from the patient, which is extremely important-no matter if the disease is monogenetic, with an identified mutation or if the genetic cause remains unknown.…”