Spinal Muscular Atrophy Patient iPSC-Derived Motor Neurons Have Reduced Expression of Proteins Important in Neuronal Development

Abstract

Spinal muscular atrophy (SMA) is an inherited neuromuscular disease primarily characterized by degeneration of spinal motor neurons, and caused by reduced levels of the SMN protein. Previous studies to understand the proteomic consequences of reduced SMN have mostly utilized patient fibroblasts and animal models. We have derived human motor neurons from type I SMA and healthy controls by creating their induced pluripotent stem cells (iPSCs). Quantitative mass spectrometry of these cells revealed increased expression of 63 proteins in control motor neurons compared to respective fibroblasts, whereas 30 proteins were increased in SMA motor neurons vs. their fibroblasts. Notably, UBA1 was significantly decreased in SMA motor neurons, supporting evidence for ubiquitin pathway defects. Subcellular distribution of UBA1 was predominantly cytoplasmic in SMA motor neurons in contrast to nuclear in control motor neurons; suggestive of neurodevelopmental abnormalities. Many of the proteins that were decreased in SMA motor neurons, including beta III-tubulin and UCHL1, were associated with neurodevelopment and differentiation. These neuron-specific consequences of SMN depletion were not evident in fibroblasts, highlighting the importance of iPSC technology. The proteomic profiles identified here provide a useful resource to explore the molecular consequences of reduced SMN in motor neurons, and for the identification of novel biomarker and therapeutic targets for SMA.

Life and death in the trash heap: The ubiquitin proteasome pathway and UCHL1 in brain aging, neurodegenerative disease and cerebral Ischemia

“…These and other observations have led to the hypothesis that UCHL1 may be important in the pathogenesis of ALS. In addition, UCHL1 expression was significantly decreased in motor neurons derived from patients of spinal muscular atrophy (SMA), an inherited neuromuscular disease primarily characterized by degeneration of spinal motor neurons (Fuller et al, 2015). Corticospinal motor neurons are susceptible to ER stress and display early, selective, progressive, and profound degeneration in the absence of normally functioning UCHL1 (Genc et al, 2016; Jara et al, 2015).…”

Structural variations causing inherited peripheral neuropathies: A paradigm for understanding genomic organization, chromatin interactions, and gene dysregulation

“…To address examining gene expression in neural tissue, motor neurons derived from patient‐induced pluripotent stem cells (iPSCs) are now being used. Several studies have used iPSC‐derived motor neurons (iPSC‐MNs) to model neuromuscular diseases including ALS (Chen et al., ; Ichiyanagi et al., ; S. Lee & Huang, ), SMA (Fuller et al., ; Nizzardo et al., ) and various IPNs (G. Lee et al., ; Saporta et al., ). iPSCs‐MNs have the potential to model neural specific phenotypic changes, gene expression, and chromatin interactions in disease relevant tissue.…”

“…Several studies have used iPSC-derived motor neurons (iPSC-MNs) to model neuromuscular diseases including ALS (Chen et al, 2014;Ichiyanagi et al, 2016;S. Lee & Huang, 2017), SMA (Fuller et al, 2015;Nizzardo et al, 2015) and various IPNs (G. Lee et al, 2009;Saporta et al, 2015). iPSCs-MNs have the potential to model neural specific phenotypic changes, gene expression, and chromatin interactions in disease relevant tissue.…”

A Comparison of mRNA Sequencing with Random Primed and 3’-Directed Libraries

“…We attempted to answer this question by taking a similar experimental design approach with a different set of RNA, this time from induced pluripotent stem cell (iPSC) lines created from control individuals or those that had a mutation for and clinical presentation of spinal muscular atrophy (SMA), where slightly different random primed library preparation and sequencing approaches were employed (see Methods). SMA is a childhood early onset motor neuron disease (Sareen et al 2012;Fuller et al 2015) where symptoms can be observed as early as 3 months or up to 2-3 years of age. The disease is typically caused by mutations in the SMN1 (Survival Motor Neuron 1) gene, however disease severity varies based on numbers of copies of the related SMN2 gene.…”

“…The disease is typically caused by mutations in the SMN1 (Survival Motor Neuron 1) gene, however disease severity varies based on numbers of copies of the related SMN2 gene. As SMN genes control critical RNA biogenesis processes during early development (Fuller et al 2015), we anticipate differential gene expression changes even at the iPSC stage without subsequent differentiation. For these analyses, two SMA subject clonal lines and three control lines, with varying numbers of growth replicates, were compared.…”