Evaluating the effects of inhibitors of the sodium hydrogen exchangers on survival motor neuron expression in spinal muscular atrophy
Date
2018
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
University of Delaware
Abstract
Spinal muscular atrophy (SMA) is an inherited neuromuscular disease caused by the degeneration of alpha motor neurons in the anterior horn of the spinal cord which leads to generalized muscle weakness, hypotonia, and atrophy. SMA is caused by mutations or the loss of the survival motor neuron 1 (SMN1) which encodes the SMN protein. Unique to the human genome is a duplicate copy of the SMN1 gene known as the SMN2. The major difference between SMN1 and SMN2 is a cytosine to thymine (C-to-T) nucleotide transition located in exon 7. This single C-to-T transition is positioned in the middle of an exonic splicing enhancer sequence (ESE) which is responsible for regulating the inclusion of exon 7 in the SMN transcripts. In SMN1, there is a cytosine located in this region allowing for the inclusion exon 7 producing mRNA that encodes full length SMN (FL-SMN) protein. Because SMN2 has a thymine in this position instead of a cytosine, the majority of the SMN2 mRNA transcripts (80-90%) lack exon 7 (SMN∆7) forming a truncated product. Due to the majority of SMN2 mRNA transcripts lacking exon 7, the SMN2 gene is unable to produce enough FL-SMN protein to compensate for the loss of SMN1 leading to the development of SMA. Numerous studies have concluded that a higher copy number of the SMN2 gene correlates with a milder phenotype of the disease. A current target for modifying the severity of the SMA is developing therapeutics that enhance SMN2 gene transcription and /or promote exon 7 inclusion. Inhibitors of the sodium hydrogen exchanger (NHE) like 5(N-ethyl-N-isopropyl)-amiloride (EIPA) have previously been studied for their ability to modulate exon 7 inclusion and SMN2 protein expression. In this study several NHE inhibitors were evaluated for their capability in modulating SMN2 expression. As reported in the previous study, EIPA was identified as a modulator of exon 7 inclusion as well as another compound known as 5(N, N-hexamethylene)-amiloride (HMA). EIPA and HMA may modulate the inclusion of exon 7 due to their ability to specifically inhibit the NHE5 isoform which is the isoform found in neural and skeletal muscle tissues. ☐ To improve current tools used to screen small molecular compounds that increase full length SMN2 mRNAs through the activation of the SMN2 promoter or by inducing the inclusion of exon 7 in SMN2 pre-mRNAs two novel reporter cell lines were also developed. The two cell lines developed will more closely mimic SMN2 gene regulation in vivo than the reporter assays currently used since it will be able to account for distal elements that may play a role in the regulation of SMN2. Development of these novel reporter cell lines will allow for a more accurate evaluation of previously discovered SMN2 regulators like the NHE inhibitors as well as allowing for the development of new therapeutics for SMA patient.
Description
Keywords
Biological sciences, Spinal muscular atrophy, Sodium hydrogen exchanger, Survival motor neuron 1