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The role of human spliceosomal component SRm300 in neurodegenerative disease, response to serotonin treatment. Horvath, Gabriela Ana


Background Genetic research in neurodegenerative disorders identified candidate genes in many familial cases, providing insight into the pathogenesis. Many of them share common pathologic mechanisms which may result from alterations in gene expression. Single gene disorders can be great models for complex neurodegenerative pathophysiology, however, questions remain, and progress in their treatment is still a challenge. This research project started in the clinic, with a family with an apparently genetic neurodegenerative disorder, including hemiplegic migraines and systemic serotonin deficiency. Serotonin has roles in physiological and behavioural functions, neurodevelopment, as well as neuropsychiatric, gastrointestinal and cardiovascular disorders and migraines. Serotonin metabolism includes synthesis, transport and degradation. Methods Building hypothesis: started with translational research, taking basic science into practical applications. To answer the question of the systemic serotonin deficiency, genes of serotonin synthesis, transport and developmental pathway were sequenced, and platelet serotonin uptake studies were performed. Furthermore, SERT protein, actin and other cytoskeleton proteins were quantified with Western blots and proteomic analysis, in different platelet fractions. Generating hypothesis: continued with Whole Exome Sequencing. For validation, transcriptome analysis was performed. Along with investigations, treatment with serotonin replacement, 5-hydroxytryptophan was started in the patients. Results Sequencing was negative for genes associated with serotonin production, transport, and development. Serotonin uptake was deficient in patient platelets. Western blots showed diminished cytoskeleton proteins in Triton-soluble platelet fractions. WES analysis yielded a candidate gene, SRRM2, a splicing coactivator protein with potentially damaging missense mutation. Transcriptome analysis revealed several differentially expressed genes. Treatment with serotonin replacement significantly improved the lower limb strength. Conclusions Cytoskeleton proteins were aggregated trapping membrane proteins inside the cell, explaining the biochemical phenotype. The transcriptome analysis demonstrated significant changes in transcription levels in multiple ontology pathways. Some of these genes are known to cause neurodegenerative diseases. The changes in the transcription levels suggest that a defect at the core of the spliceosome complex is a reasonable hypothesis explaining the basis of this family’s neurodegeneration. The success with serotonin treatment is also new and deserves further research.

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