Elucidating the consequence and cause of microRNA dysregulation in amyotrophic lateral sclerosis (ALS)

Amyotrophic Lateral Sclerosis (ALS) is a progressive motor neurodegenerative disorder with an average life expectancy of 2-5 years post-diagnosis. Common pathological features associated with ALS are the formation of cytoplasmic inclusions of intermediate filaments and RNA-binding proteins within motor neurons. The formation of intermediate filament cytoplasmic inclusions is believed to be driven by a loss of stochiometric expression between five neuronal intermediate filament proteins—NFL, NFM, NFH, INA and PRPH—where there is a selective suppression of the steady-state levels of NEFL, INA and PRPH mRNA. Further, three RNA-binding proteins—TDP-43, FUS and RGNEF—have been shown to co-aggregate with each other in ALS motor neurons indicating a possible common mechanism that leads to their dysregulation. In the last decade, microRNAs (miRNAs)—small RNA molecules generally responsible for post-transcriptional regulation of gene expression—were observed to be massively dysregulated in the spinal cord tissue of ALS patients, providing a possible explanation for the changes observed in intermediate filament steady-state mRNA levels and RNA-binding protein dysregulation in ALS. Further, TDP-43 and FUS regulate miRNA biogenesis, indicating there may be a regulatory network between RNA-binding proteins and miRNAs that is disrupted in ALS. I hypothesize that a regulatory network between specific RNA-binding proteins and miRNAs is disrupted in ALS leading to changes in miRNA processing which contributes to intermediate filament and RNA-binding protein pathology. In this dissertation, I have examined: 1) whether ALS-linked miRNA(s) contribute to the selective suppression of NEFL, PRPH, and INA; 2) whether ALS-linked miRNAs regulate the expression of NEFM and NEFH; 3) whether ALS-linked miRNAs regulate the expression of RNA-binding proteins whose metabolism is dysregulated in ALS (TDP-43, FUS, and RGNEF); and, 4) whether TDP-43 and FUS are in a regulatory network with ALS-linked miRNAs. Overall, 12 ALS-linked miRNAs were identified to regulate either intermediate filament or RNA-binding protein expression, and further, a novel negative feedback loop between TDP-43 and two miRNAs (miR-27b-3p and miR-181c-5p) was identified. This dissertation highlights that changes to miRNA levels, as seen in ALS, would contribute to overall ALS pathology, making them viable avenues for potential therapeutics