Cytoskeleton and molecular motors in the causation of motor neuron diseases

• Main Author: Simoes, Fabio Andre Amaral Lopes
• Other Authors: Leigh, P. Nigel
• Published: University of Brighton 2018
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.754032

Amyotrophic lateral sclerosis (ALS) and spinal muscular atrophy with lower extremity predominance (SMA-LED) are motor neuron diseases defined by the loss of motor neurons. RNA metabolism and molecular transport have both become increasingly implicated in the pathogenesis of motor neuron diseases. As such, this thesis explores the role of TAR-DNA binding protein 43 (TDP-43) in the regulation of peripherin expression in ALS, and the molecular consequences of mutations in DYNC1H1, a component of the cytoplasmic dynein motor complex, in SMA-LED. TDP-43 is a DNA/RNA binding protein implicated in ALS pathogenesis. Recent evidence suggests that TDP-43 regulates peripherin, an ALS associated intermediate filament protein. Here, analysis of peripherin in the lumbar spinal cord of TDP-43^+/F210I mice revealed a significant increase in the levels of Per-45, a shift towards an increase in Per-58 in the Triton X-100 soluble fraction that did not reach statistical significance, and an increase in an isoform of 50 kDa in the insoluble fraction. These changes in the expression of peripherin in TDP-43^+/F210I mice may indicate a regulatory role for TDP-43 in peripherin expression, which could contribute to ALS pathology. Furthermore, there is evidence that defects in neurodevelopment are present in SMA-LED. Analysis of paxillin, a key focal adhesion protein in mouse embryonic fibroblasts from the Legs at odd angles (Loa) model of SMA-LED was performed, which indicated a reduction in its expression which may underpin the previously reported migration phenotypes in these cells. This data provides further evidence that SMA-LED may be a neurodevelopmental disorder. Furthermore, analysis revealed that the Golgi apparatus in DYNC1H1^+/D338N patient fibroblasts was significantly condensed, while in BICD2^+/I189F fibroblasts there was a decrease in localisation of dynein to the Golgi. The lack of dynein at the Golgi in BICD2^+/I189F fibroblasts indicates that BICD2 may be necessary for the recruitment of the molecular motor to the organelle. These Golgi phenotypes may also contribute to impaired migration in disease. Importantly, analysis of DYNC1H1^+/D338N patient fibroblasts and mouse embryonic fibroblasts (MEFs) from the Loa mouse strain showed a significant decrease in α-tubulin acetylation, a phenotype previously seen in another DYNC1H1 substitution. In conclusion, these data support previous data which suggested that peripherin expression is altered in the context of TDP-43 mutations, potentially contributing to ALS pathology. Additionally, Golgi phenotypes were found in both DYNC1H1^+/D338N and BICD2^+/I189F fibroblasts with potential consequences for cellular migration. Finally, decreased microtubule acetylation may be a common factor in SMA-LED linked with DYNC1H1 mutations. The conserved nature of this phenotype could indicate a potential target for therapeutics.