Abstract
Amyotrophic lateral sclerosis (ALS) and spinal muscular atrophy with lowerextremity 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.
| Date of Award | Feb 2018 |
|---|---|
| Original language | English |
| Awarding Institution |
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| Supervisor | P Nigel Leigh (Supervisor) |