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Abstract

Cytoskeletal protein abnormalities are common features of a number of
neurodegenerative conditions. However, the potential roles of neurofilaments (NFs)
in neurodegenerative disease and in ageing-related cellular changes are poorly
understood. Many models of NF abnormalities in mice have been reported, but how
ageing affects the NF pathology and the role of ageing in neurodegenerative diseases
are still unknown. This thesis, therefore, sought to examine the effects of the absence
of a major class of NF proteins, in NF light (NF-L) knockout (KO) mice, on the
ageing-related adaptive capacity of other cytoskeletal elements in neurons, and also
on neurodegeneration-linked alteration of cytoskeletal proteins, cytoskeletal RNAbinding
proteins (TDP-43) and myelin proteins.
The NF-L subunit is considered as an obligate subunit polymer for the assembly of
NF triplet proteins into neuronal intermediate filaments (IFs). Previous studies have
shown that NF-L KO mice have substantially reduced axonal intermediate filaments.
NF abnormalities such as NF accumulation, reduced NF-L mRNA, and NF
mutations have been described in human neurodegenerative disease.
This thesis has used immunohistochemical and quantitative Western blot techniques
to examine cytoskeletal changes in the brains of NF-L KO and wild-type (WT) mice
at different ages. It was demonstrated that depletion of NF-L protein resulted in
alteration of the expression of a range of cytoskeletal proteins, and disrupts other
neuronal IF proteins, through ageing. However, there were no gross structural changes in neurons or cytoarchitecture in regions such as the cerebral cortex. In this
regard, alterations in the expression of other cytoskeletal proteins may compensate
for decreased NFs.
TDP-43, an NF-L mRNA binding protein, has recently been pathologically
associated with a number of neurodegenerative diseases of ageing. However,
mechanisms of TDP-43 pathogenesis are unknown. As TDP-43 is known to bind to
NF-L mRNA, this thesis used immunohistochemical and quantitative Western blot
approaches to characterize and quantify the changes of TDP-43 expression and
distribution in brain and spinal cord of ageing NF-L KO mice as compared to WT
animals. It was found that a significant increase of TDP-43 protein levels occurred in
the cortex and lumbar spinal cord in NF-L KO mice at 12 months of age, compared
to WT mice. Moreover, an increase of phosphorylated TDP-43 was found in the
cervical spinal cord of NF-L KO mice at 12 months, compared to WT controls.
NFs have a critical role in myelination by regulating axonal diameter. To investigate
whether deficiency of NF-L protein results in myelin alteration during ageing, this
thesis measured the relative protein level of myelin basic protein (MBP) by using
quantitative Western blot. It was demonstrated that the level of MBP was
significantly reduced in the cortex of NF-L KO mice at 12 months, compared to WT
mice.
In summary, these findings indicate that pathological and compensatory neuronal
effects of NF-L KO and reduced NFs are affected by ageing. The absence of NF-L
protein results in the alteration of NFs and other cytosekeletal, mRNA-binding and myelin proteins during ageing. These results indicate that the absence of NF proteins
can lead to abnormalities in neurodegenerative disease-related proteins, but also that
the central nervous system (CNS) is capable of adaptive alterations in the absence of
NFs.

Item Type:	Thesis - PhD
Authors/Creators:	Liu, Yao
Keywords:	neurofilament, knockout mouse, TDP-43, myelin proteins, ageing, neurodegenerative disease
Additional Information:	Copyright the Author
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