Alalwany, Roaa
(2021)
Alternative splicing and the inhibition of splicing kinases in Alzheimer’s Disease.
PhD thesis, University of Nottingham.
Abstract
Alzheimer’s disease (AD) is the most common cause of dementia, the chronic and progressive deterioration of memory and cognitive abilities. AD can be pathologically characterised by neuritic plaques and neurofibrillary tangles, formed by the aberrant aggregation of β-amyloid and tau proteins, respectively. As the global population living with dementia is projected to reach 132 million by the year 2050, treatment of AD has become a top public health priority. Unfortunately, there are currently no disease-modifying drugs available for AD patients, so it is critical to develop novel therapeutic strategies for better disease management.
Alternative splicing (AS) was first implicated in AD through key genes APP and MAPT which have splicing isoforms that differentially affect susceptibility for disease. More recently, transcriptome analyses of the ROSMAP dataset revealed an altered splicing profile in association with AD. Indeed, my analysis of this dataset found that individuals with mild cognitive impairment (MCI) and AD expressed a greater number of known splicing transcripts per gene, indicating more AS than individuals with no cognitive impairment. Additionally, multivariate analysis oftranscript splicing of the BDR dataset discovered that the frontal cortex, a brain region with high susceptibility for AD pathology, exhibited differential splicing events compared to the cerebellum, a protected region of the brain. Differential splicing most notably occurred in genes related to synaptic function and calcium signalling. Therefore, I hypothesised that the expression of splicing kinases, known regulators of AS, can be associated with AD. Accounting for sex and age, individuals with lows plicing kinase expression were identified to have a higher proportion of clinical AD and AD-related pathologies compared to high expression groups.
Next, I hypothesised that regulation of splicing kinase activity could have protective effects on AD-related neurotoxicity in vitro. Using oxidative stress, β-amyloid, and tau hyperphosphorylation models, I investigated the effect of VEGF-A splicing isoforms, previously established to be neurotrophic agents, as well as novel small molecule kinase inhibitors, which selectively inhibit SRPK1 and CLK. Both VEGFA165a and VEGF-A165b isoforms, produced by differential splice site selection in exon 8, were protective against AD-related neurotoxicity, measured by increased metabolic activity and neurite outgrowth. However, VEGF-A165b was more protective against decreased neurite outgrowth. SRPK1 inhibition was found to significantly protect neurite outgrowth through shifting AS of VEGFA towards the VEGF-A165bisoform. The use of CLK inhibitors also exerted neuroprotective effects in vitro, but this was not VEGF-A isoform dependent. Since CLK inhibition modulated AS of MAPT through increased exon 10 inclusion, I postulated that CLK inhibitors may be neuroprotective through tau-mediated mechanisms.
Overall, these findings demonstrate that splicing kinase inhibitors can be used tomodulate AS and could potentially have beneficial effects in AD-related pathologies Global changes in AS are implicated in AD and these are likely to occur upstream of pathogenic pathways, including the toxic accumulation of β-amyloid and tau proteins. As a result, I propose further investigation of splicing kinase inhibitors as a novel therapeutic strategy for treatment of AD and other tauopathies that similarly cause neurodegeneration.
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