Neurofibrillary tangles consist of hyperphosphorylated tau, one of the pathological hallmarks of Alzheimer’s disease (AD). Alternative splicing of the tau pre-mRNA produces six tau isoforms with or without exon 10 (E10); tau4R or tau3R, microtubule binding repeats respectively. In normal human brains the ratio of 4R/3R tau is approximately one. Aberrant E10 splicing is also observed in some sporadic AD cases as well as Pick’s disease. The rationale for this study is that abnormal splicing may predispose to neurological diseases such as AD either through abnormal expression and/or activity of splicing factors that control tau alternative splicing. In particular, expression levels of splicing factors regulating tau pre-mRNA splicing may be altered in AD and contribute to pathogenesis. The AD model used was dependent on the presence or absence of TDP43 inclusions because approximately 30 % of AD cases have inclusions of the RNA binding protein, TDP-43 which may contribute to the clinical phenotypes observed in these cases. However TDP-43 is an RNA binding protein known to regulate alternative splicing. In addition, TDP-43 pathology has now been shown to co-occur with tau pathology in some tauopathies. Whether the TDP-43 inclusions in AD is incidental or whether it contributes to more severe clinical phenotype remains unresolved. This model was used to determine if TDP43 pathology in AD exacerbates the changes in splicing factor expression in AD cases with TDP43 pathology. Splicing factors including serine and arginine (SR) rich proteins that either repress or promote E10 inclusion and CELF proteins are of particular interest. The brain selective CELF3 promotes tau E10 inclusion in vitro by binding to an intronic element in tau pre-mRNA. The levels of expression of CELF proteins and SR proteins that modulate tau splicing were characterised in five brain regions (frontal cortex, temporal cortex, amygdala, hippocampus and cerebellum) using post-mortem brain tissue from AD patients. Tau E10 alternative splicing pattern was also analysed in these brain regions. We investigated the expression levels of CELF proteins (CELF1, CELF3 and CELF4) and SR proteins (SC35, SRp40, and SRp55) in AD cases with (+) and without (-) TDP-43 inclusions compared to aged-matched controls. Tau E10 alternative splicing pattern analysis revealed that tau4R was increased in the amygdala and hippocampus of AD brain. We found, by quantitative RT-PCR, that the expression level of CELF3 RNA is increased in the amygdala and frontal cortex of AD cases, regardless of TDP-43 inclusions. Interestingly, in the amygdala of ADTDP43- cases where an increase in tau4R is found, we also found an increased expression of CELF4, SRp40 and SRp55 RNA. Although CELF3, CELF4 and SRp40 promote tau E10 inclusion in vitro, SRp55 inhibits tau E10 inclusion in vitro; whether this occurs in vivo is unknown. The association of abnormal expression of SR proteins and CELF proteins as well as aberrant tau E10 splicing in brain regions affected during AD pathogenesis may be a contributing factor to disease. Independent of the role of SR proteins and CELF proteins in sporadic AD, these tau splicing factors may be therapeutic targets to correct aberrant tau splicing in tauopathies. Future work will determine whether these splicing factors (CELF3, CELF4, SRp40 and SRp55) show abnormal expression in other neurodegenerative diseases.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:628040 |
| Date | January 2012 |
| Creators | Adelodun, Aderonke |
| Publisher | King's College London (University of London) |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | https://kclpure.kcl.ac.uk/portal/en/theses/characterisation-of-tau-splicing-factors-in-alzheimers-disease(75640d4d-dacd-44aa-b64c-f6e14c8b3d8a).html |
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