An investigation of the effects of the transcription factor PAX6 in an Alzheimer's disease mouse model (CRND8)

Alzheimer’s disease is the most common form of dementia, a debilitating neurodegenerative disease which affects the creation and retention of memories. It affects millions of people across the world, and despite its prevalence an effective treatment or therapy has yet to be discovered. To gain a better understanding of the disease we have investigated a potential candidate gene in the pathway of Alzheimer’s disease, paired homeobox 6 (PAX6), and its role in the mouse model TgCRND8. PAX6 is a developmental gene, necessary for normal development of the eye and several organs in the body. However, it was found to be elevated in Alzheimer’s disease patients, and is a potential candidate gene for an investigation. TgCRND8 mice are a transgenic strain of mice with a double mutation to produce human amyloid protein and convert it in high levels of amyloid-beta, forming plaques similar to those seen in human patients. By utilizing mice brains of different ages and therefore different stages of amyloid plaque development, we were able to visualize the change and increase of PAX6 protein levels in the TgCRND8 mice over time by counting PAX6 containing neuronal cells. In addition to the visualization of PAX6 within a transgenic mouse model, in vitro investigations on the downstream pathways of PAX6 were also performed, specifically regarding the effects on glycogen synthase kinase 3-beta (GSK3β) and its effect on the hyperphosphorylation of tau protein. As the hyperphosphorylation of tau protein has been hypothesized to not only contribute to but also be a cause of Alzheimer’s disease, this study focused on the effects of knocking down PAX6 in vitro on wild-type primary cortical neurons. It was found that there is a dramatic increase in the levels of PAX6 in an in vitro model of Alzheimer’s disease as well as an in vivo model of Alzheimer’s disease, the TgCRND8 mice. By investigating the role that PAX6 plays on the progression of Alzheimer’s disease as well as the localization of the protein in the neuronal cells of a transgenic mouse model, we hope to contribute to a better understanding of the complex causes and pathways of Alzheimer’s disease.published_or_final_versionBiomedical SciencesMasterMaster of Philosoph

Behavioral Stress Fails to Accelerate the Onset and Progression of Plaque Pathology in the Brain of a Mouse Model of Alzheimer's Disease

<div><p>Conflicting findings exist regarding the link between environmental factors and development of Alzheimer's disease (AD) in a variety of transgenic mouse models of AD. In the present study, we investigated the effect of behavioral stress on the onset and progression of Aβ pathology in the brains of TgCRND8 mice, a transgenic mouse model of AD. One group of TgCRND8 mice was subjected to restraint stress starting at 1 month of age until they were 3 months old, while restraint stress in the second group started at 4 months of age until they were 6 months old. After 2 months of treatment, no differences in the soluble, formic acid extracted, or histologically detected Aβ deposition in the cortical and hippocampal levels were found between non-stressed and stressed mice. These results showed that restraint stress alone failed to aggravate amyloid pathology when initiated either before or after the age of amyloid plaque deposition in TgCRND8 mice, suggesting that if stress aggravated AD phenotype, it may not be via an amyloid-related mechanism in the TgCRND8 mice. These findings are indicative that plaque load per se may not be used as a significant criterion for evaluating the effect of stress on AD patients.</p></div

Restraint stress activated hypothalamic neurons in TgCRND8 mice.

<p>A–D: Cross sections of the brains stained with c-fos immunohistochemical staining in PVN (A and C) and SON (B and D) of TgCRND8 mice at the age of 4 months undergone restraint stress (A and B) and non-stress treatment (C and D). E: Quantitative analysis of number of c-fos immunoreactive nuclei in SON of stressed and non-stressed TgCRND8 mice. * indicates statistical differences when compared with their age-matched non-stressed controls at <i>p</i><0.01. Scale bar = 150 µm.</p

The number of Thioflavin S-positive plaques/section in the brains of TgCRND8 mice at the age of 1, 3 or 6 month-old.

<p>The number of Thioflavin S-positive plaques/section in the brains of TgCRND8 mice at the age of 1, 3 or 6 month-old.</p

Effects of restraint stress on Aβ1-40 or Aβ1-42 levels in TgCRND8 mice.

<p>ELISA was used to measure Aβ levels in hippocampal tissues after completion of the restraint stress procedure. The data were expressed as means ± SEM. Restraint stress had no significant effect on Aβ levels in either soluble fraction or nonsoluble fraction.</p

Cross sections of the brains were stained with Thioflavin S staining in TgCRND8 mice at the age of 1 (A), 3 (B) and 6 (C) months.

<p>Scale bar = 100 µm.</p

Plasma corticosterone levels in the stressed TgCRND8 mice increased compared with that in their non-stressed controls at the age of 3 and 6 month-old.

<p>* indicates statistical differences when compared with their age-matched non-stressed controls at <i>p</i><0.01.</p

Restraint stress did not influence cortical and hippocampal amyloid plaque loads.

<p>A–D, Cross sections of the brains stained with bam-10 immunohistochemical staining in TgCRND8 mice at the age of 3 (A, B) or 6 months (C, D) under stress (A, C) and non-stress (B, D). E–F, Quantitative analysis of Aβ deposit burden in either cortex or hippocampus in TgCRND8 mice at the age of 3 (E) or 6 months (F) under stress or non-stress. Scale bar = 300 µm.</p