In the earliest stages of AD, tangle pathology is limited to the hippocampal formation. As the disease progresses however, pathology is seen in cortical areas and these later stages correlate with the onset of overt dementia. Although the progressive spread of pathology has been mapped in humans, most transgenic mouse models of the disease do not model what is seen in humans due to the use of promoters that drive high level expression of AD-related transgenes in inappropriate, or regionally diverse areas of the brain. To model the initial stages of the disease, and to map the spread of pathology out of the hippocampal formation, we have created a novel line of mice with regionally restricted expression of human tau in parahippocampal/hippocampal regions of relevance to the earliest affected regions in the AD brain. A second mouse model will change the regions in which tau is expressed through injection of tau-containing extract into synaptically connected, and unconnected areas of the brain to allow further insight into the significance of network activity in pathology propagation.
Three specific aims will address the following issues 1) if the anatomical progression of pathology out of the entorhinal cortex supports the hypothesis that tau pathology spreads transynaptically. 2) the spatio-temporal relationship between basal metabolic function (cerebral blood volume assessed by functional imaging) and pathological progression to test the hypothesis that functional decline is associated with accumulation of pathological tau species in vulnerable brain regions and 3) the spatio-temporal relationship between metabolic function and cognitive impairment, and the relationship with pathological progression to test the hypothesis that cognitive impairment occurs after metabolic dysfunction, when pathology is extensive in extrahippocampal regions. All three measures (neuropathology, metabolic function and cognitive performance) will be assessed relative to each other to provide a spatial and temporal ordering of events. These studies will allow us to not only address a key issue in AD pathobiology - whether transynaptic spread is implicated in propagation of the disease, but mapping the anatomical progression of the disease and correlating it with functional measures of metabolic function (fMRI) and cognitive performance will give insight into spatial and temporal relationships between these measures. These insights could inform on future therapeutic approaches that could prevent the progression of the disease when administered at an early stage.
Alzheimer's Disease is a progressive disease characterized by the accumulation of amyloid/Abeta and tau tangles in defined regions of the brain. In the earliest stages, tangle pathology is limited to the hippocampal formation but as the disease progresses, pathology is seen in cortical areas and these later stages correlate with the onset of overt dementia. Although the progressive spread of pathology has been mapped in humans, most transgenic mouse models of the disease do not model this feature of the disease. To model the initial stages of the disease, and to map the spread of pathology, metabolic dysfunction and cognitive impairment through the brain, we have created a novel line of mice with regionally restricted expression of human tau. Insights from these mice could inform on future diagnostic or therapeutic approaches that could prevent the progression to severe stages.
