Human apolipoprotein E (APOE) has three common isoforms (APOE2, APOE3, APOE4), and the APOE4 isoform is the strongest genetic risk factor for developing late-onset Alzheimer's disease (AD). The medial temporal lobe (MTL) is among the first areas of the brain affected by AD, and young adult human APOE4 carriers have altered MTL structure (DiBattista et al., 2014, [35]; [2-10]) and function (Stevens, DiBattista, et al., 204, [36]; [2-10]). I hypothesize that APOE genotype can also alter MTL structure and function in an animal model of young adults (APOE mice), and can this be rescued with a candidate preventative treatment shown to be effective in epidemiological studies (such as ibuprofen). My preliminary data show that APOE mice expressing human APOE without pathological AD features (i.e., amyloid plaques and tau tangles) have deficits in MTL-dependent memory and MTL dendritic spine density, as well as biochemical alterations in MTL apoE, that can be rescued with ibuprofen (Figures 1-3). If the APOE4 genotype also induces MRI-detectable changes in the MTL that are recued with ibuprofen in mice, these biomarkers could be readily translated to human studies testing how the MTL changes during treatment with candidate AD preventative therapies and whether these MTL biomarkers are directly associated with AD incidence. I propose to test the effect of APOE genotype and ibuprofen on brain structure and function in APOE mice. I hypothesize that APOE4 mice will have altered MTL structure and function that can be rescued by ibuprofen. The rationale for this hypothesis lies in epidemiological studies that have shown early ibuprofen use can reduce AD risk in humans, but that this protective effect may be limited to APOE4 carriers [26, 32-35]. My preliminary data also show that APOE4 mice have abnormalities in brain biochemistry, neuronal morphology, and spatial learning that can be rescued with ibuprofen (Figures 1-3). Young human APOE4 carriers have abnormal medial temporal lobe structure and function (e.g., DiBattista et al., 2014, [35], Stevens, DiBattista, et al., 2014, [36]; [2-10]), bu it is unknown how this could change with ibuprofen. To test this, I will treat young adult APOE3 and APOE4 mice with ibuprofen or control diets (2 months, 375 ppm, based on [31]) until 6 months of age. I will then conduct three dimensional imaging before and after this treatment to measure brain structure (voxel-based morphometry, VBM), allowing for within subjects (before vs. after treatment) and between subjects (control vs. ibuprofen diet) comparisons (Aim 1). In addition, I will conduct activity-induced Manganese (MnCl2) Enhanced MRI (activity-induced MEMRI) before and after the Barnes Maze [29] to measure function during spatial learning. MnCl2 is a paramagnetic tracer that is taken up by voltagegated calcium channels during neuronal activity. Instead of relying on the BOLD signal, this form of functional MRI allows for the accumulation of tracer in brain regions that have the most activity based on open voltage-gated calcium channels (see [37]). In the unlikely event that there are no differences between APOE3 and APOE4 mice, with and without ibuprofen treatment, this work will remain valuable by demonstrating that structural changes in dendritic spine density in the MTL (Figure 2) were specific to layer II/III of the medial entorhinal cortex (MEC) only, and that candidate therapies should instead be targeted to this particular brain region rather than the MTL as a whole. Similarly, in the unlikely event that there are no functional differences between APOE3 and APOE4 mice, functional changes in behavior (Figure 3) may be due to disrupted functional connectivity. Therefore, I would then conduct a whole brain analysis to determine whether there were functional changes in other brain regions known to be altered in human APOE4 carriers [2-10]. The overall goals of this proposal are to determine whether ibuprofen can compensate for APOE related risk by changing neurocognitive biomarkers in APOE4 mice to those of APOE3 mice. My training will benefit from the addition of small animal imaging techniques. The findings from this research project will not only enhance our understanding of the role of APOE in the normal brain, but will also inform future research assessing novel drug targets for preventative AD therapies (i.e., determining whether APOE-dependent differences in the MTL change after candidate drug intervention to track disease progression).
Apolipoprotein E (APOE) is the strongest genetic risk factor for Alzheimer's disease, and it is inherited by 25% of the population. The goals of this research project are to discover new APOE-associated biomarkers detectable through MRI, and to test how these respond to a preventative treatment in mice, to inform future research assessing novel drug targets for preventative Alzheimer's therapies in humans.
| Di Battista, Amanda M; Heinsinger, Nicolette M; Rebeck, G William (2016) Alzheimer's Disease Genetic Risk Factor APOE-?4 Also Affects Normal Brain Function. Curr Alzheimer Res 13:1200-1207 |
| DiBattista, Amanda M; Dumanis, Sonya B; Newman, Joshua et al. (2016) Identification and modification of amyloid-independent phenotypes of APOE4 mice. Exp Neurol 280:97-105 |
