Assessing cerebrovascular contribution to late dementia of the Alzheimer's type: the role of combined hemodynamic and structural MR analysis

Age-Related Increase of Insulin-Degrading Enzyme Is Inversely Correlated with Cognitive Function in APPswe/PS1dE9 Mice

Background

Insulin-degrading enzyme (IDE) is an important regulator for Aβ clearance and diabetes. Although it is indispensable in removing plaques related to onset Alzheimer’s disease (AD) and in degrading insulin related to diabetes, there have been few studies on the dynamic level of IDE in different stages of AD.

Material/Methods

The present study explored the level IDE protein in different stages of APPswe/PS1dE9 mice and their correlations with cognitive decline. The 4-month-old, 10-month-old, and 18-month-old mice were used as the different age stages of mice. Cognitive function was evaluated using the Morris water maze test. We also observed the level of Aβ plaques in brain regions of different stages.

Results

The data revealed that the expression of IDE was dramatically higher than in age-matched wild mice at the age of 10 months and 18 months. In terms of distribution, Aβ plaques were deposited mostly in the cortex and hippocampus, especially in 10-month-old and 18-month-old APPswe/PS1dE9 mice. The cognitive function of 4-month-old APPswe/PS1dE9 mice was not significantly differ in spatial learning. However, the cognitive function, both spatial learning and spatial memory, was dramatically lower in 10-month-old and 18-month-old groups.

Conclusions

There was a positive correlation between the expression of IDE and spatial memory in 10-month-old and 18-month-old APPswe/PS1dE9 mice. The study of this protein may provide reference values for the further study of IDE in Alzheimer’s disease.

The Disconnection Hypothesis in Alzheimer's Disease Studied Through Multimodal Magnetic Resonance Imaging: Structural, Perfusion, and Diffusion Tensor Imaging

According to the so-called disconnection hypothesis, the loss of synaptic inputs from the medial temporal lobes (MTL) in Alzheimer's disease (AD) may lead to reduced activity of target neurons in cortical areas and, consequently, to decreased cerebral blood flow (CBF) in those areas. The aim of this study was to assess whether hypoperfusion in parietotemporal and frontal cortices of patients with mild cognitive impairment who converted to AD (MCI-c) and patients with mild AD is associated with atrophy in the MTL and/or microstructural changes in the white matter (WM) tracts connecting these areas. We assessed these relationships by investigating correlations between CBF in hypoperfused areas, mean cortical thickness in atrophied regions of the MTL, and fractional anisotropy (FA) in WM tracts. In the MCI-c group, a strong correlation was observed between CBF of the superior parietal gyri and FA in the parahippocampal tracts (left: r = 0.90, p <  0.0001; right: r = 0.597, p = 0.024), and between FA in the right parahippocampal tract and the right precuneus (r = 0.551, p = 0.041). No significant correlations between CBF in hypoperfused regions and FA in the WM tract were observed in the AD group. These results suggest an association between perfusion deficits and altered WM tracts in prodromal AD, while microvasculature impairments may have a greater influence in more advanced stages. We did not find correlations between cortical thinning in the medial temporal lobes and decreased FA in the WM tracts of the limbic system in either group.

Is the cerebellum the optimal reference region for intensity normalization of perfusion MR studies in early Alzheimer's disease?

The cerebellum is the region most commonly used as a reference when normalizing the intensity of perfusion images acquired using magnetic resonance imaging (MRI) in Alzheimer's disease (AD) studies. In addition, the cerebellum provides unbiased estimations with nuclear medicine techniques. However, no reports confirm the cerebellum as an optimal reference region in MRI studies or evaluate the consequences of using different normalization regions. In this study, we address the effect of using the cerebellum, whole-brain white matter, and whole-brain cortical gray matter in the normalization of cerebral blood flow (CBF) parametric maps by comparing patients with stable mild cognitive impairment (MCI), patients with AD and healthy controls. According to our results, normalization by whole-brain cortical gray matter enables more sensitive detection of perfusion abnormalities in AD patients and reveals a larger number of affected regions than data normalized by the cerebellum or whole-brain white matter. Therefore, the cerebellum is not the most valid reference region in MRI studies for early stages of AD. After normalization by whole-brain cortical gray matter, we found a significant decrease in CBF in both parietal lobes and an increase in CBF in the right medial temporal lobe. We found no differences in perfusion between patients with stable MCI and healthy controls either before or after normalization.