Abstract
Alterations in density and morphology of the cerebral microvasculature have been reported to occur in Alzheimer's disease patients and animal models of the disease. In this study we compared magnetic resonance imaging (MRI) techniques for their utility to detect age-dependent changes of the cerebral vasculature in the arcAβ mouse model of cerebral amyloidosis. Dynamic susceptibility contrast (DSC)-MRI was performed by tracking the passage of a superparamagnetic iron oxide nanoparticle in the brain with dynamic gradient echo planar imaging (EPI). From this measurements relative cerebral blood volume [rCBV(DSC)] and relative cerebral blood flow (rCBF) were estimated. For the same animal maps of the relaxation shift index Q were computed from high resolution gradient echo and spin echo data that were acquired before and after superparamagnetic iron oxide (SPIO) nanoparticle injection. Q-values were used to derive estimates of microvessel density. The change in the relaxation rates obtained from pre- and post-contrast gradient echo data was used for the alternative determination of rCBV [rCBV()]. Linear mixed effects modeling found no significant association between rCBV(DSC), rCBV(), rCBF, and Q with genotype in 13-month old mice [compared to age-matched non-transgenic littermates (NTLs)] for any of the evaluated brain regions. In 24-month old mice there was a significant association for rCBV(DSC) with genotype in the cerebral cortex, and for rCBV() in the cerebral cortex and cerebellum. For rCBF there was a significant association in the cerebellum but not in other brain regions. Q-values in the olfactory bulb, cerebral cortex, striatum, hippocampus, and cerebellum in 24-month old mice were significantly associated with genotype. In those regions Q-values were reduced between 11 and 26% in arcAβ mice compared to age-matched NTLs. Vessel staining with CD31 immunohistochemistry confirmed a reduction of microvessel density in the old arcAβ mice. We further demonstrated a region-specific association between parenchymal and vascular deposition of β-amyloid and decreased vascular density, without a correlation with the amount of Aβ deposition. We found that Q mapping was more suitable than the hemodynamic read-outs to detect amyloid-related degeneration of the cerebral microvasculature.
Highlights
Alzheimer’s disease (AD) is a progressive neurodegenerative disorder and the most common form of dementia (Lopez, 2011; Mangialasche et al, 2012)
In different brain regions relative CBV (rCBV)(DSC) and relative cerebral blood flow (rCBF) values were measured by ROI analysis
In 24-month old mice there was a significant association for rCBV(DSC) with genotype in the cerebral cortex, while there was no association in the hippocampus and cerebellum (Table 1)
Summary
Alzheimer’s disease (AD) is a progressive neurodegenerative disorder and the most common form of dementia (Lopez, 2011; Mangialasche et al, 2012). AD pathology is characterized by changes in β-amyloid (Aβ) metabolism, abundance of soluble Aβ oligomers, parenchymal Aβ deposits and neurofibrillary tangles, synaptic dysfunction and neurodegeneration, and loss of cognitive function (Haass and Selkoe, 2007). Cerebral hypoperfusion is an early sign of cerebrovascular dysfunction in AD patients (Hirao et al, 2005; Johnson et al, 2005). Postmortem histological studies have revealed that microvessel density is altered in the AD brain. Cerebral amyloid angiopathy that is present in up to 90% of AD patients, involves the deposition of Aβ within the leptomeninges and parenchymal microvessels (Vinters, 1987). Cerebral amyloid angiopathy induces degeneration of smooth muscle cells, impairment of blood-brain barrier function, and the occurrence of cerebral microbleeds, all of which can compromise cognitive function (Cordonnier and van der Flier, 2011)
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