Microvascular degeneration occurs before plaque onset and progresses with age in 3xTg AD mice

Abstract

Heart disease and vascular disease positively correlate with the incidence of Alzheimer's disease (AD). Although there is ostensible involvement of dysfunctional cerebrovasculature in AD pathophysiology, the characterization of the specific changes and development of vascular injury during AD remains unclear. In the present study, we established a time-course for the structural changes and degeneration of the angioarchitecture in AD. We used cerebrovascular corrosion cast and µCT imaging to evaluate the geometry, topology, and complexity of the angioarchitecture in the brain of wild type and 3xTg AD mice. We hypothesized that changes to the microvasculature occur early during the disease, and these early identifiable aberrations would be more prominent in the brain subregions implicated in the cognitive decline of AD. Whole-brain analysis of the angioarchitecture indicated early morphological abnormalities and degeneration of microvascular networks in 3xTg AD mice. Our analysis of the hippocampus and cortical subregions revealed microvascular degeneration with onset and progression that was subregion dependent.

Keywords: Aging; Alzheimer's disease; Cerebrovascular degeneration; Corrosion cast; MicroCT; Microvessel.

Figure 1.. The cerebrovasculature in 3xTg AD mice develops pathology.

Reconstructed cerebrovascular corrosion cast in three-dimensions, color-coded by vessel diameter of (A) whole brain, (B-E) cortex, and (F) hippocampus. Color-coded (cooler colors = small diameter / warmer colors = larger diameter) penetrating arteriole demonstrating (B) normal morphology compared to a (C and D) tortuous vessel from a 3xTg AD mouse. Color-coded (cooler colors = small diameter / warmer colors = larger diameter) vasculature demonstrating (D) arteriolar aneurysm and (E and F) capillary aneurysm from 3xTg AD mice.

Figure 2.. Brain-wide vascular degeneration in 3xTg AD mice that progresses with age.

Bar graph(s) (mean ± SEM) depicting (A) average vessel distance, (B) number of vessel segments, (C) total surface area, (D) total vascular volume, (E) intervessel distance, (F) number of junctions, (G) network redundancy, and (H) fractal dimension from 3- (WT, n = 4; 3xTg AD, n = 4), 6- (WT, n = 3; 3xTg AD, n = 4), 12- (WT, n = 4; 3xTg AD, n = 3), and 24- (WT, n = 4; 3xTg AD, n = 4) month old mice. Line graph(s) (mean ± SEM) depicting total vascular volume as a function of average vessel diameter from (I) 3- (WT, n = 3; 3xTg AD, n = 4), (J) 6- (WT, n = 3; 3xTg AD, n = 4), (K) 12- (WT, n = 4; 3xTg AD, n = 3), and (L) 24- (WT, n = 4; 3xTg AD, n = 4) month old mice. Bar graph(s) (mean ± SEM) depicting expanded data denoted by the box inserts (M-P). To compare means, significant 2-way ANOVAs were probed for effects of Genotype with planned student’s t-test at each age or vessel diameter (*, p < 0.05; **, p < 0.01; ***, p < 0.001).

Figure 3.. Topological analysis of the cerebrovasculature of the entire brain describes changes that progress with age in 3xTg AD mice.

Reconstructed cerebrovascular corrosion cast, color-coded by vessel diameter from a 3-month and 12-month WT and 3xTg AD mouse. (A) The total volume of capillaries and (B) non-capillaries in WT and 3xTg AD mice at 3- (WT, n = 3; 3xTg AD, n = 4), 6- (WT, n = 3; 3xTg AD, n = 4), 12- (WT, n = 4; 3xTg AD, n = 3), and 24- (WT, n = 4; 3xTg AD, n = 4) months of age. To compare means, significant 2-way ANOVAs were probed for effects of Genotype with planned student’s t-test at each age (*, p < 0.05; **, p < 0.01; ***, p < 0.001).

Figure 4.. Vascular network analysis of the hippocampus indicates early and age-dependent changes to the vasculature in 3xTg AD mice.

Bar graph(s) (mean ± SEM) depicting (A-D) number of vessel segments, (E-H) number of vessel junctions, (I-L) total vascular volume, (M-P) total vascular surface area, and (Q-T) intervessel distance from 3- (WT, n = 4; 3xTg AD, n = 5), 6- (WT, n = 7; 3xTg AD, n = 5), 12- (WT, n = 5; 3xTg AD, n = 5), and 24- (WT, n = 6; 3xTg AD, n = 3) month WT and 3xTg AD mice. To compare means, significant 2-way ANOVAs within each brain region were probed for effects of Genotype with planned student’s t-test at each age (*, p < 0.05; **, p < 0.01; ***, p < 0.001).

Figure 5.. Microvascular degeneration in the hippocampus occurs early and progresses with age in a hippocampal subregion specific manner.

Reconstructed vascular network, color-coded by vessel diameter (cooler color = small / warmer color = large) from hippocampal subregions (A) CA1, (B) CA3, (K) DG, (L) and entorhinal cortex from WT and 3xTg AD mice. Grouped bar graph(s) (mean ± SEM) depicting the total length of vessels as a function of average vessel diameter in hippocampal subregion(s) (C-F) CA1, (G-J) CA3, (M-P) DG, and (Q-T) entorhinal cortex from 3- (WT, n = 4; 3xTg AD, n = 5), 6- (WT, n = 7; 3xTg AD, n = 5), 12- (WT, n = 5; 3xTg AD, n = 5), and 24- (WT, n = 5; 3xTg AD, n = 3) month old WT and 3xTg AD mice. To compare means, significant 2-way ANOVAs within each age group and in each region were probed for effects of Genotype with planned student’s t-test at each vessel diameter (*, p < 0.05; **, p < 0.01; ***, p < 0.001).

Figure 6.. Vascular network analysis of the cortex indicates early and age-dependent changes to the vasculature in 3xTg AD mice.

Bar graph(s) (mean ± SEM) depicting (A-C) number of vessel segments, (D-F) number of vessel junctions, (G-I) total vascular volume, (J-L) total vascular surface area, and (M-O) intervessel distance from 3- (WT, n = 4; 3xTg AD, n = 5), 6- (WT, n = 7; 3xTg AD, n = 5), 12- (WT, n = 5; 3xTg AD, n = 5), and 24- (WT, n = 5; 3xTg AD, n = 4) month WT and 3xTg AD mice. To compare means, significant 2-way ANOVAs within each brain region were probed for effects of Genotype with planned student’s t-test at each age (*, p < 0.05; **, p < 0.01; ***, p < 0.001).

Figure 7.. Microvascular degeneration in the cortex occurs early and progresses with age in a subregion specific manner.

Reconstructed vascular network color-coded by vessel diameter (cooler color = small / warmer color = large) from cortical subregions (A) somatosensory cortex (SS CTX), (B) medial orbital prefrontal cortex (MO PFC), and (K) cingulate cortex from WT and 3xTg AD mice. Grouped bar graph(s) (mean ± SEM) depicting the total length of vessels as a function of average vessel diameter in cortical subregion(s) (C-F) SS CTX, (G-J) MO PFC, and (L-O) cingulate cortex from 3- (WT, n = 4; 3xTg AD, n = 5), 6- (WT, n = 7; 3xTg AD, n = 5), 12- (WT, n = 5; 3xTg AD, n = 5), and 24- (WT, n = 5; 3xTg AD, n = 4) month old WT and 3xTg AD mice. To compare means, significant 2-way ANOVAs within each age group and in each region were probed for effects of Genotype with planned student’s t-test at each vessel diameter (*, p < 0.05; **, p < 0.01; ***, p < 0.001).