Relationship between cerebral small vessel disease and proteinopathies in the medial temporal lobe

Abstract

The medial temporal lobe (MTL) is strategically important for cognition and the pathogenesis of Alzheimer's Disease (AD). Cerebral small vessel disease (CSVD) independently contributes to cognitive impairment and is believed to play a role in AD. CSVD and proteinopathies related to AD often coexist in the MTL but neither the severity of CSVD, nor the associations between these pathologies have been quantitatively addressed in this brain region. We hypothesized that the severity of CSVD in the MTL is associated with the local burden of proteinopathies implicated in neurodegeneration (tau-tangles, amyloid-β-plaques, phospho-Tar-DNA-Binding-Protein-43 [pTDP-43]), regardless of disease stage. One potential mechanism linking CSVD and proteinopathies is a failure in perivascular brain clearance. Therefore, the relationship between CSVD and the enlargement of perivascular spaces (PVS) was investigated. AI-models and manual ratings were applied to digitized histological MTL-sections of 152 autopsy cases with and without Alzheimer's Disease Neuropathological Changes to quantify proteinopathies and the two common forms of CSVD, cerebral amyloid angiopathy (CAA) and arteriolosclerosis. The associations between CSVD and proteinopathies were assessed using linear-mixed-effects models. The relationship between CSVD and PVS enlargement was also investigated. Regional CAA-burden increased along Braak-stages and was positively associated with amyloid-β-plaques percentage area and tau-tangles density, irrespective of Braak-stage, but not with density of pTDP-43 inclusions. Local arteriolosclerosis severity was not associated with Braak-stages and had no direct effect on parenchymal proteinopathies. However, arteriolosclerosis severity and its interaction with CAA were positively associated with PVS enlargement. These results suggest that CAA, but not arteriolosclerosis, is more directly implicated in the pathophysiology of proteinopathies in the MTL. Moreover, arteriolosclerosis may contribute to perivascular clearance dysfunction.

Keywords: Alzheimer’s disease (AD); Arteriolosclerosis; Cerebral amyloid angiopathy (CAA); Hippocampus; Medial Temporal lobe (MTL); Perivascular space (PVS).

Fig. 1

Assessment of relevant Alzheimer’s disease-related and vascular pathologies. Whole slide image of a hippocampal section on which immunohistochemistry against amyloid-β was performed with examples of AI-based measurements of percentage area of cerebral amyloid angiopathy (CAA), in red, and of amyloid-β plaques, in blue (A). Whole slide image of a section with amygdala and entorhinal cortex, stained with AT-8 antibody against phosphorylated tau (B). The insets show examples of tau-tangles identified as objects by the AI-algorithm. Immunohistochemistry against phosphorylated-TAR-DNA-binding protein 43 (pTDP-43) was used for the amygdala/entorhinal cortex represented in (C), on which the density of cytoplasmatic pTDP-43 inclusions was calculated (inset). For all of them, the tissue area is marked in green. The severity of arteriolosclerosis was assessed for each vessel > 15 μm in diameter on sections stained with luxol blue and hematoxylin&eosin (LHE) (D). To this aim, a semiquantitative score from 0 to 3 was used, for which examples are shown in the insets

Fig. 2

Severity of cerebral amyloid angiopathy (CAA) and arteriolosclerosis across Braak-stages. CAA percentage area was significantly different according to Braak-stage group in each region of interest of the medial temporal lobe and was higher in later stages (A-D). Conversely, no significant difference was detected across Braak-stage groups in the severity of arteriolosclerosis (E-H). The dimension of the blue circles represents the number of cases for each severity. Braak-stage groups were defined as follows: 0 = Braak-stage 0; 1 = Braak-stages I/II; 2 = Braak-stages III/IV; 3 = Braak-stages V/VI. *= 0.001 < p < 0.05; **= 0.01 < p < 0.001; ***= p < 0.001. Key: posterior parahippocampal cortex (PHC)

Fig. 3

Association between cerebral amyloid angiopathy (CAA) and proteinopathies. The plots visualize the association between CAA and Aβ-plaques, tau-tangles, and pTDP-43 in linear mixed effects models, that included CAA percentage area, age at death, and sex as fixed-factors and Braak-stage group, case, and region of interest as random-factors. CAA percentage area was positively associated with both Aβ plaques percentage area (A) and with density of tau-tangles (B). There was no significant association between CAA and density of phosphorylated-TAR-DNA-binding protein 43 (pTDP-43) cytoplasmatic inclusions (C). The models explained a large part of the variance of the dependent variable. Key: AM = amygdala; RC = rhinal cortex; Est. = estimate; HC = hippocampal body; PHC = posterior parahippocampal cortex

Fig. 4

Association between arteriolosclerosis and perivascular spaces (PVS). Example of a section of the hippocampal body/posterior parahippocampal cortex (A) and of the amygdala/rhinal cortex (B), both stained for luxol fast blue with Hematoxylin&Eosin (LHE). PVS were present in the hippocampus and in white matter of the parahippocampal gyrus, as well as in the white matter adjacent to the rhinal cortex. PVS often displayed a vessel with severe arteriolosclerosis in the middle (insets in A and B). Big spaces at the folding sites of the hippocampus, which could potentially represent hippocampal cysts (example in A, arrow) were manually excluded from the analysis. Arteriolosclerosis severity had a main positive effect on the percentage area of the PVS, in a linear mixed effect model that included arteriolosclerosis, age at death, and sex as fixed-factors and Braak-stage group, case, and region of interest (ROI) as random-factors (C). The interaction between arteriolosclerosis and cerebral amyloid angiopathy percentage area was also positively associated with the PVS across ROIs. The effect was driven by the rhinal cortex (D) and posterior parahippocampal cortex (not shown)