Deposition of amyloid β in the walls of human leptomeningeal arteries in relation to perivascular drainage pathways in cerebral amyloid angiopathy

Abstract

Deposition of amyloid β (Aβ) in the walls of cerebral arteries as cerebral amyloid angiopathy (CAA) suggests an age-related failure of perivascular drainage of soluble Aβ from the brain. As CAA is associated with Alzheimer's disease and with intracerebral haemorrhage, the present study determines the unique sequence of changes that occur as Aβ accumulates in artery walls. Paraffin sections of post-mortem human occipital cortex were immunostained for collagen IV, fibronectin, nidogen 2, Aβ and smooth muscle actin and the immunostaining was analysed using Image J and confocal microscopy. Results showed that nidogen 2 (entactin) increases with age and decreases in CAA. Confocal microscopy revealed stages in the progression of CAA: Aβ initially deposits in basement membranes in the tunica media, replaces first the smooth muscle cells and then the connective tissue elements to leave artery walls completely or focally replaced by Aβ. The pattern of development of CAA in the human brain suggests expansion of Aβ from the basement membranes to progressively replace all tissue elements in the artery wall. Establishing this full picture of the development of CAA is pivotal in understanding the clinical presentation of CAA and for developing therapies to prevent accumulation of Aβ in artery walls. This article is part of a Special Issue entitled: Vascular Contributions to Cognitive Impairment and Dementia edited by M. Paul Murphy, Roderick A. Corriveau and Donna M. Wilcock.

Keywords: Amyloid-β; Basement membranes; Cerebral amyloid angiopathy; Leptomeningeal arteries; Perivascular drainage.

Fig. 1

Quantification for collagen IV, fibronectin, nidogen 2 in the gray and white matter of young, old and CAA cases. The percentage areas stained with nidogen 2 in gray and white matter were significantly higher in old compared to young brains and significantly lower in CAA brains compared to old brains.

Fig. 2

Single colour channel images in series (A–C) and the overlay (D) showing triple immunofluorescence labelling of two leptomeningeal arteries from a severe CAA brain. A) Smooth muscle actin (SMA); B) collagen IV; C) Aβ; D) overlay. Vessel 1 diameter = 71.866 μm, vessel 2 diameter = 80.151 μm. (→) marks a key region of interest where initial Aβ deposition correlates to the only region of reduced SMA in vessel 2. Scale bar: 50 μm.

Fig. 3

The spectrum of different patterns of deposition of Aβ in CAA. Maximal projection overlaid confocal images of a human leptomeningeal artery from severe CAA brain: A) the basement membrane (collagen IV, blue) of the tunica media is interposed between the smooth muscle cells (green immunolabelling). Aβ (red, arrows) is observed within the basement membranes of tunica media, with blue immunolabelling for collagen IV on both sides; the endothelial BM is free of Aβ; B) co-localization (pink) between the red Aβ and blue Col IV within the BM with the absence of SMA immunolabelling for more of half of the circumference of the arterial wall; C) complete loss of SMA immunolabelling, with Aβ co-localizing with collagen IV in tunica media; D) transverse section through an artery, with Aβ deposited in the adventitia. Blue = Col IV, green = SMA, red = Aβ. Scale bars: 50 μm.

Fig. 4

A) The percentage of fluorescently labelled leptomeningeal artery wall comprised of smooth muscle actin, collagen IV and Aβ. B) the relationship between the percentage of fluorescently labelled leptomeningeal artery wall comprised of Aβ and SMA. Each data point corresponds to the values from an individual leptomeningeal artery from the occipital sulcus of a severe CAA brain, 100 vessels in total.

Fig. 5

The relationship between blood vessel diameter and expression of SMA, Col IV and Aβ within human leptomeningeal arteries of severe AD brain tissue sections. The average percentage represents the percentage of total fluorescently labelled vessel wall comprised of each protein from an average of ‘n’ vessels. For cohort 50–60 n = 8, 60–70 n = 62, 70–80 n = 21 and > 80 n = 9. The error bars shown represent the standard error. Table: Statistical analysis of the relationship between amount of Col IV, SMA and Aβ expressed in a leptomeningeal artery wall relative to the blood vessel diameter, analysed using Graph Pad Prism 6.0 one-way ANOVA analysis. The percentage area covered by SMA increases with the diameter of the vessel; the percentage area covered by Aβ also increases with the diameter of the vessel, although this did not reach statistical significance. SE: standard error of the mean.

Fig. 6

Development of cerebral amyloid angiopathy.