An In vitro model of intramural periarterial drainage. Significance for Alzheimer’s Disease

Abstract

Alzheimer’s disease is the commonest form of dementia and one of the key features is the deposition of amyloid-beta peptides in the walls of capillaries and arteries as cerebral amyloid angiopathy (CAA). This is due to a failure of clearance of amyloid-beta (Aβ) from the ageing brain.

The basement membranes of capillaries and arteries represent the intramural periarterial drainage (IPAD) pathways of the brain and IPAD fails with increasing age and possession of Apolipoprotein E4 genotype. The motive force for IPAD is provided by the contraction of vascular smooth muscle cells (VSMC) that receive adrenergic innervation from locus coeruleus, a structure that degenerates very early in Alzheimer’s disease. As IPAD pathways are both small (100nm thickness) and inaccessible, there is an urgent need to employ new methods to investigate their targeting for treatment. The aim of this thesis is to firstly study the pattern of synthesis of basement membrane proteins by cells of the vascular wall, secondly to assess how these proteins change in response to ApoE genotype and hypoxia and thirdly to characterise the distribution of adrenergic receptors on the vascular smooth muscle cells as a look to their future therapeutic targeting of IPAD.

Materials and Methods: Human vascular smooth muscle cells, pericytes, endothelial cells and astrocytes were cultured and their expression of collagen IV, laminin, fibronectin and perlecan was examined after immunofluorescence and confocal microscopy. Astrocytes expressing ApoE2/3/4 were also examined by correlated light and electron microscopy. A novel millifluidics system called Quasi-Vivo was employed to pilot flow of Aβ peptides over vascular smooth muscle cells. Adrenergic receptors on VSMCs were studied by immunofluorescence and confocal microscopy.

Results: All cells synthesised proteins of the basement membranes in varying amounts. APOE4 astrocytes express high amounts of fibronectin. Vascular smooth muscle cells produce the highest amount of basement membrane proteins compared to pericytes, endothelial cells and astrocytes, with collagen IV and laminin expressed at their highest amount in VSMC compared to the other cells. Flow of Aβ 1-40 or Aβ1-42 did not alter the composition of the basement membranes under normoxic conditions. Hypoxia alone resulted in an upregulation of laminin with no effect of the addition of Aβ 1-40, but a decrease in laminin and collagen IV when Aβ1-42 was added.
Adrenergic receptors are expressed on VSMCs, with the highest concentration of α1B receptors.

Discussion: This study demonstrates that cells contributing to the IPAD pathways express basement membrane proteins in different concentrations, with VSMCs synthesising the highest amounts of collagen IV and laminin, responding to hypoxia and to flow of Aβ 1-42 and expressing a high concentration of α1B adrenergic receptors.

Conclusion: The unique basement membrane characteristics of the VSMCs and their response to hypoxia and flow of Aβ supports the working hypothesis that Aβ may be a signalling molecule for IPAD pathways that are sensitive to hypoxic changes and may be targeted therapeutically by adrenergic interventions.

More information

Identifiers

ORCID for Roxana-Octavia Carare: orcid.org/0000-0001-6458-3776

ORCID for James Nicoll: orcid.org/0000-0002-9444-7246

Catalogue record

Export record