Brain Perivascular Macrophages Initiate the Neurovascular Dysfunction of Alzheimer Aβ Peptides

Abstract

Rationale

Increasing evidence indicates that alterations of the cerebral microcirculation may play a role in Alzheimer’s disease (AD), the leading cause of late-life dementia. The amyloid-β peptide (Aβ), a key pathogenic factor in AD, induces profound alterations in neurovascular regulation through the innate immunity receptor CD36, which, in turn, activates a Nox2-containing NADPH oxidase leading to cerebrovascular oxidative stress. Brain perivascular macrophages (PVM) located in the perivascular space, a major site of brain Aβ collection and clearance, are juxtaposed to the wall of intracerebral resistance vessels and are a powerful source of reactive oxygen species (ROS).

Objective

We tested the hypothesis that PVM are the main source of ROS responsible for the cerebrovascular actions of Aβ, and that CD36 and Nox2 in PVM are the molecular substrates of the effect.

Methods and Results

Selective depletion of PVM using intracerebroventricular injection of clodronate abrogates the ROS production and cerebrovascular dysfunction induced by Aβ applied directly to the cerebral cortex, administered intravascularly or overproduced in the brain of transgenic mice expressing mutated forms of the amyloid precursor protein (Tg2576 mice). In addition, using bone marrow chimeras we demonstrate that PVM are the cells expressing CD36 and Nox2 responsible for the dysfunction. Thus, deletion of CD36 or Nox2 from PVM abrogates the deleterious vascular effects of Aβ, whereas wild-type PVM reconstitute the vascular dysfunction in CD36-null mice.

Conclusions

The data identify PVM as a previously unrecognized effector of the damaging neurovascular actions of Aβ and unveil a new mechanism by which brain-resident innate immune cells and their receptors may contribute to the pathobiology of AD.