Investigation into pathogenic mechanisms leading to neuro-glial-vascular damage and cognitive decline in a mouse model of vascular cognitive impairment
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Date
31/07/2021Author
Beverley, Joshua
Metadata
Abstract
Vascular cognitive impairment (VCI) refers to the contribution of cerebrovascular disease
to a spectrum of cognitive impairments, ranging from subjective cognitive decline to dementia.
Compromised cerebral blood flow (CBF) has been heavily implicated in the pathogenesis of
cerebrovascular disease, however, the key underlying mechanisms remain to be fully
elucidated.
Bilateral common carotid artery stenosis (BCAS) is a surgical method in which micro-coils
are applied permanently to both carotid arteries to reduce CBF. The BCAS mouse model
recapitulates many of the pathological and functional hallmarks of VCI, making it a valuable
experimental model. A prominent feature of the BCAS model is a robust increase in white
matter microglial numbers, which are significantly associated with cognitive impairments.
The first aim of this thesis was to test the hypothesis that microglial proliferation directly
leads to white matter damage and cognitive impairment following BCAS. BCAS surgery was
found to elicit a significant and persistent reduction in CBF, alongside increased microglial
proliferation. Pharmacological inhibition of microglial proliferation, through GW2580
treatment, prevented microglial proliferation, reduced microglial lysosomal expression,
preserved white matter integrity, and restored spatial learning deficits.
The second aim was to investigate, using the Cx3Cr1
eGFP microglial reporter line and
intravital multiphoton imaging, structural and functional changes within microglial cells
following BCAS. The additional pathogenic effects of amyloidosis as a co-morbidity using
the transgenic App23 mouse model were also assessed. Microglial structure and process
motility were found to be unaltered, at 1-week following BCAS, within both Cx3Cr1
eGFP/+ and
Cx3Cr1
eGFP/+App23 mice. Following 3-months of BCAS, microglial density was found to be
unaltered, alongside intact neurovascular coupling responses and spatial learning, although,
spatial memory was impaired within Cx3Cr1
eGFP/+ mice. Microglial density was also found to
be unchanged within Cx3Cr1
eGFP/+App23 mice following 3-months of BCAS. Neurovascular
coupling, however, was significantly impaired within Cx3Cr1
eGFP/+App23 mice following
BCAS surgery. Spatial learning and memory deficits were found within Cx3Cr1
eGFP/+App23
mice alone, with no additional BCAS mediated deficit. As a means of explaining the lack of
microglial response within the Cx3Cr1
eGFP/+ mice, qPCR analysis was carried out and
confirmed a ≈5-fold reduction in Cx3Cr1 receptor expression.
Considerable evidence has implicated cerebrovascular dysfunction as a pivotal mechanism
in the pathophysiology of VCI and dementia. The studies in chapter 3 aimed to test the
hypothesis that BCAS causes vascular dysfunction leading to the onset of neuro-glial-vascular
damage. Multiphoton imaging of C57BL/6J wild-type mice found significantly reduced RBC
velocity alongside impaired arterial pulsation, and increased leukocyte trafficking, 1-month
following BCAS surgery.
In conclusion, the work described within this thesis demonstrates that microglial
proliferation plays a causative role in white matter damage and cognitive decline following
BCAS, and that this can be successfully targeted to reverse pathological damage and functional
deficits. Furthermore, Cx3Cr1 receptor signalling was found to play a significant role in the
regulation of microglial responses following BCAS. Finally, BCAS was found to not simply
be a model of reduced CBF, with impairments in arterial pulsation and increased endothelial
activation providing a new framework to contextualise BCAS mediated effects in future
studies.