Abstract
Cerebral blood flow is important for the maintenance of brain function and its dysregulation has been implicated in Alzheimer’s disease (AD). Subpopulations of microglia have well-characterised associations with the vasculature in the central nervous system but the precise relationship between microglia and cells which exist on the vasculature is not yet clear. In this study we explored the relationship between microglia and pericytes, a vessel-resident cell type that has a major role in the regulation of cerebral blood flow and maintenance of the blood brain barrier. Using fixed tissue sections and in vivo live imaging, we discovered a subset of microglia that closely associated with pericytes, termed PEricyte-associated Microglia (PEM). PEM are present throughout all regions of the brain and spinal cord in NG2DsRed x CX3CR1+/GFP mice, and in the human frontal cortex. They reside adjacent to pericytes at all levels of the capillary tree and can maintain their position for at least 28 days. PEM associate with pericytes lacking astroglial endfeet coverage but are segregated from pericytes by capillary basement membranes and capillary vessel width is similarly increased beneath pericytes with or without an associated PEM. Deletion of the microglia fractalkine receptor (CX3CR1) did not disrupt the association between pericytes and PEM, suggesting the association is not reliant on fractalkine signalling. Finally, we found that the proportion of microglia that are capillary-associated and PEM declines in the superior frontal gyrus (SFG) in AD, which is exacerbated by the APOE ε3/ε4 genotype. In summary, we identify and characterise a subpopulation of microglia that specifically associate with pericytes and find this population is reduced in the SFG in AD. This reduction may be a novel mechanism contributing to vascular dysfunction in diseases such as AD.
Competing Interest Statement
The authors have declared no competing interest.
Abbreviations
- 2PLSM
- two-photon laser scanning microscopy
- Aβ
- Amyloid beta
- AD
- Alzheimer’s disease
- ANOVA
- Analysis of variance
- APOE
- Apolipoprotein E
- ARRIVE
- Animal Research: Reporting of In Vivo Experiments
- AQP4
- aquaporin-4
- CAM
- Capillary-associated microglia
- Cy5
- Cyanine 5
- CX3CL1
- C-X3-C Motif Chemokine Ligand 1
- CX3CR1
- C-X3-C chemokine receptor 1
- DAPI
- 4′,6-diamidino-2-phenylindole
- FITC
- Fluorescein isothiocyanate
- GFP
- Green Fluorescent Protein
- IBA1
- Ionized calcium binding adaptor molecule 1
- KO
- Knockout
- NHMRC
- National Health and Medical Research Council
- NIA
- National Institute on Aging
- NIH
- National Institutes of Health
- OME TIFF
- Open Microscopy Environment Tag Image File Format
- PBS
- phosphate buffered saline
- PDGFRβ
- Platelet-derived growth factor receptor beta
- PEM
- Pericyte-associated microglia
- PFA
- Paraformaldehyde
- ROI/s
- Region/s of interest
- ROUT
- Robust regression and outlier removal
- RT
- Room temperature
- SFG
- Superior frontal gyrus
- TRITC
- Tetramethylrhodamine
- UEA-1
- Ulex Europaeus Agglutinin I