Pericyte alterations and endothelial activation are partially dissociated processes in human cerebral small vessel disease, defining three distinct microvascular phenotypes across disease severity.
Key Findings
Results
Microvascular density increased with cSVD severity and age specifically in the white matter, while vessel diameter remained stable across severity groups.
Analysis was performed on 11,409 microvascular fragments from post-mortem brain tissue derived from 20 cases.
White matter vessels were less dense and wider compared to cortical grey matter vessels in controls.
Vessel diameter remained stable across cSVD severity groups despite changes in density.
The increase in microvascular density with severity and age was specific to white matter, not grey matter.
Results
PDGFR-β signal, a marker of pericyte coverage, decreased markedly with increasing cSVD severity in both grey and white matter.
PDGFR-β was used as the pericyte marker, assessed via multiplex immunohistochemistry with spectral unmixing and automated image analysis.
The reduction in PDGFR-β signal correlated with both disease severity and age.
The decrease was observed in both cortical grey matter and the underlying white matter.
Intermediate severity groups displayed marked heterogeneity, with vessels exhibiting either preserved or markedly reduced PDGFR-β signal.
Results
Endothelial markers PECAM-1 and VCAM-1 increased significantly with disease severity, reflecting endothelial activation.
PECAM-1 was used as an endothelial cell marker and VCAM-1 as a marker of endothelial activation.
Both PECAM-1 and VCAM-1 signals increased significantly with increasing cSVD severity.
The increase in endothelial markers was parallel to, but not wholly coincident with, the decrease in pericyte marker PDGFR-β.
Results
Unsupervised Gaussian mixture clustering identified three distinct vascular states defined by combinations of pericyte coverage and endothelial activation.
Cluster 1 was characterized by preserved PDGFR-β signal with low endothelial activation.
Cluster 2 was characterized by reduced PDGFR-β signal without endothelial activation.
Cluster 3 was characterized by reduced PDGFR-β signal combined with endothelial activation.
These clusters broadly aligned with neuropathological severity but revealed heterogeneity not captured by post-mortem diagnosis alone.
Results
Pericyte alterations and endothelial activation represent partially dissociated processes in human cSVD, suggesting they do not necessarily co-occur at the level of individual vessels.
The existence of a cluster (Cluster 2) with reduced PDGFR-β but low VCAM-1 indicates that pericyte loss can occur without concurrent endothelial activation.
The heterogeneity in intermediate severity groups indicates vessels can have either preserved or markedly reduced PDGFR-β signal within the same neuropathological category.
The authors describe these as 'partially dissociated processes,' not a single unified blood-brain barrier dysfunction pathway.
The findings are cross-sectional and do not resolve the temporal or mechanistic relationship between pericyte loss and endothelial activation.
Methods
Multiplex immunohistochemistry combined with spectral unmixing and automated image analysis enabled quantitative single-vessel resolution analysis across 11,409 microvascular fragments from 20 post-mortem human brain cases.
The study used post-mortem brain tissue spanning increasing cSVD severity and ageing.
Markers assessed were PECAM-1 (endothelial cells), PDGFR-β (pericytes), and VCAM-1 (endothelial activation).
Both cortical grey matter and the underlying white matter were analyzed.
The quantitative single-vessel approach allowed detection of within-group heterogeneity not visible in bulk tissue analyses.
What This Means
This research suggests that the small blood vessels in the brain deteriorate in distinct ways as cerebral small vessel disease (cSVD) — a major cause of stroke and memory problems — becomes more severe. By examining over 11,000 tiny blood vessel fragments from the post-mortem brains of 20 individuals with varying degrees of disease, the researchers found that two key aspects of blood vessel dysfunction — the loss of cells called pericytes that wrap around vessels, and the activation of the cells lining the vessel walls — do not always happen together. Instead, some vessels lose their pericyte coverage without showing signs of wall activation, while others show both changes simultaneously, suggesting these are separate processes rather than a single unified breakdown.
The study also found that the density of small blood vessels in the brain's white matter increases with both disease severity and aging, even though vessel size stays roughly the same. Using a statistical clustering approach, the researchers identified three distinct 'vascular states' that map onto disease progression, but also revealed significant variation within the same disease stage — meaning that two people with the same diagnosis can have very different patterns of vessel damage at the microscopic level. This heterogeneity was especially prominent in intermediate-severity cases.
This research suggests that cSVD does not follow a single, linear path of vascular damage, and that different types of vessel injury may need to be targeted separately in future treatments. The framework of three vascular states could help researchers design better studies to understand when and why pericyte loss and endothelial activation occur, and whether one leads to the other. The authors note that because this was a cross-sectional study using post-mortem tissue, the order in which these changes happen over time remains to be determined.
Chagnot A, Jaime Garcia D, McQuaid C, Cholewa-Waclaw J, McDade K, Dando O, et al.. (2026). Pericyte loss and endothelial activation define distinct vascular states in cerebral small vessel disease.. Acta neuropathologica. https://doi.org/10.1007/s00401-026-03102-6