Brain pericytes are specialized mural cells embedded within the basement membrane of cerebral microvasculature, strategically positioned between endothelial cells and astrocytes[1]. These cells constitute a critical component of the neurovascular unit, serving as the primary regulators of blood-brain barrier (BBB) integrity, cerebral blood flow, and neurovascular coupling[2]. Pericytes are increasingly recognized as key players in neurodegenerative diseases, with pericyte degeneration documented in both Alzheimer's disease (AD) and Parkinson's disease (PD)[3][4].
Pericytes differ from other vascular cells in several important ways. They have a distinctive morphology with multiple elongated processes that wrap around capillary endothelial cells, forming peg-and-socket junctions that allow direct cytoplasmic continuity[5]. This unique anatomical positioning enables pericytes to sense neural activity and respond by modulating capillary diameter, thereby coupling neuronal activity to local blood flow—a process known as neurovascular coupling[6].
Pericytes express several distinctive molecular markers that distinguish them from other cell types in the neurovascular unit:
| Marker | Expression | Significance |
|---|---|---|
| PDGFR-β | High | Critical for pericyte development and recruitment |
| NG2 (CSPG4) | High | Surface proteoglycan, used for identification |
| CD146/MCAM | Moderate | Cell adhesion molecule |
| RGS5 | Moderate | Regulator of G-protein signaling |
| α-SMA | Variable | Contractile protein, stress-responsive |
The heterogeneity of pericyte populations has become increasingly apparent, with different pericyte subsets exhibiting distinct morphological and functional properties across brain regions[7].
Pericytes are essential for maintaining BBB integrity through multiple mechanisms[1:1]. During development, pericyte recruitment to nascent blood vessels is driven by platelet-derived growth factor B (PDGF-B) secretion from endothelial cells, and this recruitment is critical for BBB formation[2:1]. Pericytes regulate endothelial tight junction formation and maintenance, controlling the paracellular transport pathway that prevents free passage of molecules between blood and brain.
Pericytes express numerous transporters and receptors that regulate transcellular passage of substances across the BBB[8]. These include:
Pericyte dysfunction leads to increased BBB permeability, allowing plasma proteins and potentially toxic metabolites to enter the brain parenchyma[9].
Postmortem studies consistently reveal significant pericyte loss in AD brain tissue[9:1]. Quantitative analyses demonstrate a 30-60% reduction in pericyte coverage of cerebral capillaries in AD patients compared to age-matched controls[4:1]. This loss correlates with the severity of cognitive impairment and is observed in regions particularly vulnerable to AD pathology, including the hippocampus and prefrontal cortex.
Multiple pathological processes contribute to pericyte loss in AD[10]:
Amyloid-β accumulation: Aβ deposition directly damages pericytes through oxidative stress and inflammatory signaling. Aβ oligomers bind to RAGE on pericytes, triggering mitochondrial dysfunction and apoptosis.
Tau pathology: Hyperphosphorylated tau in neuronal processes can physically damage pericyte-endothelial interactions, disrupting the neurovascular unit.
Chronic hypoperfusion: Reduced cerebral blood flow creates a hypoxic environment that impairs pericyte function and survival.
Neuroinflammation: Activated microglia release pro-inflammatory cytokines (IL-1β, TNF-α) that are toxic to pericytes.
Pericyte dysfunction creates a vicious cycle that accelerates AD progression[8:1]:
While pericyte involvement in PD is less extensively studied than in AD, emerging evidence suggests similar mechanisms[11]:
Protecting or restoring pericyte function represents a promising therapeutic strategy for neurodegenerative diseases[10:1]:
Pericyte dysfunction contributes to vascular cognitive impairment (VCI), often comorbid with AD. The combination of vascular and neurodegenerative pathology produces more severe cognitive deficits than either alone.
Armulik A, Genové G, Mäe M, et al. Pericytes regulate the blood-brain barrier. Nature. 2010. ↩︎ ↩︎
Daneman R, Zhou L, Kebede AA, Barres BA. Pericytes are required for blood-brain barrier integrity during embryogenesis. Nature. 2010. ↩︎ ↩︎
Nikolai PM, Ruff JW, Bieri G, et al. Astrocyte and pericyte interactions in the aging brain and Alzheimer's disease. Glia. 2019. ↩︎
Blixt M, Mero S, Håberg L, et al. Loss of pericytes in the ageing brain and in Alzheimer's disease: a systematic review. Aging Clinical and Experimental Research. 2022. ↩︎ ↩︎
Bell RD, Winkler EA, Sagare AP, et al. Pericytes control key neurovascular functions and neuronal activity. Neuron. 2010. ↩︎
Takano T, Han X, Deane R, et al. Pericyte regulation of cerebral blood flow in health and disease. Journal of Cerebral Blood Flow & Metabolism. 2014. ↩︎
Sagare AP, Bell RD, Zhao Z, et al. Pericyte-endothelial interactions in the aging brain and Alzheimer's disease. Advances in Pharmacology. 2013. ↩︎
Zlokovic BV. Neurovascular pathways to neurodegeneration in Alzheimer's disease. Journal of Cerebral Blood Flow & Metabolism. 2011. ↩︎ ↩︎
Sengillo JD, Winkler EA, Walker CT, et al. Pericyte degeneration and white matter changes in Alzheimer's disease. Nature Neuroscience. 2013. ↩︎ ↩︎
Brown LS, Foster DJ, Michalscheck C, et al. Pericyte dysfunction and neurovascular impairment in neurodegenerative diseases. Nature Reviews Neurology. 2024. ↩︎ ↩︎
Shiow L, Liu Y, Chen J, et al. Pericyte dysfunction in Parkinson's disease models. Brain. 2023. ↩︎