Demonstration of age-related blood-brain barrier disruption and cerebromicrovascular rarefaction in mice by longitudinal intravital two-photon microscopy and optical coherence tomography

Abstract

Age-related blood-brain barrier disruption and cerebromicrovascular rarefaction contribute importantly to the pathogenesis of both vascular cognitive impairment and dementia (VCID) and Alzheimer's disease (AD). Recent advances in geroscience research enable development of novel interventions to reverse age-related alterations of the cerebral microcirculation for prevention of VCID and AD. To facilitate this research there is an urgent need for sensitive and easy-to-adapt imaging methods, which enable longitudinal assessment of changes in BBB permeability and brain capillarization in aged mice, that could be used in vivo to evaluate treatment efficiency. To enable longitudinal assessment of changes in BBB permeability in aged mice equipped with a chronic cranial window, we adapted and optimized two different intravital two-photon imaging approaches. By assessing relative fluorescence changes over the baseline within a volume of brain tissue, after qualitative image subtraction of the brain microvasculature, we confirmed that in 24 month old C57BL/6J mice cumulative permeability of the microvessels to fluorescent tracers of different molecular weights (0.3 kDa to 40 kDa) is significantly increased as compared to that of 5 month old mice. Real-time recording of vessel cross-sections showed that apparent solute permeability of single microvessels is significantly increased in aged mice vs. young mice. Cortical capillary density, assessed both by intravital two-photon microscopy and optical coherence tomography (OCT) was also decreased in aged mice vs. young mice. The presented methods are optimized for longitudinal in vivo assessment of cerebromicrovascular health in preclinical geroscience research.

Age-related decline in circulating IGF-1 associates with impaired neurovascular coupling responses in older adults

“…We also confirmed that age-related impairment of NVC responses is also associated with decreased basal cerebral blood flow, suggesting shared etiology (e.g., endothelial dysfunction [53,54]). Experimental studies suggest that aging is associated with cerebromicrovascular rarefaction [55][56][57], which likely also attenuates cerebral blood flow. Agerelated damage of the neurovascular unit, especially injury of capillary endothelial cells and pericytes, both of which have been suggested to contribute to basal cerebral blood flow as well as neurovascular coupling can underly our clinical observations.…”

Cell non-autonomous regulation of cerebrovascular aging processes by the somatotropic axis

“…The BBB is a functional part of the NVU and is critical for the protection of neurons, maintenance of homeostasis, and the integrity of the brain itself ( 19 , 237 , 238 ). BBB dysfunction is one of the hallmarks of the aging brain, in both humans and animal models ( 19 , 33 , 34 , 239 – 241 ). The BBB comprises brain capillary endothelial cells with support from pericytes embedded in the basement membrane and astrocytes.…”

“…In addition to large vessel disease, age-related VCID is associated with a wide variety of microvascular pathologies ( 9 – 17 ). Microvascular contributions to cognitive decline and dementia include microvascular rarefaction ( 18 – 21 ), impaired endothelial regulation of cerebral blood flow ( 5 , 22 – 30 ), disruption of the blood brain barrier (BBB) ( 19 , 31 – 36 ), decreased neurovascular coupling (NVC) ( 37 – 41 ), cerebral microhemorrhages (CMH) ( 42 – 44 ), lacunar infarcts ( 45 – 49 ), increased pulsatility ( 50 – 53 ) and small vessel disease-related white matter damage ( 54 – 57 ), and amyloid pathologies ( 58 – 62 ). Critically, the severity of age-related increases in microvascular pathological alterations predict cognitive decline in aging ( 44 , 63 , 64 ), leading to great interest in understanding the associated cellular and molecular mechanisms.…”

Advances in brain barriers and brain fluids research in 2021: great progress in a time of adversity

“…Those effects were ameliorated in mice with endothelial specific loss of the complement C3a receptor. Nyul-Toth et al [ 128 ] have performed longitudinal studies in mice using intravital two-photon microscopy and optical coherence tomography to monitor changes in BBB permeability and brain vascularity during aging. They found that the permeability of single capillaries increased with age while capillary density decreased.…”