#079 Blood-Brain Barrier Dysfunction in Alzheimer's Disease and Dementia | Axel Montagne, Ph.D.
Dr. Axel Montagne, a group leader at the UK Dementia Research Institute, discusses how vascular dysfunction and blood-brain barrier breakdown are critical common threads in dementias, including Alzheimer's. He highlights early detection opportunities and emphasizes lifestyle factors like vigorous exercise and inflammation control to preserve brain function.
Deep Dive Analysis
18 Topic Outline
Introduction to Vascular Dysfunction in Dementia
Early Blood-Brain Barrier Leakage in Alzheimer's and APOE4
Detecting Blood-Brain Barrier Dysfunction with Biomarkers
Therapeutic Strategies for Blood-Brain Barrier Integrity
Pericyte Vulnerability and Role in Blood-Brain Barrier
Omega-3 DHA Transport and Pericyte Health
Exercise's Critical Role in Preserving Brain Vasculature
Understanding Cerebral Small Vessel Disease Features
Overlap of Alzheimer's and Small Vessel Disease
Blood-Brain Barrier Breakdown and Brain Glucose Metabolism
Fibrinogen's Neurotoxic Impact from Leaky Barrier
Environmental Pollution and Vascular Brain Damage
APOE4's Mechanism of Blood-Brain Barrier Disruption
Alisporavir's Potential to Restore Vascular Function
Blood-Brain Barrier Dysfunction Impairs Toxin Clearance
Cumulative Impact of Hypertension on Brain Health
Obesity and Blood-Brain Barrier Leakage
Future of Vascular Biomarkers for Dementia
8 Key Concepts
Blood-brain barrier (BBB)
The blood-brain barrier is a protective structure formed by brain vessels that meticulously controls the passage of substances from the bloodstream into the brain. It prevents toxic proteins and inflammatory factors from crossing, while facilitating the transport of essential nutrients like glucose and oxygen, crucial for brain energy metabolism and preventing neurotoxicity.
Pericytes
Pericytes are vital protective cells that wrap around the smallest blood vessels, known as capillaries, in the brain. They are essential for maintaining the integrity of the blood-brain barrier, preventing leakages, and regulating blood flow by their ability to constrict and dilate vessels. Their detachment and death are considered early indicators of vascular dysfunction in the brain.
Neurovascular unit
The neurovascular unit is a complex functional system composed of various cell types, including endothelial cells, pericytes, astrocytes, and neurons. These components work in concert to regulate cerebral blood flow and uphold the integrity of the blood-brain barrier, thereby ensuring optimal brain function and health.
Cerebral Small Vessel Disease (SVD)
Cerebral Small Vessel Disease is a significant form of dementia characterized by the dysfunction of the brain's microvessels. This condition manifests with features such as microbleeds, small strokes (lacunes), and white matter hyperintensities, and is distinct from Alzheimer's disease, although it can sometimes co-occur.
White Matter Hyperintensities (WMH)
White Matter Hyperintensities are lesions or bright spots observed on MRI scans within the brain's white matter. These are frequently associated with cerebral small vessel disease, normal brain aging, and Alzheimer's disease, and are linked to leaky blood vessels and damage to myelin sheets and axons.
Cyclophilin A pathway
The cyclophilin A pathway is an intracellular signaling cascade within pericytes that becomes activated in individuals carrying the APOE4 gene variant. This activation leads to the increased expression and release of Matrix Metalloproteinase 9 (MMP9), and blocking this pathway has shown potential in restoring blood-brain barrier function.
Matrix Metalloproteinase 9 (MMP9)
MMP9 is an enzyme produced and released by pericytes and endothelial cells, with elevated levels observed in APOE4 carriers and following a stroke. This enzyme plays a detrimental role by disrupting the tight junctions between endothelial cells and degrading the basement membrane, both of which contribute to the breakdown and leakage of the blood-brain barrier.
Fibrinogen
Fibrinogen is a protein typically found in the blood, crucial for coagulation and inflammatory responses. When the blood-brain barrier becomes leaky, fibrinogen can aberrantly enter the brain, where it acts as a neurotoxin to neurons and oligodendrocytes, contributing to white matter damage and activating brain-resident immune cells (microglia), thereby driving neuroinflammation.
13 Questions Answered
Many dementias, including Alzheimer's and small vessel disease, share an early vascular component, specifically the dysfunction and leakiness of the brain's blood vessels.
The blood-brain barrier maintains brain health by regulating glucose and oxygen transport, preventing toxic proteins and inflammatory factors from entering the brain, and playing a role in brain energy metabolism.
Yes, using advanced MRI techniques and new biomarkers in blood or cerebrospinal fluid, vascular problems like blood-brain barrier leakiness can be detected in cognitively normal individuals, including APOE4 carriers, potentially 10 or more years before cognitive decline.
Targeting amyloid alone has yielded mixed results because vascular dysfunction often occurs very early and independently of amyloid accumulation, and a leaky blood-brain barrier can itself impair the clearance of amyloid.
Pericytes are crucial cells that maintain the integrity of the blood-brain barrier and regulate blood flow; their detachment and death, which accelerate in aging and dementia, lead to barrier leakage and reduced blood flow.
In APOE4 carriers, the APOE4 protein has a different affinity for the LRP1 receptor on pericytes, triggering a cascade involving cyclophilin A and MMP9, which then leads to blood-brain barrier breakdown.
Regular, vigorous exercise that achieves a high heart rate helps maintain the integrity of the brain's tiny blood vessels (capillaries), preventing them from constricting, collapsing, and disappearing, which in turn preserves surrounding neurons and brain function.
SVD is a major form of dementia characterized by problems with the brain's microvessels, leading to microbleeds, small strokes (lacunes), and white matter hyperintensities, and it is largely independent of amyloid plaques, which are hallmarks of Alzheimer's.
Chronic hypertension, especially if sustained over many years from a younger age, can stiffen blood vessels, impair pericyte function, and accelerate blood-brain barrier breakdown, increasing the risk of cognitive decline and white matter damage.
Yes, a dysfunctional blood-brain barrier can reduce the transport of glucose into the brain, partly due to decreased GLUT1 transporters, which is a key feature of impaired brain energy metabolism seen in dementia.
When the blood-brain barrier is leaky, fibrinogen (a blood coagulation protein) can enter the brain, where it is neurotoxic to neurons and oligodendrocytes, contributes to white matter damage, and activates brain-resident immune cells (microglia), thereby driving neuroinflammation.
An experimental hepatitis C drug, alisporavir (which blocks cyclophilin A), has been shown in APOE4 mice to restore vascular function, reduce neuronal damage, and improve cognitive problems by sealing the blood-brain barrier.
If the blood vessels are dysfunctional and the blood-brain barrier is leaky, the transport systems responsible for clearing waste products like amyloid-beta from the brain (e.g., via LRP1 receptors) are impaired, leading to toxin accumulation.
9 Actionable Insights
1. Engage in Vigorous Exercise
Engage in regular, ideally vigorous exercise that achieves a high heart rate to support the vascular system, prevent tiny blood vessels from collapsing, and maintain healthy brain function, especially if prone to cognitive decline.
2. Control Blood Pressure Early
Prioritize early blood pressure control, particularly in younger adulthood (30s-40s), as sustained hypertension over many years is a critical cumulative exposure factor that promotes white matter damage and accelerates cognitive decline.
3. Ensure Adequate Omega-3 DHA
Ensure adequate intake of omega-3 DHA, as it supports blood-brain barrier integrity, helps resolve inflammation, and may prevent white matter dysfunction and reduce fibrinogen levels.
4. Reduce Chronic Inflammation
Adopt a healthy lifestyle that reduces chronic inflammation, as inflammation is a central pillar of aging and neurodegenerative diseases, leading to vascular dysfunction, pericyte detachment, and blood-brain barrier leakage.
5. Maintain Healthy Weight
Maintain a healthy weight and avoid obesity, as obesity is linked to gray matter atrophy in critical brain regions and its effects on the brain mimic those of Alzheimer’s disease, also associated with higher levels of pro-inflammatory markers impacting barrier function.
6. Avoid Chronic Heavy Alcohol
Avoid chronic heavy alcohol consumption, as it impacts vascular function, leads to a leakier blood-brain barrier, and increases inflammation, which impairs pericyte functions and can accelerate dementia development.
7. Reduce Air Pollution Exposure
Reduce exposure to air pollution and airborne particles, potentially by using filters or masks in highly polluted areas, as pollution causes rapid blood-brain barrier breakdown and pericyte degeneration.
8. Practice Regular Sauna Use
Consider regular sauna use, ideally 4-7 times a week, as it is associated with a significantly lower dementia and Alzheimer’s risk and offers physiological benefits comparable to moderate aerobic exercise for vascular function.
9. Lower High Homocysteine
Lower high homocysteine levels, potentially through supplementation with B6, B12, and folate, as high homocysteine is associated with brain dysfunction and dementia, and lowering it can improve cognition and blood-brain barrier markers.
5 Key Quotes
Exercise is the number one thing. If you're prone to go to cognitive decline because, let's say, you have a major genetic risk, but if on top of that you don't exercise, you're going to accelerate, as we know from study.
Dr. Axel Montaigne
The commonality about all these dementias is they have a vascular component that is quite early in the disease, and we want me as a lab and different groups in the world to try to understand how vascular dysfunction contribute to dementia.
Dr. Axel Montaigne
If we fix the blood vessels, we may not be able to cure, that's a big word, cure Alzheimer's disease, but at least we will be able to postpone the symptoms by quite a few years, for sure, which is a big deal.
Dr. Axel Montaigne
The whole idea of different labs in the world is to make sure that these pericytes wrapping the smallest vessels in the brain don't detach. They have to stay there to maintain the integrity and to avoid leakages.
Dr. Axel Montaigne
If your brain is full of plaques, it's probably too late already. So that's the importance of the research we do right now.
Dr. Axel Montaigne
1 Protocols
Alisporavir Treatment in APOE4 Mice
Dr. Axel Montaigne- Utilize humanized APOE4 mice that exhibit reduced brain blood flow, a leakier blood-brain barrier, and cognitive problems.
- Administer the cyclophilin A inhibitor (alisporavir, DebuO025) to the APOE4 mice daily for one month.
- Observe for restoration of vascular function, tight junctions, pericyte coverage, reduced neuronal damage, and improved cognition.