http://www.bme.cornell.edu/schafferlab

Your brain on Alzheimer's disease: the potential role of slowed blood flow

Chris B. Schaffer

Alzheimer’s disease is the leading cause of dementia in the elderly

Auguste D., first Alzheimer’s patient described by Alois Alzheimer

Alzheimer’s is caused by neuronal loss due to neurotoxic effects of aggregated A-beta peptide

K. Blennow, et al., Lancet (2006)

Alzheimer’s pathology molecular mechanisms

K. Blennow, et al., Lancet (2006)

Alzheimer’s pathology molecular mechanisms

Alzheimer’s is caused by neuronal loss due to neurotoxic effects of aggregated A-beta peptide

A-beta is produced by neurons andcleared through the vasculaturecleared through the vasculature

Blood flow deficits to the brain also observed in Alzheimer’s patients

Blood flow deficits to the brain also observed in Alzheimer’s patients

• 20-30% decreased brain blood flow compared to non Alzheimer controls

• This blood flow decrease could be cognitively important, but the origin remains unclear

We used advanced imaging techniques to study disruptions in microvascular blood flow in mice that are engineered to get

Alzheimer’s disease

Two-photon excitation of fluorescent dyes leads to emission that originates only from the focal volume

Z. Huang, et al., belfield.cos.ucf.edu/one vs two-photon excitation.html

Image is formed by scanning laser focus through the sample and recording fluorescence intensity

Image is formed by scanning laser focus through the sample and recording fluorescence intensity

Image fluorescently-labeled features in brain of anesthetized rodent with glass-covered craniotomy

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Imaging fluorescent blood plasma yields a 3-D cortical “micro-angiography”

In vivo imaging of vasculature and amyloid plaques in AD mouse modelsamyloid plaques in AD mouse models

plaques labeled by methoxy-X04vasculature with intravenous dye injection

Aged APPswe/PS1 mice with craniotomies

Dye labels blood plasma, but not blood cells, allowing identification of flowing vs. stalled vessels

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Fraction of capillaries with stalled blood flow increased to ~2% in mouse models of AD

Temporary stalls that shift between capillary segments, rather than permanent occlusions

2843 capillaries in 6 AD mice2475 capillaries in 4 WT mice

Labeling to distinguish red blood cells, leukocytes, and thrombi as potential cause of stalls

leukocytes: rhodamine-6G and Hoechst

thrombi: rhodamine-6G

red blood cells: unlabeled

In vivo imaging of capillary stalls with rhodamine-6G and Hoechst labeling

red - Texas-Red dextrangreen - rhodamine 6Gblue - methoxy-X04 and Hoescht

Majority of capillary stalls in AD mouse models are caused by leukocyte plugs

How does a single stalled capillary affect blood flow?affect blood flow?

mm/s

N. Nishimura, et al., Nature Methods 3, 99 (2006)

Laser injury to vessel triggers clotting

Map changes in flow after capillary clot

baseline flow post-clot flow

A single stalled capillary causes reduced blood flow in multiple downstream vessel branches

N. Nishimura, et al., Nature Methods 3, 99 (2006)

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Map of blood vessels and amyloidplaques from AD mouseplaques from AD mouse

Location of stalled capillaries

Simulate blood flow changes in capillaries downstream from plugged vessels

Simulate blood flow changes in capillaries downstream from plugged vessels

Simulate blood flow changes in capillaries downstream from plugged vessels

Increases in number of stalled capillaries causes decreases in average cerebral blood flow

2% of capillaries stalled predicts a 30% decrease in flow compared to controls

Leukocyte plugging of capillary segments could explain blood flow deficits observed in AD

• In humans, blood flow reduced by 20-30% compared to non-AD age-matched controls [1]

• In mouse models of AD, flow reduced by ~30% compared to wild-type animals [2]

1. Farkas E, Luiten PG. (2001) Cerebral microvascular pathology in aging and Alzheimer's disease. Prog Neurobiol 64:575-611

2. Niwa K, Kazama K, Younkin SG, Carlson GA, Iadecola C. (2002) Alterations in cerebral blood flow and glucose utilization in mice overexpressing the amyloid precursor protein. Neurobiol Dis 9:61-68

Summary

• 2% of capillaries are stalled in AD mouse models

• Stalls are caused by leukocytes plugging capillary segments

• This rate of capillary stalling could produce ~30% decrease in cerebral blood flow, consistent with observations in humans and mouse models

• Suggests that Aβ aggregates cause vascular inflammation that leads to firm adhesion of leukocytes to the endothelium

• Provides a novel potential target for treatment of blood flow deficits in AD, which could improve cognitive function

Cyclic relationship between vascular stalls and Aβ aggregates as a driver of AD progression

leukocyteplugs

Aβ aggregates

Collaborators

• Cornell

• Dr. Nozomi Nishimura

• Calvin Kersbergen

• Gabriel Otte

• Joan Zhou

• Jeff Beverly

• Elizabeth Slack

• Weill Cornell Medical College

• Prof. Costantino Iadecola

Thanks to William Klunk for donation of methoxy-X04

Acknowledgements

To occlude a small blood vessel, we optically injure the vessel to initiate endogenous clotting cascade

N. Nishimura, et al., Nature Methods 3, 99 (2006)

Femtosecond laser irradiation to produce a clot in a targeted, sub-surface brain capillary

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