Berislav V. Zlokovic

Alzforum Webinar Feb 17 2015

Leaky Blood-Brain Barrier a Harbinger of Alzheimer's?

Courtesy of Zlokovic lab

Neuronal computation and normal functioning of

the CNS requires tight control of the chemical

composition of the neuronal ‘milieu’ that is

maintained by the BLOOD-BRAIN BARRIER.

Zlokovic, Nat Rev Nsci, 2011

Brain endothelial cells and pericytes form the

BBB, which limits entry of neurotoxic plasma-

derived proteins, circulating metals, red blood

cells and leukocytes into the brain.

Blood-brain barrier breakdown in disease

Studies in Tg models have shown that a chronic BBB breakdown leads to

accumulation of blood-derived neurotoxic proteins in the CNS (e.g., fibrin,

thrombin, hemoglobin, free iron, plasmin) causing progressive

neurodegeneration with loss of neurons mediated by direct neuronal toxicity,

oxidant stress and/or detachment of neurons from the extracellular matrix.

Pericyte-deficient mice: a small vessel disease model -PDGFRb-PDGF-BB

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Age (months):

1 mo Pdgfrb+/-8 mo Pdgfrb

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16 mo Pdgfrb+/-Pdgfrb

+/+

50 mm 50 mm 50 mm20

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Pdgfrb+/+ 8 mo Pdgfrb+/-

16 mo Pdgfrb+/-

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20 mm 20 mm 20 mm 20 mm

Capillary degeneration 1 moBBB breakdown 1 mo

Pdgfrb+/+

8 mo Pdgfrb+/-

1 mo Pdgfrb+/-

16 mo Pdgfrb+/-

50 mm 50 mm 50 mm 50 mm

2-4 mo Pdgfrβ+/+ 2-4 mo PdgfrβF7/F7Perfusion deficit 1 mo

Normal neuronal phenotype 1 mo

Loss of white matter fibers at 2-4 mo

Loss of hippocampal neurons at 6-8 mo

Bell et al., Neuron, 2010

Armulik et al., Nature 2010

Daneman et al., Nature 2010

Blood-brain barrier breakdown in Alzheimer’s disease

Post-mortem studies have shown BBB damage in AD• Accumulation in the hippocampus and cortex of blood-derived proteins

(e.g., immunoglobulins, albumin, fibrinogen, and thrombin)

• Degeneration of pericytes

Brain imaging studies

• Microbleeds and accumulation of iron in AD

• Particularly in the hippocampus

CSF studies (increased Qalb - CSF/plasma albumin ratio)

• Associated with vascular risk factors, white matter lesions, vascular dementia and

vascular disorders (e.g., hypertension, diabetes, ischemic heart disease)

• In all dementias – AD and vascular

• In individuals at genetic risk for AD (i.e., APOE4)

• Mild cognitive impairment (MCI)

Ryu and McLarnon, J. Cell. Mol. Med., 2009

Fiala…..Vinters, J., Eur. J. Clin. Invest., 2002

Cortes-Cantelli et al., J Alzheimer’s Dis., 2012

BBB breakdown in Alzheimer's’ disease: postmortem brain tissue studies

Pericyte degeneration and BBB breakdown in post-mortem AD brain tissue Sengillo, Winkler….Zlokovic (Brain Pathology 2013)

Hulltman et al., JCBFM, 2013

Postmortem brain tissue studies in Alzheimer’s disease

– accelerated BBB breakdown in APOE4 carriers

Halliday, Rege et al., JCBFM, 2015 in press

At what stage BBB breakdown occurs in the living human brain and

whether it contributes to cognitive impairment?

Early neuroimaging attempts to measure the BBB permeability Ktrans constant

in MCI and AD patients failed to detect significant changes in BBB integrity.

These studies might have been hampered by their relatively long time resolution and

the semi-quantitative nature of their analyses.

More recent studies acquired at higher field strengths and using more sophisticated

kinetic modeling have determined that the Ktrans of healthy BBB is low but not zero,

and detected differences in the white matter in patients with multiple sclerosis.

Montagne et al., Neuron 2015 developed an advanced method using • individual arterial input function (AIF)

• improved spatial resolution

• improved SNR (signal-to-noise) ratio

• new software ‘ROCKETSHIP’

• simultaneous measurements of BBB integrity in different gray and white matter regions

Dynamic contrast enhanced MRI 64 subjects of various ages with no cognitive impairment (NCI), mild

cognitive impairment (MCI) and multiple sclerosis (MS) without history of

cognitive complaints were injected with gadolinium-based contrast agent

(MultiHance 0.05 mmol/kg).

Patlak unidirectional linear

analysis

KtransTissue (CNS), Ct

Blo

od

, C

p

𝐶𝑡 𝑡 = 𝐾𝑡𝑟𝑎𝑛𝑠 0

𝑡

𝐶𝑝 𝑢 𝑑𝑢 + 𝑣𝑝𝐶𝑝 𝑡

Modified DCE-MRI protocol +

post-processing imaging (homemade

software)

Montagne et al., Neuron 2015

Dynamic MRI

Common Carotid Artery (CCA)

Individual Arterial Input Function (AIF)

Extensive simulation results (Barnes et al., Magnetic Resonance Med., in revision)

suggests that the present Patlak model using AIF individual curves can accurately

determine Ktrans in the presence of various blood volumes, blood flows, and noise.

Blood-Brain Barrier Breakdown in the Aging Human Hippocampus in

NCI

• improved spatial resolution

• improved SNR ratio

• new software ‘ROCKETSHIP’

Aging effect- Cognitively normal participants -

a- CA1; b- CA3; c- Dentate Gyrus

BBB breakdown during normal aging

begins in the hippocampus.

Montagne et al., Neuron 2015

Blood-Brain Barrier Breakdown in the Hippocampus

worsens in MCIAge-matched NCI and MCI participants were evaluated using the Uniform Data Set (UDS) and

additional neuropsychological tests: California Verbal Learning Test, block design, letter-number

sequencing, letter fluency, and token test

Accelerated BBB breakdown in

the hippocampus may

contribute to cognitive

impairment.

Montagne et al., Neuron 2015

Hippocampus volume and lateral ventricular volume

SMP8 was used to segment T2-weighted images

BBB breakdown before atrophy

Montagne et al., Neuron 2015

sPDGFRβ, a marker of cell injury to BBB-associated pericytes

NCI, older

MCI

Increased Qalb and CSF levels of sPDGFRb , a pericyte injury marker,

in MCI vs. NCI subjects correlate with an increase in Ktrans BBB

permeability values

Montagne et al., Neuron 2015

sPDGFRb is elevated in CSF in pericyte-deficient mice and Tg2576 mice that both show

progressive pericyte degeneration by brain tissue biomarkers analysis

Pericyte-deficient mice

Mouse model of AD

Montagne et al., Neuron 2015

CSF biomarkers in MCI compared to age-matched NCI• Increased Qalb CSF/plasma quotient and sPDGFRb

• No changes in endothelial biomarkers, inflammatory response, Ab or

tau

Neurovascular Unit

CSF biomarkers of cell- and system-specific injury

Montagne et al., Neuron 2015

Small vessels disease - a target for mutifactorial pathogenesis of Alzheimer's’ disease and dementia

Modified from

Videoabstract: Montagne……Zlokovic, Neuron, 2015

Blood-brain barrier breakdown in the aging hippocampus

Highlights

High resolution MRI analysis of regional BBB permeability in the living

human brain.

BBB breakdown during normal aging begins in the hippocampus, a

region critical for learning and memory.

BBB breakdown in the hippocampus worsens with mild cognitive

impairment and correlates with injury to BBB-associated cell pericyte.

Montagne et al., Neuron 2015