THE FORMATION OF ALZHEIMER’S PLAQUES IN SYNTHETIC MEMBRANES

Jennifer Tang, Richard Alsop, Matilda Backholm, Hannah Dies, and Maikel C. Rheinstädter

Laboratory for Membrane and Protein DynamicsMcMaster University, Hamilton ON

CAP 2015, University of Alberta, Edmonton AB

ALZHEIMER’S IN THE BRAIN

Neurotoxic plaque made of amyloid-beta aggregates

Alzheimer’s is a type of dementia that causes problems with memory, thinking and behaviour.

One of the hallmarks of Alzheimer’s disease are Amyloid-Beta plaques that are neurotoxic.

Brain of Alzheimer’s patient Amyloid-β (1-

42)

Amyloid-β (25-35)

50μm

kurzweilai.net

100μm

PROTEIN-PROTEIN INTERACTIONS

Positive Curvature

Negative Curvature

Membrane mediated elastic interaction

The curvature of the membrane depends on membrane composition which affects the plaque formation

properties

RESEARCH QUESTIONS

1. Do Alzheimer's plaques form in synthetic membranes? If so, under what conditions do they form?

2. What is the structure of these plaques?oMicroscopy (Surface)o X-ray diffraction (Inside)

Alzheimer’s plaques depend on

1. Cholesterol level

2. Diet

3. Hormones

4. Protein concentration http://webneel.com/

SYNTHETIC “ALZHEIMER’S MEMBRANES”

Saturated: 50mol% Unsaturated: 50 mol% Charged: 3 mol%-Amyloid-b: 1-3mol%

POPC has one saturated tail and one unsaturated tail

DMPS is charged

Hydrophobic tails

Hydrophilic head groups

SYNTHETIC MEMBRANE PREPARATION

Multi-lamellar, solid supported synthetic membranes

MICROSCOPY

POPC/DMPS POPC/DMPS 20%Aβ

No plaques formed

Plaques formed

0.1mm

0.1mm

At 10 mol%, plaques

start appearing

0 mol% 20 mol%

PLAQUE SIZE AND DENSITY

Average plaque size: 11.05 µm

59 ± 3 plaques/mm2

Average plaque size: 10.91 µm

920 ± 64 plaques/mm2

Plaque size is independent of protein concentration

MOLECULAR STRUCTURE USING X-RAYS

PEPTIDE SIGNALS10% Amyloid-Beta

20% Amyloid-Beta

50% : 50%

ANGULAR DISTRIBUTION

Membrane Tailsa-Helices

b-Sheets

Membrane Curvature

ORIENTATION AND INTENSITY

PROPOSED PLAQUE MODEL

11 mm

• One type of plaque found in 10mol% and 20mol% samples with diameter ~11 µm

• Plaques are embedded in membranes

• Contain a mixture of a and b-peptides

CONCLUSIONS

Alzheimer’s patient Synthetic Alzheimer’s Membrane

• Alzheimer's senile plaques form in synthetic membranes concentrations 10mol% or more

• Two distinct protein conformations (a-helices and b-sheets)

• Synthetic membranes may be used as model system for in vitro drug testing in the future.

kurzweilai.net

100μm

ACKNOWLEDGEMENTS

NETLOGO SIMULATION

Short range interaction

Long range interaction

REFLECTIVITY MEASUREMENTS:FROM RECIPROCAL SPACE TO REAL SPACE

Fourier analysis to determine electron density:

• ρ(z) is the electron density perpendicular to the plane of the membrane

• ρw is the electron density of water (0.22 e/A3 )

• F is the form factor• I is the integrated intensity of a Bragg

peak• v is the phase (+/- 1)• dz is the spacing of the bilayers

Bragg’s Law: