Billy NguyenPranav Singh

Derived from Amyloid Protein Precursor (APP)

Cleaved by Secretases to Amyloid B

not neurotoxic as a monomer

Neurotoxic as plaques and it’s oligomeric form, ADDL

Implicated in the onset of Alzheimer’s Disease

Beta Amyloid

“…physiologically relevant levels of naturally secreted AB interfere with insulin receptor function in hippocampal neurons and prevent the rapid activation of specific kinases required for long term potentiation “

Matthew Townsend, Tapan Mehta, and Dennis J. Selkoe1

ADDL On Insulin Receptors

ADDL has been shown to attack insulin receptors in the dendrites of hippocampal neurons This leads to the loss of IR’s

Fernanda G. De Felicea,b,1, Marcelo N. N. Vieirab,c, Theresa R. Bomfimb, Helena Deckerb,c, Pauline T. Velascoa, Mary P. Lamberta, Kirsten L. Violaa, Wei-Qin Zhaoa,2, Sergio T. Ferreirab, and William L. Klein

ADDL on Long Term Potentiation

Further studies have shown that ADDL can disrupt LTP

This is shown by ADDL induced down regulation ERK, CAMKII, and AKT/PKb

Kinases that are critical in LTP

Insulin to the Rescue

Treatment with insulin has been shown to inhibit some of the detrimental effects ADDL has on neurons

“the mechanism of protection does not involve simple competition between ADDLs and insulin for a common binding site on the neuronal surface, but rather is a signaling-dependent downregulation of ADDL binding sites.” The protection requires insulin receptor activity

This figure shows that insulin and the drug, Rosiglitazone have a neuroprotective effect and prevent ADDLs from binding to and altering the insulin receptors in hippocampal neurons

Rosiglitazone is a drug that activates PPARy, which in turn, increases insulin sensitivity. Rosiglitazone is effect in potentiating the protective effects of insulin on the CNS

T1DM is characterized by lack of insulin while

T2DM is characterized by insulin resistance. Both of which reduce the protection from ADDL

Diabetes Mellitus

The glymphatic system has been discovered to be a

specific route for waste removal from the intestinal space of the CNS

Research shows that the activity of the glymphaticsystem is dependent on sleep/wake cycles

The glymphatics are gaining attention because it is believed that it can protect against Alzheimer's by clearing out beta amyloid from the interstitial space.

GlymphaticsIntroduction

Glymphatic = glia + lymphatic

A possible mechanism of how the brain clearance

occurs

Similar to the lymphatic system

Glymphatic System

Lymphatic system

Glymphatic System

Fluorescent Tracers and Two Photon Imaging Electromyography (EMG) and Electrocorticography

(ECoG)Real time iontophoretic tetramethylammonium

(TMA)

Methods

Fluorescent Tracers and Two Photon Imaging

Use in study: This technique was utilized to detect movement of the CSF into the ISF

Fluorescent markers emit electromagnetic waves (including visible light) when excited by external energy sources

A very fast-response laser is utilized to excite the markers with two photons fired in short succession (within .5 *s)

Similar to normal microscopes a succession of lenses are utilized to magnify the sample

A Photomultiplier tube (similar in concept to a camera) is utilized to capture the sample’s behavior at an extremely high refresh rate

Fluorescent Tracers and Two Photon Imaging

< Example setup from: Deep tissue two-photon microscopyFritjof Helmchen1 & Winfried Denk2-Nature Methods (2005)

< Example of Two Photon Imaging OutputNeurons Stained with Green Fluorescent Protein:http://www.dana.org/Publications/Brainwork/Details.aspx?id=43610

Electromyography (EMG) and Electrocorticography (ECoG)

Uses in study: To determine whether the mice were asleep or awake

Both EMG and ECoG rely on electrodes that capture the electrical activity of cells.

EMG is a needle probe that is applied below the skin and directly into the muscle and sense muscle contractions

ECoG is applied directly on an exposed surface of the brain. It picks up the neuron firing events

Both techniques have waveforms that have been extensively studied

Implementations

ECoG on a human brain:http://www.kurzweilai.net/brain%E2%80%99s-%E2%80%98radio-stations%E2%80%99-have-much-to-tell-scientists

Rat with multiple EMG probes:http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0102-86502008000300007

Real time iontophoretictetramethylammonium (TMA)

Use in study: To determine the volume of the interstitial space

In this method the diffusion of tetramethylammonium is measured through two electrodes that are stuck into the brain,

Plotting the diffusion rate versus time allows for the calculation of the volume of the interstitial space

Two metrics are outputted from this: is the volume coefficient and the or the tortuosity (twistedness) of the plotted curve

In general, the less diffusion of TMA through the interstitial fluid, a greater volume is recorded.

Experimental Setup

Taken from Reference # 17:.C. Nicholson, J. M. Phillips, J. Physiol. 321, 225–257 (1981)

Setup of the electrodes with the background circuit (sensors) utilized

Governing equations the two metrics

Sleep increases the rate of clearance Via: Shrinkage of neurons Increase in volume of interstitial space

Both of which reduce the resistance of the flow of Cerebrospinal fluid.

Effects of Sleep on Glymphatics

Delta waves are low frequency, high amplitude waves that indicate deep sleep.

To ensure that mice were actually alseep/anesthetized during the study, EcOGwas used to measure brain waves. Presence of Delta waves confirmed that the subjects were sleeping.

Norepinephrine (NE) is believed to contribute to the

increased neuron size, and resulting decreased ISP volume.

NE antagonists were used to test this and the results are as follows:

Norepinphrinecontributes to cell size

“AB was cleared twofold faster in the sleeping mice as compared with the awake mice (n =23to 29 mice, P < 0.05, ANOVA with Bonferroni test) (Fig. 3, A and B, P <0.05)”

AWAKE

14.1 +/- 1.8%

SLEEP

23.4 +/- 1.9%

AWAKE

13.6 T 1.6%

K/X

22.7 T 1.3%

AWAKE

14.3 T 5.2%

NE ANTAGONIST

22.6 T 1.2%

Changes to Interstitial Volume

Conclusions

The glymphatic system is believed to offer a mode of waste clearance from the brain

The efficacy of the system changes with the sleep/wake cycle, where it is much faster at clearing the brain during sleep

Sleep is restorative and lack of sleep can lead to cognitive dysfunction

Modifications to the glymphatic system can offer promise in the treatment of Alzheimer’s Disease