Murder or suicide - how does APP/Amyloid beta cause neuronal dysfunction?
Separating cell-autonomous from -extrinsic effects of APP/Ab
The amyloid precursor protein and its derivative, amyloid beta, are intimately associated with the onset and progression of Alzheimer's, yet there are still many basic questions about their role in neuronal dysfunction that remain unanswered because we lack appropriate model systems in which to address them. We are investigating a new viral mosaic APP" transgenic mouse model that allows us to tackle fundamental questions about whether APP and amyloid beta act locally in a single cell or exert their effects between cells to alter neuronal structure and function. We are exploring whether their overexpression in the mature brain has distinct effects from those effects that might be seen during early embryological and post-natal development. Answers to these deceptively basic questions will be critical to understanding how APP/amyloid beta contributes to Alzheimer's pathogenesis and determine how best to target its action therapeutically."
Our study is designed to address a fundamental question in Alzheimer's research: are nerve cells in the brain being killed by murder or suicide? Restated, are neurons succumbing to the effects of proteins that they make themselves, or are they being damaged by protein made by their neighbors? This simple question is surprisingly difficult to address. The transgenic mice commonly used to study the effects of Alzheimer's disease-associated proteins in the brain cannot distinguish whether neuronal damage starts from within the cell or from outside because all of the neurons in these mice make the same proteins. Yet we will need to find the answer to this question in order to design future therapeutics that get to the right place and inhibit the correct target. We are taking advantage of newly developed technology to create a mouse model that will allow us to separate these effects by expressing the disease-related protein in a mosaic pattern within the brain. In this model some cells will carry the protein while others will not. We can then test which population of cells becomes sick -- those with the protein or their neighbors. Answers to this question will determine whether we're looking at a murder or a suicide. In addition to this spatial control over protein expression, the mice also carry a gene that allows us to determine when the Alzheimer's-related protein is active. This feature will help us to determine whether the Alzheimer's-protein acts in the same way in young neurons as it does in mature ones and ensure that changes we ascribe to the disease are not influenced by damage caused by exposure to the protein during development of the brain. Dr. Jankowsky's expertise in developing new mouse models for Alzheimer's disease, and her collaborator's experience with the study's viral technology, are perfectly suited to the challenges of developing this much-needed experimental system. When completed, we will have created the first controllable mosaic transgenic mouse model for Alzheimer's disease, and will have answered several fundamental questions about where and when Alzheimer's-related proteins damage the structure and function of neurons to cause the disease's devastating cognitive symptoms.
Dr. Jankowsky and collaborators want to know whether cells in the Alzheimer’s disease (AD) brain die by murder or suicide. That is, they are testing whether the nerve cells are killed from the outside or from the inside by two proteins—the Alzheimer’s-associated amyloid precursor protein (APP) and a fragment of the protein called amyloid beta (ABeta). They used non-toxic viruses to deliver the proteins into the brains of mice engineered to have AD. In addition, they made the cells containing virus glow fluorescent yellow so they could distinguish which cells expressed APP or ABeta and which did not. So far, they have optimized the delivery method to control how many nerve cells in the brain contain the APP protein. They can also deliver two types of viruses at the same time so that they can look at cells sitting side-by-side that either contain APP or ABeta or do not. Importantly, the viruses allow them to overexpress APP at high levels for several months—enough time for the mice to form amyloid plaques typical of AD. Finally, they were able to image the size and shape of these glowing nerve cells in live animals using high-resolution microscopy. The next step will be to determine whether APP and ABeta destroy a nerve’s structure and function from the inside or outside of the cell.
Kim JY, Ash RT, Ceballos-Diaz C, Levites Y, Golde TE, Smirnakis SM, Jankowsky
JL. Viral transduction of the neonatal brain delivers controllable genetic mosaicism for visualising and manipulating neuronal circuits in vivo. Eur J
Neurosci. 2013 Apr;37(8):1203-20. doi: 10.1111/ejn.12126. Epub 2013 Jan 24.
First published on: April 2, 2010
Last modified on: June 5, 2013