A Brief Description of Currently Funded Research Grants 2015-2016

 

Is the entorhinal navigational circuit disrupted in the early stages of Alzheimer’s disease?

Dr. Mark Brandon
McGill University / Douglas Hospital Research Centre
Montreal, QC

Introduction. An early symptom of Alzheimer’s disease is frequent disorientation in familiar settings, often resulting in patients getting lost on their routine commutes to work or home. What pathology in the brain causes this debilitating deficit in spatial cognition? Recent experiments have identified a neural circuit in the entorhinal cortex that is essential for spatial memory and navigation. This circuit contains three navigation-related neuronal types including `grid cells’ that track your movement through space (similar to a GPS), `head direction cells’ that act as the brain’s `internal compass’, and `border cells’ that signal proximity to edges of the environment.

Objectives. We propose to test the hypothesis that a disruption of this entorhinal navigational circuit underlies the spatial memory and spatial cognition deficits reported in Alzheimer’s disease. The first objective is to identify whether the spatial firing patterns of neurons in this circuit undergo a disruption in a mouse model of Alzheimer’s disease. The second objective is to link changes at the neuronal firing level to deficits in spatial memory performance on a radial arm maze and Morris water maze. The combined goal of these objectives is to identify whether this entorhinal navigational circuit needs to be restored in the early stages of Alzheimer’s disease.

Outline of Research. To assess this hypothesis, we propose a semi-longitudinal study to examine the firing properties of grid cells, head direction cells, and border cells throughout the progression of Alzheimer’s-like pathology in the J20 animal model of Alzheimer’s disease. In these mice, human APP is over-expressed with two mutations (Swedish and Indiana) linked to the familial Alzheimer’s disease, driven by the PDGF-β promoter. J20 mice exhibit increased neuronal Aβ starting at the age of six weeks, have spatial memory impairments as early as 3 months, showing deficits on the radial arm maze spatial reference memory task, and exhibit impairments in spatial memory acquisition and retention in the Morris water maze by 6-7 months. To match this time course of pathology, three groups of J20 mice will be chronically implanted with microdrives at 2, 4, or 6 months of age. Each cohort of animals will be monitored for 2-3 months, permitting the characterization of each neuronal type from J20 mice aged 2-9 months. In addition to unit-recordings, all implanted animals will be tested on the Morris water maze to assess spatial memory performance on a weekly basis. Finally, post-mortem analysis of the magnitude and location of Aβ plaque accumulation will be assessed in all animals. This data set will allow a detailed analysis of the relationship between spatial coding, spatial memory deficits, and Aβ plaque buildup in the entorhinal cortex. These data will provide unprecedented insight into the mechanisms that underlie deficits in spatial cognition in Alzheimer’s disease.

Projected benefits and applications of findings. These experiments will help identify whether future efforts should focus on the development of strategies to restore this navigation-supporting circuit in order to re-establish spatial cognition in the early stages of Alzheimer’s disease. We expect that by using the activity of grid cells, head direction cells, and border cells, researchers will be equipped with a reliable high-throughput biomarker of spatial processing in Alzheimer’s mouse models that provides many advantages over the conventional use of purely behavior tasks. This is especially true if the propose experiments reveal that neuronal dysfunction precedes behavior impairments. We expect that our findings will be useful for drug discovery, gene therapy, and stem cell therapy laboratories that can use these neuronal responses to determine whether a candidate approach is effective in ameliorating dysfunction in the entorhinal spatial cognition circuit in Alzheimer’s disease.

Dr. Viviane Labrie
Centre for Addiction and Mental Health
Toronto, ON

Introduction: Alzheimer’s disease is a brain illness that is one of the leading causes of disability in later life, affecting 36 million people worldwide. Since Alzheimer’s disease is partially heritable, researchers trying to understand the causes of this disease commonly search for changes in the DNA sequence. The DNA sequence holds a wealth of biological information, acting like the hardware of a computer for our cells. Scientists use tools to check if the DNA sequence in Alzheimer’s disease patients is different than in healthy individuals. However, there are so many possible changes in the DNA sequence between individuals that these tools would be much improved if the search could be narrowed down to the disease relevant sites.
For this, the epigenetic code could be useful, as it is like the software of our DNA; running the programs held within the hardware. We recently discovered that DNA sequence changes are often predictive of specific patterns in the epigenetic code of the brain. This shows that these two systems are very much intertwined, and we find that DNA sequence problems related to Alzheimer’s disease have a significant capacity to induce epigenetic defects, particularly within enhancers. Enhancers are central to cell function because they deliver the message to genes to turn on at specific time points and cell types. If DNA hardware problems were to produce epigenetic software glitches at enhancers, then this would cause our computer to send emails to the wrong people and we would be turning off our monitor when we mean to open our word processor. DNA sequence and epigenetic defects at enhancers would therefore alter the ability of enhancers to communicate with genes, and this could be critically involved in the biological mechanism of Alzheimer’s disease.

Objective and Research Outline. In this project we ask: could DNA sequence and epigenetic disturbances specifically at enhancers alter brain function to cause Alzheimer’s disease? To test this we will carefully examine the epigenetic code within enhancers located at 1000 DNA sequence changes associated with Alzheimer’s disease. We will map different types of epigenetic marks in the brain, to determine the role of each of these to enhancer function in Alzheimer’s disease. We will survey the two main brain cell types; neurons and glia, to see if one of these is more impacted by enhancer disruption. We will then map the 3-dimensional physical interactions of DNA to determine which genes are affected by the abnormally regulated enhancers. This will reveal the communication breakdown that occurs between enhancers and their target genes in Alzheimer’s disease, which will provide insight into the mechanism by which DNA sequence and epigenetic alterations can lead to this disease.

Project benefits and applications. This research increases the capacity to identify DNA sequence changes that are meaningful to Alzheimer’s disease. The results of our scan of the epigenetic code at enhancers will be like handing a map and a compass to scientists trying to determine which DNA sequence changes are important to Alzheimer’s disease. They will go from having an overload of possible sites to knowing exactly where to focus their research.
Though certain DNA sequence changes are linked with an increased risk for Alzheimer’s disease, the biological basis for these associations is not well understood. By revealing that DNA sequence changes can cause epigenetic abnormalities at enhancers in Alzheimer’s disease, we will have a much better understanding of the biology behind DNA sequence risk factors. Our findings will also identify which DNA sequence changes are most disruptive to brain health. This information can be used to make new tests to predict and diagnose Alzheimer’s disease.
Moreover, this study will decipher the gene pathways implicated in this disease, which will reveal new and important information on the primary causes of Alzheimer’s disease. Current Alzheimer’s disease treatments only alleviate some of the symptoms, but do not prevent or cure this disease. These treatments are more like a band-aid, in that they attempt to mask the illness without actually healing the patient. Truly effective treatments and especially the cure for Alzheimer’s disease will depend on good knowledge of the primary causes of this disease. By providing such insight our study could pave the way for developing effective treatments.

Dr. Leigh Anne Swayne
University of Victoria
Victoria, BC

Introduction: Autism spectrum disorders (ASD) are the most common set of neurological disorders in children (approximately 1 in 132) and are characterized by abnormal social behaviours and intellectual disabilities. Although we know that ASD are caused by abnormalities in the development of the brain, the root cause(s) is not fully understood and there are no known cures. Hence, there is an urgent need to better understand ASD in order to facilitate the development of effective treatments to improve quality of life. One of the things most affected in ASD is the organization and wiring of the brain. My lab has found a new protein called Pannexin 1 that regulates these processes. Pannexin 1 forms pores in the cell membrane that control passage of certain molecules. If we block these pores, or remove Pannexin 1 altogether, the cells extend processes called neurites, structures that are critical for proper organization and wiring of the brain. Together these data suggest that Pannexin 1 inhibits the growth of neurites.

Recently, we discovered a physical interaction between Pannexin 1 and another protein called “collapsin response mediator protein 2” (Crmp2). In contrast to Pannexin 1, Crmp2 promotes the growth of neurites. Notably, Pannexin 1 and Crmp2 have both been recently linked to ASD, but exactly how they are involved is not yet understood. Our preliminary data suggests that during normal brain development, Panx1 ‘keeps the brakes’ on neurite outgrowth by sequestering Crmp2 to prevent the formation of aberrant connections. An appropriately timed developmental decrease in the levels of Pannexin 1 then releases Crmp2 to allow the brain to wire properly.

Objective: In the current proposal, we will investigate how Pannexin 1 regulates neurodevelopment using a Pannexin 1 knockout mouse and by interfering with a new interaction we discovered between Pannexin 1 and Crmp2.

Outline of Research: Aim 1. We will determine whether loss of Pannexin 1 perturbs several aspects of normal brain development. We will accomplish this by examining a comprehensive set of markers for development in Pannexin 1 knockout mice (mice that have the gene for Pannexin 1 removed) in comparison to control mice (mice that express Pannexin 1). We predict that knockout of Pannexin 1 will cause abnormalities in the maturation and wiring of cortical neurons, which will cause defects in brain development. Aim 2. We will determine whether the novel interaction we discovered between Pannexin 1 and Crmp2 is important in brain development. We will accomplish this using a molecular tool we designed to block the interaction. We anticipate blocking the Pannexin 1 interaction with Crmp2 will cause similar impairments in neurodevelopment as seen with the loss of Pannexin 1. If the predicted abnormalities in neuronal growth and development are indeed observed in aims 1 and 2, we will proceed with testing for ASD-like behaviours.

Project Benefits and Applications of Findings: The primary goal of this research is to bridge key gaps in knowledge of the role of these proteins in creating structural changes in brain cells and the connections between them. Successful outcomes of this work will ultimately lay the groundwork for the development of novel therapeutics that could be used to improve health outcomes in patients affected by disorders of brain development like ASD.

Dr. John Vessey
University of Guelph
Guelph, ON

Introduction: Autism spectrum disorder affects larges numbers of individuals in Canada, with diagnosis rates approaching 1 in 80 individuals. With little in regard for treatment options, it is a debilitating disease for those unfortunate to suffer from it. Unlike many diseases, there is not one singe cause. It consists of both genetic causes that are augmented by the environment in which the individual lives. At the genetic level, again, there is not one single gene that gives rise to autism. Rather, it is a combination of many defective genes that results in disease. Understanding how these genes interact with each other is paramount to the development of new treatment paradigms.

Objective: It is becoming apparent that many of the genes responsible for the onset of autism are important for the proper function of neural precursor cells, the stem cells that build the cerebral cortex of the brain. The cerebral cortex is, in evolutionary terms, the newest structure of central nervous system. It is the seat of higher cognitive functions such as cognition, reasoning and social interaction. Even slight alterations in the biology of these neural precursor cells can have catastrophic effects on the developing and adult brain. My goal is to investigate genes linked to the onset of autism with regards to their involvement in neural stem cell biology.

Outline of Research: Using mouse models, I will investigate how brain development is impaired when these genes are rendered defective. The mouse cerebral cortex is both developmentally and anatomically similar to the human cortex. Given their shorter developmental time period, mice are an ideal model for studying the development of the central nervous system. The neural precursor cells that are the focus of this proposal can be readily cultured in a dish, allowing for easy observation of their biology when specific genes are rendered dysfunctional. Also, mice can be altered genetically, allowing for behaviour observations to be studied when genes have been manipulated to mimic those found in individuals suffering from autism.

Projected Benefits: This research will allow for us to gain a thorough understanding of how neural stem cells are regulated by genes implicated in the onset of autism and how their dysfunction causes aberrant development and, eventually, cognitive impairments. The goal is to unravel new insight into brain development and function and, more importantly, identify potential therapeutic targets.