The role of apolipoprotein E4-canonical Wnt pathway crosstalk at the blood-brain barrier in Alzheimer’s disease
Dr. Ayman ElAli
Introduction: Alzheimer’s disease (AD) is a progressive neurological disorder that causes the degeneration of brain’s nerve cells. The causes of AD are still not fully understood, thus hindering the development of efficacious treatments that can cure, or at least delay disease onset. Historically, research in the field emphasized on studying brain’s nerve cells. Recently, it was demonstrated that destabilization of the cerebral blood vessels, which decisively supports the survival of brain’s nerve cells, causatively contributes to AD initiation and progression. The destabilized cerebral blood vessels deprive the brain from nutrients, and alter the removal of toxic amyloid-beta (Aβ) peptides leading to its aggregation, which constitute with tau protein aggregation the main pathological hallmarks of AD. The mechanisms underlying cerebral blood vessels destabilization are not fully characterized. Recent reports have demonstrated that the apolipoprotein E gene variant ɛ4 (ApoEɛ4), which constitute the main genetic risk factor for AD, destabilizes the cerebral blood vessels via non-identified mechanism.
Objectives: Our recent work has demonstrated that a specialized mechanism called canonical Wnt pathway, which plays a crucial role in forming and stabilizing the cerebral blood vessels during embryogenesis, is deactivated in AD. Our findings data are suggesting that the pathway is progressively deactivated during ageing – a major risk factor for AD – in a mouse model for AD. Furthermore, we found that ApoEɛ4 specifically deactivates the pathway in cells that from the cerebral blood vessels. Using post-mortem human brain samples, we found that the pathway is deactivated in the cerebral blood vessels of AD patients. Importantly, pathway deactivation positively correlates with the duration of symptoms and is exacerbated in patients carrying ApoEɛ4. As such, the project aims to, a) assess whether ApoEɛ4 destabilizes the cerebral blood vessels by specifically deactivating the canonical Wnt pathway, and b) test whether restoration of the cerebral blood vessels stability via canonical Wnt pathway activation attenuates AD progression and whether ApoEɛ4 can affect this process.
Outline of research: The defined objectives will be achieved by using state-of-the-art approaches and techniques, as follows: a) Aim 1: We will assess whether canonical Wnt pathway deactivation is required for ApoEɛ4-mediated cerebral blood vessel destabilization. For this purpose, we will use a novel transgenic mouse model that express the human ApoEɛ4 variant and in which the activity of the pathway can be genetically restored in the cerebral blood vessels. As the pathway is genetically activated in these mice, it enables us analyzing if ApoEɛ4 mediates its effects specifically through the pathway. We will investigate how ApoEɛ4 affects the expression of specific genes regulating the stability and function of cerebral blood vessels during ageing. b) Aim 2: We will test whether the pharmacological activation of canonical Wnt pathway stabilizes the cerebral blood vessels and attenuates AD progression dependently upon ApoEɛ4. For this purpose, we will use a novel transgenic mouse model for AD in which the human ApoEɛ4 is expressed. We will activate the pathway using drugs that are evaluated in clinical trials in other medical conditions.
Projected benefits and applications of findings: Our proposed project will have a number of benefits for AD. We anticipate that early deactivation of the canonical Wnt pathway by ApoEɛ4 will destabilize the cerebral blood vessels progressively over ageing. Thus, the expected results will provide new insights into a previously non-described pathological role of ApoEɛ4 in AD. Furthermore, we anticipate that pathway activation using potent drugs will restore the stability of the cerebral blood vessels thus providing the basis for the development of novel therapeutic interventions for AD. As the drugs that will be tested in this proposal are already evaluated in clinical trials in other medical conditions, the proposed pharmacological interventions could rapidly be translated to AD patients without the necessity of extensive preclinical drug development and safety studies. As such, the translation of our results from bench to bedside is warranted.
Contribution of Cerebrovascular Deficits to the Pathophysiology of Autism Spectrum Disorders.
Dr. Baptiste Lacoste
Ottawa Hospital Research Institute
Introduction: Autism spectrum disorders (ASD) are recognized as a group of complex disorders of the child’s development, affecting language, motor skills and social interactions, with manifestations of overly focused interests and repetitive behaviors. The causes of ASD are still enigmatic, but scientists agree that they include both environmental and genetic triggers. Certain anomalies in the genome (mutations) have been identified as possible causes for autism, some of which lead to a loss of DNA (deletion), the most common of which is known as the “16p11.2 deletion”. These mutations are associated with symptoms such as, but not limited to, delays in the maturation of neurons, altered communication between these cells, and increased rates of brain growth. About 1% to 2% of the children worldwide have been identified with ASD, and despite intense research efforts, the causes of ASD remain mysterious.
Brain maturation and function heavily depend on a steady supply of oxygen, glucose and nutrients from the blood stream. But the brain lacks efficacy in storing the energy that is necessary to sustain its function. As such, the brain is particularly vulnerable to failures of the vascular system. Key vascular features ensure proper brain maturation: the growth of blood vessels, the maintenance of blood vessel permeability, and the regulation of blood flow in these vessels. Early life impairments in one or several of these vascular features will automatically alter the normal course of brain development. Surprisingly, despite the wealth of knowledge on the neuronal underpinnings of ASD, very few studies have investigated the contribution of the brain vasculature to this group of disorders. A postmortem study using brains of young autistic patients pointed to impairment in angiogenesis, biological process through which new vessels are formed. In these brains, angiogenesis seemed to persist after an age when it normally decreases dramatically. Also, few studies suggested a link between ASD and reduced cerebral blood flow, which might lead to brain hypoperfusion. But these observations have neither been thoroughly verified, nor tested in animal models of ASD. Hence, involvement of the brain vasculature to the onset and/or progression of ASD remains to be elucidated.
Objective: We propose to address this gap of knowledge by developing an innovative research program divided into two main objectives: i) To thoroughly examine the health of the brain vasculature in a genetically-engineered animal model of ASD, using a mouse that possesses the 16p11.2 deletion; and ii) To investigate the consequences on brain development when the 16p11.2 deletion only affects the cells that constitute the blood vessels (i.e. endothelial cells). By following these independent objectives, our overarching goal is to test two fundamental questions that stay unanswered to date: 1) How does the brain vasculature “react” or “behave” in the ASD brain? And 2) What role(s) do vascular deficits play in the development of ASD?
Outline of Research: In pursuing the first objective, our well-established methods will allow us to assess the impairments of cerebro-vascular structure (angiogenesis) and function (blood flow) in a validated ASD mouse model harboring the 16p11.2 deletion constitutively in all cells. Then, to conduct our second objective, we will test whether ASD-associated neuronal deficits result, at least in part, from vascular deficits, by using a mouse model harboring the 16p11.2 deletion selectively in endothelial cells. For this second aim, collaborations were set up with experts in neurophysiology and neuroimaging to help us to detect fine neuronal responses to ASD-related vascular defects.
Projected benefits and applications of findings: The research program that we propose will provide novel insight into the involvement of brain blood vessels in ASD, and into how these blood vessels control critical features of brain organization and function in brain regions that have been involved in ASD. The proposed research plan will also position us to address long-term goals of even further investigating the vascular underpinnings of ASD at a mechanistic level. Identification of new cellular and molecular players in ASD pathogenesis represents an essential pre-requisite for the development of transformative therapeutic strategies, hence directly benefitting the Canadian population.
The role of estrogen on brain insulin signaling in obese insulin resistant female mice.
Dr. Rebecca MacPherson
St. Catharines, ONIntroduction: Women represent 72% of Canadians living with Alzheimer’s disease (AD). This high prevalence of AD in women has been attributed to the sharp reduction in estrogen levels during menopause. One of the pathological hallmarks of AD is the aggregation of small peptides (short chains of amino acids) in the brain, known as beta-amyloid peptides. These peptides are detrimental to neuronal networks and leads to neuronal death and dysfunction. The mechanisms leading to the accumulation of these peptides are multifaceted. My lab aims to understand the how these brain beta-amyloid peptides are produced, accumulated, cleared, and degraded. Beta-site amyloid precursor protein cleaving enzyme 1 (BACE1) initiates amyloid precursor protein processing leading to the production of beta-amyloid peptides. However, the sub-cellular mechanisms that regulate the expression, activity, and turnover of BACE1 in the brain are unknown. We have recently reported that high fat feeding of male mice results in altered brain insulin signaling and increased BACE1 activity. We further demonstrated that one bout of exercise leads to a recovery of brain insulin signaling with declines in BACE1 content and activity in high fat fed male mice. However, the majority of mechanistic research utilizes male models and our understanding of the role that estrogen may play in attenuating or exacerbating the pathological features of AD are largely unknown.Objective: The purpose of the current research is to examine a role for estrogen in the cellular and molecular pathways associated with disturbed brain metabolic signaling with a primary focus on insulin signaling. To examine this over the next three years we will: 1) examine the direct effect of estrogen on brain insulin signaling; 2) determine if the loss of estrogen accelerates the alterations in insulin signaling and BACE1 content/activity in female mice fed a high fat diet; and 3) determine if exercise rescue the altered insulin signaling in female mice with and without the presence of estrogen.Outline of Research: Over a series of three studies we will use a combination of tissue culture techniques in combination with in vivo diet and exercise treatments in wild type female mice. Our tissue culture experiments will examine the direct effects of estrogen on insulin signaling in the prefrontal cortex and hippocampus of lean and obese mice. To examine the in vivo role of estrogen on brain insulin signaling female mice will undergo either bilateral ovariectomy (model postmenopausal women) or SHAM surgery. Finally, we will determine if acute exercise rescues altered insulin signaling in female mice depleted of estrogen. These approaches will provide an outstanding training environment for undergraduate and graduate students in my lab. It is my overall hypothesis that estrogen can directly affect brain insulin signaling and that the loss of estrogen will exacerbate high fat diet induced changes in neural insulin signaling and increases in BACE1 activity/content and beta-amyloid peptide formation in the brain.Projected Benefits and Application of findings: The results of these investigations will greatly increase our fundamental understanding of the processes that underlie how the brain responds to physiological stressors such as high fat feeding and exercise. Information gained from these studies is valuable in terms of both understanding the underlying cellular mechanisms leading to declines in BACE1 but also in terms of designing evidence based preventative or therapeutic interventions for the growing proportion of our population who are at elevated risk for AD and related dementias. These results will provide the foundation for future work aimed at elucidating the underlying mechanisms and therapeutic efficacy of nutrition and exercise interventions to improve neural health outcomes in male and female models of obesity and type 2 diabetes with translation relevance to preclinical/clinical populations.
The Roles of Glyoxalase 1 and Maternal Diabetes in Neuronal Morphogenesis: A Mechanism for the Gene-Environment Interaction in Autism
Dr. Guang Yang
University of Calgary
Introduction: Growing evidence indicates that complex neurodevelopmental disorders, such as autism spectrum disorder (ASD), have roots in prenatal development. Despite recent advances in identifying numerous genetic and prenatal environmental risk factors for ASD, how these factors cause abnormal neural development and subsequent cognitive impairment remains largely unknown. In this regard, defects in neural circuit assembly are thought to underlie cognitive dysfunction in ASD, and therefore, the research emphasis has been placed on the understanding of mechanisms that disrupt the formation and connection of synapses, the last steps of neuronal development to wire up the brain. However, recent human studies suggest that pathological perturbations in ASD patients may occur even at an earlier developmental stage when newborn neurons undergo morphological remodeling and migrate to their destination before they make synaptic connections. Nonetheless, little is known about the mechanisms by which ASD risk factors alter these neuronal developmental events. This proposal is to understand the molecular mechanisms that when deregulated in ASD lead to abnormal neuronal morphogenesis and migration and, ultimately, cognitive dysfunction in later life. In this regard, we have recently gained exciting insights into such mechanisms by studying an ASD susceptible gene Glyoxalase 1 (GLO1) and an environmental risk factor for ASD, maternal diabetes. Importantly, our initial work in the mouse model suggests that maternal diabetes converges on the GLO1 pathway to influence neurodevelopment. We thus hypothesize that ASD-associated perturbations of GLO1 and maternal diabetes may interact and have a profound impact on neuronal morphogenesis during brain development and, ultimately, cognitive function in offspring.
Objective: In this proposed study, we will test this hypothesis and specifically ask: 1) if and how the ASD-relevant genetic perturbation of the GLO1 pathway regulates early neuronal development, focusing on the morphological transition and migration of newborn neurons; 2) if the gene-environment interaction may increase penetrance of neurodevelopmental deficits and long-term cognitive dysfunction relevant to ASD; 3) if targeting the GLO1 pathway might restore neuronal development and enhance functional outcome in affected offspring.
Outlines of Research: To address these questions, we will use the mouse cerebral cortex as the model system. We will combine both in vitro and in vivo approaches to assess the role of GLO1 in normal and abnormal neuronal morphogenesis in the developing cortex. Using a genetic mouse model for gestational diabetes and a GLO1 mutant mouse line, we will further investigate the ASD-relevant interaction of maternal diabetes and GLO1 deficiency in neuronal development in offspring. Finally, we will test if ASD-relevant perturbation of brain development and function in offspring might be alleviated by maternal supplementation with vitamin B6 that is known to act against the cellular stress caused by a defective GLO1 pathway.
Projected Benefits: This proposed study will provide novel insights into the molecular mechanisms underlying early neuronal developmental abnormalities in ASD. Importantly, with a better understanding of the ASD-relevant interaction between maternal diabetes and genetic vulnerability, this proposed study will shed light on novel strategies for early diagnosis and prevention of ASD in high-risk populations by controlling adverse prenatal environmental factors. It will also provide novel insights into ways for developing in utero therapeutic approaches to improve cognitive outcomes of affected offspring. This proposed research will have significant clinical and public health benefits with regard to the improvement of maternal and child health in the long-term.