A Brief Description of Currently Funded Research Grants 2021 – 2022

Investigating altered cortical sensory processing in autism spectrum disorder

Dr. Allen Chan
University of Alberta
Edmonton, ABC

INTRODUCTION: Autism Spectrum Disorder (ASD) represents a collection of developmental disorders that span a wide range of symptoms and severity. The core features of ASD include social communication deficits and repetitive patterns of behavior that can lead to significant impaired social and occupational function. ASD is often co-morbid with a global developmental delay and intellectual disability. According to the Public Health Agency of Canada, 1 in 66 children and youth in Canada is diagnosed with ASD. The personal and societal costs of treatment and caregiving are immense with lifetime financial costs of $1.2-4.7 million to care for “typical” individuals with ASD (Dudley & Emery. 2018. The School of Public Policy Publications, 8:1)

Healthy brain function requires the precise integration of the activity of millions to billions of neurons across the entire central nervous system. Extensive interconnectivity between brain regions allows for global communication and functional integration that is necessary for functions such as learning, memory, sensorimotor processing, and emotional regulation. Coincident with the core symptomology in ASD are sensory abnormalities wherein one’s perceptions of the tactile, auditory, and visual world are abnormal. Thus, a comprehensive understanding of the functional integration of multiple brain regions would provide insight into how these complex functions are integrated in healthy individuals, and altered interconnectivity in sensory-related brain regions in ASD may show how this dysfunction in the brain manifests in behaviours.

OBJECTIVE: The objective of this study is to understand, using animal models, how sensory processing is altered in the brain in persons with ASD and the degree by which this altered sensory processing is responsible for the behavioural symptoms associated with ASD. In doing so, we will identify key spatial and temporal features of cortical processing abnormalities and target these areas for therapeutic restoration and consequently the reduction of symptomatic behaviours.

OUTLINE OF RESEARCH: Our primary hypothesis is that brain structures involved in processing sensory information such as touch, vision, and audition are functioning abnormally in ASD populations. This is consistent with reports from clinicians regarding maladaptive sensory perceptions in ASD populations and could manifest in terms of over-responsiveness, under-responsiveness, and failure to habituate/adapt.
We know that high-level sensory processing occurs in the brain’s cortex and are comprised of large-scale networks. We will employ leading-edge neuroimaging approaches that allow for brain-wide measures of activity to assess altered sensory processing in the brain and its causal relationship with symptomatic behaviors associated with autism spectrum disorder. This form of neuroimaging is referred to as `mesoscale’ imaging and it allows the use of light to assess and manipulate brain activity in order to determine function. We will employ these techniques in a clinically relevant mouse model of autism spectrum disorder based on an ASD-linked gene mutation of a critical protein involved in neuronal communication, Shank3. We will employ sensitive measures to record sensory responsiveness and compare these to wild-type, neurotypical controls to assess ASD-specific alterations. We will then employ advanced chemical and genetic manipulations to restore function in altered sensory cortices and test whether this restoration can also alleviate neurobehavioural symptoms most typically associated with cognitive deficits.

PROJECTED BENEFITS AND APPLICATION OF FINDINGS: The underlying neurobiology of autism spectrum disorder is unknown and there are no therapeutic interventions that directly target underlying causes. Thus, the development of treatments that can prevent or restore the pathologies at the root of ASD symptoms is a major area of need in ASD research. This proposal leverages leading-edge neuroimaging approaches and clinically relevant animal models to identify key brain features associated with altered sensory processing in the brain in ASD animal models. These experiments and findings will form a platform from which to test the therapeutic intervention of restoring sensory processing to the ASD population and its role in restoring associated cognitive deficits.  

Epigenetic reprogramming of microglia in early development primes neuroimmune responses to THC in adolescence

Dr. Annie Ciernia
University of British Columbia
Vancouver, BC

INTRODUCTION: Evidence from both animal and human studies implicates the immune system in a number of disorders with known or suspected developmental origins, including Schizophrenia and Autism. An emerging body of evidence supports a “two-hit” hypothesis for these disorders where an adverse early life event, such as inflammation, combines with a second adverse event in adolescence to impair brain development. We propose this form of early life “priming” occurs in a sex-specific manner in part through altered DNA methylation and gene regulation in microglia, the brain resident immune cells.

In addition to their primary immune functions, microglia shape developing neuronal circuits during early brain development. Microglia dynamically tune their gene expression during development and in response to early life immune activation using epigenetic mechanisms such as DNA methylation. We have previously demonstrated that early life immune insults produce changes in microglial DNA methylation and gene expression that last into adolescence. However, it remains unclear how early life epigenetic reprogramming of microglia alters microglial interactions with developing neural circuits and impairs behavioural development.

One of the most prevalent second hits that occurs in adolescence is experimentation with drugs of abuse. Cannabis is the most commonly used drug in adolescence and has been linked to increased risk of neuropsychiatric disorders. However, only a small portion of users go on to experience neuropsychiatric symptoms, suggesting adverse impacts occur only in predisposed individuals. We hypothesize that early life immune activation primes microglia via changes in DNA methylation such that adolescent THC alters microglial pruning of developing synaptic circuits and impairs behavioural development.

OBJECTIVES:
Aim 1: Early life inflammation reprograms microglia through DNA methylation

Aim 2: Early life inflammation alters microglial priming in adolescence

Aim 3: Early life microglial inflammatory reprogramming negatively impacts behaviour

OUTLINE OF RESEARCH: In Aim1, we aim to examine how early life inflammation impacts microglial DNA methylation, gene expression and activation state using a rat model. We then aim to artificially manipulate DNA methylation in cultured microglia to causally test the relationship between microglial DNA methylation and gene expression. We then aim to tie these gene expression changes to functional changes in microglial phagocytosis. We predict that early life inflammation will epigenetically reprogram microglia resulting in a hyper-responsive phenotype.

In Aim2 we aim to test the hypothesis that early life inflammation primes microglia to respond differently to THC use in adolescence. We will combine early life inflammation with adolescent administration of THC in rats and measure changes in microglial gene expression and DNA methylation. We will also examine how microglia interact with developing neuronal circuits. We predict that early life inflammation will prime microglia to inappropriately respond to adolescent THC use, resulting in altered neuronal circuit formation in the adolescent brain.

In Aim 3 we aim to test the impact of early life inflammation and adolescent THC use on decision making and attention using a novel behavioural paradigm in rats. This paradigm is modelled after a decision making task commonly used in Schizophrenia patients and has been used recently by our collaborators to identify novel therapeutics for Schizophrenia. We predict that early life inflammation combined with adolescent THC use will significantly impair impulse control in young adulthood.

PROJECTED BENEFITS AND APPLICATION OF FINDINGS: Understanding how perturbations experienced in early life shape long-term microglial function is fundamental to understanding how the immune system contributes to brain disorders in males and females. Findings from this project will significantly advance our understanding of how microglia contribute to neuropsychiatric disorders and will identify novel genes and molecular regulators for future therapeutic development. 

Elucidation of glial-mediated dysfunction in brain development in Fragile X Syndrome

Dr. Angela Scott
McMaster University
Hamilton, ON

INTRODUCTION: The intricate choreography of signals that are shared between nerve cells (neurons) in the brain are responsible for the formation and preservation of the circuitry required for every job the brain performs. Although the communication between neurons is essential for proper function, neurons alone aren’t responsible for regulating this. Other cells within the brain, called astrocytes, help neurons both develop and function properly once the circuit is formed. The work of astrocytes are essential for controlling much of the transmission of signals that neurons use to communicate, similarly to how traffic lights control the pattern of traffic flow. Without the synchronization of information highways, some signals get jammed while others run out of control. Defects in astrocyte function and neuronal signal imbalances have been associated with many autism-spectrum disorders (ASDs), such as Fragile X Syndrome (FXS). FXS can lead to learning deficits, anxiety and seizures in children and is the leading genetic cause of ASDs and intellectual disability. FXS is triggered by a mutation that prevents the expression of fragile X mental retardation protein (FMRP). FMRP regulates hundreds of proteins expressed by neurons and astrocytes, many of which are the signals responsible for controlling information flow as described above. The resulting effects of this single mutation are therefore extensive making targeted therapies harder to establish. Currently there are no available treatments for FXS; however, we have growing evidence that targeting the purinergic signaling system may be a good approach. Purinergic signaling is known to directly influence neuronal growth, patterning, synaptogenesis, and neurotransmission by regulating much of the bidirectional astrocyte-neuronal communication. Indeed, purines represent one of the most abundant astrocyte-neuronal signals in the CNS and our findings to date demonstrate that purinergic signaling is severely affected in FXS during key developmental periods. By identifying exactly how and where this system is faulty within the brain, we ascertain not only how it contributes to the disorder, but what to target for future treatments. Our preliminary work has highlighted the purinergic P2X7 receptor as a particular protein of interest, and in this study we will test how P2X7 signaling contributes to FXS-associated dysfunction and whether blockade of this signal works to correct it.

OBJECTIVE: The objective of this study is to identify the extent of dysregulated astrocyte-neuronal signaling via P2X7 in FXS, elucidate the functional consequences on neuronal development and neuro-inflammation, and determine the efficacy of P2X7 blockade as a potential treatment for FXS.

OUTLINE OF RESEARCH: We will address these objectives using an integrative approach that will rely on a range of methods already established in the lab. Using the animal model for FXS (mice that share the same mutation), we will characterize the expression of purines and P2X7 across different brain regions during development. We will specifically test the function of P2X7 signaling on astrocyte control of neuronal communication, immune responses and behavior by using both genetic and drug-based approaches in cell culture systems and animal models. The variety of testing will include live-cell imaging, neural network activity recording, high-resolution nucleotide and protein analysis, drug manipulation, and behavioral analysis.

PROJECTED BENEFITS AND APPLICATION OF FINDINGS: In recent years, clinical interest in the role of purinergic signaling system in ASDs has grown because of elevations of purines found in the blood or urine of individuals with ASD. Unfortunately, how this corresponds to levels in the brain or neurological dysfunction is relatively unknown. A Phase I clinical trial using a single dose of a non-specific purine receptor antagonist (Suramin) in adolescents with ASD had promising short-term results; but the lack of drug specificity makes the mode of action difficult to unravel and the serious side-effects associated with this drug (low blood pressure, loss of consciousness and kidney failure) make long-term use in children infeasible. As one of the only labs working on this signaling system in Canada, our study will offer needed insight into the role of purines in the brain and explore a new avenue of targeted drug treatment for individuals with FXS, ASD and related neurological disorders.

Cerebellar short-term plasticity, endocannabinoids, and Fragile X syndrome

Dr. Aparna Suvrathan
McGill University
Montreal, QC

INTRODUCTION: Fragile X syndrome is a common cause of autism spectrum disorder and intellectual disability, resulting from the loss of Fragile X Mental Retardation Protein (FMRP). FMRP controls the translation of a number of other proteins, particularly those at synapses, the points of contact and communication between neurons. The Fragile X knockout mouse, Fmr1 KO, replicates the human phenotype, thus providing a useful tool to interrogate the properties of synapses and their relationship to behavioral deficits.
While many brain regions are involved in the symptoms of Fragile X syndrome, a key understudied region is the cerebellum. For many years, the cerebellum was thought to be important primarily for motor learning, but it is now known to be critical in the etiology of autism. Moreover, the cerebellum is important for a range of non-motor functions, such as cognition and language.
Previous studies on mouse models of autism, and Fragile X syndrome in particular, demonstrate that deficits in synaptic plasticity are pervasive. Synaptic plasticity enables the brain to learn and adapt, and therefore, perturbations in synaptic plasticity are a major cause of the behavioral symptoms. Nevertheless, even in mouse models, it remains challenging to link synaptic plasticity at a given set of synapses in the brain to a specific learning phenotype. This challenge arises from the complexity of brain circuits, and the behaviors that they support. The mammalian cerebellum provides a unique opportunity to resolve this challenge. Cerebellar circuitry is relatively simple and well mapped, and the forms of motor learning that it supports can be measured with a high degree of precision.

OBJECTIVE: In this proposal, we aim to identify how a form of physiologically-realistic, short-term synaptic plasticity is perturbed in Fragile X syndrome. This form of plasticity is dependent on endocannabinoids, and supports short-term motor learning. Because motor learning occurs by improvement of movement from one behavioral trial to the next, we hypothesize that deficits in short-term plasticity are the reason for the motor learning deficits previously observed both in patients suffering from Fragile X syndrome, and in Fmr1 KO mice. Endocannabinoids have proven a promising new line of therapy in Fragile X syndrome, although the underlying neural mechanisms remain unclear. Moreover, activating endocannabinoid signaling has varied consequences, in different neurons, and on different time scales. Therefore, it is critical to understand how endocannabinoid-dependent, short-term plasticity is impacted in the cerebellum in Fragile X syndrome.

OUTLINE OF RESEARCH: Using a combination of single-cell patch-clamp electrophysiology, behavioral analysis, and molecular-genetic and pharmacological tools, we aim to combine in vivo and ex vivo analysis of Fmr1 KO mice. Our focus will be on the parallel fiber-to-Purkinje cell synapse, because plasticity at this synapse has long been implicated in short-term motor learning.
Our experiments will be a dialogue between analysis of plasticity at parallel fiber synapses, and measurement of motor learning. Motor learning is induced using a standard paw-reach learning task, where mice learn to make a targeted forelimb movement for a food reward. We will analyze the properties of plasticity, and of learning, as well as their dependence on the endocannabinoid signaling cascade. The results of our experiments will guide pharmacological and genetic attempts to ameliorate or rectify both plasticity and learning.

PROJECTED BENEFITS AND O PROJECTED BENEFITS AND APPLICATION OF FINDINGS: Synaptic plasticity is of the most promising avenues of research into the causes of autism, but major gaps in understanding remain. This project will address some of these gaps. We will identify the cerebellar synaptic substrate for short-term learning, which is perturbed in Fmr1 KO mice. Furthermore, our experiments will determine the role of the endocannabinoid signaling pathway, and identify potential targets for treatment. Thus, this project will also be able to uncover a neural basis of a promising new direction in treatment. Overall, our results will be critical for determining how the cerebellum contributes to Fragile X syndrome.