Award Partner: CLEAR Foundation

Validation of connexins and pannexins as a target for Alzheimer’s disease

Dr. Christian Naus is one of five BC researchers leading teams supported through the British Columbia Alzheimer’s Research Award. Established in 2013 by the Michael Smith Foundation for Health Research (MSFHR), Genome British Columbia (Genome BC), The Pacific Alzheimer Research Foundation (PARF) and Brain Canada, the goal of the $7.5 million fund is to discover the causes of and seek innovative treatments for Alzheimer’s disease and related dementias.

 

Alzheimer’s disease (AD) is the most common form of dementia, accounting for almost two thirds of total cases. There are currently no successful treatments, making the discovery of effective therapeutic interventions critical.

 

The brain contains billions of neurons (nerve cells), and substantially more non-neuronal cells called glia. Astrocytes, the most abundant type of glial cells, closely interact with neurons to control the transmission of electrical impulses within the brain. The major disease hallmark of AD is cognitive decline linked to neuronal wasting, impairment and finally, death.

 

Dr. Christian Naus, a professor in the Department of Cellular and Physiological Sciences at the University of British Columbia (UBC) and Canada Research Chair in Gap Junctions and Neurological Disease, studies the molecular and cellular mechanisms by which astrocytes lose their ability to support neurons that are vulnerable to destruction in Alzheimer’s disease, with the aim to identify new drugs to aid in treatment.

 

Naus’ team examines a unique set of cellular channels in astrocytes and neurons formed by special proteins, called connexins and pannexins. These channels help control the environment in which the cells of the brain must function by allowing a variety of small molecules to pass freely from one cell to another, and allowing them to coordinate cellular responses to various signals. However, when these channels stop working properly, they can become damaging to the environment thus compromising the normal functions of neurons. Naus’ research explores the role of these channels in neurons and astrocytes in order to identify how to manipulate these channels to provide protection for neurons in cases of disease, such as AD.

 

The outcome of these studies will contribute to the potential identification and development of new drugs that will not only target neurons, but also enhance the ability of astrocytes to protect neurons that are vulnerable to cell death in AD.

Elucidating the effect of O-GlcNAc modification on protein stability

The glycosylation of proteins with O-GlcNAc is a ubiquitous post-translational modification found throughout the metazoans. Deregulation of O-GlcNAcylation is implicated in several human diseases including type II diabetes, Alzheimer’s disease, and cancer.

 

However, the basic biochemical roles of O-GlcNAcylation remain largely unanswered. Several recent studies have demonstrated a clear link between O-GlcNAc and cellular thermotolerance.

 

It is likely that a basic function of the O-GlcNAc modification prevents the unfolding or aggregation of target proteins. Dr. King will investigate its role in protein stability through series of biochemical and biophysical experiments to probe the effect of O-GlcNAc on protein unfolding, folding, and aggregation. The results of this research will provide important insights into the basic molecular mechanisms governing O-GlcNAc deregulation in human disease.

 

End of Award Update: July 2022

 

Most exciting outputs

The modification of proteins by O-linked N-acetylglucosamine (O-GlcNAc) is a widespread post-translational modification (PTM) that is dysregulated in several human diseases including type II diabetes, Alzheimer’s disease and cancer. However, research progress in this area is hampered by the fact that it is challenging to detect O-GlcNAc on proteins. Further, the basic biochemical roles of O-GlcNAcylation remain largely unanswered.

 

Therefore, we developed a mass spectrometry based method to precisely map sites of O-GlcNAc on proteins. This method employs a UV laser to produce a diversity of O-GlcNAc retained fragment ions, enabling mapping protein modification sites with unprecedented precision.

 

We then explored the role of O-GlcNAc as a biochemical regulator of protein stability. We developed a new high-throughput approach to profile the effect of O-GlcNAc on the thermostability of the proteome. Using this method, we identify several proteins that are regulated by O-GlcNAc. Interestingly, the majority of these proteins display an O-GlcNAc dependent decrease in stability, challenging the prevailing view of O-GlcNAc as being a predominantly stabilizing modification. Thus, we show that O-GlcNAc is a bi-directional regulator of protein stability. We deliver a powerful approach that provides a blueprint for determining the impact of, in principle, any PTM on the thermostability of thousands of proteins in parallel.

 

Impacts so far
This work delivers powerful tools for exploring the role of O-GlcNAc and other labile PTMs as regulators of protein biochemistry.

 

Potential future influence
Decreased levels of protein O-GlcNAcylation is associated with Alzheimer’s disease. However, the basic biochemical mechanisms underlying this association remain unknown. Here we show that O-GlcNAc regulates the stability of several proteins within human cells, a phenomenon that may impact cellular protein levels in Alzheimer’s disease. This fundamental research is important for understanding the impact O-GlcNAc has on protein structure and stability, particularly in the context of its dysregulation in neurodegenerative disorders.

 

Next steps
We plan to continue exploring the influence O-GlcNAc has on protein structure and function. In doing so, we hope to improve our understanding of the fundamental mechanisms underlying neurodegeneration. This research may ultimately provide knowledge that contributes toward the development of new therapeutic strategies.

 

Useful links

Neurally-produced estradiol enhances the neuroprotective actions of insulin

Alzheimer’s disease is a debilitating disorder that is on the rise in British Columbia’s aging population. A growing pool of evidence suggests that Alzheimer’s disease may involve insulin, a hormone whose activity in the pancreas is linked with type 1 and type 2 diabetes. Insufficient action of insulin in the brain can be a cause of Alzheimer’s disease, which is increasingly being called “type 3 diabetes” because of this.

 

During my graduate studies, I observed that insulin is produced in the brains of mice and humans, with highest expression in the hippocampus. My preliminary results also suggested that deletion of brain insulin in mice leads to cognitive deficits.

 

Estradiol enhances insulin production and response in the pancreas. However, these effects of estradiol in the brain have never been confirmed. Yet when expressed together in the hippocampus (a brain structure critically involved in memory), estradiol and insulin promote neuron growth and survival as well as synapse formation and maintenance.

 

I will test the hypothesis that estradiol produced by neurons enhances the production and action of insulin in the brain, and that this has beneficial effects in a rat model of Alzheimer’s disease.

 

I will inhibit estradiol production in the brain and then test how local insulin expression and signalling are affected in the brains of the rats. I will also examine the neurons and synapses in adult rats and will perform behavioural and cognitive tests. A drug that blocks insulin receptors will be used to confirm that insulin signalling is the true cause of any changes I observe.

 

I predict that inhibition of brain estradiol production will reduce brain insulin expression/action and increase negative effects associated with Alzheimer’s disease in this rat model.

 

Studying the role of brain estradiol production and its potential to increase brain insulin activity in the brain could ultimately lead to new treatments for Alzheimer’s disease.

End of Award Update

Source: CLEAR Foundation

 

Dr. Mehran’s hypothesis was that estradiol produced by neurons enhances the production and action of insulin in the brain, and that this would have beneficial effects in a rat model of Alzheimer’s disease. However, even using some of the most sensitive assays, they failed to yield a difference.

 

However, Dr. Mehran discovered that second-generation antipsychotic medications inhibit insulin maturation. This finding is important because these medications are used to treat patients with psychosis and Alzheimer disease. These medications may be contributing to cognitive harm, by reducing levels of brain insulin.

 

 

Chemical suppression of nonsense mutations for the treatment of frontotemporal dementia

Michael Smith Foundation for Health Research/Pacific Alzheimer Research Foundation Scholar Award

 

Frontotemporal dementia is a progressive neurodegenerative syndrome, and the second most common cause of young-onset dementia after Alzheimer’s disease. Members of our team recently reported that loss-of-function mutations in the gene for a protein called progranulin cause 25 percent of frontotemporal dementia cases. Of these mutations, 30-40 percent are “nonsense mutations” that act as stop signs to prematurely end a process required to produce normal progranulin. When progranulin production ends too early, it leads to a shortened protein that cannot carry out the normal brain functions, eventually leading to dementia in the sixth decade.

 

The goal of this project is to investigate small molecule combinations that can bypass the abnormal “stop sign” in the progranulin gene, increasing the normal production of this important protein. The small molecule combinations will be refined and optimized to find the most effective combination. This approach, also referred to as “suppression of nonsense mutations”, offers the possibility of developing a new drug for patients with frontotemporal dementia cause by a progranulin mutation. The team also plans to develop a mouse model of frontotemporal dementia to test the small molecule combinations in a living organism.

 

The long-term goal of the project is to bring new drugs for frontotemporal dementia into clinical trials. An effective therapy would alleviate the devastating impact of dementia in many patients and their families, in BC and beyond.

End of Award Update

Source: CLEAR Foundation

 

We studied frontotemporal dementia (FTD) with the aim of developing novel drugs for this devastating condition. A subset of FTD patients have a genetic mutation that leads to reduced levels of an important protein called progranulin. Our project aimed to develop a drug that could counteract this genetic mutation. We used brain cells cultured in a dish to test new drugs and found a known antibiotic to have properties that could increase progranulin in this model.

 

This work laid the foundation for ongoing research to develop drugs to increase progranulin in patients with certain forms of FTD.

 

 

Human islet amyloid polypeptide aggregation, the missing link between type 2 diabetes and Alzheimer’s disease?

Michael Smith Foundation for Health Research/The Pacific Alzheimer Research Foundation Post-Doctoral Fellowship Award

 

Type 2 diabetes (T2D) patients have an increased risk of developing Alzheimer’s disease (AD). However, the underlying mechanism is poorly understood. Human islet amyloid polypeptide (hIAPP) aggregates, occurring in ~95% of T2D patients, induce a variety of pathological processes that are contributing factors to AD neuropathology. In current proposal, we attempt to investigate the effect of hIAPP aggregation on the Alzheimer’s development in T2D and the potential mechanism by conducting cell and animal experiments. Additionally, novel transgenic mouse models of diabetic AD will be generated to mimic the natural process of AD development in diabetics.

 

This study will help us to define the prevention and treatment of diabetic AD. Dissemination of the findings from this study will be done in different ways to make sure that the largest number of people will hear, understand and benefit from this novel research project. The experimental results will be published as research articles on academic journals and presented at scientific conferences, such as Society for Neuroscience annual meeting and Canadian Diabetes Association professional conference. Educational events and learning series will be held in the community, such as Cafe Science and public lecture series where we can engage the public with our research study, answer their questions directly and stimulate discussions.

End of Award Update

Source: CLEAR Foundation

 

Dr. Zhang’s research focused on creating a better understanding of why type 2 diabetes patients have an increased risk of developing Alzheimer disease. This research identified the important role of human islet amyloid polypeptide (hIAPP) in diabetes-induced dementia. Targeting hIAPP may be a valid approach for preventing and treating dementia in diabetes mellitus.

Are there indicators of Alzheimer’s disease in the eye?: New computational imaging and analysis algorithms

Michael Smith Foundation for Health Research/The Pacific Alzheimer Research Foundation Post-Doctoral Fellowship Award

 

Alzheimer’s disease (AD) is progressive degeneration of the brain that results in loss of memory and cognitive abilities. The prevalence of the disease presents a daunting challenge — as of 2015, 46.8 million people in the world live with AD, with the number expected to double by 2035. In Canada, 14.9 percent of those 65 and older have the disease. The global health-care cost for dementia has exceeded 1 percent of the global gross domestic product (GDP).

 

AD significantly affects the quality of life for the patients and caregivers, and this makes early detection critical. However, the brain imaging required for the diagnosis is costly, and AD is often discovered only after it has progressed considerably.

 

The overarching theme of this project is finding the connection between the eye and AD, by investigating it for potential biomarkers of the disease. The eye is an extension of the brain, with the optic nerve forming a direct physical connection between the retina and the brain’s visual cortex. Recent advances in ophthalmic imaging techniques, such as optical coherence tomography (OCT), provides high-resolution 3D visualization of the inner structures of the eye, including the retina, nerve fibres, and blood vessels, in a noninvasive manner. OCT and other imaging techniques give us a comprehensive picture of the eye’s health and function.

 

We will develop image processing and analysis tools to examine chemical biomarkers, structural degradation, and functional loss in the eye that may be associated with AD. The project will potentially lead to discovery of novel AD biomarkers in the eye, and a cost-effective and accessible diagnostic tool for early detection of AD.

 

End of Award Update

Source: CLEAR Foundation

 

What did we learn?

We know that amyloid beta, a hallmark of Alzheimer’s disease, is present not only in the brain but also in the retina of the patients, and its deposition can vary by location and comorbidity such as cerebral amyloid atrophy.

 

Why is this knowledge important?

Retina can be readily imaged in high detail, and it contains rich information about the person’s neuronal health. Retinal imaging has potential as an early and accessible screening tool for neurodegenerative diseases. Studying the mechanisms of Alzheimer’s disease pathology in the retina also gives us insight into those in the brain.

 

What are the next steps?

Professor Joanne A. Matsubara’s group at the University of British Columbia and I are continuing to collaborate to study retinal biomarkers of Alzheimer’s disease. We are currently looking into how amyloid beta affects glial cells and blood vessels in the retina.

 

Publications

Altered glutamate dynamics in a mouse model of Alzheimer’s disease: Novel early biomarkers with therapeutic potential

Michael Smith Foundation for Health Research/The Pacific Alzheimer Research Foundation Post-Doctoral Fellowship Award

 

Alzheimer’s disease (AD) is a progressive neurodegenerative disorder. With no cure available, it imposes a major burden on society. In AD, a protein called amyloid beta accumulates into plaques in the brain. This event is an early and predictive marker for AD and can be detected up to 20 years before clinical symptoms arise.

 

We are exploring the dysfunction and hyperactivity of various cell types in the presence of amyloid plaques. We will investigate the possible role of altered glutamate dynamics in mouse models of AD. Fluorescent labelling will shed light on changes in glutamate signalling in awake and behaving AD mice. We will also test whether Ceftriaxone can restore normal glutamate dynamics in these mice.

 

Ultimately, our work with AD mouse models and novel glutamate imaging could shed light on possible drug targets and enable early intervention for people with Alzheimer’s disease.

End of Award Update

Source: CLEAR Foundation

 

What did we learn?

During our study it became clear that amyloid deposits have a drastic impact on glutamate signaling. This early cellular signaling deficit was only visible using in vivo 2-Photon imaging and a region-specific analysis of real time glutamate transients in direct proximity to amyloid plaques. We found areas of chronically high glutamate levels directly surrounding amyloid plaques and adjacent areas in which glutamate signaling was impaired. In larger scale wide-field real-time imaging experiments this effect was lost, indicating the importance of region-specific effects on cellular function in the early stages of the disease. Moreover, we used luminescent conjucated oligothiophens (provided by Dr. Peter Nilson, Linköping University) to visualize prefibrillary forms of amyloid. We found a direct overlap of these prefibrillary forms of amyloid surrounding the dense core plaque and a decrease in astrocytic GLT-1 transporter. We hypothesized that this decrease in GLT-1 is responsible for the observed glutamate dysfunction that was found in our experiments using stimulation experiments in awake and anesthetized animals. We thus used Ceftriaxone to restore GLT-1 expression in our mouse model of AD. We provided longitudinal imaging data of glutamate transients before and after Ceftriaxone treatment and could show that this partially restores glutamate signaling.

 

Why is this knowledge important?

As prefibrillary species are present in the brain before dense core plaques are formed it is important to further our understanding of their impact on cellular function. Moreover, it is essential to develop strategies that aim at the earlies stage that amyloids have on cellular function as these can be treated. Once neurons and other cells undergo cell death, strategies of recovery are much harder to implement. Our results provided a new therapeutical target that not only treats the disease on a symptomatic level but in an amyloid centric way that prevents/delays cellular dysfunction at an early stage in the disease.

 

What are the next steps?

We are currently expanding our research to investigate the impact of prefibrillary amyloid species on vessel function to search for more potential therapeutic targets.

 

Publications