Neural plasticity in chronic hypoxemia due to lung disease

Chronic sustained hypoxia (CSH) is a major complication of chronic obstructive pulmonary disease. The body’s first line of defence against hypoxemia, or lack of oxygen supply,  is the hypoxic ventilatory response (HVR), a reflex increase in respiration. With prolonged hypoxemia due to issues such as chronic lung disease, ventilatory drive and the HVR are further increased. This secondary increase is termed ventilatory acclimatization to hypoxia (VAH) and persists for weeks after re-oxygenation. VAH thus represents a form of functional memory in respiratory control circuits. Although systemic hypoxemia can be alleviated with oxygen therapy, it is costly and unwieldy. One promising alternative is to control the internal VAH response in a patient-specific manner to reduce hypoxemia; however, altering VAH requires knowledge of the synaptic pathways that mediate VAH, which are currently unknown.

Dr. Pamenter’s research aims to seek out the neural mechanisms that increase ventilatory drive and enhance arterial oxygen  during chronic hypoxemia. This project will determine the cellular signals for plasticity in the central nervous system mechanisms of ventilatory reflexes  caused by chemicals during CSH in rats.

In pilot experiments, Dr. Pamenter has examined a role for glutamatergic receptors in CSH in rats. Glutamatergic receptors are synaptic receptors located primarily on the membranes of neuronal cells. During the experminent, plasticity pathways are manipulated by direct microinjection of drugs into the Nucleus tractus solitarius (NTS), a nucleus in the brainstem. He will then examine changes of related second messengers (calcium and nitric oxide) in the NTS using an in vivo imaging system. Finally, he will examine glutamatergic mechanisms of synaptic plasticity directly in NTS neurons in isolated respiratory brainstem slices taken from control and CSH rats.

This research is a first step towards understanding the role of neural plasticity in systemic responses to hypoxemia due to chronic lung disease. Thus, elucidating these pathways is physiologically and clinically significant.

Co-registered optical coherence tomography and autofluorescence imaging

Lung cancer is the most common cause of cancer death with more than 1.3 million mortalities annually. Autofluorescence (AF) bronchoscopy is an established clinical technique that has proven to be extremely effective for early detection and staging of cancer by identifying high-risk areas where biopsies should be collected.

Currently, AF imaging is the most sensitive means of lung cancer detection. However, the improved sensitivity of AF broncoscopy comes at the cost of a decrease in specificity due to false-positive fluorescence in areas of inflammation or an increase in epithelial thickness. Moreover, performing biopsies and conducting histology on the removed tissue are costly and time-consuming.

The efficacy of the treatment would be significantly enhanced by differentiating carcinoma from other non-dangerous anomalies. OCT, the optical equivalent of ultrasound, enables high resolution in vivo imaging of airway morphology to study the high-risk tissue sites without performing biopsy and removing tissue. Therefore, when used in combination, AF-OCT imaging can provide rich biochemical information. The aim of Dr. Pahlevaninezhad’s research is to combine AF imaging and optical coherence tomography (OCT) to manage this disease through earlier detection. Dr. Pahlevaninezhad’s research method begins with combining the two modalities in free space to test ex vivo samples and to calibrate the system. The next step will be to build a fibre-based system for in vivo imaging of lung and to test the system on a small number of consenting patients.

Through the combination of these imaging techniques, Pahlevaninezhad’s research will provide both architectural and biochemical information which will aid in avoiding unnecessary biopsies. Significantly, the applications of the proposed device are not just limited to lung cancer; it also could target other applications like the oral cavity, considerably enhancing the ability to detect cancers effectively and efficiently. 

Regulation of intestinal regeneration and cancer by the lysine methyltransferase Set7

Intestinal epithelial cells (IECs) form a protective covering over the small and large intestine. They are the primary interface between the body and the external environment, and  are constantly turning over, completely renewing every three to five days. This impressive turnover requires tight control of stem and progenitor cell production and variation, which is mediated by various cell signalling pathways including the Hippo and Wnt pathways.

In his study, Dr. Oudoffaims to dissect the exact role the protein-coding gene Set7 has in control of the Hippo and Wnt pathways in IEC homeostasis, regeneration, and cancer. The role of Set7 will be examined in two different in vivo intestinal regeneration models.

Systematically, his team will perform in vitro biochemical and cell biological assays to define the mechanism through which Set7 acts to regulate Hippo and Wnt pathways. In preliminary studies, Dr. Oudhoff identified that Set7 negatively regulates IEC production and turnover by regulating the Hippo pathway in vivo. Based on these results, his team tested whether the increased IEC proliferation would cause tumor development. Crossing mice lacking Set7 to mice that tended to spontaneously develop intestinal tumors, Dr. Oudhoff’s team hypothesized that mice having overactive Setd7 and overactive Wnt would develop more adenomas (benign tumors) or would develop them faster.

Ultimately, these studies will attempt to provide novel therapeutic targets to treat intestinal cancers.

The influence of stress on the connectivity of developmentally-born and adult-born neurons within the hippocampal dentate gyrus-CA3 pathway

The discovery that humans are able to regenerate new neurons through a process called neurogenesis has transformed our understanding of the brain’s potential for plasticity. In the dentate gyrus (DG) subregion of the hippocampus, adult neurogenesis plays an important role both in memory and emotional processes such as depression. The neural pathway, DG-CA3 in this region shows remarkable learning-induced plasticity and is an important component of the brain’s stress-regulation circuitry. Though the mechanisms by which new neurons regulate stress and depression-related behaviour are largely unclear, they are likely to be critically dependent on their connections with downstream dorsal vs. ventral hippocampal subregions, which are involved in cognitive vs. emotional behaviours. Since the adult-born and pre-existing neuronal populations are each very large, understanding the role of the DG-CA3 pathway in stress-regulation and depression will require dissection of the circuits created during development vs. those created during adulthood.

This study will examine the influence of stress on the connectivity and plasticity of adult-born neurons in a rat model.

First, Dr. O’Leary will use a microscopal imaging technique to determine whether patterns of connectivity differ between pre-existing and adult-born neurons. Second, Dr. O’Leary will determine how stress in adult-hood modifies the pattern of connectivity in pre-existing and adult-born neurons. Following either acute or chronic restraint stress in adult-hood, anxiety-like behaviour, depressive-like behaviour, and patterns of neuronal connectivity will be measured.

Dr. O’Leary hypothesizes that stress will influence the pattern of connectivity of adult-born neurons within the ventral hippocampus, and these changes will correlate with anxiety- and depressive-like behaviours. This research will elucidate a novel mechanism by which stress contributes to depression in humans.

Unraveling the molecular mechanisms for variation in lung function

Lung function measures reflect the physiological state of the lungs, and are essential for the diagnosis and management of obstructive lung diseases such as asthma and chronic obstructive pulmonary disease (COPD), two common diseases with a huge burden on patients and health care systems. The measures are thought to have a genetic component, yet it is not known exactly how genes affect lung function. One mechanism by which genetic variation can influence lung function is through changing the amount of protein produced by that gene. This can be discovered by relating DNA sequence variations to mRNA or protein expression. Hence, to unravel the molecular mechanisms underlying lung function, it is very informative to study the genetic control of lung-specific gene expression.
Dr. Obeidat hypothesizes that a subset of lung function and obstructive lung diseases associated genetic loci act to change the level of expression of their gene product within the lung.
Dr. Obeidat is a member of a team that conducted genome-wide genotyping and gene expression analysis of lung tissue samples from ~1,200 individuals; the worlds largest study of its kind. The study identified ~17,000 loci where variants were related to the level of gene expression.  Variants that are associated with both lung function and gene expression will be prioritized as being potentially causal for variation in lung function and will be investigated further. Further, bioinformatics methods will be used to identify molecular pathways and networks enriched in the genes driving lung function variation.
This approach represents the next frontier in complex diseases genetics and has been successfully implemented in other disease areas. With this integrative genomics method, Dr. Obeidat aims to use the new genetics derived knowledge to develop new therapies to alleviate common respiratory diseases.

Role of HIV Nef in establishment and maintenance of HIV latency

HIV establishes a latent infection in CD4+ T cells that is not affected by current antiretroviral treatments. Because drug withdrawal allows viruses released from these cellular reservoirs to replicate, patients must remain on therapy for life to prevent re-emergence of the progressive disease. Although strategies to cure HIV infection are being discussed, development of an effective approach will require novel treatments that can eradicate reservoirs of latent virus. For this to occur, there is a need for a better understanding of HIV persistence, including knowledge of host and viral mechanisms required to establish and maintain latency. Formation of latent HIV reservoirs is thought to occur, in part, through infection of T cells that are either poorly activated or that revert to a non-activated state prior to death by viral cytopathic or host immune-mediated effects.

This study will investigate the role of the HIV pathogenic protein Nef in the establishment and maintenance of viral latency.

Dr. Mwimanzi hypothesizes that the Nef protein functions as a molecular “switch”, which regulates the activation threshold of virus-infected T cells. Using in vitro cell culture systems and panels of Nef variants that include site-directed mutants and patient-derived isolates, he will examine whether differences in Nef function affect the ability of a cell to establish or maintain latency.

It is anticipated that the results will help identify critical Nef motifs, evaluate interactions between Nef and host cell proteins, and elucidate viral and cellular mechanisms of HIV latency. With increased understanding of the mechanisms of HIV latency, this research has the potential to improve the health of those infected with HIV.

Do goblet cell mediators co-operatively prevent gut microbiota from causing spontaneous colitis?

Inflammatory Bowel Diseases, including Crohn’s disease and ulcerative colitis are characterized by chronic intestinal inflammation and tissue damage. There are trillions of bacteria found  within the human intestine and IBDs are thought to develop when mucus barriers that normally keep these  bacteria inside the gastrointestinal tract become impaired,  allowing bacteria to escape out of the gut lumen and causing  chronic inflammation. While the role of epithelial cells in promoting barrier function is well known, the protective actions of the mucus barrier are relatively understudied.

Specialized secretory epithelial cells known as goblet cells within the gut lumen produce  mucins known as Muc2 and pro-inflammatory proteins called  RELM-ß. Through in vitro and in vivo studies, and  microbiota analysis, Morampudi plans to define how these goblet cell proteins cooperatively protect the intestine from  developing spontaneous colitis through the development of  these products.Through tests with micelacking either Muc2 or RELM-ß, Dr. Morampudi has  hypothesized that both proteins act together to protect the  intestine from gut commensal bacteria. Muc2 provides a  structural barrier, preventing bacteria from contacting the immune system, but when the mucus barrier is impaired,  RELM-ß is induced to create an antimicrobial zone above the  intestinal epithelium. Under conditions where expression of  both proteins is impaired (such as by ER stress), the  commensal bacteria are able to escape from the intestine and cause colitis/IBD.Ultimately, this research will provide insights as to how  the development of spontaneous colitis can be prevented.