Many diseases such as cancer, atherosclerosis (narrowing and hardening of the arteries) and neurodegenerative disorders stem from problems with the uptake, transportation, storage and recycling of molecules. Proper sorting is necessary for normal cell function since many molecules are only required in specific areas or compartments of the cell. In the case of neurodegenerative disorders, defective protein sorting in nerve cells can lead to brain tissue deterioration. Disease caused by abnormal protein sorting can be studied in very simple organisms such as yeast, and the findings directly applied to human cells. Dr. Leslie Grad is researching a yeast protein, Vps13, which is very similar to a protein encoded by the human gene VPS13A. Defects in this gene can lead to chorea acanthocytosis, a neurodegenerative disorder associated with abnormal red blood cells, epilepsy, and muscle and nerve cell degradation leading to premature death. The findings could provide insight into the complicated mechanisms that regulate sorting of molecules inside cells and explain the molecular function of Vps13. Ultimately, Dr. Grad hopes to apply his findings to human cells and contribute to the development of therapies for neurological disorders caused by abnormal protein sorting.
Research Pillar: Biomedical
To define the role of caspases and caspase cleavage of htt in the pathogenesis of HD
Research has identified a genetic defect in the HD gene that causes Huntington’s disease, a devastating and ultimately fatal neuropsychiatric disease. Symptoms include progressive deterioration in the ability to control movements and emotions, recall recent events or make decisions, and leads to death 15 to 20 years after onset. One in 10,000 Canadians has HD. There is neither a cure nor treatments to prevent Huntington disease. Several years ago Dr. Hayden and his team discovered that huntingtin, the protein involved in Huntington disease (HD), is cleaved by ‘molecular scissors’ which are proteins called caspases. This discovery led to the hypothesis that cleavage of huntingtin may play a key role in causing HD. To explore the role of huntingtin cleavage in the disease process, we established an animal model of HD that replicated the key disease features seen in patients. A unique aspect of this particular animal model is that it embodied the human HD gene in exactly the same way seen in patients. This replication allowed researchers to examine the progression of HD symptoms including the inevitable cleavage of the mutant huntingtin protein. Dr. Rona Graham is continuing her earlier MSFHR-funded research into understanding the reason why the mutant form of the HD gene causes death of particular neurons in the brain. Her Masters and PhD work demonstrated that preventing cleavage of the mutant huntingtin protein responsible for HD in a mouse model, the degenerative symptoms underlying the illness do not appear and the mouse displays normal brain function. Dr. Graham’s goal now is to investigate the role of caspase activation and the caspase-6 cleaved huntingtin fragment in the disease process. Since a similar splitting of disease proteins is involved in many other central nervous system diseases including Alzheimer’s and Spinocerebellar ataxia (which causes progressive deterioration in hand, speech and eye movement) Dr. Graham hopes the findings will lead to new treatments for other neurological disorders as well as HD.
A molecular basis for replacement tooth formation in reptiles
There are a great number of genetic diseases that affect tooth number in humans. Ectodermal dysplasia (ED), for instance, is characterized by a reduction in the overall number of teeth (i.e., hypodontia). In contrast, people with cleidocranial dysplasia (CCD) may form dozens more teeth than normal. In both disorders, only the secondary generation of teeth (‘adult teeth’) is affected, while baby teeth are largely unaffected. Since conventional mammalian lab models, such as the rat and mouse, form only a single generation of teeth during their lives, they can tell us little about the molecular cues controlling tooth replacement. For this reason, Dr. Gregory Handrigan has turned to an unusual animal model: reptiles. Like humans, reptiles form multiple generations of teeth throughout their lives. As part of the first research to directly address the molecular control of generational tooth formation, Dr. Handrigan is identifying genes from reptiles such as the python and bearded dragon that underlie their ability to continually form new teeth. Given the overwhelming similarity in tooth development between reptiles and mammals, these genes are likely to be performing comparable roles in humans. Handrigan’s research could then generate important knowledge about the molecular control of tooth number in human development as well as for diseases like ED and CCD. Ultimately, his findings may provide a foundation for strategies to regenerate lost teeth in humans.
MeCP2 and chromatin: An alternative to the global binding hypothesis
Rett syndrome is a severe neurodevelopmental disease that affects approximately one in 10,000 girls. Progressive symptoms begin at a very young age and worsen through childhood. These include loss of speech, purposeful hand use, ability to walk, and the development of seizures. In 85 per cent of cases, the cause of Rett syndrome has been traced to mutations of a protein known as MeCP2. Dr. Toyotaka Ishibashi is studying the relationship at the cell level among the MeCP2 protein, DNA and chromatin (a complex of DNA and protein that regulates the binding of the MeCP2 protein to DNA). Despite some research carried out in recent years, details of the interaction of MeCP2 with chromatin remain largely unknown. Toyotaka is investigating how MeCP2 works in normal cells, which is critical for later study of how gene mutations interfere with the normal function of the protein to cause the symptoms of Rett syndrome. Ultimately, Toyotaka hopes to clarify the role of the MeCP2’s nucleosome — the most elementary structure involved in regulating the protein’s activity — to provide potential cellular targets for drug targeting and new prospects for the development of clinical therapies.
Role of ABCA1 in brain cholesterol metabolism and brain function
Although the brain accounts for only 2 per cent of total body weight, it contains almost 25 per cent of total body cholesterol. This cholesterol is critical to healthy functioning in the brain, and plays an important role in learning. Abnormalities in the synthesis of brain cholesterol are associated with several devastating diseases, including Alzheimer’s and Huntington’s. However, not much is known about how the central nervous system regulates the metabolism and movement of cholesterol in the brain. Two-thirds of brain cholesterol is located in myelin, an insulating layer that surrounds the nerve fibers of brain cells where it supports transmission of signals between neurons across connections called synapses. Cholesterol also helps repair neurons. Although the synthesis of cholesterol occurs at a high level in the developing brain, it declines significantly in the adult brain. Consequently, the brain must rely on efficient transport and recycling to meet its need for cholesterol in the brain cells. Dr. Joanna Karasinska is investigating whether ABCA1, a major cholesterol transporter in the brain, controls the metabolism of cholesterol and how this affects brain function. This knowledge could lead to new therapies for neurological disorders associated with a cholesterol imbalance in the brain, and for the repair of neurons following a brain injury.
Development of potential therapeutics for influenza via sialidase inactivators
Influenza is a severe infection of the upper respiratory tract that occurs each year, affecting approximately 20 per cent of the world’s population. Although vaccination is the primary prevention strategy, a number of scenarios exist for which vaccination is insufficient and for which the development of new antiviral agents would be extremely important. Two classes of drugs are available for controlling the spread of influenza. Amatidines work by blocking the ion channel function of the viral M2 protein. However, these drugs are only effective against influenza A virus and have substantial side effects. The other class of therapeutics, sialidase inhibitors, includes enzyme inhibitors Relenza and Tamiflu. However, influenza viruses are developing resistance to both inhibitors. One solution to the problem of viruses becoming resistant is to use several drugs at once (a drug cocktail), making it more difficult for the virus to develop resistance to all of them. Another solution, which could be used in concert, is to design new inhibitors that are less likely to induce viruses to mutate and develop resistance. This is the goal of Dr. Jin Hyo Kim’s research.
Structural basis of the glycerol-phosphate and the ribitol-phosphate chain polymerization in teichoic acid biosynthesis in rram-positive bacteria
One way of classifying bacteria is by their colour after applying a chemical stain (called the Gram stain). Some bacteria stain blue (Gram-positive), while others stain pink (Gram-negative). Gram-positive and Gram-negative bacteria produce different kinds of infections. Worldwide, more than half of infections treated in hospital involve Gram-positive bacteria. These include Staph infections caused by Gram-positive Staphylococcus aureus bacteria, as well as Strep throat and toxic shock syndrome caused by Streptococcus bacteria. Many Gram-positive bacteria, such as methicillin-resistant Staphylococcus aureus (MRSA), are becoming resistant to antibiotics. The cell wall of all Gram-positive bacteria contains about 50 percent of teichoic acids, a diverse group of polymers (long-chain molecules). Dr. Leo Lin is investigating whether two common teichoic acids help these bacteria adhere to host cells in humans or even to the synthetic coatings of transplanted medical devices, such as pacemakers. For many bacteria, the ability to attach to the surface of a host cell is an essential first step in the infection process. Dr. Lin will determine the three-dimensional structure of the enzymes that synthesize these teichoic acid polymers using x-ray crystallography, a technique that can deduce the atomic structure of molecules. A lack of teichoic acid significantly destabilizes the bacterial cell wall. Dr. Lin is looking for ways in which this information can be used to develop ways of interfering with the ability of bacteria to attach to host cell surfaces as a first line of defense in protecting against the establishment of bacterial infections.
Molecular mechanisms of retrograde transport
A single human cell is made up of many small organelles (compartments). Through a process known as vesicle transport, proteins and lipids move from one compartment to another to support and maintain cell function. Motor nerve cell diseases are progressive disorders involving the nerve cells responsible for carrying impulses that instruct the muscles in the upper and lower body to move. Abnormal vesicle transport causes a family of these devastating diseases, including Lou Gehrig’s disease (Amyotrophic Lateral Sclerosis or ALS). Abnormal vesicle transport has also been found in Alzheimer’s, Down syndrome, and Neimann-Pick C disease, suggesting that these abnormalities also play a role in the development of these diseases. To better understand these diseases and hopefully lead to improved treatments, Dr. Benjamen Montpetit is focusing his research on determining how vesicle transport works. Montpetit, who received MSFHR trainee awards in 2002 and 2006 in support of his PhD research, is studying the process in yeast with the aid of robotic-based systems. Yeast makes an excellent model for his research because the yeast genome has been fully sequenced and, therefore, its genetic code is known.
Interomics: System-wide proteomic discovery of interactors and substrates of proteases
A protease is an enzyme that can split a protein into peptides. Alterations in normal protease expression are known to be involved in the development of cancer, arthritis and various lung, neurological and cardiovascular diseases. As a result, many proteases and their substrates are an important focus of attention as potential drug targets. Among proteases, matrix metalloproteases (MMPs) are responsible for the proteolytic modification of the extracellular matrix, a complex network of polysaccharides and proteins secreted by cells that serves as a structural element in tissues and also influences their development and physiology. While more is being learned about the multiple functions of MMPs –, many of which are beneficial – their roles and biological functions are not fully understood. David Rodriguez’s research seeks to unravel the complex web of connections among MMPs, their natural substrates, inhibitors and other proteases. He is using a technique known as Mass Spectrometry to detect and identify hundreds, even thousands, of proteins in a sample. By identifying and describing the complex set of signaling pathways in which MMPs are involved, Rodriguez is hoping to better understand the role of these proteases and to predict the consequences when they function abnormally. Such knowledge is critical for designing more effective drugs to treat diseases which result from abnormal protease function.
Regulation of lymphocyte activation and proliferation and synthesis of pro-inflammatory cytokines by the Caprin-1/G3BP-1 heteromeric complex
To fend off infections, our immune system has evolved effective strategies. These include rapidly increasing the number of infection fighting immune cells, including cytokines that promote an inflammatory response to destroy harmful bacteria, viruses and other infectious agents. The key to the effectiveness of this strategy is striking a balance between creating an inflammatory response sufficient to destroy the infectious agents without causing severe damage to the surrounding tissues. In some cases, poorly controlled or misdirected immune responses cause long term damage and disease, including arthritis and asthma. Samuel Solomon is studying how the body regulates the immune response, in particular the role of RNA binding proteins such as Caprin-1 and G3BP-1 in the process. Caprin-1 and G3BP-1 are thought to be key players in the signaling process, which controls the action of inflammatory cytokines. Solomon is studying how they affect the production of cytokines and what are the effects when these proteins are absent or functioning abnormally. This research will contribute to our understanding of immune function, which could lead to the design of novel, better and more effective cures for infections and auto-immune diseases.