August 9, 2013
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Cognitive decline, memory impairment, and anxiety are all typical parts of normal aging. New research published in the Journal of Neuroscience from the lab of Dr. Remi Quirion at McGill University sheds light on cellular mechanisms in the brain that may underlie this decline. Dynorphins, endogenous opioid-like proteins, appear to be increased in aged brains, and through activation of specific opioid receptors can decrease the function of synaptic connections releasing the amino acid neurotransmitter glutamate. Glutamate is the most common neurotransmitter in the brain and acts on several different receptor types, but the effect of dynorphin appears to arise through reduction in activity of a specific group of glutamate receptors, the metabotropic glutamate receptors (mGluRs). mGluRs can be important for different forms of synaptic plasticity, or the remodeling of neural connections, and appear to be important for decreasing the strength of certain synapses in order to properly shape neural circuits that underlie learning and memory formation. The hypothesis that Dr. Quirion’s group pursued was that increased dynorphin expression in aging brains leads to decreased mGluR activation which in turn limits the synaptic plasticity required for memory and other cognitive processes. To examine this, the group compared anatomical, physiological, and behavioral characteristics of wild-type mice and mice that had the dynorphin precursor, prodynorphin, knocked out. In general, young and middle-aged wild-type mice did not differ from young and middle-aged prodynorphin knockout mice. However, many differences were observed between old wild-type mice and old prodynorphin knockout mice. Old prodynorphin knockout mice had higher mGluR expression than old wild-type mice, and they exhibited mGluR-mediated plasticity at a level similar to young and middle-aged mice. Additionally, on behavioral tests of memory, learning, and anxiety, the prodynorphin knockout mice performed better than and displayed less anxiety behaviors than old wild-type mice. In fact, old prodynorphin knockout mice performed similarly to young and middle-aged mice on the behavioral tasks. To confirm that these changes were mediated by mGluRs and dynorphin receptors, the authors also performed behavioral tests in mice that had received pharmacological treatment. In old wild-type mice, pharmacologically increasing the activity of mGluRs or blocking the activity of dynorphin receptors resulted in greatly improved performance on the memory and learning tasks and in decreased anxiety behaviors. Conversely, in old prodynorphin knockout mice pharmacologically inhibiting the activity of mGluRs resulted in poorer performance on memory tasks and in increased anxiety behaviors. Together, these data clearly demonstrate that increases in dynorphin during normal mammalian aging can cause a reduction in mGluR-mediated synaptic changes that underlie learning, memory, and anxiety, and they identify a pathway that can be targeted to improve cognitive ability in the aging population.
July 5, 2013
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A few weeks ago I reviewed a paper that demonstrated that pluripotent stem cells could be induced by repressing muscleblind-like RNA binding (MBNL) proteins in differentiated cells. Continuing in this vein, new research published in Nature Cell Biology from the lab of Dr. Connie Eaves at the BC Cancer Agency identifies a pathway crucial for the maintenance of the self-renewal properties of hematopoietic stem cells (HSCs). Using array analysis and quantitative polymerase chain reaction, the authors found that the Lin28b gene is expressed much more highly in mouse fetal liver HSCs than in adult bone marrow HSCs, which have greatly reduced self-renewal capabilities compared to fetal liver HSCs. Adult bone marrow HSCs transfected with the Lin28 gene and subsequently transplanted in to mice of at least 10 weeks of age have increased self-renewal capabilities and also show decreased levels of let-7 microRNA, the production of which is inhibited by Lin28b. Additionally, flow cytometry experiments demonstrated that Hmga2, a protein that is known to be inhibited by let-7, was increased in adult bone marrow HSCs following Lin28 transfection. Directly increasing Hmga2 levels in adult bone marrow HSCs increased the self-renewing capabilities of these cells, whereas fetal liver cells lacking Hmga2 have greatly reduced self-renewing capability. Overall, this study demonstrates that the self-renewing capability of mouse hematopoietic stem cells is regulated by the Lin28 – let-7 – Hmga2 axis, which is down-regulated within a few weeks following birth. Thus, this pathway offers a potential target for the development of tissue-specific self-replicating cells, which promise to be very important for the treatment of a variety of diseases.
June 21, 2013
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Arthritis is a highly prevalent disorder, affecting about 1 in 5 people in North America, and is characterized by joint inflammation, which results in pain and reduction in joint mobility. Underlying these symptoms is the release of a peptide called substance P, so called because of its role in signalling pain. New research published in the Journal of Neuroscience from the lab of Dr. Alfredo Ribeiro-da-Silva at McGill University indicates that joint pain associated with arthritis may be due in part to increased activation of substance P-releasing nerve cells caused by inappropriate sprouting of sympathetic nerve fibers. The authors induced arthritis, which was characterized by joint edema and increased pain responses, in the hind ankle joint of rats. Using immunohistochemistry, the authors found that sympathetic nerve fibers, which normally innervate blood vessels in the skin to regulate blood-flow, sprouted to innervate the synovial membrane surrounding the ankle joint and the upper dermis covering the ankle joint four weeks after the arthritic phenotype was induced. Interestingly, these newly sprouted sympathetic nerve fibers closely associated with peptidergic nerve cells, which release substance P and are associated with transmitting pain responses. This result suggests that sympathetic nerve sprouting can increase the activity of substance P-containing neurons, exaggerating pain responses and inflammation. Consistent with this, pharmacologically blocking sympathetic nerve responses in these rats shifted the pain threshold back near normal. The authors also found that the expression of mature nerve growth factor (NGF), which is necessary for sympathetic neuron growth and survival, was increased near the ankle joint in which arthritis had been induced. The authors suggest that activity of peptidergic nerve cells increases joint and skin inflammation which initiates an immune response leading to increased production of mature NGF. The increase in NGF leads to sympathetic nerve sprouting, a further increase in peptidergic nerve cell activity, and ultimately to hyperactive pain signaling. These findings suggest that decreasing the production of mature NGF near arthritic sites can decrease sympathetic nerve sprouting and reduce arthritis associated pain. Additionally, localized inhibition of sympathetic neurotransmission may be a way to provide short-term arthritis pain relief.
June 14, 2013
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Embryonic stem cells are pluripotent, meaning they have the ability to differentiate into multiple cell types. Due to this, embryonic stem cells have the potential to be used in cell-based therapies to treat diseases in which specific cell types are lost, such as Alzheimer’s or diabetes, or to promote recovery following traumatic events, such as spinal cord injury or stroke. However, the use of embryonic stem cells is controversial for a number of ethical reasons, with specific concern surrounding how they are harvested. Induced pluripotent stem cells (iPSCs) offer an alternative to embryonic stem cells, because they can be derived from differentiated host tissue. Because changes in gene expression within embryonic stem cells lead to their differentiation and loss of pluripotency, iPSCs can be produced from differentiated cells by essentially reversing these changes. New work published in Nature from the lab of Dr. Benjamin Blencowe at the University of Toronto identifies muscleblind-like RNA binding proteins (MBNL1 and MBNL2) as regulators of specific gene splicing events that differ between embryonic stem cells and differentiated cells. Using high-throughput sequence profiling and quantitative polymerase chain reaction, the authors found that MBNL proteins are expressed less in embryonic stem cells and iPSCs than in differentiated cells. This led the authors to hypothesize that MBNL proteins repress expression of certain sequences of RNA that maintain the pluripotent state of embryonic stem cells. To examine if this was the case, the authors used small interfering RNA to decrease the amount of MBNL1 and 2 protein expressed in cultured mouse and human cells. In approximately half of these cells, decreasing the MBNL proteins altered the splicing of the FOXP1 gene, a gene important for triggering a switch between embryonic stem cells and differentiated cells, and returned the cells to an embryonic stem cell-like pattern of FOXP1 expression. It was also possible to do the opposite: over-expression of the MBNL1 and 2 proteins in mouse embryonic stem cells caused these cells to quickly adopt the FOXP1 splicing pattern seen in differentiated cells. Importantly, knockdown of MBNL proteins increased the level of several transcription factors that are critical for maintaining pluripotency of embryonic stem cells, and significantly increased the number of iPSC colonies. These results demonstrate that MBNL proteins 1 and 2 are directly involved in the control of embryonic stem cell pluripotency, and that reduction of their expression in differentiated cells can lead to induction of iPSCs. MBNL expression is therefore an attractive therapeutic target to create pluripotent cells for use in cell-based therapies, as the use of iPSCs eliminates many of the ethical concerns surrounding the use of embryonic stem cells for such therapies.
May 31, 2013
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During development several proteins guide the mapping of blood vessels throughout our body, providing different cues to direct them where they should go and, equally as important, not go. New research published in Nature from the lab of Dr. Sabine Cordes at Mt. Sinai Hospital in Toronto describes the role of a protein called gumby in the formation of the microvasculature. Mice lacking gumby displayed normal patterning of the major vasculature, but patterning of the smaller vascular networks in the head and trunk of the mice was greatly disrupted. Genetic mapping allowed the authors to determine that mutations in the Fam105b gene were underlying the defects observed in the “gumby mice”, and identified the gumby protein as a deubiquitinase. This means that gumby can counteract ubiquitination, a process in which proteins are tagged for a certain fate; this fate may be degradation, movement within a cell, or initiation of cellular processes. The authors also found that gumby interacts with a ubiquitinating complex called LUBAC, and that together these proteins can modulate the Wnt pathway, a pathway important in the development of the vasculature. Because LUBAC and gumby serve opposing functions, the interaction of these two proteins effectively creates a signaling axis that allows for flexibility in the management of the Wnt pathway, and ultimately the development of the vasculature. Identification of these pathways and the genes underlying them creates new possible targets for the management of disorders of vasculature mapping, as well as disorders in other systems that require significant mapping, such as the nervous system.
May 17, 2013
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Parkinson’s disease, a neurodegenerative disease characterized by motor and cognitive deficits, may be caused by mutations in the Parkin gene. The Parkin gene transcribes the Parkin protein, an enzyme which has been implicated in cellular processes including autophagy, or “cell housekeeping,” and cell survival. Recent work from the Montreal Neurological Institute and McGill University’s Department of Biochemistry published in Science magazine demonstrates the crystal structure of the Parkin protein. The crystal structure of a protein offers an excellent idea of the natural conformation a protein adopts; determining the structure of Parkin protein, surely an immense amount of work, will allow for advanced studies of how the protein normally functions, and will increase understanding of how mutations in the Parkin protein lead to the deficits seen in Parkinson’s disease.
Parkin protein normally has low basal activity. Following determination of the structure of Parkin, the authors found that it can maintain this low baseline by inhibiting itself. Additionally, by testing a number of mutations in the Parkin protein, they found that most mutations greatly reduce or abolish its already low basal activity. However, mutations directed at eliminating auto-inhibition of Parkin were able to increase activity of the protein, indicating that it is possible to bidirectionally change its activity. These experiments demonstrate the utility of knowing the crystal structure of the Parkin protein, as future studies will be able to better evaluate how the activity of the protein can be managed, which may prove very important in the treatment of Parkinson’s disease.
May 10, 2013
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Stroke is the leading cause of disability in North America, but no good treatment exists for stroke beyond a few hours of its occurrence. The damaging effects of stroke occur because nerve cells in the brain require oxygen to survive; once blood-flow to the brain is disrupted and oxygen delivery to nerve cells stops, the cells enter a state called excitotoxicity and begin to die. The best way to improve stroke outcome is to limit the amount of nerve cell death that occurs. Much pharmacological treatment has been directed at inhibiting a specific neurotransmitter receptor central to excitotoxicity, but this approach can have broad effects within the brain. New research from Dr. Yu Tian Wang’s lab at the University of British Columbia published in the Journal of Neuroscience offers a potential new target to limit nerve cell death following stroke. The researchers found that PTEN, a protein that promotes cell death once it enters the nucleus of a cell, becomes targeted to nerve cell nuclei after excitotoxicity starts; additionally, they found that a specific portion of PTEN is critical for its entry in to the nucleus. In nerve cells that were pharmacologically treated to become excitotoxic, ones that had this portion of PTEN mutated were less likely to die. Furthermore, mice injected with a peptide that inhibits the entry of PTEN in to the cell nucleus experienced less extensive physical brain damage, increased nerve cell protection, and more rapid and complete motor skill recovery following an induced stroke; these effects were seen if the peptide was delivered to mice up to 6 hours after the stroke was induced. These results indicate that limiting nerve cell death through inhibition of a downstream protein involved in excitotoxicity may be a viable new approach for stroke treatment, one which may also extend the treatment window following the occurrence of a stroke.
The use of oncolytic viruses is becoming an increasingly attractive avenue for the treatment of cancer, because these viruses are able to destroy tumor cells and also generate immune-responses directed at those same tumor cells. Using human viruses for this type of treatment may be inefficacious, because immunity may exist or quickly develop toward the virus that is being used. The use of animal viruses similar to human viruses may prove to be an effective way to avoid these potential immunity problems.
A proportion of cells within a tumor are cancer stem cells, which are often enriched in what is called a “side population” of tumor cells. These cells can self-renew, produce new cells derived from multiple cell lineages, and may increase the growth rate of tumors. Previous research from Dr. Karen Mossman’s lab at the McMaster University Immunology Research Centre demonstrated that bovine herpesvirus type 1 targets transformed human cells but not normal human cells, and new research from her lab published in Cancer Gene Therapy now demonstrates that this virus can infect and kill cancer stem cells within the tumor side population.
The researchers found that exposing a number of different breast cancer cell lines to the bovine herpesvirus 1 led to a decrease in tumor cell viability and an increase in tumor cell death. The virus also killed human breast cancer stem cells, and limited the self-renewal and cellular differentiation capabilities of these cells. Additionally, mice injected with breast cancer stem cells that had been exposed to bovine herpesvirus 1 formed much smaller tumors than mice that were injected with breast cancer stem cells that were untreated. These results offer hope that bovine herpesvirus 1 or similar viruses may be particularly useful in treating cancers, because, in addition to not targeting normal cells, they are effective in killing the particularly harmful cancer stem cell population, and their use could also limit immunity issues that may reduce treatment efficacy.
April 26, 2013
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Inflammatory bowel diseases (IBD), such as Crohn’s disease and ulcerative colitis, are autoimmune disorders in which persistent bowel inflammation leads to physical damage of the intestinal tract. Research out of the Inflammation Research Network at the University of Calgary, and published in the Proceedings of the National Academy of Sciences, offers a cool novel target for the treatment of IBD. Just like we have receptors that signal heat, evident when we get a hot or burning sensation when eating a chili pepper, we also have receptors that signal cold, which can be activated by compounds such as menthol. The researchers found that a receptor that signals cold (TRPM8) is expressed more highly in colon samples from humans with Crohn’s disease than in samples from those that do not have IBD. This finding suggests that the TRPM8 receptor is up-regulated in inflamed tissue in an attempt to cool it, similar to how controlled cooling is used to treat sites of traumatic injury.
To investigate the potential of the TRPM8 receptor as a target for inflammation reduction, the researchers performed experiments in mice in which colitis had been induced. Mice with induced colitis expressed the TRPM8 receptor more highly in their colon than mice that did not have induced colitis. The mice with induced colitis also had high levels of cytokines, signalling molecules that can promote inflammation, in their colon; activating the TRPM8 receptor with a molecule called icilin reduced these cytokine levels to normal. Activation of the TRPM8 receptor in mice with induced colitis also decreased the release of a pro-inflammatory neuropeptide in the gut, and, most importantly, limited the amount of physical damage that occurred to the colon. These findings characterize the TRPM8 receptor as an anti-inflammatory receptor, and highlight its potential as a target for therapeutics directed at reducing inflammation in IBD and other chronic inflammatory diseases.
April 19, 2013
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Author’s note: I will be taking over writing duties from John Holyoake for the Friday Science Review. If you wish to know more about me, you can find my short bio on our contributors page – http://crossborderbiotech.ca/about/
Anxiety disorders are becoming increasingly prevalent in our society, and are highly detrimental to an individual’s well being, both physically and mentally. Children with autism spectrum disorder (ASD) are particularly susceptible to anxiety disorders, but their deficits in communication often make it difficult for them to express feelings of anxiousness. Being unable to express these feelings may lead to an exacerbated anxiety response in children with ASD, because they are often exceedingly aware of their surroundings and may become more socially withdrawn. A study published in PLoS One led by Dr. Azadeh Kushki at the Holland Bloorview Kids Rehabilitation Centre in Toronto sought to address this problem by determining a physiological marker that signals anxiety in children with ASD, which would allow for improvement in their care.
Children with ASD and typically developing children performed an anxiety-inducing task while activity of the autonomic nervous system, the part of our nervous system that unconsciously controls visceral functions, was evaluated using three different measures. The researchers found that two of these measures, heart rate and perspiration, were elevated even at rest in children with ASD, whereas the third measure, skin temperature, was comparable at rest between children with ASD and typically developing children. However, during the anxiety-inducing task the skin temperature of children with ASD increased, whereas the skin temperature of typically developing children decreased, the normal response during stress.
The results of this study offer three important findings. First, the observation that heart rate and perspiration are elevated at rest in children with ASD supports previous reports that these children have elevated generalized anxiety. Second, the difference in changes in skin temperature between children with ASD and typically developing children observed during the stressful task offer a potential non-invasive measure of anxiety in children with ASD. Finally, the generalized difference in visceral functions observed between children with ASD and typically developing children indicates that children with ASD experience inappropriate regulation of their autonomic nervous system, specifically over-activity in the division of the autonomic nervous system that controls stress responses. This final finding warrants further investigation in order to understand whether inappropriate regulation of the autonomic nervous system contributes to increased generalized anxiety in children with ASD, or if it simply accompanies general anxiety caused by other characteristics of the disorder.