Kissing Cousins: When two cells become one they can change their stars
Posted on Aug 3 2016 by Steffany Bennett
Connexins and pannexins in neuronal development and adult neurogenesis
In neurodegenerative disorders, specific cell lineages (i.e., neurons or glia) and subtypes (i.e., neurons expressing certain transmitters) are deleted. Little can be done to replace damaged brain cells or restore cellular connectivity in the weeks that follow a stroke or over the course of a progressive neurodegenerative disorder such as Alzheimer Disease. The adult human brain supports neural stem and progenitor cells - cells capable of producing new neurons and glia that functionally integrate into the existing circuitry. Mobilizing or introducing these populations into damaged tissue represents a novel, potentially transformative, approach to brain repair. Yet injury-induced neurogenesis can also result in the integration of inappropriate neuronal subtypes into existing brain circuitry (i.e., inhibitory neurons replacing excitatory neurons). The presence of these "ectopic" neurons can precipitate further neurological impairment. Clearly, brain repair strategies will depend upon a comprehensive understanding of how appropriate cell lineages are effectively generated in degenerating tissue. Connexin and pannexin proteins are the structural units of gap junction channels that bridge two cells allowing direct exchange of material when the bridge opens and two cells become one. We review here compelling evidence implicating the passage of ions, metabolites, and second messengers between cells via gap junctions or through open hemichannels in non-junctional membranes in the control of neural stem and progenitor cell proliferation, survival, and commitment to either a glial or neuronal lineage.
Swayne LA*, Bennett SAL (2016) "Connexins and pannexins in neuronal development and adult neurogenesis." BMC Cell Biology 2016, 17(Suppl 1):10 DOI 10.1186/s12860-016-0089-5 *Corresponding author [download] [neurogenesis movie]
Complex lipid domains simplified: A step-by-step guide to preparing intact membrane microdomains from tissue homogenates
Posted on July 22 2016 by Steph Fowler
Preparation of gap junctions in membrane microdomains for immunoprecipitation and mass spectrometry interactome analysis.
As we develop more complex biochemical and analytical techniques for identifying protein interaction networks of hub proteins, it is becoming increasingly clear that these hubs are critical platforms for intracellular signaling cascades. Progress in this field has been limited by several technical challenges, namely that the cellular environment is too complex to properly identify protein interactions of less abundant proteins. In addition, the lipid environment of each subcellular organelle presents a unique complement of structural lipids that must be appropriately solubilized to enable integral membrane proteins to be liberated from their lipid environments, without de-stabilizing any associated protein complexes. Here, we present a step-by-step protocol for isolating membrane microdomains from liver tissue, to facilitate the identification of gap junction protein interactomes by immunoprecipitation and mass spectrometry. We provide technical notes for adapting this protocol to other integral membrane proteins, tissues, and cell culture models. These procedures are valuable tools for enrichment and purification of less abundant membrane proteins, and greatly facilitate the identification of integral membrane protein signaling interactomes.
Fowler S*, Akins M, Bennett SAL* (2016) "Preparation of gap junctions in membrane microdomains for immunoprecipitation and mass spectrometry interactome analysis." In Gap Junctions Protocols, edited by Mathieu Vinken and Scott Johnstone, 1147: 113-132, New York, NY: Springer Press. *Joint corresponding authors [download]
SEX MATTERS: DISCOVERING A MOUSE MODEL THAT EMULATES THE SEXUALLY DICHOTOMOUS NATURE OF ALZHEIMER'S DISEASE
Posted on March 21 2016 by Matthew Granger
A TgCRND8 Mouse Model of Alzheimer's Disease Exhibits Sexual Dimorphisms in Behavioral Indices of Cognitive Reserve
Alzheimer's disease (AD) is sexually dimorphic in that while more men succumb to a prodromal form of the disease yet females more readily convert to late onset AD. Due to an enhanced cognitive reserve, it seems that males are more resistant to toxic AD pathologies in the brain than females. Cognitive reserve is defined as the ability adapt to different cognitive strategies using alternative brain networks to cope with progressively toxic pathologies. Our lab has recently reported and characterized a transgenic mouse model that mimics this effect. These mice are transgenically altered to give them a genetic susceptibility to the human pathologies that afflict AD patients. In comparing male and female mice, we have found that while both are impaired relative to sex-matched control mice in a learning and memory task, female mice are more impaired than males. This was due to the ability of males to adopt different cognitive strategies in the face of AD pathology while females could not which demonstrates that males have greater cognitive reserve than females in this mouse model. We have also found that this is not the influence of greater AD pathology in females, further demonstrating the common relationship with the human condition. This research is crucial to further understanding the relationship between AD cognitive decline and sex. It provides an ideal model to discover and target sex-specific processes involved the susceptibility to AD pathology.
Granger MW, Franko B, Taylor MW, Messier C, St George-Hyslop P, Bennett SAL (2016) A TgCRND8 mouse model of Alzheimer's disease exhibits sexual dimorphisms in behavioral indices of cognitive reserve, J Alz Dis, 51:757-773 doi: 10.3233/JAD-150587 [download]
(+) older blog posts
What the yeast lipidome can tell us about Alzheimer's disease
Posted on March 11 2016 by Michael Kennedy
A perfect storm: Elevating one platelet activating factor sets off a ceramide chain reaction
Although dysregulated lipid metabolism is now a recognized hallmark of many neurodegenerative diseases disentangling the effect of altered intracellular lipid metabolism upon neuronal cell function has proven challenging. In our most recent report we leveraged complementary genome-wide approaches in Saccharomyces cerevisiae to reveal an unappreciated effect of PC(O-16:0/2:0) or C16:0 platelet activating factor (PAF) upon mitochondrial function. While mitochondrial involvement in Alzheimer's disease is well documented the underlying mechanisms which disrupt mitochondrial function have not been fully elucidated. Our recent findings suggest that the dysregulated metabolism of glycerophosphocholines observed in Alzheimer's disease may be instrumental in promoting the mitochondrial fragmentation and increased production of reactive oxygen species. Interestingly, we found that the deleterious effects of PC(O-16:0/2:0) upon mitochondrial function could be suppressed by deleting cellular sphingosine phosphate lyase activity, a lipid metabolite of the ceramide biosynthetic pathway with potent effects upon cellular function and viability, suggesting that therapeutic interventions aimed at modulating intraneuronal sphingosine phosphate levels may be of benefit to patients with Alzheimer's disease however more work will be needed to investigate this possibility.
Kennedy MA, Moffat TC, Gable K, Ganesan S, Niewola-Staszkowska K, Johnston A, Nislow C, Giaever G, Harris LJ, Loewith R, Zaremberg V, Harper ME, Dunn T, Bennett SA, Baetz K (2016) A Signaling Lipid Associated with Alzheimer's Disease Promotes Mitochondrial Dysfunction. Sci Rep, 6:19332 [download]
Lipids and Depression: Can the circulating lipidome read out our mental state?
Posted on December 18 2015 by Graham Mazereeuw
Platelet activating factors are associated with depressive symptoms in coronary artery disease patients: a hypothesis-generating study
The importance of the heart-brain relationship is increasingly being recognized. Years of vascular risk factor burden, oxidative stress, and pro-inflammatory activity, each of which are part of coronary artery disease (CAD) pathophysiology, can contribute to neuroinflammation, lesions to white matter tracts involved in mood- and cognitive-regulation, and progressive neurodegeneration in the brain. Accordingly, CAD is a strong risk factor for brain disorders such as depression, cognitive impairment, and progression to dementia. Until recently, the relevance of lipids to the mechanisms responsible for those brain disorders was unclear. In a novel hypothesis (Mazereeuw et al., 2013), we proposed that platelet activating factor (PAF) lipids might be relevant to depression and cognitive deficits in CAD patients due to their associations with vascular risk factors, oxidative stress, and pro-inflammatory pathways. We now have promising preliminary data to support that hypothesis. In a cross-sectional sample of 26 CAD patients, a greater plasma abundance of several PAF species, PC(O-12:0/2:0), PC(O-14:1/2:0), PC(O-17:3/2:0), PC(O-18:3/2:0), was associated with greater depressive symptom severity (Mazereeuw et al., 2015). In a cross-sectional sample of 24 CAD patients, a greater plasma abundance of two well-characterized PAFs, PC(O-16:0/2:0) and PC(O-18:0/2:0), was associated with poorer global cognitive performance, a relationship that was stronger among depressed patients (Mazereeuw et al., 2014). Though additional work with larger sample sizes is needed, these promising findings suggest that PAFs may be relevant biomarkers of mechanisms underlying the heart-brain relationship. They also point to lipidomics as a potentially rich source for the identification and development of depression and cognition-related biomarkers. Continued investigation in this area may lead to biomarkers able to predict disease progression, or possibly novel therapeutic targets.
Mazereeuw G, Herrmann N, Xu H, Blanchard AP, Figeys D, Oh PI, Bennett SAL, Lanctôt KL (2015) Platelet activating factors are associated with depressive symptoms in coronary artery disease patients: a hypothesis generating study, Neuropsychiatr DisTreat, 11:2309-2314 [download]
An in silico approach to annotating lipidomes
Posted on July 1 2015 by Alexandre P. Blanchard and Graeme McDowell
Visualization and Phospholipid Identification (VaLID): An online integrated search engine capable of identifying and visualizing glycerophospholipids with given mass over charge.
Lipids are intriguing cell constituents. Despite species composition being in constant flux, tight regulation maintains vital integrity of plasma membrane and organelle boundaries. Glycerophospholipids are key players in cellular signaling mechanisms. There are nine major classes of glycerophospholipids, each represented by a rich diversity of multiple species. Aberrant lipid metabolisms are associated with the major brain injuries and diseases such as, stroke, epilepsy, Alzheimer Disease, and Parkinson's Disease. Because each species has distinct chemical, physical, and biological proprieties, identification is crucial to elucidating discrete roles in neurodegenerative disease. Where genomics and proteomics capitalize on sequence-based signatures, glycerophospholipids lack easily definable molecular fingerprints. While advances in detecting lipid fragmentation patterns by mass spectrometry is enabling lipid identification at the molecular level, many m/z values are not represented in existing prediction engines. To address this gap, we created Visualization and Phospholipid Identification (VaLID), a freely accessible, web-based application that includes a search engine link to an exhaustive phospholipid database (CDP-DG, PA, PC, PE, PG, PGP, PPA and PS) and multiple visualization features. VaLID's search engineconsiders the user-defined m/z and MS conditions and returns all theoretically possible species. Visualization algorithms produce multiple chemical structure files for each species. Curated lipids detected by the Canadian Institutes of Health Research Training Program in Neurodegenerative Lipidomics (CTPNL) are provided as high-resolution structures. The 3D models give the opportunity to see the species in a more biologically realistic representation. VaLID has the overarching goal of facilitating the identification of the lipid species, understanding the research more deeply and assisting in its dissemination.
McDowell GSV, Blanchard AP, Figeys D, Fai S, Bennett SAL (2014) Advancing Lipidomic Bioinformatic Technologies: Visualization and Phospholipid Identification (VaLID) version 3.0, Proceedings IWBBIO 2014: International Work-Conference on Bioinformatics and Biomedical Engineering. Granada, Spain, 642-659. [download]
McDowell GSV, Blanchard AP, Taylor GP, Figeys D, Fai S, Bennett SAL. (2014) Predicting glycerophosphoinositol identities in lipidomic datasets using VaLID (Visualization and Phospholipid Identification) – an online bioinformatic search engine, Biomed Res Int (Bioinformatics, Special Issue Computational Systems Biology Methods in Molecular Biology, Chemistry Biology, Molecular Biomedicine, and Biopharmacy), Article ID 2014; 2014:818670. doi:10.1155/2014/818670. [download]
Blanchard AP, McDowell GSV, Valenzuela N, Xu H, Gelbard S, Bertrand M, Slater GW, Figeys D, Fai S, Bennett SAL (2013) Visualization and Phospholipid Identification (VaLID): An online integrated search engine capable of identifying and visualizing glycerophospholipids with given mass. Bioinformatics, 29: 284-285 [download]
Exploring the Phospholipidome for Biomarkers of Human disease
Posted on December 16, 2014 by Graham Mazereeuw
Platelet activating factors in depression and coronary artery disease: a potential biomarker related to inflammatory mechanisms and neurodegeneration.
Up to 50% of coronary artery disease (CAD) patients will experience a depressive episode after a cardiac event, often for prolonged periods of time. Depression in CAD patients is of high clinical importance as it doubles the risk of acute ischemic events and is linked with accelerated cognitive decline and the transition to dementia. Unfortunately, antidepressant pharmacotherapies have only modest effects in CAD patients and novel approaches arelimited by a poor understanding of underlying mechanisms. In a novel hypothesis to explain this relationship, we recently proposed that the platelet activating factor (PAF) family of alkylacylglycerophosphocholines (AAGPCs) may be associated with the onset and/or persistence of a depressive episode in CAD patients due to their association with CAD and with proposed mechanisms for depression. Emerging preclinical evidence supports this by indicating that disrupted lipid metabolism may be a converging point for several pathophysiological processes active in both depression and CAD. PAFs and other AAGPCs are remodelled at the cellular membrane in response to multiple extracellular inputs such as inflammatory activity, oxidative stress, and platelet reactivity, all of which are present in depressed CAD patients. PAFs also mediate cerebrovascular pathology and neurodegenerative processes that are commonly observed in patients with prolonged depression. Currently, PAFs represent unexplored potential mechanistic markers of depression in CAD. As such, elucidation of their role may lead to a better understanding of its underlying mechanisms and the potential identification of novel therapeutic targets.
Mazereeuw G, Xu H, Herrmann N, Figeys D, Oh P, Bennett SAL, Lanctôt KL (2014) Platelet-activating factors are associated with cognitive deficits in depressed coronary artery disease patients: a hypothesis-generating study. J. Neuroinflam, 11:119 doi: 10.1186/1742-2094-11-119 [download]