Alexandre P. Blanchard

Lipidomics era: Accomplishments and challenges

Lipid mediators participate in signal transduction pathways, proliferation, apoptosis, and membrane trafficking in the cell. Lipids are highly complex and diverse owing to the various combinations of polar headgroups, fatty acyl chains, and backbone structures. This structural diversity continues to pose a challenge for lipid analysis. Here we review the current state of the art in lipidomics research and discuss the challenges facing this field. The latest technological developments in mass spectrometry, the role of bioinformatics, and the applications of lipidomics in lipid metabolism and cellular physiology and pathology are also discussed.

Amyloid-β42 signals tau hyperphosphorylation and compromises neuronal viability by disrupting alkylacylglycerophosphocholine metabolism

Perturbation of lipid second messenger networks is associated with the impairment of synaptic function in Alzheimer disease. Underlying molecular mechanisms are unclear. Here, we used an unbiased lipidomic approach to profile alkylacylglycerophosphocholine second messengers in diseased tissue. We found that specific isoforms defined by a palmitic acid (16:0) at the sn-1 position, namely 1-O-hexadecyl-2-acetyl-sn-glycero-3-phosphocholine (C16:0 PAF) and 1-O-hexadecyl-sn-glycero-3-phosphocholine (C16:0 lyso-PAF), were elevated in the temporal cortex of Alzheimer disease patients, transgenic mice expressing human familial disease-mutant amyloid precursor protein, and human neurons directly exposed to amyloid-β42 oligomers. Acute intraneuronal accumulation of C16:0 PAF but not C16:0 lyso-PAF initiated cyclin-dependent kinase 5-mediated hyperphosphorylation of tau on Alzheimer disease-specific epitopes. Chronic elevation caused a caspase 2 and 3/7-dependent cascade resulting in neuronal death. Pharmacological inhibition of C16:0 PAF signaling, or molecular strategies increasing hydrolysis of C16:0 PAF to C16:0 lyso-PAF, protected human neurons from amyloid-β42 toxicity. Together, these data provide mechanistic insight into how disruptions in lipid metabolism can determine neuronal response to accumulating oligomeric amyloid-β42.

Visualization and Phospholipid Identification (VaLID)

Motivation: Establishing phospholipid identities in large lipidomic datasets is a labour-intensive process. Where genomics and proteomics capitalize on sequence-based signatures, glycerophospholipids lack easily definable molecular fingerprints. Carbon chain length, degree of unsaturation, linkage, and polar head group identity must be calculated from mass to charge (m/z) ratios under defined mass spectrometry (MS) conditions. Given increasing MS sensitivity, many m/z values are not represented in existing prediction engines. To address this need, Visualization and Phospholipid Identification is a web-based application that returns all theoretically possible phospholipids for any m/z value and MS condition. 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 are provided as high-resolution structures. Availability: VaLID is available through the Canadian Institutes of Health Research Training Program in Neurodegenerative Lipidomics resources web site at https://www.med.uottawa.ca/lipidomics/resources.html. Contacts: lipawrd@uottawa.ca Supplementary Information: Supplementary data are available at Bioinformatics online.

Phosphoproteome analysis of an early onset mouse model (TgCRND8) of Alzheimer's disease reveals temporal changes in neuronal and glia signaling pathways

Sustained exposure to soluble amyloid β (Aβ42) oligomers is predicted to impair synaptic function in the hippocampal‐entorhinal circuit, signaling synaptic loss and precipitating cognitive impairment in Alzheimers disease. Regional changes in overall patterns of protein phosphorylation are likely crucial to promote transition from a presymptomatic to a symptomatic state in response to accumulating Aβ42. Here, we used unbiased proteomic approaches to compare the phosphoproteome of presymptomatic and symptomatic TgCRND8 mice and identify network disruptions in signaling pathways implicated in the manifestation of behavioral indices of learning and memory impairment. Phosphopeptide enrichment with triple isotopic dimethylation labeling combined with online multidimensional separation and MS was used to profile phosphoproteome changes in 2‐ and 6‐month‐old TgCRND8 mice and congenic littermate controls. We identified 1026 phosphopeptides representing 1168 phosphorylation sites from 476 unique proteins. Of these, 595 phosphopeptides from 293 unique proteins were reliably quantified and 139 phosphopeptides were found to change significantly in the hippocampus of TgCRND8 mice following conversion from a presymptomatic to a symptomatic state.

Platelet activating factors are associated with depressive symptoms in coronary artery disease patients: a hypothesis-generating study

Introduction Depression is a frequent complication of coronary artery disease (CAD) with an unknown etiology. Platelet activating factor (PAF) lipids, which are associated with CAD, have recently been linked with novel proposed etiopathological mechanisms for depression such as inflammation, oxidative/nitrosative stress, and vascular endothelial dysfunction. Methods and results This hypothesis-generating study investigated the relationships between various PAF species and depressive symptoms in 26 CAD patients (age: 60.6±9.2 years, 69% male, mean Hamilton Depression Rating Scale [HAM-D] score: 11.8±5.2, HAM-D range: 3–20). Plasma PAF analyses were performed using high performance liquid chromatography electrospray ionization mass spectrometry in precursor ion scan. Significant associations between depressive symptom severity (HAM-D score) and a greater plasma abundance of the PAFs phosphocholine (PC) PC(O-12:0/2:0) (r=0.49, P=0.01), PC(O-14:1/2:0) (r=0.43, P=0.03), PC(O-17:3/2:0) (r=0.44, P=0.04), and PC(O-18:3/2:0) (r=0.50, P=0.01) were observed. Associations between those PAFs and HAM-D score persisted after adjusting for age and sex. Conclusion These preliminary findings support the exploration of the PAF lipidome for depressive symptom biomarkers in CAD patients. Patients were recruited as part of the following clinical trial: NCT00981383.

Predicting Glycerophosphoinositol Identities in Lipidomic Datasets Using VaLID (Visualization and Phospholipid Identification)—An Online Bioinformatic Search Engine

The capacity to predict and visualize all theoretically possible glycerophospholipid molecular identities present in lipidomic datasets is currently limited. To address this issue, we expanded the search-engine and compositional databases of the online Visualization and Phospholipid Identification (VaLID) bioinformatic tool to include the glycerophosphoinositol superfamily. VaLID v1.0.0 originally allowed exact and average mass libraries of 736,584 individual species from eight phospholipid classes: glycerophosphates, glyceropyrophosphates, glycerophosphocholines, glycerophosphoethanolamines, glycerophosphoglycerols, glycerophosphoglycerophosphates, glycerophosphoserines, and cytidine 5′-diphosphate 1,2-diacyl-sn-glycerols to be searched for any mass to charge value (with adjustable tolerance levels) under a variety of mass spectrometry conditions. Here, we describe an update that now includes all possible glycerophosphoinositols, glycerophosphoinositol monophosphates, glycerophosphoinositol bisphosphates, and glycerophosphoinositol trisphosphates. This update expands the total number of lipid species represented in the VaLID v2.0.0 database to 1,473,168 phospholipids. Each phospholipid can be generated in skeletal representation. A subset of species curated by the Canadian Institutes of Health Research Training Program in Neurodegenerative Lipidomics (CTPNL) team is provided as an array of high-resolution structures. VaLID is freely available and responds to all users through the CTPNL resources web site.

Distinct disruptions in Land's cycle remodeling of glycerophosphocholines in murine cortex mark symptomatic onset and progression in two Alzheimer's Disease mouse models

Changes in glycerophosphocholine metabolism are observed in Alzheimers disease; however, it is not known whether these metabolic disruptions are linked to cognitive decline. Here, using unbiased lipidomic approaches and direct biochemical assessments, we profiled Lands cycle lipid remodeling in the hippocampus, frontal cortex, and temporal‐parietal‐entorhinal cortices of human amyloid beta precursor protein (ΑβPP) over‐expressing mice. We identified a cortex‐specific hypo‐metabolic signature at symptomatic onset and a cortex‐specific hyper‐metabolic signature of Lands cycle glycerophosphocholine remodeling over the course of progressive behavioral decline. When N5 TgCRND8 and ΑβPPSwe/PSIdE9 mice first exhibited deficits in the Morris Water Maze, levels of lyso‐phosphatidylcholines, LPC(18:0/0:0), LPC(16:0/0:0), LPC(24:6/0:0), LPC(25:6/0:0), the lyso‐platelet‐activating factor (PAF), LPC(O‐18:0/0:0), and the PAF, PC(O‐22:6/2:0), declined as a result of reduced calcium‐dependent cytosolic phospholipase A2α (cPLA2α) activity in all cortices but not hippocampus. Chronic intermittent hypoxia, an environmental risk factor that triggers earlier learning memory impairment in ΑβPPSwe/PSIdE9 mice, elicited these same metabolic changes in younger animals. Thus, this lipidomic signature of phenoconversion appears age‐independent. By contrast, in symptomatic N5 TgCRND8 mice, cPLA2α activity progressively increased; overall Lyso‐phosphatidylcholines (LPC) and LPC(O) and PC(O‐18:1/2:0) levels progressively rose. Enhanced cPLA2α activity was only detected in transgenic mice; however, age‐dependent increases in the PAF acetylhydrolase 1b α1 to α2 expression ratio, evident in both transgenic and non‐transgenic mice, reduced PAF hydrolysis thereby contributing to PAF accumulation. Taken together, these data identify distinct age‐independent and age‐dependent disruptions in Lands cycle metabolism linked to symptomatic onset and progressive behavioral decline in animals with pre‐existing Αβ pathology.

A CREE TRADITIONAL MEDICINAL PLANT, SARRACENIA PURPUREA L., ALTERS LEARNING AND MEMORY IN TGCRND8 MICE, LIKELY BY INCREASING LEVELS OF PC(O-16:0/2:0) PAF

SARRACENIA PURPUREA L., ALTERS LEARNING AND MEMORY IN TGCRND8 MICE, LIKELY BY INCREASING LEVELS OF PC(O-16:0/2:0) PAF Carolina Cieniak, Fida Ahmed, Hongbin Xu, Matthew W. Granger, Alexandre P. Blanchard, Zhibin Ning, Pierre S. Haddad, Brian C. Foster, John T. Arnason, Steffany A.L. Bennett, University of Ottawa, Ottawa, Ontario, Canada; 2 Universit e de Montr eal, Montreal, Quebec, Canada. Contact e-mail: carolina07@gmail.com