Lipidome and Proteome Map of Myelin Membranes Gopakumar Gopalakrishnan, 1,2,3 * Anshul Awasthi, 1 Wiam Belkaid, 1,3 Omar De Faria Jr., 1,3 Dalinda Liazoghli, 1,3 David R. Colman, 1,3y and Ajit S. Dhaunchak 1,3{ 1 Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill University, Montreal, Quebec, Canada 2 Department of Chemistry, McGill University, Montreal, Quebec, Canada 3 McGill Program in Neuroengineering, McGill University, Montreal, Quebec, Canada To understand the molecular anatomy of myelin mem- branes, we performed a large-scale, liquid chromatogra- phy-coupled tandem mass spectrometry (LC-MS/MS)- based lipidome and proteome screen on freshly purified human and murine myelin fractions. We identified more than 700 lipid moieties and above 1,000 proteins in the two species, including 284 common lipids and 257 com- mon proteins. This study establishes the first comprehen- sive map of myelin membrane components in human and mice. Although this study demonstrates many similarities between human and murine myelin, several components have been identified exclusively in each species. Future quantitative validation studies focused on interspecies dif- ferences will authenticate the myelin membrane anatomy. The combined lipidome and proteome map presented here can nevertheless be used as a reference library for myelin health and disease. V V C 2012 Wiley Periodicals, Inc. Key words: lipidomics; proteomics; metabolomics; multiple sclerosis; autoantigen; leukodystrophy; lipids Lipidomics and proteomics are important tools in the emerging field of systems biology, in which large-scale profiling of lipids and proteins is performed from fractio- nated tissue or cell samples (Han and Gross, 2005a,b; Fon- teh and Fisher, 2009; Vinayavekhin et al., 2010). Proteo- mics involves high-throughput identification of proteins in complex samples, whereas lipidomics involves identifi- cation of lipids in membrane fractions. In a particular cell type, the presence and abundance of a given protein can be indirectly decoded from levels of transcripts, whereas information about lipid composition can be deduced only via direct identification methods. Because there are no encoded transcripts available for lipids, the lipid moieties have to be identified via lipidomic approaches at individual cell levels. Furthermore, regulation of most cellular proc- esses, including migration, signaling, and differentiation, is performed as a result of collective and synchronized inter- actions among lipids, proteins, and other metabolites; it is evident that an ‘‘-omics’’-based future therapy would be difficult to achieve without having a better understanding of these individual components. In the context of the present study, we focus on understanding the molecular composition of myelin membranes by using a combined lipidomic and proteo- mic approach. Myelin is a specialized membrane struc- ture formed when oligodendrocytes wrap multiple layers of their membranes around axons in the vertebrate CNS. Because of its unique membrane composition of 70–85% lipids and 15–30% proteins (O’Brien and Samp- son, 1965; Norton and Autilio, 1966; Cuzner and Davi- son, 1968; Norton et al., 1975; Boggs and Moscarello, 1980), myelin membrane is a suitable candidate for dem- onstrating a combined lipidomic–proteomic approach. Studies involving myelin membranes are vital in under- standing the mechanistic pathways regulating axoglial interactions and in studying signaling pathways mediating long-term axonal support (Nave and Trapp, 2008; Nave, 2010). In addition to its classical role in insulation, mye- lin membranes are now known to play a critical role in long-term axonal integrity and survival (Nave and Trapp, 2008; Nave, 2010). These highly specialized properties of myelin membranes require unique lipid and protein composition that exhibits specific structural and mechanical properties compared with other nerve membranes (Norton et al., 1975). Myelin lipid composi- y Deceased June 1, 2011. { Deceased August 18, 2012. Contract grant sponsor: Government of Canada (to MNI); Contract grant sponsor: Rio Tinto Alcan; Contract grant sponsor: The Molson Founda- tion; Contract grant sponsor: Myelin Repair Foundation; Contract grant sponsor: MS Society of Canada (to A.S.D.). *Correspondence to: Gopakumar Gopalakrishnan, Montreal Neurological Institute/Department of Chemistry, McGill Program in Neuroengineering, McGill University, Montreal, Quebec, H3A 0B8 Canada. E-mail: gopaku- mar.gopalakrishnan@ mcgill.ca Additional Supporting Information may be found in the online version of this article. Received 29 May 2012; Revised 17 September 2012; Accepted 20 September 2012 Published online 27 November 2012 in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/jnr.23157 Journal of Neuroscience Research 91:321–334 (2013) ' 2012 Wiley Periodicals, Inc.