Date Published: July 3, 2017
Publisher: Public Library of Science
Author(s): Roman Šmidák, Harald C. Köfeler, Harald Hoeger, Gert Lubec, Michael Bader.
Brain lipids are integral components of brain structure and function. However, only recent advancements of chromatographic techniques together with mass spectrometry allow comprehensive identification of lipid species in complex brain tissue. Lipid composition varies between the individual areas and the majority of previous reports was focusing on individual lipids rather than a lipidome. Herein, a mass spectrometry-based approach was used to evaluate age-related changes in the lipidome of the rat amygdala obtained from young (3 months) and old (20 months) males of the Sprague-Dawley rat strain. A total number of 70 lipid species with significantly changed levels between the two animal groups were identified spanning four main lipid classes, i.e. glycerolipids, glycerophospholipids, sphingolipids and sterol lipids. These included phospholipids with pleiotropic brain function, such as derivatives of phosphatidylcholine, phosphatidylserine, and phosphatidylethanolamine. The analysis also revealed significant level changes of phosphatidic acid, diacylglycerol, sphingomyelin and ceramide that directly represent lipid signaling and affect amygdala neuronal activity. The amygdala is a crucial brain region for cognitive functions and former studies on rats and humans showed that this region changes its activity during normal aging. As the information on amygdala lipidome is very limited the results obtained in the present study represent a significant novelty and may contribute to further studies on the role of lipid molecules in age-associated changes of amygdala function.
Brain lipids are attracting focused attention in neurochemistry as information carrying molecules that affect the biological processes by both, modifying membrane structures and direct interaction with other signaling molecules [1,2]. The numerous functions of lipids reflect their high structural and combinatorial diversity that makes lipidomic analyses experimentally challenging . These analyses have been frequently hampered by sampling problem, extraction procedures as well as instability in postmortem tissues . However, the advancements in chromatographic separations and mass spectrometry (MS) currently allow more complex identification and quantitation of lipid species in different types of biological samples .
The aim of this study was to perform a high throughput non-targeted lipidomic analysis to identify significantly changed lipid species in the amygdala of the aged rat brain. The dissected amygdalae of young (3 months) and old (20 months) animals of Sprague-Dawley rats, each group containing 12 individuals were analyzed by liquid chromatography coupled to electrospray ionization mass spectrometry (ESI-MS). To achieve a comprehensive detection, the MS experiment was run in both, negative and positive ionization mode. Significantly changed lipid species were identified by accurate (+/- 5 ppm) precursor mass matching with an internal lipid database which covers more than 20,000 molecular lipid species originating from 58 individual lipid (sub)classes. All identified lipid molecules, the polarity of the molecules, fold change and P-values are summarized in Table 1 and more detailed experimental data are provided as supporting information in S1 Table.
Lipids form a substantial part of the brain and are pleiotropic in function. So far, very few studies analyzed the impact of aging on distinct areas in rat brain using lipidomic approach. Although amygdala is one of the primary brain structures responsible for the formation of memory and controlling emotional behaviour, lipidomic data for this area is very limited. In the current study, a comprehensive lipidomic analysis of rat amygdala was performed to better understand the age-related changes of lipid signaling in this region.