Lipid raft localization of TLR2 and its co-receptors is independent of membrane lipid composition.

BACKGROUND: Toll like receptors (TLRs) are an important and evolutionary conserved class of pattern recognition receptors associated with innate immunity. The recognition of Gram-positive cell wall constituents strongly depends on TLR2. In order to be functional, TLR2 predominantly forms a heterodimer with TLR1 or TLR6 within specialized membrane microdomains, the lipid rafts. The membrane lipid composition and the physicochemical properties of lipid rafts are subject to modification by exogenous fatty acids. Previous investigations of our group provide evidence that macrophage enrichment with polyunsaturated fatty acids (PUFA) induces a reordering of lipid rafts and non-rafts based on the incorporation of supplemented PUFA as well as their elongation and desaturation products. METHODS: In the present study we investigated potential constraining effects of membrane microdomain reorganization on the clustering of TLR2 with its co-receptors TLR1 and TLR6 within lipid rafts. To this end, RAW264.7 macrophages were supplemented with either docosahexaenoic acid (DHA) or arachidonic acid (AA) and analyzed for receptor expression and microdomain localization in context of TLR stimulation. RESULTS AND CONCLUSIONS: Our analyses showed that receptor levels and microdomain localization were unchanged by PUFA supplementation. The TLR2 pathway, in contrast to the TLR4 signaling cascade, is not affected by exogenous PUFA at the membrane level.

Lipid composition of membrane microdomains isolated detergent-free from PUFA supplemented RAW264.7 macrophages.

Profound alterations in the lipid profile of raft and non-raft plasma membrane microdomains were found when RAW264.7 macrophages were supplemented with polyunsaturated fatty acids (PUFAs) in physiologically relevant concentrations. For the first time lipids in the detergent-free isolated membrane domains of phagocytic immune cells were characterized by mass spectrometry. The extent of remodeling of the membrane lipids differed with different n3 and n6 PUFA supplements. The mildest effects were detected for α-linolenic acid (LNA) and linoleic acid (LA), the C18 precursors of the n3 and n6 families, respectively. When the effects of highly unsaturated PUFAs were compared, eicosapentaenoic acid (EPA) caused more extensive restructuring of membrane lipids than docosahexaenoic acid (DHA) or arachidonic acid (AA). The supplements altered the lipid species composition of both the raft and non-raft membrane fractions. The rafts containing elevated proportions of highly unsaturated lipid species may relocate sterically incompatible lipids and proteins originally belonging to this microdomain. Such effect was evident for sphingomyelin, which favored non-rafts instead of rafts after EPA supplementation. The current work suggests that the different functional consequences found previously when supplementing macrophages with either EPA or DHA have their origin in the different effects of these PUFAs on membrane architecture.

Impact of Polyunsaturated Fatty Acids on miRNA Profiles of Monocytes/Macrophages and Endothelial Cells-A Pilot Study.

Alteration of miRNAs and dietary polyunsaturated fatty acids (PUFAs) underlies vascular inflammation. PUFAs are known to be incorporated into the cell membrane of monocytes/macrophages or endothelial cells, the major cellular players of vascular diseases, thereby affecting cellular signal transduction. Nevertheless, there are no investigations concerning the PUFA impact on miRNA expression by these cells. With regard to the key role miRNAs play for overall cellular functionality, this study aims to elucidate whether PUFAs affect miRNA expression profiles. To this end, the monocyte/macrophage cell line RAW264.7 and the endothelial cell line TIME were enriched with either docosahexaenoic acid (DHA; n3-PUFA) or arachidonic acid (AA; n6-PUFA) until reaching a stable incorporation into the plasma membrane and, at least in part, exposed to an inflammatory milieu. Expressed miRNAs were determined by deep sequencing, and compared to unsupplemented/unstimulated controls. Data gained clearly show that PUFAs in fact modulate miRNA expression of both cell types analyzed regardless the presence/absence of an inflammatory stimulator. Moreover, certain miRNAs already linked to vascular inflammation were found to be affected by cellular PUFA enrichment. Hence, vascular inflammation appears to be influenced by dietary fatty acids, inter alia, via PUFA-mediated modulation of the type and amount of miRNAs synthesized by cells involved in the inflammatory process.