Key roles of mono-unsaturated fatty acids in lipid metabolism and lipid-dependent signalling

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Cellular lipid metabolism as well as multiple cell signalling events are impacted by the intracellular levels of monounsaturated fatty acids (MUFA). However, the mechanisms by which MUFA exert these effects remain poorly understood. Our research program aims to elucidate the role of the stearoyl-CoA desaturase 1 (SCD1) enzyme, which produces MUFA, in these cellular events. We use oleate, a major product of the SCD1 enzyme, as a bioactive MUFA in our studies.******OBJECTIVES***1- To determine the role of MUFA in the cellular storage of lipids. We will address the role of SCD1 in intracellular lipid storage, and establish if SCD1 is part of a larger protein complex controlling this process. As oleate preferentially stimulates lipid storage in the form of lipid droplets, we will identify the oleate metabolite responsible for this effect. Further, seipin, a key protein in lipid droplet formation, functionally interacts with SCD1 and, together with SCD1, localizes to the vicinity of lipid droplets; thus, we will examine the role of SCD1 in lipid droplet formation by identifying SCD1 protein interactors under different metabolic states. We will combine information garnered from two cellular models (hepatocytes and yeast) to better understand the contribution of SCD1 to lipid droplet formation.******2- To characterize protein acylation events involving MUFA. We will evaluate the prevalence of MUFA acylation, an emerging type of protein covalent modification, in cellular signalling events. Oleate stimulates lipid synthesis by modulating the activity of SREBP-1, a key lipogenic transcription factor. This modulation of activity likely occurs via direct acylation of SREBP1. Using complementary mass spectrometry analyses, we will identify the lipid moiety on the SREBP-1 protein, as well as its acylated residue(s). We will also use an -alkynyl-biotin pull-down approach to capture palmitoylated and oleylated proteins and identify new MUFA-modified proteins.******3- To determine the impact of MUFA on signalling events associated with cell membranes. We will characterize the impact of oleate on the regulation of signalling events involving lipid second messengers. These events influence cell migration by controlling the formation of cell membrane protrusions. Oleate impacts both cell membrane lipid composition and micro-domain organization, and modulates the activity of membrane signalling complexes. We will characterize the signalling proteins recruited to membrane rafts of oleate-treated cells. Using biosensors, we will also visualize the formation of phospholipase D2 and phosphoinositide 3-kinase products, two enzymes implicated in oleate-stimulated cell migration. We will observe the impact of oleate on the spatial generation of lipid second messengers at the subcellular scale.******Our studies are expected to provide understanding of the molecular mechanisms by which MUFA, particularly oleate, act on signalling pathways regulating cellular homeostasis.**