title: A comprehensive lipidomic screen of pancreatic β-cells using mass spectroscopy defines novel features of glucose-stimulated turnover of neutral lipids, sphingolipids and plasmalogens.
abstract: OBJECTIVE
  Glucose promotes lipid remodelling in pancreatic β-cells, and this is thought to contribute to the regulation of insulin secretion, but the metabolic pathways and potential signalling intermediates have not been fully elaborated.
  
  
  METHODS
  Using mass spectrometry (MS) we quantified changes in approximately 300 lipid metabolites in MIN6 β-cells and isolated mouse islets following 1 h stimulation with glucose. Flux through sphingolipid pathways was also assessed in (3)H-sphinganine-labelled cells using TLC.
  
  
  RESULTS
  Glucose specifically activates the conversion of triacylglycerol (TAG) to diacylglycerol (DAG). This leads indirectly to the formation of 18:1 monoacylglycerol (MAG), via degradation of saturated/monounsaturated DAG species, such as 16:0_18:1 DAG, which are the most abundant, immediate products of glucose-stimulated TAG hydrolysis. However, 16:0-containing, di-saturated DAG species are a better direct marker of TAG hydrolysis since, unlike the 18:1-containing DAGs, they are predominately formed via this route. Using multiple reaction monitoring, we confirmed that in islets under basal conditions, 18:1 MAG is the most abundant species. We further demonstrated a novel site of glucose to enhance the conversion of ceramide to sphingomyelin (SM) and galactosylceramide (GalCer). Flux and product:precursor analyses suggest regulation of the enzyme SM synthase, which would constitute a separate mechanism for localized generation of DAG in response to glucose. Phosphatidylcholine (PC) plasmalogen (P) species, specifically those containing 20:4, 22:5 and 22:6 side chains, were also diminished in the presence of glucose, whereas the more abundant phosphatidylethanolamine plasmalogens were unchanged.
  
  
  CONCLUSIONS
  Our results highlight 18:1 MAG, GalCer, PC(P) and DAG/SM as potential contributors to metabolic stimulus-secretion coupling.
authors.affiliation: Diabetes and Metabolism Division, Garvan Institute of Medical Research, 384 Victoria St, Darlinghurst, NSW, 2010, Australia; St. Vincent's Clinical School, Faculty of Medicine, University of New South Wales, Australia.
authors.forename: Gemma L
authors.initials: GL
authors.lastname: Pearson
authors.affiliation: Baker IDI Heart and Diabetes Institute, Melbourne, Australia.
authors.forename: Natalie
authors.initials: N
authors.lastname: Mellett
authors.affiliation: Diabetes and Metabolism Division, Garvan Institute of Medical Research, 384 Victoria St, Darlinghurst, NSW, 2010, Australia.
authors.forename: Kwan Yi
authors.initials: KY
authors.lastname: Chu
authors.affiliation: Diabetes and Metabolism Division, Garvan Institute of Medical Research, 384 Victoria St, Darlinghurst, NSW, 2010, Australia; St. Vincent's Clinical School, Faculty of Medicine, University of New South Wales, Australia.
authors.forename: Ebru
authors.initials: E
authors.lastname: Boslem
authors.affiliation: Baker IDI Heart and Diabetes Institute, Melbourne, Australia. Electronic address: peter.meikle@bakeridi.edu.au.
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Meikle
authors.affiliation: Diabetes and Metabolism Division, Garvan Institute of Medical Research, 384 Victoria St, Darlinghurst, NSW, 2010, Australia; St. Vincent's Clinical School, Faculty of Medicine, University of New South Wales, Australia. Electronic address: t.biden@garvan.org.au.
authors.forename: Trevor J
authors.initials: TJ
authors.lastname: Biden
keywords: (O), ether lipid; (P), plasmalogen; ATGL, adipose tissue glycerolipase; CE, cholesterol ester; COH, free cholesterol; Ceramide; DAG, diacylglycerol; Diacylglycerol; FA, fatty acid; GSIS, glucose-stimulated insulin secretion; GalCer, galactosylceramide; GluCer, glucosylceramide; HSL, hormone sensitive lipase; Insulin secretion; KRHB, Krebs Ringer Hepes Buffer; MAG, monacylglycerol; MHC, monohexosylceramide; MS, mass spectrometry; Monacylglycerol; PC, phosphatidylcholine; PE, phosphatidylethanolamine; PI, phosphatidylinositol; PKD, protein kinase D; PLA2, phospholipase A2; Pancreatic β-cell; Plasmalogen; SM, sphingomyelin; TAG, triacylglycerol