Elsevier

Molecular Metabolism

Volume 5, Issue 6, June 2016, Pages 404-414
Molecular Metabolism

Original article
A comprehensive lipidomic screen of pancreatic β-cells using mass spectroscopy defines novel features of glucose-stimulated turnover of neutral lipids, sphingolipids and plasmalogens

https://doi.org/10.1016/j.molmet.2016.04.003Get rights and content
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Highlights

  • Using mass spectroscopy lipidomics we have defined new aspects of glucose simulated lipid turnover in pancreatic beta cells.

  • Glucose directly stimulates triacylglycerol hydrolysis, of which di-saturated diacylglycerol species are excellent markers.

  • C18:1 is the most abundant monacylglycerol, and the one most obviously increased by glucose.

  • Phosphatidylcholine plasmalogens with poly-unsaturated side chains are preferentially decreased by glucose.

  • Glucose specifically enhances the conversion of ceramide to both sphingomyelin and galactosylceramide.

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 3H-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.

Conclusion

Our results highlight 18:1 MAG, GalCer, PC(P) and DAG/SM as potential contributors to metabolic stimulus-secretion coupling.

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Keywords

Pancreatic β-cell
Insulin secretion
Diacylglycerol
Monacylglycerol
Ceramide
Plasmalogen

Abbreviations

ATGL
adipose tissue glycerolipase
CE
cholesterol ester
COH
free cholesterol
DAG
diacylglycerol
FA
fatty acid
GalCer
galactosylceramide
GluCer
glucosylceramide
GSIS
glucose-stimulated insulin secretion
HSL
hormone sensitive lipase
KRHB
Krebs Ringer Hepes Buffer
MAG
monacylglycerol
MHC
monohexosylceramide
MS
mass spectrometry
PC
phosphatidylcholine
PE
phosphatidylethanolamine
PI
phosphatidylinositol
(P)
plasmalogen
(O)
ether lipid
PKD
protein kinase D
PLA2
phospholipase A2
TAG
triacylglycerol
SM
sphingomyelin

Cited by (0)

4

Gemma Pearson and Natalie Mellett contributed equally to this project.

5

Current address: Brehm Diabetes Research Center, University of Michigan Medical School, 1000 Wall St, Ann Arbor, Michigan, 48105-1912, USA.

6

Peter Meikle and Trevor Biden contributed equally to this project.