The expression of hormone-sensitive lipase in clonal beta-cells and rat islets is induced by long-term exposure to high glucose.
Hormone-sensitive lipase (HSL) is expressed and enzymatically active in beta-cells and has been proposed to be involved in the generation of the lipid-derived signal that seems to be necessary for glucose-stimulated insulin secretion. In this study, we investigated whether the expression of HSL in INS-1 cells and in rat islets is affected by exposure to high glucose concentrations. Incubation of INS-1 cells in 25 mmol/l glucose for 16 and 32 h induced HSL protein expression twofold, whereas no effect was observed after 4 and 8 h of incubation. The HSL activity, defined as the diglyceride lipase activity inhibited by anti-rat HSL antibodies, constituted approximately 25% of total diglyceride lipase activity and was induced to a similar extent as HSL protein levels. The glucose effect at 16 h on HSL protein expression level was confirmed in freshly isolated rat islets. Exposure of INS-1 cells to different glucose concentrations for 16 h showed that the inductive effect on HSL protein levels was maximum at 20 mmol/l glucose (2- to 2.5-fold). Northern blot analysis demonstrated a more than threefold elevation of HSL mRNA levels. The induction was blocked by actinomycin D, and the half-life of the transcript seemed to be unchanged by high glucose, suggesting a transcriptional nature of the glucose effect on HSL gene expression. The nonmetabolizable glucose analog 2-deoxyglucose, which has no mitogenic effect, induced HSL approximately 1.3-fold, whereas mannose was similar to glucose, stimulating HSL expression 1.7- to 2-fold. The results suggest that HSL is involved in the beta-cell responses to hyperglycemia and also in generating the lipid signal that is needed in stimulus-secretion coupling.
Winzell
M S
MS
Department of Cell and Molecular Biology, Section for Molecular Signalling, Lund University, Lund, Sweden. sorhede_winzell@medkem.lu.se
Svensson
H
H
Arner
P
P
Ahrén
B
B
Holm
C
C
D000818:Animals; D002478:Cells, Cultured; D002999:Clone Cells; D004305:Dose-Response Relationship, Drug; D005947:Glucose / Q000378:metabolism / Q000494:pharmacology*; D007515:Islets of Langerhans / Q000187:drug effects* / Q000201:enzymology* / Q000378:metabolism; D008066:Lipolysis / Q000187:drug effects; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D002787:Sterol Esterase / Q000378:metabolism*; D013997:Time Factors
D002787:Sterol Esterase; D005947:Glucose