Localization of lipoprotein lipase and GPIHBP1 in mouse pancreas: effects of diet and leptin deficiency

Abstract

BackgroundLipoprotein lipase (LPL) hydrolyzes triglycerides in plasma lipoproteins and enables uptake of lipolysis products for energy production or storage in tissues. Our aim was to study the localization of LPL and its endothelial anchoring protein glycosylphosphatidylinositol-anchored high density lipoprotein-binding protein 1 (GPIHBP1) in mouse pancreas, and effects of diet and leptin deficiency on their expression patterns. For this, immunofluorescence microscopy was used on pancreatic tissue from C57BL/6 mouse embryos (E18), adult mice on normal or high-fat diet, and adult ob/ob-mice treated or not with leptin. The distribution of LPL and GPIHBP1 was compared to insulin, glucagon and CD31. Heparin injections were used to discriminate between intracellular and extracellular LPL.ResultsIn the exocrine pancreas LPL was found in capillaries, and was mostly co-localized with GPIHBP1. LPL was releasable by heparin, indicating localization on cell surfaces. Within the islets, most of the LPL was associated with beta cells and could not be released by heparin, indicating that the enzyme remained mostly within cells. Staining for LPL was found also in the glucagon-producing alpha cells, both in embryos (E18) and in adult mice. Only small amounts of LPL were found together with GPIHBP1 within the capillaries of islets. Neither a high fat diet nor fasting/re-feeding markedly altered the distribution pattern of LPL or GPIHBP1 in mouse pancreas. Islets from ob/ob mice appeared completely deficient of LPL in the beta cells, while LPL-staining was normal in alpha cells and in the exocrine pancreas. Leptin treatment of ob/ob mice for 12 days reversed this pattern, so that most of the islets expressed LPL in beta cells.ConclusionsWe conclude that both LPL and GPIHBP1 are present in mouse pancreas, and that LPL expression in beta cells is dependent on leptin.

Evidence for Two Distinct Binding Sites for Lipoprotein Lipase on Glycosylphosphatidylinositol-anchored High Density Lipoprotein-binding Protein 1 (GPIHBP1)

“…It is assumed, but seldom demonstrated, that heparin removes essentially all LPL from the capillary endothelium in tissues (1,38). Determination of LPL activity in post-heparin plasma has been used for many years as a surrogate measure of the functional pool of LPL on the capillary bed in the body.…”

TREM2 regulates microglial cell activation in response to demyelination in vivo

“…The following primary antibodies were used: anti-MBP (1:100; Abcam, ab7349), -dMBP (1:2000; Millipore, ab5864) [31], -βAPP (1:100; Invitrogen, 51-2700), -SMI-31 (1:1000; Covance, smi-31R), -Iba1 (1:600; Wako, 019-19741), -BrdU (1:250; Abcam, ab1893), -GFAP (1:200; Invitrogen, 13-0300), -iNOS (1:100; BD Pharmingen, 610329), -LPL (1:400, from Dr. G. Olivecrona) [57] and -MHC II (1:100; BD Pharmingen, 553549). Images were acquired using a Nikon Eclipse 90 i fluorescent and bright field microscope and analyzed for quantitation with the Metamorph 7.7 software.…”

Lipotoxicity in the Pancreatic Beta Cell: Not Just Survival and Function, but Proliferation as Well?

“…At the level of lipid entry into beta cells, one histological analysis has found that lipoprotein lipase (LPL), important for cleaving triglyceride to allow fatty acid entry into cells, is surprisingly not intravascular in mouse islets, but instead appears to be intracellular, where it would not have access to circulating triglyceride [41]. Islet expression of LPL was not altered by fasting-fed state, but was regulated by leptin [41].…”

“…Islet expression of LPL was not altered by fasting-fed state, but was regulated by leptin [41]. Islet lipid uptake may be regulated by signals that change LPL location to extracellular; disruption of these signals may contribute to reduction of the lipid component of glucose stimulated insulin secretion (GSIS).…”