Effects of Stable Suppression of Group VIA Phospholipase A2 Expression on Phospholipid Content and Composition, Insulin Secretion, and Proliferation of INS-1 Insulinoma Cells

Abstract

Studies involving pharmacologic inhibition or transient reduction of Group

Modulation of the Pancreatic Islet β-Cell-delayed Rectifier Potassium Channel Kv2.1 by the Polyunsaturated Fatty Acid Arachidonate

“…Prolonged exposure of ␤-cells to AA stimulates their proliferation and amplifies secretagogue-induced insulin release (62), both of which also occur during the evolution of type II diabetes. Similarly, overexpression of iPLA 2 ␤ in insulinoma cell lines is associated with increased proliferation rates and amplified secretory responses (21,56), and suppression of iPLA 2 ␤ expression is associated with reduced proliferation rates and insulin secretion (22). The progressive rise in insulin resistance during the evolution of type II diabetes requires development of a compensatory hypersecretion of insulin to maintain glucose homeostasis, and a rise in AA levels might stimulate such a response.…”

“…Pharmacologic, biochemical, and genetic evidence suggests that glucose-stimulated hydrolysis of esterified arachidonic acid from ␤-cell membrane phospholipids is required for physiological insulin secretion (7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25). Pancreatic islet ␤-cells contain high levels of arachidonic acid compared with other tissues (7, 9 -12 24, 25), and about two-thirds of islet ␤-cell glycerophospholipids contain arachidonic acid as the sn-2 substituent (23)(24)(25).…”

“…The products of iPLA 2 ␤ action on its phospholipid substrates include a nonesterified fatty acid, such as AA, and a 2-lysphophosplipid, such as lysophosphatidylcholine (LPC), and ␤-cell levels of both products correlate with iPLA 2 ␤ expression level (21,22,31,32). Modulation of iPLA 2 ␤ activity and the rate of secretagogue-induced hydrolysis of arachidonic acid from ␤-cell membrane phospholipids might thus represent a tunable signal to amplify or attenuate islet insulin secretion in various (patho)physiologic settings (19,24).…”

Diminished Acyl-CoA Synthetase Isoform 4 Activity in INS 832/13 Cells Reduces Cellular Epoxyeicosatrienoic Acid Levels and Results in Impaired Glucose-stimulated Insulin Secretion

“…Based on studies that show that glucose stimulates the release and metabolism of AA, it has been hypothesized that AA and/or its metabolites play a significant role in insulin secretion (10 -12). The initial hydrolysis of AA from glycerophospholipids seems to be critical for insulin secretion, because knockdown or knock-out of phospholipase A 2 in INS-1 cells (13) or mouse islets (14) diminishes GSIS. Free AA is metabolized by one of several different enzyme systems that yield potent bioactive compounds with critical signaling roles.…”

Algorithm for processing raw mass spectrometric data to identify and quantitate complex lipid molecular species in mixtures by data-dependent scanning and fragment ion database searching

“…Unfractionated lipid extracts are directly infused and analyzed by ESI/MS with data-dependent switching to MS/MS mode. MS/MS data are searched against a library of reference spectra for complex lipids constructed from studies of standard glycerophospholipids of all major head-group classes [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28], which we used to establish fragmentation rules [29] that facilitate identification of glycerophospholipids in biological mixtures [30,31]. Structure assignment permits determination of an elemental formula, and a theoretical isotope profile is then calculated and used in a deisotoping algorithm.…”