Cytosolic and Calcium-Independent Phospholipases A2 Activation and Prostaglandins E2 Are Associated with Escherichia coli-Induced Reduction of Insulin Secretion in INS-1E Cells

It is suspected that microbial infections take part in the pathogenesis of diabetes mellitus type 1 (T1DM). Glucose-induced insulin secretion is accompanied by the release of free arachidonic acid (AA) mainly by cytosolic- and calcium independent phospholipases A 2 (cPLA 2 and iPLA 2 ). Insulinoma cell line (INS-1E) was infected with E . coli isolated from the blood culture of a patient with sepsis. Invasion assay, Scanning Electron Microscopy and Transmission Electron Microscopy demonstrated the capacity of E . coli to enter cells, which was reduced by PLA 2 inhibitors. Glucose-induced insulin secretion was significantly increased after acute infection (8h) but significantly decreased after chronic infection (72h). PLA 2 activities, cPLA 2 , iPLA 2 , phospho-cPLA 2 , and COX-2 expressions were increased after acute and, even more, after chronic E . coli infection. The silencing of the two isoforms of PLA 2 s, with specific cPLA 2 - or iPLA 2 - si RNAs, reduced insulin secretion after acute infection and determined a rise in insulin release after chronic infection. Prostaglandins E 2 (PGE 2 ) production was significantly elevated in INS-1E after long-term E . coli infection and the restored insulin secretion in presence of L798106, a specific EP3 antagonist, and NS-398, a COX-2 inhibitor, and the reduction of insulin secretion in presence of sulprostone, a specific EP3 agonist, revealed their involvement in the effects triggered by bacterial infection. The results obtained demonstrated that cPLA 2 and iPLA 2 play a key role in insulin secretion process after E . coli infection. The high concentration of AA released is transformed into PGE 2 , which could be responsible for the reduced insulin secretion.