Cytosolic and Calcium-Independent Phospholipases A(2) Activation and Prostaglandins E(2) 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)-siRNAs, 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.