Enhanced expression of group IIA secreted phospholipase A2 by elevated glucose levels in cytokine-stimulated rat mesangial cells and in kidneys of diabetic rats

Background: Group IIA secreted phospholipase A(2) (sPLA(2)-IIA) has been implicated in various inflammatory processes including the kidney. Previously it has been shown that potent proinflammatory cytokines such as interleukin 1 beta (IL-1 beta) increase sPLA(2)-IIA expression and secretion in rat mesangial cells. Aim: The present study examines the effects of glucose on sPLA2-IIA regulation in interleukin-1 beta (IL-1 beta) treated mesangial cell cultures and in diabetic kidneys of Sprague-Dawley rats. Materials and Methods: Rat mesangial cells were grown either in low glucose (5,55 mM D-Glucose) or high glucose (25 mM) conditions followed by assessment of sPLA(2)-IIA transcription, expression and secretion after 24 h. The model of streptozotocin induced diabetes mellitus in Sprague-Dawley rats was used for the in vivo experiments. Diabetic kidneys where examined for sPLA(2)-IIA-mRNA and -protein expression as well as IL-1 beta-levels at 2, 4 and 6 weeks after induction of diabetes mellitus. Results: Increased concentration of glucose had a weak, but significant stimulatory effect on sPLA(2)-IIA expression, which was markedly up-regulated (2-3-fold) in IL-1 beta treated mesangial cells compared to the levels obtained in low glucose medium. Concerning the underlying mechanism, we found that high concentration of glucose increased the activity of the rat sPLA(2)-IIA-promoter, whereas mRNA stability was not affected. Furthermore, the in vivo experiments revealed a marked up-regulation of sPLA(2)-IIA mRNA and protein in the diabetic rat kidneys 2-4 weeks after induction. Since the strong up-regulation of sPLA(2)-IIA in vitro under high glucose conditions occurred mainly in presence of cytokine, we measured the levels of IL-1 beta in diabetic kidneys by ELISA. We detected rat IL-1 beta only in diabetic, but not in control rat kidneys. Conclusions: The changes of sPLA(2)-IIA expression under increased glucose concentrations as well as in diabetic rat kidneys suggest a function of this enzyme as an acute phase protein providing lipid autacoids that may contribute to early changes in the course of diabetic nephropathy.