Prostaglandin D2 synthase induces apoptosis in pig kidney LLC-PK1 cells

Background. Prostaglandin D-2 synthase (PGD(2)S), a unique member of the lipocalin family, is found at elevated levels in the serum of patients with renal impairment and has recently been implicated as a new biochemical marker of renal insufficiency. The aim of this study was to investigate the apoptotic effects of PGD(2)S on a pig kidney epithelial cell line (LLC-PK1) and to investigate the effects of prostaglandins and growth factors on this process. Methods. Apoptosis was detected by terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick end-labeling (TUNEL), annexin V staining, and electron microscopy. Results. A four- to fivefold increase in apoptosis was observed in PGD(2)S-treated cells as compared with controls and the apoptosis appeared to act via caspase-3. A cyclooxygenase-2 inhibitor, anti-PGD(2)S antibody, and selenium all significantly inhibited the apoptosis induced by PGD(2)S; however, none had any effect on the apoptosis induced by the known apoptotic inducer camptothecin. Furthermore, prostaglandins E-1 and E-2, known to induce mitogen-activated protein (MAP) kinase phosphorylation and exhibit cytoprotective effects, both inhibited PGD(2)S-induced apoptosis, while prostaglandin H-2 had no significant effect. Growth factors such as insulin, insulin-like growth factor-1, and platelet-derived growth factor also decreased PGD(2)S-induced apoptosis. In addition, PGD(2)S isolated from human serum seemed slightly more effective at inducing apoptosis than recombinantly expressed protein. Conclusions. We report on the induction of apoptosis by PGD(2)S in LLC-PK1 pig kidney epithelial cells, and speculate that the accumulation of PGD(2)S in the serum of kidney failure patients may further exacerbate renal problems and is most likely regulated by other prostaglandins and growth factors.