Prostaglandin D-2 synthase induces apoptosis in pig kidney LLC-PK1 cells

Background. Prostaglandin D-2 synthase (PGD(2)S), a unique member of the li pocalin family, is found at elevated levels in the serum of patients with r enal impairment and has recently been implicated as a new biochemical marke r of renal insufficiency. The aim of this study was to investigate the apop totic 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 pr ocess. Methods. Apoptosis was detected by terminal deoxynucleotidyl transferase (T dT)-mediated dUTP nick end-labeling (TUNEL), annexin V staining, and electr on 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 v ia caspase-3. A cyclooxygenase-2 inhibitor, anti-PGD(2)S antibody, and sele nium all significantly inhibited the apoptosis induced by PGD(2)S; however, none had any effect on the apoptosis induced by the known apoptotic induce r camptothecin. Furthermore, prostaglandins E-1 and E-2, known to induce mi togen-activated protein (MAP) kinase phosphorylation and exhibit cytoprotec tive effects, both inhibited PGD(2)S-induced apoptosis, while prostaglandin H-2 had no significant effect. Growth factors such as insulin, insulin-lik e 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 probl ems and is most likely regulated by other prostaglandins and growth factors .