Cyclopentenone prostaglandins induce lymphocyte apoptosis by activating the mitochondrial apoptosis pathway independent of external death receptor signaling.

15-Deoxy-Delta(12,14)-PGJ(2) (15d-PGJ(2)) is a naturally occurring cyclopentenone metabolite of PGD(2) that possesses both peroxisome proliferator-activated receptor gamma (PPAR-gamma)-dependent and PPAR-gamma-independent anti-inflammatory properties. Recent studies suggest that cyclopentenone PGs may play a role in the down-regulation of inflammation-induced immune responses. In this study, we report that 15d-PGJ(2) as well as synthetic PPAR-gamma agonists inhibit lymphocyte proliferation. However, only 15d-PGJ(2), but not the specific PPAR-gamma activators, induce lymphocyte apoptosis. We found that blocking of the death receptor pathway in Fas-associated death domain(-/-) or caspase-8(-/-) Jurkat T cells has no effect on apoptosis induction by 15d-PGJ(2). Conversely, overexpression of Bcl-2 or Bcl-x(L) completely inhibits the initiation of apoptosis, indicating that 15d-PGJ(2)-mediated apoptosis involves activation of the mitochondrial pathway. In line with these results, 15d-PGJ(2) induces mitochondria disassemblage as demonstrated by dissipation of mitochondrial transmembrane potential (Deltapsi(m)) and cytochrome c release. Both of these events are partially inhibited by the broad spectrum caspase inhibitor benzyloxycarbonil-Val-Ala-Asp-fluoromethylketone, suggesting that caspase activation may amplify the mitochondrial alterations initiated by 15d-PGJ(2). We also demonstrate that 15d-PGJ(2) potently stimulates reactive oxygen species production in Jurkat T cells, and Deltapsi(m) loss induced by 15d-PGJ(2) is prevented by the reactive oxygen species scavenger N-acetyl-L-cysteine. In conclusion, our data indicate that cyclopentenone PGs like 15d-PGJ(2) may modulate immune responses even independent of PPAR-gamma by activating the mitochondrial apoptosis pathway in lymphocytes in the absence of external death receptor signaling.