Expression and functional activity of PPAR γ in pancreatic β cells

Rosiglitazone is an agonist of peroxisome proliferator activated receptor‐ γ (PPAR γ ) and ameliorates insulin resistance in type II diabetes. In addition, it may also promote increased pancreatic β ‐cell viability, although it is not known whether this effect is mediated by a direct action on the β cell. We have investigated this possibility. Semiquantitative real‐time reverse transcription–polymerase chain reaction analysis (Taqman®) revealed that freshly isolated rat islets and the clonal β ‐cell line, BRIN‐BD11, express PPAR γ , as well as PPAR α and PPAR δ . The levels of expression of PPAR γ were estimated by reference to adipose tissue and were found to represent approximately 60% (islets) and 30% (BRIN‐BD11) of that found in freshly isolated visceral adipose tissue. Western blotting confirmed the presence of immunoreactive PPAR γ in rat (and human) islets and in BRIN‐BD11 cells. Transfection of BRIN‐BD11 cells with a PPAR γ ‐sensitive luciferase reporter construct was used to evaluate the functional competence of the endogenous PPAR γ . Luciferase activity was modestly increased by the putative endogenous ligand, 15‐deoxy‐Δ 12,14 prostaglandin J 2 (15dPGJ 2 ). Rosiglitazone also caused activation of the luciferase reporter construct but this effect required concentrations of the drug (50–100 μ M ) that are beyond the expected therapeutic range. This suggests that PPAR γ is relatively insensitive to activation by rosiglitazone in BRIN‐BD11 cells. Exposure of BRIN‐BD11 cells to the lipotoxic effector, palmitate, caused a marked loss of viability. This was attenuated by treatment of the cells with either actinomycin D or cycloheximide suggesting that a pathway of programmed cell death was involved. Rosiglitazone failed to protect BRIN‐BD11 cells from the toxic actions of palmitate at concentrations up to 50 μ M . Similar results were obtained with a range of other PPAR γ agonists. Taken together, the present data suggest that, at least under in vitro conditions, thiazolidinediones do not exert direct protective effects against fatty acid‐mediated cytotoxicity in pancreatic β cells.British Journal of Pharmacology (2004) 142 , 1162–1170. doi: 10.1038/sj.bjp.0705844