Expression and functional activity of PPARgamma in pancreatic beta cells.
Rosiglitazone is an agonist of peroxisome proliferator activated receptor-gamma (PPARgamma) and ameliorates insulin resistance in type II diabetes. In addition, it may also promote increased pancreatic beta-cell viability, although it is not known whether this effect is mediated by a direct action on the beta 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 beta-cell line, BRIN-BD11, express PPARgamma, as well as PPARalpha and PPARdelta. The levels of expression of PPARgamma 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 PPARgamma in rat (and human) islets and in BRIN-BD11 cells. Transfection of BRIN-BD11 cells with a PPARgamma-sensitive luciferase reporter construct was used to evaluate the functional competence of the endogenous PPARgamma. Luciferase activity was modestly increased by the putative endogenous ligand, 15-deoxy-Delta12,14 prostaglandin J2 (15dPGJ2). Rosiglitazone also caused activation of the luciferase reporter construct but this effect required concentrations of the drug (50-100 microm) that are beyond the expected therapeutic range. This suggests that PPARgamma 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 microm. Similar results were obtained with a range of other PPARgamma 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 beta cells.
Welters
Hannah J
HJ
Institute of Biomedical and Clinical Science, Peninsula Medical School, Plymouth, Devon, UK.
McBain
Stuart C
SC
Tadayyon
Moh
M
Scarpello
John H B
JH
Smith
Stephen A
SA
Morgan
Noel G
NG
D000818:Animals; D015153:Blotting, Western; D016923:Cell Death; D002460:Cell Line; D004305:Dose-Response Relationship, Drug; D006801:Humans; D007004:Hypoglycemic Agents / Q000008:administration & dosage / Q000494:pharmacology; D007515:Islets of Langerhans / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D047495:PPAR gamma / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D019308:Palmitic Acid / Q000633:toxicity; D016133:Polymerase Chain Reaction; D020033:Protein Isoforms / Q000096:biosynthesis; D051381:Rats; D017208:Rats, Wistar; D000077154:Rosiglitazone; D013045:Species Specificity; D045162:Thiazolidinediones / Q000008:administration & dosage / Q000494:pharmacology; D014162:Transfection
D007004:Hypoglycemic Agents; D047495:PPAR gamma; D020033:Protein Isoforms; D045162:Thiazolidinediones; D000077154:Rosiglitazone; D019308:Palmitic Acid