Troglitazone induces cytotoxicity in part by promoting the degradation of peroxisome proliferator-activated receptor γ co-activator-1α protein.
OBJECTIVE
Troglitazone (Tro), rosiglitazone (Rosi) and pioglitazone (Pio) are anti-diabetic thiazolidinediones that function as ligands for peroxisome proliferator-activated receptor γ (PPARγ); however, Tro has been withdrawn from the market due to liver toxicity issues. Mitochondrial dysfunction induced by Tro has been suggested to be an important mechanism behind its cytotoxicity. Constitutively active nuclear hormone receptors, oestrogen-related receptor α and γ are thought to regulate mitochondrial mass and oxidative phosphorylation together with their co-activators PPARγ co-activator-1α and -1β (PGC-1α and PGC-1β). Hence, in this study, we investigated whether Tro affects the expression and activity levels of these regulators.


METHODS
Cellular viability was measured by an ATP-based assay. Mitochondrial mass and reactive oxygen species (ROS) were quantified by two different fluorogenic probes. Apoptosis was measured by an Annexin-V-based kit. Gene expression at the levels of mRNA and protein was measured by quantitative RT-PCR and Western analysis. Over-expression of PGC-1α was mediated by an adenovirus.


RESULTS
Tro, but not Rosi or Pio, selectively stimulated PGC-1α protein degradation. As a result, Tro reduced mitochondrial mass, and superoxide dismutases 1 and 2 expressions, but induced ROS to initiate apoptosis. Using a ubiquitin-proteasome inhibitor MG132, it was established that blocking PGC-1α degradation partially suppressed the reduction of mitochondrial mass. Importantly, over-expressing PGC-1α partially restored the Tro-suppressed mitochondrial mass and attenuated the cytotoxic effects of Tro.


CONCLUSIONS
Collectively, these results suggest that PGC-1α degradation is an important mechanism behind the cytotoxic effects of Tro in the liver.
Liao
Xuemei
X
Guangzhou Institute of Biomedicine and Health, Chinese Academy of Sciences, Guangzhou, China.
Wang
Yanfei
Y
Wong
Chi-Wai
CW
D000255:Adenosine Triphosphate / Q000378:metabolism; D017209:Apoptosis / Q000187:drug effects; D002352:Carrier Proteins / Q000187:drug effects / Q000378:metabolism; D002470:Cell Survival / Q000187:drug effects; D002839:Chromans / Q000633:toxicity*; D005786:Gene Expression Regulation / Q000187:drug effects; D006360:Heat-Shock Proteins / Q000187:drug effects* / Q000378:metabolism; D056945:Hep G2 Cells; D006801:Humans; D007004:Hypoglycemic Agents / Q000633:toxicity*; D008930:Mitochondria, Liver / Q000187:drug effects* / Q000378:metabolism; D000071248:Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha; D000077205:Pioglitazone; D016601:RNA-Binding Proteins; D017382:Reactive Oxygen Species / Q000378:metabolism; D000077154:Rosiglitazone; D045162:Thiazolidinediones / Q000633:toxicity*; D014157:Transcription Factors / Q000187:drug effects* / Q000378:metabolism; D000077288:Troglitazone
D002352:Carrier Proteins; D002839:Chromans; D006360:Heat-Shock Proteins; D007004:Hypoglycemic Agents; C486497:PPARGC1A protein, human; C455622:PPARGC1B protein, human; D000071248:Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha; D016601:RNA-Binding Proteins; D017382:Reactive Oxygen Species; D045162:Thiazolidinediones; D014157:Transcription Factors; D000077154:Rosiglitazone; D000255:Adenosine Triphosphate; D000077288:Troglitazone; D000077205:Pioglitazone