| Mitochondria are vital for the control of bioenergetics and cellular metabolism, but their role in tumorigenesis is poorly understood. The results of the current study show that ablation of cyclophilin D (CypD), a mitochondrial matrix peptidylprolyl isomerase and cell death regulator, results in hepatic tumorigenesis in 16 month old CypD KO mice. Both autophagic flux and mitochondrial biogenesis were found to be impaired in the aged CypD KO mice, indicating dysfunctional mitochondrial turnover. Impaired mitochondrial quality control was inferred from upregulation of mitochondria-associated 8'-oxoguanine glycosylase, suggesting accumulation of mtDNA oxidative damage due to reactive oxygen species (ROS). We also found inflammatory mediator STAT3 activation in both CypD KO mice and mouse embryonic fibroblasts (MEFs) from Parkin KO mice. Based on these results, we hypothesis that the STAT3 activation resulted from inflammatory cytokine production initiated by oxidized mtDNA activation of the NLRP3 inflammasome. Proteostasis was abnormal as indicated by upregulation of ER stress markers Grp78 and CHOP in aged CypD KO mice, although heat shock proteins were not different between WT and KO mice. In conclusion, this study showed that ablation of CypD interfered with mitochondrial quality control and proteostasis, leading to sustained inflammation that culminated in hepatic tumorigenesis in aged CypD KO mice. This implicates cyclophilin D as a novel tumor suppressor gene. This may shed light on the increased risk of malignancy in organ transplant patients receiving cyclosporine A (cyclophilin D inhibitor) for immunosuppression. |
