Fraxetin reduces endometriotic lesions through activation of ER stress, induction of mitochondria-mediated apoptosis, and generation of ROS

Background: Fraxetin, a phytochemical obtained from Fraxinus rhynchophylla, is well known for its anti-inflammatory and anti-fibrotic properties. However, fraxetin regulates the progression of endometriosis, which is a benign reproductive disease that results in low quality of life and infertility. Hypothesis/purpose: We hypothesized that fraxetin may have therapeutic effects on endometriosis and aimed to elucidate the underlying mechanisms of mitochondrial function and tiRNA regulation. Study design: Endometriotic animal models and cells (End1/E6E7 and VK2/E6E7) were used to identify the mode of action of fraxetin. Methods: An auto-implanted endometriosis animal model was established and the effects of fraxetin on lesion size reduction were analyzed. Cell-based assays including proliferation, cell cycle, migration, apoptosis, mitochondrial function, calcium efflux, and reactive oxygen species (ROS) were performed. Moreover, fraxetin signal transduction was demonstrated by western blotting and qPCR analyses. Results: Fraxetin inhibited proliferation and migration by inactivating the P38/JNK/ERK mitogen-activated protein kinase (MAPK) and AKT/S6 pathways. Fraxetin dissipates mitochondrial membrane potential, downregulates oxidative phosphorylation (OXPHOS), and disrupts redox and calcium homeostasis. Moreover, it triggered endoplasmic reticulum stress and intrinsic apoptosis. Furthermore, we elucidated the functional role of tiRNA^HisGTG in endometriosis by transfection with its inhibitor. Finally, we established an endometriosis mouse model and verified endometriotic lesion regression and downregulation of adhesion molecules with inflammation. Conclusion: This study suggests that fraxetin is a novel therapeutic agent that targets mitochondria and tiRNAs. This is the first study to demonstrate the mechanisms of tiRNA^HisGTG with mitochondrial function and cell fates and can be applied as a non-hormonal method against the progression of endometriosis.