Tanshinone IIA potentiates the therapeutic efficacy of glucocorticoid in lipopolysaccharide-treated HEI-OC1 cells through modulation of Foxp3/Nrf2 signaling pathway

Glucocorticoids (GC) are commonly used to treat sudden sensorineural hearing loss (SSNHL) , although some patients show resistance to this therapeutic approach. Clinical studies demonstrate the efficacy of tanshinone IIA (TA) in combination with GC for managing various human ailments. However, it remains unclear whether TA can mitigate GC resistance in SSNHL. Aim of the study: Our aim is to elucidate the role of NRF2-induced transcriptional regulation of HDAC2 in influencing GC resistance and investigate the involvement of TA-related molecular pathways in GC resistance. Materials and Methods: HEI-OC1 cells are treated with lipopolysaccharide (LPS) to establish an in vitro model for SSNHL. Subsequently, the cells are treated with dexamethasone (DXE) or DXE+TA. RT-qPCR and western blot analyses are employed to measure mRNA and protein levels of Forkhead box P3 (FOXP3), nuclear factor erythroid 2-related factor 2 (NRF2), and histone deacetylase 2 (HDAC2). Cell Counting Kit-8 (CCK-8) and 5-ethynyl-2-deoxyuridine (EdU) assays are conducted to assess cell proliferation. Flow cytometry analysis is performed for apoptosis evaluation. Mechanistic studies involve Chromatin immunoprecipitation (ChIP), luciferase reporter, and DNA pull-down assays. Results: Treatment with TA+DEX significantly enhances proliferation and suppresses apoptosis in LPS-treated HEI OC1 cells. TA upregulates HDAC2 expression by activating NRF2-mediated transcription of HDAC2, with the NRF2-HDAC2 binding site located at bases 419-429 (ATGACACTCCA) in the promoter sequence of HDAC2. Furthermore, TA upregulates FOXP3 expression to activate NRF2 transcription, with the predicted FOXP3-binding site located at bases 864-870 (GCAAACA) in the promoter sequence of NRF2. Conclusion: This study's findings suggest that TA enhances the therapeutic effects of GC on proliferation and apoptosis in HEI OC1 cells by up-regulating FOXP3/Nrf2 expression. These results indicate that TA may be promising in ameliorating GC resistance in patients with SSNHL.