Transcriptional regulation of Hb-α and Hb-β through nuclear factor E2-related factor-2 (Nrf2) activation in human vaginal cells: A novel mechanism of cellular adaptability to oxidative stress

Problem: Hemoglobin (Hb), a major protein involved in transport of oxygen (O-2), is expressed by erythroid lineages. Until recently, it was not known whether non-erythroid cells express Hb. The objective was to evaluate the expression and functional significance of Hb-alpha and Hb-beta in human primary vaginal epithelial cells (hPVECs) and decipher downstream signaling. Methods of study: RT-PCR, qRT-PCR, flow cytometry, Western blot, immunofluorescence were used to evaluate the expression of Hb-alpha, Hb-beta, and nuclear factor E2-related factor-2(Nrf2) after hydrogen peroxide (H2O2) induction. Electrophoretic mobility shift assay (EMSA) and chromatin immunoprecipitation (ChIP) assay were used to determine the binding efficiency of Nrf2 on the Hb-alpha promoter. Results: Stimulation of hPVECs and human vaginal epithelial cell line, VK2/E6E7 with H2O2 augmented the expression of Hb-alpha, Hb-beta, Nrf2, heme oxygenase-1 (HO-1), and reactive oxygen species (ROS). Treatment of these cells with Nrf2 inhibitor, trigonelline (Trig) inhibited Hb-alpha and Hb-beta expressions. Hb-alpha and Hb-beta overexpression downregulated H2O2-induced ROS. The presence of Nrf2 binding domain was demonstrated within Hb-alpha promoter. Conclusion: The results revealed for the first time that Hb-alpha and Hb-beta were induced by oxidative stress through the activation of Nrf2. Overexpression of Hb-alpha and Hb-beta ameliorated H2O2-induced oxidative stress, indicating one of the possible mechanism(s) to protect hPVECS from oxidative stress.