A positive feedback loop promotes HIF-1α stability through miR-210-mediated suppression of RUNX3 in paraquat-induced EMT.

Irreversible pulmonary fibrosis induced by paraquat (PQ) poisoning is the major cause of death in patients with PQ poisoning. The epithelial-mesenchymal transition (EMT) is postulated to be one of the main mechanisms of pulmonary fibrosis. Here, we investigated the role of miR-210 in PQ-induced EMT and its relationship with hypoxia-inducible factor-1α (HIF-1α). Western blotting, immunofluorescence, immunoprecipitation and other methods were used in this study. We found that miR-210 expression was significantly increased after PQ poisoning, and it may be regulated by HIF-1α. Overexpression of miR-210 further increased the HIF-1α protein level and promoted EMT. Moreover, miR-210 knock-down reduced the HIF-1α protein level and decreased the degree of EMT. Runt-related transcription factor-3 (RUNX3), a direct target of miR-210, was inhibited by miR-210 in response to PQ poisoning. RUNX3 increased the hydroxylation ability of prolyl hydroxylase domain-containing protein 2 (PHD2), a key enzyme that promotes HIF-1α degradation. PHD2 immunoprecipitated with RUNX3 and its level changed similarly to that of RUNX3. The expression of the HIF-1α protein was significantly reduced when RUNX3 was overexpressed. HIF-1α protein levels were markedly increased when RUNX3 was silenced. Based on these results, a positive feedback loop may exist between miR-210 and HIF-1α. The mechanism may function through miR-210-mediated repression of RUNX3, which further decreases the hydroxylation activity of PHD2, enhances the stability of HIF-1α, and promotes PQ-induced EMT, aggravating the progression of pulmonary fibrosis. This study further elucidates the mechanism of PQ-induced pulmonary fibrosis and may provide a new perspective for the future development of therapies.