Expression and significance of HIF-1α in pulmonary fibrosis induced by paraquat

It is commonly accepted that epithelial-mesenchymal transition contributes to fibrotic remodeling, but the molecular pathways involved in paraquat (PQ)-induced epithelial-mesenchymal transition remain uncharacterized. The objective of this study was to evaluate the potential involvement of HIF-1 alpha in TGF-beta 1/beta-Catenin and Snail pathway after PQ poisoning. In our study, 86 Spragne-Dawley rats were randomly divided into control group and PQ group, which received intragastric infusion of 20% PQ solution 50 mg/kg. Rats in the PQ group were subsequently divided into eight subgroups (10 for each subgroup) and samples were collected at different predetermined time points (2, 6, 12, 24, 48, 72, 96 h and 7 d). Fibrosis markers, including beta-catenin, snail and alpha-SMA, were measured by western blot. The activity of HIF-1 alpha was determined by western blot and immunofluorescence. We found that in PQ-induced pulmonary fibrosis, the level of PaO2 was significantly reduced in the 6-h subgroup, when compared to the control group (P < 0.01). Interestingly, between 6 and 72 h, there was no significant difference in PaO2. On the other hand, the level of PaCO2 started to increase from 72-h subgroup (P < 0.01). Fibrosis markers including beta-catenin, snail and alpha-SMA, measured by western blot, were significantly increased at 2 h, while the level of p-GSK-3 beta was increased at 6 h. And the level of GSK-3 beta showed significant reduction beginning at 24 h. The activity of HIF-1 alpha measured by western blot assays was significantly increased starting from 2 h with sustained expression. The result of Pearson coefficient analysis showed that HIF-1 alpha was positively correlated with Snail (r = 0.935, P < 0.01) and beta-catenin (r = 0.761, P < 0.05). Meanwhile, immunofluorescent analysis of HIF-1 alpha revealed partial staining appearing from 2 h. Our data illustrated a positive correlation between Snail, beta-catenin signaling and HIF-1 alpha, suggesting a potential synergistic role of HIF-1 alpha in PQ-induced pulmonary fibrosis, which may be independent of GSK-3 beta. It might also represent a potential therapeutic window for treatment of paraquat poisoning.