Salidroside attenuates HALI via IL-17A-mediated ferroptosis of alveolar epithelial cells by regulating Act1-TRAF6-p38 MAPK pathway

Abstract

Background and Purpose: Hyperoxia-induced acute lung injury (HALI) is a critical life-threatening disorder characterized by severe infiltration immune cells and death of type II alveolar epithelial cells (AECII). However, little is known about the relations between immune cells and AECII in HALI. IL-17A is a pro-inflammatory cytokine mainly secreted by Th17 cells, contributing to the pathogenesis of various inflammatory diseases. The present study investigated the role of IL-17A in cell-cell communication between immune cells and AECII in HALI, and explored the therapeutic effect of salidroside (Sal, a natural anti-inflammatory agents) on HALI.Methods: Mice with HALI were induced by exposure to hyperoxia over 90% for 12 h, 24 h, 48 h or 72 h, and the optimal timing was detected by H&E and Masson staining. Ferroptosis was confirmed by detecting the levels of MDA, Fe2+ and GPX4, and the morphological alterations of AECII under transmission electron microscopy (TEM). The expression of pro-inflammatory cytokine, including IL-6, TGF-β1, IL-17A and IL-17A receptor (IL-17RA) were measured by Western blotting and immunohistochemical stanning. The ferroptosis-related Act1/TRAF6/p38 MAPK pathway was detected by Western blotting. The role of pro-inflammatory cytokine IL-17A for AECII ferroptosis, and the effect of Sal on HALI were investigated by administration of Y-320 (IL-17 inhibitor) and Sal respectively 3 days before mice exposed to hyperoxia.Results: Mice exposed to hyperoxia for 24 h suffered sufficient HALI with inflammatory cell infiltration and collagen deposition, and exhibited features of ferroptosis under TME. Meanwhile, compared with sham mice, mice exposed to hyperoxia showed down-regulation of GPX4, and up-regulation of IL-6, TGF-β1, IL-17A, IL-17RA, Act1, TRAF6, p38 MAPK and p-p38 MAPK. Moreover, inhibition of IL-17A with Y-320 or administration with Sal could reverse the effect caused by hyperoxia respectively. Conclusions: IL-17A is associated with immune cells infiltration in HALI, and contributes to ferroptosis of AECII that related to Act1/TRAF6/p38 MAPK pathway. Additionally, Sal protects against HALI throughout the whole pathogenic process.

IRF4-mediated Treg phenotype switching can aggravate hyperoxia-induced alveolar epithelial cell injury

“…We determined that the expression levels of SP-C and T1α protein in the lung tissue of mice with BPD induced by hyperoxia were decreased, implying that alveolar epithelial cells were damaged and AECII trans-differentiation was abnormal. Long-term exposure to hyperoxia can induce a pro-inflammatory response in lung tissue, manifesting as the increase of various inflammatory factors and the apoptosis of alveolar epithelial cells [44, [46]. We determined that the levels of IL-17 A and IL-6 in the lung tissue of the hyperoxia group were remarkably increased, suggesting that the inflammatory response mediated by IL-17 A and IL-6 affected the process of AECII trans-differentiation and alveolarization.…”

“…After exposure to hyperoxia, IRF4-KO mice exhibit a higher proportion of FOXP3 + Treg as the predominant phenotype in lung tissue, leading to a more effective inhibitory function. FOXP3 + Treg can promote the normal proliferation and differentiation of lung epithelial cells, inhibit lung inflammation, and resolve acute lung injury [17,46]. It can be concluded that knocking out IRF4 can inhibit the phenotype switching of Tregs in the lung tissue of mice induced by hyperoxia, thereby reducing inflammatory response and alveolar epithelial cell damage.…”