ITIH4 attenuates acute lung injury by Fe-containing particulate matter in mice via Hippo pathway in type II alveolar epithelial cells

Background: Metals in particulate matter (PM), like iron (Fe), were associated with lung injury. Inter-alpha-trypsin inhibitor heavy chain H4 (ITIH4) was suggested to inhibit lung inflammation. However, the effect of metals in PM, particularly Fe, on lung inflammation involving ITIH4 remained unclear. Methods: We investigated the effects of recombinant ITIH4 (rITIH4) against acute lung injury in C57BL/6JNarl and B6.Sftpc-CreER^T2;Ai14(RCL-tdT)-D mice exposed to Fe-containing PM. Mice were exposed to diesel exhaust particles (DEP) or soluble iron (FeCl) via intratracheal instillation, while rITIH4 treatment was administered intranasally after exposure. Lung function, Fe levels (both bulk and single-cell by inductively-coupled plasma mass spectrometry (ICP-MS) and single-cell ICP-MS, respectively), inflammatory cell infiltration, and Hippo pathway regulation in type II alveolar epithelial cells (AECII) were assessed. Results: We observed correlation between lung function changes and Fe levels, both in bulk and single-cell Fe in peripheral blood mononuclear cells. Single-cell RNA sequencing of the control group identified AECII-related cells characterized by high Sftpc, Sftpa1, Mzb1, B3 gnt5, Cacna1e, and Agbl1 expression. rITIH4 treatment in DEP-exposed mice restored Hippo pathway Cdh1, Itih4, Pdpn, Wwtr1, and Yap1 in AECII. rITIH4 reversed DEP- and Fe-induced increases in neutrophil infiltration, neutrophil-to-lymphocyte ratio, and monocyte depletion in bronchoalveolar lavage fluid (BALF). rITIH4 reduced BALF CXCL1/KC levels by DEP and serum 8-isoprostane levels by Fe. rITIH4 also reduced DEP-induced lung damage, increased º-catenin and p-YAP in Fe-exposed mice, and pTAZ/TAZ ratio in both DEP- and Fe-exposed mice. rITIH4 increased pYAP/YAP ratio in DEP-exposed mice while decreasing LC3BII/I ratio in Fe-exposed mice. Conclusion: ITIH4 attenuated acute lung injury in mice exposed to PM, specifically Fe, by modulating the Hippo pathway in AECII. © The Author(s) 2025.