Role of ITIH4 in Modulating YAP/TAZ-Mediated Apoptosis of Type II Alveolar Epithelium during Acute Respiratory...

Inter-alpha-trypsin inhibitor heavy chain 4 (ITIH4) is a type II acute-phase protein with anti-inflammatory and anti-apoptotic properties. This study investigated the role of ITIH4 in regulating Hippo signaling and alveolar epithelial type II cell (AECII) apoptosis during acute respiratory distress syndrome (ARDS) METHODS: A549 cells were used for ITIH4 knockdown, ITIH4 overexpression, and lipopolysaccharide (LPS) exposure following recombinant ITIH4 (rITIH4) treatment. The expressions of Hippo signaling components (YAP/TAZ), apoptotic markers (ATM, p53, caspase-3), and the senescence marker SIRT1 were examined. Next, C57BL/6JNarl and B6.Sftpc-CreERT2;Ai14(RCLtdT)-D mice were administered intratracheal LPS and daily intranasal rITIH4. Lung injury severity was assessed through H&E staining with K-means clustering and immunofluorescence quantified ITIH4, caspase-3, and YAP expression in SPC⁺ cells from different lung regions RESULTS: The expression of YAP and TAZ decreased with ITIH4 knockdown in A549, whereas p-YAP and SIRT1 increased, and p-TAZ/TAZ decreased with ITIH4 overexpression. We also observed the expression of p-TAZ/TAZ and SIRT1 increased, while ATM and caspase-3 decreased in LPS-injured A549 following rITIH4 treatment. Furthermore, rITIH4 administration restored ITIH4 in SPC⁺ cells and reduced caspase-3 expression in LPS-induced ARDS mice. rITIH4 elevated YAP in SPC⁺ cells within damaged and severely injured lung regions on day 3; this upregulation was attenuated by day 7, suggesting spatiotemporal regulation of Hippo signaling activity during lung repair CONCLUSION: rITIH4 mitigated LPS-induced lung injury by regulating YAP/TAZ activity and suppression of caspase-3 and ATM expression. The observed modulation of Hippo signaling and reduction of AECII apoptosis highlight ITIH4 as a therapeutic potential for ARDS.