Humanin-G protects septic ARDS by mediating mitochondrial function in lung vascular endothelial cells

Recent investigations show that mitochondrial impairment significantly contributes to endothelial damage in septic acute respiratory distress syndrome (ARDS). Humanin (HN) and its derivative Humanin-G (HNG) are mitochondrial polypeptides which have been identified as inhibitors of cellular apoptosis and neuroprotective agents against oxidative stress. This study aims to elucidate the effects of HNG on pulmonary vascular endothelial damage. In septic ARDS patients, serum concentrations of HN increased markedly on Day 1, followed by a progressive decrease from Day 3 to Day 7. A murine model of septic ARDS was established through intraperitoneal injection of lipopolysaccharide. The results showed that HNG pretreatment significantly reduced inflammatory factor expression in both in vivo and in vitro settings, as confirmed by qPCR and Western blot. Furthermore, HNG treatment conferred protection against lung injury, restored mitochondrial morphology, improved mitochondrial respiratory function, and corrected impaired membrane potential, as assessed by H&E staining, transmission electron microscopy, Seahorse analysis, and JC-1 staining, respectively. Additionally, protein-peptide interaction analysis suggested that HNG binds to the interleukin-6 receptor alpha, and immunoprecipitation confirmed that HNG competitively interacts with the IL-6 receptor family in comparison to IL-6. Furthermore, WB analysis indicated that the protective effects of HNG on mitochondria may be largely due to the suppression of STAT3 expression in septic lung endothelial cells. In summary, this study suggests that the administration of the mitochondrial peptide HNG confers protective effects and mitigates mitochondrial damage by inhibiting the downstream pro-inflammatory pathways of IL-6/STAT3 in the pulmonary vascular endothelial cells of septic ARDS.