Critical Role of S100A9 in Sepsis-associated Acute Kidney Injury: Mechanistic Insights through Pyroptosis Pathway Modulation.

This study investigates the role of S100A9 in sepsis-associated AKI (SA-AKI) through the lens of pyroptosis, a controlled form of cell death mediated by the gasdermin protein family. Using C57BL/6 mice and S100A9 knockout mice subjected to cecal ligation and puncture (CLP), RNA sequencing and bioinformatics analyses revealed differentially expressed genes (DEGs) related to inflammation and immune responses, with notable upregulation of S100A9. Functional enrichment analyses (GO and KEGG) indicated these DEGs are involved in interferon-beta response, immune processes, and cell adhesion. Protein-protein interaction (PPI) network analyses further emphasized S100A9's pivotal role in SA-AKI.Clinical validation measured S100A9 levels in serum and urine samples from SA-AKI patients and healthy volunteers, finding elevated S100A9 levels in the former. In vivo experiments showed that S100A9 knockout mice exhibited reduced kidney injury and inflammation, indicated by lower serum creatinine, urea nitrogen, and inflammatory markers (IL-1β and IL-18). Histopathological analyses and immunohistochemistry confirmed less renal damage and reduced expression of cleaved IL-1β and GSDMD-N in S100A9-deficient mice. Electron microscopy and Western blotting validated that S100A9 deficiency mitigates caspase-1-dependent pyroptosis.Cellular experiments with HK-2 cells demonstrated that S100A9 knockdown alleviated LPS-induced cell damage and reduced pyroptosis markers. These findings illuminate S100A9's involvement in NLRP3 inflammasome activation and pyroptosis, suggesting potential therapeutic targets for SA-AKI. Targeting S100A9 may offer new therapeutic avenues, improving outcomes for sepsis-related kidney injury patients. Future research should aim to validate these findings in larger clinical settings.