Regulation of Necroptosis by Aspergillus fumigatus Exopolysaccharide in Human Macrophages Derived from THP-1 Cells: Involvement of the RIP1-RIP3-MLKL Signaling Axis.

Previous research has indicated that the exopolysaccharide galactosaminogalactan (GAG) from Aspergillus fumigatus plays a pivotal role in the pathogenesis of experimental invasive aspergillosis by promoting virulence. However, it remains unclear whether the exopolysaccharide is directly virulent to host cells. In this study, we established a co-incubation system using human THP-1-derived macrophages and GAG extracted from A. fumigatus ATCC 1022 to assess the capacity of GAG to induce necroptosis in THP-1 cells, as well as to elucidate the underlying mechanisms of this process. Our findings indicate that the proportion of N-acetylgalactosamine in the GAG fraction derived from strain ATCC 1022 was lower, while GAG demonstrated a significantly greater ability to induce the production of the pro-inflammatory cytokines TNF-α and IL-1β, which was accompanied by the induction of necroptosis. Western blotting analysis revealed a significant increase in the phosphorylation of RIP1, RIP3, and MLKL proteins in GAG-treated THP-1 cells, and RIP1-RIP3-MLKL signaling activation and GAG-induced caspase activity-independent cell death were effectively inhibited by the TNF-α receptor-1 (TNFR1) inhibitor R-7050, the neutralizing antibody against TNF-α or necroptosis inhibitor Necrostatin-1. It's worth noting that the expression of CLEC4E, the gene encoding the Mincle receptor in macrophages, was elevated in the co-incubation system, potentially enhancing TNF-α-mediated necroptotic cell death. In addition to the RIP1-RIP3-MLKL axis, BAX, cleaved PARP, and JNK were also activated following GAG treatment, warranting further investigation into their roles in the regulation of necroptosis. Our findings demonstrate that GAG produced by A. fumigatus conidia during germination triggers necroptotic cell death in human THP-1 cells via TNF-α-mediated RIP1-RIP3-MLKL signaling.