Impaired AMP-Dependent Protein Kinase-Mediated Neutrophil Extracellular Trap Clearance by Aged Macrophages in Sepsis-Induced Liver Injury

BACKGROUND: This study investigates the role and mechanism of neutrophil extracellular trap (NET) clearance by aged macrophages during sepsis-induced liver injury, as elderly patients show higher rates of organ damage and mortality in sepsis. METHODS: A sepsis model was established using cecal ligation and puncture (CLP) in aged (100-week-old) and young mice (8-week-old) to study NET clearance by macrophages, assessing liver injury and inflammatory responses with interventions targeting AMP-dependent protein kinase (AMPK) and phagocytosis pathways. Additionally, the study included 40 sepsis patients, with 25 elderly (65-89 years) and 15 young (31-62 years) individuals, and collected peripheral blood samples from all for in vitro experiments. RESULTS: In aged mice, a significant increase in 7-day mortality was observed (hazard ratio [HR] = 2.50, 95% confidence interval [CI], 1.10-5.65, P = .009), alongside heightened inflammatory response and liver injury (histopathology score: 3.2 ± 0.4 vs 2.4 ± 0.6; P = .021), compared to young mice post-CLP. Hepatic NET accumulation markedly increased (mean difference [MD] = 0.43%, 95% CI, 0.25%-0.61%; P < .001), which was attenuated by DNase I-mediated NET inhibition, reducing hepatic enzymes and inflammatory responses. Consistently, transplantation of young bone marrow into aged recipients significantly reduced NET accumulation (MD = -0.33%, 95% CI, -0.43% to -0.22%; P < .001). Mechanistically, the phosphorylation of AMPK (0.68-fold vs young; P < .001) and Ca2+/calmodulin-dependent protein kinase kinase 2 (CaMKK2) was suppressed in aged septic mice. Activation of AMPK via 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR) led to a decrease in hepatic NET accumulation (MD = -0.30%, 95% CI, -0.41% to -0.19%; P < .001), improved liver injury (histopathology score: 2.49 ± 0.24 vs 3.07 ± 0.28; P = .006), and reduced 7-day mortality (HR = 0.37, 95% CI, 0.15-0.94, P = .038). Critically, elderly patients exhibited elevated NET-related markers, compounded by suppressed AMPK phosphorylation and impaired NET phagocytosis (MD = -16.34%, 95% CI, -24.31% to -8.37%; P = .002). CONCLUSIONS: Aging impairs AMPK-mediated macrophage clearance of NETs in the liver, exacerbating liver inflammatory injury. Focusing on NETs could offer a therapeutic strategy to mitigate liver damage and reduce mortality in elderly sepsis patients.