Abstract
Gut microbiota dysbiosis contributes to acute pancreatitis (AP) severity, but the specific microbes and mechanisms remain unclear. In this study, we employed both germ-free (GF) and specific-pathogen-free (SPF) murine models of AP to investigate the role of the intestinal microbiota. Our findings demonstrate that GF mice exhibited markedly attenuated pancreatic injury, inflammatory cell infiltration, and neutrophil extracellular traps (NETs) formation. Through fecal microbiota transplantation (FMT) from AP patients, differential antibiotic modulation, and single-bacterial colonization experiments, we identified Gram-negative bacteria, particularly Escherichia coli (E. coli), as critical microbial drivers of disease exacerbation. Single-cell RNA sequencing revealed that microbiota dysbiosis profoundly reprogrammed both local pancreatic and systemic immune landscapes. Specifically, dysbiosis promoted emergency granulopoiesis in the bone marrow, enhanced neutrophil mobilization and activation, and facilitated the expansion of pro-inflammatory neutrophil subpopulations (Neutrophils_2 and Neutrophils_3). These subsets exhibited upregulated signaling through NETosis-associated pathways, including TLR, NF-κB, and IL-17 axes. Conversely, in GF conditions, we observed a predominance of an anti-inflammatory neutrophil subset (Neutrophils_4), characterized by the expression of tissue repair-associated genes such as Reg1 and Reg2. Shotgun metagenomic profiling of fecal samples from patients with AP revealed an enrichment of E. coli during the acute phase, positively correlating with circulating cell-free DNA, a marker of NETosis. Together, these insights suggest that gut microbiota dysbiosis, notably increased E. coli abundance, may aggravate AP by reshaping immunity and promoting aberrant NETs formation, supporting microbiota or NETs targeted therapies.