Single cell and spatial transcriptomics reveal macrophage extracellular trap as pivotal driver of encapsulated peritoneal sclerosis progression

Encapsulating peritoneal sclerosis (EPS), the most severe complication of peritoneal dialysis (PD), poses a significant threat to the life safety of PD patients. However, the mechanism underlying the formation of intra-abdominal adhesions in EPS remains elusive. This study aimed to dissect the characteristics of the peritoneal microenvironment in EPS at the single-cell level and investigate the mechanism driving intra-abdominal adhesion formation.

In this study, we employed single-cell RNA sequencing (scRNA-seq) combined with 10x Visium HD spatial transcriptomic sequencing to perform high-throughput analyses of peritoneal tissues and PD effluents from healthy controls, PD patients without EPS, and PD-related EPS patients. Based on these analyses, we constructed an "intra-abdominal adhesion niche atlas" specific to EPS patients. Furthermore, these technologies were applied to an EPS mouse model to further characterize the dynamic changes in the peritoneal microenvironment during adhesion formation. Subsequently, multi-staining immunofluorescence, flow cytometry, and PAD4 knockout (PAD4⁻/⁻) mice were used to validate the findings from the sequencing analyses. Finally, in vitro and in vivo experiments were conducted to demonstrate the therapeutic potential of targeting signaling involved in macrophage extracellular traps (METs) formation for EPS treatment.

ScRNA sequencing revealed a significant increase in the proportions of proinflammatory macrophages (S100A8⁺ macrophages) and myofibroblasts in the peritoneum of EPS patients. Spatial transcriptomics further uncovered the spatial characteristics of the intra-abdominal adhesion regions in EPS: S100A8⁺ macrophages aggregated into clusters and localized at the core of adhesions, with a large number of fibroblasts adhering around these macrophage clusters. Notably, fibroblasts located closer to macrophages exhibited higher activation levels, collectively forming a characteristic "adhesion niche" in EPS. Spatial transcriptomic sequencing of the EPS mouse model further confirmed that this niche plays a critical driving role throughout the de novo formation process of EPS. Subsequent pathway enrichment analysis and corresponding validation experiments demonstrated that S100A8⁺ macrophages form METs under EPS conditions. The METs structures can adhere to and entrap various peritoneal cells; specifically, the protein and DNA components within METs target the TLR2 receptor on fibroblasts, leading to sustained activation of fibroblasts via the TLR2/MyD88-Rac-ROS-p38/MAPK signaling pathway. This sustained activation ultimately promotes irreversible peritoneal fibrosis and adhesion formation.

Additionally, the concentration of METs in the peritoneal cavity of EPS patients was identified as a predictive marker for the onset and progression of EPS. Moreover, inhibition of METs formation—achieved through PAD4 gene knockout, treatment with deoxyribonuclease I (DNase I) exerted significant therapeutic effects on EPS.

Proinflammatory macrophages mediate EPS pathogenesis by forming METs, which interact with fibroblasts to establish a spatially distinct "EPS adhesion niche." The ability of METs to adhere to and entrap various peritoneal cells, together with their activation of fibroblasts via protein/DNA components-driven TLR2/MyD88-Rac-ROS-p38/MAPK signaling, constitutes the structural and functional basis for the formation of this niche. Measurement of peritoneal METs concentration in PD patients enables the prediction of EPS onset and progression. Furthermore, strategies targeting METs formation—including DNase I and gene editing techniques—hold promise as potential therapeutic approaches for EPS.