Single-cell transcriptomics uncovers the roles of mesothelial cells and microenvironmental changes in the ultrafiltration failure after long-term peritoneal dialysis
Chronic exposure to biological incompatibility of peritoneal dialysis solution is one of the principal causes of ultrafiltration failure (UF). However, the changes of peritoneal cell composition and molecular mechanism of peritoneal microenvironment after long-term PD are unclear. Single-cell RNA sequencing was performed to profile cell composition and transcriptome characteristics in effluent obtained from patients undergoing PD with short vintage (SV), long vintage without ultrafiltration failure (LV_NOT_UF), and long vintage with ultrafiltration failure (LV_UF).  A total of 6 SV patients, 6 LV_NOT_UF patients, and 4 LV_UF patients were enrolled. The median PD duration of the three groups were 5 months (range:1.0–6.0 months), 137 months (range: 92–189 months) and 132 months (range: 120–161 months), with no significant differences in age (38.3 ± 21.5 years, 45.7 ± 10.6 years and 41.0 ± 16.7 years, P>0.05) and gender (male%: 33.3%, 50.0% and 25.0%, P>0.05). scRNA-seq data annotated 8 main cell types including epithelial-like mesothelial cells (E-MCs), mesenchymal-like mesothelial cells (M-MCs), fibroblast, plasma B cells, conventional dendritic cells, plasmacytoid dendritic cells, natural killer T cells, and myeloid cells. LV_UF patients showed higher proportion of E-MCs, which exhibited activated autophagy and had properties of both anti-inflammatory and pro-inflammatory, and neutrophil- and autophagy-related DEGs of E-MCs were upregulated in the LV_UF group. In contrast, the M-MCs and the AQP1 expression in the peritoneal mesenchyme were reduced in the LV_UF group compared to the other groups. The neutrophils in PD effluent were elevated in the LV_UF group, while the M2-like MRC1-macrophages gradually decreased from the SV, LV_NOT_UF to LV_UF group. Compared with the LV_NOT_UF group, the upregulated DEGs of monocytes/macrophages in the LV_UF group not only involved in pro-inflammatory response, but also promoted EMT progress. Additionally, neutrophils and monocytes/macrophages both interacted with MCs. Our study uncovers peritoneal different individual cell populations and cellular functions in different stages of PD which indicates the dynamic changes of microenvironments of peritoneal membrane. These findings provide new insights into the novel roles of mesothelial cells and inflammatory cells in UF. Overall design: We collected overnight effluent from 16 PD patients, including 6 SV patients, 6 patients in the LV_NOT_UF group, and 4 patients in the LV_UF group. SV group: patients received PD for less than 6 months. LV_NOT_UF group: patients received PD for more than 90 months and modified PET (Mod-PET) test showed that the ultrafiltration volume was greater than 400 mL. LV_UF group: patients received PD for more than 90 months, Mod-PET test showed that the ultrafiltration volume was less than 400 mL.