Single-cell RNA sequencing reveals prolonged polyacrylamide hydrogel stimulation in vivo leads to an immunosuppressive microenvironment and potential tumorigenesis.

[BACKGROUND] Polyacrylamide hydrogel (PAAG) was once a prevalent filler for augmentation surgery. It was banned in China in 2006 due to persistent adverse reactions. However, numerous patients who received PAAG injection still suffer from PAAG related complications, and studies on the toxic effects of PAAG in human body remains severely deficient.

[METHODS] Single-cell RNA sequencing was employed to dissect the genomic characteristics of PAAG peripheral capsules, with poly-dimethylsiloxane implant peripheral capsules serving as a control. The InferCNV method was used to identify high-CNV cells, SCENIC method was used to deduce typical transcription factors across different groups and cell types. Hematoxylin and eosin staining, along with multiplex immunofluorescence staining was used to present the pathological features of the capsular samples and to validate the results of the bioinformatics analysis.

[RESULTS] High copy number variation (CNV) cells within the PAAG capsules were identified, characterized by highly activated Ras and ErbB signaling pathways. The PAAG capsules were characterized with immune cell infiltration. The functional variations of macrophages, T cells and NK cells, endothelial cells and fibroblasts were also depicted. Prolonged PAAG stimulation led to the formation of foreign body giant cells, an immunosuppressive microenvironment, cellular acidification, and a robust collagen synthesis/degradation process, etc. A series of genes and ligand-receptor pairs collectively derived these biological processes, facilitated the inflammatory response to PAAG stimulation and the accumulation of high-CNV cells.

[CONCLUSION] This study presented the first single-cell atlas of the PAAG capsule, offered insights into the pathophysiological process of PAAG stimulation.