Oxidative stress induces monocyte-to-myofibroblast transdifferentiation through p38 in pancreatic ductal adenocarcinoma

Background Cancer-associated fibroblasts (CAFs) are among the most prominent cells during the desmoplastic reaction in pancreatic ductal adenocarcinoma (PDAC). However, CAFs are heterogeneous and the precise origins are not fully elucidated. This study aimed to explore whether monocytes can transdifferentiate into fibroblasts in PDAC and evaluate the clinical significance of this event. Methods CD14(+) monocytes were freshly isolated from human peripheral blood. Immunofluorescence, reverse transcription-quantitative PCR, western blot, flow cytometry and enzyme-linked immunosorbent assay were used to detect the expression of alpha SMA, fibronectin, and other relevant molecules. In addition, latex beads with a mean particle size of 2.0 mu m were used to assess the phagocytic capacity. Moreover, RNA sequencing (RNA-seq) was performed to identify the differences induced by H2O2 and the underlying mechanisms. Results Immunofluorescence identified alpha SMA and fibroblast-specific protein 1 expression by tumor-associated macrophages in PDAC. The in vitro experiment revealed that oxidative stress (H2O2 or radiation) induced monocyte-to-myofibroblast transdifferentiation (MMT), as identified by upregulated alpha SMA expression at both the RNA and protein levels. In addition, compared with freshly isolated monocytes, human monocyte-derived macrophages increased fibronectin expression. RNA-seq analysis identified p53 activation and other signatures accompanying this transdifferentiation; however, the p53 stabilizer nutlin-3 induced alpha SMA expression through reactive oxygen species generation but not through the p53 transcription/mitochondria-dependent pathway, whereas the p38 inhibitor SB203580 could partially inhibit alpha SMA expression. Finally, MMT produced a unique subset of CAFs with reduced phagocytic capacity that could promote the proliferation of pancreatic cancer cells. Conclusions Oxidative stress in the tumor microenvironment could induce MMT in PDAC, thus inducing reactive stroma, modulating immunosuppression, and promoting tumor progression. Reducing oxidative stress may be a promising future therapeutic regimen.