αSMA fibroblasts suppress Lgr5 cancer stem cells and restrain colorectal cancer progression.

The development and progression of solid tumors is dependent on cancer cell autonomous drivers and the tumor microenvironment (TME). Cancer-associated fibroblasts (CAFs) in the TME possess both tumor-promoting and tumor-restraining functions. In the current study, we interrogated the role of αSMA CAFs in a genetic mouse model of metastatic colorectal cancer (CRC). Selective depletion of αSMA CAFs resulted in increased tumor invasiveness, lymph node metastasis, and reduced overall survival. Depletion of αSMA CAFs reduced BMP4 and increased TGFβ1 secretion from stromal cells, and was associated with increased Lgr5 cancer stem-like cells (CSCs) and the generation of an immunosuppressive TME with increased frequency of Foxp3 regulatory T cells and suppression of CD8 T cells. This study demonstrates that αSMA CAFs in CRC exert tumor-restraining functions via BMP4/TGFβ1 paracrine signaling that serves to suppress Lgr5 CSCs and promote anti-tumor immunity, ultimately limiting CRC progression.