A feed-forward loop based on aerobic glycolysis and TGF-β between tumor-associated macrophages and bladder cancer cells promoted malignant progression and immune escape.

Purpose: Immunotherapy with programmed cell death 1/ligand 1 (PD-1/PD-L1) checkpoint inhibitors has revolutionized the systemic treatment of solid tumors, including bladder cancer. Previous studies have shown that enhanced glycolysis, tumor-associated macrophage (TAM) infiltration, and TGF-β secretion in the tumor microenvironment (TME) are closely related to PD-1/PD-L1 inhibitor immunotherapy resistance. However, the potential mechanism of their interaction in bladder cancer has not been fully uncovered.

Methods: By coculturing bladder cancer cells and TAMs, we studied the relationship and interaction mechanism between tumor cell glycolysis, TAM functional remodeling, TGF-β positive feedback secretion, and PD-L1 mRNA m6A methylation in the bladder cancer microenvironment.

Results: Bioinformatics analysis and IHC staining found a close correlation between tumor glycolysis, M2 TAM infiltration, and the prognosis of bladder cancer patients. In Vitro experiments demonstrated that bladder cancer cells could re-educate M2 TAMs through lactate and promote TGF-β secretion via the HIF-1α signaling pathway. Reciprocally, in vitro, and in vivo experiments validated that M2 TAMs could promote glycolysis in bladder cancer cells by TGF-β via the Smad2/3 signaling pathways. Furthermore, M2 TAMs could also promote CSCs and EMT of bladder cancer cells. More importantly, we found M2 TAMs enhance PD-L1 mRNA m6A methylation by promoting METLL3 expression in bladder cancer via the TGF-β/Smad2/3 pathway in the TME.

Conclusions: Our study highlights a feed-forward loop based on aerobic glycolysis and TGF-β between M2 TAMs and bladder cancer cells, which may be a potential mechanism of malignant progression and immunotherapy resistance in bladder cancer.