Lactic acid inhibits ferroptosis and promotes M2 macrophage polarization in colon cancer via GPX4 regulation

Abstract

Background: Metabolite lactic acid is closely related to the metabolism and polarization of macrophages in cancers. Glutathione peroxidase 4 (GPX4), the core regulator of ferroptosis driven by lipid peroxidation and iron accumulation, has been reported as an oncogene in colon cancer. This study explored the role of lactic acid in GPX4-mediated ferroptosis and macrophage polarization in colon cancer.

Methods: Cell proliferation and apoptosis were respectively detected by CCK-8, EdU and flow cytometry. Ferroptosis markers were assessed by assay kits, qRT-PCR and Western Blot. Mitochondrial dysfunction was measured by JC-1 assay. Bioinformatics tools analyzed the correlation between GPX4 and immune cell infiltration. qRT-PCR and flow cytometry analyzed macrophage polarization. A tumorigenic model was constructed in nude mice, followed by histopathological analyses.

Results: Lactic acid promoted cell proliferation, inhibited cell apoptosis, and suppressed ferroptosis, while Erastin exerted the opposite effects and reversed the in vitro impacts of lactic acid on the proliferation, apoptosis and ferroptosis in CRC cells. The suppressive role of lactic acid on cell apoptosis and ferroptosis was also restored by GPX4 interference, indicating that the functions of lactic acid in colon cancer might be mediated by GPX4-dependent ferroptosis. GPX4 was associated with immune cell infiltration and its knockdown inhibited M2 macrophage polarization that was promoted by lactic acid both in vitro and in vivo. The pro-tumorigenic effects of lactic acid in vivo were also partially abrogated by GPX4 silencing, indicating that through targeting GPX4, lactic acid might alter immune cell infiltration to accelerate colon cancer tumorigenesis.

Discussion: Lactic acid was demonstrated to regulate tumor microenvironment and drive tumor growth in colon cancer via mediating GPX4-dependent ferroptosis. Targeting GPX4 and tumor metabolism could provide a new approach in anti-colon cancer therapies based on ferroptosis induction. However, the role of lactic acid needs to be verified in clinical settings and the specific regulatory mechanism between lactic acid and GPX4 remains to be further identified. Moreover, the in vivo model relies solely on subcutaneous xenografts in nude mice, which do not recapitulate immune-competent tumor microenvironments.

Conclusion: Lactic acid might regulate GPX4-mediated ferroptosis to promote M2 macrophage polarization, contributing to tumor growth and immune escape in colon cancer.

Keywords: Colon cancer; Ferroptosis; GPX4; Lactic acid; Macrophage polarization.