Hedgehog signaling induced metabolic reprogramming is essential for M2 polarization of macrophages in breast cancer

Abstract

Abstract Current treatments for breast cancer offer little relief to patients with metastatic disease. The aberrant activation of Hedgehog (Hh) signaling enables cancer cells to survive, proliferate, and metastasize. Effective metastasis depends upon the surrounding immune microenvironment. Macrophages (MΦ) can be polarized to M1 (inflammatory) or M2 (suppressive), and increased populations of M2 tumor infiltrating MΦs are correlated with worse prognosis. We have discovered that Hh signaling contributes to M2 polarization. M1 and M2 MΦs have inherently different metabolic profiles, so we hypothesize that Hh signaling alters M2 MΦ metabolism to reflect M1 MΦ metabolism, leading to diminished M2 phenotype and function within the tumor microenvironment (TME). Methodology includes a mouse model of mammary carcinoma, RNA-seq, mass spectrometry-based metabolomics, confocal imaging, and flow cytometry. We elucidated the impact of Hh signaling blockade on the metabolism of MΦs diminishing their M2 polarization. Inhibition of Hh signaling reduces MΦ O-GlcNAcylation which directly correlates with the diminished suppressive attributes of M2 MΦs through the reduced activity of STAT6. Since STAT6 plays a dual role in governing the M2 phenotype and fatty acid oxidation, this ultimately enacts a metabolic cascade, including lipid utilization, cellular bioenergetics and mitochondrial morphology and function, that metabolically alters M2 MΦs to resemble M1 MΦs. We have discovered that blockade of Hh signaling initiates a metabolic cascade diminishing the M2 phenotype and function. This knowledge will help us to better understand how to target and diminish the pro-tumorigenic phenotypes of MΦs in the TME and at the metastatic site.