All ETDs from UAB

Advisory Committee Chair

Lalita A Shevde-Samant

Advisory Committee Members

Etty N Benveniste

Selvaranagan Ponnazhagan

Robert S Welner

Eddy Yang

Document Type

Dissertation

Date of Award

2022

Degree Name by School

Doctor of Philosophy (PhD) Heersink School of Medicine

Abstract

Current treatments for breast cancer offer little relief to patients with metastatic disease. A contributory factor to tumor growth and metastasis is aberrant up-regulation of developmental signaling pathways such as the Hedgehog (Hh) signaling pathway. This pathway is aberrantly activated in breast cancer and contributes to tumor progression and metastasis. The success of these events is highly influenced by the surrounding immune microenvironment. Macrophages exist along a spectrum of M1 (tumor-eradicating) to M2 (tumor-promoting), while regulatory T cells (Tregs) are an immunosuppressive cell type. The predominant functions of M2 macrophages and Tregs include dampening the immune response and promoting wound healing and tissue repair. These two critical immunosuppressive cell types contribute to worse prognosis in patients with breast cancer. We discovered a novel role for Hh signaling in promoting macrophage polarization to an M2 phenotype and in enhancing Treg differentiation and activity. Metabolomic and scRNAseq analyses highlighted changes in the Hexosamine Biosynthetic Pathway (HBP) and consequently cellular O-GlcNAcylation, in response to Hh blockade. We discovered that O-GlcNAc modifications on key M2 and Treg-specific proteins contribute to their immunosuppression within the TME, and that this phenomenon can be reversed with Hh blockade. Hh blockade in these cell types not only iii diminishes their suppressive potency, but also increases their inflammatory profiles. Hh blockade rewires M2 macrophage metabolism to be reminiscent of M1 macrophage metabolism and promotes Treg to Th17 conversion. Th17s and Tregs are plastic in nature with one another, and Th17s often play an inflammatory role in the context of cancer. Although, there are still conflicting reports regarding Th17s in breast cancer. This study is the first to elucidate Hh signaling’s role in recalibrating the metabolism of tumor-supporting M2 macrophages and Tregs. Inhibiting Hh signaling dampens the HBP, resulting in weakened suppressive properties and concomitant enhanced inflammatory nature of M2 macrophages and Tregs. Our work provides evidence for modulating Hh activity, and consequently the metabolism of two critical immunosuppressive cell types to sculpt their plasticity. This knowledge will help us to better understand how to target and diminish the protumorigenic phenotypes of macrophages and Tregs in the TME.

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