Macrophages induce inflammation by efferocytosis of apoptotic prostate cancer cells via HIF-1a stabilization

Clearance of apoptotic cancer cells by macrophages, known as efferocytosis, fuels the bone-metastatic growth of prostate cancer cells via pro-inflammatory and immunosuppressive mechanisms that are still unclear. In this study, single-cell transcriptomics of bone marrow macrophages undergoing efferocytosis of apoptotic prostate cancer cells revealed a significant enrichment of a cellular response to hypoxia. Here we show that efferocytic macrophages promote HIF-1a stabilization under normoxic conditions through interaction with phosphorylated STAT3. Inflammatory cytokine gene expression analysis of efferocytic HIF-1a-mutant macrophages revealed a reduced expression of the pro-tumorigenic Mif. Furthermore, stabilization of HIF-1a using the HIF-prolyl-hydroxylase inhibitor, Roxadustat, enhanced MIF expression in macrophages. Finally, macrophages treated with recombinant MIF protein activated NF-?B (p65) signaling increased the expression of pro-inflammatory cytokines. Altogether, these findings suggest that the clearance of apoptotic cancer cell by tumor-associated macrophages triggers p-STAT3/HIF-1a/MIF signaling to enhance tumor-promoting inflammation in bone, suggesting this axis as a target for metastatic prostate cancer. Overall design: Single cell sequencing of macrophages following efferocytosis