Ablation of hematopoietic stem cell derived adipocytes reduces tumor burden in syngeneic mouse models of high-grade serous carcinoma

In this study we examined the influence of hematopoietic stem cell derived adipocytes (HSCDAs) on the proliferation and metastasis of high-grade serous carcinoma (HGSC), the most common type of ovarian cancer. HSCDAs are a subtype of adipocytes which begin as myeloid cells that traffic from bone marrow to adipose tissue, particularly visceral depots, and then differentiate and accumulate therein. We hypothesized that HSCDAs promote HGSC progression and establish a pro-tumoral niche within peritoneal adipose tissues such as the omentum. We took primary human adipose biopsies and flow sorted the myeloid and mesenchymal populations. We differentiated these adipose precursors in vitro into mature HSCDAs and CMAs, respectively. RNA-Seq analysis showed that HSCDAs have a distinct transcriptional profile from CMAs, including downregulation of cell cycle and upregulation of multiple metabolic and adipogenic pathways. Using ELISA, we found that HSCDAs secreted greater amounts of inflammatory cytokines IL-6 and IL-8 than CMAs. We incubated HGSC cell lines in conditioned media from HSCDAs and CMAs and performed reverse phase protein array (RPPA) and proliferation assays. HGSC cells in HSCDA media had elevated protein markers of epithelial to mesenchymal plasticity, including fibronectin, as well as increased serine phosphorylation of pro-survival AKT1/2. Conversely, HGSC cells in HSCDA media downregulated tumor suppressors including Wnt regulator GSK3β. Depending on the cell line and adipose donor, HGSC cells also showed altered growth rates in conditioned media. We next investigated the role of HSCDAs in HGSC progression and metastasis in vivo. We generated immunocompetent mice that were either HSCDA Proficient (can make both adipocyte subtypes) or Deficient (can only make CMAs). We performed two independent tumor studies using the ID8 (Tp53-/-, Brca2-/-) and SO (Tp53-/-, Brca1/2 wild-type, Hras and Myc amplified) syngeneic models. In both models, overall tumor burden was lower in HSCDA Deficient mice. In the ID8 model, omentum tumors from HSCDA Deficient mice, relative to those from Proficient mice, showed reduced proliferation (Ki67) and apoptosis (cleaved caspase 3). Analysis of bulk RNA-Seq of ID8 omentum tumors from HSCDA Deficient mice revealed downregulation of oxidative phosphorylation, adipogenesis, and fatty acid metabolism. These pathways were enriched in HSCDA cells in vitro, suggesting that ablation of HSCDAs had a significant influence on the tumor metabolic environment. We also observed reduced inflammatory pathways in ID8 tumors from HSCDA Deficient mice, so we interrogated immune cell infiltration into omentum tumors. Compared to HSCDA Proficient mice, tumors from HSCDA Deficient mice showed reduced densities of dendritic cells (DC) and natural killer (NK) cells. By spatial analysis we found fewer DCs, NKs, and B-cells near tumor cells. Overall, our data suggest that HSCDAs can promote HGSC survival and plasticity while downregulating tumor suppressors, and also alter the peritoneal immune and metabolic environment to promote HGSC progression.