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Chronic Intermittent Hypoxia Impacts Bone Marrow Macrophages

Sleep apnea is highly prevalent in patients with multiple myeloma, a rare and incurable cancer of malignant plasma cells, and is associated with poor outcomes. Chronic intermittent hypoxia (CIH), a feature of sleep apnea, facilitates myeloma development in mice. However, the mechanism by which CIH contributes to myeloma progression remains unknown. Our objective was to test the hypothesis that CIH provides a fertile environment for malignant cell engraftment via polarization of bone marrow macrophages. We exposed mice to chronic intermittent hypoxia (12 cycles/hr,10 hr/day) or 21% oxygen (control), harvested bone marrow, and assessed the impact of CIH on the percentage of bone marrow macrophages, B cells, plasma cells, T cells flow cytometry. Expression of Arg1, Mrc1, and Chi3l3 in bone marrow macrophages (CD11b+ F4/80+) of CIH‐exposed mice was quantified by qPCR. We evaluated the transcriptome alteration in bone marrow cells of mice exposed to CIH and normoxia by conducting bulk RNA sequencing and single‐cell RNA sequencing. Overall, CIH did not impact the number of macrophages in the bone marrow microenvironment but increased transcription of Arg1, Mrc1, and Chi3l3, transcripts associated with tumor associated‐macrophages, relative to the transcription of IL‐1β, TNF‐α, and iNOS, transcripts associated with anti‐tumorigenic macrophages. RNA sequencing of whole bone marrow supports the increased expression of macrophage markers consistent with tumor‐associated macrophages, and pathway analysis further highlights the role of macrophages. Single‐cell sequencing demonstrated that CIH‐induced genes co‐localize to a single cell population. In conclusion, we found that CIH exposure causes changes to myeloid cell populations in the bone marrow of mice and increases the transcription of genes relevant to myeloma tumor development in macrophages.