Bone marrow milieu reprogramming triggered by chronic intermittent hypoxia
Creators: name: Zhang, Zishan
Publisher: name: University of Iowa
Year: 2023
Subjects: arterial oxygen saturation
bone marrow macrophage heterogeneity
bone marrow microenvironment
gas response kinetics
intermittent hypoxia
oxygen exposure chambers
public abstract
Molecular Biology

description: Intermittent hypoxia is defined by episodic exposures to a lowered oxygen tension, followed by reoxygenation. Sleep apnea causes chronic intermittent hypoxia (CIH), and CIH is thought to mediate many cardiovascular complications associated with sleep apnea. In adult rodents, CIH induces hypertension, augments the sympathetic and ventilatory drives, and promotes cancer progression. We studied the effects of CIH on multiple myeloma cells. Myeloma is a cancer of bone marrow plasma cells associated with obesity. We found that CIH promoted fatal myeloma cell expansion in mice, but In vitro, CIH failed to increase the proliferation of myeloma cells grown in culture. These results led to my overarching hypothesis that the pro-tumor effects of CIH in a myeloma model are the result of CIH modifying the bone marrow microenvironment. However, the specific role of CIH in the murine bone marrow niche remains incompletely understood. Elucidating the effects of sleep apnea on the bone marrow environment, where myeloma cells and other immune cells grow, will advance our understanding of the physiological and pathophysiological consequences of intermittent hypoxia and allow us to develop strategies to prevent myeloma and other diseases. In this thesis, we aim to investigate the impact of chronic intermittent hypoxia on the bone marrow microenvironment. We exposed mice to chronic intermittent hypoxia and assessed the impact on the bone marrow immune cells.Chamber systems are commonly used to perform intermittent hypoxia exposures. The first step is to understand the sources of variability in intermittent hypoxia experiments that can impact reproducibility. There are several points at which variability may be introduced into the experiment. These include the experimental model, the sex of animals, the presence of mice in the chamber, the frequency of the cycling, and the sensitivity of the gas sensor, particularly if it provides feedback to control the chamber. We demonstrate critical sex-dependent differences in the commonly used C57BL/6J mouse model. The time delay of the oxygen sensor that provides feedback to the system during the ramp-down and ramp-up phases was different, limiting the number of cycles per hour that can be conducted and the overall stability of the oxygen concentration. The cycle number impacted the time to reach the hypoxic and normoxic hold stages and the overall oxygen concentration. These variables were further affected by whether animals were present in the chamber, highlighting the importance of verifying the cycling frequency with animals in the chamber. These data demonstrate the critical sources of variability that justify reporting and verifying the target oxygen concentration, cycling frequency, and arterial oxygen concentration, particularly when comparing different animal models and chamber configurations. Using the current chamber, model, and protocol, we need to include both male and female mice and limit the cycling frequency based on the sensor response time and chamber volume in our future experiments to reduce variabilities in the intermittent hypoxia studies.
description: After exposing C57BL/6J mice to CIH (12 cycles/hr,10 hr/day), we found decreased myeloid cell number and increased expression of macrophage signature genes in the bone marrow. The macrophage gene signature is also present in KaLwRij myeloma-prone mice. Pathway analysis further highlights the role of macrophages and B cells. Single-cell sequencing demonstrated that CIH-induced genes co-localize to several subsets of B cell lineage and a single macrophage cell population consistent with erythroid island macrophages and different from “traditional macrophages.” Furthermore, macrophage gene expression on the cell surface is increased by CIH in the macrophages which are different from traditional myeloid cells. This work contributes to disclosing bone marrow macrophage properties and understanding the physiological and pathophysiological consequences of CIH in the murine bone marrow niche and multiple myeloma.