Temporary effects of random positioning on the function and plasticity of proliferating monocytes

The Random Positioning Machine (RPM) is used in the field of gravitational biology and space medicine. Rotational bioreactors such as the RPM create dynamic suspension cultures, providing shear stress, a crucial factor in circulatory homeostasis, but also in efficient mixing of nutrients and gases. This creates more physiologically relevant growth conditions than standard culture conditions translating the results to both microgravity and physiological systems on Earth. Immortalized monocyte-like THP-1 cells and primary blood-derived monocytes (PBMC) were cultured on the RPM for up to 7 days and evaluated for cell morphology, plasticity and functionality. For proliferating THP-1 cells, two different cell culture phases became obvious during random positioning: RPM early-phase (1-3 days) cells showed an increased responsiveness to lipopolysaccharide (LPS), plasticity for macrophage differentiation and phagocytic activity. RPM late-phase (4-7 days) cells demonstrated an impaired responsiveness to LPS, plasticity for macrophage differentiation and no phagocytic activity, emphasizing possible inhibitory effects of long-term random positioning on monocyte maturation and functionality. Interestingly, RPM cell culture had no significant effect on the phenotype of non-proliferating PBMCs, possibly related to their quiescence in G₀ phase. These insights provide valuable information about the behavior and susceptibility of human monocytic cells under changing mechanical influences, which is important not only for gravitational research, but also for a better understanding of disease mechanisms.