Controlling pericellular oxygen tension in cell culture reveals distinct breast cancer responses to low oxygen tensions

Abstract

Oxygen (O2) tension plays a key role in tissue function and pathophysiology. O2-controlled cell culture, in which the O2concentration in an incubator’s gas phase is controlled, is an indispensable tool to study the role of O2in vivo. For this technique, it is presumed that the incubator setpoint is equal to the O2tension that cells experience (i.e., pericellular O2). We discovered that physioxic (5% O2) and hypoxic (1% O2) setpoints regularly induce anoxic (0.0% O2) pericellular tensions in both adherent and suspension cell cultures. Electron transport chain inhibition ablates this effect, indicating that cellular O2consumption is the driving factor. RNA-seq revealed that primary human hepatocytes cultured in physioxia experience ischemia-reperfusion injury due to anoxic exposure followed by rapid reoxygenation. To better understand the relationship between incubator gas phase and pericellular O2tensions, we developed a reaction-diffusion model that predicts pericellular O2tensiona priori. This model revealed that the effect of cellular O2consumption is greatest in smaller volume culture vessels (e.g.,96-well plate). By controlling pericellular O2tension in cell culture, we discovered that MCF7 cells have stronger glycolytic and glutamine metabolism responses in anoxiavs.hypoxia. MCF7 also expressed higher levels ofHIF2A,CD73,NDUFA4L2,etc.and lower levels ofHIF1A,CA9,VEGFA, etc.in response to hypoxiavs.anoxia. Proteomics revealed that 4T1 cells had an upregulated epithelial-to-mesenchymal transition (EMT) response and downregulated reactive oxygen species (ROS) management, glycolysis, and fatty acid metabolism pathways in hypoxiavs.anoxia. Collectively, these results reveal that breast cancer cells respond non-monotonically to low O2, suggesting that anoxic cell culture is not suitable to model hypoxia. We demonstrate that controlling atmospheric O2tension in cell culture incubators is insufficient to control O2in cell culture and introduce the concept ofpericellular O2-controlled cell culture.