Mammalian Cell Death Pathways Induced by Different Types of Shear Flow

During cultivation of mammalian cells in a bioreactor, cells are constantly subjected to shear stresses arising through agitation and aeration. In this work we investigated whether the type of shear flow, to which cells are exposed, will influence the cellular response. It will be shown that mammalian cells, indeed, distinguish between discrete types of flow and respond differently. Two flow devices were employed to impose accurate hydrodynamic flow fields: uniform steady simple shear flow and oscillating extensional flow. The cell response was evaluated by measuring the release of DNA in the culture supernatant, as indicator for membrane rupture and necrotic death, and by means of fluorescence activated cell sorting, to distinguish between necrotic and apoptotic cell death. Results show that Chinese Hamster Ovaries and Human Embryonic Kidney cells will enter the apoptotic pathway when subjected to low levels of hydrodynamic stress (around 2.0 Pa) in oscillating, extensional flow. In contrast, necrotic death prevails when the cells are exposed to hydrodynamic stresses around 1.0 Pa in simple shear flow or around 500 Pa in extensional flow. These threshold values at which cells will enter the respective death pathway should be avoided when culturing cells for recombinant protein production to enhance culture longevity and productivity.