Adaptation for survival: Phenotype and transcriptome response of CHO cells to elevated stress induced by agitation and sparging

• Maximum hydrodynamic stress in mammalian cell culture bioreactors was characterized.
• Separate regimes for hydrodynamic stress from agitation or sparging were identified.
• Cultivations in these regimes resulted in different characteristic stress responses.
• Responses were analyzed in a transcriptome fingerprinting approach.
• Pathways involved in hydrodynamic stress adaptation of CHO cells were outlined.

In this work, the response and adaption of CHO cells to hydrodynamic stress in laboratory scale bioreactors originating from agitation, sparging and their combination is studied experimentally. First, the maximum hydrodynamic stress, τmaxτmax, is characterized over a broad range of operating conditions using a shear sensitive particulate system. Separate stress regimes are determined, where τmaxτmax is controlled either by sparging, agitation, or their combination. Such conditions are consequently applied during cultivations of an industrial CHO cell line to determine the cellular responses to corresponding stresses. Our results suggest that the studied CHO cell line has different threshold values and response mechanisms for hydrodynamic stress resulting from agitation or sparging, respectively. For agitation, a characteristic local minimum in viability was found after stress induction followed by viability recovery, while at highest sparging stress a monotonic decrease in viability was observed. If both stresses were combined, also both characteristic stress responses could be observed, amplifying each other. On the other hand, cellular metabolism, productivity and product quality did not change significantly. Transcriptome analysis using mRNA microarrays confirmed that separate adaptation mechanisms are activated in the different stress situations studied, allowing identification of these stresses using a transcriptome fingerprinting approach. Functional analysis of the transcripts was consequently used to improve our understanding of the molecular mechanisms of shear stress response and adaptation.