Hypoxia influences protein transport and epigenetic repression of CHO cell cultures in shake flasks

Shake flasks and bench‐top bioreactors are widely used for cell culture process development, however, culture performances significantly differ between them. In order to apply the results received from small‐scale cultures to production scale, it is important to understand the mechanisms underlying the differences between various culture systems. This study analyzes the expression patterns of Chinese hamster ovary (CHO) cells producing IgG‐fusion protein B0 cultured in shake flasks and 5‐L bench‐top bioreactors by CHO‐specific DNA microarrays. The data show that hypoxia was present in shake flask cultures but not in controlled, bench‐top bioreactors. Hypoxic conditions appeared to be associated with epigenetic repression resulting in decreased cell culture performance and protein productivity, which is also present during large‐scale bioreactor operations due to oxygen gradients. High protein productivity was associated with increased cellular machinery for protein transport and secretion in conjunction with decreased epigenetic repression in bench‐top bioreactor cultivation. Metal ions could improve cell growth and protein production under hypoxia and this condition could be mimicked in small‐scale bioreactors to facilitate cell culture process scale‐up. In order to successfully increase the production scale of cell cultures, it is important to understand the mechanisms underlying the differences in the culture systems. Experimental evidence from the current study demonstrates that a low‐oxygen condition is present in the cultures of shake flasks, which makes gene transcription more difficult to perform due to increased DNA methylation and condensed chromatin. A low‐oxygen condition is also present during large‐scale bioreactor operations, and therefore the shake flask results can be applied to production scale.