On metabolic shift to lactate consumption in fed-batch culture of mammalian cells.

Fedbatch culture is the prevalent cell cultivation method in producing protein therapeutics. A metabolic shift to lactate consumption in late stage of cultivation has been shown to extend the culture viability and increase product concentrations. To better understand the factors, which trigger metabolic shift we performed transcriptome and metabolic flux analysis on a fedbatch culture of mouse myeloma cell line (NS0) and developed a mechanistic kinetic model for energy metabolism. Experimental observation indicates that the shift to lactate consumption occurs upon the cessation of rapid growth and under conditions of low glycolysis flux and high extracellular lactate concentrations. Although the transition is accompanied by a general down regulation of enzymes in energy metabolism, that alone was insufficient to elicit a metabolic shift. High lactate level has been reported to exert an inhibitory effect on glycolysis enzyme phosphofructokinase; model simulation suggests that a high lactate level can contribute to reduced glycolytic flux as well as providing a driving force for its conversion to pyruvate. The transcriptome data indicate that moderate alteration in the transcript levels of AKT1 and P53 signaling pathways genes occurs in the late stage of culture. These signaling pathways are known to regulate glycolytic activity. Model simulations further suggest that AKT1 signaling plays a key role in facilitating lactate consumption. Collectively, our results strongly suggest that lactate consumption in fedbatch culture is an outcome of reduced glycolysis flux, which is a product of lactate inhibition and regulatory action of signaling pathway caused by reduced growth rate.