Associate Professor University of Copenhagen Copenhagen, Denmark
Abstract: Metabolism has recently emerged as an important functional regulator of early embryo development, supporting not only nutritional requirements but also pluripotent cell state transitions and gastrulation. Previous studies focusing on metabolism either used transcriptomics as a proxy for metabolic state or small molecule treatments. Therefore, our understanding of the intricate metabolic reprogramming that occurs throughout the developmental continuum remains rudimentary. In this study, we reconstruct the intracellular metabolite routings in blastocyst and peri-implantation mouse embryos and in stem cell models using 13C-isotope tracing combined with advanced imaging and mass spectrometry techniques (MALDI-MSI and LC-MS). Our findings reveal that implantation is linked to alterations in nutrient contributions to core metabolic pathways and further engagement of alternative metabolic routes. Specifically, we identify dramatic rewiring of the TCA cycle both in vivo and in vitro. Firstly, while the oxidative TCA cycle is extinguished, carbon starts flowing from glutamine in the reverse reductive direction. Indeed, further 13C labeling showed that this TCA reversal fuels rapid histone acetylation turnover in primed pluripotency. Here, we find that glutamine uptake is vital for maintaining the active epigenome in preparation for gastrulation. Secondly, we uncover that about a third of carbon enters the TCA cycle entirely bypassing pyruvate dehydrogenase through anaplerotic flow dependent on pyruvate carboxylase and malic enzymes. Disrupting these alternative pathways using CRISPRi impairs the exit from naive pluripotency and affects the transcriptional and metabolic cell states. Together, our study uncovers that implantation is not associated with a simple switch from oxidative phosphorylation to glycolysis but rather involves far more complex metabolite routings vital for fueling the epigenome and directly coupled to cell state transitions.
Funding Source: This work was supported by Novo Nordisk Fonden (NNF21CC0073729, NNF18CC0034900), Lundbeckfonden (R345-2020-1497, R380-2021-1519), European Research Council(101077271) and Danmarks Frie Forskningsfond (0169-00031B).
