Amino acid intake strategies define pluripotent cell states

Mammalian preimplantation development is associated with marked metabolic robustness, and embryos can develop under a wide variety of nutrient conditions, including even the complete absence of soluble amino acids. Here we show that mouse embryonic stem cells (ESCs) capture the unique metabolic state of preimplantation embryos and proliferate in the absence of several essential amino acids. Amino acid independence is enabled by constitutive uptake of exogenous protein through macropinocytosis, alongside a robust lysosomal digestive system. Following transition to more committed states, ESCs reduce digestion of extracellular protein and instead become reliant on exogenous amino acids. Accordingly, amino acid withdrawal selects for ESCs that mimic the preimplantation epiblast. More broadly, we find that all lineages of preimplantation blastocysts exhibit constitutive macropinocytic protein uptake and digestion. Taken together, these results highlight exogenous protein uptake and digestion as an intrinsic feature of preimplantation development and provide insight into the catabolic strategies that enable embryos to sustain viability before implantation. RNA-seq of mouse embryonic stem cells expressing a tamoxifen-responsive version of murine Tfe3. Tamoxifen induces nuclear translocation of Tfe3.

哺乳动物植入前发育（Mammalian preimplantation development）具有显著的代谢鲁棒性，胚胎可在多样营养条件下完成发育，甚至可在完全缺乏可溶性氨基酸的环境中存活发育。本研究证实，小鼠胚胎干细胞（mouse embryonic stem cells, ESCs）能够捕获植入前胚胎特有的代谢状态，并在多种必需氨基酸缺失的条件下增殖。其氨基酸不依赖性的实现，依赖于通过巨胞饮作用（macropinocytosis）持续摄取外源蛋白质，同时辅以功能完备的溶酶体消化系统。当胚胎干细胞向更特化的细胞状态转变时，其对胞外蛋白质的消化能力会减弱，转而依赖外源氨基酸获取营养。据此，氨基酸剥夺筛选可获得模拟植入前上胚层的胚胎干细胞。从更广泛的视角来看，植入前囊胚的所有谱系均存在组成型巨胞饮蛋白摄取与消化过程。综上，本研究结果证实外源蛋白质摄取与消化是植入前发育的内在固有特征，并为阐明胚胎在着床前维持存活的分解代谢策略提供了新见解。本数据集包含表达他莫昔芬（tamoxifen）响应型小鼠Tfe3的小鼠胚胎干细胞的RNA测序（RNA-seq）数据，其中他莫昔芬可诱导Tfe3发生核转位（nuclear translocation）。