Abstract
In mice, inhibition of both the fibroblast growth factor (FGF) mitogen-activated protein kinase kinase/extracellular-signal regulated kinase (MEK/Erk) and the Wnt signaling inhibitor glycogen synthase-3β (GSK3β) enables the derivation of mouse embryonic stem cells (mESCs) from nonpermissive strains in the presence of leukemia inhibitory factor (LIF). Whereas mESCs are in an uncommitted naïve state, human embryonic stem cells (hESCs) represent a more advanced state, denoted as primed pluripotency. This burdens hESCs with a series of characteristics, which, in contrast to naïve ESCs, makes them not ideal for key applications such as cell-based clinical therapies and human disease modeling. In this study, different small molecule combinations were applied during human ESC derivation. Hereby, we aimed to sustain the naïve pluripotent state, by interfering with various key signaling pathways. First, we tested several combinations on existing, 2i (PD0325901 and CHIR99021)-derived mESCs. All combinations were shown to be equally adequate to sustain the expression of naïve pluripotency markers. Second, these conditions were tested during hESC derivation. Overall, the best results were observed in the presence of medium supplemented with 2i, LIF, and the noncanonical Wnt signaling agonist Wnt5A, alone and combined with epinephrine. In these conditions, outgrowths repeatedly showed an ESC progenitor-like morphology, starting from day 3. Culturing these "progenitor cells" did not result in stable, naïve hESC lines in the current conditions. Although Wnt5A could not promote naïve hESC derivation, we found that it was sustaining the conversion of established hESCs toward a more naïve state. Future work should aim to distinct the effects of the various culture formulations, including our Wnt5A-supplemented medium, reported to promote stable naïve pluripotency in hESCs.