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Sci Signal. 2019 Jun 25;12(587). pii: eaaw3306. doi: 10.1126/scisignal.aaw3306.

Kynurenine signaling through the aryl hydrocarbon receptor maintains the undifferentiated state of human embryonic stem cells.

Author information

1
Research & Development Center for Cell Therapy, Foundation for Biomedical Research and Innovation, 2-2 Minatojima Minami-machi, Chuo-ku, Kobe 650-0047, Japan.
2
Innovative Technology Planning Department, Tokyo Electron Limited, Akasaka Biz Tower, 5-3-1 Akasaka, Minato-Ku, Tokyo 107-6325, Japan.
3
Analytical and Measuring Instruments Division, Shimadzu Corporation, 1 Nishinokyo, Kuwahara-cho, Nagagyo-ku, Kyoto 604-8511, Japan.
4
Research & Development Center for Cell Therapy, Foundation for Biomedical Research and Innovation, 2-2 Minatojima Minami-machi, Chuo-ku, Kobe 650-0047, Japan. kawamata@fbri.org.
5
Riken Center for Developmental Biology, 2-1 Minatojima Minami-machi, Chuo-ku, Kobe 650-0047, Japan.

Abstract

Kynurenine, which is generated from tryptophan by indoleamine 2,3-dioxygenase 1 (IDO1), binds to the aryl hydrocarbon receptor (AhR). Here, we report that kynurenine was produced by undifferentiated human embryonic stem cells (hESCs) and by induced pluripotent stem cells (iPSCs). In undifferentiated hESCs, kynurenine stimulated the AhR to promote the expression of self-renewal genes. The kynurenine-AhR complex also stimulated the expression of IDO1 and AHR, activating a positive feedback loop. Inhibition of IDO1 activity reduced the proliferation of undifferentiated ESCs but did not stimulate their differentiation. Substantial amounts of free kynurenine were present in the culture medium, providing a paracrine signal for maintenance of the undifferentiated state. Kynurenine was not present in the medium of differentiated ESCs or iPSCs. When ESCs were induced to undergo ectodermal differentiation, the abundance of kynurenine in the medium was reduced through activation of the main kynurenine catabolic pathway mediated by kynurenine aminotransferase 2 (KAT2, also known as AADAT), resulting in the secretion of 2-aminoadipic acid (2-AAA) into the culture medium. Inhibition of KAT2 activity blocked ectodermal differentiation. Thus, kynurenine metabolism plays an important role in the maintenance of the undifferentiated state and in ectodermal differentiation. Furthermore, kynurenine in the culture medium is a biomarker for the undifferentiated state, whereas the presence of 2-AAA in the culture medium is a biomarker of ESCs and iPSCs that have committed to differentiate along the ectoderm lineage.

PMID:
31239324
DOI:
10.1126/scisignal.aaw3306

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