Murine Embryonic Stem Cells Synthesize Retinoic Acid to Promote their Own Differentiation

Abstract

Objective:Embryonic stem cells (ESC) pluripotency is maintained through a complex interplay of different signaling pathways and a network of transcription factors. Although much is known about this pluripotency selfrenewal circuitry, the molecular events that lead ESC to exit from pluripotency and begin differentiation are currently less known. All-trans retinoic acid (atRA), plays important and pleiotropic roles in embryonic development and ESC differentiation. The objective of the present study is to check the autocrine synthesis of atRA by ESC, test its role in spontaneous differentiation of ESC as embryoid bodies (EBs), and analyze the expression of the enzymes and proteins involved in atRA synthesis pathway. Methods: ESC, undifferentiated or differentiating as EBs, were grown in absence or presence of atRA, retinol, or the RAR antagonist CD2665, and Brachyury expression was analyzed as marker of ESC differentiation state. ESC or EBs-conditioned medium was produced in absence or presence of retinol and tested on RARE-luciferase reporter cells. RT-qPCR analysis of atRA biosynthetic pathway components was performed on undifferentiated or differentiating ESC. Finally, microarray gene expression profile was used to identify direct atRA target genes in ESC. Results: Here, we demonstrate that atRA promotes early steps of ESC differentiation, and that ESC increase their capacity to synthesize atRA during spontaneous differentiation as EBs, up-regulating RDH1, RDH10, ADH3, RALDH2, and CRABP2. Among 35 transcription factors (TFs) regulated by atRA in ESC, 3 TFs up-regulated (Snai1, Gata6, Cdx1) are known to be involved in ESC pluripotency exit and 3 TFs down-regulated (Otx2, Id2 and Arid1a) are involved in ESC pluripotency maintaining. Conclusion: Cultivation and controlled differentiation of ESC has opened new frontiers both in regenerative medicine and biology of development. Here, we demonstrated that RA is synthesized by ESC during spontaneous differentiation as EBs and takes an active role to promote their own differentiation process.