Embryonic Trophectoderm Secretomics Reveals Chemotactic Migration and Intercellular Communication of Endometrial and Circulating MSCs in Embryonic Implantation.

Alexandra Calle,Víctor Toribio,María Yáñez-Mó,Miguel Ángel Ramírez

doi:10.3390/ijms22115638

Abstract

Embryonic implantation is a key step in the establishment of pregnancy. In the present work, we have carried out an in-depth proteomic analysis of the secretome (extracellular vesicles and soluble proteins) of two bovine blastocysts embryonic trophectoderm primary cultures (BBT), confirming different epithelial–mesenchymal transition stages in these cells. BBT-secretomes contain early pregnancy-related proteins and angiogenic proteins both as cargo in EVs and the soluble fraction. We have demonstrated the functional transfer of protein-containing secretome between embryonic trophectoderm and maternal MSC in vitro using two BBT primary cultures eight endometrial MSC (eMSC) and five peripheral blood MSC (pbMSC) lines. We observed that eMSC and pbMSC chemotax to both the soluble fraction and EVs of the BBT secretome. In addition, in a complementary direction, we found that the pattern of expression of implantation proteins in BBT-EVs changes depending on: (i) their epithelial–mesenchymal phenotype; (ii) as a result of the uptake of eMSC- or pbMSC-EV previously stimulated or not with embryonic signals (IFN-τ); (iii) because of the stimulation with the endometrial cytokines present in the uterine fluid in the peri-implantation period.

Highlights

Embryo implantation is a crucial step for pregnancy establishment
Our group characterized for the first time endometrial mesenchymal stem cell lines [11] as well as peripheral blood MSC lines [12]
While endometrial mesenchymal stem cell lines (eMSC) showed a reduced migratory capacity in response to the implantation cytokine IFN-τ [11], peripheral blood MSC (pbMSC) showed chemotactic behavior to both inflammation (TNFα, IL1β), embryo implantation stimuli (IFN-τ) or blastocysts embryonic trophectoderm primary cultures (BBT)-secretome, suggesting that the embryo secretome plays a role in ensuring the retention of eMSC and the active recruitment of MSCs from bone marrow during early pregnancy to repress the immune response to prevent the embryo rejection by the maternal organism [12]

Summary

Introduction

Embryo implantation is a crucial step for pregnancy establishment. In ruminants, noninvasive trophoblast attaches and adheres to the uterine endometrium, followed by the formation of the placenta. Lee et al demonstrated that cell–cell interaction continues during conceptus implantation into the endometrium and that EMT is the key process for many events that facilitate embryonic development, for which the expansion of epidermal basal compartments is required [2]. During this period, trophectoderm cells must be more flexible, enabling the formation of binucleated and trinucleated cells. It was found that binucleated trophoblast cells exhibit intermediate characteristics between epithelial and mesenchymal phenotypes [3]. EMT occurs in different biological processes, the first type of EMT is associated with implantation, embryo formation, organ development, and the generation of a variety of cell types with mesenchymal phenotypes [4]

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