SMAD2/3 signaling in the uterine epithelium controls endometrial cell homeostasis and regeneration

Abstract

The regenerative potential of the endometrium is attributed to endometrial stem cells; however, the signaling pathways controlling its regenerative potential remain obscure. In this study, genetic mouse models and endometrial organoids are used to demonstrate that SMAD2/3 signaling controls endometrial regeneration and differentiation. Mice with conditional deletion of SMAD2/3 in the uterine epithelium using Lactoferrin-iCre develop endometrial hyperplasia at 12-weeks and metastatic uterine tumors by 9-months of age. Mechanistic studies in endometrial organoids determine that genetic or pharmacological inhibition of SMAD2/3 signaling disrupts organoid morphology, increases the glandular and secretory cell markers, FOXA2 and MUC1, and alters the genome-wide distribution of SMAD4. Transcriptomic profiling of the organoids reveals elevated pathways involved in stem cell regeneration and differentiation such as the bone morphogenetic protein (BMP) and retinoic acid signaling (RA) pathways. Therefore, TGFβ family signaling via SMAD2/3 controls signaling networks which are integral for endometrial cell regeneration and differentiation.

Impaired bone morphogenetic protein (BMP) signaling pathways disrupt decidualization in endometriosis

“…SMAD4 is the common SMAD that can transmit BMP signaling (via SMAD1/5) or activin/TGFβ signaling 62 . Our previous studies, which show that BMP/SMAD1/5 signaling and TGFβ/SMAD2/3 signaling are critical for decidualization and fertility, are in line with these results 78 – 80 , 122 – 124 . We focused on the roles of BMP/SMAD1/5 signaling given that we observed altered expression of BMP ligands ( BMP4, BMP6) as well as decreased expression of canonical SMAD1/SMAD5 targets in the decidualizing stromal cells from individuals with endometriosis.…”

Bioengineering approaches for the endometrial research and application

“…This approach is beneficial for precisely simulating in vivo tissues and allows for the investigation of the roles played by different types of cells [ 33 , 34 ]. Endometrial organoids are expected to reveal crucial intracellular signaling pathways and depict the entire morphological characteristics of the tissue, greatly enhancing our understanding of the physiological and pathological traits of the human endometrium at the cellular level [ 35 , 36 ]. Controversies regarding the cellular sources of endometrial regeneration exist owing to the existence of a hierarchical network of SC differentiation; therefore, more efforts are needed to build an accessible and ideal research model that allows the analysis of gene expression patterns [ 15 , 37 ].…”

Endometrial TGFβ signaling fosters early pregnancy development by remodeling the fetomaternal interface

“…[55][56][57] Hence, BMP signaling, via the ALK2 and ALK3 receptors and the SMAD1/SMAD5 transcription factors, is critical for reprogramming endometrial stroma into functional decidua during early pregnancy. 49 Conditional uterine SMAD1/5 knock-out using PR-cre mouse model results in sterile females due to embryo implantation defects caused by cystic endometrial glands, endometrial hyperproliferation during the window of implantation, and faulty apicobasal transformation Monsivais et al 55 Epithelial-specific conditional double knock-out of SMAD1 and SMAD5 results in subfertility linked to impaired endometrial receptivity, delayed implantation, and peri-implantation defects Tang et al 56 Triple conditional knock-outs of SMAD1, SMAD5, and SMAD4 using the Amhr2-cre mouse model results in sterile females due to oviductal malformations, impaired decidualization, and an inability to assemble a closed uterine lumen following implantation Rodriguez et al 57 SMAD2/3 Conditional uterine epithelial SMAD2/3 knock-out using Lactoferrin-iCre mouse model results in endometrial hyperplasia by 12-weeks of age and metastatic tumors by 9 months of age Kriseman et al 146 levels of progesterone, whereas the stromal cells in mice require not only the increase in progesterone signaling, but also the mechanical stimulation of an implanting embryo. 26,58 The morphological and functional reprogramming of stromal cells into decidual cells is triggered by the combined effects of E2 and P4, as well as multiple growth factors that are stimulated in response to these hormones.…”

“…145 To further investigate the effects of the TGFβ pathway on uNK populations, multiple studies have altered various points this pathway in mice and observed their effects both broadly on reproductive function, but also more specifically on uNK localization to implantation sites during early pregnancy. Uterine-specific knock-out studies of TGFβ receptors and downstream effectors, such as the SMAD proteins, result in a range of reproductive phenotypes from infertility to uterine tumors, 52,54,55,94,95,146 and clearly play an important role in proper female reproductive function. Some of these phenotypes are associated with a lack of uNK cell infiltration into early implantation sites, such as in the implantation sites of mice with a conditional knock-out of a conserved activin receptor type 2 B (ACVR2B), which lacks uNKs and is associated with implantation defects and infertility.…”