Alternatively Activated Macrophages Are the Primary Retinoic Acid-Producing Cells in Human Decidua

Retinoic Acid Action in Cumulus Cells: Implications for Oocyte Development and In Vitro Fertilization

In the field of human in vitro fertilization (IVF), selecting the best oocyte for freezing or embryo for transfer remains an important focus of clinical practice. Although several techniques are and have been used for this goal, results have generally not been favorable and/or are invasive such that damage to some embryos occurs, resulting in a reduced number of healthy births. Therefore, the search continues for non-invasive oocyte and embryo quality markers that signal the development of high-quality embryos. Multiple studies indicate the important positive effects of retinoic acid (RA) on oocyte maturation and function. We previously showed that a high follicular fluid (FF) RA concentration at the time of oocyte retrieval in IVF protocols was associated with oocytes, giving rise to the highest quality embryos, and that cumulus granulosa cells (CGCs) are the primary source of follicle RA synthesis. Data also demonstrated that connexin-43 (Cx43), the main connexin that forms gap junctions in CGCs, is regulated by RA and that RA induces a rapid increase in gap junction communication. Here, we hypothesize that CGC RA plays a causal role in oocyte competency through its action on Cx43 and, as such, may serve as a biomarker of oocyte competence. Multiple studies have demonstrated the requirement for Cx43 in CGCs for the normal progression of folliculogenesis, and that the increased expression of this connexin is linked to the improved developmental competence of the oocyte. The data have shown that RA can up-regulate gap junction intercellular communication (GJIC) in the cumulus-oocyte complex via a non-genomic mechanism that results in the dephosphorylation of Cx43 and enhanced GJIC. Recognizing the positive role played by gap junctions in CGCs in oocyte development and the regulation of Cx43 by RA, the findings have highlighted the possibility that CGC RA levels may serve as a non-invasive indicator for selecting high-quality oocytes for IVF procedures. In addition, the data suggest that the manipulation of Cx43 with retinoid compounds could provide new pharmacological approaches to improve IVF outcomes in cases of failed implantation, recurrent miscarriage, or in certain diseases that are characterized by reduced fecundity, such as endometriosis.

Spatiotemporal insight into early pregnancy governed by immune-featured stromal cells

Endometrial decidualization connecting embryo implantation and placentation is transient but essential for successful pregnancy, which, however, is not systematically investigated. Here, we use a scStereo-seq technology to spatially visualize and define the dynamic functional decidual hubs assembled by distinct immune, endothelial, trophoblast, and decidual stromal cells (DSCs) in early pregnant mice. We unravel the DSC transdifferentiation trajectory and surprisingly discover a dual-featured type of immune-featured DSCs (iDSCs). We find that immature DSCs attract immune cells and induce decidual angiogenesis at the mesenchymal-epithelial transition hub during decidualization initiation. iDSCs enable immune cell recruitment and suppression, govern vascularization, and promote cytolysis at immune cell assembling and vascular hubs, respectively, to establish decidual homeostasis at a later stage. Interestingly, dysfunctional and spatially disordered iDSCs cause abnormal accumulation of immune cells in the vascular hub, which disrupts decidual hub specification and eventually leads to pregnancy complications in DBA/2-mated CBA/J mice.

Intercellular communication involving macrophages at the maternal-fetal interface may be a pivotal mechanism of URSA: a novel discovery from transcriptomic data

Unexplained recurrent spontaneous abortion (URSA) is a severe challenge to reproductive females worldwide, and its etiology and pathogenesis have not yet been fully clarified. Abnormal intercellular communication between macrophages (Mφ) and decidual stromal cells (DSCs) or trophoblasts has been supposed to be the key to URSA. However, the exact molecular mechanisms in the crosstalk are not yet well understood. This study aimed to explore the potential molecule mechanism that may be involved in the communication between Mφ and DSC or trophoblast cells and determine their diagnostic characteristics by using the integrated research strategy of bioinformatics analysis, machine learning and experiments. First, microarrays of decidual tissue (GSE26787, GSE165004) and placenta tissue (GSE22490) in patients with URSA, as well as microarrays involving induced decidualization (GSE94644) and macrophage polarization in vitro (GSE30595) were derived from the gene expression omnibus (GEO) database. And 721 decidua-differentially expressed genes (DEGs), 613 placenta-DEGs, 510 Mφ polarization DEGs were obtained in URSA by differential expression analysis. Then, the protein-protein interaction (PPI) network was constructed, and the hub genes were identified by CytoHubba in Cytoscape software and validated by real-time PCR assay. Subsequently, immune enrichment analysis on decidua-DEGs and placenta-DEGs by ClueGO verified their regulation effects on Mφ. Besides, functional enrichment analysis was performed on Mφ polarization DEGs and the essential module genes derived from the weighted gene co-expression network analysis (WGCNA) to uncover the biological function that were related to abnormal polarization of Mφ. Furthermore, we screened out 29, 43 and 22 secreted protein-encoding genes from DSC-DEGs, placenta-DEGs and Mφ polarization DEGs, respectively. Besides, the hub secreted-protein-encoding genes were screened by CytoHubba. Moreover, we conducted functional enrichment analysis on these genes. And spearman correlation analysis between hub secreted-protein-encoding genes from donor cells and hub genes in recipient cells was performed to further understand the molecular mechanism of intercellular communication further. Moreover, signature genes with diagnostic value were screened from secreted protein-encoding genes by machine learning and validated by immunofluorescence co-localization analysis with clinical samples. Finally, three biomarkers of DSCs (FGF9, IL1R2, NID2) and three biomarkers of Mφ (CFB, NID2, CXCL11) were obtained. In conclusion, this project provides new ideas for understanding the mechanism regulatory network of intercellular communication involving macrophages at the maternal-fetal interface of URSA. Also, it provides innovative insights for the diagnosis and treatment of URSA.

Functional characterization of interleukin 4 and retinoic acid signaling crosstalk during alternative macrophage activation

Retinoic acid possesses potent immunomodulatory properties in various cell types, including macrophages. In this study, we first investigated the effects at the transcriptional and functional levels of exogenous retinoic acid in murine bone marrow-derived macrophages (BMDMs) in the presence or absence of interleukin 4 (IL4), a cytokine with potent anti-inflammatory properties. We examined the effect of IL4 on vitamin A homeostasis in macrophages by quantifying retinoid synthesis and secretion. Our RNAseq data show that exogenous retinoic acid synergizes with IL4 to regulate anti-inflammatory pathways such as oxidative phosphorylation and phagocytosis. Efferocytosis and lysosomal degradation assays validated gene expression changes at the functional level. IL4 treatment altered the expression of several genes involved in vitamin A transport and conversion to retinoic acid. Radiolabeling experiments and mass spectrometry assays revealed that IL4 stimulates retinoic acid production and secretion in a signal transducer and activator of transcription 6 (STAT6)-dependent manner. In summary, our studies highlight the key role of exogenous and endogenous retinoic acid in shaping the anti-inflammatory response of macrophages.

Decidual macrophages in recurrent spontaneous abortion

Recurrent spontaneous abortion (RSA) is defined as two or more pregnancy loss, affecting the happiness index of fertility couples. The mechanisms involved in the occurrence of RSA are not clear to date. The primary problem for the maternal immune system is how to establish and maintain the immune tolerance to the semi-allogeneic fetuses. During the pregnancy, decidual macrophages mainly play an important role in the immunologic dialogue. The purpose of this study is to explore decidual macrophages, and to understand whether there is a connection between these cells and RSA by analyzing their phenotypes and functions. Pubmed, Web of Science and Embase were searched. The eligibility criterion for this review was evaluating the literature about the pregnancy and macrophages. Any disagreement between the authors was resolved upon discussion and if required by the judgment of the corresponding author. We summarized the latest views on the phenotype, function and dysfunction of decidual macrophages to illuminate its relationship with RSA.

Altered RBP1 Gene Expression Impacts Epithelial Cell Retinoic Acid, Proliferation, and Microenvironment

Vitamin A is an essential diet-derived nutrient that has biological activity affected through an active metabolite, all-trans retinoic acid (atRA). Retinol-binding protein type 1 (RBP1) is an intracellular chaperone that binds retinol and retinal with high affinity, protects retinoids from non-specific oxidation, and delivers retinoids to specific enzymes to facilitate biosynthesis of RA. RBP1 expression is reduced in many of the most prevalent cancers, including breast cancer. Here, we sought to understand the relationship between RBP1 expression and atRA biosynthesis in mammary epithelial cells, as well as RBP1 expression and atRA levels in human mammary tissue. We additionally aimed to investigate the impact of RBP1 expression and atRA on the microenvironment as well as the potential for therapeutic restoration of RBP1 expression and endogenous atRA production. Using human mammary ductal carcinoma samples and a series of mammary epithelial cell lines representing different stages of tumorigenesis, we investigated the relationship between RBP1 expression as determined by QPCR and atRA via direct liquid chromatography-multistage-tandem mass spectrometry-based quantification. The functional effect of RBP1 expression and atRA in epithelial cells was investigated via the expression of direct atRA targets using QPCR, proliferation using Ki-67 staining, and collagen deposition via picrosirius red staining. We also investigated the atRA content of stromal cells co-cultured with normal and tumorigenic epithelial cells. Results show that RBP1 and atRA are reduced in mammary tumor tissue and tumorigenic epithelial cell lines. Knock down of RBP1 expression using shRNA or overexpression of RBP1 supported a direct relationship between RBP1 expression with atRA. Increases in cellular atRA were able to activate atRA direct targets, inhibit proliferation and inhibit collagen deposition in epithelial cell lines. Conditions encountered in tumor microenvironments, including low glucose and hypoxia, were able to reduce RBP1 expression and atRA. Treatment with either RARα agonist AM580 or demethylating agent Decitabine were able to increase RBP1 expression and atRA. Cellular content of neighboring fibroblasts correlated with the RA producing capacity of epithelial cells in co-culture. This work establishes a direct relationship between RBP1 expression and atRA, which is maintained when RBP1 expression is restored therapeutically. The results demonstrate diseases with reduced RBP1 could potentially benefit from therapeutics that restore RBP1 expression and endogenous atRA.

Functional regulation of decidual macrophages during pregnancy

A successful pregnancy requires that the maternal immune system recognizes and tolerates the semi-allogeneic fetus without compromising the capability of protecting both mother and fetus from various pathogens. Decidual macrophages present unique phenotypes to play a key role in the establishment of the immunological aspects of maternal-fetal interaction. Dysfunction of decidual macrophages gives rise to pregnancy complications such as preeclampsia, recurrent spontaneous miscarriage, preterm labor and fetal growth restriction. Here, we reviewed the latest knowledge on the origin, differentiation, unique phenotype and function of macrophages in normal pregnancy and in pregnancy complications. We mainly focused on the significant roles of decidual macrophages in the process of extravillous trophoblast invasion, spiral arterial remodeling, decidual stromal cells cultivation and immune tolerance maintenance in normal pregnancy, and their pathological roles in pregnancy-related complications, offering more integrated information in maternal-fetal immunity.

Aberrant retinoic acid production in the decidua: Implications for pre-eclampsia

Fine-tuning of the endometrium during the evanescent 'window of implantation' relies upon an array of diverse and redundant signaling molecules, particularly the ovarian steroids E2 and P4, but also growth factors, eicosanoids, and vitamins including the vitamin A compounds (retinoids). Pregnancy complications such as preeclampsia (PE) can result from aberrations in the production or function of these molecules that arise during this critical period of decidual development. Such aberrations may be reflected by incomplete decidualization, reduced spiral artery modification, and/or loss of immune tolerance to the developing fetus. Our understanding of the role of the active retinoid metabolite all-trans retinoic acid (RA) in maintaining immune balance in certain tissues, along with data describing its role in decidualization, present a compelling argument that aberrant RA signaling in the decidua can play a significant role in the etiology of PE. Recent findings that decidualization and expression of the anti-angiogenic gene product, 'soluble fms-like tyrosine kinase-1' (sFLT1) are negatively correlated and that sFLT1 expression is directly inhibited by RA, provide additional evidence of the critical role of this retinoid in regulating early vascular development in the decidua. This review provides insight into the production and function of RA in the decidua and how modifications in its metabolism and signaling might lead to certain pregnancy disorders such as PE.