Uterine natural killer cell partnerships in early mouse decidua basalis

Innate immune cellular therapeutics in transplantation

Successful organ transplantation provides an opportunity to extend the lives of patients with end-stage organ failure. Selectively suppressing the donor-specific alloimmune response, however, remains challenging without the continuous use of non-specific immunosuppressive medications, which have multiple adverse effects including elevated risks of infection, chronic kidney injury, cardiovascular disease, and cancer. Efforts to promote allograft tolerance have focused on manipulating the adaptive immune response, but long-term allograft survival rates remain disappointing. In recent years, the innate immune system has become an attractive therapeutic target for the prevention and treatment of transplant organ rejection. Indeed, contemporary studies demonstrate that innate immune cells participate in both the initial alloimmune response and chronic allograft rejection and undergo non-permanent functional reprogramming in a phenomenon termed "trained immunity." Several types of innate immune cells are currently under investigation as potential therapeutics in transplantation, including myeloid-derived suppressor cells, dendritic cells, regulatory macrophages, natural killer cells, and innate lymphoid cells. In this review, we discuss the features and functions of these cell types, with a focus on their role in the alloimmune response. We examine their potential application as therapeutics to prevent or treat allograft rejection, as well as challenges in their clinical translation and future directions for investigation.

Functional prominence of natural killer cells and natural killer T cells in pregnancy and infertility: A comprehensive review and update

During pregnancy, complicated connections are formed between a mother and a fetus. In a successful pregnancy, the maternal-fetal interface is affected by dynamic changes, and the fetus is protected against the mother's immune system. Natural killer (NK) cells are one of the immune system cells in the female reproductive system that play an essential role in the physiology of pregnancy. NK cells not only exist in peripheral blood (PB) but also can exist in the decidua. Studies have suggested multiple roles for these cells, including decidualization, control of trophoblast growth and invasion, embryo acceptance and maintenance by the mother, and facilitation of placental development during pregnancy. Natural killer T (NKT) cells are another group of NK cells that play a crucial role in the maintenance of pregnancy and regulation of the immune system during pregnancy. Studies show that NK and NKT cells are not only effective in maintaining pregnancy but also can be involved in infertility-related diseases. This review focuses on NK and NKT cells biology and provides a detailed description of the functions of these cells in implantation, placentation, and immune tolerance during pregnancy and their role in pregnancy complications.

Spatial transcriptomic profiles of mouse uterine microenvironments at pregnancy day 7.5†

Uterine dysfunctions lead to fertility disorders and pregnancy complications. Normal uterine functions at pregnancy depend on crosstalk among multiple cell types in uterine microenvironments. Here, we performed the spatial transcriptomics and single-cell RNA-seq assays to determine local gene expression profiles at the embryo implantation site of the mouse uterus on pregnancy day 7.5 (D7.5). The spatial transcriptomic annotation identified 11 domains of distinct gene signatures, including a mesometrial myometrium, an anti-mesometrial myometrium, a mesometrial decidua enriched with natural killer cells, a vascular sinus zone for maternal vessel remodeling, a fetal-maternal interface, a primary decidual zone, a transition decidual zone, a secondary decidual zone, undifferentiated stroma, uterine glands, and the embryo. The scRNA-Seq identified 12 types of cells in the D7.5 uterus including three types of stromal fibroblasts with differentiated and undifferentiated markers, one cluster of epithelium including luminal and glandular epithelium, mesothelium, endothelia, pericytes, myelomonocytic cell, natural killer cells, and lymphocyte B. These single-cell RNA signatures were then utilized to deconvolute the cell-type compositions of each individual uterine microenvironment. Functional annotation assays on spatial transcriptomic data revealed uterine microenvironments with distinguished metabolic preferences, immune responses, and various cellular behaviors that are regulated by region-specific endocrine and paracrine signals. Global interactome among regions is also projected based on the spatial transcriptomic data. This study provides high-resolution transcriptome profiles with locality information at the embryo implantation site to facilitate further investigations on molecular mechanisms for normal pregnancy progression.

Role of Natural Killer Cells during Pregnancy and Related Complications

A high number of leucocytes reside in the human endometrium and are distributed differentially during the menstrual cycle and pregnancy. During early pregnancy, decidual natural killer (dNK) cells are the most common type of natural killer (NK) cells in the uterus. The increase in the number of uterine NK (uNK) cells during the mid-secretory phase of the menstrual cycle, followed by further increase of dNK cells in early pregnancy, has heightened interest in their involvement during pregnancy. Extensive research has revealed various roles of dNK cells during pregnancy including the formation of new blood vessels, migration of trophoblasts, and immunological tolerance. The present review article is focused on the significance of NK cells during pregnancy and their role in pregnancy-related diseases. The article will provide an in-depth review of cellular and molecular interactions during pregnancy and related disorders, with NK cells playing a pivotal role. Moreover, this study will help researchers to understand the physiology of normal pregnancy and related complications with respect to NK cells, so that future research work can be designed to alleviate the complications.

Obesogenic diet exposure alters uterine natural killer cell biology and impairs vasculature remodeling in mice†

Prepregnancy obesity associates with adverse reproductive outcomes that impact maternal and fetal health. While obesity-driven mechanisms underlying adverse pregnancy outcomes remain unclear, local uterine immune cells are strong but poorly studied candidates. Uterine immune cells, particularly uterine natural killer cells (uNKs), play central roles in orchestrating developmental events in pregnancy. However, the effect of obesity on uNK biology is poorly understood. Using an obesogenic high-fat/high-sugar diet (HFD) mouse model, we set out to examine the effects of maternal obesity on uNK composition and establishment of the maternal-fetal interface. HFD exposure resulted in weight gain-dependent increases in systemic inflammation and rates of fetal resorption. While HFD did not affect total uNK frequencies, HFD exposure did lead to an increase in natural cytotoxicity receptor-1 expressing uNKs as well as overall uNK activity. Importantly, HFD-associated changes in uNK coincided with impairments in uterine artery remodeling in mid but not late pregnancy. Comparison of uNK mRNA transcripts from control and HFD mice identified HFD-directed changes in genes that play roles in promoting activity/cytotoxicity and vascular biology. Together, this work provides new insight into how obesity may impact uNK processes central to the establishment of the maternal-fetal interface in early and mid pregnancy. Moreover, these findings shed light on the cellular processes affected by maternal obesity that may relate to overall pregnancy health.

Evolutionary transcriptomics implicates HAND2 in the origins of implantation and regulation of gestation length

The developmental origins and evolutionary histories of cell types, tissues, and organs contribute to the ways in which their dysfunction produces disease. In mammals, the nature, development and evolution of maternal-fetal interactions likely influence diseases of pregnancy. Here we show genes that evolved expression at the maternal-fetal interface in Eutherian mammals play essential roles in the evolution of pregnancy and are associated with immunological disorders and preterm birth. Among these genes is HAND2, a transcription factor that suppresses estrogen signaling, a Eutherian innovation allowing blastocyst implantation. We found dynamic HAND2 expression in the decidua throughout the menstrual cycle and pregnancy, gradually decreasing to a low at term. HAND2 regulates a distinct set of genes in endometrial stromal fibroblasts including IL15, a cytokine also exhibiting dynamic expression throughout the menstrual cycle and gestation, promoting migration of natural killer cells and extravillous cytotrophoblasts. We demonstrate that HAND2 promoter loops to an enhancer containing SNPs implicated in birth weight and gestation length regulation. Collectively, these data connect HAND2 expression at the maternal-fetal interface with evolution of implantation and gestational regulation, and preterm birth.

Male fetal sex affects uteroplacental angiogenesis in growth restriction mouse model†

Abnormally increased angiotensin II activity related to maternal angiotensinogen (AGT) genetic variants, or aberrant receptor activation, is associated with small-for-gestational-age babies and abnormal uterine spiral artery remodeling in humans. Our group studies a murine AGT gene titration transgenic (TG; 3-copies of the AGT gene) model, which has a 20% increase in AGT expression mimicking a common human AGT genetic variant (A[-6]G) associated with intrauterine growth restriction (IUGR) and spiral artery pathology. We hypothesized that aberrant maternal AGT expression impacts pregnancy-induced uterine spiral artery angiogenesis in this mouse model leading to IUGR. We controlled for fetal sex and fetal genotype (e.g., only 2-copy wild-type [WT] progeny from WT and TG dams were included). Uteroplacental samples from WT and TG dams from early (days 6.5 and 8.5), mid (d12.5), and late (d16.5) gestation were studied to assess uterine natural killer (uNK) cell phenotypes, decidual metrial triangle angiogenic factors, placental growth and capillary density, placental transcriptomics, and placental nutrient transport. Spiral artery architecture was evaluated at day 16.5 by contrast-perfused three-dimensional microcomputed tomography (3D microCT). Our results suggest that uteroplacental angiogenesis is significantly reduced in TG dams at day 16.5. Males from TG dams are associated with significantly reduced uteroplacental angiogenesis from early to late gestation compared with their female littermates and WT controls. Angiogenesis was not different between fetal sexes from WT dams. We conclude that male fetal sex compounds the pathologic impact of maternal genotype in this mouse model of growth restriction.

Recent Insights on the Maternal Microbiota: Impact on Pregnancy Outcomes

Hormonal changes during and after pregnancy are linked with modifications in the maternal microbiota. We describe the importance of the maternal microbiota in pregnancy and examine whether changes in maternal microbiotic composition at different body sites (gut, vagina, endometrium) are associated with pregnancy complications. We analyze the likely interactions between microbiota and the immune system. During pregnancy, the gastrointestinal (gut) microbiota undergoes profound changes that lead to an increase in lactic acid-producing bacteria and a reduction in butyrate-producing bacteria. The meaning of such changes needs clarification. Additionally, several studies have indicated a possible involvement of the maternal gut microbiota in autoimmune and lifelong diseases. The human vagina has its own microbiota, and changes in vaginal microbiota are related to several pregnancy-related complications. Recent studies show reduced lactobacilli, increased bacterial diversity, and low vaginal levels of beta-defensin 2 in women with preterm births. In contrast, early and healthy pregnancies are characterized by low diversity and low numbers of bacterial communities dominated by Lactobacillus. These observations suggest that early vaginal cultures that show an absence of Lactobacillus and polymicrobial vaginal colonization are risk factors for preterm birth. The endometrium is not a sterile site. Resident endometrial microbiota has only been defined recently. However, questions remain regarding the main components of the endometrial microbiota and their impact on the reproductive tract concerning both fertility and pregnancy outcomes. A classification based on endometrial bacterial patterns could help develop a microbiota-based diagnosis as well as personalized therapies for the prevention of obstetric complications and personalized treatments through nutritional, microbiotic, or pharmaceutical interventions.

An Ancient Fecundability-Associated Polymorphism Creates a GATA2 Binding Site in a Distal Enhancer of HLA-F

Variation in female reproductive traits, such as fertility, fecundity, and fecundability, are heritable in humans, but identifying and functionally characterizing genetic variants associated with these traits have been challenging. Here, we explore the functional significance and evolutionary history of a G/A polymorphism at SNP rs2523393, which is an eQTL for HLA-F and is significantly associated with fecundability (the probability of being pregnant within a single menstrual cycle). We replicated the association between the rs2523393 genotype and HLA-F expression by using GTEx data and demonstrate that HLA-F is upregulated in the endometrium during the window of implantation and by progesterone in decidual stromal cells. Next, we show that the rs2523393 A allele creates a GATA2 binding site in a progesterone-responsive distal enhancer that loops to the HLA-F promoter. Remarkably, we found that the A allele is derived in the human lineage and that the G/A polymorphism arose before the divergence of modern and archaic humans and segregates at intermediate to high frequencies across human populations. Remarkably, the derived A allele is has also been identified in a GWAS as a risk allele for multiple sclerosis. These data suggest that the polymorphism is maintained by antagonistic pleiotropy and a reproduction-health tradeoff in human evolution.

Natural cytotoxicity receptor 1 in mouse uNK cell maturation and function

Early and midgestational decidua of mice genetically ablated for expression of the natural killer (NK) cell natural cytotoxicity receptor (NCR; Ncr1^Gfp/Gfp mice) shows restricted angiogenesis and atypically small uterine (u)NK cells. We hypothesized that NCR1 inactivation disturbs maturation and angiokine production by uterine natural killer (uNK) cells. Using histological and morphometric approaches, we observed that Ncr1^Gfp/Gfp but not control C57BL/6 (B6) implantation sites sustain immature, non-granulated uNK cells into midpregnancy. Mouse uNK cells can be subclassified by their reactivity with Dolichos biflorus agglutinin (DBA) lectin; DBA+ uNK cells with greater Ncr1 expression were investigated. DBA+ uNK cells from Ncr1^Gfp/Gfp mice show delayed maturation as indicated by shorter diameters and fewer cytoplasmic granules. Granules in mature Ncr1^Gfp/Gfp uNK cells are ultrastructurally abnormal and abundance of granule-associated proteins (perforin, granzyme) and of cytoplasmic proteins (vascular endothelial growth factor; placental growth factor) differs from controls. Leukocyte-leukocyte conjugate formation in gestation day 6.5 and 8.5 intact Ncr1^Gfp/Gfp decidua was less frequent than in B6; however, this difference involved leukocytes other than DBA+ uNK cells. These studies strongly support roles for NCR1 and its ligands in normal pregnancy promotion.

Decidual natural killer cells and the immune microenvironment at the maternal-fetal interface

During early pregnancy, an orchestrated evolutionary maternal adaption toward tolerance of the semiallogeneic fetus is required to ensure decidualization and early embryo development. Remodeling of the immune system involves natural killer cells (NKs), macrophages, T cells and dendritic cells (DCs) altering the microenvironment in the deciduas. In particular, a unique population of NK cells with a CD56^brightCD16^- phenotype in the decidua has been proposed to play a key role in the maternal adaptation to pregnancy. However, there is a tendency for pregnancy immunology to reflect transplantation immunology regarding the assumption that the maternal immune system should be suppressed. This tendency is misleading. We discuss how the immune system is formed in early deciduas and the interactions between maternal NK cells and fetal growth. We propose that the maternal immune response must not be fully suppressed and is even necessary for the local response of uterine NK cells.

An Ancient Fecundability-Associated Polymorphism Switches a Repressor into an Enhancer of Endometrial TAP2 Expression

Variation in female reproductive traits, such as fertility, fecundity, and fecundability, is heritable in humans, but identifying and functionally characterizing genetic variants associated with these traits has been challenging. Here, we explore the functional significance and evolutionary history of a T/C polymorphism of SNP rs2071473, which we have previously shown is an eQTL for TAP2 and significantly associated with fecundability (time to pregnancy). We replicated the association between the rs2071473 genotype and TAP2 expression by using GTEx data and demonstrated that TAP2 is expressed by decidual stromal cells at the maternal-fetal interface. Next, we showed that rs2071473 is located within a progesterone-responsive cis-regulatory element that functions as a repressor with the T allele and an enhancer with the C allele. Remarkably, we found that this polymorphism arose before the divergence of modern and archaic humans, segregates at intermediate to high frequencies across human populations, and has genetic signatures of long-term balancing selection. This variant has also previously been identified in genome-wide association studies of immune-related disease, suggesting that both alleles are maintained as a result of antagonistic pleiotropy.