-RAMP3 promotes hepatocellular carcinoma tumor cell-mediated CCL2 degradation by supporting membrane distribution of ACKR2

This study aimed to explore the potential bind of Receptor Activity-Modifying Protein 3 (RAMP3) with atypical chemokine receptor 2 (ACKR2), and their cooperative regulation on the degradation of the immunosuppressive chemokine CCL2 in the tumor microenvironment of HCC. Bioinformatic analysis was conducted using available bulk-tissue RNA-seq, single-cell RNA-seq, and protein-protein interaction datasets. Human HCC cell line Huh7 and HepG2 and mouse HCC cell line Hepa1-6 were utilized for experiments. Results showed that RAMP3 binds with ACKR2 in HCC tumor cells and promotes the membrane distribution of ACKR2 through RAB4-positive vesicles. RAMP3 promotes CCL2 scavenging through ACKR2 in HCC cells. Mouse RAMP3 inhibited the proliferation of mouse liver cancer cell line (Hepa1-6)-derived syngeneic tumors through ACKR2, reduced the intratumoral concentration of CCL2 in the tumor, and inhibited the phosphorylation of Signal Transducer and Activator of Transcription 3 (STAT3) and protein kinase B (AKT). In addition, mouse RAMP3 inhibited CD11b+/Gr-1 + myeloid cell infiltration and neovascularization in the tumors through ACKR2. In TCGA-LIHC, RAMP3low/ACKR2low group had the worst progression-free interval (PFI), while the RAMP3high/ACKR2high group had the best overall survival (OS). In summary, restoring RAMP3 expression in HCC cells may generate synergistic support for the anticancer effect of ACKR2.

Atypical chemokine receptors in the immune system

Leukocyte migration is a fundamental component of innate and adaptive immune responses as it governs the recruitment and localization of these motile cells, which is crucial for immune cell priming, effector functions, memory responses and immune regulation. This complex cellular trafficking system is controlled to a large extent via highly regulated production of secreted chemokines and the restricted expression of their membrane-tethered G-protein-coupled receptors. The activity of chemokines and their receptors is also regulated by a subfamily of molecules known as atypical chemokine receptors (ACKRs), which are chemokine receptor-like molecules that do not couple to the classical signalling pathways that promote cell migration in response to chemokine ligation. There has been a great deal of progress in understanding the biology of these receptors and their functions in the immune system in the past decade. Here, we describe the contribution of the various ACKRs to innate and adaptive immune responses, focussing specifically on recent progress. This includes recent findings that have defined the role for ACKRs in sculpting extracellular chemokine gradients, findings that broaden the spectrum of chemokine ligands recognized by these receptors, candidate new additions to ACKR family, and our increasing understanding of the role of these receptors in shaping the migration of innate and adaptive immune cells.

Multi-Layered Mechanisms of Immunological Tolerance at the Maternal-Fetal Interface

Pregnancy represents an immunological paradox where the maternal immune system must tolerate the semi-allogeneic fetus expressing paternally-derived Ags. Accumulating evidence over decades has revealed that successful pregnancy requires the active development of robust immune tolerance mechanisms. This review outlines the multi-layered processes that establish fetomaternal tolerance, including the physical barrier of the placenta, restricted chemokine-mediated leukocyte trafficking, lack of sufficient alloantigen presentation, the presence of immunosuppressive regulatory T cells and tolerogenic decidual natural killer cells, expression of immune checkpoint molecules, specific glycosylation patterns conferring immune evasion, and unique metabolic/hormonal modulations. Interestingly, many of the strategies that enable fetal tolerance parallel those employed by cancer cells to promote angiogenesis, invasion, and immune escape. As such, further elucidating the mechanistic underpinnings of fetal-maternal tolerance may reciprocally provide insights into developing novel cancer immunotherapies as well as understanding the pathogenesis of gestational complications linked to dysregulated tolerance processes.

Pan-cancer analysis of the prognostic significance of ACKR2 expression and the related genetic/epigenetic dysregulations

OBJECTIVE

ACKR2 is a scavenger for most inflammation-related CC chemokines. This study aimed to assess the pan-cancer prognostic significance of ACKR2 and the genetic and epigenetic mechanisms underlying its dysregulation.

METHODS

Pan-cancer data from The Cancer Genome Atlas (TCGA), Therapeutically Applicable Research to Generate Effective Treatments (TARGET) and The Genotype-Tissue Expression (GTEx) were integrated and analyzed.

RESULTS

ACKR2 is consistently associated with favorable progression-free interval (PFI) and overall survival (OS) in TCGA-uveal melanoma (UVM) and TCGA-liver hepatocellular carcinoma (LIHC). ACKR2 is negatively correlated with the expression of CCL1, CCL4, CCL5, CXCL8, CCL17, and CCL20 in TCGA-UVM and TCGA-LIHC. The group with gene copy gain had significantly higher ACKR2 expression than those with loss. The lower ACKR2 expression groups were associated with a significantly higher ratio of BAP1 mutations. In addition, ACKR2 was negatively corrected with DNMT1 expression but was positively corrected with ZC3H13, an m6A writer gene and NSUN3, an RNA m5C writer gene.

CONCLUSIONS

ACKR2 expression was associated with favorable prognosis in patients with uveal melanoma and hepatocellular carcinoma. ACKR2 dysregulation might be an accumulated result of gene copy number alterations, transcriptional disruption, and RNA modifications.

Regulation of human trophoblast gene expression by endogenous retroviruses

The placenta is a fast-evolving organ with large morphological and histological differences across eutherians, but the genetic changes driving placental evolution have not been fully elucidated. Transposable elements, through their capacity to quickly generate genetic variation and affect host gene regulation, may have helped to define species-specific trophoblast gene expression programs. Here we assess the contribution of transposable elements to human trophoblast gene expression as enhancers or promoters. Using epigenomic data from primary human trophoblast and trophoblast stem-cell lines, we identified multiple endogenous retrovirus families with regulatory potential that lie close to genes with preferential expression in trophoblast. These largely primate-specific elements are associated with inter-species gene expression differences and are bound by transcription factors with key roles in placental development. Using genetic editing, we demonstrate that several elements act as transcriptional enhancers of important placental genes, such as CSF1R and PSG5. We also identify an LTR10A element that regulates ENG expression, affecting secretion of soluble endoglin, with potential implications for preeclampsia. Our data show that transposons have made important contributions to human trophoblast gene regulation, and suggest that their activity may affect pregnancy outcomes.

Prospects for targeting ACKR1 in cancer and other diseases

The chemokine network is comprised of a family of signal proteins that encode messages for cells displaying chemokine G-protein coupled receptors (GPCRs). The diversity of effects on cellular functions, particularly directed migration of different cell types to sites of inflammation, is enabled by different combinations of chemokines activating signal transduction cascades on cells displaying a combination of receptors. These signals can contribute to autoimmune disease or be hijacked in cancer to stimulate cancer progression and metastatic migration. Thus far, three chemokine receptor-targeting drugs have been approved for clinical use: Maraviroc for HIV, Plerixafor for hematopoietic stem cell mobilization, and Mogalizumab for cutaneous T-cell lymphoma. Numerous compounds have been developed to inhibit specific chemokine GPCRs, but the complexity of the chemokine network has precluded more widespread clinical implementation, particularly as anti-neoplastic and anti-metastatic agents. Drugs that block a single signaling axis may be rendered ineffective or cause adverse reactions because each chemokine and receptor often have multiple context-specific functions. The chemokine network is tightly regulated at multiple levels, including by atypical chemokine receptors (ACKRs) that control chemokine gradients independently of G-proteins. ACKRs have numerous functions linked to chemokine immobilization, movement through and within cells, and recruitment of alternate effectors like β-arrestins. Atypical chemokine receptor 1 (ACKR1), previously known as the Duffy antigen receptor for chemokines (DARC), is a key regulator that binds chemokines involved in inflammatory responses and cancer proliferation, angiogenesis, and metastasis. Understanding more about ACKR1 in different diseases and populations may contribute to the development of therapeutic strategies targeting the chemokine network.

CCL2: An important cytokine in normal and pathological pregnancies: A review

C-C motif ligand 2 (CCL2), also known as monocytic chemotactic protein 1 (MCP-1), is an integral chemotactic factor which recruits macrophages for the immune response. Together with its receptors (e.g., CCR2, ACKR1, and ACKR2), they exert noticeable influences on various diseases of different systems. At the maternal-fetal interface, CCL2 is detected to be expressed in trophoblasts, decidual tissue, the myometrium, and others. Meanwhile, existing reports have determined a series of physiological regulators of CCL2, which functions in maintaining normal recruitment of immunocytes, tissue remodeling, and angiogenesis. However, abnormal levels of CCL2 have also been reported to be associated with adverse pregnancy outcomes such as spontaneous abortion, preeclampsia and preterm labor. In this review, we concentrate on CCL2 expression at the maternal-fetal interface, as well as its precise regulatory mechanisms and classic signaling pathways, to reveal the multidimensional aspects of CCL2 in pregnancy.

The Role of Atypical Chemokine Receptor D6 (ACKR2) in Physiological and Pathological Conditions; Friend, Foe, or Both?

Chemokines exert crucial roles in inducing immune responses through ligation to their canonical receptors. Besides these receptors, there are other atypical chemokine receptors (ACKR1–4) that can bind to a wide range of chemokines and carry out various functions in the body. ACKR2, due to its ability to bind various CC chemokines, has attracted much attention during the past few years. ACKR2 has been shown to be expressed in different cells, including trophoblasts, myeloid cells, and especially lymphoid endothelial cells. In terms of molecular functions, ACKR2 scavenges various inflammatory chemokines and affects inflammatory microenvironments. In the period of pregnancy and fetal development, ACKR2 plays a pivotal role in maintaining the fetus from inflammatory reactions and inhibiting subsequent abortion. In adults, ACKR2 is thought to be a resolving agent in the body because it scavenges chemokines. This leads to the alleviation of inflammation in different situations, including cardiovascular diseases, autoimmune diseases, neurological disorders, and infections. In cancer, ACKR2 exerts conflicting roles, either tumor-promoting or tumor-suppressing. On the one hand, ACKR2 inhibits the recruitment of tumor-promoting cells and suppresses tumor-promoting inflammation to blockade inflammatory responses that are favorable for tumor growth. In contrast, scavenging chemokines in the tumor microenvironment might lead to disruption in NK cell recruitment to the tumor microenvironment. Other than its involvement in diseases, analyzing the expression of ACKR2 in body fluids and tissues can be used as a biomarker for diseases. In conclusion, this review study has tried to shed more light on the various effects of ACKR2 on different inflammatory conditions.

CXCL10 Is an Agonist of the CC Family Chemokine Scavenger Receptor ACKR2/D6

Simple Summary

The atypical chemokine receptor ACKR2 plays an important role in the tumour microenvironment. It has long been considered as a scavenger of inflammatory chemokines exclusively from the CC family. In this study, we identified the CXC chemokine CXCL10 as a new strong agonist ligand for ACKR2. CXCL10 is known to drive the infiltration of immune cells into the tumour bed and was previously reported to bind to CXCR3 only. We demonstrated that ACKR2 acts as a scavenger reducing the availability of CXCL10 for CXCR3. Our study sheds new light on the complexity of the chemokine network and the potential role of CXCL10 regulation by ACKR2 in tumour immunology.

Abstract

Atypical chemokine receptors (ACKRs) are important regulators of chemokine functions. Among them, the atypical chemokine receptor ACKR2 (also known as D6) has long been considered as a scavenger of inflammatory chemokines exclusively from the CC family. In this study, by using highly sensitive β-arrestin recruitment assays based on NanoBiT and NanoBRET technologies, we identified the inflammatory CXC chemokine CXCL10 as a new strong agonist ligand for ACKR2. CXCL10 is known to play an important role in the infiltration of immune cells into the tumour bed and was previously reported to bind to CXCR3 only. We demonstrated that ACKR2 is able to internalize and reduce the availability of CXCL10 in the extracellular space. Moreover, we found that, in contrast to CC chemokines, CXCL10 activity towards ACKR2 was drastically reduced by the dipeptidyl peptidase 4 (DPP4 or CD26) N-terminal processing, pointing to a different receptor binding pocket occupancy by CC and CXC chemokines. Overall, our study sheds new light on the complexity of the chemokine network and the potential role of CXCL10 regulation by ACKR2 in many physiological and pathological processes, including tumour immunology. Our data also testify that systematic reassessment of chemokine-receptor pairing is critically needed as important interactions may remain unexplored.

Abnormal uterine inflammation in obstetric syndromes: molecular insights into the role of chemokine decoy receptor D6 and inflammasome NLRP3

The adaptation of the uterine environment into a favorable immunological and inflammatory milieu is a physiological process needed in normal pregnancy. A uterine hyperinflammatory state, whether idiopathic or secondary to hormonal or organic uterine disorders (polycystic ovary syndromes, endometriosis/adenomyosis and fibroids), negatively influences the interactions between decidua and trophoblast, early in gestation, and between chorion and decidua later in pregnancy. Abnormal activation of uterine inflammatory pathways not only contributes to the pathogenesis of the obstetric syndromes, i.e. recurrent pregnancy loss (RPL), pre-term delivery (PTD) and pre-eclampsia (PE), but also to correlates with severity. In this review, we summarize recent advances in the knowledge of uterine molecular mechanisms of inflammatory modulation in normal pregnancy and obstetric syndromes (RPL, PTD and PE). In particular, we focus on two regulators of uterine/placental inflammation: the NLRP3 inflammasome and the chemokines decoy receptor D6. We performed comprehensive review of the literature in PubMed and Google Scholar databases from 1994 to 2018. The available evidence suggests that: (i) the expression of inflammasome NLRP3 is increased in the endometrium of women with unexplained RPL, in the chorioamniotic membranes of women with PTL and in the placenta of women with PE; (ii) there is a role for abnormal expression and function of D6 decoy receptor at the feto-maternal interface in cases of RPL and PTD and (iii) the function of placental D6 decoy receptor is impaired in PE. A wider comprehension of the inflammatory molecular mechanisms involved in the pathogenesis of the obstetric syndromes might lead to the identification of new potential therapeutic targets.

Histone Deacetylase Sirtuin 2 Enhances Viability of Trophoblasts Through p65-Mediated MicroRNA-146a/ACKR2 Axis

Reduced activity of trophoblast cells is well-recognized to lead to preeclampsia (PE) progression. This study aims to evaluate the roles of histone deacetylase sirtuin 2 (SIRT2) in activity of trophoblast cells and the molecules involved. Differentially expressed genes in placental tissues between PE patients and healthy individuals were screened using microarray analyses. SIRT2 and atypical chemokine receptor 2 (ACKR2) were downregulated while miR-146a was upregulated in PE patients. SIRT2 was localized in placental syncytiotrophoblasts. Upregulation of SIRT2 enhanced viability, migration and invasion, while reduced apoptosis of HTR-8/SVneo cells. SIRT2 was found to trigger p65 deacetylation level and suppress miR-146a expression according to the luciferase and ChIP assays, whereas miR-146a was found to target ACKR2. Downregulation of p65 promoted migration and invasion of cells. Overexpression of miR-146a inhibited cell viability and blocked the function of SIRT2. ACKR2 was downregulated in tissues from PE women and its upregulation blocked the role of miR-146a. To conclude, SIRT2 promotes p65 deacetylation to suppress miR-146a expression and upregulates ACKR2 expression, therefore enhancing proliferation, migration, and invasion of HTR-8/SVneo cells. This study may offer novel thoughts into the management of PE.

Intrauterine Inflammation Alters the Transcriptome and Metabolome in Placenta

Placental insufficiency is implicated in spontaneous preterm birth (SPTB) associated with intrauterine inflammation. We hypothesized that intrauterine inflammation leads to deficits in the capacity of the placenta to maintain bioenergetic and metabolic stability during pregnancy ultimately resulting in SPTB. Using a mouse model of intrauterine inflammation that leads to preterm delivery, we performed RNA-seq and metabolomics studies to assess how intrauterine inflammation alters gene expression and/or modulates metabolite production and abundance in the placenta. 1871 differentially expressed genes were identified in LPS-exposed placenta. Among them, 1,149 and 722 transcripts were increased and decreased, respectively. Ingenuity pathway analysis showed alterations in genes and canonical pathways critical for regulating oxidative stress, mitochondrial function, metabolisms of glucose and lipids, and vascular reactivity in LPS-exposed placenta. Many upstream regulators and master regulators important for nutrient-sensing and mitochondrial function were also altered in inflammation exposed placentae, including STAT1, HIF1α, mTOR, AMPK, and PPARα. Comprehensive quantification of metabolites demonstrated significant alterations in the glucose utilization, metabolisms of branched-chain amino acids, lipids, purine and pyrimidine, as well as carbon flow in TCA cycle in LPS-exposed placenta compared to control placenta. The transcriptome and metabolome were also integrated to assess the interactions of altered genes and metabolites. Collectively, significant and biologically relevant alterations in the placenta transcriptome and metabolome were identified in placentae exposed to intrauterine inflammation. Altered mitochondrial function and energy metabolism may underline the mechanisms of inflammation-induced placental dysfunction.

Chemokine receptors coordinately regulate macrophage dynamics and mammary gland development

Macrophages are key regulators of developmental processes, including those involved in mammary gland development. We have previously demonstrated that the atypical chemokine receptor ACKR2 contributes to the control of ductal epithelial branching in the developing mammary gland by regulating macrophage dynamics. ACKR2 is a chemokine-scavenging receptor that mediates its effects through collaboration with inflammatory chemokine receptors (iCCRs). Here, we reveal reciprocal regulation of branching morphogenesis in the mammary gland, whereby stromal ACKR2 modulates levels of the shared ligand CCL7 to control the movement of a key population of CCR1-expressing macrophages to the ductal epithelium. In addition, oestrogen, which is essential for ductal elongation during puberty, upregulates CCR1 expression on macrophages. The age at which girls develop breasts is decreasing, which raises the risk of diseases including breast cancer. This study presents a previously unknown mechanism controlling the rate of mammary gland development during puberty and highlights potential therapeutic targets.

Deletion of atypical chemokine receptor 3 (ACKR3) increases immune cells at the fetal-maternal interface

Establishment of immune cell populations and adaptations in immune cells are critical aspects during pregnancy that lead to protection of the semi-allogenic fetus. Appropriate immune cell activation and trophoblast migration are regulated in part by chemokines, the availability of which can be fine-tuned by decoy receptors. Atypical chemokine receptor 3 (ACKR3), previously named C-X-C chemokine receptor 7 (CXCR7), is a chemokine decoy receptor expressed in placenta, but little is known about how this receptor affects placental development. In this study, we investigated the phenotypic characteristics of placentas from Ackr3^-/- embryos to determine how Ackr3 contributes to early placentation. In placentas from Ackr3^-/- embryos, we observed an increase in decidual compaction and in the size of the uterine natural killer cell population. Ackr3 knockdown in trophoblast cells led to a decrease in trophoblast migration. These findings suggest that this decoy receptor may therefore be an important factor in normal placentation.

ACKR2 contributes to pulmonary dysfunction by shaping CCL5:CCR5-dependent recruitment of lymphocytes during influenza A infection in mice

Inflammation triggered by influenza A virus (IAV) infection is important for viral clearance, induction of adaptive responses, and return to lung homeostasis. However, an exaggerated immune response, characterized by the overproduction of chemokines, can lead to intense lung injury, contributing to mortality. Chemokine scavenger receptors, such as ACKR2, control the levels of CC chemokines influencing the immune responses. Among the chemokine targets of ACKR2, CCL5 is important to recruit and activate lymphocytes. We investigated the role of ACKR2 during IAV infection in mice. Pulmonary ACKR2 expression was increased acutely after IAV infection preceding the virus-induced lung dysfunction. ACKR2-knockout (ACKR2−/−) mice were protected from IAV, presenting decreased viral burden and lung dysfunction. Mechanistically, the absence of ACKR2 resulted in augmented airway CCL5 levels, secreted by mononuclear and plasma cells in the lung parenchyma. The higher chemokine gradient led to an augmented recruitment of T and B lymphocytes, formation of inducible bronchus-associated lymphoid tissue and production of IgA in the airways of ACKR2−/− mice post-IAV. CCL5 neutralization in ACKR2−/− mice prevented lymphocyte recruitment and increased bronchoalveolar lavage fluid protein levels and pulmonary dysfunction. Finally, CCR5−/− mice presented increased disease severity during IAV infection, displaying increased neutrophils, pulmonary injury and dysfunction, and accentuated lethality. Collectively, our data showed that ACKR2 dampens CCL5 levels and the consequent recruitment of CCR5+ T helper 1 (Th1), T regulatory cells (Tregs), and B lymphocytes during IAV infection, decreasing pathogen control and promoting lung dysfunction in wild type mice. Therefore, ACKR2 is detrimental and CCR5 is protective during IAV infection coordinating innate and adaptive immune responses in mice.

Distinctive phenotypes and functions of innate lymphoid cells in human decidua during early pregnancy

During early pregnancy, decidual innate lymphoid cells (dILCs) interact with surrounding maternal cells and invading fetal extravillous trophoblasts (EVT). Here, using mass cytometry, we characterise five main dILC subsets: decidual NK cells (dNK)1–3, ILC3s and proliferating NK cells. Following stimulation, dNK2 and dNK3 produce more chemokines than dNK1 including XCL1 which can act on both maternal dendritic cells and fetal EVT. In contrast, dNK1 express receptors including Killer-cell Immunoglobulin-like Receptors (KIR), indicating they respond to HLA class I ligands on EVT. Decidual NK have distinctive organisation and content of granules compared with peripheral blood NK cells. Acquisition of KIR correlates with higher granzyme B levels and increased chemokine production in response to KIR activation, suggesting a link between increased granule content and dNK1 responsiveness. Our analysis shows that dILCs are unique and provide specialised functions dedicated to achieving placental development and successful reproduction.

As an interface between maternal and fetal tissues, decidua hosts immune cells specialized in fostering a successful pregnancy. Here the authors carry out high-dimensional characterization of function, morphology and surface markers of human decidual innate lymphoid cells (ILCs), identifying subsets with features distinct from blood ILC.

Expression of ACKR2 in placentas from different types of preeclampsia

OBJECTIVE

The purpose of this study was to investigate the expression of atypical chemokine receptor 2 (ACKR2, D6) in different types of preeclampsia (PE) and its effects on trophoblast proliferation and apoptosis.

METHODS

The subjects were divided into four groups: early-onset PE group (EOPE, n = 30), late-onset PE group (LOPE, n = 30), preterm birth group (PB, n = 30), and normal group (N, n = 30). The expression of ACKR2 in placentas was evaluated using immunohistochemistry, qRT-PCR, and Western blot. The trophoblast cell line JAR was cultured to detect the expression of ACKR2 after simulating hypoxic conditions with cobalt chloride (CoCl₂). The effects on cell proliferation, apoptosis, and expression of the chemokine CCL2 were analyzed after silencing ACKR2 with siRNA.

RESULTS

ACKR2 was decreased in placentas of EOPE and PB groups at the protein and mRNA level，compared to the normal group. No statistical differences were found between EOPE and PB groups, or between LOPE and normal groups. In our in vitro work, we found that the expression of ACKR2 decreased after treatment with 150 μmol/L, 200 μmol/L, and 250 μmol/L of CoCl₂. After ACKR2 was silenced, the degree of cellular proliferation decreased, while apoptosis and CCL2 expression increased.

CONCLUSION

The changes of ACKR2 expression in placentas of PE may be related to gestational weeks. Hypoxia inhibits the expression of ACKR2 in placentas. Abnormal expression of ACKR2 in PE may lead to dysfunction of trophoblast, and ACKR2 is an essential player in the immunoregulation of the placental chemokine CCL2.

Atypical chemokine receptors 1, 2, 3 and 4: Expression and regulation in the endometrium during the estrous cycle and pregnancy and with somatic cell nucleus transfer-cloned embryos in pigs

Atypical chemokine receptor (ACKR) 1, ACKR2, ACKR3, and ACKR4, chemokine decoy receptors that lack G-protein-mediated signaling pathways, internalize and degrade chemokines to control their availability and function. Chemokines play important roles in the endometrium during the estrous cycle and pregnancy, but the expression and regulation of ACKRs have not been determined in pigs. Therefore, we examined the expression of ACKRs in the endometrium throughout the estrous cycle and pregnancy and in conceptus tissues in pigs. ACKR1, ACKR2, ACKR3, and ACKR4 mRNA was expressed in the endometrium, with higher levels of ACKR3 on day 12 of the estrous cycle than in pregnancy and higher levels of ACKR4 on day 15 of pregnancy than in the estrous cycle. ACKR1, ACKR2, and ACKR3, but not ACKR4, mRNA was detected in conceptus and chorioallantoic tissues during pregnancy. ACKR2 and ACKR3 mRNA and ACKR4 protein were mainly localized to luminal epithelial cells and weakly to glandular epithelial cells in the endometrium. Increasing doses of progesterone increased the expression of ACKR2 and ACKR4 and decreased the expression of ACKR3 in endometrial tissues. On day 12 of pregnancy, the expression of ACKR4 mRNA was lower in the endometria of gilts with somatic cell nucleus transfer-derived conceptuses than in the endometria of gilts carrying conceptuses derived from natural mating. These results indicate that the expression of ACKRs is dynamically regulated at the maternal-conceptus interface, suggesting that ACKR proteins might play critical roles in regulating endometrial chemokines to support the establishment and maintenance of pregnancy in pigs.

A guide to chemokines and their receptors

The chemokines (or chemotactic cytokines) are a large family of small, secreted proteins that signal through cell surface G protein-coupled heptahelical chemokine receptors. They are best known for their ability to stimulate the migration of cells, most notably white blood cells (leukocytes). Consequently, chemokines play a central role in the development and homeostasis of the immune system, and are involved in all protective or destructive immune and inflammatory responses. Classically viewed as inducers of directed chemotactic migration, it is now clear that chemokines can stimulate a variety of other types of directed and undirected migratory behavior, such as haptotaxis, chemokinesis, and haptokinesis, in addition to inducing cell arrest or adhesion. However, chemokine receptors on leukocytes can do more than just direct migration, and these molecules can also be expressed on, and regulate the biology of, many nonleukocytic cell types. Chemokines are profoundly affected by post-translational modification, by interaction with the extracellular matrix (ECM), and by binding to heptahelical 'atypical' chemokine receptors that regulate chemokine localization and abundance. This guide gives a broad overview of the chemokine and chemokine receptor families; summarizes the complex physical interactions that occur in the chemokine network; and, using specific examples, discusses general principles of chemokine function, focusing particularly on their ability to direct leukocyte migration.

Simultaneous Ablation of Uterine Natural Killer Cells and Uterine Mast Cells in Mice Leads to Poor Vascularization and Abnormal Doppler Measurements That Compromise Fetal Well-being

Intrauterine growth restriction (IUGR) is a serious pregnancy complication with short- and long-term health consequences. The mechanisms underlying this condition are not well understood. Animal models are the basis for understanding the causes of IUGR and for developing useful therapeutic strategies. Here, we aimed to ascertain the in utero growth of fetuses from NK (natural killer cells)/MC (mast cells)-deficient mothers that give birth to growth-restricted pups and to determine the time point at which IUGR starts. We used high frequency ultrasound imaging to follow-up fetal and placenta size and employed Doppler measurements to document blood supply to the fetus in females that were deficient for NK cells and MCs. In mice lacking NKs and MCs, we observed significantly reduced implantation sizes from mid gestation onward, which was further associated with smaller placentas. Additionally, NK/MC-deficiency was associated with absent and reversed end diastolic flow in umbilical arteries of the fetuses and an increased systolic/diastolic ratio as well as an elevated resistance index. Together, our results indicate that NKs/MCs promote blood flow, placental growth, and subsequent fetal development. The results of this study offer new insights as to how fetal growth is affected in vivo in NK/MC-deficient mice, whose pups are growth restricted at birth. The use of IUGR models and modern technologies enabling the in vivo follow-up of fetal development are important tools for understanding mechanisms behind pregnancy complications that in the future may lead to the development of effective therapies.

Overview and potential unifying themes of the atypical chemokine receptor family

Chemokines modulate immune responses through their ability to orchestrate the migration of target cells. Chemokines directly induce cell migration through a distinct set of 7 transmembrane domain G protein-coupled receptors but are also recognized by a small subfamily of atypical chemokine receptors, characterized by their inability to support chemotactic activity. Atypical chemokine receptors are now emerging as crucial regulatory components of chemokine networks in a wide range of physiologic and pathologic contexts. Although a new nomenclature has been approved recently to reflect their functional distinction from their conventional counterparts, a systematic view of this subfamily is still missing. This review discusses their biochemical and immunologic properties to identify potential unifying themes in this emerging family.