Molecular Analysis of HLA-G in Women with High-Risk Pregnancy and Their Partners with Regard to Possible Complications

Genetic causes of sporadic and recurrent miscarriage

Approximately 80% of miscarriages happen within the first 12 weeks of gestation. More than half of early losses result from genetic defects, usually presenting as abnormal chromosome numbers or gene rearrangements in the embryo. However, the impact of genetics on pregnancy loss goes well beyond embryonic aneuploidy. For example, the use of big data has recently led to the discovery of specific gene mutations that may be implicated in sporadic and recurrent miscarriages. Further, emerging data suggest that genetic factors play a role in conditions for which there is a causative association with recurrent pregnancy loss. Here, we summarize the evidence on the genetics of miscarriage and provide an overview of the diagnosis and prevention of genetic causes associated with sporadic and recurrent pregnancy loss.

Association of parental HLA-G polymorphisms with soluble HLA-G expressions and their roles on recurrent implantation failure: A systematic review and meta-analysis

Introduction

HLA-G plays a central role in immune tolerance at the maternal-fetal interface. The HLA-G gene is characterized by low allelic polymorphism and restricted tissue expression compared with classical HLA genes. HLA-G polymorphism is associated with HLA-G expression and linked to pregnancy complications. However, the association of parental HLA-G polymorphisms with soluble HLA-G (sHLA-G) expression and their roles in recurrent implantation failure (RIF) is unclear. The study aims to systematically review the association of HLA-G polymorphisms with RIF, the association of sHLA-G expression with RIF, and the association of HLA-G polymorphisms with sHLA-G expressions in patients attending in-vitro fertilization (IVF) treatment.

Methods

Studies that evaluated the association of HLA-G polymorphisms with RIF, the association between sHLA-G expression with RIF, and the association between HLA-G polymorphisms with sHLA-G expressions in patients attending IVF treatment were included. Meta-analysis was performed by random-effect models. Sensitivity analysis was performed by excluding one study each time. Subgroup analysis was performed based on ethnicity.

Results

HLA-G 14bp ins variant is associated with a lower expression of sHLA-G in seminal or blood plasma of couples attending IVF treatment. The maternal HLA-G*010101 and paternal HLA-G*010102 alleles are associated with RIF risk compared to other alleles. However, single maternal HLA-G 14bp ins/del polymorphism, HLA-G -725 C>G/T polymorphism, or circulating sHLA-G concentration was not significantly associated with RIF in the general population. HLA-G 14bp ins/ins homozygous genotype or ins variant was associated with a higher risk of RIF in the Caucasian population.

Discussion

Specific HLA-G alleles or HLA-G polymorphisms are associated with sHLA-G expression in couples attending IVF treatment. Several HLA-G polymorphisms may be related to RIF, considering different ethnic backgrounds. A combined genetic effect should be considered in future studies to confirm the association of HLA-G polymorphisms and sHLA-G expressions in relation to RIF.

Role of polymorphisms on the Recurrent Pregnancy Loss: A systematic review, Meta-analysis and bioinformatic analysis

Recurrent miscarriage (RM) is a major reproductive health issue. RM is a multi-factorial disease, and is affected by environmental, genetic, and epigenetic factors. Genetics has a common role in recurrent miscarriage occurrence. It seems that molecular genetics has a great role in RSA incidence. So, in these years, RM has become for a major subject of genetics research. There are many genes that are involved in each phase for successful reproduction. This research aimed to evaluate the effect of all studied polymorphisms in studies on RSA that have not been included in any meta-analysis. PubMed, Scopus, and Web of Science databases were recruited to investigate the related articles. The systematic review results identified 143 studies worldwide. Thirteen genes have been included in assessing the case-control studies. Sixty-four SNPs were recruited to assess the association between genetic factors and RSA susceptibility. Ninety-two studies containing twenty two SNPs (from 10 genes) were included in the quantitative analysis. Bioinformatic analysis indicated that rs12722482 showed "Damaging Status" by double servers, and rs315952 and rs854560 had "Possibly damaging" status in the PolyPhen-2 server. MethPrimer server indicated that there is "CpG Island" in the rs10895068, rs1130355, and rs41557518 variants, and rs10895068-G allele makes a CpG dinucleotide which can change the gene methylation and result in altering the gene expression. So, further studies on rs12722482 and rs10895068 can demonstrate valuable results. To the best of our knowledge, this systematic review has covered the all studied polymorphisms of HLA-C, HLA-G, PON1, AGTR1, TAFI, FAS, FAS-L, ESR1, PGR, CTLA-4, MMP-2, MMP-3, MMP-9, and IL1RN for the first time. Also, we did a novel meta-analysis for AGTR1 rs5186, TAFI rs1926447, rs3742264, HLA-G rs1063320, rs1233334, rs1736936, rs2249863, PON1 rs662, rs854560, FAS rs2234767, rs1800682, FAS-L rs763110, ESR1, rs9340799, rs3798759, PGR rs1042838, CTLA4 rs4553808, rs5742909, rs231775, rs3087243, and MMP-2 rs243865 and updated statistical finding for rs2234693 and rs371194629. Rs2234693, rs9340799, rs231775, and rs371194629 demonstrated a significant association with RSA risk. Some variations showed significant association, while further studies are suggested to confirm the results. Finally, Rs4553808 and rs5742909 revealed no significant deviation in the results. It is suggested that these SNPs may be excluded from subsequent case-control studies or other analyses.

HLA-G genetic diversity and evolutive aspects in worldwide populations

HLA-G is a promiscuous immune checkpoint molecule. The HLA-G gene presents substantial nucleotide variability in its regulatory regions. However, it encodes a limited number of proteins compared to classical HLA class I genes. We characterized the HLA-G genetic variability in 4640 individuals from 88 different population samples across the globe by using a state-of-the-art method to characterize polymorphisms and haplotypes from high-coverage next-generation sequencing data. We also provide insights regarding the HLA-G genetic diversity and a resource for future studies evaluating HLA-G polymorphisms in different populations and association studies. Despite the great haplotype variability, we demonstrated that: (1) most of the HLA-G polymorphisms are in introns and regulatory sequences, and these are the sites with evidence of balancing selection, (2) linkage disequilibrium is high throughout the gene, extending up to HLA-A, (3) there are few proteins frequently observed in worldwide populations, with lack of variation in residues associated with major HLA-G biological properties (dimer formation, interaction with leukocyte receptors). These observations corroborate the role of HLA-G as an immune checkpoint molecule rather than as an antigen-presenting molecule. Understanding HLA-G variability across populations is relevant for disease association and functional studies.

Role of the HLA-G immune checkpoint molecule in pregnancy

The non-classical HLA class I molecule HLA-G is expressed in trophoblasts where it contributes to maternal-fetal tolerance. HLA-G has been implicated in the control of trophoblast invasion, uterine vascular remodeling, and maintenance of a local immunosuppressive state. Understanding HLA-G biology at the maternal-fetal interface is therefore a critical issue in reproduction. In this regard, we review here: (i) the effects of HLA-G on decidual leucocytes and stromal cells, (ii) the contribution of trogocytosis in HLA-G expression on decidual cells, (iii) its interaction with the ILT2, ILT4 and KIR2DL4 receptors, (iv) the link between HLA-G polymorphism and pregnancy disorders, and (v) the expression of newly-described HLA-G isoforms at the maternal-fetal interface.

HLA-G: Function, polymorphisms and pathology

HLA-G immune modulatory genes and molecules are presently being studied by a widespread number of research groups. In the present study, we do not aim to be exhaustive since the number of manuscripts published every year is overwhelming. Instead, our aim is pointing out facts about HLA-G function, polymorphism and pathology that have been confirmed by several different researchers, together with exposing aspects that may have been overlooked or not sufficiently remarked in this productive field of study. On the other hand, we question whether performing mainly studies on HLA-G and disease associations is going to give a clear answer in the future, since 40 years of study of classical HLA molecules association with disease has still given no definite answer on this issue.

Soluble HLA-G expression levels and HLA-G/irinotecan association in metastatic colorectal cancer treated with irinotecan-based strategy

We here explore the soluble Human Leukocyte Antigen-G (sHLA-G) expression level as clinical biomarker in metastatic colorectal cancer (mCRC). To this aim the sHLA-G protein was measured in plasma samples of 40 patients with mCRC treated with the FOLFIRI (irinotecan (CPT-11) plus 5-fluorouracil (5-FU) and leucovorin (LV)) regimen. The results suggest a link between HLA-G levels and irinotecan (CPT-11) pharmacokinetic, leading to hypothesize a molecular interaction between sHLA-G and CPT-11. This interaction was confirmed experimentally by fluorescence spectroscopy. HLA-G is known to exist in a number of polymorphs that affect both the protein expression levels and its peptide-binding cleft. The interaction between HLA-G polymorphs and CPT-11 was explored by means of computational modelling, confirming the hypothesis that CPT-11 could actually target the peptide binding cleft of the most common HLA-G polymorphs.

Association of Soluble HLA-G Plasma Level and HLA-G Genetic Polymorphism With Pregnancy Outcome of Patients Undergoing in vitro Fertilization Embryo Transfer

Infertility is currently a growing problem observed around the world and is estimated to affect between 8 and 12% of reproductive-aged couples worldwide. Artificial reproductive techniques are the last chance for couples seeking their own child. Human leukocyte antigen (HLA)-G expression has been suggested as an immunomodulatory molecule that influences pregnancy outcome. The HLA-G gene encodes either membrane-bound or/and soluble proteins. The aim of this study was the evaluation of the role of soluble HLA-G (sHLA-G) and its gene polymorphism in successful implantation after in vitro fertilization embryo transfers (IVF-ETs) in different clinical protocols. We tested the HLA-G polymorphism in three positions: rs1632947: c.-964G>A; rs1233334: c.-725G>C/T in promoter region; rs371194629: c.^*65_^*66insATTTGTTCATGCCT in 3′ untranslated region of exon 8, in 389 patients who underwent IVF-ETs and 320 women with healthy children born after natural conception. Among the patient group, 239 women were with recurrent implantation failure and 117 women had an ongoing pregnancy or a child born after IVF-ET. We found that certain rs1632947-rs1233334-rs371194629 HLA-G haplotypes and diplotypes were associated with infertility, while others were protective. The lowest secretors of sHLA-G were G-C-ins haplotype carriers (37.21 IU/ml), while the highest -G-C-del carriers (73.80 IU/ml). Other haplotype carriers were intermediate secretors. In our study, regardless of possessed haplotype by the patient, 59.73 IU/ml sHLA-G was the threshold value with the best sensitivity (58.82%) and specificity (66.10%) to discriminate patients who achieved and maintained pregnancy from those who did not conceive or they had miscarriage (p = 0.0085; likelihood ratio, 1.74; 95% CI = 0.55–0.78). However, we do not exclude that factors other than sHLA-G may also contribute to complications in pregnancy. In addition, we found that IVF patients in cycles when frozen/thawed embryo was transferred secreted higher soluble HLA-G levels than patients with fresh embryo transferred (p = 0.021). Moreover, correlation analysis of sHLA-G concentration measured before and after embryo transfer for particular patients indicated short ovarian stimulation with gonadotropin-releasing hormone antagonist as more beneficial than long protocol with gonadotropin-releasing hormone agonist. Our study confirms a role of HLA-G polymorphism in infertility and soluble HLA-G in the early stages of pregnancy.