Maternal human leukocyte antigen-G polymorphism is not associated with pre-eclampsia in a Chinese Han population

Pre-Existing Diabetes Mellitus, Hypertension and KidneyDisease as Risk Factors of Pre-Eclampsia: A Disease of Theories and Its Association with Genetic Polymorphism

Pre-existing diabetes, hypertension and kidney disorders are prominent risk factors of pre-eclampsia (PE). It is a multifactorial pregnancy disorder associated with high blood pressure, proteinuria, and multiorgan failure, which develops after the 20th week of pregnancy. It is one of the most feared pregnancy disorders, as it consumes thousands of fetomaternal lives per annum. According to clinical and pathological studies, the placenta appears to be a key player in the pathogenesis of PE; however, the exact origin of this disorder is still under debate. Defective placentation and angiogenesis are the hallmarks of PE progression. This angiogenic imbalance, together with maternal susceptibility, might determine the severity and clinical presentation of PE. This article comprehensively examines the mechanisms of pathogenesis of PE and current evidence of the factors involved in its progression. Finally, this article will explore the genetic association of PE, various candidate genes, their proposed mechanisms and variants involved in its pathogenesis.

Genetic association between HLA-G 14-bp polymorphism and diseases: A systematic review and meta-analysis

BACKGROUND

HLA-G is an immune checkpoint molecule. Since a differential molecule expression has been reported even for healthy individuals, many studies have focused on polymorphisms at HLA-G regulatory regions, particularly the 3' untranslated region (3'UTR). The presence/absence of a 14-bp sequence was the first polymorphism described and it is the most studied in association between HLA-G and disorders.

METHODS

In this study, we performed a systematic review and meta-analysis of all association studies published regarding the HLA-G 14-bp.

RESULTS

We verified association between 14-bp alleles and diseases in the following situations: (1) presence of 14-bp (insertion) conferred susceptibility to preeclampsia (child alleles evaluated) and systemic lupus erythematosus (OR = 1.42; 95%CI = 1.04-1.93; p = 0.026 and OR = 1.13; 95%CI = 1.01-1.27, p = 0.028); (2) 14-bp absence (deletion) was associated with increased risk to breast cancer (OR = 1.23; 95%CI = 1.06-1.43; p = 0.006) and human Cytomegalovirus infection (OR = 2.06; 95%CI = 1.60-2.64; p < 0.0001); and (3) a risk association was observed between the group of reproductive disorders and the 14-bp insertion (OR = 1.12; 95%CI = 1.01-1.24; p = 0.034).

CONCLUSIONS

Considering that others 14-bp associations were inconclusive and that other variation sites observed at HLA-G 3'UTR exhibit a proven role on post-transcriptional regulation of HLA-G expression, the complete 3'UTR segment should be analyzed in terms of disease susceptibility, instead of a single polymorphism.

Association between HLA-G 14bp Gene Polymorphism and Serum sHLA-G Protein Concentrations in Preeclamptic Patients and Normal Pregnant Women

BACKGROUND

Preeclampsia (PE) is a multisystem syndrome that is a primary source of fetal-maternal morbidity and mortality. Human leukocyte antigen-G (HLA-G) is a nonclassical Major histocompatibility complex (MHC) class-Ib molecule expressed on the extravillous trophoblast and seems to have immunomodulatory functions during pregnancy. The purpose of our study was to investigate whether HLA-G may be a vital marker in the modulation of the pregnancy.

METHODS

In this case-control study, a number of 150 healthy pregnant women and 150 patients with PE had been genotyped for the 14 base-pair (bp) insertion/deletion polymorphism in exon 8 of the HLA-G gene, and the serum level of soluble HLA-G (sHLA-G) protein was measured using the enzyme-linked immunosorbent assay.

RESULTS

Data showed that the PE syndrome was not related to the HLA-G 14 bp genotype. But, the serum level of sHLA-G in PE patients was significantly lower than that in healthy pregnant women in the third trimester (11.74 and 24.48 U/ml, respectively, p < 0.001). However, no significant association was observed between the HLA-G 14 bp genotype and serum sHLA-G level.

CONCLUSION

Our results demonstrate that measurement of sHLA-G protein level may be helpful as a primary diagnosis for the pathogenesis of PE. Overall, this study suggests that the association between HLA-G 14 bp polymorphism and serum sHLA-G level in different ethnic populations of PE should be taken into consideration.

HLA Class Ib Molecules and Immune Cells in Pregnancy and Preeclampsia

Despite decades of research, the highly prevalent pregnancy complication preeclampsia, “the disease of theories,” has remained an enigma. Indeed, the etiology of preeclampsia is largely unknown. A compiling amount of studies indicates that the pathological basis involves a complex array of genetic predisposition and immunological maladaptation, and that a contribution from the mother, the father, and the fetus is likely to be important. The Human Leukocyte Antigen (HLA)-G is an increasing focus of research in relation to preeclampsia. The HLA-G molecule is primarily expressed by the extravillous trophoblast cells lining the placenta together with the two other HLA class Ib molecules, HLA-E and HLA-F. Soluble isoforms of HLA-G have been detected in the early endometrium, the matured cumulus–oocyte complex, maternal blood of pregnant women, in umbilical cord blood, and lately, in seminal plasma. HLA-G is believed to be involved in modulating immune responses in the context of vascular remodeling during pregnancy as well as in dampening potential harmful immune attacks raised against the semi-allogeneic fetus. In addition, HLA-G genetic variants are associated with both membrane-bound and soluble forms of HLA-G, and, in some studies, with preeclampsia. In this review, a genetic contribution from the mother, the father, and the fetus, together with the presence and function of various immune cells of relevance in pregnancy are reviewed in relation to HLA-G and preeclampsia.

Insights into HLA-G Genetics Provided by Worldwide Haplotype Diversity

Human leukocyte antigen G (HLA-G) belongs to the family of non-classical HLA class I genes, located within the major histocompatibility complex (MHC). HLA-G has been the target of most recent research regarding the function of class I non-classical genes. The main features that distinguish HLA-G from classical class I genes are (a) limited protein variability, (b) alternative splicing generating several membrane bound and soluble isoforms, (c) short cytoplasmic tail, (d) modulation of immune response (immune tolerance), and (e) restricted expression to certain tissues. In the present work, we describe the HLA-G gene structure and address the HLA-G variability and haplotype diversity among several populations around the world, considering each of its major segments [promoter, coding, and 3′ untranslated region (UTR)]. For this purpose, we developed a pipeline to reevaluate the 1000Genomes data and recover miscalled or missing genotypes and haplotypes. It became clear that the overall structure of the HLA-G molecule has been maintained during the evolutionary process and that most of the variation sites found in the HLA-G coding region are either coding synonymous or intronic mutations. In addition, only a few frequent and divergent extended haplotypes are found when the promoter, coding, and 3′UTRs are evaluated together. The divergence is particularly evident for the regulatory regions. The population comparisons confirmed that most of the HLA-G variability has originated before human dispersion from Africa and that the allele and haplotype frequencies have probably been shaped by strong selective pressures.

HLA-G expression on blasts and tolerogenic cells in patients affected by acute myeloid leukemia

Human Leukocyte Antigen-G (HLA-G) contributes to cancer cell immune escape from host antitumor responses. The clinical relevance of HLA-G in several malignancies has been reported. However, the role of HLA-G expression and functions in Acute Myeloid Leukemia (AML) is still controversial. Our group identified a subset of tolerogenic dendritic cells, DC-10 that express HLA-G and secrete IL-10. DC-10 are present in the peripheral blood and are essential in promoting and maintaining tolerance via the induction of adaptive T regulatory (Treg) cells. We investigated HLA-G expression on blasts and the presence of HLA-G-expressing DC-10 and CD4⁺ T cells in the peripheral blood of AML patients at diagnosis. Moreover, we explored the possible influence of the 3′ untranslated region (3′UTR) of HLA-G, which has been associated with HLA-G expression, on AML susceptibility. Results showed that HLA-G-expressing DC-10 and CD4⁺ T cells are highly represented in AML patients with HLA-G positive blasts. None of the HLA-G variation sites evaluated was associated with AML susceptibility. This is the first report describing HLA-G-expressing DC-10 and CD4⁺ T cells in AML patients, suggesting that they may represent a strategy by which leukemic cells escape the host's immune system. Further studies on larger populations are required to verify our findings.

The maternal HLA-G 1597ΔC null mutation is associated with increased risk of pre-eclampsia and reduced HLA-G expression during pregnancy in African-American women

The non-classical major histocompatibility complex molecule, human leukocyte antigen (HLA)-G, is thought to contribute to maternal immune tolerance and successful placentation during pregnancy. Genetic polymorphisms in HLA-G are known to influence expression levels as well as the relative expression of individual protein isoforms. As diminished or aberrant HLA-G expression patterns may contribute to the development of certain pregnancy complications, we sought to investigate the association between functional HLA-G polymorphisms and the risk of pre-eclampsia (PE) in African-American women. The association between maternal and fetal genotype at six HLA-G polymorphisms and risk of PE was assessed in 372 pregnancies (314 normotensive; 58 pre-eclamptic). We observed an elevated risk of PE (P = 0.00027) in pregnancies where the mother carried the 1597ΔC allele, a null allele that abolishes expression of full-length HLA-G isoforms. Furthermore, the frequency of the maternal 1597ΔC allele was highest in the subset of pre-eclamptic pregnancies that were delivered preterm, suggesting an association between the null allele and the severity of PE. We then replicated the association between higher maternal 1597ΔC allele frequency and increased severity of PE (P = 0.038) in an independent sample of 533 African-American women. Finally, to investigate the mechanistic basis of this association, we measured circulating soluble HLA-G (sHLA-G) concentrations in maternal serum collected during pregnancy in 51 healthy, normotensive African-American control women and found significantly lower levels in women carrying the 1597ΔC allele (P = 0.012). These results demonstrate that maternal HLA-G genotype is significantly associated with risk of PE in African-American women and is predictive of circulating sHLA-G levels during pregnancy.

HLA-G polymorphisms and soluble HLA-G protein levels in women with recurrent pregnancy loss from Basrah province in Iraq

HLA-G is a nonclassical, class I major histocompatibility complex (MHC) gene that exhibits immunomodulatory properties and likely plays a role in the maintenance of successful pregnancy. In this study, we investigated the role of HLA-G polymorphisms on risk for recurrent pregnancy loss (RPL) and on circulating levels of soluble (s)HLA-G in Iraqi women. DNA and plasma were obtained from blood samples collected at 9-12 weeks gestation from 50 women with RPL and 50 healthy pregnant women in Basrah province, Iraq. As measured by ELISA, median sHLA-G levels were significantly lower in the RPL cases compared to healthy controls (21.4 vs. 38.8 U/ml, respectively; P=0.025), and decreased with increasing maternal age (P=0.0051). However, HLA-G allele and haplotype frequencies did not differ significantly between cases and controls (P values ≥0.12 for all tests). In contrast, homozygosity for the C allele (CC) at a tri-allelic promoter polymorphism, -725C/G/T, was associated with lower concentrations of sHLA-G compared to the CG or CT genotypes (median levels 21.1 vs. 40.1 vs. 42.6 U/ml, respectively; P=0.0089). These results demonstrate that HLA-G genotype influences circulating sHLA-G levels during pregnancy but is not significantly associated with risk of RPL.

The importance of HLA-G expression in embryos, trophoblast cells, and embryonic stem cells

The nonclassical HLA-G molecule is a trophoblast-specific molecule present in almost every pregnancy. It differs from classical HLA class I molecules by the low degree of allelic variants and the high diversity of protein structures. HLA-G is reported to be a tolerogenic molecule that acts on cells of both innate and adaptive immunity. At the maternal-fetal interface HLA-G seems to be responsible largely for the reprogramming of local maternal immune response. This review will focus on the HLA-G gene expression profile in pregnancy, in preimplantation embryos, and in human embryonic stem cells with emphasis on the structural diversity of the HLA-G protein and its potential functional and diagnostic implications.

Human leukocyte antigen-G polymorphism in relation to expression, function, and disease

Human leukocyte antigen-G (HLA-G) is a nonclassical class Ib molecule belonging to the major histocompatibility complex. HLA-G appears to play a role in the suppression of immune responses and contribute to long-term immune escape or tolerance. The focus of this review is polymorphism in the HLA-G gene and protein and its possible importance in expression, function, and disease associations.

HLA-G gene polymorphism in human placentas: possible association of G*0106 allele with preeclampsia and miscarriage

Definite causes for several pathologies of pregnancy remain unknown. In light of several recent studies, however, diminished or aberrant HLA-G expression may be associated with certain complication of pregnancy and be linked to HLA-G polymorphism. We analyzed DNA from 60 normal placentas (controls), 140 placentas from miscarriage, 36 placentas from preeclampsia, 76 placentas from fetal hypotrophy, and 34 placentas with hypoxia for variations in coding regions (allelic groups G*0101 to G*0107) and the 14-bp deletion/insertion into the 3'-untranslated region. No statistically significant differences were observed in the distribution of allelic group between pathological placentas and controls with the exception of G*0106 allele frequency in preeclamptic compared with control placentas (21.2% and 6.6%, respectively). A greater frequency of this allele also was observed in the two subgroups of miscarriage and hypoxia compared with that in controls. In addition, presence of the 14-bp sequence was prominent in preeclampsia compared with controls (60.8% vs. 35%, respectively), and homozygotes with deletion were not detected in the pathology. The results suggest that the G*0106 allele, which is coupled with the presence of the 14-bp sequence, contributes and/or is a relevant marker in some specific complications of pregnancy, especially preeclampsia.

Paternal contribution of HLA-G*0106 significantly increases risk for pre-eclampsia in multigravid pregnancies

Pre-eclampsia (PE) is a leading cause of maternal and fetal mortality and morbidity. Structural or functional alterations of human leukocyte antigen (HLA)-G present at the maternal-fetal interface may predispose women to PE. We tested the HLA-G gene for association with PE in a case-control study of 83 PE and 240 normotensive Malay women. HLA-G was amplified in a single-tube multiplex-PCR reaction and genotyped for 18 single nucleotide polymorphisms (SNPs) by multiplex-minisequencing. Case-control comparisons were performed, and associations with disease were expressed as odds ratios (ORs). Risk for PE was significantly associated with fetal allele G*0106 only in multigravid pregnancies (P = 0.002, OR = 5.0, 95% CI = 1.8-13.8). Among multigravid pregnancies, the frequency of PE babies heterozygous or homozygous for G*0106 was also significantly higher compared with normal control babies (P = 0.002, OR = 5.4, 95% CI = 1.9-15.4). Multivariate analyses with adjustment for factors associated with PE revealed similar results (P = 0.003, OR = 10.1, 95% CI = 2.2-46.8). Additionally, a significantly higher frequency of fetal-maternal G*0106 genotype mismatch was observed in PE compared with normal multigravid pregnancies (P = 0.001, OR = 9.6, 95% CI = 2.4-38.7). Thus, paternal HLA-G G*0106 contribution significantly increases risk for PE in multigravidas who do not carry this allele, potentially mediated by a gradual maternal alloimmune response to repeated exposure to the paternal HLA-G variant.

Absence of the HLA-G*0105N allele in Amerindian populations from the Brazilian Amazon Region: a possible role of natural selection

The human leukocyte antigen G (HLA-G) null allele (G*0105N) is defined by a DeltaC deletion at exon 3. Its high frequency in populations from areas with high pathogen loads and the putative role of HLA-G in placental development suggest that the reduced G1 expression in G*0105N heterozygous placentas may improve the intrauterine defense against infections. The G*0105N allele frequencies were evaluated in 143 Amerindians from six isolated tribes that inhabit the Central Amazon to determine the existence of genotype frequencies that suggest balancing selection in favor of G*0105N heterozygotes. No copy of the null allele was found by exon 3 sequencing. Although this finding may be because of demographic or other selective factors, it also suggests no evidence of G*0105N heterozygous advantage.

14 bp deletion polymorphism in the HLA-G gene is a risk factor for idiopathic dilated cardiomyopathy in a Chinese Han population

Human leukocyte antigen (HLA) has been reported to be associated with the pathogenesis of autoimmune-associated idiopathic dilated cardiomyopathy (IDC). However, the HLA-G in this context is limited. In the current study, a total of 117 IDC patients and age and sex matched 401 unrelated healthy controls in a Chinese Han population were HLA-G genotyped for the 14 bp insertion and deletion polymorphism. IDC patients showed markedly increased frequencies of -14 bp/-14 bp genotype [Pc = 0.00049, odds ratio (OR) = 2.17] and -14 bp alleles (Pc = 4.1 x 10(-5), OR = 1.97) when compared with healthy controls. Whereas the frequencies of +14 bp/+14 bp genotype (Pc = 0.0036, OR = 0.35) and +14 bp alleles (Pc = 4.1 x 10(-5), OR = 0.51) were significantly lower in IDC. These data, for the first time, indicated that 14 bp insertion/deletion polymorphism in HLA-G gene could be a genetic risk factor for the susceptibility to IDC.