Toll-Like Receptor 4 Gene Polymorphisms and Preeclampsia: Lack of Association in a Caucasian Population

A review of key cytokines based on gene polymorphism in the pathogenesis of pre-eclampsia

Although a number of theories have been suggested, including roles for oxidative stress, an abnormal maternal-fetal interface, and genetic and environmental factors, the etiopathology of pre-eclampsia (PE) remains unclear. Maternal immune tolerance is important for maintaining pregnancy, and researchers have increasingly focused on the critical roles of cytokines in the pathogenesis of PE in recent years. The assessment of candidate genetic polymorphisms in PE could partially elucidate the mechanisms of susceptibility to disease, and contribute to seeking for new diagnosis and treatment methods of PE. PE can lead to severe complications, and even the death of both mother and fetus. Although the complex pathology is not yet clear, some evidence suggested that the occurrence of PE is related to inflammatory factors. We reviewed the current understandings of roles of cytokines in PE, and provided an extensive overview of the role of single nucleotide chain polymorphisms (SNPs) in the genes potentially underlying the pathophysiology of PE.

Association Between TLR4 Gene Polymorphisms and Risk of Preeclampsia: Systematic Review and Meta-Analysis

BACKGROUND Toll-like receptor 4 (TLR4) plays a pivotal role in the innate immune response and is hyperactivated in preeclampsia (PE). Several researchers have published conflicting evidence for TLR4 rs4986790 and rs4986791 single nucleotide polymorphisms (SNPs) as risk factors for PE. The present meta-analysis was conducted to obtain a more definitive conclusion about the effects of these SNPs on PE susceptibility. MATERIAL AND METHODS To determine the correlation between rs4986790 and rs4986791 polymorphisms in the TLR4 gene and susceptibility to PE, the PubMed, Web of Science, EMBASE, Chinese National Knowledge Infrastructure, and Chinese WANFANG databases were searched for eligible articles. Statistical analysis was performed with STATA software, version 12.0. Pooled odds ratios with corresponding 95% confidence intervals (CIs) were extracted for assessment of correlation strength. RESULTS We identified 5 studies including 578 cases and 631 controls for the rs4986790 SNP and 4 studies including 469 cases and 457 controls for the rs4986791 SNP, mainly from a White population. The pooled analyses showed no statistical relationship between the polymorphisms rs4986790 and rs4986791 and PE susceptibility in 5 genetic models (all P>0.05). Moreover, the allelic and dominant gene models of rs4986790 and the allelic, heterozygous, and dominant gene models of rs4986791 had high heterogeneity. The sensitivity analysis explored potential sources of heterogeneity and confirmed the findings of this meta-analysis. CONCLUSIONS TLR4 rs4986790 and rs4986791 polymorphisms may not be implicated in PE susceptibility, primarily in a White population. More high-quality studies of genetic associations with PE are warranted.

Insight Into TLR4-Mediated Immunomodulation in Normal Pregnancy and Related Disorders

Unlike organ transplants where an immunosuppressive environment is required, a successful pregnancy involves an extremely robust, dynamic, and responsive maternal immune system to maintain the development of the fetus. A specific set of hormones and cytokines are associated with a particular stage of pregnancy. Any disturbance that alters this fine balance could compromise the development and function of the placenta. Although there are numerous underlying causes of pregnancy-related complications, untimely activation of Toll-like receptors (TLR), primarily TLR4, by intrauterine microbes poses the greatest risk. TLR4 is an important Pattern Recognition Receptor (PRR), which activates both innate and adaptive immune cells. TLR4 activation by LPS or DAMPs leads to the production of pro-inflammatory cytokines via the MyD88 dependent or independent pathway. Immune cells modulate the materno–fetal interface by TLR4-mediated cytokine production, which changes at different stages of pregnancy. In most pregnancy disorders, such as PTB, PE, or placental malaria, the TLR4 expression is upregulated in immune cells or in maternal derived cells, leading to the aberrant production of pro-inflammatory cytokines at the materno–fetal interface. Lack of functional TLR4 in mice has reduced the pro-inflammatory responses, leading to an improved pregnancy, which further strengthens the fact that abnormal TLR4 activation creates a hostile environment for the developing fetus. A recent study proposed that endothelial and perivascular stromal cells should interact with each other in order to maintain a homeostatic balance during TLR4-mediated inflammation. It has been reported that depleting immune cells or supplying anti-inflammatory cytokines can prevent PTB, PE, or fetal death. Blocking TLR4 signaling or its downstream molecule by inhibitors or antagonists has proven to improve pregnancy-related complications to some extent in clinical and animal models. To date, there has been a lack of knowledge regarding whether TLR4 accessories such as CD14 and MD-2 are important in pregnancy and whether these accessory molecules could be promising drug targets for combinatorial treatment of various pregnancy disorders. This review mainly focuses on the activation of TLR4 during pregnancy, its immunomodulatory functions, and the upcoming advancement in this field regarding the improvement of pregnancy-related issues by various therapeutic approaches.

Association of maternal Toll-like receptor-4 alleles with susceptibility to early-onset preeclampsia in central Greece

INTRODUCTION

Altered maternal inflammatory responses may play a role in the development of hypertensive disorders of pregnancy like preeclampsia, its more severe early-onset form and intrauterine growth restriction. We evaluated the relation of common allelic variants of Toll-like receptor 4 (TLR4), known to impair the inflammatory response, with the susceptibility to early-onset preeclampsia in Central Greece.

METHODS

We compared the occurrence of TLR4 (Asp299Gly and Thr399Ile) alleles in heterozygous (A/G, C/T) and homozygous (G/G, T/T) states in 84 women with a history of early-onset preeclampsia and 94 age matched controls with a history of only uneventful pregnancies, by direct sequencing.

RESULTS

Heterozygous TLR4 allelic variants were more common in women with a history of early-onset preeclampsia than in controls (GA for Asp299Gly: 14.3% vs 6.4% (AA), p = 0.053 & CT for Thr399Ile: 16.7% vs. 6.4% (CC), p = 0.019) and a stronger association was obtained when homozygous allelic carriers were also included (GA/GG for Asp299Gly: 16.7% vs. 6.4% (AA), p = 0.03 & TC/TT for Thr399Ile: 19.0% vs. 6.4% (CC), p = 0.01).

DISCUSSION

We recorded association between common TLR4 gene variants and early-onset preeclampsia. Our findings support the involvement of maternal innate immune system in severe hypertensive disorders of pregnancy and point to the potential value of maternal TLR4 polymorphisms as predictors-risk factors of susceptibility to early-onset preeclampsia in Central Greece.

Toll-like receptors signaling network in pre-eclampsia: An updated review

Toll-like receptors (TLRs) are innate immune cells receptors. They are expressed on leukocytes, epithelial cells, and more particularly on placental immune cells and chorion trophoblast. Upregulation of innate immune response occurs during normal pregnancy, but its excessive activity is involved in the pathology of pregnancy complications including pregnancy-induced hypertension and pre-eclampsia (PE). The recent studies about the overmuch inflammatory responses and aberrant placentation are associated with increased expression of TLRs in PE patients. This review has tried to focus on the relationship between some activities of TLRs and the risk of preeclampsia development.

Role of Innate Immunity in Preeclampsia: A Systematic Review

Innate immune system dysfunction has been known to be a key player in preeclampsia (PE). Activation of the maternal innate immunity may be triggered by invading microorganisms or endogenous ligands, which are detected by different pattern recognition receptors (PRRs). Although some studies have linked PRR activation to PE, it is still unclear if dysregulated PRR expression is associated with the development of this complication. Therefore, we conducted a systematic review of the literature, searching articles that evaluated associations of PRRs with PE. Twenty-six studies met the inclusion criteria: 20 of them analyzed PRR expressions and 6 studies investigated the association between PRR polymorphisms and PE. Among the PRRs, only few studies analyzed retinoic acid-inducible gene I-like helicase (RLH) and/or toll-like receptor (TLR)-1, 5, 6, 7, 8, and 9 expressions in immune cells or placentas from women with PE and controls; thus, it is inconclusive if these PRRs are involved in PE. Results from the 10 studies that analyzed TLR-2 expressions in women with PE and controls are also contradictory. The majority of the studies that investigated TLR-3 and -4 expressions indicate that these PRRs are increased in placenta or immune cells from women with PE compared to pregnant control woman. To date, polymorphisms in TLR-2, - 3, and - 4 and nucleotide-binding oligomerization domain-like receptor 2 genes do not seem to be associated with PE development. No study has evaluated the association between polymorphisms in genes codifying other TLRs or RLHs genes. In conclusion, available data in literature support a role for TLR-3 and TLR-4 in the pathogenesis of PE.

Innate immunity, decidual cells, and preeclampsia

Preeclampsia (PE) manifested by hypertension and proteinuria complicates 3% to 8% of pregnancies and is a leading cause of fetal-maternal morbidity and mortality worldwide. It may lead to intrauterine growth restriction, preterm delivery, and long-term sequelae in women and fetuses, and consequently cause socioeconomic burden to the affected families and society as a whole. Balanced immune responses are required for the maintenance of successful pregnancy. Although not a focus of most studies, decidual cells, the major resident cell type at the fetal-maternal interface, have been shown to modulate the local immune balance by interacting with other cell types, such as bone marrow derived-immune cells, endothelial cells, and invading extravillous trophoblasts. Accumulating evidence suggests that an imbalanced innate immunity, facilitated by decidual cells, plays an important role in the pathogenesis of PE. Thus, this review will discuss the role of innate immunity and the potential contribution of decidual cells in the pathogenesis of PE.

Oxidative damage, inflammation, and Toll-like receptor 4 pathway are increased in preeclamptic patients: a case-control study

Problem. There was no direct correlation between plasma and placental oxidative damage parameters and inflammation and evidence of TLR4 pathway activation in the placenta in preeclamptic (PE) patients. Method of Study. 33 PE patients and 33 normotensive pregnant women were included. The maternal section of the placenta and blood were collected to the determination of oxidative damage markers (thiobarbituric acid reactive species and protein carbonyls), inflammatory response (interleukin-6 and myeloperoxidase activity), and activation of the TLR-4-NF-kB pathway. Results. An increase of IL-6 levels in both plasma and placenta was observed, but myeloperoxidase activity was not significantly different comparing the groups. Oxidative damage parameters were increased in plasma and placenta in PE patients. A significant increase of the protein levels of TLR-4 and NF-kB was observed in the placenta. Conclusion. The TLR4-NF-kB pathway is upregulated in PE, probably generating local and systemic inflammatory response that is followed by local and systemic oxidative damage.

Genetic variants, immune function, and risk of pre-eclampsia among American Indians

PROBLEM

To determine the prevalence in an American Indian population of genetic variants with putative effects on immune function and determine if they are associated with pre-eclampsia (PE).

METHOD OF STUDY

In a study of 66 cases and 130 matched controls, six single nucleotide polymorphisms (SNP) with either previously demonstrated or postulated modulating effects on the immune system were genotyped. Allele frequencies and various genetic models were evaluated by conditional logistic regression in both univariate and multiply adjusted models.

RESULTS

Although most genetic variants lacked evidence of association with PE, the minor allele of the CRP related, rs1205 SNP in a dominant model with adjustment for age at delivery, nulliparity, and body mass index, exhibited an odds ratio of 0.259 (95% CI of 0.08-0.81, P=0.020) in relation to severe PE (48 cases). The allelic prevalence of this variant was 46.1% in this population.

CONCLUSION

Of the six SNPs related to immune function in this study, a functional variant in the 3'UTR of the CRP gene was shown to be associated with severe PE in an American Indian population.

Expression of toll-like receptor TLR-2, TLR-3, TLR-4 and TLR-9 is increased in placentas from patients with preeclampsia

BACKGROUND AND AIMS

Few studies have examined the presence of Toll-like receptors (TLRs) in term placentas from women with preeclampsia, such, have focused on TLR-4 and TLR-2 analysis. Whereas an increase in TLR-4 immunostaining has been observed in preeclampsia, it is even higher in placentas with chorioamnionitis compared with normal pregnancy. Expression of TLR-2 has not been associated with preeclampsia. The relationship of TLR-3 and TLR-9, which may recognize dsRNA or DNA, either derived either from microorganisms or from apoptotic cells and thus may be involved with this pathology, has not been studied in term placentas. We undertook this study to determine if there are changes in the expression and localization of TLR-2, TLR-4, TLR-3 and TLR-9 in preeclamptic term placentas as compared with normal placentas.

METHODS

A prospective, cross-sectional and comparative study was done in a group of ten patients with 38-40 gestation weeks, both in preeclamptic and control cases. Immunofluorescence detection of TLRs was performed in samples of placenta and analyzed by confocal microscopy.

RESULTS

It was observed that TLR-2, TLR-3, TLR-4 and TLR-9 were expressed both in normal and preeclamptic placentas, in the trophoblast, at the vascular endothelium (where TLR-2 and TLR-9 staining was pronounced), and at placental villous stroma, although increased expression was detected in preeclampsia. In addition, co-localization of TLR-2 and TLR-4 as well as of TLR-3 and TL9 was found in the trophoblast.

CONCLUSIONS

TLR-2, -3, -4 and -9 expressions are increased in preeclamptic placentas. However, more studies are required to determine the role of TLRs in pregnancy immunology and to establish its relationship with preeclampsia.

G protein-coupled receptor kinase 4 gene variants are not associated with preeclampsia in Northern Han Chinese

Genetic variations in preeclampsia (PE) may affect PE risk. The G protein-coupled receptor kinase 4 (GRK4) gene encodes a member of the Ser/Thr protein kinase family and has been linked to both genetic and acquired hypertension. The aim of this study was to investigate the association between polymorphisms (T-rs1024323-C and T-rs1801058-C) in GRK4 and PE in Northern Han Chinese. Using a case-control design, the association between the GRK4 exon-4 T-rs1024323-C and exon-13 T-rs1801058-C polymorphisms and the risk of PE in Northern Han Chinese was assessed in 105 individuals with PE and 103 age- and area-matched normotensive controls. Genotypes were determined by allelic discrimination. The odds ratio and 95% confidence interval were estimated by binary logistic regression. No association was found between the GRK4 polymorphisms (T-rs1024323-C and T-rs1801058-C) and PE, and there was also no relationship with the severity of PE. The risk of homozygous and heterozygous variant allele carriers of the analyzed single-nucleotide polymorphisms did not differ significantly from that of the homozygous wild-type allele carriers, even after adjustment for age, body mass index, (family) history of hypertension and smoking status. The GRK4 (T-rs1024323-C and T-rs1801058-C) polymorphisms were not associated with a risk of PE in the present Northern Han Chinese study group. Thus, the GRK4 polymorphisms do not seem to have an important role in PE in this population.