Genetics and Epigenetics of Recurrent Hydatidiform Moles: Basic Science and Genetic Counselling

Expression patterns of maspin and mutant p53 are associated with the development of gestational trophoblastic neoplasia

Gestational trophoblastic disease (GTD) is a group of conditions that originate from the abnormal proliferation of trophoblastic cells. GTDs encompass hydatidiform moles (HMs) and gestational trophoblastic neoplasia (GTN). GTNs are a group of malignant diseases that require chemotherapy, or more aggressive treatment. There is a requirement for more tumor markers to predict the development of GTN from HMs. The current study evaluated the expression of maspin and tumor protein p53 (p53) in GTD, and their role in predicting the development of GTN. Expression of maspin and mutant p53 (m-p53) was detected by immunohistochemistry in 48 normal first trimester placentas, matched for gestational age to 49 HMs that regressed, 39 malignant HMs and 11 invasive moles or choriocarcinomas. Spearman's rank correlation analysis and logistic regression were performed on the expression patterns of maspin and m-p53, and on the clinical prognostic factors in GTD. Compared with normal placenta levels, the expression levels of maspin were decreased, whereas the expression levels of m-p53 were increased in GTDs (P<0.05). The expression levels of maspin and m-p53 in complete and partial HMs were not significantly different (P>0.05). In HMs, maspin expression was inversely correlated with serum β human chorionic gonadotropin, uterine size and diameter of theca-lutein cysts; however, m-p53 expression demonstrated a positive correlation with these factors (all P<0.05). Compared with the high-risk metastatic group (FIGO score ≥7), the low-risk group (FIGO score <7) exhibited a higher rate of positive maspin expression (P=0.041), and the frequency of positive m-p53 expression was significantly higher in patients with an advanced FIGO stages (FIGO stage ≥III) compared with patients in early stages (FIGO stage ≤II; 87.9 vs. 58.8%; P=0.019). The combination of maspin negative expression with m-p53 positive expression had an 84% specificity value, 76% positive predictive value and 70% negative predictive value for the development of GTN. In conclusion, maspin-negative and m-p53-positive expression is associated with the development of GTN in HMs.

Recent Advances in Imprinting Disorders

Imprinting disorders (ImpDis) are a group of currently 12 congenital diseases with common underlying (epi)genetic etiologies and overlapping clinical features affecting growth, development and metabolism. In the last years it has emerged that ImpDis are characterized by the same types of mutations and epimutations, i.e. uniparental disomies, copy number variations, epimutations, and point mutations. Each ImpDis is associated with a specific imprinted locus, but the same imprinted region can be involved in different ImpDis. Additionally, even the same aberrant methylation patterns are observed in different phenotypes. As some ImpDis share clinical features, clinical diagnosis is difficult in some cases. The advances in molecular and clinical diagnosis of ImpDis help to circumvent these issues, and they are accompanied by an increasing understanding of the pathomechanism behind them. As these mechanisms have important roles for the etiology of other common conditions, the results in ImpDis research have a wider effect beyond the borders of ImpDis. For patients and their families, the growing knowledge contributes to a more directed genetic counseling of the families and personalized therapeutic approaches.

Novel Nonsense Mutation in the NLRP7 Gene Associated with Recurrent Hydatidiform Mole

AIM

This study aimed to clarify the genetic and epigenetic features of recurrent hydatidiform mole (RHM) in Japanese patients.

METHODS

Four Japanese isolated RHM cases were analyzed using whole-exome sequencing. Villi from RHMs were collected by laser microdissection for genotyping and DNA methylation assay of differentially methylated regions (DMRs). Single nucleotide polymorphisms of PEG3 and H19 DMRs were used to confirm the parental origin of the variants.

RESULTS

A novel homozygous nonsense mutation in NLRP7 (c.584G>A; p.W195X) was identified in 1 patient. Genotyping of one of her molar tissue revealed that it was biparental but not androgenetic in origin. Despite the fact that the RHM is biparental, maternally methylated DMRs of PEG3, SNRPN and PEG10 showed complete loss of DNA methylation. A paternally methylated DMR of H19 retained normal methylation.

CONCLUSIONS

This is the first Japanese case of RHM with a novel homozygous nonsense NLRP7 mutation and a specific loss of maternal DNA methylation of DMRs. Notably, the mutation was identified in an isolated case of an ethnic background that has not previously been studied in this context. Our data underscore the involvement of NLRP7 in RHM pathophysiology and confirm that DNA methylation of specific regions is critical.

Absence of Maternal Methylation in Biparental Hydatidiform Moles from Women with NLRP7 Maternal-Effect Mutations Reveals Widespread Placenta-Specific Imprinting

Familial recurrent hydatidiform mole (RHM) is a maternal-effect autosomal recessive disorder usually associated with mutations of the NLRP7 gene. It is characterized by HM with excessive trophoblastic proliferation, which mimics the appearance of androgenetic molar conceptuses despite their diploid biparental constitution. It has been proposed that the phenotypes of both types of mole are associated with aberrant genomic imprinting. However no systematic analyses for imprinting defects have been reported. Here, we present the genome-wide methylation profiles of both spontaneous androgenetic and biparental NLRP7 defective molar tissues. We observe total paternalization of all ubiquitous and placenta-specific differentially methylated regions (DMRs) in four androgenetic moles; namely gain of methylation at paternally methylated loci and absence of methylation at maternally methylated regions. The methylation defects observed in five RHM biopsies from NLRP7 defective patients are restricted to lack-of-methylation at maternal DMRs. Surprisingly RHMs from two sisters with the same missense mutations, as well as consecutive RHMs from one affected female show subtle allelic methylation differences, suggesting inter-RHM variation. These epigenotypes are consistent with NLRP7 being a maternal-effect gene and involved in imprint acquisition in the oocyte. In addition, bioinformatic screening of the resulting methylation datasets identified over sixty loci with methylation profiles consistent with imprinting in the placenta, of which we confirm 22 as novel maternally methylated loci. These observations strongly suggest that the molar phenotypes are due to defective placenta-specific imprinting and over-expression of paternally expressed transcripts, highlighting that maternal-effect mutations of NLRP7 are associated with the most severe form of multi-locus imprinting defects in humans.

ATP binding by NLRP7 is required for inflammasome activation in response to bacterial lipopeptides

Nucleotide-binding oligimerization domain (NOD)-like receptors (NLRs) are pattern recognition receptors (PRRs) involved in innate immune responses. NLRs encode a central nucleotide-binding domain (NBD) consisting of the NAIP, CIITA, HET-E and TP1 (NACHT) domain and the NACHT associated domain (NAD), which facilitates receptor oligomerization and downstream inflammasome signaling. The NBD contains highly conserved regions, known as Walker motifs, that are required for nucleotide binding and hydrolysis. The NLR containing a PYRIN domain (PYD) 7 (NLRP7) has been recently shown to assemble an ASC and caspase-1-containing high molecular weight inflammasome complex in response to microbial acylated lipopeptides and Staphylococcus aureus infection. However, the molecular mechanism responsible for NLRP7 inflammasome activation is still elusive. Here we demonstrate that the NBD of NLRP7 is an ATP binding domain and has ATPase activity. We further show that an intact nucleotide-binding Walker A motif is required for NBD-mediated nucleotide binding and hydrolysis, oligomerization, and NLRP7 inflammasome formation and activity. Accordingly, THP-1 cells expressing a mutated Walker A motif display defective NLRP7 inflammasome activation, interleukin (IL)-1β release and pyroptosis in response to acylated lipopeptides and S. aureus infection. Taken together, our results provide novel insights into the mechanism of NLRP7 inflammasome assembly.

Effect of puerarin on human choriocarcinoma cells

OBJECTIVE

To discuss the effect of puerarin on human choriocarcinoma cells.

METHODS

Survival rates under puerarin monotherapy, fluorouracil (5-FU) monotherapy and puerarin in combination with 5-FU were detected by MTT assay. Apoptotic morphology was observed with Hoechst 33258 staining. Apoptosis rates were detected with flow cytometry. Expressions of AKT, mechanistic target of rapamycin (mTOR), and P70S6K mRNAs and phosphorylated proteins were detected by RT-PCR and Western blot. Tumor-bearing mice were administered puerarin and puerarin+5-FU, and serum levels of β-human chorionic gonadotropin (β-HCG) were measured.

RESULTS

Proliferation inhibition and apoptosis rates of JEG-3 cells were positively correlated with puerarin concentration, which increased in the puerarin+5-FU group. Expression levels of AKT, mTOR, P70S6K mRNAs, and phosphorylated proteins decreased significantly after action of puerarin at different concentrations. With increasing puerarin concentration, expression of cleaved-caspase-3 in JEG-3 cells increased, whereas that of Bcl-2 decreased. Puerarin significantly inhibited tumor growth in choriocarcinoma-bearing SCID mice. Serum β-HCG levels were significantly lower than those of control group after administration. Magnitude of β-HCG decline was positively correlated with concentration..

CONCLUSION

Puerarin+5-FU inhibited proliferation of JEG-3 choriocarcinoma cells and promoted their apoptosis, being associated with the mTOR signaling pathway.

Molecular genetic studies of complete hydatidiform moles

Complete hydatidiform moles (CHM) are abnormal pregnancies with no fetal development resulting from having two paternal genomes with no maternal contribution. It is important to distinguish CHM from partial hydatidiform moles, and non-molar abortuses, due to the increased risk of gestational trophoblastic neoplasia. We evaluated a series of products of conception (POC) (n=643) investigated by genome-wide microarray comparative genomic hybridisation (CGH) with the aim of refining our strategy for the identification of complete moles. Among 32 suspected molar pregnancies investigated by STR genotyping to supplement microarray CGH testing, we found 31.3% (10/32) CHM; all identified among 3.6% (10/272) early first trimester POC. We suggest that when using microarray CGH that genotyping using targeted STR analysis should be performed for all POC referrals to aid in the identification of CHM.

Identification of a human subcortical maternal complex

Maternal effect genes play essential roles in early embryonic development. However, the mechanisms by which maternal effect genes regulate mammalian early embryonic development remain largely unknown. Recently, we identified a subcortical maternal complex (SCMC) that is composed of at least four proteins encoded by Mater, Floped, Tle6 and Filia and is critical for mouse preimplantation development. The present study demonstrates that human SCMC homologous genes (NLRP5, OOEP, TLE6 and KHDC3L) are specifically expressed in the oocytes of human fetal ovaries. The proteins of this complex co-localize in the subcortex of human oocytes and early embryos. Furthermore, the SCMC proteins physically interact with each other when they are co-expressed in cell lines. These results indicate that human NLRP5, OOEP, TLE6 and KHDC3L function as a complex in the oocytes and early embryos of Homo sapiens. Considering the important roles of the SCMC in mouse early embryogenesis, the characterization of the human SCMC will provide a basis for investigating human early embryonic development and will have clinical implications in human female infertility or recurrent spontaneous abortion.

NLRP7 and KHDC3L, the two maternal-effect proteins responsible for recurrent hydatidiform moles, co-localize to the oocyte cytoskeleton

STUDY QUESTION

What is the subcellular localization in human oocytes and preimplantation embryos, of the two maternal-effect proteins, NLRP7 and KHDC3L, responsible for recurrent hydatidiform moles (RHMs)?

SUMMARY ANSWER

NLRP7 and KHDC3L localize to the oocyte cytoskeleton and are polar and absent from the cell-to-cell contact region in early preimplantation embryos.

WHAT IS KNOWN ALREADY

NLRP7 and KHDC3L expression has been described at the RNA level in some stages of human oocytes and preimplantation embryos and at the protein level by immunohistochemistry in human and bovine ovaries. NLRP7 and KHDC3L co-localize to the microtubule organizing center and/or the Golgi apparatus in human hematopoietic cells.

STUDY DESIGN, SIZE, DURATION

A total of 164 spare human oocytes and embryos from patients undergoing in vitro fertilization were used.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Oocytes and early cleavage-stage embryos were fixed, immunostained with NLRP7 and/or KHDC3L antibodies, and analyzed using high-resolution confocal immunofluorescence and electron microscopies.

MAIN RESULTS AND THE ROLE OF CHANCE

NLRP7 and KHDC3L localize to the cytoskeleton and are predominant at the cortical region in growing oocytes. After the first cellular division, these two maternal-effect proteins become asymmetrically confined to the outer cortical region and excluded from the cell-to-cell contact region until the blastocyst stage where NLRP7 and KHDC3L homogeneously redistribute to the cytoplasm and the nucleus, respectively.

LIMITATIONS, REASONS FOR CAUTION

We could not analyze fresh human oocytes and embryos. The analyzed materials were donated by patients undergoing assisted reproductive technologies and released for research 1-3 days after their collection and the transfer of embryos to the patients.

WIDER IMPLICATIONS OF THE FINDINGS

Our study is the first comprehensive and high-resolution localization of the only two known maternal-effect proteins, NLRP7 and KHDC3L, in human oocytes and preimplantation embryos. Our data contribute to a better understanding of the roles of these two proteins in the integrity of the oocytes, post-zygotic divisions, and cell-lineage differentiation.

STUDY FUNDING/COMPETING INTERESTS

This work was supported by the Canadian Institute of Health Research (86546 to R.S.); E.A. was supported by fellowships from the Research Institute of the McGill University Health Centre and a CREATE award from the Réseau Québécois en Reproduction. All authors declare no conflict of interest.

NOD-like receptors interfacing the immune and reproductive systems

Nucleotide-binding oligomerization domain receptors (NOD-like receptors, NLRs) are intracellular proteins that are chiefly known for their critical functions in inflammatory responses and host defense against microbial pathogens. Several NLRs have been demonstrated to assemble inflammasomes or to engage transcriptional signaling cascades that result in the production of pro-inflammatory cytokines and bactericidal factors. In recent years, NLRs have also emerged as key regulators of early mammalian embryogenesis and reproduction. A subset of phylogenetically related NLRs represents a new class of maternal effect genes that are highly expressed in maturing oocytes and pre-implantation embryos. Mutations in several of these NLRs have been linked to hereditary reproductive defects and imprinting diseases. In this review, we discuss the expression profiles, the emerging functions and molecular mode of action of these NLRs with newly recognized roles at the interfaces of the immune and reproductive systems. In addition, we provide an overview of coding mutations in NLRs that have been associated with human reproductive diseases, and outline crucial outstanding questions in this emerging research field.

NLRP7 inter-domain interactions: the NACHT-associated domain is the physical mediator for oligomeric assembly

Mutations in NLRP7 (NOD-like-receptor family, pyrin domain containing 7) are responsible for a type of recurrent pregnancy loss known as recurrent hydatidiform mole (HYDM1). This condition is characterized by abnormal growth of the placenta, a lack of proper embryonic development and abnormal methylation patterns at multiple imprinted loci in diploid biparental molar tissues. The role of NLRP7 protein in the disease manifestation is currently not clear. In order to better understand how the effects of HYDM1 are associated with mutations on the structure of NLRP7, we performed an inter-domain interaction screen using a yeast two-hybrid system. Additionally, we generated in silico structural models of NLRP7 in its non-activated and activated forms. Our observations from the yeast two-hybrid screen and modeling suggest that the NACHT-associated domain (NAD) of the NLRP7 protein is central to its oligomeric assembly. Upon activation, the NAD and a small part of the leucine rich repeat (LRR) of one molecule emerged out of the protective LRR domain and interact with the NACHT domain of the second molecule to form an oligomer. Furthermore, we investigated the molecular basis for the pathophysiological effect of four missense mutations, three HYDM1-causing and one rare non-synonymous variant, on the protein using confocal microscopy of transiently transfected NLRP7 in HEK293T cells and in silico structural analysis. We found that with the two clinically severe missense mutations, L398R and R693W, the normal molecule to molecule interaction was apparently affected thus decreasing their oligomerization potential while aggresome formation was increased; these changes could disturb the normal downstream functions of NLRP7 and therefore be a possible molecular effect underlying their pathophysiological impact.