Impact of the Reticular Stress and Unfolded Protein Response on the inflammatory response in endometrial stromal cells

NLRP3 inflammasome pathway, the hidden balance in pregnancy: A comprehensive review

The balance of the inflammatory response is indispensable during pregnancy. Inflammasomes are the cytosolic supramolecular protein complexes activated by pattern recognition receptors. These receptors recognize the pathogen and damage/danger-associated molecular patterns. NLRP3 inflammasome complex consists mainly of NLRP3 (leucine-rich repeat-containing and pyrin domain-containing protein 3), a cytosolic sensor molecule, ASC (apoptosis-associated speck-like protein containing a CARD) protein and a cysteine protease pro-caspase-1 as an effector molecule. This complex has a role in producing inflammatory cytokines, interleukin 1 beta and interleukin 18, and inflammasome-dependent programmed cell death pathway pyroptosis. In this review, we focused on and summarised the NLRP3 inflammasome and its roles in normal and pathological pregnancies. The NLRP3 inflammasome pathway influences endometrial receptivity and embryo invasion by inducing epithelial-mesenchymal transition. Abnormal inflammasome activation in the endometrium may adversely affect endometrial receptivity. In addition, NLRP3 inflammasome pathway overactivation may mediate the abnormal inflammatory response at the maternal-fetal interface and be associated with pregnancy complications, such as recurrent implantation failure, pregnancy loss, pre-term birth and pre-eclampsia. Therefore, targeting the NLRP3 inflammasome pathway could develop a new therapeutic approach to prevent the aforementioned pregnancy pathologies.

Validation of the Sw71-spheroid model with primary trophoblast cells

PROBLEM

Human implantation is a limiting factor for the success of natural and IVF reproduction since about 60% of pregnancy losses occur in the peri-implantation period. The in vitro modeling of human implantation challenges the researchers in accurate recreation of the complex in vivo differentiation and function of human blastocyst in the peri-implantation period. In previous studies, we constructed Sw71-spheroid models, which like human blastocyst undergo compactization, attaches to the endometrial epithelium, invade, and migrate. The aim of this study was to validate the trophoblast Sw71-spheroid model with primary trophoblast cells, derived from healthy women in early pregnancy.

METHOD OF STUDY

We performed a direct comparison of Sw71-spheroid model with placenta-derived primary trophoblasts regarding their hybrid phenotype and HLA status, as well as the ability to generate spheroids able to migrate and invade. From the primary trophoblast cells, isolated by mild enzymatic treatment and Percoll gradient separation, were generated long-lived clones, which phenotype was assessed by FACS and immunocytochemistry.

RESULTS

Our results showed that cultured primary trophoblasts have the EVT phenotype (Vim+/CK7+/HLA-C+/HLA-G+), like Sw71 cells. In both 3D culture settings, we obtained stable, round-shaped, multilayered spheroids. Although constructed from the same number of cells, the primary trophoblast spheroids were smaller. The primary trophoblast spheroids migrate successfully, and in term of invasion are equally potent but less stable as compared to Sw71 spheroids.

CONCLUSIONS

The Sw71 cell line and cultured native trophoblast cells are interchangeable regarding their EVT phenotype (HLA-C+/HLA-G+/Vim+/CK7+). The blastocyst-like spheroids sourced by both types of cells differentiate in the same time frame and function similarly. We strongly advise the use of Sw71 spheroids as blastocyst surrogate for observation on trophectoderm differentiation and function during early human implantation.

miRNAs associated with endoplasmic reticulum stress and unfolded protein response during decidualization

RESEARCH QUESTION

Do microRNAs (miRNAs) play a role in regulating endoplasmic reticulum stress (ERS) and unfolded protein response (UPR) in decidualized cells and endometrium associated with reproductive failures?

DESIGN

Endometrial stromal cell line St-T1b was decidualized in vitro with 8-Br-cAMP over 5 days, or treated with the ERS inducer thapsigargin. Expression of ERS sensors, UPR markers and potential miRNA regulators was analysed by quantitative PCR. Endometrial biopsies from patients with recurrent pregnancy loss (RPL) and recurrent implantation failure (RIF) were investigated for the location of miRNA expression.

RESULTS

Decidualization of St-T1b cells resulted in increased expression of ERS sensors including ATF6α, PERK and IRE1α, and the UPR marker, CHOP. TXNIP, which serves as a link between the ERS pathway and inflammation, as well as inflammasome NLRP3 and interleukin 1β expression increased in decidualized cells. An in-silico analysis identified miR-17-5p, miR-21-5p and miR-193b-3p as miRNAs potentially involved in regulation of the ERS/UPR pathways and inflammation associated with embryo implantation. Their expression decreased significantly (P ≤ 0.0391) in non-decidualized cells in the presence of thapsigargin. Finally, expression of the selected miRNAs was localized by in-situ hybridization in stromal and glandular epithelial cells in endometrial samples from patients with RPL and RIF. Expression in stroma cells from patients with RPL was lower in comparison with stroma cells from patients with RIF.

CONCLUSIONS

Decidualization in St-T1b cells is accompanied by ERS/UPR processes, associated with an inflammatory response that is potentially influenced by miR-17-5p, miR-21-5p and miR-193b-3p. These miRNAs are expressed differentially in stromal cells from patients with RPL and RIF, indicating an alteration in regulation of the ERS/UPR pathways.

Inflammasomes in human reproductive diseases

Inflammasomes are multi-protein complexes localized within immune and non-immune cells that induce caspase activation, proinflammatory cytokine secretion, and ultimately pyroptosis-a type of cell death. Inflammasomes are involved in a variety of human diseases, especially acute or chronic inflammatory diseases. In this review, we focused on the strong correlation between the NLRP3 inflammasome and various reproductive diseases, including ovarian aging or premature ovarian insufficiency, PCOS, endometriosis, recurrent spontaneous abortion, preterm labor, pre-eclampsia, and male subfertility, as well as the multifaceted role of NLRP3 in the pathogenesis and treatment of these diseases. In addition, we provide an overview of the structure and amplification of inflammasomes. This comprehensive review demonstrates the vital role of NLRP3 inflammasome activation in human reproductive diseases together with the underlying mechanisms, offers new insights for mechanistic studies of reproduction, and provides promising possibilities for the development of drugs targeting the NLRP3 inflammasome for the treatment of reproductive disorders in the future.

Paradoxical expression of NRP1 in decidual stromal and immune cells reveals a novel inflammation balancing mechanism during early pregnancy

OBJECTIVE AND DESIGN

To investigate the balancing mechanisms between decidualization-associated inflammation and pregnancy-related immunotolerance.

MATERIAL OR SUBJECTS

Decidual samples from women with normal pregnancy (n = 58) or unexplained spontaneous miscarriage (n = 13), peripheral blood from normal pregnancy and endometria from non-pregnancy (n = 10) were collected. Primary endometrial stromal cells (ESCs), decidual stromal cells (DSCs), decidual immune cells (DICs) and peripheral blood mononuclear cells (PBMCs) were isolated.

TREATMENT

The plasmid carrying neuropilin-1 (NRP1) gene was transfected into ESC for overexpression. To induce decidualization in vitro, ESCs were treated with a combination of 10 nM estradiol, 100 nM progesterone and 0.5 mM cAMP. Anti-Sema3a and anti-NRP1 neutralizing antibodies were applied to block the ligand-receptor interactions.

METHODS

RNA-seq analysis was performed to identify differentially expressed genes in DSCs and DICs, and NRP1 expression was verified by Western blotting and flow cytometry. The secretion of inflammatory mediators was measured using a multifactor cytometric bead array. The effects of Sema3a-NRP1 pathway on DICs were determined by flow cytometry. Statistical differences between groups were compared using the T test and one way or two-way ANOVA.

RESULTS

Combined with five RNA-seq datasets, NRP1 was the only immune checkpoint changing oppositely between DSCs and DICs. The decreased expression of NRP1 in DSCs allowed intrinsic inflammatory responses required for decidualization, while its increased expression in DICs enhanced tolerant phenotypes beneficial to pregnancy maintenance. DSC-secreted Sema3a promoted immunosuppression in DICs via NRP1 binding. In women with miscarriage, NRP1 was abnormally elevated in DSCs but diminished in decidual macrophages and NK cells.

CONCLUSION

NRP1 is a multifunctional controller that balances the inflammatory states of DSCs and DICs in gravid uterus. Abnormal expression of NRP1 is implicated in miscarriage.

Understanding the natural selection of human embryos: blastocyst quality modulates the inflammatory response during the peri-implantation period

PROBLEM

Decidualized cells display an active role during embryo implantation sensing blastocyst quality, allowing the implantation of normal developed blastocysts and preventing the invasion of impaired developed ones. Here, we characterized the immune microenvironment generated by decidualized cells in response to soluble factors secreted by blastocysts that shape the receptive milieu.

METHOD OF STUDY

We used an in vitro model of decidualization based on the Human Endometrial Stromal Cells line (HESC) differentiated with medroxiprogesterone and dibutyryl-cAMP, then treated with human blastocysts-conditioned media (BCM) classified according to their quality.

RESULTS

Decidualized cells treated with BCM from impaired developed blastocysts increased IL-1β production. Next, we evaluated the ability of decidualized cells to modulate other mediators associated with menstruation as chemokines. Decidualized cells responded to stimulation with BCM from impaired developed blastocysts increasing CXCL12 expression and CXCL8 secretion. The modulation of these markers was associated with the recruitment and activation of neutrophils, while regulatory T cells recruitment was restrained. These changes were not observed in the presence of BCM from normal developed blastocysts.

CONCLUSION

Soluble factors released by impaired developed blastocysts induce an exacerbated inflammatory response associated with neutrophils recruitment and activation, providing new clues to understand the molecular basis of the embryo-endometrial dialogue.

VIP conditions human endometrial receptivity by privileging endoplasmic reticulum stress through ATF6α pathway

Endometrial stromal cells undergo endoplasmic reticulum (ER) stress and unfolded protein response (UPR) during the decidualization linked with the inflammation and angiogenesis processes. Considering VIP (vasoactive intestinal peptide) induces the decidualization program, we studied whether modulates the ER/UPR pathways to condition both processes for embryo implantation. When Human Endometrial Stromal Cell line (HESC) were decidualized by VIP we observed an increased expression of ATF6α, an ER stress-sensor, and UPR markers, associated with an increase in IL-1β production. Moreover, AEBSF (ATF6α -inhibitor pathway) prevented this effect and decreased the expansion index in the in vitro model of implantation. VIP-decidualized cells also favor angiogenesis accompanied by a strong downregulation in thrombospondin-1. Finally, ATF6α, VIP and VPAC2-receptor expression were reduced in endometrial biopsies from women with recurrent implantation failures in comparison with fertile. In conclusion, VIP privileged ATF6α-pathway associated with a sterile inflammatory response and angiogenesis that might condition endometrial receptivity.

Brucella abortus Proliferates in Decidualized and Non-Decidualized Human Endometrial Cells Inducing a Proinflammatory Response

Brucella spp. have been associated with abortion in humans and animals. Although the mechanisms involved are not well established, it is known that placental Brucella infection is accompanied by inflammatory phenomena. The ability of Brucella abortus to infect and survive in human endometrial stromal cells (T-HESC cell line) and the cytokine response elicited were evaluated. B. abortus was able to infect and proliferate in both non-decidualized and decidualized T-HESC cells. Intracellular proliferation depended on the expression of a functional virB operon in the pathogen. B. abortus internalization was inhibited by cytochalasin D and to a lower extent by colchicine, but was not affected by monodansylcadaverine. The infection did not induce cytotoxicity and did not alter the decidualization status of cells. B. abortus infection elicited the secretion of IL-8 and MCP-1 in either decidualized or non-decidualized T-HESC, a response also induced by heat-killed B. abortus and outer membrane vesicles derived from this bacterium. The stimulation of T-HESC with conditioned media from Brucella-infected macrophages induced the production of IL-6, MCP-1 and IL-8 in a dose-dependent manner, and this effect was shown to depend on IL-1β and TNF-α. The proinflammatory responses of T-HESC to B. abortus and to factors produced by infected macrophages may contribute to the gestational complications of brucellosis.