Increased expression of complement component 3 in human ectopic endometrium compared with the matched eutopic endometrium

Spatial Transcriptomic Analysis Identifies Epithelium-Macrophage Crosstalk in Endometriotic Lesions

The mechanisms underlying the pathophysiology of endometriosis, characterized by the presence of endometrium-like tissue outside the uterus, remain poorly understood. This study aimed to identify cell type-specific gene expression changes in superficial peritoneal endometriotic lesions and elucidate the crosstalk among the stroma, epithelium, and macrophages compared to patient-matched eutopic endometrium. Surprisingly, comparison between lesions and eutopic endometrium revealed transcriptional similarities, indicating minimal alterations in the sub-epithelial stroma and epithelium of lesions. Spatial transcriptomics highlighted increased signaling between the lesion epithelium and macrophages, emphasizing the role of the epithelium in driving lesion inflammation. We propose that the superficial endometriotic lesion epithelium orchestrates inflammatory signaling and promotes a pro-repair phenotype in macrophages, providing a new role for Complement 3 in lesion pathobiology. This study underscores the significance of considering spatial context and cellular interactions in uncovering mechanisms governing disease in endometriotic lesions.

Insights into the role of complement system in the pathophysiology of endometriosis

Endometriosis (EM) is a gynecologic disorder characterized by the presence of endometrium-like tissue outside of normal location that affects up to 10 % of all women in reproductive age. The pathogenesis of endometriosis is not completely known. The relationship between complement and EM has already been demonstrated in some studies, indicating an important role in the pathophysiology of the disease, however, researches are scarce and sometimes controversial. The objective of this review is to bring state-of-the-art knowledge on the subject and promote better understanding of the complement system role in the pathophysiology of EM. We searched in databases up to December 2020 and found 1213 articles that were screened, from which were selected 54 articles from title and abstract. We found that there is a dysfunction of the immune system on endometriosis, including the complement system. Apparently, the complement system is dysregulated in endometriosis and several proteins of the three complement pathways presented serum levels altered in women with endometriosis compared with those without the disease. The most studied protein is C3. Future investigations on the innate immune response and complement system could offer a further understanding on the inflammatory pathogenesis of EM, which will support a new therapeutic plan.

Immunological Basis of the Endometriosis: The Complement System as a Potential Therapeutic Target

Endometriosis (EM) is a chronic disease characterized by the presence and proliferation of functional endometrial glands and stroma outside the uterine cavity. Ovaries and pelvic peritoneum are the most common locations for endometrial ectopic tissue, followed by deep infiltrating EM sites. The cyclic and recurrent bleeding, the progressive fibrosis and the peritoneal adhesions of ectopic endometrial glands, may cause different symptoms depending on the origin involved. EM is a frequent clinical condition affecting around 10% of women of mainly reproductive age, as well as in post-menopausal women and adolescents, especially with uterine anomalies. The risk of developing EM depends on a complex interaction between genetic, immunological, hormonal, and environmental factors. It is largely considered to arise due to a dysfunction of immunological surveillance. In fact, women with EM exhibit altered functions of peritoneal macrophages, lymphocytes and natural killer cells, as well as levels of inflammatory mediators and growth factors in the peritoneal fluid. In EM patients, peritoneal macrophages are preponderant and highly active compared to healthy women. Peritoneal macrophages are able to regulate the events that determine the production of cytokines, prostaglandins, growth factors and complement components. Several studies have shown alteration in the regulation of the complement activation, leading to chronic inflammation characteristic of EM. Aberrant regulation/activation of the complement system has been observed in the peritoneal cavity of women affected by EM. Thus, complement inhibition may represent a new approach for the treatment of EM, given that a number of complement inhibitors are under pre-clinical and clinical development. Such an intervention may provide a broader therapeutic control of complement-mediated inflammatory damage in EM patients. This review will focus on our current understanding of the role of complement activation in EM and possible modalities available for complement-based therapy.

High-throughput mRNA sequencing of stromal cells from endometriomas and endometrium

The aetiology of endometriosis is still unclear and to find mechanisms behind the disease development, it is important to study each cell type from endometrium and ectopic lesions independently. The objective of this study was to uncover complete mRNA profiles in uncultured stromal cells from paired samples of endometriomas and eutopic endometrium. High-throughput mRNA sequencing revealed over 1300 dysregulated genes in stromal cells from ectopic lesions, including several novel genes in the context of endometriosis. Functional annotation analysis of differentially expressed genes highlighted pathways related to cell adhesion, extracellular matrix-receptor interaction and complement and coagulation cascade. Most importantly, we found a simultaneous upregulation of complement system components and inhibitors, indicating major imbalances in complement regulation in ectopic stromal cells. We also performed in vitro experiments to evaluate the effect of endometriosis patients' peritoneal fluid (PF) on complement system gene expression levels, but no significant impact of PF on C3, CD55 and CFH levels was observed. In conclusion, the use of isolated stromal cells enables to determine gene expression levels without the background interference of other cell types. In the future, a new standard design studying all cell types from endometriotic lesions separately should be applied to reveal novel mechanisms behind endometriosis pathogenesis.

The endometriotic tissue lining the internal surface of endometrioma: hormonal, genetic, epigenetic status, and gene expression profile

Ovarian endometriomas are found in a consistent proportion of patients with endometriosis and are associated with a more severe form of the disease. The endometriotic tissue lining the inside of the endometrioma has been extensively studied over the years mostly for the need to compare the molecular and cellular characteristics of eutopic and ectopic endometria. Several aspects of hormonal regulation, response to local inflammation, carcinogenesis, and modifications of the local environment have been investigated in order to characterize also the processes associated with peritoneal endometriosis. In this review, we have summarized the current knowledge of pathophysiology of endometrioma, with a particular focus on the cellular components lining the internal surface of the cyst in order to provide a comprehensive overview of the hormonal, genetic, epigenetic, and gene expression profiles of this essential part of the cyst.

Single-nucleotide polymorphisms in the lysyl oxidase-like protein 4 and complement component 3 genes are associated with increased risk for endometriosis and endometriosis-associated infertility

This study was conducted to assess genetic associations with endometriosis in a Puerto Rican population. Statistically significant differences in the allelic frequencies and genotype distribution of genetic variants in lysyl oxidase-like protein 4 (LOXL4) and complement component 3 (C3) were documented in patients with endometriosis-associated infertility versus controls, and in patients with endometriosis versus controls, respectively. In women who have the risk genotype at both single-nucleotide polymorphisms, the estimated risk for endometriosis nearly doubled.

Plasma C3a-des-Arg levels in women with and without endometriosis

PROBLEM

The lack of a reliable method for early non-invasive detection of endometriosis often results in delayed diagnosis. The aim of this study was to test the hypothesis that the plasma concentration of complement factor C3a (anaphylatoxin) can be used as a non-invasive test in the diagnosis of endometriosis.

METHOD OF STUDY

The C3a concentration was analyzed using ELISA in 160 patients with (n = 109) or without (n = 51) endometriosis during menstruation (n = 49), follicular phase (n = 55), and luteal (n = 56) phase.

RESULTS

Plasma C3a concentration was comparable between patients with [102 (27-2213) ng/mL] and without [105 (32-2340) ng/mL] (P = 0.84) endometriosis, also when assessed separately during menstruation, follicular phase, and luteal phase.

CONCLUSION

We found no difference in C3a levels between women with and without endometriosis and did not confirm our hypothesis that plasma C3a levels can be used as diagnostic test for endometriosis.

Preimplantation embryos cooperate with oviductal cells to produce embryotrophic inactivated complement-3b

Human oviductal epithelial (OE) cells produce complement protein 3 (C3) and its derivatives, C3b and inactivated complement-3b (iC3b). Among them, iC3b is the most potent embryotrophic molecule. We studied the production of iC3b in the oviductal cell/embryo culture system. In the immune system, C3 convertase converts C3 into C3b, and the conversion of C3b to iC3b requires factor I (fI) and its cofactors, such as factor H or membrane cofactor protein. Human oviductal epithelium and OE cells expressed mRNA and protein of the components of C3 convertase, including C2, C4, factor B, and factor D. The OE cell-conditioned medium contained active C3 convertase activity that was suppressed by C3 convertase inhibitor, H17 in a dose and time-dependent manner. Although the oviductal epithelium and OE cells produced fI, the production of its cofactor, factor H required for the conversion of C3b to iC3b, was weak. Thus, OE cell-conditioned medium was inefficient in producing iC3b from exogenous C3b. On the contrary, mouse embryos facilitated such conversion to iC3b, which was taken up by the embryos, resulting in the formation of more blastocysts of larger size. The facilitatory activity was mediated by complement receptor 1-related gene/protein Y (Crry) with known membrane cofactor protein activity on the trophectoderm of the embryos as anti-Crry antibody inhibited the conversion and embryotrophic activity of C3b in the presence of fI. In conclusion, human oviduct possesses C3 convertase activity converting C3 to C3b, and Crry of the preimplantation embryos may be involved in the production of embryotrophic iC3b on the surface of the embryos.

Human endometriosis is associated with plasma cells and overexpression of B lymphocyte stimulator

Endometriosis affects 10-20% of women of reproductive age and is associated with pelvic pain and infertility, and its pathogenesis is not well understood. We used genomewide transcriptional profiling to characterize endometriosis and found that it exhibits a gene expression signature consistent with an underlying autoimmune mechanism. Endometriosis lesions are characterized by the presence of abundant plasma cells, many of which produce IgM, and macrophages that produce BLyS/BAFF/TNFSF13B, a member of the TNF superfamily implicated in other autoimmune diseases. B lymphocyte stimulator (BLyS) protein was found elevated in the serum of endometriosis patients. These observations suggest a model for the pathology of endometriosis where BLyS-responsive plasma cells interact with retrograde menstrual tissues to give rise to endometriosis lesions.

Molecular profiling of experimental endometriosis identified gene expression patterns in common with human disease

OBJECTIVE

To validate a rat model of endometriosis using complimentary DNA (cDNA) microarrays by identifying common gene expression patterns between experimental and natural disease.

DESIGN

Autotransplantation rat model.

SETTING

Medical school department.

ANIMALS

Female Sprague-Dawley rats.

INTERVENTION(S)

Endometriosis was surgically induced by suturing uterine horn implants next to the small intestine's mesentery. Control rats received sutures with no implants. After 60 days, endometriotic implants and uterine horn were obtained.

MAIN OUTCOME MEASURE(S)

Gene expression levels determined by cDNA microarrays and real-time quantitative polymerase chain reaction (qPCR). The Cy5-labeled cDNA was synthesized from total RNA obtained from endometriotic implants. The Cy3-labeled cDNA was synthesized using uterine RNA from a control rat. Gene expression levels were analyzed after hybridizing experimental and control labeled cDNA to PIQOR (Parallel Identification and Quantification of RNAs) Toxicology Rat Microarrays (Miltenyi Biotec, Cologne, Germany) containing 1,252 known genes. The Cy5/Cy3 ratios were determined, and genes with >2-fold higher or <0.5-fold lower expression levels were selected. Microarray results were validated by QRT-PCR.

RESULT(S)

We observed differential expression of genes previously shown to be up-regulated in patients, including growth factors, inflammatory cytokines/receptors, tumor invasion/metastasis factors, adhesion molecules, and antiapoptotic factors.

CONCLUSION(S)

This study presents evidence in support of using this rat model to study the natural history of endometriosis and to test novel therapeutics for this incurable disease.

Levels of complement components iC3b, C3c, C4, and SC5b-9 in peritoneal fluid and serum of infertile women with endometriosis

OBJECTIVE

To assess whether complement components iC3b, C3c, C4, and SC5b-9 may be involved in the pathogenesis of endometriosis.

DESIGN

Prospective, experimental trial.

SETTING

Medical university.

PATIENT(S)

112 women infertile women undergoing laparoscopy.

INTERVENTION(S)

Venipuncture and laparoscopic peritoneal fluid collection.

MAIN OUTCOME MEASURE(S)

Peritoneal fluid and serum iC3b, C3c, C4, and SC5b-9 levels were measured by the enzyme-linked immunosorbent assay (ELISA) method.

RESULT(S)

Higher levels of C3c, C4, and SC5b-9 complement components were found in the serum compared with the peritoneal fluid, but the levels of iC3b were higher in the peritoneal fluid. We observed higher concentrations of C3c, C4, and SC5b-9 in the peritoneal fluid and serum of women with endometriosis compared with healthy women. However, the levels of iC3b in both peritoneal fluid and serum were statistically significantly lower than in the control group.

CONCLUSION(S)

The impairment of the mechanisms involved in the regulation of activation of complement system may be an important factor in the pathogenesis of endometriosis and endometriosis-associated infertility.

The Embryotrophic Activity of Oviductal Cell-derived Complement C3b and iC3b, a Novel Function of Complement Protein in Reproduction

The oviduct-derived embryotrophic factor, ETF-3, enhances the development of trophectoderm and the hatching process of treated embryos. Monoclonal anti-ETF-3 antibody that abolishes the embryotrophic activity of ETF-3 recognized a 115-kDa protein from the conditioned medium of immortalized human oviductal cells. Mass spectrometry analysis showed that the protein was complement C3. Western blot analysis using an antibody against C3 confirmed the cross-reactivities between anti-C3 antibody with ETF-3 and anti-ETF-3 antibody with C3 and its derivatives, C3b and iC3b. Both derivatives, but not C3, were embryotrophic. iC3b was most efficient in enhancing the development of blastocysts with larger size and higher hatching rate, consistent with the previous reported embryotrophic activity of ETF-3. Embryos treated with iC3b contained iC3b immunoreactivity. The oviductal epithelium produced C3 as evidenced by the presence of C3 immunoreactivity and mRNA in the human oviduct and cultured oviductal cells. Cyclical changes in the expression of C3 immunoreactivity and mRNA were also found in the mouse oviduct with the highest expression at the estrus stage. Molecules involving in the conversion of C3b to iC3b and binding of iC3b were present in the human oviduct (factor I) and mouse preimplantation embryo (Crry and CR3), respectively. In conclusion, the present data showed that the oviduct produced C3/C3b, which was converted to iC3b to stimulate embryo development.

Signal transduction pathways involved in macrophage migration induced by peritoneal fluid chemotactic factors in stages I and II endometriosis

OBJECTIVE

To explore the role of G-protein coupled signaling pathways in activation of macrophage migration in endometriosis stages I and II.

DESIGN

Case controlled study.

SETTING

University hospital.

PATIENT(S)

Fifteen patients undergoing laparoscopy for elective sterilization (n = 5) or for diagnosis of endometriosis stages I and II associated with infertility (n = 10).

INTERVENTION(S)

Peritoneal fluid samples were collected during laparoscopy.

MAIN OUTCOME MEASURE(S)

Macrophage migration induced by peritoneal fluid from patients with endometriosis stages I and II (PF SI-II) and potential G-protein coupled receptors and second messengers involved in macrophage activation.

RESULT(S)

Potential G-protein coupled receptors and second messengers involved in macrophage activation were evaluated after incubation of U-937 cells differentiated into macrophages with inhibitors of phospholipase A and C, adenylate cyclase, and protein kinase A and C. Macrophage chemotactic activity induced by PF SI-II was inhibited in the presence of a phospholipase C and A2 inhibitor (IC50= 30 microM) and after treatment with myristoylated protein kinase C peptide inhibitor (50 nM). An increase in inositol phosphate (IP3) was also observed in macrophages exposed to PF SI-II. Activation of multiple G-proteins in macrophages was examined after exposure of cells to PF SI-II in the presence and absence of Bordettela pertussis and cholera toxins. No effect on macrophage migration was observed.

CONCLUSION(S)

Macrophage chemotaxis induced by PF SI-II appears to involve activation of pertussis toxin-insensitive G-protein coupled receptors in macrophages. Our data suggest that these events lead to subsequent activation of phospholipases followed by generation of IP3 and potential mobilization of intracellular Ca2+. Subsequent phosphorylation of target proteins by protein kinase C may regulate the chemotactic responses. The adenylate cyclase pathway does not appear to play a role in this process.

Theories of endometriosis

Endometriosis is characterised by the presence of abnormally located tissue resembling the endometrium with glands and stroma. Several hypotheses have attempted to explain the development of such tissue. The oldest theory, that of metaplasia, suggests that under diverse influences coelomic tissue could be transformed into endometrium. The most often cited theory, that of implantation, proposes that the physiological phenomenon of endometrial reflux in the fallopian tubes during menstruation may, in certain conditions, overcome local defense mechanisms, implant, and proliferate. The peritoneal fluid in unaffected women possesses the capacity to prevent endometriotic tissue from becoming established. The reasons for the occurrence of endometriosis and its consequences (pain, sterility, adhesions) are probably numerous and involve the endometrium, the immune system (macrophages, natural killer cells), the peritoneum, and fallopian tubes. The failure to clear the peritoneal cavity of fragments of endometrium could cause a state of local inflammation with hyperactivation of macrophages secreting a variety of different compounds. Some of these compounds may bring about metaplasia of the peritoneum or the development of Mullerian residues.

Is endometriosis an endometrial disease?

Endometriosis is characterised by the presence of abnormally located tissue resembling the endometrium with glands and stroma. Several hypotheses have attempted to explain the development of such tissue. The most often cited theory, that of implantation, proposes that the physiological phenomenon of endometrial reflux in the fallopian tubes during menstruation may, in certain conditions, overcome local defense mechanisms, implant, and proliferate. The implantation theory does not explain why endometriosis will develop only in approximately 10-15% of women, while the reflux of endometrial tissue via the fallopian tubes during menstruation is a quasi-universal phenomenon. The endometrium of women affected by endometriosis could be abnormal compared with endometrium of healthy women. The abnormal endometrium could be able to protect itself from harmful effects of immune cells by expressing specific antigens, by harbouring a different immune cell population and by synthetizing and secreting immunosuppressive factors. Several others characteristic features of endometrium have been described in women with endometriosis: (1) production of its own estrogens in too heavy amount; (2) aptitude for setting up on peritoneum; (3) tendencies to proliferate and to invade tissue; (4) aggressiveness for the peritoneum; (5) auto-protection from physiological apoptosis; (6) abnormal expression of heat shock proteins; and (7) excessive angiogenesis.