Nonsurgical mouse model of endometriosis-associated pain that responds to clinically active drugs.

Endometriosis is an estrogen-dependent inflammatory disease that affects approximately 10% of women. Debilitating pelvic or abdominal pain is one of its major clinical features. Current animal models of endometriosis-associated pain require surgery either to implant tissue or to remove the ovaries. Moreover, existing models do not induce spontaneous pain, which is the primary symptom of patients with chronic pain, including endometriosis. A lack of models that accurately recapitulate the disease phenotype must contribute to the high failure rate of clinical trials for analgesic drugs directed at chronic pain, including those for endometriosis. We set out to establish a murine model of endometriosis-associated pain. Endometriosis was induced nonsurgically by injecting a dissociated uterine horn into a recipient mouse. The induced lesions exhibited histological features that resemble human lesions along with an increase in proinflammatory cytokines and recruitment of immune cells. We also observed the presence of calcitonin gene-related peptide-, TRPA1-, and TRPV1-expressing nerve fibers in the lesions. This model induced mechanical allodynia, spontaneous abdominal pain, and changes in thermal selection behavior that indicate discomfort. These behavioral changes were reduced by drugs used clinically for endometriosis, specifically letrozole (aromatase inhibitor) and danazol (androgen). Endometriosis also induced neuronal changes as evidenced by activation of the NF-κB signaling pathway in TRPA1- and TRPV1-expressing dorsal root ganglion neurons. In conclusion, we have established a model of endometriosis-associated pain that responds to clinically active drugs and can, therefore, be used to identify novel therapies.

The Use of Antibody Arrays in the Discovery of New Plasma Biomarkers for Endometriosis.

A noninvasive diagnostic test for endometriosis is needed to shorten the current diagnostic delay of 8-11 years. The goal of this study was to discover new biomarkers for endometriosis using an antibody array approach. A total of 103 plasma samples from patients with laparoscopically confirmed presence (n = 68) or absence (n = 35) of endometriosis were selected. Samples were pooled according to disease status, cycle phase, disease stage, and phenotype. Pooled samples were screened for possible biomarkers using the L-series 1000 and Quantibody 660 arrays from RayBiotech. Technical verification of ten markers was done using a custom-made multiplex immunoassay identifying ten proteins (10-plex) and later by single ELISA. Due to the limited reproducibility of the L-series 1000 immunoassay, the biomarker screening was performed using the Quantibody 660, a sandwich-based multiplex immunoassay, which showed that 280 proteins were upregulated, and 29 proteins downregulated in the endometriosis pool versus the control pool. In order to assess the reproducibility of these results, ten preselected proteins were analyzed using a custom 10-plex. Four proteins (CD48, DNAM-1, IL-31, and XIAP) were confirmed to be differentially expressed when comparing the endometriosis and control pool. However, only IL-31 showed a univariate statistical difference between endometriosis and control groups in individual samples that were part of the initial pools. In conclusion, discovery and verification of potential markers proved challenging using multiplex immunoassay methods, mainly due to issues with reproducibility. Only IL-31 showed potential as possible biomarker for endometriosis.

Technical Verification and Assessment of Independent Validation of Biomarker Models for Endometriosis.

There is a great need for a noninvasive diagnosis for endometriosis. Several biomarkers and biomarker panels have been proposed. Biomarker models consisting of CA-125, VEGF, Annexin V, and glycodelin/sICAM-1 were previously developed by our group. The objective of our current study was to assess the impact of technical and biological variability on the performance of those previously developed prediction models in a technical verification and a validation setting. The technical verification cohort consisted of peripheral blood plasma samples from a subset of the patients included in the original study of Vodolazkaia et al. (99 women with and 37 women without endometriosis). The validation study was done in plasma samples of an independent patient cohort (170 women with and 86 women without endometriosis). Single immunoassays were used for CA-125, VEGF-A, sICAM-1, Annexin V, and glycodelin. Statistical analyses were done using univariate and multivariate (logistic regression) approaches. The previously reported prediction models for endometriosis had a low performance in both the technical verification and validation setting. New prediction models were developed, which included CA-125, Annexin V, and sICAM-1, but CA-125 was the only marker that was retained in the models across the technical verification and validation study. Overall, successful validation of a biomarker model depends on several factors such as patient selection, collection methods, assay selection/handling, stability of the marker, and statistical analysis and interpretation. There is a need for standardized studies in large, well-defined patient cohorts with robust assay methodologies.

Lack of an Association between a Polymorphism in the KRAS 3' Untranslated Region (rs61764370) and Endometriosis in a Large European Case-Control Study.

BACKGROUND: Endometriosis is a common disorder that affects 6-10% of reproductive age women. In a previous study, we demonstrated that a polymorphism in let-7 microRNA-binding site in the 3' untranslated region of the KRAS gene was found in 31% of subjects with endometriosis resistant to medical therapy. This polymorphism was now tested in a large, case-control study. METHODS: Peripheral blood or peritoneal biopsies from 2,077 European subjects with or without endometriosis and known infertility were tested for the presence of the variant allele using polymerase chain reaction. RESULTS: Histologically proven endometriosis was found in 1,140 subjects, while 937 subjects were disease free. Variant allele carrier rates in subjects with and without endometriosis were 15.7 and 15.1%, respectively. No association between the variant KRAS allele and stage of the disease, age at surgery, body mass index, or type of infertility was identified. CONCLUSION: A germ-line single-nucleotide polymorphism in the let-7 microRNA-binding site of the KRAS gene was not associated with sporadic endometriosis in an infertile Caucasian population in this large case-control study. However, it remains possible that this gene variant may be a marker of treatment resistance. Further studies on the role of this polymorphism in endometriosis are needed.

Functional Expression of TRP Ion Channels in Endometrial Stromal Cells of Endometriosis Patients.

Endometriosis is a common gynecological disease that is characterized by the presence of functional endometrial-like lesions in the abdominal cavity. Aside from epithelial cells, these lesions consist of stromal cells that have the capacity to migrate, adhere, proliferate, and induce neuro- and lymphangiogenesis, which allows them to survive at ectopic locations. However, the exact underlying mechanisms that regulate these changes are yet to be elucidated. The common ground of these processes, however, is the second messenger, calcium. In this regard, members of the superfamily of transient receptor potential (TRP) ion channels, which are known to be calcium-permeable and expressed in the endometrium, have emerged as key regulators. Here, we assessed the molecular and functional expression of TRP channels in stromal cells isolated from the eutopic endometrium of endometriosis patients and controls. Using RT-qPCR, high mRNA levels of TRPV2, TRPV4, TRPM4, TRPM7, TRPC1, TRPC3, TRPC4, and TRPC6 were observed in the whole endometrium throughout the menstrual cycle. Additionally, and in line with previous reports of control patients, TRPV2, TRPV4, TRPC1/4, and TRPC6 were present in human endometrial stromal cells (hESC) from endometriosis patients both at the molecular and functional level. Moreover, proliferation and migration assays illustrated that these parameters were not affected in stromal cells from endometriosis patients. Furthermore, comparison between eutopic and ectopic endometrial samples revealed that the RNA expression pattern of TRP channels did not differ significantly. Collectively, although a functional expression of specific ion channels in hESCs was found, their expression did not correlate with endometriosis.

Optimization of Endometrial Decidualization in the Menstruating Mouse Model for Preclinical Endometriosis Research.

BACKGROUND: To induce endometrial decidualization in rodents, an intrauterine oil stimulus can be delivered via the nontraumatic vagina or via the traumatic laparotomy. However, there is considerable variation in amount of decidualization using these inducing methods. Therefore, we studied which oil delivery route could achieve the highest rate of endometrial decidualization along the full length of both uterine horns. METHODS: To induce decidualization, ovariectomized C57Bl/6J mice were injected with estrogen (100 ng/day; 3 days). A progesterone pellet (5 mg) was implanted subcutaneously, followed by estrogen injections (5 ng/day; 3 days). Oil (20 µL/horn) was injected in the uterus via laparotomy, laparoscopy, or vagina. Four days later, the pellet was removed, followed by hysterectomy after 4 to 6 hours. Endometrial decidualization was evaluated macroscopically and microscopically using hematoxylin and eosin and desmin staining. Furthermore, uterine weight and hormone levels were measured. RESULTS: The proportion of animals with macroscopic bicornuate decidualization was higher after laparoscopic (83%) and laparotomic (89%) injection than after sham injection (11%). Furthermore, macroscopic bicornuate decidualization was significantly higher after laparotomic injection (89%) compared to the vaginal injection (38%). Uterine weight and endometrial surface area were significantly higher in both laparotomy and laparoscopy groups compared to the sham group, while the relative desmin-positive endometrial surface area was only significantly different between the laparotomy and the sham animals. CONCLUSION: Methods using laparoscopic and laparotomic intrauterine oil injection resulted in a higher amount of decidualized endometrium compared to sham injection, although further optimization is needed to reach full bicornuate decidualization.

Evaluation of Total, Active, and Specific Myeloperoxidase Levels in Women with and without Endometriosis.

Myeloperoxidase (MPO) is a proinflammatory enzyme and a marker for neutrophil activation and oxidative stress. Since oxidative stress and inflammation are linked to the pathogenesis of endometriosis, we hypothesized that the total, active, and specific (active/total) MPO levels were significantly different in plasma of women with and without endometriosis. Samples were selected from our biobank from women with endometriosis (n = 212) and controls without endometriosis (n = 121) across the menstrual cycle. Total MPO plasma levels were measured by immunoassay and MPO activity by enzymatic assay. Total and active MPO levels did not differ significantly among endometriosis cases and controls, whereas the specific MPO activity was significantly lower in women with endometriosis than that in controls (p = 0.0159). After the subdivision of control patients into women with a normal pelvis and women with other benign gynecological disorders, a significant difference was observed only between women with endometriosis and women with other benign gynecological disorders (p = 0.0266). In conclusion, systemic MPO levels may not be suited as a single biomarker for endometriosis. Our data support the involvement of MPO in other gynecological disorders but do not provide any evidence for an association with endometriosis.

Of Mice and Women: A Laparoscopic Mouse Model for Endometriosis.

STUDY OBJECTIVE: To demonstrate how a novel laparoscopic approach allows the development of a mouse model for endometriosis after seeding menstrual endometrium from donor mice into the abdominal cavity of syngeneic recipient mice. DESIGN: A step-by-step video description of the techniques used to adapt the estrous cycle of mice towards a menstrual cycle and to subsequently induce endometriosis via laparoscopic seeding of menstrual endometrium. SETTING: University research institute. ETHICS: All animal experiments were ethically approved by KU Leuven, Belgium (ethical approval number: P031/2013). INTERVENTIONS, MEASUREMENTS, AND MAIN RESULTS: Oophorectomized female C57BL/6JRj mice received a series of estrogen injections. Next, a progesterone pellet was administered, together with a second series of estrogen injections. In addition, decidualization of the endometrium was induced with an intrauterine sesame oil stimulus. Four days later the progesterone pellet was removed and menstruation started [1]. Five hours after the progesterone pellet was removal the uterus was harvested, and the menstrual endometrium was dissected and seeded into the abdominal cavity of syngeneic recipient mice to induce endometriosis [2] using a laparoscopic approach [3]. Uterus and lesions were removed from the recipient mice 1 week after induction, and tissues were immunohistochemically stained for H&E, vimentin, and cytokeratin. CONCLUSION: In this video we show a novel methodology to induce endometriosis in mice using laparoscopic inoculation of syngeneic menstrual endometrium, mimicking Sampson's theory of retrograde menstruation [4]. Compared with currently available rodent models, our model offers a less invasive and more physiologic way for fundamental and preclinical endometriosis research, with a high endometriosis incidence and lesion take rate.

Analysis of potential protein-modifying variants in 9000 endometriosis patients and 150000 controls of European ancestry.

Genome-wide association (GWA) studies have identified 19 independent common risk loci for endometriosis. Most of the GWA variants are non-coding and the genes responsible for the association signals have not been identified. Herein, we aimed to assess the potential role of protein-modifying variants in endometriosis using exome-array genotyping in 7164 cases and 21005 controls, and a replication set of 1840 cases and 129016 controls of European ancestry. Results in the discovery sample identified significant evidence for association with coding variants in single-variant (rs1801232-CUBN) and gene-level (CIITA and PARP4) meta-analyses, but these did not survive replication. In the combined analysis, there was genome-wide significant evidence for rs13394619 (P = 2.3 × 10-9) in GREB1 at 2p25.1 - a locus previously identified in a GWA meta-analysis of European and Japanese samples. Despite sufficient power, our results did not identify any protein-modifying variants (MAF > 0.01) with moderate or large effect sizes in endometriosis, although these variants may exist in non-European populations or in high-risk families. The results suggest continued discovery efforts should focus on genotyping large numbers of surgically-confirmed endometriosis cases and controls, and/or sequencing high-risk families to identify novel rare variants to provide greater insights into the molecular pathogenesis of the disease.

Meta-analysis identifies five novel loci associated with endometriosis highlighting key genes involved in hormone metabolism.

Endometriosis is a heritable hormone-dependent gynecological disorder, associated with severe pelvic pain and reduced fertility; however, its molecular mechanisms remain largely unknown. Here we perform a meta-analysis of 11 genome-wide association case-control data sets, totalling 17,045 endometriosis cases and 191,596 controls. In addition to replicating previously reported loci, we identify five novel loci significantly associated with endometriosis risk (P<5 × 10-8), implicating genes involved in sex steroid hormone pathways (FN1, CCDC170, ESR1, SYNE1 and FSHB). Conditional analysis identified five secondary association signals, including two at the ESR1 locus, resulting in 19 independent single nucleotide polymorphisms (SNPs) robustly associated with endometriosis, which together explain up to 5.19% of variance in endometriosis. These results highlight novel variants in or near specific genes with important roles in sex steroid hormone signalling and function, and offer unique opportunities for more targeted functional research efforts.

The Presence of Endometrial Cells in Peritoneal Fluid of Women With and Without Endometriosis.

To reinforce Sampson's theory of retrograde menstruation in the pathogenesis of endometriosis, proof should be provided that during menstruation endometrial cells are present in peritoneal fluid (PF). We hypothesize that the prevalence of PF samples containing endometrial cells is higher in patients with endometriosis than in controls without endometriosis during menstruation. We selected from our biobank PF samples of 17 reproductive-age women with (n = 9) or without (n = 8) endometriosis who had received a diagnostic laparoscopy for investigation of pain/infertility. Peritoneal fluid had been collected during laparoscopy in the menstrual phase of the cycle, centrifuged, and the resulting pellet was stored at -80°C. About 5-µm sections of frozen PF pellets were stained using the Dako Envision Flex system with primary antibodies against epithelial cell adhesion molecule (Ep-CAM; endometrial epithelial cells), CD10 (endometrial stromal cells), prekeratin (epithelial/mesothelial cells), vimentin (endometrial/mesothelial/immune cells), calretinin (mesothelial cells), and CD68 (macrophages). The PF cells positive for Ep-CAM were detected in 5 of 9 patients with endometriosis and 6 of 8 controls ( P = .62). CD10 stained positively in 6 of the 9 patients with endometriosis and 3 of the 8 controls ( P = .35). Calretinin and prekeratin staining showed the presence of mesothelial cells in all pellets. Vimentin stained approximately 100% of the PF cells. CD68+ macrophages represented >50% of cells in all pellets. The prevalence of PF samples containing endometrial epithelial and stromal cells was not higher in patients with endometriosis than in controls without endometriosis during menstruation. Our findings question the relevance of endometrial cells in PF for the pathogenesis of endometriosis and support the importance of other mechanisms such as immune dysfunction and/or endometrial stem cells.

Laparoscopic Surgery: A New Technique to Induce Endometriosis in a Mouse Model.

BACKGROUND: This prospective pilot study was designed to induce endometriosis in a mouse model using laparoscopy, a less invasive and more precise approach than laparotomy. We aimed to achieve a peritoneal implant rate of at least 50% by varying both duration of anesthesia and intra-abdominal insufflation pressure. METHODS: Female BALB/cANnCrl mice in metestrus or diestrus were used as donors (n = 5) or recipients (n = 20) of uterine transplant tissue. Each recipient mouse was laparoscopically inoculated with 10 uterine pieces (range: 10-12) from donor mice into the abdominal cavity. Before starting the study, recipient mice were randomly assigned to 4 groups with variable duration of anesthesia (ketamine/xylazine or pentobarbital) and variable intra-abdominal pressure (5 or 15 mm Hg). One week after laparoscopy, endometriosis incidence and peritoneal implant take rate were documented visually during laparotomy. The retrieved lesions were histologically analyzed. RESULTS: Laparoscopic inoculation of uterine pieces in recipient mice resulted in an endometriosis incidence of 100% (20/20 animals) and an individual peritoneal implant take rate of 60% (121/206), ranging from 17% (2/12) till 83% (10/12), without differences between the 4 subgroups, and with a histological confirmation rate of 92% (58/63). CONCLUSIONS: To the best our knowledge, this is the first report showing that endometriosis can be induced by laparoscopic surgery in rodents, with a 100% incidence and a median peritoneal implant take rate of 60%. This laparoscopic model offers important advantages over traditional laparotomy models that are limited by surgery-associated trauma and/or adhesion formation.

Independent Replication and Meta-Analysis for Endometriosis Risk Loci.

Endometriosis is a complex disease that affects 6-10% of women in their reproductive years and 20-50% of women with infertility. Genome-wide and candidate-gene association studies for endometriosis have identified 10 independent risk loci, and of these, nine (rs7521902, rs13394619, rs4141819, rs6542095, rs1519761, rs7739264, rs12700667, rs1537377, and rs10859871) are polymorphic in European populations. Here we investigate the replication of nine SNP loci in 998 laparoscopically and histologically confirmed endometriosis cases and 783 disease-free controls from Belgium. SNPs rs7521902, rs13394619, and rs6542095 show nominally significant (p < .05) associations with endometriosis, while the directions of effect for seven SNPs are consistent with the original reports. Association of rs6542095 at the IL1A locus with 'All' (p = .066) and 'Grade_B' (p = .01) endometriosis is noteworthy because this is the first successful replication in an independent population. Meta-analysis with the published results yields genome-wide significant evidence for rs7521902, rs13394619, rs6542095, rs12700667, rs7739264, and rs1537377. Notably, three coding variants in GREB1 (near rs13394619) and CDKN2B-AS1 (near rs1537377) also showed nominally significant associations with endometriosis. Overall, this study provides important replication in a uniquely characterized independent population, and indicates that the majority of the original genome-wide association findings are not due to chance alone.

Dysregulation of Lysyl Oxidase Expression in Lesions and Endometrium of Women With Endometriosis.

UNLABELLED: Lysyl oxidases (LOXs) are enzymes involved in collagen deposition, extracellular membrane remodeling, and invasive/metastatic potential. Previous studies reveal an association of LOXs and endometriosis. We aimed to identify the mechanisms activated by upregulation of lysyl oxidases (LOX) in endometriotic cells and tissues. We hypothesized that LOX plays a role in endometriosis by promoting invasiveness and epithelial to mesenchymal transition (EMT). METHODS: The LOX protein expression levels were measured by immunohistochemistry in lesions and endometrium on a tissue microarray (TMA) and in endometrial biopsies from patients and controls during the window of implantation (WOI). Estradiol regulation of LOX expression was determined by quantitative polymerase chain reaction (qPCR). Proliferation, invasion, and migration assays were performed in epithelial (endometrial epithelial cell), endometrial (human endometrial stromal cell), and endometriotic cell lines (ECL and 12Z). Pathway-focused multiplex qPCR was used to determine transcriptome changes due to LOX overexpression. RESULTS: LOX protein was differentially expressed in ovarian versus peritoneal lesions. During WOI, LOX levels were higher in luminal epithelium of patients with endometriosis-associated infertility compared to controls. Invasive epithelial cell lines expressed higher levels of LOX than noninvasive ones. Transfection of LOX into noninvasive epithelial cells increased their migration in an LOX inhibitor-sensitive manner. Overexpression of LOX did not fully induce EMT but the expression of genes related to fibrosis and extracellular matrix remodeling were dysregulated. CONCLUSIONS: This study documents that expression of LOX is differentially regulated in endometriotic lesions and endometrium. A role for LOX in mediating proliferation, migration, and invasion of endometrial and endometriotic cells was observed, which may be implicated in the establishment and progression of endometriotic lesions.

The autonomic stress-induced hyperthermia response is not enhanced by several anxiogenic drugs.

While anxiety models are often based on locomotor activity responses, the stress-induced hyperthermia (SIH) paradigm uses the autonomic stress response by measuring body temperature. The effects of putative anxiogenic compounds in the SIH paradigm are inconclusive in mice and have not been examined in rats. Furthermore, it has been suggested that drug-induced effects on body temperature could be dependent on locomotor activity levels. Therefore, the effects of three anxiogenic substances, yohimbine (an α(2) receptor antagonist), mCPP (a 5HT(2C) receptor agonist) and FG-7142 (a GABA(A) receptor inverse agonist acting at the benzodiazepine site) on the stress-induced body temperature and locomotor activity response were studied in rats using novel cage stress. All anxiogenic compounds resulted in hypothermia. In contrast, FG-7142 and yohimbine increased locomotor activity levels, whereas mCPP reduced locomotor activity levels. The lack of an increased body temperature response of anxiogenic compounds indicates that the anxiogenic capacity of a drug does not necessarily yield increased autonomic stress responsivity. Moreover, the present study shows that a drug-induced decreased body temperature can be accompanied by increased locomotor activity, suggesting that both parameters represent independent parameters of the stress response.

Cross-species behavioural genetics: A starting point for unravelling the neurobiology of human psychiatric disorders.

Identifying the genetic and neurobiological mechanisms underlying certain behavioural traits is an important strategy to understand the aetiology of various psychiatric disorders and to find potential new treatment possibilities. It has proven a great challenge to develop paradigms that allow translational research for behavioural phenotypes that are relevant for disorders across the psychiatric spectrum. Recently, there has been increasing attention for studies that implement rodent behavioural paradigms in the home cage to assess the association between genetic backgrounds and behavioural traits. The application of interspecies genetics to unravel these traits has revealed novel insights in the genetic mechanisms that are encoding phenotypes relevant to biological processes underlying psychiatric disorders. By means of two examples, namely the stress-induced hyperthermia paradigm and the home cage environment, this review aims to show that by using individual genetic variations with phenotypes obtained from mice and across categories of neuropsychiatric disorders, novel insights in the neurobiological trajectory of psychiatric disorders can be obtained.