**4. Genomic and epigenetic changes of adult stem cells in ectopic and eutopic endometrium: heredity in endometriosis**

Women suffering from endometriosis were observed since then to have peculiarities including genetic predisposition, aberrant immunological response, and altered peritoneal environment that make them susceptible to attachment and growth of ectopic endometrial cells, with their exosomes, and that the ectopic endometriotic lesions are histologically similar to their putative eutopic precursors, yet significant biochemical differences exist between these two tissues. The findings provide a framework for causality and mechanisms underlying attenuate progesterone response in endometriosis, especially in the deeply infiltrating groups, but there are still unclear or controverted aspects in the genetics and consequences of progesterone resistance in endometriosis [139].

#### **4.1 Genomic regulation in endometriosis**

*Molecular Bases of Endometriosis - The Integration Between Research and Clinical Practice*

homodimers or heterodimers that have distinct transcriptional activities at

The PR initiates paracrine signaling within the uterine microenvironment during the preimplantation period and of extrauterine microenvironment in cases of ectopic endometrium. P4 facilitates the subsequent downstream expression of PR targets within the epithelium and stroma. The potential molecular pathways which are involved in the pathological mechanisms and in endometriosis were assessed and determined: c-Jun, CREB-binding protein, protein kinase B (AKT), and cyclin

The dysregulation of the PR isoforms has been shown to occur in women with endometriosis, demonstrating the integral requirement for proper balance of these

PRs are differentially expressed in the endometrial structures—glands and stroma, and during menstrual cycle. The transformation of endometrial stromal fibroblasts (ESC) into specialized secretory cells (decidualization) is fundamental for the establishment of a receptive endometrial microenvironment which can sup-

PR-A is exerting a negative control on PR-B-mediated transcription and the mediated transcription of the ER and glucocorticoid receptors [137], a fact that may underlie, at least in part, the mechanism by which progesterone functionally antagonizes the effects of estrogen. PR-A and PR-B can interact as dimers with DNA progesterone-responsive element and with signaling proteins of the Src/Ras/

De novo motif analysis indicated that, although the two isoforms bind to the same DNA sequence motif, they are both common and unique neighboring motifs where other transcription factors, such as FOSL1/FOSL2, JUN, C/EBPβ, and STAT3, bind to and dictate the transcriptional activities of these isoforms. Chromatin immunoprecipitation sequencing in combination with gene expression profiling revealed that PR-B controls a substantially larger cistrome and transcriptome than PR-A during human endometrial stem cell differentiation

*Progesterone action on the epithelial and stromal cells of the endometrium to prepare it for embryo receptivity. Progesterone has both a direct influence on endometrial epithelium via PR-B, and an indirect influence via the* 

*endometrial stromal cells. Adapted from Groll and Lessey [196].*

specific sets of gene promoters.

D1 (CCND1) signaling [136].

port and maintain pregnancy.

(**Figure 4**).

Erk pathway outside the nucleus [138].

isoforms in hormone-responsive tissues [114].

**56**

**Figure 4.**

The genetic aspects in endometriosis must be referred to the complex pathogenomic architecture and multiple interactions of the genetic qualities of the migratory and adhesive mesenchymal/stromal cells, to the qualities of the tissues/ organs where the ectopic endometrial cells arrive, and to other factors involved in the development of the disease, as the complex combinations of functional protein modules, and alteration of different metabolic pathways by sexual steroid hormones, their receptors and co-regulators, and immune systems. The genes of endometrial stem cells, such as *OCT4*, *SOX2*, *SOX15*, *NOTCH1*, and *TWIST1*, which can be deregulated in endometriosis, leading to altered SC behavior of migration and adhesivity in ectopic location, which is associated with miRNA of angiogenic factors [42]. The transcriptome analysis of eutopic and ectopic endometrium shows genetic peculiarities in women with endometriosis versus disease-free women [140–142], with relevant dysregulation of the proliferative-to-secretory transition in the endometrium in cases with endometriosis, PR gene polymorphism, and epigenetic alterations in stem cell populations, and their resulting exosomes in endometriosis, including imbalance of miRNA expression of PRs, histone and DNA modifications, and chromosomal aberrations, are some possible answers to the unclear pathophysiologic aspects and to some clinical relevance complications—as chronic severe pelvic pain, dyspareunia, infertility, miscarriages, recurrent pregnancy loss, preterm birth, and progression to malignancy, specially of the ovary, which were assessed by recent, large international collaborative studies [143, 144]. There are questions about the relationships between eutopic and ectopic endometria, regarding the trigger of progesterone-attenuated response and infertility [145]. It is unknown if the defective endometrium gives rise to a predisposition toward endometriosis and infertility or, alternatively, if endometriosis causes the altered endometrial receptivity, in cases with failure of ART. In experiments on mice, the methylation of *Hoxa 10* and *Hoxa 11* (known as a potential mechanism responsible for altered gene expression) decreased the endometrial receptivity in the endometriosis group.

The eutopic endometrium of ill women has an attenuate response to P4 because estrogen-responsive genes are nor suppressed in their stromal cells comparative to normal women in early secretory phase of menstrual cycle, a fact that suggests a resistant phenotype to progesterone [111, 114, 115].

#### **4.2 Heredity in endometriosis**

Since the 1990s, there is increasing evidence of a germline predisposition to endometriosis. A familial clustering of endometriosis in humans [146] and rhesus monkeys [147] as well as increased prevalence among first-degree relatives of women with all disease severities compared to the general population [148] has been reported. The age at onset of symptoms is similar in affected, non-twin sisters [149], and there is concordance in monozygotic twins [147]. The complex gynecologic disorder of endometriosis was since then recognized as showing heritable tendencies, with recurrent risks of 5–7% for first-degree relatives [150]. Familial and epidemiologic studies support that this disease is a genetic disorder of polygenic/ multifactorial inheritance, being determined the number and locations of causative genes. Using microarray for real-time PCR validation for the genome-wide linkage analysis, in a study of 1176 families with affected sibling pairs versus disease-free women, Treloar et al. [151] identified a region of significant linkage to endometriosis on chromosome 10q26, and four genes [a disintegrin and metalloproteinase domain 12 (ADAM12; 10q26.3; 2.29 ESE), arginyltransferase 1 (ATE1; 10q26.13; 1.61 PE, 1.57 ESE), and fibronectin type III and ankyrin repeat domains 1 (FANK1; 10q26.2; −1.85 ESE)] which have statistical significant changes, but the gene CYP26A1 had a fold change in the real-time PCR analysis that did not reach statistical significance. After the publication of this study, there are debates on the familial aggregation [152, 153].

#### **4.3 Progesterone receptor polymorphism**

Endometriosis is considered a polygenic disorder [154] requiring alterations in multiple biological pathways for the establishment and proliferation of ectopic endometrial cells, a fact documented in a meta-analysis of European and Japanese cohorts [155]. The human progesterone receptor gene is located on chromosomes 11q22–11q23 [156].

Multiple genes are expressed differentially in the eutopic endometrium of ill patients vs. disease-free women; and the most studied gene expression, the HOX gene, was proven to be altered in stromal stem cells from the ectopic endometrium [157]. To date, many deregulated genes have been identified in endometriotic cells with a wide variety of functions, including apoptosis, vascularization, cell cycle regulation, DNA repair, encoding detoxification enzymes, immune system regulation, and cell adhesion. PR polymorphism is controverted in literature [152]; some authors consider to have little or no relevance in endometriosis development. The multinational study [144] of a total of 45,923 cis-eQTLs for 417 unique genes and 2968 trans-eQTLs affecting 82 unique genes showed dynamic changes in expression of individual genes along the cycle, which include alteration in both mean expression and transcriptional silencing. The genetic polymorphisms predispose women to endometriosis [158], a fact that was not sustained by the results of three meta-analyses on association of endometriosis and some genetic polymorphisms coding for dioxin detoxification enzymes, sex steroid biosynthesis, and their receptors [159–161], even though meta-analyses is known to have upward biases in risk estimates. A quite old review on this topic found "a strikingly large amount of conflicting results" and concluded that "polymorphisms may have a limited value in assessing possible development of endometriosis" [152].

The endometrial specimens in different phases of the menstrual cycle, mainly in the secretory phase, were analyzed and there was demonstrated a signature of enhanced cellular survival, persistent expression of genes involved in DNA synthesis, and cellular mitosis in the setting of endometriosis, were analyzed, and, on another hand, the genes for susceptibility of attenuated progesterone response when in endometriosis from the families *FOXO1A*, *MIG6*, and *CYP26A1* (151), *HOX* [142], *WNT* [68], and 12 single nucleotide polymorphisms at 10 independent genetic loci associated with endometriosis have also been identified were identified [162].

Comparative gene expression analysis of progesterone-regulated genes in secretory-phase endometrium confirmed the observation of attenuated progesterone

**59**

**Table 2.**

*Progesterone Resistance and Adult Stem Cells' Genomic and Epigenetic Changes in the Puzzle…*

response, which is the main issue of this chapter. The genetic polymorphism of PRs was studied also on *PROGINS* receptor gene [163], recently on the PROGINS allele [143], and on *+331G/A* genes (especially for comparison between superficial and deeply infiltrating endometrioses [86]). The +331C/T has been shown to influence the transcription of PR-B relative to PR-A with the T allele favoring PR-B [137, 164]. PR-B acts as a classic hormone receptor, mediating the effects of progesterone, whereas PR-A acts as a repressor of PR-B, and as a result, the presence of the +331T

In the recent published multinational and multicenter collaborative study focused on the genotypes for the +331C/T SNP (associated with low risk of endometriosis, because of increased synthesis of PR-B) and PROGINS allele (equivocal from other analyses) in cases with a history of endometriosis [144]. The occurrence of endometriosis was reduced in women carrying one or more copies of the +331T allele, whereas there was no association between the PROGINS allele and endometriosis (**Table 2**). The conclusion regarding PRs was that the +331T allele drives to a reduced PR-A to PR-B ratio, and if the observed association with endometriosis is confirmed, it would suggest that this ratio is important for endometriosis; more than this the authors' conclusion was that a reduced risk is biologically plausible

In the last 15–20 years, the relationship between PR-A and PR B is more and more understood. The exclusive expression of PR-B in the luminal epithelium may act as a reservoir of PR-A heterodimerizing partners, or PR-B may homodimerize and regulate epithelial target genes. The expression ratio of the PR isoforms within the uterine compartments could potentially regulate the gene expression profile; it was observed in ill women. The expression of progesterone target genes is blunted, and decidualization is inadequate [115]. The prototype progesterone-responsive gene, glycodelin, was discovered to be strikingly downregulated in the endometrium of women with endometriosis compared with disease-free women [165], and recently glycodelin is the third biomarker for early diagnosis of endometriosis,

Other earlier studies were considering the additional effect of environmental factors as dioxin to genes [166] or the interaction between multiple genes and/or the interaction between genes to other factors to produce the disease phenotype [167]. The location of endometrial stem cells outside the uterus may be another explanation of their different actions in ectopic and eutopic endometrium in ill women in

> **Cases without endometriosis (n)**

345 5369 0.65 (0.43,

343 5339 0.94 (0.76,

*OR = odds ratio, compares heterozygotes and rare homozygotes to common homozygotes for +331C/T, per copy of the allele carried for PROGINS, stratified on study site and age group; p-value for heterogeneity across study sites.*

*Association between the two PRs SNPs and endometriosis in the multinational study population* 

**OR (95% CI) p-Value phet**

0.042 0.46

0.56 0.24

0.98)

1.16)

*DOI: http://dx.doi.org/10.5772/intechopen.84203*

allele is hypothesized to lead to increase the effect of P4.

since endometriosis is responsive to progesterone.

besides zinc-ɑ and brain-derived neurotrophic factor (BDNF).

**Cases with endometriosis (n)**

comparison to disease-free women [78].

**Single nucleotide polymorphism (SNP)**

+331 C/T (rs10895068)

PROGINS C/A (rs1042838)

*(adapted from Fung et al. [144]).*

**4.4 Progesterone target genes**

response, which is the main issue of this chapter. The genetic polymorphism of PRs was studied also on *PROGINS* receptor gene [163], recently on the PROGINS allele [143], and on *+331G/A* genes (especially for comparison between superficial and deeply infiltrating endometrioses [86]). The +331C/T has been shown to influence the transcription of PR-B relative to PR-A with the T allele favoring PR-B [137, 164]. PR-B acts as a classic hormone receptor, mediating the effects of progesterone, whereas PR-A acts as a repressor of PR-B, and as a result, the presence of the +331T allele is hypothesized to lead to increase the effect of P4.

In the recent published multinational and multicenter collaborative study focused on the genotypes for the +331C/T SNP (associated with low risk of endometriosis, because of increased synthesis of PR-B) and PROGINS allele (equivocal from other analyses) in cases with a history of endometriosis [144]. The occurrence of endometriosis was reduced in women carrying one or more copies of the +331T allele, whereas there was no association between the PROGINS allele and endometriosis (**Table 2**). The conclusion regarding PRs was that the +331T allele drives to a reduced PR-A to PR-B ratio, and if the observed association with endometriosis is confirmed, it would suggest that this ratio is important for endometriosis; more than this the authors' conclusion was that a reduced risk is biologically plausible since endometriosis is responsive to progesterone.

#### **4.4 Progesterone target genes**

*Molecular Bases of Endometriosis - The Integration Between Research and Clinical Practice*

monkeys [147] as well as increased prevalence among first-degree relatives of women with all disease severities compared to the general population [148] has been reported. The age at onset of symptoms is similar in affected, non-twin sisters [149], and there is concordance in monozygotic twins [147]. The complex gynecologic disorder of endometriosis was since then recognized as showing heritable tendencies, with recurrent risks of 5–7% for first-degree relatives [150]. Familial and epidemiologic studies support that this disease is a genetic disorder of polygenic/ multifactorial inheritance, being determined the number and locations of causative genes. Using microarray for real-time PCR validation for the genome-wide linkage analysis, in a study of 1176 families with affected sibling pairs versus disease-free women, Treloar et al. [151] identified a region of significant linkage to endometriosis on chromosome 10q26, and four genes [a disintegrin and metalloproteinase domain 12 (ADAM12; 10q26.3; 2.29 ESE), arginyltransferase 1 (ATE1; 10q26.13; 1.61 PE, 1.57 ESE), and fibronectin type III and ankyrin repeat domains 1 (FANK1; 10q26.2; −1.85 ESE)] which have statistical significant changes, but the gene CYP26A1 had a fold change in the real-time PCR analysis that did not reach statistical significance. After the publication of this study, there are debates on the familial aggregation [152, 153].

Endometriosis is considered a polygenic disorder [154] requiring alterations in multiple biological pathways for the establishment and proliferation of ectopic endometrial cells, a fact documented in a meta-analysis of European and Japanese cohorts [155]. The human progesterone receptor gene is located on chromosomes

Multiple genes are expressed differentially in the eutopic endometrium of ill patients vs. disease-free women; and the most studied gene expression, the HOX gene, was proven to be altered in stromal stem cells from the ectopic endometrium [157]. To date, many deregulated genes have been identified in endometriotic cells with a wide variety of functions, including apoptosis, vascularization, cell cycle regulation, DNA repair, encoding detoxification enzymes, immune system regulation, and cell adhesion. PR polymorphism is controverted in literature [152]; some authors consider to have little or no relevance in endometriosis development. The multinational study [144] of a total of 45,923 cis-eQTLs for 417 unique genes and 2968 trans-eQTLs affecting 82 unique genes showed dynamic changes in expression of individual genes along the cycle, which include alteration in both mean expression and transcriptional silencing. The genetic polymorphisms predispose women to endometriosis [158], a fact that was not sustained by the results of three meta-analyses on association of endometriosis and some genetic polymorphisms coding for dioxin detoxification enzymes, sex steroid biosynthesis, and their receptors [159–161], even though meta-analyses is known to have upward biases in risk estimates. A quite old review on this topic found "a strikingly large amount of conflicting results" and concluded that "polymorphisms may have a limited value in assessing possible development of endometriosis" [152]. The endometrial specimens in different phases of the menstrual cycle, mainly in the secretory phase, were analyzed and there was demonstrated a signature of enhanced cellular survival, persistent expression of genes involved in DNA synthesis, and cellular mitosis in the setting of endometriosis, were analyzed, and, on another hand, the genes for susceptibility of attenuated progesterone response when in endometriosis from the families *FOXO1A*, *MIG6*, and *CYP26A1* (151), *HOX* [142], *WNT* [68], and 12 single nucleotide polymorphisms at 10 independent genetic loci associated with endometriosis have also been identified were identified [162].

Comparative gene expression analysis of progesterone-regulated genes in secretory-phase endometrium confirmed the observation of attenuated progesterone

**4.3 Progesterone receptor polymorphism**

11q22–11q23 [156].

**58**

In the last 15–20 years, the relationship between PR-A and PR B is more and more understood. The exclusive expression of PR-B in the luminal epithelium may act as a reservoir of PR-A heterodimerizing partners, or PR-B may homodimerize and regulate epithelial target genes. The expression ratio of the PR isoforms within the uterine compartments could potentially regulate the gene expression profile; it was observed in ill women. The expression of progesterone target genes is blunted, and decidualization is inadequate [115]. The prototype progesterone-responsive gene, glycodelin, was discovered to be strikingly downregulated in the endometrium of women with endometriosis compared with disease-free women [165], and recently glycodelin is the third biomarker for early diagnosis of endometriosis, besides zinc-ɑ and brain-derived neurotrophic factor (BDNF).

Other earlier studies were considering the additional effect of environmental factors as dioxin to genes [166] or the interaction between multiple genes and/or the interaction between genes to other factors to produce the disease phenotype [167].

The location of endometrial stem cells outside the uterus may be another explanation of their different actions in ectopic and eutopic endometrium in ill women in comparison to disease-free women [78].


*OR = odds ratio, compares heterozygotes and rare homozygotes to common homozygotes for +331C/T, per copy of the allele carried for PROGINS, stratified on study site and age group; p-value for heterogeneity across study sites.*

#### **Table 2.**

*Association between the two PRs SNPs and endometriosis in the multinational study population (adapted from Fung et al. [144]).*

## **4.5 MicroRNA (miRNA) dysregulation of steroid hormone receptor expression in endometriosis**

The receptors of sexual steroid hormones (ERs, PRs) are involved in endometriosis, and correlated to them is the exploration of the correlation between microRNA (miRNA) and ER/PR in eutopic and ectopic endometrium. There are recently discovered stranded noncoding RNAs (ncRNAs) [168]. MicroRNAs (miRNAs) are single-stranded noncoding RNA molecules with approximately 22 nucleotides in length, and they control posttranscriptional gene regulation, which were proposed to contribute to human reproductive physiology; their abnormal expression was involved in the pathogenesis of many diseases of female reproductive tract, including endometriosis. While the majority of the literature supports the notion that miRNAs inhibit translation, there is some evidence that miRNAs can actually enhance translation in certain biological scenarios.

miRNAs are postulated to play a role in normal biological processes, to be critical regulators of cellular development and physiology, while their mis-expression has been associated with numerous diseases [169]. A recently published paper [170] at the Department of Molecular and Integrative Physiology, at the University of Kansas Medical Center (USA) tries to determine if the "mis-expressed" endometriotic tissue is a cause (driver of the disease) or a result of endometriosis (passenger).

More than 10 years ago, there are comparative microanalyses of genetic expressions—the miRNAs in women with ectopic endometrial cells and eutopic endometrium—that have proven an alternative pattern in the two groups [171–173], as well as the differences of ill women versus disease-free women [172–175]. miRNA regarding ER shows a ratio of 100:1 in *ESR2* (RE*-*β) to *ESR1* (RE-α) in endometriomas vs. superficial endometriotic lesions and eutopic endometrium [112, 113].

Different miRNAs are identified by microarray with real-time reverse transcription-polymerase chain reaction (real-time RT-PCR), and they were done in paired eutopic/ectopic endometrium from the same patients. In the published papers, there are identified upregulated (over expressed) and downregulated (underexpressed) miRNA expressions in eutopic and different ectopic lesion locations (peritoneal, ovarian), and some are "mis-expressed." Using the Ingenuity Pathway Analysis (IPA) software, potential molecular pathways were assessed and determined to involve c-Jun, CREB-binding protein, protein kinase B (AKT), and cyclin D1 (CCND1) signaling, all of which have previously been associated with endometriosis pathogenesis [136]. According to the involvement in endometriosis, the molecules directly involved in endometriosis (cytokines, enzymes, growth factors, kinases, ion channels, ligand-dependent nuclear receptors, peptidases, phosphatases) are assessed.

There are differences between authors; there were conflicting reports on whether or not miRNA expression was influenced by the stage of the menstrual cycle (proliferative [136] or secretory [176]), the type of endometrial cell (miRNA of endometrial stromal cells was for the first time assessed by Hawkins et al. [177]), the type of miRNA, and the level in eutopic and ectopic tissue [miRNA from *miR-29* family (was evaluated using primary human endometrial stromal cells in vitro)], which had different levels—(high for [136] and [176] and decreased for [178], who compared it to disease-free women). The role of *miR-29c* in endometrial cell proliferation, invasion, and apoptosis in vitro was examined. *miR-29c* suppressed endometrial cell proliferation and invasion, promoting cell apoptosis. The conclusion was that *miR-29c* exhibits inhibitory action on endometrial cell proliferation and invasion by inhibiting the expression of *c-Jun*. Another studied miRNA—the stromal cell *miR-183*, was examined in response to ovarian steroids (17β-estradiol and P4), and inflammatory cytokines (TNF-α) were concluded from this study that repressed levels of *miR-183* may modulate the growth and invasive potential of

**61**

*Progesterone Resistance and Adult Stem Cells' Genomic and Epigenetic Changes in the Puzzle…*

endometriotic endometrial stromal cells contributing to the development and progression of endometriosis [179]. The microarray to identify differentially expressed miRNAs between endometriotic lesion tissues from women with stage III/IV disease compared with eutopic endometrium from women without endometriosis has shown that lesion tissue expressed significantly higher levels of expression of seven miRNAs and significantly lower levels of expression of ten miRNAs [180]; some miRNAs were predictors of angiogenesis in endometriotic lesions. Expression of VEGFA was significantly upregulated, whereas EGFR2, PTEN, and CXCR4 were markedly downregulated in lesion tissue compared with the endometrium from women without endometriosis. The authors concluded that the differentially expressed miRNAs could modulate VEGFA, EGFR2, PTEN, and/or CXCR4 expression and contribute to the pathogenesis of endometriosis. Their conclusion is quite similar to other researchers from Spain [181]: the expression levels of miRNAs related to angiogenesis (the pro-angiogenic factors (VEGF-A) and the angiogenesis inhibitor thrombospondin-1 (TSP-I) are different in eutopic endometrium from that observed in ovarian endometrioma, rectovaginal nodule. Ovarian endometriomas exhibited significantly lower levels of pro-angiogenic VEGF-A mRNA and protein and higher levels of *miR-125a* and *miR-222* than the corresponding eutopic endometrium. In contrast, levels of the angiogenesis inhibitor were significantly higher in endometriomas, and this was associated with reduced levels of *miR-17*-*5p*. According to the results of the last mentioned study [170], it was considered that from the initial generation of miRNA profiles, investigations were focused on specific miRNAs and putative targets, which can become relevant to the pathophysiology of endometriosis and may aid in determining whether these miRNAs

*miR-126* was proposed to be analyzed as a regulator of angiogenesis, growth, adhesion, and invasion in ectopic endometriotic lesions versus eutopic endometrium of disease-free women, and the results of this parameter are discordant higher in earlier studies [136], and reduced in the more recent one, the level of

reduction being parallel to the severity of endometrioma [182].

**4.6 Epigenetics in endometriosis: methylation pattern of sexual steroid** 

There is accumulating evidence that various epigenetic aberrations exist in endometriosis. In the last 10 years, evidence from reviewed and retrieved studies has emerged that endometriosis may be an epigenetic disease [153], epigenetics appearing to have a better explanatory power than genetics, and to be a common denominator for hormonal and immunological aberrations in the puzzle of endometriosis. Genomic imprinting; DNA methylation; histone modifications with different nominations (acetylation/ histone phosphorylation/histone ubiquitylation/ histone sumoylation); microRNAs [183] and recently discovered, stranded, noncoding RNAs (ncRNAs) [168]; transcription factor network; and chromatin remodeling are known to regulate transcription of target genes. Genomic imprinting is an epigenetic phenomenon known to regulate DNA methylation of either maternal or paternal alleles [184], and the male and female germ lines guide the allele-specific DNA methylation marking and histone modification onto specific gene regions of parental alleles [185]. The epigenome, the collection of DNA methylation, and the histone modifications can be influenced by environmental factors. Exposure to xenobiotics, chronic inflammation, and transient hypoxia are associated with DNA hypomethylation of stromal endometrial stem cells through the destabilization of *DNMT1* mRNA; *DNMT1*, *DNMT3A*, and *DNMT3B* are overexpressed in the epithelial component of endometriotic implants as compared to normal controls or in the

*DOI: http://dx.doi.org/10.5772/intechopen.84203*

function as drivers of the disease.

**hormone receptors**

endometriotic endometrial stromal cells contributing to the development and progression of endometriosis [179]. The microarray to identify differentially expressed miRNAs between endometriotic lesion tissues from women with stage III/IV disease compared with eutopic endometrium from women without endometriosis has shown that lesion tissue expressed significantly higher levels of expression of seven miRNAs and significantly lower levels of expression of ten miRNAs [180]; some miRNAs were predictors of angiogenesis in endometriotic lesions. Expression of VEGFA was significantly upregulated, whereas EGFR2, PTEN, and CXCR4 were markedly downregulated in lesion tissue compared with the endometrium from women without endometriosis. The authors concluded that the differentially expressed miRNAs could modulate VEGFA, EGFR2, PTEN, and/or CXCR4 expression and contribute to the pathogenesis of endometriosis. Their conclusion is quite similar to other researchers from Spain [181]: the expression levels of miRNAs related to angiogenesis (the pro-angiogenic factors (VEGF-A) and the angiogenesis inhibitor thrombospondin-1 (TSP-I) are different in eutopic endometrium from that observed in ovarian endometrioma, rectovaginal nodule. Ovarian endometriomas exhibited significantly lower levels of pro-angiogenic VEGF-A mRNA and protein and higher levels of *miR-125a* and *miR-222* than the corresponding eutopic endometrium. In contrast, levels of the angiogenesis inhibitor were significantly higher in endometriomas, and this was associated with reduced levels of *miR-17*-*5p*.

According to the results of the last mentioned study [170], it was considered that from the initial generation of miRNA profiles, investigations were focused on specific miRNAs and putative targets, which can become relevant to the pathophysiology of endometriosis and may aid in determining whether these miRNAs function as drivers of the disease.

*miR-126* was proposed to be analyzed as a regulator of angiogenesis, growth, adhesion, and invasion in ectopic endometriotic lesions versus eutopic endometrium of disease-free women, and the results of this parameter are discordant higher in earlier studies [136], and reduced in the more recent one, the level of reduction being parallel to the severity of endometrioma [182].
