No abstract

Mayer-Rokitansky-Küster-Hauser (MRKH) syndrome is a pathological condition characterized by primary amenorrhea and infertility and by congenital aplasia of the uterus and of the upper vagina. The development of secondary sexual characters is normal as well as that the karyotype (46,XX). Etiologically, this syndrome may be caused by the lack of development of the Müllerian ducts between the fifth and the sixth weeks of gestation. To explain this condition, it has been suggested that in patients with MRKH syndrome, there is a very strong hyperincretion of Müllerian-inhibiting factor (MIF), which would provoke the lack of development of the Müllerian ducts from primitive structures (as what normally occurs in male phenotype). These alterations are commonly associated with renal agenesis or ectopia. Specific mutations of several genes such as WT1, PAX2, HOXA7-HOXA13, PBX1, and WNT4 involved in the earliest stages of embryonic development could play a key role in the etiopathogenesis of this syndrome. Besides, it seems that the other two genes, TCF2 (HNF1B) and LHX1, are involved in the determinism of this pathology. Currently, the most widely nonsurgical used techniques include the “Frank's dilators method,” while the surgical ones most commonly used are those developed by McIndoe, Williams, Vecchietti, Davydov, and Baldwin.

In the genetic regulation of Müllerian structures development, a key role is played by Hoxa and Wnt clusters, because they lead the transcription of different genes according to the different phases of the organogenesis, addressing correctly cell-to-cell interactions, allowing, finally, the physiologic morphogenesis. Accumulating evidence is suggesting that dysregulation of Wnt and/or Hox genes may affect cell migration during organogenesis and differentiation of Müllerian structures of the female reproductive tract, with possible dislocation and dissemination of primordial endometrial stem cells in ectopic regions, which have high plasticity to differentiation. We hypothesize that during postpubertal age, under the influence of different stimuli, these misplaced and quiescent ectopic endometrial cells could acquire new phenotype, biological functions, and immunogenicity. So, these kinds of cells may differentiate, specializing in epithelium, glands, and stroma to form a functional ectopic endometrial tissue. This may provoke a breakdown in the peritoneal cavity homeostasis, with the consequent processes of immune alteration, documented by peripheral mononuclear cells recruitment and secretion of inflammatory cytokines in early phases and of angiogenic and fibrogenic cytokines in the late stages of the disease.

During endometriosis, a breakdown occurs in endometrial and peritoneal homeostasis caused by cytokine-induced cell proliferation and dysregulation of apoptosis. We studied tumor necrosis factor (TNF)-a, TNF receptor (TNFR) 1, and TNFR2 gene expression at both messenger RNA (mRNA) and protein levels in peritoneal fluid (PF) mononuclear cells (PFMCs), the percentages of these cells bearing the same markers, and soluble TNF-a (sTNF-a) values in PF of 80 women with endometriosis. We found that TNFR1 mRNA and protein levels, the percentages of TNFR1-bearing PFMCs, and sTNF-a values decreased from minimal to severe stages of the disease. Instead, TNF-a and TNFR2 mRNA and protein levels, the percentages of membrane TNF-a (mTNF-a)-and TNFR2-bearing PFMCs increased as the disease worsened. These data allow us to hypothesize that, in early stages, the high percentages of TNFR1-bearing PFMCs and the high levels of sTNF-a could address signal toward complex I pathway, favoring the inflammatory response. With the worsening of the disease, the low percentages of TNFR1-bearing PFMCs are probably due to decreased TNFR1 mRNA transcription and protein translation rate. In early stages (minimal and mild), the percentages of both TNFR2-and mTNF-a-bearing PFMCs are so low, due to decreased mRNA transcription and protein translation rate, that subsequent cellular events may depend minimally by this interaction. The high levels of sTNF-a may be rerouted to bind TNFR1. In contrast, in the moderate and severe stages, the high percentages of TNFR2-bearing PFMCs may be saturated by high percentages of mTNF-a-bearing PFMCs, triggering death process. So, in endometriosis, each component of the TNF-a/TNFRs system may trigger opposite cellular fate.

The evidence collected in this review suggests that TCDD could modulate transcription at multiple levels, including the epigenetic level, and via microRNAs, thus disturbing the physiologic processes mediated through the aryl hydrocarbon receptor pathways. Exposure to TCDD also modulates the immune response by influencing the production and action of endometrial cytokines and chemokines, destroying mucosal immunity of the reproductive tract and re-directing the tissue distribution and behavior of leukocytes. Despite this large body of evidence, current human-based epidemiological studies on the association between TCDD and endometriosis remain controversial.