The role of oxidation-sensitive nociception and epigenetics in endometriosis-associated pain

Endometriosis is an enigmatic disease that is associated with severe symptoms and consequences such as total hysterectomy. Upwards of 10% of women of reproductive age have endometriosis, most of whom are afflicted with chronic pelvic pain and/or infertility. Despite many treatment options available to endometriosis patients, there is no cure for this condition and recurrence of symptoms is extremely common. In CHAPTER 1, we describe the mechanisms involved in endometriotic pain and the currently available treatment strategies. Our laboratory has provided evidence for the role of oxidative stress in the etiology of endometriosis and its associated pain. In this dissertation research, we wanted to specifically understand the mechanistic role for the abundance of oxidized lipoproteins (ox-LDLs) in the peritoneal fluid (PF) of women with endometriosis. We hypothesize that the ox-LDLs and the peritoneal milieu play a dynamic role in endometriosis. These components are epigenetic modulators of inflammatory and nociceptive processes. Our IRB-approved study used eutopic and ectopic endometrial tissues and peritoneal fluid from patients with (endo) and without (control) endometriosis (IRB-[114954-20](9074)). Tissue sources included eutopic endometrium of control patients (EuNN), eutopic endometrium from patients with endometriosis (EuYY), and ectopic tissue from women with endometriosis (EcYY). Peritoneal fluid (PF), was collected from patients categorized as having neither endometriosis nor pain (NN-PF), endometriosis and pain (YY-PF), or endometriosis without pain (YN-PF). In CHAPTER 2, we provide evidence for the ability of the ox-LDL components of PF to induce inflammation and nociception in Sprague-Dawley rats (IACUC 485[397498-7]). The ox-LDL nociceptive and inflammatory responses were similar to that observed with PF from women with endometriosis and pain. Antioxidants were able to alleviate these nociceptive responses. In CHAPTER 3, we provide a mechanism by which these ox-LDL components induce inflammatory and nociceptive responses. Global miRNA expression was measured in tissues and PF-treated cells and key miRNAs and their targets were validated by qPCR. Several miRNAs (e.g. isoforms of let-7, miR-98, and miR-374) and their gene targets (e.g. IL-10, Mip1α, and MCP1) were differentially expressed in both ox-LDL and endo PF-treated cells. In CHAPTER 4, an epigenetic mechanism involving Enhancer of zeste 2 (EZH2) is proposed to contribute to endometriosis and associated pain. RT-qPCR and Western blots were used to measure the expression of key epigenetic factors in patient tissues and PF-treated cells while ChIP-qPCR identified interactions between upstream regulator Jumonji protein 2 and epigenetic genes. This study provides mechanistic evidence for oxidized lipoprotein components playing a role in endometriosis associated pain. We also provide evidence for epigenetic changes in the endometriosis pain. Future studies will test drugs that target oxidation and/or epigenetic pathways in animal models of endometriosis and patients with endometriosis.