There are three main types of endometriosis: ovarian, peritoneal and deep nodal. This study mainly studied ovarian endometriosis. At present, most scholars believe that EMs is due to endometrial ectopic implantation, but Lang Jinghe, a famous scholar in China, proposed the eutopic endometrial determinism. He pointed out that the "3A" mode (Attachment, Aggression, Angiogenesis) of EMs. This model proposed that the refluxed endometrium needs to break through the inflammatory factors in the ascites, the immune cells in the peritoneal cavity and the extracellular matrix of the peritoneum to adhere to the extraendometrial tissue before further invasion and vascular. Subsequently, it was found that the expression levels of inflammatory factors such as transforming growth factor beta (TGF-β) IL-1, IL-6, IL-8, and IL-17 in peritoneal fluid, blood and endometriotic lesions differed between patients with and without EMs[9]. It was suggested that these inflammatory factors may have a coordinated role in the development of endometriosis [10]. In recent years, it has been suggested that EMs is a systemic auto-inflammatory immune disease and that some immune cells such as macrophages and lymphocytes secrete inflammatory mediators such as IL-8, tumor necrosis factor α (TNF-α), and VEGF that are involved in the pathogenesis of EMs[11,12]. These inflammatory factors recruit and stimulate ectopic endometrial cells to proliferate and release a large number of cytokines including a large number of inflammatory mediators. Positive feedback is involved in the proliferation, adhesion, invasion and angiogenesis of the ectopic endothelium, promoting the progression of the disease[11]. Among them, macrophages and their associated factors play a particularly important role in this process. Macrophages have been found to release a series of angiogenic factors, including VEGFa, IGF-1, IL-6 and bFGF[13]. Angiogenesis is essential for the survival of ectopic endothelial cells and the formation of ectopic nodules. Endometriosis has similar biological characteristics to tumor, specifically, it has the characteristics of invasion, migration and susceptibility to recurrence. In recent years, NUCKS1 has been found to play an important role in the development and progression of many types of female reproductive cancers, such as ovarian cancer[14] and endometrial cancer cancer[15].
Nuclear Ubiquitous Casein and Cyclin-dependent Kinase Substrate 1 (NUCKS1) belongs to the HMG family, located on chromosome 1q32.1, and is widely present in almost all human cell types[3]. NUCKS1 acts as a substrate for second messenger-activated kinases, which mainly regulate several cellular activities such as replication, transcription, and chromatin condensation[4]. NUCKS1 was initially found to play an important role in glucose metabolism and maintenance of energy endostasis in vivo[16]. Later , an abnormal expression of NUCKS1 in many malignant tumors was found[17-19]. NUCKS1 is not only expressed at increased levels in malignant tumors, but also correlates with the cellular immune activity of tumors. Studies have found a positive correlation between IL-6, IL-12, lipocalin 2 ( LCN2) and NUCKS1 mRNA expression[20]. Subsequent studies found that NUCKS1 also plays an important function in some metabolic and inflammatory diseases. For example, NUCKS1 can control the cellular physiological functions through NF-κB and c-MYC regulatory signaling cascades[21, 22]. After knockdown of NUCKS1, some cells release some specific paracrine factors, mainly involved in inflammatory response, inflammation, regulation of cell proliferation, cell migration and secretion, and the expression of VEGFa was found to be elevated after knockdown of NUCKS1[23]. And VEGF, IL-6, TNF-α and other inflammatory factors have very important roles in the development of EMs.
NUCKS1 is highly expressed in various tumors[5,6]. To investigate the expression of NUCKS1 in endometriosis, which has similar characteristics with tumor, we collected ectopic endometrium and eutopic endometrium from patients with endometriosis, along with normal endometrial tissues. The expression of NUCKS1 in each group of tissues was detected by RT-qPCR. The results showed that NUCKS1 expression in ectopic, eutopic and normal endometrium tissues, but NUCKS1 expression in ectopic endometrial tissues was significantly higher than the eutopic and normal endometrium. This indicates that NUCKS1 is highly activated in the ectopic endometrial tissues of EMs patients, suggesting that NUCKS1 plays a very important role in the development and progression of endometriosis. Unfortunately, we failed to further investigate the relationship between NUCKS1 and clinicopathological parameters, such as stage, fertility index, cyst size, and degree of adhesion. We will further improve this part in the subsequent experiments. Subsequently, we performed functional tests through the Immortalized cells of eutopic endometrial mesenchymal cells from human endometriosis patients, including CCK8 assay, flow cytometry and transwell assay. The functional test results are shown that inhibition of NUCKS1 decreased cell viability and capability of invasion, and increased apoptosis in endometriosis cells. It shows that NUCKS1 has some relationship with the occurrence and development of EMs.
We have verified that NUCKS1 is involved in the development of endometriosis, but the specific mechanism is unclear. Studies on lung cancer[7], breast cancer[24] and gastric cancer[25] have shown that NUCKS1 functions through the PI3K signaling pathway. In addition, study[21] showed that following alkali-injury, inhibition of NUCKS1 is accompanied by a decrease of NF-κB. Therefore, we selected two signaling pathway proteins, PI3K and NF-κB, for validation of the downstream mechanism. We found increased PI3K and NF-κB expression in EMs tissues through western blot. Reduced expression of PI3K and NF-κB in NUCKS1-inhibited endometriosis cells. All the above indicated that NUCKS1 may function through PI3K or NF-κB signaling in endometriosis.
As previously mentioned, both endometriosis and NUCKS1 are strongly associated with VEGF. Study[21] showed that the expression of VEGFa was found to be elevated after knockdown of NUCKS1. Therefore, we examined the level of VEGF in inhibitory NUCKS1 endometriosis cells via ELISA. The results showed that the expression level of cellular VEGF was decreased after the inhibition of NUCKS1. Thus NUCKS1 may regulate invasion of ectopic endometrial cells as well as angiogenesis of local lesions through the VEGF.