Upregulation of elafin expression in the fallopian tube of ectopic tubal pregnancies compared to the normal tubes

Highlights

• Elafin is an anti-inflammatory agent in mucosal surfaces.

• Ectopic pregnancy is one of the most important causes of maternal mortality.

• Immunohistochemical expression and the level of elafin mRNA in ectopic pregnancy increase.

• Elafin plays a role augmentation of innate immune response and involved in ectopic implantation.

Abstract

Background

Ectopic pregnancy is one of the most important causes of maternal deaths and fallopian tubes are the location of 95% of ectopic pregnancies. Elafin is a natural antimicrobial molecule that plays an important role as an anti-inflammatory agent in mucosal surfaces and has been found in the female reproductive tract.

Objectives

The aim of this study was to investigate elafin expression, in the fallopian tube mucosa of ectopic pregnancies compared to the normal tubes using immunohistochemistry (IHC) techniques and quantitative reverse transcription (qRT)-PCR.

Methods

In this case-control study, uterine tube samples were obtained from patients with an indication for surgical removal of the tubes. The case group (n = 20) consisted of patients who were undergoing salpingectomy due to an ectopic pregnancy, the control group (n = 20) included patients who had a salpingectomy and hysterectomy. Using qRT-PCR and IHC, the expression of elafin was investigated in both study groups.

Results

Immunohistochemical expression of elafin in the epithelium and connective tissue was significantly increased in the implantation site of the patients in comparison with the control group (P < 0.001). The level of elafin mRNA increased in the mucous membrane of the fallopian tube from patients with the ectopic pregnancy compared to the normal mucosa (P < 0.001).

Conclusion

Increasing expression of elafin during an ectopic pregnancy may be a mechanism for enhancing innate immune response and be involved in related pathological conditions such as infection and ectopic implantation.

Introduction

The female reproductive system must provide fertility, implantation, and normal pregnancy while maintaining the ability to respond to infections. Genital tract infection is associated with infertility, ectopic pregnancy, and early delivery (King et al., 2008). Ectopic pregnancy is one of the most important causes of maternal deaths and fallopian tubes are the location of 95% of ectopic pregnancies (Sotelo, 2019). Improved understanding of the innate immune mechanisms at the implantation site will affect the development of a public health strategy and reducing ectopic pregnancy (Dalgetty et al., 2008).

The innate immune response is an important part of the mucosal defense system. The mucosal immune system in the female reproductive tract has evolved to eliminate sexually transmitted diseases (STDs) and maintaining the ability of adaptation to specialized physiological situations such as menstruation, fertilization, implantation, pregnancy, and childbirth. Antimicrobial molecules are an integral part of the innate immune system, which is extensively involved in the reproductive potential of women (Williams et al., 2006; Givan et al., 1997).

Elastase-specific inhibitor, also known as elafin, is a natural antimicrobial molecule and an antileukoproteinase family member (Neto et al., 2014). It is known as a proteinase inhibitor 3 (PI3), skin-derived antileukoproteinase (SKALP) (Hiramatsu et al., 2019; Korkmaz et al., 2016) or Trappin-2 (pre‐elafin) (Neto et al., 2014). This protein is encoded in humans by the gene PI3 and is a part of the whey acidic protein (WAP) or WAP four-disulfide-core (WFDC) family (Korkmaz et al., 2016). Its expression has been reported in normal epithelial cells, including skin, lung, oral cavity and vagina epithelia (Neto et al., 2014; Moreau et al., 2008). Elafin is localized in vaginal secretions, amnion epithelium, decidua, chorion, and placental trophoblast during pregnancy and it is responsible for the regulation of proinflammatory paracrine interactions needed to maintain the pregnancy and to limit uterine infections. Other functions of elafin include the intrinsic pathways of protection in tubal mucous membranes against uterine infections and regulation of menstruation through antiproteolytic mechanisms and involving in the tissue repair (Neto et al., 2014; Horne et al., 2008).

The human endometrium is an important site for the cyclic pattern of cell destruction and regeneration during fertility-related events such as implantation and menstruation. These processes require the activity of some key molecules (eg, matrix metalloproteinase (MMPs)) in the fallopian tube. MMPs have an important role in the destruction of endometrial tissues during menstruation (King et al., 2003; Grudzinski et al., 2015).

Briefly, the activity of MMPs has been triggered by neutrophil elastase (NE) and subsequently disable natural inhibitors of MMPs in the tissue. Elafin is probably responsible to decrease effects of MMPs by inhibiting NE and proteinase 3 (P3) (Neto et al., 2011).

Therefore, elafin is involved in the controlling of tissue regeneration required for implantation and early pregnancy. Elafin is detected throughout the menstrual cycle and is mainly expressed by endometrial neutrophils. Neutrophils infiltrate into the endometrium during the menstrual cycle and are associated with tissue destruction and repair that occurs at this time (King et al., 2003; Grudzinski et al., 2015).

Therefore because of the limited number of studies on the role of elafin in ectopic pregnancy (Grudzinski et al., 2015), the present study aimed to determine the expression of elafin at both mRNA and protein levels in the mucosa of the normal fallopian tubes in comparison with the ectopic pregnancy using the immunohistochemistry (IHC) and quantitative reverse transcription PCR (qRT-PCR) methods.