T-cell distribution in two different segments of the equine endometrium 6 and 48 hours after insemination

Mating to Intact, but Not Vasectomized, Males Elicits Changes in the Endometrial Transcriptome: Insights From the Bovine Model

An appropriate female reproductive environment is essential for pregnancy success. In several species, including mice, pigs and horses, seminal plasma (SP) components have been shown to modulate this environment, leading to increased embryo viability and implantation. Due to the characteristics of mating in the aforementioned species, SP comes into direct contact with the uterus. However, it is questionable whether any SP reaches the uterus in species that ejaculate inside the vagina, such as humans and cattle. Hence, we hypothesized that sperm, perhaps acting as a vehicle for SP factors, play a more important role in the modulation of the maternal uterine environment in these species. In addition, changes elicited by SP and/or sperm may originate in the vagina and propagate to more distal regions of the female reproductive tract. To test these hypotheses, a bovine model in which heifers were mated to intact or vasectomized bulls or were left unmated was used. RNA-sequencing of endometrial samples collected 24 h after mating with a vasectomized bull did not reveal any differentially expressed genes (DEGs) in comparison with control samples. However, the endometrium of heifers mated with intact bulls exhibited 24 DEGs when compared to heifers mated with vasectomized bulls, and 22 DEGs when compared to unmated control heifers. The expression of a set of cytokines (IL6, IL1A, IL8, and TNFA) and candidate genes identified in the endometrial RNA-sequencing (PLA2G10, CX3CL1, C4BPA, PRSS2, BLA-DQB, and CEBPD) were assessed by RT-qPCR in the vagina and oviductal ampulla. No differences in expression of these genes were observed between treatments in any region. However, mating to both intact and vasectomized bulls induced an increase in IL1A and TNFA expression in the vagina compared to the oviduct. These data indicate that sperm, but not secretions from the accessory glands alone, induce modest changes in endometrial gene expression after natural mating in cattle. However, it is not clear whether this effect is triggered by inherent sperm proteins or SP proteins bound to sperm surface at the time of ejaculation.

Effects of Hysteroscopic and Uterine Body Insemination on the Presence of Selected Immune Cells in the Equine Endometrium

The effects of standard uterine body and hysteroscopic insemination on endometrial health were investigated. For this purpose, 33 mares were assigned to five different protocols: control (no insemination; n = 7), sham AI (sham uterine body insemination; n = 6), sham HysAI (sham hysteroscopic insemination; n = 7), standard AI (standard uterine body insemination, 300 × 10⁶ progressively motile sperms (PMS); n = 7) and HysAI (hysteroscopic insemination, 100 × 10⁶ PMS; n = 6). Sampling included uterine swabbing for microbiological examination, cytology for determination of polymorphonuclear neutrophils (PMNs) in the uterus, and endometrial biopsy collection for histology and characterization of endometrial immune cells on day 18 after ovulation (B1) as well as 8-10 hours (B2, day 20) and 72 hours after insemination (B3, day 23). Microbial contamination increased throughout the experiment in the sham insemination groups. Significant effects (P < .05) over time were detected for PMNs (cytology: sham HysAI, standard AI, and HysAI; histology: standard AI and HysAI), macrophages (immunohistochemistry: standard AI and HysAI) and T cells (immunohistochemistry: standard AI), showing an increase at B2 and a subsequent decrease toward baseline levels at B3. At B2, significant differences (P < .05) existed for PMNs (mean ± SEM) between control (1.3 ± 1.9%) and sham AI (2.2 ± 2.7%) versus standard AI (12.2 ± 4.7%) and for macrophages between control (4.1 ± 3.5%) and sham AI (2.5 ± 1.3%) versus standard AI (25.4 ± 15.8%). Thus, the cellular immune response of the endometrium depends on sperm deposition in the uterus and does not differ between hysteroscopic and standard uterine body insemination.

The Healthy and Diseased Equine Endometrium: A Review of Morphological Features and Molecular Analyses

Simple Summary

Diseases of the endometrium are a frequent cause of subfertility in mares and have an economic impact on the horse breeding industry. These include periglandular fibrosis of endometrial glands (endometrosis), degenerative diseases of vessels (angiosis), inflammation (endometritis), as well as altered differentiation of endometrial glands. Some mares are susceptible towards persistent endometritis. The etiology and pathogenesis of endometrosis are still unclear. This review describes morphological hallmarks and molecular features associated with endometrial health and different types of diseases. The presented literature data reveal characteristic differences in the expression of several extra- and intracellular molecules between the healthy and diseased equine endometrium. Some of these molecules can be detected directly within the tissue and thus have the potential to serve as excellent diagnostic markers for the presence of endometrial diseases. The knowledge of disease-associated changes in cellular differentiation, secretory functions, and immune mechanisms will help to decipher pathogenesis and will contribute to the development of novel treatments. In addition, the quantification of molecular alterations may contribute to a fertility prognosis for an individual mare. Reproductive health increases the well-being of mares and reduces financial loss for the horse breeding industry.

Abstract

Mares are seasonally polyestric. The breeding season in spring and summer and the winter anestrus are flanked by transitional periods. Endometrial diseases are a frequent cause of subfertility and have an economic impact on the horse breeding industry. They include different forms of endometrosis, endometritis, glandular maldifferentiation, and angiosis. Except for suppurative endometritis, these are subclinical and can only be diagnosed by the microscopic examination of an endometrial biopsy. Endometrosis is characterized by periglandular fibrosis and nonsuppurative endometritis by stromal infiltration with lymphocytes and plasma cells. The pathogenesis of endometrosis and nonsuppurative endometritis is still undetermined. Some mares are predisposed to persistent endometritis; this has likely a multifactorial etiology. Glandular differentiation has to be interpreted under consideration of the season. The presence of endometrial diseases is associated with alterations in the expression of several intra- and extracellular molecular markers. Some of them may have potential to be used as diagnostic biomarkers for equine endometrial health and disease. The aim of this review is to provide an overview on pathomorphological findings of equine endometrial diseases, to outline data on analyses of cellular and molecular mechanisms, and to discuss the impact of these data on reproduction and treatment.

Effects on the equine endometrium of cervical occlusion after insemination

Cervical patency is considered to be important for uterine drainage after mating or artificial insemination (AI), and failure to relax or premature tightening of the cervix can lead to persistent endometritis. This study investigated the hypothesis that cervical occlusion after AI increases accumulation of fluid, polymorphonuclear leukocytes (PMNs), and cytokines in the uterine lumen. Endometrial swabs were obtained from 29 normal cyclic mares during the first, third, and fifth estrus and biopsies during the first and fifth estrus. All mares were inseminated during the second and fourth estrus. In either the second or fourth estrus, a clamped catheter was inserted into the uterus immediately after AI. Accumulation of intrauterine fluid was evaluated by transrectal ultrasonography at 0, 6, 25, and 48 hours. Fluid was drained from the catheter at either 25 hours (TxA) or 6 and 25 hours after AI (TxB). In the control estrus (TxC, no catheters), fluid was obtained by a tampon at 25 hours after AI. The uteri were then lavaged with Ringer's solution, after which the catheters were withdrawn. Sequences of treatments in the second and fourth estrus were A followed by C, C followed by A, B followed by C, and C followed by B in groups AC, CA, BC, and CB, respectively. Five mares lost their catheters and were excluded from the study. Scores for total inflammation, gland dilation, and lymphatic lacunae in the uterine biopsies did not differ significantly between groups or estrous periods. In contrast, periglandular fibrosis scores increased in all groups during the experiment. At 25 hours after AI in the second estrus, the mares with the catheters had larger accumulations of fluid (P < 0.05) and higher concentrations and total numbers of PMNs in uterine fluid (P < 0.05) than the mares without catheters. In the fourth estrus, the total number of PMNs was lower in TxB than in TxA at 25 hours (P < 0.05). Concentrations of PMNs in TxC were 10 times higher in the fourth estrus than the second. Within mare groups AC and BC, total numbers of PMNs in treatment C (fourth estrus) were as high as in TxA and B (second estrus). Expression of IL-1β, IL-6, IL-10 and TNF-α, analyzed by Western blotting, did not differ significantly between the treatments or estrous periods. It is concluded that a closed cervix after insemination results in pronounced inflammation of the mare's endometrium. Furthermore, this kind of severe insult may lead to permanent pathologic changes in the endometrium, including fibrosis.

Seminal fluid and immune adaptation for pregnancy--comparative biology in mammalian species

Seminal fluid delivered to the female reproductive tract at coitus not only promotes the survival and fertilizing capacity of spermatozoa, but also contains potent signalling agents that influence female reproductive physiology to improve the chances of conception and reproductive success. Male to female seminal fluid signalling occurs in rodents, domestic and livestock animals, and all other mammals examined to date. Seminal plasma is instrumental in eliciting the female response, by provision of cytokines and prostaglandins synthesized in the male accessory glands. These agents bind to receptors on target cells in the cervix and uterus, activating changes in gene expression leading to functional adaptations in the female tissues. Sperm also interact with female tract cells, although the molecular basis of this interaction is not yet defined. The consequences are increased sperm survival and fertilization rates, conditioning of the female immune response to tolerate semen and the conceptus, and molecular and cellular changes in the endometrium that facilitate embryo development and implantation. Studies in porcine, equine, bovine, ovine and canine species all show evidence of male-female signalling function for seminal fluid. There are variations between species that relate to their different reproductive strategies and behaviours, particularly the site of seminal fluid deposition and female reproductive tract anatomy. Although the details of the molecular mechanisms require more study, the available data are consistent with both the sperm and plasma fractions of seminal fluid acting in a synergistic fashion to activate inflammation-like responses and downstream female tract changes in each of these species. Insight into the biological function and molecular basis of seminal fluid signalling in the female will inform new interventions and management practices to support optimal reproductive outcomes in domestic, livestock and endangered animal species.

Characterisation of lymphocyte subsets in the equine oviduct

REASONS FOR PERFORMING STUDY

The equine oviduct is the site of fertilisation and location of embryonic development during the first 5 or 6 days. It therefore has an important influence on mare fertility. Although histopathological changes have been described previously, there is limited information regarding lymphocyte subtypes present in the mucosa of the normal equine oviduct.

OBJECTIVES

To characterise the distribution of CD3+, CD4+, CD8+ and B lymphocytes in the equine oviduct from inseminated mares during oestrus and dioestrus, and from noninseminated mares during the immediate post ovulatory period.

METHODS

Oviductal tissues were collected from noninseminated mares at oestrus (> 30 mm follicle, n = 4), at Day 1 post ovulation (n = 3) and at dioestrus (Day 7 post ovulation; n = 4). Oviducts were also collected from inseminated mares at Days 1, 2, and 3 post ovulation (n = 4 for each period). Cross-sections of tissues from the ampullar-isthmic junction from each oviduct were snap frozen and cryostat sections stained by the immunoperoxidase technique with monoclonal antibodies directed against equine lymphocyte surface markers for B cells as well as CD3+, CD4+ and CD8+ cells.

RESULTS

In all oviductal sections examined, B cells were rare whereas T cells were relatively abundant. The predominant cell type found was the CD8+ phenotype, with a lesser number of CD4+ cells. Among mares, individual variation was large; therefore, although breeding status and stage of oestrous cycle appeared to alter lymphocyte populations, these differences were not significant.

CONCLUSIONS AND POTENTIAL RELEVANCE

A population of CD3+, CD4+ and CD8+ cells exists within the mucosal region of the equine oviduct. The density of these cells is similar to that described in the human oviduct. Their function is not currently known, but they may be involved with modulation of the maternal response to the presence of spermatozoa or the early conceptus within the equine oviduct. As our capacity to differentiate these cell types improves, along with the ability to identify the specific cytokines they produce, their functional significance will become more apparent.

Equine endometrial biopsy: Enhancement of clinical value by more extensive histopathology and application of new diagnostic techniques?

During the 1960s and 1970s, the clinical value of equine endometrial histopathology was firmly established after it was shown that fertility outcome was correlated with the presence and severity of specific microscopic lesions. The objective of this paper is to summarize reports from the veterinary literature published after the mid 1980s that describe new diagnostic methods of assessing equine uterine health using material collected by endometrial biopsy.

Lactoferrin expression in the horse endometrium: Relevance in persisting mating-induced endometritis

Lactoferrin (LF) is an estrogen-regulated glycoprotein with well-described antibacterial and immunomodulatory properties. The present study is the first report on LF expression in horse endometrial specimens. Mares chosen for the study were either resistant or susceptible for persisting mating-induced endometritis (PMIE) during the natural ovulatory cycle and in early pregnancy. Our investigations included immunostaining for LF protein and CD18, a leukocyte marker, as neutrophils are a possible source for LF in the endometrium. Quantification of LF mRNA was performed by use of real-time RT-PCR. This study demonstrated that LF protein in equine endometrium was expressed in glandular and luminal epithelium and in neutrophils. Similar to other mammalian species, the level of endometrial LF transcription in the mare was modulated according to the stage of the estrus cycle and was 5500-fold higher during estrus compared with diestrus and early pregnancy. The endometria from mares susceptible for PMIE and delayed uterine clearance exhibited an increased LF transcription during all stages of the estrus cycle that reached statistical significance in proestrus. In the endometria of mares susceptible for PMIE the upregulated LF mRNA expression was not associated with a higher number of CD18 positive leukocytes but correlated with the number of uterine glands. Enhanced LF transcription within the endometrial epithelium might therefore be a response to recurrent persisting inflammation following insemination in mares with delayed uterine clearance.