Prostaglandins have a central role in many endocrine functions in mammals, including regulation of the life span of the corpus luteum by prostaglandin F(2alpha) (PGF) and prostaglandin E2 (PGE), which are secreted by the uterine endometrium. However, the uterus is readily infected with bacteria such as Escherichia coli, which disrupt luteolysis. Immune cells detect E. coli by Toll-like receptor 4 (TLR4) binding its pathogenic ligand, lipopolysaccharide (LPS), although signaling requires accessory molecules such as CD14. The objective of this study was to determine the effect of E. coli or LPS on the function of bovine endometrial cells, and whether purified populations of epithelial and stromal cells express the molecules involved in LPS recognition. In addition, because the female sex hormones estradiol and progesterone modify the risk of uterine infection, their effect on the LPS response was investigated. Endometrial explants produced prostaglandins in response to LPS, with an increased ratio of PGE to PGF. Addition of LPS or E. coli to stromal and epithelial cells stimulated production of PGE and PGF and increased their cyclooxygenase 2 mRNA expression. The production of prostaglandins was abrogated by an LPS antagonist. In addition, estradiol and progesterone inhibited the production of PGE and PGF in response to LPS, indicating a role for steroid hormones in the response to bacterial infection. For the first time, Toll-like receptor 4 mRNA and CD14 mRNA and protein were detected in bovine endometrial stromal and epithelial cells by RT-PCR and flow cytometry. In conclusion, epithelial and stromal cells detect and respond to bacteria, which modulate their endocrine function.

/pdf/expression-and-function-of-toll-like-receptor-4-in-the-3snn2hueop.pdf

Expression and function of Toll-like receptor 4 in the endometrial cells of the uterus.

Background 
Escherichia coli are widespread in the environment and pathogenic strains cause diseases of mucosal surfaces including the female genital tract. Pelvic inflammatory disease (PID; metritis) or endometritis affects ∼40% of cattle after parturition. We tested the expectation that multiple genetically diverse E. coli from the environment opportunistically contaminate the uterine lumen after parturition to establish PID.


Methodology/Principal Findings 
Distinct clonal groups of E. coli were identified by Random Amplification of Polymorphic DNA (RAPD) and Multilocus sequence typing (MLST) from animals with uterine disease and these differed from known diarrhoeic or extra-intestinal pathogenic E. coli. The endometrial pathogenic E. coli (EnPEC) were more adherent and invasive for endometrial epithelial and stromal cells, compared with E. coli isolated from the uterus of clinically unaffected animals. The endometrial epithelial and stromal cells produced more prostaglandin E2 and interleukin-8 in response to lipopolysaccharide (LPS) purified from EnPEC compared with non-pathogenic E. coli. The EnPEC or their LPS also caused PID when infused into the uterus of mice with accumulation of neutrophils and macrophages in the endometrium. Infusion of EnPEC was only associated with bacterial invasion of the endometrium and myometrium. Despite their ability to invade cultured cells, elicit host cell responses and establish PID, EnPEC lacked sixteen genes commonly associated with adhesion and invasion by enteric or extraintestinal pathogenic E. coli, though the ferric yersiniabactin uptake gene (fyuA) was present in PID-associated EnPEC. Endometrial epithelial or stromal cells from wild type but not Toll-like receptor 4 (TLR4) null mice secreted prostaglandin E2 and chemokine (C-X-C motif) ligand 1 (CXCL1) in response to LPS from EnPEC, highlighting the key role of LPS in PID.


Conclusions/Significance 
The implication arising from the discovery of EnPEC is that development of treatments or vaccines for PID should focus specifically on EnPEC and not other strains of E. coli.

/pdf/specific-strains-of-escherichia-coli-are-pathogenic-for-the-1x9sfoxovo.pdf

Specific strains of Escherichia coli are pathogenic for the endometrium of cattle and cause pelvic inflammatory disease in cattle and mice.

The transition of a preovulatory follicle into a corpus luteum is a complex process involving mechanisms similar to wound healing and tumor formation. The objective of this review is to focus on mechanisms associated with corpus luteum development with specific attention to the follicular lineage of luteal cells, mechanisms associated with luteinization, and neovascular changes during luteal development. Corpora lutea are a continuation of follicular maturation and form from granulosal and theca interna cells. There is morphological and immunological evidence in ruminant species for the differentiation of granulosal and theca interna cells into large and small steroidogenic luteal cells, respectively. Different morphological, physiological, and biochemical characteristics of large and small luteal cells may reflect different follicular lineages with separate embryological origins. Following the preovulatory gonadotropin surge, follicular cells begin morphological, endocrinological, and biochemical changes associated with luteinization. Luteinization involves the transition of a preovulatory follicle into a highly vascular corpus luteum capable of secreting large quantities of progesterone. In addition, various cell types undergo hyperplasia, hypertrophy, and(or) migration during corpus luteum formation. An essential component of corpus luteum development is the recruitment of a blood supply. The development of a new microcirculatory bed involves breakdown of the follicular basement membrane, endothelial cell migration, endothelial cell proliferation, and development of capillary lumina. This process is regulated by the interaction of angiogenic and antiangiogenic substances. Further clarification of the preceding mechanisms may result in the development of improved methodologies for controlling the time of ovulation and(or) increasing pregnancy rates.

Mechanisms associated with corpus luteum development

To determine the physiological significance of tumor necrosis factor a (TNFa) in the regulation of luteolytic prostaglandin (PG) F2a release by the bovine endometrium, the effect of TNFa on PGF2a output by the endometrial tissues in vitro was investigated and compared with the effect of oxytocin (OT). Furthermore, the presence of specific receptors for TNFa in the bovine endometrium during the estrous cycle was determined. Endometrial slices (20‐30 mg) taken from six stages of the estrous cycle (estrus: Day 0; early I: Days 2‐3; early II: Days 5‐ 6; mid-: Days 8‐12; late: Days 15‐17; and follicular: Days 19‐ 21), as determined by macroscopic examination of the ovaries and uterus, were exposed to TNFa (0.06‐6 nM) and/or OT (100 nM). OT stimulated PGF2a output at the follicular stage and at estrus (P , 0.001), but not at the late luteal stage. On the other hand, the stimulatory effects of TNFa on PGF2a output were observed not only at the follicular stage but also at the late luteal stage (P , 0.001). When the endometrial tissues at late luteal stage were simultaneously exposed to TNFa (0.6 nM) and OT (100 nM), the stimulatory effect on PGF2a output was higher than the effect of TNFa or OT alone (P , 0.05). Specific binding of TNFa to the bovine endometrial membranes was observed throughout the estrous cycle. The concentration of TNF-a receptor at the early I luteal stage was less than the concentrations at other luteal stages (P , 0.01). The dissociation constant (Kd) values of the endometrial membranes were constant during the estrous cycle. The overall results lead us to hypothesize that TNFa may be a trigger for the output of PGF2a by the endometrium at the initiation of luteolysis in cattle.

https://bioone.org/journals/Biology-of-Reproduction/volume-62/issue-5/biolreprod62.5.1109/Is-Tumor-Necrosis-Factor-%ce%b1-a-Trigger-for-the-Initiation/10.1095/biolreprod62.5.1109.pdf

R.L. Murphee

Papers

Accuracy of Predicting Stages of Bovine Estrous Cycle by Gross Appearance of the Corpus Luteum