Characterization of foamy epithelial surface cells in the canine endometrium

Ovarian and uterine changes during the oestrous cycle in female dogs

CONTEXT

An accurate staging of sexual cycle is essential for the optimum timing of medical interventions.

AIMS

Here, an updated insight into clinical, endocrinological and vagino-cytological parameters, and their correlation with histomorphology of ovarian and uterine tissue samples is presented.

METHODS

Samples from 39 dogs were collected at various stages of the oestrous cycle: pro-oestrus (n =8), oestrus (n =12), dioestrus (n =9) (luteal phase) and anoestrus (n =10), according to clinical observations. Final allocation of samples was done after histomorphological evaluation of all tissues. Peripheral oestradiol-17ß (E2) and progesterone (P4) concentrations were measured, P4 by both chemiluminescent immunoassay (CLIA) and radioimmunoassay (RIA).

KEY RESULTS

Differences were observed between determination of the stage of the oestrous cycle, either by clinical, endocrinological or histomorphological evaluation. Individuals considered to be in clinical and endocrinological oestrus, had entered the luteal phase according to histomorphology. P4 concentrations measured by two different assays differed, underlying the importance to understand that absolute P4 concentrations may deviate depending on the used assay. Comparison of E2 and P4 concentrations is suggested to be useful when defining the transition from early follicular phase to the time of ovulation.

CONCLUSIONS AND IMPLICATIONS

Based on parallel histomorphological observations, combined with clinical and endocrinological findings on the same individuals, the present study emphasises that an accurate classification of the stage of the cycle in female dogs based solely on clinical and endocrinological assessments can be difficult. The histomorphological findings presented herein provide new insights into the transitional phases between the different stages of the oestrous cycle in the dog.

Lipid droplet dynamics in healthy and pyometra-affected canine endometrium

BACKGROUND

Accumulation of lipid droplets (LDs) was recently observed in pyometra-affected uteri. As data about their nature and function are missing we intended to compare the localization, quality and quantity of LDs in canine healthy and pyometra-affected tissues and in an in vitro model.

METHODS AND RESULTS

We characterized LDs in healthy and pyometra uterine tissue samples as well as in canine endometrial epithelial cells (CEECs) in vitro by means of histochemistry, immunohistochemistry, transmission electron microscopy, western blot, and RT-qPCR. Oil Red O (ORO) staining and quantification as well as p-phenylenediamine staining showed a higher number of LDs in epithelial cells of pyometra samples. Immunohistochemistry revealed that the amount of LDs coated by perilipin2 (PLIN2) protein was also higher in pyometra samples. Transmission electron microscopy showed an increase of LD size in surface and glandular epithelial cells of pyometra samples. In cell culture experiments with CEECs, supplementation with oleic acid alone or in combination with cholesterol lead to an increased LD accumulation. The expression of PLIN2 at protein and mRNA level was also higher upon oleic acid supplementation. Most LDs were double positive for ORO and PLIN2. However, ORO positive LDs lacking PLIN2 coating or LDs positive for PLIN2 but containing a lipid class not detectable by ORO staining were identified.

CONCLUSIONS

We found differences in the healthy and pyometra-affected endometrium with respect to LDs size. Moreover, several kinds of LDs seem to be present in the canine endometrium. In vitro studies with CEECs could show their responsiveness to external lipids. Since epithelial cells reacted only to oleic acid stimulation, we assume that the cyclic lipid accumulation in the canine endometrium is based mainly on triglycerides and might serve as energy provision for the developing early embryo. Further studies are necessary to verify the complex role of lipids in the healthy and pyometra-affected canine endometrium.

Pseudo-Placentational Endometrial Hyperplasia in the Bitch: Case Series

Simple Summary

Pseudo-placentational endometrial hyperplasia is an uncommon lesion of the canine uterus. The lesion is characterized by a bizarre tissue organization resembling the layers of the mature maternal placenta. It may be inducible by foreign body insertion in the dioestrus uterus and probably encloses the mechanism of canine placentation. The ordinated proliferation may subvert to disorganized forms when the stimulus is biological and triggers an immune response. In this view, the pseudo-placentational endometrial hyperplasia may explain some unknown features of the cystic endometrial hyperplasia/pyometra complex. The report of six new spontaneous cases will help the knowledge and the clinicopathological framing of this unique lesion. Considering the physiological changes of endometrium in late dioestrus and early anoestrus, in the authors’ opinion, the pseudo-placentational endometrial hyperplasia term should be limited to the well-organized forms detectable by gross examination or ultrasound imaging.

Abstract

Canine pseudo-placentational endometrial hyperplasia differs from the classical form of cystic endometrial hyperplasia for the well-organized tissue architecture resembling the canine placenta. After the discovery, it has been inconstantly reported. The present work reports the clinicopathological details of six spontaneous cases retrieved retrospectively from a large database. The lesion was found in young non-pregnant female dogs (median 2.0 years) at the end of dioestrus. It could be imaged by ultrasound and was always grossly detectable as single or multiple uterine enlargements of 2–3 cm in diameter with a villous whitish tissue growing on the mucosa and occluding the lumen. Histology confirmed the tissue architecture of the canine placenta with a basal glandular layer, a connective band, a spongy layer and a tortuous and compact labyrinth, often poorly recognizable. The pseudo-placentational hyperplasia is a non-inflammatory proliferative lesion although numerous mast cells inhabit the connective band, and a superimposed inflammatory infiltrate was seen in a case. Canine pseudo-placentational endometrial hyperplasia has very peculiar features, and it is a model for canine placentation and may help to better understand the cystic endometrial hyperplasia/pyometra complex.

Morphological Characteristics and Expression of Estrogen and Progesterone Receptors in the Canine Endometrium During the Estrus Cycle, Cystic Endometrial Hyperplasia and Pyometra

The estrus cycle of bitches is divided into four phases: proestrus, estrus, diestrus and anestrus, during which different morphological changes, and also cyclic changes of estrogen and progesterone receptors are present. Several pathological changes can be differentiated on the endometrium, but one of these is the most important - cystic endometrial hyperplasia, which frequently develops into pyometra. The aim of the present study was to describe morphological characteristics, and expression of estrogen and progesterone receptors on the endometrium of mixedbreed bitches during the different phases of the estrus cycle, cystic endometrial hyperplasia and pyometra. The uterus and ovaries of 36 mixed breed bitches in different phases of the estrus cycle and also with cystic endometrial hyperplasia (CEH) and chronic purulent endometritis - pyometra were examined macroscopically, histopathologically, and immunohistochemically for estrogen receptors (ΕR) and progesterone receptors (PR). During proestrus uterine cells showed a weak reaction for both estrogen and progesterone receptors, but during estrus a large number of uterine cells showed a strong reaction on estrogen receptors and moderate reaction on progesterone receptors. On the contrary, during diestrus the scores for the estrogen receptors decreased, while the progesterone receptors level increased - uterine cells expressed strong reaction for progesterone receptors, and moderate reaction for estrogen receptors. Uterine cells in cystic endometrial hyperplasia expressed a strong reaction for estrogen receptors, and moderate reaction for progesterone receptors, but on the other hand the uterine cells in the uterus with pyometra expressed a moderate to strong reaction for progesterone receptors, and a weak reaction for estrogen receptors. In further investigations it would be interesting to perform quantitative analysis for both estrogen and progesterone receptors during different phases of the estrus cycle and also in the uterus with cystic endometrial hyperplasia and pyometra.

The physiological expression of scavenger receptor SR-B1 in canine endometrial and placental epithelial cells and its potential involvement in pathogenesis of pyometra

Pyometra, the purulent inflammation of the uterus, is a common uterine disease of bitches that has potentially life-threatening consequences. The opportunistic bacterial infection of the uterus often progresses into the serious systemic inflammatory response syndrome. In a previous study, we characterized epithelial foam cells in the canine endometrial surface occurring in metestrus, and we regularly observed pronounced epithelial foam-cell formations in pyometra-affected uteri. Therefore, it was assumed that the mechanism behind lipid droplet accumulation in surface epithelial cells might even increase bacterial binding capacity and promote pyometra development. Lipid droplet accumulation in epithelial cells is accomplished via specialized lipid receptors called scavenger receptors (SR). Scavenger receptor class B type 1 (SR-B1) is an important receptor for lipid accumulation in diverse cell types, but it is also a strong binding partner for bacteria, and thereby enhances bacterial adhesion and clinical signs of systemic inflammatory response syndrome. In the present study, after the isolation of metestrous surface epithelial cells from canine uteri by laser capture microdissection, SR-B1 was identified at the messenger RNA (mRNA) level by quantitative real time polymerase chain reaction and also at the protein level by means of immunohistochemistry. In pyometra-affected uteri, SR-B1 mRNA expression was higher than that in the healthy control samples, and SR-B1 protein was expressed in the surface and crypt epithelial cells. Furthermore, to understand the physiological role of SR-B1 expression in the metestrus surface epithelial cells, we investigated its expression in the epithelial cells of the glandular chambers of canine placenta in different stages of gestation because these cells are also characterized by lipid droplet accumulation. SR-B1 was present in the placental epithelial cells of the glandular chambers from 25 to 30 and 45 to 50 days of gestation, where basal and basal and/or apical expression patterns were observed. The physiological expression of SR-B1 in metestrous endometrial surface epithelia might be related to the implantation process and embryo development, as SR-B1 was also identified in the epithelial cells of the canine placental chambers. The increased levels of SR-B1 in pyometra-affected uteri indicate a potential role for this scavenger receptor in endometrial bacterial adhesion.

Leptin in the canine uterus and placenta: possible implications in pregnancy

BACKGROUND

Leptin (Lep) is known for its involvement in the regulation of reproductive functions. It is important for uterine receptivity, implantation, placental growth and maternal energy homeostasis in several species, but Lep's function in the pregnant dog has not been investigated.

METHODS

Pregnant bitches were ovariohysterectomized at pre-implantation, post-implantation, mid-gestation and prepartum luteolysis. Two additional groups were treated with aglepristone in mid-gestation, and ovariohysterectomized 24 or 72 h later. Lep and leptin receptor (LepR) gene expression was detected by semi-quantitative real-time PCR in pre-implantation and inter-placental uterine sections (Ut) and in utero-placental compartments (Ut/Pl). Immunohistochemistry and in situ hybridization (ISH) were performed for Lep and LepR protein and mRNA localization. Parametric one-way ANOVA, paired t-test and Wilcoxon signed-rank test were used for statistical analysis.

RESULTS

In the Ut/Pl, Lep expression was higher at post-implantation and prepartum luteolysis than at mid-gestation, while in the Ut, Lep mRNA levels did not change during pregnancy. LepR expression in the Ut/Pl was up-regulated at prepartum luteolysis compared to the earlier stages. In the Ut, highest LepR mRNA was found at pre- and post-implantation. LepR expression was down-regulated in the Ut/Pl compared to the Ut at post-implantation and at mid-gestation. Aglepristone treatment resulted in a decrease of Lep mRNA levels from 24 to 72 h in the Ut without concomitant changes in the Ut/Pl or in LepR levels. Lep and LepR immunoreactivities were strong in the luminal and glandular epithelium in the Ut with abundant LepR signals in the subepithelial stroma. In the Ut/Pl, fetal trophoblasts stained stronger for Lep and LepR than decidual cells, and signals for both proteins were also detected in the glandular chambers. The myometrium, blood vessel media, and sporadically also the endothelium stained for Lep and LepR. ISH showed similar signal distribution in the Ut and Ut/Pl.

CONCLUSIONS

Lep and LepR are differentially expressed in the canine uterus and placenta during pregnancy, and their presence in various cell types indicates paracrine/autocrine roles. The Lep signaling system may be one of the pathways involved in feto-maternal cross-talk, implantation and maintenance of pregnancy, and may have a regulatory role around parturition.