Progesterone, estrogen, and androgen receptors in the corpus luteum of the domestic cat, Iberian lynx ( Lynx pardinus ) and Eurasian lynx ( Lynx lynx )

Molecular Factors Involved in the Reproductive Morphophysiology of Female Domestic Cat (Felis catus)

The domestic cat (Felis catus) is considered an important model for the study of feline reproductive morphophysiology. However, although the morphological changes and clinical signs that occur during the estrous cycle and pregnancy are well known, little is known about the molecular mechanisms involved in the reproductive physiology of this animal species. Thus, this paper reviews the current knowledge about the modulation and expression profile of hormonal, immunological, redox, and growth mediators involved in the uterine, ovarian, and placental morphophysiology of domestic cats.

Spheroid formation and luteinization of granulosa cells of felids in a long-term 3D culture

In the present study, granulosa cells (GCs) from domestic cats and Persian leopard were cultured and characterized from selected days. The culture period was divided into two phases: maintenance, which lasted for 7 days, and luteinization, which followed for up to 11 days. Luteinization was performed on ultra-low attachment plates, supporting the formation of spheroids in a medium supplemented with insulin, forskolin, and luteinizing hormone (LH). GCs of domestic cat produced estradiol (E2) and progesterone (P4) during the maintenance phase. The gene expressions of some proteins involved in steroidogenesis were stable (STAR, HSD3B1) or decreased over time (CYP11A1, HSD17B1, CYP17A1, and CYP19A1), which was similar to the expressions of gonatropin receptors (LHCGR and FSHR). During the luteinization phase, P4 concentration significantly increased (P < 0.05), and E2, in contrast to the proliferation phase, was below detection range. The expression of genes of proteins involved in steroidogenesis (STAR, CYP11A1, HSD3B1, HSD17B1, CYP17A1, and CYP19A1) and of gonadotropin receptors (LHCGR and FSHR) significantly increased during the luteinization period, but some expressions exhibited a decrease at the end of the phase (LHCGR, FSHR, HSD17B1, CYP19A1). The morphology of the luteinized GCs of domestic cat resembled large luteal cells and had numerous vacuole-like structures. Also, the GCs of Persian leopard underwent luteinization, shown by increasing P4 production and HSD3B1 expression. This study confirms that GCs from felids can be luteinized in a 3D spheroid system which can be a basis for further studies on luteal cell function of felids. Additionally, we could show that the domestic cat can serve as a model species for establishing cell culture methods which can be transferred to other felids.

Estrogen and progesterone receptors and antioxidant enzymes are expressed differently in the uterus of domestic cats during the estrous cycle

Sex steroids and antioxidant enzymes are important in female sexual development and adequate modulation of the estrous cycle, pregnancy, and fetal development. Therefore, modifications in its signaling or expression in the genital system are associated with reproductive dysfunctions. However, the spatial-temporal expression profile of receptors for sex steroids and antioxidant enzymes in the uterus of domestic cats throughout the estrous cycle needs to be studied. Cats in proestrus/estrus (N = 6), diestrus, (N = 7), and anestrus (N = 6) were used to evaluate the uterine expression of estrogen alpha (ERα), progesterone (PR), and androgen (AR) receptors and of the antioxidant enzymes superoxide dismutase 1 (SOD1), catalase and glutathione peroxidase 1 (GPX1) by immunohistochemistry and qPCR. The uterus of cats in diestrus showed lower protein and mRNA expression of ERα and PR compared to proestrus/estrus and anestrus, mainly in the luminal and glandular epithelium and myometrium, different from catalase and SOD1, which showed higher expression in diestrus in relation to other phases of the cycle. GPX1, on the other hand, showed lower uterine gene expression in diestrus compared to proestrus/estrus and anestrus. No significant differences in AR expression were observed. In conclusion, ERα and PR sex steroid receptors and antioxidant enzymes are expressed differently in the uterus of domestic cats during the estrous cycle.

Current knowledge in the biology of gametes and embryos from Carnivora

In addition to companion animals and laboratory species, about 270 carnivore species play fundamental ecological roles in different ecosystems. However, almost 40% of carnivore species are now threatened or endangered in the wild because of human activities. While protection of natural habitats is critical, it is equally important to better understand carnivore reproduction, including a solid knowledge in sperm, oocyte, and embryo biology, to maintain sustainable populations in the wild and in conservation breeding centers. Characterizing gamete and embryo biology is also needed to develop cryopreservation and assisted reproductive technologies to enhance conservation efforts. The objective of this review is to provide the most recent knowledge in the biology of sperm cells, oocytes, and early embryos across all carnivore families. Overall, most data originate from populations maintained in breeding centers or zoos. Characterizations of sperm biology and cryopreservation are far more advanced than for oocytes and embryos. Currently, sperm biology is mainly studied in Canids, Felids, Ursids, and Mustelids, with more emphasis on structural than functional properties. Importantly, fundamental studies of gamete and embryo biology in domestic dogs, cats, and ferrets have paved the way for more precise characterizations in wild counterparts as well as the development of cryopreservation and assisted reproductive technologies. A striking feature of spermatozoa across a wide range of Canids and Felids is the presence of teratospermia (>60% of abnormal sperm cells), which is related to the loss of genetic diversity in some populations. Although sperm structures differ across carnivore families, sperm biology remains difficult to compare because of the small amount of data in many species. Regarding oocyte biology and embryology, data are much scarcer than in sperm cells, with too few studies going beyond structural descriptions. More carnivore species and more individuals (especially from wild populations in addition to captive ones) must be studied to improve our understanding about comparative germplasm biology and develop adequate conservation breeding strategies including the use of cryobanking and assisted reproductive technologies.

Progesterone Signaling and Mammalian Ovarian Follicle Growth Mediated by Progesterone Receptor Membrane Component Family Members

How progesterone influences ovarian follicle growth is a difficult question to answer because ovarian cells synthesize progesterone and express not only the classic nuclear progesterone receptor but also members of the progestin and adipoQ receptor family and the progesterone receptor membrane component (PGRMC) family. Which type of progestin receptor is expressed depends on the ovarian cell type as well as the stage of the estrous/menstrual cycle. Given the complex nature of the mammalian ovary, this review will focus on progesterone signaling that is transduced by PGRMC1 and PGRMC2 specifically as it relates to ovarian follicle growth. PGRMC1 was identified as a progesterone binding protein cloned from porcine liver in 1996 and detected in the mammalian ovary in 2005. Subsequent studies focused on PGRMC family members as regulators of granulosa cell proliferation and survival, two physiological processes required for follicle development. This review will present evidence that demonstrates a causal relationship between PGRMC family members and the promotion of ovarian follicle growth. The mechanisms through which PGRMC-dependent signaling regulates granulosa cell proliferation and viability will also be discussed in order to provide a more complete understanding of our current concept of how progesterone regulates ovarian follicle growth.

Role of sex steroids and prostaglandins during the luteal life cycle in domestic cats and lynxes

Although lynxes and domestic cats are both felids, their luteal life cycles differ. As in many species, corpora lutea (CLs) of domestic cats regress after pregnancy or pseudopregnancy. By contrast, CLs of lynxes do not functionally regress following the cycle of their formation. They stay physiologically active and persist for several years. To obtain an improved understanding of the life cycle of both species, we comparatively studied the CLs of these species in detail. In this review, we summarize the similarities and differences of their CLs regarding sex steroid and prostaglandin generation and receptors. The most evident differences were visible in the CLs of lynxes, which persist from previous cycles, compared with CLs of lynxes and domestic cats from the recent luteal cycle. We assume that these differences could indicate processes ensuring long-term luteal survival and functionality, for example, by high estrogen production/metabolism or by antioxidative effects.

Early preantral follicles of the domestic cat express gonadotropin and sex steroid signalling potential

Key biomolecular processes which regulate primordial ovarian follicle dormancy and early folliculogenesis in mammalian ovaries are not fully understood. The domestic cat is a useful model to study ovarian folliculogenesis and is the most relevant for developing in vitro growth methods to be implemented in wild felid conservation breeding programs. Previously, RNA-sequencing of primordial, primary, and secondary follicle samples from domestic cat implicated ovarian steroidogenesis and steroid reception during follicle development. Here we aimed to identify which sex steroid biosynthesis and metabolism enzymes, gonadotropin receptors, and sex steroid receptors are present and may be potential regulators. Differential gene expression, functional annotation, and enrichment analyses were employed and protein localisation was studied too. Gene transcripts for PGR, PGRMC1, AR (steroid receptors), CYP11A1, CYP17A1, HSD17B1 and HSD17B17 (steroidogenic enzymes), and STS (steroid metabolising enzyme) were significantly differentially expressed (Q values of ≤0.05). Differential gene expression increased in all transcripts during follicle transitions apart from AR which decreased by the secondary stage. Immunohistochemistry localised FSHR and LHCGR to oocytes at each stage. PGRMC1 immunostaining was strongest in granulosa cells whereas AR was strongest in oocytes throughout each stage. Protein signals for steroidogenic enzymes were only detectable in secondary follicles. Products of these significantly differentially expressed genes may regulate domestic cat preantral folliculogenesis. In vitro growth could be optimised as all early follicles express gonadotropin and steroid receptors meaning hormone interaction and response may be possible. Protein expression analyses of early secondary follicles supported its potential for producing sex steroids.

Expression of nuclear progesterone receptor, progesterone receptor membrane components 1 and 2 and prostaglandin-endoperoxide synthase 2 in the endometrium and oviduct of spontaneously ovulating cats

Although ovulations not followed by pregnancy occur regularly in cats, differences in endometrial function between cats in the luteal and non-luteal phase have not been studied so far. Progesterone exerts its effects through a nuclear progesterone receptor (PGR) and via cell-membrane bound receptors referred to as progesterone receptor membrane component (PGRMC) 1 and 2. Progesterone receptor expression is regulated by gonadal steroid hormones and therefore may change throughout the oestrous cycle. Protein expression of PGR, PGRMC-1 and 2 and prostaglandin-endoperoxide synthase 2 (PTGS2) was analysed in the endometrium and oviduct of non-pregnant female cats in the follicular (n = 8) and luteal phase (n = 9). We hypothesized that the presence of corpora lutea (CL) is associated with downregulation of progesterone receptors and PTGS2. Cells of the luminal endometrial epithelium, endometrial stroma and oviductal epithelium were assessed by immunohistochemistry. The PGR protein expression was more pronounced in the endometrial epithelium than stroma (p < 0.001) and less pronounced in cats with a CL than without CL (p < 0.001) but did not differ between groups in the oviduct. The PTGS2 was localized only in the endometrial and oviductal epithelium and its expression was reduced in cats with CL (p = 0.001). In the endometrial epithelium, PGRMC-1 expression was reduced in cats with CL (p < 0.05). Expression of PGRMC-2 was highest in the endometrial epithelium and lowest in the endometrial stroma (p = 0.01) but did not differ between cats with and without CL. In conclusion, progesterone receptor and PTGS2 downregulation in the female cat closely resembles findings in other spontaneously ovulating domestic animal species.

Cloprostenol, a synthetic analog of prostaglandin F2α induces functional regression in cultured luteal cells of felids†

In the present study, we investigated the effect of the synthetic analog of prostaglandin F2α (PGF2α)-cloprostenol-on cultured steroidogenic luteal cells of selected felid species over a 2-day culture period. The changes induced by cloprostenol were measured based on progesterone concentration and mRNA expression analysis of selected genes. Cloprostenol significantly reduced concentration of progesterone in cell culture medium of small luteal cells isolated from domestic cat corpora lutea (CL) at the development/maintenance stage (P < 0.05), but did not influence progesterone production in cultured cells from the regression stage. A decrease or complete silencing of progesterone production was also measured in cultured luteal cells of African lion (formation stage) and Javan leopard (development/maintenance stage). Gene-expression analysis by real-time PCR revealed that treatment with cloprostenol did not have an influence on expression of selected genes coding for enzymes of steroidogenesis (StAR, HSD3B, CYP11A1) or prostaglandin synthesis (PTGS2, PGES), nor did it effect hormone receptors (AR, ESR1, PGR, PTGER2), an anti-oxidative enzyme (SOD1) or factors of cell apoptosis (FAS, CASP3, TNFRSF1B, BCL2) over the studied period. Significant changes were measured only for expressions of luteinizing hormone (P < 0.05), prolactin (P < 0.05) and PGF2α receptors (P < 0.005) (LHCGR, PRLR, and PTGFR). The obtained results confirm that PGF2α/cloprostenol is a luteolytic agent in CL of felids and its impact on progesterone production depends on the developmental stage of the CL. Cloprostenol short-term treatment on luteal cells was associated only with functional but not structural changes related to luteal regression.

Breakthroughs and new horizons in reproductive biology of rare and endangered animal species

Because of higher extinction rates due to human and natural factors, more basic and applied research in reproductive biology is required to preserve wild species and design proper strategies leading to sustainable populations. The objective of the review is to highlight recent, inspiring breakthroughs in wildlife reproduction science that will set directions for future research and lead to more successes in conservation biology. Despite new tools and approaches allowing a better and faster understanding of key mechanisms, we still know little about reproduction in endangered species. Recently, the most striking advances have been obtained in nonmammalian species (fish, birds, amphibians, or corals) with the development of alternative solutions to preserve fertility or new information about parental nutritional influence on embryo development. A novel way has also been explored to consider the impact of environmental changes on reproduction-the allostatic load-in a vast array of species (from primates to fish). On the horizon, genomic tools are expected to considerably change the way we study wildlife reproduction and develop a concept of "precision conservation breeding." When basic studies in organismal physiology are conducted in parallel, new approaches using stem cells to create artificial gametes and gonads, innovations in germplasm storage, and more research on reproductive microbiomes will help to make a difference. Lastly, multiple challenges (for instance, poor integration of new tools in conservation programs, limited access to study animals, or few publication options) will have to be addressed if we want reproductive biology to positively impact conservation of biodiversity.

Expression of genes that regulate follicle development and maturation during ovarian stimulation in poor responders

RESEARCH QUESTION

Sex hormone-binding globulin (SHBG), androgen receptor (AR), LH beta polypeptide (LHB), progesterone receptor membrane component 1 (PGRMC1) and progesterone receptor membrane component 2 (PGRMC2) regulate follicle development and maturation. Their mRNA expression was assessed in peripheral blood mononuclear cells (PBMC) of normal and poor responders, during ovarian stimulation.

DESIGN

Fifty-two normal responders and 15 poor responders according to the Bologna criteria were enrolled for IVF and intracytoplasmic sperm injection and stimulated with 200 IU of follitrophin alpha and gonadotrophin-releasing hormone antagonist. HCG was administered for final oocyte maturation. On days 1, 6 and 10 of stimulation, blood samples were obtained, serum hormone levels were measured, RNA was extracted from PBMC and real-time polymerase chain reaction was carried out to identify the mRNA levels. Relative mRNA expression of each gene was calculated by the comparative 2^-DDCt method.

RESULTS

Differences between mRNA levels of each gene on the same time point between the two groups were not significant. PGRMC1 and PGRMC2 mRNA levels were downregulated, adjusted for ovarian response and age. Positive correlations between PGRMC1 and AR (standardized beta = 0.890, P < 0.001) from day 1 to 6 and PGRMC1 and LHB (standardized beta = 0.806, P < 0.001) from day 1 to 10 were found in poor responders. PGRMC1 and PGRMC2 were positively correlated on days 6 and 10 in normal responders.

CONCLUSIONS

PGRMC1 and PGRMC2 mRNA are significantly decreased during ovarian stimulation, with some potential differences between normal and poor responders.

The antioxidative enzyme SOD2 is important for physiological persistence of corpora lutea in lynxes

Corpora lutea (CL) are transient endocrine glands supporting pregnancy by progesterone production. They develop at the site of ovulation from the remaining follicle, are highly metabolically active and undergo distinct, transformative processes during their lifetime. In contrast to other species, CL of lynxes do not regress at the end of cycle, but remain functionally active (persist) for years. Reactive oxygen species (ROS) and anti-oxidative enzymes are described to be important for the functionality of CL. We examined ten anti-oxidative enzymes in fresh and persistent CL of lynxes as well as in domestic cat CL of different luteal stages. The gene expression profiles, especially those of SOD1 and SOD2, showed some remarkable differences between CL stages during non-pregnant and pregnant cycles of domestic cats and between fresh and persistent CL of lynxes. Lynx gene expression profiles of SODs were confirmed by western blot analysis, immunohistochemistry and activity assays. SOD2 was characterized by a conspicuous high expression and enzyme activity exclusively in persistent CL. We suggest that SOD2 is required to detoxify potential elevated superoxide anion levels by producing H₂O₂ in the physiologically persistent CL. This product might also act as a signaling molecule, securing the CL from apoptosis and insuring long-term luteal cell survival.

Progesterone signaling during pregnancy in the lab opossum, Monodelphis domestica

To investigate subtle pregnancy-associated changes in the lab opossum, Monodelphis domestica, an induced ovulator, we compared pregnant with non-pregnant and pseudopregnant animals with regard to serum P₄ levels and progesterone receptor (PR) expression. Using video-verified, time-mated lab opossums as sources of biological material, we compared ovaries, uteri and sera obtained on odd-numbered days of the 14.5-day pregnancy in this animal. Females that mated successfully but did not produce embryos were classified as pseudopregnant. P₄ levels differed significantly between pregnant (N = 21) and either non-pregnant (N = 3) or pseudopregnant (N = 3) opossums, but not between the non-pregnant and pseudopregnant groups. A significant decline in serum P₄ occurred between pregnancy days 3 and 5, coinciding with an elevated probability of pregnancy failure between days 5 and 9. PR was detected in the nuclei of uterine-gland epithelial cells on pregnancy days 5 and 7 as well as variably in the corpora lutea (CL) of animals on pregnancy days 3-11. PR expression in the CL suggests that P₄ may be autostimulatory in lab opossums and that certain levels of this steroid are required during normal pregnancy. The significant day-3 drop in P₄ may explain why pregnancy failure in this polyovular metatherian is likeliest to occur between days 5 and 9, an interval during which the extended period of blastocyst morphogenesis and expansion occurs. Taken together, these results suggest that P₄ may have unrecognized signaling roles not only in pregnancy but perhaps embryonic development as well in the lab opossum.

Steroidogenic enzymes, their products and sex steroid receptors during testis development and spermatogenesis in the domestic cat (Felis catus)

In the present study we comprehensively characterize intratesticular sex steroid production, metabolism and receptors in the domestic cat to elucidate the role of testosterone, estradiol and progesterone in testis development, steroid synthesis and spermatogenesis. There is a great demand for new concepts of fertility control in domestic (feral) cats and wild felids. The acquired knowledge will help to understand the regulation of spermatogenesis in felids, and may reveal new target points for male contraception. Progesterone and androgens are produced throughout all stages of testicular development; their synthesizing enzymes are mainly expressed in Leydig cells, and to a much lesser extent also in tubular cells. Aromatase (CYP19A1), the estrogen synthesizing enzyme, is only present in the tubuli and is first detectable in spermatocytes and round spermatids at puberty. As shown by elevated expression of the enzymes steroid 5-α-reductase type 1 (SRD5A) and aldo-keto-reductase family 1 member C3 (AKR1C3), the capacity to metabolize particular steroids increases during testis development. Apparently, this refers to a decreasing intra-testicular testosterone concentration per mg tissue with increasing testis weight during postpuberty. The increasing potential of sulfation of E2 by estrogen sulfotransferase (SULT1E1) with ongoing development might be responsible for the low level of unconjugated intratesticular estradiol in all stages of development probably due to facilitated excretion of conjugated estrogens. For the first time, expression of the progesterone membrane receptor components 1 and 2 (PGRMC1, PGRMC2) was studied in mammalian testis tissue. Both of these and also the progesterone receptor (PGR) are expressed depending on the developmental stage and cell type, suggesting an important regulatory role of progesterone in the testis. Androgen receptor (AR) is present in almost all cell types except for some spermatogenic cells. The co-localization of aromatase with estrogen receptor alpha (ESR1) in spermatocytes and round spermatids of domestic cat testis indicates an auto-/paracrine function of estrogen in spermatogenesis. In summary, the testis of the domestic cat is an important source of sex steroids. All of them could act within the testis but additionally, at least androgens and estrogens are likely secreted by the testis, partly as conjugated steroids.

Ovarian Follicular Theca Cell Recruitment, Differentiation, and Impact on Fertility: 2017 Update

The major goal of this review is to summarize recent exciting findings that have been published within the past 10 years that, to our knowledge, have not been presented in detail in previous reviews and that may impact altered follicular development in polycystic ovarian syndrome (PCOS) and premature ovarian failure in women. Specifically, we will cover the following: (1) mouse models that have led to discovery of the derivation of two precursor populations of theca cells in the embryonic gonad; (2) the key roles of the oocyte-derived factor growth differentiation factor 9 on the hedgehog (HH) signaling pathway and theca cell functions; and (3) the impact of the HH pathway on both the specification of theca endocrine cells and theca fibroblast and smooth muscle cells in developing follicles. We will also discuss the following: (1) other signaling pathways that impact the differentiation of theca cells, not only luteinizing hormone but also insulinlike 3, bone morphogenic proteins, the circadian clock genes, androgens, and estrogens; and (2) theca-associated vascular, immune, and fibroblast cells, as well as the cytokines and matrix factors that play key roles in follicle growth. Lastly, we will integrate what is known about theca cells from mouse models, human-derived theca cell lines from patients who have PCOS and patients who do not have PCOS, and microarray analyses of human and bovine theca to understand what pathways and factors contribute to follicle growth as well as to the abnormal function of theca.