Steroidogenic capacity and ultrastructural morphology of cultured ovine luteal cells

Comprehensive proteomic profiling of early antral follicles from sheep

The present study evaluates the proteome of early antral follicles from Ovis aries. Fifty follicles were collected from ovaries of adult ewes and extracted proteins were trypsin-digested, desalted and analyzed by LC-MS/MS. Genes were screened for potential modulation by miRNAs and protein data, subjected to functional enrichment analysis. Label-free mass spectrometry allowed the identification of 2503 follicle proteins, confirming vimentin, actin, lamin, heat shock proteins and histones as the most abundant ones. In silico analyses indicated that miRNAs modulate the expression of genes coding proteins of the sheep follicles involved in cell cycle, cell differentiation, aging, apoptosis, cell death, adipocyte differentiation, cell division. The most important biological processes associated with the follicle proteins were innate immune response, translation, adaptive immune response and protein folding, while molecular functions linked to the proteome of sheep antral follicles related to metal ion binding, ATP binding, oxygen binding, RNA binding and GTP binding, among others. Upload of 2503 Uniport accession codes through DAVID platform matched 1274 genes, associated with translation, metabolic process, proteolysis involved in cellular protein catabolic process, zona pellucida receptor complex and others. KEEG pathways analysis indicated genes correlated with ovine follicular development, with major pathways listed as carbon metabolism, biosynthesis of amino acids, glutathione metabolism, oxidative phosphorylation, fatty acid degradation and oocyte meiosis. This represents a comprehensive atlas of proteins expressed in sheep early antral follicles and will contribute to future identification of biomarkers for follicular development and oocyte maturation.

History, insights, and future perspectives on studies into luteal function in cattle

The corpus luteum (CL) forms following ovulation from the remnant of the Graafian follicle. This transient tissue produces critical hormones to maintain pregnancy, including the steroid progesterone. In cattle and other ruminants, the presence of an embryo determines if the lifespan of the CL will be prolonged to ensure successful implantation and gestation, or if the tissue will undergo destruction in the process known as luteolysis. Infertility and subfertility in dairy and beef cattle results in substantial economic loss to producers each year. In addition, this has the potential to exacerbate climate change because more animals are needed to produce high-quality protein to feed the growing world population. Successful pregnancies require coordinated regulation of uterine and ovarian function by the developing embryo. These processes are often collectively termed "maternal recognition of pregnancy." Research into the formation, function, and destruction of the bovine CL by the Northeast Multistate Project, one of the oldest continuously funded Hatch projects by the USDA, has produced a large body of evidence increasing our knowledge of the contribution of ovarian processes to fertility in ruminants. This review presents some of the seminal research into the regulation of the ruminant CL, as well as identifying mechanisms that remain to be completely validated in the bovine CL. This review also contains a broad discussion of the roles of prostaglandins, immune cells, as well as mechanisms contributing to steroidogenesis in the ruminant CL. A triadic model of luteolysis is discussed wherein the interactions among immune cells, endothelial cells, and luteal cells dictate the ability of the ruminant CL to respond to a luteolytic stimulus, along with other novel hypotheses for future research.

Functional and Morphological Characterization of Small and Large Steroidogenic Luteal Cells From Domestic Cats Before and During Culture

The current study aimed to isolate, culture and characterize small (SLC) and large (LLC) steroidogenic cells from the corpora lutea (CL) of non-pregnant domestic cats. Isolation of feline SLC was based on an enzymatic digestion of luteal tissue, whereas LLC were obtained by mechanical disruption of CL. To assess function of both cell types, progesterone secretion and mRNA expression of selected genes involved in steroid and prostaglandin synthesis were measured, as well as relative transcript abundance of hormone receptors and anti-oxidative enzymes, before and during culture. The cells were cultured for 3 or 5 days without gonadotropins. Isolated feline SLC and LLC had different sizes (12 ± 3 μm vs. 34 ± 5 μm, respectively), morphologies (amount of lipid droplets) and behaved differently in culture. SLC attached and proliferated or spread quickly, but lost their steroidogenic function during culture (significant decrease in progesterone secretion and expression of steroidogenic genes). The expression of receptors for gonadotropins and prolactin also decreased. Prostaglandin synthase (PTGS2) decreased steadily over time, whereas mRNA expression of PGE2 synthase (PGES) increased. The gene expression of anti-oxidative enzyme glutathione peroxidase 4 (GPX4), also increased during culture, but not of superoxide dismutase 1 (SOD1). In comparison to SLC, LLC did not attach to culture plates, secreted more progesterone per inoculated cells and maintained steroidogenic function during culture. Expression of prostaglandin synthases (PTGS2 and PGES) was almost non-detectable. The gene expression of hormone receptors for prostaglandin F2 alpha (PTGFR), gonadotropins (LHCHR and FSHR), and prolactin (PRLR), as well as of anti-oxidative enzymes (GPX4, SOD1), increased over time. To conclude, we successfully isolated and cultured different types of feline steroidogenic luteal cells and comprehensively characterized both isolated cell types. This knowledge can be used to better understand the CL lifecycle in felines more broadly, and the established cell cultures will provide a foundation for future studies on luteolytic and luteotrophic factors in the domestic cat, and for comparison with other feline species, particularly lynx.

Establishment and characterization of a telomerase immortalized porcine luteal cells

Luteal cells play a crucial role in pregnancy through secreting progesterone to maintain pregnancy and support of fetus. However, low cellular yields and inability to passage primary porcine luteal cells (PLCs) in vitro limit the luteal cell study. Therefore, developing an immortalized porcine luteal cell line is necessary for studying luteal cells activity and function in different diseases. In this study, primary PLCs were obtained from gilts at day 30 to day 50 of gestation and immortalized by human telomerase reverse transcriptase (hTERT). The porcine corpus luteal cell line (hTERT-PLCs) expressed hTERT gene steady, maintained high hTERT activity and normal karyotype. The phase contrast microscope and transmission electron microscope observation showed primary PLCs and hTERT-PLCs were polygonal and exhibited abundant mitochondria, smooth endoplasmic reticulum and lipid droplets. 3β hydroxysteroid dehydrogenase (3βHSD) and Oil-Red-O staining showed that hTERT-PLCs at passage 30 and 50 were similar to primary PLCs. The hTERT-PLCs expressed steroidogenesis-related proteins, enzymes and receptors, such as steroidogenic acute regulatory protein, P450 cholesterol side-chain cleavage, 3βHSD, 20αHSD, luteinizing hormone receptor, progesterone receptor, prolactin receptor, estrogen receptorα/β, as well as primary PLCs. Consequently, hTERT-PLCs could secret progesterone and exhibited similar responses to luteinizing hormone and prostaglandin F2α as primary PLCs. In addition, the hTERT-PLCs did not show neoplastic transformation or anchorage independent growth. In summary, we developed an immortalized porcine luteal cell line which maintained its originally morphological, biological and functional characteristics.

Size distribution of steroidogenic and non-steroidogenic ovine luteal cells throughout pregnancy

The present study examines the size distribution of ovine steroidogenic and non-steroidogenic luteal cells throughout pregnancy. Cells were isolated from corpora lutea collected from early (< 8 weeks), mid (9 to 14 weeks) or late (15 to 18 weeks) stages of pregnancy. Cells were stained for 3β-hydroxysteroid dehydrogenase (3β-HSD) activity, a marker for steroidogenic cells. Both 3β-HSD positive and β-HSD negative cells covered a wide spectrum of size ranging from 7 to 37 μm in diameter. There was a significant increase (P > 0·01) in mean diameter of non-steroidogenic luteal cells as pregnancy progressed. Mean diameter of 3β-HSD negative cells increased from 17·8 (s.e. 0·4) μm in the corpus luteum of early stage of pregnancy to 22·4 (s.e. 0·3) μm in the corpus luteum of advanced pregnancy. However, there was no significant increase in the mean diameter of 3β-HSD positive cells. Corpora lutea obtained from early stages of the pregnancy contained more steroidogenic cells than the cells obtained from mid and late pregnancy (P < 0·01). Percentage of 3β-HSD negative cells had increased 2·07-fold by 18 weeks of pregnancy when compared with the early stage of pregnancy. In contrast, percentage of 3β-HSD positive cells had decreased to 50% of starting values during the same period (P < 0·05). These results indicate that the ovine corpus luteum of pregnancy is morphologically dynamic over the course of pregnancy. Steroidogenic activity of luteal cells may decrease as pregnancy progresses, especially activity of the large luteal cells.

Ovarian proteomic study reveals the possible molecular mechanism for hyperprolificacy of Small Tail Han sheep

Small Tail Han sheep is a widely bred farm animal in China which has attracted lots of attention due to their high prolificacy and year-round estrus. However, the molecular mechanism of its fecundity remains unrevealed. The FecB gene polymorphism has been found to be associated with the ovulation rate and litter size of sheep. In the present study, we constructed an iTRAQ-based quantitative proteomics analysis to compare the ovarian proteomes of FecB+FecB+ genotype Small Tail Han sheep ewes (Han ++), FecB^BFecB^B Han ewes (Han BB) and Dorset ewes (Dorset). Hundreds of differentially expressed proteins between each two groups were identified; GO and KEGG pathway analysis indicated that the expressions of those proteins involved in ribosome assembly, protein translation and mTOR pathway between Dorset and both Han groups were highly different. Between Han ++ and Han BB groups, higher level of protein expressions were related to mitochondrial oxidation functions such as oxidoreductase activity, cytochrome-c oxidase activity and electron carrier activity. This was identified in Han BB group, which may contribute to the elevated ovulation rate of Han BB ewes. In conclusion, our work provided a prospective understanding of the molecular mechanism for high prolificacy of Small Tail Han sheep.

Proliferation and progesterone production of ovine luteal cells from several stages of the estrous cycle: effects of fibroblast growth factors and luteinizing hormone

This study was conducted to evaluate the effects of fibroblast growth factor 1 (FGF-1), fibroblast growth factor 2 (FGF-2), or luteinizing hormone (LH) on proliferation and progesterone secretion of ovine luteal cells from days 5, 10, or 15 after estrus (estrus = day 0; n = 4 or 5 ewes/day). After enzymatic dispersion, luteal cells were incubated in the presence or absence of various doses of FGF-1, FGF-2, LH, or fetal bovine serum (FBS) (positive control) in serum-free media for 7 days in 24-well plates. Cells were counted on day 7 of culture and media analyzed for progesterone concentration. For all treatments, maximal effects (Emax) and dissociation constants (KD) were calculated. In addition, luteal cells were cultured in eight-chamber slides and treated as above, but on day 7 of culture cells were fixed and stained for the presence of 3beta-hydroxy-delta 5-steroid dehydrogenase (3beta HSD). The number of steroidogenic (3beta HSD positive) cells per unit area was counted for control cultures (no treatment) and cultures treated with the most effective doses of FGF-1, FGF-2, LH, OR FBS in proliferation and (or) progesterone assays. FGF-1, FGF-2, AND FBS stimulated (p < 0.05) proliferation of luteal cells from all stages of luteal development in a dose-dependent manner. In addition, LH increased (p < 0.01) the number of 3beta HSD-positive cells across all stages of luteal development. Moreover, LH and FBS increased (p < 0.05) progesterone secretion by luteal cells from all stages in a dose-responsive manner, but the effects of FGF-1 and FGF-2 were variable. For proliferation, the Emax of all factors was greatest (p < 0.01) on day 5, whereas the KD values were similar across days of the estrous cycle. For progesterone production, the Emax and KD of LH and FBS were similar and did not differ across the estrous cycle. These data demonstrate the luteal cells from the early luteal phase of the estrous cycle exhibit the greatest ability to proliferate and (or) increase their progesterone secretion in response to FGF-1, FGF-2, LH, or FBS. In addition, although LH does not affect the total number of luteal cells in culture, it does increase the number of steroidogenic cells. These data indicate that in addition to LH, fibroblast growth factors may be involved in regulation of luteal growth and differentiation in ewes.

Isolation of granulosa-like cells from the bovine secretory corpus luteum and their characterization in long-term culture

BACKGROUND

The isolation of cells termed type 5 from the bovine corpus luteum was recently reported. Since these cells were reminiscent of immature granulosa cells, their morphological and functional relationship requires further investigation in view of the novel concept of corpus luteum growth. It suggests that putative stem cells of unknown origin supply the pool of small luteal cells.

METHODS

Bovine corpora lutea were mechanically dispersed, cell suspensions separated over a Percoll density gradient, and type 5 cells purified by colony transfer. Granulosa cells were harvested from small-sized antral follicles. Observations were carried out at the light and electron microscopical level. 3 beta-Hydroxy-steroid-dehydrogenase was localized histochemically in addition to intracellular lipid droplets stained with nile red. Immunolocalization was used to study Factor VIII antigen presence, the architecture of the cytoskeleton, as well as the occurrence of neuronal cell adhesion molecules, and of neuronal cadherin-like molecules. The uptake of acetylated low density lipoprotein was examined. As for progesterone concentration, cells were seeded at low density on day zero. Cell numbers and progesterone levels of supernatants were determined on day 10 in culture.

RESULTS AND CONCLUSIONS

Type 5 cells behaved morphologically like immature granulosa cells, yet the total cell number and the progesterone concentration differed for type 5 cells compared to granulosa cells. The addition of LH had no influence on the progesterone concentration as seen for either type 5 cells or for granulosa cells. It is concluded that type 5 cells, which were originally mistaken for microvascular endothelial cells, display similarities with immature granulosa cells. Type 5 cells may play a role in renewal of luteal cells.

Evaluation of the physiological value of porcine luteal cells isolated in various stages of the luteal phase: Tissue culture approach

Porcine luteal cells were collected from corpora lutea in four different stages of the luteal phase and cultured as monolayers. Progesterone (P4) secretion was assayed using radioimmunoassays (Gregoraszczuk, 1991). Luteal cells cultured from porcine corpora lutea collected in the early luteal phase maintained steroidogenic capacity for 6 days in culture until the time comparable with midluteal corpora lutea. Luteal cells collected from mature and regressing corpora lutea did not dedifferentiate during 2 days of culture. After this time secretion of progesterone decreased to undetectable amounts characteristic of old corpora lutea. The regression in the culture progressed. The results demonstrate that the degree of the decline of progesterone depends on the type of corpus luteum, which is connected to particular time intervals of the luteal phase. Before starting experiments it is necessary to take into consideration the stage of the luteal phase from which the material is collected for culture. This study provides evidence that long term culture is useful for investigating a variety of aspects of luteal function only if cells are collected in the early luteal phase. Short term culture is suitable for investigation of cells collected from mid and late luteal phase. Regulation of luteal function is dependent on stage of the luteal phase.

Cellular composition and steroidogenic capacity of the ovary of Macrotus californicus (Chiroptera: Phyllostomatidae) during and after delayed embryonic development

In the leaf-nosed bat, Macrotus californicus, a 4.5-month period of delayed early embryogenesis (October-March) precedes a 3.5-month period of normal embryogenesis (March-June). This prolonged gestation provides a unique opportunity to correlate ovarian changes with the events following implantation. The present study investigated luteal cell development and follicular biology during gestation. Circulating progesterone (P) levels following implantation were unchanged before transition to normal development, and were maximal at the start of active gestation. Luteal cell diameters increased during this period. Serum P levels declined prior to parturition, when cells staining positive for 3 beta-hydroxy-5-steroid dehydrogenase-5,4-isomerase (3 beta-HSD) activity were reduced in number and diameter, and enzyme staining was less intense in tissue slices. Subcellular steroidogenic organelles were present during delayed development, but smooth endoplasmic reticulum (SER) was markedly increased after the resumption of normal development at which time also luteal cells reacted positively to staining for 17 beta-HSD. Before parturition, lipid droplet accumulation and reduced SER suggested a reduction in steroid secretion. Large multilaminar follicles stained positive for 3 beta-HSD activity throughout gestation and for 17 beta-HSD except in late delayed development. Thus, the delay in embryogenesis may be due to an inadequately developed corpus luteum or to the steroidogenic activity of the multilaminar follicles.