Ovulatory changes in the wall at the apex of the human Graafian follicle

Hyaluronan and Collagen Are Prominent Extracellular Matrix Components in Bovine and Porcine Ovaries

The extracellular matrix (ECM) is a major component of the ovarian stroma. Collagen and hyaluronan (HA) are critical ovarian stromal ECM molecules that undergo age-dependent changes in the mouse and human. How these matrix components are regulated and organized in other mammalian species with reproductive characteristics similar to women such as cows and pigs, has not been systematically investigated. Therefore, we performed histological, molecular, and biochemical analyses to characterize collagen and HA in these animals. Bovine ovaries had more collagen than porcine ovaries when assessed biochemically, and this was associated with species-specific differences in collagen gene transcripts: Col3a1 was predominant in cow ovaries while Col1a1 was predominant in pig ovaries. We also observed more HA in the porcine vs. bovine ovary. HA was distributed across three molecular weight ranges (<100 kDa, 100-300 kDa, and >300 kDa) in ovarian tissue and follicular fluid, with tissue having more >300 kDa HA than the other two ranges. Transcripts for HA synthesis and degradation enzymes, Has3 and Hyal2, respectively, were predominant in cow ovaries, whereas Has2, Kiaa1199, and Tmem2 tended to be predominant in pig ovaries. Together, our findings have implications for the composition, organization, and regulation of the ovarian ECM in large mammalian species, including humans.

The ovarian stroma as a new frontier

Historically, research in ovarian biology has focused on folliculogenesis, but recently the ovarian stroma has become an exciting new frontier for research, holding critical keys to understanding complex ovarian dynamics. Ovarian follicles, which are the functional units of the ovary, comprise the ovarian parenchyma, while the ovarian stroma thus refers to the inverse or the components of the ovary that are not ovarian follicles. The ovarian stroma includes more general components such as immune cells, blood vessels, nerves, and lymphatic vessels, as well as ovary-specific components including ovarian surface epithelium, tunica albuginea, intraovarian rete ovarii, hilar cells, stem cells, and a majority of incompletely characterized stromal cells including the fibroblast-like, spindle-shaped, and interstitial cells. The stroma also includes ovarian extracellular matrix components. This review combines foundational and emerging scholarship regarding the structures and roles of the different components of the ovarian stroma in normal physiology. This is followed by a discussion of key areas for further research regarding the ovarian stroma, including elucidating theca cell origins, understanding stromal cell hormone production and responsiveness, investigating pathological conditions such as polycystic ovary syndrome (PCOS), developing artificial ovary technology, and using technological advances to further delineate the multiple stromal cell types.

Induction of proteinases in the human preovulatory follicle of the menstrual cycle by human chorionic gonadotropin

OBJECTIVE

To explore the temporal expression in granulosa and theca cells of key members of the MMP and ADAMTS families across the periovulatory period in women to gain insight into their possible roles during ovulation and early luteinization.

DESIGN

Experimental prospective clinical study and laboratory-based investigation.

SETTING

University medical center and private IVF center.

ANIMAL AND PATIENT(S)

Thirty-eight premenopausal women undergoing surgery for tubal ligation and six premenopausal women undergoing assisted reproductive techniques.

INTERVENTION(S)

Administration of hCG and harvesting of follicles by laparoscopy and collection of granulosa-lutein cells at oocyte retrieval.

MAIN OUTCOME MEASURE(S)

Expression of mRNA for matrix metalloproteinase (MMPs) and the A disintegrin and metalloproteinase with thrombospondin-like motifs (ADAMTS) in human granulosa cells and theca cells collected across the periovulatory period of the menstrual cycle and in cultured granulosa-lutein cells after hCG. Localization of MMPs and ADAMTSs by immunohistochemistry.

RESULT(S)

Expression of MMP1 and MMP19 mRNA increased in both granulosa and theca cells after hCG administration. ADAMTS1 and ADAMTS9 mRNA increased in granulosa cells after hCG treatment, however, thecal cell expression for ADAMTS1 was unchanged, while ADAMTS9 expression was decreased. Expression of MMP8 and MMP13 mRNA was unchanged. Immunohistochemistry confirmed the localization of MMP1, MMP19, ADAMTS1, and ADAMTS9 to the granulosa and thecal cell layers.

CONCLUSION(S)

The collection of the dominant follicle throughout the periovulatory period has allowed the identification of proteolytic remodeling enzymes in the granulosa and theca compartments that may be critically involved in human ovulation. These proteinases may work in concert to regulate breakdown of the follicular wall and release of the oocyte.

Structural changes and cell properties of human ovarian surface epithelium in ovarian pathophysiology

The surface epithelial cells of the ovary, which are modified peritoneal cells, form a single, focally pseudostratified layer. The Müllerian ducts differentiate after invagination of the coelomic mesothelium over the gonadal ridges during the 6th week of embryonic life. On the basis of the embryologically putative Müllerian potential of this epithelium, endometriosis can be explained by coelomic metaplasia from the peritoneum, including ovarian surface epithelium. Some pelvic endometriosis specimens have shown that epithelial cells on the ovary or pelvis are serially changed to endometriotic gland cells. Immunohistochemistry as well as scanning electron microscopy also reinforce the light-microscopical findings. A three-dimensional culture system demonstrated that human ovarian surface epithelial cells exhibited a glandular-stromal structure when they were cocultured with endometrial stromal cells in an estrogen-rich environment. Ovarian carcinomas in the epithelial-stromal category are thought to arise from the surface epithelium and its inclusions. The ovarian surface epithelium is physiologically involved in follicular rupture, oocyte release, and the subsequent repair of follicle wall during reproductive age. Simultaneously, ovulation may cause a loss of integrity of the surface epithelium, followed by accumulation of multiple mutations. The cortical invagination, surface stromal proliferation, and Müllerian differentiation of these cells are likely not to be an early step in the cancer development. However, the inclusion cysts are closely related with carcinogenesis because they are significantly more common in ovaries contralateral to those containing epithelial cancers than in control ovaries. As an in vitro study, ovarian carcinoma cell lines were established from simian virus 40 large T antigen-transformed human surface epithelial cells of the ovary. Further investigations of these cell lines may lead to insights into the preneoplastic and early stages of carcinomas. To clarify the pathogenesis of endometriosis and epithelial ovarian cancer, specifically designed studies of ovarian surface epithelium are required.

Pathophysiological Dynamics of Human Ovarian Surface Epithelial Cells in Epithelial Ovarian Carcinogenesis

Epithelial ovarian cancer is responsible for almost half of all the deaths from female genital tract tumors. Major impediments to the clinical treatment of this disease are the relatively asymptomatic progression and a lack of knowledge regarding defined precursor or malignant lesions. Most epithelial ovarian cancers are thought to arise from the transformation of ovarian surface epithelial cells, a single continuous layer of flat-to-cuboidal mesothelial cells surrounding the ovary. To improve our understanding of the pathogenesis of epithelial ovarian cancer, it is necessary to study the biological characteristics of normal ovarian surface epithelial cells. However, this approach has been hampered by the inability to purify and culture such human cells. During the past decade, procedures to isolate and culture human ovarian surface epithelial cells have been developed, and, subsequently, using viral oncogenes, several immortalized cells have been established. This new experimental system is being employed to improve our understanding of the genetic changes leading to the initiation of epithelial ovarian cancer and to identify events in the cancer's development. This review mainly describes the biological dynamics of ovarian surface epithelial cells in the pathogenesis of epithelial ovarian cancer, focusing on humans and excluding small animal models.

Morphodynamics of the follicular-luteal complex during early ovarian development and reproductive life

Female reproductive activity depends upon cyclic morphofunctional changes of the ovarian tissue during the female's fertile period, but the primum movens of an active gonadal rearrangement can be found from early phases of embryo development. To offer a basic account of the main steps of ovarian dynamics, we review the morphofunctional behavior of the follicular-luteal complex in an integrated study using light microscopy and transmission and scanning electron microscopy as well as through the use of numerous drawings. Particular emphasis is given to some reproductive aspects including (1) germ-somatic cell relationships and onset of folliculogenesis during early gonadal development; (2) follicular development and oocyte-follicle cell associations through adult folliculogenesis, finally leading to ovulation; (3) morphodynamics of corpus luteum formation, development, and regression, and (4) degenerative processes involving germ and somatic cells. The results reported, many of which originated in our laboratory, arise from some experiments on laboratory mammals but mostly from a large selection of human specimens. The data obtained are integrated and correlated with classic reports as well as with current views. Crucial biochemical, histophysiological, and clinical aspects are also emphasized.

Characterization and tumorigenicity of human ovarian surface epithelial cells immortalized by SV40 large T antigen

OBJECTIVES

Epithelial ovarian cancers are considered to arise from neoplastic transformation of the ovarian surface epithelium (OSE). However, the earliest events in ovarian carcinogenesis have not been clearly defined because patients are often diagnosed in the advanced stages and useful in vivo and in vitro experimental systems using human OSE cells are lacking. We aimed to improve the availability of experimental models for the study of human ovarian carcinogenesis.

METHODS

Subcultured human OSE cells were transfected with SV40 large T antigen. Resulting OSE cell lines were characterized using immunocytochemistry and tested tumorigenicity.

RESULTS

Six immortalized OSE cell lines were obtained. All cell lines essentially retained the original morphological features of normal OSE cells and showed higher proliferation rates and saturation density. Although they were all nontumorigenic in athymic mice, OSE2b-2 sv cells, which were selected in soft agar from colonies of an SV40 large T antigen-expressing transfectant, OSE2b sv, produced tumors on the peritoneal surface, mesothelium, and diaphragm and induced ascites after being injected intraperitoneally. Solid tumors also grew when mice were inoculated subcutaneously. The tumor cells were formed in a solid sheet arrangement and no evidence of glandular or squamous differentiation was present. They were weakly immunostained with an antibody against cytokeratin, and intercellular junctions resembling attachment devices were ultrastructurally present between cells. The tumors were histologically diagnosed as undifferentiated carcinomas.

CONCLUSIONS

The established cell lines may provide a model system to investigate the mechanisms of cytogenic and molecular changes from normal OSE cells through the various steps of transformation.

On the specificity of prostaglandin and steroid induced inhibition of 3H-proline incorporation in the human follicular wall

Experiments were carried out to elucidate whether the previously reported inhibitory effect of prostaglandin (PG) E2 on 3H-proline incorporation into total protein of specimens from the isolated preovulatory human follicular wall could be exerted also by other prostanoids. Moreover, investigations were designed to explore if the previously documented inhibitory effect of steroids on 3H-proline incorporation could be mediated by endogenously formed PGs. Tissue specimens from the apical wall of follicles were incubated in the presence of PGF2 alpha, 6-keto-PGF1 alpha, progesterone (P) or 17 beta-estradiol (E2). The steroids were added alone or in combination with the PG synthetase blockers, indomethacin or 5, 8, 11, 14-eicosatetraynoic acid. Following incubation with 3H-proline for 2-4 h, the incorporated radioactivity was determined. PGF2 alpha and 6-keto-PGF1 alpha had no effect on 3H-proline incorporation. Both P and E2 induced a significant decrease of 3H-proline incorporation in preovulatory follicles, whereas similar effects in unripe follicles were statistically significant only for P. The steroid effects were not influenced when blockers of PG synthesis were added concomitantly. It is concluded that among the "classical" PGs PGE2 has a unique effect on collagen metabolism in the human follicular wall. E2 and especially P have a similar inhibitory effect on collagen formation as reflected by measurements of 3H-proline incorporation, an effect which does not appear to be primarily mediated by endogenous PGs.

Formation of the rupture site in preovulatory hamster and mouse follicles: loss of the surface epithelium

Changes in the morphology of epithelial cells covering the sides and apex of ovarian follicles were examined in mice and hamsters during the final 13 hr before rupture using light and electron microscopy. At the time of the surge of luteinizing hormone, approximately 13 hr before follicle rupture, epithelial cells along the follicle sides are spherical, covered with microvilli, and remain so throughout the entire cycle. As ovulation approaches, cells at the apex become progressively flatter, increase in diameter, and undergo a reduction in the number and length of microvilli. By 2 hr before ovulation, the microvilli are present only along the boundary between adjacent cells and the cells are in different stages of degeneration. In some cells, the cytoplasm is electron dense and the nuclei are pyknotic. Other cells become electron lucent and cytoplasmic elements are leached from the cell. The apical plasma membrane is lost first over the center of the cell and later over the periphery. Epithelial cells detach from the apex individually until a large patch devoid of cells is formed. This includes the site of eventual rupture. The loss of epithelial cells from the apex of ovarian follicles of other species is compared with our results, and the processes involved in stretching, degeneration, and sloughing of the epithelial cells are discussed.

Visualization of the three-dimensional distribution of collagen fibrils over preovulatory follicles in the hamster

Before an oocyte can escape from a preovulatory follicle, the apical wall must thin to the point of rupture. Although numerous layers of cells are present, it is the collagen fibrils in the theca externa that provide most of the strength to the developing follicle. The three-dimensional distribution and integrity of these fibrils over a follicle cannot be appreciated with standard used methods such as examination of thin sections by transmission electron microscopy In this paper we describe a technique that removes cells superficial to the collagen fibrils so that their distribution may be examined by scanning electron microscopy. On the third day of the hamster's 4-day estrous cycle, bundles of fibrils pass from intrafollicular areas and ascend follicles. Approximately halfway up the follicle wall, the bundles fan out and form a meshwork of fibrils which covers the apex. As the time of ovulation approaches, the number of layers of fibrils decreases over the apex until a tear forms in the weakened matrix. Experimental results demonstrating that the meshwork is composed of collagen fibrils are presented. The usefulness of this technique in visualizing the collagen content in preovulatory follicles is discussed as well as factors that may aid in weakening this layer so that follicle rupture may occur.

Influence of prostaglandin E2 on proteoglycan synthesis in the human ovarian follicle wall

The effect of prostaglandin (PG) E2 on the incorporation of 3H-glucosamine in the human follicular wall was investigated in vitro. Follicles were obtained from women undergoing sterilization via minilaparotomy. Tissue pieces of the follicular wall were incubated in the presence of PGE2 and 3H-glucosamine and the tissue-bound radioactivity was determined. PGE2 induced a significant increase of radiolabelling in the apex of the mature follicle wall but did not significantly affect the incorporation in other parts of the wall, nor in the wall of less developed follicles. The incorporation of glucosamine, a precursor of glucosaminoglycans, is regarded to reflect the synthesis of proteoglycans. The demonstrated increase in the incorporation of 3H-glucosamine in the apical wall of the mature follicle in response to PGE2 indicates that PG-mediated stimulation of proteoglycan synthesis is of importance for follicular rupture.

An ultrastructural study of ovarian perifollicular capillaries in the indomethacin-treated rabbit

The perifollicular capillaries of the rabbit ovary were observed by light and electron microscopy following administration of human chorionic gonadotropin (hCG) and indomethacin (IM). Fenestrations and interendothelial gaps were not observed at 4, 10, or 12 hours, at which times carbon particles were confined to capillary lumina. By 24 hours, dilated capillaries were noted among granulosa cells and theca. In the theca, interendothelial gaps permeable to carbon particles were observed. At 48 hours, ribosome-rich, newly developed capillaries were noted. Many collagen fibrils were observed in the tunica albuginea and theca externa in hCG/IM-treated rabbits in contrast to those treated with hCG alone. Ovarian prostaglandins normally produced in response to gonadotropins may be responsible for alterations in perifollicular capillaries and degradation of collagen in the follicle wall, changes considered essential for ovulation.

Ultrastructural changes of the stigma of the follicle during the process of ovulation in the hen

No structural changes could be observed in the stigma until 2 h before ovulation. Within a few minutes of ovulation, the stratum granulosum and theca interna disappear completely in the middle part of the stigma. By 30 min before ovulation, the rough endoplasmic reticulum in the fibroblasts of the theca externa develops conspicuously. Then a few minutes before ovulation, the theca externa becomes much thinner with a conspicuous disintegration of the collagenous fibers into individual fibrils. These structural changes may contribute to the fragility of the stigma tissue and induce rupture of the follicle.

Collagenolytic enzyme activity in human ovary: an ovulatory enzyme system

Collagenolytic enzyme activities presumed to play an important role in ovulation were investigated in the human follicular apex, base, and granulosa cell layer throughout the ovarian cycle. Those analyzed were human ovarian collagenase, 2,4-dinitrophenyl-Pro-Gln-Gly-Ile-Ala-Gly-Gln-D-Arg-OH peptidase, N-carbobenzoxy-Gly-Pro-Gly-Gly-Pro-Ala peptidase, and alpha-N-benzoyl-DL-arginine beta-naphthylamide hydrolase. Collagenase activity was also measured in human granulosa cell cultures. The activities of all four enzymes showed a marked preovulatory decrease in the apex. The activities in the apex were slightly higher than those in the base throughout the ovarian cycle. However, the activities in the granulosa cell layer and collagenase activity in the granulosa cell cultures increased toward preovulation and decreased after ovulation. These findings suggest that collagenase is synthesized in the granulosa cells maximally at preovulation and is consumed in the follicular apex at the same time, resulting in collagen degradation and disruption of the follicular wall in collaboration with other collagenolytic enzymes investigated here.