Mechanisms controlling the function and life span of the corpus luteum.

The primary function of the corpus luteum is secretion of the hormone progesterone, which is required for maintenance of normal pregnancy in mammals. The corpus luteum develops from residual follicular granulosal and thecal cells after ovulation. Luteinizing hormone (LH) from the anterior pituitary is important for normal development and function of the corpus luteum in most mammals, although growth hormone, prolactin, and estradiol also play a role in several species. The mature corpus luteum is composed of at least two steroidogenic cell types based on morphological and biochemical criteria and on the follicular source of origin. Small luteal cells appear to be of thecal cell origin and respond to LH with increased secretion of progesterone. LH directly stimulates the secretion of progesterone from small luteal cells via activation of the protein kinase A second messenger pathway. Large luteal cells are of granulosal cell origin and contain receptors for PGF(2alpha) and appear to mediate the luteolytic actions of this hormone. If pregnancy does not occur, the corpus luteum must regress to allow follicular growth and ovulation and the reproductive cycle begins again. Luteal regression is initiated by PGF(2alpha) of uterine origin in most subprimate species. The role played by PGF(2alpha) in primates remains controversial. In primates, if PGF(2alpha) plays a role in luteolysis, it appears to be of ovarian origin. The antisteroidogenic effects of PGF(2alpha) appear to be mediated by the protein kinase C second messenger pathway, whereas loss of luteal cells appears to follow an influx of calcium, activation of endonucleases, and an apoptotic form of cell death. If the female becomes pregnant, continued secretion of progesterone from the corpus luteum is required to provide an appropriate uterine environment for maintenance of pregnancy. The mechanisms whereby the pregnant uterus signals the corpus luteum that a conceptus is present varies from secretion of a chorionic gonadotropin (primates and equids), to secretion of an antiluteolytic factor (domestic ruminants), and to a neuroendocrine reflex arc that modifies the secretory patterns of hormones from the anterior pituitary (most rodents).

Regulation of ovarian extracellular matrix remodelling by metalloproteinases and their tissue inhibitors: effects on follicular development, ovulation and luteal function.

In most organs, remodelling of tissues after morphogenesis is minimal; however, normal ovarian function depends upon cyclical remodelling of the extracellular matrix (ECM). The ECM has a profound effect on cellular functions and probably plays an important role in the processes of follicular development and atresia, ovulation, and development, maintenance and regression of corpora lutea. Matrix metalloproteinases (MMPs; collagenases, gelatinases, stromelysins and membrane-type MMPs) cleave specific components of the ECM and are inhibited by tissue inhibitors of metalloproteinases (TIMPs). MMPs have been detected at all stages of follicular development and probably modulate follicular expansion or atresia within the ovarian stroma. In addition, increased MMP activity appears to be required for ovulation since follicular rupture occurred in the absence of plasminogen activator activity and inhibitors of MMPs blocked follicular rupture. Development and luteolysis of the corpus luteum are accompanied by extensive remodelling of the ECM. Differentiation and regression of luteal cells are associated with construction and degradation of ECM, respectively. There is increasing evidence that ECM components enhance luteinization; whereas loss of ECM results in luteal cell death. Ovine large luteal cells may be the primary type of cell responsible for controlling the extent of remodelling of luteal ECM since they produce TIMP-1, TIMP-2 and plasminogen activator inhibitor 1. The ratio of active MMPs to TIMPs may be important in maintaining an ECM microenvironment conducive to the differentiation of follicular-derived cells into luteal cells, and maintenance of the phenotype of luteal cells.

Concentration of mRNA encoding 3 beta-hydroxysteroid dehydrogenase/delta 5,delta 4 isomerase (3 beta-HSD) and 3 beta-HSD enzyme activity following treatment of ewes with prostaglandin F2 alpha.

The objectives of these experiments were (1) to determine if prostaglandin F2 alpha (PGF2 alpha) decreased mRNA encoding 3 beta-hydroxysteroid dehydrogenase/d5,delta 4 isomerase (3 beta-HSD) specifically in large steroidogenic luteal cells, which contain the high affinity receptors for PGF2 alpha; and (2) to determine if the decreased concentration of mRNA encoding 3 beta-HSD following administration of PGF2 alpha was associated with a decrease in 3 beta-HSD enzyme activity. Ewes on days 11 or 12 of the estrous cycle were administered PGF2 alpha (25 mg i.v. followed by 10 mg i.m. 2 h later) and corpora lutea collected 4, 12, 24, or 48 h later (n = 4-5/time). Corpora lutea were also collected from non-injected (n = 4) or saline-injected (n = 4) control ewes. Administration of PGF2 decreased (P < 0.05) steady-state concentrations of mRNA encoding 3 beta-HSD to 35, 15, 9, and 5 percent of the concentrations in the control group at 4, 12, 24, and 48 h, respectively. Concentrations of mRNA encoding 3 beta-HSD in large luteal cells were decreased to 43% of controls 4 h following injection, which was similar to the decrease seen in steady-state concentrations of this mRNA in total luteal mRNA (35%). However, 3 beta-HSD enzyme activity was not significantly decreased by 48 h after PGF2 alpha injection. Thus, the dramatic decreased in mRNA encoding 3 beta-HSD was not associated with an immediate decrease in 3 beta-HSD enzyme activity and, therefore, does not appear to be responsible for the acute decrease in secretion of progesterone from ovine luteal tissue during PGF2 alpha-induced luteolysis.

Tissue inhibitor of metalloproteinase-1 concentrations are attenuated in peritoneal fluid and sera of women with endometriosis and restored in sera by gonadotropin-releasing hormone agonist therapy.

OBJECTIVE: To establish tissue inhibitor of metalloproteinase-1 (TIMP-1) concentrations in peritoneal fluid (PF) and sera of women with endometriosis and compare them to disease-free controls. DESIGN: Prospective randomized study. SETTING: Academic medical center. PATIENT(S): Women with laparoscopically documented endometriosis and disease-free women of reproductive age. INTERVENTION(S): Peritoneal fluid and sera were collected, and some women received gonadotropin-releasing hormone agonist (GnRH-a) therapy for endometriosis. MAIN OUTCOME MEASURE(S): Peritoneal fluid and sera TIMP-1 concentrations were measured with a specific RIA. RESULT(S): The TIMP-1 concentrations were significantly lower in PF and sera of women with endometriosis compared with disease-free women. The GnRH-a therapy restored serum TIMP-1 concentrations. CONCLUSION(S): Aberrant expression and localization of TIMP-1 may derange the proteolytic milieu of the peritoneal cavity and contribute to the etiology and underlying physiologic sequelae associated with endometriosis. Measurement of TIMP-1 in serum may aid in diagnosing endometriosis and assist with monitoring treatment efficacy in women with this disease.

Matrix metalloproteinases and tissue inhibitors of metalloproteinases in ovarian function.

Growth and ovulation of follicles, and development, maintenance, and regression of the corpus luteum depend on cyclical remodelling of the extracellular matrix. The extracellular matrix consists of proteinaceous and non-proteinaceous components and provides the tissue-specific, extracellular architecture to which cells attach, and modulates the activities of cells through cell surface receptors. Specific components of the extracellular matrix are cleaved by matrix metalloproteinases, the activities of which are inhibited by tissue inhibitors of metalloproteinases. This review presents evidence for the involvement of matrix metalloproteinases and their inhibitors in extracellular matrix remodelling associated with ovarian function.

Messenger ribonucleic acid encoding monocyte chemoattractant protein-1 is expressed by the ovine corpus luteum in response to prostaglandin F2alpha.

To investigate expression of monocyte chemoattractant protein-1 (MCP-1) in the ovine corpus luteum, a partial cDNA was produced by reverse transcription-polymerase chain reaction. This cDNA was 89% identical to that reported for bovine MCP-1 mRNA. In experiment 1, steady-state concentrations of mRNA encoding MCP-1 were measured in pools of luteal tissue collected on Days 3, 6, 9, 12, and 15 of the estrous cycle (estrus = O; n = 4/day). There were no differences in mRNA concentrations for MCP-1 among any of the days studied (p = 0.43). In experiment 2, midluteal-phase corpora lutea were collected from ewes at 0 (untreated), 2, 4, 8, and 16 h after administration of a luteolytic dose of prostaglandin F2alpha (PGF2alpha; n = 4/time point). Concentrations of MCP-1 mRNA were undetectable in untreated controls, were detectable at 2 h post-treatment, had increased 4 and 8 h after administration of PGF2alpha when compared to those at 2 h (p < 0.05), and were decreased 16 h after administration of PGF2alpha when compared to those at 4 h (p < 0.05). In situ hybridization for MCP-1 mRNA combined with immunocytochemical labeling of tissue inhibitor of metalloproteinase-1 (TIMP-1) in large luteal cells was used to determine whether the steroidogenic cells that have PGF2alpha receptors express MCP-1 mRNA in response to PGF2alpha. Messenger RNA encoding MCP-1 and TIMP-1 were not colocalized, indicating that MCP-1 was not expressed by large steroidogenic luteal cells during luteolysis.

Expression of tissue inhibitor of metalloproteinase-1 protein and messenger ribonucleic acid by the oviduct of cyclic, early-pregnant, and ovariectomized steroid-treated gilts.

It has been suggested that tissue inhibitor of metalloproteinases (TIMP)-1 has a role in reproductive tissues, regulating tissue remodeling or enhancing embryonic development. Oviductal TIMP-1 mRNA levels and protein expression were examined in gilts during the estrous cycle and early pregnancy and in steroid-treated ovariectomized (OVX) gilts by explant culture, two-dimensional SDS-PAGE and fluorography, dot-blot hybridization, immunoblot analysis, RIA, and immunocytochemical studies. TIMP-1 mRNA levels in the oviduct during the estrous cycle were greater (p < 0.02) on Days 2, 15, and 18 than on other days examined, and analysis of oviductal functional segments indicated an effect of day (p < 0.003), an effect of segment (p < 0.007), and a day x segment effect (p < 0.03). The level of TIMP-1 mRNA was greater (p < 0.003) in the isthmus (I) on Day 2 than in the ampulla (A) or infundibulum (INF) or on other days examined (0 and 12). In steroid-treated OVX gilts, an effect of treatment with estradiol valerate (EV) + progesterone (P4) was shown with increased (p < 0.003) TIMP-1 mRNA levels. De novo synthesis of TIMP-1 protein was found throughout the estrous cycle and early pregnancy in all functional segments, but protein expression was greater in the I and greatest on Day 2. In steroid-treated OVX gilts, TIMP-1 protein synthesis was greatest in the I regardless of treatment, but with increased intensity after EV+P4 treatment. TIMP-1 protein was found in oviductal flushings during the estrous cycle and early pregnancy, and in steroid-treated OVX gilts regardless of day, status, or treatment. Differences in TIMP-1 concentrations in oviductal fluid were found by day (p < 0.001), with breed differences detected between the Meishan and standard Western breeds. TIMP-1 protein was immunolocalized primarily to luminal epithelium of the INF, A, and I on all days of the estrous cycle and early pregnancy and to some cells in the stroma and blood vessel walls. Staining intensity correlated with TIMP-1 protein levels in oviductal flushings. The role of TIMP-1 in the oviduct remains to be established.

Concentration of tissue inhibitor of metalloproteinases (TIMP)-1 in ovine follicular fluid and serum.

Tissue inhibitor of metalloproteinases (TIMP)-1 mRNA and protein localize within granulosal cells of post-gonadotropin-surge follicles and luteal tissue in ewes. Our objectives were to test the hypotheses that 1) follicular fluid concentration of TIMP-1 increases following a gonadotropin surge induced by LHRH agonist (Exp. 1) and 2) luteal status affects peripheral serum concentration of TIMP-1 (Exp. 2 and 3). In Exp. 1, the concentration of TIMP-1 within antral fluid from post-surge follicles (28.7 +/- 6.65 microg/mL) was greater (P < .02) than from pre-surge follicles (2.37 +/- 2.47 microg/mL). In Exp. 2, serum concentration of TIMP-1 did not differ among d 0 to 6 (1.27 +/- .55 microg/mL) of the estrous cycle or among periods of luteal maintenance (1.29 +/- .06 microg/mL), spontaneous luteal regression (1.19 +/- .09 microg/mL), or luteal development (1.22 +/- .08 microg/mL). However, serum concentration of TIMP-1 was greater ( P < .001) during the period of luteal maintenance (1.14 +/- .04 microg/mL) than during PGF2alpha-induced luteolysis (d 26; .85 +/- .06 microg/mL) and induced luteal absence (d 27 to 33; .95 +/- .05 microg/mL). In Exp. 3, ewes (n = 14) were bled daily from d 1 to 19 (d 0 = estrus) and at 12-min intervals for 6 h on d 3, 10, and 17. Although concentration of TIMP-1 varied considerably within and among ewes, mean concentration of TIMP-1 per ewe per day increased ( P < .05) from d 3 to 17. These data indicate that follicular fluid concentration of TIMP-1 increases following a gonadotropin surge, but the contribution of ovarian derived TIMP-1 to peripheral serum concentration is negligible.

Immunolocalization of tissue inhibitor of metalloproteinases-1 within ovine periovulatory follicular and luteal tissues.

In previous studies, tissue inhibitor of metalloproteinases (TIMP)-1 mRNA increased in follicular tissue after the preovulatory gonadotropin surge and was expressed in luteal tissue. However, the localization of TIMP-1 protein within ovine periovulatory follicular and luteal tissues is unknown. The objectives of the present study were to 1) localize TIMP-1 within follicles collected before and after a preovulatory gonadotropin surge and within Day 3 and Day 10 corpora lutea (CL), 2) determine whether TIMP-1 was colocalized to Day 10 luteal cells with oxytocin or TIMP-2, and 3) determine whether TIMP-1 was present within secretory granules of large luteal cells. Ovaries were removed from ewes before (presurge; n = 4) or 12-14 h after (postsurge; n = 5) an LHRH-induced gonadotropin surge (36 h following PGF2 alpha-induced luteolysis; objective 1). Additionally, ovaries containing CL were collected on Days 3 (n = 5; objective 1) and 10 (n = 4, 3, and 2 for objectives 1, 2, and 3, respectively). TIMP-1 immunoreactivity was observed within the granulosa cells of postsurge but not presurge follicles. On Days 3 and 10, TIMP-1 was localized within luteal tissue in a cell-specific manner. On Day 10, many of the cells that were immunopositive for TIMP-1 were judged to be large luteal cells on the basis of morphology (diameter > 22 microns; round nucleus) and colocalization with oxytocin and TIMP-2. Electron microscopy demonstrated that TIMP-1 was localized to secretory granules undergoing exocytosis from Day 10 large luteal cells. These data indicate that TIMP-1 is produced by granulosa cells following a gonadotropin surge and is packaged in secretory granules by large steroidogenic cells of the ovine CL.

Mechanisms associated with corpus luteum development.

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.