Angiogenesis in the corpus luteum

Defective blood vessel development and pericyte/pvSMC distribution in alpha 4 integrin-deficient mouse embryos

Blood vessel development is in part regulated by pericytes/presumptive vascular smooth muscle cells (PC/pvSMCs). Here, we demonstrate that interactions between PC/pvSMCs and extracellular matrix play a critical role in this event. We show that the cranial vessels in alpha4 integrin-deficient mouse embryos at the stage of vessel remodeling are increased in diameter. This defect is accompanied by a failure of PC/pvSMCs, which normally express alpha4beta1 integrin, to spread uniformly along the vessels. We also find that fibronectin but not VCAM-1 is localized in the cranial vessels at this stage. Furthermore, cultured alpha4 integrin-null PC/pvSMCs plated on fibronectin display a delay in initiating migration, a reduction in migration speed, and a decrease in directional persistence in response to a polarized force of shear flow. These results suggest that specific motile activities of PC/pvSMCs regulated by mechanical signals imposed by the interstitial extracellular matrix may also be required in vivo for the distribution and function of the PC/pvSMCs during blood vessel development.

Temporal and spatial expression of MMP-2,-9,-14 and their inhibitors TIMP-1,-2,-3 in the corpus luteum of the cycling rhesus monkey

The corpus luteum (CL) is a transient endocrine organ that secretes progesterone to support early pregnancy. If implantation is unsuccessful, luteolysis is initiated. Extensive tissue remodeling occurs during CL formation and luteolysis. In this study, we have studied the possible involvement of MMP-2, -9, -14, and their inhibitors, TIMP-1, -2, -3 in the CL of cycling rhesus monkey at various stages by in situ hybridization, immunohistochemistry and microscopic assessment. The results showed that the MMP-2 mRNA and protein were mainly expressed in the endothelial cells at the early and middle stages of the CL development, while their expressions were observed in the luteal cells at the late stage during luteal regression. MMP-9 protein was detected in the CL at the early and middle stages, and obviously increased at the late stage. The expressions of MMP-14 and TIMP-1 mRNA were high at the early and late stages, and low at the middle stage. TIMP-2 mRNA was high throughout all the stages, the highest level could be observed at the late stage. The TIMP-3 production was detected throughout all the stages, but obviously declined during CL regression. MMP-9, -14 and TIMP-1, -2, -3 were mainly localized in the cytoplasm of the steroidogenic cells. The results suggest that the MMP/TIMP system is involved in regulation of CL development in the primate, and the coordinated expression of MMP-2, -14 and TIMP-1, -3 may have a potential role in the CL formation and the functional maintaining, while the interaction of MMP-2, -9, -14 and TIMP-1, -2, -3 might also play a role in CL regression at the late stage of CL development in the primate.

hCG-dependent regulation of angiogenic factors in human granulosa lutein cells

As prerequisite for development and maintenance of many diseases angiogenesis is of particular interest in medicine. Pathologic angiogenesis takes place in chronic arthritis, collagen diseases, arteriosclerosis, retinopathy associated with diabetes, and particularly in cancers. However, angiogenesis as a physiological process regularly occurs in the ovary. After ovulation the corpus luteum is formed by rapid vascularization of initially avascular granulosa lutein cell tissue. This process is regulated by gonadotropic hormones. In order to gain further insights in the regulatory mechanisms of angiogenesis in the ovary, we investigated these mechanisms in cell culture of human granulosa lutein cells. In particular, we determined the expression and production of several angiogenic factors including tissue inhibitor of matrix metalloproteinases-1 (TIMP-1), Leptin, connective tissue growth factor (CTGF), meningioma-associated complimentary DNA (Mac25), basic fibroblast growth factor (bFGF), and Midkine. In addition, we showed that human chorionic gonadotropin (hCG) has distinct effects on their expression and production. hCG enhances the expression and production of TIMP-1, whereas it downregulates the expression of CTGF and Mac25. Furthermore it decreases the expression of Leptin. Our results provide evidence that hCG determines growth and development of the corpus luteum by mediating angiogenic pathways in human granulosa lutein cells. Hence we describe a further approach to understand the regulation of angiogenesis in the ovary.

The role of pericytes in blood-vessel formation and maintenance

Blood vessels are composed of two interacting cell types. Endothelial cells form the inner lining of the vessel wall, and perivascular cells--referred to as pericytes, vascular smooth muscle cells or mural cells--envelop the surface of the vascular tube. Over the last decades, studies of blood vessels have concentrated mainly on the endothelial cell component, especially when the first angiogenic factors were discovered, while the interest in pericytes has lagged behind. Pericytes are, however, functionally significant; when vessels lose pericytes, they become hemorrhagic and hyperdilated, which leads to conditions such as edema, diabetic retinopathy, and even embryonic lethality. Recently, pericytes have gained new attention as functional and critical contributors to tumor angiogenesis and therefore as potential new targets for antiangiogenic therapies. Pericytes are complex. Their ontogeny is not completely understood, and they perform various functions throughout the body. This review article describes the current knowledge about the nature of pericytes and their functions during vessel growth, vessel maintenance, and pathological angiogenesis.

Animal models of placental angiogenesis

The study of the development of the fetal membranes is an ancient one, and the importance of placental vascular development to placental function has long been recognized. Animal models have been important in these studies, as they allow for controlled experiments and analysis of multiple time-points during pregnancy. Since the demonstration nearly 20 years ago that the placenta produces angiogenic factors, the major factors regulating placental angiogenesis have been identified. These major factors include vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), the angiopoietins (ANG), and their receptors. Recently, sophisticated computerized image analysis methods have been developed to establish the pattern of placental vascular development in sheep. The maternal placental capillary bed develops primarily by increased size of capillaries, with only small increases in capillary number or surface densities. In contrast, the microvasculature of the fetal placenta develops primarily by increased branching, resulting in a large increase in capillary number and surface densities. These observations help to explain the relatively large increase in umbilical blood flow and nutrient delivery to the fetus that occurs during the last half of gestation. In addition, expression of mRNAs for VEGF, bFGF, ANG, and their receptors have recently been correlated with normal placental vascular development in sheep, and further refinement of these mathematical models is warranted. Lastly, the recent development of animal models of compromised pregnancies, including those resulting from maternal nutrition (both restriction and excess), multiple fetuses, environmental stress (heat stress and high altitude), and fetal and maternal breed effects, has already indicated that reductions in placental vascular development and expression of angiogenic factors are probably a root cause of fetal growth restriction. With these methods and models now in place, we should soon be able to establish the mechanisms involved in both normal and abnormal placental angiogenesis.

Follicular fluid levels of vascular endothelial growth factor and early corpus luteum function during assisted reproductive technology cycles

Background

The relation between vascular endothelial growth factor (VEGF) and early luteal function has rarely been proven in humans. The purpose of this study was to define the relation between follicular fluid concentrations of VEGF (FF VEGF) and early luteal function at the preimplantation stage during assisted reproductive technology (ART) cycles.

Methods

71 women were divided into two groups, based on reproductive outcome: women who became pregnant after embryo transfer (ET) (n = 18, Group A) and non-pregnant women (n = 53, Group B). Serum progesterone (Se P) and inhibin A on ET day, and FF VEGF levels were measured in all women. Data were expressed as mean ± standard deviation. Statistical analysis was performed using Excel Office 98 for Student's t-test, linear regression test and chi-square test. A p value of < 0.05 was considered statistically significant.

Results

The groups were comparable for age, ovarian reserve, number and quality of the oocytes retrieved and of the embryos obtained and transferred. FF VEGF levels were increased (4235 ± 1433 vs 3432 ± 1231 pg/ml), while Se P and inhibin A levels were significantly reduced (83.1 ± 34.1 vs 112.0 ± 58.8 ng/ml and 397.4 ± 223 vs 533.5 ± 283 pg/ml, respectively) in the non-pregnant group and were negatively correlated with FF VEGF (r = -0.482, p < 0.05; r = -0.468, p < 0.05) only in pregnant women.

Conclusion

Much has to be learned about the regulation and role of VEGF during the early luteal phase. We advance the hypothesis that the existence of a negative correlation between FF VEGF/Se P and FF VEGF/inhibin A in pregnant women might indicate the existence of a normal VEGF-mediated paracrine response when Se P and inhibin A levels are decreased. Excess production of FF VEGF and the absence of a correlation between FF VEGF/Se P and FF VEGF/inhibin A in non-pregnant women may be a paracrine reaction to immature luteal vasculature, resulting in luteal dysfunction.

Blood flow: a key regulatory component of corpus luteum function in the cow

Prostaglandin F2alpha (PGF2alpha) is the primary luteolysin in the cow. During the early luteal phase, the corpus luteum (CL) is resistant to the luteolytic effect of PGF2alpha. Once mature, the CL becomes responsive to PGF2alpha and undergoes luteal regression. These actions of PGF2alpha coincide with changes in luteal blood flow (BF): PGF2alpha has no effect on BF in the early CL, but acutely increases BF in the peripheral vasculature of the mature CL within 30 min of PGF2alpha injection. During spontaneous luteolysis, luteal BF increases on Days 17-18 of the estrous cycle, prior to any decrease in plasma progesterone (P). The increase in luteal BF is synchronous with an increase in plasma PGFM levels, suggesting that pulsatile release of PGF2alpha from uterus stimulates the increase in luteal BF. Serial biopsies of these CL showed that mRNA expression for endothelial nitric oxide synthase (eNOS) together with endothelin-1 (ET-1) and angiotensin converting enzyme (ACE) increases on Days 17-18 when the luteal BF is elevated. On Day 19 when plasma P level firstly decreases, eNOS mRNA returns to the basal level whereas ET-1 and ACE mRNA remains elevated. Cyclooxygenase-2 (COX-2) mRNA expression increases on Day 19. In support of these data, an in vivo microdialysis study revealed that luteal ET-1 and angiotensin II (Ang II) secretion increases and precedes PGF2alpha secretion during spontaneous luteolysis. In conclusion, we show for the first time that an acute increase of BF occurs in the peripheral vasculature of the mature CL together with increases in eNOS expression and ET-1 and Ang II secretion in the CL during the early stages of luteolysis in the cow. We propose that the increase in luteal BF may be induced by NO from large arterioles surrounding the CL, and simultaneously uterine or exogenous PGF2alpha directly increases ET-1 and Ang II secretion from endothelial cells of microcapillary vessels within the CL, thereby suppressing P secretion by luteal cells. Taken together, our results indicate that an acute increase in luteal BF occurs as a first step of luteolysis in response to PGF2alpha. Therefore, local BF plays a key role to initiate luteal regression in the cow.

The yin and yang of corpus luteum-derived endothelial cells: balancing life and death

A dense network of capillaries irrigates the corpus luteum (CL) allowing an intricate cross talk between luteal steroiodgenic and endothelial cell (EC) types. Indeed, luteal endothelial cells (LEC) play pivotal roles throughout the entire CL life-span. Microvascular endothelial cells are locally specialized to accommodate the needs of individual tissues, therefore unraveling the characteristics of LEC is imperative in CL physiology. Numerous studies demonstrated that endothelium-derived endothelin-1 (ET-1) is upregulated by the luteolytic hormone-prostaglandin F2alpha (PGF2alpha) and functions as an important element of the luteolytic cascade. To have a better insight on its synthesis and action, members of ET system (ET-1, ET converting enzyme -ECE-1 and ET(A) and ET(B) receptors) were quantified in LEC. The characteristic phenotype of these cells, identified by high ET-1 receptor expression (both ET(A), ET(B)) and low ET-1 and ECE-1 levels, was gradually lost during culture suggesting that luteal microenvironment sustains the selective phenotype of its resident endothelial cells. Proper vascularization and endothelial cell activity per se are essential for normal CL function. Therefore, factors affecting vascular growth are expected to play major role in the regulation of luteal function. Concomitantly with the angiogenic process, luteal PGF2alpha and its receptors (PGFR) are induced and maintained during most of the CL life-span, suggesting a possible role of PGF2alpha in LEC proliferation and function. Dispersed LEC expressed PGFR and incubation with the prostaglandin stimulated mitogen-activated protein kinase (MAPK) signaling cascade. PGF2alpha activated p42/44 MAPK phosphorylation also in long-term cultured LEC. In this cell type, PGF2alpha increased cell number, 3H-Thymidine incorporation and cell survival. Additionally, PGF2alpha rapidly and transiently stimulated the expression of immediate-early response genes, i.e. c-fos and c-jun mRNA, further suggesting a mitogenic effect for this prostaglandin in LEC. These data imply that PGF2alpha may assume different and perhaps opposing roles depending on luteal microenvironment.

Stimulatory effects of eicosanoids on ovarian angiogenesis in early luteal phase in cyclooxygenase-2 inhibitor-treated rats

Our previous study demonstrated that impaired ovarian vasculature is responsible for the decrease in serum progesterone observed in cyclooxygenase (COX)-2 inhibitor-treated rats. To explore the role of arachidonic acid metabolites in the formation of the corpus luteum, we determined in the present study the effects of prostaglandin (PG) and thromboxane (TX) receptor agonists together with vascular endothelial growth factor (VEGF) on progesterone secretion and angiogenesis in the newly formed corpus luteum in NS-398 (a selective inhibitor of COX-2)-treated rats. Uterine injection of PGE2 or U-46619 (TXA2 receptor agonist) prevented decreased levels of serum progesterone and ovarian hemoglobin, an indicator of amounts of vasculature in NS-398-treated rats. Luteal capillary vessel establishment was inhibited by NS-398, as determined by histological examination of ovarian vascular plexuses, while administration of PGE2 reversed the effect. VEGF enhanced the levels of serum progesterone and ovarian hemoglobin, and increased the density of ovarian capillaries. However, VEGF-induced angiogenesis was inhibited by NS-398 treatment. These results suggest that PGE2 and TXA2 stimulate angiogenesis in the newly formed corpus luteum and that there is a possibility that these eicosanoids are involved in VEGF-induced progesterone production and the increase in luteal blood flow.

Role of pericytes in vascular morphogenesis

Pericytes are solitary, smooth muscle-like mural cells that invest the wall of microvessels. For a long time, the functional significance of the presence and distribution of pericytes in the microvasculature was unclear. However, in recent years, the application of experimental genetics to the PDGF-B/PDGFRbeta signaling pathway in mice has provided a range of mutants with primary defects in pericytes, allowing for studies of the physiological consequences of pericyte deficiency in developmental angiogenesis and adult physiology. Interestingly, some of the phenotypic consequences of these mutations resemble human diseases, such as diabetic retinopathy. The studies have also led to the discovery of critical mechanisms involved in pericyte recruitment and differentiation. The present review focuses on genetic data suggesting that pericytes take active part in developmental angiogenic processes.

Spatiotemporal expression of heparanase during human and rodent ovarian folliculogenesis

Heparanase (HPSE) is an endoglycosidase that cleaves heparan sulfate proteoglycans (HSPGs), major components of the basement membrane (BM) and extracellular matrix (ECM). Heparanase activity results in release of HSPG-bound molecules, including basic fibroblast growth factor (FGF2). Structural and functional development of the corpus luteum (CL) involves tissue remodeling, active angiogenesis, and steroid production. Heparanase-induced ECM and BM breakdown as well as FGF2-stimulated endothelial proliferation may have an important role in the regulation of luteal function. Heparanase mRNA was detected by reverse-transcription-polymerase chain reaction in granulosa cells recovered from follicular fluid of in vitro fertilization patients. Using sulfate-labeled ECM, heparanase enzymatic activity was determined in human luteinized granulosa cells. Employing immunohistochemistry, heparanase protein was localized predominantly in the theca interna cell layer of the mature antral follicle, whereas in human corpora lutea, both luteinized granulosa and theca cells were immunostained for heparanase. During luteolysis, heparanase was identified in macrophages surrounding the forming corpus albicans. In serially sectioned ovaries from unstimulated rats as well as from eCG-treated rats, expression of heparanase was noted exclusively in the ovarian steroid-producing interstitial tissue. Following an ovulatory dose of hCG, heparanase was immunostained also in lutein cells of the forming corpora lutea. Temporal expression of heparanase in granulosa cells during the luteal phase and in macrophages during luteal regression supports the hypothesis that heparanase plays a role in human ovarian ECM remodeling and may potentiate cellular migration and growth factor bioavailability.

Effects of luteinizing hormone and human chorionic gonadotropin on corpus luteum cells in a spheroid cell culture system

The human corpus luteum (CL) is a highly vascularized, temporarily active endocrine gland and consists mainly of granulosa cells (GCs), theca cells (TCs), and endothelial cells (ECs). Its cyclic growth and development takes place under the influence of gonadotropic hormones. If pregnancy does occur, human chorionic gonadotropin (hCG) takes over the function of luteinizing hormone (LH) and, in contrast to LH, extends the functional life span of the CL. In this study, we investigated the effects of hCG and LH in a spheroidal cell culture model of CL development. Our data indicate that GCs secrete factors under the control of hCG that increase sprout formation of EC-spheroids. We demonstrate that the most prominent of these factors is VEGF-A. Furthermore, we found that both LH and hCG decrease sprout formation of GC-spheroids. After forming EC-GC coculture spheroids and consequently bringing GCs and ECs in close contact, sprouting increased under the influence of hCG, however not under LH. These experiments provide evidence for an hCG dependent functional switch in the GCs after coming in contact with ECs. Moreover, it demonstrates the considerably different effects of hCG and LH on GCs although their signaling is transmitted via the same receptor.

Immunolocalization of von Willebrand Factor and Vascular Endothelial Growth Factor during Follicular Atresia in the Swamp Buffalo Ovary

The aim of this study was to investigate the distribution pattern of von Willebrand factor (vWF) and vascular endothelial growth factor (VEGF) in the healthy antral and atretic follicles of Philippine swamp buffaloes (SB) in comparison with Holstein-Friesian cows (HF). Paraffin sections of healthy follicles and atretic follicles at various stages were immunostained with vWF antibody and VEGF antibody. The density of vWF-positive capillary vessels in the theca interna significantly increased as atresia progressed in SB, whereas the density significantly decreased in late atretic follicles compared with advanced ones in HF. On the other hand, the area of vWF-positive capillary vessels in the theca interna significantly increased as atresia progressed in both SB and HF. Immunoreactions of VEGF in the granulosa cells (in all follicle types) were observed in both SB and HF. In the granulosa layer, a reduction in the VEGF immunoreaction was noted as follicles progressed from healthy to advanced atretic follicles in both animals. Granulosa cells (in both SB and HF) showed a higher immunopositive staining than theca cells. In the theca interna, VEGF immunostaining diminished as follicles progressed to the late atretic follicles in both animals. These results indicate that during atresia, changes of vWF expression are the opposite of VEGF expression in SB. Both vWF and VEGF are suggested to be associated with follicular atresia in SB.

Alterations in the Ovarian Transcriptome During Primordial Follicle Assembly and Development1

The assembly of the developmentally arrested primordial follicle and subsequent transition to the primary follicle are poorly understood processes critical to ovarian biology. Abnormal primordial follicle development can lead to pathologies such as premature ovarian failure. The current study used a genome-wide expression profile to investigate primordial follicle assembly and development. Rat ovaries with predominantly unassembled, primordial, or primary follicles were obtained. RNA from these ovaries was hybridized to rat microarray gene chips, and the gene expression (i.e., ovarian transcriptome) was compared between the developmental stages. Analysis of the ovarian transcriptome demonstrated 148 genes up-regulated and 50 genes down-regulated between the unassembled and primordial follicle stages. Observations demonstrate 80 genes up-regulated and 44 genes down-regulated between the primordial and primary follicle stages. The analysis demonstrated 2332 genes common among the three developmental stages, 146 genes specific for the unassembled follicles, 94 genes specific for the primordial follicles, and 151 genes specific for the primary follicles. Steroidogenic genes are up-regulated between unassembled and primordial follicles, and then many are again down-regulated between primordial and primary follicles. The hormones inhibin and Mullerian inhibitory substance (MIS) display a similar pattern of expression with the highest levels of mRNA in the primordial follicles. Several novel unknown genes that had dramatic changes in expression during primordial follicle development were also identified. Gene families/clusters identified that were up-regulated from unassembled to primordial follicles include growth factors and signal transduction gene clusters, whereas a down-regulated gene family was the synaptonemal complex genes associated with meiosis. Gene families/clusters that were up-regulated between primordial and primary follicles included immune response genes, metabolic enzymes, and proteases, whereas down-regulated gene families include the globulin genes and some steroidogenic genes. The expression of several growth factors changed during primordial follicle development, including vascular endothelial growth factor and insulin-like growth factor II. Elucidation of how these changes in gene expression coordinate primordial follicle assembly and the primordial to primary follicle transition provides a better understanding of these critical biological processes and allows selection of candidate regulatory factors for further investigation.

Microarray analysis of in vitro pericyte differentiation reveals an angiogenic program of gene expression

The vasculature consists of endothelial cells (ECs) lined by pericyte/vascular smooth muscle cells (vSMCs). Pericyte/vSMCs provide support to the mature vasculature but are also essential for normal blood vessel development. To determine how pericyte-EC communication influences vascular development, we used the well-established in vitro model of TGFbeta-stimulated differentiation of 10T1/2 cells into pericyte/vSMCs. Microarray analysis was performed to identify genes that were differentially expressed by induced vs. uninduced 10T1/2 cells. We discovered that these cells show an angiogenic program of gene expression, with up-regulation of several genes previously implicated in angiogenesis, including VEGF, IL-6, VEGF-C, HB-EGF, CTGF, tenascin C, integrin alpha5, and Eph receptor A2. Up-regulation of some genes was validated by Western blots and immunocytochemistry. We also examined the functional significance of these gene expression changes. VEGF and IL-6 alone and in combination were important in 10T1/2 cell differentiation. Furthermore, we used a coculture system of 10T1/2 and human umbilical vein ECs (HUVECs), resulting in the formation of cordlike structures by the HUVECs. This cordlike structure formation was disrupted when neutralizing antibodies to VEGF or IL-6 were added to the coculture system. The results of these studies show that factors produced by pericytes may be responsible for recruiting ECs and promoting angiogenesis. Therefore, a further understanding of the genes involved in pericyte differentiation could provide a novel approach for developing anti-angiogenic therapies.

Vascular control of ovarian function: ovulation, corpus luteum formation and regression

Hemodynamic changes are involved in the cyclic remodeling of ovarian structures. A transrectal color Doppler ultrasonography was used to assess the blood flow and changes in the vasculature that take place in the follicle wall and within the corpus luteum (CL) during specific physiological events such as ovulation, CL development, and CL regression in cows. To investigate the local release of vasoactive peptides, steroid hormones, and prostaglandins (PGs) in the ovarian microenvironment, the capillary membranes (0.2mm diameter and 5-10mm length) of a microdialysis system (MDS) were implanted into the follicle wall and the CL in vitro. Furthermore, in vivo experiments were conducted with the same MDS membranes surgically implanted in follicle wall or on CL along with ovarian venous and jugular catheters to collect simultaneous, real-time information on the ovarian and systemic changes in the secretion of factors regulating vascular function. Based on the results obtained from the series of in vitro and in vivo experiments, we propose that a functional "cross-talk" occurs between the vascular components (endothelial cells) and steroidogenic cells to control follicular and luteal functions in the bovine ovary.

Characterization of endothelin-1 and nitric oxide generating systems in corpus luteum-derived endothelial cells

Endothelium-derived endothelin-1 (ET-1) and nitric oxide (NO) are pivotal regulators of corpus luteum (CL) function. To have a better insight into their synthesis and action, members of the ET system (ET-1, ET converting enzyme (ECE-1) isoforms a–d, ETAand ETBreceptors) along with NO synthase (NOS) isoforms – endothelial (e)NOS and inducible (i)NOS – were quantified in CL-derived endothelial cells (CLEC). The expression of these genes in microvascular CLEC, obtained by lectin-coated magnetic beads, was compared with cells removed from the luteal microenvironment and maintained in culture for different durations, and with endothelial cells (EC) derived from a large blood vessel (i.e. bovine aortic endothelial cells, BAEC). The profile of gene expression in the different EC types was determined by quantitative real-time PCR. Freshly isolated EC from mid-cycle CL exhibited high ET-1 receptor expression (both ETAand ETB), low ET-1 synthesizing ability (both prepro (pp) ET-1 and ECE-1), but elevated iNOS – the high throughput NOS isoform. The distinct phenotype of CLEC was lost soon after an overnight culture. ETAand ETBreceptor levels declined, ppET-1 levels increased while iNOS was reduced. These changes were extenuated during long-term culture of CLEC. The general pattern of gene expression in BAEC and long-term cultured CLEC was similar yet some differences, reminiscent of freshly isolated CLEC, remained: ECE-1c, ETBreceptor and NOS isoforms were expressed differently in BAEC as compared with lines of CLEC.

This study suggests that the luteal microenvironment is necessary to sustain the selective phenotype of its resident endothelial cells. The inverse relationship between ppET-1 and iNOS observed in freshly isolated CLEC and in cultured cells is physiologically significant and suggests that ET-1 and NO may modulate the production of each other.

Effect of nutrient intake during pregnancy on fetal and placental growth and vascular development

Remarkable diversity of size and health of offspring exists after normal pregnancies. When pregnancies are complicated by an extrinsic variable such as inappropriate maternal nutrition, birth weight and health of the neonate are substantially affected. The placenta is the organ through which respiratory gases, nutrients, and wastes are exchanged between the maternal and fetal systems. Thus, transplacental exchange provides for all the metabolic demands of fetal growth. Transplacental exchange is dependent upon uterine and umbilical blood flow, and blood flow rates are in turn dependent in large part upon vascularization of the placenta. Therefore, factors that influence placental vascular development will have a dramatic impact on fetal growth and development, and thereby on neonatal mortality and morbidity. Recent work from our laboratories has focused on the effects of nutrient intake during pregnancy on placental growth and vascular development. Both nutrient restriction of the adult dam and overnourishment of the adolescent dam during pregnancy suppress placental cell proliferation and vascularity. Furthermore, placental expression of angiogenic factors and their receptors, factors that are known to affect vascular growth, are perturbed by level of nutrition. Studies in this area will lead to improved methods to manage nutritionally-compromised pregnancies.

Regulator of G-protein signaling-5 induction in pericytes coincides with active vessel remodeling during neovascularization

We identified regulator of G-protein signaling-5 (RGS-5) as an angiogenic pericyte marker at sites of physiologic and pathologic angiogenesis. In a mouse model of pancreatic islet cell carcinogenesis, RGS-5 is specifically induced in the vasculature of premalignant lesions during the "angiogenic switch" and further elevated in tumor vessels. Similarly, RGS-5 is overexpressed in highly angiogenic astrocytomas but not in hypoxia-inducible factor-1alpha (HIF-1alpha)-deficient tumors, which grow along preexisting brain capillaries without inducing neovessels. Elevated levels of RGS-5 in pericytes are also observed during wound healing and ovulation indicating a strong correlation between RGS-5 expression and active vessel remodeling beyond tumor angiogenesis. Moreover, antitumor therapy, which reverses tumor vasculature to an almost normal morphology, results in down-regulation of RGS-5 transcription. Taken together, these data demonstrate for the first time a factor that is specific for "activated" pericytes. This further supports the notion that pericytes, like endothelial cells, undergo molecular changes during neovascularization that makes them a novel target for antiangiogenic therapy.

Prognostic value of von Willebrand factor, CD34, CD31, and vascular endothelial growth factor expression in women with uterine leiomyosarcomas

BACKGROUND AND OBJECTIVES

To compare uterine leiomyosarcomas (LMS) and leiomyomas (LM) with normal myometrium in terms of microvessel density (MVD), and to correlate this parameter with vascular endothelial growth factor (VEGF) expression and clinical/pathological parameters.

METHODS

An immunohistochemical technique, using antibodies against von Willebrand factor (FvW), CD34, CD31, and VEGF, was applied to formalin-fixed paraffin-embedded samples of 32 normal myometria, 32 uterine LM, and 12 LMS. MVD was calculated by a digital image analyzer.

RESULTS

Using anti-FvW, mean +/- SD MVD in myometrium, LM, and LMS was 107.0 +/- 53.6, 66.2 +/- 55.4, and 64.4 +/- 44.2, respectively (P = 0.001). MVD was lower in LMS (P = 0.021) and in LM (P = 0.0004) than in normal myometrium. Using anti-CD34, mean +/- SD MVD in myometrium, LM, and LMS was 187.6 +/- 91.2, 106.1 +/- 55.5, and 114.2 +/- 98.8, respectively (P = 0.001). MVD was lower in LMS (P = 0.012) and LM (P = 0.0004) than in normal myometrium. No such differences were found using anti-CD31 and anti-VEGF. No correlation was found between MVD and VEGF expression. In women with uterine LMS, low MVD (assessed with anti-FvW) correlated with recurrence (P = 0.04) and poor overall survival (P = 0.03).

CONCLUSIONS

Uterine smooth muscle tumors exhibit a lower MVD than normal myometrium, as assessed using anti-FvW or anti-CD34 antibodies. A reduced MVD, as assessed by FvW staining, has prognostic value in uterine LMS.

Chemokines in the corpus luteum: implications of leukocyte chemotaxis

Chemokines are small molecular weight peptides responsible for adhesion, activation, and recruitment of leukocytes into tissues. Leukocytes are thought to influence follicular atresia, ovulation, and luteal function. Many studies in recent years have focused attention on the characterization of leukocyte populations within the ovary, the importance of leukocyte-ovarian cell interactions, and more recently, the mechanisms of ovarian leukocyte recruitment. Information about the role of chemokines and leukocyte trafficking (chemotaxis) during ovarian function is important to understanding paracrine-autocrine relationships shared between reproductive and immune systems. Recent advances regarding chemokine expression and leukocyte accumulation within the ovulatory follicle and the corpus luteum are the subject of this mini-review.

Microvascular endothelial cells of the corpus luteum

The cyclic nature of the capillary bed in the corpus luteum offers a unique experimental model to examine the life cycle of endothelial cells, involving discrete physiologically regulated steps of angiogenesis, blood vessel maturation and blood vessel regression. The granulosa cells and theca cells of the developing antral follicle and the steroidogenic cells of the corpus luteum produce and respond to angiogenic factors and vasoactive peptides. Following ovulation the neovascularization during the early stages of corpus luteum development has been compared to the rapid angiogenesis observed during tumor formation. On the other end of the spectrum, the microvascular endothelial cells are the first cells to undergo apoptosis at the onset of corpus luteum regression. Important insights on the morphology and function of luteal endothelial cells have been gained from a combination of in vitro and in vivo studies on endothelial cells. Endothelial cells communicate with cells comprising the functional unit of the corpus luteum, i.e., other vascular cells, steroidogenic cells, and immune cells. This review is designed to provide an overview of the types of endothelial cells present in the corpus luteum and their involvement in corpus luteum development and regression. Available evidence indicates that microvascular endothelial cells of the corpus luteum are not alike, and may differ during the process of angiogenesis and angioregression. The contributions of vasoactive peptides generated by the luteal endothelin-1 and the renin-angiotensin systems are discussed in context with the function of endothelial cells during corpus luteum formation and regression. The ability of two cytokines, tumor necrosis factor alpha and interferon gamma, are evaluated as paracrine mediators of endothelial cell function during angioregression. Finally, chemokines are discussed as a vital endothelial cell secretory products that contribute to the recruitment of eosinophils and macrophages. The review highlights areas for future investigation of ovarian microvascular endothelial cells. The potential clinical applications of research directed on corpus luteum endothelial cells are intriguing considering reproductive processes in which vascular dysfunctions may play a role such as ovarian failure, polycystic ovary syndrome (PCOS), and ovarian hyperstimulation syndrome (OHSS).

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.

Possible role of cyclooxygenase II in the acquisition of ovarian luteal function in rodents

The development of the corpus luteum (CL), which involves angiogenesis, is essential for the establishment of early pregnancy. We investigated the roles of the prostaglandin synthases cyclooxygenase (COX) I and COX-II in angiogenesis and progesterone production in the newly formed CL, using inhibitors of the COX enzymes and the gonadotropin-induced pseudopregnant rat as a model. Injection of indomethacin, a nonselective COX inhibitor, on the day of ovulation and the following day decreased serum levels of progesterone, as did injection of the selective COX-II inhibitor NS-398. In contrast, a selective COX-I inhibitor, SC-560, had no effect on serum progesterone concentrations. None of the inhibitors had any effect on the weight of the superovulated ovaries or on the synthesis of progesterone by cultured luteal cells. To determine whether changes in angiogenesis are responsible for the decrease in progesterone synthesis, we measured hemoglobin and CD34 levels in luteinized ovaries following injection of COX inhibitors and measured the relative frequency of cells positive for platelet-endothelial cell adhesion molecule as a specific marker for endothelial cells. All of these parameters were reduced by the COX-II inhibitors, suggesting that changes in the vasculature are responsible for the decrease in serum progesterone. Histological examination of ovarian corrosion casts indicated that NS-398 inhibited the establishment of luteal capillary vessels following the injection of hCG. The results are consistent with the hypothesis that the activity of COX-II is associated with the formation of functional CL via its stimulation of angiogenesis.

Expression and regulation of plasminogen activators, plasminogen activator inhibitor type-1, and steroidogenic acute regulatory protein in the rhesus monkey corpus luteum

The corpus luteum (CL) is a transient endocrine organ that secretes progesterone to support early pregnancy. Using primate materials obtained from rhesus monkeys, we have in this study investigated the expression and regulation of the plasminogen activators (PAs) and PA inhibitor type 1 (PAI-1) during CL development and regression. Adult (5-7 yr old) female rhesus monkeys were treated with pregnant mare serum gonadotropin/human chorionic gonadotropin to induce ovulation and follicular luteinization. At various luteal developmental stages, CL or whole ovaries were obtained for preparing luteal cells, Northern blot, in situ hybridization, and immunohistochemistry. We demonstrated that luteal cells from the rhesus monkey were able to produce both tissue type PA (tPA) and urokinase type PA, as well as the physiological PAI-1. During luteal development in the monkey, urokinase type PA was the major PA species taking part in the active angiogenesis and tissue remodeling processes in the forming CL. However, the mRNA as well as the enzymatic activity levels of tPA increased dramatically in monkey CL with the advent of luteolysis. This change of tPA levels was in a temporal coordination with the regulation of PAI-1 expression, resulting in an increased tPA activity at the initiation of luteolysis. Therefore, we suggest that tPA might be a luteolytic factor to the monkey CL. A PAI-1 modulated tPA activity might be important for the initiation of luteolysis in the monkey. In addition, we have also demonstrated that the expression of steroidogenic acute regulatory protein in the monkey CL was in accordance with the changes of progesterone production, suggesting that steroidogenic acute regulatory protein expression may be considered as a reliable marker for CL function in primates.

Luteogenesis in cyclic ewes: echotextural, histological, and functional correlates

To date, it has not been possible to detect corpus luteum (CL) by ultrasonography, immediately following ovulation, in the ewe. Early CL detection is essential to be able to relate luteal outcome to the developmental pattern of the ovulated follicle and to confirm ovulation. Image analysis of the CL may be useful in providing a noninvasive picture of CL differentiation and function. The present study was designed to use high-resolution ultrasonography to monitor and to correlate the echotextural, histological, and functional attributes of the developing ovine CL from Days 1 to 3 after ovulation. Ten ewes underwent twice-daily transrectal ultrasonography and blood sampling from the day of synchronized estrus. Ewes were ovariectomized at 12-24, 36-48, and 60-72 h after ovulation. Ovaries collected were scanned in a water bath before processing for histology. Ultrasonographic images of CL were analyzed for echotexture. Histological sections were analyzed for the percentage area of the CL occupied by blood clot or luteal tissue. Serum samples were analyzed for progesterone concentration. Numerical pixel value, heterogeneity, and percentage of the CL occupied by blood clot declined (P<0.05) from 12-24 to 60-72 h after ovulation. Luteal area and serum progesterone concentration increased (P<0.05) from 12-24 to 60-72 h. The results indicated that it was possible to visualize developing CL as early as 12-24 h after ovulation in the ewe. Echotexture of the CL was closely associated with its morphological and functional characteristics; image analysis holds promise for noninvasive monitoring of CL differentiation and growth.

Transcription profiling of platelet-derived growth factor-B-deficient mouse embryos identifies RGS5 as a novel marker for pericytes and vascular smooth muscle cells

All blood capillaries consist of endothelial tubes surrounded by mural cells referred to as pericytes. The origin, recruitment, and function of the pericytes is poorly understood, but the importance of these cells is underscored by the severe cardiovascular defects in mice genetically devoid of factors regulating pericyte recruitment to embryonic vessels, and by the association between pericyte loss and microangiopathy in diabetes mellitus. A general problem in the study of pericytes is the shortage of markers for these cells. To identify new markers for pericytes, we have taken advantage of the platelet-derived growth factor (PDGF)-B knockout mouse model, in which developing blood vessels in the central nervous system are almost completely devoid of pericytes. Using cDNA microarrays, we analyzed the gene expression in PDGF-B null embryos in comparison with corresponding wild-type embryos and searched for down-regulated genes. The most down-regulated gene present on our microarray was RGS5, a member of the RGS family of GTPase-activating proteins for G proteins. In situ hybridization identified RGS5 expression in brain pericytes, and in pericytes and vascular smooth muscle cells in certain other, but not all, locations. Absence of RGS5 expression in PDGF-B and PDGFR beta-null embryos correlated with pericyte loss in these mice. Residual RGS5 expression in rare pericytes suggested that RGS5 is a pericyte marker expressed independently of PDGF-B/R beta signaling. With RGS5 as a proof-of-principle, our data demonstrate the usefulness of microarray analysis of mouse models for abnormal pericyte development in the identification of new pericyte-specific markers.

The yolkless egg and the evolution of eutherian viviparity

All vertebrate follicles have the same basic structure. Viviparity also occurs in all vertebrates except birds, but it is the only form of reproduction in eutherians ("placental mammals"). Their mature follicles are vesicular, and their oocytes are yolkless. Clues to the origin of these unique characteristics are in the incidence of atresia and the role of yolk in reproduction. In broadcast spawning, atresia is as rare as it is common among eutherians and other nonspawning vertebrates. In all but the eutherians, at least the initial-and in most cases all-stages of embryogenesis depend crucially on the zygote's yolk. Eutherian reproduction, therefore, must have evolved in connection with genetic changes that caused fragility of the oocyte, instability of the follicle, and loss of the ability to produce vitellogenin (VTG), the main lipoprotein of yolk. Mutations can result in adaptations by uncovering hidden properties in a trait and/or its environment. Useful mutations in recessive alleles can spread through a population as heterozygotes, invisible until the number of homozygotes for the mutation is large enough for them to suddenly appear and form the nucleus of a new breeding population. Such a mutation probably truncated a long, oviductal-based, aplacental gestation of a small, lightly yolked zygote in an endothermic, mammal-like reptile and converted it into an early monotreme or marsupial-like mammal (pantothere). Against tremendous odds, another mutation later caused loss of the genes for VTG. The resultant yolkless zygote survived because 1). the mutation also affected a network of homeiotic genes controlling the ontogeny of the entire reproductive system and 2). the system contained enough hidden properties for the mutation to change the character of the oocyte, its granulosa cells and corpus luteum, the zygote, and the uterus in a way that virtually assured the new zygote's survival. Eutherian reproduction, however, is neither better nor worse than other forms; it is only different.

Angiogenesis in the female reproductive organs: pathological implications

The female reproductive organs (ovary, uterus, and placenta) are some of the few adult tissues that exhibit regular intervals of rapid growth. They also are highly vascular and have high rates of blood flow. Angiogenesis, or vascular growth, is therefore an important component of the growth and function of these tissues. As with many other tissues, vascular endothelial growth factors (VEGFs) and fibroblast growth factors (FGFs) appear to be major angiogenic factors in the female reproductive organs. A variety of pathologies of the female reproductive organs are associated with disturbances of the angiogenic process, including dysfunctional uterine bleeding, endometrial hyperplasia and carcinoma, endometriosis, failed implantation and subnormal foetal growth, myometrial fibroids (uterine leiomyomas) and adenomyosis, ovarian hyperstimulation syndrome, ovarian carcinoma, and polycystic ovary syndrome. These pathologies are also associated with altered expression of VEGFs and/or FGFs. In the near future, angiogenic or antiangiogenic compounds may prove to be effective therapeutic agents for treating these pathologies. In addition, monitoring of angiogenesis or angiogenic factor expression may provide a means of assessing the efficacy of these therapies.

Luteotropic roles of prolactin in early pregnant hamsters

Prolactin (PRL) has long been regarded as a luteotropin maintaining early pregnancy in rodents. To delineate luteotropic roles of PRL in terms of luteal vascularization and immune privilege, luteal expression of Thy-1 differentiation protein, Fas, and Fas ligand (FasL) in early pregnancy was studied in hamsters on Day 4 of pregnancy (P4 group). Release of pituitary PRL was blocked by daily treatment with bromocriptine (1 mg s.c. given at 1000 h) on Days 1-4 of pregnancy (PB group). PRL withdrawal induced functional luteolysis, as evidenced by a precipitous drop in serum progesterone to background levels. In situ 3' end-labeling of fragmented DNA (TUNEL method) also clearly showed that many apoptotic nuclei accumulated in the disintegrated luteal vessels in the corpus luteum in the PB group. Immunohistochemical studies showed that luteal Thy-1-positive vascular pericytes were abundant in the P4 group but rare in the PB group. Thus, PRL is essential for luteal vascularization in early pregnancy. Western blotting and quantitative real-time reverse transcription-polymerase chain reaction data showed that Fas protein and mRNA levels increased, whereas those of FasL decreased after PRL withdrawal. Accordingly, apoptosis initiated by Fas-FasL interaction is involved in the bromocriptine-induced luteolysis. Therefore, luteotropic roles of PRL are to support Thy-1 positive pericytes in maintaining proper luteal vascularization and to prevent immune insult by preserving a balance between luteal Fas and FasL expression in early pregnancy.

Bovine membrane-type 1 matrix metalloproteinase: molecular cloning and expression in the corpus luteum

Matrix metalloproteinase-2 (MMP-2) is produced as a zymogen, which is subsequently activated by membrane-type 1 metalloproteinase (MT1-MMP). The objectives of the present study were to clone bovine MT1-MMP and to investigate its expression in the corpus luteum. Corpora lutea were harvested from nonlactating dairy cows on Days 4, 10, and 16 of the estrous cycle (Day 0 = estrus; n = 3 for each age). The bovine MT1-MMP cDNA contained an open reading frame of 1749 base pairs, which encoded a predicted protein of 582 amino acids. Northern blotting revealed no differences (P > 0.05) in MT1-MMP mRNA levels between any ages of corpora lutea. Western blotting demonstrated that two species of MT1-MMP, the latent form ( approximately 63 kDa) and the active form ( approximately 60 kDa), were present in corpora lutea throughout the estrous cycle. Active MT1-MMP was lower (P < 0.05) in early stages of the corpus luteum than the mid and late stages, where MMP-2 activity, as revealed by gelatin zymography, was also elevated. Furthermore, immunohistochemistry revealed that MT1-MMP was localized in endothelial, large luteal, and fibroblast cells of the corpus luteum at different stages. Taken together, the differential expression and localization of MT1-MMP in the corpus luteum suggest that it may have multiple functions throughout the course of the estrous cycle, including activation of pro-MMP-2.

Microvascular endothelial cells differ in basal and hypoxia-regulated expression of angiogenic factors and their receptors

Phenotypically and functionally different types of microvascular endothelial cells (MVECs) derived from the developing corpus luteum were isolated and characterized by our group. We investigated whether these cytokeratin-positive (CK+) and cytokeratin-negative (CK-) MVECs differed in the expression of angiogenic factors and their regulation under hypoxia. Using quantitative RT-PCR, VEGF and its receptors, Flk-1 and Flt-1, were detected in CK- MVECs. The mRNA expression of Flk-1 mRNA was 100 times as high as that of Flt-1 mRNA. CK+ MVECs expressed VEGF and Flt-1 mRNA, but were devoid of Flk-1 transcripts. No Ang-1 mRNA was demonstrated in either cell type, and Ang-2 mRNA was found only in CK- MVECs. Tie-2 mRNA was detected in both MVEC types, but levels were 150 times as high in CK- MVECs as in CK+ MVECs. mRNA of hypoxia-inducible factors Hif-1alpha and Hif-1beta was expressed in both MVEC types. After hypoxia, neither VEGF, nor Flk-1, nor Tie-2 mRNA expression was altered in either MVEC type. Flt-1 expression and Ang-2 mRNA expression were significantly increased at about 2.5-fold (P < 0.05) in CK- MVECs, but not in CK+ MVECs. Our study demonstrates the varying expression and regulation of angiogenesis-related factors and receptors in phenotypically different MVEC types.

Abnormalities in pericytes on blood vessels and endothelial sprouts in tumors

Endothelial cells of tumor vessels have well-documented alterations, but it is less clear whether pericytes on these vessels are abnormal or even absent. Here we report that alpha-smooth muscle actin (alpha-SMA) and desmin-immunoreactive pericytes were present on >97% of blood vessels viewed by confocal microscopy in 100-microm-thick sections of three different spontaneous or implanted tumors in mice. However, the cells had multiple abnormalities. Unlike pericytes on capillaries in normal pancreatic islets, which had desmin but not alpha-SMA immunoreactivity, pericytes on capillary-size vessels in insulinomas in RIP-Tag2 transgenic mice expressed both desmin and alpha-SMA. Furthermore, pericytes in RIP-Tag2 tumors, as well as those in MCa-IV breast carcinomas and Lewis lung carcinomas, had an abnormally loose association with endothelial cells and extended cytoplasmic processes deep into the tumor tissue. alpha-SMA-positive pericytes also covered 73% of endothelial sprouts in RIP-Tag2 tumors and 92% of sprouts in the other tumors. Indeed, pericyte sleeves were significantly longer than the CD31-immunoreactive endothelial cell sprouts themselves in all three types of tumors. All three tumors also contained alpha-SMA-positive myofibroblasts that resembled pericytes but were not associated with blood vessels. We conclude that pericytes are present on most tumor vessels but have multiple abnormalities, including altered expression of marker proteins. In contrast to some previous studies, the almost ubiquitous presence of pericytes on tumor vessels found in the present study may be attributed to our use of both desmin and alpha-SMA as markers and 100-microm-thick tissue sections. The association of pericytes with endothelial sprouts raises the possibility of an involvement in sprout growth or retraction in tumors.

Local changes in blood flow within the early and midcycle corpus luteum after prostaglandin F(2 alpha) injection in the cow

One of the postulated main luteolytic actions of prostaglandin (PG) F(2 alpha) is to decrease ovarian blood flow. However, before Day 5 of the normal cycle, the corpus luteum (CL) is refractory to the luteolytic action of PGF(2 alpha). Therefore, we aimed to determine in detail the real-time changes in intraluteal blood flow after PGF(2 alpha) injection at the early and middle stages of the estrous cycle in the cow. Normally cycling cows at Day 4 (early CL, n = 5) or Days 10--12 (mid CL, n = 5) of the estrous cycle (estrus = Day 0) were examined by transrectal color and pulsed Doppler ultrasonography to determine the blood flow area, the time-averaged maximum velocity (TAMXV), and the volume of the CL after an i.m. injection of a PGF(2 alpha) analogue. Ultrasonographic examinations were carried out just before PG injection (0 h) and then at 0.5, 1, 2, 4, 8, 12, 24, and 48 h after the injection. Blood samples were collected at each of these times for progesterone (P) determination. The ratio of the colored area to a sectional plane at the maximum diameter of the CL was used as a quantitative index of the changes in blood flow within the luteal tissue. Blood flow within the midcycle CL initially increased (P < 0.05) at 0.5-2 h, decreased at 4 h to the same levels observed at 0 h, and then further decreased to a lower level from 8 h (P < 0.05) to 48 h (P < 0.001). Plasma P concentrations decreased (P < 0.05) from 4.7 +/- 0.5 ng/ml (0 h) to 0.6 +/- 0.2 ng/ml (24 h). The TAMXV and CL volume decreased at 8 h (P < 0.05) and further decreased (P < 0.001) from 12 to 24 h after PG injection, indicating structural luteolysis. These changes were not detected in the early CL, in which luteolysis did not occur. In the early CL, the blood flow gradually increased in parallel with the CL volume, plasma P concentration, and TAMXV from Day 4 to Day 6. The present results indicate that PGF(2 alpha) induces an acute blood flow increase followed by a decrease in the midcycle CL but not in the early CL. This transitory increase may trigger the luteolytic cascade. The lack of intraluteal vascular response to PG injection in the early CL appears to be directly correlated with the ability to be resistant to PG.

Evidence for a role of capillary pericytes in vascular growth of the developing ovine corpus luteum

Because of rapid growth followed by spontaneous regression, the ovarian corpus luteum (CL) is an excellent model to study angiogenesis in vivo. To evaluate the expression of vascular endothelial growth factor (VEGF) protein during luteal development, ovaries were collected from FSH-stimulated ewes throughout the estrous cycle. VEGF was immunolocalized in tissue sections by using an affinity-purified antibody. VEGF protein localized exclusively to the thecal layer of preovulatory follicles, while the granulosa was devoid of staining. Associated with the periovulatory period was intense expression of VEGF by thecal cells at the basement membrane and subsequent invasion of the granulosa layers by these VEGF-positive cells immediately after ovulation. The early CL showed staining for VEGF in thecal-derived compartments, and strong staining for VEGF was also seen in cells within the granulosa-derived parenchymal lobules. Dual immunohistochemical localization of VEGF and smooth muscle cell alpha-actin indicated that the VEGF-positive cells were capillary pericytes or vascular smooth muscle cells. In another experiment, we quantified proliferation of endothelial cells and pericytes throughout luteal development. Pericytes represented a large proportion of the proliferating cells during the early luteal phase and then decreased dramatically. Perivascular cells, therefore, may play a critical role in angiogenesis that occurs during transformation of the follicle into the highly vascular CL of the sheep. As angiogenesis occurs only at the level of capillaries, and pericytes are integral members of these microvessels, regulation of pericytes may provide a novel mechanism for regulating luteal growth and tissue growth in general.

Isolation and characterization of vascular smooth muscle cell growth promoting factor from bovine ovarian follicular fluid and its cDNA cloning from bovine and human ovary

A protein possessing vascular smooth muscle cell (SMC) growth-promoting activity (VSGP) was purified from bovine ovarian follicular fluid. The purified protein showed a broad band on SDS-PAGE with an apparent molecular mass of 90-100 kDa. The purified protein was characterized by amino acid sequence analysis of its N-terminal and internal peptides. Based on the information of the peptide sequences, bovine ovarian cDNA library was screened and cDNA clones encoding the protein were isolated. Human homolog of the protein was also cloned from human ovarian cDNA library. Nucleotide sequence analysis revealed that bovine VSGP transcript has a 2421-bp open reading frame, which encodes a protein of 807 amino acid residues. A homology search indicated that bovine and human VSGP are counterparts of rat F-spondin, which has been previously identified as a promoter molecule of neurite extension in rat fetal floor plate. RNA blot analysis showed wide distribution of VSGP/F-spondin transcripts in fetal and adult human tissues. Especially the expression was highest in the adult human ovary. The purified bovine VSGP/F-spondin showed vascular SMC growth promoting activity with an ED(50) value of 10(-8) M. Together with these findings, we demonstrated here that VSGP/F-spondin is a major factor for vascular SMC proliferation in the ovary. In conclusion, our present study provides a distinct and important function of VSGP/F-spondin as a strong VSMC proliferation promoting factor, in addition to the previously proposed function in neuronal system, and also provides insight into mechanisms underlying vascular SMC proliferation during ovarian folliculogenesis.

Angiogenesis in the placenta

The mammalian placenta is the organ through which respiratory gases, nutrients, and wastes are exchanged between the maternal and fetal systems. Thus, transplacental exchange provides for all the metabolic demands of fetal growth and development. The rate of transplacental exchange depends primarily on the rates of uterine (maternal placental) and umbilical (fetal placental) blood flows. In fact, increased uterine vascular resistance and reduced uterine blood flow can be used as predictors of high risk pregnancies and are associated with fetal growth retardation. The rates of placental blood flow, in turn, are dependent on placental vascularization, and placental angiogenesis is therefore critical for the successful development of viable, healthy offspring. Recent studies, including gene knockouts in mice, indicate that the vascular endothelial growth factors represent a major class of placental angiogenic factors. Other angiogenic factors, such as the fibroblast growth factors or perhaps the angiopoietins, also may play important roles in placental vascularization. In addition, recent observations suggest that these angiogenic factors interact with the local vasodilator nitric oxide to coordinate placental angiogenesis and blood flow. In the future, regulators of angiogenesis that are currently being developed may provide novel and powerful methods to ensure positive outcomes for most pregnancies.