Angiogenesis in the corpus luteum

Immunohistochemical study of angiogenesis and angiogenic factors in equine granulosa cell tumours

The first part of our study (Müller et al., 2009) characterized angiogenesis in the equine cycling ovary through histomorphological and immunohistochemical examinations (vascular endothelial growth factors A and B [VEGF A, VEGF B], vascular endothelial growth factor receptors 1 and 2 [VEGF-R1, VEGF-R2], vascular angiopoietins 1 and 2 [Ang1, Ang2], angiopoietin receptor [Tie2], and von Willebrand Factor). Since angiogenesis plays an important role in development and growth of numerous tumours, the second part of our study involved a similar examination of 70 equine granulosa cell tumours (GCTt). The results of the second study were compared with those of the normal equine ovary. Certain similarities in the expression pattern could be detected between normal, cyclical ovaries (Müller et al., 2009) and GCTt. The immunoreactivity of granulosa cells and Leydig-like cells in GCTt resembles granulosa cells and luteinized thecal cells in periovulatory cycling ovaries. The neoplastic cells support circulation, supply and growth of GCTt by contributing to angiogenesis.

A role for cysteine-rich 61 in the angiogenic switch during the estrous cycle in cows: regulation by prostaglandin F2alpha

The development and demise of the corpus luteum (CL) are accompanied by angiogenic and angioregressive processes; however, the mediators of these processes have not been fully identified and characterized. Transcriptional profiling studies revealed the upregulation of cysteine-rich 61 (CYR61) in the CL, about which nothing was previously known. In the present study, we found that over a 12-h period following a single injection of prostaglandin F(2alpha) (PGF(2alpha)), RT-PCR revealed the upregulation of CYR61 at 0.5 and 1 h, after which it declined. We also determined that luteal-derived endothelial cells as well as luteal steroidogenic cells are sources of CYR61. Treatment with PGF(2alpha) in vitro had no effect on CYR61 expression in luteal-derived endothelial cells, but it increased CYR61 expression in luteal steroidogenic cells. During the estrous cycle, CYR61/CYR61 (transcript/protein) was increased in the Day 4 but not in the Day 10 and Day 16 CL, suggesting that it may be associated with the switch to the angiogenic phenotype. In addition, the specific but transient upregulation of CYR61 by PGF(2alpha) in vivo, and in luteal steroidogenic cells but not endothelial cells in vitro, may be part of the mechanism underlying the previously reported transient increase in blood flow during the early onset of luteolysis. This is supported by our preliminary finding that CYR61 transiently inhibited endothelial cell expression of endothelin-converting enzyme 1 mRNA but not endothelin 1. Collectively, the increased expression of CYR61 in the Day 4 CL and its transient increase by PGF(2alpha) in Day 6, Day 10, and Day 16 CL indicate that CYR61 may play a role in regulating angiogenesis over the life span of the CL.

Administration of a gonadotropin-releasing hormone agonist affects corpus luteum vascular stability and development and induces luteal apoptosis in a rat model of ovarian hyperstimulation syndrome

Ovarian hyperstimulation syndrome (OHSS) is a complication of ovarian stimulation with gonadotropins followed by the administration of human chorionic gonadotropin (hCG) to trigger the final steps of oocyte maturation. Gonadotropin-releasing hormone (GnRH) analogs are thought to be effective in preventing this complication and a clinical trial has found a lower incidence of OHSS in patients treated with these molecules. Our aim was to analyze the in vivo effect of a GnRH-I agonist on corpus luteum development and regression, ANGPT-1, ANGPT-2 and Tie-2 protein expression and luteal blood vessel stabilization, the expression of the steroidogenic acute regulatory protein (StAR) and the cytochrome P450 side-chain cleavage enzyme (P450scc) and cell proliferation, in ovaries from an OHSS rat model. To this end immature female Sprague-Dawley rats were hyperstimulated and treated with a GnRH-I agonist from the start of pregnant mare serum gonadotropin (PMSG) administration until the day of hCG injection for 5 consecutive days. Blood and tissue samples were collected 48h after hCG injection. Vascular endothelial growth factor VEGF levels were evaluated in the peritoneal fluid by ELISA. Serum progesterone and estradiol were measured by RIA. Histological features of sectioned ovaries were assessed in hematoxylin and eosin (H&E) stained slides. Luteal blood vessel stability, cell proliferation and apoptosis were assessed by immunohistochemistry for SMCA, PCNA, and TUNEL, respectively. P450scc, StAR, FLK-1, ANGPT-1, ANGPT-2, Tie-2 and PCNA protein levels were evaluated by Western blot from dissected corpora lutea (CL). The treatment with the GnRH-I agonist significantly decreased serum progesterone and estradiol levels as well as P450scc and StAR protein expression in the untreated OHSS group. In addition, the agonist significantly decreased the number of CL in the OHSS group, as compared with the untreated OHSS group. In the OHSS group, the area of periendothelial cells in the CL was larger than that of the control group. However, the treatment with the GnRH-I agonist significantly reduced the area of periendothelial cells in the CL in the OHSS group. The luteal levels of ANGPT-1 and its receptor Tie-2 significantly increased in the OHSS group when compared with the control group. Conversely, the administration of the GnRH-I agonist significantly decreased the levels of these factors in the CL from the OHSS group, as compared with the untreated OHSS group. In addition, the treatment with the GnRH-I agonist reduced the diameter of CL and decreased CL cell proliferation as compared with that observed in the untreated OHSS group. Finally, the GnRH-I agonist increased apoptosis in the CL from the OHSS group. In conclusion, these results show that GnRH-I agonist exerts diverse actions on the CL from a rat OHSS model. The decrease in P450scc, StAR, ANGPT-1 and Tie-2 expression, blood vessel stability and luteal proliferation leads to CL regression in the ovaries from OHSS rats. Moreover, our results suggest that the downregulation of ANGPT-1 and its receptor is a possible mechanism whereby GnRH-I agonists could prevent early OHSS.

Vascular smooth muscle Notch signals regulate endothelial cell sensitivity to angiogenic stimulation

The evolutionarily conserved Notch signaling pathway is required for normal vascular development and function, and genetic associations link select Notch receptors and ligands to human clinical syndromes featuring blood vessel abnormalities and stroke susceptibility. A previously described mouse model engineered to suppress canonical Notch signaling in vascular smooth muscle cells (vSMCs) revealed surprising anatomical defects in arterial patterning and vessel maturation, suggesting that vSMCs have the functional capacity to influence blood vessel formation in a Notch signaling-dependent manner. In further analyses using this model system, we now show that explanted aortic ring tissue and Matrigel implants from the smooth muscle Notch signaling-deficient mice yield markedly diminished responses to angiogenic stimuli. Furthermore, cultured Notch signaling-deficient primary vSMCs have reduced proliferation and migration capacities and reveal diminished expression of PDGF receptor β and JAGGED1 ligand. These observations prompted a series of endothelial cell (EC)-vSMC co-culture experiments that revealed a requirement for intact vSMC Notch signals via JAGGED1 for efficient EC Notch1 receptor activation and EC proliferation. Taken together, these studies suggest a heterotypic model wherein Notch signaling in vSMCs provides early instructive cues to neighboring ECs important for optimal postnatal angiogenesis.

Blood vessel maturation, vascular phenotype and angiogenic potential in malignant melanoma: one step forward for overcoming anti-angiogenic drug resistance?

Angiogenesis is a pivotal process for growth, invasion and spread of the majority of solid tumors including melanoma. Anti-angiogenic agents have not been systematically tested in patients with advanced melanoma. Clinical efficacy of angiogenesis inhibitors targeting endothelial cells has not been as affirmative as initially hoped and improved clinical outcomes have been observed in combination with chemotherapy or additional drugs for many types of human cancer. However, angiogenesis is not only dependent on endothelial cell invasion and proliferation, it also requires pericyte coverage of vascular sprouts for stabilization and maturation of vascular walls. Recent data suggest that pericytes might be able to confer resistance to anti-vascular endothelial growth factor (VEGF) therapy. This review will focus on the significance of the vascular phenotype but also on the impact of pericyte-mediated vessel maturation for the susceptibility to anti-angiogenic therapy, including malignant melanoma, which we identified as crucial factor regarding therapeutic efficacy.

Defective female reproductive function in 1,25(OH)2D-deficient mice results from indirect effect mediated by extracellular calcium and/or phosphorus

We used mice with targeted deletion of 25-hydroxyvitamin D 1α-hydroxylase [1α(OH)ase(-/-)] to investigate the effects of calcium and phosphorus on defects in the reproductive system of 1,25-dihydroxyvitamin D [1,25(OH)(2)D]-deficient female mice. The 1α(OH)ase(-/-) mice and their wild-type littermates were fed either a normal diet or a rescue diet (high calcium, phosphate, and lactose) starting from weaning until 3 mo of age. We then determined serum calcium and phosphorus levels, assessed gonadotropin and gonadal hormone production, and evaluated folliculogenesis, corpus luteum formation, ovarian angiogenesis, uterus development, and fertility. Results showed that hypocalcemic and hypophosphatemic female 1α(OH)ase(-/-) mice developed infertility accompanied by decreased estrogen and progestogen levels, elevated follicle-stimulating hormone and luteinizing hormone levels, defects in follicular development and corpus luteum formation, uterine hypoplasia, and decreased ovarian expression of angiogenic factors including vascular endothelial growth factor (VEGF), angiopoietin-1 and -2, and Tie-2. When serum calcium and phosphorus were normalized by the rescue diet, the defective reproductive phenotype in the female 1α(OH)ase(-/-) mice, including the dysfunction in the hypothalamic-pituitary-ovarian axis, and ovarian angiogenesis were reversed. These results indicate that the infertility seen in 1,25(OH)(2)D-deficient mice is not a direct effect of active vitamin D deficiency on the reproductive system but is an indirect effect mediated by extracellular calcium and phosphorus.

Development and hormonal regulation of the ovarian lymphatic vasculature

The lymphatic vasculature plays a number of essential physiological roles including maintaining fluid homeostasis, providing a network for the transport of immune cells, and facilitating the uptake of fat-soluble nutrients from the gastrointestinal tract. Although the critical importance and remodeling capacity of the blood vasculature has been well described within the ovary, just a few reports describe the lymphatic vasculature. Using histological and molecular techniques, we report the kinetics of ovarian lymphangiogenesis and the hormonal regulation of lymphangiogenic growth factors associated with key stages of ovarian follicle growth. We exploited the Adamts1-null mouse model, a model with a previously characterized lymphatic defect to further interrogate the mechanisms controlling ovarian lymphangiogenesis. The establishment and development of the ovarian lymphatic vascular network in postnatal developing ovaries was associated with the presence and hormonal regulation of the lymphangiogenic growth factors and their receptors, including Vegfc, Vegfd, and Vegfr3. We characterized the hormonally regulated remodeling of the ovarian lymphatic vasculature in response to FSH and estradiol. The lymphatic network was defective in the Adamts1-null ovary, clearly demonstrating both the involvement of FSH/estradiol and the Adamts1 (a disintegrin and metalloproteinase with thrombospondin motifs 1) protease in ovarian lymphangiogenesis. This study provides the first evidence of a malleable lymphatic system responsive to hormonal changes of the female reproductive cycle, at least in the mouse ovary, suggesting a role for lymphatic vessel functions in normal folliculogenesis.

Expression of vascular endothelial growth factor A during ligand-induced down-regulation of luteinizing hormone receptor in the ovary

Vascular endothelial growth factor A (VEGF-A) is one of the most important regulators of ovarian angiogenesis. In this study, we examined the temporal relationship between VEGF-A and luteinizing hormone receptor (LHR) mRNA expression during ligand-induced down-regulation of LHR. Immature female rats were treated with pregnant mare's serum gonadotropin followed by 25 IU hCG 56 h later (day 0). On day 5, treatment with hCG (50 IU) to down-regulate LHR showed a temporal decrease in VEGF-A mRNA and protein levels in parallel with decreasing LHR mRNA. This effect was specific since the expression of CYP11A1 mRNA showed no decline. Examination of VEGF-A mRNA expression, using in situ hybridization histochemistry with (35)S-labeled antisense VEGF-A mRNA probe, showed intense signal in the corpora lutea on day 5. Treatment with 50 IU hCG to down-regulate LHR mRNA showed a decline in the intensity of VEGF-A mRNA in the corpora lutea. VEGF-A mRNA expression returned to control level 53 h later when the expression of LHR mRNA also recovered. These results show that the transient down-regulation of VEGF-A mRNA and protein closely parallels the ligand-induced down-regulation of LHR mRNA. The present study establishes a close association between VEGF-A and LHR mRNA expression, suggesting the possibility that VEGF-A-induced vascularization of the ovary is dictated by the expression of LHR and this might play a regulatory role in ovarian physiology.

Deleterious effects of progestagen treatment in VEGF expression in corpora lutea of pregnant ewes

The aim of the current study was to determine the possible effects of progestagen oestrous synchronization on vascular endothelial growth factor (VEGF) expression during sheep luteogenesis and the peri-implantation period and the relationship with luteal function. At days 9, 11, 13, 15, 17 and 21 of pregnancy, the ovaries from 30 progestagen treated and 30 ewes cycling after cloprostenol injection were evaluated by ultrasonography and, thereafter, collected and processed for immunohistochemical evaluation of VEGF; blood samples were drawn for evaluating plasma progesterone. The progestagen-treated group showed smaller corpora lutea than cloprostenol-treated and lower progesterone secretion. The expression of VEGF in the luteal cells increased with time in the cloprostenol group, but not in the progestagen-treated group, which even showed a decrease between days 11 and 13. In progestagen-treated sheep, VEGF expression in granulosa-derived parenchymal lobule capillaries was correlated with the size of the luteal tissue, larger corpora lutea had higher expression, and tended to have a higher progesterone secretion. In conclusion, the current study indicates the existence of deleterious effects from exogenous progestagen treatments on progesterone secretion from induced corpora lutea, which correlate with alterations in the expression of VEGF in the luteal tissue and, this, presumably in the processes of neoangiogenesis and luteogenesis.

Proliferation of vascular smooth muscle cells in glioblastoma multiforme

OBJECT

Glioblastomas multiforme (GBM) contain a higher number of alpha-smooth muscle actin (SMA)-positive vascular smooth muscle cells (VSMCs) than those in the respective normal neuronal tissue. The role of VSMCs during angiogenesis is unclear, and it is also uncertain whether and to what extent angiogenic factors might be involved in GBM VSMCs. In GBMs, the contribution of VSMCs in angiogenesis accompanying endothelial proliferation and the correlation of VSMC proliferation with vascular endothelial growth factor (VEGF) expression were examined using an immunohistochemical method.

METHODS

The examined material, including surrounding brain tissue, came from 12 cases (6 men and 6 women) with classic GBM. Microvessel densities (MVDs) of CD31-immunoreactive vessels (CD31-MVD) and SMA-immunoreactive vessels (SMA-MVD) were obtained in areas selected from white matter, boundary, tumor (concentrated area of tumor cells), and perinecrosis. Subsequently, the SMA-MVD/CD31-MVD (SMA/CD31) rate, representing the percentage of vessels with VSMCs in the region, was calculated in each area. The VEGF immunoreactivity of tumor cells was examined, and cases were divided into 2 groups: < 30% VEGF expression of tumor cells (low VEGF group) and > 30% VEGF expression of tumor cells (high VEGF group).

RESULTS

The SMA/CD31 rate of the boundary was significantly lower than that of the tumor (p < 0.005) and perinecrosis (p < 0.001). The SMA/CD31 rate of the high VEGF group was significantly higher than that of the low VEGF group (p < 0.05) in the tumor.

CONCLUSIONS

In GBMs, the transformation and proliferation of VSMCs may accompany neovascularization and may also be induced by angiogenic factors.

Pericytes and vessel maturation during tumor angiogenesis and metastasis

Despite promising results in preclinical and clinical studies, the therapeutic efficacy of antiangiogenic therapies has been restricted by a narrow focus on inhibiting the growth of endothelial cells. Other cell types in the tumor stroma are also critical to the progression of cancer, including mural cells. Mural cells are vascular support cells that range in phenotype from pericytes to vascular smooth muscle cells. Although the role of pericytes and pericyte-like cells in the pathophysiology of cancer is still unclear, evidence indicates that aberrations in pericyte-endothelial cell signaling networks could contribute to tumor angiogenesis and metastasis. The purpose of this review is to evaluate critically recent evidence on the role of pericytes in tumor biology and discuss potential therapeutic targets for anticancer intervention.

N-acetylcysteine impairs survival of luteal cells through mitochondrial dysfunction

N-acetylcysteine (NAC) is known as an antioxidant and used for mucus viscosity reduction. However, this drug prevents or induces cell death depending on the cell type. The response of steroidogenic luteal cells to NAC is unknown. Our data shows that NAC can behave as an antioxidant or prooxidant in dependency on the concentration and mitochondrial energization. NAC elevated the flowcytometric-measured portion of hypodiploid (dying) cells. This rise was completely abolished by aurintricarboxylic acid, an inhibitor of topoisomerase II. NAC increased the secretion of nitric oxide and cellular nitrotyrosine. An image analysis indicated that cells pretreated with NAC and loaded with DHR showed a fluorescent structure probably elicited by the oxidative product of DHR, rhodamine 123 that sequesters mitochondrially. Pretreating luteal cells with NAC or adding NAC directly to mitochondrial fractions followed by assessing the mitochondrial transmembrane potential difference (Deltapsi) by the JC-1 technique demonstrated a marked decrease in Deltapsi. A protonophore restored Deltapsi and rotenone (an inhibitor of respiratory chain complex I) inhibited mitochondrial recovering. Thus, in steroidogenic luteal cells from healthy mature corpus luteum, NAC impairs cellular survival by interfering with mitochondrial metabolism. The protonophore-induced recovering of NAC-provoked decrease in Deltapsi indicates that an ATP synthase-favored route of H(+) re-entry to the matrix is essentially switched off by NAC while other respiratory chain complexes remain intact. These data may be important for therapeutic timing of treatments with NAC. (c) 2010 International Society for Advancement of Cytometry.

Molecular mediators of angiogenesis

Angiogenesis, or the formation of new blood vessels from the preexisting vasculature, is a key component in numerous physiologic and pathologic responses and has broad impact in many medical and surgical specialties. In this review, we discuss the key cellular steps that lead to the neovascularization of tissues and highlight the main molecular mechanisms and mediators in this process. We include discussions on proteolytic enzymes, cell-matrix interactions, and pertinent cell signaling pathways and end with a survey of the mechanisms that lead to the stabilization and maturation of neovasculatures.

Induction of heparanase in bovine granulosa cells by luteinizing hormone: possible role during the ovulatory process

Follicular development, follicular rupture, and corpus luteum (CL) formation are accompanied by extensive tissue remodeling. We examined whether heparanase (HPSE), which cleaves heparan sulfate glycosaminoglycans, is induced during these processes. Prostaglandin F2alpha injection, which initiated luteolysis and the development of a preovulatory follicle, moderately increased HPSE mRNA in bovine granulosa cells (GCs). GnRH, used to induce gonadotropin surge, markedly augmented HPSE mRNA levels 12 h after its injection. The temporal pattern of HPSE gene expression in follicular-luteal transition was further examined in follicles collected before, and 4, 10, 20, 25, and 60 h after GnRH injection. HPSE mRNA increased transiently 10-20 h after GnRH injection to levels 10-fold higher than in untreated heifers. HPSE protein levels were similarly elevated 20 h after GnRH injection in GCs, but not in the theca layer. Cyclooxygenase-2 (PTGS2) mRNA peaked before ovulation when HPSE levels returned to baseline levels. HPSE mRNA abundance also remained low in the CLs. The antiprogesterone, RU-486, elevated HPSE levels in GC culture, suggesting that progesterone secreted by CLs may inhibit HPSE. HPSE immunostaining was more abundant in GCs than thecae. In cultured GCs, LH induced a transient increase in HPSE mRNA 3-6 h after its addition, but not at 24 h. However, PTGS2 mRNA was clearly induced at this time. These findings suggest that: 1) HPSE may play a role in ovulation but much less so during CL development, and 2) GC-derived HSPE may be a novel member of the LH-induced extracellular matrix-degrading enzyme family and may contribute to follicular rupture.

Vascular dynamics in relation to immunolocalisation of VEGF-A, VEGFR-2 and Ang-2 in the bovine corpus luteum

Vascular dynamics during development and regression of the bovine corpus luteum were investigated morphometrically in relation to immunolocalisation of vascular endothelial growth factor A (VEGF-A), vascular endothelial growth factor receptor 2 (VEGFR-2) and angiopoietin 2 (Ang-2) in the different cell types. Angiogenesis and remodelling of the capillary network between day 8 and 17 of the oestrous cycle was driven by luteal cells, which were highly immunopositive for VEGF-A. Thereafter, immunoreactivity for VEGF-A and VEGFR-2 was mainly found in vascular smooth muscle cells, the predominant cell type in late luteolysis. During early regression, apoptosis of luteal and endothelial cells was closely correlated, resulting in a significant decrease of capillarity. In late regression, an increase in capillary density was found, suggesting that regression and transformation into the corpus albicans requires adequate perfusion. In the phases of vascular remodelling, i.e. mature and late regressing corpus luteum, high scores of Ang-2-immunopositive endothelial and smooth muscle cells were found. Therefore, it may be hypothesised that Ang-2 supports the angiogenic effects of VEGF-A in these luteal stages. Results emphasise that precise staging and a differentiated view on the cellular populations is important in evaluating the controlled regression and transformation of the corpus luteum.

Impaired microRNA processing causes corpus luteum insufficiency and infertility in mice

The microRNA (miRNA) processing enzyme Dicer1 is required for zygotic and embryonic development, but the early embryonic lethality of Dicer1 null alleles in mice has limited our ability to address the role of Dicer1 in normal mouse growth and development. To address this question, we used a mouse mutant with a hypomorphic Dicer1 allele (Dicer(d/d)) and found that Dicer1 deficiency resulted in female infertility. This defect in female Dicer(d/d) mice was caused by corpus luteum (CL) insufficiency and resulted, at least in part, from the impaired growth of new capillary vessels in the ovary. We found that the impaired CL angiogenesis in Dicer(d/d) mice was associated with a lack of miR17-5p and let7b, 2 miRNAs that participate in angiogenesis by regulating the expression of the antiangiogenic factor tissue inhibitor of metalloproteinase 1. Furthermore, injection of miR17-5p and let7b into the ovaries of Dicer(d/d) mice partially normalized tissue inhibitor of metalloproteinase 1 expression and CL angiogenesis. Our data indicate that the development and function of the ovarian CL is a physiological process that appears to be regulated by miRNAs and requires Dicer1 function.

Angiogenesis in the human corpus luteum

Angiogenesis is important for the formation and development of the corpus luteum and for maintenance of luteal function. Blood vessel regression is an important physiological phenomenon in the corpus luteum, which is associated with tissue involution during structural luteolysis. Angiogenesis actively occurs during the early luteal phase and is completed by the mid-luteal phase. Perivascular cells (pericytes) increase in number from the early luteal phase to the mid-luteal phase, suggesting that blood vessels are gradually stabilized until the mid-luteal phase. In the corpus luteum undergoing luteolysis, blood vessels and pericytes decrease in number, which is related to structural involution. In the corpus luteum of early pregnancy, the number of blood vessels with pericytes increases, suggesting that angiogenesis occurs again, accompanied by blood vessel stabilization. These changes in vasculature of the corpus luteum are regulated by the collaboration with vascular endothelial growth factor, which is involved in proliferation of vascular endothelial cells, and angiopoietins, which are involved in stabilization of blood vessels. This review focuses on angiogenesis, blood vessel stabilization and blood vessel regression during the divergent phases of luteal formation, luteal regression and luteal rescue by pregnancy. (Reprod Med Biol 2008; 7: 91-103).

Acid sphingomyelinase involvement in tumor necrosis factor alpha-regulated vascular and steroid disruption during luteolysis in vivo

TNF is well known for its role in inflammation, including direct effects on the vasculature. TNF also is implicated in the regulation of reproduction by its actions to affect ovarian steroidogenic cells and to induce apoptosis of corpus luteum (CL)-derived endothelial cells in vitro. We hypothesized that the disruption of TNF signaling would postpone the regression of the highly vascularized CL in vivo, and this effect could be replicated in mutant mouse models lacking TNF receptor (TNFRI(-/-)) and/or a critical enzyme of TNF signaling, acid sphingomyelinase (ASMase(-/-)). In the current study, the treatment of pseudopregnant mice with the luteolytic mediator prostaglandin F2-alpha (PGF) significantly increased TNF in the ovaries when compared with saline-treated controls. Treatment with PGF also reduced serum progesterone (P4) concentrations and caused involution of the CL. However, pretreatment of pseudopregnant mice with Etanercept (ETA), a TNF-neutralizing antibody, inhibited the PGF-induced decrease in P4 and delayed luteal regression. A similar outcome was evident in pseudopregnant TNFRI(-/-) animals. Treatment of luteal microvascular endothelial cells (MVECs) with TNF provoked a significant increase in ASMase activity when compared with the corresponding controls. Furthermore, TNF-induced MVEC death was inhibited in the ASMase(-/-) mice. The ASMase(-/-) mice displayed no obvious evidence of luteal regression 24 h after treatment with PGF and were resistant to the PGF-induced decrease in P4. Together these data provide evidence that TNF plays an active role in luteolysis. Further studies are required to determine the deleterious effects of anti-inflammatory agents on basic ovarian processes.

A novel physiological culture system that mimics luteal angiogenesis

Luteal inadequacy is a major cause of poor embryo development and infertility. Angiogenesis, the formation of new blood vessels, is an essential process underpinning corpus luteum (CL) development and progesterone production. Thus, understanding the factors that regulate angiogenesis during this critical time is essential for the development of novel strategies to alleviate luteal inadequacy and infertility. This study demonstrates the development of a physiologically relevant primary culture system that mimics luteal angiogenesis. This system incorporates all luteal cell types (e.g. endothelial, steroidogenic cells, fibroblasts and pericytes). Using this approach, endothelial cells, identified by the specific marker von Willebrand factor (VWF), start to form clusters on day 2, which then proliferate and develop thread-like structures. After 9 days in culture, these tubule-like structures lengthen, thicken and form highly organized intricate networks resembling a capillary bed. Development of the vasculature was promoted by coating wells with fibronectin, as determined by image analysis (P<0.001). Progesterone production increased with time and was stimulated by LH re-enforcing the physiological relevance of the model in mimicking in vivo luteal function. LH also increased the area stained positively for VWF by twofold (P<0.05). Development of this endothelial cell network was stimulated by fibroblast growth factor 2 and vascular endothelial growth factor A, which increased total area of VWF positive staining on day 9, both independently (three- to fourfold; P<0.01) and in combination (tenfold; P<0.001). In conclusion, the successful development of endothelial cell networks in vitro provides a new opportunity to elucidate the physiological control of the angiogenic process in the developing CL.

VEGF system expression in different stages of estrous cycle in the corpus luteum of non-treated and superovulated water buffalo

Water buffaloes are easily adaptable animals, whose raising and economical exploitation have been growing in the last three decades all over the world. Hyperstimulation of ovarian function in this species is a common technique aiming to improve reproductive performance. Superovulatory treatment affects corpus luteum (CL) function, which is highly correlated to angiogenic process. The aim of this study was therefore to assess the temporal protein and mRNA expression of VEGF and its receptors in the CL of non-treated and superovulated buffaloes. For that purpose blood samples and CL from 36 healthy (30 untreated, groups 1-5, and 6 superovulated, group 6) non-pregnant buffaloes were collected and the samples were divided into 6 groups according to the age of CL. Plasma samples were submitted to RIA to measure progesterone concentration and CL were subjected to immunohistochemistry and real time PCR for VEGF (vascular endothelial growth factor), Flt-1 (fms-like tyrosine kinase receptor 1) and KDR (kinase insert domain containing region). The VEGF system protein and mRNA expression during CL life span of untreated animals showed a specific time-dependent profile, although protein did not always reflect mRNA concentrations. VEGF expression in luteal cells was high correlated to plasma progesterone levels. Superovulated CL showed a significant increase of the VEGF-system protein and a significant decrease of mRNA expression compared to untreated animals in the same stage of the oestrous cycle. We conclude that VEGF, Flt-1 and KDR protein and mRNA expression in buffalo CL is dependent of estrous cycle stage and superovulatory treatment is able to increase the translation rate of this system.

Application of Doppler Ultrasonography in Cattle Reproduction

The development of Doppler processing extended the scope of sonographic imaging from an anatomical to a physiological basis. This technique became established as a clinical tool in human gynaecology. For example, it has been discussed that the implantation of an embryo is influenced by the uterine blood flow. In cows, this uterine blood flow was investigated, using surgically implanted Doppler ultrasonic or electromagnetic blood flow probes prior to the introduction of colour Doppler sonography in bovine medicine. Therefore, the aims of our studies were to use transrectal Doppler sonography for the non-invasive measurement of uterine and ovarian blood flow in cows and to determine changes in genital perfusion during the oestrous cycle, pregnancy and puerperium, respectively. The results of our studies show that transrectal flow imaging can be used to obtain blood flow velocity waveforms from the uterine arteries at any time during the oestrous cycle, pregnancy and puerperium. During all these phases, characteristic changes in the uterine blood flow could be observed. This uterine blood flow was low during diestrus and high during proestrus and oestrus. During pregnancy, an exponential rise in uterine blood supply could be detected. There was a positive relationship between the uterine blood flow volume (BFV) at the end of gestation and the birth weight of calves. During puerperium, the uterine BFV declined tremendously, especially during the first week after birth. In cows, with pathological disturbances of the pueperium a delayed decrease in the uterine BFV was observed. Characteristic alterations occurred also in the luteal blood flow during the oestrous cycle, which were highly related to those of the progesterone levels. Furthermore, it has been detected by the colour Doppler technique that there is no decrease, but an increase of the luteal blood flow at the beginning of luteolysis in cows. Another group has found that there are close relationships between the LH-surge and the follicular blood flow before ovulation. In conclusion, these studies show that transrectal colour Doppler sonography is a useful technique for the investigation of the genital blood flow and provides new information about physiological changes of the genital organs during, all reproductive phases. The influence of the genital blood flow on fertility in cows needs to be examined further in future studies.

Fibroblast Growth Factor 2 Is More Dynamic than Vascular Endothelial Growth Factor A During the Follicle-Luteal Transition in the Cow1

Luteal inadequacy is a major cause of infertility in a number of species. During the early luteal phase, progesterone production requires the rapid growth of the corpus luteum (CL), which is in turn dependent on angiogenesis. In the present study, we examined the temporal changes in vascular endothelial growth factor A (VEGFA), fibroblast growth factor 2 (FGF2) and secreted protein, acidic, cysteine-rich (osteonectin) (SPARC) during the follicular-luteal transition and CL development in the cow. Luteal VEGFA concentrations increased as the CL developed but were lower in the regressing CL. Conversely, luteal FGF2 concentrations were highest immediately postovulation in the collapsed follicle and declined as the CL developed. Furthermore, three FGF2 isoforms were present in the collapsed follicle, but only one isoform was detected in older CL. Interestingly, FGF2 concentrations increased in the regressing CL. Western blot analysis for SPARC showed the presence of two isoforms, which were constitutively expressed throughout CL development. Further studies investigated the regulation of FGF2 by LH, which showed that FGF2 concentrations in preovulatory follicular fluid were higher in those animals that had experienced an LH surge. Moreover, LH stimulated FGF2 production in dispersed luteal cells. Conversely, the LH surge had no effect on follicular fluid VEGFA concentrations. In conclusion, FGF2 was more dynamic than VEGFA and SPARC during the follicular-luteal transition, which suggests that FGF2 plays a key role in the initiation of angiogenesis at this time. Furthermore, it is likely that this is stimulated by the LH surge. The results also suggest that VEGFA and SPARC have a more constitutive, but essential, role in the development of the CL vasculature.

The gonadotropins: tissue-specific angiogenic factors?

The gonadotropins, whose members are human chorionic gonadotropin (hCG), lutenizing hormone (LH) and follicle-stimulating hormone (FSH) are a well characterized hormone family known to regulate reproductive functions in both females and males. Recent studies indicate that they can modulate the vascular system of reproductive organs. It was shown that gonadotropins not only influence the expression of vascular endothelial growth factor (VEGF) and both its receptors VEGFR-1 and -2, but also modulate other ubiquitously expressed angiogenic factors like the angiopoietins and their receptor Tie-2, basic fibroblast growth factor or placental-derived growth factor. Some recent data indicates a possible direct action of gonadotropins on endothelial cells. Thus, the gonadotropins act as tissue-specific angiogenic factors providing an optimal vascular supply during the menstrual cycle and early pregnancy in the female reproductive tract as well as in testis. In pathological conditions (e.g. preeclampsia, intrauterine growth restriction, ovarian hyperstimulation or endometriosis), these tightly regulated interactions between the gonadotropins and the ubiquitous angiogenic factors appear to be disturbed. The intent of this short manuscript is to review the current knowledge of the regulatory role of the gonadotropins in vasculo- and angiogenesis. We also review angiogenic actions of thyroid-stimulating hormone (TSH), a glycoprotein closely related to gonadotropins, which display strong gonodal actions.

Endothelium-microenvironment interactions in the developing embryo and in the adult

The vascular endothelium is best known for its role in oxygen and nutrient delivery to the various tissues. Growing evidence supports a far more complex role in tissue homeostasis. In particular, reciprocal interactions between endothelial cells and the local microenvironment may regulate organ development and pattern formation. Such interactions appear to be important also in the adult, in normal and pathological conditions.

Platelet-Derived Growth Factors and Receptors in the Rat Corpus Luteum: Localization and Identification of an Effect on Luteogenesis1

Platelet-derived growth factors (PDGFs) and their receptors (PDGFRs) play a vital role in regulating cell growth and angiogenesis. In this study, the expression of the family of PDGFs and PDGFRs in the ovarian corpus luteum were identified and characterized, and an effect of their activity on development of the corpus luteum revealed. Gonadotropin-stimulated immature rats were utilized as a model of induced ovulation, luteogenesis, and pseudopregnancy. Levels of ovarian mRNA for Pdgfb and Pdgfd, and their receptor, Pdgfrb, increased significantly as early as 4 h after human chorionic gonadotropin (hCG) injection in immature rats primed with equine chorionic gonadotropin (eCG). Gonadotropin regulation of Pdgfb expression was confirmed by in vitro promoter-reporter assays, which showed a 2- to 3-fold increase in Pdgfb promoter activity in response to luteinizing hormone (LH). Inhibition studies implicated protein kinase A, phosphatidylinositol 3-kinase and mitogen activated protein kinase signaling pathways in the LH-induced upregulation. In the corpus luteum, PDGFA, PDGFB, PDGFC, and PDGFRA were localized to a population of luteal parenchymal/steroidogenic cells. PDGFRB was expressed primarily in what appeared to be cells of the luteal microvasculature. Intraovarian injection of an inhibitor of PDGF receptor activity, the tyrphostin AG1295, prior to injection of hCG in eCG-primed immature rats resulted in a significant 21.86%+/-11.15% decrease in corpora lutea per treated ovary in comparison to the contralateral vehicle-injected control ovary. In addition, the treated ovary of 3 of 16 rats showed widespread hemorrhage throughout the entire ovary, indicating a possible role for PDGF receptor activity in maintenance of the ovarian vasculature.

The molecular control of corpus luteum formation, function, and regression

The corpus luteum (CL) is one of the few endocrine glands that forms from the remains of another organ and whose function and survival are limited in scope and time. The CL is the site of rapid remodeling, growth, differentiation, and death of cells originating from granulosa, theca, capillaries, and fibroblasts. The apparent raison d'etre of the CL is the production of progesterone, and all the structural and functional features of this gland are geared toward this end. Because of its unique importance for successful pregnancies, the mammals have evolved a complex series of checks and balances that maintains progesterone at appropriate levels throughout gestation. The formation, maintenance, regression, and steroidogenesis of the CL are among the most significant and closely regulated events in mammalian reproduction. During pregnancy, the fate of the CL depends on the interplay of ovarian, pituitary, and placental regulators. At the end of its life span, the CL undergoes a process of regression leading to its disappearance from the ovary and allowing the initiation of a new cycle. The generation of transgenic, knockout and knockin mice and the development of innovative technologies have revealed a novel role of several molecules in the reprogramming of granulosa cells into luteal cells and in the hormonal and molecular control of the function and demise of the CL. The current review highlights our knowledge on these key molecular events in rodents.

Effects of Storage and Passage of Bovine Luteal Endothelial Cells on Endothelin-1 and Prostaglandin F2.ALPHA. Production

To establish a storage system for isolated bovine luteal endothelial cells (LECs), we investigated the basal and tumor necrosis factor (TNF) alpha-stimulated production of endothelin-1 (ET-1) and prostaglandin (PG) F2alpha in unfrozen and frozen-thawed LECs until passage 10. LECs were obtained from developing corpora lutea (CL; days 5-7 of the estrous cycle) using enzymatic digestion and magnetic beads coated with lectin BS-1. The LECs were frozen at -80 C or further cultured and/or passaged until passage 10 in DMEM/Ham's F-12 supplemented with 10% calf serum. The hormonal productions of unfrozen and frozen/thawed LECs were compared through passages 2-10. When both the unfrozen and frozen/thawed cells reached confluence, the culture medium was replaced with fresh medium containing 0.1% bovine serum albumin (BSA), and the cells were incubated with TNFalpha (50 ng/ml) for 12 h. The basal productions of ET-1 and PGF2alpha by the unfrozen and frozen/thawed LECs were similar at passage 2. The basal production of PGF2alpha by LECs was not altered by passage and storage at -80 C, whereas the basal production of ET-1 decreased from passage 2 and 3 to passage 4 in the unfrozen LECs and from passage 2 to passage 3 in the frozen/thawed LECs. However, production of ET-1 by the unfrozen and frozen/thawed LECs was similar between passages 4-10 and passages 3-10, respectively. Exposure of LECs to TNFalpha increased (P<0.05) ET-1 and PGF2alpha production by the unfrozen and frozen-thawed LECs in all passages examined. Thus, LECs obtained from developing CLs and stored until passage 10 can be used for study of the physiology of LECs in vitro.

Localization of Ang-1, -2, Tie-2, and VEGF expression at endothelial-pericyte interdigitation in rat angiogenesis

Endothelial cells and pericytes play critical role in angiogenesis, which is controlled, in part, by the angiopoietin (Ang)/Tie-2 system and vascular endothelial growth factor (VEGF). Here, we investigated Ang, Tie-2, and VEGF expression within endothelial cells and pericyte interdigitations (EPI), which consist of cytoplasmic projections of pericytes and corresponding endothelial indentations. After subcutaneous implantation of a thermoreversible gelation polymer disc in rats, the capillary density was low on day 5, increased to a peak on day 7, and then decreased on days 10-20. A small number of EPI were observed on day 5, then increased sharply to a peak on day 10, but had decreased on day 20. Light and electron microscopy immunohistochemical and RNA in situ hybridization analyses revealed that Tie-2 localized at endothelial cells, and Ang-2 localized at endothelial cells and pericytes, while Ang-1 and VEGF localized at pericytes, and Ang-1 was most intensely observed at EPI of pericytes. Conventional quantitative RT-PCR and Western blot analyses revealed that the level of Ang-1 was low on days 5-7, then increased on days 10-20, while the level of VEGF was high on days 5-10, but had decreased on day 20. The level of Ang-2 remained high and Tie-2 remained at the level of the control on days 5-20. The present study showed that the angiogenic phase might be initiated by increases in Ang-2 and VEGF, while the microvessel maturation phase might be initiated by a relative increase in Ang-1 and a decrease in VEGF. Moreover, EPI might serve as a pathway for the Ang-1/Tie-2 system, with VEGF promoting pericyte recruitment for microvascular integrity.

Inverse relationship between nitric oxide synthases and endothelin-1 synthesis in bovine corpus luteum: interactions at the level of luteal endothelial cell

Endothelin-1 (ET-1) and nitric oxide (NO) play pivotal roles in corpus luteum (CL) function. The present study examined the interplay between NO and ET-1 synthesis in the bovine CL. We found similar inducible and endothelial NO synthase (iNOS and eNOS, respectively) activities in the young CL (d 1-5) expressing the highest levels of both eNOS and iNOS mRNA. These values later declined at mid-cycle (d 8-15) and remained low at later stages (d 16-18). Luteolysis, initiated by prostaglandin F2alpha analog administration, further reduced NOS mRNA and by 24 h, NOS values dropped to approximately 15% of those at mid-cycle. eNOS protein levels followed a similar pattern to its mRNA. Because endothelial cells (ECs) are the main site for ET-1 and NO production in the CL, we examined the direct effects of the NO donor, NONOate on luteal ECs (LECs). Elevated NO levels markedly decreased ET-1 mRNA, and peptide concentrations in cultured and freshly isolated LECs in a dose-dependent manner. In agreement, NOS inhibitor, NG-nitro-l-arginine methyl ester, stimulated ET-1 mRNA expression in these cells. Interestingly, NO also up-regulated prostaglandin F2alpha receptors in LECs. These data show that there is an inverse relationship between NOS and ET-1 throughout the CL life span, and imply that this pattern may be the result of their interaction within the resident LECs. NOS are expressed in a physiologically relevant manner: elevated NO at an early luteal stage is likely to play an important role in angiogenesis, whereas reduced levels of NO during luteal regression may facilitate the sustained up-regulation of ET-1 levels during luteolysis.

Vascular composition, apoptosis, and expression of angiogenic factors in the corpus luteum during prostaglandin F2alpha-induced regression in sheep

Corpora lutea and blood samples were collected from superovulated ewes 0, 4, 8, 12 and 24 h after prostaglandin F(2alpha) (PGF) analog injection on day 10 of the estrous cycle. Changes in vascular cell and fibroblast composition, apoptosis and mRNA expression for several angiogenic factors in the corpus luteum (CL) were determined. While peripheral progesterone concentration decreased at 24 h after PGF injection, CL weight did not change. The area of positive BS-1 lectin staining (endothelial cell marker), smooth muscle cell actin (SMCA; pericyte and SMC marker), collagen type 1 (fibroblast marker), and the rate of cell death changed in luteal tissues after PGF treatment. In association with these cellular changes, mRNA for several angiogenic factors including vascular endothelial growth factor (VEGF) and receptors (Flt and KDR), basic fibroblast growth factor (FGF2) and receptor, angiopoietin (ANGPT) 1 and receptor Tie-2, endothelial nitric oxide synthase (NOS3), and angiotensin II receptor 1 (AT1) were altered. Changes in endothelial cell marker expression were positively correlated with changes in VEGF and NO systems. In addition, changes in mRNA expression for VEGF, Flt and KDR were positively correlated with changes in ANGPT2, Tie-2, and NOS3, indicating a functional relationship. This data demonstrates that after an initial increase, the endothelial component of the vascular bed decreases during PGF-induced luteal regression. However, SMCA expression remained high during luteal regression, potentially indicating a role of pericytes and vascular SMC in luteolysis, likely to regulate tissue remodeling and to maintain the integrity of larger blood vessels. Further, it appears that early regression may increase collagen type 1 production and/or expression by fibroblasts. Expression of angiogenic factors is influenced by PGF-induced luteolysis and may serve to maintain vascular structure in order to aid luteal regression.

Expression of endothelial nitric oxide synthase in the ovine ovary throughout the estrous cycle

This study was conducted to evaluate the expression of endothelial nitric oxide synthase (eNOS) in ovarian follicles and corpora lutea (CL) throughout the estrous cycle in sheep. Three experiments were conducted to (1) immunolocalize eNOS protein, (2) determine expression of mRNA for eNOS and its receptor guanylate cyclase 1 soluble β3 (GUCY1B3), and (3) co-localize eNOS and vascular endothelial growth factor (VEGF) proteins in the follicles and/or CL throughout the estrous cycle. In experiment 1, ovaries were collected from ewes treated with FSH, to induce follicular growth or atresia. In experiment 2, ovaries were collected from ewes treated with FSH and hCG to induce follicular growth and ovulation. In experiment 3, ovaries were collected from superovulated ewes to generate multiple CL on days 2, 4, 10, and 15 of the estrous cycle. In experiments 1 and 2, the expression of eNOS protein was detected in the blood vessels of the theca externa and interna of healthy ovarian follicles. However, in early and advanced atretic follicles, eNOS protein expression was absent or reduced. During the immediate postovulatory period, eNOS protein expression was detected in thecal-derived cells that appeared to be invading the granulosa layer. Expression of eNOS mRNA tended to increase in granulosa cells at 12 and 24 h, and in theca cells 48 h after hCG injection. In experiment 3, eNOS protein was located in the blood vessels of the CL during the estrous cycle. Dual localization of eNOS and VEGF proteins in the CL demonstrated that both were found in the blood vessels.

Expression of gap junctional connexins 26, 32, and 43 mRNA in ovarian preovulatory follicles and corpora lutea in sheep

The objective of the current study was to evaluate the expression of connexins (Cx)26, Cx32, and Cx43 mRNA in granulosa and theca cells during the peri-ovulatory period (experiment 1) and in the corpus luteum (CL) during the estrous cycle (experiment 2) and during prostaglandin F2alpha (PGF)-induced luteal regression (experiment 3) in FSH-treated ewes. In experiment 1, Cx26, Cx32, and Cx43 mRNA was expressed in granulosa and theca cells, and expression of Cx32 and Cx43 mRNA, but not Cx26, was greater (p<0.001) in granulosa than in theca cells throughout the peri-ovulatory period. Expression of Cx43 mRNA in granulosa and theca cells decreased (p<0.01) 24 h after hCG treatment. In experiment 2, expression of Cx26 mRNA in the CL tended to be greater (p<0.06) on day 10 than on days 5 or 15, but expression of Cx43 mRNA was greater (p<0.01) on day 5 than on days 10 and 15 of the estrous cycle. In experiment 3, expression of Cx26, but not Cx32 or Cx43 mRNA decreased (p<0.001) during PGF-induced luteal regression. In all 3 experiments, expression of Cx32 mRNA was much less than Cx26 and Cx43 mRNA. Moreover, Cx32 mRNA expression was unchanged during the peri-ovulatory period or during several stages of luteal development and PGF-induced regression of the CL. Thus, we have shown that the mRNA expression pattern of Cx26 and Cx43 changes during peri-ovulatory period and during several stages of the luteal development. This suggests that Cx26 and Cx43 play a role in ovarian tissue remodeling during the critical time around ovulation and throughout luteal tissue growth, differentiation, and regression in sheep.

Endocrine and cellular characteristics of corpora lutea from cows with a delayed post-ovulatory progesterone rise

The timing of the post-ovulatory progesterone rise is critical to the embryonic development and survival. The aim of this study was to determine the underlying causes of delayed post-ovulatory progesterone rises. Two groups of non-lactating dairy cows with early (n = 11) or late (n = 9) post-ovulatory progesterone rises were created by inducing luteolysis in the presence of either a large (> 10 mm) or small (< 10 mm) follicle, respectively. LH pulses were measured on days 4 (all cows) and 7 (n = 7, early; n = 5, late) (day 1= ovulation). The cows were slaughtered on day 5 (n = 4 each group) or 8 (n = 7, early; n = 5, late). Immunohistochemical analysis for endothelial cells (von Willebrand Factor, VWF), steroidogenic cells (3beta-HSD) and proliferation marker (Ki67) were performed. The basal progesterone production and LH responsiveness (0.001-100 ng/ml) of dispersed luteal cells was investigated. The luteal concentrations of FGF-2 and VEGF were measured by ELISA and RIA, respectively. There were no differences in LH pulse characteristics, area of VWF staining, proliferation index, steroidogenic cell characteristics, basal or LH-stimulated progesterone production by luteal cells between cows with an early or late progesterone rise (P > 0.10). However, the area of VWF staining increased from days 5 to 8, while the proliferation index decreased (P < 0.05). Furthermore, the luteal cells were more responsive to LH on day 8 (P < 0.01). Luteal concentrations of FGF-2 were higher on day 5 (P = 0.05), while VEGF was greater on day 8 (P < 0.01). In conclusion, we have clearly shown that LH support, degree of vascularization or luteal cell steroidogenic capacity were not the major factors responsible for inadequate secretion of progesterone by the developing bovine CL.

Morphological patterns of angiogenesis in ovarian follicle capillary networks. A scanning electron microscopy study of corrosion cast

To describe the morphological characteristics of the ovarian follicle (F) capillary neoformation and regression, the angiogenic figures were studied by means of scanning electron microscopy of corrosion casts in developing and mature F of rabbit, pig, and cow. Developing F showed gradual neoformation of thecal capillaries characterized by budding and then sprouting, likely from preexisting interstitial vessels. Postcapillary venules frequently showed vasoconstriction rings (sphincters). Vasodilation followed capillary elongation. Mature F, in addition to vessel elongation and dilation, also presented infolding of dilated capillary walls, followed by capillary duplication and sinusoidalization. Periovulatory F mainly showed functional changes, such as capillary dilation, signs of iperpermeabilization, and ischemia, the latter being limited to the apical follicular area. Vessel regression was characterized by thinning of capillaries and presence of avascular areas within the atretic F wall at any stage. This study showed two main types of angiogenic patterns. (a) longitudinal elongation (in series, sprouting angiogenesis) characterizing the initial phase of F development and (b) parallel duplication (in parallel, infolding or intussusceptive angiogenesis), ending in capillary lateral replication or splitting, secondary to functional microvascular changes. Indirect evidence of the establishment of postcapillary resistances contributing to capillary remodeling, was also shown. It is concluded that the sequence of capillary neoformation in mammalian ovarian F occurs in six steps: (1) budding, (2) sprouting (and elongation), (3) dilation, (4) infolding (intussusception), (5) duplication (splitting and elongation), and (6) sinusoidalization. Capillary regression hits F at any stage and characterizes F atresia.

Microvascularization and angiogenic activity of equine corpora lutea throughout the estrous cycle

Corpus luteum growth and endocrine function are closely dependent on the formation of new capillaries. The objectives of this study were to evaluate (i) tissue growth and microvascular development in the equine cyclic luteal structures; (ii) in vitro angiogenic activity of luteal tissues in response to luteotrophic (LH, PGE(2)) and luteolytic (PGF(2alpha)) hormones and (iii) to relate data to luteal endocrinological function. Our results show that microvascular density was increased in the early and mid luteal phase, followed by a fall in the late luteal phase and a further decrease in the corpus albicans. Hyperplasia of luteal tissue increased until the mid luteal phase and it was followed by tissue regression. Luteal explants were cultured with no hormone added, or with PGF(2alpha), LH, PGE(2), LH+PGE(2) or LH+PGF(2alpha). Media conditioned by equine luteal tissue from different stages of the luteal phase were able to stimulate mitogenesis of bovine aortic endothelial cells (BAEC), suggesting the presence of angiogenic activity. No difference was observed among luteal structures on their mitogenic capacity, for any treatment used. Nevertheless, Late-CL conditioned-media with PGF(2alpha) showed a significant decrease in BAEC proliferation (p<0.05) and LH+PGF(2alpha) a tendency to reduce mitogenesis. Thus, prostaglandin F(2alpha) may play a role on vascular regression of the CL during the late luteal phase in the mare. These data suggest that luteal angiogenesis and vascular regression in the mare are coordinated with the development of non-vascular tissue and might be regulated by many different factors.

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.