Angiogenesis in the human corpus luteum

Angiogenesis and Apoptosis: Data Comparison of Similar Microenvironments in the Corpus Luteum and Tumors

The corpus luteum is a temporary endocrine gland formed in the ovary after ovulation, and it plays a critical role in animal reproductive processes. Tumors rely on the development of an adequate blood supply to ensure the delivery of nutrients and oxygen and the removal of waste products. While angiogenesis occurs in various physiological and pathological contexts, the corpus luteum and tumors share similarities in terms of the signaling pathways that promote angiogenesis. In the corpus luteum and tumors, apoptosis plays a crucial role in controlling cell numbers and ensuring proper tissue development and function. Interestingly, there are similarities between the apoptotic-regulated signaling pathways involved in apoptosis in the corpus luteum and tumors. However, the regulation of apoptosis in both can differ due to their distinct physiological and pathological characteristics. Thus, we reviewed the biological events of the corpus luteum and tumors in similar microenvironments of angiogenesis and apoptosis.

Developmental and functional roles of androgen and interactive signals for external genitalia and erectile tissues

Background

Recent progress in molecular and signal analyses revealed essential functions of cellular signals including androgen and related growth factors such as Wnt regulators for external genitalia (ExG) development and its pathogenesis. Accumulated data showed their fundamental functions also for erectile tissue (corporal body) development and its abnormalities. The current review focuses on such signals from developmental and functional viewpoints.

Methods

Experimental strategies including histological and molecular signal analyses with conditional mutant mice for androgen and Wnt signals have been extensively utilized.

Main findings

Essential roles of androgen for the development of male-type ExG and urethral formation are shown. Wnt signals are associated with androgen for male-type ExG organogenesis. Androgen plays essential roles in the development of erectile tissue, the corporal body and it also regulates the duration time of erection. Wnt and other signals are essential for the regulation of mesenchymal cells of erectile tissue as shown by its conditional mutant mouse analyses. Stress signals, continuous erection, and the potential of lymphatic characteristics of the erectile vessels with sinusoids are also shown.

Conclusion

Reiterated involvement of androgen, Wnt, and other regulatory factors is stated for the development and pathogenesis of ExG and erectile tissues.

Novel erectile analyses revealed augmentable penile Lyve-1, the lymphatic marker, expression

Purpose

The pathophysiology of penis extends to erectile dysfunction (ED) to conditions including sexually transmitted diseases (STDs) and cancer. To date, there has been little research evaluating vascular drainage from the penis. We aimed to evaluate penile blood flow in vivo and analyze its possible relationship with the lymphatic maker.

Materials and Methods

We established an in vivo system designed to assess the dynamic blood outflow from the corpus cavernosum (CC) by dye injection. To analyze lymphatic characteristics in the CC, the expression of Lyve-1, the key lymphatic endothelium marker, was examined by the in vitro system and lipopolysaccharide (LPS) injection to mimic the inflammatory conditions.

Results

A novel cavernography methods enable high-resolution morphological and functional blood drainage analysis. The expression of Lyve-1 was detected along the sinusoids. Furthermore, its prominent expression was also observed after penile LPS injection and in the erectile condition.

Conclusions

The current in vivo system will potentially contribute to the assessment of penile pathology from a novel viewpoint. In addition, current analyses revealed inducible Lyve-1 expression for LPS injection and the erection state, which requires further analyses on penile lymphatic system.

Effect of vitamin E, D-limonene, and their combination on nulliparous rabbit reproductive performance

Oxidative status is important in reproductive performance and using two natural antioxidants is more beneficial than one in nulliparous rabbits. The goal, effect of vitamin E (VitE), D-limonene (DL), and VitE+DL on maternal LBW (MLBW), conception (CR), pregnancy (PR), and kindling rates (KR), gestation length (GL), total litter size at birth (TLSB) and weaning (TLSW), live kits at birth (LKB) and weaning (LKW), dead kits at birth (DKB) and weaning (DKW), kits mortality rate at weaning (KMRW), Kit weight at birth (KWB) and weaning (KWW), total kit weight at birth (TKWB) and weaning (TKWW), and concentrations of progesterone (P4) and Malondialdehyde (MDA), during first two pregnancies. A total of 24 healthy female WNZ rabbits were randomly selected and assigned into four groups (6/each). Control (animals injected with 1.0 mL propylene glycol), VitE (60 mg IM injection/animal, 2X/week pre-mating and 3X post-mating until mid-pregnancy, DL (20 mg IM injection/animal, 2X/week pre-mating and 1X at mating, and VitE+DL (IM injection/animal with the same doses and times applied in VitE and DL groups. All animals were treated during 1st pregnancy only. The results confirmed that animals treated with VitE+DL gained significant maternal LBW in 1st pregnancy, reduced dead kit number at birth and kit mortality rate at weaning, increased live kits and total kit weight at birth and weaning in the two pregnancies, and also increased significantly kit weight at birth and weaning in the treatments than controls in the two pregnancies, and DL was greater in 1st pregnancy. Progesterone concentrations in mid-pregnancy rose significantly in VitE+DL during 1st pregnancy and DL in 2nd pregnancy. Malondialdehyde concentrations dropped significantly in VitE and VitE+DL in mid-pregnancy in the two pregnancies. Eventually, the integration of VitE and DL displayed their unique properties for improving productive and reproductive performance in nulliparous rabbits.

Relationship between ovarian ultrasonographic findings on the seventh post-estrus day and plasma progesterone concentration, nutritional metabolic factors, and pregnancy outcome in dairy cows

To improve the accuracy of ultrasonographic assessment of luteal function, we investigated the relationship between ovarian ultrasonographic findings on Day 7 (Day 1 = ovulation) and plasma progesterone (P₄) concentration, nutritional metabolic factors, and pregnancy outcome. A total of 47 spontaneous estrus events were investigated in 38 lactating Holstein cows (artificial insemination, n = 31; embryo transfer, n = 16). Transrectal ultrasonography was performed on Days 0 and 7 to measure the pre-ovulatory follicle area on Day 0 and the luteal tissue area (LTA), luteal blood flow area (LBF), relative LBF (rLBF) (= LBF/LTA), and dominant follicle area (DFA) on Day 7. Blood samples were collected on Day 7 to measure plasma P₄, insulin-like growth factor-I (IGF-I), insulin, and metabolites. Plasma P₄ concentration was positively correlated with LTA but was not associated with LBF or rLBF. Plasma P₄ concentration was positively correlated with blood glucose and IGF-I and negatively correlated with blood urea nitrogen and free fatty acid, and no significant relationship was found between the ultrasonographic findings of the corpus luteum (CL) and these blood metabolites. Pregnant cows had smaller DFA than non-pregnant cows. In conclusion, LTA measurement can help predict plasma P₄ concentration, but it was difficult to detect variations in plasma P₄ concentration in relation to changes in energy status by evaluating the CL ultrasonographically. A combined assessment of CL and first-wave dominant follicle may be important in evaluating fertility.

Biomechanical forces and signals operating in the ovary during folliculogenesis and their dysregulation: implications for fertility

BACKGROUND

Folliculogenesis occurs in the highly dynamic environment of the ovary. Follicle cyclic recruitment, neo-angiogenesis, spatial displacement, follicle atresia and ovulation stand out as major events resulting from the interplay between mechanical forces and molecular signals. Morphological and functional changes to the growing follicle and to the surrounding tissue are required to produce oocytes capable of supporting preimplantation development to the blastocyst stage.

OBJECTIVE AND RATIONALE

This review will summarize the ovarian morphological and functional context that contributes to follicle recruitment, growth and ovulation, as well as to the acquisition of oocyte developmental competence. We will describe the changes occurring during folliculogenesis to the ovarian extracellular matrix (ECM) and to the vasculature, their influence on the mechanical properties of the ovarian tissue, and, in turn, their influence on the regulation of signal transduction. Also, we will outline how their dysregulation might be associated with pathologies such as polycystic ovary syndrome (PCOS), endometriosis or premature ovarian insufficiency (POI). Finally, for each of these three pathologies, we will highlight therapeutic strategies attempting to correct the altered biomechanical context in order to restore fertility.

SEARCH METHODS

For each area discussed, a systematic bibliographical search was performed, without temporal limits, using PubMed Central, Web of Science and Scopus search engines employing the keywords extracellular matrix, mechanobiology, biomechanics, vasculature, angiogenesis or signalling pathway in combination with: ovary, oogenesis, oocyte, folliculogenesis, ovarian follicle, theca, granulosa, cumulus, follicular fluid, corpus luteum, meiosis, oocyte developmental competence, preimplantation, polycystic ovary syndrome, premature ovarian insufficiency or endometriosis.

OUTCOMES

Through search engines queries, we yielded a total of 37 368 papers that were further selected based on our focus on mammals and, specifically, on rodents, bovine, equine, ovine, primates and human, and also were trimmed around each specific topic of the review. After the elimination of duplicates, this selection process resulted in 628 papers, of which 287 were cited in the manuscript. Among these, 89.2% were published in the past 22 years, while the remaining 8.0%, 2.4% or 0.3% were published during the 1990s, 1980s or before, respectively. During folliculogenesis, changes occur to the ovarian ECM composition and organization that, together with vasculature modelling around the growing follicle, are aimed to sustain its recruitment and growth, and the maturation of the enclosed oocyte. These events define the scenario in which mechanical forces are key to the regulation of cascades of molecular signals. Alterations to this context determine impaired folliculogenesis and decreased oocyte developmental potential, as observed in pathological conditions which are causes of infertility, such as PCOS, endometriosis or POI.

WIDER IMPLICATIONS

The knowledge of these mechanisms and the rules that govern them lay a sound basis to explain how follicles recruitment and growth are modulated, and stimulate insights to develop, in clinical practice, strategies to improve follicular recruitment and oocyte competence, particularly for pathologies like PCOS, endometriosis and POI.

Emerging structural and pathological analyses on the erectile organ, corpus cavernous containing sinusoids

Background

The corpus cavernosum (CC) containing sinusoids plays fundamental roles for erection. Analysis of pathological changes in the erectile system is studied by recent experimental systems. Various in vitro models utilizing genital mesenchymal-derived cells and explant culture systems are summarized.

Methods

3D reconstruction of section images of murine CC was created. Ectopic chondrogenesis in aged mouse CC was shown by a gene expression study revealing the prominent expression of Sox9. Various experimental strategies utilizing mesenchyme-derived primary cells and tissue explants are introduced.

Main Findings

Possible roles of Sox9 in chondrogenesis and its regulation by several signals are suggested. The unique character of genital mesenchyme is shown by various analyses of external genitalia (ExG) derived cells and explant cultures. Such strategies are also applied to the analysis of erectile contraction/relaxation responses to many signals and aging process.

Conclusion

Erectile dysfunction (ED) is one of the essential topics for the modern aged society. More comprehensive studies are necessary to reveal the nature of the erectile system by combining multiple cell culture strategies.

Characterization of the roles of amphiregulin and transforming growth factor β1 in microvasculature-like formation in human granulosa-lutein cells

Vascular endothelial-cadherin (VE-cadherin) is an essential component that regulates angiogenesis during corpus luteum formation. Amphiregulin (AREG) and transforming growth factor β1 (TGF-β1) are two intrafollicular factors that possess opposite functions in directing corpus luteum development and progesterone synthesis in human granulosa-lutein (hGL) cells. However, whether AREG or TGF-β1 regulates the VE-cadherin expression and subsequent angiogenesis in the human corpus luteum remains to be elucidated. Results showed that hGL cells cultured on Matrigel spontaneously formed capillary-like and sprout-like microvascular networks. Results of specific inhibitor treatment and small interfering RNA-mediated knockdown revealed that AREG promoteed microvascular-like formation in hGL cells by upregulating the VE-cadherin expression mediated by the epidermal growth factor receptor (EGFR)-extracellular signal-regulated kinase1/2 (ERK1/2) signaling pathway. However, TGF-β1 suppressed microvascular-like formation in hGL cells by downregulating VE-cadherin expression mediated by the activin receptor-like kinase (ALK)5-Sma- and Mad-related protein (SMAD)2/3/4 signaling pathway. Collectively, this study provides important insights into the underlying molecular mechanisms by which TGF-β1 and AREG differentially regulate corpus luteum formation in human ovaries.

Parenteral Copper Administration at the Beginning of a Fixed-Time Artificial Insemination Protocol in Beef Cattle: Effect on Ovarian Function and Pregnancy Rates

The aim of this study was to evaluate the association between plasma copper (Cu) concentration and ovarian function during a fixed-time artificial insemination (FTAI) protocol and the effect of parenteral Cu administration (100 mg) at the start of such protocol (day 0) on area of preovulatory follicle (APF); area of corpus luteum (ACL), plasma estradiol (E2), and progesterone (P4) concentrations; CL blood flow (CLBF); and pregnancy rate in beef heifers and cows. In cows, plasma Cu concentration on days 0 and 7 correlated positively with APF. Copper administration increased plasma Cu concentration and decreased APF and plasma E2 concentration (day 9), without modifying ACL, plasma P4 concentration, and CLBF (day 16) in cows. Pregnancy rate was higher in Cu-supplemented cattle on day 41 after FTAI as compared with controls (58.76 and 45.28%, respectively). In conclusion, Cu administration at the beginning of the FTAI protocol increased pregnancy rate in beef heifers and cows, modifying APF and plasma E2 concentration in the latter.

Luteal blood flow as a predictive factor for methotrexate treatment outcomes in women with unruptured tubal pregnancy

BACKGROUND

Blood flow in the corpus luteum is associated with luteal function. However, the impact of luteal blood flow on methotrexate (MTX) treatment in women with unruptured tubal pregnancy has not been reported. The aim of the present study was to observe the impact of luteal blood flow on the therapeutic effect of MTX in women with unruptured tubal pregnancy.

METHODS

A prospective observational study recruited 129 women with unruptured tubal pregnancy in the First Affiliated Hospital of Xi'an Jiaotong University from September 2016 to June 2018. One hundred and fifteen women were treated successfully with MTX, and women were divided into 2 groups according to luteal blood flow: the poor luteal blood flow group and the abundant luteal blood flow group. The therapeutic effects were compared between the two groups.

RESULTS

Women in the abundant luteal blood flow group had a significantly higher serum β-human chorionic gonadotropin (β-hCG) level 4 days, 1 week and 2 weeks after MTX treatment compared with women in the poor luteal blood flow group (P < 0.05). The average diameter of the ectopic mass 1 week, 2 weeks and 3 weeks after MTX treatment in women with abundant luteal blood flow was significantly larger (P < 0.05), and the time of serum β-hCG clearance and ectopic mass disappearance were significantly longer compared with those in women in the poor luteal blood flow group (P < 0.05).

CONCLUSIONS

Luteal blood flow might be a predictive factor for MTX treatment outcomes in women with unruptured tubal pregnancy, and those with abundant luteal blood flow need a longer recovery time.

Inflammation and angiogenesis in the corpus luteum

Angiogenesis is a very important process that helps establish and maintain the normal structure and function of the corpus luteum (CL). Early luteal development can be considered a kind of physiological injury with an inflammatory response; therefore, the inflammatory response may play an important role in the luteal angiogenesis. The inflammatory response is companied by activated leukocytes and their mediators. For luteal tissue, numerous activated leukocytes such as macrophages, neutrophils and eosinophils are present in the early luteal phase and are widely involved in neovascularization. The objective of this review is to describe the role of the inflammatory factors in the angiogenesis and to discuss their mechanism. Knowledge of action and mechanism of these inflammatory factors on angiogenic activity will be beneficial for the understanding of luteal function.

C/EBPβ regulates Vegf gene expression in granulosa cells undergoing luteinization during ovulation in female rats

The ovulatory LH-surge increases Vegf gene expression in granulosa cells (GCs) undergoing luteinization during ovulation. To understand the factors involved in this increase, we examined the roles of two transcription factors and epigenetic mechanisms in rat GCs. GCs were obtained from rats treated with eCG before, 4 h, 8 h, 12 h and 24 h after hCG injection. Vegf mRNA levels gradually increased after hCG injection and reached a peak at 12 h. To investigate the mechanism by which Vegf is up-regulated after hCG injection, we focused on C/EBPβ and HIF1α. Their protein expression levels were increased at 12 h. The binding activity of C/EBPβ to the Vegf promoter region increased after hCG injection whereas that of HIF1α did not at this time point. The C/EBPβ binding site had transcriptional activities whereas the HIF1α binding sites did not have transcriptional activities under cAMP stimulation. The levels of H3K9me3 and H3K27me3, which are transcriptional repression markers, decreased in the C/EBPβ binding region after hCG injection. The chromatin structure of this region becomes looser after hCG injection. These results show that C/EBPβ regulates Vegf gene expression with changes in histone modifications and chromatin structure of the promoter region in GCs undergoing luteinization during ovulation.

Locally existing endothelial cells and pericytes in ovarian stroma, but not bone marrow-derived vascular progenitor cells, play a central role in neovascularization during follicular development in mice

Background

Neovascularization is necessary for follicular growth. Vascularization is first observed in preantral follicles, and thereafter the vasculature markedly increases in follicles undergoing development. Neovascularization includes angiogenesis and vasculogenesis. Vasculogenesis is the formation of new blood vessels by bone marrow-derived endothelial progenitor cells. It is unclear whether vasculogenesis occurs during follicular growth. Blood vessels must be mature to be functional blood vessels. Mature blood vessels are characterized by the recruitment of pericytes. However, it is unclear where pericytes come from and whether they contribute to neovascularization in the follicle during follicular growth. In this study, we investigated whether bone marrow-derived progenitor cells that differentiate into vascular endothelial cells or pericytes contribute to neovascularization during follicular growth.

Methods

A parabiosis model was used in this study. Six-week-old wild-type and transgenic female mice expressing green fluorescent protein (GFP) were conjoined between the lateral abdominal regions to create a shared circulatory system. After 6 weeks, the ovaries were obtained and immunostained for CD31/CD34 (a vascular endothelial cell marker), platelet-derived growth factor receptor-β (PDGFR-β) (a pericyte marker), and GFP (a bone marrow-derived cell marker).

Results

Cells that were positive for CD34 and PDGFR-β were observed in the stroma adjacent to the primary or early preantral follicles and in the theca cell layer of the follicles from the late preantral stage to the preovulatory stage. CD31/CD34 and GFP double-positive cells were observed in the theca cell layer of the follicle from the antral stage to the preovulatory stage while the number of double-positive cells in the preovulatory follicles did not increase. PDGFR-β and GFP double-positive cells were observed in the theca cell layer of the preovulatory follicle but not in the smaller follicle.

Conclusions

Locally existing endothelial cells and pericytes in the stroma play a central role in the neovascularization during follicular growth, while bone marrow-derived endothelial cells and pericytes partially contribute to this process.

Involvement of bone marrow-derived vascular progenitor cells in neovascularization during formation of the corpus luteum in mice

Neovascularization is necessary for formation of the corpus luteum (CL) and includes angiogenesis and vasculogenesis. Vasculogenesis is the formation of new blood vessels by bone marrow-derived endothelial progenitor cells. Here we investigated whether vasculogenesis occurs in neovascularization during CL formation. Mice transplanted with bone marrow from transgenic mice expressing green fluorescent protein (GFP) were injected with equine chorionic gonadotropin and human chorionic gonadotropin (hCG) to induce ovulation and subsequent CL formation. Immunohistochemistry was performed on the ovaries obtained before hCG injection and at 6, 12, and 24 h after hCG injection using antibodies for CD34 or CD31 (an endothelial cell marker), platelet-derived growth factor receptor beta (PDGFR-beta, a pericyte marker), F4/80 (a macrophage marker), and GFP (a bone marrow-derived cell marker). Cells immunostained for CD34, PDGFR-beta, F4/80, and GFP were present in the theca cell layer of the preovulatory follicle before hCG injection. Each of these cell types invaded the granulosa cell layer after hCG injection, and a number of them were observed in the CL 24 h after hCG injection. Fluorescence-based immunohistochemistry or double immunohistochemical staining revealed that a few CD34/CD31-positive cells and PDGFR-beta-positive cells were also positive for GFP in the preovulatory follicle and CL, and that many of the GFP-positive cells recruited to the CL during CL formation were F4/80-positive macrophages. In conclusion, bone marrow-derived vascular progenitor cells and macrophages contribute to neovascularization during CL formation.

Luteal blood flow in patients undergoing GnRH agonist long protocol

BACKGROUND

Blood flow in the corpus luteum (CL) is closely related to luteal function. It is unclear how luteal blood flow is regulated. Standardized ovarian-stimulation protocol with a gonadotropin-releasing hormone agonist (GnRHa long protocol) causes luteal phase defect because it drastically suppresses serum LH levels. Examining luteal blood flow in the patient undergoing GnRHa long protocol may be useful to know whether luteal blood flow is regulated by LH.

METHODS

Twenty-four infertile women undergoing GnRHa long protocol were divided into 3 groups dependent on luteal supports; 9 women were given ethinylestradiol plus norgestrel (Planovar) orally throughout the luteal phase (control group); 8 women were given HCG 2,000 IU on days 2 and 4 day after ovulation induction in addition to Planovar (HCG group); 7 women were given vitamin E (600 mg/day) orally throughout the luteal phase in addition to Planovar (vitamin E group). Blood flow impedance was measured in each CL during the mid-luteal phase by transvaginal color-pulsed-Doppler-ultrasonography and was expressed as a CL-resistance index (CL-RI).

RESULTS

Serum LH levels were remarkably suppressed in all the groups. CL-RI in the control group was more than the cutoff value (0.51), and only 2 out of 9 women had CL-RI values < 0.51. Treatments with HCG or vitamin E significantly improved the CL-RI to less than 0.51. Seven of the 8 women in the HCG group and all of the women in the vitamin E group had CL-RI < 0.51.

CONCLUSION

Patients undergoing GnRHa long protocol had high luteal blood flow impedance with very low serum LH levels. HCG administration improved luteal blood flow impedance. This suggests that luteal blood flow is regulated by LH.

Luteal blood flow and luteal function

BACKGROUND

Blood flow in the corpus luteum (CL) is associated with luteal function. The present study was undertaken to investigate whether luteal function can be improved by increasing CL blood flow in women with luteal phase defect (LFD).

METHODS

Blood flow impedance in the CL was measured by transvaginal color-pulsed-Doppler-ultrasonography and was expressed as a resistance index (RI). The patients with both LFD [serum progesterone (P) concentrations < 10 ng/ml during mid-luteal phase] and high CL-RI (>/= 0.51) were given vitamin-E (600 mg/day, n = 18), L-arginine (6 g/day, n = 14) as a potential nitric oxide donor, melatonin (3 mg/day, n = 13) as an antioxidant, or HCG (2,000 IU/day, n = 10) during the subsequent menstrual cycle.

RESULTS

In the control group (n = 11), who received no medication to increase CL blood flow, only one patient (9%) improved in CL-RI and 2 patients (18%) improved in serum P. Vitamin-E improved CL-RI in 15 patients (83%) and improved serum P in 12 patients (67%). L-arginine improved CL-RI in all the patients (100%) and improved serum P in 10 patients (71%). HCG improved CL-RI in all the patients (100%) and improved serum P in 9 patients (90%). Melatonin had no significant effect.

CONCLUSION

Vitamin-E or L-arginine treatment improved luteal function by decreasing CL blood flow impedance. CL blood flow is a critical factor for luteal function.