COVID-19-related premature ovarian insufficiency: case report and literature review

OBJECTIVE

The aim of this study is to present the case report of a 36-year-old woman developing premature ovarian insufficiency (POI) after COVID-19 and review the literature referring to the possible impact of SARS-CoV-2 infection on female reproduction.

METHODS

A 36-year-old nulligravida with normal menstrual cycles, non-smoker, with a normal body mass index and no pelvic surgery or oncological treatment in her medical history presented to the Infertility Center of the Institute of Mother and Child in Warsaw after a year of unsuccessful attempts to get pregnant. During diagnostic process she was affected by COVID-19 with a mild manifestation and thereafter she presented amenorrhea with intense hot flushes. Further diagnostic confirmed the diagnosis of POI.

RESULTS

There is a strong molecular basis for a possible effect of SARS-CoV-2 infection on the female reproductive system; however, the results of available research are conflicting. All of these aspects are discussed in detail.

CONCLUSIONS

SARS-CoV-2 infection may cause serious complications that cast a long shadow on a patient's future life and health. Further research is needed to assess the real impact of SARS-CoV-2 infection on female reproductive health, as well as potential preventive and therapeutic strategies for women affected with COVID-19.

Impaired immune response against SARS-CoV-2 infection is the major factor indirectly altering reproductive function in COVID-19 patients: a narrative review

Coronavirus disease 2019 (COVID-19) is an infectious disease affecting multiple systems and organs, including the reproductive system. SARS-CoV-2, the virus that causes COVID-19, can damage reproductive organs through direct (angiotensin converting enzyme-2, ACE-2) and indirect mechanisms. The immune system plays an essential role in the homeostasis and function of the male and female reproductive systems. Therefore, an altered immune response related to infectious and inflammatory diseases can affect reproductive function and fertility in both males and females. This narrative review discussed the dysregulation of innate and adaptive systems induced by SARS-CoV-2 infection. We reviewed the evidence showing that this altered immune response in COVID-19 patients is the major indirect mechanism leading to adverse reproduction outcomes in these patients. We summarized studies reporting the long-term effect of SARS-CoV-2 infection on women's reproductive function and proposed the chronic inflammation and chronic autoimmunity characterizing long COVID as potential underlying mechanisms. Further studies are needed to clarify the role of autoimmunity and chronic inflammation (long COVID) in altered female reproduction function in COVID-19.

Advanced bioengineering of female germ cells to preserve fertility

Oogenesis and folliculogenesis are considered as complex and species-specific cellular differentiation processes, which depend on the in vivo ovarian follicular environment and endocrine cues. Considerable efforts have been devoted to driving the differentiation of female primordial germ cells toward mature oocytes outside of the body. The recent experimental attempts have laid stress on offering a suitable microenvironment to assist the in vitro folliculogenesis and oogenesis. Despite developing a variety of bioengineering techniques and generating functional mature gametes through in vitro oogenesis in earlier studies, we still lack knowledge of appropriate microenvironment conditions for building biomimetic culture systems for female fertility preservation. Therefore, this review paper can provide a source for a large body of scientists developing cutting-edge in vitro culture systems for female germ cells or setting up the next generation of reproductive medicine as feasible options for female infertility treatment. The focal point of this review outlines advanced bioengineering technologies such as 3D biofabricated hydrogels/scaffolds and microfluidic systems utilized with female germlines for fertility preservation through in vitro folliculogenesis and oogenesis.

The Inflammatory Cytokine Imbalance for Miscarriage, Pregnancy Loss and COVID-19 Pneumonia

Pregnancy can be defined a vascular event upon endocrine control. In the human hemo-chorial placentation the chorionic villi penetrate the wall of the uterine spiral arteries, to provide increasing amounts of nutrients and oxygen for optimal fetal growth. In any physiological pregnancy the natural maternal response is of a Th1 inflammatory type, aimed at avoiding blood loss through the arteriolar wall openings. The control of the vascular function, during gestation as in any other condition, is achieved through the action of two main types of prostanoids: prostaglandin E2 and thromboxane on the one hand (for vasoconstriction and coagulation), prostacyclin on the other (for vasodilation and blood fluidification). The control of the maternal immune response is upon the responsibility of the fetus itself. Indeed, the chorionic villi are able to counteract the natural maternal response, thus changing the inflammatory Th1 type into the anti-inflammatory Th2. Clinical and experimental research in the past half century address to inflammation as the leading cause of abortion, pregnancy loss, premature delivery and related pulmonary, cerebral, intestinal fetal syndromes. Increased level of Interleukin 6, Interleukin 1-beta, Tumor Necrosis Factor-alfa, Interferon-gamma, are some among the well-known markers of gestational inflammation. On the other side, COVID-19 pneumonia is a result of extensive inflammation induced by viral replication within the cells of the respiratory tract. As it may happen in the uterine arteries in the absence of an effective fetal control, viral pneumonia triggers pulmonary vascular coagulation. The cytokines involved in the process are the same as those in gestational inflammation. As the fetus breathes throughout the placenta, fetal death from placental thrombosis is similar to adult death from pulmonary thrombosis. Preventing and counteracting inflammation is mandatory in both conditions. The most relevant literature dealing with the above-mentioned concepts is reviewed in the present article.

The Effects of SARS-CoV-2 Infection on Female Fertility: A Review of the Literature

As the coronavirus pandemic is far from ending, more questions regarding the female reproductive system, particularly fertility issues, arise. The purpose of this paper is to bring light upon the possible link between COVID-19 and women’s reproductive health. This review emphasizes the effect of SARS-CoV-2 on the hormones, endometrium and menstrual cycle, ovarian reserve, follicular fluid, oocytes, and embryos. The results showed that endometrial samples did not express SARS-CoV-2 RNA. Regarding the menstrual cycle, there is a large range of alterations, but they were all reversible within the following months. The ovarian reserve was not significantly affected in patients recovering from both mild and severe infection in most cases, except one, where the levels of AMH were significantly lower and basal follicle-stimulating hormone (FSH) levels were increased. All COVID-19 recovered patients had positive levels of SARS-CoV-2 IgG in the follicular fluid. The amount of retrieved and mature oocytes and the fertilization rate were unharmed in three studies, except for one study, where the quantity of retrieved and mature oocytes was reduced in patients with higher levels of SARS-CoV-2 antibodies. The numbers of blastocysts, top-quality embryos, and euploid embryos were affected in most of the studies reviewed.

Impact of COVID-19 on the Endocrine System: A Mini-review

The coronavirus disease 2019 (COVID-19) pandemic continues to exert a significant impact on global health care systems, causing devastating mortality and morbidity. As time passes and our understanding of this novel respiratory virus deepens, it is increasingly clear that its effects extend beyond that of the respiratory system. The coronavirus responsible for COVID-19, severe acute respiratory syndrome coronavirus 2, obtains cellular access through the angiotensin-converting enzyme 2 (ACE2) receptor in a process requiring the transmembrane serine protease 2 (TMPRSS2) protein. Both ACE2 and TMPRSS2 are widely expressed in many endocrine glands. This, along with several case reports of thyroid and pituitary disruption in patients with COVID-19, has resulted in significant interest in its impact on the endocrine system. Indeed, as mortality is abated by the increasing availability of effective vaccines, there is increasing focus on the long-term effects on health in COVID-19 survivors. This review summarizes data investigating the effects of COVID-19 on each of the endocrine axes to guide appropriate investigations and optimal management.

Female fertility under the impact of COVID-19 pandemic: a narrative review

Coronavirus disease 2019 (COVID-19) is a serious respiratory disease mediated by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. The worldwide spread of COVID-19 has caused millions of confirmed cases and morbidity, and the crisis has greatly affected global economy and daily life and changed our attitudes towards life. The reproductive system, as a potential target, is at a high risk of SARS-CoV-2 infection, and females are more vulnerable to viral infection compared with males. Therefore, female fertility and associated reproductive health care in the COVID-19 era need more attention. This review summarises the mechanism of SARS-CoV-2 infection in the female reproductive system and discusses the impact of the COVID-19 crisis on female fertility. Studies have proven that COVID-19 might affect female fertility and interfere with assisted reproductive technology procedures. The side effects of vaccines against the virus on ovarian reserve and pregnancy have not yet been well investigated. In the future, the female fertility after SARS-CoV-2 infection and vaccination needs more attention because of the uncertainty of COVID-19.

Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) and its effect on gametogenesis and early pregnancy

SARS-CoV-2 infection and pregnancy has been the topic of hundreds of publications over the last several months; however, few studies have focused on the implications of infection in early pregnancy and reproductive tissues. Here, we analyzed available evidence pertaining to SARS-CoV-2 infection, in early pregnancy, and in reproductive tissues. We searched PubMed and Embase databases in accordance with guidelines of Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) for publications from inception to June 4, 2020. Four reviewers screened titles and abstracts and obtained full-text articles for analysis. Sixty-two studies were included in the review. Biological plausibility for infection with SARS-CoV-2 exists in testis, ovaries, and placenta as they express ACE2 receptor activity. In males, SARS-CoV-2 infection could lead to functional abnormalities leading to spermatogenic failure and male infertility. In females, an alteration of the ACE2 cascade via SARS-CoV-2 infection could lead to impairment in important follicular and luteal processes. There is also evidence of significant placental pathology in SARS-CoV-2 infection, but it is unclear what effects there may be for early pregnancy, though available data suggest less severe effects compared to other respiratory virus outbreaks. Further investigation is needed regarding SARS-CoV-2 in reproductive function and early pregnancy.

Potential influence of COVID-19/ACE2 on the female reproductive system

The 2019 novel coronavirus (2019-nCoV) appeared in December 2019 and then spread throughout the world rapidly. The virus invades the target cell by binding to angiotensin-converting enzyme (ACE) 2 and modulates the expression of ACE2 in host cells. ACE2, a pivotal component of the renin-angiotensin system, exerts its physiological functions by modulating the levels of angiotensin II (Ang II) and Ang-(1-7). We reviewed the literature that reported the distribution and function of ACE2 in the female reproductive system, hoping to clarify the potential harm of 2019-nCoV to female fertility. The available evidence suggests that ACE2 is widely expressed in the ovary, uterus, vagina and placenta. Therefore, we believe that apart from droplets and contact transmission, the possibility of mother-to-child and sexual transmission also exists. Ang II, ACE2 and Ang-(1-7) regulate follicle development and ovulation, modulate luteal angiogenesis and degeneration, and also influence the regular changes in endometrial tissue and embryo development. Taking these functions into account, 2019-nCoV may disturb the female reproductive functions through regulating ACE2.

Supportive techniques to investigate in vitro culture and cryopreservation efficiencies of equine ovarian tissue: A review

During the reproductive lifespan of a female, only a limited quantity of oocytes are naturally ovulated; therefore, the mammalian ovary possesses a substantial population of preantral follicles available to be handled and explored in vitro. Hence, the manipulation of preantral follicles enclosed in ovarian tissue aims to recover a considerable population of oocytes of high-value animals for potential application in profitable assisted reproductive technologies (ARTs). For this purpose, the technique of preantral follicle in vitro culture (IVC) has been the most common research tool, achieving extraordinary results with offspring production in the mouse model. Although promising outcomes have been generated in livestock animals after IVC of preantral follicles, the quantity and quality of embryo production with those oocytes are still poor. In recent years, the mare has become an additional model for IVC studies due to remarkable similarities with women and livestock animals regarding in vivo and in vitro ovarian folliculogenesis. For a successful IVC system, several factors should be carefully considered to provide an optimum culture environment able to support the viability and growth of preantral follicles enclosed in ovarian tissue. The cryopreservation of the ovarian tissue is another important in vitro manipulation technique that has been used to preserve the reproductive potential in humans and, in the future, may be used in highly valuable domestic animals or endangered species. Several improvements in cryopreservation protocols are necessary to support the utilization of ovarian tissue of different species in follow-up ARTs (e.g., ovarian fragment transplantation). This review aims to provide an update on the most current advances regarding supportive in vitro techniques used in equids to evaluate and manipulate preantral follicles and ovarian tissue, as well as methodological approaches used during IVC and cryopreservation techniques.

Establishment of a protocol for the isolation of ovarian preantral follicles derived from collared peccaries (Pecari tajacu)

We compare the efficiency of mechanical or enzymatic methods, and their combination, for the isolation of ovarian preantral follicles (PFs) from collared peccaries. The ovaries from six females were subjected to the different methods investigated here. For the enzymatic method, ovary fragments were exposed to collagenase type IV in TCM-HEPES medium; the mechanical procedure was based on ovarian cortex dissociation by using a scalpel blade. The residual solution obtained after the mechanical isolation was subjected to the enzymatic procedure. The number of isolated PFs was quantified and classified as primordial, primary, or secondary; their viability was assessed using trypan blue dye assay. To confirm the results, PFs derived from the most efficient method were evaluated for integrity using scanning electron microscopy (SEM) and subjected to a 24 h in vitro culture for subsequent evaluation of viability by using fluorescent probes. A higher number of PFs (P < 0.05) was obtained from the enzymatic method (961.7 ± 132.9) in comparison with the mechanical method (434.3 ± 88.9), but no difference was observed between the two methods and their combination (743.2 ± 92.8). The trypan blue assay showed that the enzymatic method (98.7 ± 0.6%) provided the highest percentage of viable follicles (P < 0.05). Furthermore, SEM confirmed the ultrastructural integrity of the surface architecture of peccary PFs isolated by the enzymatic procedure; epifluorescence microscopy was used to confirm their viability (86.0%). In conclusion, we suggest that the enzymatic method investigated here is useful for the isolation of viable ovarian PFs from collared peccaries.

Effects of Estradiol on the Paracrine Regulator Expression of In Vitro Maturated Murine Ovarian Follicles

The preservation of female germ cells is important in the individuals with ovarian dysfunction and failure. For this purpose, ovarian follicle in vitro maturation (OFIVM) is an important technology for the retrieval of mature oocytes. In the in vivo follicular development, paracrine factors such as angiotensin (AT) and anti-Müllerian hormone (AMH) play important roles. We attempted to add estrogen during the OFIVM and to assess their expression on the follicular cells. The ovaries and pre-antral follicles were collected from 13-day C57BL/6 mice and cultured in vitro with estradiol (E2) treatment for up to two weeks. In the whole ovaries, the expression of AT II was decreased and the expression of AMH was similar between control and E2-treated ovaries after in vitro culture. Although there was no difference in the survival, ovulation, maturation and fertilization rates between control and E2-treated groups, the expression of AT II in the follicular cells was down-regulated after E2 treatment at mRNA level, and AMH showed similar expression. In conclusion, adding E2 in OFIVM may regulate paracrine factors and their receptors that are related to follicular development. Further investigations are necessary to elucidate the roles of various sex hormones in the regulation of AT and AMH expression during the OFIVM.

The expression profile of angiotensin system on thawed murine ovaries

Freezing and thawing is one of the most widely used tissue engineering techniques for the preservation of ovaries. Many cells and tissues demonstrate changes in functional gene expression after thawing. Several studies have reported the important roles of angiotensin (AT) system during the ovarian follicular growth. AT system consists of ATII, and ATII receptors type I (ATII-RI) and type II (ATII-RII). However, little is known whether frozen-thawed ovaries show any alteration of AT system member gene expression when treated with survival-enhancing factors. We aimed to investigate whether mass freezing and thawing with or without the use of Rho-associated kinase (ROCK) inhibitors up- or down-regulate the expression of ATII, ATII-RI, and ATII-RII genes on frozen-thawed ovarian tissues. Significant changes in the expression of ATII, ATII-RI, and ATII-RII genes were observed on thawed ovaries when compared to fresh control. The treatment with ROCK inhibitors did not significantly alter their expression. In conclusion, freezing and thawing of ovarian tissue may affect the mRNA expression levels of intra-ovarian AT system genes, and modulation of ROCK inhibitor activity may not regulate AT system on the frozenthawed ovarian tissue.

Ovarian follicle development in vitro and oocyte competence: advances and challenges for farm animals

During the last 2 decades, research on in vitro preantral follicle growth and oocyte maturation has delivered fascinating advances concerning the knowledge of processes regulating follicle growth and the developmental competence of oocytes. These advances include (1) information about the role of several hormones and growth factors on in vitro activation of primordial follicles; (2) increased understanding of the intracellular pathway involved in the initiation of primordial follicle growth; (3) the growth of primary and secondary follicles up to antral stages; and (4) production of embryos from oocytes from in vitro grown preantral follicles. This review article describes these advances, especially in regard farm animals, and discusses the reasons that limit embryo production from oocytes derived from preantral follicles cultured in vitro.

Spatio-Temporal Gene Expression Profiling during In Vivo Early Ovarian Folliculogenesis: Integrated Transcriptomic Study and Molecular Signature of Early Follicular Growth

Background

The successful achievement of early ovarian folliculogenesis is important for fertility and reproductive life span. This complex biological process requires the appropriate expression of numerous genes at each developmental stage, in each follicular compartment. Relatively little is known at present about the molecular mechanisms that drive this process, and most gene expression studies have been performed in rodents and without considering the different follicular compartments.

Results

We used RNA-seq technology to explore the sheep transcriptome during early ovarian follicular development in the two main compartments: oocytes and granulosa cells. We documented the differential expression of 3,015 genes during this phase and described the gene expression dynamic specific to these compartments. We showed that important steps occurred during primary/secondary transition in sheep. We also described the in vivo molecular course of a number of pathways. In oocytes, these pathways documented the chronology of the acquisition of meiotic competence, migration and cellular organization, while in granulosa cells they concerned adhesion, the formation of cytoplasmic projections and steroid synthesis. This study proposes the involvement in this process of several members of the integrin and BMP families. The expression of genes such as Kruppel-like factor 9 (KLF9) and BMP binding endothelial regulator (BMPER) was highlighted for the first time during early follicular development, and their proteins were also predicted to be involved in gene regulation. Finally, we selected a data set of 24 biomarkers that enabled the discrimination of early follicular stages and thus offer a molecular signature of early follicular growth. This set of biomarkers includes known genes such as SPO11 meiotic protein covalently bound to DSB (SPO11), bone morphogenetic protein 15 (BMP15) and WEE1 homolog 2 (S. pombe)(WEE2) which play critical roles in follicular development but other biomarkers are also likely to play significant roles in this process.

Conclusions

To our knowledge, this is the first in vivo spatio-temporal exploration of transcriptomes derived from early follicles in sheep.

Expression of angiotensin II receptors in the caprine ovary and improvement of follicular viability in vitro

This study aimed to evaluate mRNA levels of angiotensin II (ANG II) receptors (AGTR1 and AGTR2) in caprine follicles and to investigate the influence of ANG II on the viability and in vitro growth of preantral follicles. Real-time polymerase chain reaction (PCR) was used to quantify AGTR1 and AGTR2 mRNA levels in the different follicular stages. For culture, caprine ovaries were collected, cut into 13 fragments and then either directly fixed for histological and ultrastructural analysis (fresh control) or placed in culture for 1 or 7 days in α-minumum essential medium plus (α-MEM+) with 0, 1, 5, 10, 50 or 100 ng/ml ANG II. Then, the fragments were destined to morphological, viability and ultrastructural analysis. The results showed that primordial follicles had higher levels of AGTR1 and AGTR2 mRNA than secondary follicles. Granulosa/theca cells from antral follicles had higher levels of AGTR1 mRNA than their respective cumulus-oocyte complex (COCs). After 7 days of culture, ANG II (10 or 50 ng/ml) maintained the percentages of normal follicles compared with α-MEM+. Fluorescence and ultrastructural microscopy confirmed follicular integrity in ANG II (10 ng/ml). In conclusion, a high expression of AGTR1 and AGTR2 is observed in primordial follicles. Granulosa/theca cells from antral follicles had higher levels of AGTR1 mRNA. Finally, 10 ng/ml ANG II maintained the viability of caprine preantral follicles after in vitro culture.

Role of angiotensin in ovarian follicular development and ovulation in mammals: a review of recent advances

Angiotensin (Ang) II is widely known for its role in the control of systemic blood vessels. Moreover, Ang II acts on the vascular control of ovarian function, corpus luteum formation, and luteolysis. Over the past 10 years, our research group has been studying the new concept of the renin–angiotensin system (RAS) as an autocrine/paracrine factor regulating steroidogenesis and promoting different cellular responses in the ovary, beyond vascular function. We have developed and used differentin vivoandin vitroexperimental models to study the role of RAS in the ovary and a brief overview of our findings is presented here. It is widely accepted that there are marked species differences in RAS function in follicle development. Examples of species-specific functions of the RAS in the ovary include the involvement of Ang II in the regulation of follicle atresia in rats vs the requirement of this peptide for the dominant follicle development and ovulation in rabbits and cattle. More recently, Ang-(1–7), its receptor, and enzymes for its synthesis (ACE2, NEP, and PEP) were identified in bovine follicles, implying that Ang-(1–7) has an ovarian function. Other novel RAS components (e.g. (pro)renin receptor and renin-binding protein) recently identified in the bovine ovary show that ovarian RAS is poorly understood and more complex than previously thought. In the present review, we have highlighted the progress toward understanding the paracrine and autocrine control of ovarian antral follicle development and ovulation by ovarian tissue RAS, focusing onin vivostudies using cattle as a model.

Isolation and culture of preantral follicles for retrieving oocytes for the embryo production: present status in domestic animals

The development of efficient ovarian preantral follicle (PF) isolation and culture systems provide a large number of oocytes for the manipulation and embryo production. It also helps for understanding the mechanisms of follicle and oocyte development. Isolation and culture protocols for PFs were developed for many domestic species like cattle, buffalo, sheep, goat, pig, horse, camel, dog and cats; however, embryo production from oocytes derived from in vitro grown PFs was reported only in pigs, buffalo, sheep and goat. The rate of oocyte maturation from PFs grown in vitro is low and requires considerable research. This paper presents an overview of isolation and culture systems of PFs that have been developed for domestic species (cattle, buffalo, sheep, goat, pigs, horse, camel, dog and cat) along with the current status of progress achieved in the direction of producing embryos using PFs as the source of oocyte in these species.

In vitro maturation of oocytes via the pre-fabricated self-assembled artificial human ovary

PURPOSE

create a 3-Dimensional artificial human ovary to mature human oocytes.

METHODS

theca and granulosa cells were isolated from antral follicles of reproductive-aged women, seeded into micro-molded gels and self-assembled into complex 3D microtissues. Immunohistochemistry and live-dead staining confirmed theca cell identity and cellular viability at one week respectively. Placement of granulosa cell spheroids or cumulus-oocyte complexes into theca cell honeycomb openings resulted in creation of an artificial human ovary. Oocytes from this construct were assessed for polar body extrusion.

RESULTS

theca and granulosa cells self-assembled into complex microtissues, remaining viable for one week. At 72 h after artificial human ovary construction, theca cells completely surrounded the granulosa spheroids or COCs without stromal invasion or disruption. Polar body extrusion occurred in one of three COCs assessed.

CONCLUSIONS

an artifical human ovary can be created with self-assembled human theca and granulosa cell microtissues, and used for IVM and future oocyte toxicology studies.

The in vitro growth and maturation of follicles

The development of technologies to grow oocytes from the most abundant primordial follicles to maturity in vitro holds many attractions for clinical practice, animal production technology and research. The production of fertile oocytes and live offspring has been achieved in mice following the long-term culture of oocytes in primordial follicles from both fresh and cryopreserved ovarian tissue. In contrast, in non-rodent species advances in follicle culture are centred on the growth of isolated preantral follicles. As a functional unit, mammalian preantral follicles are well-suited to culture but primordial and primary follicles do not grow well after isolation from the ovarian stroma. The current challenges for follicle culture are numerous and include: optimisation of culture media and the tailoring of culture environments to match the physiological needs of the cell in vivo; the maintenance of cell-cell communication and signalling during culture; and the evaluation of the epigenetic status, genetic health and fertility of in vitro derived mature oocytes. In large animals and humans, the complete in vitro growth and maturation of oocytes is only likely to be achieved following the development of a multistage strategy that closely mimics the ovary in vivo. In this approach, primordial follicle growth will be initiated in situ by the culture of ovarian cortex. Isolated preantral follicles will then be grown to antral stages before steroidogenic function is induced in the somatic cells. Finally, cytoplasmic and nuclear maturation will be induced in the in vitro derived oocytes with the production of fertile metaphase II gametes.

The current knowledge on radiosensitivity of ovarian follicle development stages

BACKGROUND

The aim of this paper is to review the available information on ovarian radiation sensitivity and the genetic hazard of ionizing radiation in female mammals including humans.

METHODS

The literature present in the author's laboratories (international papers from the 1970s) was complemented by a Medline literature search using the keywords 'ionizing radiation genetic effects', 'oocyte radiosensitivity' and 'oocyte DNA repair' (1990-2008). Further articles were acquired from citations in the research papers and reports.

RESULTS

Animal data show that oocyte radiosensitivity varies widely according to the follicle/oocyte stage and the species. Oocytes near ovulation show the highest susceptibility to radiation induction of mutational events. Congenital anomalies have been observed after exposure to high doses (1-5 Gy), but extrapolation of these data to humans requires caution. In humans, the dose required to induce permanent ovarian failure would vary from 20.3 Gy at birth to 14.3 Gy at 30 years. Most epidemiological studies found little evidence of genetic diseases at the doses at which medical, occupational or accidental exposure occurred.

CONCLUSIONS

The fact that genetic effects were observed in irradiated animals suggests that these could also occur in humans. The probability of such events remains low compared with the 'spontaneous' risks of genetic effects.

Vascular supply as a discriminating factor for pig preantral follicle selection

This research analyses how somatic and vascular compartments change during preantral follicle growth. To address this aim, theca-granulosa (somatic) proliferation indexes (PIs), proportion of proliferating endothelial cells (PE), vascular area (VA) and vascular endothelial growth factor A (VEGFA) expression were simultaneously recorded on single healthy preantral follicles, classified into six different stages on the basis of the diameter and the granulosa layers. An autonomous blood vessel network starts to appear only in class 3. Vascular remodelling requires VEGFA expression, and VEGFA mRNA and VA significantly increase between class 3 and classes 4 and 5 and, further, in class 6. In addition, a positive correlation exists between these parameters in classes 3-5. Despite variation in angiogenesis results from classes 3 to 5, the statistical analysis reveals that the vascular parameters are positively and strictly correlated with somatic PIs. Conversely, class 6, also characterized by higher values of somatic PIs, displays a stable proportion of PEs ( congruent with 40%) without showing any correlation among the different parameters analysed. To identify follicular subpopulations within different classes, a multivariate hierarchical cluster analysis was performed. This analysis reveals that the majority of classes 3 and 4 are quiescent follicles or structures that grow very slowly. Class 5 represents a transitory category, where half of the follicles maintain a low activity and the remaining express significantly higher levels of granulosa PI and VA. The follicles with this high activity are probably able to reach class 6 becoming dominant structures where somatic and vascular parameters are constantly on high levels and the VA remains the unique differentiating element.

Survival and developmental competence of buffalo preantral follicles using three-dimensional collagen gel culture system

The aim of the present study was to develop a three-dimensional (3D) collagen gel culture system for the in vitro growth and survival of buffalo preantral follicles with or without growth factors. Buffalo ovaries were collected from a local abattoir and preantral follicles were isolated through microdissection. Isolated preantral follicles were put either in collagen gel coated culture dish or embedded in a microdrop of collagen gel. The culture medium was TCM-199 fortified with fetal calf serum (10%), insulin transferin selenium solution (ITS, 1%), epidermal growth factor (EGF, 20 ng/ml) and follicle stimulating hormone (FSH, 0.5 microg/ml). Follicles were divided into three groups and cultured in the medium described above (group a, control), with addition of insulin like growth factor (IGF-I, 100 ng/ml, group b), or with addition of IGF-I and basic fibroblast growth factor (bFGF, 10 ng/ml, group c). Preantral follicles were incubated at 38.5 degrees C in 5% CO(2) and maximum humidity. Culture medium was replenished after every 72 h and spent medium was stored at -30 degrees C for hormone analysis. We found that the extracellular matrix of collagen gel maintained follicle viability and growth by providing surface interaction and increasing attachment of follicles. Preantral follicles embedded in collagen gel droplets had better antrum formation and development as compared to the whole surface coated culture method. Follicles cultured with IGF-I on collagen gel matrix showed a significantly (P<0.05) higher survival rate and larger mean diameter of follicles on day 10 of culture with improved growth and mucification as compared to the control group. However, follicles cultured in the combination of IGF-I with bFGF had decreased survival rate and smaller mean follicles diameter than the IGF-I group (b). Progesterone (P(4)) accumulation was greater on day 9 of culture in follicles cultured in IGF-I as compared to control; whereas, P(4) was markedly decreased in the combination of IGF-I with bFGF. Follicles of the control group could survive for up to 10-15 days before degenerating, but follicles cultured with growth factors were able to survive up to 20 days and showed signs of early antrum formation. In summary, we have shown that collagen gel was a novel and efficacious 3D microenvironment for the extended culture of buffalo preantral follicles. Supplementation of culture medium with growth factors was found to be essential for antrum formation.

Effects of follicular fluids on the growth of porcine preantral follicle and oocyte

We examined the effect of supplementing the culture medium with follicular fluid (FF) on the growth of porcine preantral follicles and oocytes. Firstly, preantral follicles were retrieved from ovaries and then FF was collected from all antral follicles that were 2–7 mm in diameter (AFF), which included large follicles of 4–7 mm in diameter (LFF) and small follicles of 2–3 mm in diameter (SFF). When preantral follicles with a diameter of 250 μm were cultured in medium containing AFF, the growth of follicles and oocytes was greater than when follicles were cultured in medium containing fetal calf serum (FCS). When this growth-promoting effect in AFF was compared for LFF and SFF, the LFF were shown to be significantly more effective than SFF. This LFF effect was lost, however, when the concentration of LFF in the medium was decreased from 5% to 0.5% or when LFF were heat treated (60 °C for 30 min) or trypsin was added. In contrast, a decrease in SFF concentration from 5% to 0.5% and heat treatment of the SFF enhanced preantral follicle growth. Furthermore, proteins obtained from LFF that had molecular weights greater than 10 kDa (LFF > 10 kDa) had similar, but relatively reduced, growth-promoting properties. The remaining three LFF protein fractions (<10 kDa or <100 kDa or >100 kDa), however, did not have these growth-promoting properties. In conclusion, the supplementation of medium with LFF, rather than serum, enhanced preantral follicle and oocyte growth. Factors that enhanced follicle development in LFF and factors that suppressed follicle development in SFF were proteins and these LFF factors ranged in size from 10 kDa to over 100 kDa.

High-Resolution Ultrasonography of Xenografted Domestic Cat Ovarian Cortex

Transplantation of ovarian tissue has high potential for female gamete conservation. However, optimal timing of oocyte recovery for in vitro maturation and fertilization is still critical. Therefore the aim of the present study was to use high-resolution transcutaneous ultrasonography to monitor follicular development within xenografted ovarian tissue. Ovarian cortex fragments (n=44) from domestic cats were transplanted into athymic nude rats (n=12). Graft development in the animals was assessed weekly by high frequency ultrasound (10-22 MHz) under two different FSH regimes. Blood collection for serum estradiol determination and vaginal smears were performed simultaneously. The xenografts were removed at different time points according to the ultrasound findings. The survival rate of the transplants 4 weeks after surgery was 54.5% and antral follicular growth was observed within 10 grafts from 5 different hosts (8.6 +/- 6.43 follicles per graft). Early follicle antrums could be detected from 0.4 mm onwards. The growth rate of the antral cavity was calculated from weekly measurements (0.56 +/- 0.44 mm per week). Although vaginal cells and estradiol levels followed a cyclic pattern, no correlation was found between follicular diameter, estradiol and keratinized vaginal cells. We recovered 5, 1 and 4 cumulus oocyte complexes from three different individuals during weeks 19, 21, and 23 respectively. Extrusion of a polar body (1 oocyte) and germinal vesicle break down (7 oocytes) indicated progression of maturation after in vitro culture. We conclude that ultrasonography und provided a reliable method to examine xenograft survival and follicular development within the grafts. Furthermore, this technique is suitable for assessment of the efficiency of hormonal treatment and narrowing of the optimal time frame for oocyte retrieval. To our knowledge, this is the first report of the in vivo development of early antral follicles in mammalian species.

Effect of epidermal growth factor and insulin-like growth factor I on porcine preantral follicular growth, antrum formation, and stimulation of granulosal cell proliferation and suppression of apoptosis in vitro

The object of this study was to investigate the role of epidermal growth factor (EGF) and IGF-I in the regulation of preantral follicular growth, antrum formation, and granulosal cell proliferation/ apoptosis. Porcine preantral follicles were manually dissected and cultured for up to 8 d in Waymouth's (Exp. 1) or alpha-minimum Eagle's essential medium (Exp. 2 and 3) supplemented with 10 microg/mL of transferrin, 100 microg/mL of L-ascorbic acid, and 2 mU/mL of ovine FSH, in the presence (Exp. 1 and 3) or absence (Exp. 2) of 7.5% fetal calf serum. According to the experimental protocol, IGF-I (0, 1, 10, or 100 ng/mL; Exp. 1), or IGF-I (50 ng/mL), EGF (10 ng/mL) and EGF+IGF-I (Exp. 2 and 3) were added to the culture media. In Exp. 1, follicles exhibited a concentration-dependent response (P < 0.05) to IGF-I, with the highest rates of granulosal cell proliferation, follicular integrity, and recovery rate of cumulus cell-oocyte complexes and lowest incidence of apoptosis occurring at the highest IGF-I dose. In Exp. 2 serum-free medium, granulosal cell proliferation was low (1 to 5%), irrespective of whether EGF and/or IGF-I were present and cellular apoptosis was increased (P < 0.05) on d 4 and 8 in the EGF+IGF-I group compared with the addition of either factor alone. In Exp. 3, granulosal cell proliferation was high in all follicles cultured in serum-containing medium for the first 3 d, but fell sharply (P < 0.05) on d 4, except in media containing IGF-I. Collectively, EGF and IGF-I increased granulosal cell proliferation, decreased apoptosis, and promoted follicular antrum formation. These results may provide useful information for developing a preantral follicular culture system in which the oocytes are capable of fertilization and embryonic development.

Immunohistochemical localization of inducible and endothelial nitric oxide synthase in porcine ovaries and effects of NO on antrum formation and oocyte meiotic maturation

The present study is to investigate the immunolocalization of endothelial and inducible nitric oxide synthase (eNOS, iNOS) in porcine ovary and the effect of nitric oxide (NO) on antrum formation and oocyte meiotic resumption. In Experiment 1, preantral follicles (250-300 microm in diameter) were cultured in 0 (Control), 0.1, 0.3, 0.5 or 1 mM sodium nitroprusside (SNP), a NO donor. In Experiment 2, the cumulus-oocyte complexes (COCs) aspirated from medium follicles (3-6 mm in diameter) were incubated in 0.1mM SNP or two inhibitors for NOS, 10 mM aminoguanidine bicarbonate salt (AG) or 1 mM Nomega-nitro-l-arginine methyl ester (L-NAME), alone or concomitantly. In Experiment 3, ovarian tissues, corpus luteum (CL), corpus albican (CA) and COCs from small (1-2 mm in diameter), medium (3-6 mm) and large follicles (7-10 mm) were isolated, rinsed, fixed, paraffin embedded and stained by the conventional avidin-biotin complex method for the detection of eNOS and iNOS production. The results showed that 0.1mM SNP had no effect on antrum formation (P > 0.05) while 0.3, 0.5 or 1 mM significantly inhibited the antrum formation (P < 0.05). AG markedly inhibited porcine oocyte meiotic resumption (P < 0.05) while L-NAME inhibited first polar body (PB1) extrusion (P < 0.05). The immunoreactivity of eNOS in early antral follicles was restricted to oocyte and it increased from small, medium to large follicle-enclosed oocytes. Cumulus cells from large follicles showed weak eNOS immunoreactivity but those from small or medium follicles not. In CL, eNOS-positive staining was shown in granulosa lutein cells. In CA, it was in some parenchymal cells. In contrast, no immunoreactivity for iNOS was found in primordial, early antral follicle or the COCs aspirated from small and medium follicles. The large follicle-enclosed oocyte showed weak immunoreactivity. In CL, some granulosa lutein cells showed iNOS-positive cytoplasm. Such immunostaining was not found in CA. The results demonstrate that porcine ovaries have distinct cell-specific expression of both eNOS and iNOS, and that NO derived from both NOS is actively involved in meiotic resumption. Nitric oxide is not involved in the antrum formation of preantral follicles but exogenous NO inhibits the antrum formation. Endothelial nitric oxide synthase and inducible nitric oxide synthase might be differently functional in CL development and regression.

Lack of an association between plasma follicle-stimulating hormone concentrations and ovarian weight in prepubertal gilts1

Selection for increased number of corpora lutea in gilts is associated with increased plasma FSH concentrations during pubertal development. In the current study, 270 gilts from a control (CO) line and a line selected for increased ovulation rate (OR) were unilaterally ovariectomized at 85 d of age, and this ovarian weight was related to FSH concentrations at 65, 75, and 85 d of age. Gilts were produced during two farrowing seasons, spring and fall, and the age at first estrus was monitored from 160 to 250 d. Plasma FSH was greater in OR than in CO gilts at 65 (P < 0.01) and 75 d (difference in spring greater than in fall, P < 0.01), but FSH at these ages was not correlated with ovarian weight at 85 d. At 85 d, FSH did not differ in gilts of these lines; however, FSH was negatively correlated (r = -0.27, P < 0.01) with ovarian weight. The proportion of gilts detected in estrus was less for spring-born CO gilts than for spring-born OR or for fall-born CO and OR gilts (78 vs. 92%, season x line, P < 0.02). The age at first estrus was similar in the two lines but was earlier (P < 0.01) for spring-born than for fall-born gilts (194 vs. 204 d). Concentrations of FSH at each of the ages examined were not correlated with the age at first estrus. These observations support the conclusion that selection for a greater number of corpora lutea produces a correlated increase in plasma FSH during early pubertal development. This increase in FSH most likely reflects differences in FSH synthesis and release and not differences in the stage of pubertal development.

Localization of angiotensin II in pig ovary and its effects on oocyte maturation in vitro

The renin-angiotensin system (RAS) has been found in mammalian ovarian tissue; however, its physiological role is unclear. This study examined the content of angiotensin II (Ang II) in porcine follicular fluid (pFF), Ang II localization and its receptors in ovary, and the effects of Ang II on porcine oocyte maturation. The concentrations of Ang II were 6951.82 +/- 1295.83, 3502.99 +/- 679.10, 3147.89 +/- 690.60, and 2545.92 +/- 407.01 pg/ml in pFF from small, medium, large, and extra-large follicles, respectively. In addition, Ang II was found on zona pellucidae (ZP) and granulosa cells by immunoreactive staining. The distribution of AT1, an Ang II receptor subtype, was in accordance with that of Ang II. However, AT2, another Ang II receptor, was mainly distributed in the stroma and thecal layers of follicles. When oocytes were cultured in media containing various concentrations of Ang II, a higher (P<0.05) proportion of oocytes reached metaphase II (MII) in the medium with 100 ng/ml (87.0%) than without Ang II (61%). When oocytes from different sizes of follicles were separately cultured in media containing 100 ng/ml Ang II, maturation rates were significantly higher in oocytes from small (61.5%) and medium (85.1%) follicles than that of their controls (45.1 and 72.6%, respectively). However, addition of Ang II inhibited nuclear maturation in oocytes from large follicles (77.8% versus 87.3%). Fertilization and male pronuclear (MPN) formation rates of oocytes matured in medium containing 100 or 1000 ng/ml of Ang II were higher (P<0.05) than that of oocytes matured in medium containing 0 or 10 ng/ml Ang II. Glutathione content in oocytes cultured for 44 h in medium containing 100 or 1000 ng/ml of Ang II was also higher (P<0.01) than that of oocytes cultured in medium containing 0 or 10 ng/ml Ang II. In conclusion, Ang II was present in porcine ovaries and may regulate follicle growth and oocyte maturation.

Bringing up small oocytes to eggs in pigs and cows

It has been known that the mammalian ovary contains a huge number of non-growing small oocytes, of which only a small number grow to their final size, mature, and are ovulated. Artificial maturation of small oocytes could provide a new source of mature eggs for livestock production and assisted reproduction in humans and in endangered species. Two methods have been used for oocyte growth, in vitro growth (IVG) culture and xenotransplantation. By these methods, oocytes in some species grow up to their final size and acquire developmental competence, although the methods are still at the experimental stage. The experiments remind us of many basic questions in mammalian oogenesis: Does the oocyte require certain stimuli to initiate growth? How are the few oocytes selected to grow to final size? How do they grow up in follicular units? How do they acquire meiotic competence during the growth phase? This paper will give some clues to answer these questions by presenting our recent data from IVG and xenotransplantation experiments, and by illustrating differences between the oocytes of mice and larger animals.

Interactions between the Oocyte and Surrounding Somatic Cells in Follicular Development: Lessons from In Vitro Culture

Mammalian oogenesis occurs concomitantly with folliculogenesis in a coordinated manner in the ovaries. In vitro growth (IVG) culture systems of the oocytes have been developed as a new technology for utilizing incompetent oocytes in the ovary as a source of mature oocytes as well as for studying oogenesis, folliculogenesis, and oocyte-somatic cell interactions. The results of IVG experiments have suggested that direct association of oocytes and surrounding granulosa cells supports oocyte viability and growth through the gap junctions, which are efficient conduits for low molecular weight substances. It has been revealed that granulosa cells metabolize some molecules which are in turn transported into the oocytes. IVG systems have also provided evidence that FSH promotes the development of follicles at secondary or later stages by its stimulation of proliferation and differentiation of granulosa cells, and perhaps by its anti-apoptotic effects. In addition, interactions between granulosa cell-derived KIT ligands and oocyte KIT receptors have been suggested as initiating oocyte growth and follicular development. Furthermore, recent findings suggest there are growth factors derived from oocytes such as GDF-9 and BMP-15. With such factors, oocytes participate in follicular development by regulating the differentiation of surrounding somatic cells. These bidirectional communications between oocytes and somatic cells are important for oocyte growth and follicular development. IVG systems should provide further information regarding oogenesis and folliculogenesis in the ovary.