Elimination of apoptotic granulosa cells by intact granulosa cells and macrophages in atretic mature follicles of the guinea pig ovary

Autophagy is involved in granulosa cell death and follicular atresia in ewe ovaries

In mammalian ovaries, most follicles do not ovulate and are eliminated by atresia, which primarily depends on granulosa cell (GC) apoptosis. Autophagy is an alternative mechanism involved in follicle depletion in mammals through independent or tandem action with apoptosis. However, follicular autophagy has not yet been investigated in sheep; therefore, the present study aimed to investigate the involvement of autophagy in atresia among a pool of growing antral follicles in ewe ovaries. The abundance of the autophagic marker LC3B-II was determined using western blotting in GCs collected from ewe antral follicles. The antral follicles were classified as healthy or atretic based on morphological criteria and steroid measurements in follicular fluid (FF). Immunofluorescence and confocal microscopy analyses were performed on GCs to evaluate the presence of autophagic proteins and their subcellular localisation. Caspase-3 and DNA fragmentation were assessed using western blotting and TUNEL assays, respectively, in the same GC population to investigate the simultaneous apoptosis. The novel results of this study demonstrated enhanced LC3B-II protein expression in GCs of atretic follicles compared to that of healthy ones (1.3-fold increase; P = 0.0001, ANOVA), indicating a correlation between autophagy enhancement in GCs and antral follicular atresia. Autophagy, either functioning independently or in tandem with apoptosis, may be involved in the atresia of growing antral follicles in ewe ovaries because atretic GCs also showed high levels of apoptotic markers. The findings of this study might have important implication on scientific understanding of ovarian follicle dynamics.

Chitosan alleviates ovarian aging by enhancing macrophage phagocyte-mediated tissue homeostasis

BACKGROUND

Age-related changes in the ovarian microenvironment are linked to impaired fertility in women. Macrophages play important roles in ovarian tissue homeostasis and immune surveillance. However, the impact of aging on ovarian macrophage function and ovarian homeostasis remains poorly understood.

METHODS

Senescence-associated beta-galactosidase staining, immunohistochemistry, and TUNEL staining were used to assess senescence and apoptosis, respectively. Flow cytometry was employed to evaluate mitochondrial membrane potential (MMP) and apoptosis in granulosa cells lines (KGN), and macrophages phagocytosis. After a 2-month treatment with low molecular weight Chitosan (LMWC), ovarian tissues from mice were collected for comprehensive analysis.

RESULTS

Compared with the liver and uterus, the ovary displayed accelerated aging in an age-dependent manner, which was accompanied by elevated levels of inflammatory factors and apoptotic cells, and impaired macrophage phagocytic activity. The aged KGN cells exhibited elevated reactive oxygen species (ROS) and apoptotic levels alongside decreased MMP. H2O2-induced aging macrophages showed reduced phagocytosis function. Moreover, there were excessive aging macrophages with impaired phagocytosis in the follicular fluid of patients with diminished ovarian reserve (DOR). Notably, LMWC administration alleviated ovarian aging by enhancing macrophage phagocytosis and promoting tissue homeostasis.

CONCLUSIONS

Aging ovarian is characterized by an accumulation of aging and apoptotic granulosa cells, an inflammatory response and macrophage phagocytosis dysfunction. In turn, impaired phagocytosis of macrophage contributes to insufficient clearance of aging and apoptotic granulosa cells and the increased risk of DOR. Additionally, LMWC emerges as a potential therapeutic strategy for age-related ovarian dysfunction.

Classification of Atretic Small Antral Follicles in the Human Ovary

The reproductive lifespan in humans is regulated by a delicate cyclical balance between follicular recruitment and atresia in the ovary. The majority of the small antral follicles present in the ovary are progressively lost through atresia without reaching dominance, but this process remains largely underexplored. In our study, we investigated the characteristics of atretic small antral follicles and proposed a classification system based on molecular changes observed in granulosa cells, theca cells, and extracellular matrix deposition. Our findings revealed that atresia spreads in the follicle with wave-like dynamics, initiating away from the cumulus granulosa cells. We also observed an enrichment of CD68+ macrophages in the antrum during the progression of follicular atresia. This work not only provides criteria for classifying three stages of follicular atresia in small antral follicles in the human ovary but also serves as a foundation for understanding follicular degeneration and ultimately preventing or treating premature ovarian failure. Understanding follicular remodeling in the ovary could provide a means to increase the number of usable follicles and delay the depletion of the follicular reserve, increasing the reproductive lifespan.

Macrophage activation drives ovarian failure and masculinization in zebrafish

BMP15 is a conserved regulator of ovarian development and maintenance in vertebrates. In humans, premature ovarian insufficiency is caused by autoimmunity and genetic factors, including mutation of BMP15. The cellular mechanisms underlying ovarian failure caused by BMP15 mutation and immune contributions are not understood. Using zebrafish, we established a causal link between macrophage activation and ovarian failure, which, in zebrafish, causes sex reversal. We define a germline-soma signaling axis that activates macrophages and drives ovarian failure and female-to-male sex reversal. Germline loss of zebrafish Bmp15 impairs oogenesis and initiates this cascade. Single-cell RNA sequencing and genetic analyses implicate ovarian somatic cells that express conserved macrophage-activating ligands as mediators of ovarian failure and sex reversal. Genetic ablation of macrophages or elimination of Csf1Rb ligands, Il34 or Csf1a, delays or blocks premature oocyte loss and sex reversal. The axis identified here provides insight into the cells and pathways governing oocyte and ovary maintenance and potential therapeutic targets to preserve female fertility.

Macrophage activation drives ovarian failure and masculinization

In humans, premature ovarian insufficiency (POI) is caused by autoimmunity and genetic factors, such as mutation of BMP15, a key ovarian determining gene. The cellular mechanisms associated with ovarian failure caused by BMP15 mutation and immune contributions to the disorder are not understood. BMP15's role in ovarian follicle development is conserved in vertebrates, including zebrafish. Using zebrafish, we established a causal link between macrophage activation and ovarian failure. We identified a germline-somatic gonadal cell-macrophage axis underlying ovarian atresia. Germline loss of Bmp15 triggers this axis that single-cell RNA sequencing and genetic analyses indicate involves activation of ovarian somatic cells that express conserved macrophage-activating ligands. Genetic ablation of macrophages blocks premature oocyte loss. Thus, the axis identified here represents potential therapeutic targets to preserve female fertility.

Granulosa cells provide elimination of apoptotic oocytes through unconventional autophagy-assisted phagocytosis

STUDY QUESTION

Do human granulosa cells (GCs) ingest and destroy apoptotic oocytes?

SUMMARY ANSWER

Somatic GCs ingest and destroy apoptotic oocytes and other apoptotic substrates through unconventional autophagy-assisted phagocytosis.

WHAT IS KNOWN ALREADY

Most (99%) ovarian germ cells undergo apoptosis through follicular atresia. The mode of cleaning of atretic follicles from the ovary is unclear. Ovarian GCs share striking similarities with testicular Sertoli cells with respect to their origin and function. Somatic Sertoli cells are responsible for the elimination of apoptotic spermatogenic cells through unconventional autophagy-assisted phagocytosis.

STUDY DESIGN, SIZE, DURATION

Human GCs were tested for the ability to ingest and destroy the apoptotic oocytes and other apoptotic substrates. A systemic study of the main phagocytosis steps has been performed at different time points after loading of apoptotic substrates into the GC.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Primary cultures of GC retrieved following controlled ovarian stimulation of five women for IVF/ICSI and a human granulosa KGN cell line were incubated with different apoptotic substrates: oocytes which underwent spontaneous apoptosis during the cultivation of immature germ cells for IVF/ICSI; apoptotic KGN cells; and apoptotic membranes from rat retinas. Cultured GC were analyzed for the presence of specific molecular markers characteristic of different steps of phagocytic and autophagy machineries by immunocytochemistry, confocal microscopy, transmission electron microscopy and western blotting, before and after loading with apoptotic substrates.

MAIN RESULTS AND THE ROLE OF CHANCE

Incubation of human GC with apoptotic substrates resulted in their translocation in cell cytoplasm, concomitant with activation of the phagocytosis receptor c-mer proto-oncogene tyrosine kinase MERTK (P < 0.001), clumping of motor molecule myosin II, recruitment of autophagy proteins: autophagy-related protein 5 (ATG5), autophagy-related protein 6 (Beclin1) and the rise of a membrane form of microtubule-associated protein 1 light chain 3 (LC3-II) protein. Ingestion of apoptotic substrates was accompanied by increased expression of the lysosomal protease Cathepsin D (P < 0.001), and a rise of lysosomes in the GCs, as assessed by different techniques. The level of autophagy adaptor, sequestosome 1/p62 (p62) protein remained unchanged.

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

The number of patients described here is limited. Also the dependence of phagocytosis on reproductive hormone status of patients should be analyzed.

WIDER IMPLICATIONS OF THE FINDINGS

Removal of apoptotic oocytes by surrounding GC seems likely to be a physiological mechanism involved in follicular atresia. Proper functioning of this mechanism may be a new strategy for the treatment of ovarian dysfunctions associated with an imbalance in content of germ cells in the ovaries, such as premature ovarian failure and polycystic ovary syndrome.

STUDY FUNDING/COMPETING INTEREST(S)

The study was funded by Rennes Metropole (AIS 2015) and Agence de BioMédecine. This work was supported by funding from Université de Rennes1, Institut National de la Santé et de la Recherche Médicale (INSERM) and CHU de Rennes. A.B. is funded in part by the program Actions Concertées Interpasteuriennes (ACIP) and a research grant from the European Society of Pediatric Endocrinology. This work is supported by the Agence Nationale de la Recherche Grants ANR-17-CE14-0038 and ANR-10-LABX-73. The authors declare no competing interests.

Proteomic analysis of healthy and atretic porcine follicular granulosa cells

Follicular atresia is initiated with the apoptosis of granulosa cells (GCs) after birth in mammals. The molecular mechanisms underlying GC apoptosis during follicular selection are unclear at present. The objective of this study is to identify the proteins and pathways that may be involved in porcine follicular atresia. Proteins isolated from GCs collected from healthy and atretic follicles were detected by tandem mass tag (TMT) protein labeling and LC-MS/MS. A total of 4591 proteins in the healthy follicle granulosa cell (HFGC) and atretic follicle granulosa cell (AFGC) groups were identified, and 399 differentially abundant proteins were found between the HFGC and AFGC groups; of which 262 proteins were significantly up-regulated and 137 proteins were significantly down-regulated. Differential protein enrichment analysis showed that proteins involved in proteolysis, protein destabilization, phagocytosis, and engulfment were more abundant in the AFGC group. Also, these proteins were mainly involved in the lysosome, phagosome, autophagy, and apoptosis pathways. Specially, PTGFRN is potential important regulated protein in the development of the antral follicle, and down-regulation of PTGFRN in GCs may lead to follicular atresia. Our study shows that the identified proteins and their related signaling pathways may play crucial roles during health follicle develop to atretic follicle. SIGNIFICANCE: Follicular atresia during 'selection' reduces the reproductive potential of sows. In this study, we found 399 proteins differentially abundant. between the HFGC and AFGC groups. These results establish a foundation for elucidating the mechanism of follicular atresia in swine.

There is No Association between Premature Ovarian Insufficiency and Levels of Fetuin-A/α2-Heremans-Schmid Glycoprotein

Objective:

Fetuin-A is a well-known negative acute-phase protein and has been used liberally to predict vascular disease. The aim of this study was to evaluate the association between serum human fetuin-A/alpha2-Heremans–Schmid glycoprotein levels and idiopathic premature ovarian insufficiency (POI).

Methods:

A total of 75 women were included in this case–control study between January 2013 and December 2013. Serum fetuin-A concentrations were measured in 36 women with idiopathic POI and 39 healthy women with regular cycles. Blood samples were drawn after a 12-h overnight fast and were kept at −80°C for subsequent assay. The serum levels of fetuin-A were assessed by commercial ELISA kits (BioVendor Laboratory Medicine Inc., Brno, Czech Republic) and serum concentration values were expressed as μg/ml.

Results:

The mean serum fetuin-A levels of idiopathic POI and control women were 229.02 ± 27.79 and 232.37 ± 65.56, respectively, with P = 0.771 (independent samples t-test). Our results showed no statistically significant difference between serum fetuin-A levels of idiopathic POI women and controls.

Conclusion:

The mean values of serum fetuin-A in idiopathic POI women were not significantly different from controls, which implies that there is no significant association between serum fetuin-A levels and idiopathic POI.

Oocyte atresia in WT (HdrR) and P53 (-/-) medaka (Oryzias latipes) exposed to UVA

The negative effects of ambient ultraviolet (UVA) on the water environment have been recently highlighted; UVA can create deleterious effects by stimulating stress on pelagic organisms. Little is known about UVA effects on oocyte characteristics of female fish. In the present study we explored the effects of exposure to ecologically relevant levels of simulated UVA radiation on ovaries of two major strains WT (HdrR) and P53 (-/-) of medaka (Oryzias latipes) mature female. Fish were assigned to control and three UVA-exposed groups as (15 min, 30 min, and 60 min/day) for three days and sample selection was 24 h and 14 days after exposure. Histological alterations and oocyte atresia percentage were analyzed in the UVA-exposed fish compared to control. Alteration comprised hyperthrophied follicular cells with increased thickness, breakdown of egg chorion (zona radiata), damage of cortical alveoli, and distorted nucleus and cytoplasm. The atresia percentages significantly increased with higher UVA exposure dose and time for both the wild type and the p53 deficient fish. The wild type displayed significantly higher oocyte atresia percentage than the p53 mutant. These results suggested that UVA exposure provoked histological alterations in both p53 and WT medaka oocytes leading to follicular atresia, which reduce female reproductive ability and larval production. UVA oocyte response showed p53 dependent and independent histological alteration, however, the p53 mutant was less sensitive to UVA than the wild type in medaka fish.

CD11c+ M1-like macrophages (MΦs) but not CD206+ M2-like MΦ are involved in folliculogenesis in mice ovary

Macrophages (MΦs) are involved in folliculogenesis and ovulation. However, it is unknown which type of MΦ, M1 or M2, plays a more essential role in the ovary. CD206 or CD11c diphtheria toxin receptor transgenic (DTR) mice, which enable depletion of CD206+ M2 MΦs and CD11c+ MΦ or CD11c+ Dendritic cells (DCs), respectively, were used. Oocytes were used for in vitro fertilization and embryo transfer. In vitro fertilized embryos derived from M2 MΦ depleted oocytes were transferred to pseudo pregnant wild type mice. CD11c DTR mice were also used to investigate the role of CD11c cells, M1 MΦ and DCs in folliculogenesis. In WT mice, the proportion of CD206+ M2-like MΦs was not increased in follicular induction, while that of CD11c+ M1-like MΦs was increased. In CD206 DTR mice, folliculogenesis was normal and the ovulation number, fertilization rate, and implantation rate were similar to those in WT mice. In CD11c DTR mice, folliculogenesis was impaired with ovarian hemorrhage and the staining of platelet derived growth factor-receptor β (PDGF-Rβ), a marker of pericytes, and CD34, a marker of endothelial cells, was reduced. CD11c+ cells, M1 MΦs or DCs, may be involved in folliculogenesis, while M2 MΦs are not involved in folliculogenesis.

The Growth of Preantral Follicles and the Impact of Different Supplementations and Circumstances: A Review Study with Focus on Bovine and Human Preantral Follicles

One of the most important concerns cancer survivors face is fertility. Current treatment modalities often result in damage to the reproductive system. Different options have been proposed to preserve the fertility of affected women, and many attempts have been made to improve their chance of childbearing after therapy. Cryopreservation of ovarian tissue and follicles before the onset of cancer treatment and then either transplantation of ovarian tissue or culture of ovarian tissue and individual follicles in vitro is a commonly cited approach. Extensive research is being done to design an optimal condition for the culture of ovarian follicles. Improving follicle culture systems by understanding their actual growth needs might be a crucial step toward fertility preservation in cancer patients. This review article will try to provide a summary of the role of different factors and conditions on growth of human and bovine preantral follicles in vitro.

Histomorphology and innate immunity during the progression of osteoarthritis: Does synovitis affect cartilage degradation?

Osteoarthritis (OA) is a common chronic degenerative disease that affects all joints. At present, the pathological processes and mechanisms of OA are still unclear. Innate immunity, a key player in damage to the structure of the joint and the mechanism by which the host attempts to repair OA, affects all pathological stages of the disease. In the present study, our aim was to assess changes in innate immunity during the pathological processes of OA in articular cartilage (AC) and the synovial membrane (SM), which are the major structures in joints, and to systematically examine the histological changes in AC and SM in mild, moderate and severe cases of OA, in order to further speculate about the manner in which the interactions of AC and SM are facilitated by innate immunity. Histological methods (including HE and Safranin O-fast green staining), immunofluorescent double staining, TUNEL stain, and Western blots were used to assess the morphological changes within AC and SM tissues in healthy and mild, moderate, or severe OA rats. Our results showed that the damage to AC and SM within the joints progressively worsened in different degrees during the course of the disease, and that the innate immune system was closely involved in the AC and SM during each stage of OA. These findings also confirmed that SM may affect the pathological changes in AC through the innate immune system, and therefore affect the progress of OA.

Melanins as biomarkers of ovarian follicular atresia in the catfish Heteropneustes fossilis: biochemical and histochemical characterization, seasonal variation and hormone effects

Follicular atresia is a common feature of the vertebrate ovary that occurs at different stages of folliculogenesis and ovarian regression. It has physiological significance to maintain homeostasis and control fecundity, and ensure removal of post-ovulatory follicular remnants for preparing the ovary for the next cycle. Pigments appear late in the atretic process as indigestible waste formed out of the degradation of the oocytes, follicle wall and granulocytes. In the present study, pigment accumulation was demonstrated by Schmorl's and Perls' staining methods in the atretic ovarian follicles of Heteropneustes fossilis during follicular development and regression. Melanins were characterized spectrophotometrically for the first time in fish ovary. The predominant form is eumelanin, followed by pheomelanin and alkali-soluble melanin. Melanins showed significant seasonal variations with levels low in gonad resting phase, increasing to the peak in the post-spawning phase. The concentration of melanins increased time-dependently in post-ovulated ovary after human chorionic gonadotropin treatment. In the spawning phase, in vitro incubation of ovary slices with estradiol-17β or dexamethasone for 8 or 16 h decreased both eumelanin and pheomelanin levels time-dependently. The alkali-soluble melanin showed a significant decrease only in the dexamethasone group at 16 h. The results show that melanin assay can be used as a biomarker of follicular atresia in fish ovary, natural or induced by environmental toxicants.

Chronic exposures to low levels of estradiol and their effects on the ovaries and reproductive hormones: Comparison with aging

Aging in female rats is characterized by a state called "constant estrous" in which rats are unable to ovulate, have polycystic ovaries and moderately elevated estrogen levels. We hypothesized that chronic exposure of young animals to low levels of E2 can produce reproductive changes similar to that seen in aging animals. Adult female rats were sham-implanted (control) or implanted with slow-release E2 (20 ng/day) pellets for 30, 60, or 90 days. Old constant estrous (OCE) rats were used for comparison. Estrous cyclicity was monitored periodically. At the end of treatment, animals were sacrificed, trunk blood was collected for hormone measurements and ovaries for immunohistochemistry. Young animals became acyclic with increasing duration of E2 exposure while OCE rats were in a state of acyclicity. Ovaries became increasingly more cystic with E2 exposure, and were comparable to OCE rats; however, there was a marked reduction in interstitial tissue with exogenous E2 treatment. Exogenous E2 also decreased Mullerian inhibiting substance expression, increased infiltration of macrophages without much impact on apoptosis in the ovaries. Serum testosterone levels decreased in E2-treated young animals, while it increased significantly in OCE rats. There was a marked reduction in LH but not FSH levels with E2 exposure in both young and old animals. These results indicate that even very low doses of E2 are capable of inducing aging-like changes in young animals.

Ovarian phagocyte subsets and their distinct tissue distribution patterns

Ovarian macrophages, which play critical roles in various ovarian events, are probably derived from multiple lineages. Thus, a systemic classification of their subsets is a necessary first step for determination of their functions. Utilizing antibodies to five phagocyte markers, i.e. IA/IE (major histocompatibility complex class II), F4/80, CD11b (Mac-1), CD11c, and CD68, this study investigated subsets of ovarian phagocytes in mice. Three-color immunofluorescence and flow cytometry, together with morphological observation on isolated ovarian cells, demonstrated complicated phenotypes of ovarian phagocytes. Four macrophage and one dendritic cell subset, in addition to many minor phagocyte subsets, were identified. A dendritic cell-like population with a unique phenotype of CD11c(high)IA/IE⁻F4/80⁻ was also frequently observed. A preliminary age-dependent study showed dramatic increases in IA/IE⁺ macrophages and IA/IE⁺ dendritic cells after puberty. Furthermore, immunofluorescences on ovarian sections showed that each subset displayed a distinct tissue distribution pattern. The pattern for each subset may hint to their role in an ovarian function. In addition, partial isolation of ovarian macrophage subset using CD11b antibodies was attempted. Establishment of this isolation method may have provided us a tool for more precise investigation of each subset's functions at the cellular and molecular levels.

Secondary follicle growth and oocyte maturation during encapsulated three-dimensional culture in rhesus monkeys: effects of gonadotrophins, oxygen and fetuin

BACKGROUND

An alginate-based matrix supports the three-dimensional (3D) architecture of non-human primate follicles and, in the presence of FSH, permits the in vitro development of pre-antral follicles to the small antral stage, including the production of ovarian steroids and paracrine factors. The current study investigated the ability of gonadotrophins, fetuin and oxygen (O₂) to improve primate follicle growth and oocyte maturation in vitro.

METHODS

Macaque secondary follicles were isolated from the early follicular phase ovaries, encapsulated in a sodium alginate matrix and cultured individually for 40 days in supplemented medium. The effects of recombinant human (rh) FSH (15, 3 and 0.3 ng/ml for high, medium and low FSH, respectively), bovine fetuin (1 or 0 mg/ml) and O₂ (5 or 20% v/v) were examined. Half of the follicles in each culture condition received rhLH on Day 30-40. Follicles that reached antral stage were treated with rh chorionic gonadotrophin for 34 h to initiate oocyte meiotic maturation. Media were analyzed for ovarian steroids and anti-müllerian hormone (AMH).

RESULTS

Improved culture conditions supported non-human primate, secondary follicle growth to the antral stage and, for the first time, promoted oocyte maturation to the MII stage. In the presence of fetuin at 5% O₂, follicles had the highest survival rate if cultured with high or medium FSH, whereas follicles grew to larger diameters at Week 5 in low FSH. Oocyte health and maturation were promoted under 5% O₂. High FSH stimulated steroid production by growing follicles, and steroidogenesis by follicles cultured with low FSH was promoted by LH. AMH biosynthesis was elevated with high compared with low FSH and for longer under 5% O₂ than under 20% O₂.

CONCLUSIONS

This encapsulated 3D culture model permits further studies on the endocrine and local factors that influence primate follicle growth and oocyte maturation, with relevance to enhancing fertility preservation options in women.

Morphologic observation and classification criteria of atretic follicles in guinea pigs

There is a lack of appropriate classification criteria for the determination of atretic follicles in guinea pigs. In the present study, new criteria were established based on the latest morphologic criteria for cell death proposed by the Nomenclature Committee on Cell Death (NCCD) in 2009. Ovaries of guinea pigs were sampled on different stages of estrous cycle, and the morphologic observations of atretic follicles were investigated in serial sections. The results showed that the process of follicular atresia could be classified into four continuous stages: (1) the granulosa layer became loose, and some apoptotic bodies began to appear; (2) the granulosa cells were massively eliminated; (3) the theca interna cells differentiated; and (4) the residual follicular cells degenerated. In addition, the examination revealed that these morphologic criteria were accurate and feasible. In conclusion, this study provides new criteria for the classification of atretic follicles in guinea pigs, and this knowledge can inform future research in the area.

Involvement of cell proliferation in the process of follicular atresia in the guinea pig

Cell morphology and proliferation was investigated in the atretic follicles during estrous cycles in the guinea pig. Ovarian samples on days 1, 4, 8, 12 and 16 of the estrous cycle in the guinea pig were taken in the morning for histologic staining with hematoxylin and eosin (HE), and immunohistochemical staining of the protein proliferating cell nuclear antigen (PCNA). The results indicated that the granulosa cells degenerated and eliminated first in atretic follicles, while the fibroblast-like cells appeared in the innermost layer of theca interna cells. When the fibroblast-like cells migrated to the antrum, they proliferated and formed a new tissue in peripheral to the zona pellucida of the oocyte. Our results also revealed that the orientation of the theca interna cell arrangement changed twice during the process of atresia, and the loose connective tissue in the antrum was critical for follicular atresia. Therefore, follicular atresia was not a simple process of cell death and elimination, but coexisted with cell proliferation. To our knowledge, we have for the first time confirmed cell proliferation and the presence of new tissue in atretic follicles in guinea pigs.

Ultrastructural features of atretic follicles in the sexually immature ostrich (Struthio camelus)

The aim of this study was to describe the ultrastructural features of atresia in follicles of the immature ostrich (12-14 months old); a ratite that displays seasonal, precocious ovarian activity. The early stage of atresia in primordial, pre-vitellogenic and vitellogenic follicles was characterized by the accumulation of lipid droplets in the granulosa cells. Granulosa cells with condensed cytoplasm and nuclei were a prominent feature during the intermediate phase of atresia. The degenerating follicles were then infiltrated by stroma during the terminal stages of atresia. The results of this study provide further information on the morphology of atretic ovarian follicles in the immature ostrich.

Expression and Glycosylation with Polylactosamine of CD44 Antigen on Macrophages During Follicular Atresia in Pig Ovaries1

Macrophages are essential in cleaning up apoptotic debris during follicular atresia. However, the key factors of this process are still unclear. In the present study, we evaluated CD44 mRNA, CD44 protein, and CD44 antigen glycosylation on macrophages during follicular atresia in the pig. Atresia was classified into five stages: stage I, healthy follicles; stage II, early atretic follicles having apoptotic granulosa cells with an unclear basement membrane; stage III, progressing atretic follicles having apoptotic granulosa cells completely diffused from the basement membrane; stage IV, late atretic follicles with increasing lysosomal activity; and stage V, disintegrated atretic follicles having collapsed theca cells and strong lysosomal activity. Immunohistological analysis showed that macrophages expressing CD44 invaded the inside of stage III follicles, accompanied by a collapse of basement membrane. Semiquantitative RT-PCR showed that only mRNA of the CD44 standard isoform (CD44s) was present in inner cells of follicles, and not any CD44 variant isoform (CD44v) mRNAs. The amount of CD44s mRNA was increased at stage III. Western blot and lectin blot analyses showed that CD44 was markedly expressed at stage III and glycosylated with polylactosamine at the same time. After macrophages invaded atretic follicles at stages III-V, the CD44 expressed on macrophages was glycosylated with polylactosamine. The lysosomal activity began to increase at stage IV, and reached the highest level at stage V. Increased CD44s protein and posttranslational modification of CD44 with polylactosamine on macrophages from stage III could be involved in the cleaning up apoptotic granulosa cells.

Fetuin and fetuin messenger RNA in granulosa cells of the rat ovary

The hardening reaction that occurs in the zona pellucida to block polyspermy can be overcome in oocyte cultures in the presence of fetal serum or the serum component fetuin. Fetuin may also prevent precocious zona hardening by inhibiting a ZP2 proteinase released spontaneously by cortical granules during maturation of the oocyte. We demonstrated fetuin mRNA in the rat ovary by reverse transcriptase-polymerase chain reaction and localized it by in situ hybridization. Fetuin mRNA was present in all granulosa cells of growing and large follicles. Immunohistochemical analysis revealed that the fetuin protein was only present in some of the small, growing follicles. In large, healthy follicles, fetuin protein was confined to cumulus cells and granulosa cells bordering the antrum. Fetuin was present in atretic follicles, but the staining pattern differed from that of healthy follicles. The follicular antrum contained a substantial amount of fetuin, but whether granulosa cells secreted it or it originated in the ovarian blood supply could not be confirmed. We concluded that at least a portion of the fetuin is produced by granulosa cells of growing and large follicles, suggesting that fetuin may function in a paracrine manner to maintain the zona pellucida in a penetrable state for fertilization.

Caspase-3 gene knockout defines cell lineage specificity for programmed cell death signaling in the ovary

Previous studies have proposed the involvement of caspase-3, a downstream executioner enzyme common to many paradigms of programmed cell death (PCD), in mediating the apoptosis of both germ and somatic cells in the ovary. Herein we used caspase-3 gene knockout mice to directly test for the functional requirement of this protease in oocyte and/or granulosa cell demise. Using both in vivo and in vitro approaches, we determined that oocyte death initiated as a result of either developmental cues or pathological insults was unaffected by the absence of caspase-3. However, granulosa cells of degenerating antral follicles in both mouse and human ovaries showed a strong immunoreaction using an antibody raised against the cleaved (activated) form of caspase-3. Furthermore, caspase-3 mutant female mice possessed aberrant atretic follicles containing granulosa cells that failed to be eliminated by apoptosis, as confirmed by TUNEL (terminal deoxynucleotidyl transferase-mediated deoxy-UTP nick end labeling) analysis of DNA cleavage and 4',6-diamidino-2-phenylindole staining of nuclear morphology (pyknosis). These in vivo results were supported by findings from in vitro cultures of wild-type and caspase-3-deficient antral follicles or isolated granulosa cells. Contrasting the serum starvation-induced occurrence of apoptosis in wild-type granulosa cells, caspase-3-null granulosa cells deprived of hormonal support were TUNEL-negative, showed attenuated chromatin condensation by 4',6-diamidino-2-phenylindole staining and exhibited delayed internucleosomal DNA cleavage. Such ex vivo findings underscore the existence of a cell autonomous (granulosa cell intrinsic) defect in apoptosis execution resulting from caspase-3 deficiency. We conclude that caspase-3 is functionally required for granulosa cell apoptosis during follicular atresia, but that the enzyme is dispensable for germ cell apoptosis in the female.

Elimination of atretic follicles from the mouse ovary: a TEM and immunohistochemical study in mice

We examined numerous ovarian follicles from 32-35 d virgin mice by transmission electron microscopy and light microscopic immunohistochemistry. No macrophages were seen, but various stages of apoptotic granulosa cells were encountered. Presumably a granulosa cell or its debris in an advanced stage of apoptosis was destined to be phagocytosed by adjacent normal-looking granulosa cells. Other granulosa cells of normal appearance were seen in the region of the zona pellucida in contact with and apparently phagocytosing atrophic oocytes. Such granulosa cells were characterised by the presence of gap junctions with other cells and frequently contained annular gap junctions in the cytoplasm. To confirm the lack of involvement of macrophages in the process of follicular atresia and elimination, specially prepared ovarian sections were incubated with antimouse macrophage monoclonal antibodies (F4/80, Mac-1, Mac-2). None of the follicles examined showed positive immunoreactivity with these antibodies. Atretic follicles may shrink and eventually disappear from the ovary as a result of repeated apoptosis and phagocytosis by granulosa cells. There is no evidence for the presence or involvement of macrophages in the atretic follicles, at least in prereproductive mice as examined.

Crosstalk Among Multiple Signaling Pathways Controlling Ovarian Cell Death

Ovarian cell death is an essential process for the homeostasis of ovarian function in human and other mammalian species. It ensures the selection of the dominant follicle and the demise of excess follicles. In turn, this process minimizes the possibility of multiple embryo development during pregnancy and assures the development of few but healthy embryos. Degeneration of the old corpora lutea in each estrous/menstrual cycle by programmed cell death is essential to maintain the normal cyclicity of ovarian steroidogenesis. Although there are multiple pathways that can determine cell death or survival, crosstalk among endocrine, paracrine and autocrine factors, as well as among protooncogenes, tumor suppressor genes, survival genes and death genes, plays an important role in determining the fate of ovarian somatic and germ cells. The establishment of immortalized rat and human steroidogenic granulosa cell lines and the investigation of pure populations of primary granulosa cells allows systematic studies of the mechanisms that control steroidogenesis and apoptosis of granulosa cells. These cells are the most abundant type of somatic follicular cell. Moreover, crosstalk between p53 and extracellular matrix components such as laminin, fibronectin and basic fibroblast growth factor, between cAMP- and p53-generated signals and between steroid hormones and Bcl-2, can explain some of the fine tuning that controls ovarian steroidogenesis and apoptosis. Further study of the mechanisms of ovarian cell death will lead to a better understanding of the processes involved and permit the formulation of novel strategies for the treatment of ovarian malfunctions, such as polycystic ovarian syndrome and ovarian cancer.

Limited uptake of foreign materials by resident macrophages in murine ovarian tissues

In the present study, the distributions of exogenously administered horseradish peroxidase (HRP) and colloidal carbon in gonadal tissues were observed in both male and female mice using light microscopy. HRP was injected intravenously and colloidal carbon was directly injected into the gonadal parenchyma. Thereafter, the gonads were obtained for histological examination. The results showed that staining of HRP and carbon was detected in the ovaries at a low level. In contrast, much staining was observed in the interstitial cells of the testes for a long period. This suggests that ovarian tissues are less active in the uptake of exogenous materials than testicular tissues in vivo. However, immunohistochemical examination using anti-macrophage antibodies revealed that the ovaries contained a large number of macrophages, as did the testes, under normal conditions. Therefore, the results indicate that resident macrophages in the ovaries exhibit weak endocytic activity of foreign materials in vivo.