Effects of reduction of the number of primordial follicles on follicular development to achieve puberty in female rats

hUMSCs Transplantation Regulates AMPK/NR4A1 Signaling Axis to Inhibit Ovarian Fibrosis in POI Rats

BACKGROUND

The mechanism of human Umbilical Cord Mesenchymal Stem Cells (hUMSCs) transplantation to improve ovarian function in the rats with Premature Ovarian Insufficiency (POI) is still unclear. The aim of this study is to investigate the signal axis mechanism that is involved in the ovarian function recovery of POI rats following hUMSCs transplantation.

METHODS

The rat model with POI was established by intraperitoneal injection of cisplatin. The hUMSCs were transplanted by caudal vein injection into POI rats. Hematoxylin-eosin (H&E) staining was performed to examine the morphology of rat ovarian tissue. Masson staining, Sirus red staining and immunofluorescence were used to observe the fibrosis extent of ovarian tissue. The levels of serum sex hormones and the expression of fibrosis related markers in ovarian tissues were measured by enzyme-linked immunosorbent assay (ELISA). The expression of NR4A1, Phospho-NR4A1 and AMP-activated protein kinase (AMPK) signaling in rat ovarian tissues was measured by immunohistochemistry and immunofluorescence. The role of AMPK/NR4A1 signaling axis in the regulation of ovarian function recovery in POI rats following hUMSCs transplantation was further investigated by adenovirus and siRNA intervention in isolated stromal cells.

RESULTS

The results showed that the hUMSCs transplantation significantly inhibited ovarian tissue fibrosis and restored the ovarian function in POI rats. The level of NR4A1 and AMPK expression in ovarian tissue of POI rats after hUMSCs transplantation was significantly increased compared with the control group. In the cultured ovarian stromal cells, the similar results were obtained on the expression of NR4A1 and its regulation on fibrosis related molecular markers in Cisplatin (CDDP) damaged stromal cells following hUMSCs supernatant treatment. Both hUMSCs supernatant treatment and the addition of AMPK inhibitors increased NR4A1 expression in stromal cells. And after NR4A1 molecular intervention, fibrosis-related indicators in stromal cells changed. The data suggests that the AMPK/NR4A1 signaling axis is involved in the ovarian function changes in POI rats following hUMSCs transplantation.

CONCLUSION

The data from this study indicate that the inhibition of tissue fibrosis and recovery of ovarian function is regulated by AMPK/NR4A1 signaling axis in POI rats following hUMSCs transplantation.

Human Menstrual Blood Stem Cell-Derived Granulosa Cells Participate in Ovarian Follicle Formation in a Rat Model of Premature Ovarian Failure In Vivo

We recently reported the application of human menstrual blood stem cells' (HuMenSCs) transplantation as a treatment modality in a rat model of premature ovarian failure (POF). We continued to investigate further in this respect. Female rats were injected intraperitoneally with 36 mg/kg busulfan. HuMenSCs were obtained, grown, and analyzed for immunophenotypic features at passage three. The cells were labeled with CM-Dil and infused into the rats. There were four groups: normal, negative control, treatment, and Sham. One month after treatment, the ovaries were collected and weighed. Histological sections were prepared from the ovary and HuMenSCs were tracking. Subsequently, we examined the changes of expression of Bax and B cell lymphoma 2 (Bcl2) genes by real-time polymerase chain reaction assay. One month after HuMenSCs transplantation, these cells were located in the ovarian interstitium and granulosa cells (GCs). The number of TUNEL-positive cells significantly decreased in the treatment group. Also the expression level of Bax genes, unlike Bcl2 gene, significantly decreased compared with negative and sham groups. In our study, HuMenSCs were tracked in ovarian tissues within 2 months after transplantation, and they differentiated into GCs. Therefore, the use of these cells can be a practical and low-cost method for the treatment of POF patients.

Mesenchymal Stem Cell Therapy Using Human Umbilical Cord in a Rat Model of Autoimmune-Induced Premature Ovarian Failure

Premature ovarian failure (POF) is one of the principal causes of female infertility, and although its causes are complex and diverse, autoimmune deficiency may be involved. Human umbilical cord mesenchymal stem cells (UCMSCs) can be used for tissue regeneration and repair. Therefore, the present study was designed to determine the role of UCMSCs in immune factor-induced POF in rats. In this study, different concentrations of UCMSCs were injected into induced POF rats. Ovarian functions were examined by evaluating the estrus cycle, follicular morphology, hormonal secretion, and the proliferation and apoptosis of granulosa cells. Our results showed that the estrus cycle of rats returned to normal and follicular development was significantly improved after transplantation of UCMSCs. In addition, serum concentrations of 17-estradiol (E2), progesterone (P4), and anti-Müllerian hormone (AMH) increased significantly with treatment. Transplantation of UCMSCs also reduced the apoptosis of granulosa cells and promoted the proliferation of granulosa cells. All of these improvements were dose dependent. Furthermore, the results of related gene expression showed that transplanted human UCMSCs upregulated the expression of Bcl-2, AMH, and FSHR in the ovary of POF rats and downregulated the expression of caspase-3. These results further validated the potential mechanisms of promoting the release of cell growth factors and enhancing tissue regeneration and provide a theoretical basis for the clinical application of stem cells in the treatment of premature ovarian failure.

Toxic effects of VCD on kidneys and liver tissues: a histopathological and biochemical study

OBJECTIVE

We explored detrimental effects of VCD on non-ovarian tissues such as kidneys and liver 14 days post-drug administration. Twelve rats were randomly assigned into two groups. In VCD group, rats received 160 mg/kgbw VCD intraperitoneally for 15 consequent days. Control rats were injected with VCD-free normal saline. At the respective time point, rats were euthanized, blood and tissue samples were collected. H&E staining was performed to evaluate pathological changes. Serum level of ALT, AST, creatinine and urea were also measured.

RESULTS

Histological analysis revealed hyperemia and follicular atresia in the ovaries, indicating successful POF induction in rats. In renal tissue, extensive tubular necrosis, focal hemorrhage, hyaline casts, and interstitial nephritis were observed. Analysis of hepatic tissue showed numerous hemorrhagic foci, chronic cholangitis, and hepatocyte necrosis, indicating apparent VCD toxicity of both hepatic and renal tissues. The biochemical evaluation revealed a tendency of increase in ALT, AST, creatinine, and Urea in VCD-treated rats; however, the values did not reach significant level. In conclusion, the induction of POF in rats by VCD correlates with renal and hepatic damages. Commensurate with data from this study, any conclusions from experiments based on VCD-induced premature ovarian failure rats should be reported with caution.

Study of the reparative effects of menstrual-derived stem cells on premature ovarian failure in mice

Background

Young female patients who receive chemotherapy frequently face premature ovarian failure (POF). The therapeutic potential of stem cells in these patients has been explored in stem cells derived from different sources. However, many of these types of stem cells are either difficult to obtain or obtaining them involves invasive procedures. Here, we show that menstrual-derived stem cells (MenSCs) are easy to access and exhibit mesenchymal stem cell-like properties. MenSCs are therefore a novel source of stem cells that can be used for tissue repair. The aim of this study was to explore the reparative capacity and the mechanism underlying the activities of MenSCs.

Methods

POF mouse models were established by 7 consecutive days of intraperitoneal injection of cisplatin, and then MenSCs or MenSC-derived conditioned media (CM) were infused via the tail vein. The ovaries were excised after either 7 or 21 days of treatment and the follicles were counted and categorized. Apoptosis of granulosa cells was observed by terminal deoxynucleotidyl transferase mediated dUTP nick end labelling staining. Ovarian function was evaluated by monitoring serum sex hormone levels. Furthermore, MenSC tracking, Q-PCR, and small interfering RNA transfection were used to reveal the inner mechanism of repair.

Results

MenSC transplantation could improve the ovarian microenvironment by reducing apoptosis in granulosa cells and the fibrosis of ovarian interstitium, which contributes to increase the follicular numbers and return sex hormone levels to normal values. Meanwhile, the transplanted MenSCs directively migrate to ovarian interstitium to play a role in repair rather than differentiate to oocytes directly. Additionally, MenSCs and CM derived from these cells exerted protective effects on damaged ovaries partially by secreting FGF2.

Conclusion

MenSCs repair ovarian injury, improve ovarian function, and stimulate regeneration, suggesting that transplantation of MenSCs may provide an effective and novel method for treating POF.

Overexpression of Oct4 in porcine ovarian stem/stromal cells enhances differentiation of oocyte-like cells in vitro and ovarian follicular formation in vivo

Background

Recent findings have revealed that the female gonad may have regenerative activity with having germ line stem cells in juveniles and adults. Application of these germ line stem cells could be an alternative therapy for reproductive disorders in regenerative medicine.

Methods

To enhance the potency of differentiation into oocyte-like cells (OLCs) and folliculogenesis, we overexpressed Oct4 in ovarian stem/stromal cell (OvSCs) and examined the cellular properties related to stemness and self-renewal ability and finally demonstrated the ability of in vitro differentiation and folliculogenesis.

Results

Ovarian cortex included putative stem cells in terms of AP activity, cell cycle status, cell proliferation, expression of mesenchymal lineage surface markers and pluripotent transcriptional markers. Further, Oct4 transfected OvSCs (Oct4-OvSCs) were enhanced their AP activity and cell proliferation compared to OvSCs. The potential on in vitro differentiation into OLCs and in vivo folliculogenesis was also evaluated in OvSCs and Oct4-OvSCs, respectively. Oct4-OvSCs possessed higher oogenesis potential in vitro than OvSCs, in terms of expression of germ cell markers by RT-PCR and the number of OLCs. When OvSCs and Oct4-OvSCs were xeno-transplanted into infertile mice ovaries, the OvSCs transplantation induced new primary follicle formation and hormonal levels of estradiol and FSH remained similar to that of normal mice. However, Oct4-OvSCs possessed higher ability for folliculogenesis based on inducing developing follicles with thecal layer and granulosa cells and more similar estradiol level to normal mice.

Conclusions

These findings demonstrated that putative stem cells were present in ovarian cortex and exhibited differentiation ability into OLCs and folliculogenesis in vivo, and Oct4-overexpression enhanced these ability, suggesting their cellular models based on gene therapy in understanding the mechanisms of oogenesis and folliculogenesis, and finally in view of reproductive cell therapy.

Polyinosinic-Polycytidylic Acid Perturbs Ovarian Functions Through Toll-Like Receptor 3-Mediated Tumor Necrosis Factor A Production in Female Mice

Viral infections may perturb ovarian functions and female fertility. Mechanisms underlying viral perturbation of ovarian functions are incompletely understood. This study found that intraperitoneal injection of polyinosinic-polycytidylic acid [poly (I:C)] in female mice inhibits estradiol synthesis and induces ovarian granulosa cell apoptosis. Poly (I:C) is a synthetic viral double-stranded RNA analog, which induces innate antiviral responses mimicking a viral infection through activation of pattern recognition receptors, including toll-like receptor 3 (TLR3), retinoic acid-inducible gene I, and melanoma differentiation-associated gene 5. Injection of poly (I:C) significantly induced granulosa cell apoptosis in antral follicles and reduced antral follicle numbers. These effects were significantly diminished in Tlr3 knockout or tumor necrosis factor-alpha (Tnfa) knockout mice. We demonstrated that poly (I:C) induced TNFA production at a relatively high level in wild-type mice compared with that in Tlr3 knockout mice. Notably, TNFA neutralizing antibody significantly reduced poly (I:C)-induced ovarian dysfunction. In vitro assays confirmed that TNFA inhibits estradiol synthesis and induces granulosa cell apoptosis. Results provide novel insights into the mechanisms by which a mimicked viral infection perturbs ovarian functions in mice.

Human endometrial mesenchymal stem cells restore ovarian function through improving the renewal of germline stem cells in a mouse model of premature ovarian failure

Background

Human endometrial mesenchymal stem cells (EnSCs) derived from menstrual blood have mesenchymal stem/stromal cells (MSCs) characteristics and can differentiate into cell types that arise from all three germ layers. We hypothesized that EnSCs may offer promise for restoration of ovarian dysfunction associated with premature ovarian failure/insufficiency (POF/POI).

Methods

Mouse ovaries were injured with busulfan and cyclophosphamide (B/C) to create a damaged ovary mouse model. Transplanted EnSCs were injected into the tail vein of sterilized mice (Chemoablated with EnSCs group; n = 80), or culture medium was injected into the sterilized mice via the tail vein as chemoablated group (n = 80). Non-sterilized mice were untreated controls (n = 80). Overall ovarian function was measured using vaginal smears, live imaging, mating trials and immunohistochemical techniques.

Results

EnSCs transplantation increased body weight and improved estrous cyclicity as well as restored fertility in sterilized mice. Migration and localization of GFP-labeled EnSCs as measured by live imaging and immunofluorescent methods indicated that GFP-labeled cells were undetectable 48 h after cell transplantation, but were later detected in and localized to the ovarian stroma. 5’-bromodeoxyuridine (BrdU) and mouse vasa homologue (MVH) protein double-positive cells were immunohistochemically detected in mouse ovaries, and EnSC transplantation reduced depletion of the germline stem cell (GSCs) pool induced by chemotherapy.

Conclusion

EnSCs derived from menstrual blood, as autologous stem cells, may restore damaged ovarian function and offer a suitable clinical strategy for regenerative medicine.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-015-0516-y) contains supplementary material, which is available to authorized users.

Post-natal oogenesis: a concept for controversy that intensified during the last decade

For decades, scientists have considered that female mammals are born with a lifetime reserve of oocytes in the ovary, irrevocably fated to decline after birth. However, controversy in the matter of the possible presence of oocytes and granulosa cells that originate from stem cells in the adult mammalian ovaries has been expanded. The restricted supply of oocytes in adult female mammals has been disputed in recent years by supporters of neo-oogenesis, who claim that germline stem cells (GSCs) exist in the ovarian surface epithelium (OSE) or the bone marrow (BM). Differentiation of ovarian stem cells (OSCs) into oocytes, fibroblast-like cells, granulosa phenotype, neural and mesenchymal type cells and generation of germ cells from OSCs under the contribution of an OSC niche that consists of immune system-related cells and hormonal signalling has been claimed. Although these arguments have met with intense suspicion, their confirmation would necessitate the revision of the current classic knowledge of female reproductive biology.

Accelerated ovarian aging in mice by treatment of busulfan and cyclophosphamide

Busulfan/cyclophosphamide (Bu/Cy) conditioning regimen has been widely used to treat cancer patients, while their effects on major internal organs in females are not fully understood. We treated female mice with Bu/Cy, and examined the histopathology of major internal organs on Day 30 after the treatment. The results show that Bu/Cy treatment affected the ovaries most extensively, while it had less effect on the spleen, lungs, and kidneys, and no effect on the heart, liver, stomach, and pancreas. To better understand the effect of Bu/Cy on the ovaries, we counted follicles, and determined the levels of ovarian steroids. The Bu/Cy-treated mice showed a reduction of primordial and primary follicles (P<0.01) on Day 30 and a marked loss of follicles at all developmental stages (P<0.01) on Day 60. Plasma levels of estradiol and progesterone in Bu/Cy-treated mice decreased by 43.9% and 61.4%, respectively. Thus, there was a gradual process of follicle loss and low estradiol in Bu/Cy-treated mice; this is a profile similar to what is found in women with premature ovarian failure (POF). The Bu/Cy-treated mice may serve as a useful animal model to study the dynamics of follicle loss in women undergoing POF.

Intraovarian transplantation of primordial follicles fails to rescue chemotherapy injured ovaries

Busulfan and cyclophosphamide (B/C)-treated mice exhibited a marked increase in apoptosis and a concomitant decrease in the ovarian weight. Histological and RT-PCR analysis indicate that the period of germ cell depletion in the B/C-treated ovaries coincides with decreased expression of genes Figla, Lhx8, Nobox, c-kit, and Sox3. However, depletion of the ovarian germ cells is mediated by autophagy-independent pathways that involve Fas/FasL-, TNF-, and/or p53-signalings. Treatment with B/C resulted in the cease of the reproductive function to produce their offspring during the 15(th) week post-treatment period in female mice. Furthermore, injection of the 3 × 10(6) GFP positive primordial follicles into the ovaries of the B/C treated mouse did not show apparent colonization of the transplanted follicles within the recipient ovaries. The present results suggest that B/C treatment is closely associated with an increased risk of premature ovarian failure.

Follicular populations, recruitment and atresia in the ovaries of different strains of mice

Follicular atresia is a key event in the selection of the ovulatory follicles and occurs during all developmental stages. The aims of the study were to evaluate the follicular population as well as the rates of follicular recruitment and atresia in different strains of mice. Ovaries were obtained from four strains of mice: G1/ Swiss, G2/ F1 Swiss×C57BL/6, G3/ inbred strain C57BL/6, and G4/ F1 C57BL/6×Swiss. All mice used in the study were 60 days old. Ovaries collected from the mice were fixed and processed for histological analysis. The G2 ovaries were also used to examine immunolocalization of active caspase-3. The pimordial follicle population was smaller in G3 mice than in G1, G2 and G4 groups (7 565±1 845 vs. 17 180±3 159, 14 785±3 319 and 13 325±2 685, respectively; p<0.05). The rate of follicular recruitment in G3, however, was higher than in the other groups (29.2% vs. 18.2%, 17.3% and 13.0% in G1, G2 and G4, respectively; p<0.05), resulting in a similar (p>0.05) number of antral follicles among groups. The small follicular pool in G3 mice was also associated with a lower rate of follicular atresia (11.4% vs. 17.2%, 16.7% and 13.6% for G3, G1, G2 and G4, respectively; p<0.05). The number of follicles stained with active caspase-3 was higher (p<0.05) during the final stage of preantral folliculogenesis than in other stages of follicular development suggesting that apoptosis in mice occurs earlier in comparison to large animals. Thus, it was concluded that differences in follicle reservoir among mice strains are compensated by an increased rate of follicular recruitment and a decreased rate of follicular atresia; and atresia occurs in mice mainly at the end of the preantral stage of folliculogenesis.

Final Report of the Safety Assessment of Cosmetic Ingredients Derived From Zea Mays (Corn)

Many cosmetic ingredients are derived from Zea mays (corn). While safety test data were not available for most ingredients, similarities in preparation and the resulting similar composition allowed extrapolation of safety data to all listed ingredients. Animal studies included acute toxicity, ocular and dermal irritation studies, and dermal sensitization studies. Clinical studies included dermal irritation and sensitization. Case reports were available for the starch as used as a donning agent in medical gloves. Studies of many other endpoints, including reproductive and developmental toxicity, use corn oil as a vehicle control with no reported adverse effects at levels used in cosmetics. While industry should continue limiting ingredient impurities such as pesticide residues before blending into a cosmetic formulation, the CIR Expert Panel determined that corn-derived ingredients are safe for use in cosmetics in the practices of use and concentration described in the assessment.

Polychlorinated biphenyls have inhibitory effect on testicular steroidogenesis by downregulation of P45017α and P450scc

Polychlorinated biphenyls (PCBs) are environmental pollutants that are quite toxic to biological systems. This study examined the inhibitory effect of PCB126 and PCB114 on testicular steroidogenesis in male rats. Male Sprague Dawley rats received weekly intraperitoneal injections of PCB126 (0.2 mg/kg) or PCB114 (20 mg/kg) or vehicle (corn oil). Animals from each group were sacrificed at 2, 5 and 8 weeks after the injections. Blood and testis tissue samples were collected for the hormone assay, Western blotting and reverse transcriptase polymerase chain reaction (RT-PCR). The testosterone, luteinizing hormone (LH) and follicle-stimulating hormone (FSH) levels were assayed, and the expression levels of the mRNA and proteins associated with the testosterone biosynthesis pathway were measured to determine the effect of PCB126 and PCB114 on testicular steroidogenesis. The results showed that the testis weight was significantly higher in the PCB126-treated rats given eight shots. Moreover, the serum testosterone levels were significantly lower in the PCB126 and PCB114-treated groups than the control. The transcription and translation levels of P45017α and P450scc were significantly lower in the PCB126-treated groups than the control. These results suggest that PCB126 may affect testicular steroidogenesis by downregulating P45017α, P450 scc and have inhibitory effect on the testicular functions.

Collaborative work on evaluation of ovarian toxicity. 5) Two- or four-week repeated-dose studies and fertility study of busulfan in female rats

Busulfan, an antineoplastic agent that targets small follicles (primordial and primary follicles), was given orally to female Sprague-Dawley rats (0, 0.1, 0.5, or 1.5 mg/kg/day; n = 10 in each group) for 2 or 4 weeks to assess the optimal administration period for detection of the toxic effects on ovarian morphology. Isolated ovaries were used for histopathological analysis and follicle counts. In addition, a female fertility study was conducted by giving the same dose levels of busulfan from 2 weeks before mating to day 7 of pregnancy to determine the non-observed-adverse-effect-level (NOAEL) for female reproduction. In the 2-week study, all rats treated with busulfan showed normal estrous cyclicity and no toxicological changes in weight or histopathology of the ovaries. In the 4-week study, a decrease in small follicles was found histopathologically in 1 rat, even at 0.5 mg/kg, and in 4 rats at 1.5 mg/kg. Proliferating cell nuclear antigen immunohistochemistry of the follicles confirmed the above decrease in number of small follicles at 1.5 mg/kg. In the female fertility study, increases in dead embryos and post-implantation loss were found in rats at 1.5 mg/kg. Taken together, the NOAELs were 1.5 mg/kg for reproductive performance and 0.5 mg/kg for early embryonic development. In conclusion, the present study indicates that a 4-week administration period and appropriate assessment, including careful histopathological analysis of stage-based follicles are needed to detect small follicle depletion in a general toxicity study used as a first-titer screen.

Effects of Vertically Transferred 3,3',4,4',5-Pentachlorobiphenyl on Gene Expression in the Ovaries of Immature Sprague-Dawley Rats

We have previously shown that 3,3',4,4',5-pentachlorobiphenyl (PCB-126) vertically transferred from dams potentially exerts a direct effect on the ovaries of offspring and adversely affects female puberty. To investigate its toxicological targets in ovarian tissues, mRNAs encoding representative peptides that regulate follicular development in granulosa cells, theca cells, and oocytes were quantified using ovaries collected on postnatal days (PND) 5, 15, and 24 from the offspring of dams administered oral doses of 0, 1 or 3 microg/kg PCB-126 starting 2 weeks prior to mating and continuing until 20 days after delivery. Quantification using the real-time RT-PCR method revealed that PCB-126 lowered the amounts of mRNAs that encoded the inhibin alpha- and inhibin/activin beta A-subunits from PND 15 onwards; the amounts of mRNAs for inhibin/activin beta B-subunit, follicle-stimulating hormone (FSH) receptor, and aromatase on PND 15; and the amounts of luteinizing hormone receptor mRNA on PND 24 compared with those of the age-matched controls. In contrast, no differences were noted for mRNAs encoding c-kit, growth differentiation factor-9, bone morphogenetic protein-15, or kit ligand for any of the age groups examined. The serum FSH level on PND 24 was higher than that in the control. Since the earliest effects on the mRNAs in the rat ovaries were observed in those expressed in the granulosa cells of the growing follicles after the antral follicles had developed, molecules in granulosa cells but not in oocytes during the early stages of the antral follicles might be the primary targets of vertically transferred PCB-126.

Quantification of healthy follicles in the neonatal and adult mouse ovary: evidence for maintenance of primordial follicle supply

Proliferation and partial meiotic maturation of germ cells in fetal ovaries is believed to establish a finite, non-renewable pool of primordial follicles at birth. The supply of primordial follicles in postnatal life should be depleted during folliculogenesis, either undergoing atresia or surviving to ovulation. Recent studies of mouse ovaries propose that intra- and extraovarian germline stem cells replenish oocytes and form new primordial follicles. We quantified all healthy follicles in C57BL/6 mouse ovaries from day 1 to 200 using unbiased stereological methods, immunolabelling of oocyte meiosis (germ cell nuclear antigen (GCNA)) and ovarian cell proliferation (proliferating cell nuclear antigen (PCNA)) and electronmicroscopy. Day 1 ovaries contained 7924+/-1564 (s.e.m.) oocytes or primordial follicles, declining on day 7 to 1987+/-203, with 200-800 oocytes ejected from individual ovaries on that day and day 12. Discarded oocytes and those subjacent to the surface epithelium were GCNA-positive indicating their incomplete meiotic maturation. From day 7 to 100 mean numbers of primordial follicles per ovary were not significantly depleted but declined at 200 days to 254+/-71. Mean numbers of all healthy follicles per ovary were not significantly different from day 7 to 100 (range 2332+/-349-3007+/-322). Primordial follicle oocytes were PCNA-negative. Occasional unidentified cells were PCNA-positive with mitotic figures observed in the cortex of day 1 and 12 ovaries. Although we found no evidence for ovarian germline stem cells, our data support the hypothesis of postnatal follicle renewal in postnatal and adult ovaries of C57BL/6 mice.

Regulation of primordial follicle assembly and development

The assembly of the primordial follicles early in ovarian development and the subsequent development and transition of the primordial follicle to the primary follicle are critical processes in ovarian biology. These processes directly affect the number of oocytes available to a female throughout her reproductive life. Once the pool of primordial follicles is depleted a series of physiological changes known as menopause occur. The inappropriate coordination of these processes contributes to ovarian pathologies such as premature ovarian failure (POF) and infertility. Primordial follicle assembly and development are coordinated by locally produced paracrine and autocrine growth factors. Endocrine factors such as progesterone have also been identified that influence follicular assembly. Locally produced factors that promote the primordial to primary follicle transition include growth factors such as kit ligand (KL), leukaemia inhibitory factor (LIF), bone morphogenic proteins (BMP's), keratinocyte growth factor (KGF) and basic fibroblast growth factor (bFGF). Factors mediating both precursor theca-granulosa cell interactions and granulosa-oocyte interactions have been identified. A factor produced by preantral and antral follicles, Müllerian inhibitory substance, can act to inhibit the primordial to primary follicle transition. Observations suggest that a complex network of cell-cell interactions is required to control the primordial to primary follicle transition. Elucidation of the molecular and cellular control of primordial follicle assembly and the primordial to primary follicle transition provides therapeutic targets to regulate ovarian function and treat ovarian disease.

Numbers of antral follicles during follicular waves in cattle: evidence for high variation among animals, very high repeatability in individuals, and an inverse association with serum follicle-stimulating hormone concentrations

The extent, causes, and physiological significance of the variation in number of follicles growing during ovarian follicular waves in human beings and cattle are unknown. Therefore, the present study examined the variability and repeatability in numbers of follicles 3 mm or greater in diameter during the follicular waves in bovine estrous cycles, and we determined if the variation in number of follicles during waves was associated with alterations in secretion of FSH, estradiol, inhibin, and insulin-like growth factor I (IGF-I). Dairy cattle were subjected to twice-daily ultrasound analysis to count total number of antral follicles 3 mm or greater in diameter throughout 138 different follicular waves. In another study, blood samples were taken at frequent intervals from cows that consistently had low or very high numbers of follicles during waves and were subjected to immunoassays. Results indicate the following: First, despite an approximately sevenfold variation in number of follicles during waves among animals and marked differences in age, stage of lactation, and season of the year, a very highly repeatable (0.95) number of follicles 3 mm or greater in diameter is maintained during the ovulatory and nonovulatory follicular waves of individuals. Second, variation in number of follicles 3 mm or greater in diameter during waves and the inverse association of number of follicles during waves with FSH are not directly explained by alterations in the patterns of secretion of estradiol, inhibin, or IGF-I. Third, ovarian ultrasound analysis can be used reliably by investigators to identify cattle that consistently have low or high numbers of follicles during waves, thus providing a novel experimental model to determine the causes and physiological significance of the high variation in antral follicle number during follicular waves among single-ovulating species, such as cattle or humans.

Reduction of Primordial Follicles Caused by Maternal Treatment with Busulfan Promotes Endometrial Adenocarcinoma Development in Donryu Rats

Ovarian dysfunction leading to hormonal imbalance plays a crucial role in uterine carcinogenesis in rats as well as women. However, the effects of a reduction in primordial follicles at birth on uterine adenocarcinoma development have hitherto not been determined. The present study was therefore conducted using female Donryu rats, a high incidence rat strain of uterine adenocarcinoma. The animals were maternally exposed to 2.5 or 5.0 mg/kg of busulfan on gestation day 14 to reduce primordial follicles, and were then initiated by intrauterine treatment with N-ethyl-N'-nitro-N-nitrosoguanidine at 11 weeks of age. Both busulfan treatment doses caused earlier occurrence of persistent estrus, with dose-dependence as compared to controls. At 15 months of age, the rats were euthanized. The incidence of uterine adenocarcinomas and multiplicity of uterine neoplastic lesions were significantly increased by the 5.0 mg/kg, but not the 2.5 mg/kg busulfan treatment. Morphologically, the ovaries exposed to busulfan treatment exhibited severe atrophy, with few or no follicles and corpus lutea. Serum 17beta-estradiol (E2), progesterone, and inhibin levels were significantly decreased in the busulfan treatment groups, with a clear dose-relation. Interestingly, only the 5.0 mg/kg busulfan treatment elevated the E2/progesterone ratio. These results provide evidence that the reduction of primordial follicles promotes uterine adenocarcinoma development in rats in association with an earlier occurrence of the persistent estrus status.