Matrix-free 3D culture supports human follicular development from the unilaminar to the antral stage in vitro yielding morphologically normal metaphase II oocytes

STUDY QUESTION

Can group culture with stage-specific anti-Müllerian hormone (AMH) modulation support human follicular development and oocyte maturation in vitro?

SUMMARY ANSWER

In the presence of FSH, AMH supplementation at the secondary-to-early antral stage followed by AMH depletion promotes the coordinated growth and function of human follicles during group culture, thereby yielding mature oocytes.

WHAT IS KNOWN ALREADY

Stage-specific AMH modulation promotes in-vitro development of nonhuman primate follicles. The group culture method supports nonhuman primate follicle growth from the primary to antral stage, producing developmentally competent oocytes.

STUDY DESIGN, SIZE, DURATION

Ovarian tissue samples were collected from 19 patients of reproductive age (22-47 years old having menstrual cycles) who underwent oophorectomy or hysterectomy for clinical purposes. Tissue pieces were cultured in a matrix-free system for 3 weeks followed by isolation of follicles for the subsequent 6-week individual or group culture.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Pieces of ovarian cortical tissue were cultured to support primordial follicle activation and early-stage follicle growth. Secondary follicles isolated from cultured tissue were then randomly assigned to two groups for individual culture: control and AMH modulation, i.e., recombinant human AMH protein supplementation during the secondary-to-early antral stage followed by the addition of neutralizing anti-human AMH antibody. Secondary follicles were also cultured in groups with the same AMH modulation. Follicle survival, growth, steroid hormone and paracrine factor production, steroidogenic protein expression, as well as oocyte maturation and morphology were assessed.

MAIN RESULTS AND THE ROLE OF CHANCE

Follicles grew to the secondary stage during 3 weeks of ovarian tissue culture. In-vitro-developed follicles expressed AMH and levels of secreted AMH increased (P < 0.05) in the culture media over time. Secondary follicles isolated from cultured ovarian tissue survived and grew to the antral stage during 6 weeks of individual follicle culture. In-vitro-developed antral follicles produced granulosa and theca cell-derived steroid hormones and paracrine factors, which were detectable in the culture media. Germinal vesicle oocytes obtained from cultured follicles exhibited a perinucleolar chromatin rim configuration. AMH modulation did not alter follicle survival or oocyte maturation relative to those of the control follicles. However, follicle diameters, as well as steroid hormone and paracrine factor production, increased (P < 0.05) in the AMH-modulation group compared with the control group. Secondary follicles isolated from cultured ovarian tissue formed aggregates and grew to the antral stage during 6 weeks of group culture. In-vitro-developed antral follicles expressed steroidogenic enzymes and secreted steroid hormones were detectable in the culture media. Oocytes obtained from cultured follicle aggregates with AMH-modulation progressed to the metaphase II stage after IVM, containing a normal-sized first polar body and meiotic spindle. Oocytes exhibited a typical ultrastructure.

LIMITATIONS, REASONS FOR CAUTION

Follicles were obtained from fresh ovarian tissue of adult patients. Oocyte maturation rates were relatively low and oocytes were assessed by morphological evaluation. Owing to the lack of a control group, the beneficial effects of AMH modulation remained undetermined for the group culture in this study.

WIDER IMPLICATIONS OF THE FINDINGS

Stage-specific AMH modulation supports human follicular development in the matrix-free group culture, which is consistent with previously reported AMH actions on growing follicles in nonhuman primates. Oocytes generated by in-vitro-developed follicles achieve meiotic maturation with a typical morphology and ultrastructure, which supports in-vitro follicle maturation as a potential approach for fertility preservation in women.

STUDY FUNDING/COMPETING INTEREST(S)

NICHD R01HD082208 and NIH Office of the Director P51OD011092. The authors have no competing interest to declare.

TRIAL REGISTRATION NUMBER

N/A.

Short-term Western-style diet negatively impacts reproductive outcomes in primates

A maternal Western-style diet (WSD) is associated with poor reproductive outcomes, but whether this is from the diet itself or underlying metabolic dysfunction is unknown. Here, we performed a longitudinal study using regularly cycling female rhesus macaques (n = 10) that underwent 2 consecutive in vitro fertilization (IVF) cycles, one while consuming a low-fat diet and another 6–8 months after consuming a high-fat WSD. Metabolic data were collected from the females prior to each IVF cycle. Follicular fluid (FF) and oocytes were assessed for cytokine/steroid levels and IVF potential, respectively. Although transition to a WSD led to weight gain and increased body fat, no difference in insulin levels was observed. A significant decrease in IL-1RA concentration and the ratio of cortisol/cortisone was detected in FF after WSD intake. Despite an increased probability of isolating mature oocytes, a 44% reduction in blastocyst number was observed with WSD consumption, and time-lapse imaging revealed delayed mitotic timing and multipolar divisions. RNA sequencing of blastocysts demonstrated dysregulation of genes involved in RNA binding, protein channel activity, mitochondrial function and pluripotency versus cell differentiation after WSD consumption. Thus, short-term WSD consumption promotes a proinflammatory intrafollicular microenvironment that is associated with impaired preimplantation development in the absence of large-scale metabolic changes.

Insulin-like growth factor 2 is produced by antral follicles and promotes preantral follicle development in macaques†

Insulin-like growth factors (IGFs) are known for their involvement in endocrine and paracrine regulation of ovarian function. Although IGF2 is the predominant circulating and intraovarian form of IGFs in primate species, the stage-specific follicular expression, action, and regulation of IGF2 are not well defined. Therefore, experiments were conducted to investigate the follicular IGF production in response to steroid hormone regulation and the direct IGF actions on follicular development and function in vitro. Preantral follicles were isolated from rhesus macaque ovaries and cultured to the antral stage in media supplemented with follicle-stimulating hormone and insulin. Follicles were randomly assigned to treatment groups: (a) control, (b) trilostane (a steroid synthesis inhibitor), (c) trilostane + estradiol, (d) trilostane + progesterone, and (e) trilostane + dihydrotestosterone. Media was analyzed for IGF concentrations, which were correlated to follicle growth. Follicles produced IGF2, but not IGF1, at the antral stage. Steroid depletion decreased, whereas steroid replacement increased, IGF2 production by antral follicles. Media IGF2 levels correlated positively with antral follicle diameters. Macaque preantral follicles and granulosa cells were subsequently cultured without (control) and with recombinant human IGF2 supplementation. Follicle survival, growth, and paracrine factor production, as well as granulosa cell proliferation and gonadotropin receptor gene expression, were assessed. IGF2 addition increased follicle survival rates, diameters and inhibin B production, as well as granulosa cell proliferation. These data demonstrate that IGF2 produced by antral follicles, in response to steroid hormone regulation, could act as a paracrine factor that positively impacts preantral follicle development and function in primates.

Direct actions of androgen, estrogen and anti-Müllerian hormone on primate secondary follicle development in the absence of FSH in vitro

STUDY QUESTION

What are effects of androgen, estrogen and anti-Müllerian hormone (AMH), independent of FSH action, on the development and function of primate follicles from the preantral to small antral stage in vitro?

SUMMARY ANSWER

Androgen and estrogen, but not AMH, promote follicle survival and growth in vitro, in the absence of FSH. However, their growth-promoting effects are limited to the preantral to early antral stage.

WHAT IS KNOWN ALREADY

FSH supports primate preantral follicle development in vitro. Androgen and estrogen augment follicle survival and growth in the presence of FSH during culture.

STUDY DESIGN SIZE, DURATION

Nonhuman primate model; randomized, control versus treatment groups. Rhesus macaque (n = 6) secondary follicles (n = 24 per animal per treatment group) were cultured for 5 weeks.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Follicles were encapsulated in 0.25% (w/v) alginate and cultured individually in modified alpha minimum essential media with (i) FSH (1 ng/ml; control), (ii) no FSH, (iii) no FSH + estradiol (E2; 100 pg/ml)/dihydrotestosterone (DHT; 50 ng/ml) and (iv) no FSH + AMH (50 ng/ml). In a second experiment, follicles were cultured with (i) FSH (1 ng/ml), (ii) no FSH, (iii) no FSH + E2 (1 ng/ml), (iv) no FSH + DHT (50 ng/ml) and (v) no FSH + E2/DHT. Follicle survival, antrum formation and growth pattern were evaluated. Progesterone (P4), E2 and AMH concentrations in culture media were measured.

MAIN RESULTS AND THE ROLE OF CHANCE

In the first experiment, FSH deprivation significantly decreased (P < 0.05) follicle survival rates in the no FSH group (16 ± 5%), compared to CTRL (66 ± 9%). E2/DHT (49 ± 5%), but not AMH (27 ± 8%), restored follicle survival rate to the CTRL level. Similarly, antrum formation rates were higher (P < 0.05) in CTRL (56 ± 6%) and E2/DHT groups (54 ± 14%), compared to no FSH (0 ± 0%) and AMH (11 ± 11%) groups. However, follicle growth rate after antrum formation and follicle diameter at week 5 was reduced (P < 0.05) in the E2/DHT group (405 ± 25 μm), compared to CTRL (522 ± 29 μm). Indeed, the proportion of fast-grow follicles at week 5 was higher in CTRL (29% ± 5), compared to E2/DHT group (10 ± 3%). No fast-grow follicles were observed in no FSH and AMH groups. AMH levels at week 3 remained similar in all groups. However, media concentrations of P4 and E2 at week 5 were lower (P < 0.05, undetectable) in no FSH, E2/DHT and AMH groups, compared to CTRL (P4 = 93 ± 10 ng/ml; E2 = 4 ± 1 ng/ml). In the second experiment, FSH depletion diminished follicle survival rate (66 ± 8% in control versus 45 ± 9% in no FSH, P = 0.034). E2 plus DHT (31.5 ± 11%) or DHT alone (69 ± 9%) restored follicle survival rate to the control (FSH) level as expected. Also, E2 plus DHT or DHT alone improved antrum formation rate. However, in the absence of FSH, E2 plus DHT or DHT alone did not support growth, in terms of follicle diameter, or steroid (P4 or E2) production after the antral stage.

LIMITATIONS REASONS FOR CAUTION

This study is limited to in vitro effects of E2, DHT and AMH during the interval from the secondary to small antral stage of macaque follicular development. In addition, the primate follicle pool is heterogeneous and differs between animals; therefore, even though only secondary follicles were selected, follicle growth and developmental outcomes might differ from one animal to another.

WIDER IMPLICATIONS OF THE FINDINGS

This study provides novel information on the possible actions of estrogen and androgen during early follicular development in primates. Our results suggest that sequential exposure of preantral follicles to local factors, e.g. E2 and DHT, followed by gonadotropin once the follicle reaches the antral stage, may better mimic primate folliculogenesis in vivo.

STUDY FUNDING/COMPETING INTEREST(S)

Research reported in this publication was supported by the Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Center for Translational Research on Reproduction and Infertility 5P50HD071836, and the NIH Primate Centers Program 8P510D011092. There are no conflicts of interest.

Characterization of FOXO1, 3 and 4 transcription factors in ovaries of fetal, prepubertal and adult rhesus macaques

The phosphoinositide 3-kinase/AKT (protein kinase B) signaling pathway negatively regulates follicle activation via the forkhead box O (FOXO) transcription factor in rodents. FOXO3 knockout mice exhibit global activation of primordial follicles leading to early depletion of ovarian follicles and subsequent infertility. Whether a similar mechanism for follicle activation exists in the primate ovary is unclear. In the current study, protein localization of FOXO1, 3, and 4 as well as their upstream regulator, AKT/p-AKT, was examined in rhesus macaque ovaries of three developmental stages: fetal, prepubertal, and adult. FOXO1 protein is expressed in granulosa cells of fetal, prepubertal, and adult ovaries. FOXO3 is distributed sparsely in the mitotically active germ cells, but its expression decreases following follicle formation in the macaque fetal ovary. In addition, FOXO3 is seldom with interanimal variation in the prepubertal ovary and is absent in the adult ovary. FOXO4 is nondetectable in fetal ovaries, although it is expressed in some theca cells of antral follicles and some stromal cells in prepubertal and adult ovaries. Our results suggest that the regulation and/or function of FOXO3 in the primate primordial follicle may differ than that of the rodent. Nevertheless, AKT/p-AKT is expressed in macaque primordial oocytes, suggesting that similar upstream events but different downstream effects may regulate primordial follicle activation in nonhuman primates compared to rodents. Elucidation of the mechanism responsible for follicle activation in primates will be crucial for understanding primary ovarian insufficiency, improving female fertility, and applying techniques for in vitro maturation of follicles for fertility preservation in cancer survivors.

Anti-Müllerian hormone is a survival factor and promotes the growth of rhesus macaque preantral follicles during matrix-free culture

Anti-Müllerian hormone (AMH) plays a key role during ovarian follicular development, with local actions associated with a dynamic secretion profile by growing follicles. While results for AMH effects on antral follicle growth and function are consistent among studies in various species, any effects on preantral follicle development remain controversial. Therefore, experiments were conducted to investigate the direct actions and role of AMH during follicle development at the preantral stage. Macaque-specific short-hairpin RNAs (shRNAs) targeting AMH mRNA were incorporated into adenoviral vectors to decrease AMH gene expression in rhesus macaque follicles. Secondary follicles were isolated from adult macaque ovaries and cultured individually in the ultra-low-attachment dish containing defined medium supplemented with follicle-stimulating hormone and insulin for 5 weeks. Follicles were randomly assigned to treatment groups: (a) control, (b) nontargeting control shRNA-vector, (c) AMH shRNA-vector, (d) AMH shRNA-vector + recombinant human AMH, and (e) recombinant human AMH. Follicle survival and growth were assessed. Culture media were analyzed for steroid hormone and paracrine factor concentrations. For in vivo study, the nontargeting control shRNA-vector and AMH shRNA-vector were injected into macaque ovaries. Ovaries were collected 9 days postinjection for morphology and immunohistochemistry assessment. Decreased AMH expression reduced preantral follicle survival and growth in nonhuman primates. Supplemental AMH treatment in the culture media promoted preantral follicle growth to the small antral stage in vitro with increased steroid hormone and paracrine factor production, as well as oocyte maturation. These data demonstrate that AMH is a critical follicular paracrine/autocrine factor positively impacting preantral follicle survival and growth in primates.

Good manufacturing practice requirements for the production of tissue vitrification and warming and recovery kits for clinical research

Products that are manufactured for use in a clinical trial, with the intent of gaining US Food and Drug Administration (FDA) approval for clinical use, must be produced under an FDA approved investigational new drug (IND) application. We describe work done toward generating reliable methodology and materials for preserving ovarian cortical tissue through a vitrification kit and reviving this tissue through a warming and recovery kit. We have described the critical steps, procedures, and environments for manufacturing products with the intent of submitting an IND. The main objective was to establish an easy-to-use kit that would ensure standardized procedures for quality tissue preservation and recovery across the 117 Oncofertility Consortium sites around the globe. These kits were developed by breaking down the components and steps of a research protocol and recombining them in a way that considers component stability and use in a clinical setting. The kits were manufactured utilizing current good manufacturing practice (cGMP) requirements and environment, along with current good laboratory practices (cGLP) techniques. Components of the kit were tested for sterility and endotoxicity, and morphological endpoint release criteria were established. We worked with the intended down-stream users of these kits for development of the kit instructions. Our intention is to test these initial kits, developed and manufactured here, for submission of an IND and to begin clinical testing for preserving the ovarian tissue that may be used for future restoration of fertility and/or hormone function in women who have gonadal dysgenesis from gonadotoxic treatment regimens or disease.

Western-style diet, with and without chronic androgen treatment, alters the number, structure, and function of small antral follicles in ovaries of young adult monkeys

OBJECTIVE

To examine the small antral follicle (SAF) cohort in ovaries of adult rhesus monkeys after consumption of a Western-style diet (WSD), with or without chronically elevated androgen levels since before puberty.

DESIGN

Cholesterol or T (n = 6 per group) implants were placed SC in female rhesus macaques beginning at 1 year of age (prepubertal), with addition of a WSD (high fat/fructose) at 5.5 years (menarche approximately 2.6 years). Ovaries were collected at 7 years of age. One ovary per female was embedded in paraffin for morphologic and immunohistochemical analyses. The SAFs (<2.5 mm) were dissected from the other ovary obtained at or near menses in a subgroup of females (n = 3 per group) and processed for microarray analyses of the SAF transcriptome. Ovaries of adult monkeys consuming a standard macaque diet (low in fats and sugars) were obtained at similar stages of the menstrual cycle and used as controls for all analyses.

SETTING

Primate research center.

ANIMAL(S)

Adult, female rhesus monkeys (Macaca mulatta).

INTERVENTION(S)

None.

MAIN OUTCOME MEASURES

Histologic analyses, SAF counts and morphology, protein localization and abundance in SAFs, transcriptome in SAFs (messenger RNAs [mRNAs]).

RESULT(S)

Compared with controls, consumption of a WSD, with and without T treatment, increased the numbers of SAFs per ovary, owing to the presence of more atretic follicles. Numbers of granulosa cells expressing cellular proliferation markers (pRb and pH3) was greater in healthy SAFs, whereas numbers of cells expressing the cell cycle inhibitor (p21) was higher in atretic SAFs. Intense CYP17A1 staining was observed in the theca cells of SAFs from WSD with or without T groups, compared with controls. Microarray analyses of the transcriptome in SAFs isolated from WSD and WSD plus T-treated females and controls consuming a standard diet identified 1,944 genes whose mRNA levels changed twofold or more among the three groups. Further analyses identified several gene pathways altered by WSD and/or WSD plus T associated with steroid, carbohydrate, and lipid metabolism, plus ovarian processes. Alterations in levels of several SAF mRNAs are similar to those observed in follicular cells from women with polycystic ovary syndrome.

CONCLUSION(S)

These data indicate that consumption of a WSD high in fats and sugars in the presence and absence of chronically elevated T alters the structure and function of SAFs within primate ovaries.

Differential effects of estrogen and progesterone on development of primate secondary follicles in a steroid-depleted milieu in vitro

STUDY QUESTION

What are the direct effects of progesterone (P4) and estradiol (E2) on the development and function of primate follicles in vitro from the pre-antral to early antral stage?

SUMMARY ANSWER

In a steroid-depleted milieu, E2 improved follicle survival, growth, antrum formation and oocyte health, whereas P4 exerted minimal beneficial effects on follicle survival and reduced oocyte health.

WHAT IS KNOWN ALREADY

Effects of P4 and E2 on follicle development have been studied primarily in large antral and pre-ovulatory follicles. Chronic P4 exposure suppresses antral follicle growth, but acute P4 exposure promotes oocyte maturation in pre-ovulatory follicles. Effects of E2 can be stimulatory or inhibitory depending upon species, dose and duration of exposure.

STUDY DESIGN, SIZE, DURATION

Non-human primate model, randomized, control versus treatment. Macaque (n = 6) secondary follicles (n = 24 per animal per treatment group) were cultured for 5 weeks.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Adult rhesus macaque secondary follicles were encapsulated in 0.25% alginate and cultured individually in media containing follicle stimulating hormone plus (i) vehicle, (ii) a steroid-synthesis inhibitor, trilostane (TRL, 250 ng/ml), (iii) TRL + low E2 (100 pg/ml) or progestin (P, 10 ng/ml R5020) and (iv) TRL + high E2 (1 ng/ml E2) or P (100 ng/ml R5020). Follicles reaching the antral stage (≥750 µm) were treated with human chorionic gonadotrophin for 34 h. End-points included follicle survival, antrum formation, growth pattern, plus oocyte health and maturation status, as well as media concentrations of P4, E2 and anti-Müllerian hormone (AMH).

MAIN RESULTS AND THE ROLE OF CHANCE

In a steroid-depleted milieu, low dose, but not high dose, P improved (P < 0.05) follicle survival, but had no effect (P > 0.05) on antrum formation and AMH production. Low-dose P increased (P < 0.05) P4 production in fast-grow follicles, and both doses of P elevated (P < 0.05) E2 production in slow-grow follicles. Additionally, low-dose P increased (P < 0.05) the percentage of no-grow follicles, and high-dose P promoted oocyte degeneration. In contrast, E2, in a steroid-depleted milieu, improved (P < 0.05) follicle survival, growth, antrum formation and oocyte health. E2 had no effect on P4 or E2 production. Follicles exposed to E2 yielded mature oocytes capable of fertilization and early cleavage, at a rate similar to untreated control follicles.

LIMITATIONS, REASONS FOR CAUTION

This study is limited to in vitro effects of P and E2 during the interval from the secondary to small antral stage of macaque follicles.

WIDER IMPLICATIONS OF THE FINDINGS

This study provides novel information on the direct actions of P4 and E2 on primate pre-antral follicle development. Combined with our previous report on the actions of androgens, our findings suggest that androgens appear to be a survival factor but hinder antral follicle differentiation, E2 appears to be a survival and growth factor at the pre-antral and early antral stage, whereas P4 may not be essential during early folliculogenesis in primates.

STUDY FUNDING/COMPETING INTERESTS

NIH P50 HD071836 (NCTRI), NIH ORWH/NICHD 2K12HD043488 (BIRCWH), ONPRC 8P51OD011092. There are no conflicts of interest.

Challenges and Potential for Ovarian Preservation with SERMs

Tamoxifen (TAM) is a selective estrogen receptor modulator with tissue-specific effects on estrogen signaling used predominantly for treatment and chemoprevention of breast cancers. Recent studies have shown that TAM prevents infertility and decreases follicular loss from common cancer chemotherapy and radiation therapy in preclinical models. Here we review current and novel uses of selective estrogen receptor modulator s and advantages and challenges for translation of TAM for human fertility preservation.

Expression of the beta-2 adrenergic receptor (ADRB-2) in human and monkey ovarian follicles: a marker of growing follicles?

Background

ADRB-2 was implicated in rodent ovarian functions, including initial follicular growth. In contrast, ADRB-2 expression and function in nonhuman primate and human ovary were not fully known but innervation and significant levels of norepinephrine (NE), which is a ligand at the ADRB-2, were reported in the ovary.

Methods

We studied expression of ADRB-2 in human and rhesus monkey ovary (RT-PCR, immunohistochemistry; laser micro dissection) and measured levels of norepinephrine (NE; ELISA) in monkey follicular fluid (FF). 3D cultures of monkey follicles (4 animals) were exposed to NE or the ADRB-2 agonist isoproterenol (ISO), and follicular development (size) was monitored. Upon termination expression of ADRB-2, FSH receptor and aromatase genes were examined.

Results

Immunohistochemistry and RT-PCR of either human follicular granulosa cells (GCs) obtained by laser micro dissection or isolated monkey follicles revealed ADRB-2 in GCs of primordial, primary, secondary and tertiary follicles. Staining of GCs in primordial and primary follicles was intense. In large preantral and antral follicles the staining was heterogeneous, with positive and negative GCs present but GCs lining the antrum of large follicles were generally strongly immunopositive. Theca, interstitial, and ovarian surface epithelial cells were also positive. NE was detected in FF of preovulatory antral monkey follicles (0.37 + 0.05 ng/ml; n = 7; ELISA) but not in serum. We examined preantral follicles ranging from 152 to 366 μm in diameter in a 3D culture in media supplemented with follicle stimulating hormone (FSH). Under these conditions, neither NE, nor ISO, influenced growth rate in a period lasting up to one month. Upon termination of the cultures, all surviving follicles expressed aromatase and FSH receptors, but only about half of them also co-expressed ADRB-2. The ADRB-2 expression was not correlated with the treatment but was positively correlated with the follicular size at the beginning and at the end of the culture period. Hence, expression of ADRB-2 was found in the largest and fastest-in vitro growing follicles.

Conclusions

The results imply ADRB-2-mediated actions in the development of primate follicles. Drugs interfering with ADRB-2 are used to treat medical conditions and may have unexplored effects in the human ovary.

Fibrin promotes development and function of macaque primary follicles during encapsulated three-dimensional culture

STUDY QUESTION

Does fibrin introduced into the extracellular matrix affect the growth and maturation of individual primate follicles during encapsulated three-dimensional (3D) culture?

SUMMARY ANSWER

While not altering follicle survival, fibrin-alginate (FIBRIN) improves macaque primary, but not secondary, follicle development during encapsulated 3D culture in terms of growth, steroidogenesis, anti-Müllerian hormone (AMH)/vascular endothelial growth factor (VEGF) production and oocyte maturation.

WHAT IS KNOWN ALREADY

Efforts to grow non-human primate ovarian follicles from the secondary to the antral stage during encapsulated 3D culture have been successful. However, the growth and maturation of primary follicles in vitro has not been reported in primates, especially in chemically defined conditions.

STUDY DESIGN, SIZE, DURATION

In vitro follicle maturation was investigated using the rhesus macaque (Macaca mulatta). Ovaries (n = 7 pairs) were obtained during the early follicular phase of the menstrual cycle (cycle day 1-4). Primary (80-120 µm diameter) and secondary (125-225 µm diameter) follicles were isolated mechanically, randomly assigned to experimental groups, encapsulated into alginate (0.25% w/v) or FIBRIN (25 mg/ml fibrinogen-0.25% alginate) and cultured for 13 and 5 weeks, respectively.

MATERIALS, SETTING, METHODS

Individual follicles were cultured in alpha minimum essential medium supplemented with FSH. Follicle survival and growth were assessed by microscopy. Follicles that reached the antral stage were treated with recombinant hCG. Metaphase II (MII) oocytes were inseminated via ICSI. Follicle morphology was evaluated by hematoxylin and eosin (H&E) staining. Immunohistochemistry was performed for cytochrome P450 family 17 subfamily A polypeptide 1 (CYP17A1) and 19 subfamily A polypeptide 1 (CYP19A1). Culture medium was analyzed for estradiol (E2) and progesterone by chemiluminescence, androstenedione (A4) by radioimmunoassay, as well as anti-Müllerian hormone (AMH) and vascular endothelial growth factor (VEGF) by enzyme-linked immunosorbent assay.

MAIN RESULTS AND THE ROLE OF CHANCE

A total of 105 primary and 133 secondary follicles were collected. The presence of fibrin in the alginate matrix had no effect on either primary or secondary follicle survival. Growing primary and secondary follicles formed an antrum at Weeks 9 and 3, respectively. The percentage of growing follicles was higher (P < 0.05) for primary follicles cultured in FIBRIN than alginate at Week 13. The diameters were larger for the growing secondary follicles cultured in alginate than FIBRIN at Week 5 (P < 0.05). H&E staining revealed the typical morphology for small antral follicles. CPY17A1 immunostaining was detected in theca cells, while CYP19A1 was observed in granulosa cells. E2 increased (P < 0.05) during antrum formation in growing follicles at Week 9 for primary and Week 3 for secondary follicles. AMH levels in medium from growing primary follicles increased (P < 0.05) after Week 4 with peak levels at Weeks 9-11. AMH increased (P < 0.05) in growing secondary follicles at Weeks 3-5. VEGF levels in medium were elevated (P < 0.05) in growing primary follicles at Week 9. VEGF increased (P < 0.05) in medium from growing secondary follicles at Weeks 3-5. E2, AMH and VEGF production was higher (P < 0.05) in primary follicle culture with FIBRIN than alginate alone. One primary follicle cultured in FIBRIN (1 of 5 follicles harvested) and a secondary follicle cultured in alginate alone (1 of 15 follicles harvested) yielded an MII oocyte. The fertilized oocyte from primary follicle culture arrested without cell division after fertilization, while the oocyte from secondary follicle culture cleaved and reached the morula stage.

LIMITATIONS, REASONS FOR CAUTION

The study reports on in vitro development and function of individual macaque follicles, that is limited to the interval from the primary and secondary stage to the small antral stage. The findings await translation to human ovarian follicles.

WIDER IMPLICATIONS OF THE FINDINGS

The 3D model for primate follicle development offers a unique opportunity to investigate the growth and regulation of primate primary, as well as secondary follicles, and their enclosed oocytes, as they grow to the antral stage by monitoring and manipulating factors or signaling pathways in vitro. Since primate primary follicles, in addition to secondary follicles, can be cultured to the antral stage to provide mature oocytes, they represent an additional source of pre-antral follicles for in vitro follicle maturation with the potential to provide gametes for assisted reproductive technology as an option for fertility preservation in women, including patients with cancer.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by The Oncofertility Consortium (NIH U54 RR024347-HD058294, PL1-EB008542), NIH U54-HD18185 (Eunice Kennedy Shriver Specialized Cooperative Centers Program in Reproduction and Infertility Research), NIH ORWH/NICHD 2K12HD043488 (BIRCWH), Oregon National Primate Research Center 8P51OD011092. There are no conflicts of interest.

Morphological and functional preservation of pre-antral follicles after vitrification of macaque ovarian tissue in a closed system

STUDY QUESTION

What are the appropriate conditions to vitrify the macaque ovarian cortex in a large-volume, closed system that will preserve functional pre-antral follicles?

SUMMARY ANSWER

The combination of glycerol, ethylene glycol (EG) and polymers with cooling in liquid nitrogen (LN2) vapor and a two-step warming procedure was able to preserve tissue and follicle morphology as well as function of a small population of secondary follicles in the macaque ovarian cortex following vitrification in a closed system.

WHAT IS KNOWN ALREADY

For prepubertal cancer patients or those who require immediate cancer therapy, ovarian tissue cryopreservation offers the only hope for future fertility. However, the efficacy of live birth from the transplantation of cryopreserved ovarian tissue is still unclear. In addition, live birth from cryopreserved ovarian tissue has only been demonstrated after tissue autotransplantation, which poses the risk of transmitting metastatic cancer cells back to the cancer survivor in certain cancers.

STUDY DESIGN, SIZE, DURATION

Non-human primate model, n = 4, randomized, control versus treatment. End-points were collected from tissue histology, tissue culture (48 h) and isolated secondary follicle culture (6 weeks).

PARTICIPANTS/MATERIALS, SETTING, METHODS

Two vitrification solutions (VSs) containing EG + glycerol (VEG) and EG + dimethylsulfoxide (VED) were examined for vitrification, devitrification and thermodynamic properties. Once the optimal VS was determined, macaque ovarian cortical pieces (3 × 3 × 0.5 mm(3)) were divided into fresh and two vitrified groups (VEG and VED). For the vitrification groups, tissues were exposed to 1/4, 1/2 and 1× VS for 5 min/step as well as 1× VS + polymers for 1 min at 37°C, loaded into high-security straws with 1 ml of VS + polymers, heat sealed and cooled in LN2 vapor. Samples were warmed in a 40°C water bath and cryoprotective agents were diluted with 1, 0.5, 0.25 and 0 M sucrose. Tissues were fixed for histological analysis and cultured with bromodeoxyuridine (BrdU). Secondary follicles from VEG tissues were encapsulated and cultured (n = 24/treatment/animal). Follicle health, diameter and steroid [progesterone, androstenedione (A4), estradiol (E2)] production were analyzed weekly.

MAIN RESULTS AND THE ROLE OF CHANCE

Dense stroma and intact pre-antral follicles were observed using VS containing 27% glycerol, 27% EG and 0.8% polymers with cooling in LN2 vapor and a two-step warming. Higher cooling and warming rates led to fracturing. BrdU uptake was evident in granulosa cells of growing follicles in fresh and vitrified tissues. Secondary follicles from fresh tissues (70 ± 12%) and tissues vitrified with VEG (52 ± 2%) showed similar survival rates (all data: mean ± SEM; P > 0.05). For both groups, the initial follicle diameter was similar and increased (P < 0.05) by Week 3, but diameters in vitrified follicles were smaller (P < 0.05) by Week 6 (566 ± 27 µm) than those of the fresh follicles (757 ± 26 µm). Antrum formation rates were lower (P < 0.05) for vitrified (37 ± 6%) relative to fresh (64 ± 8%) follicles. There was no significant change in levels in culture media of E2, P4 and A4 between fresh and VEG groups at any time point during culture.

LIMITATIONS, REASONS FOR CAUTION

Only in vitro studies are reported. Future in vivo tissue transplantation studies will be needed to confirm long-term function and fertility potential of vitrified ovarian tissues.

WIDER IMPLICATIONS OF THE FINDINGS

This is the first demonstration of antral follicle development during 3D culture following ovarian tissue vitrification in a closed system using primate ovarian tissue. While diminished antrum formation and slower growth in vitro reflect residual cryodamage, continued development of ovarian tissue vitrification based on cryobiology principles using a non-human primate model will identify safe, practical and efficient protocols for eventual clinical use. Tissue function following heterotopic transplantation is currently being examined.

STUDY FUNDING/COMPETING INTEREST(S)

National Institutes of Health (NIH) Oncofertility Consortium UL1 RR024926 (1RL1-HD058293, HD058295, PL1 EB008542), the Eunice Kennedy Shriver NICHD/NIH (U54 HD018185) and ONPRC 8P51OD011092-53. G.M.F. works for the company that makes the polymers used in the current study.

Amphiregulin promotes the maturation of oocytes isolated from the small antral follicles of the rhesus macaque

BACKGROUND

In non-primates, the epidermal growth factor (EGF) and EGF-related ligands such as amphiregulin (AREG) serve as critical intermediates between the theca/mural cells and the cumulus-oocyte-complex (COC) following the mid-cycle LH surge. Studies were designed in primates (1) to analyze AREG levels in follicular fluid (follicular fluid) obtained from pre-ovulatory follicles, as well as (2) to assess dose-dependent effects of AREG on oocytes from small antral follicles (SAFs) during culture, including meiotic and cytoplasmic maturation.

METHODS

Controlled ovulation protocols were performed on rhesus monkeys (n=12) to determine AREG content within the single, naturally selected dominant follicle after an ovulatory stimulus. Using healthy COCs (n=271) obtained from SAFs during spontaneous cycles (n=27), in vitro maturation (IVM) was performed in the absence or presence of physiological concentrations of AREG (10 or 100 ng/ml) with or without gonadotrophins (FSH, 75 mIU/ml; LH, 75 mIU/ml). At the end of the culture period, oocyte meiotic maturation was evaluated and ICSI was performed (n=111), from which fertilization and early embryo development was followed in vitro.

RESULTS

AREG levels in follicular fluid from pre-ovulatory follicles increased (P<0.05) following an ovulatory bolus of hCG at 12, 24 and 36 h post-treatment. At 12 h post-hCG, AREG levels in follicular fluid ranged from 4.8 to 121.4 ng/ml. Rhesus macaque COCs incubated with 10 ng/ml AREG in the presence of gonadotrophins displayed an increased percentage of oocytes that progressed to the metaphase II (MII) stage of meiosis (82 versus 56%, P<0.05) and a decreased percentage of metaphase I (MI) oocytes (2 versus 23%, P<0.05) relative to controls, respectively. The percentage of either MI or MII oocytes at the end of the culture period was not different between oocytes cultured with 100 ng/ml AREG or in media alone. Fertilization and first cleavage rates obtained by ICSI of all IVM MII oocytes were 93 and 98%, respectively, and did not vary among treatment groups. Of the MII oocytes that fertilized (n=103), 37 were randomly selected and maintained in culture to assess developmental potential. A total of 13 early blastocysts were obtained, with four embryos developing to expanded blastocysts.

CONCLUSIONS

These data indicate that AREG levels increase in rhesus macaque pre-ovulatory follicles after an ovulatory stimulus, and a specific concentration of AREG (10 ng/ml) enhances rhesus macaque oocyte nuclear maturation but not cytoplasmic maturation from SAFs obtained during the natural menstrual cycle. However, owing to the small number of samples in some treatment groups, further studies are now required.

In vitro development of secondary follicles from cryopreserved rhesus macaque ovarian tissue after slow-rate freeze or vitrification

BACKGROUND

Ovarian tissue cryopreservation is the only option for preserving fertility in prepubertal girls and cancer patients requiring immediate treatment. Following ovarian tissue cryopreservation, fertility can be restored after tissue transplant or in vitro follicle maturation.

METHODS

Macaque (n= 4) ovarian cortex was cryopreserved using slow-rate freezing (slow freezing) or vitrification. Tissues were fixed for histology or phosphohistone H3 (PPH3) analysis, cultured with bromodeoxyuridine (BrdU) or used for three-dimensional secondary follicle culture. Follicular diameter and steroid hormones were measured weekly.

RESULTS

Slow freezing induced frequent cryo-injuries while vitrification consistently maintained morphology of the stroma and secondary follicles. PPH3 was similar in fresh and vitrified, but sparse in slow-frozen tissues. BrdU uptake appeared diminished following both methods compared with that in fresh follicles. In vitro follicle survival and growth were greater in fresh than in cryopreserved follicles. Antrum formation appeared similar after vitrification compared with the fresh, but was reduced following slow freezing. Steroid production was delayed or diminished following both methods compared with fresh samples.

CONCLUSIONS

Secondary follicle morphology was improved after vitrification relative to slow freezing. Following vitrification, stroma was consistently more compact with intact cells typical to that of fresh tissue. BrdU uptake demonstrated follicle viability post-thaw/warming. For the first time, although not to the extent of fresh follicles, macaque follicles from cryopreserved tissue can survive, grow, form an antrum and produce steroid hormones, indicating some functional preservation. The combination of successful ovarian tissue cryopreservation with in vitro maturation of follicles will offer a major advancement to the field of fertility preservation.

Temporal and anatomical sensitivities to the aryl hydrocarbon receptor agonist 2,3,7,8-tetrachlorodibenzo-p-dioxin leading to premature acyclicity with age in rats

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that mediates diverse dioxin toxicities. While the acute effects of activation of the AhR pathway by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) have been a focus of past study, the role of this pathway in normal physiology and ageing is unclear. The purpose of this study was to identify the portion of the reproductive axis [ovary vs. hypothalamus and pituitary gland (H-H axis)] and the stages of the reproductive lifespan (foetal and early post-natal life vs. adolescence and adulthood) that are particularly sensitive to the effects of TCDD during female reproductive ageing. Adult pregnant Lewis rat dams were dosed with corn oil vehicle or TCDD (50 ng/kg-week by gavage) on days 14 and 21 of gestation and post-natal days 7 and 14 to provide in utero and lactational (IUL) exposure to pups. Female pups (n = 96) were weaned on post-natal day 21 and dosed with TCDD or vehicle weekly. Half of the pups were used as donors for ovary transplantation while the remainder were recipients. Following ovary transplantation, rats (n = 6-8 per group) received weekly TCDD or vehicle again until sacrifice at 8 months of age. Beginning at vaginal opening, reproductive cycles were monitored by vaginal cytology for 10 days each month. Blood samples were collected at 22.00 h on proestrus to measure concentration of 17beta-oestradiol in serum. Real-time PCR was used to determine differences in Cyp1a1, Cyp19a1, Cyp17a1, LH receptor (LHR), FoxA2 and FoxJ1 genes expression between control and remaining groups. IUL exposure of the H-H axis plus adult exposure of the whole body to TCDD significantly delayed puberty in females rats. Data analysis revealed an accelerated onset of acyclicity by 5 months in all groups involving IUL exposure of the developing ovary to TCDD. 17beta-oestradiol was significantly decreased in animals receiving TCDD during IUL exposure of the H-H axis. CYP1a1 expression was markedly greater in the liver than in ovarian tissue and correlated with ongoing TCDD exposure. Aromatase, 17alpha-hydroxylase and LHR gene expressions were largely unchanged (or occasionally elevated) by TCDD. FoxA2 and FoxJ1 mRNAs were similarly of limited value mechanistically, although FoxJ1 was much higher in TTT females (receiving TCDD as donor, recipient and adult). This study reveals a particular sensitivity of the developing ovary to TCDD leading to early loss of reproductive function with age.

Effect of chronic exposure to the aryl hydrocarbon receptor agonist 2,3,7,8-tetrachlorodibenzo-p-dioxin in female rats on ovarian gene expression

The aryl hydrocarbon receptor (AHR) mediates the effects of many endocrine disruptors and contributes to the loss of fertility in polluted environments. Female rats exposed chronically to environmentally relevant doses of the AHR agonist 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) across their lifespan experience accelerated reproductive senescence preceded by ovarian endocrine disruption. The purpose of this study was to determine the changes in ovarian gene expression that accompany the loss of ovarian function caused by chronic exposure to TCDD. Beginning in utero, female Sprague-Dawley rats received TCDD (1, 5, 50, or 200 ng/kg-week; n=4 per group) or vehicle weekly throughout their lifespan, and were sacrificed on diestrus just prior to loss of reproductive cyclicity at 11 months of age. Microarray analysis was used to determine differences in ovarian gene expression between control and TCDD-treated (200 ng/kg-week) animals. To confirm microarray results, real-time PCR was used to assess changes in gene expression among treatment groups. TCDD treatment decreased (p<0.05) proestrus serum estradiol concentrations with no effect on serum progesterone. In ovaries from rats treated with 200 ng/kg-week TCDD compared to controls, 19 genes of known function were found to be up-regulated, while 31 ovarian genes were found to be down-regulated >or=1.5-fold (p<or=0.05). Gene expression of 17 alpha-hydroxylase decreased following chronic TCDD treatment, suggesting the decrease in estradiol biosynthesis may be a consequence of decreased substrate. Taken together with past studies indicating a lack of effect on hypothalamus or pituitary function, the apparent regulation of key ovarian genes support the hypothesis that chronic TCDD exposure directly affects ovarian function.

Tamoxifen prevents premalignant changes of breast, but not ovarian, cancer in rats at high risk for both diseases

Women at increased risk for breast cancer are at increased risk for ovarian cancer as well, reflecting common risk factors and intertwined etiology of the two diseases. We previously developed a rat model of elevated breast and ovarian cancer risk, allowing evaluation of dual-target cancer prevention strategies. Tamoxifen, a Food and Drug Administration-approved breast cancer chemoprevention drug, has been shown to promote ovarian cysts in premenopausal women; however, the effect of tamoxifen on ovarian cancer risk is still controversial. In the current experiment, Fischer 344 rats (n = 8 per treatment group) received tamoxifen (TAM) or vehicle (control) in factorial combination with combined breast and ovarian carcinogen (17beta-estradiol and 7,12 dimethylbenza[a]anthracene, respectively). Mammary and ovarian morphologies were normal in the control and TAM groups. Carcinogen (CARC) treatment induced mammary dysplasia with elevated cell proliferation and reduced estrogen receptor-alpha expression and promoted preneoplastic changes in the ovary. In the CARC + TAM group, tamoxifen reduced preneoplastic changes and proliferation rate in the mammary gland, but not in the ovary, compared with rats treated with carcinogen alone. Putative stem cell markers (Oct-4 and aldehyde dehydrogenase 1) were also elevated in the mammary tissue by carcinogen and this expansion of the stem cell population was not reversed by tamoxifen. Our study suggests that tamoxifen prevents early progression to mammary cancer but has no effect on ovarian cancer progression in this rat model.

Ovarian Endocrine Disruption Underlies Premature Reproductive Senescence Following Environmentally Relevant Chronic Exposure to the Aryl Hydrocarbon Receptor Agonist 2,3,7,8-Tetrachlorodibenzo-p-Dioxin1

The aryl hydrocarbon receptor (AHR) mediates the effects of many endocrine disruptors and contributes to the loss of fertility in polluted environments. While previous work has focused on mechanisms of short-term endocrine disruption and ovotoxicity in response to AHR ligands, we have shown recently that chronic exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) induces premature reproductive senescence in female rats without depletion of ovarian follicular reserves. In the current study, premature reproductive senescence was induced using a range of low-dose exposure to TCDD (0, 1, 5, 50, and 200 ng kg(-1) wk(-1)) beginning in utero and continuing until the transition to reproductive senescence. Doses of 50 and 200 ng TCDD kg(-1) wk(-1) delayed the age at vaginal opening and accelerated the loss of normal reproductive cyclicity with age without depletion of follicular reserves. Serum estradiol concentrations were decreased in a dose-dependent fashion (> or = 5 ng kg(-1) wk(-1)) across the estrous cycle in perisenescent rats still displaying normal cyclic vaginal cytology. Serum FSH, LH, and progesterone profiles were unchanged by TCDD. The loss of reproductive cyclicity following chronic exposure to TCDD was not accompanied by decreased responsiveness to GnRH. Ovarian endocrine disruption is the predominant functional change preceding the premature reproductive senescence induced by chronic exposure to low doses of the AHR-specific ligand TCDD.

Characterization of a preclinical model of simultaneous breast and ovarian cancer progression

Women at increased risk for breast cancer are often also at increased risk for ovarian cancer, reflecting common risk factors and intertwined etiologies for both diseases. Unlike breast cancer prevention, primary ovarian cancer prevention has been impractical due to the low incidence, lack of risk and response biomarkers and difficulties in sampling ovarian tissue. Challenges in the development of ovarian cancer prevention drugs, however, may be circumvented through the development of breast cancer prevention strategies that simultaneously decrease ovarian cancer. In the present study, three commonly used mammary cancer carcinogen models [7,12-dimethylbenz[alpha]anthracene (DMBA), N-methyl-N-nitrosourea (MNU) and estradiol (E2)] were combined with local ovarian DMBA administration to induce progression to mammary and ovarian cancer concurrently in the rat. Animals were treated for 3 or 6 months, and tissue histology as well as proliferation, hormonal and inflammation biomarkers were assessed. Mammary and ovarian morphologies (measured as descriptive histology and dysplasia scores) were normal in vehicle controls. Mammary hyperplasia was observed in DMBA/DMBA (mammary carcinogen/ovarian carcinogen) and MNU/DMBA-treated rats; however, ovarian preneoplastic changes were seldom observed after these treatments. All E2/DMBA-treated rats had mammary hyperplasia, atypia, ductal carcinoma in situ and/or invasive adenocarcinoma, while 50% also developed preneoplastic changes in the ovary (ovarian epithelial and stromal hyperplasia and inclusion cyst formation). In both the mammary gland and ovary, decreased estrogen receptor alpha expression was detected, and in the mammary gland elevated Ki-67 and cyclooxygenase-2 expressions were observed. This combined breast and ovarian cancer rat model (systemic E2 treatment and local ovarian DMBA) may be useful for future dual target breast and ovarian cancer prevention studies.

Estrogen alters trkA and p75 neurotrophin receptor expression within sympathetic neurons

Survival and growth of sympathetic neurons is regulated by nerve growth factor acting through trkA and p75NTR receptors. Sympathetic neurons are also affected by gonadal steroid hormones, particularly estrogen. To determine if estrogen may influence sympathetic neurons via altered neurotrophin receptor expression, we investigated effects of acute or chronic estrogen administration on levels of trkA and p75NTR proteins, numbers of immunoreactive neurons, and numbers of neurons expressing trkA, p75NTR, and estrogen receptor-alpha transcripts. Superior cervical ganglia from ovariectomized or estradiol-treated rats were processed for in situ hybridization or immunohistochemistry, and percentages of stained neurons quantitated or processed for Western blot analysis. In ovariectomized rats, approximately 50% of sympathetic neurons expressed trkA mRNA and protein. Acute estrogen administration did not affect trkA transcript expression, but reduced trkA protein significantly. Chronic treatment did not alter neuronal trkA expression. Approximately 70% of sympathetic neurons in ovariectomized rats expressed p75NTR transcripts and about 50% showed p75NTR immunoreactivity. Acute estrogen did not affect p75NTR expression. However, chronic estrogen reduced p75NTR mRNA and protein expression significantly. Fifty to sixty percent of sympathetic neurons in ovariectomized rats displayed estrogen receptor-alpha mRNA. After acute estrogen administration, estrogen receptor-alpha transcript expression increased by 35%, although this was not maintained chronically. These findings indicate that estrogen can influence sympathetic neuronal neurotrophin receptor expression as well as estrogen receptor-alpha. Reduced trkA expression after acute estrogen may transiently predispose neurons to degenerative events, while diminished p75NTR expression by chronic estrogen administration may exert long-term effects on survival or axonal outgrowth in sympathetic neurons.

Estrogen Regulates Vaginal Sensory and Autonomic Nerve Density in the Rat1

Vaginal function is strongly influenced by reproductive hormone status. Vaginal dysfunction during menopause is generally assumed to occur because of diminished estrogen-mediated trophic support of vaginal target cells. However, peripheral neurons possess estrogen receptors and are potentially responsive to gonadal steroid hormones. In the present study, we investigated whether sensory and autonomic innervation of the vagina varies among rats during the estrus phase of the estrous cycle, following chronic ovariectomy, and after sustained estrogen replacement. Relative to rats in estrus, ovariectomized rats showed a 59% elevation in nerve density, as determined using the panneuronal marker PGP 9.5. This increase persisted even after correcting for differences in vaginal tissue size, indicating true axonal proliferation after ovariectomy rather than changes secondary to altered volume. Increased total innervation after ovariectomy was attributable to increased densities of sympathetic nerves immunostained for tyrosine hydroxylase (70%), cholinergic parasympathetic nerves immunoreactive for vesicular acetylcholine transporter (93%), and calcitonin gene-related peptide-immunoreactive sensory nociceptor nerves (84%). Myelinated primary sensory innervation revealed by RT-97 immunoreactivity did not appear to be affected. Sustained 17beta-estradiol administration reduced innervation density to an extent comparable to that of estrus, implying that estrogen is the hormone mediating vaginal neuroplasticity. These findings indicate that some aspects of vaginal dysfunction during menopause may be attributable to changes in innervation. Increased sympathetic innervation may augment vasoconstriction and promote vaginal dryness, while sensory nociceptor axon proliferation may contribute to symptoms of pain, burning, and itching associated with menopause and some forms of vulvodynia.

Phage-display evolution of tyrosine kinases with altered nucleotide specificity

The problem of identifying downstream targets of kinase phosphorylation remains a challenge despite technological advances in genomics and proteomics. A recent approach involves the generation of kinase mutants that can uniquely use "orthogonal" ATP analogs to phosphorylate substrates in vivo. Using structure-based design, mutants of several protein kinase superfamily members have been found; robust and general methods are needed, however, for altering the nucleotide specificity of the remaining kinases in the genome. Here we demonstrate the application of a new phage display technique for direct functional selection to the identification of a tyrosine kinase mutant with the ability to use N6-benzyl-ATP. Our method produces, in five rounds of selection, a mutant identical to the best orthogonal Src kinase found to date. In addition, we isolate from a larger library of kinase mutants a promiscuous clone capable of using many different ATP analogs. This approach to engineering orthogonal kinases, combined with others, will facilitate the mapping of phosphorylation targets of any kinase in the genome.

Genetically encoded fluorescent reporters of protein tyrosine kinase activities in living cells

The complexity and specificity of many forms of signal transduction are widely believed to require spatial compartmentation of protein kinase and phosphatase activities, yet existing methods for measuring kinase activities in cells lack generality or spatial or temporal resolution. We present three genetically encoded fluorescent reporters for the tyrosine kinases Src, Abl, and epidermal growth factor (EGF) receptor. The reporters consist of fusions of cyan fluorescent protein (CFP), a phosphotyrosine binding domain, a consensus substrate for the relevant kinase, and yellow fluorescent protein (YFP). Stimulation of kinase activities in living cells with addition of growth factors causes 20-35% changes in the ratios of yellow to cyan emissions because of phosphorylation-induced changes in fluorescence resonance energy transfer (FRET). Platelet-derived growth factor (PDGF) stimulated Abl activity most strongly in actin-rich membrane ruffles, supporting the importance of this tyrosine kinase in the regulation of cell morphology. These results establish a general strategy for nondestructively imaging dynamic protein tyrosine kinase activities with high spatial and temporal resolution in single living cells.

Probing ion permeation and gating in a K+ channel with backbone mutations in the selectivity filter

Potassium channels selectively conduct K+ ions across cell membranes, and use diverse mechanisms to control their gating. We studied ion permeation and gating of an inwardly rectifying K+ channel by individually changing the amide carbonyls of two conserved glycines lining the selectivity filter to ester carbonyls using nonsense suppression. Surprisingly, these backbone mutations do not significantly alter ion selectivity. However, they dramatically change the kinetics of single-channel gating and produce distinct subconductance levels. The mutation at the glycine closer to the inner mouth of the pore also abolishes high-affinity binding of Ba2+ to the channel, indicating the importance of this position in ion stabilization in the selectivity filter. Our results demonstrate that K+ ion selectivity can be retained even with significant reduction of electronegativity in the selectivity filter, and that conformational changes of the filter arising from interactions between permeant ions and the backbone carbonyls contribute directly to channel gating.

Single-molecule fluorescence spectroscopy of enzyme conformational dynamics and cleavage mechanism

Fluorescence resonance energy transfer and fluorescence polarization anisotropy are used to investigate single molecules of the enzyme staphylococcal nuclease. Intramolecular fluorescence resonance energy transfer and fluorescence polarization anisotropy measurements of fluorescently labeled staphylococcal nuclease molecules reveal distinct patterns of fluctuations that may be attributed to protein conformational dynamics on the millisecond time scale. Intermolecular fluorescence resonance energy transfer measurements provide information about the dynamic interactions of staphylococcal nuclease with single substrate molecules. The experimental methods demonstrated here should prove generally useful in studies of protein folding and enzyme catalysis at single-molecule resolution.

Molecular cloning of a Schizosaccharomyces pombe cDNA encoding lanosterol synthase and investigation of conserved tryptophan residues

A Schizosaccharomyces pombe cDNA encoding lanosterol synthase was cloned by complementing a Saccharomyces cerevisiae lanosterol synthase mutant. The predicted 83-kDa protein is 54-58% identical to other lanosterol synthases. The previously known lanosterol synthases contain 229 conserved residues, which should encompass the catalytically essential amino acids. This number is decreased dramatically by including the Sc. pombe lanosterol synthase in the analysis; 42 residues are no longer conserved and therefore are catalytically nonessential. We have begun mutagenic studies to identify catalytic residues from the remaining conserved residues. Mutant Sa. cerevisiae lanosterol synthase genes were generated in which phenylalanine was specifically substituted for conserved tryptophan residues. All of the resultant mutant enzymes retained the ability to complement the Sc. cerevisiae lanosterol synthase mutant, suggesting that these conserved tryptophan residues are not catalytically essential.