An intravital microscopy method permitting continuous long-term observations of ovulation in vivo in the rabbit

Two waves of transcriptomic changes in periovulatory human granulosa cells

STUDY QUESTION

How does the human granulosa cell (GC) transcriptome change during ovulation?

SUMMARY ANSWER

Two transcriptional peaks were observed at 12 h and at 36 h after induction of ovulation, both dominated by genes and pathways known from the inflammatory system.

WHAT IS KNOWN ALREADY

The crosstalk between GCs and the oocyte, which is essential for ovulation and oocyte maturation, can be assessed through transcriptomic profiling of GCs. Detailed transcriptional changes during ovulation have not previously been assessed in humans.

STUDY DESIGN, SIZE, DURATION

This prospective cohort study comprised 50 women undergoing fertility treatment in a standard antagonist protocol at a university hospital-affiliated fertility clinic in 2016-2018.

PARTICIPANTS/MATERIALS, SETTING, METHODS

From each woman, one sample of GCs was collected by transvaginal ultrasound-guided follicle aspiration either before or 12 h, 17 h or 32 h after ovulation induction (OI). A second sample was collected at oocyte retrieval, 36 h after OI. Total RNA was isolated from GCs and analyzed by microarray. Gene expression differences between the five time points were assessed by ANOVA with a random factor accounting for the pairing of samples, and seven clusters of protein-coding genes representing distinct expression profiles were identified. These were used as input for subsequent bioinformatic analyses to identify enriched pathways and suggest upstream regulators. Subsets of genes were assessed to explore specific ovulatory functions.

MAIN RESULTS AND THE ROLE OF CHANCE

We identified 13 345 differentially expressed transcripts across the five time points (false discovery rate, <0.01) of which 58% were protein-coding genes. Two clusters of mainly downregulated genes represented cell cycle pathways and DNA repair. Upregulated genes showed one peak at 12 h that resembled the initiation of an inflammatory response, and one peak at 36 h that resembled the effector functions of inflammation such as vasodilation, angiogenesis, coagulation, chemotaxis and tissue remodelling. Genes involved in cell-matrix interactions as a part of cytoskeletal rearrangement and cell motility were also upregulated at 36 h. Predicted activated upstream regulators of ovulation included FSH, LH, transforming growth factor B1, tumour necrosis factor, nuclear factor kappa-light-chain-enhancer of activated B cells, coagulation factor 2, fibroblast growth factor 2, interleukin 1 and cortisol, among others. The results confirmed early regulation of several previously described factors in a cascade inducing meiotic resumption and suggested new factors involved in cumulus expansion and follicle rupture through co-regulation with previously described factors.

LARGE SCALE DATA

The microarray data were deposited to the Gene Expression Omnibus (www.ncbi.nlm.nih.gov/gds/, accession number: GSE133868).

LIMITATIONS, REASONS FOR CAUTION

The study included women undergoing ovarian stimulation and the findings may therefore differ from a natural cycle. However, the results confirm significant regulation of many well-established ovulatory genes from a series of previous studies such as amphiregulin, epiregulin, tumour necrosis factor alfa induced protein 6, tissue inhibitor of metallopeptidases 1 and plasminogen activator inhibitor 1, which support the relevance of the results.

WIDER IMPLICATIONS OF THE FINDINGS

The study increases our understanding of human ovarian function during ovulation, and the publicly available dataset is a valuable resource for future investigations. Suggested upstream regulators and highly differentially expressed genes may be potential pharmaceutical targets in fertility treatment and gynaecology.

STUDY FUNDING/COMPETING INTEREST(S)

The study was funded by EU Interreg ÔKS V through ReproUnion (www.reprounion.eu) and by a grant from the Region Zealand Research Foundation. None of the authors have any conflicts of interest to declare.

In vivo imaging reveals an essential role of vasoconstriction in rupture of the ovarian follicle at ovulation

Rupture of the ovarian follicle releases the oocyte at ovulation, a timed event that is critical for fertilization. It is not understood how the protease activity required for rupture is directed with precise timing and localization to the outer surface, or apex, of the follicle. We hypothesized that vasoconstriction at the apex is essential for rupture. The diameter and blood flow of individual vessels and the thickness of the apical follicle wall were examined over time to expected ovulation using intravital multiphoton microscopy. Vasoconstriction of apical vessels occurred within hours preceding follicle rupture in wild-type mice, but vasoconstriction and rupture were absent in Amhr2(cre/+)SmoM2 mice in which follicle vessels lack the normal association with vascular smooth muscle. Vasoconstriction is not simply a response to reduced thickness of the follicle wall; vasoconstriction persisted in wild-type mice when thinning of the follicle wall was prevented by infusion of protease inhibitors into the ovarian bursa. Ovulation was inhibited by preventing the periovulatory rise in the expression of the vasoconstrictor endothelin 2 by follicle cells of wild-type mice. In these mice, infusion of vasoconstrictors (either endothelin 2 or angiotensin 2) into the bursa restored the vasoconstriction of apical vessels and ovulation. Additionally, infusion of endothelin receptor antagonists into the bursa of wild-type mice prevented vasoconstriction and follicle rupture. Processing tissue to allow imaging at increased depth through the follicle and transabdominal ultrasonography in vivo showed that decreased blood flow is restricted to the apex. These results demonstrate that vasoconstriction at the apex of the follicle is essential for ovulation.

Induction of proteinases in the human preovulatory follicle of the menstrual cycle by human chorionic gonadotropin

OBJECTIVE

To explore the temporal expression in granulosa and theca cells of key members of the MMP and ADAMTS families across the periovulatory period in women to gain insight into their possible roles during ovulation and early luteinization.

DESIGN

Experimental prospective clinical study and laboratory-based investigation.

SETTING

University medical center and private IVF center.

ANIMAL AND PATIENT(S)

Thirty-eight premenopausal women undergoing surgery for tubal ligation and six premenopausal women undergoing assisted reproductive techniques.

INTERVENTION(S)

Administration of hCG and harvesting of follicles by laparoscopy and collection of granulosa-lutein cells at oocyte retrieval.

MAIN OUTCOME MEASURE(S)

Expression of mRNA for matrix metalloproteinase (MMPs) and the A disintegrin and metalloproteinase with thrombospondin-like motifs (ADAMTS) in human granulosa cells and theca cells collected across the periovulatory period of the menstrual cycle and in cultured granulosa-lutein cells after hCG. Localization of MMPs and ADAMTSs by immunohistochemistry.

RESULT(S)

Expression of MMP1 and MMP19 mRNA increased in both granulosa and theca cells after hCG administration. ADAMTS1 and ADAMTS9 mRNA increased in granulosa cells after hCG treatment, however, thecal cell expression for ADAMTS1 was unchanged, while ADAMTS9 expression was decreased. Expression of MMP8 and MMP13 mRNA was unchanged. Immunohistochemistry confirmed the localization of MMP1, MMP19, ADAMTS1, and ADAMTS9 to the granulosa and thecal cell layers.

CONCLUSION(S)

The collection of the dominant follicle throughout the periovulatory period has allowed the identification of proteolytic remodeling enzymes in the granulosa and theca compartments that may be critically involved in human ovulation. These proteinases may work in concert to regulate breakdown of the follicular wall and release of the oocyte.

Alterations of follicular microcirculation and apex structure during ovulation in the rat

OBJECTIVE

We utilized methods for intravital microscopy and microcirculation measurements to study changes during ovulation.

STUDY DESIGN

Immature gonadotrophin-primed rats were laparotomized and one ovary was examined for morphological alterations during a 3 h period (covering a period from 1h before to 27 h after hCG) through water-immersion lenses (maximum magnification 812×). Microcirculatory blood flow was assessed by measurements of blood cell velocity and laser Doppler flowmetry.

RESULTS

Follicular hyperaemia was observed 30 min after hCG and then vasomotion was observed. A gradual decline of apical blood flow was seen, which later was associated with an avascular area over the top of the apex. Cells from the surface over the follicular apex were then detached from the exterior of the follicle and this phenomenon was initiated more than one hour prior to follicular rupture. The subsequent structural alterations varied with or without formation of a cone over the stigma. In ovulations with a stigma-cone, a translucent, irregular mass formed over the stigma. Prior to follicular rupture, granulosa cells and follicular fluid were extruded from the follicular cavity at a velocity of around 70 μm/s. Occasionally, intra-antral haemorrhage occurred prior to or during follicular rupture.

CONCLUSION

Characteristic features of ovulation in the rat are microcirculatory vasomotion, gradual formation of apical avascular area, specific changes of the stigma, and extrusion of the oocyte-granulosa cell complex with or without haemorrhage.

Cryopreserved ovarian tissues can maintain a long-term function after heterotopic autotransplantation in rat

The functional longevity of cryopreserved ovarian grafts is one of the most challenging questions regarding ovarian transplantation at present. This study used a rat ovarian grafting model to investigate whether ovarian tissues from adult rats, which had been cryopreserved by vitrification and followed by heterotopic transplantation, could establish long-term hormone secretion and follicle development. Fresh and cryopreserved ovarian tissues were autologously transplanted under the kidney capsule. One-third of the animals in each group (sham-operated, fresh autografts, cryopreserved autografts, or castrated) were killed 5, 8, or 10 months after transplantation. Vaginal cytology, serum estradiol (E2), progesterone, and the morphology of the reproductive tract were used to assess ovarian function. Both fresh and cryopreserved ovarian grafts survived well in all the animal models with comparable proportion of follicles at each stage of folliculogenesis at all three time points. The serum E2 and progesterone concentrations in the groups with fresh or cryopreserved grafts remained comparable with those in sham-operated controls at all investigated time points. However, a loss of grafts and primordial follicles following heterotopic transplantation was noted. In conclusion, the heterotopic autotransplantation of vitrified ovarian tissues from adult rat without vascular anastomosis can maintain long-term ovarian function and exert endocrine function in target organs, in spite of the reduction in follicle pool.

Blood vessel remodeling in pig ovarian follicles during the periovulatory period: an immunohistochemistry and SEM-corrosion casting study

BACKGROUND

The present research aims to describe the process of vascular readjustment occurring in pig ovary during the periovulatory phase (from LH surge to ovulation) that drives the transformation of the follicle, a limited blood supplied structure, into the corpus luteum, a highly vascularised endocrine gland required to maintain high levels of progesterone in pregnancy. The swine model was chosen because it is characterized by a long periovulatory window (about 40-44 hrs-similar to human) that permits to recover follicles at a precise endocrinological timing.

METHODS

By validated hormonal protocol (eCG+hCG), able to mimic the physiologic gonadotropin stimulation, preovulatory follicles (PreOFs, 60 h-eCG), follicles in the middle (early periovulatory follicles, EPerOFs, 18 h-hCG) or late (LPerOFs, 36 h-hCG) periovulatory phase were isolated from prepubertal gilts. To understand the angiogenic process, morphological/morphometrical analyses were performed by combining immunohistochemistry (IHC) and SEM of vascular corrosion casts (VCC) techniques.

RESULTS

PreOFs showed a vascular plexus with proliferating endothelial cells (EPI). This plexus was characterized by a dense inner capillary network, with angiogenic figures, connected to the outer network by anastomotic vessels (arterioles and venules of the middle network). EPerOFs decreased their EPI, blood vessel extension in the outer network, and evidenced a reduced compactness of blood vessels. In LPerOFs, a rapid neovascularization was associated to an intensive tissue remodeling: the follicle acquired an undulated aspect presenting arterioles/venules near the basal membrane, increased vascular extension by EPI, sprouting and non-sprouting angiogenesis.The analysis of vascular geometric relations and branching angles evidenced similar values at all stages.

CONCLUSION

These data allow us to hypothesize that EPerOFs are in a quiescent status. LPerOFs represent the "metamorphic" follicles that rapidly turn-on angiogenesis to sustain a successful corpus luteum formation. Particularly, it is interesting to underlie that the non-sprouting angiogenesis, typical of structures in rapid neovascularization, occurred only in the LPerOFs. Moreover, vascular geometric relations showed as blood vessel remodeling occurs with the "maximum output and the minimum energetic expense".This knowledge will allow to better understand the mechanisms regulating the reproductive success and to clarify the complex physiological angiogenic process in adult tissues.

Intravital high-resolution optical imaging of individual vessel response to photodynamic treatment

Intravital imaging using confocal microscopy facilitates high-resolution studies of cellular and molecular events in vivo. We use this, complemented by Doppler optical coherence tomography (OCT), to assess blood flow in a mouse dorsal skin-fold window chamber model to image the response of individual blood vessels to localized photodynamic therapy (PDT). Specific fluorescent cell markers were used to assess the effect on the vascular endothelial cell lining of the treated vessels. A fluorescently tagged antibody against an endothelial transmembrane glycoprotein (CD31) was used to image endothelial cell integrity in the targeted blood vessel. A cell permeability (viability) indicator, SYTOX Orange, was also used to further assess damage to endothelial cells. A fluorescently labeled anti-CD41 antibody that binds to platelets was used to confirm platelet aggregation in the treated vessel. These optical techniques enable dynamic assessment of responses to PDT in vivo, at both the vascular endothelial cell and whole vessel levels.