Insulin promotes preantral follicle growth and antrum formation through temporal expression of genes regulating steroidogenesis and water transport in the cat

Lipid modulation during IVM increases the metabolism and improves the cryosurvival of cat oocytes

This study investigated the time course of lipid accumulation during IVM and assessed the role of lipid modulators added during IVM on lipid content, nuclear maturation, oxidative stress, mitochondrial activity, gene expression, and cryosurvival of cat oocytes. First, the lipid content of immature COCs was compared to those subjected to different IVM duration times (24, 28, and 32 h). Then, the lipid content was investigated after the use of different lipid modulators [conjugated linoleic acid (CLA), forskolin (FSK), l-carnitine (LC)]. Subsequently, both the CONTROL group and MIX 18 (CLA+FSK+LC) were compared regarding nuclear maturation, mitochondrial activity, reactive oxygen 19 species (ROS), and glutathione (GSH) levels, to the expression of SDHA, GDF9, BMP15, ZAR-1, 20 PRDX1, SIRT1, and SIRT3 genes (normalized by ACTB and YWHAZ genes); and to vitrification and 21 post-warming viability assessment. When not using any lipid modulator, an increase (P < 0.05) in lipid content could be observed after 28 h of IVM. The MIX group showed the greatest (P < 0.05) reduction in oocyte lipid content after 28 h of IVM. No difference (P > 0.05) was observed in the MII rate in the CONTROL (45%) and MIX (41%) groups and in mitochondrial activity ((1.00 ± 0.35 A U vs 1.19 ± 0.14 A U). Although ROS and GSH levels were higher (P < 0.05) in MIX than in CONTROL, the redox balance (ROS/GSH) was greater (P < 0.05) in the latter (C:1.00 ± 0.20b vs M:0.26 ± 0.06 a A.U). The GDF9, HSP70, PRDX1, and SIRT1 transcripts were downregulated (P < 0.05) in MIX-oocytes, compared to the CONTROL. After vitrification, MIX (74%) presented a higher (P < 0.05) viability compared to control (53%). In conclusion, MIX can reduce the total lipid content and improve viability after cryopreservation, however, it seems to affect the oocyte metabolism in a way that still needs to be better understood in the cat biological model.

Comparative Tensile Properties and Collagen Patterns in Domestic Cat (Felis catus) and Dog (Canis lupus familiaris) Ovarian Cortical Tissues

The importance of the ovarian extracellular environment and tissue rigidity on follicle survival and development has gained attention in recent years. Our laboratory has anecdotally observed differences in the rigidity of domestic cat and dog ovarian cortical tissues, which have been postulated to underlie the differences in in vitro culture responses between the species, wherein cat ovarian tissues display higher survival in extended incubation. Here, the tensile strengths of cat and dog ovarian cortical tissues were compared via micropipette aspiration. The underlying collagen patterns, including fiber length, thickness, alignment, curvature, branch points and end points, and overall tissue lacunary and high-density matrix (HDM) were quantified via picrosirius red staining and TWOMBLI analysis. Finally, we explored the potential of MMP (-1 and -9) and TIMP1 supplementation in modulating tissue rigidity, collagen structure, and follicle activation in vitro. No differences in stiffness were observed between cat or dog cortical tissues, or pre- versus post-pubertal status. Cat ovarian collagen was characterized by an increased number of branch points, thinner fibers, and lower HDM compared with dog ovarian collagen, and cat tissues exposed to MMP9 in vitro displayed a reduced Young's modulus. Yet, MMP exposure had a minor impact on follicle development in vitro in either species. This study contributes to our growing understanding of the interactions among the physical properties of the ovarian microenvironment, collagen patterns, and follicle development in vitro.

The FSH-mTOR-CNP signaling axis initiates follicular antrum formation by regulating tight junction, ion pumps, and aquaporins

The initial formation of the follicular antrum (iFFA) serves as a dividing line between gonadotropin-independent and gonadotropin-dependent folliculogenesis, enabling the follicle to sensitively respond to gonadotropins for its further development. However, the mechanism underlying iFFA remains elusive. Herein, we reported that iFFA is characterized by enhanced fluid absorption, energy consumption, secretion, and proliferation and shares a regulatory mechanism with blastula cavity formation. By use of bioinformatics analysis, follicular culture, RNA interference, and other techniques, we further demonstrated that the tight junction, ion pumps, and aquaporins are essential for follicular fluid accumulation during iFFA, as a deficiency of any one of these negatively impacts fluid accumulation and antrum formation. The intraovarian mammalian target of rapamycin-C-type natriuretic peptide pathway, activated by follicle-stimulating hormone, initiated iFFA by activating tight junction, ion pumps, and aquaporins. Building on this, we promoted iFFA by transiently activating mammalian target of rapamycin in cultured follicles and significantly increased oocyte yield. These findings represent a significant advancement in iFFA research, further enhancing our understanding of folliculogenesis in mammals.

Determination of the appropriate concentration of sodium alginate used for in vitro culture of cat preantral follicles in a serum-free medium containing FSH, EGF and IGF-I

Culture of domestic cat preantral follicles can be a suitable technology to assist oocyte conservation strategies in the family Felidae. This research was aimed to comparatively analyse cat preantral follicular development of follicles directly seeded on growth surface or encapsulated in 0.5 or 1% of sodium alginate in a serum-free medium containing FSH, EGF and IGF-I. Preantral follicles were isolated from cat ovarian cortical tissue after ovariectomy. Alginate was dissolved at 0.5 or 1% in PBS. Follicles, 4 per well, with 0% (G-0%), 0.5% (G-0.5%) or 1% (G-1%) of sodium alginate were cultured in M199 with FSH (100 ng/mL), EGF (100 ng/mL) and IGF-I (100 ng/mL) for 7 days at 37°C, 5% CO₂ and 99% humidity. Culture medium was replaced every 48 h and samples were stored at -20°C until ELISA of steroid hormones. Morphometric evaluation of follicles was performed every 24 h. G-0% follicles showed granulosa cell migration away from the oocyte and disrupted morphology, whereby they reached apparently larger diameters (203.70 ± 5.82 μm; p < .05) than G-0.5% and G-1% follicles (157.89 ± 8.47 μm and 95.23 ± 1.67 μm, respectively) which maintained three-dimensional organization, being larger in G-0.5% than in G-1% (p < .05). G-0.5% follicles attained the multi-layer preantral follicle stage on day 7 of culture, whereas G-1% follicles underwent progressive atresia. On day 6, steroid concentrations were higher (p < .05) in G-0% than in G-1%: 60 ± 19 vs 0.88 ± 0.32 pg/mL oestradiol; 2.6 ± 0.84 vs 0.04 ± 0.02 ng/mL progesterone; 1.3 ± 0.22 vs 0.61 ± 0.04 ng/mL testosterone and 1.6 ± 0.54 vs 0.22 ± 0.07 ng/mL androstenedione respectively. Steroid concentrations in G-0.5% were comprised between those of G-0% and G-1% (p > .05). In conclusion, two-layer cat preantral follicles encapsulated in 0.5% alginate cultured in medium containing FSH, EGF and IGF-I can develop up to the multi-layer preantral stage in 7 days of culture, whereas follicles directly seeded on growth surface or encapsulated in 1% alginate lost their three-dimensional organization, and experienced regression with compromised steroidogenesis, respectively.

Insulin induces steroidogenesis in canine luteal cells via PI3K-MEK-MAPK

Glucose uptake increases in canine luteal cells under insulin treatment. We hypothesize that insulin also increases luteal cell steroidogenesis. Dogs underwent elective ovariohysterectomy from days 10-60 post ovulation and their corpora lutea (CL) and blood samples were collected. Deep RNA sequencing determined differentially expressed genes in CL; those related to insulin signaling and steroidogenesis were validated in vivo by qPCR and their respective proteins by Western blotting and immunofluorescence. Next, luteal cell cultures were stimulated with insulin with or without inhibition of MAPK14, MAP2K1 and PI3K. Studied proteins except P450 aromatase showed the same expression pattern of coding genes in vivo. The expression of HSD3B and CYP19A1 was higher in insulin-treated cells (P < 0.005). Following respective pathway blockades, the culture medium had decreased concentrations of progesterone (P4) and 17b-estradiol (E2) (P < 0.01). Our results indicate that insulin increases HSD3B and CYP19A1 expression via MAPK and PI3K, and contributes to the regulation of P4 and E2 production in canine luteal cells.

Different expression and localization of aquaporin 7 and aquaporin 9 in granulosa cells, oocytes, and embryos of patients with polycystic ovary syndrome and the negatively correlated relationship with insulin regulation

OBJECTIVE

To investigate the expression of aquaporin 7 (AQP7) and aquaporin 9 (AQP9) in the granulosa cells of patients with polycystic ovary syndrome (PCOS) and healthy women and detect their localization in oocytes at the germinal vesicle (GV), metaphase I (MI), MII, embryo, and blastocyst stages and the in vitro response to insulin stimulation.

DESIGN

Randomized, assessor-blinded study.

SETTING

Reproductive medical center.

PATIENT(S)

A total of 40 women (aged 20-38 years) comprising 29 cases of primary infertility and 11 cases of secondary infertility, of whom 17 had an initial diagnosis of PCOS and three received a PCOS diagnosis after an infertility examination.

INTERVENTION(S)

Controlling different concentrations of insulin and different treatment times in cultures of normal human granulosa cells in vitro.

MAIN OUTCOME MEASURE(S)

Expression of AQP7 and AQP9 genes and proteins in granulosa cells detected by real-time quantitative polymerase chain reaction, and localization in oocytes at the GV, MI, MII, embryo, and blastocyst stages by Western blot, immunohistochemical, and immunofluorescence assays, and concentrations of insulin in follicular fluid by enzyme-linked immunosorbent assay.

RESULT(S)

The expression levels of the AQP7 mRNA and protein in the granulosa cells of patients with PCOS were higher than found in healthy controls. We found AQP7 protein expressed in human oocytes at GV, MI, MII, embryo, and blastocyst stages; it was mainly located in the nucleoplasm. In the PCOS group, the expression level of AQP9 mRNA and protein in granulosa cells was lower, and AQP9 protein was expressed in oocytes at the GV, MI, MII, embryo, and blastocyst stages; it was localized on the nuclear membrane. Compared with healthy women, the insulin expression in patients with PCOS was higher. In cultures of normal human granulosa cells in vitro, the expression of AQP7 and AQP9 mRNA and protein decreased with the increase in insulin concentration; expression statistically significantly decreased when the insulin concentration was 100 nmol/L, and after 6 to 24 hours of exposure the lowest expression levels were found at 12 hours.

CONCLUSION(S)

The different localization and expression of AQP7 and AQP9 between the two groups suggests that they might be involved in oocyte maturation and embryonic development through different regulatory pathways. The expression levels of AQP7 and AQP9 were negatively correlated with insulin regulation, suggesting that insulin might affect the maturation of PCOS follicles by changing AQP7 and AQP9 expression.

In vitro development of mechanically and enzymatically isolated cat ovarian follicles

Isolation of ovarian follicles is a key step in culture systems for large mammalian species to promote the continued growth of follicles beyond the preantral stage in fertility preservation efforts. Still, mechanical isolation methods are user-skill dependent and time-consuming, whereas enzymatic strategies carry increased risk of damaging theca cell layers and the basement membranes. Here, we sought to determine an optimal method to rescue domestic cat (Felis catus) early antral and antral stage follicles from ovarian tissue and to evaluate the influence of isolation strategy on follicle development, survival, and gene expression during 14 days of in vitro culture in alginate hydrogel. Mechanical isolation was compared with 90 min digestion in 0.7 and 1.4 Wünsch units/mL Liberase blendzyme (0.7L and 1.4L, respectively). Mechanical isolation resulted in improved follicle growth and survival, and better antral cavity and theca cell maintenance in vitro, compared with 1.4L (P < 0.05) but displayed higher levels of apoptosis after incubation compared with enzymatically isolated follicles. However, differences in follicle growth and survival were not apparent until 7+ days in vitro. Expressions of CYP19A1, GDF9, LHR, or VEGFA were similar among isolation-strategies. Cultured follicles from all isolation methods displayed reduced STAR expression compared with freshly isolated follicles obtained mechanically or via 0.7L, suggesting that prolonged culture resulted in loss of theca cell presence and/or function. In sum, early antral and antral stage follicle development in vitro is significantly influenced by isolation strategy but not necessarily observable in the absence of extended culture. These results indicate that additional care must be taken in follicle isolation optimizations for genome rescue and fertility preservation efforts.

In vitro ovarian follicle growth: a comprehensive analysis of key protocol variables†

Folliculogenesis is a complex process that requires integration of autocrine, paracrine, and endocrine factors together with tightly regulated interactions between granulosa cells and oocytes for the growth and survival of healthy follicles. Culture of ovarian follicles is a powerful approach for investigating folliculogenesis and oogenesis in a tightly controlled environment. This method has not only enabled unprecedented insight into the fundamental biology of follicle development but also has far-reaching translational applications, including in fertility preservation for women whose ovarian follicles may be damaged by disease or its treatment or in wildlife conservation. Two- and three-dimensional follicle culture systems have been developed and are rapidly evolving. It is clear from a review of the literature on isolated follicle culture methods published over the past two decades (1980-2018) that protocols vary with respect to species examined, follicle isolation methods, culture techniques, culture media and nutrient and hormone supplementation, and experimental endpoints. Here we review the heterogeneity among these major variables of follicle culture protocols.

Cilostamide and forskolin maintain gap junction function of incubated dog follicles

Disruption of the communication between the oocyte and granulosa cells is one of the major causes of poor development of in vitro grown ovarian follicles and oocytes. The present study investigated the effect of two cAMP modulators, cilostamide and forskolin, on in vitro growth of isolated dog secondary follicles and enclosed oocytes, communication between the gamete and surrounding granulosa cells, expression of GJA1 and GDF9, as well as cAMP level. Secondary follicles were incubated with cilostamide or forskolin alone or a combination of 20 μM cilostamide +1 μM forskolin, and the diameter of the incubated follicles and enclosed oocytes assessed every 72 h. Gap junction activity, GJA1 and GDF9 expression and cAMP level were assessed on Days 6 and 12 and transzonal projection (TZP) density was evaluated on Day 12. Neither cilostamide nor forskolin alone enhanced in vitro growth of dog follicles and the enclosed oocytes (P > 0.05). However, these two cAMP modulators dose dependently sustained gap junction activity and stimulated cAMP production compared with the non-supplemented control. Cilostamide at the high dosage (20 μM) also upregulated GJA1 expression. The combination of cilostamide and forskolin supported oocyte growth during the first 9 days and upregulated GJA1 and GDF9 expression at Day 12 of in vitro culture. This combination treatment also sustained gap junction activity, cAMP production, and increased TZP function (calcein intensity: TZP density ratio). The findings indicated that a combination of cilostamide and forskolin supported growth and survival of oocytes enclosed within cultured follicles by sustaining cAMP production and gap junction activity.

RFRP3 influences basal lamina degradation, cellular death, and progesterone secretion in cultured preantral ovarian follicles from the domestic cat

The hypothalamic neuropeptide RFRP3 can suppress hypothalamic GnRH neuron activation and inhibit gonadotropin release from the anterior pituitary. RFRP3 is also produced locally in the ovary and can inhibit steroidogenesis and follicle development in many vertebrates. However, almost nothing is known about the presence and regulatory action of RFRP3 in gonads of any carnivore species. Such knowledge is important for developing captive breeding programs for endangered carnivores and for inhibiting reproduction in feral species. Using the domestic cat as a model, our objectives were to (1) demonstrate the expression of feline RFRP3 (fRFRP3) and its receptor in the cat ovary and (2) assess the influence of fRFRP3 on ovarian follicle integrity, survival, and steroidogenesis in vitro. We first confirmed that fRFRP3 and its receptors (NPFFR1 and NPFFR2) were expressed in cat ovaries by sequencing PCR products from ovarian RNA. We then isolated and cultured preantral ovarian follicles in the presence of 10 or 1 µM fRFRP3 + FSH (1 µg/mL). We recorded the percentage of morphologically viable follicles (basal lamina integrity) over 8 days and calculated percentage survival of follicles on Day 8 (using fluorescent markers for cell survival and death). Last, we quantified progesterone accumulation in media. 10 µM fRFRP3 had no observable effect on viability, survival, or steroid production compared to follicles exposed to only FSH. However, 1 µM fRFRP3 decreased the percentage of morphologically viable follicles and the percentage of surviving follicles on Day 8. At the same time, 1 µM fRFRP3 increased the accumulation of progesterone in media. Our study shows, for the first time, direct action of RFRP3 on the follicle as a functional unit, and it is the first in a carnivore species. More broadly, our results support a conserved, inhibitory action of RFRP3 on ovarian follicle development and underscore the importance of comparative functional studies.