CULTURE OF BOVINE IVM/IVF EMBRYOS UP TO BLASTOCYST STAGE IN DEFINED MEDIUM USING INSULIN, TRANSFERRIN AND SELENIUM OR GROWTH FACTORS

Endometrium On-a-Chip Reveals Insulin- and Glucose-induced Alterations in the Transcriptome and Proteomic Secretome

The molecular interactions between the maternal environment and the developing embryo are key for early pregnancy success and are influenced by factors such as maternal metabolic status. Our understanding of the mechanism(s) through which these individual nutritional stressors alter endometrial function and the in utero environment for early pregnancy success is, however, limited. Here we report, for the first time, the use of an endometrium-on-a-chip microfluidics approach to produce a multicellular endometrium in vitro. Isolated endometrial cells (epithelial and stromal) from the uteri of nonpregnant cows in the early luteal phase (Days 4-7) were seeded in the upper chamber of the device (epithelial cells; 4-6 × 104 cells/mL) and stromal cells seeded in the lower chamber (1.5-2 × 104 cells/mL). Exposure of cells to different concentrations of glucose (0.5, 5.0, or 50 mM) or insulin (Vehicle, 1 or 10 ng/mL) was performed at a flow rate of 1 µL/minute for 72 hours. Quantitative differences in the cellular transcriptome and the secreted proteome of in vitro-derived uterine luminal fluid were determined by RNA-sequencing and tandem mass tagging mass spectrometry, respectively. High glucose concentrations altered 21 and 191 protein-coding genes in epithelial and stromal cells, respectively (P < .05), with a dose-dependent quantitative change in the protein secretome (1 and 23 proteins). Altering insulin concentrations resulted in limited transcriptional changes including transcripts for insulin-like binding proteins that were cell specific but altered the quantitative secretion of 196 proteins. These findings highlight 1 potential mechanism by which changes to maternal glucose and insulin alter uterine function.

Metabolic biomarkers, body condition, uterine inflammation and response to superovulation in lactating Holstein cows

The objective was to determine associations between response to superovulation and body condition, subclinical endometritis and circulating metabolic biomarkers [adiponectin, leptin, insulin, IGF1, tumor necrosis factor (TNF) α, interleukin (IL) 1β, IL6, and urea] in lactating dairy cows. Ten multiparous lactating Holstein cows in each body condition score (1-5; 1 emaciated; 5 obese) category (BCSC) 2.00 to < 2.50 (BCSC1), 2.50 to < 3.00 (BCSC2), 3.00 to <3.50 (BCSC3), 3.50 to <4.00 (BCSC4) and 4.00 to 5.00 (BCSC5) groups (total n = 50) were randomly selected and superovulated, timed artificially inseminated with frozen-thawed semen from three sires and embryos collected (n = 50 collections). At embryo collection, blood samples and embryo recovery fluid were collected for determination of metabolic markers and presence of subclinical endometritis (lavage technique; > 6% PMN). In total, 379 embryos were collected (average of 7.6 embryos per superovulation). Mean numbers of total ova and embryos was greater for cows in BCSC2, BCSC3 and BCSC4 groups compared with cows in BCSC1 and BCSC5 groups (P < 0.01). Total number of transferrable embryos were greater for cows in BCSC 2 and BCSC3 groups compared with cows in BCSC1, BCSC4 and BCSC5 groups (P < 0.01). Mean number of total ova and embryos and of transferrable embryos was higher for cows with 0 or 1-6% PMN compared to cows with >6% PMN (P < 0.01). In addition, there was a quadratic association between blood urea nitrogen concentrations and % transferrable embryos (r² = 0.85; P < 0.05) and between BCS and % transferrable embryos (r² = 0.73; P < 0.05). Circulating adiponectin, leptin, insulin, IGF1 and TNFα were greater in cows with moderate to good body condition compared to thin or obese cows (P < 0.05). Circulating adiponectin, leptin, IGF1 and insulin were greater in normal cows (≤6% PMNs), whereas, TNFα and IL1β and IL6 were greater in cows with subclinical endometritis (P < 0.05). In conclusion, BCS and subclinical endometrial inflammation were associated with superovulatory response and embryo quality. Further, circulating metabolic biomarkers were associated with superovulatory response and embryo quality, likely due to donor's metabolic status and uterine environment. Optimizing superovulatory responses and embryo quality in lactating dairy cows requires management of nutrition and uterine health.

Insulin concentrations used in in vitro embryo production systems: a pilot study on insulin stability with an emphasis on concentrations measured in vivo

BACKGROUND

Insulin has been used as a stimulatory factor for in vitro cell culture since many years. Even for routine in vitro embryo production (IVP), insulin is added to the media during different steps. There is a strong difference in concentrations used in vitro compared to what is measured in vivo in follicular fluid or serum. We performed a pilot study on insulin stability to explain possible reasons for that variation.

RESULTS

We measured insulin concentrations before and after bovine oocyte maturation in an experiment by using a quantitative ELISA (Mercodia bovine insulin ELISA immunoassay) and found that concentrations were stable up to 22 h of incubation. We compared our results with eleven in vivo studies measuring insulin in either serum or follicular fluid and nine IVP-protocols using insulin. In all studies, in vitro concentrations were much higher compared with those found physiologically in vivo. Limited knowledge is available concerning the different activity and stability of insulin in vitro versus in vivo.

CONCLUSIONS

The concentrations of insulin used in vitro are quite high in comparison to physiological concentrations found in serum or follicular fluid. One explanation may be a different stability or activity of insulin in vitro even if we could measure stable concentrations of insulin in our pilot study. More precise dose-effect studies have to be performed to draw clear conclusions about the consequences of the use of such high doses as they might have negative consequences for the developing embryo. Insulin has direct effects on the regulation of the metabolism and could even influence the epigenetic programming of the metabolism with unknown consequences for the offspring later in life.

The functional role of insulin in fertility and embryonic development-What can we learn from the bovine model?

Insulin is a key metabolic hormone that plays a crucial role in regulating energy homeostasis in the body. In addition, insulin-dependent signaling has important functions in reproduction and early embryo development. As metabolism and reproduction are closely linked, metabolic challenges may be the source of reproductive disorders and decreased fertility. This is known for the dairy cow and for other species including the human. Although metabolic disorders in the dairy cow often derive from a failure to adapt to a high milk production, the situation in the human is often linked to emerging conditions and associated diseases in our modern society such as obesity and diabetes, where an excess energy intake causes decreased fertility in women. Both energy excess and energy deficit are associated with a deviation of insulin concentrations in serum and follicular fluid from normal levels. Although many studies have shown that extreme variation in energy supply can negatively influence early embryo development by inducing changes in circulating concentrations of several metabolites or hormones like insulin, several in vitro culture media are still supplemented with insulin in high concentrations. In this review, direct and indirect effects of insulin on fertility will be described. Differences between the in vivo and in vitro situations will also be discussed.

Replacing serum in culture medium with albumin and insulin, transferrin and selenium is the key to successful bovine embryo development in individual culture

Individual culture of bovine embryos is usually associated with low blastocyst development. However, during preliminary experiments in our laboratory we observed high blastocyst development after individual embryo culture in a serum-free culture system. We therefore hypothesised that serum has a negative effect on embryos cultured individually whereas embryos in groups can counteract this. First, we determined whether the timing of removal of serum (during maturation or culture) had an influence on individual embryo development. The results clearly showed that removal of serum during embryo culture was the main contributing factor since high blastocyst development was observed after individual culture in synthetic oviductal fluid supplemented with bovine serum albumin (BSA) and insulin, transferrin and selenium (ITS), independent of the maturation medium. Second, we investigated whether an individual factor of the ITS supplement was essential for individual embryo development. We demonstrated that repeatable high blastocyst percentages were due to the synergistic effect of ITS. Finally, we investigated if a group-culture effect can still be observed under serum-free conditions. Group culture generated blastocysts with higher total cell numbers and less apoptosis. These data show that individual culture in serum-free conditions leads to high blastocyst development, but group culture still improves blastocyst quality.

Developmental competence and embryo quality of small oocytes from pre-pubertal goats cultured in IVM medium supplemented with low level of hormones, insulin-transferrin-selenium and ascorbic acid

The aim of this study was to test the effect of insulin-transferrin-selenium (ITS) and L-ascorbic acid (AA) supplementation and the hormonal level during in vitro maturation (IVM) of small oocytes from pre-pubertal goat on the blastocyst yield and quality. Concretely, we used four maturation media: conventional IVM medium (CM), growth medium (GM: CM+ITS+AA and low level of hormones), modified CM (mCM: CM with low level of hormones) and modified GM (mGM: CM+ITS+AA and normal level of hormones). Cumulus-oocyte complexes (COCs) were classified into two categories according to oocyte diameter: <125 μm and ≥ 125 μm. Large oocytes were matured 24 h in CM (Treatment A). Small oocytes were matured randomly in six experimental groups: Treatment B: 24 h in CM; Treatment C: 12 h in GM and 12 h in CM; Treatment D: 24 h in mGM; Treatment E: 12 h in mGM and 12 h in CM; Treatment F: 12 h in mCM and 12 h in CM; and Treatment G: 12 h in GM and 12 h in mGM. After IVM, oocytes were fertilized and cultured for 8 days. The blastocyst quality was assessed by the survival following vitrification/warming and the mean cell number. When different maturation media were combined, the blastocyst rate did not improve. The large oocytes produced the highest blastocysts yield. However, the culture of small oocytes in GM (53.3%) enhanced the post-warming survival of blastocysts compared to large oocytes matured in CM (35.7%). In conclusion, IVM of pre-pubertal goat small oocytes in GM would be useful to improve the quality of in vitro-produced blastocysts.

Evaluation of Bovine Embryos Produced in High Performance Serum-Free Media

This review evaluates the quality of bovine embryos developed from in vitro-matured (IVM) and -fertilized (IVF) oocytes cultured in either serum-free or serum-containing media. Bovine embryos cultured in serum-supplemented medium contain numerous cytoplasmic lipid droplets and immature mitochondria compared to those cultured in serum-free medium. The accumulation of cytoplasmic lipids in embryos developed in serum-containing medium may be a result of incorporation of lipoproteins from the serum and may result in impaired function of mitochondria. The improved serum-free media (IVMD101 and IVD101) offer several advantages over culture in serum-containing medium, including increased rates of blastocyst formation and higher cell numbers. Additionally, the survival and hatching rates of embryos produced in serum-free media after post-thaw culture were superior to those of embryos produced in the serum-containing medium, suggesting that the abnormal accumulation of cytoplasmic lipids in embryos may have a negative effect on the sensitivity of embryos to chilling and freezing. These serum-free culture systems have proven to be beneficial for the production of good quality embryos from IVM-IVF bovine oocytes. Furthermore, recent studies have shown a correlation between mitochondrial function (oxygen consumption) and embryo quality. A new method using scanning electrochemical microscopy may be capable of assessing the viability and developmental potential of bovine embryos.

Effect of insulin, transferrin and selenium and epidermal growth factor on development of buffalo oocytes to the blastocyst stage in vitro in serum-free, semidefined media

The in vitro development of buffalo oocytes up to the blastocyst stage was studied in serum-free, semidefined media containing bovine serum albumin, follicle-stimulating hormone (FSH), insulin, transferrin and selenium (ITS) and epidermal growth factor (EGF). In experiment 1, oocytes aspirated from abattoir-derived ovaries were cultured in eight serum-free, semidefined culture media containing different combinations of these four factors. In experiment 2, the maturation of buffalo oocytes and the development of the embryos were compared in a complex co-culture system and in the serum-free, semidefined media. Supplementation with FSH and EGF significantly (P < 0.05) increased the maturation rates of buffalo oocytes, and the yield of blastocysts was higher (P < 0.05) in media containing EGF and ITS. The yield of blastocysts was lower in the serum-free semidefined media (P < 0.05) than in the complex co-culture system.

Ultrastructure of bovine embryos developed from in vitro-matured and -fertilized oocytes: comparative morphological evaluation of embryos cultured either in serum-free medium or in serum-supplemented medium

The ultrastructure of bovine embryos developed from in vitro-matured and -fertilized oocytes, cocultured with bovine cumulus/granulosa cells either in a serum-free medium (IVMD101) or in a serum-containing medium (TCM199+CS) was compared. Embryos up to the eight-cell stage had many cellular organelles and cytoplasmic components that were randomly distributed in the cytoplasm. Mitochondria were spherical or ovoid and had only a few peripheral cristae. There were no obvious differences in the ultrastructure between embryos developed in IVMD101 and TCM199+CS up to the eight-cell stage. However, conspicuous differences in the ultrastructural features between the embryos cultured in IVMD101 and TCM199+CS were observed at the morula and blastocyst stages. At the morula stage, embryos cultured in IVMD101 had cells containing elongated mitochondria, well-developed Golgi apparatus, lipid droplets, and large vesicles resembling lysosomes. The lysosome-like vesicles were partially filled with electron-dense materials and were frequently fused with lipid droplets. The blastomeres of morulae cultured in TCM199+CS contained numerous large lipid droplets and fewer lysosome-like vesicles than those cultured in IVMD101. In blastocysts cultured in IVMD101, lysosome-like vesicles were frequently observed in the trophoblast cells and lipid droplets were present in the cytoplasm of trophoblast and inner cell mass (ICM)-cells, but they were not abundant. On the other hand, the blastocysts developed in TCM199+CS contained fewer lysosome-like vesicles and large numbers of lipid droplets. This accumulation of lipid droplets was higher in the trophoblast cells than in the ICM-cells. This study showed major differences in the ultrastructural features between the morulae and blastocysts from serum-free and serum-supplemented cultures, suggesting that the ultrastructural differences may reflect physiological characteristics of embryos.

Growth of preimplantation bovine embryos

Development of mammalian embryos in vitro is functionally and temporally inferior to embryo development as it occurs inside the female reproductive tract. The deficiencies of cultured embryos range from slow cleavage rates to complete developmental arrests or blocks, occurring at particular stages in many species. A variety of approaches have been used to overcome the blocks, including most extensively the coculture of preimplantation embryos with various somatic cells. However, even with coculture, development of embryos in vitro is still not equivalent to that in vivo. In most laboratories, only 25-40% of inseminated oocytes develop into morulae and blastocysts in spite of numerous variations on the basic technique. A better understanding of the factors governing embryonic growth is required before we can hope to achieve results comparable with those occurring in vivo.

Effect of growth factors on bovine blastocyst development in a serum-free medium

To investigate the effect of growth factors on pre-implantation development, bovine zygotes, produced by in vitro fertilization (IVF) of in vitro-matured (IVM) oocytes, were cultured in a serum-free medium to which the following growth factors were added one at a time: epidermal growth factor (EGF), acidic fibroblast growth factor (a-FGF), insulin-like growth factor-II (IGF-II), platelet-derived growth factor from human platelets (PDGF), and platelet-derived growth factor-AB, human, recombinant (PDGF-AB). All growth factors were added at a dose of either 10 or 50 ng/ml, except PDGF which was added at a dose of either 5 or 15 ng/ml. The control medium was TCM 199 supplemented with sodium pyruvate (0.25 mmol/l), BSA (10 mg/ml), insulin (5 micrograms/ml), transferrin (5 micrograms/ml), and sodium selenite (5 ng/ml). Embryos were cultured for 8 days (day of insemination = Day 0). The mean percentages of first cleavage on Day 2 varied from 67% to 86% and the differences between the 2 doses, or between the control and growth factor-treated groups were not significant (p > or = 0.13). The effects of the two doses on subsequent development up to the blastocyst stage did not differ either (p > or = 0.12). There was no stimulatory effect of any of the used exogenous growth factors on embryo development up to the morula or blastocyst stage on Day 7, or blastocyst stage on Day 8. Moreover, medium supplemented with PDGF had fewer blastocysts than the control (p < or = 0.03).(ABSTRACT TRUNCATED AT 250 WORDS)

Fine structure of bovine blastocysts developed either in serum-free medium or in conventional co-culture with oviduct epithelial cells

The ultrastructure of day 7 bovine blastocysts developed in vitro in either of two culture systems was compared with that of morphologically normal blastocytes collected non-surgically from superovulated cows on day 7 (Day 0 = day of insemination). The in vitro-embryos were obtained after culture of in vitro-matured and -fertilized oocytes either in a serum-free, cell-free medium (SFM, i.e. TCM 199 supplemented with BSA (10 mg/ml), insulin (5 micrograms/ml), transferrin (5 micrograms/ml) and selenium (5 ng/ml) or in a serum-supplemented medium (TCM 199 and 10% (v/v) oestrous cow serum) together with bovine oviduct epithelial cells (BOEC). Five of the 8 blastocysts developed in SFM fulfilled the criteria set for normal morphology of the in vivo-developed blastocytes. In contrast, 6 out of 8 blastocysts developed in co-culture with BOEC were classified as morphologically deviated, and only 2 reached the criteria for morphological normality. In vitro-developed blastocysts with deviated morphology showed a higher degree of cytoplasmic vacuolation, short, less developed cell-to-cell contacts between trophoblast as well as between inner cell mass (icm)-cells, less developed apical microvilli on the trophoblast and wide inter-cellular spaces. Additionally, numerous cytoplasmic vesicles, phagosomes, lipid droplets and hooded mitochondria were commonly present, both in trophoblast and in icm-cells. The results indicate that a high proportion of blastocysts developed in co-culture with BOEC were morphologically deviated compared to those cultured in medium where serum and somatic cells were replaced by BSA, insulin, transferrin and selenium.