The effect of insulin on maturation and development of -fertilized bovine oocytes

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.

Insulin exposure during in vitro bovine oocyte maturation changes blastocyst gene expression and developmental potential

Metabolic imbalance impairs fertility, because changes in concentrations of metabolites and hormones in the blood and follicular fluid create an unfavourable environment for early embryonic development. Insulin is a key metabolic hormone known for its effects on fertility: insulin concentrations are increased during energy balance disturbances in diabetes or metabolic syndrome. Still, insulin is frequently used at supraphysiological concentrations for embryo in vitro culture with unknown consequences for the developmental potential of the offspring. In the present study we investigated the effects of insulin exposure during in vitro bovine oocyte maturation on developmental rates, embryo quality and gene expression. Supplementation of the maturation media with insulin at 10 or 0.1 µg mL-1 decreased blastocyst rates compared with an insulin-free control (19.8 ± 1.3% and 20.4 ± 1.3% vs 23.8 ± 1.3%, respectively; P < 0.05) and led to increased cell numbers (nearly 10% more cells on Day 8 compared with control; P < 0.05). Transcriptome analysis revealed significant upregulation of genes involved in lipid metabolism, nuclear factor (erythroid-derived 2)-like 2 (NRF2) stress response and cell differentiation, validated by quantitative polymerase chain reaction. To conclude, the results of the present study demonstrate that insulin exposure during in vitro oocyte maturation has a lasting effect on the embryo until the blastocyst stage, with a potential negative effect in the form of specific gene expression perturbations.

Increased cleavage and blastocyst rate in ewes treated with bovine somatotropin 5 days before the end of progestin-based estrous synchronization

Treatment with bovine somatotropin (bST) during estrous synchronization increased fertility and prolificacy in sheep. In the present study, a single dose of bST 5 days before the end of progestin treatment improved cleavage and embryo development. Stage of estrous cycle was synchronized in ewes (n=32) with progestin and superovulation was induced by use of FSH. Five days before the end of progestin treatment, ewes were randomly assigned to two groups: bST group (n=16) received a depot injection of 125 mg of bST sc (Lactotropina, Elanco, México) and the control group (n=16) received saline solution. Estrous was detected with rams fitted with an apron every 2 h and estrous sheep were mated every 8 h whilst in estrous. Embryos were recovered on Day 7 post mating, assessed microscopically and fixed in 4% paraformaldehyde. Cell number in blastocysts was counted after Hoechst 33342 staining. Plasma concentrations of IGF-I, insulin and progesterone were determined in eight sheep per group from the day of bST treatment to the day of embryo recovery. Cleavage rate, percentage of transferable embryos (transferable embryos/cleaved) and percentage of embryos reaching the blastocyst stage (blastocyst/cleaved) were compared between groups by logistic regression. IGF-I, insulin and progesterone plasma concentrations were analyzed by ANOVA for repeated measurements and cell number by ANOVA. Cleavage rate was greater (P<0.01) in bST treatment group (86%) than in the control group (62%). Similarly, the proportion of embryos reaching the blastocyst stage (bST=68.7 vs control=42.5) and the number of cells per blastocyst (bST group 91.8±5.5 compared to control group 75±6) were greater (P<0.01) in the bST-treated sheep. Plasma concentrations of IGF-I and insulin were greater (P<0.01) in the bST-treated group. No changes were observed in progesterone concentrations (P=0.5). It is concluded that bST injection 5 days before progestin removal increases cleavage rate and the proportion of embryos that reach the blastocyst stage. These effects are associated with an increase in IGF-I and insulin concentrations.

Embryonic and genetic manipulation in fish

Fishes, the biggest and most diverse community in vertebrates are good experimental models for studies of cell and developmental biology by many favorable characteristics. Nuclear transplantation in fish has been thoroughly studied in China since 1960s. Fish nuclei of embryonic cells from different genera were transplanted into enucleated eggs generating nucleo-cytoplasmic hybrids of adults. Most importantly, nuclei of cultured goldfish kidney cells had been reprogrammed in enucleated eggs to support embryogenesis and ontogenesis of a fertile fish. This was the first case of cloned fish with somatic cells. Based on the technique of microinjection, recombinant MThGH gene has been transferred into fish eggs and the first batch of transgenic fish were produced in 1984. The behavior of foreign gene was characterized and the onset of the foreign gene replication occurred between the blastula to gastrula stages and random integration mainly occurred at later stages of embryogenesis. This eventually led to the transgenic mosaicism. The MThGH-transferred common carp enhanced growth rate by 2-4 times in the founder juveniles and doubled the body weight in the adults. The transgenic common carp were more efficient in utilizing dietary protein than the controls. An "all-fish" gene construct CAgcGH has been made by splicing the common carp beta-actin gene (CA) promoter onto the grass carp growth hormone gene (gcGH) coding sequence. The CAgcGH-transferred Yellow River Carp have also shown significantly fast-growth trait. Combination of techniques of fish cell culture, gene transformation with cultured cells and nuclear transplantation should be able to generate homogeneous strain of valuable transgenic fish to fulfil human requirement in 21st century.

Expression of IGFs and their receptors is a potential marker for embryo quality

PROBLEM

Insulin-like growth factors (IGFs) and insulin have been demonstrated to stimulate oocyte maturation and embryo development. Therefore, the expression of IGFs and their receptors may be an important intrinsic factor for embryo growth and may be a potential marker for embryo quality.

METHOD OF STUDY

Thirty donated day 3 embryos were cultured in vitro for an additional 3 days to observe their developmental potential and were semiquantitatively analyzed for the expression of IGF-I, IGF-II, IGF-IR, IGF-IIR, and insulin-R.

RESULTS

Our results show that the activity of these gene expressions correlates well with the morphological assessment and that high and more gene expressions were often associated with embryos of high growth potential.

CONCLUSION

The IGF system may indeed play an important role in human embryogenesis; IGF gene expressions can be a good indicator of embryonic developmental stage and/or growth potential; finally, the IGF system can serve as a marker for embryo quality.

Functions of proteins secreted by oviduct epithelial cells

Studies on embryonic development in vitro as well as observations in vivo, suggested that two aspects of oviduct physiology are important for early development. On one side has to be considered the oviduct "environment": temperature, pH, osmotic pressure, nutrients, oxygen tension, free radical scavengers, etc. On the other, the oviduct "active components": stimulatory and/or regulatory molecules, supposed to finely regulate the fertilisation process and the first differentiative steps. While the physical environment of the oviduct has been under investigation for some decades, studies on oviduct-specific molecules and their functions have only been developed much more recently. The amount of information on this topic, however, has rapidly reached the size that demands a summary. In this review the descriptive literature on oviduct specific proteins will be examined as a basis for illustrating the possible functions of these molecules. In particular their role in fertilisation and early embryonic cleavages will be analysed in some details. Finally a section is devoted to the presence and physiological significance of growth factors in oviduct fluid.

Transcription and localization of growth factor mRNA in the bovine oviduct

It has become evident that certain growth factors are involved in the regulation of the initial bovine embryogenesis. In the present study, we examined by means of Northern blot and in situ hybridization, the expression and localization in the bovine oviduct of mRNAs encoding for platelet-derived growth factor (PDGF-B), basic fibroblast growth factor (bFGF), and insulin-like growth factor (IGF-I). Northern blot analysis on oviduct tissue demonstrated transcripts for PDGF-B and bFGF, but not IGF-I mRNAs. Two bands with estimated sizes of 5.0 and 1.5 kb were detected for PDGF-B and two bands with sizes of 7.5 and 4.9 kb for bFGF. In situ hybridization analysis demonstrated localization of PDGF-B mRNA in the lamina epithelialis and tunica muscularis of the oviduct whereas bFGF mRNA was detected in the lamina propria. It is concluded that the lamina epithelialis and lamina propria of the oviduct represent sites of synthesis of PDGF-B and bFGF mRNA, respectively.

The role of growth factors in preimplantation development

It has become clear that the mammalian embryo participates in a complex dialogue with the maternal physiology. The language of the dialogue is growth factor signalling. The embryo expresses receptors for insulin, IGFs, GH, EGF and cytokines including LIF, and CSFs; whilst ligands are secreted by the supporting tissues of the oviduct and uterus, and in some cases, the embryo itself. In the preimplantation period when the embryo is travelling to the uterus and passing through its first differentiation, these ligands affect embryonic physiology, apparently in ways that optimise developmental potential and synchronise embryonic and maternal physiologies. It is not yet clear in most cases whether this is by autocrine, paracrine or endocrine mode. In the crucial peri-implantation phase the embryo is preparing to invade the maternal system for which extensive uterine remodelling is necessary. A model is proposed in which a cascade of growth factor activities, orchestrated by the ovarian steroid patterns, choreographs the biochemical players (ECM proteinases and their inhibitors) which initiate this activity.

Expression of IGF ligand and receptor genes during preimplantation mammalian development

The temporal patterns of expression of genes encoding insulin-like growth factor (IGF) ligands and receptors during very early development have been investigated in several laboratories in several different mammalian species. Both reverse transcription-polymerase chain reaction (RT-PCR) and immunocytochemical techniques have been used to identify the time of appearance of gene transcripts or end-products. In preimplantation mouse embryos, IGF-II ligand and receptor gene activity is detectable as early as at the two-cell stage, the time when transcription from the embryonic genome is activated, but receptors for insulin and IGF-I are not detectable until the compacted eight-cell stage. Transcripts for insulin or IGF-I are not detectable in preimplantation mouse embryos, although the ligands are present in the reproductive tract. The pattern of IGF gene expression is not, however, identical in all mammalian species. In cow embryos, for example, transcripts for IGF-I and IGF-II ligands and receptors and insulin receptors have been detected at all stages of preimplantation development from mature oocyte to blastocyst (Watson et al., 1992). Attempts to quantitate transcript abundance in these early embryos are in progress in our laboratory. In the preimplantation mouse embryo, transcripts for several different IGF-binding proteins (IGFBP-2, -3, -4, and -6) have been detected by RT-PCR procedures. In addition, transcripts for IGFBPs have been identified in RNA derived from cumulus cells, the ovary, the oviduct, the uterus, and the decidua. These findings suggest that the interactions of IGF ligands and receptors in preimplantation development might, indeed, be modulated by IGFPs.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of maturation and co-culture treatments on the developmental capacity of early bovine embryos

A total of 901 cumulus-oocyte complexes (COCs) were collected from bovine ovaries obtained at a local abattoir. COCs randomly assigned to Treatment I (n = 451), were cultured in TCM-199 + 10% fetal bovine serum (FBS) and hormones, while oocytes in Treatment II (n = 450) were cultured in TCM-199 + 20% estrous cow serum (ECS). Assessment of maturation revealed that 91.3% (42/46) of oocytes in Treatment I had reached metaphase II of meiosis, which was greater (P less than 0.05) than the 73.3% (33/45) in Treatment II. Following in vitro fertilization, 203 oocytes from Treatment I were co-cultured on bovine granulosa cells (Treatment IA) while the remaining 202 oocytes were co-cultured on bovine oviductal cells (Treatment IB). Similarly, 203 oocytes from Treatment II were co-cultured on granulosa cells (Treatment IIA) or oviductal cells (Treatment IIB, n = 202). Co-culture was maintained for 8 days. The proportion of cleaved zygotes was higher (P less than 0.05) in Treatment IB (86.6%) compared to Treatments IA (78.8%), IIA (58.1%), and IIB (64.8%). The proportion of cleaved zygotes that progressed beyond the 16-cell stage was also greater (P less than 0.001) in Treatment IB (71.4%) compared to Treatments IA (50.0%), IIA (35.4%) and IIB (55.8%). Treatment IB also produced the highest proportion of blastocysts (P less than 0.0001) (41.1%) versus 24.6% (IA), 11.3% (IIA) and 18.3% (IIB). The proportion of day 6 morulae that progressed to form day 8 blastocysts was similar for both co-culture treatments (IA, 70.1%; IB 70.2%; IIA, 51.5%; IIB 50.8%) and varied only between in vitro maturation groups.(ABSTRACT TRUNCATED AT 250 WORDS)