The interplay of maternal and offspring obesogenic diets: the impact on offspring metabolism and muscle mitochondria in an outbred mouse model

Consumption of obesogenic (OB) diets increases the prevalence of maternal obesity worldwide, causing major psychological and social burdens in women. Obesity not only impacts the mother's health and fertility but also elevates the risk of obesity and metabolic disorders in the offspring. Family lifestyle is mostly persistent through generations, possibly contributing to the growing prevalence of obesity. We hypothesized that offspring metabolic health is dependent on both maternal and offspring diet and their interaction. We also hypothesized that the sensitivity of the offspring to the diet may be influenced by the match or mismatch between offspring and maternal diets. To test these hypotheses, outbred Swiss mice were fed a control (C, 10% fat, 7% sugar, and n = 14) or OB diet (60% fat, 20% sugar, and n = 15) for 7 weeks and then mated with the same control males. Mice were maintained on the same corresponding diet during pregnancy and lactation, and the offspring were kept with their mothers until weaning. The study focused only on female offspring, which were equally distributed at weaning and fed C or OB diets for 7 weeks, resulting in four treatment groups: C-born offspring fed C or OB diets (C » C and C » OB) and OB-born offspring fed C or OB diets (OB » C and OB » OB). Adult offspring's systemic blood profile (lipid and glucose metabolism) and muscle mitochondrial features were assessed. We confirmed that the offspring's OB diet majorly impacted the offspring's health by impairing the offspring's serum glucose and lipid profiles, which are associated with abnormal muscle mitochondrial ultrastructure. Contrarily, maternal OB diet was associated with increased expression of mitochondrial complex markers and mitochondrial morphology in offspring muscle, but no additive effects of (increased sensitivity to) an offspring OB diet were observed in pups born to obese mothers. In contrast, their metabolic profile appeared to be healthier compared to those born to lean mothers and fed an OB diet. These results are in line with the thrifty phenotype hypothesis, suggesting that OB-born offspring are better adapted to an environment with high energy availability later in life. Thus, using a murine outbred model, we could not confirm that maternal obesogenic diets contribute to female familial obesity in the following generations.

Preconception Diet Interventions in Obese Outbred Mice and the Impact on Female Offspring Metabolic Health and Oocyte Quality

Obese individuals often suffer from metabolic health disorders and reduced oocyte quality. Preconception diet interventions in obese outbred mice restore metabolic health and oocyte quality and mitochondrial ultrastructure. Also, studies in inbred mice have shown that maternal obesity induces metabolic alterations and reduces oocyte quality in offspring (F1). Until now, the effect of maternal high-fat diet on F1 metabolic health and oocyte quality and the potential beneficial effects of preconception dietary interventions have not been studied together in outbred mice. Therefore, we fed female mice a high-fat/high-sugar (HF/HS) diet for 7 weeks and switched them to a control (CONT) or caloric-restriction (CR) diet or maintained them on the HF/HS diet for 4 weeks before mating, resulting in three treatment groups: diet normalization (DN), CR, and HF/HS. In the fourth group, mice were fed CONT diet for 11 weeks (CONT). HF/HS mice were fed an HF/HS diet from conception until weaning, while all other groups were then fed a CONT diet. After weaning, offspring were kept on chow diet and sacrificed at 11 weeks. We observed significantly elevated serum insulin concentrations in female HF/HS offspring and a slightly increased percentage of mitochondrial ultrastructural abnormalities, mitochondrial size, and mitochondrial mean gray intensity in HF/HS F1 oocytes. Also, global DNA methylation was increased and cellular stress-related proteins were downregulated in HF/HS F1 oocytes. Mostly, these alterations were prevented in the DN group, while, in CR, this was only the case for a few parameters. In conclusion, this research has demonstrated for the first time that a maternal high-fat diet in outbred mice has a moderate impact on female F1 metabolic health and oocyte quality and that preconception DN is a better strategy to alleviate this compared to CR.

Risks of using mitoquinone during in vitro maturation and its potential protective effects against lipotoxicity-induced oocyte mitochondrial stress

PURPOSE

Oxidative stress and mitochondrial dysfunction play central roles in reduced oocyte quality and infertility in obese patients. Mitochondria-targeted treatments containing co-enzyme Q10 such as mitoquinone (MitoQ) can increase mitochondrial antioxidative capacity; however, their safety and efficiency when supplemented to oocytes under lipotoxic conditions have not been described.

METHODS

We tested the effect of different concentrations of MitoQ or its cationic carrier (TPP) (0, 0.1, 0.5, 1.0 μM each) during bovine oocyte IVM. Then, we tested the protective capacity of MitoQ (0.1 μM) against palmitic acid (PA)-induced lipotoxicity and mitochondrial dysfunction in oocytes.

RESULTS

Exposure to MitoQ, or TPP only, at 1 μM significantly (P<0.05) reduced oocyte mitochondrial inner membrane potential (JC-1 staining) and resulted in reduced cleavage and blastocyst rates compared with solvent control. Lower concentrations of MitoQ or TPP had no effects on embryo development under control (PA-free) conditions. As expected, PA increased the levels of MMP and ROS in oocytes (CellROX staining) and reduced cleavage and blastocyst rates compared with the controls (P<0.05). These negative effects were ameliorated by 0.1 μM MitoQ. In contrast, 0.1 μM TPP alone had no protective effects. MitoQ also normalized the expression of HSP10 and TFAM, and partially normalized HSP60 in the produced blastocysts, indicating at least a partial alleviation of PA-induced mitochondrial stress.

CONCLUSION

Oocyte exposure to MitoQ may disturb mitochondrial bioenergetic functions and developmental capacity due to a TPP-induced cationic overload. A fine-tuned concentration of MitoQ can protect against lipotoxicity-induced mitochondrial stress during IVM and restore developmental competence and embryo quality.

In vitro reduction of bovine oocyte ATP production with oligomycin affects embryo epigenome

In brief

Epigenetic programming is a crucial process during early embryo development that can have a significant impact on the results of assisted reproductive technology (ART) and offspring health. Here we show evidence using a bovine in vitro experiment that embryo epigenetic programing is dependent on oocyte mitochondrial bioenergetic activity during maturation.

Abstract

This study investigated if oocyte and early embryo epigenetic programming are dependent on oocyte mitochondrial ATP production. A bovine in vitro experiment was performed in which oocyte mitochondrial ATP production was reduced using 5 nmol/L oligomycin A (OM; ATP synthase inhibitor) during in vitro maturation (IVM) compared to control (CONT). OM exposure significantly reduced mitochondrial ATP production rate in MII oocytes (34.6% reduction, P = 0.018) and significantly decreased embryo cleavage rate at 48 h post insemination (7.6% reduction, P = 0.031). Compared to CONT, global DNA methylation (5mC) levels were decreased in OM-exposed MII oocytes (9.8% reduction, P = 0.019) while global histone methylation (H3K9me2) was increased (9.4% increase, P = 0.024). In zygotes, OM exposure during IVM increased 5mC (22.3% increase, P < 0.001) and histone acetylation (H3K9ac, 17.3% increase, P = 0.023) levels, while H3K9me2 levels were not affected. In morulae, 5mC levels were increased (10.3% increase, P = 0.041) after OM exposure compared to CONT, while there was no significant difference in H3K9ac and H3K9me2 levels. These epigenetic alterations were not associated with any persistent effects on embryo mitochondrial ATP production rate or mitochondrial membrane potential (assessed at the four-cell stage). Also, epigenetic regulatory genes were not differentially expressed in OM-exposed zygotes or morulae. Finally, apoptotic cell index in blastocysts was increased after OM exposure during oocyte maturation (41.1% increase, P < 0.001). We conclude that oocyte and early embryo epigenetic programming are dependent on mitochondrial ATP production during IVM.

Oxidative stress in donor mares for ovum pick-up delays embryonic development

The in vitro production of equine embryos via ovum pick-up (OPU) and intracytoplasmic sperm injection (ICSI) has increased rapidly. There is a marked effect of the individual mare on the outcome of OPU-ICSI, but little is known about the influence of the mare's health condition. This study aimed to investigate the potential associations between the concentrations of interleukin-6 (IL-6), reactive oxygen metabolites (d-ROMs), and biological antioxidant potential (BAP) in serum of oocytes' donor mares and the subsequent embryonic development. Just before OPU, a blood sample was collected from 28 Warmblood donor mares, that were subjected to a routine OPU-ICSI program. The serum concentrations of IL-6, d-ROMs, and BAP were assayed photometrically. The maturation, cleavage and blastocyst rate as well as the kinetics of blastocyst development were recorded. The average blastocyst rate was 24.68 ± 5.16% and the average concentrations of IL-6, d-ROMs, and BAP were 519.59 ± 157.08 pg/mL, 171.30 ± 4.55 carratelli units (UCARR), and 2711.30 ± 4.55 μmol/L, respectively. Serum concentrations of IL-6, d-ROMs, and BAP were not significantly different between mares yielding at least one blastocyst (552.68 ± 235.18 pg/mL, 168.36 ± 5.56 UCARR, and 2524.80 ± 159.55 μmol/L) and mares yielding no blastocysts (468.47 ± 179.99 pg/mL, 175.85 ± 7.89 UCARR, and 2999.50 ± 300.13 μmol/L, respectively). Serum concentrations of d-ROMs were significantly lower in mares with fast growing (at day 7-8 post ICSI; 148.10 ± 8.13 UCARR) compared to those with slow growing blastocysts (≥ day 9 post ICSI; 179.41 ± 4.89 UCARR; P = 0.003). Taken together, the serum concentration of IL-6, d-ROMs, and BAP do not determine the mare's ability to produce blastocysts in vitro. Although it may be questioned whether a single sample is representative of the mare's health status, changes in serum metabolites related to oxidative stress at the time of oocyte retrieval were linked to a delayed blastocyst development in a clinical OPU-ICSI outcome.

Effect of lipotoxicity on mitochondrial function and epigenetic programming during bovine in vitro embryo production

Maternal metabolic disorders may cause lipotoxic effects on the developing oocyte. Understanding the timing at which this might disrupt embryo epigenetic programming and how this is linked with mitochondrial dysfunction is crucial for improving assisted reproductive treatments, but has not been investigated before. Therefore, we used a bovine in vitro model to investigate if pathophysiological palmitic acid (PA) concentrations during in vitro oocyte maturation and in vitro embryo culture alter embryo epigenetic patterns (DNA methylation (5mC) and histone acetylation/methylation (H3K9ac/H3K9me2)) compared to control (CONT) and solvent control (SCONT), at the zygote and morula stage. Secondly, we investigated if these epigenetic alterations are associated with mitochondrial dysfunction and changes in ATP production rate, or altered expression of epigenetic regulatory genes. Compared to SCONT, H3K9ac and H3K9me2 levels were increased in PA-derived zygotes. Also, 5mC and H3K9me2 levels were increased in PA-exposed morulae compared to SCONT. This was associated with complete inhibition of glycolytic ATP production in oocytes, increased mitochondrial membrane potential and complete inhibition of glycolytic ATP production in 4-cell embryos and reduced SOD2 expression in PA-exposed zygotes and morulae. For the first time, epigenetic alterations in metabolically compromised zygotes and morulae have been observed in parallel with mitochondrial dysfunction in the same study.

Lipid metabolites, interleukin-6 and oxidative stress markers in follicular fluid and their association with serum concentrations in mares

The application of trans-vaginal ovum pick up (OPU) and intracytoplasmic sperm injection (ICSI) is well established for commercial in vitro embryo production in horses. These assisted reproductive techniques are especially applied during the non-breeding season of the mare. However, little is known about how the health of the oocyte donor may affect the biochemical composition of the follicular fluid (FF) in small and medium-sized follicles routinely aspirated during OPU. This study aimed to investigate associations between systemic and FF concentrations of interleukin-6 (IL-6), total cholesterol, triglycerides, non-esterified fatty acids (NEFA), reactive oxygen metabolites (d-ROMs), biological antioxidant potential (BAP), and oxidative stress index (OSI) during the non-breeding season in mares. At the slaughterhouse, serum and FF of small (5-10 mm in diameter), medium (> 10-20 mm in diameter), and large (> 20-30 mm in diameter) follicles were sampled from 12 healthy mares. There was a strong positive association (P < 0.01) between the concentration of IL-6 in serum and those measured in small (r = 0.846), medium (r = 0.999), and large (r = 0.996) follicles. Serum concentrations of NEFA were positively correlated (P < 0.05) with those measured in small (r = 0.726), medium (r = 0.720), and large (r = 0.974) follicles. Values of total cholesterol and OSI in serum and medium follicles were significantly associated (r = 0.736 and r = 0.696, respectively). The serum concentrations of all lipid metabolites were markedly higher than those measured in FF of small- and medium-sized follicles. Values of IL-6 and OSI did not change significantly between serum and all follicle classes (P ≥ 0.05). To conclude, changes in the blood composition associated with inflammation, oxidative stress, and disturbed lipid metabolism of mares may lead to an inadequate oocyte microenvironment, which could affect oocyte quality and the success rate of OPU/ICSI programs. Further research should indicate whether these changes may ultimately affect in vitro oocyte developmental capacity and subsequent embryo quality.

The impact of a maternal and offspring obesogenic diet on daughter's oocyte mitochondrial ultrastructure and bioenergetic responses. Insights from an outbred mouse model

Obesity affects oocyte mitochondrial functions and reduces oocyte quality and fertility. Obesity may also increase the risk of metabolic disorders in the offspring. Children are likely to follow their parents lifestyle and diet, which also contributes to the increased prevelance of obesity across generations. We hypothesise that the impact of obesogenic (OB) diet and obesity on oocyte mitochondrial functions is different in offspring born to obese mothers compared to those born to healthy mothers. To test this hypothesis, we fed a control (C, 10% fat, 7% sugar) or an OB diet (60% fat, 20% sugar) to female mice (for 7 weeks (w)) and then to their female offspring (for 7w after weaning) in a 2 × 2 factorial design (C » C, n = 35, C » OB, n = 35, OB » C n = 49 and OB » OB, n = 50). Unlike many other studies, we used an outbred Swiss mouse model to increase the human pathophysiological relevance. Offspring were sacrificed at 10w and their oocytes were collected. Offspring OB diet increased oocyte lipid droplet content, mitochondrial activity and reactive oxygen species (ROS) levels, altered mitochondrial ultrastructure and reduced oocyte pyruvate consumption. Mitochondrial DNA copy numbers and lactate production remained unaffected. Mitochondrial ultrastructure was the only factor where a significant interaction between maternal and offspring diet effect was detected. The maternal OB background resulted in a small but significant increase in offspring's oocyte mitochondrial ultrastructural abnormalities without altering mitochondrial inner membrane potential, active mitochondrial distribution, mitochondrial DNA copy numbers, or ROS production. This was associated with reduced mitochondrial complex III and V expression and reduced pyruvate consumption which may be compensatory mechanisms to control mitochondrial inner membrane potential and ROS levels. Therefore, in this Swiss outbred model, while offspring OB diet had the largest functional impact on oocyte mitochondrial features, the mitochondrial changes due to the maternal background appear to be adaptive and compensatory rather than dysfunctional.

How the Oviduct Lipidomic Profile Changes over Time after the Start of an Obesogenic Diet in an Outbred Mouse Model

We investigated whether a high-fat/high-sugar (HF/HS) diet alters the lipidomic profile of the oviductal epithelium (OE) and studied the patterns of these changes over time. Female outbred Swiss mice were fed either a control (10% fat) or HF/HS (60% fat, 20% fructose) diet. Mice (n = 3 per treatment per time point) were sacrificed and oviducts were collected at 3 days and 1, 4, 8, 12 and 16 weeks on the diet. Lipids in the OE were imaged using matrix-assisted laser desorption ionisation mass spectrometry imaging. Discriminative m/z values and differentially regulated lipids were determined in the HF/HS versus control OEs at each time point. Feeding the obesogenic diet resulted in acute changes in the lipid profile in the OE already after 3 days, and thus even before the development of an obese phenotype. The changes in the lipid profile of the OE progressively increased and became more persistent after long-term HF/HS diet feeding. Functional annotation revealed a differential abundance of phospholipids, sphingomyelins and lysophospholipids in particular. These alterations appear to be not only caused by the direct accumulation of the excess circulating dietary fat but also a reduction in the de novo synthesis of several lipid classes, due to oxidative stress and endoplasmic reticulum dysfunction. The described diet-induced lipidomic changes suggest alterations in the OE functions and the oviductal microenvironment which may impact crucial reproductive events that take place in the oviduct, such as fertilization and early embryo development.

Genesis of clinical and subclinical endometritis in dairy cows

Up to half of dairy cows may develop one or more types of reproductive tract inflammatory disease within 5 weeks after calving. Clinical endometritis (CE) results from uterine bacterial dysbiosis with increased relative abundance of pathogenic bacteria associated with luminal epithelial damage. These bacteria cause endometrial stromal cell lysis, followed by massive polymorphonuclear neutrophil (PMN) migration, and pyogenesis. Clinical endometritis is defined as endometrial inflammation accompanied by purulent discharge. Purulent discharge is not always accompanied by uterine inflammation (being (rarely) vaginitis or (commonly) cervicitis), hence referred to as purulent vaginal discharge (PVD). Subclinical endometritis (SCE) is an asymptomatic uterine disease defined by a threshold of PMN on cytology that is associated with worse reproductive performance; it has not been linked with bacterial dysbiosis. Current evidence suggests that SCE is a result of metabolic and inflammatory dysfunction that impairs innate immune function and the ability of endometrial PMN to undergo apoptosis, necrosis, and ultimately achieve resolution of inflammation. Clinical endometritis and SCE are diagnosed between 3 and 5 weeks postpartum and commonly overlap, but they are considered distinct manifestations of reproductive tract inflammatory disease. This review addresses the genesis of CE and SCE in postpartum dairy cows considering metabolic stress, innate immune dysfunction, and shifts in the composition of the uterine microbiota.

Viability and function dynamics of circulating versus endometrial polymorphonuclear leukocytes in postpartum dairy cows with subclinical or clinical endometritis

We aimed to compare the viability of circulating polymorphonuclear leukocyte (cPMN) and endometrial PMN (ePMN) and their function dynamics in postpartum dairy cows with subclinical (SCE) or clinical endometritis (CE). To do so, blood samples from 38 Holstein cows were collected at -7, 9, 21, and 36 d relative to calving, and endometrial cytology samples from 32 Holstein cows were harvested at 9, 21, and 36 d postpartum. Uterine health status was assessed at 36 d postpartum, and cows were classified as healthy (absence of abnormal vaginal discharge and ≤5% ePMN), SCE (absence of abnormal vaginal discharge and >5% ePMN), or CE (mucopurulent or purulent vaginal discharge and >5% ePMN). Viability (viable, apoptotic, and necrotic) and function parameters phagocytosis (PC), oxidative burst, and intracellular proteolytic degradation were evaluated for cPMN via flow cytometry. For ePMN, only viability and PC were evaluated. The association of cPMN and ePMN viability and functional parameters with reproductive tract health classification were fitted in mixed linear regression models, accounting for repeated measures, sampling day, and interactions of reproductive tract status and day. Cows with CE had a lower proportion of cPMN viability (84.5 ± 2.1%; least squares means ± standard error) and a higher proportion of apoptosis (14.4 ± 2.0%) than healthy (92.4 ± 1.3 and 6.7 ± 1.3%, respectively) or SCE (95.3 ± 2.4 and 3.8 ± 2.3%, respectively) at 9 d postpartum. Interestingly, cPMN intracellular proteolytic degradation was lower [6.2 ± 0.1 median fluorescence intensity (MFI)] in SCE compared with healthy (6.7 ± 0.08 MFI) or CE (6.8 ± 0.1 MFI) at d 9 postpartum. No other differences in cPMN function were found among experimental groups. The proportion of necrotic ePMN was higher for healthy (49.6 ± 5.1%) than SCE (27.4 ± 7.3%) and CE (27.7 ± 7.3%) cows at 36 d postpartum. Also, at 36 d postpartum, the proportion of ePMN performing PC was higher in CE (47.0 ± 8.6%) than in healthy (18.4 ± 7.6%) cows, but did not differ from SCE cows (25.9 ± 8.7%). Results of the present study suggest that cPMN viability and function at 9 d postpartum are associated with the development of uterine disease. Furthermore, ePMN at 36 d postpartum are mostly necrotic in healthy cows but viable and functional in cows with CE, probably due to active uterine inflammation. Remarkably, ePMN in cows with SCE at 36 d postpartum are also mostly viable but seem to display a numerically lower proportion of PC compared with ePMN in CE cows.

Oocyte developmental capacity is influenced by intrinsic ovarian factors in a bovine model for individual embryo production

The ovary and its hormones may have major effects on the in vitro developmental capacity of the oocytes it contains. We related intrinsic ovarian factors namely the presence of corpus luteum (CL) and/or dominant follicle (>8 mm) and the follicular count to cumulus expansion (CE), embryo development, and blastocyst quality in a bovine model. Cumulus-oocyte-complexes (COCs) were aspirated from follicles between 4 and 8 mm in diameter. In vitro embryo production was performed in a fully individual production system. The follicular fluid from which COCs were collected was pooled (per ovary) to evaluate the estrogen, progesterone, and insulin-like growth factor-1 (IGF-1) concentrations. Cumulus oocyte complexes collected from ovaries without a CL presented a greater CE than COCs derived from ovaries bearing CL. The absence of ovarian structures increased the blastocyst rate when compared to oocytes derived from ovaries with a CL, a dominant follicle, or both. Blastocysts derived from ovaries without a dominant follicle presented higher total cell numbers and a lower proportion of apoptosis than blastocysts derived from ovaries containing a dominant follicle. Cumulus oocyte complexes collected from ovaries with high follicular count resulted in higher cleavage than from ovaries with low follicular count, but the blastocyst rate was similar between groups. Ovaries bearing a CL had greater progesterone and IGF-1 follicular fluid concentrations in neighboring follicles than ovaries without a CL. Selection for bovine ovaries without CL or dominant follicle can have positive effects on CE, embryo development, and blastocyst quality in an individual embryo production system set-up.

Endometrial receptivity in cattle: the mutual reprogramming paradigm

Prior to implantation in cattle, the mucous medium contained in the uterine lumen serves as a working interface for molecular exchange and signaling between the lining endometrium and the embryo. The composition of this luminal fluid changes temporally according to the secretory and reabsorptive activities of the uterus and the embryo, which are under complex regulation. Via this interface, both the embryo and the endometrium reprogram each other's functions to support pregnancy continuation beyond the pre-implantation period. More specifically, the embryo receives elongation signals and the uterus receives anti-luteolytic stimuli. Here, characteristics of the luminal compartment as well as the regulation of its composition to determine the pregnancy outcome will be discussed.

Maternal metabolic health and fertility: we should not only care about but also for the oocyte!

Metabolic disorders due to obesity and unhealthy lifestyle directly alter the oocyte's microenvironment and impact oocyte quality. Oxidative stress and mitochondrial dysfunction play key roles in the pathogenesis. Acute effects on the fully grown oocytes are evident, but early follicular stages are also sensitive to metabolic stress leading to a long-term impact on follicular cells and oocytes. Improving the preconception health is therefore of capital importance but research in animal models has demonstrated that oocyte quality is not fully recovered. In the in vitro fertilisation clinic, maternal metabolic disorders are linked with disappointing assisted reproductive technology results. Embryos derived from metabolically compromised oocytes exhibit persistently high intracellular stress levels due to weak cellular homeostatic mechanisms. The assisted reproductive technology procedures themselves form an extra burden for these defective embryos. Minimising cellular stress during culture using mitochondrial-targeted therapy could rescue compromised embryos in a bovine model. However, translating such applications to human in vitro fertilisation clinics is not simple. It is crucial to consider the sensitive epigenetic programming during early development. Research in humans and relevant animal models should result in preconception care interventions and in vitro strategies not only aiming at improving fertility but also safeguarding offspring health.

Obese outbred mice only partially benefit from diet normalization or calorie restriction as preconception care interventions to improve metabolic health and oocyte quality

STUDY QUESTION

Can diet normalization or a calorie-restricted diet for 2 or 4 weeks be used as a preconception care intervention (PCCI) in Western-type diet-induced obese Swiss mice to restore metabolic health and oocyte quality?

SUMMARY ANSWER

Metabolic health and oocyte developmental competence was already significantly improved in the calorie-restricted group after 2 weeks, while obese mice that underwent diet normalization showed improved metabolic health after 2 weeks and improved oocyte quality after 4 weeks.

WHAT IS KNOWN ALREADY

Maternal obesity is linked with reduced metabolic health and oocyte quality; therefore, infertile obese women are advised to lose weight before conception to increase pregnancy chances. However, as there are no univocal guidelines and the specific impact on oocyte quality is not known, strategically designed studies are needed to provide fundamental insights in the importance of the type and duration of the dietary weight loss strategy for preconception metabolic health and oocyte quality.

STUDY DESIGN, SIZE, DURATION

Outbred female Swiss mice were fed a control (CTRL) or high-fat/high-sugar (HF/HS) diet. After 7 weeks, some of the HF mice were put on two different PCCIs, resulting in four treatment groups: (i) only control diet for up to 11 weeks (CTRL_CTRL), (ii) only HF diet for up to 11 weeks (HF_HF), (iii) switch at 7 weeks from an HF to an ad libitum control diet (HF_CTRL) and (iv) switch at 7 weeks from an HF to a 30% calorie-restricted control diet (HF_CR) for 2 or 4 weeks. Metabolic health and oocyte quality were assessed at 2 and 4 weeks after the start of the intervention (n = 8 mice/treatment/time point).

PARTICIPANTS/MATERIALS, SETTING, METHODS

Changes in body weight were recorded. To study the impact on metabolic health, serum insulin, glucose, triglycerides, total cholesterol and alanine aminotransferase concentrations were measured, and glucose tolerance and insulin sensitivity were analyzed at PCCI Weeks 2 and 4. The quality of in vivo matured oocytes was evaluated by assessing intracellular lipid droplet content, mitochondrial activity and localization of active mitochondria, mitochondrial ultrastructure, cumulus cell targeted gene expression and oocyte in vitro developmental competence.

MAIN RESULTS AND THE ROLE OF CHANCE

Significant negative effects of an HF/HS diet on metabolic health and oocyte quality were confirmed (P < 0.05). HF_CTRL mice already showed restored body weight, serum lipid profile and glucose tolerance, similar to the CTRL_CTRL group after only 2 weeks of PCCI (P < 0.05 compared with HF_HF) while insulin sensitivity was not improved. Oocyte lipid droplet volume was reduced at PCCI Week 2 (P < 0.05 compared with HF_HF), while mitochondrial localization and activity were still aberrant. At PCCI Week 4, oocytes from HF_CTRL mice displayed significantly fewer mitochondrial ultrastructural abnormalities and improved mitochondrial activity (P < 0.05), while lipid content was again elevated. The in vitro developmental capacity of the oocytes was improved but did not reach the levels of the CTRL_CTRL mice. HF_CR mice completely restored cholesterol concentrations and insulin sensitivity already after 2 weeks. Other metabolic health parameters were only restored after 4 weeks of intervention with clear signs of fasting hypoglycemia. Although all mitochondrial parameters in HF_CR oocytes stayed aberrant, oocyte developmental competence in vitro was completely restored already after 2 weeks of intervention.

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

In this study, we applied a relevant HF/HS Western-type diet to induce obesity in an outbred mouse model. Nevertheless, physiological differences should be considered when translating these results to the human setting. However, the in-depth study and follow-up of the metabolic health changes together with the strategic implementation of specific PCCI intervals (2 and 4 weeks) related to the duration of the mouse folliculogenesis (3 weeks), should aid in the extrapolation of our findings to the human setting.

WIDER IMPLICATIONS OF THE FINDINGS

Our study results with a specific focus on oocyte quality provide important fundamental insights to be considered when developing preconception care guidelines for obese metabolically compromised women wishing to become pregnant.

STUDY FUNDING/COMPETING INTEREST(S)

This study was supported by the Flemish Research Fund (FWO-SB grant 1S25020N and FWO project G038619N). The authors declare there are no conflicts of interest.

Effects of an obesogenic diet on the oviduct depend on the duration of feeding

Research question

How long does it take for an obesogenic (high-fat/high-sugar, HF/HS) diet to influence the oviductal microenvironment? What are the affected cellular pathways and are they dependent on the genetic background of the mouse model?

Design

Female Swiss (outbred) and C57BL/6N (B6, inbred) mice were fed either a control (10% fat) or HF/HS (60% fat, 20% fructose) diet. Body weight was measured weekly. Mice were sacrificed at 3 days (3d), 1 week (1w), 4w, 8w, 12w and 16w on the diet (n = 5 per treatment per time point). Total cholesterol concentrations and inflammatory cytokines were measured in serum. Oviductal epithelial cells (OECs) were used to study the expression of genes involved in (mitochondrial) oxidative stress (OS), endoplasmic reticulum (ER) stress and inflammation using qPCR.

Results

Body weight and blood cholesterol increased significantly in the HF/HS mice in both strains compared to controls. In Swiss mice, HF/HS diet acutely increased ER-stress and OS-related genes in the OECs already after 3d. Subsequently, mitochondrial and cytoplasmic antioxidants were upregulated and ER-stress was alleviated at 1w. After 4-8w (mid-phase), the expression of ER-stress and OS-related genes was increased again and persisted throughout the late-phase (12-16w). Serum inflammatory cytokines and inflammatory marker-gene expression in the OECs were increased only in the late-phase. Some of the OEC stress responses were stronger or earlier in the B6.

Conclusions

OECs are sensitive to an obesogenic diet and may exhibit acute stress responses already after a few days of feeding. This may impact the oviductal microenvironment and contribute to diet-induced subfertility.

Metabolic and antioxidant status during transition is associated with changes in the granulosa cell transcriptome in the preovulatory follicle in high-producing dairy cows at the time of breeding

In this study, we hypothesized that early postpartum (pp) metabolic and oxidative stress conditions in dairy cows (particularly those with severe negative energy balance, NEB) are associated with long-term changes in granulosa cell (GC) functions in the preovulatory follicle at the time of breeding. Blood samples were collected at wk 2 and wk 8 pp from 47 healthy multiparous cows. Follicular fluid (FF) and GC were collected from the preovulatory follicle after estrous synchronization at wk 8. Several metabolic and antioxidant parameters were measured in blood and FF, and their correlations were studied. Subsequently, 27 representative GC samples were selected for RNA sequencing analysis. The GC gene expression data of LH-responsive genes and the estradiol:progesterone ratio in FF were used to identify pre- and post-LH surge cohorts. We compared the transcriptomic profile of subgroups of cows within the highest and lowest quartiles (Q4 vs. Q1) of each parameter, focusing on the pre-LH surge cohort (n = 16, at least 3 in each subgroup). Differentially expressed genes (DEG: adjusted P-value < 0.05, 5% false discovery rate) were determined using DESeq2 analysis and were functionally annotated. Blood and FF β-carotene and vitamin E concentrations at wk 2, but not at wk 8, were associated with the most pronounced transcriptomic differences in the GC, with up to 341 DEG indicative for lower catabolism, increased oxidoreductase activity and signaling cascades that are known to enhance oocyte developmental competence, increased responsiveness to LH, and a higher steroidogenic activity. In contrast, elevated blood NEFA concentrations at wk 2 (and not at wk 8) were associated with a long-term carryover effect detectable in the GC transcriptome at wk 8 (64 DEG). These genes are related to response to lipids and ketones, oxidative stress, and immune responses, which suggests persistent cellular stress and oxidative damage. This effect was more pronounced in cows with antioxidant deficiencies at wk 8 (up to 148 DEG), with more genes involved in oxidative stress-dependent responses, apoptosis, autophagy and catabolic processes, and mitochondrial damage. Interestingly, within the severe NEB cows (high blood NEFA at wk 2), blood antioxidant concentrations (high vs. low) at wk 8 were associated with up to 194 DEG involved in activation of meiosis and other signaling pathways, indicating a better oocyte supportive capacity. This suggests that the cow antioxidant profile at the time of breeding might alleviate, at least in part, the effect of NEB on GC functions. In conclusion, these results provide further evidence that the metabolic and oxidative stress in dairy cows early postpartum can have long-term effects on GC functions in preovulatory follicles at the time of breeding. The interplay between the effects of antioxidants and NEFA illustrated here might be useful to develop intervention strategies to minimize the effect of severe NEB on fertility.

Maladaptation to the transition period and consequences on fertility of dairy cows

After parturition, dairy cows undergo a plethora of metabolic, inflammatory, and immunologic changes to adapt to the onset of lactation. These changes are mainly due to the homeorhetic shift to support milk production when nutrient demand exceeds dietary intake, resulting in a state of negative energy balance. Negative energy balance in postpartum dairy cows is characterized by upregulated adipose tissue modelling, insulin resistance, and systemic inflammation. However, half of the postpartum cows fail to adapt to these changes and develop one or more types of clinical and subclinical disease within 5 weeks after calving, and this is escorted by impaired reproductive performance in the same lactation. Maladaptation to the transition period exerts molecular and structural changes in the follicular and reproductive tract fluids, the microenvironment in which oocyte maturation, fertilization, and embryo development occur. Although the negative effects of transition diseases on fertility are well-known, the involved pathways are only partially understood. This review reconstructs the mechanism of maladaptation to lactation in the transition period, explores their key (patho)physiological effects on reproductive organs, and briefly describes potential carryover effects on fertility in the same lactation.

Cellular Stress Responses in Oocytes: Molecular Changes and Clinical Implications

The oocyte may be exposed to several sources of stress during its growth and maturation, which may lead to reduced fertility. Unfolded protein responses (UPRs) play a central role to maintain cell survival and repair. Transcription of heat shock proteins (HSPs) is a key element to facilitate reestablishment of cellular homeostasis. Unlike somatic cells, cellular mechanisms by which oocytes can sense and respond to stress are not well described. In here, we provide an overview about the impact of cellular stress, particularly due to lipotoxicity, oxidative stress, and heat stress on oocyte developmental competence. Next, we focus on the expression of HSPs in oocytes and their potential role in UPRs in oocytes and embryos. This is based on a comprehensive shotgun proteomic analysis of mature bovine oocytes performed in our laboratory, as well as a literature review. The topic is discussed in light of our understanding of similar mechanisms in other cell types and the limited transcriptional activity in oocytes. More fundamental research is needed both at the transcriptomic and proteomic levels to further understand cell stress response mechanisms in oocytes and early developing embryos, their critical interactions, and their long-term effects. Strategies to provide targeted external support to prevent or reduce cell stress levels during oocyte maturation or early embryo development under maternal metabolic stress conditions should be developed to maximize the odds of producing good quality embryos and guarantee optimal viability.

Diet normalization or caloric restriction as a preconception care strategy to improve metabolic health and oocyte quality in obese outbred mice

BACKGROUND

Maternal metabolic disorders are linked to reduced metabolic health and oocyte quality. Obese women are advised to lose weight before conception to increase pregnancy chances. However, as human studies show no univocal guidelines, more research is necessary to provide fundamental insights in the consequences of dietary weight loss on oocyte quality. Therefore, we investigated the impact of diet normalization or calorie restricted diet for two, four or six weeks, as preconception care intervention (PCCI), in obese mice on metabolic health and oocyte quality.

METHODS

Outbred female mice were fed a control (CTRL) or high-fat (HF) diet for 7 weeks (7w). Afterwards, HF-mice were put on different PCCIs, resulting in four treatment groups: 1) control diet up to 13w, 2) HF diet up to 13w (HF_HF), switch from a HF (7w) to 3) an ad libitum control diet (HF_CTRL) or 4) 30% calorie restricted control diet (HF_CR) for two, four or six weeks. Body weight, metabolic health, oocyte quality and overall fertility results were assessed.

RESULTS

Negative effects of HF diet on metabolic health, oocyte quality and pregnancy rates were confirmed. HF_CTRL mice progressively improved insulin sensitivity, glucose tolerance, serum insulin and cholesterol from PCCI w2 to w4. No further improvements in metabolic health were present at PCCI w6. However, PCCI w6 showed best oocyte quality improvements. Mature oocytes still showed elevated lipid droplet volume and mitochondrial activity but a significant reduction in ROS levels and ROS: active mitochondria ratio compared with HF_HF mice. HF_CR mice restored overall insulin sensitivity and glucose tolerance by PCCI w4. However, serum insulin, cholesterol and ALT remained abnormal. At PCCI w6, glucose tolerance was again reduced. However, only at PCCI w6, oocytes displayed reduced ROS levels and restored mitochondrial activity compared with HF_HF mice. In addition, at PCCI w6, both PCCI groups showed decreased mitochondrial ultrastructural abnormalities compared with the HF_HF group and restored pregnancy rates.

CONCLUSIONS

Diet normalization for 4 weeks showed to be the shortest, most promising intervention to improve metabolic health. Most promising improvements in oocyte quality were seen after 6 weeks of intervention in both PCCI groups. This research provides fundamental insights to be considered in developing substantiated preconception guidelines for obese women planning for pregnancy.

Molecular interactions at the bovine embryo-endometrial epithelium interface

In cattle, pre-implantation embryo development occurs within the confinement of the uterine lumen. Current understanding of the bi-lateral molecular interactions between embryo and endometrium that are required for a successful pregnancy is limited. We hypothesized that the nature and intensity of reciprocal embryo-endometrium interactions depend on the extent of their physical proximity. Bovine endometrial epithelial cells (bEECs) and morulae were co-cultured in juxtacrine (Contact+) or non-juxtacrine (Contact-) apposition. Co-culture with bEECs improved blastocyst rates on day 7.5, regardless of juxtaposition. Contact+ regulated transcription of 1797 endometrial genes vs only 230 in the Contact- group compared to their control (no embryos) counterparts. A subset of 50 overlapping differentially expressed genes (DEGs) defined embryo-induced effects on bEEC transcriptome irrespective of juxtaposition. Functional analysis revealed pathways associated with interferon signaling and prostanoid biosynthesis. A total of 175 genes displayed a graded expression level depending on Contact+ or Contact-. These genes were involved in interferon-related and antigen presentation pathways. Biological processes enriched exclusively in Contact+ included regulation of cell cycle and sex-steroid biosynthesis. We speculate that, in vivo, embryonic signals fine-tune the function of surrounding cells to ultimately maximize pregnancy success.

O-155 Dietary caloric normalization or restriction as preconception care strategies: impact on oocyte developmental competence and quality in high fat/high sugar-induced obese outbred mice

Study question

Can diet normalization or caloric restriction (CR) for two weeks be used as a preconception care intervention in obese Swiss mice to restore oocyte development and quality

Summary answer

Diet normalization or CR as short-term preconception care interventions in obese mice only partially restored oocyte quality but did improve overall developmental competence.

What is known already

Maternal metabolic disorders like obesity and metabolic syndrome may result in decreased oocyte and embryo quality, and thus reproductive failure. Overweight and obese patients are advised to lose weight before conception to increase the chance of a healthy pregnancy. However, as human studies show no univocal guidelines, more fundamental research might provide additional answers. In order to avoid interference with increased maternal age, the question remains if oocyte quality can be restored after only a short preconception care intervention (PCCI).

Study design, size, duration

Outbred mice were fed a control (CTRL) or high-fat/high-sugar (HF) diet for seven weeks. Afterwards, HF-mice were put on different PCCIs for two weeks, resulting in four treatment groups: control diet (9w; CTRL_CTRL), HF diet (9w; HF_HF), switch from HF (7w) to an ad libitum control diet for 2w (HF_CTRL) or to a 30% CR diet for 2w (HF_CR). Oocyte developmental competence (n = 357) and quality (12-16 oocytes /treatment, scored blinded) were determined, using 6-8 mice/treatment.

Participants/materials, setting, methods

Body weight changes were recorded. In vivo matured oocytes were collected after superovulation and analysed for quality or in vitro fertilized and cultured. Oocyte quality was determined by staining for lipid content (Bodipy) and mitochondrial inner membrane potential and active mitochondria localization (JC-1). Oocyte developmental competence [cleavage (24h p.i.) and blastocyst rates (5 days p.i.)] was scored. Categorical and numerical data were analysed using binary logistic regression and ANOVA, respectively and corrected for multiple testing.

Main results and the role of chance

Compared to the CTRL group, HF diet increased body weight after 7 weeks by 24.19% (P &lt; 0.001). After the start of the PCCI, both HF_CTRL and HF_CR mice progressively lost weight and reached values similar to control mice after two weeks. HF_HF diet increased the intracellular lipid content in oocytes with 54.3% compared to the CTRL_CTRL group (P &lt; 0.05). This increased content was (partially) normalized in both preconception care intervention groups, even similar to the control levels in the HF_CTRL group. Both HF_HF and HF_CR oocytes showed a tendency to an increased ratio of active/total mitochondria when compared to the CTRL_CTRL group (P = 0.081, P = 0.083 respectively). In addition, active oocyte mitochondria in the HF_HF group were less pericortically distributed compared to controls. This was also the case in both preconception care intervention groups (P &lt; 0.05). After two weeks of PCCI, oocytes from HF_HF mice displayed lower cleavage rates than those from CTRL_CTRL mice (36.26% vs. 64.52%, P &lt; 0.05) but blastocyst rates (26.37% vs. 35.48%, P &gt; 0.1) were not different. HF_CR, but not HF_CTRL, oocytes showed higher cleavage rates (68.48%, P &lt; 0.001) compared with HF_HF oocytes. Moreover, both HF_CTRL (44.64%, P &lt; 0.05) and HF_CR (59.78%, P &lt; 0.001) oocytes showed improved blastocyst rates when compared to the HF_HF group (26.37%).

Limitations, reasons for caution

Although using a mouse model has several advantages, translating these results to the human setting is a limitation of this study. However, to improve this translatability, an outbred mouse model was used. Additional data will be collected to gain more information regarding the best preconception care intervention advice.

Wider implications of the findings

This research aims to provide fundamental insights in order to be able to formulate clear preconception guidelines to obese women planning for pregnancy. In addition, we aim to find the shortest possible intervention period to improve fertility.

Trial registration number

Not applicable

Oocyte maturation under lipotoxic conditions induces carryover transcriptomic and functional alterations during post-hatching development of good-quality blastocysts: novel insights from a bovine embryo-transfer model

STUDY QUESTION

Does oocyte maturation under lipolytic conditions have detrimental carry-over effects on post-hatching embryo development of good-quality blastocysts after transfer?

SUMMARY ANSWER

Surviving, morphologically normal blastocysts derived from bovine oocytes that matured under lipotoxic conditions exhibit long-lasting cellular dysfunction at the transcriptomic and metabolic levels, which coincides with retarded post-hatching embryo development.

WHAT IS KNOWN ALREADY

There is increasing evidence showing that following maturation in pathophysiologically relevant lipotoxic conditions (as in obesity or metabolic syndrome), surviving blastocysts of good (transferable) morphological quality have persistent transcriptomic and epigenetic alteration even when in vitro embryo culture takes place under standard conditions. However, very little is known about subsequent development in the uterus after transfer.

STUDY DESIGN, SIZE, DURATION

Bovine oocytes were matured in vitro in the presence of pathophysiologically relevant, high non-esterified fatty acid (NEFA) concentrations (HIGH PA), or in basal NEFA concentrations (BASAL) as a physiological control. Eight healthy multiparous non-lactating Holstein cows were used for embryo transfers. Good-quality blastocysts (pools of eight) were transferred per cow, and cows were crossed over for treatments in the next replicate. Embryos were recovered 7 days later and assessed for post-hatching development, phenotypic features and gene expression profile. Blastocysts from solvent-free and NEFA-free maturation (CONTROL) were also tested for comparison.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Recovered Day 14 embryos were morphologically assessed and dissected into embryonic disk (ED) and extraembryonic tissue (EXT). Samples of EXT were cultured for 24 h to assess cellular metabolic activity (glucose and pyruvate consumption and lactate production) and embryos' ability to signal for maternal recognition of pregnancy (interferon-τ secretion; IFN-τ). ED and EXT samples were subjected to RNA sequencing to evaluate the genome-wide transcriptome patterns.

MAIN RESULTS AND THE ROLE OF CHANCE

The embryo recovery rate at Day 14 p.i. was not significantly different among treatment groups (P > 0.1). However, higher proportions of HIGH PA embryos were retarded in growth (in spherical stage) compared to the more elongated tubular stage embryos in the BASAL group (P < 0.05). Focusing on the normally developed tubular embryos in both groups, HIGH PA exposure resulted in altered cellular metabolism and altered transcriptome profile particularly in pathways related to redox-regulating mechanisms, apoptosis, cellular growth, interaction and differentiation, energy metabolism and epigenetic mechanisms, compared to BASAL embryos. Maturation under BASAL conditions did not have any significant effects on post-hatching development and cellular functions compared to CONTROL.

LARGE-SCALE DATA

The datasets of RNA sequencing analysis are available in the NCBI's Gene Expression Omnibus (GEO) repository, series accession number GSE127889 (https://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE127889). Datasets of differentially expressed genes and their gene ontology functions are available in the Mendeley datasets at http://dx.doi.org/10.17632/my2z7dvk9j.2.

LIMITATIONS, REASONS FOR CAUTION

The bovine model was used here to allow non-invasive embryo transfer and post-hatching recovery on Day 14. There are physiological differences in some characteristics of post-hatching embryo development between human and cows, such as embryo elongation and trophoblastic invasion. However, the main carry-over effects of oocyte maturation under lipolytic conditions described here are evident at the cellular level and therefore may also occur during post-hatching development in other species including humans. In addition, post-hatching development was studied here under a healthy uterine environment to focus on carry-over effects originating from the oocyte, whereas additional detrimental effects may be induced by maternal metabolic disorders due to adverse changes in the uterine microenvironment. RNA sequencing results were not verified by qPCR, and no solvent control was included.

WIDER IMPLICATIONS OF THE FINDINGS

Our observations may increase the awareness of the importance of maternal metabolic stress at the level of the preovulatory oocyte in relation to carry-over effects that may persist in the transferrable embryos. It should further stimulate new research about preventive and protective strategies to optimize maternal metabolic health around conception to maximize embryo viability and thus fertility outcome.

STUDY FUNDING/COMPETING INTEREST(S)

This study was supported by the Flemish Research Fund (FWO grant 11L8716N and FWO project 42/FAO10300/6541). The authors declare there are no conflicts of interest.

Effect of overconditioning on the hepatic global gene expression pattern of dairy cows at the end of pregnancy

Overconditioning is a risk factor for upregulated pre- and postpartum fat mobilization. Therefore, we hypothesized that overconditioning at the end of pregnancy leads to the accumulation of lipids in the liver and modifications of the hepatic gene expression pattern. The aim of this study was to evaluate the effect of normal- versus overconditioning on the hepatic transcriptomic profile of dairy cows at the end of pregnancy. Ten dry multiparous Holstein cows were killed 2 wk before expected calving. Body condition score (BCS) and backfat thickness (BFT) were evaluated, and blood samples for nonesterified fatty acids (NEFA) were taken before cows were killed. After cows were killed, liver biopsy samples were collected for further assessment of total lipids and RNA sequencing. Five cows were classified as normal-conditioned (median BCS = 3, range 2.75-3.5) and 5 as overconditioned (median BCS = 4, range 4-5). Regression models confirmed that normal-conditioned cows had lower BFT (1.29 ± 0.29 cm; least squares means ± standard error) and serum NEFA (0.16 ± 0.04 mmol/L) in comparison to overconditioned cows (3.14 ± 0.43 cm and 0.38 ± 0.07 mmol/L for BFT and NEFA, respectively). Total liver lipid percentage tended to be lower in normal- versus overconditioned cows (4.63 ± 0.40% and 6.06 ± 0.44%, respectively). In comparison to the mean liver lipid percentage of the normal- and overconditioned cows, 1 overconditioned cow had a relatively low (5.21%) and 1 normal-conditioned cow had a relatively high (6.07%) liver lipid percentage. Differentially expressed genes analysis (edgeR quasi-likelihood method) showed that normal-conditioned cows presented 11 upregulated and 12 downregulated genes in comparison to overconditioned cows. Linear discriminant analysis effects size revealed 133 differentially expressed genes between normal- versus overconditioned cows. Notably, the liver of normal-conditioned cows had upregulated genes associated with liver functionality (ALB, SELENOP, IGF1, and IGF2). On the other hand, overconditioned cows had upregulated genes associated with the acute-phase response (C3, HPX, and, LBP). High basal lipolysis in overconditioned cows at the end of pregnancy increased liver lipid content, and this may alter the hepatic gene expression pattern to a pro-inflammatory state.

Follicular fluid during individual oocyte maturation enhances cumulus expansion and improves embryo development and quality in a dose-specific manner

We evaluated the effect of supplementation of different concentrations of bovine follicular fluid (FF) during in vitro maturation (IVM) on oocyte development and blastocyst quality in group and individual culture conditions. To do so, in vitro maturation medium (TCM-199 with 20 ng/mL epidermal growth factor and 50 μg/mL gentamycin) was supplemented with 0 (control), 1, 5, or 10% of FF. Follicular fluid was collected from slaughterhouse-derived ovaries, selecting follicles between 12 and 20 mm in diameter. Oocytes were either produced in groups or individually matured, fertilized, and cultured to the blastocyst stage, allowing for separate follow-up of each oocyte. Development (cleavage and blastocyst rates) among experimental groups were fitted in mixed-effects models, and blastocyst quality parameters (assessed via differential apoptotic staining) were evaluated in mixed linear regression models. We also assessed the cumulus expansion (prior and after maturation) for individual culture conditions, and their difference was fitted in mixed linear regression models. The FF was collected from two batches, with an estradiol/progesterone ratio higher than 1. The FF batch did not affect the development or blastocyst quality in group or individual culture conditions (P > 0.05). In group culture, development was similar among experimental groups (P > 0.05). Five or 10% of FF supplementation improved (P ˂ 0.05) aspects of blastocyst quality such as total cell numbers (TCN), trophectoderm (TE), inner cell mass (ICM), and ICM/TCN and apoptotic cells/TCN ratio in comparison to control. In the individual culture system, 5% FF supplementation increased (P ˂ 0.05) day 8 blastocyst rate (33 ± 3.4% (LSM ± SE)) in comparison to control (20 ± 2.7%) and 1% FF supplementation (19 ± 2.6%) but it was not different (P > 0.05) from 10% FF supplementation (28 ± 3.4%). Five percent of FF supplementation resulted in greater TCN, ICM, and ICM/TCN than control (P ˂ 0.05). It also resulted in a greater expansion of cumulus cell investment than the other groups (P ˂ 0.05), with a 3-fold increase compared to control. In conclusion, 5% of FF supplementation during IVM improved the cumulus expansion and the blastocyst development and quality in an individual culture system. However, FF supplementation during maturation in a group culture system did not increase development, but it modestly improved some embryo quality aspects when 5 or 10% of FF was added.

Altered embryotrophic capacities of the bovine oviduct under elevated free fatty acid conditions: an in vitro embryo--oviduct co-culture model

Maternal metabolic stress conditions are of growing importance in both human and dairy cattle settings as they can have significant repercussions on fertility. Upregulated lipolysis is a common trait associated with metabolic disorders and results in systemically elevated concentrations of non-esterified fatty acids (NEFAs). The effects of high NEFA concentrations on the follicular environment, oocyte and embryo development is well documented. However, knowledge on the effects of NEFAs within the oviduct, representing the initial embryonic growth environment, is currently lacking. Therefore, the experiments outlined here were designed to obtain fundamental insights into both the direct and indirect interactions between NEFAs, bovine oviductal cells and developing zygotes. Hence, zygotes were co-cultured with NEFA-pre-exposed bovine oviductal cells or subjected to simultaneous NEFA exposure during the co-culture period. The outcome parameters assessed were embryo development with cleavage (48h post insemination (pi)), morula (120-126h pi) and blastocyst (192h pi) rates, as well as morula intracellular lipid content and blastocyst quality using Bodipy and differential staining respectively. Our data suggest a direct embryotoxicity of NEFAs as well as impaired embryo development through a reduced oviductal ability to support and protect early embryo development.

Capacity of Trolox to improve the development and quality of metabolically compromised bovine oocytes and embryos invitro during different windows of development

Trials to improve oocyte developmental competence under metabolic stress by using antioxidants may start before or after oocyte maturation. In the present conceptual study, we aimed to identify the most efficient timing of antioxidant application in relation to a metabolic insult using a bovine invitro embryo production model. Pathophysiological concentrations of palmitic acid (PA) were used to induce metabolic stress during oocyte maturation or embryo development. Trolox (TR; antioxidant) treatment prior to, during or after the PA insult was tested to evaluate the protective, neutralising and rescuing capacity of TR respectively. Changes in embryo developmental competence, mitochondrial activity, reactive oxygen species (ROS) concentrations, blastocyst cell allocation and apoptosis and cell stress-related gene expression were monitored. The improvement in developmental capacity was most obvious when oocytes were preloaded with TR before the PA insult. This protective effect could be explained by the observed combination of increased mitochondrial activity with reduced ROS production. This resulted in blastocysts with normal cell counts and apoptosis, as well as increased nuclear factor erythroid 2-related factor 2 (NRF2) expression (a marker for redox regulatory processes) and normalised the expression of the mitochondrial transcription factor A (TFAM), a marker of mitochondrial biogenesis. These results indicate that 'pretreatment' of oocytes with antioxidants produces embryos that seem to be more resilient to a metabolic stress insult.

Cellular uptake of polymeric nanoparticles by bovine cumulus-oocyte complexes and their effect on in vitro developmental competence

Polymeric nanoparticles (NPs) are produced using bio-compatible and bio-degradable materials such as PLGA (Poly(lactic-co-glycolic acid)). This technology provides a valuable tool to deliver molecules to the subcellular level with a relatively low risk of cytotoxicity. However their use in the field of reproductive biotechnology is not yet scientifically substantiated. The aim of the present study was to test if PLGA NPs can be taken-up by cumulus-enclosed oocytes as a first step towards potential oocyte-targeted applications to enhance oocyte quality and fertility. We conducted a series of experiments using bovine in vitro oocyte maturation as a model to study FITC-conjugated PLGA internalization (using laser-scanning confocal microscopy) and the effect of some important physical (particle size) and chemical (conjugation with PEG) modifications. We show evidence that PLGA NPs can be taken-up by cumulus cells and to a less extent by the enclosed oocytes regardless of the NP size. The NP transfer to the oocyte appear to be transcellular (via cumulus cells and transzonal projections) and paracellular (via zona pellucida). The PLGA NPs were detected in the vicinity of the oocyte as quick as 2 h post-exposure in a protein-free medium and did not compromise cumulus cell viability nor subsequent early embryo development or embryo quality. These results suggest that PLGA NPs may have promising applications as carriers for drug or molecule delivery targeting cumulus cells and oocytes.

Preservation of connexin 43 and transzonal projections in isolated bovine pre-antral follicles before and following vitrification

PURPOSE

Gap junctions and transzonal projections play a crucial role in intercellular communication between different follicular components and are necessary for follicle development. We aimed to demonstrate gap junction protein connexin 43 (Cx43) and transzonal projections (TZPs) in viable, category 1, isolated bovine pre-antral follicles (PAFs) during short-term culture and after vitrification and warming.

METHODS

This study involved four experimental groups: fresh control, 2-day culture, 4-day culture, and vitrified secondary PAFs. Isolated PAFs were vitrified using a simple and efficient cryopreservation method by means of mini cell strainers.

RESULTS

Cx43 and TZPs were detected in pre-antral follicles of all stages, as well as in every experimental group. The group fresh follicles showed a higher percentage of follicles that were positive for Cx43 (91.7%) than the follicles that were vitrified (77.4%). All follicles that were cultured for 2 days were Cx43-positive (100%). Follicles cultured for 4 days (65.8%) (P = 0.002) showed the lowest percentage of follicles that were Cx43-positive. The percentages of the presence or (partial) absence of the TZP network were shown to be very heterogeneous between follicles in different treatment groups.

CONCLUSIONS

These results suggest the maintenance of communication between the oocyte and the somatic companion cells after vitrification and warming. The varying percentages of the expression of the TZP network within groups suggests that it will be of interest to investigate whether this is truly due to variability in TZP integrity and follicle quality or due to methodological limitations.

Mitochondria-targeted therapy rescues development and quality of embryos derived from oocytes matured under oxidative stress conditions: a bovine in vitro model

STUDY QUESTION

Can we use a mitochondrial-targeted antioxidant (Mitoquinone) during in vitro embryo culture to rescue developmental competence of oocytes matured under lipotoxic conditions, exhibiting mitochondrial dysfunction and oxidative stress?

SUMMARY ANSWER

Supplementation of embryo culture media with Mitoquinone reduced oxidative stress and prevented mitochondrial uncoupling in embryos derived from metabolically compromised oocytes in vitro, leading to higher blastocyst rates and lower blastomeric apoptosis.

WHAT IS KNOWN ALREADY

Maternal metabolic disorders, such as obesity and type-II diabetes are associated with hyperlipidemia and elevated free fatty acid (FFA) concentrations in the ovarian follicular fluid (FF). Oocyte maturation under these lipotoxic conditions results in increased oxidative stress levels, mitochondrial dysfunction, reduced developmental competence and disappointing IVF results.

STUDY DESIGN, SIZE, DURATION

A well-described bovine oocyte IVM model was used, where a pathophysiologically relevant elevated FF concentrations of palmitic acid (PA; 150 μM or 300 μM) were added to induce oxidative stress. After fertilization (Day 0, D0), zygotes were in vitro cultured (IVC, from D1 to D8) in standard fatty acid-free media in the presence or absence of Mitoquinone or its carrier triphenyl-phosphonium.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Embryo cleavage and fragmentation (D2) and blastocyst rates (D8) were recorded. Mitochondrial activity and oxidative stress in cleaved embryos at D2 were determined using specific fluorogenic probes and confocal microscopy. D8 blastocysts were used to (i) examine the expression of marker genes related to mitochondrial unfolded protein responses (UPRmt; HSPD1 and HSPE1), mitochondrial biogenesis (TFAM), endoplasmic reticulum (ER) UPR (ATF4, ATF6 and BiP) and oxidative stress (CAT, GPX1 and SOD2) using real time RT-PCR; (ii) determine cell differentiation and apoptosis using CDX-2 and cleaved caspase-3 immunostaining; and (iii) measure mtDNA copy numbers. This was tested in a series of experiments with at least three independent replicates for each, using a total of 2525 oocytes. Differences were considered significant if a P value was <0.05 after Bonferroni correction.

MAIN RESULTS AND THE ROLE OF CHANCE

Exposure to PA during IVM followed by culture under control conditions resulted in a significant increase in oxidative stress in embryos at D2. This was associated with a significant reduction in mitochondrial inner membrane potential (uncoupling) compared with solvent control (P < 0.05). The magnitude of these effects was PA-concentration dependent. Consequently, development to the blastocysts stage was significantly hampered. Surviving blastocysts exhibited high apoptotic cell indices and upregulated mRNA expression indicating persistent oxidative stress, mitochondrial and ER UPRs. In contrast, supplementation of PA-derived zygotes with Mitoquinone during IVC (i) prevented mitochondrial uncoupling and alleviated oxidative stress at D2; and (ii) rescued blastocyst quality; normalized oxidative stress and UPR related genes and apoptotic cell indices (P > 0.01 compared with solvent control). Mitoquinone also improved blastocyst rate in PA-exposed groups, an effect that was dependent on PA concentration.

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

This is a fundamental study performed using a bovine in vitro model using PA-induced lipotoxicity during oocyte maturation. PA is the most predominant FFA in the FF that is known to induce lipotoxicity; however, in vivo maturation in patients suffering from maternal metabolic disorders involve more factors that cannot be represented in one model. Nevertheless, focusing on the carryover oxidative stress as a known key factor affecting developmental competence, and considering the novel beneficial rescuing effects of Mitoquinone shown here, we believe this model is of high biological relevance.

WIDER IMPLICATIONS OF THE FINDINGS

Human oocytes collected for IVF treatments from patients with maternal metabolic disorders are vulnerable to lipotoxicity and oxidative stress during in vivo maturation. The results shown here suggest that mitochondrial targeted therapy, such as using Mitoquinone, during IVC may rescue the developmental competence and quality of these compromised oocytes. After further clinical trials, this may be a valuable approach to increase IVF success rates for infertile patients experiencing metabolic disorders.

STUDY FUNDING/COMPETING INTEREST(S)

This study was financially supported by a BOF/KP grant number 34399, from the University of Antwerp, Belgium. W.F.A.M. was supported by a postdoctoral fellowship from the Research Foundation-Flanders (FWO), grant number 12I1417N, Antwerp, Belgium. The Leica SP 8 confocal microscope used in this study was funded by the Hercules Foundation of the Flemish Government (Hercules grant AUHA.15.12). All authors have no financial or non-financial competing interests to declare.

Metabolic Stress in the Transition Period of Dairy Cows: Focusing on the Prepartum Period

All modern, high-yielding dairy cows experience a certain degree of reduced insulin sensitivity, negative energy balance, and systemic inflammation during the transition period. Maladaptation to these changes may result in excessive fat mobilization, dysregulation of inflammation, immunosuppression, and, ultimately, metabolic or infectious disease in the postpartum period. Up to half of the clinical diseases in the lifespan of high-yielding dairy cows occur within 3 weeks of calving. Thus, the vast majority of prospective studies on transition dairy cows are focused on the postpartum period. However, predisposition to clinical disease and key (patho)physiological events such as a spontaneous reduction in feed intake, insulin resistance, fat mobilization, and systemic inflammation already occur in the prepartum period. This review focuses on metabolic, adaptive events occurring from drying off until calving in high-yielding cows and discusses determinants that may trigger (mal)adaptation to these events in the late prepartum period.

Differential effects of high fat diet-induced obesity on oocyte mitochondrial functions in inbred and outbred mice

Maternal obesity can cause reduced oocyte quality and subfertility. Mitochondrial dysfunction plays a central role here, and most often inbred mouse models are used to study these pathways. We hypothesized that the mouse genetic background can influence the impact of high fat diet (HFD)-induced obesity on oocyte quality. We compared the inbred C57BL/6 (B6) and the outbred Swiss strains after feeding a HFD for 13w. HFD-mice had increased body weight gain, hypercholesterolemia, and increased oocyte lipid droplet (LD) accumulation in both strains. LD distribution was strain-dependent. In Swiss mouse oocytes, HFD significantly increased mitochondrial inner membrane potential (MMP), reactive oxygen species concentrations, mitochondrial ultrastructural abnormalities (by 46.4%), and endoplasmic reticulum (ER) swelling, and decreased mtDNA copy numbers compared with Swiss controls (P < 0.05). Surprisingly, B6-control oocytes exhibited signs of cellular stress compared to the Swiss controls (P < 0.05); upregulated gene expression of ER- and oxidative stress markers, high mitochondrial ultrastructural abnormalities (48.6%) and ER swelling. Consequently, the HFD impact on B6 oocyte quality was less obvious, with 9% higher mitochondrial abnormalities, and no additive effect on MMP and stress marks compared to B6 control (P > 0.1). Interestingly, mtDNA in B6-HFD oocytes was increased suggesting defective mitophagy. In conclusion, we show evidence that the genetic background or inbreeding can affect mitochondrial functions in oocytes and may influence the impact of HFD on oocyte quality. These results should create awareness when choosing and interpreting data obtained from different mouse models before extrapolating to human applications.

The pre-hatching bovine embryo transforms the uterine luminal metabolite composition in vivo

In cattle, conceptus development after elongation relies on well-characterized, paracrine interactions with the hosting maternal reproductive tract. However, it was unrecognized previously that the pre-hatching, pre-implantation bovine embryo also engages in biochemical signalling with the maternal uterus. Our recent work showed that the embryo modified the endometrial transcriptome in vivo. Here, we hypothesized that the embryo modulates the biochemical composition of the uterine luminal fluid (ULF) in the most cranial portion of the uterine horn ipsilateral to the corpus luteum. Endometrial samples and ULF were collected post-mortem from sham-inseminated cows and from cows inseminated and detected pregnant 7 days after oestrus. We used quantitative mass spectrometry to demonstrate that the pre-hatching embryo changes ULF composition in vivo. Embryo-induced modulation included an increase in concentrations of lipoxygenase-derived metabolites [12(S)-HETE, 15(S)-HETE] and a decrease in the concentrations of amino acids (glycine), biogenic amines (sarcosine), acylcarnitines and phospholipids. The changed composition of the ULF could be due to secretion or depletion of specific molecules, executed by either the embryo or the endometrium, but initiated by signals coming from the embryo. This study provides the basis for further understanding embryo-initiated modulation of the uterine milieu. Early embryonic signalling may be necessary to guarantee optimal development and successful establishment of pregnancy in cattle.

Action mechanisms of n-3 polyunsaturated fatty acids on the oocyte maturation and developmental competence: Potential advantages and disadvantages

Infertility is a growing problem worldwide. Currently, in vitro fertilization (IVF) is widely performed to treat infertility. However, a high percentage of IVF cycles fails, due to the poor developmental potential of the retrieved oocyte to generate viable embryos. Fatty acid content of the follicular microenvironment can affect oocyte maturation and the subsequent developmental competence. Saturated and monounsaturated fatty acids are mainly used by follicle components as primary energy sources whereas polyunsaturated fatty acids (PUFAs) play a wide range of roles. A large body of evidence supports the beneficial effects of n-3 PUFAs in prevention, treatment, and amelioration of some pathophysiological conditions including heart diseases, cancer, diabetes, and psychological disorders. Nevertheless, current findings regarding the effects of n-3 PUFAs on reproductive outcomes in general and on oocyte quality more specifically are inconsistent. This review attempts to provide a comprehensive overview of potential molecular mechanisms by which n-3 PUFAs affect oocyte maturation and developmental competence, particularly in the setting of IVF and thereby aims to elucidate the reasons behind current discrepancies around this topic.

Effect of nutritionally induced hyperlipidaemia on in vitro bovine embryo quality depends on the type of major fatty acid in the diet

The present study examined whether the effects of dietary-induced hyperlipidaemia on preimplantation embryo development depend on the predominant fatty acid (FA) type in the diet. In a combined in vivo-in vitro bovine model, two groups of cows (n=3 in each group) were fed with three diets consecutively (4 weeks feeding for each): (1) a maintenance control diet (CONT); (2) a high-starch diet rich in saturated fat (SAT); and (3) a high-starch diet rich in omega-3 unsaturated fat (UNSAT). Two feeding sequences were used to test for carry-over effects: Group A was fed CONT, SAT1 and then UNSAT2, whereas Group B was fed CONT, UNSAT1 and then SAT2. Serum was collected after each dietary period, analysed and tested in bovine in vitro embryo culture. Introducing SAT and UNSAT diets induced hyperlipidaemia (specifically hypercholesterolaemia and elevated free FAs) and reduced insulin sensitivity. Carry-over effects in serum metabolites and FA profile were dependent on the diet and feeding sequence. SAT1 and SAT2 serum decreased blastocyst rates and altered blastocyst mRNA expression related to apoptosis and oxidative stress. UNSAT1 and UNSAT2 serum resulted in normal embryo development and quality. Other in vitro effects depended on the sequence of feeding. In conclusion, substitution of saturated fat with omega-3 fat in a high-caloric diet induced hyperlipidaemia with an FA profile yielding similar rates and quality of blastocysts compared with normolipidaemic controls.

Differential effects of high and low glucose concentrations during lipolysis-like conditions on bovine in vitro oocyte quality, metabolism and subsequent embryo development

Lipolytic metabolic conditions are traditionally associated with elevated non-esterified fatty acid (NEFA) concentrations, but may also be accompanied by hyperglycaemia in obesity or by hypoglycaemia during a negative energy balance status. Elevated NEFA concentrations disrupt oocyte and embryo development and quality, but little is known about whether the effects of lipolytic conditions on oocyte developmental competence are modulated by glucose availability. To answer this, bovine cumulus-oocyte complexes (COCs) were matured under different conditions: physiological NEFA (72µM) and normal glucose (5.5mM), pathophysiologically high NEFA (420µM) and normal glucose, high NEFA and high glucose (9.9mM), high NEFA and low glucose (2.8mM). Developmental potential, cumulus expansion and metabolism of COCs exposed to high NEFA and low glucose were affected to a greater extent compared with COCs matured under high NEFA and high glucose conditions. High NEFA and high glucose conditions caused a moderate increase in oocyte reactive oxygen species compared with their high NEFA and low glucose or control counterparts. Blastocyst metabolism and the transcriptome of metabolic and oxidative stress-related genes were not affected. However, both lipolytic conditions associated with hyper- or hypoglycaemia led to surviving embryos of reduced quality with regards to apoptosis and blastomere allocation.

Effects of vitrification on the viability of alginate encapsulated isolated bovine pre-antral follicles

PURPOSE

Individual follicle cryopreservation techniques, without hydrogel support, are labor-intensive and a substantial proportion of isolated follicles are lost during handling and after warming. Therefore, the viability and morphology of isolated bovine (as a model for human) pre-antral follicles after vitrification and warming, when encapsulated in alginate beads, were investigated.

METHODS

Bovine pre-antral follicles were mechanically isolated and divided into four different groups: (1) culture in 2% alginate beads (3D system) and vitrification in beads using mesh cups (3DVIT), (2) culture in 2% alginate beads (3DCUL), (3) culture in 96-well plates (2D system) and vitrification using High Security Vitrification straws® (2DVIT), (4) culture in a 2D system (2DCUL). The same vitrification and warming protocols were used for embedded (3DVIT) and non-embedded follicles (2DVIT).

RESULTS

No differences were observed in follicle viability between group 2DCUL and 3DCUL. Group 3DVIT showed the lowest viability (45.9%) according to calcein and neutral red staining among all groups. Group 2DVIT displayed the highest viability (87.5%) and largest percentage of follicles with a well-preserved morphology.

CONCLUSIONS

Our results show that, using a vitification protocol optimized for non-embedded follicles, 2D culture is more effective in vitrifying isolated follicles. However, embedding in alginate allow to handle follicles more efficiently, i.e., without excessive manipulation and thus less labor-intensive in combination with a reduced loss of follicles during the procedure. Based on the increased work efficiency, but lower viability and higher proportion of follicles showing impaired morphology, we consider it advantageous to optimize the protocol for the vitrification of embedded follicles to increase survival and maintain morphology after vitrification.

Alpha-linolenic acid protects the developmental capacity of bovine cumulus-oocyte complexes matured under lipotoxic conditions in vitro

Elevated concentrations of free fatty acids (FFAs), predominantly palmitic, stearic, and oleic acids (PSO), exert detrimental effects on oocyte developmental competence. This study examined the effects of omega-3 alpha-linolenic acid (ALA) during in vitro oocyte maturation (IVM) in the presence of PSO on subsequent embryo development and quality, and the cellular mechanisms that might be involved. Bovine cumulus-oocyte complexes (COCs) were supplemented during IVM with ALA (50 μM), PSO (425 μM), or PSO+ALA. Compared with FFA-free controls (P < 0.05), PSO increased embryo fragmentation and decreased good quality embryos on day 2 postfertilization. Day 7 blastocyst rate was also reduced. Day 8 blastocysts had lower cell counts and higher apoptosis but normal metabolic profile. In the PSO group, cumulus cell (CC) expansion was inhibited with an increased CC apoptosis while COC metabolism was not affected. Mitochondrial inner membrane potential (MMP; JC-1 staining) was reduced in the CCs and oocytes. Heat shock protein 70 (HSP70) but not glucose-regulated protein 78 kDa (GRP78, known as BiP; an endoplasmic reticulum stress marker) was upregulated in the CCs. Higher reactive oxygen species levels (DCHFDA staining) were detected in the oocytes. In contrast, adding ALA in the presence of PSO normalized embryo fragmentation, cleavage, blastocyst rates, and blastocyst quality compared to controls (P > 0.05). Combined treatment with ALA also reduced CC apoptosis, partially recovered CC expansion, abrogated the reduction in MMP in the CCs but not in the oocytes, and reduced BiP and HSP70 expression in CCs, compared with PSO only (P < 0.05). In conclusion, ALA supplementation protected oocyte developmental capacity under lipotoxic conditions mainly by protecting cumulus cell viability.

Non-esterified fatty acids in early luteal bovine oviduct fluid mirror plasma concentrations: An ex vivo approach

We investigated whether and to which extent plasma non-esterified fatty acids (NEFAs) are reflected in oviduct fluid (OF) using an improved ex vivo flushing method. OF and plasma NEFA concentrations were respectively 0.29±0.19 and 0.31±0.14mmol/L, they didn't differ significantly (P=0.13) and tended to be positively correlated (Pearson correlation coefficient=0.56; P=0.07). Results suggest that OF NEFAs mirror the concentrations seen in plasma of healthy cattle.

Nutrition and maternal metabolic health in relation to oocyte and embryo quality: critical views on what we learned from the dairy cow model

Although fragmented and sometimes inconsistent, the proof of a vital link between the importance of the physiological status of the mother and her subsequent reproductive success is building up. High-yielding dairy cows are suffering from a substantial decline in fertility outcome over past decades. For many years, this decrease in reproductive output has correctly been considered multifactorial, with factors including farm management, feed ratios, breed and genetics and, last, but not least, ever-rising milk production. Because the problem is complex and requires a multidisciplinary approach, it is hard to formulate straightforward conclusions leading to improvements on the 'work floor'. However, based on remarkable similarities on the preimplantation reproductive side between cattle and humans, there is a growing tendency to consider the dairy cow's negative energy balance and accompanying fat mobilisation as an interesting model to study the impact of maternal metabolic disorders on human fertility and, more specifically, on oocyte and preimplantation embryo quality. Considering the mutual interest of human and animal scientists studying common reproductive problems, this review has several aims. First, we briefly introduce the 'dairy cow case' by describing the state of the art of research into metabolic imbalances and their possible effects on dairy cow reproduction. Second, we try to define relevant in vitro models that can clarify certain mechanisms by which aberrant metabolite levels may influence embryonic health. We report on recent advances in the assessment of embryo metabolism and meantime critically elaborate on advantages and major limitations of in vitro models used so far. Finally, we discuss hurdles to be overcome to successfully translate the scientific data to the field.

Maternal metabolic stress may affect oviduct gatekeeper function

We hypothesized that elevated non-esterified fatty acids (NEFA) modify in vitro bovine oviduct epithelial cell (BOEC) metabolism and barrier function. Hereto, BOECs were studied in a polarized system with 24-h treatments at Day 9: (1) control (0 µM NEFA + 0% EtOH), (2) solvent control (0 µM NEFA + 0.45% EtOH), (3) basal NEFA (720 µM NEFA + 0.45% EtOH in the basal compartment) and (4) apical NEFA (720 µM NEFA + 0.45% EtOH in the apical compartment). FITC-albumin was used for monolayer permeability assessment and related to transepithelial electric resistance (TER). Fatty acid (FA), glucose, lactate and pyruvate concentrations were measured in spent medium. Intracellular lipid droplets (LD) and FA uptake were studied using Bodipy 493/503 and immunolabelling of FA transporters (FAT/CD36, FABP3 and CAV1). BOEC-mRNA was retrieved for qRT-PCR. Results revealed that apical NEFA reduced relative TER increase (46.85%) during treatment and increased FITC-albumin flux (27.59%) compared to other treatments. In basal NEFA, FAs were transferred to the apical compartment as free FAs: mostly palmitic and oleic acid increased respectively 56.0 and 33.5% of initial FA concentrations. Apical NEFA allowed no FA transfer, but induced LD accumulation and upregulated FA transporter expression (↑CD36, ↑FABP3 and ↑CAV1). Gene expression in apical NEFA indicated increased anti-apoptotic (↑BCL2) and anti-oxidative (↑SOD1) capacity, upregulated lipid metabolism (↑CPT1, ↑ACSL1 and ↓ACACA) and FA uptake (↑CAV1). All treatments had similar carbohydrate metabolism and oviduct function-specific gene expression (OVGP1, ESR1 and FOXJ1). Overall, elevated NEFAs affected BOEC metabolism and barrier function differently depending on NEFA exposure side. Data substantiate the concept of the oviduct as a gatekeeper that may actively alter early embryonic developmental conditions.

The Importance of the Periconception Period: Immediate Effects in Cattle Breeding and in Assisted Reproduction Such as Artificial Insemination and Embryo Transfer

In livestock breeding, the successful outcome is largely depending on the "periconception environment" which, in a narrow sense, refers to the genital tract, where gametogenesis and embryogenesis occur. During these early stages of development, gametes and embryos are known to be particularly sensitive to alterations in their microenvironment. However, as the microenvironment somehow reflects what is going on in the external world, we must widen our definition of "periconception environment" and refer to all events taking place around the time of conception, including metabolic state and health and nutrition of the dam. In modern dairy cows that have to manage an optimal reproductive performance with continued growth and high milk yield, the periconception period is particularly challenging. The metabolic priority for growth and lactation is known to generate adverse conditions hampering optimal ovarian function, oocyte maturation, and development of embryo/fetus. In addition, by using artificial reproductive technologies (ARTs), gametes and/or embryos of livestock are exposed to unnatural conditions outside the male and female genital tract. Artificial insemination, the most widely used technique, is currently yielding pregnancy rates similar to natural mating, and calves produced by AI are equally viable after natural mating. In contrast, other ART, such as multiple ovulation and embryo transfer, have been reported to induce changes in gene expression and DNA methylation patterns with potential consequences for development.Finally, the "periconceptional" environment has been shown to not only influence the successful establishment of pregnancy but also the long-term health and productivity of the offspring. Hence, the optimization of management around the time of conception might open doors to improve animal production and product quality.

Targeted deletion of the Kv6.4 subunit causes male sterility due to disturbed spermiogenesis

Electrically silent voltage-gated potassium (KvS) channel subunits (i.e. Kv5–Kv6 and Kv8–Kv9) do not form functional homotetrameric Kv channels, but co-assemble with Kv2 subunits, generating functional heterotetrameric Kv2­–KvS channel complexes in which the KvS subunits modulate the Kv2 channel properties. Several KvS subunits are expressed in testis tissue but knowledge about their contribution to testis physiology is lacking. Here, we report that the targeted deletion of Kv6.4 in a transgenic mouse model (Kcng4–/–) causes male sterility as offspring from homozygous females were only obtained after mating with wild-type (WT) or heterozygous males. Semen quality analysis revealed that the sterility of the homozygous males was caused by a severe reduction in total sperm-cell count and the absence of motile spermatozoa in the semen. Furthermore, spermatozoa of homozygous mice showed an abnormal morphology characterised by a smaller head and a shorter tail compared with WT spermatozoa. Comparison of WT and Kcng4–/– testicular tissue indicated that this inability to produce (normal) spermatozoa was due to disturbed spermiogenesis. These results suggest that Kv6.4 subunits are involved in the regulation of the late stages of spermatogenesis, which makes them a potentially interesting pharmacological target for the development of non-hormonal male contraceptives.

Exposure of bovine oocytes and embryos to elevated non-esterified fatty acid concentrations: integration of epigenetic and transcriptomic signatures in resultant blastocysts

Background

Metabolic stress associated with negative energy balance in high producing dairy cattle and obesity in women is a risk factor for decreased fertility. Non-esterified fatty acids (NEFA) are involved in this pathogenesis as they jeopardize oocyte and embryo development. Growing evidence indicates that maternal metabolic disorders can disturb epigenetic programming, such as DNA methylation, in the offspring. Oocyte maturation and early embryo development coincide with methylation changes and both are sensitive to adverse environments. Therefore, we investigated whether elevated NEFA concentrations affect establishment and maintenance of DNA methylation in oocytes and embryos, subsequently altering transcriptomic profiles and developmental competence of resultant blastocysts.

Results

Bovine oocytes and embryos were exposed to different NEFA concentrations in separate experiments. In the first experiment, oocytes were matured in vitro for 24 h in medium containing: 1) physiological (“BASAL”) concentrations of oleic (OA), palmitic (PA) and stearic (SA) acid or 2) pathophysiological (“HIGH COMBI”) concentrations of OA, PA and SA. In the second experiment, zygotes were cultivated in vitro for 6.5 days under BASAL or HIGH COMBI conditions. Developmental competence was evaluated by assessing cleavage and blastocyst rate. Overall gene expression and DNA methylation of resultant blastocysts were analyzed using microarray. DNA methylation data were re-evaluated by pyrosequencing. HIGH COMBI-exposed oocytes and embryos displayed a lower competence to develop into blastocysts compared to BASAL-exposed counterparts (19.3% compared to 23.2% and 18.2% compared to 25.3%, respectively) (P < 0.05). HIGH COMBI-exposed oocytes and embryos resulted in blastocysts with altered DNA methylation and transcriptomic fingerprints, compared to BASAL-exposed counterparts. Differences in gene expression and methylation were more pronounced after exposure during culture compared to maturation suggesting that zygotes are more susceptible to adverse environments. Main gene networks affected were related to lipid and carbohydrate metabolism, cell death, immune response and metabolic disorders.

Conclusions

Overall, high variation in methylation between blastocysts made it difficult to draw conclusions concerning methylation of individual genes, although a clear overview of affected pathways was obtained. This may offer clues regarding the high rate of embryonic loss and metabolic diseases during later life observed in offspring from mothers displaying lipolytic disorders.

The effect of a negative energy balance status on β-carotene availability in serum and follicular fluid of nonlactating dairy cows

Maternal metabolic pressure due to a cow's negative energy balance (NEB) has a negative effect on oocyte quality as a result of increased oxidative stress. In this study, we hypothesized that a NEB status may negatively affect the availability of β-carotene (bC, an antioxidant) in the micro-environment of the oocyte or follicular fluid (FF) and that daily bC supplementation can increase bC availability. We aimed to (1) determine the effect of a nutritionally induced NEB on bC concentrations in serum and FF as well as on the presence of bC metabolites, oxidative stress levels, and follicular growth in a nonlactating dairy cow model, and (2) investigate how this effect could be altered by dietary bC supplementation. Six multiparous nonlactating Holstein Friesian cows were subjected to 4 consecutive dietary treatments, 28 d each: (1) 1.2 × maintenance (M) or positive energy balance (PEB) without bC supplement (PEB-bC), (2) 1.2 × M with daily supplement of 2,000mg of bC comparable to the level of bC intake at grazing (PEB+bC), (3) 0.6 × M with 2,000mg of bC (NEB+bC), and (4) 0.6 × M (NEB-bC). At the end of each treatment, estrous cycles were synchronized and blood and FF of the largest follicle were sampled and analyzed for bC, retinol, α-tocopherol, free fatty acids, estradiol, and progesterone. Serum cholesterol, triglycerides, urea, insulin growth factor 1, growth hormone, total antioxidant status (TAS), and red blood cell glutathione (GSH) concentrations were determined as well. All cows lost body weight during both energy restriction periods and showed increased serum free fatty acid concentrations, illustrating a NEB. A dietary induced NEB reduced FF bC, but not plasma bC or plasma and FF retinol concentrations. However, bC and retinol concentrations drastically increased in both fluid compartments after bC supplementation. Follicular diameter was increased in supplemented PEB cows. Energy restriction reduced the TAS and red blood cell GSH, whereas daily bC supplementation could restore GSH concentrations, but not the TAS, to levels present in healthy PEB cows. In conclusion, daily bC supplementation can substantially improve bC and retinol availability in the oocyte's micro-environment, irrespective of the energy balance, which may affect follicular development and oocyte quality in the presence of maternal metabolic stress. This knowledge can be of importance to optimize nutritional strategies in the dairy industry to feed for optimal oocyte quality and fertility.

Suboptimal culture conditions induce more deviations in gene expression in male than female bovine blastocysts

Background

Since the development of in vitro embryo production in cattle, different supplements have been added to culture media to support embryo development, with serum being the most popular. However, the addition of serum during embryo culture can induce high birthweights and low viability in calves (Large Offspring Syndrome). Analysis of global gene expression in bovine embryos produced under different conditions can provide valuable information to optimize culture media for in vitro embryo production.

Results

We used RNA sequencing to examine the effect of in vitro embryo production, in either serum-containing or serum-free media, on the global gene expression pattern of individual bovine blastocysts. Compared to in vivo derived embryos, embryos produced in serum-containing medium had five times more differentially expressed genes than embryos produced in serum-free conditions (1109 vs. 207). Importantly, in vitro production in the presence of serum appeared to have a different impact on the embryos according to their sex, with male embryos having three times more genes differentially expressed than their female counterparts (1283 vs. 456). On the contrary, male and female embryos produced in serum-free conditions showed the same number (191 vs. 192) of genes expressed differentially; however, only 44 of those genes were common in both comparisons. The pathways affected by in vitro production differed depending on the type of supplementation. For example, embryos produced in serum-containing conditions had a lower expression of genes related to metabolism while embryos produced in serum-free conditions showed aberrations in genes involved in lipid metabolism.

Conclusions

Serum supplementation had a major impact on the gene expression pattern of embryos, with male embryos being the most affected. The transcriptome of embryos produced in serum-free conditions showed a greater resemblance to that of in vivo derived embryos, although genes involved in lipid metabolism were altered. Male embryos appeared to be most affected by suboptimal in vitro culture, i.e. in the presence of serum.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-2393-z) contains supplementary material, which is available to authorized users.

Interaction between differential gene expression profile and phenotype in bovine blastocysts originating from oocytes exposed to elevated non-esterified fatty acid concentrations

Maternal metabolic disorders linked to lipolysis are major risk factors for reproductive failure. A notable feature of such disorders is increased non-esterified fatty acid (NEFA) concentrations in the blood, which are reflected in the ovarian follicular fluid. Elevated NEFA concentrations impact on the maturing oocyte and even alter subsequent embryo physiology. The aetiological mechanisms have not been fully elucidated. Therefore, in the present study, bovine in vitro maturing cumulus-oocyte complexes were exposed (24 h) to three different maturation treatments containing: (1) physiological (72 µM) NEFA concentrations (=control); (2) elevated (75 µM) stearic acid (SA) concentrations (=HIGH SA); and (3) elevated (425 µM) NEFA concentrations (=HIGH COMBI). Zygotes were fertilised and cultured following standard procedures. Transcriptomic analyses in resulting Day 7.5 blastocysts revealed that the major pathways affected are related to lipid and carbohydrate metabolism in HIGH COMBI embryos and to lipid metabolism and cell death in HIGH SA embryos. Furthermore, lower glutathione content and a reduced number of lipid droplets per cell were observed in HIGH SA-exposed oocytes and resulting morulae, respectively, compared with their HIGH COMBI-exposed counterparts. Vitrified embryos originating from HIGH SA-exposed oocytes tended to exhibit lower survival rates compared with controls. These data suggest possible mechanisms explaining why females across species suffering lipolytic disorders experience difficulties in conceiving.

Perfluoroalkyl acid contamination of follicular fluid and its consequence for in vitro oocyte developmental competence

Perfluoroalkyl acids (PFAAs) have been shown to induce negative effects in laboratory animals and in vitro experiments. Also, PFAAs have been detected in human tissues and body fluids. The ovarian follicle constitutes a fragile micro-environment where interactions between hormones, growth factors, the oocyte and surrounding somatic cells are essential to generate a fully competent oocyte. In vitro experiments suggest that PFAAs can influence this balance, but very scarce in vivo data are available to confirm this assumption. In fact, the potential PFAA-presence in the follicular micro-environment is currently unknown. Therefore, we investigated if PFAAs are present in human follicular fluid and if their presence could be a risk factor for in vivo exposed developing oocytes. Furthermore, we compared the PFAA-distribution within serum and follicular fluid. PFAAs were analyzed by LC/MS in follicular fluid (n=38) and serum (n=20) samples from women undergoing assisted reproductive technologies (ARTs). Statistical models were used to investigate PFAA-distribution in both body fluids, to compare this behavior with the distribution of lipophilic organic pollutants and to explore the relationship between patient characteristics, ART-results and follicular fluid contamination. Perfluorooctane sulfonate (PFOS) was the PFAA found in the highest concentration in follicular fluid [7.5 (0.1-30.4) ng/mL] and serum [7.6 (2.8-12.5) ng/mL]. A new variable, Principal Component 1, representing the overall PFAA-contamination of the follicular fluid samples, was associated with a higher fertilization rate (p<0.05) and a higher proportion of top embryos relative to the amount of retrieved oocytes (p<0.05), after adjusting for age, estradiol-concentration, BMI, male subfertility and the presence of other organic pollutants as explanatory variables. To conclude, overall higher PFAA-contamination in the follicular micro-environment was associated with a higher chance of an oocyte to develop into a high quality embryo. Also, PFAAs have different distribution patterns between serum and follicular fluid compared to the lipophilic organic pollutants. Further research is of course crucial to confirm these new observations.

Effects of neutral red assisted viability assessment on the cryotolerance of isolated bovine preantral follicles

PURPOSE

Fertility preservation strategies warrant non-invasive viability assessment of preantral follicles (PAF) such as staining with Neutral Red (NR) that is incorporated by viable follicles. To optimize the procedure, we firstly determined the lowest concentration and shortest exposure time needed for optimal viability screening of isolated bovine PAF. Secondly, we combined this protocol to a vitrification procedure to assess cryotolerance of the stained follicles.

METHODS

Isolated PAF (900, divided over 6 replicates) were cultured in DMEM/Ham's F12 (Culture Medium - Cm) for 4 days (38.5 °C, 5% CO2). On D0, D2 and D4, follicles were stained, by adding NR medium (NRm = Cm with different concentrations NR) after which viability was assessed by counting stained/non-stained PAF every 30 min for a period of 2 h.

RESULTS

Following a binary logistic regression analysis with staining as a result (yes/no) versus log-concentration, a probability model could be fitted, indicating that the proportion of stained follicles remained stable after 30 min when 15 μg/ml NR was used, without compromising follicular health and viability. Consequently, using this protocol, no significant effect of staining prior to vitrification, was found on PAF viability immediately after warming or following 4 days of culture.

CONCLUSIONS

In conclusion, we propose NR staining as a non-invasive, non-detrimental viability assessment tool for PAF, when applied at 15 μg/ml for 30 min, being perfectly compatible with PAF vitrification.

Elevated non-esterified fatty acid concentrations during in vitro murine follicle growth alter follicular physiology and reduce oocyte developmental competence

OBJECTIVE

To study how long-term elevated non-esterified fatty acid (NEFA) concentrations, typical in metabolic disorders such as obesity or type 2 diabetes, affect murine follicular development, follicle quality, and subsequent oocyte developmental competence in vitro.

DESIGN

Experimental study.

SETTING

In vitro culture setting.

ANIMAL(S)

Female and male 13-day old, B6CBAF1 mice of proven fertility were sacrificed for harvesting ovaries and epididymal sperm, respectively.

INTERVENTION(S)

Early secondary murine follicles were cultured in vitro in the presence of NEFAs until the antral stage (12 days). Treatments consisted of one or a mixture of NEFAs (stearic acid [SA], palmitic acid [PA], oleic acid [OA]) in physiological (basal) or pathological (high SA, high OA, high NEFA) concentrations.

MAIN OUTCOME MEASURE(S)

Follicular development; follicle and oocyte diameters; secretion of progesterone, estradiol, and inhibin B; and luteinized granulosa cell gene expression patterns were investigated. Oocytes from NEFA-exposed follicles were fertilized in vitro, and presumptive zygotes were cultured until the blastocyst stage.

RESULT(S)

Exposure to high SA reduced follicle diameters and day-12 antrum formation. Elevated NEFA concentrations changed luteinized granulosa cell messenger-ribonucleic acid abundance of genes related to energy/fatty acid/steroid metabolism, apoptosis, and oxidative stress. High NEFA and high SA treatments increased progesterone synthesis, compared with high OA follicles. Oocyte developmental competence was substantially reduced in oocytes retrieved from high OA-, high SA-, and high NEFA-exposed follicles compared with basal-treated follicles.

CONCLUSION(S)

This study showed, for the first time, that lipolysis-linked, elevated NEFA concentrations can potentially impair fertility, by altering follicular physiology and reducing oocyte developmental competence.