Low Oxygen Levels Induce Early Luteinization Associated Changes in Bovine Granulosa Cells

Reduced oxygen concentrations regulate the phenotype and function of human granulosa cells in vitro and cause a diminished steroidogenic but increased inflammatory cellular reaction

Oxygen (O2) concentrations have recently been discussed as important regulators of ovarian cells. Human IVF-derived granulosa cells (human GCs) can be maintained in vitro and are a widely used cellular model for the human ovary. Typically, GCs are cultured at atmospheric O2 levels (approximately around 20%), yet the O2 conditions in vivo, especially in the preovulatory follicle, are estimated to be much lower. Therefore, we comprehensively evaluated the consequences of atmospheric versus hypoxic (1% O2) conditions for 4 days on human GCs. We found lower cellular RNA and protein levels but unchanged cell numbers at 1% O2, indicating reduced transcriptional and/or translational activity. A proteomic analysis showed that 391 proteins were indeed decreased, yet 133 proteins were increased under hypoxic conditions. According to gene ontology (GO) enrichment analysis, pathways associated with metabolic processes, for example amino acid-catabolic-processes, mitochondrial protein biosynthesis, and steroid biosynthesis, were downregulated. Pathways associated with glycolysis, chemical homeostasis, cellular response to hypoxia, and actin filament bundle assembly were upregulated. In accordance with lower CYP11A1 (a cholesterol side-chain cleavage enzyme) levels, progesterone release was decreased. A proteome profiler, as well as IL-6 and IL-8 ELISA assays, revealed that hypoxia led to increased secretion of pro-inflammatory and angiogenic factors. Immunofluorescence studies showed nuclear localization of hypoxia-inducible factor 1α (HIF1α) in human GCs upon acute (2 h) exposure to 1% O2 but not in cells exposed to 1% O2 for 4 days. Hence, the role of HIF1α may be restricted to initiation of the hypoxic response in human GCs. The results provide a detailed picture of hypoxia-induced phenotypic changes in human GCs and reveal that chronically low O2 conditions inhibit the steroidogenic but promote the inflammatory phenotype of these cells.

Multisite and multitimepoint proteomics reveal that patent foramen ovale closure improves migraine and epilepsy by reducing right-to-left shunt-induced hypoxia

Patent foramen ovale (PFO) is a congenital defect in the partition between two atria, which may cause right-to-left shunt (RLS), leading to neurological chronic diseases with episodic manifestations (NCDEMs), such as migraine and epilepsy. However, whether PFO closure was effective in improving NCDEMs and the mechanism were unclear. Twenty-eight patients with migraine or epilepsy who underwent PFO closure were recruited. Notably, approximately half of patients received 50% or more reduction in seizure or headache attacks. Meanwhile, the postoperative blood oxygen partial pressure and oxygen saturation were elevated after PFO closure. Multisite (peripheral, right, and left atrial) and multitimepoint (before and after surgery) plasma proteomics from patients showed that the levels of free hemoglobin and cell adhesion molecules (CAMs) were significantly increased after PFO closure, which may be related to the relief of the hypoxic state. Furtherly, the omics data from multiple brain regions of mice revealed that a large number of proteins were differentially expressed in the occipital region in response to PFO, including redox molecules and CAMs, suggesting PFO-caused hypoxia may have great impacts on occipital region. Collectively, PFO may cause NCDEMs due to RLS-induced hypoxia, and PFO closure could prevent RLS to improve migraine and epilepsy.

Investigating and Modelling an Engineered Millifluidic In Vitro Oocyte Maturation System Reproducing the Physiological Ovary Environment in the Sheep Model

In conventional assisted reproductive technologies (ARTs), oocytes are in vitro cultured in static conditions. Instead, dynamic systems could better mimic the physiological in vivo environment. In this study, a millifluidic in vitro oocyte maturation (mIVM) system, in a transparent bioreactor integrated with 3D printed supports, was investigated and modeled thanks to computational fluid dynamic (CFD) and oxygen convection-reaction-diffusion (CRD) models. Cumulus-oocyte complexes (COCs) from slaughtered lambs were cultured for 24 h under static (controls) or dynamic IVM in absence (native) or presence of 3D-printed devices with different shapes and assembly modes, with/without alginate filling. Nuclear chromatin configuration, mitochondria distribution patterns, and activity of in vitro matured oocytes were assessed. The native dynamic mIVM significantly reduced the maturation rate compared to the static group (p < 0.001) and metaphase II (MII) oocytes showed impaired mitochondria distribution (p < 0.05) and activity (p < 0.001). When COCs were included in a combination of concave+ring support, particularly with alginate filling, oocyte maturation and mitochondria pattern were preserved, and bioenergetic/oxidative status was improved (p < 0.05) compared to controls. Results were supported by computational models demonstrating that, in mIVM in biocompatible inserts, COCs were protected from shear stresses while ensuring physiological oxygen diffusion replicating the one occurring in vivo from capillaries.

The Role of Reduced Oxygen Supply and Transcription Factors cJUN and CREB in Progesterone Production during the Corpus Luteum Rescue in Gilts

The corpus luteum plays a fundamental role in regulating reproduction via progesterone production. Still, there is little data on factors regulating the maintenance of luteal function during early pregnancy in gilts. Previous studies emphasize the role of hypoxia and HIF-1 in the regulation of steroidogenic and angiogenic genes expression and progesterone production by ovarian cells. Using the corpus luteum of cyclic and early pregnant gilts we analyzed: (1) the in vitro effects of reduced oxygen tension on progesterone production and mRNA expression of HIF1A and luteal function regulators, STAR and VEGFA; (2) the ex vivo profiles of mRNA and protein expression of HIF-1α, STAR, VEGFA and transcription factors-cJUN and CREB, regulating STAR expression, in the corpus luteum of cyclic and pregnant gilts. The synthesis of progesterone was gradually inhibited in cyclic or pregnant gilt luteal tissue (on day 13 of cycle or pregnancy) incubated in a decreasing concentration−20%, 10%, and 3% of oxygen (O2). Luteal tissues of pregnant gilts produced trace amounts of progesterone in 10% O2, which was similar to cyclic gilts in 3% O2. HIF1A expression increased after 24 h of incubation in tissues of cyclic gilts in 3% vs. 20% O2 (p < 0.01), whereas levels of STAR and VEGFA increased significantly in cyclic and pregnant gilt tissues incubated in 10% and 3% vs. 20% O2. The ex vivo mRNA expression of HIF1A and VEGFA was elevated (p < 0.001) on day 14 vs. day 12 of pregnancy. The protein expression of HIF-1 and VEGFA increased (p < 0.001), whereas the level of STAR (mRNA and protein) and progesterone dropped (p < 0.001) on day 14 of the estrous cycle vs. a parallel day of pregnancy and/or day 12 of the estrous cycle. The content of phosphorylated cJUN and CREB was elevated (p < 0.01) in the luteal tissue on day 12 or 14 of pregnancy vs. parallel days of the estrous cycle. These increases of phosphorylated cJUN and CREB may be involved in STAR expression in the luteal tissue during early pregnancy in gilts.

Follicular Hyperstimulation Dysgenesis: New Explanation for Adverse Effects of Excessive FSH in Ovarian Stimulation

High follicle-stimulating hormone (FSH) doses during ovarian stimulation protocols for assisted reproductive technologies (ART) are detrimental to ovulatory follicle function and oocyte quality. However, the mechanisms are unclear. In a small ovarian reserve heifer model, excessive FSH doses lead to phenotypic heterogeneity of ovulatory size follicles, with most follicles displaying signs of premature luteinization and a range in severity of abnormalities. By performing whole transcriptome analyses of granulosa cells, cumulus cells, and oocytes from individual follicles of animals given standard or excessive FSH doses, we identified progressive changes in the transcriptomes of the 3 cell types, with increasing severity of follicular abnormality with the excessive doses. The granulosa and cumulus cells each diverged progressively from their normal phenotypes and became highly similar to each other in the more severely affected follicles. Pathway analysis indicates a possible dysregulation of the final stages of folliculogenesis, with processes characteristic of ovulation and luteinization occurring concurrently rather than sequentially in the most severely affected follicles. These changes were associated with disruptions in key pathways in granulosa and cumulus cells, which may account for previously reported reduced estradiol production, enhanced progesterone and oxytocin production and diminished ovulation rates. Predicted deficiencies in oocyte survival, stress response, and fertilization suggest likely reductions in oocyte health, which could further compromise oocyte quality and ART outcomes.

Current knowledge and the future potential of extracellular vesicles in mammalian reproduction

Extracellular vesicles (EVs), which contain various functional classes of vesicles, namely exosomes, microvesicles, and apoptotic bodies, represent the major nano-shuttle to transfer bioactive molecules from donor to recipient cells to facilitate cell-to-cell communication in the follicular, oviduct, and uterine microenvironments. In addition to transferring various molecular cargos in the form of miRNAs, mRNAs, proteins, lipids, and DNA molecules, the relative proportion of those molecular cargos in the reproductive fluids can be associated with the physiological and pathological condition of the host animal. Inside the follicle, EV-mediated circulation of miRNAs has been reported to be associated with the growth status of the enclosed oocytes, the metabolic status, and the advanced maternal aging of the animal. Importantly, EVs have the potential to protect their cargo molecules from extracellular degradation or modification while travelling to the recipient cells. This fact together with the enormous availability in almost all biological fluids and spent culture media make them attractive in the search for biomarkers of oocyte/embryo developmental competence, receptive maternal environment and a multitude of reproductive pathophysiological conditions. One of the key factors that have contributed to the lower efficiency of assisted reproductive technologies (ART) is the absence of several maternal in vivo factors in the ART procedures. For this, several studies have been conducted to supplement various components present in the follicular and oviductal fluids into the existing ART procedures and significant positive impacts have been observed in terms of embryo cleavage rate, blastocyst rate, resistance to stress, and survival after cryopreservation. The potential of EVs in shuttling protective messages against environmental and physiological stressors has been evidenced. The effective use of the EV-coupled molecular signals against stress-associated conditions has the potential to pave the path for the application of these protective signals against oxidative stress-associated pathological conditions including PCOS, ageing, and endometritis. In this review, we provide current knowledge and potential future use of EVs as remedies in reproductive pathophysiological conditions, mainly in follicular and oviductal microenvironments.

Insulin-like growth factor-I prevents hypoxia-inducible factor-1 alpha-dependent G1/S arrest by activating cyclin E/cyclin-dependent kinase2 via the phoshatidylinositol-3 kinase/AKT/forkhead box O1/Cdkn1b pathway in porcine granulosa cells†

As the follicle develops, the thickening of the granulosa compartment leads to progressively deficient supply of oxygen in granulosa cells (GCs) due to the growing distances from the follicular vessels. These conditions are believed to cause hypoxia in GCs during folliculogenesis. Upon hypoxic conditions, several types of mammalian cells have been reported to undergo cell cycle arrest. However, it remains unclear whether hypoxia exerts any impact on cell cycle progression of GCs. On the other hand, although the GCs may live in a hypoxic environment, their mitotic capability appears to be unaffected in growing follicles. It thus raises the question whether there are certain intraovarian factors that might overcome the inhibitory effects of hypoxia. The present study provides the first evidence suggesting that cobalt chloride (CoCl2)-mimicked hypoxia prevented G1-to-S cell cycle progression in porcine GCs. In addition, we demonstrated that the inhibitory effects of CoCl2 on GCs cell cycle are mediated through hypoxia-inducible factor-1 alpha/FOXO1/Cdkn1b pathway. Moreover, we identified insulin-like growth factor-I (IGF-I) as an intrafollicular factor required for cell cycle recovery by binding to IGF-I receptor in GCs suffering CoCl2 stimulation. Further investigations confirmed a role of IGF-I in preserving G1/S progression of CoCl2-treated GCs via activating the cyclin E/cyclin-dependent kinase2 complex through the phoshatidylinositol-3 kinase/protein kinase B (AKT)/FOXO1/Cdkn1b axis. Although the present findings were based on a hypoxia mimicking model by using CoCl2, our study might shed new light on the regulatory mechanism of GCs cell cycle upon hypoxic stimulation.

Transcriptome analysis of buffalo granulosa cells in three dimensional culture systems

Hanging drop (HD) three-dimensional (3D) culture model for buffalo granulosa cells (GC) was reported to mimic the preovulatory stage of ovarian follicles in our previous study. To further verify its reliability, the present study attempted a comparative transcriptome profile of buffalo GC freshly isolated from ovarian follicles (<8 mm diameter) (FC) and their cultures in normal culture dish (ND or 2D), polyHEMA coated dish (PH) and HD culture systems (3D). Out of 223 significantly (-log2 fold change: >3; p < .0005; false discovery rate [FDR]: <0.1) differentially expressed genes (SDEGs) among different culture systems, 137 were found unannotated, and 94, 29, and 66 were exclusively expressed in FC, PH, and HD, respectively. However, on eliminating the fixed points of p values and FDR from the entire raw data, only 11 genes related to long noncoding RNA, 12 genes related to luteinization, and 3 genes related to follicular maturation were exclusively expressed in FC, PH, and HD culture systems, respectively. The quantitative real time-PCR validation and the next generation sequencing data had more than 90% correlation. Bioinformatics analyses of the exclusively expressed SDEG revealed that the freshly aspirated GCs were a true representative of GCs from small follicles (<8 mm diameter), the GC spheroids under PH maintained mitochondrial function, and those cultured in HD system for 6 days simulated the inflammatory milieu required for ovulation. Therefore, the comparative transcriptome profile also reinforced that HD culture system is better in vitro culture method than the other methods analyzed in this study for buffalo GC.

HIF-1α Protects Granulosa Cells From Hypoxia-Induced Apoptosis During Follicular Development by Inducing Autophagy

Owing to the avascular structure of the ovarian follicle, proliferation of granulosa cells (GCs) and development of follicles occur under hypoxia, which is obviously different from the cell survival requirements of most mammalian cells. We hypothesized that autophagy may exert an inhibitory effect on GC apoptosis. To decipher the underlying mechanism, we constructed a rat follicular development model using pregnant mare serum gonadotropin and a cell culture experiment in hypoxic conditions (3% O₂). The present results showed that the autophagy level was obviously increased and was accompanied by the concomitant elevation of hypoxia inducible factor (HIF)-1α and BNIP3 (Bcl-2/adenovirus E1B 19kDa-interacting protein 3) in GCs during follicular development. The levels of Bax (Bcl2-associated X) and Bcl-2 (B-cell lymphoma-2) were increased, while the activation of caspase-3 exhibited no obvious changes during follicular development. However, inhibition of HIF-1α attenuated the increase in Bcl-2 and promoted the increase in Bax and cleaved caspase-3. Furthermore, we observed the downregulation of BNIP3 and the decrease in autophagy after treatment with a specific HIF-1α activity inhibitor (echinomycin), indicating that HIF-1α/BNIP3 was involved in autophagy regulation in GCs in vivo. In an in vitro study, we also found that hypoxia did not obviously promote GC apoptosis, while it significantly enhanced the activation of HIF-1α/BNIP3 and the induction of autophagy. Expectedly, this effect could be reversed by 3-methyladenine (3-MA) treatment. Taken together, these findings demonstrated that hypoxia drives the activation of HIF-1α/BNIP3 signaling, which induces an increase in autophagy, protecting GC from apoptosis during follicular development.

The ovarian stroma as a new frontier

Historically, research in ovarian biology has focused on folliculogenesis, but recently the ovarian stroma has become an exciting new frontier for research, holding critical keys to understanding complex ovarian dynamics. Ovarian follicles, which are the functional units of the ovary, comprise the ovarian parenchyma, while the ovarian stroma thus refers to the inverse or the components of the ovary that are not ovarian follicles. The ovarian stroma includes more general components such as immune cells, blood vessels, nerves, and lymphatic vessels, as well as ovary-specific components including ovarian surface epithelium, tunica albuginea, intraovarian rete ovarii, hilar cells, stem cells, and a majority of incompletely characterized stromal cells including the fibroblast-like, spindle-shaped, and interstitial cells. The stroma also includes ovarian extracellular matrix components. This review combines foundational and emerging scholarship regarding the structures and roles of the different components of the ovarian stroma in normal physiology. This is followed by a discussion of key areas for further research regarding the ovarian stroma, including elucidating theca cell origins, understanding stromal cell hormone production and responsiveness, investigating pathological conditions such as polycystic ovary syndrome (PCOS), developing artificial ovary technology, and using technological advances to further delineate the multiple stromal cell types.

Effect of increased oxygen availability and astaxanthin supplementation on the growth, maturation and developmental competence of bovine oocytes derived from early antral follicles

In vitro growth (IVG) culture of bovine oocyte-cumulus-granulosa complexes (OCGCs) is generally carried out for 12 or 14 days using conventional gas impermeable culture devices. The culture duration may be longer compared to follicular development in vivo. During follicular development, follicles receive oxygen from micro vessels; however, oxygen supply is limited under the culture using conventional gas impermeable devices. The purpose of this study was to investigate the effect of increasing dissolved oxygen availability using a gas permeable (GP) culture device with or without antioxidant (astaxanthin, Ax) supplementation on 8-day IVG culture systems for bovine OCGCs derived from early antral follicles. We cultured OCGCs in GP, GP supplemented with Ax (GP + Ax), and a conventional gas impermeable device (control) for 8 or 12 days. OCGC viability were significantly higher when cultured for 8 days than 12 days (p < 0.001) in all culture condition, but significant difference was not observed between groups (p > 0.05). Antrum formation rates of OCGCs were higher after 12 days than 8 days of culture in all culture condition (p < 0.001) and were significantly higher in the control than GP groups regardless of Ax supplementation (p < 0.05). Oocyte diameters were similar among day-8 GP + Ax, day-8 control and day-12 control groups (p > 0.05). Nuclear maturation rates of oocytes grown in vitro for 8 days were significantly higher in the GP + Ax group than in the control and the GP groups (p < 0.05) and similar to oocytes grown for 12 days regardless of the culture conditions (p > 0.05). The generation of reactive oxygen species in OCGCs on day 8 of IVG culture was significantly lower in the GP + Ax group than those of the GP and control groups (p < 0.05). IVG oocytes after eight days of culture developed into blastocysts, and the cleavage and blastocyst rates were similar in all treatment groups. However, in vivo-grown oocytes had significantly higher (p < 0.05) cleavage and blastocyst rates than the IVG oocytes in all groups. The present study demonstrates that increased oxygen availability using a GP culture device with Ax supplementation promotes oocyte growth and maturation competence but inhibits proliferation of granulosa cells and antrum formation compared with a conventional gas impermeable culture device, and that OCGCs can attain developmental competence after 8 days of IVG culture.

HIF1 driven transcriptional activity regulates steroidogenesis and proliferation of bovine granulosa cells

Hypoxia-inducible factor 1 (HIF1) is a heterodimeric transcription factor, consisting of a constitutively expressed β-subunit (HIF1B) and a regulated α-subunit (HIF1A). In the present study, we analyzed the HIF1 driven transcriptional activity in bovine granulosa cells (GC). Treatment of GC with FSH (follicle stimulating hormone) and IGF1 (insulin-like growth factor 1) resulted in the upregulation of HIF1A mRNA expression under normoxia. Immunohistochemistry of bovine ovarian sections showed distinct staining of HIF1A in the GC layer of different staged ovarian follicles. Suppression of HIF1 using echinomycin and gene knockdown procedures revealed that HIF1 transcriptionally regulates the genes associated with steroidogenesis (STAR, HSD3B and CYP19A1) and proliferation (CCND2 and PCNA) of GC. Further, our data suggest that CYP19A1, the key gene of estradiol production, is one of the plausible downstream targets of HIF1 in bovine GC as shown by gene expression, radioimmunoassay, and chromatin precipitation analysis. Based on these results, we propose that HIF1 driven transcriptional activity plays a crucial role in GC functionality, especially steroidogenesis and proliferation in developing bovine ovarian follicles.

Extracellular vesicle mediated molecular signaling in ovarian follicle: Implication for oocyte developmental competence

The bidirectional communication between the oocyte and the companion somatic cells in the follicular environment is known to be mediated by either a direct communication via gap junction or transzonal projections or indirectly through endocrine, paracrine and autocrine signaling factors. Extracellular vesicles (EVs), which are found in various biological fluids, including follicular fluid (FF) are known to play important roles in mediating the communication between the oocyte and the surrounding somatic cells through shuttling bioactive molecules to facilitate follicular growth and oocyte maturation. As vesicles in the extracellular space are known to reflect the physiological status of the donor or the releasing cells, molecules carried by the EVs in the follicular environment could be markers of the internal and external stressors. EVs exhibit greater degree of heterogeneity in their size, biogenesis and the bioactive molecule they carry. The process of biogenesis of EVs is known to be regulated by several proteins associated with the endosomal sorting complex required for transport (ESCRT) proteins. The type of EVs and surface proteins markers vary according to the type of protein involved in their biogenesis. EVs are recently reported to play indispensable role in promoting cell-to-cell communication during follicular growth. Recent advancements in EV research opened the possibilities to load EVs with specific molecules like miRNA, siRNA, CRISPR-cas9 complex and protein, which showed a new horizon for their application in therapeutics. The present review explores the biogenesis, the role and the future prospects of EVs with a special emphasis given to follicular growth and oocyte maturation.

Effects of Dietary Fatty Acids on Bovine Oocyte Competence and Granulosa Cells

Here we assessed the effects of dietary essential fatty acids on the developmental competence of oocytes in cows and on the functionality of follicular granulosa cells (GC). Lactating German Holstein cows were supplemented from week 9 ante partum (ap) until week 8 post-partum (pp) in four dietary groups designed as (i) control (CTRL: coconut oil), (ii) essential fatty acid (EFA: linseed and safflower oil), (iii) conjugated linoleic acid (CLA: Lutalin®), and (iv) EFA+CLA (mixture of linseed oil, safflower oil and Lutalin®). EFA, CLA or EFA+CLA supplementation did not improve in vitro embryo production. However, higher proportions of α-linolenic acid (ALA) and cis-9, trans-11 CLA were observed in the follicular fluid suggesting the exposure of GC to relatively high levels of ALA and cis-9, trans-11 CLA. Consequently, we tested different concentrations of ALA and cis-9, trans-11 CLA in a bovine GC culture model for their effects on steroid production, marker gene expression and viability. Both fatty acids upregulated CD36 and downregulated the expression of FOXL2, while ALA significantly increased SOX 9 transcript levels. Both ALA and cis-9, trans-11 CLA reduced the CCND2 expression and cis-9, trans-11 CLA induced apoptosis. ALA and cis-9, trans-11 CLA significantly down-regulated the expression of STAR, CYP19A1, FSHR, LHCGR and decreased the 17β-Estradiol (E2) and progesterone (P4) production. In conclusion, dietary lipids did not improve in vitro embryo production, while ALA and cis-9, trans-11 CLA affected the morphology and functionality of GC. This could suggestively lead to compromised follicle development and ovarian cyclicity in dairy cows.

Elevated free fatty acids affect bovine granulosa cell function: a molecular cue for compromised reproduction during negative energy balance

High-yielding dairy cows postpartum face the challenge of negative energy balance leading to elevated free fatty acids levels in the serum and follicular fluid thus affecting the ovarian function. Here, we investigated effects of physiological concentrations of palmitic acid (PA), stearic acid (SA) and oleic acid (OA) on the viability, steroid production and gene expression in a bovine granulosa cell (GC) culture model. Treatment with individual and combined fatty acids increased the CD36 gene expression, while no significant apoptotic effects were observed. Both PA and SA significantly upregulated the expression of FSHR, LHCGR, CYP19A1, HSD3B1, CCND2 and increased 17β-estradiol (E2) production, while OA downregulated the expression of these genes and reduced E2. Interestingly, STAR was equally downregulated by all fatty acids and combination treatment. E2 was significantly reduced after combination treatment. To validate the effects of OA, in vivo growing dominant follicles (10-19 mm) were injected with bovine serum albumin (BSA) with/without conjugated OA. The follicular fluid was recovered 48 h post injection. As in our in vitro model, OA significantly reduced intrafollicular E2 concentrations. In addition, expression of CD36 was significantly up- and that of CYP19A1 and STAR significantly downregulated in antral GC recovered from aspirated follicles. The ovulation rates of OA-injected follicles tended to be reduced. Our results indicate that elevated free fatty acid concentrations specifically target functional key genes in GC both in vitro and in vivo. Suggestively, this could be a possible mechanism through which elevated free fatty acids affect folliculogenesis in dairy cows postpartum.

L-lactate induces specific genome wide alterations of gene expression in cultured bovine granulosa cells

Background

Previously, we could show that L-lactate affects cultured bovine granulosa cells (GC) in a specific manner driving the cells into an early pre-ovulatory phenotype. Here we studied genome wide effects in L-lactate-treated GC to further elucidate the underlying mechanisms that are responsible for the L-lactate induced transformation. Cultured estrogen producing GC treated either with L-lactate or vehicle control were subjected to mRNA microarray analysis.

Results

The analysis revealed 487 differentially expressed clusters, representing 461 annotated genes. Of these, 333 (= 318 genes) were identified as up- and 154 (= 143 genes) as down-regulated. As the top up-regulated genes we detected TXNIP, H19 and AHSG as well as our previously established marker transcripts RGS2 and PTX3. The top down-regulated genes included VNN1, SLC27A2 and GFRA1, but also MYC and the GC marker transcript CYP19A1. Pathway analysis with differentially expressed genes indicated “cAMP-mediated signaling” and “Axon guidance signaling” among the most affected pathways. Furthermore, estradiol, progesterone and Vegf were identified as potential upstream regulators. An effector network analysis by IPA provided first hints that processes of “angiogenesis” and “vascularization”, but also “cell movement” appeared to be activated, whereas “organismal death” was predicted to be inhibited.

Conclusions

Our data clearly show that L-lactate alters gene expression in cultured bovine GC in a broad, but obviously specific manner. Pathway analysis revealed that the mode of L-lactate action in GC initiates angiogenic processes, but also migratory events like cell movement and axonal guidance signaling, thus supporting the transformation of GC into an early luteal phenotype.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5657-6) contains supplementary material, which is available to authorized users.