Beneficial Effects of Neurotrophin-4 Supplementation During in vitro Maturation of Porcine Cumulus-Oocyte Complexes and Subsequent Embryonic Development After Parthenogenetic Activation

Supplementation with fibroblast growth factor 7 during in vitro maturation of porcine cumulus-oocyte complexes improves oocyte maturation and early embryonic development

In vitro generation of porcine embryos is an indispensable method in the realms of both agriculture and biomedicine. Nonetheless, the extant procedures encounter substantial obstacles pertaining to both the caliber and efficacy of the produced embryos, necessitating extensive research to in vitro maturation (IVM), the seminal commencement phase. One potentially fruitful approach may lie in refining the media and supplements composition utilized for oocyte maturation. Fibroblast growth factor-7 (FGF7), alternatively termed keratinocyte growth factor, is a theca-derived cytokine integral to folliculogenesis. This study aimed to examine the ramifications of supplementing FGF7 during the IVM phase. To determine the FGF7 location and its receptor in porcine ovaries, immunohistochemistry was executed based on follicle size categories (1-2, 3-6, and 7-9 mm). Regardless of follicle size, it was determined that FGF7 was expressed in theca and granulosa cells (GCs), whereas the FGF7 receptor was only expressed in the GCs of the larger follicles. During the IVM process, the maturation medium was supplied with various concentrations of FGF7, aiming to mature porcine cumulus-oocyte complexes (COCs). The data indicated a significant augmentation in the nuclear maturation rate only within the group treated with 10 ng/mL of FGF7 (p < 0.05). Post-IVM, the oocytes diameter exhibited a significant expansion in all groups that received FGF7 supplementation (p < 0.05). Additionally, all FGF7-supplemented groups exhibited a substantial elevation in intracellular glutathione levels, coupled with a noticeable reduction in reactive oxygen species levels (p < 0.05). With respect to gene expressions related to apoptosis, FGF7 treatment elicited a downregulation of pro-apoptotic genes and an upregulation of anti-apoptotic genes. The expression of genes associated with antioxidants underwent a significant enhancement (p < 0.05). In terms of the FGF7 signaling pathway-associated genes, there was a significant elevation in the mRNA expression of ERK1, ERK2, c-kit, and KITLG (p < 0.05). Remarkably, the group of 10 ng/mL of FGF7 demonstrated an appreciable uptick in the blastocyst formation rate during embryonic development post-parthenogenetic activation (p < 0.05). In conclusion, the FGF7 supplementation during IVM substantially augments the quality of matured oocytes and facilitates the subsequent development of parthenogenetically activated embryos. These results offer fresh perspectives on improved maturation and following in vitro evolution of porcine oocytes.

Neurotrophin-4 promotes the specification of trophectoderm lineage after parthenogenetic activation and enhances porcine early embryonic development

Neurotrophin-4 (NT-4), a neurotrophic factor, appears to affect early embryonic development because it is secreted not only by neurons but also by oviductal and uterine epithelial cells. However, no studies have characterized the effects of NT-4 on early embryonic development in pigs. In this study, we applied the experimental model of parthenogenetic-activation (PA)-derived embryos. Herein, we investigated the effect of NT-4 supplementation during the in vitro culture (IVC) of embryos, analyzed the transcription levels of specific genes, and outlined the first cell lineage specification for porcine PA-derived blastocysts. We confirmed that NT-4 and its receptor proteins were localized in both the inner cell mass (ICM) and trophectoderm (TE) in porcine blastocysts. Across different concentrations (0, 1, 10, and 100 ng/mL) of NT-4 supplementation, the optimal concentration of NT-4 to improve the developmental competence of porcine parthenotes was 10 ng/mL. NT-4 supplementation during porcine IVC significantly (p < 0.05) increased the proportion of TE cells by inducing the transcription of TE lineage markers (CDX2, PPAG3, and GATA3 transcripts). NT-4 also reduced blastocyst apoptosis by regulating the transcription of apoptosis-related genes (BAX and BCL2L1 transcripts) and improved blastocyst quality via the interaction of neurotrophin-, Hippo-yes-associated protein (Hippo-YAP) and mitogen-activated protein kinase/extracellular regulated kinase (MAPK/ERK) pathway. Additionally, NT-4 supplementation during IVC significantly (p < 0.05) increased YAP1 transcript levels and significantly (p < 0.01) decreased LATS2 transcript levels, respectively, in the porcine PA-derived blastocysts. We also confirmed through fluorescence intensity that the YAP1 protein was significantly (p < 0.001) increased in the NT-4-treated blastocysts compared with that in the control. NT-4 also promoted differentiation into the TE lineage rather than into the ICM lineage during porcine early embryonic development. In conclusion, 10 ng/mL NT-4 supplementation enhanced blastocyst quality by regulating the apoptosis- and TE lineage specification-related genes and interacting with neurotrophin-, Hippo-YAP-, and MAPK/ERK signaling pathway during porcine in vitro embryo development.

The effect of C–C motif chemokine ligand 2 supplementation on in vitro maturation of porcine cumulus-oocyte complexes and subsequent developmental competence after parthenogenetic activation

Porcine embryos are used for a variety of applications. However, the maturation rate in vitro remains low, and novel in vitro maturation (IVM) techniques that facilitate the collection of mature oocytes are necessary. C-C motif chemokine ligand 2 (CCL2) is a key periovulatory chemokine present in cumulus-oocyte complexes (COCs). We aimed to examine the effects of CCL2 supplementation during IVM on oocyte maturation and embryonic development. The CCL2 concentration was significantly higher in porcine follicular fluid (pFF) derived from follicles &gt;8 mm in size than in pFF derived from smaller follicles. There was a significant increase in CCL2 mRNA levels in all follicular cells after IVM compared with that before IVM. We analyzed the localization of CCL2 and its receptor, the CCL2 receptor, in follicular cells. During IVM, different concentrations of CCL2 were added to COCs cultured in a maturation medium. After IVM, the group treated with 100 ng/mL CCL2 showed significantly higher metaphase II rates than the control group. All CCL2-treatment groups showed a significant increase in intracellular glutathione levels and a significant decrease in reactive oxygen species levels, compared to the control. In CCs treated with 100 ng/mL CCL2, the mRNA levels of BAX, CASP3, and NPR2 were significantly decreased. Furthermore, the mRNA levels of SOD1, SOD2, and CD44 were significantly increased. In oocytes treated with 10 ng/mL CCL2, mRNA levels of BAX and CASP3 were significantly decreased, whereas, NRF2 and NPM2 were significantly increased. ERK1 exhibited significantly increased mRNA expression in both CCs and oocytes treated with 10 ng/mL CCL2. The protein expression ratio of phosphorylated ERK1/2 to total ERK1/2 was significantly increased in CCs treated with 10 ng/mL CCL2. After parthenogenetic activation, cleavage rates were significantly improved in the 100 ng/mL CCL2 treatment group, and blastocyst formation rates were significantly enhanced in the 10 ng/mL CCL2 treatment group. Overall, our results suggest that IVM medium along with CCL2 improves porcine oocyte maturation and the development of parthenogenetically-activated embryos.

Interleukin-7 enhances in vitro development and blastocyst quality in porcine parthenogenetic embryos

Interleukin-7 (IL-7), a vital factor that affects cell development, proliferation, and survival, plays an important role in oocyte maturation. However, its role in embryonic development remains unknown. Therefore, in this study, we aimed to investigate the effects of IL-7 supplementation on in vitro culture (IVC) of porcine embryos after parthenogenetic activation (PA) based on characteristics such as cleavage, blastocyst formation rate, intracellular glutathione (GSH) and reactive oxygen species (ROS) levels in cleaved embryos, total cell number, apoptosis rate, and cell lineage specification in blastocysts. Immunofluorescence revealed that IL-7 and its receptor, IL-7Rα (IL-7R) localized in the cytoplasm of porcine parthenote embryos. By supplementing the IVC medium (PZM5) with various concentrations of IL-7, an optimal concentration that enhanced embryonic development, promoted intracellular GSH, and decreased ROS levels in the cleavage stage during porcine embryo IVC was determined. Investigation of mRNA expression patterns via qRT-PCR suggested that IL-7 possibly regulated maternal mRNA clearance and zygotic genome activation. Furthermore, IL-7 supplementation reduced blastocyst apoptosis, enhanced the expression of the inner cell mass marker SOX2, and phosphorylated STAT5 levels in the blastocysts. Moreover, it altered the transcription patterns of genes that regulate apoptosis, IL-7 signaling, and development. Thus, we demonstrated the localization of IL-7 and IL-7R in porcine preimplantation embryos in vitro for the first time. Furthermore, we suggest that IL-7 supplementation can be employed to enhance embryonic development and blastocyst quality based on the activation of the transcripts of genes that are involved in developmental competence and IL-7 signaling during in vitro porcine embryo development following PA.

Neurotrophic factors in the porcine ovary: Their effects on follicular growth, oocyte maturation, and developmental competence

Pigs are cost-effective industrial animals because they produce a large number of offspring and have shorter rebreeding intervals compared with other animals, such as non-human primates. The reproductive physiology of pigs has been studied over the past several decades. However, there is not enough research on the effects of the neurotrophic factors on the ovarian physiology and development in pigs. As the ovary is a highly innervated organ, various neurotrophic factors during ovarian development can promote the growth of nerve fibers and improve the development of ovarian cells. Thus, investigating the role of neurotrophic factors on ovarian development, and the relationship between neurotrophic factors and porcine female reproduction is worth studying. In this review, we focused on the physiological roles of various neurotrophic factors in porcine ovaries and summarized the current status of the studies related to the relationship between neurotrophic factors and porcine ovarian development.

Physiological and Functional Roles of Neurotrophin-4 During In Vitro Maturation of Porcine Cumulus–Oocyte Complexes

Neurotrophin-4 (NT-4), a granulosa cell-derived factor and a member of the neurotrophin family, is known to promote follicular development and oocyte maturation in mammals. However, the physiological and functional roles of NT-4 in porcine ovarian development are not yet known. The aim of this study was to investigate the physiological role of NT-4-related signaling in the in vitro maturation (IVM) of porcine cumulus–oocyte complexes (COCs). The NT-4 protein and its receptors were detected in matured porcine COCs via immunofluorescence analysis. NT-4 was shown to promote the maturation of COCs by upregulating NFKB1 transcription via the neurotrophin/p75NTR signaling pathway. Notably, the mRNA expression levels of the oocyte-secreted factors GDF9 and BMP15, sperm–oocyte interaction regulator CD9, and DNA methylase DNMT3A were significantly upregulated in NT-4-treated than in untreated porcine oocytes. Concurrently, there were no significant differences in the levels of total and phosphorylated epidermal growth factor receptor and p38 mitogen-activated protein kinase between NT-4-treated and untreated cumulus cells (CCs); however, the level of phosphorylated ERK1/2 was significantly higher in NT-4-treated CCs. Both total and phosphorylated ERK1/2 levels were significantly higher in NT-4-treated than in untreated oocytes. In addition, NT-4 improved subsequent embryonic development after in vitro fertilization and somatic cell nuclear transfer. Therefore, the physiological and functional roles of NT-4 in porcine ovarian development include the promotion of oocyte maturation, CC expansion, and ERK1/2 phosphorylation in porcine COCs during IVM.