G protein-coupled estrogen receptor signaling dependent epidermal growth-like factor expression is required for NPR2 inhibition and meiotic resumption in goat oocytes

Estrogen influences the transzonal projection assembly of cumulus-oocyte complexes through G protein-coupled estrogen receptor during goat follicle development

Estrogen is an important hormone that plays a role in regulating follicle development and oocyte maturation. Transzonal projections (TZPs) act as communication bridges between follicle somatic cells and oocytes, and their dynamic changes are critical for oocyte development and maturation. However, the roles and mechanisms of estrogen in regulating TZPs during follicular development are not yet understood. We found that the proportion of oocytes spontaneously resuming meiosis increases as the follicle grows, which is accompanied by rising estrogen levels in follicles and decreasing TZPs in cumulus-oocyte complex. To further explore the effect of elevated estrogen levels on TZP assembly, additional estrogen was added to the culture system. The increased estrogen level significantly decreased the mRNA and protein expression levels of TZP assembly-related genes. Subsequent research revealed that TZP regulation by estrogen was mediated by the membrane receptor GPER and downstream ERK1/2 signaling pathway. In summary, our study suggests that estrogen may regulate goat oocyte meiosis arrest by decreasing TZP numbers via estrogen-mediated GPER activation during follicle development.

Growth differentiation factor 9 regulates the expression of estrogen receptors via Smad2/3 signaling in goat cumulus cells

Both oocyte secretory factors (OSFs) and estrogen are essential for the development and function of mammalian ovarian follicles, playing synergistic role in regulating oocyte growth. OSFs can significantly affect the biological processes regulated by estrogen in cumulus cells (CCs). It is a scientific question worth investigating whether oocyte secretory factors can influence the expression of estrogen receptors in CCs. In our study, we observed a significant increase in the mRNA and protein expressions of estrogen receptor β (Esr2/ERβ) and G-protein-coupled estrogen receptor (GPER) in cumulus cells of goat cumulus-oocyte complexes (COCs) cultured in vitro for 6 h. Furthermore, the addition of 10 ng/mL growth-differentiation factor 9 (GDF9) and 5 ng/mL bone morphogenetic protein 15 (BMP15) to the culture medium of goat COCs resulted in a significant increase in the expressions of ERβ and GPER in cumulus cells. To explore the mechanism further, we performed micromanipulation to remove oocyte contents and co-cultured the oocytectomized complexes (OOXs) with denuded oocytes (DOs) or GDF9/BMP15. The expressions of ERβ and GPER in the co-culture groups were significantly higher than those in the OOXs group, but there was no difference compared to the COCs group. Mechanistically, we found that SB431542 (inhibitor of GDF9 bioactivity), but not LDN193189 (inhibitor of BMP15 bioactivity), abolished the upregulation of ERβ and GPER in cumulus cells and the activation of Smad2/3 signaling. In conclusion, our results demonstrate that the oocyte secretory factor GDF9 promotes the activation of Smad2/3 signaling in cumulus cells during goat COCs culture in vitro, and the phosphorylation of Smad2/3 induces the expression of estrogen receptors ERβ and GPER in cumulus cells.

Sulforaphane Suppresses H2O2-Induced Oxidative Stress and Apoptosis via the Activation of AMPK/NFE2L2 Signaling Pathway in Goat Mammary Epithelial Cells

Oxidative stress in high-yielding dairy goats adversely affects lactation length, milk quality, and the economics of dairy products. During the lactation period, goat mammary epithelial cells (GMECs) are often in a state of disordered metabolic homeostasis primarily caused by the overproduction of reactive oxygen species (ROS). Sulforaphane (SFN), an electrophilic compound that is enriched in broccoli, is a promising antioxidant agent for future potential clinical applications. The objective of the present study was to investigate the function of SFN on hydrogen peroxide (H₂O₂)-induced oxidative damage in primary GMECs and the underlying molecular mechanisms. Isolated GMECs in triplicate were pretreated with SFN (1.25, 2.5, and 5 μM) for 24 h in the absence or presence of H₂O₂ (400 μM) for 24 h. The results showed that SFN effectively enhanced superoxide dismutase (SOD) activity, elevated the ratio of glutathione (GSH)/glutathione oxidized (GSSG), and reduced H₂O₂-induced ROS and malondialdehyde (MDA) production and cell apoptosis. Mechanically, SFN-induced nuclear factor erythroid 2-related factor 2 (NRF2/NFE2L2) translocation to the nucleus through the activation of the adenosine monophosphate-activated protein kinase (AMPK) signaling pathway coupled with inhibition of the caspase apoptotic pathway. In addition, GMECs were transfected with NFE2L2 small interfering RNA (NFE2L2 siRNA) for 48 h and/or treated with SFN (5 μM) for 24 h before being exposed to H₂O₂ (400 μM) for 24 h. We found that knockdown of NFE2L2 by siRNA abrogated the preventive effect of SFN on H₂O₂-induced ROS overproduction and apoptosis. Taken together, sulforaphane suppressed H₂O₂-induced oxidative stress and apoptosis via the activation of the AMPK/NFE2L2 signaling pathway in primary GMECs.

E2/ER signaling mediates the meiotic arrest of goat intrafollicular oocytes induced by follicle-stimulating hormone

The increased production of high-quality oocytes lies at the heart of the search to accelerate the reproduction of high-quality breeding livestock using assisted reproductive technology. Follicle-stimulating hormone (FSH) maintains the arrest of oocyte meiosis during early follicular development in vivo and promotes the synchronous maturation of nucleus and cytoplasm to improve oocyte quality. However, the mechanism by which FSH maintains meiotic arrest in oocytes is still not fully understood. Oocytes spontaneously resume meiosis once released from the arrested state. In this study, we isolated goat antral follicles with a diameter of 2.0-4.0 mm, cultured them in vitro either with or without added FSH, and finally collected the oocytes to observe their meiotic state. The results showed that FSH effectively inhibited the meiotic recovery of oocytes in follicles [4 h: control (n = 84) vs. with FSH (n = 86), P = .0115; 6 h: control (n = 86) vs. FSH (n = 85), P = 0.0308; and 8 h: control (n = 95) vs. FSH (n = 101), P = 0.0039]. FSH significantly inhibited the downregulation of natriuretic peptide receptor 2 (NPR2) expression and cyclic guanosine monophosphate (cGMP) synthesis during follicular culture in vitro (P < 0.05). Further exploration found that FSH promoted the synthesis of 17β-estradiol (E2) (P = .0249 at 4 h and P = .0039 at 8 h) and maintained the expression of the estrogen nuclear receptor ERβ, but not the estrogen nuclear receptor ERα during follicle culture in vitro (P = .0190 at 2 h, and P = .0100 at 4 h). In addition, E2/ER (estrogen nuclear receptors ERα and ERβ) mediated the inhibitory effect of FSH on the downregulation of NPR2 expression and cGMP synthesis, ultimately preventing the meiotic recovery of oocytes (P < .05). In summary, our study showed that FSH-induced estrogen production in goat follicles, and the E2/ER signaling pathway, both mediated meiotic arrest in FSH-induced goat oocytes.