Glycine regulates in vitro nutrient sensing of porcine oocytes through AMPK-mTORC1

In vitro maturation (IVM) of oocytes is essential for enhancing reproductive efficiency in livestock. Investigating the nutrient-sensing mechanisms of oocytes is crucial for understanding the regulatory networks governing oocyte growth and metabolism. This study aimed to elucidate how Glycine is sensed nutritionally by porcine oocytes, thereby offering nutritional compensation under low glucose stress to sustain normal biological functions during in vitro development. We assessed indicators related to oocyte maturation, early embryonic development, mitochondrial function, and energy metabolism across four groups: control (Con), low glucose (LG), Glycine (Gly), and low glucose plus Glycine (LG + Gly). The findings indicated that the LG stress group experienced significant impairments in both oocyte and embryonic development, which were associated with excessive accumulation of reactive oxygen species (ROS), a notable decrease in adenosine triphosphate (ATP) levels, substantial mitochondrial accumulation of Ca²⁺, and compromised mitochondrial function. Analysis of the key cross-talk pathway AMPK-mTORC1, which is involved in energy metabolism, revealed that LG stress led to excessive activation of AMPK and inhibition of mTORC1. Glycine supplementation restored the activities of AMPK and mTORC1 to levels comparable to the Control group, significantly reduced ROS production, increased ATP content, and markedly upregulated the mRNA expression of PGC-1 and RHEB, indicating the recovery of normal mitochondrial function and the occurrence of "nutritional compensation."These findings indicate that Glycine can mitigate the imbalance in energy metabolism pathways caused by low glucose stress. Additionally, the detection of eIF4E at both the protein and transcriptional levels revealed that Glycine enhances its expression. Furthermore, the results demonstrated a suppression of H3K27me3 expression alongside an activation of H3K36me3, which further elucidates the improvement in embryonic development. In conclusion, Glycine-mediated nutritional compensation supplies additional energy for oocyte in vitro maturation (IVM) and early embryonic development by regulating AMPK and mTORC1. This regulation alleviates the issues of reduced mitochondrial function, insufficient energy supply, and abnormal oocyte-to-embryo transition induced by low glucose stress during porcine oocyte IVM. This study lays a foundation for advancing the theory of oocyte nutrient sensing.