A novel role of follicular fluid chemokine CCL21 in promoting porcine oocyte in vitro maturation through activating ERK1/2 signaling pathway

Follicular fluid (FF) is recognized for its ability to enhance oocyte in vitro maturation (IVM), yet the specific factors responsible for this effect remain largely unidentified. In this study, 44 extracellular specifically expressed proteins were identified in FF, among which CCL21 was predicted to play a role in regulating oocyte maturation. Treatment with 50 ng/mL CCL21 significantly increased the rate of oocyte polar body extrusion (PBE). Furthermore, CCL21 significantly promoted spindle assembly, and reduced the level of DNA damage marker γ-H2AX. And more, CCL21 obviously increased endoplasmic reticulum (ER) content, decreased ER stress (ERS) and Reactive Oxygen Species (ROS) level, and enhanced Golgi apparatus submembrane distribution and glutathione (GSH) content. Notably, CCL21 elevated the level of p-ERK1/2. Further investigation showed that inhibition of ERK1/2 signaling with FR180204 markedly reduced p-ERK1/2 level, disrupted spindle morphology, and increased γ-H2AX level. Additionally, inhibition of ERK1/2 signaling significantly decreased ER and GSH contents, impaired Golgi apparatus submembrane distribution and increased ERS and ROS levels. These changes collectively led to a significant decrease in the PBE rate. When FR180204 was applied together with CCL21, it largely reversed the beneficial effects of CCL21 on these parameters and suppressed PBE. In conclusion, CCL21 promotes porcine oocyte maturation by activating ERK1/2 signaling pathway. This study provides new insights for optimizing oocyte IVM system, with potential applications in Animal Husbandry and human assisted reproductive technology.

CCL21; Cytoplasmic maturation; ERK1/2 signaling pathway; Nuclear maturation; Oocyte; Pig.