Polydopamine-based nano-protectant for prolonged boar semen preservation by eliminating ROS and regulating protein phosphorylation via D2DR-mediated cAMP/PKA signaling pathway

Preservation of porcine semen is essential for artificial insemination and genetic improvement in pig breeding programs. However, the overproduction of reactive oxygen species (ROS) and lower levels of protein phosphorylation emerge as two challenges during semen preservation. Inspired by the innate ligand-receptor binding biofunction of dopamine, herein, a dual-task nano-protectant that combines ROS-scavenging and protein phosphorylation-regulating properties via incorporating the natural antioxidant epigallocatechin gallate (EGCG) into polydopamine nanoparticles (EGCG@PDA NPs) was proposed to enhance the quality of pig semen during storage at 4 ℃. The results suggested that EGCG@PDA NPs significantly maintained sperm motility, acrosome integrity and mitochondrial membrane potential, extending semen storage time from 3 days to 10 days. Furthermore, EGCG@PDA NPs effectively scavenged excess ROS and inhibited ROS-mediated sperm apoptosis through the extracellular regulated protein kinases (ERK) signaling pathway. Intriguingly, EGCG@PDA NPs could degrade into ultrasmall particles (< 10 nm) in the semen or H₂O₂ systems. These particles could target and activate the dopamine D2 receptor (D2DR) on membrane surface of sperm midpiece, thereby enhancing protein phosphorylation via the downstream cyclic adenosine monophosphate/protein kinase A (cAMP/PKA) signaling pathway, ultimately improving sperm motility parameters. This study presents a novel nano-strategy to boost the quality of pig semen, offering significant implications for the pig industry.