Prematuration with urokinase-type plasminogen activator improves oocyte development alongside cAMP-associated gap junctional communication

Urokinase-type plasminogen activator (PLAU) has established roles in reproduction, but its function during oocyte maturation remains unclear. We investigated whether PLAU–PLAUR signaling during a 2-h pretreatment before conventional in vitro maturation (IVM) is associated with cyclic adenosine monophosphate (cAMP)-related cumulus–oocyte gap-junctional communication (GJC), intraoocyte reduced glutathione (GSH), and subsequent developmental competence in bovine cumulus–oocyte complexes (COCs). PLAU and PLAUR proteins both localized to cumulus cells, but only PLAUR was present in bovine oocytes. Follicular-fluid PLAU concentrations were higher in large antral follicles (875 pg/mL) than in small-to-medium antral follicles (247 pg/mL). Compared with conventional IVM, with or without PLAU, a 2-h PLAU pretreatment before conventional IVM was associated with improved subsequent embryo development and quality. PLAU treatment increased intra-COC cAMP and delayed meiotic resumption; both responses were attenuated by amiloride or a PLAUR-blocking antibody. PLAU treatment was associated with higher semi-quantitative LY-transfer scores before and during IVM, and Rp-cAMP attenuated this response, consistent with the involvement of a PKA-sensitive component of cAMP signaling in functional cumulus–oocyte coupling. PLAU treatment was also associated with increased intraoocyte GSH, and this increase was attenuated by carbenoxolone (CBX). Amiloride and PLAUR blockade eliminated the developmental benefit associated with PLAU pretreatment. PLAU–PLAUR signaling during a 2-h pretreatment before conventional IVM was associated with increased intra-COC cAMP, prolonged functional cumulus–oocyte coupling, higher intraoocyte GSH, and improved developmental competence. These findings support the involvement of the PLAU–PLAUR system in the established cAMP–GJC axis but do not establish a strictly linear causal pathway. This association may inform further efforts to improve IVM outcomes.