Coordinated dysfunction in oxidative phosphorylation-related proteins and a delayed acrosome reaction during sperm...

Although dynamic changes of proteomes during sperm capacitation are well documented by the advanced proteomic research, spatiotemporal changed proteins during capacitation according to sperm fertility remain elusive. This study aimed to investigate temporal protein changes in spermatozoa during capacitation in relation to fertility status. Initially, proteomic analysis was conducted on spermatozoa at early (20 min) and late (120 min) stages of capacitation to comprehensively identify protein modifications during capacitation, irrespective of fertility status (n = 6). After late capacitation, a decrease in acrosome vesicle-associated proteins and an increase in oxidative phosphorylation (OXPHOS)-related proteins were observed. To determine whether these temporal protein changes are linked to fertility status, western blot were conducted using normal fertility (NF, n = 5) and below-normal fertility (BNF, n = 5) bulls during capacitation. We found that mitochondrial respiratory complex proteins II-IV were abundant in BNF spermatozoa before and during capacitation. During capacitation, NF sperm showed gradual acrosomal protein degradation, while BNF sperm retained intact proteins and showed higher ROS accumulation in the acrosome after late capacitation. These results suggest that systemic instability in OXPHOS may promote ROS accumulation in the acrosome during late capacitation, potentially delaying the acrosome reaction and thereby reducing fertility.