Role of the Ca2+-ATPase Pump (SERCA) in Capacitation and the Acrosome Reaction of Cryopreserved Bull Spermatozoa

Cryopreservation of sperm is a resource used for artificial insemination. In the case of bovines, it ensures the reproduction of animals through cells from males with a highlighted genetic background. The fertilisation capacity of sperm cells is achieved after capacitation, a process that includes subcellular modifications that could be altered by cryopreservation. Intracellular calcium handling plays a crucial role in the development of capacitation, culminating in the acrosomal reaction. SERCA protein is responsible for calcium reuptake into the acrosome, which is one of the main calcium reservoirs of sperm cells. In this work, we studied the relationships between SERCA activity and sperm motility, capacitation progression, actin polymerisation, and intracellular calcium handling in cryopreserved bovine spermatozoa. Inhibition of SERCA activity reduced sperm motility and induced hyperactivation patterns. It also increased the proportion of cells with acrosomal reaction and earlier actin depolymerisation, an event necessary to induce the acrosomal reaction. All changes occurred in concordance with a significant increase in intracellular calcium concentration (Ca²⁺). Our findings suggest that a thapsigargin-sensitive Ca²⁺ pump consistent with SERCA activity remains responsive in cryopreserved spermatozoa from the bull studied, under specific cryopreservation and incubation conditions tested, and may contribute to Ca²⁺ handling, motility changes, and premature acrosomal exocytosis.