Heat shock affects the Ca 2+ /calmodulin-dependent protein kinase II dynamic during bovine sperm capacitation and acrosome reaction

Thais Sousa Santos ¹ Isabelle Scarpini Contrim ¹ Daniela Franco Silva ² Mayra Elena Ortiz DAvila Assumpção ³ Fabíola Freitas de Paula-Lopes ¹ Weber Beringui Feitosa ^4*

• ¹ Department of Biological Science, Institute of Environmental, Chemical and Pharmaceutical Sciences, Federal University of São Paulo, Diadema, Brazil
• ² Institute of Biosciences, State University of Sao Paulo, Botucatu, Brazil
• ³ Department of Animal Reproduction, Faculty of Veterinary Medicine and Animal Science, University of Sao Paulo, Sao Paulo, São Paulo, Brazil
• ⁴ Department of Biological Science, Institute of Environmental, Chemical and Pharmaceutical Sciences - Federal University of São Paulo, Diadema, Brazil

Heat shock during sperm capacitation affects the spermatozoa quality, resulting in increased early acrosome reaction and consequently decreasing their fertilizing capacity. Although the mechanisms involved in the regulation of sperm capacitation and acrosome reaction are not fully understood, it has been reported that Ca 2+ /calmodulin-dependent protein kinase II (CaMKII) is an important regulator of these processes. Thus, the present aimed to evaluate the effect of heat shock in the CaMKII signaling during the bovine sperm capacitation and acrosome. For that, bovine spermatozoa were submitted to in vitro capacitation and acrosome reaction at 38.5 °C (Control) or at 41 °C (Heat stress). It was observed that CaMKII and not phosphorylated CaMKII (pCaMKII) localization at the acrosome region was affected by sperm capacitation. In contrast, the localization of both, CaMKII and its phosphorylated form was affected by the acrosome reaction (p ˂ 0.05). The acrosome membrane integrity, as well as the pCamKII localization in bovine spermatozoa, was affected by incubation time. This effect of incubation time was stronger in heated shock sperm, although it was observed only after 2h of incubation. Heat shock also affected the acrosomal localization of pCaMKII in the acrosomal region of spermatozoa with intact acrosome. Taken together, the data present here show that CaMKII and pCaMKII localization is dynamic during bovine sperm capacitation and acrosome reaction and that this pattern of localization is affected by heat shock, suggesting that failure in CaMKII signaling is probably involved in the early acrosome reaction observed in heated-shock spermatozoa.