HSP90 maintains boar spermatozoa motility and mitochondrial membrane potential during heat stress

Heat Shock Proteins (HSP) is a family of proteins that protects cells from high temperatures. The present work aimed to elucidate the role that HSP90 exerts on boar sperm incubated under heat stress conditions on viability, total motility (TM), progressive motility (PM), acrosome status, mitochondrial membrane potential and plasma membrane lipid organization. Sperm were incubated in non-capacitating conditions (Tyrode's basal medium or TBM) for 3, 8 and 24 h or in capacitating conditions (Tyrode's complete medium or TCM) for 4 h at 38.5 °C or 40 °C (Heat stress) in the presence or absence of 5 or 20 μM of 17-AAG, a specific HSP90 inhibitor. Sperm viability was not affected by the presence of 17-AAG in any condition tested compared with its own control (at the same temperature and incubation time). In non-capacitating conditions TM (22.7 ± 4.1 vs. 1.9 ± 1.1; % mean ± SEM), PM (3.1 ± 0.9 vs. 0) and high mitochondrial membrane potential (19.5 ± 2.2 vs. 11.8 ± 0.8) decreased significantly in sperm incubated at 40 °C for 24 h in the presence of 20 μM 17-AAG (control vs. 20 μM 17-AAG, respectively; p < 0.05). In sperm incubated at 38.5 °C only a mild decrease in TM was observed (48.7 ± 3.1 vs. 32.1 ± 4.8; control vs. 20 μM 17-AAG, respectively; p < 0.05). However, under capacitating conditions none of the sperm parameters studied were affected by 17-AAG after 4 h of incubation. These results demonstrate for the first time the role of HSP90 in the maintenance of boar sperm motility and mitochondrial membrane potential during prolonged heat stress in non-capacitating conditions.