GRP78 plays a key role in sperm function via the PI3K/PDK1/AKT pathway.

Glucose-regulated protein 78 (GRP78), which is commonly found in the endoplasmic reticulum (ER), is involved in stabilizing ER proteins and inducing the unfolded protein response. Furthermore, GRP78 is expressed on the surface of most common cancer cells, such as cells of breast, lung, liver, and prostate cancers, and plays a role in apoptosis and cell proliferation via the PI3K/PDK1/AKT signaling pathway. Therefore, various trials have been performed for evaluating cancer treatment by inhibiting GRP78. Moreover, GRP78 is expressed on the surface of spermatozoa; however, its role in spermatozoa physiology remains unclear. Therefore, this study was designed to investigate the effects of GRP78 on sperm function during capacitation and elucidate the underlying mechanisms. Boar spermatozoa were exposed to various concentrations of HA15, a GRP78 antagonist, and sperm kinematic parameters, capacitation status, cell viability, levels of PI3K/PDK1/AKT-pathway related proteins, and tyrosine phosphorylation were evaluated. GRP78 inhibition significantly decreased sperm motility, kinematic parameters, capacitated and acrosome-reacted spermatozoa counts, and cell viability. Moreover, GRP78 expression was significantly decreased in HA15-treated spermatozoa compared to that in the control group, and levels of PI3K/PDK1/AKT-pathway related proteins changed significantly. Furthermore, tyrosine phosphorylation was significantly altered in the HA15-treated group. The results of this study suggest that GRP78 inhibition in cancer therapy may negatively affect sperm function. These results lay a strong foundation for future studies aiming to identify the molecular mechanisms related to GRP78 in spermatozoa.