Direct binding of boar ejaculate and epididymal spermatozoa to porcine epididymal epithelial cells is also needed to maintain sperm survival in in vitro co-culture

The aim of the present study was to compare the influence of cultured epididymal epithelial cells (EEC) from corpus, caput or cauda, oviductal epithelial cells (OEC) and non-reproductive epithelial cells (LLC-PK1) on function and survival of epididymal and ejaculated spermatozoa, in the latter case to determine whether such influence differed between morphologically normal and abnormal spermatozoa. For this purpose, either spermatozoa were directly co-cultured with EEC from caput, corpus, or cauda, OEC and LLC-PK1 cells (experiment 1) or a membrane-diffusible insert was included in these co-cultures (experiment 2). EEC cultured from the three epididymal regions did not differently affect the sperm parameters. Morphologically normal spermatozoa presented a higher ability to bind EEC, OEC, and LLC-PK1 than abnormal spermatozoa with cytoplasmic droplets or with tail/head malformations. Epididymal spermatozoa were more able to bind EEC during the first 24 h of co-culture, while ejaculated spermatozoa presented a higher capacity to bind OEC between 30 min and 3 h of co-incubation. In all cases, the ability to bind to epithelial cells was higher when they were co-cultured with EEC and OEC than with LLC-PK1. After 2 h of co-culture, the viability of epididymal spermatozoa was better maintained when they bound EEC than when they bound OEC. Conversely, the viability of ejaculated spermatozoa was better maintained when bound OEC than when bound EEC after 24 and 48 h of co-culture. Our work, apart from corroborating the involvement of morphologically normal spermatozoa in the formation of sperm reservoir, highlights the importance of direct contact spermatozoa-EEC in maintaining the sperm survival in in vitro co-culture, and also suggests that a specific binding between EEC and epididymal spermatozoa exists.