Seminal Plasma, Sperm Concentration, and Sperm-PMN Interaction in the Donkey: An In Vitro Model to Study Endometrial Inflammation at Post-Insemination.

Jordi Miró,Marion Papas,Henar Marín,Marc Yeste,Jaime Catalán,Sabrina Gacem

doi:10.3390/ijms21103478

Abstract

In the donkey, artificial insemination (AI) with frozen-thawed semen is associated with low fertility rates, which could be partially augmented through adding seminal plasma (SP) and increasing sperm concentration. On the other hand, post-AI endometrial inflammation in the jenny is significantly higher than in the mare. While previous studies analyzed this response through recovering Polymorphonuclear Neutrophils (PMN) from uterine washings, successive lavages can detrimentally impact the endometrium, leading to fertility issues. For this reason, the first set of experiments in this work intended to set an in vitro model through harvesting PMN from the peripheral blood of jennies. Thereafter, how PMN, which require a triggering agent like formyl-methionyl-leucyl-phenylalanine (FMLP) to be activated, are affected by donkey semen was interrogated. Finally, we tested how four concentrations of spermatozoa (100 × 106, 200 × 106, 500 × 106 and 1000 × 106 spermatozoa/mL) affected their interaction with PMN. We observed that semen, which consists of sperm and SP, is able to activate PMN. Whereas there was a reduced percentage of spermatozoa phagocytosed by PMN, most remained attached on the PMN surface or into a surrounding halo. Spermatozoa not attached to PMN were viable, and most of those bound to PMN were also viable and showed high tail beating. Finally, only sperm concentrations higher than 500 × 106 spermatozoa/mL showed free sperm cells after 3 h of incubation, and percentages of spermatozoa not attached to PMN were higher at 3 h than at 1 h, exhibiting high motility. We can thus conclude that semen activates PMN in the donkey, and that the percentage of spermatozoa phagocytosed by PMN is low. Furthermore, because percentages of spermatozoa not attached to PMN were higher after 3 h than after 1 h of incubation, we suggest that PMN-sperm interaction plays an instrumental role in the reproductive strategy of the donkey.

Highlights

Most European donkey breeds are currently in danger of extinction
We suggest that in a similar fashion to that investigated in other species [31,32,38], additional receptors involved in the induction of phagocytosis, which would lead to the activation of NETosis in a similar fashion to that reported by Branzk et al [33] when Dectin-1 is inhibited
Were the percentages of viable spermatozoa higher in the bound-to-Polymorphonuclear Neutrophils (PMN) than in the free sperm population, but sperm cells that were apparently released from PMN after 3 h of incubation showed good motility

Summary

Introduction

Most European donkey breeds are currently in danger of extinction. There has been, in the recent years, an increased global demand for donkey products. Our current knowledge of the donkey reproductive physiology is still scarce and, despite horse reproduction technologies being used, many differences between these two species exist. While frozen-thawed donkey spermatozoa have good post-thaw viability and motility [4,5,6], are able to penetrate zona pellucida free bovine oocytes in vitro [7] and yield good conception rates (50%) following artificial insemination (AI) of mares [1], their pregnancy rates are poor (0–28%) when used to inseminate jennies [8]

Objectives

Methods

Conclusion