Single layer colloid centrifugation technique improves motility, viability and chromatin integrity of ram spermatozoa after thawing

Quantitative phosphoproteomics explain cryopreservation-induced reductions in ram sperm motility

Sperm cryopreservation decreases motility, probably due to changes in protein phosphorylation. Our objective was to use quantitative phosphoproteomics for systematic comparative analyses of fresh versus frozen-thawed sperm to identify factors causing cryo-injury. Ejaculates were collected (artificial vagina) from six Dorper rams, pooled, extended, and frozen over liquid nitrogen. Overall, 915, 3382, and 6875 phosphorylated proteins, phosphorylated peptides, and phosphorylation sites, respectively, were identified. At least two modified sites were present in 57.94% of the 6875 phosphosites identified, of which AKAP4 protein contained up to 331 modified sites. There were 732 phosphorylated peptides significantly up-regulated and 909 significantly down-regulated in frozen-thawed versus fresh sperm. Moreover, the conserved motif [RxxS] was significantly down-regulated in frozen-thawed sperm. Phosphorylation of sperm-specific proteins, e.g., AKAP3/4, CABYR, FSIP2, GSK3A/B, GPI, and ODF1/2 make them potential biomarkers to assess the quality of frozen-thawed ram sperm. Furthermore, these differentially phosphorylated proteins and modification sites were implicated in cryopreservation-induced changes in sperm energy production, fiber sheath composition, and various biological processes. We concluded that abnormal protein phosphorylation modifications are key regulators of reduced sperm motility. These novel findings implicated specific protein phosphorylation modifications in sperm cryo-injury. SIGNIFICANCE: This study used phosphorylated TMT quantitative proteomics to explore regulation of epigenetic modifications in frozen-thawed ram sperm. This experiment demonstrated that ram sperm freezing affects phosphorylation site modifications of proteins, especially those related to functions such as sperm motility and energy production. Furthermore, it is important to link functions of phosphorylated proteins with changes in sperm quality after freezing and thawing, and to clarify intrinsic reasons for sperm quality changes, which is of great importance for elucidating mechanisms of sperm freezing damage. Based on these protein markers and combined with cryoprotectant design theory, it provides a theoretical basis and data reference to study sperm cryoprotectants.

A novel experimental design for boar sperm cryopreservation

Cryopreservation of sperm is a routine technology in many livestock species, but not in swine. Frozen sperm must result in acceptable conception rates and produce 11-12 piglets/litter to be competitive with traditional cooled semen. The development of an extender that results in high post-thaw sperm quality and acceptable litter size requires identification of factors that markedly impact post-thaw semen quality. The present study aims to first identify factors in boar sperm cryopreservation that significantly impacts post-thaw sperm quality using an efficient, cost-effective, and relatively rapid approach. The Plackett-Burman experimental design is ideal for the screening of factors at their extreme, greatly reducing the amount of time and resources needed for a follow-up, full factorial design. Using commercial semen, a 9 factor, 12 run Plackett-Burman design was used on 10 boars split between 12 treatments. Via this method glycerol concentration, cooling rate, antioxidant supplementation with GameteGuard(Membrane Protective Technologies, Inc. Fort Collins, CO), and straw size were identified as highly influential factors that impact post-thaw sperm quality. Extender type, starting osmolality, sodium dodecyl sulfate addition, and stepwise addition of glycerol were also influential for some but not all post-thaw sperm parameters (p<0.05). Equilibration time in the straws before freezing was determined to have no impact on post thaw sperm quality parameters. Using the Plackett-Burman design, it can be concluded that four of the nine factors warrant detailed investigation in a full factorial experiments in development of boar sperm cryopreservation extenders.

Cryopreservation of ram semen: Manual versus programmable freezing and different lengths of equilibration

The aim of our study was to examine effects of the length of semen equilibration as well as two freezing techniques on ram sperm post-thaw quality. The ejaculates of Wallachian sheep rams (n = 12) were collected by an electro-ejaculation, equilibrated in a Triladyl® (0, 2, 4, 6, and 8 h) containing glycerol and egg yolk and frozen by programmable freezing (PF) or manual freezing (MF). After thawing, sperm samples were subjected to the motility (computer-assisted sperm analysis [CASA]), viability (SYBR-14/PI), and fertilizing ability (FA) (in vitro penetration/fertilization test on bovine oocytes) assays. It was found that the equilibration of 6 h (E-6) ensured higher post-thaw sperm motility and progressive movement compared with other lengths tested, irrespective of a freezing technique. The E-6 sperm viability did not differ between PF and MF but was lower (P < 0.05) than control. Sperm FA (E-6) was similar in PF (60.44%) and MF (62%) but slightly lower than in fresh (72.8%). Our data demonstrate that the use of MF was comparable with PF, which can be applied in the field conditions without need in a piece of cost-expensive equipment, which can greatly benefit the gene bank of animal genetic resources.

An Exploration of Current and Perspective Semen Analysis and Sperm Selection for Livestock Artificial Insemination

Artificial insemination of livestock has been a staple technology for producers worldwide for over sixty years. This reproductive technology has allowed for the rapid improvement of livestock genetics, most notably in dairy cattle and pigs. This field has experienced continuous improvements over the last six decades. Though much work has been carried out to improve the efficiency of AI, there are still many areas which continue to experience improvement, including semen analysis procedures, sperm selection techniques, sperm sexing technologies, and semen storage methods. Additionally, the use of AI continues to grow in beef cattle, horses, and small ruminants as the technology continues to become more efficient and yield higher pregnancy rates. In this review, AI trends in the various livestock species as well as cutting edge improvements in the aforementioned areas will be discussed at length. Future work will continue to refine the protocols which are used for AI and continue to increase pregnancy rates within all livestock species.

Single Layer Centrifugation Improves the Quality of Fresh Donkey Semen and Modifies the Sperm Ability to Interact with Polymorphonuclear Neutrophils

Simple Summary

Donkey Artificial Insemination (AI) with frozen/thawed semen results in poor fertility outcomes. Jennies show a significant post-AI endometrial reaction, with a large amount of defense cells—polymorphonuclear neutrophils (PMN)—migrating to the uterine lumen. Seminal plasma (SP) has a detrimental effect on sperm conservation and its removal is a necessary step in the semen freezing protocol. However, several SP proteins seem to control sperm-PMN binding. Single layer centrifugation (SLC) with colloids, which has been used to select spermatozoa and improve reproductive performance in different species, is known to remove SP proteins attached to the sperm membrane. In this study, two experiments were performed. The first one compared the quality of SLC-selected and non-selected fresh donkey spermatozoa. In the second experiment, PMN obtained from the peripheral blood were co-incubated with selected and unselected spermatozoa, and the interaction between PMN and spermatozoa was analyzed. In conclusion, SLC of fresh donkey semen increases the proportion of functionally intact spermatozoa and appears to remove the SP proteins that inhibit sperm-PMN binding, thus increasing sperm phagocytosis by PMN.

Abstract

This study sought to determine whether single layer centrifugation (SLC) of fresh donkey semen with Equicoll has any impact on sperm quality parameters and on the modulation of endometrial reaction following semen deposition using an in vitro model. Seventeen ejaculates from five jackasses were obtained using an artificial vagina and diluted in a skim-milk extender. Samples were either selected through SLC (Equicoll) or non-treated (control). Two experiments were performed. The first one consisted of incubating selected or non-selected spermatozoa at 38 °C for 180 min. Integrity and lipid disorder of sperm plasma membrane, mitochondrial membrane potential, and intracellular levels of calcium and reactive oxygen species were evaluated at 0, 60, 120, and 180 min. In the second experiment, polymorphonuclear neutrophils (PMN) isolated from jennies blood were mixed with selected and unselected spermatozoa. Interaction between spermatozoa and PMN was evaluated after 0, 60, 120, and 180 min of co-incubation at 38 °C. SLC-selection increased the proportions of spermatozoa with an intact plasma membrane and low lipid disorder, of spermatozoa with high mitochondrial membrane potential and with high calcium levels, and of progressively motile spermatozoa. In addition, selection through SLC augmented the proportion of phagocytosed spermatozoa, which supported the modulating role of seminal plasma proteins on sperm-PMN interaction. In conclusion, SLC of fresh donkey semen increases the proportions of functionally intact and motile spermatozoa, and appears to remove the seminal plasma proteins that inhibit sperm-PMN binding.