Bovine epididymal spermatozoa: Resistance to cryopreservation and binding ability to oviductal cells

A longer period of epididymal sperm interaction with extender components during cryopreservation improves sperm quality, decreases the size of sperm distal cytoplasmic droplets, and changes the number of nanoparticles in the extender

While cryopreservation of cauda epididymal sperm (SpCau) allows the preservation of post-mortem bulls' gametes, the process triggers sperm damage. Although improving post-thaw sperm quality, using egg yolk extenders (EY) raises biosafety concerns which forces the use of EY-free extenders (EYFE). Since EYFE are less efficient in preserving post-thaw sperm quality, a strategy for ejaculated sperm (SpEj) frozen with EYFE is to add an Equilibrium Time (ET) step period to the cryopreservation process. However, the ET effect on the quality of SpCau cryopreserved in EYFE remains unknown. Distinct from SpEJ, SpCau physiologically displays cytoplasmic droplets (CDs) in the flagellum that may benefit cell exchange during ET. We hypothesized that using ET in SpCau cryopreserved with EYFE impacts sperm morphofunctional features, CD area, and in vitro fertility ability. Extender nanoparticles were also assessed. Following collection from the cauda epididymis of six Nellore bulls by retrograde flow, SpCau were cryopreserved in EYFE BoviFree® (Minitube, Germany) using three ET protocols: ET0 (no-ET); ET2.5 (2.5 h-ET); and ET5 (5 h-ET). SpCau from ET2.5 and ET5 showed a higher (P ≤ 0.05) percentage of motility and integrity of plasma and acrosome membranes and a smaller (P ≤ 0.05) distal CD area. There are no differences in sperm abnormalities, oxidative stress, capacitation-like events, and in vitro fertility ability. However, a better sperm recovery was found after Percoll® selection for ET2.5 and ET5. Interestingly, the number of nanoparticles in the extender decreased in post-thawed samples. In conclusion, an ET of 2.5 or 5 h is required for an efficient SpCau cryopreservation using an EYFE.

Seminal cell-free DNA as a potential marker for in vitro fertility of Nellore bulls

PURPOSE

This study aimed to identify a marker for freezability and in vitro fertility of sperm samples before freezing.

METHODS

Semen was collected from nine Nelore bulls; half of the ejaculate was used for seminal plasma cell-free DNA (cfDNA) quantification, and the other half was cryopreserved. Evaluation of sperm movement using computer-assisted semen analysis and plasma membrane integrity and stability, acrosomal integrity, apoptosis, and mitochondrial potential using flow cytometry were performed on fresh and frozen/thawed semen at 0, 3, 6, and 12 h after thawing. Frozen/thawed sperm was also used for in vitro embryo production. cfDNA was extracted from each bull, and the total DNA and number of cell-free mitochondrial DNA (cfmtDNA) copies were quantified. Semen from each animal was used for IVF, and cleavage, blastocyst formation, and cell counts were evaluated.

RESULTS

Two groups were formed and compared based on the concentrations of cfDNA and cfmDNA present: low-cfDNA and high-cfDNA and low-cfmtDNA and high-cfmtDNA. Up to 12 h post-thawing, there were no differences between the groups in the majority of the sperm parameters evaluated. Cleavage, day 6 and 7 blastocyst rates, and the number of cells were higher in the high cfDNA group than in the low cfDNA group. Similar results were observed for cfmtDNA, except for the number of cells, which was similar between the groups.

CONCLUSION

The concentration of cfDNA and the relative number of copies of cfmtDNA in seminal plasma cannot predict the freezability of semen but can be used to predict in vitro embryo production.

Vitrification of Iberian wolf (Canis lupus signatus) sperm: A possible alternative to conventional cryopreservation

Sperm vitrification is a simple, inexpensive method that allows the cryopreservation of sperm in the field and for endangered species is a useful alternative to conventional freezing. The study, therefore, is focused on the suitability of vitrification for cryopreserving Iberian wolf sperm and utilizing plasma testosterone concentration as a marker for procedure efficacy. Sperm and blood samples were collected from 17 wolves. There were 14 samples suitable for cryopreservation (12 ejaculated and two epididymal). Immediately after collection, these samples were proportioned into two aliquots for conventional freezing using a Tris-citric acid-glucose based extender (TCG) or vitrification utilizing an animal protein free extender (HTF®). Vitrification occurred by directly plunging a sperm suspension into liquid nitrogen. Sperm were assessed for motility, membrane integrity, acrosomal status and DNA integrity before and after cryopreservation. With both techniques, there were similar post-thaw/warming results (P > 0.05) with respect to progressive motility, kinetic variables VCL, VSL, VAP and BCF, DNA fragmentation, sperm membrane functionality and morphological abnormalities. Total motile sperm, progression ratios LIN, STR, and WOB, the ALH, sperm viability and sperm with intact membrane and acrosome were greater (P < 0.05) in the conventional frozen-thawed sperm than vitrified-warmed sperm. Plasma testosterone concentrations varied from 0.0 ng/mL to 7.7 ng/mL. For epididymal sperm, sperm motility and viability following thawing were greater in vitrified-warmed samples than conventionally-frozen samples; however, small sample numbers precluded statistical analysis. When considered together, these results indicate vitrification may be a possible alternative for wolf sperm cryopreservation.

Assessment of tebuconazole exposure on bovine testicular cells and epididymal spermatozoa

This study is the first to investigate the effects of tebuconazole (TEB) on the physiological functions of bovine testicular cells and epididymal spermatozoa. Motility and plasma membrane integrity of spermatozoa exposed to TEB (0.001-100 µM) were evaluated at different incubation times (0-6 h), while TEB-induced spermiotoxicity was assessed after 24 h in cell cultures. Testicular cells, obtained from the parenchyma of bovine testes, were seeded at 1.0 × 104 and 1.5 × 106 cells/well in 96- and 12-well culture plates and incubated for 48 h in culture media containing TEB (0.001-100 µM) to evaluate cytotoxicity and hormone release, respectively. TEB did not affect the motility and plasma membrane integrity. However, significant spermiotoxicity occurred at higher TEB (1-100 µM) concentrations (P < 0.05) compared to control and lower doses. Although no dose caused cytotoxicity in testicular cells (P > 0.05), 1 and 100 µM TEB caused a significant increase in testosterone secretion (P < 0.05). As a result, high doses of TEB (1-100 µM) had slightly suppressive effects on spermatozoa; however, these doses had stimulatory effects on testosterone secretion by testicular cells. It appears that the disruption of hormonal homeostasis of testicular cells after TEB exposure may result in metabolic and especially reproductive adverse effects in bulls.

Differential proteome between ejaculate and epididymal sperm represents a key factor for sperm freezability in wild small ruminants

Epididymal sperm shows higher cryoresistance than ejaculated sperm. Although the sperm proteome seems to affect cell cryoresistance, studies aiming at identifying proteins involved in sperm freezing-tolerance are scarce. The aims of this study were to investigate differences of sperm freezability and proteome between epididymal and ejaculated sperm in three mountain ungulates: Iberian ibex, Mouflon and Chamois. Sperm samples were cryopreserved in straws by slow freezing. Tandem mass tag-labeled peptides from sperm samples were analyzed by high performance liquid chromatography coupled to a mass spectrometer in three technical replicates. The statistical analysis was done using the moderated t-test of the R package limma. Differences of freezability between both types of sperm were associated with differences of the proteome. Overall, epididymal sperm showed higher freezability than ejaculated sperm. Between 1490 and 1883 proteins were quantified in each species and type of sperm sample. Cross species comparisons revealed a total of 76 proteins that were more abundant in epididymal than in ejaculated sperm in the three species of study whereas 3 proteins were more abundant in ejaculated than epididymal sperm in the three species of study (adjusted P < 0.05; |log₂| fold-change > 0.5). Many of the proteins that were associated with higher cryoresistance are involved in stress response and redox homeostasis. In conclusion, marked changes of sperm proteome were detected between epididymal and ejaculated sperm. This work contributes to update the sperm proteome of small ruminants and to identify candidate markers of sperm freezability.

Shape and size of epididymal sperm from Gir bulls using atomic force microscopy: A nanoscale characterization of epididymal sperm

As epididymal sperm (EP) are not exposed to seminal plasma, they are physiologically different from ejaculated spermatozoa (EJ). Therefore, the aim of this study was to morphologically characterize the head of EP recovered from the epididymis tail, and to evaluate if the physiological differences between EP and EJ were also expressed in the head's shape and size. EP and EJ were recovered from seven Gir bulls and were individually assessed. Sperm cells were washed, fixed, and 20 cells from each animal were analyzed by atomic force microscopy (AFM). The images were acquired through contact mode. Then, an off-line processing software was used and the images acquired were manually segmented using digital zoom of the original images. Twenty-four structural features were assessed including one, two, and three dimensional parameters, and also shape descriptors which were calculated based on the one and two dimensional parameters. Data were compared by t-test, then, a collective analysis was performed using principal component analysis (PCA). The EP group presented higher roughness and elongation (P ≤ 0.05), and smaller form factor and circularity rate than that of the EJ group (P ≤ 0.05). For the other parameters no differences (P ≥ 0.05) were observed. In addition, in the PCA analysis no differences among EP and EJ were observed either (P ≤ 0.05). This study showed that EP and EJ collected from the same sire presented similar characteristics in nineteen of the twenty-four parameters evaluated, indicating that absence of seminal plasma does not affect the morphology of EP.

Epididymal and ejaculated sperm differ on their response to the cryopreservation and capacitation processes in mouflon (Ovis musimon)

Spermatozoa must undergo the process of capacitation to fertilize the egg which involves a cell destabilizing process. Capacitation-like changes such as protein tyrosine phosphorylation (PTP) are associated with cryopreservation. The aim of this study was to compare the cryoresistance and capacitation response of epididymal and ejaculated sperm of European mouflon (Ovis musimon). Post-thaw sperm parameters were analysed from epididymal and ejaculated samples cryopreserved by slow-freezing or ultrarapid-freezing for comparison. Sperm capacitation status was assessed by the semiquantification of PTP levels, cell localization of PTP and kinematic clustering. Epididymal sperm had higher cryoresistance than ejaculated sperm in both freezing techniques, and slow-freezing rendered better results than ultrarapid-freezing in both sperm samples. Ejaculated sperm had higher PTP levels than epididymal sperm and, additionally, ejaculated sperm showed higher phosphorylation in capacitating (CA) than in non-capacitating (NCA) conditions while there was no effect of medium in epididymal sperm. There was a higher tail PTP in CA than in NCA conditions in both types of sperm. Kinematic analysis revealed that the cluster associated with hyperactivated movement increased in ejaculated sperm incubated in CA whereas no effect of medium was observed in epididymal sperm clusters. In conclusion, epididymal sperm showed better freezability and lower capacitation status compared to ejaculated sperm.

Bovine epididymal spermatozoa treatment for in vitro fertilization: Heparin accelerates fertilization and enables a reduction in coincubation time

This study aimed to establish a protocol for in vitro embryo production using epididymal sperm (EP). Samples were obtained from ejaculated sperm (EJ) and the epididymis of 7 Gir bulls. First, the effect of heparin (+) on the viability, longevity (Experiment 1) and fertilization rates (Experiment 2) of the EP was evaluated. In experiment 2, a pool of EP and EJ sperm (n = 7) was coincubated with cumulus-oocyte complexes (COCs) for 0, 3, 6, 12 and 18 h, and the fertilization rate (FR) was evaluated. A third experiment was performed to test sperm treatments for IVP using the Percoll (P) or PureSperm (PS) gradients or a spTALP wash for sperm selection. Cleavage, blastocyst rate (BR) and embryo sex were evaluated. In experiment 4, embryos were produced using 6, 12, and 18 h of sperm-oocyte coincubation. The cleavage, BR, and total number and percentage of apoptotic cells were determined. Heparin affected EP viability, longevity and FR. After 6 h, 82% of the oocytes were fertilized in the EP+ group, a higher value (P<0.05) than that in the EJ (19%) and EP- (42%) groups. At 12 and 18 h, FR remained higher in the EP+ group, and a gradual increase in polyspermy was observed. The use of a P or PS gradient yielded a similar BR on D7 (54% and 52%), which was higher than the rate obtained using the washing method (37%). The embryos produced by EP and selected in a P or PS gradient resulted in a sex deviation in favor of male embryos (P>0.05). No differences (P>0.05) were observed among the groups that were coincubated for 6, 12 and 18 h with respect to embryo production, kinetics of development, total cell number and percentage of apoptotic cells. In conclusion, IVF time can be reduced to 6 h without affecting embryo production and quality. In addition, EP sperm selection can be performed by either a PS or P gradient.