Sperm flagellum volume determines freezability in red deer spermatozoa

The factors affecting the inter-individual differences in sperm freezability is a major line of research in spermatology. Poor sperm freezability is mainly characterised by a low sperm velocity, which in turn is associated with low fertility rates in most animal species. Studies concerning the implications of sperm morphometry on freezability are quite limited, and most of them are based on sperm head size regardless of the structural parts of the flagellum, which provides sperm motility. Here, for the first time, we determined the volumes of the flagellum structures in fresh epididymal red deer spermatozoa using a stereological method under phase contrast microscopy. Sperm samples from thirty-three stags were frozen and classified, as good freezers (GF) or bad freezers (BF) at two hours post-thawing using three sperm kinetic parameters which are strongly correlated with fertility in this species. Fourteen stags were clearly identified as GF, whereas nineteen were BF. No significant difference in sperm head size between the two groups was found. On the contrary, the GF exhibited a lower principal piece volume than the BF (6.13 μm3 vs 6.61 μm3, respectively, p = 0.006). The volume of the flagellum structures showed a strong negative relationship with post-thawing sperm velocity. For instance, the volume of the sperm principal piece was negatively correlated with sperm velocity at two hours post-thawing (r = -0.60; p<0.001). Our results clearly show that a higher volume of the sperm principal piece results in poor freezability, and highlights the key role of flagellum size in sperm cryopreservation success.JLRS was supported by I3P program (Spanish National Research Council, CSIC, Spain), post-doctoral fellowship no. 99830/1181/1822 (Czech University of Life Sciences, Prague, Czech Republic), and by the project CIGA 20145001 (Czech University of Life Sciences, Prague, Czech Republic).Peer Reviewe

Catalase supplementation on thawed bull spermatozoa abolishes the detrimental effect of oxidative stress on motility and DNA integrity

P. 353-359The potential protective effect of catalase supplementation during in vitro culture of frozen/thawed bull spermatozoa was investigated. Frozen/thawed semen collected from three fighting bulls was diluted in phosphate buffered saline (PBS) and incubated at 37 °C under different experimental conditions: Control, Catalase (CAT) (200 U/mL), Oxidant (OXI) (100 μm Fe2+/1 mm ascorbate), and Catalase + Oxidant (CAT/OXI). We assessed sperm motility, acrosomal integrity, viability and chromatin status (SCSA®) at 0, 2 and 6 h of incubation. Our results showed that catalase abolished the effect of the oxidant, protecting spermatozoa against reactive oxygen species, and improving both sperm motility and chromatin status during incubation. The OXI treatment significantly reduced the percentage of motile sperm after 6 h of incubation. The statistical model also showed that there were differences in sperm motility between CAT/OXI (20.8 ± 2.9%) and OXI (11.6 ± 7.6%) (p < 0.001). There were no significant effects of OXI on sperm viability, acrosomal status or proportion of abnormal tails. %DFI (spermatozoa with moderate or high DNA Fragmentation Index) was significantly higher on OXI (p < 0.001). Catalase prevented DNA fragmentation even in the presence of the oxidant (%DFI: 30.3 ± 0.8% OXI vs. 17.4 ± 0.7% CAT/OXI). We conclude that catalase supplementation after thawing could protect bull spermatozoa against oxidative stress, and it could improve media used for processing thawed spermatozoa

Washing increases the susceptibility to exogenous oxidative stress in red deer spermatozoa

P. 1073-1084The effects of routine sperm work are often overlooked. We assessed the effect of washing cryopreserved epididymal spermatozoa from red deer (Cervus elaphus hispanicus, Helzheimer 1909). After thawing, epididymal samples (four stags) were diluted in TALP-HEPES. A split was left untouched, another was centrifuged (300 × g, 5 min) and resuspended, and a third was centrifuged and the supernatant substituted by fresh TALP-HEPES (washing). Each split was supplemented either with nothing, 1 mM of the antioxidant Trolox, 100 μM of the oxidant Fe (with ascorbate), or both. The 3 × 4 treatments were incubated at 37°C and assessed each hour up to 3 h for motility (computer-aided sperm assessment) and viability/apoptosis plus mitochondrial status (YO-PRO-1, propidium iodide, Mitotracker Deep Red; flow cytometry). DNA damage at 4 h was assessed using the terminal deoxynucleotidyl transferase–mediated dUTP nick end-labeling assay. Centrifugation alone affected neither sperm quality nor DNA, and the oxidant had no effect in control or centrifuged samples. Washed samples were not different than control, but oxidant decreased motility, mitochondrial status and viability, and altered the motility subpopulation pattern, being partially suppressed by Trolox. Spermatozoa with damaged DNA dramatically increased in the washed-oxidized sample (from 22.30 ± 3.52% to 67.94 ± 5.07%), but not when antioxidant was present. Although samples from different males behaved similarly, male-to-male variability was detected regarding susceptibility to oxidative damage after washing. We concluded that, although red deer thawed spermatozoa seemed resilient to centrifugation, the vulnerability to oxidative stress after washing makes it advisable to supplement manipulation media with antioxidants, especially taking into account male-to-male variability.S

Mitochondrial activity and forward scatter vary in necrotic, apoptotic and membrane-intact spermatozoan subpopulations

P. 547-556In the present study, we have related mitochondrial membrane potential (ΔΨm) and forward scatter (FSC) to apoptotic-related changes in spermatozoa. Thawed red deer spermatozoa were incubated in synthetic oviductal fluid medium (37°C, 5% CO2), with or without antioxidant (100 μm Trolox). At 0, 3, 6 and 9 h, aliquots were assessed for motility and were stained with a combination of Hoechst 33342, propidium ioide (PI), YO-PRO-1 and Mitotracker Deep Red for flow cytometry. The proportion of spermatozoa YO-PRO-1+ and PI+ (indicating a damaged plasmalemma; DEAD) increased, whereas that of YO-PRO-1– and PI– (INTACT) spermatozoa decreased. The proportion of YO-PRO-1+ and PI– spermatozoa (altered plasmalemma; APOPTOTIC) did not change. Both DEAD and APOPTOTIC spermatozoa had low ΔΨm. Most high-ΔΨm spermatozoa were INTACT, and their proportion decreased with time. The FSC signal also differed between different groups of spermatozoa, in the order APOPTOTIC > DEAD > INTACT/low ΔΨm > INTACT/high ΔΨm; however, the actual meaning of this difference is not clear. APOPTOTIC spermatozoa seemed motile at 0 h, but lost motility with time. Trolox only slightly improved the percentage of INTACT spermatozoa (P < 0.05). The population of APOPTOTIC spermatozoa in the present study may be dying cells, possibly with activated cell death pathways (loss of ΔΨm). We propose that the sequence of spermatozoon death here would be: (1) loss of ΔΨm; (2) membrane changes (YO-PRO-1+ and PI–); and (3) membrane damage (PI+). INTACT spermatozoa with low ΔΨm or altered FSC may be compromised cells. The present study is the first that directly relates membrane integrity, apoptotic markers and mitochondrial status in spermatozoa. The results of the present study may help us understand the mechanisms leading to loss of spermatozoon viability after thawing.S

Improving the effect of incubation and oxidative stress on thawed spermatozoa from red deer by using different antioxidant treatments

P. 856-870Antioxidants could improve sperm media, extending the viability of spermatozoa and protecting their DNA. The protective ability of lipoic acid, melatonin, Trolox and crocin was tested on red deer spermatozoa incubated at 37°C. Cryopreserved spermatozoa were thawed and incubated with 1 mM or 0.1 mM of each antioxidant, with or without oxidative stress (100 μM Fe2+). Motility (CASA), viability, mitochondrial membrane potential and acrosomal status were assessed. Lipoperoxidation (malondialdehyde production), intracellular reactive oxygen species (ROS) and DNA status (TUNEL) were checked at 4 h. Incubation alone increased ROS and decreased motility. Oxidative stress intensified these effects, increasing lipoperoxidation and DNA damage. Lipoic acid had little protective effect, whereas 1 mM melatonin showed limited protection. Trolox lowered ROS and lipoperoxidation both in oxidised and non-oxidised samples. In oxidised samples, Trolox prevented DNA and acrosomal damage, and ameliorated motility. Crocin at 1 mM showed similar results to Trolox, but noticeably stimulated motility and had no effect on lipoperoxidation. In a second experiment, a broader range of crocin and melatonin concentrations were tested, confirming the effects of crocin (positive effects noticeable at 0.5–0.75 mM), but showing an increase in lipoperoxidation at 2 mM. Melatonin was increasingly effective at 2.5 and 5 mM (ROS, lipoperoxidation and DNA status). Crocin seems a promising new antioxidant, but its particular effects on sperm physiology must be further studied, especially the consequences of motility stimulation and confirming its effect on lipoperoxidation. Melatonin might be useful at relatively high concentrations, compared to Trolox.S

Sperm Flagellum Volume Determines Freezability in Red Deer Spermatozoa

<div><p>The factors affecting the inter-individual differences in sperm freezability is a major line of research in spermatology. Poor sperm freezability is mainly characterised by a low sperm velocity, which in turn is associated with low fertility rates in most animal species. Studies concerning the implications of sperm morphometry on freezability are quite limited, and most of them are based on sperm head size regardless of the structural parts of the flagellum, which provides sperm motility. Here, for the first time, we determined the volumes of the flagellum structures in fresh epididymal red deer spermatozoa using a stereological method under phase contrast microscopy. Sperm samples from thirty-three stags were frozen and classified as good freezers (GF) or bad freezers (BF) at two hours post-thawing using three sperm kinetic parameters which are strongly correlated with fertility in this species. Fourteen stags were clearly identified as GF, whereas nineteen were BF. No significant difference in sperm head size between the two groups was found. On the contrary, the GF exhibited a lower principal piece volume than the BF (6.13 µm³ vs 6.61 µm³, respectively, p = 0.006). The volume of the flagellum structures showed a strong negative relationship with post-thawing sperm velocity. For instance, the volume of the sperm principal piece was negatively correlated with sperm velocity at two hours post-thawing (r = −0.60; p<0.001). Our results clearly show that a higher volume of the sperm principal piece results in poor freezability, and highlights the key role of flagellum size in sperm cryopreservation success.</p></div

Subjective motility of fresh and thawed red deer spermatozoa (N = 33).

<p>Different superscript letters within the same column differ significantly (p<0.001). Data are shown as mean ± SD (standard deviation). QM, quality of motility; SMI, sperm motility index.</p><p>Subjective motility of fresh and thawed red deer spermatozoa (N = 33).</p

Relationships between sperm velocity and flagellum morphometry.

<p>Good freezers are shown in open circles and bad freezers in closed circles: A (0 hours post-thaw); B, C, D, and E (2 hours post-thaw).</p

Results of principal component analysis (PCA) to determine overall sperm velocity at 0 and 2 hours post-thaw.

<p>VAP, average path velocity; VCL, curvilinear velocity; VSL, straight linear velocity; ALH, amplitude of lateral head displacement; SMI, sperm motility index.</p><p>Results of principal component analysis (PCA) to determine overall sperm velocity at 0 and 2 hours post-thaw.</p

Classification of sperm principal piece volume according to red deer sperm freezability.

<p>Good freezers are shown in open circles and bad freezers in closed circles.</p