What is the importance of sperm subpopulations?

Exposure to silver and titanium dioxide nanoparticles at supra-environmental concentrations decreased sperm motility and affected spermatozoa subpopulations in gilthead seabream, Sparus aurata

Marine pollution by nanoparticles (NPs) can be reprotoxic for fish and disturb successful reproduction of wild populations. In gilthead seabream (Sparus aurata), a mild effect on sperm motility was observed after exposure to high concentrations of silver NPs. Considering the great heterogeneity traits within a sperm sample, it is possible that NPs affect spermatozoa accordingly, modulating subpopulation profile. Thus, this work aimed to analyse NP effects in sperm motility in general and considering spermatozoa population structure, using a subpopulation approach. Seabream sperm samples from mature males were exposed for 1 h to increasing concentrations of titanium dioxide (1, 10, 100, 1000 and 10,000 μg L-1) and silver (0.25, 25 and 250 μg L-1) NPs, including Ag NP and Ag+, dissolved in a non-activating medium (0.9 % NaCl). Concentrations chosen include realistic (10-100 and 0.25 μg L-1, respectively, for TiO2 and Ag) and supra-environmental values. The mean particle diameter was determined as 19.34 ± 6.72 and 21.50 ± 8.27 nm in the stock suspension, respectively, for titanium dioxide and silver. After the ex vivo exposure, sperm motility parameters were determined using computer-assisted sperm analysis, and sperm subpopulations were later identified using a two-step cluster analysis. Results revealed a significant reduction in total motility after exposure to the 2 highest concentrations of titanium dioxide NPs, while curvilinear and straight-line velocities were not altered. Exposure to silver NPs (Ag NP and Ag+) lowered significantly total and progressive motilities at all concentrations, while curvilinear and straight-line velocities were significantly lower only at the highest concentration. Sperm subpopulations were also affected by the exposure to both titanium dioxide and silver NPs. In both cases, the highest levels of NPs triggered a decrease in the percentage of fast sperm subpopulations (38.2% in TiO2 1000 μg L-1, 34.8.% in Ag NP 250 μg L-1, and 45.0% in Ag+ 250 μg L-1 vs 53.4% in the control), while an increase on slow sperm subpopulations. A reprotoxic effect was proven for both NPs, but only at supra-environmental concentrations.

Therapeutic potential of Sertoli cells in vivo: alleviation of acute inflammation and improvement of sperm quality

BACKGROUND

Inflammation-induced testicular damage is a significant contributing factor to the increasing incidence of infertility. Traditional treatments during the inflammatory phase often fail to achieve the desired fertility outcomes, necessitating innovative interventions such as cell therapy.

METHODS

We explored the in vivo properties of intravenously administered Sertoli cells (SCs) in an acute lipopolysaccharide (LPS)-induced inflammatory mouse model. Infiltrating and resident myeloid cell phenotypes were assessed using flow cytometry. The impact of SC administration on testis morphology and germ cell quality was evaluated using computer-assisted sperm analysis (CASA) and immunohistochemistry.

RESULTS

SCs demonstrated a distinctive migration pattern, importantly they preferentially concentrated in the testes and liver. SC application significantly reduced neutrophil infiltration as well as preserved the resident macrophage subpopulations. SCs upregulated MerTK expression in both interstitial and peritubular macrophages. Applied SC treatment exhibited protective effects on sperm including their motility and kinematic parameters, and maintained the physiological testicular morphology.

CONCLUSION

Our study provides compelling evidence of the therapeutic efficacy of SC transplantation in alleviating acute inflammation-induced testicular damage. These findings contribute to the expanding knowledge on the potential applications of cell-based therapies for addressing reproductive health challenges and offer a promising approach for targeted interventions in male infertility.

"Modeling Diffusive Search by Non-Adaptive Sperm: Empirical and Computational Insights"

During fertilization, mammalian sperm undergo a winnowing selection process that reduces the candidate pool of potential fertilizers from ~106-1011 cells to 101-102 cells (depending on the species). Classical sperm competition theory addresses the positive or 'stabilizing' selection that acts on sperm phenotypes within populations of organisms but does not strictly address the developmental consequences of sperm traits among individual organisms that are under purifying selection during fertilization. It is the latter that is of utmost concern for improving assisted reproductive technologies (ART) because 'low fitness' sperm may be inadvertently used for fertilization during interventions that rely heavily on artificial sperm selection, such as intracytoplasmic sperm injection (ICSI). Importantly, some form of sperm selection is used in nearly all forms of ART (e.g., differential centrifugation, swim-up, or hyaluronan binding assays, etc.). To date, there is no unifying quantitative framework (i.e., theory of sperm selection) that synthesizes causal mechanisms of selection with observed natural variation in individual sperm traits. In this report, we reframe the physiological function of sperm as a collective diffusive search process and develop multi-scale computational models to explore the causal dynamics that constrain sperm 'fitness' during fertilization. Several experimentally useful concepts are developed, including a probabilistic measure of sperm 'fitness' as well as an information theoretic measure of the magnitude of sperm selection, each of which are assessed under systematic increases in microenvironmental selective pressure acting on sperm motility patterns.

Heat shock protein 70 kDa (HSP70) is involved in the maintenance of pig sperm function throughout liquid storage at 17 °C

At present, liquid storage is the most efficient method for pig semen preservation. This approach relies upon reducing sperm metabolism, allowing for the maintenance of cell lifespan. In this context, the study of proteins that could protect sperm during liquid storage is of high relevance. The 70 kDa Heat Shock Protein (HSP70) is an anti-apoptotic protein that has been reported to be relevant to sperm survival. Thus, we explored the role of HSP70 during prolonged storage of pig semen at 17 °C. Six semen pools were incubated with YM-1 (0, 0.05, 0.1 and 0.2 μM), an HSP70 inhibitor, and stored at 17 °C for 21 days. On days 0, 4, 10, 14 and 21, sperm quality and function were evaluated through flow cytometry and Computer-Assisted Sperm Analysis (CASA), and HSP70 activity and chromatin condensation were also determined. While inhibition of HSP70 increased progressive motility, Ca2+ and Reactive Oxygen Species (ROS) levels, and mitochondrial activity during the first 10 days of storage, it had a detrimental effect on sperm motility after 14 and 21 days. In spite of this, sperm viability was not altered. We can conclude that HSP70 contributes to the liquid storage of pig semen because it keeps mitochondrial activity low, which is needed for the maintenance of sperm function.

The impact of Origanum Vulgare essential oil supplementation on sperm motility and subpopulation alterations in bulls, dogs, and rabbits

Artificial insemination is a widely adopted method in livestock production for various reasons such as health security and genetic improvement. Although sperm motility is of paramount importance in this technique as it directly influences the sperm's ability to fertilize the oocyte. In previous research on human sperm, we observed that in vitro supplementation with Origanum Vulgare essential oil significantly improved sperm motility and antioxidant activities, all without negatively affecting the integrity of their DNA. Based on these promising results, we considered it crucial to explore the potential effects of supplementation with this essential oil on sperm of other species. In this study, we studied the effects of oregano essential oil supplementation on sperm motility of (bulls = 15) (dogs = 15) and (rabbits = 9) and the changes that in vitro incubation with this oil could induce on sub-motile sperm populations of different species. The results of the study showed that in vitro oregano essential oil supplementation had a significant impact on sperm motility in the three species studied. This improvement in sperm motility was accompanied by an increase in the proportion of subpopulations with high velocity and progressivity: an increase of (2.16%, 10% and 4.84%) for subpopulation 1, (6.50%, 5.5% and 3.17%) for subpopulation 4 in bulls, dogs and rabbits respectively. While the subpopulations representing low motile and non-progressive sperm have decreased. These results suggest that the use of oregano essential oil can be a beneficial approach to improve sperm motility in different species, which can have important implications for the success of artificial insemination.

The future of equine semen analysis

We are currently experiencing a period of rapid advancement in various areas of science and technology. The integration of high throughput 'omics' techniques with advanced biostatistics, and the help of artificial intelligence, is significantly impacting our understanding of sperm biology. These advances will have an appreciable impact on the practice of reproductive medicine in horses. This article provides a brief overview of recent advances in the field of spermatology and how they are changing assessment of sperm quality. This article is written from the authors' perspective, using the stallion as a model. We aim to portray a brief overview of the changes occurring in the assessment of sperm motility and kinematics, advances in flow cytometry, implementation of 'omics' technologies, and the use of artificial intelligence/self-learning in data analysis. We also briefly discuss how some of the advances can be readily available to the practitioner, through the implementation of 'on-farm' devices and telemedicine.

Post-testicular sperm maturation in ancient holostean species

Fish speciation was accompanied by changes in the urogenital system anatomy. In evolutionarily modern Teleostei, male reproductive tracts are fully separated from the excretory system, while in evolutionarily ancient Chondrostei and Holostei, the excretory and reproductive tracts are not separated. Sturgeon post-testicular sperm maturation (PTSM) occurring as a result of sperm/urine mixing is phenomenologically well described, while, in holosteans, functional intimacy of seminal ducts with kidney ducts and the existence of PTSM still need to be addressed. In Lepisosteus platostomus (Holostei), sperm samples were collected from testes (TS), efferent ducts (EDS), and Wolffian ducts (WDS). While WDS was motile, no motility was found in TS and EDS. The existence of PTSM was checked by in vitro PTSM procedure. After TS and EDS incubation in seminal fluid from WDS, no more than 5% motile spermatozoa were observed in TS, whereas in EDS the motility percentage was up to 75%. Experimental dyeing of urogenital ducts in gars and sturgeons revealed some differences in the interconnection between sperm ducts and kidneys. It is concluded that post-testicular sperm maturation occurs in gars and suggests that infraclass Holostei occupies an intermediate evolutionary position between Teleostei and Chondrostei in the anatomical arrangement of the urogenital system.

Morphometric assessment of cryopreserved livestock bull spermatozoa in the tropics

The identification of different morphometric patterns of spermatozoa serves as a basis for improving our understanding of the diversity in an ejaculate and to relate them to the potential fertility of males. In this study, we aimed to examine the semen subpopulation structure, following dilution in semen of extenders, using a mathematical approach a possible application to fertility analyses. Ten sexually mature Bos taurus bulls were randomly allotted to one of three groups: (1) Tris-citric acid-egg yolk extender (Tris-EY); (2) commercial egg yolk extender OptiXcell® and (3) commercial egg yolk extender Triladyl®. The results showed significant differences (p < .05) between extenders in terms of values for head size and head shape variables of individual sperm, indicating an influence of extender composition. Sperm head width was found to significantly differ (p < .05) according to the extender, decreasing in the following order: OptiXcell® (4.836 ± 0.017 μm), Triladyl® (4.695 ± 0.012 μm) and Tris-EY (4.638 ± 0.010 μm). Principal component analysis allowed us to identify two subpopulations in OptiXcell®, and three subpopulations were each found in Triladyl® and Tris-EY. Overall, we observed significant differences between sperm subpopulations within each extender (p < .05), with differences in sperm head size and shape between bovine species that can be related to functionality and fertility capabilities.

Cryptic female choice within individual males - A neglected component of the postmating sexual selection?

Cryptic female choice (CFC) is commonly assumed to act only in polyandrous mating systems, which allows females to bias fertilization towards the sperm of particular males. However, accumulated evidence has demonstrated that sperm show significant phenotypic and genotypic variation also within single ejaculates, which have important consequences for offspring phenotype and fitness. Here, I argue that these neglected sources of intra-male sperm variation often allow CFC to act also within individual males and facilitate fertilization bias towards genetically compatible (or otherwise preferred) sperm haplotypes. In this article, I explain prerequisites for within-male CFC, the criteria for demonstrating it and summarize accumulated evidence for this emerging selection process. Then, I evaluate prevalence of within-male CFC and review its potential evolutionary consequences. The aim of this article is to broaden the current definition of CFC by demonstrating that CFC has potential to act in all mating systems, in both internally and externally fertilizing species. Incorporation of the within-male CFC concept into the current models of sexual selection may provide novel insights into the deeper understanding of selective factors driving the evolution of mating systems and reproductive proteins. Finally, within-male CFC towards particular sperm haplotypes may increase our understanding of non-Mendelian inheritance.

Relationship between frame rates and subpopulation structure of bovine sperm divided by their motility analyzed by a computer-assisted sperm analysis system

The authors investigated the relationship between frame rates and subpopulation structure of bovine sperm divided by their motility analyzed by a computer-assisted sperm analysis (CASA). Kinematic parameters of bovine sperm incubated in Brackett & Oliphant medium with and without calcium ionophore for 0, 1, 5, 10, 15, 20, 25, and 30 min were evaluated by a CASA at 150 frames per second (fps) and analyzed structure of sperm motility subpopulation by cluster analysis. Then, we converted CASA data at 150 fps to 75, 50, and 30 fps and evaluated the structures of sperm motility subpopulation at different fps in each sperm by a discriminant analysis. As the results, the structure of sperm motility subpopulation was affected by frame rate. Sperm were divided into six clusters at 150, 75, and 50 fps; on the other hand, there were five clusters at 30 fps. Straight-line velocity was similar at all frame rates. However, as the frame rate became higher, curvilinear velocity and beat cross frequency of sperm head increased significantly, whereas lateral sperm head displacement decreased significantly. In conclusion, higher frame rate at 150 fps is recommended to capture the trajectory of sperm accurately by CASA in the present study.

The flagellar germ-line hypothesis: How flagellate and ciliate gametes significantly shaped the evolution of organismal complexity

This essay presents a hypothesis which contends that the development of organismic complexity in the eukaryotes depended extensively on propagation via flagellated and ciliated gametes. Organisms utilizing flagellate and ciliate gametes to propagate their germ line have contributed most of the organismic complexity found in the higher animals. The genes of the flagellum and the flagellar assembly system (intraflagellar transport) have played a disproportionately important role in the construction of complex tissues and organs. The hypothesis also proposes that competition between large numbers of haploid flagellated male gametes rigorously conserved the functionality of a key set of flagellar genes for more than 700 million years. This in turn has insured that a large set (>600) of highly functional cytoskeletal and signal pathway genes is always present in the lineage of organisms with flagellated or ciliated gametes to act as a dependable resource, or "toolkit," for organ elaboration.