Effects of viscosity on sperm motility studied with optical tweezers

Deletion of the Sodium Glucose Cotransporter 1 (Sglt-1) impairs mouse sperm movement

The Sodium Glucose Cotransporter Isoform 1 (Sglt-1) is a symporter that moves Na+ and glucose into the cell. While most studies have focused on the role of Sglt-1 in the small intestine and kidney, little is known about this transporter's expression and function in other tissues. We have previously shown that Sglt-1 is expressed in the mouse sperm flagellum and that its inhibition interferes with sperm metabolism and function. Here, we further investigated the importance of Sglt-1 in sperm, using a Sglt-1 knockout mouse (Sglt-1 KO). RNA, immunocytochemistry, and glucose uptake analysis confirmed the ablation of Sglt-1 in sperm. Sglt-1 KO male mice are fertile and exhibit normal sperm counts and morphology. However, Sglt-1 null sperm displayed a significant reduction in total, progressive and other parameters of sperm motility compared to wild type (WT) sperm. The reduction in motility was exacerbated when sperm were challenged to swim in media with higher viscosity. Parameters of capacitation, namely protein tyrosine phosphorylation and acrosomal reaction, were similar in Sglt-1 KO and WT sperm. However, Sglt-1 KO sperm displayed a significant decrease in hyperactivation. The impaired motility of Sglt-1 null sperm was observed in media containing glucose as the only energy substrate. Interestingly, the addition of pyruvate and lactate to the media partially recovered sperm motility of Sglt-1 KO sperm, both in the low and high viscosity media. Altogether, these results support an important role for Sglt-1 in sperm energetics and function, providing sperm with a higher capacity for glucose uptake.

Applications of laser technology in the manipulation of human spermatozoa

The application of laser technology in the field of assisted reproductive technology (ART) has experienced rapid growth over the past decades owing to revolutionary techniques such as intracytoplasmic sperm injection (ICSI), preimplantation genetic testing (PGT), and in vitro manipulation of gametes and embryos. For male gametes, in vitro manipulation techniques include spermatozoa selection, sorting, immobilization, and quality assessment. A number of studies have been conducted to investigate the application of different laser technologies in the manipulation of human spermatozoa. However, there is a lack of a unified understanding of laser application in the in vitro manipulation of sperm and safety considerations in ART and, subsequently, the inability to make clear and accurate decisions on the clinical value of these laser technologies. This review summarizes the advancements and improvements of laser technologies in the manipulation of human spermatozoa, such as photobiomodulation therapy, laser trap systems for sperm analysis and sorting, laser-assisted selection of immotile sperm and laser-assisted immobilization of sperm prior to ICSI. The safety of those technologies used in ART is also discussed. This review will provide helpful and comprehensive insight into the applications of laser technology in the manipulation of human spermatozoa.

Chirality and frequency measurement of longitudinal rolling of human sperm using optical trap

Motility is one of the most critical features to evaluate sperm quality. As longitudinal rolling of human sperm has long been ignored until recently, its detailed dynamics and cellular biological mechanisms are still largely unknown. Here we report an optical-tweezers-based method to evaluate the chirality and frequency of sperm rotation. According to the intensity distribution patterns of off-focus micron-size particles, we established a method to judge the orientation of the sperm head along the optical axis in the optical trap. Together with the rotation direction of the projection of the sperm head, the chirality of longitudinal rolling of sperm can be measured without the application of three-dimensional tracking techniques or complex optical design. By video tracking optically trapped sperm cells from different patients, both rolling chirality and rolling frequency were analyzed. In this study, all the vertically trapped human sperm cells adopt a right-hand longitudinal rolling. The orientation and rolling frequency but not the rolling chirality of sperm in the optical trap are affected by the trap height. The rotation analysis method developed in this study may have clinical potential for sperm quality evaluation.

Motility Assessment of Ram Spermatozoa

For successful fertilisation to occur, spermatozoa need to successfully migrate through the female reproductive tract and penetrate the oocyte. Predictably, poor sperm motility has been associated with low rates of fertilisation in many mammalian species, including the ram. As such, motility is one of the most important parameters used for in vitro evaluation of ram sperm quality and function. This review aims to outline the mechanical and energetic processes which underpin sperm motility, describe changes in motility which occur as a result of differences in sperm structure and the surrounding microenvironment, and assess the effectiveness of the various methods used to assess sperm motility in rams. Methods of subjective motility estimation are convenient, inexpensive methods widely used in the livestock industries, however, the subjective nature of these methods can make them unreliable. Computer-assisted sperm analysis (CASA) technology accurately and objectively measures sperm motility via two-dimensional tracing of sperm head motion, making it a popular method for sperm quality assurance in domesticated animal production laboratories. Newly developed methods of motility assessment including flagellar tracing, three-dimensional sperm tracing, in vivo motility assessment, and molecular assays which quantify motility-associated biomarkers, enable analysis of a new range of sperm motion parameters with the potential to reveal new mechanistic insights and improve ram semen assessment. Experimental application of these technologies is required to fully understand their potential to improve semen quality assessment and prediction of reproductive success in ovine artificial breeding programs.

Microenvironment of the male and female reproductive tracts regulate sperm fertility: Impact of viscosity, pH, and osmolality

BACKGROUND

Terminally differentiated mammalian sperm are exposed to gradients of viscosity, pH, and osmolality both in the male and female reproductive tract during their perilous journey to quest the ovum. The complex physicochemical factors play an integral role in preparing sperm for the fertilization process.

OBJECTIVES

To elucidate the influence of the reproductive tract microenvironment especially viscosity, pH, and osmolality in regulating sperm functional and fertilization competence.

MATERIALS AND METHODS

The data used in this review were collected from the research papers and online databases focusing on the influence of viscosity, pH, and osmolality on sperm function.

DISCUSSION

The gradients of viscosity, pH, and osmolality exist across various segments of the male and female reproductive tract. The changes in the viscosity create a physical barrier, pH aid in capacitation and hyperactivation, and the osmotic stress selects a progressive sperm subpopulation for accomplishing fertilization. The sperm function tests are developed based on the concept that the male genotype is the major contributor to the reproductive outcome. However, recent studies demonstrate the significance of sperm genotype-environment interactions that are essentially contributing to reproductive success. Hence, it is imperative to assess the impact of physicochemical stresses and the adaptive ability of the terminally differentiated sperm, which in turn would improve the outcome of the assisted reproductive technologies and male fertility assessment.

CONCLUSION

Elucidating the influence of the reproductive tract microenvironment on sperm function provides newer insights into the procedures that need to be adopted for selecting fertile males for breeding, and ejaculates for the assisted reproductive technologies.

A PMMA-Based Microfluidic Device for Human Sperm Evaluation and Screening on Swimming Capability and Swimming Persistence

The selection of high-quality sperm is essential to the success of in vitro fertilization (IVF). As human cervical mucus has a high viscosity, without enough swimming persistence, human sperm clouds cannot arrive at the ampulla to fertilize the egg. In this study, we used swimming capability and motion characteristics that are known to be associated with fertilization ability to evaluate the quality of sperm. Here, a clinically applicable polymethyl methacrylate (PMMA)-based microdevice was designed and fabricated for sperm evaluation and screening for swimming capability and persistence in a viscous environment. In this study, we applied methylcellulose (MC) to mimic the natural properties of mucus in vivo to achieve the selection of motile sperm. Sperm motion was recorded by an inverted microscope. The statistical features were extracted and analyzed. Hundreds of sperm in two treated groups with different concentrations of MC and one control group with human tubal fluid (HTF) media were video recorded. This device can achieve a one-step procedure of high-quality sperm selection and achieve the quantitative evaluation of sperm swimming capability and persistence. Sperm with good swimming capability and persistence may be more suitable for fertilization in a viscous environment. This microdevice and methods could be used to guide the evaluation of sperm motility and screening in the future.

Dynamic Assembly of Small Parts in Vortex-Vortex Traps Established within a Rotating Fluid

Stable, purely fluidic particle traps established by vortex flows induced within a rotating fluid are described. The traps can manipulate various types of small parts, dynamically assembling them into high-symmetry clusters, cages, interlocked architectures, jammed colloidal monoliths, or colloidal formations on gas bubbles. The strength and the shape of the trapping region can be controlled by the strengths of one or both vortices and/or by the system's global angular velocity. The system exhibits a range of interesting dynamical behaviors including a Hopf-bifurcation transition between equilibrium-point trapping and the so-called limit cycle in which the particles are confined to circular orbits. Theoretical considerations indicate that these vortex-vortex traps can be further miniaturized to manipulate objects with sizes down to ≈10 µm.

Effect of Gum Arabic on Stallion Sperm Survival During Cold Storage and Post Freezing

This study is aimed at investigating effects of supplementation of stallion’ semen extender with various concentrations of Gum Arabic (GA) versus egg yolk (EY) on viscosity, sperm motility and survival during cooling and freezing. Physical sperm characteristics; i.e. curvilinear velocity (VCL), straight line velocity (VSL), average path velocity (VAP), linearity (LIN) and straightness index (STR) were evaluated. Based on the sperm velocity (velocity of the average path), individual spermatozoons were classified into two major groups; i.e., progressively motile (>45 μm/sec) and immotile (0-45 μm/sec) spermatozoa. Addition of 3, 9 or 15% of GA to HF-20 extender resulted in linear decreases in VCL, VSL and VAP and a decrease in the percentage of progressively motile spermatozoa. Dilution of horse semen samples with high viscosityextenders (i.e., high percentage of GA) decreased the VCL, VSL and VAP in fresh and chilled semen. Freezing semen in high viscosity-extenders reduced percentage of progressively motile spermatozoa compared with those of low viscosity-extenders. In refrigerated and frozen semen samples, the extender containing 15% GA had detrimental effects on the percentage of progressively motile sperm cells and velocity of progressive motile sperm. Moreover, cooling sperm in extenders containing 9 or 15% of GA for 72 hours resulted in complete motility cessation. In conclusion, GA could replace EY in stallion semen extenders at a level of 3% to maintain the physical and biological characteristics of cold and frozen semen.

CASA: tracking the past and plotting the future

The human semen sample carries a wealth of information of varying degrees of accessibility ranging from the traditional visual measures of count and motility to those that need a more computational approach, such as tracking the flagellar waveform. Although computer-aided sperm analysis (CASA) options are becoming more widespread, the gold standard for clinical semen analysis requires trained laboratory staff. In this review we characterise the key attitudes towards the use of CASA and set out areas in which CASA should, and should not, be used and improved. We provide an overview of the current CASA landscape, discussing clinical uses as well as potential areas for the clinical translation of existing research technologies. Finally, we discuss where we see potential for the future of CASA, and how the integration of mathematical modelling and new technologies, such as automated flagellar tracking, may open new doors in clinical semen analysis.

Determination of motility forces on isolated chromosomes with laser tweezers

Quantitative determination of the motility forces of chromosomes during cell division is fundamental to understanding a process that is universal among eukaryotic organisms. Using an optical tweezers system, isolated mammalian chromosomes were held in a 1064 nm laser trap. The minimum force required to move a single chromosome was determined to be ≈ 0.8-5 pN. The maximum transverse trapping efficiency of the isolated chromosomes was calculated as ≈ 0.01-0.02. These results confirm theoretical force calculations of ≈ 0.1-12 pN to move a chromosome on the mitotic or meiotic spindle. The verification of these results was carried out by calibration of the optical tweezers when trapping microspheres with a diameter of 4.5-15 µm in media with 1-7 cP viscosity. The results of the chromosome and microsphere trapping experiments agree with optical models developed to simulate trapping of cylindrical and spherical specimens.

Selection of functional human sperm with higher DNA integrity and fewer reactive oxygen species

Fertilization and reproduction are central to the survival and propagation of a species. Couples who cannot reproduce naturally have to undergo in vitro clinical procedures. An integral part of these clinical procedures includes isolation of healthy sperm from raw semen. Existing sperm sorting methods are not efficient and isolate sperm having high DNA fragmentation and reactive oxygen species (ROS), and suffer from multiple manual steps and variations between operators. Inspired by in vivo natural sperm sorting mechanisms where vaginal mucus becomes less viscous to form microchannels to guide sperm towards egg, a chip is presented that efficiently sorts healthy, motile and morphologically normal sperm without centrifugation. Higher percentage of sorted sperm show significantly lesser ROS and DNA fragmentation than the conventional swim-up method. The presented chip is an easy-to-use high-throughput sperm sorter that provides standardized sperm sorting assay with less reliance on operators's skills, facilitating reliable operational steps.

Real-time calcium measurements of live optically trapped microorganisms

A system has been developed that allows for the real-time measurement of calcium dynamics in swimming sperm. Specifically, the ratiometric dye Indo-I is used as a fluorescent indicator of intracellular calcium dynamics. The dual emissions are collected by a high-sensitivity back-illuminated CCD camera coupled to a Dual-View imaging system. From the CCD, the images are sent to a custom developed algorithm which processes the images and outputs the calcium measurements in real-time. Additionally, sperm velocity and position data are processed and outputted in real-time. The velocity and position data are obtained using a separate coupled red light (>670 nm) phase contrast imaging setup that does not optically interfere with the fluorescent imaging. Using this system the effects of optical trapping on calcium dynamics was determined. Optical trapping of sperm with a decaying focused laser power of 510 mW to 3 mW over 8 seconds causes a statistically insignificant change in calcium dynamics between in-trap and out-of-trap conditions. Progesterone, a calcium activator, was added and sperm were trapped under the 8 second power decay conditions. Progesterone treated sperm has a statistically higher average calcium level than untreated sperm, but shows no statistical difference between progesterone treated in-trap and out-of-trap conditions. Trapping at 16 seconds at 510 mW without decay, which have been shown to decrease sperm motility, shows a statistical difference between baseline pre-trap and in-trap intracellular calcium levels.

Rotational dynamics of optically trapped human spermatozoa

Introduction. Optical trapping is a laser-based method for probing the physiological and mechanical properties of cells in a noninvasive manner. As sperm motility is an important criterion for assessing the male fertility potential, this technique is used to study sperm cell motility behavior and rotational dynamics. Methods and Patients. An integrated optical system with near-infrared laser beam has been used to analyze rotational dynamics of live sperm cells from oligozoospermic and asthenozoospermic cases and compared with controls. Results. The linear, translational motion of the sperm is converted into rotational motion on being optically trapped, without causing any adverse effect on spermatozoa. The rotational speed of sperm cells from infertile men is observed to be significantly less as compared to controls. Conclusions. Distinguishing normal and abnormal sperm cells on the basis of beat frequency above 5.6 Hz may be an important step in modern reproductive biology to sort and select good quality spermatozoa. The application of laser-assisted technique in biology has the potential to be a valuable tool for assessment of sperm fertilization capacity for improving assisted reproductive technology.

Optical trapping map of dielectric spheres

Many applications use a focused Gaussian laser beam to manipulate spherical dielectric particles. The axial trapping efficiency of this process is a function of (i) the particle radius r, (ii) the ratio of the refractive index of particle over the medium, and (iii) the numerical aperture of the delivered light beam. During what we believe is the first comprehensive simulation of its kind, we uncovered optical trapping regions in the three-dimensional (3D) parameter space forming an iso-surface landscape with ridge-like contours. Using specific points in the parameter space, we drew attention to difficulties in using the trapping efficiency and stiffness metrics in defining how well particles are drawn into and held in the trap. We have proposed an alternative calculation based on the maximum forward and restoration values of the trapping efficiency in the axial sense, called the trapping quality. We also discuss the manner in which the ridge regions may be harnessed for effective particle sorting, how the optical trapping blind spots can be used in applications that seek to eschew photothermal damage, and how trapping can proceed when many parameters change, such as when swelling occurs.