Collective cell dynamics and luminal fluid flow in the epididymis: A mechanobiological perspective

Diffusion tensor imaging and fiber tractography of the epididymis in men with non-obstructive azoospermia

BACKGROUND

Scrotal magnetic resonance imaging, including diffusion tensor imaging and fiber tractography has emerged as a valuable, non-invasive method in the evaluation of non-obstructive azoospermia. The epididymis has a crucial role in male infertility.

OBJECTIVES

To evaluate the role of diffusion tensor imaging and fiber tractography of the epididymis in the work-up of non-obstructive azoospermia.

MATERIALS AND METHODS

This prospective study included 22 men with non-obstructive azoospermia and 15 controls. Scrotal magnetic resonance imaging, including diffusion tensor imaging, was performed. The epididymal apparent diffusion coefficient and fractional anisotropy were measured. Fiber tractography reconstructions were created. Non-parametric statistics compared apparent diffusion coefficient and fractional anisotropy of the epididymis between: (1) non-obstructive azoospermia and normal men; (2) histologic phenotypes of non-obstructive azoospermia; (3) non-obstructive azoospermia men, with positive and negative sperm retrieval; and (4) non-obstructive azoospermia men, with idiopathic and non-genetic etiology. Visual assessment of the epididymal fiber tracts was performed.

RESULTS

Lower epididymal fractional anisotropy (p = 0.027) was observed in men with non-obstructive azoospermia in comparison to normal population. Fractional anisotropy decreased (p = 0.033) in cases with idiopathic non-obstructive azoospermia in comparison to men with non-genetic etiology. Fiber tractography showed abnormalities in epididymal fiber tracts in men with non-obstructive azoospermia, including decrease in number and/or thickness and disorganization. However, diffusion tensor imaging parameters were unable to differentiate the histologic types of non-obstructive azoospermia and to predict the results of sperm retrieval (p > 0.05).

DISCUSSION AND CONCLUSION

Our preliminary observations showed that diffusion tensor imaging and fiber tractography of the epididymis provide valuable, non-invasive biomarkers in the work-up of non-obstructive azoospermia, although the clinical significance of these findings is yet to be determined. However, diffusion tensor imaging data were not predictive for the presence of spermatozoa before microdissection testicular sperm extraction.

Biomechanical properties of the capsule and extracellular matrix play a major role during the Wolffian/epididymal duct development

BACKGROUND

The epididymis is important for sperm maturation and without its proper development, male infertility will result. Biomechanical properties of tissues/organs play key roles during their morphogenesis, including the Wolffian duct. It is hypothesized that structural/bulk stiffness of the capsule and mesenchyme/extracellular matrix that surround the duct is a major biomechanical property that regulates Wolffian duct morphogenesis. These data will provide key information as to the mechanisms that regulate the development of this important organ.

OBJECTIVES

To measure the structural/bulk stiffness in Pascals (force/area) of the capsule and the capsule and mesenchyme together that surrounds the Wolffian duct during the development. To examine the relative membrane tension of mesenchymal cells during the Wolffian duct development. Since Ptk7 was previously shown to regulate ECM integrity and Wolffian duct elongation and coiling, the hypothesis that Ptk7 regulates structural/bulk stiffness and mesenchymal cell membrane tension was tested.

MATERIALS AND METHODS

Atomic force microscopy and a microsquisher compression apparatus were used to measure the structural stiffness. Biomechanical properties within the membranes of cells within the capsule and mesenchyme were examined using a membrane-tension fluorescent probe.

RESULTS AND DISCUSSION

The structural stiffness (Pascals) of the capsule and underlying mesenchyme was relatively constant during development, with a significant increase in the capsule at the later stages. However, this increase may reflect the ECM and associated mesenchyme being close to the capsule because the coiling of the duct pushed or compressed them into that space. Keeping the capsule and mesenchyme/ECM at constant stiffness would ensure that the duct will continue to coil under similar biomechanical forces throughout the development. Cells within the capsule and mesenchyme at different Wolffian duct regions during the development had varying degrees of membrane lipid tension. It is hypothesized that the dynamic changes ensure the duct is kept at a constant stiffness regardless of any external forces. Loss of Ptk7 resulted in an increase in stiffness at E18.5, which was presumable due to the loss of integrity of the ECM within the mesenchyme.

CONCLUSION

Biomechanical properties of the capsule and the mesenchyme/extracellular matrix that surround the Wolffian duct play an important role toward Wolffian duct morphogenesis, thereby allowing for the proper development of the epididymis and subsequent male fertility.

Shear stress effects on epididymal epithelial cell via primary cilia mechanosensory signaling

Shear stress, resulting from fluid flow, is a fundamental mechanical stimulus affecting various cellular functions. The epididymis, essential for sperm maturation, offers a compelling model to study the effects of shear stress on cellular behavior. This organ undergoes extensive proliferation and differentiation until puberty, achieving full functionality as spermatozoa commence their post-testicular maturation. Although the mechanical tension exerted by testicular fluid is hypothesized to drive epithelial proliferation and differentiation, the precise mechanisms remain unclear. Here we assessed whether the responsiveness of the epididymal cells to shear stress depends on functional primary cilia by combining microfluidic strategies on immortalized epididymal cells, calcium signaling assays, and high-throughput gene expression analysis. We identified 97 genes overexpressed in response to shear stress, including early growth response (Egr) 2/3, cellular communication network factor (Ccn) 1/2, and Fos proto-oncogene (Fos). While shear stress triggered a rapid increase of intracellular Ca2+, this response was abrogated following the impairment of primary ciliogenesis through pharmacological and siRNA approaches. Overall, our findings provide valuable insights into how mechanical forces influence the development of the male reproductive system, a requisite to sperm maturation.

Regulation of NHE3 subcellular localization in epididymal principal cells: pH, cyclic adenosine 3,5 monophosphate (cAMP), and adenosine signaling

INTRODUCTION

The epididymis creates an optimal acidic luminal environment for sperm maturation and storage. In epididymal principal cells (PCs), proton secretion is activated by the accumulation of the sodium-proton exchanger type 3, NHE3 (SLC9A3), in apical stereocilia. PCs also secrete ATP, which is hydrolyzed into adenosine by ectonucleotidases. Adenosine has opposite effects depending on which purinergic receptors it activates. Activation of ADORA1 (A1) and ADORA3 (A3) receptors decreases intracellular cAMP (cAMP), while activation of ADORA2A (A2A) and ADORA2B (A2B) receptors increases cAMP. In other epithelia, cAMP triggers NHE3 internalization from the apical membrane. Here, we examined the roles of pH, cAMP, and adenosine (via A3, A2A, and A2B receptors) in the subcellular localization of NHE3 in PCs.

METHODS

3D immunofluorescence confocal microscopy was used to visualize NHE3 in stereocilia or intracellular vesicles. Single confocal microscopy images superimposed with bright-field imaging was used to quantify NHE3 subcellular localization. The lumen of the cauda (Cd) epididymis of C57Bl/6Ncrl mice was perfused in vivo at pH 6.0 and 7.8. The effect of a permeant analog of cAMP (cpt-cAMP) was studied at pH 7.8, while the effect of adenosine was investigated at pH 6.0. Expression of A2A, A2B, and A3 was examined by immunofluorescence, and their respective role was evaluated by using specific agonists and antagonists at different luminal pH. Immunofluorescence for clathrin, an endosomal marker, was examined at pH 7.8 with and without an A2B agonist.

RESULTS

At an acidic pH perfusion solution of 6.0, NHE3 was predominantly localized intracellularly, whereas an alkaline pH of 7.8 promoted its accumulation in apical stereocilia. Perfusion with cpt-cAMP at pH 7.8 reduced the amount of NHE3 in stereocilia. Immunolabeling showed the localization of A3, A2A, and A2B receptors in the apical membrane of epithelial cells in the Cd epididymis. Adenosine and an A3 agonist increased NHE3 stereocilia accumulation at pH 6.0, and the adenosine effect was abolished with an A3 antagonist. An A2A agonist had no effect on NHE3 localization, while an A2B agonist decreased the amount of NHE3 in stereocilia observed at pH 7.8. A concomitant increase in intracellular labeling for clathrin was induced by the A2B agonist at pH 7.8.

CONCLUSIONS

Our study indicates that in the Cd epididymis, NHE3 localization in PCs is modulated by luminal pH, cAMP, and adenosine receptor signaling. Acidic pH promotes NHE3 internalization, while alkaline pH facilitates its accumulation in stereocilia. Activation of A3 by luminal adenosine maintains NHE3 on the cell surface. Conversely, A2B activation by adenosine induces NHE3 internalization. We propose that the distinct effects mediated by these receptors are the consequence of their opposite effect on cAMP signaling. This intricate interplay of pH and adenosine highlights some of the regulatory mechanisms influencing the establishment of an optimal acidic environment for sperm maturation and storage in the epididymis.

Exploring the Molecular Characteristics and Role of PDGFB in Testis and Epididymis Development of Tibetan Sheep

Platelet-derived growth factor B (PDGFB), as an important cellular growth factor, is widely involved in the regulation of cellular events such as cell growth, proliferation, and differentiation. Although important, the expression characteristics and biological functions in the mammalian reproductive system remain poorly understood. In this study, the PDGFB gene of Tibetan sheep was cloned by RT-PCR, and its molecular characteristics were analyzed. Subsequently, the expression of the PDGFB gene in the testes and epididymides (caput, corpus, and cauda) of Tibetan sheep at different developmental stages (3 months, 1 year, and 3 years) was examined by qRT-PCR and immunofluorescence staining. A bioinformatic analysis of the cloned sequences revealed that the CDS region of the Tibetan sheep PDGFB gene is 726 bp in length and encodes 241 amino acids with high homology to other mammals, particularly goats and antelopes. With the increase in age, PDGFB expression showed an overall trend of first decreasing and then increasing in the testis and epididymis tissues of Tibetan sheep, and the PDGFB mRNA expression at 3 months of age was extremely significantly higher than that at 1 and 3 years of age (p < 0.05). The PDGFB protein is mainly distributed in testicular red blood cells and Leydig cells in Tibetan sheep at all stages of development, as well as red blood cells in the blood vessel, principal cells, and the pseudostratified columnar ciliated epithelial cells of each epididymal duct epithelium. In addition, PDGFB protein expression was also detected in the spermatocytes of the 3-month-old group, spermatids of the 1-year-old group, spermatozoa and interstitial cells of the 3-year-old group, and loose connective tissue in the epididymal duct space in each developmental period. The above results suggest that the PDGFB gene, as an evolutionarily conserved gene, may play multiple roles in the development and functional maintenance of testicular cells (such as red blood cells, Leydig cells, and germ cells) and epididymal cells (such as red blood cells, principal cells, and ciliated epithelial cells) during testicular and epididymal development, which lays a foundation for the further exploration of the mechanisms by which the PDGFB gene influences spermatogenesis in Tibetan sheep.

In vivo dynamic volumetric imaging of mouse testis and epididymis with optical coherence tomography†

The implementation of live imaging in reproductive research is crucial for studying the physiological dynamics. Sperm transport is a highly dynamic process regulated by tubular contractions and luminal flows within the male reproductive tract. However, due to the lack of imaging techniques to capture these dynamics in vivo, there is little information on the physiological and biomechanical regulation of sperm transport through the male reproductive tract. Here, we present a functional in vivo imaging approach using optical coherence tomography, enabling live, label-free, depth-resolved, three-dimensional, high-resolution visualization of the mouse testis and epididymis. With this approach, we spatiotemporally captured tubular contractility in mouse testis and epididymis, as well as microstructures of these reproductive organs. Our findings demonstrated that the contraction frequency varies significantly depending on the epididymal regions, suggesting the spatial regulation of epididymal contractility. Furthermore, we implemented quantitative measurements of the contraction wave and luminal transport through the epididymal duct, revealing the physiological dynamics within the male reproductive tract. The results show that the contraction wave propagates along the epididymal duct and the wave propagation velocity was estimated in vivo. In conclusion, this is the first study to develop in vivo dynamic volumetric imaging of the male reproductive tract, which allows for quantitative analysis of the dynamics associated with sperm transport. This study sets a platform for various studies investigating normal and abnormal male reproductive physiology as well as the pharmacological and environmental effects on reproductive functions in mouse models, ultimately contributing to a comprehensive understanding of male reproductive disorders.