ARL13B controls male reproductive tract physiology through primary and Motile Cilia

ARL13B is a small regulatory GTPase that controls ciliary membrane composition in both motile cilia and non-motile primary cilia. In this study, we investigated the role of ARL13B in the efferent ductules, tubules of the male reproductive tract essential to male fertility in which primary and motile cilia co-exist. We used a genetically engineered mouse model to delete Arl13b in efferent ductule epithelial cells, resulting in compromised primary and motile cilia architecture and functions. This deletion led to disturbances in reabsorptive/secretory processes and triggered an inflammatory response. The observed male reproductive phenotype showed significant variability linked to partial infertility, highlighting the importance of ARL13B in maintaining a proper physiological balance in these small ducts. These results emphasize the dual role of both motile and primary cilia functions in regulating efferent duct homeostasis, offering deeper insights into how cilia related diseases affect the male reproductive system.

Human efferent ductules and epididymis display unique cell lineages with motile and primary cilia

BACKGROUND

Previous research has illustrated the role of cilia as mechanical and sensory antennae in various organs within the mammalian male reproductive system across different developmental stages. Despite their significance in both organ development and homeostasis, primary cilia in the human male reproductive excurrent duct have been overlooked due to limited access to human specimens.

OBJECTIVE

This study aimed to characterize the unique cellular composition of human efferent and epididymal ducts, with a focus on their association with primary cilia.

MATERIALS AND METHODS

Human efferent ductules/epididymides from five donors aged 32-47 years, were obtained through our local organ transplant program. Cell lineage specificity and primary cilia features were examined by immunofluorescent staining and confocal microscopy in the efferent ductules and the distinct segments of the epididymis.

RESULTS

The epithelium of the human efferent duct exhibited estrogen receptor-positive cells with primary cilia, FoxJ1-positive multiciliated cells with numerous motile cilia, and non-ciliated intraepithelial immune cells. Notably, intraluminal macrophages, identified by CD163/CD68 positivity, were observed to engage in sperm phagocytosis. In all three segments of the human epididymis, primary cilia were found on the surface of principal and basal cells.

DISCUSSION AND CONCLUSIONS

Our research indicates that the human efferent ductules create a distinct environment, characterized by the presence of two types of ciliated cells that are in contact with immune cells. The discovery of sensory primary cilia exposed on the surface of reabsorptive cells in the efferent ductules, as well as on basal and principal cells in the epididymis, lays the foundation for complementary functional studies. This research uncovers novel characteristics exclusive to human efferent ductules and epididymides, providing a basis for exploring innovative approaches to male contraception and infertility treatment.

The single-cell atlas of the epididymis in mice reveals the changes in epididymis function before and after sexual maturity

Introduction: The epididymis is important for sperm transport, maturation, and storage. Methods: The head and tail of the epididymis of 5-week-old and 10-week-old C57 BL/6J male mice were used for single-cell sequencing. Results: 10 cell types including main, basal, and narrow/clear cells are identified. Next, we performed cell subgroup analysis, functional enrichment analysis, and differentiation potential prediction on principal cells, clear cells, and basal cells. Our study indicates that the principal cells are significantly involved in sperm maturation, as well as in antiviral and anti-tumor immune responses. Clear cells are likely to play a crucial role in safeguarding sperm and maintaining epididymal pH levels. Basal cells are implicated in the regulation of inflammatory and stress responses. The composition and functions of the various cell types within the epididymis undergo significant changes before and after sexual maturity. Furthermore, pseudo-temporal analysis elucidates the protective and supportive roles of epididymal cells in sperm maturation during sexual maturation. Discussion: This study offers a theoretical framework and forecasts for the investigation of epididymal sperm maturation and epididymal immunity.

Hedgehog signaling regulates Wolffian duct development through the primary cilium†

Primary cilia play pivotal roles in embryonic patterning and organogenesis through transduction of the Hedgehog signaling pathway (Hh). Although mutations in Hh morphogens impair the development of the gonads and trigger male infertility, the contribution of Hh and primary cilia in the development of male reproductive ductules, including the epididymis, remains unknown. From a Pax2Cre; IFT88fl/fl knock-out mouse model, we found that primary cilia deletion is associated with imbalanced Hh signaling and morphometric changes in the Wolffian duct (WD), the embryonic precursor of the epididymis. Similar effects were observed following pharmacological blockade of primary cilia formation and Hh modulation on WD organotypic cultures. The expression of genes involved in extracellular matrix, mesenchymal-epithelial transition, canonical Hh and WD development was significantly altered after treatments. Altogether, we identified the primary cilia-dependent Hh signaling as a master regulator of genes involved in WD development. This provides new insights regarding the etiology of sexual differentiation and male infertility issues.

Intra and intercellular signals governing sperm maturation

After their production in the testis, spermatozoa do not have the capacity to move progressively and are unable to fertilise an oocyte. They sequentially acquire these abilities following their maturation in the epididymis and their capacitation/hyperactivation in the female reproductive system. As gene transcription is silenced in spermatozoa, extracellular factors released from the epididymal epithelium and from secretory glands allow spermatozoa to acquire bioactive molecules and to undergo intrinsic modifications. These modifications include epigenetic changes and post-translational modifications of endogenous proteins, which are important processes in sperm maturation. This article emphasises the roles played by extracellular factors secreted by the epididymis and accessory glands in the control of sperm intercellular signallings and fertilising abilities.

Arl13b controls basal cell stemness properties and Hedgehog signaling in the mouse epididymis

Epithelial cells orchestrate a series of intercellular signaling events in response to tissue damage. While the epididymis is composed of a pseudostratified epithelium that controls the acquisition of male fertility, the maintenance of its integrity in the context of tissue damage or inflammation remains largely unknown. Basal cells of the epididymis contain a primary cilium, an organelle that controls cellular differentiation in response to Hedgehog signaling cues. Hypothesizing its contribution to epithelial homeostasis, we knocked out the ciliary component ARL13B in keratin 5-positive basal cells. In this model, the reduced size of basal cell primary cilia was associated with impaired Hedgehog signaling and the loss of KRT5, KRT14, and P63 basal cell markers. When subjected to tissue injury, the epididymal epithelium from knock-out mice displayed imbalanced rates of cell proliferation/apoptosis and failed to properly regenerate in vivo. This response was associated with changes in the transcriptomic landscape related to immune response, cell differentiation, cell adhesion, and triggered severe hypoplasia of the epithelium. Together our results indicate that the ciliary GTPase, ARL13B, participates in the transduction of the Hedgehog signaling pathway to maintain basal cell stemness needed for tissue regeneration. These findings provide new insights into the role of basal cell primary cilia as safeguards of pseudostratified epithelia.

TLR4 Modulates Senescence and Paracrine Action in Placental Mesenchymal Stem Cells via Inhibiting Hedgehog Signaling Pathway in Preeclampsia

Preeclampsia (PE) is a heterogeneous disease closely associated with the accelerated senescence of the placentas. Placental mesenchymal stem cells (PMSCs) modulate placental development, which is abnormally senescent in PE together with abnormal paracrine. Both pivotal in the placenta development, Toll-like receptor 4 (TLR4) and Hedgehog (HH) pathway are also tightly involved in regulating cellular senescence. This study was aimed at demonstrating that TLR4/HH pathway modulated senescence of placentas and PMSCs in vitro and in vivo. Preeclamptic and normal PMSCs were isolated. Smoothed agonist (SAG) and cyclopamine were used to activate and inhibit HH pathway, respectively. Lipopolysaccharide (LPS) was used to activate TLR4 in vitro and establish the classic PE-like rat model. qRT-PCR, Western blotting, and immunofluorescence were used to detect the expression of TLR4 and HH components (SHH, SMO, and Gli1). Cellular biological function such as proliferation, apoptosis, and migration was compared. Cell cycle analysis, β-galactosidase staining, and the protein expressions of p16 and p53 were detected to analyze the cellular senescence. The secretion levels of human matrix metalloproteinase 9 (MMP-9) and soluble fms-like tyrosine kinase-1 (sFlt-1) were measured in the conditioned medium. Cell migration, invasion, and tube formation were analyzed in HTR8/SVneo cells or human umbilical vein endothelial cells (HUVECs). Our study demonstrated that activation of TLR4 accelerated senescence of PMSCs via suppressing HH pathway both in vitro and in vivo, accompanied by the detrimental paracrine to impair the uterine spiral artery remodeling and placental angiogenesis. Meanwhile, induction of HH pathway could alleviate PE-like manifestations, improve pregnancy outcomes, and ameliorate multiorgan injuries, suggesting that strengthening the HH pathway may serve as a potential therapy in PE.

Generation of an Ihh-mKate2-Dre knock-in mouse line

Indian hedgehog (Ihh), a member of the Hh family, plays important roles in vertebrate development and homeostasis. To improve our understanding of the function of Ihh-expressing cells and their progeny as well, we generate an Ihh-mKate2^tomm20 -Dre knock-in mouse line that can label Ihh-positive cells with a fluorescence protein mKate2 and trace Ihh-positive cells and their progeny via Dre-mediated recombination. Consistent with previous reports, we verified Ihh expression in hypertrophic chondrocytes of growth plate and granulosa cells of ovarian follicles by mKate2 immunostaining, and meanwhile confirmed Dre activity in these cells via a Dre reporter mouse line Rosa26-confetti2. We also found, for the first time, that Ihh can mark some cell types, including retinal ganglion cells, Purkinje cells, and gallbladder epithelial cells. Taken together, the Ihh-mKate2^tomm20 -Dre mouse is a genetic tool for examining the precise expression profile of Ihh and tracing Ihh-expressing cells and their progeny.

Differential gene expression and hallmarks of stemness in epithelial cells of the developing rat epididymis

Epididymal development can be subdivided into three phases: undifferentiated, a period of differentiation, and expansion. The objectives of this study were (1) to assess gene expression profiles in epididymides, (2) predict signaling pathways, and (3) develop a novel 3D cell culture method to assess the regulation of epididymal development in vitro. Microarray analyses indicate that the largest changes in differential gene expression occurred between the 7- to 18-day period, in which 1452 genes were differentially expressed, while 671 differentially expressed genes were noted between days 18 and 28, and there were 560 differentially expressed genes between days 28 and 60. Multiple signaling pathways were predicted at different phases of development. Pathway associations indicated that in epididymides of 7- to 18-day old rats, there was a significant association of regulated genes implicated in stem cells, estrogens, thyroid hormones, and kidney development, while androgen- and estrogen-related pathways were enriched at other phases of development. Organoids were derived from CD49f + columnar cells from 7-day old rats, while no organoids developed from CD49f^- cells. Cells cultured in an epididymal basal cell organoid medium versus a commercial kidney differentiation medium supplemented with DHT revealed that irrespective of the culture medium, cells within differentiating organoids expressed p63, AQP9, and V-ATPase after 14 days of culture. The commercial kidney medium resulted in an increase in the number of organoids positive for p63, AQP9, and V-ATPase. Together, these data indicate that columnar cells represent an epididymal stem/progenitor cell population.

Cholesterol and Hedgehog Signaling: Mutual Regulation and Beyond

The Hedgehog (HH) signaling is one of the key agents that govern the precisely regulated developmental processes of multicellular organisms in vertebrates and invertebrates. The HH pathway in the receiving cell includes Patched1, a twelve-pass transmembrane receptor, and Smoothened, a seven-transmembrane G-protein coupled receptor (GPCR), and the downstream GLI family of three transcriptional factors (GLI1-GLI3). Mutations of HH gene and the main components in HH signaling are also associated with numerous types of diseases. Before secretion, the HH protein undergoes post-translational cholesterol modification to gain full activity, and cholesterol is believed to be essential for proper HH signaling transduction. In addition, results from recent studies show the reciprocal effect that HH signaling functions in cholesterol metabolism as well as in cholesterol homeostasis, which provides feedback to HH pathway. Here, we hope to provide new insights into HH signaling function by discussing the role of cholesterol in HH protein maturation, secretion and HH signaling transduction, and the potential role of HH in regulation of cholesterol as well.

Epididymal embryonic development harbors TLR4/NFKB signaling pathway as a morphogenetic player

The Wolffian duct (WD) is an embryonic tissue that undergoes androgen-induced morphological changes to become the epididymis. Toll-like receptor 4 (TLR4)- and nuclear factor kB (NFKB)-induced effectors are expressed in the adult epididymis and represent important players in epididymal innate immune responses. TLR4/NFKB signaling pathway is evolutionarily conserved and plays a critical morphogenetic role in several species; however, its function during WD morphogenesis is unknown. We hypothesized that TLR4/NFKB pathway plays a role during WD development. Here we examined TLR4 expression and regulation of TLR4-target genes during rat WD morphogenesis between embryonic days (e) 17.5-20.5. The functionality of TLR4/NFKB signaling was examined using WD organotypic cultures treated with lipopolysaccharide (LPS) from E. coli (TLR4 agonist) and PDTC (NFKB inhibitor). TLR4 was detected at mRNA level in e17.5 (uncoiled duct) and e20.5 (coiled duct) WDs, and spatio-temporal changes in TLR4 immunoreactivity were observed between these two time points. Expression level analysis of a subset of TLR4-regulated genes showed that TLR4/NFKB pathway was activated after exposure of cultured WD to LPS (4 h), an event that was abrogated by PDTC. Long-term exposure of cultured WDs to LPS (96 h) resulted in dysregulations of morphogenetic events and LAMA1 immunodistribution changes, suggesting the extracellular matrix at the intersection between WD morphogenesis and balance of innate immune components. Our results unveil the epididymal morphogenesis as an event equipped with TLR4/NFKB signaling components that may serve developmental functions, and eventually transition to host defense function when the fetus is exposed to an infectious or noninfectious threat.

Contribution of epididymal epithelial cell functions to sperm epigenetic changes and the health of progeny

BACKGROUND

Spermatozoa acquire their motility and fertilizing abilities during their maturation through the epididymis. This process is controlled by epididymal epithelial cells that possess features adapted to sense and respond to their surrounding environment and to communicate with spermatozoa. During the past decade, new intercellular communication processes have been discovered, including the secretion and transport of molecules from the epithelium to spermatozoa via extracellular vesicles (EVs), as well as sensing of the intraluminal milieu by cellular extensions.

OBJECTIVE AND RATIONALE

This review addresses recent findings regarding epididymal epithelial cell features and interactions between spermatozoa and the epididymal epithelium as well as epigenetic modifications undergone by spermatozoa during transit through the epididymal microenvironment.

SEARCH METHODS

A systematic search was conducted in Pubmed with the keyword 'epididymis'. Results were filtered on original research articles published from 2009 to 2021 and written in the English language. One hundred fifteen original articles presenting recent advancements on the epididymis contribution to sperm maturation were selected. Some additional papers cited in the primary reference were also included. A special focus was given to higher mammalian species, particularly rodents, bovines and humans, that are the most studied in this field.

OUTCOMES

This review provides novel insights into the contribution of epididymal epithelium and EVs to post-testicular sperm maturation. First, new immune cell populations have been described in the epididymis, where they are proposed to play a role in protecting the environment surrounding sperm against infections or autoimmune responses. Second, novel epididymal cell extensions, including dendrites, axopodia and primary cilia, have been identified as sensors of the environment surrounding sperm. Third, new functions have been outlined for epididymal EVs, which modify the sperm epigenetic profile and participate in transgenerational epigenetic inheritance of paternal traits.

WIDER IMPLICATIONS

Although the majority of these findings result from studies in rodents, this fundamental research will ultimately improve our knowledge of human reproductive physiopathologies. Recent discoveries linking sperm epigenetic modifications with paternal environmental exposure and progeny outcome further stress the importance of advancing fundamental research on the epididymis. From this, new therapeutic options for infertile couples and better counseling strategies may arise to increase positive health outcomes in children conceived either naturally or with ART.

Insights into differentiation and function of the transition region between the seminiferous tubule and rete testis

Seminiferous tubules physically connect to the rete testis through short segments called the transition region (TR). During fetal development, this specialized junction is considered the initial site where testis cords begin to form and to grow in length well beyond birth and into adulthood and form convoluted tubular cores. Mitotic activity of the Sertoli cell, the somatic cell of the epithelium, ceases before puberty, but modified Sertoli cells in the TR remain immature and capable of proliferation. This review presents what is known about this specialized region of the testis, with an emphasis on the morphological, molecular and physiological features, which support the hypothesis that this short region of epithelial transition serves as a specialized niche for undifferentiated Sertoli cells and spermatogonial stem cells. Also, the region is populated by an elevated number of immune cells, suggesting an important activity in monitoring and responding to any leakage of autoantigens, as sperm enter the rete testis. Several structure/function characteristics of the transition region are discussed and compared across species.

Hedgehog signaling and the primary cilium: implications for spatial and temporal constraints on signaling

The mechanisms of vertebrate Hedgehog signaling are linked to the biology of the primary cilium, an antenna-like organelle that projects from the surface of most vertebrate cell types. Although the advantages of restricting signal transduction to cilia are often noted, the constraints imposed are less frequently considered, and yet they are central to how Hedgehog signaling operates in developing tissues. In this Review, we synthesize current understanding of Hedgehog signal transduction, ligand secretion and transport, and cilia dynamics to explore the temporal and spatial constraints imposed by the primary cilium on Hedgehog signaling in vivo.

De novo purine biosynthesis is a major driver of chemoresistance in glioblastoma

Glioblastoma is a primary brain cancer with a near 100% recurrence rate. Upon recurrence, the tumour is resistant to all conventional therapies, and because of this, 5-year survival is dismal. One of the major drivers of this high recurrence rate is the ability of glioblastoma cells to adapt to complex changes within the tumour microenvironment. To elucidate this adaptation's molecular mechanisms, specifically during temozolomide chemotherapy, we used chromatin immunoprecipitation followed by sequencing and gene expression analysis. We identified a molecular circuit in which the expression of ciliary protein ADP-ribosylation factor-like protein 13B (ARL13B) is epigenetically regulated to promote adaptation to chemotherapy. Immuno-precipitation combined with liquid chromatography-mass spectrometry binding partner analysis revealed that that ARL13B interacts with the purine biosynthetic enzyme inosine-5'-monophosphate dehydrogenase 2 (IMPDH2). Further, radioisotope tracing revealed that this interaction functions as a negative regulator for purine salvaging. Inhibition of the ARL13B-IMPDH2 interaction enhances temozolomide-induced DNA damage by forcing glioblastoma cells to rely on the purine salvage pathway. Targeting the ARLI3B-IMPDH2 circuit can be achieved using the Food and Drug Administration-approved drug, mycophenolate mofetil, which can block IMPDH2 activity and enhance the therapeutic efficacy of temozolomide. Our results suggest and support clinical evaluation of MMF in combination with temozolomide treatment in glioma patients.