Progenitor cells of the testosterone-producing Leydig cells revealed

Efficient differentiation of human iPSCs into Leydig-like cells capable of long-term stable secretion of testosterone

Late-onset hypogonadism (LOH) syndrome is characterized by age-related testosterone deficiency and negatively affects the quality of life of older men. A promising therapeutic approach for LOH syndrome is transplantation of testosterone-producing Leydig-like cells (LLCs) derived from human induced pluripotent stem cells (hiPSCs). However, previous studies have encountered obstacles, such as limited cell longevity, insufficient testosterone production, and inefficiency of differentiation. To address these issues, we developed a novel protocol that includes forced NR5A1 expression, a cytokine cocktail promoting mesoderm differentiation, and a transitional shift from 3D to 2D cultures. The resultant cells survived on culture dishes for over 16 weeks, produced 22-fold more testosterone than the conventional method, and constituted a homogeneous population of LLCs with a differentiation efficiency exceeding 99% without purification. Furthermore, these LLCs were successfully engrafted subcutaneously into mice, resulting in increased serum testosterone levels. Our study will facilitate innovative therapeutic strategies for LOH syndrome.

Testicular sex cord-stromal tumors in mice with constitutive activation of PI3K and loss of Pten

Testicular tumors are the most common malignancy of young men, and tumors affecting the testis are caused by somatic mutations in germ or germ-like cells. The PI3K pathway is constitutively activated in about one-third of testicular cancers. To investigate the role of the PI3K pathway in transforming stem-like cells in the testis, we investigated tumors derived from mice with post-natal, constitutive activation of PI3K signaling and homozygous deletion of tumor suppressor Pten, targeted to Nestin-expressing cells. Mice developed aggressive tumors, exhibiting heterogeneous histopathology and hemorrhaging. The tumors resemble the rare testis tumor type, testicular sex cord-stromal Leydig cell tumors. Single-cell resolution spatial tissue analysis demonstrated that T-cells are the dominant tumor-infiltrating immune cell type, with very few infiltrating macrophages observed in the tumor tissue, with CD8+ T-cells predominating. Further analysis showed that immune cells preferentially localize to, or accumulate within stromal regions.

A New Leydig Cell-Exclusive Cre Line Allows Lineage Tracing of Fetal and Adult Leydig Cell Populations in the Mouse

Leydig cells produce hormones that are required for male development, fertility, and health. Two Leydig cell populations produce these hormones but at different times during development: fetal Leydig cells, which are active during fetal life, and adult Leydig cells, which are functional postnatally. Historically, our ability to understand the origin and function of Leydig cells has been made difficult by the lack of genetic models to exclusively target these cells. Taking advantage of the Leydig cell-exclusive expression pattern of the Insl3 gene, we used a CRISPR/Cas9 gene-editing strategy to knock-in iCre recombinase into the mouse Insl3 locus. To demonstrate the Leydig cell-exclusive nature of our iCre line, lineage-tracing experiments were performed by crossing Insl3iCre mice with a Rosa26LoxSTOPLox-TdTomato reporter. iCre activity was restricted to male offspring. TdTomato fluorescence was detected both in fetal and adult Leydig cells and colocalized with CYP17A1, a classic Leydig cell marker. Prior to birth, fluorescence was observed in fetal Leydig cells beginning at embryonic day 13.0. Fluorescence was also detected in adult Leydig cells starting at postnatal day 5 and continuing to the mature testis. Fluorescence was not detected in any other fetal or adult tissue examined, except for the unexpected finding that the adrenal cortex contains some Insl3-expressing Leydig-like cells. Our Leydig cell-exclusive iCre line therefore constitutes an invaluable new tool to study not only the origin of Leydig cells but also to target genes that have been long-proposed to be important for the development and functioning of these critical endocrine cells.

Age-related testosterone decline: mechanisms and intervention strategies

Contemporary societies exhibit delayed reproductive age and increased life expectancy. While the male reproductive system demonstrates relatively delayed aging compared to that of females, increasing age substantially impacts its function. A characteristic manifestation is age-induced testosterone decline. Testosterone, a crucial male sex hormone, plays pivotal roles in spermatogenesis and sexual function, and contributes significantly to metabolism, psychology, and cardiovascular health. Aging exerts profound effects on the hypothalamic-pituitary-gonadal axis and Leydig cells, precipitating testosterone reduction, which adversely affects male health. Exogenous testosterone supplementation can partially ameliorate age-related testosterone deficiency; however, its long-term safety remains contentious. Preserving endogenous testosterone production capacity during the aging process warrants further investigation as a potential intervention strategy.

Effects of Leydig cell elimination on testicular interstitial cell populations: characterization by scRNA-seq and immunocytochemical techniques

Background

The mammalian testicular interstitial cells are not well-defined. The present study characterized the interstitial cell types and their turnover dynamics in adult rats. Additionally, the heterogeneity of the mesenchymal population and the effects of Leydig cell elimination on interstitial homeostasis were further analyzed by scRNA-seq datasets and immunocytochemical techniques.

Methods

Interstitial cells were defined at the transcriptomic level by scRNA-seq and then confirmed and quantified with protein markers. The dividing activity of the major cell types was determined by continuous EdU labeling of the animals for one week. Some of the rats were also treated with a dose of ethylenedimethylsulfonate (EDS) to examine how the loss of Leydig cells (LCs) could affect interstitial homeostasis for three weeks.

Results

Seven interstitial cell types were identified, including cell types (percentage of the whole interstitial population) as follows: Leydig (44.6%), macrophage and dendritic (19.1%), lymphoid (6.2%), vascular endothelial (7.9%), smooth muscle (10.7%), and mesenchymal (11.5%) cells. The EdU experiment indicated that most cell types were dividing at relatively low levels (<9%) except for the mesenchymal cells (MCs, 17.1%). Further analysis of the transcriptome of MCs revealed 4 subgroups with distinct functions, including 1) glutathione metabolism and xenobiotic detoxification, 2) ROS response and AP-1 signaling, 3) extracellular matrix synthesis and binding, and 4) immune response and regulation. Stem LCs (SLCs) are primarily associated with subgroup 3, expressing ARG1 and GAP43. EDS treatment not only eliminated LCs but also increased subgroup 3 and decreased subgroups 1 and 2 of the mesenchymal population. Moreover, EDS treatment increased the division of immune cells by more than tenfold in one week.

Conclusion

Seven interstitial cell types were identified and quantified for rat testis. Many may play more diversified roles than previously realized. The elimination of LCs led to significant changes in MCs and immune cells, indicating the importance of LCs in maintaining testicular interstitial homeostasis.

In vitro effects of uncarboxylated osteocalcin on buffalo Leydig cell steroidogenesis

Uncarboxylated osteocalcin (UcOCN), a bone derived circulating protein, has been demonstrated to influence steroidogenesis in testicular Leydig cells of murine and human species. However, the role of UcOCN in testosterone biosynthesis remains unexplored in domestic animals. The present study aimed to investigate the impact of UcOCN on the expressions of steroidogenic genes (HSD3β1, HSD3β6, CYP17A1, CYP11A1), testosterone production and GPRC6A receptor localization in buffalo Leydig cells. Leydig cells from the testes of adult Murrah buffalo were isolated, with an average cell count and viability after digestion and Percoll enrichment of 1.43 × 106 cells/g of testes and 78.5%, respectively. Immunophenotyping of Percoll-enriched cell suspension by flow cytometry showed populations of Leydig cells ranging between 69 and 73.9%. Immunostaining confirmed the presence of GPRC6A receptors and CYP11A1 positive Leydig cells. When these cells were cultured and incubated with varying levels of UcOCN (6, 12, 24, and 48 ng/ml) and LH, there was a significant (P < 0.01) increase in testosterone production and up-regulation (P < 0.05) of CYP11A1, CYP17A1, HSD3β1 and HSD3β6 gene expression. In summary, the present study underscored the effects of UcOCN on testosterone biosynthesis, expression of crucial steroidogenic genes and interaction with GPRC6A receptors in buffalo Leydig cells, emphasizing its potential implications in andrology.

The role of HIF-1α-mediated autophagy in ionizing radiation-induced testicular injury

Testis, as a key organ for maintaining male fertility, are extremely sensitive to ionizing radiation (IR). IR-induced testicular dysfunction and infertility are common adverse effects of radiation therapy in patients with pelvic cancer. To study the phenotype and mechanism of IR-induced testicular injury, the mice were irradiated with different radiation doses (0, 2 and 5 Gy) below the semi-lethal dose for one month. Our present results showed that testicular weight and the serum testosterone levels significantly decreased with the structural injury of the testis in an IR dose-dependent manner, indicating that IR caused not only the structural damage of the testis, but also the functional damage. Further analysis by TUNEL staining and Western blotting found that IR induced the apoptosis in a dose-dependent manner as indicated by increased expressions of cleaved caspase3, p53 and Bax on Day 15 after IR treatment. Combined with significantly increased oxidative stress, these results indicated that IR-induced testicular damage may be a long-term, progressively aggravated process, accompanied by apoptosis. Given the role of autophagy in apoptosis, the present study also detected and analyzed the localization and expressions of autophagy-related proteins LC-3I/II, beclin1, p62 and Atg12 in testicular cells, and found that LC-3II, beclin1 and Atg12 expressions significantly increased in the testicular cells of mice irradiated with 2 Gy and 5 Gy, while p62 expression significantly decreased with 5 Gy, implying autophagy was involved in the apoptosis of testicular cells induced by IR. Furthermore, the expressions of HIF-1α and BNIP3 were significantly enhanced in the testis cells of mice irradiated with 2 Gy and 5 Gy, suggesting the potential role of HIF-1α/BNIP3-mediated autophagy in the apoptosis of testicular cells induced by IR. Taken together, our findings demonstrated that HIF-1α/BNIP3-mediated autophagy not only plays a protective effect on the testicular cells of mice irradiated with 2 Gy, but also induces the apoptosis of the testicular cells of mice irradiated with 5 Gy, indicating the double effects on apoptosis, which will help us further understanding the molecular mechanisms of IR-induced testicular injury, and will facilitate us further studies on testicular radioprotection.

Mitochondrial defects caused by PARL deficiency lead to arrested spermatogenesis and ferroptosis

Impaired spermatogenesis and male infertility are common manifestations associated with mitochondrial diseases, yet the underlying mechanisms linking these conditions remain elusive. In this study, we demonstrate that mice deficient for the mitochondrial intra-membrane rhomboid protease PARL, a recently reported model of the mitochondrial encephalopathy Leigh syndrome, develop early testicular atrophy caused by a complete arrest of spermatogenesis during meiotic prophase I, followed by degeneration and death of arrested spermatocytes. This process is independent of neurodegeneration. Interestingly, genetic modifications of PINK1, PGAM5, and TTC19 - three major substrates of PARL with important roles in mitochondrial homeostasis - fail to reproduce or modify this severe phenotype, indicating that the spermatogenic arrest arises from distinct molecular pathways. We further observed severe abnormalities in mitochondrial ultrastructure in PARL-deficient spermatocytes, along with prominent electron transfer chain defects, disrupted coenzyme Q (CoQ) biosynthesis, and metabolic rewiring. These mitochondrial defects are associated with a germ cell-specific decrease in GPX4 expression leading arrested spermatocytes to ferroptosis - a regulated cell death modality characterized by uncontrolled lipid peroxidation. Our results suggest that mitochondrial defects induced by PARL depletion act as an initiating trigger for ferroptosis in primary spermatocytes through simultaneous effects on GPX4 and CoQ - two major inhibitors of ferroptosis. These findings shed new light on the potential role of ferroptosis in the pathogenesis of mitochondrial diseases and male infertility warranting further investigation.

Carob extract induces spermatogenesis in an infertile mouse model via upregulation of Prm1, Plzf, Bcl-6b, Dazl, Ngn3, Stra8, and Smc1b

ETHNOPHARMACOLOGICAL RELEVANCE

Ethnopharmacological studies for drug discovery from natural compounds play an important role for developing current therapeutical platforms. Plants are a group of natural sources which have been served as the basis in the treatment of many diseases for centuries. In this regard, Ceratonia siliqua (carob) is one of the herbal medicine which is traditionally used for male infertility treatments. But so far the main mechanisms for effects of carob are unknown. Here, we intend to investigate the ability of carob extract to induce spermatogenesis in an azoospermia mouse model and determine the mechanisms that underlie its function.

AIM OF THE STUDY

This is a pre-clinical animal model study to evaluate the effect of carob extract in spermatogenesis recovery.

METHODS

We established an infertile mouse model with the intent to examine the ability of carob extract as a potential herbal medicine for restoration of male fertility. Sperm parameters, as well as gene expression dynamics and levels of spermatogenesis hormones, were evaluated 35 days after carob administration.

RESULTS

Significant enhanced sperm parameters (P < 0.05) showed that the carob extract could induce spermatogenesis in the infertile mouse model. Our data suggested an anti-apototic and inducer role in the expressions of cell cycle regulating genes. Carob extract improved the spermatogenesis niche by considerable affecting Sertoli and Leydig cells (P < 0.05). The carob-treated mice were fertile and contributed to healthy offspring that matured. Our data confirmed that this extract triggered the hormonal system, the spermatogenesis-related gene expression network, and signaling pathways to induce and promote sperm production with notable level (P < 0.05). We found that the aqueous extract consisted of a polar and mainly well water-soluble substance. Carob extract might upregulate spermatogenesis hormones via its amino acid components, which were detected in the extract by liquid chromatography-mass spectrometry (LC-MS).

CONCLUSION

Our results strongly suggest that carob extract might be a promising future treatment option for male infertility. This finding could pave the way for clinical trials in infertile men. This is the first study that has provided reliable, strong pre-clinical evidence for carob extract as an effective candidate for fertility recovery in cancer-related azoospermia.

Mesenchymal "stem" cells, or facilitators for the development of regenerative macrophages? Pericytes at the interface of wound healing

Cultured mesenchymal stromal cells are among the most used cells in clinical trials. Currently, their potential benefits include provision of mature cell types through differentiation, and secretion of various types of paracrine signaling molecules. Even though research on these cells has spanned some decades now, surprisingly, their therapeutic potential has not been fully translated into clinical practice yet, which calls for further understanding of their intrinsic nature and modes of action. In this review, after discussing pieces of evidence that suggest that some perivascular cells may exhibit mesenchymal stem cell characteristics in vivo, we examine the possibility that subpopulations of perivascular and/or adventitial cells activated after tissue injury behave as MSCs and contribute to the resolution of tissue injury by providing cues for the development of regenerative macrophages at injured sites. Under this perspective, an important contribution of cultured MSCs (or their acellular products, such as extracellular vesicles) used in cell therapies would be to instigate the development of M2-like macrophages that support the tissue repair process.

Effects of aging and macrophages on mice stem Leydig cell proliferation and differentiation in vitro

BACKGROUND

Testosterone plays a critical role in maintaining reproductive functions and well-beings of the males. Adult testicular Leydig cells (LCs) produce testosterone and are generated from stem Leydig cells (SLCs) during puberty through adulthood. In addition, macrophages are critical in the SLC regulatory niche for normal testicular function. Age-related reduction in serum testosterone contributes to a number of metabolic and quality-of-life changes in males, as well as age-related changes in immunological functions. How aging and testicular macrophages may affect SLC function is still unclear.

METHODS

SLCs and macrophages were purified from adult and aged mice via FACS using CD51 as a marker protein. The sorted cells were first characterized and then co-cultured in vitro to examine how aging and macrophages may affect SLC proliferation and differentiation. To elucidate specific aging effects on both cell types, co-culture of sorted SLCs and macrophages were also carried out across two ages.

RESULTS

CD51+ (weakly positive) and CD51++ (strongly positive) cells expressed typical SLC and macrophage markers, respectively. However, with aging, both cell types increased expression of multiple cytokine genes, such as IL-1b, IL-6 and IL-8. Moreover, old CD51+ SLCs reduced their proliferation and differentiation, with a more significant reduction in differentiation (2X) than proliferation (30%). Age matched CD51++ macrophages inhibited CD51+ SLC development, with a more significant reduction in old cells (60%) than young (40%). Crossed-age co-culture experiments indicated that the age of CD51+ SLCs plays a more significant role in determining age-related inhibitory effects. In LC lineage formation, CD51+ SLC had both reduced LC lineage markers and increased myoid cell lineage markers, suggesting an age-related lineage shift for SLCs.

CONCLUSION

The results suggest that aging affected both SLC function and their regulatory niche cell, macrophages.

Bone morphogenetic protein 4 inhibits rat stem/progenitor Leydig cell development and regeneration via SMAD-dependent and SMAD-independent signaling

Bone morphogenetic protein 4 (BMP4) is an important member of the transforming growth factor-β superfamily. BMP4 is expressed in the Leydig cell lineage. We hypothesized that BMP4 might regulate the development of stem/progenitor Leydig cells. The BMP4 receptors, BMPR1A, BMPR1B, and BMPR2 were found to be expressed in progenitor Leydig cells of prepubertal testis and isolated cells. BMP4 at 1 and 10 ng/mL significantly reduced androgen production and down-regulated steroidogenesis-related gene and protein expression possibly by activating the SMAD signaling pathway (increasing SMAD1/5 phosphorylation and SMAD4) at 24 h treatment. BMP4 at 0.1 ng/mL and higher concentrations markedly reduced the EdU labeling index of CD90⁺ stem Leydig cells after 24 h treatment and significantly reduced the number of EdU⁺ stem Leydig cells on the surface of seminiferous tubules after 7 days of culture. BMP4 at 0.01 ng/mL and higher concentrations significantly blocked the differentiation of stem Leydig cells into adult cells, as shown by the reduction of testosterone secretion and the downregulation of Lhcgr, Scarb1, Cyp11a1, Hsd11b1, and Insl3 and their function after 3D seminiferous tubule culture for 3 weeks, and this effect was reversed by co-treatment with the BMP4 antagonists noggin and doxomorphine. In addition, BMP4 also blocked stem Leydig cell differentiation through SMAD-independent signaling pathways (ERK1/2 and AMPK). Ethanedimethane sulfonate (EDS) single injection can result in reduction of testosterone, restoration can happen post treatment. In an in vivo model of Leydig cell regeneration following EDS treatment, intratesticular injection of BMP4 from day 14 to day 28 post-elimination significantly reduced serum testosterone levels and down-regulated the expression of Scarb1, Star, Hsd11b1, and Insl3 and its proteins, possibly through SMAD-dependent and SMAD-independent (ERK1/2 and AMPK) signaling pathways. In conclusion, BMP4 is expressed in cells of the Leydig cell lineage and blocks entry of stem/progenitor Leydig cells into adult Leydig cells through SMAD-dependent and SMAD-independent signaling pathways.

Perivascular cells support folliculogenesis in the developing ovary

Supporting cells of the ovary, termed granulosa cells, are essential for ovarian differentiation and oogenesis by providing a nurturing environment for oocyte maintenance and maturation. Granulosa cells are specified in the fetal and perinatal ovary, and sufficient numbers of granulosa cells are critical for the establishment of follicles and the oocyte reserve. Identifying the cellular source from which granulosa cells and their progenitors are derived is an integral part of efforts to understand basic ovarian biology and the etiology of female infertility. In particular, the contribution of mesenchymal cells, especially perivascular cells, to ovarian development is poorly understood but is likely to be a source of new information regarding ovarian function. Here we have identified a cell population in the fetal ovary, which is a Nestin-expressing perivascular cell type. Using lineage tracing and ex vivo organ culture methods, we determined that perivascular cells are multipotent progenitors that contribute to granulosa, thecal, and pericyte cell lineages in the ovary. Maintenance of these progenitors is dependent on ovarian vasculature, likely reliant on endothelial-mesenchymal Notch signaling interactions. Depletion of Nestin+ progenitors resulted in a disruption of granulosa cell specification and in an increased number of germ cell cysts that fail to break down, leading to polyovular ovarian follicles. These findings highlight a cell population in the ovary and uncover a key role for vasculature in ovarian differentiation, which may lead to insights into the origins of female gonad dysgenesis and infertility.

Behavior and Functional Roles of CD34+ Mesenchymal Cells in Mammalian Testes

Mammalian testes consist of seminiferous tubules within which Sertoli cells line up at the periphery and nurse germ cells, and of interstitia that harbor various cells such as peritubular myoid cells (PMCs), Leydig cells (LCs), vascular endothelial cells, immune cells such as macrophages, and mesenchymal (stromal) cells. Morphological studies have recently reported the presence of telocytes with telopodes in the interstitium of adult mouse, rat, and human testes. CD34+PDGFRα+ telocytes with long and moniliform telopodes form reticular networks with various cell types such as LCs, PMCs, and vessels, indicating their potential functions in cell-cell communications and tissue homeostasis. Functional studies have recently been performed on testicular interstitial cells and CD34+ cells, using 3D re-aggregate cultures of dissociated testicular cells, and cell cultures. Direct observation of CD34+ cells and adult LCs (ALCs) revealed that CD34+ cells extend thin cytoplasmic processes (telopodes), move toward the LC-CD34+ cell-re-aggregates, and finally enter into the re-aggregates, indicating the chemotactic behavior of CD34+ telocytes toward ALCs. In mammalian testes, important roles of mesenchymal interstitial cells as stem/progenitors in the differentiation and regeneration of LCs have been reported. Here, reports on testicular telocytes so far obtained are reviewed, and future perspectives on the studies of testicular telocytes are noted.

Deciphering the origins and fates of steroidogenic lineages in the mouse testis

Leydig cells (LCs) are the major androgen-producing cells in the testis. They arise from steroidogenic progenitors (SPs), whose origins, maintenance, and differentiation dynamics remain largely unknown. Single-cell transcriptomics reveal that the mouse steroidogenic lineage is specified as early as embryonic day 12.5 (E12.5) and has a dual mesonephric and coelomic origin. SPs specifically express the Wnt5a gene and evolve rapidly. At E12.5 and E13.5, they give rise first to an intermediate population of pre-LCs, and finally to fetal LCs. At E16.5, SPs possess the characteristics of the dormant progenitors at the origin of adult LCs and are also transcriptionally closely related to peritubular myoid cells (PMCs). In agreement with our in silico analysis, in vivo lineage tracing indicates that Wnt5a-expressing cells are bona fide progenitors of PMCs as well as fetal and adult LCs, contributing to most of the LCs present in the fetal and adult testis.

The Fate of Leydig Cells in Men with Spermatogenic Failure

The steroidogenic cells in the testicle, Leydig cells, located in the interstitial compartment, play a vital role in male reproductive tract development, maintenance of proper spermatogenesis, and overall male reproductive function. Therefore, their dysfunction can lead to all sorts of testicular pathologies. Spermatogenesis failure, manifested as azoospermia, is often associated with defective Leydig cell activity. Spermatogenic failure is the most severe form of male infertility, caused by disorders of the testicular parenchyma or testicular hormone imbalance. This review covers current progress in knowledge on Leydig cells origin, structure, and function, and focuses on recent advances in understanding how Leydig cells contribute to the impairment of spermatogenesis.

Identification of Rat Testicular Leydig Precursor Cells by Single-Cell-RNA-Sequence Analysis

Stem Leydig cells (SLCs) play a critical role in the development and maintenance of the adult Leydig cell (ALC) population. SLCs also are present in the adult testis. Their identification, characteristics, and regulation in the adult testis remain uncertain. Using single-cell RNA-seq, we found that the mesenchymal stromal population may be involved in ALC regeneration. Upon ALC elimination, a fraction of stromal cells begins to proliferate while a different fraction begins to differentiate to ALCs. Transcriptomic analysis identified five stromal clusters that can be classified into two major groups representing proliferation and differentiation populations. The proliferating group represents stem cells expressing high levels of CD90, Nes, Lum, Fn and Gap43. The differentiating group represents a progenitor stage that is ready to form ALCs, and specifically expresses Vtn, Rasl11a, Id1 and Egr2. The observation that the actively dividing cells after ALC loss were not those that formed ALCs suggests that stem cell proliferation and differentiation are regulated separately, and that the maintenance of the stromal stem cell pool occurs at the population level. The study also identified specific markers for the major interstitial cell groups and potential paracrine factors involved in the regulation of SLCs. Our data suggest a new theory about SLC identity, proliferation, differentiation, and regulation.

Mineralized Peyronie's plaque has a phenotypic resemblance to bone

Mineralized Peyronie's plaque (MPP) impairs penile function. The association, colocalization, and dynamic interplay between organic and inorganic constituents can provide insights into biomineralization of Peyronie's plaque. Human MPPs (n = 11) were surgically excised, and the organic and inorganic constituents were spatially mapped using multiple high-resolution imaging techniques. Multiscale image analyses resulted in spatial colocalization of elements within a highly porous material with heterogenous composition, lamellae, and osteocytic lacuna-like features with a morphological resemblance to bone. The lower (520 ± 179 mg/cc) and higher (1024 ± 155 mg/cc) mineral density regions were associated with higher (11%) and lower (7%) porosities in MPP. Energy dispersive X-ray and micro-X-ray fluorescent spectroscopic maps in the higher mineral density regions of MPP revealed higher counts of calcium (Ca) and phosphorus (P), and a Ca/P ratio of 1.48 ± 0.06 similar to bone. More importantly, higher counts of zinc (Zn) were localized at the interface between softer (more organic to inorganic ratio) and harder (less organic to inorganic ratio) tissue regions of MPP and adjacent softer matrix, indicating the involvement of Zn-related proteins and/or pathways in the formation of MPP. In particular, dentin matrix protein-1 (DMP-1) was colocalized in a matrix rich in proteoglycans and collagen that contained osteocytic lacuna-like features. This combined materials science and biochemical with correlative microspectroscopic approach provided insights into the plausible cellular and biochemical pathways that incite mineralization of an existing fibrous Peyronie's plaque. STATEMENT OF SIGNIFICANCE: Aberrant human penile mineralization is known as mineralized Peyronie's plaque (MPP) and often results in a loss of form and function. This study focuses on investigating the spatial association of matrix proteins and elemental composition of MPP by colocalizing calcium, phosphorus, and trace metal zinc with dentin matrix protein 1 (DMP-1), acidic proteoglycans, and fibrillar collagen along with the cellular components using high resolution correlative microspectroscopy techniques. Spatial maps provided insights into cellular and biochemical pathways that incite mineralization of fibrous Peyronie's plaque in humans.

Effects of Cadmium Exposure on Leydig Cells and Blood Vessels in Mouse Testis

Environmental exposure to cadmium (Cd) contributes to a decline in the quality of human semen. Although the testis is sensitive to Cd exposure, the mechanism underlying how cadmium affects the testis remains to be defined. In this study, male mice were treated with intraperitoneal injections of 0, 0.5, 1.5 and 2.5 mg CdCl₂/kg/day for 10 days, respectively. Both the testicular weight and the 3β-HSD activity of Leydig cells were significantly reduced with the administration of 2.5 mg CdCl₂/kg/day. The height of endothelial cells in the interstitial blood vessels significantly increased with the use of 2.5 mg CdCl₂/kg/day compared with the control. Western blot data showed that the protein levels of CD31, αSMA, caveolin and Ng2 increased with cadmium exposure, and this increase was particularly significant with the administration of 2.5 mg CdCl₂/kg/day. CD31, αSMA, caveolin and Ng2 are related to angiogenesis. Based on our data, cadmium exposure may stimulate the proliferation of the mural cells and endothelial cells of blood vessels, which may lead to abnormal function of the testis.

Dynamic Expression of the Homeobox Factor PBX1 during Mouse Testis Development

Members of the pre-B-cell leukemia transcription factor (PBX) family of homeoproteins are mainly known for their involvement in hematopoietic cell differentiation and in the development of leukemia. The four PBX proteins, PBX1, PBX2, PBX3 and PBX4, belong to the three amino acid loop extension (TALE) superfamily of homeoproteins which are important transcriptional cofactors in several developmental processes involving homeobox (HOX) factors. Mutations in the human PBX1 gene are responsible for cases of gonadal dysgenesis with absence of male sex differentiation while Pbx1 inactivation in the mouse causes a failure in Leydig cell differentiation and function. However, no data is available regarding the expression profile of this transcription factor in the testis. To fill this knowledge gap, we have characterized PBX1 expression during mouse testicular development. Real time PCRs and Western blots confirmed the presence Pbx1 mRNA and PBX1 protein in different Leydig and Sertoli cell lines. The cellular localization of the PBX1 protein was determined by immunohistochemistry and immunofluorescence on mouse testis sections at different embryonic and postnatal developmental stages. PBX1 was detected in interstitial cells and in peritubular myoid cells from embryonic life until puberty. Most interstitial cells expressing PBX1 do not express the Leydig cell marker CYP17A1, indicating that they are not differentiated and steroidogenically active Leydig cells. In adults, PBX1 was mainly detected in Sertoli cells. The presence of PBX1 in different somatic cell populations during testicular development further supports a direct role for this transcription factor in testis cell differentiation and in male reproductive function.

Short histological kaleidoscope - recent findings in histology. Part I

This article is a review of new advances in histology, concerning either classification or structure of different tissular elements (basement membrane, hemidesmosomes, urothelium, glandular epithelia, adipose tissue, astrocytes), and various organs' constituents (blood-brain barrier, human dental cementum, tubarial salivary glands, hepatic stellate cells, pineal gland, fibroblasts of renal interstitium, Leydig testicular cells, ovarian hilar cells), as well as novel biotechnological techniques (tissue engineering in angiogenesis), recently introduced.

Advances in stem cell research for the treatment of primary hypogonadism

In Leydig cell dysfunction, cells respond weakly to stimulation by pituitary luteinizing hormone, and, therefore, produce less testosterone, leading to primary hypogonadism. The most widely used treatment for primary hypogonadism is testosterone replacement therapy (TRT). However, TRT causes infertility and has been associated with other adverse effects, such as causing erythrocytosis and gynaecomastia, worsening obstructive sleep apnoea and increasing cardiovascular morbidity and mortality risks. Stem-cell-based therapy that re-establishes testosterone-producing cell lineages in the body has, therefore, become a promising prospect for treating primary hypogonadism. Over the past two decades, substantial advances have been made in the identification of Leydig cell sources for use in transplantation surgery, including the artificial induction of Leydig-like cells from different types of stem cells, for example, stem Leydig cells, mesenchymal stem cells, and pluripotent stem cells (PSCs). PSC-derived Leydig-like cells have already provided a powerful in vitro model to study the molecular mechanisms underlying Leydig cell differentiation and could be used to treat men with primary hypogonadism in a more specific and personalized approach.

Specific Transcriptomic Signatures and Dual Regulation of Steroidogenesis Between Fetal and Adult Mouse Leydig Cells

Leydig cells (LC) are the main testicular androgen-producing cells. In eutherian mammals, two types of LCs emerge successively during testicular development, fetal Leydig cells (FLCs) and adult Leydig cells (ALCs). Both display significant differences in androgen production and regulation. Using bulk RNA sequencing, we compared the transcriptomes of both LC populations to characterize their specific transcriptional and functional features. Despite similar transcriptomic profiles, a quarter of the genes show significant variations in expression between FLCs and ALCs. Non-transcriptional events, such as alternative splicing was also observed, including a high rate of intron retention in FLCs compared to ALCs. The use of single-cell RNA sequencing data also allowed the identification of nine FLC-specific genes and 50 ALC-specific genes. Expression of the corticotropin-releasing hormone 1 (Crhr1) receptor and the ACTH receptor melanocortin type 2 receptor (Mc2r) specifically in FLCs suggests a dual regulation of steroidogenesis. The androstenedione synthesis by FLCs is stimulated by luteinizing hormone (LH), corticotrophin-releasing hormone (CRH), and adrenocorticotropic hormone (ACTH) whereas the testosterone synthesis by ALCs is dependent exclusively on LH. Overall, our study provides a useful database to explore LC development and functions.

Standardized Saw Palmetto Extract Directly and Indirectly Affects Testosterone Biosynthesis and Spermatogenesis

We investigated whether a standardized saw palmetto extract (SP, mixture of supercritical extract and ethanol extract at a ratio of 9.5 to 0.5) can relieve the symptoms of andropause, including metabolic syndrome, and decreases in muscle endurance and spermatogenesis, in old rats. Twenty-four-week-old male Sprague Dawley rats received oral supplementation of SP at 40, 80, and 160 mg/kg body weight (bw) for 4 weeks. We found that SP supplementation reduced body weight gain by decreasing visceral and epididymal fat weights and the levels of serum triglycerides, total cholesterol, and low-density lipoprotein/very low-density lipoprotein cholesterol. In addition, SP supplementation increased muscle endurance, sperm counts, and testosterone biosynthesis through hormonal regulation. In Leydig cells under hydrogen peroxide-induced oxidative stress, SP treatment directly induced testosterone biosynthesis by activating the mRNA expression of the genes encoding 17,20-desmolase and 3β-hydroxysteroid dehydrogenase 4. In conclusion, our results suggest that supplementation of SP may be useful for alleviating the symptoms of andropause via direct and indirect regulation of testosterone biosynthesis.

TCF21+ mesenchymal cells contribute to testis somatic cell development, homeostasis, and regeneration in mice

Testicular development and function rely on interactions between somatic cells and the germline, but similar to other organs, regenerative capacity declines in aging and disease. Whether the adult testis maintains a reserve progenitor population remains uncertain. Here, we characterize a recently identified mouse testis interstitial population expressing the transcription factor Tcf21. We found that TCF21lin cells are bipotential somatic progenitors present in fetal testis and ovary, maintain adult testis homeostasis during aging, and act as potential reserve somatic progenitors following injury. In vitro, TCF21lin cells are multipotent mesenchymal progenitors which form multiple somatic lineages including Leydig and myoid cells. Additionally, TCF21+ cells resemble resident fibroblast populations reported in other organs having roles in tissue homeostasis, fibrosis, and regeneration. Our findings reveal that the testis, like other organs, maintains multipotent mesenchymal progenitors that can be potentially leveraged in development of future therapies for hypoandrogenism and/or infertility.

Age-Related Alterations in the Testicular Proteome of a Non-Human Primate

Aging of human testis and associated cellular changes is difficult to assess. Therefore, we used a translational, non-human primate model to get insights into underlying cellular and biochemical processes. Using proteomics and immunohistochemistry, we analyzed testicular tissue of young (age 2 to 3) and old (age 10 to 12) common marmosets (Callithrix jacchus). Using a mass spectrometry-based proteomics approach, we identified 63,124 peptides, which could be assigned to 5924 proteins. Among them, we found proteins specific for germ cells and somatic cells, such as Leydig and Sertoli cells. Quantitative analysis showed 31 differentially abundant proteins, of which 29 proteins were more abundant in older animals. An increased abundance of anti-proliferative proteins, among them CDKN2A, indicate reduced cell proliferation in old testes. Additionally, an increased abundance of several small leucine rich repeat proteoglycans and other extracellular matrix proteins was observed, which may be related to impaired cell migration and fibrotic events. Furthermore, an increased abundance of proteins with inhibitory roles in smooth muscle cell contraction like CNN1 indicates functional alterations in testicular peritubular cells and may mirror a reduced capacity of these cells to contract in old testes.

Stem Leydig cells: Current research and future prospects of regenerative medicine of male reproductive health

Stem cells are specialized cells that can renew themselves through cell division and can differentiate into multi-lineage cells. Mesenchymal stem cells are adult stem cells that exist in animal and human tissues. Mesenchymal stem cells have the ability to differentiate into mesodermal lineages, such as Leydig cells, adipocytes, osteocytes, and chondrocytes. Mesenchymal stem cells express cell surface markers, such as cluster of differentiation (CD) 29, CD44, CD73, CD90, CD105, and lack the expression of CD14, CD34, CD45 and HLA (human leukocyte antigen)-DR. Stem Leydig cells are one kind of mesenchymal stem cells, which are present in the interstitial compartment of testis. Stem Leydig cells are multipotent and can differentiate into Leydig cells, adipocytes, osteocytes, and chondrocytes. Stem Leydig cells have been isolated from rodent and human testes. Stem Leydig cells may have potential therapeutic values in several clinical applications, such as the treatment of male hypogonadism and infertility. In this review, we focus on the latest research on stem Leydig cells of both rodents and human, the expression of cell surface markers, culture, differentiation potential, and their applications.

Endosialin defines human stem Leydig cells with regenerative potential

STUDY QUESTION

Is endosialin a specific marker of human stem Leydig cells (SLCs) with the ability to differentiate into testosterone-producing Leydig cells (LCs) in vitro and in vivo?

SUMMARY ANSWER

Endosialin is a specific marker of human SLCs which differentiate into testosterone-producing LCs in vitro and in vivo.

WHAT IS KNOWN ALREADY

Human SLCs have been identified and isolated using the marker platelet-derived growth factor receptor α (PDGFRα) or nerve growth factor receptor (NGFR). However, the specificity was not high; thus, LCs and germ cells could be mistakenly sorted as SLCs if PDGFRα or NGFR was used as a marker for human SLCs isolation.

STUDY DESIGN, SIZE, DURATION

Firstly, we re-evaluated the specificity of PDGFRα and NGFR for SLCs in adult human testes. Then we analysed the previously published single-cell sequencing data and found that endosialin may identify human SLCs. Subsequently, we sorted endosialin+ cells from four human donors and characterized their self-renewal and multipotent properties. To assess whether endosialin+ cells have the potential to differentiate into functional LCs in vitro, these cells were stimulated by differentiation-inducing medium. We next assessed the in vivo regenerative potential of human endosialin+ cells after xenotransplantation into the testes of immunodeficient mice.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Single-cell sequencing analysis, immunofluorescence and flow cytometry were used to characterize human testis tissues. In vitro colony formation, multipotent differentiation (adipogenic, osteogenic and chondrogenic) and Leydig cell-lineage induction were used to assess stem cell activity. Xenotransplantation into 3-week-old immunodeficient mice was used to determine in vivo regenerative potential. Endpoint measures included testosterone measurements, cell proliferation, immunofluorescence, flow cytometry and quantitative RT-PCR.

MAIN RESULTS AND THE ROLE OF CHANCE

The results indicate that endosialin is a specific marker of SLCs compared with PDGFRα and NGFR. Additionally, endosialin+ cells isolated from human testes show extensive proliferation and differentiation potential in vitro: their self-renewal ability was inferred by the formation of spherical clones derived from a single cell. Moreover, these cells could differentiate into functional LCs that secreted testosterone in response to LH in a concentration-dependent manner in vitro. These self-renewal and differentiation properties reinforce the proposal that human testicular endosialin+ cells are SLCs. Furthermore, transplanted human endosialin+ cells appear to colonize the murine host testes, localize to peritubular and perivascular regions, proliferate measurably and differentiate partially into testosterone-producing LCs in vivo.

LARGE SCALE DATA

NA.

LIMITATIONS, REASONS FOR CAUTION

Owing to the difficulty in collecting human testis tissue, the sample size was limited. The functions of endosialin on SLCs need to be elucidated in future studies.

WIDER IMPLICATIONS OF THE FINDINGS

A discriminatory marker, endosialin, for human SLCs purification is a prerequisite to advance research in SLCs and logically promote further clinical translation of SLCs-based therapies for male hypogonadism.

STUDY FUNDING/COMPETING INTEREST(S)

A.P.X. was supported by the National Key Research and Development Program of China (2017YFA0103802 and 2018YFA0107200). C.D. was supported by the National Natural Science Foundation of China (81971314) and the Natural Science Foundation of Guangdong Province, China (2018B030311039). The authors declare no conflict of interest.

Differentiation of seminiferous tubule-associated stem cells into leydig cell and myoid cell lineages

Peritubular stem Leydig cells (SLCs) have been identified from rat testicular seminiferous tubules. However, no stem cells for peritubular myoid cells have been reported in the adult testis so far. In the present study, we tested the hypothesis that the peritubular SLCs are multipotent and able to form either Leydig or myoid cells. Using cultured tubules, we show that in the presence of PDGFAA and luteinizing hormone, SLCs became testosterone-producing Leydig cells, while in the presence of PDGFBB and TGFB, the cells formed α-smooth muscle actin-expressing myoid cells. This multipotency was also confirmed by culture of isolated CD90+ SLCs. These results suggest that these stem cells outside the myoid layer are multipotent and give rise to either Leydig or myoid cells, depending on the inducing factors. These cells may serve as a common precursor population for maintaining homeostasis of both Leydig and myoid cell populations in the adult testis.

Immune and vascular contributions to organogenesis of the testis and ovary

Gonad development is a highly regulated process that coordinates cell specification and morphogenesis to produce sex-specific organ structures that are required for fertility, such as testicular seminiferous tubules and ovarian follicles. While sex determination occurs within specialized gonadal supporting cells, sexual differentiation is evident throughout the entire organ, including within the interstitial compartment, which contains immune cells and vasculature. While immune and vascular cells have been traditionally appreciated for their supporting roles during tissue growth and homeostasis, an increasing body of evidence supports the idea that these cell types are critical drivers of sexually dimorphic morphogenesis of the gonad. Myeloid immune cells, such as macrophages, are essential for multiple aspects of gonadogenesis and fertility, including for forming and maintaining gonadal vasculature in both sexes at varying stages of life. While vasculature is long known for supporting organ growth and serving as an export mechanism for gonadal sex steroids in utero, it is also an important component of fetal testicular morphogenesis and differentiation; additionally, it is vital for ovarian corpus luteal function and maintenance of pregnancy. These findings point toward a new paradigm in which immune cells and blood vessels are integral components of sexual differentiation and organogenesis. In this review, we discuss the state of the field regarding the diverse roles of immune and vascular cells during organogenesis of the testis and ovary and highlight outstanding questions in the field that could stimulate new research into these previously underappreciated constituents of the gonad.

Deficiency in insulin-like growth factors signalling in mouse Leydig cells increase conversion of testosterone to estradiol because of feminization

AIM

A growing body of evidence pointed correlation between insulin-resistance, testosterone level and infertility, but there is scarce information about mechanisms. The aim of this study was to identify the possible mechanism linking the insulin-resistance with testosterone-producing-Leydig-cells functionality.

METHODS

We applied in vivo and in vitro approaches. The in vivo model of functional genomics is represented by INSR/IGF1R-deficient-testosterone-producing Leydig cells obtained from the prepubertal (P21) and adult (P80) male mice with insulin + IGF1-receptors deletion in steroidogenic cells (Insr/Igf1r-DKO). The in vitro model of INSR/IGF1R-deficient-cell was mimicked by blockade of insulin/IGF1-receptors on the primary culture of P21 and P80 Leydig cells.

RESULTS

Leydig-cell-specific-insulin-resistance induce the development of estrogenic characteristics of progenitor Leydig cells in prepubertal mice and mature Leydig cells in adult mice, followed with a dramatic reduction of androgen phenotype. Level of androgens in serum, testes and Leydig cells decrease as a consequence of the dramatic reduction of steroidogenic capacity and activity as well as all functional markers of Leydig cell. Oppositely, the markers for female-steroidogenic-cell differentiation and function increase. The physiological significances are the higher level of testosterone-to-estradiol-conversion in double-knock-out-mice of both ages and few spermatozoa in adults. Intriguingly, the transcription of pro-male sexual differentiation markers Sry/Sox9 increased in P21-Leydig-cells, questioning the current view about the antagonistic genetic programs underlying gonadal sex determination.

CONCLUSION

The results provide new molecular mechanisms leading to the development of the female phenotype in Leydig cells from Insr/Igf1r-DKO mice and could help to better understand the correlation between insulin resistance, testosterone and male (in)fertility.

Phthalate inhibits Leydig cell differentiation and promotes adipocyte differentiation

Studies have shown that phthalates are capable of affecting the development and functions of male reproductive system. The effect of phthalates on Leydig cell functions is well documented. However, little is known about their potential effects on the functions of stem Leydig cells (SLC). In the present study, we have examined the effects of mono-(2-ethylhexyl) phthalate (MEHP) on SLC functions in vitro by culturing seminiferous tubules and isolated SLCs. The results indicate that MEHP can significantly inhibit the proliferation and differentiation of SLCs in both the organ and cell culture systems. Interestingly, the minimal effective concentration that is able to affect SLC function was lower in the tubule culture system (1 μM) than in the isolated cells (10 μM), suggesting a possible involvement of the niche cells. Also, MEHP appeared to affect both the efficiency of SLCs to form Leydig cells and a selected group of Leydig cell-specific genes, including Lhcgr, Scarb1, Hsd3b1, Cyp17a1, Star, Srd5a1, Akr1c14, Insl3, Hao2 and Pah. Since SLCs are multipotent, we also tested the effect of MEHP on the differentiation of SLCs to adipocytes. Though MEHP by itself can not specify SLCs into adipocyte lineage, it indeed significantly increased the adipogenic activity of SLCs if used with an adipocyte inducing medium by up-regulation of multiple adipogenic-related genes, including Pparg and Cebpa. Overall, the results indicate that MEHP inhibits SLCs differentiating into Leydig lineage while stimulates the differentiating potential of SLCs to adipocytes.

Pericyte Ontogeny: The Use of Chimeras to Track a Cell Lineage of Diverse Germ Line Origins

The goal of lineage tracing is to understand body formation over time by discovering which cells are the progeny of a specific, identified, ancestral progenitor. Subsidiary questions include unequivocal identification of what they have become, how many descendants develop, whether they live or die, and where they are located in the tissue or body at the end of the window examined. A classical approach in experimental embryology, lineage tracing continues to be used in developmental biology and stem cell and cancer research, wherever cellular potential and behavior need to be studied in multiple dimensions, of which one is time. Each technical approach has its advantages and drawbacks. This chapter, with some previously unpublished data, will concentrate nonexclusively on the use of interspecies chimeras to explore the origins of perivascular (or mural) cells, of which those adjacent to the vascular endothelium are termed pericytes for this purpose. These studies laid the groundwork for our understanding that pericytes derive from progenitor mesenchymal pools of multiple origins in the vertebrate embryo, some of which persist into adulthood. The results obtained through xenografting, like in the methodology described here, complement those obtained through genetic lineage-tracing techniques within a given species.

Mesenchymal Stromal Cells as Critical Contributors to Tissue Regeneration

Adult stem cells that are tightly regulated by the specific microenvironment, or the stem cell niche, function to maintain tissue homeostasis and regeneration after damage. This demands the existence of specific niche components that can preserve the stem cell pool in injured tissues and restore the microenvironment for their subsequent appropriate functioning. This role may belong to mesenchymal stromal cells (MSCs) due to their resistance to damage signals and potency to be specifically activated in response to tissue injury and promote regeneration by different mechanisms. Increased amount of data indicate that activated MSCs are able to produce factors such as extracellular matrix components, growth factors, extracellular vesicles and organelles, which transiently substitute the regulatory signals from missing niche cells and restrict the injury-induced responses of them. MSCs may recruit functional cells into a niche or differentiate into missing cell components to endow a niche with ability to regulate stem cell fates. They may also promote the dedifferentiation of committed cells to re-establish a pool of functional stem cells after injury. Accumulated evidence indicates the therapeutic promise of MSCs for stimulating tissue regeneration, but the benefits of administered MSCs demonstrated in many injury models are less than expected in clinical studies. This emphasizes the importance of considering the mechanisms of endogenous MSC functioning for the development of effective approaches to their pharmacological activation or mimicking their effects. To achieve this goal, we integrate the current ideas on the contribution of MSCs in restoring the stem cell niches after damage and thereby tissue regeneration.

Perfluoroalkyl substances cause Leydig cell dysfunction as endocrine disruptors

Perfluoroalkyl substances (PFASs) are a group of man-made organic substances. Some of PFASs have been classified as persistent organic pollutants and endocrine disruptors. They might interfere with the male sex endocrine system, causing the abnormal development of the male reproductive tract and failure of pubertal onset and infertility. The present review discusses the development and function of two generations of Leydig cells in rodents and the effects of PFASs on Leydig cell development after their exposure in gestational and postnatal periods. We also discuss human epidemiological data for the effects of PFASs on male sex hormone levels. The structure-activity relationship of PFASs on Leydig cell steroidogenesis and enzyme activities are also discussed.

Restorative functions of Autologous Stem Leydig Cell transplantation in a Testosterone-deficient non-human primate model

Rationale: Stem Leydig cells (SLCs) transplantation can restore testosterone production in rodent models and is thus a potential solution for treating testosterone deficiency (TD). However, it remains unknown whether these favorable effects will be reproduced in more clinically relevant large-animal models. Therefore, we assessed the feasibility, safety and efficacy of autologous SLCs transplantation in a testosterone-deficient non-human primate (NHP) model.

Methods: Cynomolgus monkey SLCs (CM-SLCs) were isolated from testis biopsies of elderly (> 19 years) cynomolgus monkeys by flow cytometry. Autologous CM-SLCs were injected into the testicular interstitium of 7 monkeys. Another 4 monkeys were injected the same way with cynomolgus monkey dermal fibroblasts (CM-DFs) as controls. The animals were then examined for sex hormones, semen, body composition, grip strength, and exercise activity.

Results: We first isolated CD271⁺ CM-SLCs which were confirmed to expand continuously and show potential to differentiate into testosterone-producing Leydig cells (LCs) in vitro. Compared with CM-DFs transplantation, engraftment of autologous CM-SLCs into elderly monkeys could significantly increase the serum testosterone level in a physiological pattern for 8 weeks, without any need for immunosuppression. Importantly, CM-SLCs transplantation recovered spermatogenesis and ameliorated TD-related symptoms, such as those related to body fat mass, lean mass, bone mineral density, strength and exercise capacity.

Conclusion: For the first time, our short-term observations demonstrated that autologous SLCs can increase testosterone levels and ameliorate relevant TD symptoms in primate models. A larger cohort with long-term follow-up will be required to assess the translational potential of autologous SLCs for TD therapy.

A comparative analysis of human adult testicular cells expressing stem Leydig cell markers in the interstitium, vasculature, and peritubular layer

Background

Origin of human adult Leydig cells (ALCs) is not well understood. This might be partly due to limited data available on the identification and location of human precursor and stem Leydig cells (SLCs) which hampers the study on the development of ALCs.

Objectives

The aim of the present study was to investigate whether described human (PDGFRα, NGFR) and rodent (NES, PDGFRα, THY1, NR2F2) SLC markers are expressed by a common cell population within human adult testicular interstitial cells in vivo and before and after in vitro propagation.

Materials and methods

Immunohistochemical analyses were used to identify localization of human adult testicular interstitial cells expressing described SLC markers. Next, interstitial cells were isolated and cultured. The percentage of cells expressing one or more SLC markers was determined before and after culture using flow cytometry.

Results

NR2F2 and PDGFRα were present in peritubular, perivascular, and Leydig cells, while THY1 was expressed in peritubular and perivascular cells. Although NES and NGFR were expressed in endothelial cells, co‐localization with PDGFRα was found for both in vitro, although for NGFR only after culture. All marker positive cells were able to undergo propagation in vitro.

Discussion

The partly overlap in localization and overlap in expression in human testicular cells indicate that PDGFRα, NR2F2, and THY1 are expressed within the same ALC developmental lineage from SLCs. Based on the in vitro results, this is also true for NES and after in vitro propagation for NGFR.

Conclusion

Our results that earlier described SLC markers are expressed in overlapping human interstitial cell population opens up further research strategies aiming for a better insight in the Leydig cell lineage and will be helpful for development of strategies to cure ALC dysfunction.

Stem Leydig Cells in the Adult Testis: Characterization, Regulation and Potential Applications

Androgen deficiency (hypogonadism) affects males of all ages. Testosterone replacement therapy (TRT) is effective in restoring serum testosterone and relieving symptoms. TRT, however, is reported to have possible adverse effects in part because administered testosterone is not produced in response to the hypothalamic-pituitary-gonadal (HPG) axis. Progress in stem cell biology offers potential alternatives for treating hypogonadism. Adult Leydig cells (ALCs) are generated by stem Leydig cells (SLCs) during puberty. SLCs persist in the adult testis. Considerable progress has been made in the identification, isolation, expansion and differentiation of SLCs in vitro. In addition to forming ALCs, SLCs are multipotent, with the ability to give rise to all 3 major cell lineages of typical mesenchymal stem cells, including osteoblasts, adipocytes, and chondrocytes. Several regulatory factors, including Desert hedgehog and platelet-derived growth factor, have been reported to play key roles in the proliferation and differentiation of SLCs into the Leydig lineage. In addition, stem cells from several nonsteroidogenic sources, including embryonic stem cells, induced pluripotent stem cells, mature fibroblasts, and mesenchymal stem cells from bone marrow, adipose tissue, and umbilical cord have been transdifferentiated into Leydig-like cells under a variety of induction protocols. ALCs generated from SLCs in vitro, as well as Leydig-like cells, have been successfully transplanted into ALC-depleted animals, restoring serum testosterone levels under HPG control. However, important questions remain, including: How long will the transplanted cells continue to function? Which induction protocol is safest and most effective? For translational purposes, more work is needed with primate cells, especially human.

Suppression of transforming growth factor-beta signaling enhances spermatogonial proliferation and spermatogenesis recovery following chemotherapy

STUDY QUESTION

Could small molecules (SM) which target (or modify) signaling pathways lead to increased proliferation of undifferentiated spermatogonia following chemotherapy?

SUMMARY ANSWER

Inhibition of transforming growth factor-beta (TGFb) signaling by SM can enhance the proliferation of undifferentiated spermatogonia and spermatogenesis recovery following chemotherapy.

WHAT IS KNOWN ALREADY

Spermatogonial stem cells (SSCs) hold great promise for fertility preservation in prepubertal boys diagnosed with cancer. However, the low number of SSCs limits their clinical applications. SM are chemically synthesized molecules that diffuse across the cell membrane to specifically target proteins involved in signaling pathways, and studies have reported their ability to increase the proliferation or differentiation of germ cells.

STUDY DESIGN, SIZE, DURATION

In our experimental study, spermatogonia were collected from four brain-dead individuals and used for SM screening in vitro. For in vivo assessments, busulfan-treated mice were treated with the selected SM (or vehicle, the control) and assayed after 2 (three mice per group) and 5 weeks (two mice per group).

PARTICIPANTS/MATERIALS, SETTING, METHODS

We investigated the effect of six SM on the proliferation of human undifferentiated spermatogonia in vitro using a top–bottom approach for screening. We used histological, hormonal and gene-expression analyses to assess the effect of selected SM on mouse spermatogenesis. All experiments were performed at least in triplicate and were statistically evaluated by Student’s t-test and/or one-way ANOVA followed by Scheffe’s or Tukey’s post-hoc.

MAIN RESULTS AND THE ROLE OF CHANCE

We found that administration of SB431542, as a specific inhibitor of the TGFb1 receptor (TGFbR1), leads to a two-fold increase in mouse and human undifferentiated spermatogonia proliferation. Furthermore, injection of SB to busulfan-treated mice accelerated spermatogenesis recovery as revealed by increased testicular size, weight and serum level of inhibin B. Moreover, SB administration accelerated both the onset and completion of spermatogenesis. We demonstrated that SB promotes proliferation in testicular tissue by regulating the cyclin-dependent kinase (CDK) inhibitors 4Ebp1 and P57 (proliferation inhibitor genes) and up-regulating Cdc25a and Cdk4 (cell cycle promoting genes).

LIMITATIONS, REASONS FOR CAUTION

The availability of human testis was the main limitation in this study.

WIDER IMPLICATIONS OF THE FINDINGS

This is the first study to report acceleration of spermatogenesis recovery following chemotherapy by administration of a single SM. Our findings suggest that SB is a promising SM and should be assessed in future clinical trials for preservation of fertility in men diagnosed with cancer or in certain infertility cases (e.g. oligospermia).

STUDY FUNDING/COMPETING INTEREST(S)

This study was supported by Royan Institute and National Institute for Medical Research Development (NIMAD, grant no 963337) granted to H.B. The authors have no conflict of interest to report.

The pericyte microenvironment during vascular development

Vascular pericytes provide critical contributions to the formation and integrity of the blood vessel wall within the microcirculation. Pericytes maintain vascular stability and homeostasis by promoting endothelial cell junctions and depositing extracellular matrix (ECM) components within the vascular basement membrane, among other vital functions. As their importance in sustaining microvessel health within various tissues and organs continues to emerge, so does their role in a number of pathological conditions including cancer, diabetic retinopathy, and neurological disorders. Here, we review vascular pericyte contributions to the development and remodeling of the microcirculation, with a focus on the local microenvironment during these processes. We discuss observations of their earliest involvement in vascular development and essential cues for their recruitment to the remodeling endothelium. Pericyte involvement in the angiogenic sprouting context is also considered with specific attention to crosstalk with endothelial cells such as through signaling regulation and ECM deposition. We also address specific aspects of the collective cell migration and dynamic interactions between pericytes and endothelial cells during angiogenic sprouting. Lastly, we discuss pericyte contributions to mechanisms underlying the transition from active vessel remodeling to the maturation and quiescence phase of vascular development.

Human Adipose-derived Pericytes Display Steroidogenic Lineage Potential in Vitro and Influence Leydig Cell Regeneration in Vivo in Rats

Exogenous androgen replacement is used to treat symptoms associated with low testosterone in males. However, adverse cardiovascular risk and negative fertility impacts impel development of alternative approaches to restore/maintain Leydig cell (LC) androgen production. Stem Leydig cell (SLC) transplantation shows promise in this regard however, practicality of SLC isolation/transplantation impede clinical translation. Multipotent human adipose-derived perivascular stem cells (hAd-PSCs) represent an attractive extragonadal stem cell source for regenerative therapies in the testis but their therapeutic potential in this context is unexplored. We asked whether hAd-PSCs could be converted into Leydig-like cells and determined their capacity to promote regeneration in LC-ablated rat testes. Exposure of hAd-PSCs to differentiation-inducing factors in vitro upregulated steroidogenic genes but did not fully induce LC differentiation. In vivo, no difference in LC-regeneration was noted between Sham and hAd-PSC-transplanted rats. Interestingly, Cyp17a1 expression increased in hAd-PSC-transplanted testes compared to intact vehicle controls and the luteinising hormone/testosterone ratio returned to Vehicle control levels which was not the case in EDS + Sham animals. Notably, hAd-PSCs were undetectable one-month after transplantation suggesting this effect is likely mediated via paracrine mechanisms during the initial stages of regeneration; either directly by interacting with regenerating LCs, or through indirect interactions with trophic macrophages.

Characterization of stem cells associated with seminiferous tubule of adult rat testis for their potential to form Leydig cells

Adult testicular Leydig cells arise from stem cells in the neonatal and adult testis. The nature of these stem Leydig cells (SLCs) have not been well characterized. We have found previously that a group cells expressing CD90, a cell surface glycoprotein that may play roles in cell-cell and cell-matrix interactions and associated with the seminiferous tubule surface, have the ability to form Leydig cells. As yet, the relationship between this CD90+ cell population and SLCs reported previously by other groups is still unknown. In the present study, we systematically characterized these CD90+ cells by their ability to express multiple potential SLC markers and to proliferate and differentiate into Leydig cells in vitro. First, we have found by qPCR and immunohistochemical staining that the CD90+ cells do not express any of the markers of the common seminiferous tubular cells, including myoid, Sertoli, germ and Leydig cells, as well as macrophages. Moreover, when the CD90+ cells were isolated by fluorescent-sorting, the cells expressed high levels of all the potential SLC marker genes, including Nestin, Cd51, Coup-tf2, Arx, Pdgfra and Tcf21. Also, CD90-positive, but not -negative, cells were able to form Leydig cells in vitro with the proper inducing medium. Overall, the results indicated that the tubule-associated CD90+ cells represent a population of SLC in adult testis.

Development of fetal and adult Leydig cells

BACKGROUND

In mammals, two distinct Leydig cell populations, fetal Leydig cells (FLCs) and adult Leydig cells (ALCs), appear in the prenatal and postnatal testis, respectively. Although the functional differences between these cell types have been well described, the developmental relationship between FLCs and ALCs has not been fully understood. In this review, I focus on the cellular origins of FLCs and ALCs as well as the developmental and functional links between them.

METHODS

I surveyed previous reports about FLC and/or ALC development and summarized the findings.

MAIN FINDINGS

Fetal Leydig cells and ALCs were identified to have separate origins in the fetal and neonatal testis, respectively. However, several studies suggested that FLCs and ALCs share a common progenitor pool. Moreover, perturbation of FLC development at the fetal stage induces ALC dysfunction in adults, suggesting a functional link between FLCs and ALCs. Although the lineage relationship between FLCs and ALCs remains controversial, a recent study suggested that some FLCs dedifferentiate at the fetal stage, and that these cells serve as ALC stem cells.

CONCLUSION

Findings obtained from animal studies might provide clues to the causative mechanisms of male reproductive dysfunctions such as testicular dysgenesis syndrome in humans.

Characterization and differentiation of CD51+ Stem Leydig cells in adult mouse testes

It was reported previously that adult mouse stem Leydig cells (SLCs) express CD51 (integrin α-chain V). However, it is still unclear whether all CD51⁺ cells are SLCs. In the present study, we found that CD51⁺ cells can be classified into two sub-groups, a weakly-staining group (CD51⁺) and a strongly-staining group (CD51⁺⁺). The CD51⁺ cells expressed common SLC marker genes, including Nestin, Pdgfra and Coup-tf2, while CD51⁺⁺ cells did not express these genes. Instead, they expressed macrophage markers, such as F4/80, Cd115 and Tnfa. When these cells were induced to differentiate in vitro, the CD51⁺ cells, but not CD51⁺⁺ cells, formed Leydig cells. Overall, our results showed that although SLCs expressed CD51, not all CD51-expressing cells are SLCs. The cells that expressed high levels of CD51 are actually macrophages.

A Tri-fusion Reporter Mouse Reveals Tissue-Specific FGF1B Promoter Activity in vivo

Transgenic mice harboring imaging reporters take full advantage of imaging technologies in studies using living mice. Here, we established a tri-fusion multimodal reporter gene containing fragments from firefly luciferase, enhanced green fluorescent protein, and herpes simplex virus type 1 thymidine kinase and generated tri-fusion reporter Tg mice. Fibroblast growth factor type 1 (FGF1), a multifunctional mitogen to a wide range of tissues, regulates proliferation of neural stem cells of the brain, where FGF1 expression is initiated through activation of the FGF1B (F1B) promoter. The reporter mouse under the control of the human F1B promoter enables visualization in vivo where F1B activity is elevated, including tissues not only in the brain but also in the nasopharynx, skull, spine, and testes, particularly in Leydig cells. Treating Tg mice with the alkylating agent busulfan, which is known to eradicate Leydig cells and disrupt spermatogenesis in mice, eliminated the reporter signals. Restoring Leydig cells recovered reporter expression, indicating that the reporter can be used as a surrogate marker for Leydig cells. The F1B tri-fusion reporter mouse model can be utilized in longitudinal monitoring of the health status of the male reproductive system, such as in studies exploring the toxicity of chemicals to spermatogenesis.

Androgen receptor expression is required to ensure development of adult Leydig cells and to prevent development of steroidogenic cells with adrenal characteristics in the mouse testis

Background

The interstitium of the mouse testis contains Leydig cells and a small number of steroidogenic cells with adrenal characteristics which may be derived from the fetal adrenal during development or may be a normal subset of the developing fetal Leydig cells. Currently it is not known what regulates development and/or proliferation of this sub-population of steroidogenic cells in the mouse testis. Androgen receptors (AR) are essential for normal testicular function and in this study we have examined the role of the AR in regulating interstitial cell development.

Results

Using a mouse model which lacks gonadotropins and AR (hpg.ARKO), stimulation of luteinising hormone receptors in vivo with human chorionic gonadotropin (hCG) caused a marked increase in adrenal cell transcripts/protein in a group of testicular interstitial cells. hCG also induced testicular transcripts associated with basic steroidogenic function in these mice but had no effect on adult Leydig cell-specific transcript levels. In hpg mice with functional AR, treatment with hCG induced Leydig cell-specific function and had no effect on adrenal transcript levels. Examination of mice with cell-specific AR deletion and knockdown of AR in a mouse Leydig cell line suggests that AR in the Leydig cells are likely to regulate these effects.

Conclusions

This study shows that in the mouse the androgen receptor is required both to prevent development of testicular cells with adrenal characteristics and to ensure development of an adult Leydig cell phenotype.

Electronic supplementary material

The online version of this article (10.1186/s12861-019-0189-5) contains supplementary material, which is available to authorized users.

Microvascular bioengineering: a focus on pericytes

Capillaries within the microcirculation are essential for oxygen delivery and nutrient/waste exchange, among other critical functions. Microvascular bioengineering approaches have sought to recapitulate many key features of these capillary networks, with an increasing appreciation for the necessity of incorporating vascular pericytes. Here, we briefly review established and more recent insights into important aspects of pericyte identification and function within the microvasculature. We then consider the importance of including vascular pericytes in various bioengineered microvessel platforms including 3D culturing and microfluidic systems. We also discuss how vascular pericytes are a vital component in the construction of computational models that simulate microcirculation phenomena including angiogenesis, microvascular biomechanics, and kinetics of exchange across the vessel wall. In reviewing these topics, we highlight the notion that incorporating pericytes into microvascular bioengineering applications will increase their utility and accelerate the translation of basic discoveries to clinical solutions for vascular-related pathologies.

Histological Changes of the Testicular Interstitium during Postnatal Development in Microminipigs

Microminipigs have become an attractive animal model for the toxicology- and pharmacology-related studies because of their manageable size. In this study, the development of the testicular interstitium and steroidogenesis in microminipigs, from 0 to 12 months of age, were investigated. Testicular interstitium was mostly composed of two types of Leydig cells (large and small Leydig cells) and a few macrophages and mast cells. Large Leydig cells were observed in the peritubular area throughout all the ages. Small Leydig cells were present in the interlobular and subcapsular areas at an early age and then gradually converted into large Leydig cells. Testicular composition of the Leydig cells began to increase after 3 months of age, when spermatogenesis was completed, and reached approximately 35% at 12 months. Steroidogenic enzymes in Leydig cells were detected by immunohistochemistry from 0 month of age. Serum testosterone levels increased substantially from 1.5 to 4.5 months of age, which coincided well with the age of sexual development previously reported in microminipigs. Because the interstitial space of the testis has dramatic variations between species, the basic information obtained in the present study will be a useful reference for all the future toxicity evaluations in microminipigs.

Effects of spermatogenic cycle on Stem Leydig cell proliferation and differentiation

We reported previously that stem Leydig cells (SLC) on the surfaces of rat testicular seminiferous tubules are able to differentiate into Leydig cells. The proliferation and differentiation of SLCs seem likely to be regulated by niche cells, including nearby germ and Sertoli cells. Due to the cyclical nature of spermatogenesis, we hypothesized that the changes in the germ cell composition of the seminiferous tubules as spermatogenesis proceeds may affect tubule-associated SLC functions. To test this hypothesis, we compared the ability of SLCs associated with tubules at different stages of the cycle to differentiate into Leydig cells in vitro. SLCs associated with stages IX-XI were more active in proliferation and differentiation than SLCs associated with stages VII-VIII. However, when the SLCs were isolated from each of the two groups of tubules and cultured in vitro, no differences were seen in their ability to proliferate or differentiate. These results suggested that the stage-dependent local factors, not the SLCs themselves, explain the stage-dependent differences in SLC function. TGFB, produced in stage-specific fashion by Sertoli cells, is among the factors shown in previous studies to affect SLC function in vitro. When TGFB inhibitors were included in the cultures of stages IX-XI and VII-VIII tubules, stage-dependent differences in SLC development were reduced, suggesting that TGFB may be among the paracrine factors involved in the stage-dependent differences in SLC function. Taken together, the findings suggest that there is dynamic interaction between SLCs and germ/Sertoli cells within the seminiferous tubules that may affect SLC proliferation and differentiation.

The Pluripotent Microvascular Pericytes Are the Adult Stem Cells Even in the Testis

The pericytes of the testis are part of the omnipresent population of pericytes in the vertebrate body and are the only true pluripotent adult stem cells able to produce structures typical for the tree primitive germ layers: ectoderm, mesoderm, and endoderm. They originate very early in the embryogenesis from the pluripotent epiblast. The pericytes become disseminated through the whole vertebrate organism by the growing and differentiating blood vessels where they remain in specialized periendothelial vascular niches as resting pluripotent adult stem cells for tissue generation, maintenance, repair, and regeneration. The pericytes are also the ancestors of the perivascular multipotent stromal cells (MSCs). The variable appearance of the pericytes and their progeny reflects the plasticity under the influence of their own epigenetic and the local environmental factors of the host organ. In the testis the pericytes are the ancestors of the neuroendocrine Leydig cells. After activation the pericytes start to proliferate, migrate, and build transit-amplifying cells that transdifferentiate into multipotent stromal cells. These represent progenitors for a number of different cell types in an organ. Finally, it becomes evident that the pericytes are a brilliant achievement of the biological nature aiming to supply every organ with an omnipresent population of pluripotent adult stem cells. Their fascinating features are prerequisites for future therapy concepts supporting cell systems of organs.