Stem Leydig cells: from fetal to aged animals

Role of p57KIP2 in Stem and Progenitor Leydig Cells of Mouse Testes

PURPOSE

Precise control of proliferation and differentiation of Leydig cells is important for gonadal androgenesis and spermatogenesis. Though cyclin-dependent kinase inhibitors are crucial for cell proliferation and differentiation, their role in the development of early adult Leydig cells (ALCs) remained unanswered. To understand mechanism for ALC development, functional expression of p57KIP2 (cdkn1c) was investigated in the stem Leydig cells (SLCs) and progenitor Leydig cells (PLCs) in mice.

MATERIALS AND METHODS

The roles of p57KIP2 in the proliferation, differentiation, apoptosis, and steroidogenesis in SLCs and PLCs were investigated by antibodies and bromodeoxyuridine (BrdU) labeling in the early neonatal testes and p57kip2 siRNA in the isolated SLCs and PLCs. Steroidogenic differentiation of PLCs was examined by progesterone and testosterone production in cell culture.

RESULTS

From postnatal day (PND) 1 to 14, p57KIP2(+) spindle-shaped cells in the testis interstitium were α-smooth muscle actin (αSMA)(-), a peritubular myoid cells marker, suggesting that they are SLCs and PLCs. Besides, p57KIP2 was also expressed in HSD3β(+) fetal Leydig cells. From PND1 to 14, BrdU(+)/αSMA(-), Ki67(+)/p57KIP2(+), and BrdU(+)/p57KIP2(+) spindle-shaped cells were gradually decreased. From PND1 to 14, p57KIP in the αSMA(-)/p57KIP2(+) cells was peaked at PND7 and decreased thereafter. In THY1(+) isolated SLCs, p57kip2 siRNA significantly increased ki67 and pcna mRNA and pdgfrα mRNA, a differentiation marker and decreased nestin mRNA, a SLC marker. No significant difference in apoptosis related genes mRNA was found after p57kip2 siRNA treatment. In HSD3β(+) PLCs, p57kip2 siRNA increased proapoptotic genes mRNA, annexin V(+) early-apoptotic cells. Importantly, p57kip2 siRNA significantly decreased hsd3β6 and cyp17a1 mRNA and progesterone production.

CONCLUSIONS

p57KIP2 may suppress proliferation and support stemness of SLCs. In PLCs, p57KIP2 may suppress apoptosis and potentiate the steroidogenic differentiation.

Ontogeny of mouse Sertoli, Leydig and peritubular myoid cells from embryonic day 10 to adulthood

We present a comprehensive description of the differentiating somatic cell types (Sertoli, Leydig, and peritubular myoid cells) of the mouse testis from embryonic day 10.5 (E10.5) to adulthood, postnatal day 60 (P60). Immunohistochemistry was used to analyze expression of: Sox9 (a Sertoli cell marker), 3βHSD-1 (a fetal Leydig cell marker), 3βHSD-6 (an adult Leydig cell marker), α-actin (a peritubular myoid cell marker), and androgen receptor (a marker of all three somatic cell types). The temporal-spatial expression of these markers was used to interrogate findings of earlier experimental studies on the origin of Sertoli, Leydig and peritubular myoid cells, as well as extend previous descriptive studies across a broader developmental period (E10.5-P60). Such comparisons demonstrate inconsistencies that require further examination and raise questions regarding conservation of developmental mechanisms across higher vertebrate species.

Pubertal Bisphenol A exposure increases adult rat serum testosterone by resetting pituitary homeostasis

Bisphenol A (BPA) is widely used by manufacturers and in consumer products. Its release in the environment may affect male reproductive function. In this study, we examined the effect of low dose (0.1 mg/kg BW), short term exposure during puberty (PD21-35) on adult rat male reproduction. The results indicated that such exposure reset growth hormone (GH) and follicular stimulating hormone (FSH) homeostasis and resulted in a significantly higher level of serum testosterone without affecting serum luteinizing hormone level. QPCR and Western blot results showed that BPA significantly up-regulated selective genes/proteins in the Leydig cell steroidogenic pathway, including steroidogenic acute regulatory protein, cytochrome P450 11A1, cytochrome P450 17A, and low-density lipoprotein receptor. RNA-Seq analysis of testicular RNAs showed that BPA significantly affected the gene profiles of multiple testicular interstitial populations without affecting germ cells. Also, GO- and KEGG-analysis suggested that IGF1-related PI3K/AKT signaling was activated, which was confirmed by the increased phosphorylation of IRS1, AKT1 and CREB. The results indicated that a low-dose, short-term BPA exposure during puberty affected the adult male rat pituitary (GH and FSH) and testis (testosterone) homeostasis.

Single-cell RNA sequencing of adult rat testes after Leydig cell elimination and restoration

Spermatogenesis is an efficient, complex, and highly organized proliferation and differentiation process that relies on multiple factors including testosterone produced by the Leydig cells. Although the critical role played by testosterone in spermatogenesis is well recognized, the mechanism by which it works is still not completely understood, partially due to the inability to specifically and precisely monitor testosterone-dependent changes within developing germ cells. Here we present single-cell RNA sequencing data from10,983 adult rat testicular cells after the rats were treated with ethanedimethanesulfonate, which temporarily eliminates Leydig cells. The elimination and recovery of Leydig cells represented a complete testosterone depletion and restoration cycle. The dataset, which includes all developing germ cells from spermatogonia to spermatozoa, should prove useful for characterizing developing germ cells, their regulatory networks, and novel cell-specific markers. The dataset should be particularly useful for exploring the effects of the androgen environment on the regulation of spermatogenesis. As this is the first single-cell RNA-Seq dataset for rat testes, it can also serve as a reference for future studies.

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.

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.

Identification of novel genes and pathways regulated by the orphan nuclear receptor COUP-TFII in mouse MA-10 Leydig cells†

In males, Leydig cells are the main producers of testosterone and insulin-like 3 (INSL3), two hormones essential for sex differentiation and reproductive functions. Chicken ovalbumin upstream promoter-transcription factors I (COUP-TFI/NR2F1) and COUP-TFII (NR2F2) belong to the steroid/thyroid hormone nuclear receptor superfamily of transcription factors. In the testis, COUP-TFII is expressed and plays a role in the differentiation of cells committed to give rise to fully functional steroidogenic adult Leydig cells. Steroid production has also been shown to be diminished in COUP-TFII-depleted Leydig cells, indicating an important functional role in steroidogenesis. Until now, only a handful of target genes have been identified for COUP-TFII in Leydig cells. To provide new information into the mechanism of action of COUP-TFII in Leydig cells, we performed microarray analyses of COUP-TFII-depleted MA-10 Leydig cells. We identified 262 differentially expressed genes in COUP-TFII-depleted MA-10 cells. Many of the differentially expressed genes are known to be involved in lipid biosynthesis, lipid metabolism, male gonad development, and steroidogenesis. We validated the microarray data for a subset of the modulated genes by RT-qPCR. Downregulated genes included Hsd3b1, Cyp11a1, Prlr, Shp/Nr0b2, Fdx1, Scarb1, Inha and Gsta3. Finally, analysis of the Gsta3 and Inha gene promoters showed that at least two of the downregulated genes are potentially new direct targets for COUP-TFII. These data provide new evidence that further strengthens the important nature of COUP-TFII in steroidogenesis, androgen homeostasis, cellular defense, and differentiation in mouse Leydig cells.

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.

Exogenous testosterone replacement therapy versus raising endogenous testosterone levels: current and future prospects

Testosterone replacement therapy is an important treatment option for men with low testosterone and symptomatic hypogonadism. Various formulations of exogenous testosterone replacement therapy exist, including oral, buccal, intramuscular, transdermal, subdermal, and nasal preparations. However, exogenous testosterone replacement therapy is a double-edged sword, posing risks to fertility due to negative feedback mechanisms on the hypothalamic-pituitary-gonadal (HPG) axis, which is the main regulator of testosterone production and spermatogenesis in males. Alternative pharmacologic therapies are being used to increase endogenous testosterone levels while attempting to preserve fertility and function of the HPG axis. These include selective estrogen receptor modulators, gonadotropins, and aromatase inhibitors. This review focuses on overviewing and comparing the currently available methods of exogenous testosterone replacement therapy, alternative treatments to increasing endogenous testosterone, and novel treatments that are currently under investigation to normalize testosterone levels while preserving the function of the HPG axis. In conclusion, reports suggest that, though Testosterone replacement therapy is an important way to restore testosterone levels and reduce symptoms associated with low testosterone, it is often difficult to decide which treatment to select for patients with testosterone deficiency. Several factors need to be considered to decide on optimal therapy option for the patient which include but are not limited to safety, efficacy, cost-effectiveness, dosing flexibility, and side effects. Alternative approaches which aim to improve endogenous testosterone production and preserve fertility are promising but still are at their initial stages of development. Ultimately, patient-centered decision making is paramount to appropriate treatment selection.

Exposure to di-n-octyl phthalate during puberty induces hypergonadotropic hypogonadism caused by Leydig cell hyperplasia but reduced steroidogenic function in male rats

Humans are exposed to phthalates ubiquitously, which may threaten health. However, whether di-n-octyl phthalate can prevent pubertal sexual maturity is still elusive. In this study, male Sprague Dawley rats (age 35 days) were treated daily by gavage with 0, 10, 100, and 1000 mg/kg body weight of di-n-octyl phthalate from day 35 to day 49 after birth. Di-n-octyl phthalate significantly reduced serum testosterone levels at doses of 100 and 1000 mg/kg, but increased serum luteinizing hormone levels of 1000 mg/kg and decreased testosterone/luteinizing hormone ratio at ≥10 mg/kg, without affecting serum follicle-stimulating hormone levels. Di-n-octyl phthalate significantly induced Leydig cell hyperplasia (increased number of CYP11A1-positive Leydig cells) at 100 and 1000 mg/kg. Di-n-octyl phthalate down-regulates the gene expression of Cyp11a1, Hsd3b1 and Insl3 in individual Leydig cells. Di-n-octyl phthalate can also reduce the number of sperm in the epididymis. Di-n-octyl phthalate increased phosphorylated AKT1/AKT2 without affecting their total proteins, but increased the total protein and phosphorylated protein of ERK1/2 and GSK-3β. Primary immature Leydig cells isolated from 35-day-old rats were treated with 0-50 μM di-n-octyl phthalate for 3 h. This phthalate inhibited androgen production under basal, LH-stimulated, and cAMP-stimulated conditions by 5 and 50 μM in vitro via down-regulating Cyp11a1 expression but up-regulating Srd5a1 expression in vitro. In conclusion, di-n-octyl phthalate induces hypergonadotropic hypogonadism caused by Leydig cell hyperplasia but reduced steroidogenic function and prevents sperm production.

Effects of Midazolam on the Development of Adult Leydig Cells From Stem Cells In Vitro

BACKGROUND

Midazolam is a neurological drug with diverse functions, including sedation, hypnosis, decreased anxiety, anterograde amnesia, brain-mediated muscle relaxation, and anticonvulsant activity. Since it is frequently used in children and adolescents for extended periods of time, there is a risk that it may affect their pubertal development. Here, we report a potential effect of the drug on the development of Leydig cells (LCs), the testosterone (T)-producing cells in the testis.

METHODS

Stem LCs (SLCs), isolated from adult rat testes by a magnetic-activated cell sorting technique, were induced to differentiate into LCs in vitro for 3 weeks. Midazolam (0.1-30 μM) was added to the culture medium, and the effects on LC development were assayed.

RESULTS

Midazolam has dose-dependent effects on SLC differentiation. At low concentrations (0.1-5 μM), the drug can mildly increase SLC differentiation (increased T production), while at higher concentrations (15-30 μM), it inhibits LC development (decreased T production). T increases at lower levels may be due to upregulations of scavenger receptor class b Member 1 (SCARB1) and cytochrome P450 17A1 (CYP17A1), while T reductions at higher levels of midazolam could be due to changes in multiple steroidogenic proteins. The uneven changes in steroidogenic pathway proteins, especially reductions in CYP17A1 at high midazolam levels, also result in an accumulation of progesterone. In addition to changes in T, increases in progesterone could have additional impacts on male reproduction. The loss in steroidogenic proteins at high midazolam levels may be mediated in part by the inactivation of protein kinase B/cAMP response element-binding protein (AKT/CREB) signaling pathway.

CONCLUSION

Midazolam has the potential to affect adult Leydig cell (ALC) development at concentrations comparable with the blood serum levels in human patients. Further studies are needed to test the effects on human cells.

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.

Fetal Leydig cells in buffalo testis: Light and electron microscopic study

The present study was conducted on testis of 20 buffalo fetuses ranging from 2.5 cm to 20 cm curved crown rump length (CVRL). The tissues were processed for light and transmission electron microscopic study. The intertubular tissue was filled with primitive mesenchymal cells, developing Leydig cells and blood vessels. At 7.5 cm CVRL, some of the interstitial mesenchymal cells started developing into foetal Leydig cells and were androgen positive. These cells were characterized by their polygonal shape, eosinophilic cytoplasm and darkly stained spherical nucleus with prominent nucleoli at 9.5 cm CVRL. At 15.5 cm CVRL, the fetal Leydig cells were present in groups around the interstitial blood vessels, which increased in number and size at 20 cm CVRL and decreased afterwards. By TEM, three types of Leydig cells were observed at 14.5 cm CVRL as stem Leydig cells (Leydig cell A), progenitor Leydig cells (Leydig cell B) and immature Leydig cells (Leydig cell C). Leydig cell A had elongated nucleus with a very thin rim of cytoplasm. Leydig cell B had oval nucleus with comparatively larger amount of cytoplasm. Leydig cell C had adult Leydig cell like features and had round to oval nucleus with lager amount of cytoplasm. The cytoplasm of these cells contained mitochondria with elongated cristae, Golgi apparatus and very few lipid inclusions. The number and size of Leydig cells increased during early prenatal life.

Essential roles of interstitial cells in testicular development and function

BACKGROUND

Testicular architecture and sperm production are supported by a complex network of communication between various cell types. These signals ensure fertility by: regulating spermatogonial stem/progenitor cells; promoting steroidogenesis; and driving male-specific differentiation of the gonad. Sertoli cells have long been assumed to be the major cellular player in testis organogenesis and spermatogenesis. However, cells in the interstitial compartment, such as Leydig, vascular, immune, and peritubular cells, also play prominent roles in the testis but are less well understood.

OBJECTIVES

Here, we aim to outline our current knowledge of the cellular and molecular mechanisms by which interstitial cell types contribute to spermatogenesis and testicular development, and how these diverse constituents of the testis play essential roles in ensuring male sexual differentiation and fertility.

METHODS

We surveyed scientific literature and summarized findings in the field that address how interstitial cells interact with other interstitial cell populations and seminiferous tubules (i.e., Sertoli and germ cells) to support spermatogenesis, male-specific differentiation, and testicular function. These studies focused on 4 major cell types: Leydig cells, vascular cells, immune cells, and peritubular cells.

RESULTS AND DISCUSSION

A growing number of studies have demonstrated that interstitial cells play a wide range of functions in the fetal and adult testis. Leydig cells, through secretion of hormones and growth factors, are responsible for steroidogenesis and progression of spermatogenesis. Vascular, immune, and peritubular cells, apart from their traditionally acknowledged physiological roles, have a broader importance than previously appreciated and are emerging as essential players in stem/progenitor cell biology.

CONCLUSION

Interstitial cells take part in complex signaling interactions with both interstitial and tubular cell populations, which are required for several biological processes, such as steroidogenesis, Sertoli cell function, spermatogenesis, and immune regulation. These various processes are essential for testicular function and demonstrate how interstitial cells are indispensable for male fertility.

Single-Cell RNA Sequencing of Human, Macaque, and Mouse Testes Uncovers Conserved and Divergent Features of Mammalian Spermatogenesis

Spermatogenesis is a highly regulated process that produces sperm to transmit genetic information to the next generation. Although extensively studied in mice, our current understanding of primate spermatogenesis is limited to populations defined by state-specific markers from rodent data. As between-species differences have been reported in the duration and differentiation hierarchy of this process, it remains unclear how molecular markers and cell states are conserved or have diverged from mice to man. To address this challenge, we employ single-cell RNA sequencing to identify transcriptional signatures of major germ and somatic cell types of the testes in human, macaque, and mice. This approach reveals similarities and differences in expression throughout spermatogenesis, including the stem/progenitor pool of spermatogonia, markers of differentiation, potential regulators of meiosis, RNA turnover during spermatid differentiation, and germ cell-soma communication. These datasets provide a rich foundation for future targeted mechanistic studies of primate germ cell development and in vitro gametogenesis.

Differentiation of human umbilical cord mesenchymal stem cells into Leydig-like cells with defined molecular compounds

95% of the body's testosterone is produced by the Leydig Cells (LCs) in adult testis, and LC functional degradation can cause testosterone deficiency ultimately leading towards hypogonadism. The transplantation of LCs derived from stem cells is a very promising therapy to overcome the testosterone deficiency. The isolated umbilical cord mesenchymal stem cells (UMSCs) were identified by flow cytometry and adipogenic and osteogenic differentiation. Western blotting and reverse transcription polymerase chain reaction (RT-PCR) were used for the differentiated Leydig-like cell identification. The comparisons of the testosterone levels, gene expression levels, and cyclic adenosine monophosphate (cAMP) productions were performed through radioimmunoassay, quantitative polymerase chain reaction (qPCR), and cAMP assay kit, respectively. Here, it is stated that our isolated human UMSCs, which could positively express CD29, CD44, CD59, CD90, CD105, and CD166 but negatively express CD34 as well as could be differentiated into adipocytes and osteocytes, could be differentiated into Leydig-like cells (UMSC-LCs) using a novel differentiation method based on molecular compounds. The enrichment UMSC-LCs could secrete testosterone into the medium supernatant and produce considerable cAMP at the stimulation of luteinizing hormone (LH), and positively expressed LC lineage-typical markers LHCGR, SCARB1, SATR, CYP11A1, CYP17A1, HSD3B1, HSD17B3, and SF-1 as well as negatively expressed mesenchymal stem cell typical markers CD29, CD44, and CD105. The expression levels of NR3C4, PDGFRA, and NR3A1 in UMSC-LCs were higher than those of UMSCs and were comparable with LCs. These results illuminated that UMSCs could be differentiated into Leydig-like cells using the defined molecular compounds, which might further support MSC-derived Leydig cell transplantation therapy for testosterone insufficiency.

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.

Amhr2-Cre-Mediated Global Tspo Knockout

Although the role of translocator protein (TSPO) in cholesterol transport in steroid-synthesizing cells has been studied extensively, recent studies of TSPO genetic depletion have questioned its role. Amhr2-Cre mice have been used to generate Leydig cell-specific Tspo conditional knockout (cKO) mice. Using the same Cre line, we were unable to generate Tspo cKO mice possibly because of genetic linkage between Tspo and Amhr2 and coexpression of Amhr2-Cre and Tspo in early embryonic development. We found that Amhr2-Cre is expressed during preimplantation stages, resulting in global heterozygous mice (gHE; Amhr2-Cre^+/–,Tspo^–/+). Two gHE mice were crossed, generating Amhr2-Cre–mediated Tspo global knockout (gKO; Tspo^–/–) mice. We found that 33.3% of blastocysts at E3.5 to E4.5 showed normal morphology, whereas 66.7% showed delayed development, which correlates with the expected Mendelian proportions of Tspo^+/+ (25%), Tspo^–/– (25%), and Tspo^+/– (50%) genotypes from crossing 2 Tspo^–/+ mice. Adult Tspo gKO mice exhibited disturbances in neutral lipid homeostasis and reduced intratesticular and circulating testosterone levels, but no change in circulating basal corticosterone levels. RNA-sequencing data from mouse adrenal glands and lungs revealed transcriptome changes in response to the loss of TSPO, including changes in several cholesterol-binding and transfer proteins. This study demonstrates that Amhr2-Cre can be used to produce Tspo gKO mice instead of cKO, and can serve as a new global “Cre deleter.” Moreover, our results show that Tspo deletion causes delayed preimplantation embryonic development, alters neutral lipid storage and steroidogenesis, and leads to transcriptome changes that may reflect compensatory mechanisms in response to the loss of function of TSPO.

Aflatoxin B1 impairs leydig cells through inhibiting AMPK/mTOR-mediated autophagy flux pathway

Aflatoxin B1 (AFB1), a potential endocrine disrupter, has been shown to induce hepatotoxicity in animal models, but the effects of AFB1 on Leydig cell function are unclear. In this study, in vivo exposure to AFB1 at 15 and 150 μg/kg/day lowered serum testosterone (T), luteinizing hormone (LH), and follicle-stimulating hormone (FSH) levels, reduced Leydig cell number, and down-regulated the expression of testosterone biosynthesis-related genes. In vitro study showed that AFB1 (10 μM) significantly increased ROS levels, and decreased T production in Leydig cells by suppressing certain T-biosynthesis gene expressions. Moreover, AFB1 induced Leydig cell apoptosis through lowering pAMPK/AMPK ratio and increasing pmTOR/mTOR ratio, and then further up-regulating autophagy and apoptosis proteins, LC3, BECLIN 1, and BAX, as well as down-regulating autophagy flux protein P62 and anti-apoptosis protein BCL-2. AFB1-induced toxicity in Leydig cells was characterized by inhibiting T-biosynthesis gene expression, reducing Leydig cell number, promoting ROS production, and inducing cell apoptosis via suppressing AMPK/mTOR-mediated autophagy flux pathway.

Notch signaling inhibition induces G0/G1 arrest in murine Leydig cells

As a highly evolutionarily conserved signaling pathway, Notch widely participates in cell-fate decisions and the development of various tissues and organs. In male reproduction, research on the Notch signaling pathway has mainly concentrated on germ cells and Sertoli cells. Leydig cells are the primary producers of testosterone and play important roles in spermatogenesis and maintaining secondary sexual characteristics. In this study, we used TM3 cells, a murine adult Leydig cell line, to investigate the expression profiles of Notch receptors and ligands and observe the effect of Notch signaling on the proliferation of TM3 cells. We found that Notch 1-3 and the ligands Dll-1 and Dll-4 were expressed in TM3 cells, Notch 1-3 and the ligand Dll-1 were expressed in testis interstitial Leydig cells, and Notch signaling inhibition suppressed the proliferation of TM3 cells and induced G0/G1 arrest. Inhibition of Notch signaling increased the expression of p21^Waf1/Cip1 and p27. Overall, our results suggest that Notch inhibition suppresses the proliferation of TM3 cells and P21^Waf1/Cip1 , and p27 may contribute to this process.

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.

Differentiation of human adipose derived stem cells into Leydig-like cells with molecular compounds

Leydig cells (LCs) are the primary source of testosterone in the testis, and testosterone deficiency caused by LC functional degeneration can lead to male reproductive dysfunction. LC replacement transplantation is a very promising approach for this disease therapy. Here, we report that human adipose derived stem cells (ADSCs) can be differentiated into Leydig-like cells using a novel differentiation method based on molecular compounds. The isolated human ADSCs expressed positive CD29, CD44, CD59 and CD105, negative CD34, CD45 and HLA-DR using flow cytometry, and had the capacity of adipogenic and osteogenic differentiation. ADSCs derived Leydig-like cells (ADSC-LCs) acquired testosterone synthesis capabilities, and positively expressed LC lineage-specific markers LHCGR, STAR, SCARB1, SF-1, CYP11A1, CYP17A1, HSD3B1 and HSD17B3 as well as negatively expressed ADSC specific markers CD29, CD44, CD59 and CD105. When ADSC-LCs labelled with lipophilic red dye (PKH26) were injected into rat testes which were selectively eliminated endogenous LCs using ethylene dimethanesulfonate (EDS, 75 mg/kg), the transplanted ADSC-LCs could survive and function in the interstitium of testes, and accelerate the recovery of blood testosterone levels and testis weights. These results demonstrated that ADSCs could be differentiated into Leydig-like cells by few defined molecular compounds, which might lay the foundation for further clinical application of ADSC-LC transplantation therapy.

Differentiation of human induced pluripotent stem cells into Leydig-like cells with molecular compounds

Leydig cells (LCs) play crucial roles in producing testosterone, which is critical in the regulation of male reproduction and development. Low levels of testosterone will lead to male hypogonadism. LC transplantation is a promising alternative therapy for male hypogonadism. However, the source of LCs limits this strategy for clinical applications. Thus far, others have reported that LCs can be derived from stem cells by gene transfection, but the safe and effective induction method has not yet been reported. Here, we report that Leydig-like cells can be derived from human induced pluripotent stem cells (iPSCs) using a novel differentiation protocol based on molecular compounds. The iPSCs-derived Leydig-like cells (iPSC-LCs) acquired testosterone synthesis capabilities, had the similar gene expression profiles with LCs, and positively expressed Leydig cell lineage-specific protein markers LHCGR, STAR, SCARB1, SF-1, CYP11A1, HSD3B1, and HSD17B3 as well as negatively expressed iPSC-specific markers NANOG, OCT4, and SOX2. When iPSC-LCs labeled with lipophilic red dye (PKH26) were transplanted into rat testes that were selectively eliminated endogenous LCs using EDS (75 mg/kg), the transplanted iPSC-LCs could survive and function in the interstitium of testes, and accelerate the recovery of serum testosterone levels and testis weights. Collectively, these findings demonstrated that the iPSCs were able to be differentiated into Leydig-like cells by few defined molecular compounds, which may lay the safer groundwork for further clinical application of iPSC-LCs for hypogonadism.

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.

Fibroblast Growth Factor 1 Promotes Rat Stem Leydig Cell Development

Fibroblast growth factor 1 (FGF1) is reported to be expressed in the testis. How FGF1 affects stem Leydig cell development remains unclear. Here, we report the effects of FGF1 on rat stem Leydig cell development in an ethane dimethane sulfonate (EDS)-treated model. FGF1 (100 ng/testis) significantly increased serum testosterone level, increased PCNA-positive Leydig cell percentage and Leydig cell number, but down-regulated the expression of Lhcgr, Star, Cyp11a1, Hsd3b1, Cyp17a1, and Hsd11b1 in Leydig cells per se, after its daily intratesticular injection from post-EDS day 14 for 14 days. Primary culture of the seminiferous tubules showed that FGF1 stimulated EdU incorporation to stem Leydig cells but blocked the differentiation into the Leydig cell lineage, possibly via FGFR1-mediated mechanism. In conclusion, FGF1 promotes stem Leydig cell proliferation but blocks its differentiation.

Transcript profiling in the testes and prostates of postnatal day 30 Sprague-Dawley rats exposed prenatally and lactationally to 2-hydroxy-4-methoxybenzophenone

2-hydroxy-4-methoxybenzophenone (HMB) is an ultraviolet light-absorbing compound that is used in sunscreens, cosmetics and plastics. HMB has been reported to have weak estrogenic activity by in vivo and in vitro studies, making it a chemical with potential reproductive concern. To explore if prenatal and lactational HMB exposure alters gene expression profiles of the developing reproductive organs, we performed microarray analysis using the prostate and testis of postnatal day (PND) 30 male Sprague-Dawley rats offspring exposed to 0, 3000, or 30,000 ppm of HMB from gestational day 6 through PND 21. Gene expression profiles of the prostate and testis were differentially affected by HMB dose with significant alterations observed at the 30,000 ppm HMB group. Tissue-specific gene expression was also identified. These genes, whose expression was altered by HMB exposure, may be considered as candidate biomarker(s) for testicular or prostatic toxicity; however, further studies are necessary to explore this potential.

A perivascular niche for multipotent progenitors in the fetal testis

Androgens responsible for male sexual differentiation in utero are produced by Leydig cells in the fetal testicular interstitium. Leydig cells rarely proliferate and, hence, rely on constant differentiation of interstitial progenitors to increase their number during fetal development. The cellular origins of fetal Leydig progenitors and how they are maintained remain largely unknown. Here we show that Notch-active, Nestin-positive perivascular cells in the fetal testis are a multipotent progenitor population, giving rise to Leydig cells, pericytes, and smooth muscle cells. When vasculature is disrupted, perivascular progenitor cells fail to be maintained and excessive Leydig cell differentiation occurs, demonstrating that blood vessels are a critical component of the niche that maintains interstitial progenitor cells. Additionally, our data strongly supports a model in which fetal Leydig cell differentiation occurs by at least two different means, with each having unique progenitor origins and distinct requirements for Notch signaling to maintain the progenitor population.

Leydig cells are steroidogenic cells in the testes and produce the androgens required for male development and spermatogenesis. Here the authors show that a multipotent progenitor population producing Leydig cells, pericytes and smooth muscle cells is maintained in a perivascular niche within the mouse fetal testis.

Oncostatin M inhibits differentiation of rat stem Leydig cells in vivo and in vitro

Oncostatin M (OSM) is a pleiotropic cytokine within the interleukin six family of cytokines, which regulate cell growth and differentiation in a wide variety of biological systems. However, its action and underlying mechanisms on stem Leydig cell development are unclear. The objective of the present study was to investigate whether OSM affects the proliferation and differentiation of rat stem Leydig cells. We used a Leydig cell regeneration model in rat testis and a unique seminiferous tubule culture system after ethane dimethane sulfonate (EDS) treatment to assess the ability of OSM in the regulation of proliferation and differentiation of rat stem Leydig cells. Intratesticular injection of OSM (10 and 100 ng/testis) from post-EDS day 14 to 28 blocked the regeneration of Leydig cells by reducing serum testosterone levels without affecting serum luteinizing hormone and follicle-stimulating hormone levels. It also decreased the levels of Leydig cell-specific mRNAs (Lhcgr, Star, Cyp11a1, Hsd3b1, Cyp17a1 and Hsd11b1) and their proteins by the RNA-Seq and Western blotting analysis. OSM had no effect on the proliferative capacity of Leydig cells in vivo. In the seminiferous tubule culture system, OSM (0.1, 1, 10 and 100 ng/mL) inhibited the differentiation of stem Leydig cells by reducing medium testosterone levels and downregulating the expression of Leydig cell-specific genes (Lhcgr, Star, Cyp11a1, Hsd3b1, Cyp17a1 and Hsd11b1) and their proteins. OSM-mediated action was reversed by S3I-201 (a STAT3 antagonist) or filgotinib (a JAK1 inhibitor). These data suggest that OSM is an inhibitory factor of rat stem Leydig cell development.

Bisphenol A stimulates differentiation of rat stem Leydig cells in vivo and in vitro

Bisphenol A (BPA) is widely used in consumer products and a potential endocrine disruptor linked with sexual precocity. However, its action and underlying mechanisms on male sexual maturation is unclear. In the present study, we used a unique in vivo ethane dimethane sulfonate (EDS)-induced Leydig cell regeneration model that mimics the pubertal development of Leydig cells and an in vitro stem Leydig cell differentiation model to examine the roles of BPA in Leydig cell development in rats. Intratesticular exposure to doses (100 and 1000 pmol/testis) of BPA from post-EDS day 14-28 stimulated Leydig cell developmental regeneration process by increasing serum testosterone level and Leydig cell-specific gene (Lhcgr, Star, Cyp11a1, Hsd3b1, Cyp17a1, Hsd17b3, and Hsd11b1) and their protein expression levels. BPA did not alter serum luteinizing hormone and follicle-stimulating hormone levels as well as the proliferative capacity of Leydig cells in vivo. In vitro study demonstrated that BPA (100 nmol/L) stimulated the differentiation of stem Leydig cells by increasing medium testosterone levels and up-regulating Leydig cell-specific gene (Lhcgr, Cyp11a1, Hsd3b1, Cyp17a1, and Hsd17b3) and their proteins but did not affect their proliferation measured by EdU incorporation. In conclusion, BPA stimulates the differentiation of stem Leydig cells in rat testes, thus possibly causing sexual precocity in the male.

Interleukin 6 inhibits the differentiation of rat stem Leydig cells

Inflammation causes male hypogonadism. Several inflammatory cytokines, including interleukin 6 (IL-6), are released into the blood and may suppress Leydig cell development. The objective of the present study was to investigate whether IL-6 affected the proliferation and differentiation of rat stem Leydig cells. Leydig cell-depleted rat testis (in vivo) and seminiferous tubules (in vitro) with ethane dimethane sulfonate (EDS) were used to explore the effects of IL-6 on stem Leydig cell development. Intratesticular injection of IL-6 (10 and 100 ng/testis) from post-EDS day 14 to 28 blocked the regeneration of Leydig cells, as shown by the lower serum testosterone levels (21.6% of the control at 100 ng/testis dose), the down-regulated Leydig cell gene (Lhcgr, Star, Cyp11a1, Cyp17a1, and Hsd17b3) expressions, and the reduced Leydig cell number. Stem Leydig cells on the surface of the seminiferous tubules were induced to enter the Leydig cell lineage in vitro in the medium containing luteinizing hormone and lithium. IL-6 (1, 10, and 100 ng/ml) concentration-dependently decreased testosterone production and Lhcgr, Cyp11a1, Cyp17a1, Hsd17b3 and Insl3 mRNA levels. The IL-6 mediated effects were antagonized by Janus kinase 1 (JAK) inhibitor (filgotinib) and Signal Transducers and Activators of Transcription 3 (STAT3) inhibitor (S3I-201), indicating that a JAK-STAT3 signaling pathway is involved. In conclusion, our results demonstrated that IL-6 was an inhibitory factor of stem Leydig cell development.

Di-(2-ethylhexyl) phthalate (DEHP)-induced testicular toxicity through Nrf2-mediated Notch1 signaling pathway in Sprague-Dawley rats

Di-(2-ethylhexyl) phthalate (DEHP) is an environmental endocrine disruptor widely used in China that is harmful to the male reproductive system. Many studies have shown that DEHP causes testicular toxicity through oxidative stress, but the specific mechanism is unknown. Because the Notch pathway is a key mechanism for regulating cell growth and proliferation, we investigated whether Notch is involved in DEHP-induced testicular toxicity and whether vitamins E and C could rescue testicular impairment in Sprague-Dawley (SD) rats. Compared with the control group, we found that DEHP exposure induced testicular toxicity through oxidative stress injury, and it decreased the testosterone level (P < .01) and upregulated nuclear factor-erythroid 2 related factor (Nrf2) expression (P < .01). Therefore, because oxidative stress might be the initiating factor of DEHP-induced testicular toxicity, treatment with the antioxidant vitamins E and C activated the Notch1 signaling pathway in the testis and in Leydig cells. Treatment with vitamins E and C normalized the oxidative stress state after DEHP exposure and restored testicular development to be similar to the control group. In summary, antioxidant vitamins E and C may be used to treat DEHP-induced testicular toxicity.

Influence of fetal Leydig cells on the development of adult Leydig cell population in rats

Leydig cells are the main endogenous testosterone synthesis cells in the body. Testosterone is an essential hormone in males that affects metabolism, emotion, and pubertal development. However, little is known about the development of Leydig cells and relationship between fetal Leydig cells (FLCs) and adult Leydig cells (ALCs). The aims of this study were to investigate the effect of (FLCs) on ALC development. Our study showed that FLCs in neonatal rat testis can be eliminated by 100 mg/kg ethane dimethane sulfonate (EDS) treatment without affecting the health of newborn rats. Immunohistological results showed that eliminating FLCs led to early re-generation of the ALC population (progenitor Leydig cells [PLCs] and ALCs) accompanied at first by increased and then by decreased serum testosterone, indicating that ALCs which appeared after neonatal EDS treatment were degenerated or had attenuated functions. Our results showed that FLCs were eliminated 4 days after EDS treatment, the ALC population regenerated by 21 days, and serum testosterone levels dramatically decreased at 56 days. Collectively, our results indicate that the ablation of FLCs in neonatal rat results in abnormal development of ALCs. Our study further indicates that abnormal development of Leydig cells in the fetal stage leads to steroid hormone disorders, such as testosterone deficiency, in the adult stage. Therefore, studies of Leydig cell development are important for understanding the pathogenesis of testosterone deficiency or pubertas praecox.

Origin of a rapidly evolving homeostatic control system programming testis function

Mammals share common strategies for regulating reproduction, including a conserved hypothalamic-pituitary-gonadal axis; yet, individual species exhibit differences in reproductive performance. In this report, we describe the discovery of a species-restricted homeostatic control system programming testis growth and function. Prl3c1 is a member of the prolactin gene family and its protein product (PLP-J) was discovered as a uterine cytokine contributing to the establishment of pregnancy. We utilized mouse mutagenesis of Prl3c1 and revealed its involvement in the regulation of the male reproductive axis. The Prl3c1-null male reproductive phenotype was characterized by testiculomegaly and hyperandrogenism. The larger testes in the Prl3c1-null mice were associated with an expansion of the Leydig cell compartment. Prl3c1 locus is a template for two transcripts (Prl3c1-v1 and Prl3c1-v2) expressed in a tissue-specific pattern. Prl3c1-v1 is expressed in uterine decidua, while Prl3c1-v2 is expressed in Leydig cells of the testis. 5'RACE, chromatin immunoprecipitation and DNA methylation analyses were used to define cell-specific promoter usage and alternative transcript expression. We examined the Prl3c1 locus in five murid rodents and showed that the testicular transcript and encoded protein are the result of a recent retrotransposition event at the Mus musculus Prl3c1 locus. Prl3c1-v1 encodes PLP-J V1 and Prl3c1-v2 encodes PLP-J V2. Each protein exhibits distinct intracellular targeting and actions. PLP-J V2 possesses Leydig cell-static actions consistent with the Prl3c1-null testicular phenotype. Analysis of the biology of the Prl3c1 gene has provided insight into a previously unappreciated homeostatic setpoint control system programming testicular growth and function.

Leydig cell stem cells: Identification, proliferation and differentiation

Adult Leydig cells develop from undifferentiated mesenchymal-like stem cells (stem Leydig cells, SLCs) present in the interstitial compartment of the early postnatal testis. Putative SLCs also have been identified in peritubular and perivascular locations of the adult testis. The latter cells, which normally are quiescent, are capable of regenerating new Leydig cells upon the loss of the adult cells. Recent studies have identified several protein markers to identify these cells, including nestin, PDGFRα, COUP-TFII, CD51 and CD90. We have shown that the proliferation of the SLCs is stimulated by DHH, FGF2, PDGFBB, activin and PDGFAA. Suppression of proliferation occurred with TGFβ, androgen and PKA signaling. The differentiation of the SLCs into testosterone-producing Leydig cells was found to be regulated positively by DHH (Desert hedgehog), lithium-induced signaling and activin; and negatively by TGFβ, PDGFBB, FGF2, Notch and Wnt signaling. DHH, by itself, was found to induce SLC differentiation into LH-responsive steroidogenic cells, suggesting that DHH plays a critical role in the commitment of SLC into the Leydig lineage. These studies, taken together, address the function and regulation of low turnover stem cells in a complex, adult organ, and also have potential application to the treatment of androgen deficiency.

Transplantation of alginate-encapsulated seminiferous tubules and interstitial tissue into adult rats: Leydig stem cell differentiation in vivo?

In vivo and in vitro studies were conducted to determine whether testosterone-producing Leydig cells are able to develop from cells associated with rat seminiferous tubules, interstitium, or both. Adult rat seminiferous tubules and interstitium were isolated, encapsulated separately in alginate, and implanted subcutaneously into castrated rats. With implanted tubules, serum testosterone increased through two months. Tubules removed from the implanted rats and incubated with LH produced testosterone, and cells on the tubule surfaces expressed steroidogenic enzymes. With implanted interstitial tissue, serum levels of testosterone remained undetectable. However, co-culture of interstitium plus tubules in vitro resulted in the formation of Leydig cells by both compartments. These results indicate that seminiferous tubules contain both cellular and paracrine factors necessary for the differentiation of Leydig cells, and that the interstitial compartment contains precursor cells capable of forming testosterone-producing Leydig cells but requires stimulation by paracrine factors from the seminiferous tubules to do so.

Stem cell therapy for the treatment of Leydig cell dysfunction in primary hypogonadism

The production of testosterone occurs within the Leydig cells of the testes. When production fails at this level from either congenital, acquired, or systemic disorders, the result is primary hypogonadism. While numerous testosterone formulations have been developed, none are yet fully capable of replicating the physiological patterns of testosterone secretion. Multiple stem cell therapies to restore androgenic function of the testes are under investigation. Leydig cells derived from bone marrow, adipose tissue, umbilical cord, and the testes have shown promise for future therapy for primary hypogonadism. In particular, the discovery and utilization of a group of progenitor stem cells within the testes, known as stem Leydig cells (SLCs), has led not only to a better understanding of testicular development, but of treatment as well. When combining this with an understanding of the mechanisms that lead to Leydig cell dysfunction, researchers and physicians will be able to develop stem cell therapies that target the specific step in the steroidogenic process that is deficient. The current preclinical studies highlight the complex nature of regenerating this steroidogenic process and the problems remain unresolved. In summary, there appears to be two current directions for stem cell therapy in male primary hypogonadism. The first method involves differentiating adult Leydig cells from stem cells of various origins from bone marrow, adipose, or embryonic sources. The second method involves isolating, identifying, and transplanting stem Leydig cells into testicular tissue. Theoretically, in-vivo re-activation of SLCs in men with primary hypogonadism due to age would be another alternative method to treat hypogonadism while eliminating the need for transplantation.

Juvenile Male Rats Exposed to a Low-Dose Mixture of Twenty-Seven Environmental Chemicals Display Adverse Health Effects

Humans are exposed to a large number of environmental chemicals in their daily life, many of which are readily detectable in blood or urine. It remains uncertain if these chemicals can cause adverse health effects when present together at low doses. In this study we have tested whether a mixture of 27 chemicals administered orally to juvenile male rats for three months could leave a pathophysiological footprint. The mixture contained metals, perfluorinated compounds, PCB, dioxins, pesticides, heterocyclic amines, phthalate, PAHs and others, with a combined dose of 0.16 (Low dose), 0.47 (Mid dose) or 1.6 (High dose) mg/kg bw/day. The lowest dose was designed with the aim of obtaining plasma or urine concentrations in rats at levels approaching those observed in humans. Some single congeners were administered at doses representative of combined doses for chemical groups. With this baseline, we found effects on weight, histology and gene expression in the liver, as well as changes to the blood plasma metabolome in all exposure groups, including low-dose. Additional adverse effects were observed in the higher dosed groups, including enlarged kidneys and alterations to the metabolome. No significant effects on reproductive parameters were observed.

Integrated Analysis of Multiple Biomarkers from Circulating Tumor Cells Enabled by Exclusion-Based Analyte Isolation

PURPOSE

There is a critical clinical need for new predictive and pharmacodynamic biomarkers that evaluate pathway activity in patients treated with targeted therapies. A microscale platform known as VERSA (versatile exclusion-based rare sample analysis) was developed to integrate readouts across protein, mRNA, and DNA in circulating tumor cells (CTC) for a comprehensive analysis of the androgen receptor (AR) signaling pathway.

EXPERIMENTAL DESIGN

Utilizing exclusion-based sample preparation principles, a handheld chip was developed to perform CTC capture, enumeration, quantification, and subcellular localization of proteins and extraction of mRNA and DNA. This technology was validated across integrated endpoints in cell lines and a cohort of patients with castrate-resistant prostate cancer (CRPC) treated with AR-targeted therapies and chemotherapies.

RESULTS

The VERSA was validated in cell lines to analyze AR protein expression, nuclear localization, and gene expression targets. When applied to a cohort of patients, radiographic progression was predicted by the presence of multiple AR splice variants and activity in the canonical AR signaling pathway. AR protein expression and nuclear localization identified phenotypic heterogeneity. Next-generation sequencing with the FoundationOne panel detected copy number changes and point mutations. Longitudinal analysis of CTCs identified acquisition of multiple AR variants during targeted treatments and chemotherapy.

CONCLUSIONS

Complex mechanisms of resistance to AR-targeted therapies, across RNA, DNA, and protein endpoints, exist in patients with CRPC and can be quantified in CTCs. Interrogation of the AR signaling pathway revealed distinct patterns relevant to tumor progression and can serve as pharmacodynamic biomarkers for targeted therapies. Clin Cancer Res; 1-11. ©2016 AACR.

ACBD2/ECI2-Mediated Peroxisome-Mitochondria Interactions in Leydig Cell Steroid Biosynthesis

Fatty acid metabolism and steroid biosynthesis are 2 major pathways shared by peroxisomes and mitochondria. Both organelles are in close apposition to the endoplasmic reticulum, with which they communicate via interorganelle membrane contact sites to promote cellular signaling and the exchange of ions and lipids. To date, no convincing evidence of the direct contact between peroxisomes and mitochondria was reported in mammalian cells. Hormone-induced, tightly controlled steroid hormone biosynthesis requires interorganelle interactions. Using immunofluorescent staining and live-cell imaging, we found that dibutyryl-cAMP treatment of MA-10 mouse tumor Leydig cells rapidly induces peroxisomes to approach mitochondria and form peroxisome-mitochondrial contact sites/fusion, revealed by the subcellular distribution of the endogenous acyl-coenzyme A-binding domain (ACBD)2/ECI2 isoform A generated by alternative splicing, and further validated using a proximity ligation assay. This event occurs likely via a peroxisome-like structure, which is mediated by peroxisomal and mitochondrial matrix protein import complexes: peroxisomal import receptor peroxisomal biogenesis factor 5 (PEX5), and the mitochondrial import receptor subunit translocase of outer mitochondrial membrane 20 homolog (yeast) protein. Similar results were obtained using the mLTC-1 mouse tumor Leydig cells. Ectopic expression of the ACBD2/ECI2 isoform A in MA-10 cells led to increased basal and hormone-stimulated steroid formation, indicating that ACBD2/ECI2-mediated peroxisomes-mitochondria interactions favor in the exchange of metabolites and/or macromolecules between these 2 organelles in support of steroid biosynthesis. Considering the widespread occurrence of the ACBD2/ECI2 protein, we propose that this protein might serve as a tool to assist in understanding the contact between peroxisomes and mitochondria.

Regulation of seminiferous tubule-associated stem Leydig cells in adult rat testes

Testicular Leydig cells are the primary source of testosterone in males. Adult Leydig cells have been shown to arise from stem cells present in the neonatal testis. Once established, adult Leydig cells turn over only slowly during adult life, but when these cells are eliminated experimentally from the adult testis, new Leydig cells rapidly reappear. As in the neonatal testis, stem cells in the adult testis are presumed to be the source of the new Leydig cells. As yet, the mechanisms involved in regulating the proliferation and differentiation of these stem cells remain unknown. We developed a unique in vitro system of cultured seminiferous tubules to assess the ability of factors from the seminiferous tubules to regulate the proliferation of the tubule-associated stem cells, and their subsequent entry into the Leydig cell lineage. The proliferation of the stem Leydig cells was stimulated by paracrine factors including Desert hedgehog (DHH), basic fibroblast growth factor (FGF2), platelet-derived growth factor (PDGF), and activin. Suppression of proliferation occurred with transforming growth factor β (TGF-β). The differentiation of the stem cells was regulated positively by DHH, lithium- induced signaling, and activin, and negatively by TGF-β, PDGFBB, and FGF2. DHH functioned as a commitment factor, inducing the transition of stem cells to the progenitor stage and thus into the Leydig cell lineage. Additionally, CD90 (Thy1) was found to be a unique stem cell surface marker that was used to obtain purified stem cells by flow cytometry.

Origin and Differentiation of Androgen-Producing Cells in the Gonads

Sexual reproduction is dependent on the activity of androgenic steroid hormones to promote gonadal development and gametogenesis. Leydig cells of the testis and theca cells of the ovary are critical cell types in the gonadal interstitium that carry out steroidogenesis and provide key androgens for reproductive organ function. In this chapter, we will discuss important aspects of interstitial androgenic cell development in the gonad, including: the potential cellular origins of interstitial steroidogenic cells and their progenitors; the molecular mechanisms involved in Leydig cell specification and differentiation (including Sertoli-cell-derived signaling pathways and Leydig-cell-related transcription factors and nuclear receptors); the interactions of Leydig cells with other cell types in the adult testis, such as Sertoli cells, germ cells, peritubular myoid cells, macrophages, and vascular endothelial cells; the process of steroidogenesis and its systemic regulation; and a brief discussion of the development of theca cells in the ovary relative to Leydig cells in the testis. Finally, we will describe the dynamics of steroidogenic cells in seasonal breeders and highlight unique aspects of steroidogenesis in diverse vertebrate species. Understanding the cellular origins of interstitial steroidogenic cells and the pathways directing their specification and differentiation has implications for the study of multiple aspects of development and will help us gain insights into the etiology of reproductive system birth defects and infertility.

Steroidogenic fate of the Leydig cells that repopulate the testes of young and aged Brown Norway rats after elimination of the preexisting Leydig cells

The capacity of Brown Norway rat Leydig cells to produce testosterone (T) decreases with aging. In a previous study, we reported that a new generation of Leydig cells can be restored in both young and old rat testes after a single injection of ethane dimethanesulfonate (EDS), and that the abilities of the new Leydig cells in young and old rats to produce T were equivalent. Our objective herein was to compare the steroidogenic fate of the new Leydig cells over time. Young (3 month-old) and old (18 month-old) rats were injected with EDS to eliminate the existing Leydig cells. Ten weeks after EDS, Leydig cells had been restored and T production by the new Leydig cells isolated from young and old rat testes was equivalent. Thirty weeks after EDS treatment of young rats, the ability of the new Leydig cells to produce T had not diminished from 10 weeks post-EDS. In contrast, at 30 weeks post-EDS, T production by new cells in old rat testes was reduced significantly from the 10-week level. Serum T levels at 10 and 30 weeks were consistent with Leydig cell T production. Serum LH levels did not differ in any group. Thus, although the Leydig cells restored to both young and old rats after EDS initially produced T at high, equivalent levels, the cells in the old testes did not maintain this ability. These results suggest that: 1) the cells from which new populations of Leydig cells are derived may differ depending upon the age of the rat; and/or 2) factors extrinsic to the new Leydig cells in young and old testes differ, and it is these differences that are responsible for reductions in T by the newly formed Leydig cells in the testes of old rats.

Morphological and functional maturation of Leydig cells: from rodent models to primates

BACKGROUND

Leydig cells (LC) are the sites of testicular androgen production. Development of LC occurs in the testes of most mammalian species as two distinct growth phases, i.e. as fetal and pubertal/adult populations. In primates there are indications of a third neonatal growth phase. LC androgen production begins in embryonic life and is crucial for the intrauterine masculinization of the male fetal genital tract and brain, and continues until birth after which it rapidly declines. A short post-natal phase of LC activity in primates (including human) termed 'mini-puberty' precedes the period of juvenile quiescence. The adult population of LC evolves, depending on species, in mid- to late-prepuberty upon reawakening of the hypothalamic-pituitary-testicular axis, and these cells are responsible for testicular androgen production in adult life, which continues with a slight gradual decline until senescence. This review is an updated comparative analysis of the functional and morphological maturation of LC in model species with special reference to rodents and primates.

METHODS

Pubmed, Scopus, Web of Science and Google Scholar databases were searched between December 2012 and October 2014. Studies published in languages other than English or German were excluded, as were data in abstract form only. Studies available on primates were primarily examined and compared with available data from specific animal models with emphasis on rodents.

RESULTS

Expression of different marker genes in rodents provides evidence that at least two distinct progenitor lineages give rise to the fetal LC (FLC) population, one arising from the coelomic epithelium and the other from specialized vascular-associated cells along the gonad-mesonephros border. There is general agreement that the formation and functioning of the FLC population in rodents is gonadotrophin-responsive but not gonadotrophin-dependent. In contrast, although there is in primates some controversy on the role of gonadotrophins in the formation of the FLC population, there is consensus about the essential role of gonadotrophins in testosterone production. Like the FLC population, adult Leydig cells (ALC) in rodents arise from stem cells, which have their origin in the fetal testis. In contrast, in primates the ALC population is thought to originate from FLC, which undergo several cycles of regression and redifferentiation before giving rise to the mature ALC population, as well as from differentiation of stem cells/precursor cells. Despite this difference in origin, both in primates and rodents the formation of the mature and functionally active ALC population is critically dependent on the pituitary gonadotrophin, LH. From studies on rodents considerable knowledge has emerged on factors that are involved besides LH in the regulation of this developmental process. Whether the same factors also play a role in the development of the mature primate LC population awaits further investigation.

CONCLUSION

Distinct populations of LC develop along the life span of males, including fetal, neonatal (primates) and ALC. Despite differences in the LC lineages of rodents and primates, the end product is a mature population of LC with the main function to provide androgens necessary for the maintenance of spermatogenesis and extra-gonadal androgen actions.