Therapeutic potential of Sertoli cells in vivo: alleviation of acute inflammation and improvement of sperm quality

BACKGROUND

Inflammation-induced testicular damage is a significant contributing factor to the increasing incidence of infertility. Traditional treatments during the inflammatory phase often fail to achieve the desired fertility outcomes, necessitating innovative interventions such as cell therapy.

METHODS

We explored the in vivo properties of intravenously administered Sertoli cells (SCs) in an acute lipopolysaccharide (LPS)-induced inflammatory mouse model. Infiltrating and resident myeloid cell phenotypes were assessed using flow cytometry. The impact of SC administration on testis morphology and germ cell quality was evaluated using computer-assisted sperm analysis (CASA) and immunohistochemistry.

RESULTS

SCs demonstrated a distinctive migration pattern, importantly they preferentially concentrated in the testes and liver. SC application significantly reduced neutrophil infiltration as well as preserved the resident macrophage subpopulations. SCs upregulated MerTK expression in both interstitial and peritubular macrophages. Applied SC treatment exhibited protective effects on sperm including their motility and kinematic parameters, and maintained the physiological testicular morphology.

CONCLUSION

Our study provides compelling evidence of the therapeutic efficacy of SC transplantation in alleviating acute inflammation-induced testicular damage. These findings contribute to the expanding knowledge on the potential applications of cell-based therapies for addressing reproductive health challenges and offer a promising approach for targeted interventions in male infertility.

Sertoli Cell Immune Regulation: A Double-Edged Sword

The testis must create and maintain an immune privileged environment to protect maturing germ cells from autoimmune destruction. The establishment of this protective environment is due, at least in part, to Sertoli cells. Sertoli cells line the seminiferous tubules and form the blood-testis barrier (BTB), a barrier between advanced germ cells and the immune system. The BTB compartmentalizes the germ cells and facilitates the appropriate microenvironment necessary for spermatogenesis. Further, Sertoli cells modulate innate and adaptive immune processes through production of immunoregulatory compounds. Sertoli cells, when transplanted ectopically (outside the testis), can also protect transplanted tissue from the recipient’s immune system and reduce immune complications in autoimmune diseases primarily by immune regulation. These properties make Sertoli cells an attractive candidate for inflammatory disease treatments and cell-based therapies. Conversely, the same properties that protect the germ cells also allow the testis to act as a reservoir site for infections. Interestingly, Sertoli cells also have the ability to mount an antimicrobial response, if necessary, as in the case of infections. This review aims to explore how Sertoli cells act as a double-edged sword to both protect germ cells from an autoimmune response and activate innate and adaptive immune responses to fight off infections.

Postpubertal spermatogonial stem cell transplantation restores functional sperm production in rhesus monkeys irradiated before and after puberty

BACKGROUND

Cancer treatment of prepubertal patients impacts future fertility due to the abolition of spermatogonial stem cells (SSCs). In macaques, spermatogenesis could be regenerated by intratesticular transplantation of SSCs, but no studies have involved cytotoxic treatment before puberty and transplantation after puberty, which would be the most likely clinical scenario.

OBJECTIVES

To evaluate donor-derived functional sperm production after SSC transplantation to adult monkeys that had received testicular irradiation during the prepubertal period.

MATERIALS AND METHODS

We obtained prepubertal testis tissue by unilaterally castrating six prepubertal monkeys and 2 weeks later irradiated the remaining testes with 6.9 Gy. However, because spermatogenic recovery was observed, we irradiated them again 14 months later with 7 Gy. Three of the monkeys were treated with GnRH-antagonist (GnRH-ant) for 8 weeks. The cryopreserved testis cells from the castrated testes were then allogeneically transplanted into the intact testes of all monkeys. Tissues were harvested 10 months later for analyses.

RESULTS

In three of the six monkeys, 61%, 38%, and 11% of the epididymal sperm DNA were of the donor genotype. The ability to recover donor-derived sperm production was not enhanced by the GnRH-ant pretreatment. However, the extent of filling seminiferous tubules during the transplantation procedure was correlated with the eventual production of donor spermatozoa. The donor epididymal spermatozoa from the recipient with 61% donor contribution were capable of fertilizing rhesus eggs and forming embryos. Although the transplantation was done into the rete testis, two GnRH-ant-treated monkeys, which did not produce donor-derived epididymal spermatozoa, displayed irregular tubular cords in the interstitium containing testicular spermatozoa derived from the transplanted donor cells.

DISCUSSION AND CONCLUSION

The results further support that sperm production can be restored in non-human primates from tissues cryopreserved prior to prepubertal and post-pubertal gonadotoxic treatment by transplantation of these testicular cells after puberty into seminiferous tubules.

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

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

Therapeutic application of Sertoli cells for treatment of various diseases

Sertoli cells (SCs) are immune privileged cells found in the testis that function to immunologically protect maturing germ cells from immune destruction. This immune protection is due to the blood-testis-barrier, which prevents infiltration of cytotoxic immune cells and antibodies, and SC production of immunomodulatory factors, that favor a tolerogenic environment. The ability of SCs to create an immune privileged environment has led to the exploration of their potential use in the treatment of various diseases. SCs have been utilized to create a tolerogenic ectopic microenvironment, to protect co-grafted cells, and to deliver therapeutic proteins through gene therapy. To date, numerous studies have reported the potential use of SCs for the treatment of diabetes, neurodegenerative disorders, and restoration of spermatogenesis. Additionally, SCs have been investigated as a delivery vehicle for therapeutic products to treat other diseases like Laron syndrome, muscular dystrophy, and infections. This review will provide an overview of these therapeutic applications.

Restoration of functional sperm production in irradiated pubertal rhesus monkeys by spermatogonial stem cell transplantation

BACKGROUND

In male pre-pubertal cancer patients, radiation and chemotherapy impact future fertility by eradication of spermatogonial stem cells (SSCs). In macaques, spermatogenesis could be regenerated by intratesticular transplantation of SSCs, but only a small percentage of spermatozoa produced were of donor origin. Transient hormone suppression with a GnRH antagonist (GnRH-ant) enhanced spermatogenic recovery from transplanted SSCs.

OBJECTIVES

To evaluate donor-derived and endogenous spermatogenic recovery after SSC transplantation into irradiated monkeys and to test whether hormone suppression around the time of transplantation facilitates spermatogenic recovery.

MATERIALS AND METHODS

Testes of 15 adult rhesus monkeys were irradiated with 7 Gy and 4 months later transplanted, to one of the testes, with cryopreserved testicular cells containing SSCs from unrelated monkeys. Monkeys were either treated with GnRH-ant for 8 weeks before transplantation, GnRH-ant from 4 weeks before to 4 weeks after transplantation, or with no GnRH-ant. Tissues were harvested 10 months after transplantation.

RESULTS

Two of the 15 monkeys, a control and a pre-transplantation GnRH-ant-treated, showed substantially higher levels of testicular spermatogenesis and epididymal sperm output in the transplanted side as compared to the untransplanted. Over 84% of epididymal spermatozoa on the transplanted side had the donor genotype and were capable of fertilizing eggs after intracytoplasmic sperm injection forming morulae of the donor paternal origin. Low levels of donor spermatozoa (~1%) were also identified in the epididymis of three additional monkeys. Transplantation also appeared to enhance endogenous spermatogenesis.

DISCUSSION AND CONCLUSION

We confirmed that SSC transplantation can be used for restoration of fertility in male cancer survivors exposed to irradiation as a therapeutic agent. The success rate of this procedure, however, is low. The success of filling the tubules with the cell suspension, but not the GnRH-ant treatment, was related to the level of colonization by transplanted cells.

Donor spermatogenesis in de novo formed seminiferous tubules from transplanted testicular cells in rhesus monkey testis

STUDY QUESTION

Can transplanted primate testicular cells form seminiferous tubules de novo, supporting complete spermatogenesis?

SUMMARY ANSWER

Cryopreserved testicular cells from a prepubertal monkey can reorganize in an adult monkey recipient testis forming de novo seminiferous tubular cords supporting complete spermatogenesis.

WHAT IS KNOWN ALREADY

De novo morphogenesis of testicular tissue using aggregated cells from non-primate species grafted either subcutaneously or in the testis can support spermatogenesis.

STUDY DESIGN, SIZE, DURATION

Two postpubertal rhesus monkeys (Macaca mulatta) were given testicular irradiation. One monkey was given GnRH-antagonist treatment from 8 to 16 weeks after irradiation, while the other received sham injections. At 16 weeks, cryopreserved testicular cells from two different prepubertal monkeys [43 × 106 viable (Trypan-blue excluding) cells in 260 μl, and 80 × 106 viable cells in 400 μl] were transplanted via ultrasound-guided injections to one of the rete testis in each recipient, and immune suppression was given. The contralateral testis was sham transplanted. Testes were analyzed 9 months after transplantation.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Spermatogenic recovery was assessed by testicular volume, weight, histology and immunofluorescence. Microsatellite genotyping of regions of testicular sections obtained by LCM determined whether the cells were derived from the host or transplanted cells.

MAIN RESULTS AND THE ROLE OF CHANCE

Transplanted testis of the GnRH-antagonist-treated recipient, but not the sham-treated recipient, contained numerous irregularly shaped seminiferous tubular cords, 89% of which had differentiating germ cells, including sperm in a few of them. The percentages of donor genotype in different regions of this testis were as follows: normal tubule, 0%; inflammatory, 0%; abnormal tubule region, 67%; whole interior of abnormal tubules, >99%; adluminal region of the abnormal tubules, 92%. Thus, these abnormal tubules, including the enclosed germ cells, were derived de novo from the donor testicular cells.

LARGE SCALE DATA

Not applicable.

LIMITATIONS, REASONS FOR CAUTION

The de novo tubules were observed in only one out of the two monkeys transplanted with prepubertal donor testicular cells.

WIDER IMPLICATIONS OF THE FINDINGS

These findings may represent a promising strategy for restoration of fertility in male childhood cancer survivors. The approach could be particularly useful in those exposed to therapeutic agents that are detrimental to the normal development of the tubule somatic cells affecting the ability of the endogenous tubules to support spermatogenesis, even from transplanted spermatogonial stem cells.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by research grants P01 HD075795 from Eunice Kennedy Shriver National Institute of Child Health & Human Development (NICHD/NIH) to K.E.O and Cancer Center Support Grant P30 CA016672 from NCI/NIH to The University of Texas MD Anderson Cancer Center. The authors declare that they have no competing interests.

Zearalenone induces apoptosis of rat Sertoli cells through Fas-Fas ligand and mitochondrial pathway

Zearalenone (ZEA) is an estrogen-like toxin produced by Fusarium that is widely found in cereals worldwide. In recent years, ZEA has been found to cause reproductive dysfunction in male animals, but the underlying mechanism remains unclear. This study examined the apoptosis of rat Sertoli cells induced by different concentrations (0, 5, 10, and 20 μmol/L) of ZEA via Fas-Fas ligand and mitochondrial signaling pathway in vitro. Apoptosis rate was detected by flow cytometry. The mitochondrial membrane potential was detected by immunofluorescence assay and flow cytometry. Western Blot and qRT-PCR were used to identify the signaling pathway. The results revealed that ZEA induced apoptosis of rat Sertoli cells, significantly reduced the transcription and expression of the anti-apoptotic protein Bcl-2, increased the transcription and expression of pro-apoptotic proteins Bax and tBID, and Fas, FasL, FADD, and caspase-8. ZEA also increased the activation of caspase-8 and caspase-9, and promoted the release of cytochrome C from mitochondria to cytoplasm. Moreover, addition of caspase-8 inhibitor Z-IETD-FMK led to significant decrease in the mitochondrial membrane potential and apoptosis rate of the ZEA + Z-IETD-FMK group as compared to the ZEA treatment group. The release of cytochrome C from mitochondria to cytoplasm and the activation of caspase-9 and caspase-3 were significantly decreased in the ZEA + Z-IETD-FMK group. These results suggested that ZEA can induce apoptosis of rat Sertoli cells, activate the Fas-Fas ligand signaling pathway and participate in the regulation of mitochondrial apoptosis pathway.

Vitamin C ameliorates the adverse effects of dexamethasone on sperm motility, testosterone level, and spermatogenesis indexes in mice

BACKGROUND:

Dexamethasone (DEX) is a common medicine that is capable of causing malformation in the male reproductive system. The aim of this study was to investigate the effect of vitamin C (Vit-C) on spermatogenesis indexes and daily sperm production (DSP) in adult mice treated with DEX.

METHODS:

Male Naval Medical Research Institute (NMRI) mice were divided into four groups: Control, DEX (7 mg/kg/day), Vit-C (100 mg/kg/day), and DEX +Vit-C and treated for 7 days with intraperitoneal injection.

RESULTS:

A significant increase in the mean levels of serum and tissue malondialdehyde (MDA) and apoptosis of Leydig cells was found in the DEX group compared to the control group. Sperm motility, DSP, tubular differentiation index, meiotic index, spermatogenesis index, the mean number of spermatocytes, round and long spermatids, and Leydig cells, and also serum testosterone level decreased in the DEX group compared to the control group. The results of this study indicate that Vit-C can significantly prevent the adverse effects of DEX on the mean number of spermatocyte, spermatid, and Leydig cells, tubular differentiation, meiotic and spermatogenesis index, DSP, sperm motility, and the mean levels of serum MDA.

CONCLUSION:

In conclusion, our results showed that coadministration of Vit-C and DEX prevents the adverse effects of DEX on the spermatogenesis indexes and DSP.

Effect of hormone modulations on donor-derived spermatogenesis or colonization after syngeneic and xenotransplantation in mice

BACKGROUND

Cytotoxic cancer treatments, such as irradiation, can cause permanent sterility in male mammals owing to the loss of spermatogonial stem cells. In animal models, spermatogenesis could be restored from transplanted spermatogonial stem cells. Previously, we showed that transient suppression of FSH, LH, and testosterone in the recipient with a gonadotropin-releasing hormone antagonist (GnRH-ant), given immediately after irradiation, enhanced spermatogenesis from transplanted spermatogonial stem cells in mice and monkeys.

OBJECTIVES

To explore improvements in the preparation of the recipient for efficient and reliable spermatogenic recovery from spermatogonial stem cell transplantation, so that it can be used effectively in clinical practice.

MATERIALS AND METHODS

In mouse recipients, we evaluated the effects of hormone suppression given after germ cell depletion was complete, which is a more clinically relevant model, and also the importance of total androgen ablation and maintenance of FSH levels. Three regimens, GnRH-ant, GnRH-ant plus flutamide (androgen receptor antagonist), and GnRH-ant plus FSH, were administered prior to and around the time of transplantation of testis cells from immature mice or from prepubertal monkeys.

RESULTS

Treatment with GnRH-ant resulted in a fourfold increase in spermatogenic recovery from GFP-marked transplanted mouse cells. Total androgen ablation with the addition of flutamide, started two weeks before transplantation, did not further enhance recovery. Surprisingly, FSH supplementation, started around the time of transplantation, actually reduced spermatogenic recovery from transplanted spermatogonial stem cells in GnRH-ant-treated mice. When prepubertal monkey testicular cells were transplanted into nude mice that were given the same hormone treatments, the numbers of donor-derived colonies were independent of hormone treatment.

DISCUSSION AND CONCLUSION

The enhancements in spermatogenic recovery may only occur when syngeneic or closely related donor-recipient pairs are used. These results are useful in further investigations in choosing a hormone suppression regimen in combination with spermatogonial transplantation as a treatment to restore fertility in primates after cytotoxic therapy.

Can mesenchymal stem cells improve spermatogonial stem cell transplantation efficiency?

Improved treatments have led to an increased survival rate in cancer patients. However, in pre-pubertal boys, these gonadotoxic treatments can result in the depletion of the spermatogonial stem cell (SSC) pool causing lifelong infertility. SSC transplantation has been proposed as a promising technique to preserve the fertility of these patients. In mice, this technique has resulted in live-born offspring, but the efficiency of colonization remained low. This could be because of a deficient microenvironment, leading to apoptosis of the transplanted SSCs. Interestingly, mesenchymal stem cells (MSCs), being multipotent and easy to isolate and multiply in vitro, are nowadays successfully and widely used in regenerative medicine. Here, we shortly review the current understanding of MSC and SSC biology, and we hypothesize that a combined MSC-SSC transplantation might improve the efficiency of SSC colonization and differentiation as paracrine factors from MSCs may contribute to the SSC niche.

Underlying Mechanisms that Restore Spermatogenesis on Transplanting Healthy Niche Cells in Busulphan Treated Mouse Testis

Very small embryonic-like stem cells (VSELs) exist among spermatogonial stem cells and survive chemotherapy in both mice and human testes because of their relatively quiescent nature. Our earlier study revealed that inter-tubular transplantation of niche (Sertoli or bone marrow derived mesenchymal) cells can restore spermatogenesis from endogenous surviving VSELs. Present study was undertaken to delineate the effect of busulphan on testicular stem/germ/Sertoli cells and to comprehend the underlying mechanisms of how transplanted niche cells restore spermatogenesis. Ploidy analysis showed an increase in diploid cells on D7 and VSELs (2-6 μm; LIN-/CD45-/SCA-1+) were detected at all time-points studied and were maximum on D15 after busulphan treatment. They were visualized in cell smears, expressed nuclear NANOG and SOX2 and BrdU uptake on D15 suggested they were proliferating in response to stress induced by busulphan. Verapamil-sensitive side population detected comprised SCA-1 positive stem cells (5 ± 0.02 % in normal and 8.6 ± 2.02 % in chemoablated testis). Adverse effects of busulphan on Sertoli cells by transcriptome analysis included altered expression of Gdnf, Scf, Fgf, Bmp4, androgen binding protein, components of blood-testis-barrier and also stem cells related signaling pathways including Wnt. GFP positive transplanted cells aligned themselves as 'neo-tubules' and were visualized adjacent to 'native' germ cells depleted tubules. 'Neo-tubules' provide paracrine support to endogenous VSELs to undergo spermatogenesis. Quantitative analysis was done to track proliferation (PCNA) and differentiation (MVH) of stem cells by immuno-localization studies at different time intervals. Results provide an alternative strategy to restore spermatogenesis in cancer survivors from endogenous stem cells which needs to be further researched.

Neonatal testicular cell transplantation restores murine spermatogenesis damaged in the course of herpes simplex virus-induced orchitis

Genital tract infection and inflammation may affect male fertility, causing germ and Sertoli cell loss. We determined if testicular cell transplantation is effective at repairing testicular injury induced by herpes simplex virus (HSV) orchitis. ROSA26 mice were used as donors and the recipients were C57BL/6 mice after HSV testicular inoculation; some of the recipients were treated with the antiviral drug acyclovir (ACV). ACV reduced the amount of HSV antigen in testes on Day 3 after transplantation and enhanced the efficacy of transplantation at Day 30. In recipient testes, donor Sertoli cells formed new seminiferous tubules; significantly more new tubules were observed in the testes of ACV-treated mice compared with mice not treated with ACV (17.8% vs 3.6%). Over half (50.4%) of new tubules in ACV-treated testes contained germ cells and round spermatids were detected in 14.2% of new tubules compared with 15.9% and 5.3% in testes not treated with ACV, respectively. At Day 150 the seminiferous epithelium was completely recovered in some donor tubules and elongated spermatids were observed inside it. Thus, our findings reveal the effectiveness of the combination of antiviral therapy with neonatal testis-cell transplantation for the restoration of spermatogenesis damaged by viral infection.

Transplantation of Autologous Bone Marrow Mesenchymal Stem Cells into the Testes of Infertile Male Rats and New Germ Cell Formation

Background

Mesenchymal stem cells (MSCs), have been suggested as a potential choice for treatment of male infertility. Yet, the effects of MSCs on regeneration of germinal epithelium of seminiferous tubules and recovery of spermatogenesis have remained controversial. In this research, we have evaluated and compared the fate of autologous bone marrow (BM)-MSCs during three different periods of time- 4, 6 and 8 weeks after transplantation into the testes of busulfan-induced infertile male rats.

Methods

Rats BM samples were collected from tibia bone under anesthesia. The samples were directly cultured in culture medium. Isolated, characterized and purified BM-MSCs were labeled with PKH26, and transplanted into the testes of infertile rats. After 4, 6 and 8 weeks, the testes were removed and underwent histological evaluations.

Results

Immunohistochemical analysis showed that transplanted BM-MSCs survived in all three groups. Some of the cells homed at the germinal epithelium and expressed spermatogonia markers (Dazl and Stella). The number of homed spermatogonia-like cells in 4-week testes, was more than the 6-week testes. The 8-week testes had the least numbers of homed cells (p<0.05). Immunostaining for vimentin showed that BM-MSCs did not differentiate into the sertoli cells in the testes.

Conclusions

From our results, it could be concluded that, autologous BM-MSCs could survive in the testis, migrate onto the seminiferous tubules basement membrane and differentiate into spermatogonia. Although, no more differentiation was observed in the produced spermatogonia, generation of such endogenous GCs would be a really promising achievement for treatment of male infertility using autologous stem cells.

Only a small population of adult Sertoli cells actively proliferates in culture

Adult mammalian Sertoli cells (SCs) have been considered to be quiescent terminal differentiated cells for many years, but recently, proliferation of adult SCs was demonstrated in vitro and in vivo. We further examined mouse SC behavior in culture and found that there are two populations of adult SCs. The first population is SCs from seminiferous tubules that hardly proliferate in vitro. The second population is small and consists of SCs with atypical nuclear morphology from the terminal segments of seminiferous tubules, a transitional zone (TZ). TZ SCs multiply in culture and form colonies, display mixture of mature and immature SC characteristics, and generate cord-like structures in a collagen matrix. The specific features of TZ SCs are ACTA2 expression in vitro and DMRT1 low levels in vivo and in vitro. Although the in vivo function of TZ SCs still remains unclear, this finding has significant implications for our understanding of SC differentiation and functioning in adult mammals.

Endogenous, very small embryonic-like stem cells: critical review, therapeutic potential and a look ahead

BACKGROUND

Both pluripotent very small embryonic-like stem cells (VSELs) and induced pluripotent stem (iPS) cells were reported in 2006. In 2012, a Nobel Prize was awarded for iPS technology whereas even today the very existence of VSELs is not well accepted. The underlying reason is that VSELs exist in low numbers, remain dormant under homeostatic conditions, are very small in size and do not pellet down at 250-280g. The VSELs maintain life-long tissue homeostasis, serve as a backup pool for adult stem cells and are mobilized under stress conditions. An imbalance in VSELs function (uncontrolled proliferation) may result in cancer.

SEARCH METHODS

The electronic database 'Medline/Pubmed' was systematically searched with the subject heading term 'very small embryonic-like stem cells'.

OBJECTIVE AND RATIONALE

The most primitive stem cells that undergo asymmetric cell divisions to self-renew and give rise to progenitors still remain elusive in the hematopoietic system and testes, while the presence of stem cells in ovary is still being debated. We propose to review the available literature on VSELs, the methods of their isolation and characterization, their ontogeny, how they compare with embryonic stem (ES) cells, primordial germ cells (PGCs) and iPS cells, and their role in maintaining tissue homeostasis. The review includes a look ahead on how VSELs will result in paradigm shifts in basic reproductive biology.

OUTCOMES

Adult tissue-specific stem cells including hematopoietic, spermatogonial, ovarian and mesenchymal stem cells have good proliferation potential and are indeed committed progenitors (with cytoplasmic OCT-4), which arise by asymmetric cell divisions of pluripotent VSELs (with nuclear OCT-4). VSELs are the most primitive stem cells and postulated to be an overlapping population with the PGCs. Rather than migrating only to the gonads, PGCs migrate and survive in various adult body organs throughout life as VSELs. VSELs express both pluripotent and PGC-specific markers and are epigenetically and developmentally more mature compared with ES cells obtained from the inner cell mass of a blastocyst-stage embryo. As a result, VSELs readily differentiate into three embryonic germ layers and spontaneously give rise to both sperm and oocytes in vitro. Like PGCs, VSELs do not divide readily in culture, nor produce teratoma or integrate in the developing embryo. But this property of being relatively quiescent allows endogenous VSELs to survive various kinds of toxic insults. VSELs that survive oncotherapy can be targeted to induce endogenous regeneration of non-functional gonads. Transplanting healthy niche (mesenchymal) cells have resulted in improved gonadal function and live births.

WIDER IMPLICATIONS

Being quiescent, VSELs possibly do not accumulate genomic (nuclear or mitochondrial) mutations and thus may be ideal endogenous, pluripotent stem cell candidates for regenerative and reproductive medicine. The presence of VSELs in adult gonads and the fact that they survive oncotherapy may obviate the need to bank gonadal tissue for fertility preservation prior to oncotherapy. VSELs and their ability to undergo spermatogenesis/neo-oogenesis in the presence of a healthy niche will help identify newer strategies toward fertility restoration in cancer survivors, delaying menopause and also enabling aged mothers to have better quality eggs.

Leydig cells contribute to the inhibition of spermatogonial differentiation after irradiation of the rat

Irradiation with 6 Gy produces a complete block of spermatogonial differentiation in LBNF1 rats that would be permanent without treatment. Subsequent suppression of gonadotropins and testosterone (T) restores differentiation to the spermatocyte stage; however, this process requires 6 weeks. We evaluated the role of Leydig cells (LCs) in maintenance of the block in spermatogonial differentiation after exposure to radiation by specifically eliminating functional LCs with ethane dimethane sulfonate (EDS). EDS (but not another alkylating agent), given at 10 weeks after irradiation, induced spermatogonial differentiation in 24% of seminiferous tubules 2 weeks later. However, differentiation became blocked again at 4 weeks as LCs recovered. When EDS was followed by treatment with GnRH antagonist and flutamide, sustained spermatogonial differentiation was induced in >70% of tubules within 2 weeks. When EDS was followed by GnRH antagonist plus exogenous T, which also inhibits LC recovery but restores follicle stimulating hormone (FSH) levels, the spermatogonial differentiation was again rapid but transient. These results confirm that the factors that block spermatogonial differentiation are indirectly regulated by T, and probably FSH, and that adult and possibly immature LCs contribute to the production of such inhibitory factors. We tested whether insulin-like 3 (INSL3), a LC-produced protein whose expression correlated with the block in spermatogonial differentiation, was indeed responsible for the block by injecting synthetic INSL3 into the testes and knocking down its expression in vivo with siRNA. Neither treatment had any effect on spermatogonial differentiation. The Leydig cell products that contribute to the inhibition of spermatogonial differentiation in irradiated rats remain to be elucidated.

Starvation is more efficient than the washing technique for purification of rat Sertoli cells

Sertoli cells (SCs), one of the most important components of seminiferous tubules, are vital for normal spermatogenesis and male fertility. In recent years, numerous in vitro studies have shown the potential and actual activities of SCs. However, pure SCs are necessary for various in vitro studies. In this study, we have evaluated the efficiency of the starvation method for SC purification as compared with the washing method. Seminiferous tubule-derived cells (STDCs) of rats' testes underwent two different techniques for SC purification. In the first group (washing group), the medium was changed every 3-4 d, and cells were washed twice with phosphate-buffered saline that lacked CaC12 and MgSO4 (PBS(-)) before the addition of fresh medium. In the second group (starvation), the medium was changed every 7-8 d. Primary culture (P0), passage 1 (P1), and passage 2 (P2) cells were analyzed for the expression of SC-specific genes, vimentin, Wilm's tumor 1 (WT1), germ cell gene (vasa), Leydig cell marker, 17beta-hydroxysteroid dehydrogenase type 3 (Hsd17b3), and a marker of peritubular myoid cells, alpha smooth muscle actin (αSma), by reverse transcriptase polymerase chain reaction (RT-PCR) and real-time RT-PCR. Gene expression analysis showed that P0 cells expressed all tested genes except Hsd17b3. The starvation method caused significant downregulation of vasa and αSma expression in P0, P1, and P2 cells, whereas vimentin and WT1 were upregulated. In contrast, the washing method was less effective than the starvation method for the removal of germ and pretubular myoid cells (p < 0.001). Totally, the results have revealed that although washing is the only common technique for elimination of contaminant cells in SC cultures, starvation has a stronger effect and is a suitable, affordable technique for SC purification. We propose that starvation is an efficient, inexpensive method that can be used for purification of SCs in animal species.

Nondividing, postpubertal rat sertoli cells resumed proliferation after transplantation

Conventionally, it was believed that Sertoli cells (SC) stopped proliferating at puberty and became terminally differentiated quiescent cells. However, recent studies have challenged that dogma. In this study, we transplanted nondividing SC isolated from 23- to 27-day-old postpubertal rats transduced with a recombinant adenoviral vector (containing furin-modified human proinsulin cDNA) into diabetic severe combined immunodeficiency mice. Immunostaining the grafts for cell proliferation markers, proliferating cell nuclear antigen (PCNA) and MKI67, revealed that transplanted SC within the grafts were proliferating. Possible causes for resumption of proliferation of SC could be viral transduction, cell isolation and culture, higher abdominal temperature at the transplant site, and/or transplantation. To test for these possible causes, double- immunofluorescence staining was performed for GATA4 (SC marker) and MKI67. None of the SC were positive for MKI67 in tissue collected during SC isolation and culture or at higher temperature. However, nontransduced SC stained positive for MKI67 after transplantation into rats, suggesting viral transduction was not a key factor for induction of SC proliferation. Interestingly, resumption in proliferative ability of nondividing SC was temporary, as SC stopped proliferating within 14 days of transplantation and did not proliferate thereafter. Quantification of 5-bromo-2'-deoxyuridine-labeled SC demonstrated that 7%-9% of the total transplanted SC were proliferating in the grafts. These data indicate for the first time that nondividing SC resumed proliferation after transplantation and further validate previous findings that SC are not terminally differentiated. Hence, transplantation of SC could provide a useful model with which to study the regulation of SC proliferation in vivo.

Spermatogonial behavior in rats during radiation-induced arrest and recovery after hormone suppression

Ionizing radiation has been shown to arrest spermatogenesis despite the presence of surviving stem spermatogonia, by blocking their differentiation. This block is a result of damage to the somatic environment and is reversed when gonadotropins and testosterone are suppressed, but the mechanisms are still unknown. We examined spermatogonial differentiation and Sertoli cell factors that regulate spermatogonia after irradiation, during hormone suppression, and after hormone suppression combined with Leydig cell elimination with ethane dimethane sulfonate. These results showed that the numbers and cytoplasmic structure of Sertoli cells are unaffected by irradiation, only a few type A undifferentiated (Aund) spermatogonia and even fewer type A1 spermatogonia remained, and immunohistochemical analysis showed that Sertoli cells still produced KIT ligand (KITLG) and glial cell line-derived neurotrophic factor (GDNF). Some of these cells expressed KIT receptor, demonstrating that the failure of differentiation was not a result of the absence of the KIT system. Hormone suppression resulted in an increase in Aund spermatogonia within 3 days, a gradual increase in KIT-positive spermatogonia, and differentiation mainly to A3 spermatogonia after 2 weeks. KITL (KITLG) protein expression did not change after hormone suppression, indicating that it is not a factor in the stimulation. However, GDNF increased steadily after hormone suppression, which was unexpected since GDNF is supposed to promote stem spermatogonial self-renewal and not differentiation. We conclude that the primary cause of the block in spermatogonial development is not due to Sertoli cell factors such (KITL\GDNF) or the KIT receptor. As elimination of Leydig cells in addition to hormone suppression resulted in differentiation to the A3 stage within 1 week, Leydig cell factors were not necessary for spermatogonial differentiation.

Transcriptome profiling of mice testes following low dose irradiation

BACKGROUND

Radiotherapy is used routinely to treat testicular cancer. Testicular cells vary in radio-sensitivity and the aim of this study was to investigate cellular and molecular changes caused by low dose irradiation of mice testis and to identify transcripts from different cell types in the adult testis.

METHODS

Transcriptome profiling was performed on total RNA from testes sampled at various time points (n = 17) after 1 Gy of irradiation. Transcripts displaying large overall expression changes during the time series, but small expression changes between neighbouring time points were selected for further analysis. These transcripts were separated into clusters and their cellular origin was determined. Immunohistochemistry and in silico quantification was further used to study cellular changes post-irradiation (pi).

RESULTS

We identified a subset of transcripts (n = 988) where changes in expression pi can be explained by changes in cellularity. We separated the transcripts into five unique clusters that we associated with spermatogonia, spermatocytes, early spermatids, late spermatids and somatic cells, respectively. Transcripts in the somatic cell cluster showed large changes in expression pi, mainly caused by changes in cellularity. Further investigations revealed that the low dose irradiation seemed to cause Leydig cell hyperplasia, which contributed to the detected expression changes in the somatic cell cluster.

CONCLUSIONS

The five clusters represent gene expression in distinct cell types of the adult testis. We observed large expression changes in the somatic cell profile, which mainly could be attributed to changes in cellularity, but hyperplasia of Leydig cells may also play a role. We speculate that the possible hyperplasia may be caused by lower testosterone production and inadequate inhibin signalling due to missing germ cells.

Effects of multiple doses of cyclophosphamide on mouse testes: accessing the germ cells lost, and the functional damage of stem cells

Spermatogenesis is sensitive to the chemotherapeutic drug cyclophosphamide, which decreases the patients' sperm count. Since the recovery of fertility is dependent on regeneration from stem cells, in the present study we evaluated the ability of cyclophosphamide-exposed stem spermatogonia from mice to regenerate spermatogenesis in situ and after transplantation. When seven doses of cyclophosphamide were given at 4-day intervals, the differentiating germ cells were largely eliminated but ~50% of the undifferentiated type A spermatogonia remained. We monitored the recovery and found that sperm production recovered to 64% of control within the time expected. When the cyclophosphamide-surviving spermatogonia were transplanted into recipient mice, recovery of spermatogenesis from the cyclophosphamide-exposed donor cells was observed, but was reduced when compared to cells from cryptorchid donors. Thus, multidose regimens of cyclophosphamide did not eliminate the stem spermatogonia, but resulted in cell loss and residual damage.

A shorter interval between irradiation of recipient testis and germ cell transplantation is detrimental to recovery of fertility in rams

The objective of the current study was to identify an optimal time period for donor cell transplantation after irradiation in sheep. The testes of recipient rams were treated with a single dose of 15 Gray (Gy) irradiation followed by germ cell transplantation either 3 or 6 weeks later. Transplantation of donor cells at 6 weeks after irradiation resulted in production of donor sperm by all five recipient rams compared with 4 of 11 rams transplanted at 3 weeks. Rams transplanted 3 weeks post-irradiation appeared to show reduced libido and fertility. Two rams produced sperm with low motility (< 20%) and two other rams were azoospermic. More than 1 year after cell transfer, there were heavy infiltrates of CD45-positive cells and more fibrous tissue in 9 of 14 recipient testes (seven rams) that received cells 3 weeks after irradiation. Taken together, these results suggest that the interval between irradiation of recipients and germ cell transplantation affects the success rate of the procedure, with a 6-week interval preferable. The elevated inflammatory/immune reaction may be responsible, at least in part, for the reduced fertility and low libido observed in the rams that received cells 3 weeks post-irradiation.

Gene expression profiles of mouse spermatogenesis during recovery from irradiation

BACKGROUND

Irradiation or chemotherapy that suspend normal spermatogenesis is commonly used to treat various cancers. Fortunately, spermatogenesis in many cases can be restored after such treatments but knowledge is limited about the re-initiation process. Earlier studies have described the cellular changes that happen during recovery from irradiation by means of histology. We have earlier generated gene expression profiles during induction of spermatogenesis in mouse postnatal developing testes and found a correlation between profiles and the expressing cell types. The aim of the present work was to utilize the link between expression profile and cell types to follow the cellular changes that occur during post-irradiation recovery of spermatogenesis in order to describe recovery by means of gene expression.

METHODS

Adult mouse testes were subjected to irradiation with 1 Gy or a fractionated radiation of two times 1 Gy. Testes were sampled every third or fourth day to follow the recovery of spermatogenesis and gene expression profiles generated by means of differential display RT-PCR. In situ hybridization was in addition performed to verify cell-type specific gene expression patterns.

RESULTS

Irradiation of mice testis created a gap in spermatogenesis, which was initiated by loss of A1 to B-spermatogonia and lasted for approximately 10 days. Irradiation with 2 times 1 Gy showed a more pronounced effect on germ cell elimination than with 1 Gy, but spermatogenesis was in both cases completely reconstituted 42 days after irradiation. Comparison of expression profiles indicated that the cellular reconstitution appeared equivalent to what is observed during induction of normal spermatogenesis.

CONCLUSION

The data indicates that recovery of spermatogenesis can be monitored by means of gene expression, which could aid in designing radiation treatment regimes for cancer patients leading to better restoration of spermatogenesis.