Testicular organoid generation by a novel in vitro three-layer gradient system

Microfluidic systems in testicular in vitro culture: a powerful model tool for spermatogenesis and reprotoxicity studies

ABSTRACT

As prepubertal boys do not yet produce spermatozoa, they cannot rely on sperm cryopreservation for fertility preservation before gonadotoxic therapy, such as high-dose alkylating agents or radiotherapy in the case of childhood cancers. According to the current guidelines, cryopreservation of testicular biopsies containing spermatogonial stem cells (SSCs) may be proposed to high-risk patients for potential later therapeutic use to fulfill the patients' wish for a biological child. One promising technique for human in vitro spermatogenesis and in vitro propagation of human SSCs is microfluidic (MF) culture, in which cells or tissues are subjected to a continuous flow of medium. This provides exact control over such parameters as nutrient content and gradients, as well as the removal of waste metabolites. While MF has been shown to maintain tissues and cell populations of organs for longer than conventional in vitro culture techniques, it has not been widely used for testicular in vitro culture. MF could advance human testicular in vitro culture and is also applicable to reprotoxicity studies. This review summarizes the findings and achievements of testis-on-chip (ToC) setups to date and discusses the benefits and limitations of these for spermatogenesis in vitro and toxicity assessment.

Modeling lamotrigine-induced reprotoxicity in porcine endometrial organoids: Integrated multi-platform profiling

Lamotrigine, a newer generation anti-epileptic drug aimed at addressing reproductive complications, requires thorough evaluation of its effects on the endometrium. Using the three-dimensional endometrial organoid (EO) model provides a distinct advantage in modeling lamotrigine-induced toxicity, offering a more relevant physiological system. In this study, a porcine EO model was used and treated with lamotrigine to mimic and analyze drug-induced toxicity. Porcine uteri were processed and digested with collagenase, then combined with Matrigel and incubated with 5 % CO2 environment, at 38°C. During passaging, cells were dissociated, treated with trypsin-EDTA, and subcultured, with the medium renewed every 2-3 days. Different analytical methods were employed to evaluate lamotrigine's impact on the endometrial organoids, covering aspects such as cell viability, morphology, replication, steroidogenesis, and metabolic changes. The results showed significant alterations in cell morphology with a decrease in number and size. Metabolite analysis revealed metabolic shifts in some amino acids, glucose and galactose, ranging from approximately 1.5 to 5 times, (p < 0.05), when compared to the control groups. Molecular assays indicated increased oxidative stress, activation of apoptotic pathway, and disrupted steroidogenesis, revealing lamotrigine as an active endocrine disruptor. Moreover, lamotrigine induced changes in specific miRNAs that regulate implantation, and epithelial-mesenchymal transition pathways. In conclusion, our study highlights the potential diverse impact of lamotrigine on the endometrial microenvironment, emphasizing the need for further investigations into its implications on reproductive health and embryo implantation.

Spatially defined microenvironment for engineering organoids

In the intricately defined spatial microenvironment, a single fertilized egg remarkably develops into a conserved and well-organized multicellular organism. This observation leads us to hypothesize that stem cells or other seed cell types have the potential to construct fully structured and functional tissues or organs, provided the spatial cues are appropriately configured. Current organoid technology, however, largely depends on spontaneous growth and self-organization, lacking systematic guided intervention. As a result, the structures replicated in vitro often emerge in a disordered and sparse manner during growth phases. Although existing organoids have made significant contributions in many aspects, such as advancing our understanding of development and pathogenesis, aiding personalized drug selection, as well as expediting drug development, their potential in creating large-scale implantable tissue or organ constructs, and constructing multicomponent microphysiological systems, together with functioning at metabolic levels remains underutilized. Recent discoveries have demonstrated that the spatial definition of growth factors not only induces directional growth and migration of organoids but also leads to the formation of assembloids with multiple regional identities. This opens new avenues for the innovative engineering of higher-order organoids. Concurrently, the spatial organization of other microenvironmental cues, such as physical stresses, mechanical loads, and material composition, has been minimally explored. This review delves into the burgeoning field of organoid engineering with a focus on potential spatial microenvironmental control. It offers insight into the molecular principles, expected outcomes, and potential applications, envisioning a future perspective in this domain.

Impacts of cancer therapy on male fertility: Past and present

Over the past two decades, advances in cancer therapy have significantly improved survival rates, particularly in childhood cancers. Still, many treatments pose a substantial risk for diminishing future fertility potential due to the gonadotoxic nature of many cancer regimens, justifying fertility preservation programs for both childhood and adult cancer patients. To assure a balance between offering fertility preservation and actual chance of infertility post-treatment, guidelines are in place. However, assessing the actual risk of infertility after treatment remains challenging, given the multi-faceted approach of many cancer treatment plans, which are continuously evolving. This review discusses the evolution of cancer therapy over the past 20 years and attempts to assess their impact on fertility after treatment. Overall, cancer regimens have shifted from broadly killing fast dividing cells to more targeting therapies, reducing collateral damage in general. Although progress has been made to reduce overall toxicity, unfortunately this does not automatically translate to reduced gonadotoxicity. Therefore, current fertility preservation programs continue to be an important part of cancer care.

Is Routine Pathology Evaluation of Tissue Removed for Fertility Preservation Necessary?

BACKGROUND

For all fertility preservation (FP) cases at our institution, a biopsy is performed for routine pathology from all gonadal tissue removed. This is not standard at all centers. We reviewed our experience with biopsy for pathological evaluation of ovarian and testicular specimens in FP cases to determine clinical utility.

METHODS

The medical records of individuals who underwent ovarian tissue cryopreservation (OTC) or testicular tissue cryopreservation (TTC) between 2011 and 2023 were retrospectively reviewed under an IRB-approved study at a free-standing tertiary care children's hospital. Patient demographics, diagnosis, operative characteristics, and pathology results were collected.

RESULTS

One-hundred and eighty-three patients underwent OTC, and 134 patients underwent TTC. All patients had their gonadal tissue biopsied for routine pathology. Malignancy was identified in the biopsies of 4 OTC patients (2.2%) and 2 TTC patients (1.5%). Two OTC patients (1.1%) and 2 TTC patients (1.5%) did not have germ cells identified in their biopsy. All OTC and TTC patients and families elected to continue storing tissue for FP after discussion of pathology findings.

CONCLUSIONS

Pathology results provide another data point to help inform patients and their families when making decisions on ovarian or testicular tissue storage and on how tissue may be utilized in the future to restore fertility and/or hormones. There is a low rate of identifying malignancy in gonadal tissue biopsies taken from FP specimens even in patients with known malignancy. However, when malignancy was identified, it could be unexpected and alter the diagnosis and treatment plan significantly for patients.

LEVEL OF EVIDENCE

IV.

Establishment and Characterization of Testis Organoids with Proliferation and Differentiation of Spermatogonial Stem Cells into Spermatocytes and Spermatids

Organoids play pivotal roles in uncovering the molecular mechanisms underlying organogenesis, intercellular communication, and high-throughput drug screening. Testicular organoids are essential for exploring the genetic and epigenetic regulation of spermatogenesis in vivo and the treatment of male infertility. However, the formation of testicular organoids with full spermatogenesis has not yet been achieved. In this study, neonatal mouse testicular cells were isolated by two-step enzymatic digestion, and they were combined with Matrigel and transplanted subcutaneously into nude mice. Histological examination (H&E) staining and immunohistochemistry revealed that cell grafts assembled to form seminiferous tubules that contained spermatogonial stem cells (SSCs) and Sertoli cells, as illustrated by the co-expression of PLZF (a hallmark for SSCs) and SOX9 (a marker for Sertoli cells) as well as the co-expression of UCHL1 (a hallmark for SSCs) and SOX9, after 8 weeks of transplantation. At 10 weeks of transplantation, SSCs could proliferate and differentiate into spermatocytes as evidenced by the expression of PCNA, Ki67, c-Kit, SYCP3, γ-HA2X, and MLH1. Notably, testicular organoids were seen, and spermatids were observed within the lumen of testicular organoids after 16 weeks of transplantation, as shown by the presence of TNP1 and ACROSIN (hallmarks for spermatids). Collectively, these results implicate that we successfully established testicular organoids with spermatogenesis in vivo. This study thus provides an excellent platform for unveiling the mechanisms underlying mammalian spermatogenesis, and it might offer valuable male gametes for treating male infertility.

Spermatogenesis in mouse testicular organoids with testis-specific architecture, improved germ cell survival and testosterone production

This study presents a biphasic approach to overcome the limitations of current testicular organoid (TO) cultures, including histological heterogeneity, germ cell loss and absence of spermatogenesis. Agarose microwells were utilized to create TOs from prepubertal C57BL/6 J testicular cells. First emphasis was on improving germ cell survival during the initial 2-week reorganization phase by comparingα-MEM + 10% knockout serum replacement (KSR) medium, known to support TO generation in mice, to three optimized media (1-3). Cell densities and culture dynamics were also tested to recreate histological resemblance to testes. After optimizing germ cell survival and cell organization, the effect of growth factors and immunomodulation through CD45+immune cell depletion or dexamethasone (DEX) supplementation were assessed for enhancing spermatogenesis during the subsequent differentiation phase. Testicular cells self-reorganized into organoids resembling the testicular anatomical unit, characterized by one tubule-like structure surrounded by interstitium. Media 1-3 proved superior for organoid growth during the reorganization phase, with TOs in medium 3 exhibiting germ cell numbers (7.4% ± 4.8%) comparable to controls (9.3% ± 5.3%). Additionally, 37% ± 30% demonstrated organized histology from 32 × 103cells under static conditions. Switching toα-MEM + 10% KSR during the differentiation phase increased formation efficiency to 85 ± 7%, along with elevated germ cell numbers, testosterone production (3.1 ± 0.9 ng ml-1) and generation ofγ-H2AX+spermatid-like cells (steps 8-11, 1.2% ± 2.2% of the total). Adding differentiation factors to theα-MEM increased spermatid-like cell numbers to 2.9% ± 5.9%, confirmed through positive staining for CREM, transition protein 1, and peanut agglutinin. Although, these remained diploid with irregular nuclear maturation. DEX supplementation had no additional effect, and immune cell depletion adversely impacted TO formation. The manipulability of TOs offers advantages in studying male infertility and exploring therapies, with scalability enabling high-throughput chemical screening and reducing animal usage in reproductive toxicity and drug discovery studies.

Prior exposure to alkylating agents negatively impacts testicular organoid formation in cells obtained from childhood cancer patients

STUDY QUESTION

Can human pre- and peri-pubertal testicular cells obtained from childhood cancer patients, previously treated with chemotherapy, form testicular organoids (TOs)?

SUMMARY ANSWER

Organoid formation from testicular tissue collected from childhood cancer patients positively correlates with SRY-Box transcription factor 9 (SOX9) expression in Sertoli cells, which in turn negatively correlates with previous exposure to alkylating chemotherapy.

WHAT IS KNOWN ALREADY

Pre- and peri-pubertal boys exposed to highly gonadotoxic therapies can only safeguard their fertility potential through testicular tissue cryopreservation. Today, there is no established clinical tool to restore fertility using these testicular samples. Organoids hold promise in providing fundamental early insights in creating such platforms. However, the generation of TOs that closely resemble the innate testis, to enable a thorough monitoring of the necessary steps for germ cell differentiation and somatic functionalities, remains a challenge.

STUDY DESIGN SIZE DURATION

We used a Matrigel-based three-layer gradient culture system to generate human TOs and to reveal whether chemotherapy exposure affects TO formation capacity and the functionality of pre- and peri-pubertal testicular somatic cells. Testicular cells of 11 boys (aged 7.7 ± 4.1 (mean ± SD) years) were assessed for TO formation in relation to previous chemotherapy exposure and SOX9 expression in histological sections of paraffin-embedded testicular tissue samples collected on the day of biopsy and compared with testicular tissue samples obtained from 28 consecutive patients (aged 6.9 ± 3.8 (mean ± SD) years). All 39 patients were part of the fertility preservation project NORDFERTIL; an additional 10 samples (from boys aged 5.5 ± 3.5 (mean ± SD) years, without an underlying pathology) in an internal biobank collection were used as controls.

PARTICIPANTS/MATERIALS SETTING METHODS

We obtained 49 testicular tissue samples from boys aged 0.8-13.4 years. Fresh samples (n = 11) were dissociated into single-cell suspensions and applied to a three-layer gradient culture system for organoid formation. Histological sections of another 28 samples obtained as part of the fertility preservation project NORDFERTIL, and 10 samples from a sample collection of a pathology biobank were used to evaluate the effects of prior exposure to alkylating agents on testicular samples. Testicular organoid formation was defined based on morphological features, such as compartmentalized structures showing cord formation, and protein expression of testicular cell-specific markers for germ and somatic cells was evaluated via immunohistochemical staining. Hormone secretion was analysed by specific enzyme-linked immunosorbent assays for testosterone and anti-Müllerian hormone (AMH) production.

MAIN RESULTS AND THE ROLE OF CHANCE

Our results revealed that 4 out of 11 prepubertal testicular samples formed TOs that showed compartmentalized cord-like structures surrounded by interstitial-like areas and increasing levels of both testosterone as well as AMH over a 7-day culture period. We observed that SOX9 expression was correlated positively with TO formation. Moreover, exposure to alkylating agents before biopsy was inversely correlated with SOX9 expression (P = 0.006).

LARGE SCALE DATA

N/A.

LIMITATIONS REASONS FOR CAUTION

Due to the limited amount of material available, only 11 out of the 39 pre- and peri-pubertal testicular tissue samples could be used for the organoid formation experiments. The testicular tissue samples obtained from a sample collection of the internal biobank of Department of Pathology, Karolinska University Hospital were considered normal and included in the study if no testicular pathology was reported. However, detailed information regarding previous medical treatments and/or testicular volumes of the patients included in this biobank was not available.

WIDER IMPLICATIONS OF THE FINDINGS

Our observations suggest that SOX9 expression may serve as a putative indicator of TO formation, indicating a critical role of Sertoli cells in promoting organoid formation, seminiferous tubule integrity, and testicular function in pre- and peri-pubertal testicular tissue.

STUDY FUNDING/COMPETING INTERESTS

This study was supported by grants from the Swedish Childhood Cancer Foundation (PR2019-0123; PR2022-0115; TJ2020-0023) (J.-B.S.), Finnish Cancer Society (K.J.), Finnish Foundation for Paediatric Research (K.J.), Swedish Research Council (2018-03094; 2021-02107) (J.-B.S.), and Birgitta and Carl-Axel Rydbeck's Research Grant for Paediatric Research (2020-00348; 2020-00335; 2021-00073; 2022-00317) (J.-B.S. and K.J.). Y.C. and Y.Y. received a scholarship from the Chinese Scholarship Council. J.P.A-L. was supported by a Starting Grant in Medicine and Health (2022-01467) from the Swedish Research Council. R.T.M. was supported by a UKRI Future Leaders Fellowship (MR/S017151/1). The MRC Centre for Reproductive Health was supported by an MRC Centre Grant (MR/N022556/1). The authors declare no competing interests.

Multi-cellular engineered living systems to assess reproductive toxicology

Toxicants and some drugs can negatively impact reproductive health. Many toxicants haven't been tested due to lack of available models. The impact of many drugs taken during pregnancy to address maternal health may adversely affect fetal development with life-long effects and clinical trials do not examine toxicity effects on the maternal-fetal interface, requiring indirect assessment of safety and efficacy. Due to current gaps in reproductive toxicological knowledge and limitations of animal models, multi-cellular engineered living systems may provide solutions for modeling reproductive physiology and pathology for chemical and xenobiotic toxicity studies. Multi-cellular engineered living systems, such as microphysiological systems (MPS) and organoids, model of functional units of tissues. In this review, we highlight the key functions and structures of human reproductive organs and well-known representative toxicants afflicting these systems. We then discuss current approaches and specific studies where scientists have used MPS or organoids to recreate in vivo markers and cellular responses of the female and male reproductive system, as well as pregnancy-associated placenta formation and embryo development. We provide specific examples of organoids and organ-on-chip that have been used for toxicological purposes with varied success. Finally, we address current issues related to usage of MPS, emerging techniques for improving upon these complications, and improvements needed to make MPS more capable in assessing reproductive toxicology. Overall, multi-cellular engineered living systems have considerable promise to serve as a suitable, alternative reproductive biological model compared to animal studies and 2D culture.

Elucidating the Transcriptional States of Spermatogenesis-Joint Analysis of Germline and Supporting Cell, Mice and Human, Normal and Perturbed, Bulk and Single-Cell RNA-Seq

In studying the molecular underpinning of spermatogenesis, we expect to understand the fundamental biological processes better and potentially identify genes that may lead to novel diagnostic and therapeutic strategies toward precision medicine in male infertility. In this review, we emphasized our perspective that the path forward necessitates integrative studies that rely on complementary approaches and types of data. To comprehensively analyze spermatogenesis, this review proposes four axes of integration. First, spanning the analysis of spermatogenesis in the healthy state alongside pathologies. Second, the experimental analysis of model systems (in which we can deploy treatments and perturbations) alongside human data. Third, the phenotype is measured alongside its underlying molecular profiles using known markers augmented with unbiased profiles. Finally, the testicular cells are studied as ecosystems, analyzing the germ cells alongside the states observed in the supporting somatic cells. Recently, the study of spermatogenesis has been advancing using single-cell RNA sequencing, where scientists have uncovered the unique stages of germ cell development in mice, revealing new regulators of spermatogenesis and previously unknown cell subtypes in the testis. An in-depth analysis of meiotic and postmeiotic stages led to the discovery of marker genes for spermatogonia, Sertoli and Leydig cells and further elucidated all the other germline and somatic cells in the testis microenvironment in normal and pathogenic conditions. The outcome of an integrative analysis of spermatogenesis using advanced molecular profiling technologies such as scRNA-seq has already propelled our biological understanding, with additional studies expected to have clinical implications for the study of male fertility. By uncovering new genes and pathways involved in abnormal spermatogenesis, we may gain insights into subfertility or sterility.

Self-Organization of Sinusoidal Vessels in Pluripotent Stem Cell-derived Human Liver Bud Organoids

The induction of tissue-specific vessels in in vitro living tissue systems remains challenging. Here, we directly differentiated human pluripotent stem cells into CD32b+ putative liver sinusoidal progenitors (iLSEP) by dictating developmental pathways. By devising an inverted multilayered air-liquid interface (IMALI) culture, hepatic endoderm, septum mesenchyme, arterial and sinusoidal quadruple progenitors self-organized to generate and sustain hepatocyte-like cells neighbored by divergent endothelial subsets composed of CD32blowCD31high, LYVE1+STAB1+CD32bhighCD31lowTHBD-vWF-, and LYVE1-THBD+vWF+ cells. Wnt2 mediated sinusoidal-to-hepatic intercellular crosstalk potentiates hepatocyte differentiation and branched endothelial network formation. Intravital imaging revealed iLSEP developed fully patent human vessels with functional sinusoid-like features. Organoid-derived hepatocyte- and sinusoid-derived coagulation factors enabled correction of in vitro clotting time with Factor V, VIII, IX, and XI deficient patients' plasma and rescued the severe bleeding phenotype in hemophilia A mice upon transplantation. Advanced organoid vascularization technology allows for interrogating key insights governing organ-specific vessel development, paving the way for coagulation disorder therapeutics.

Male Infertility: New Developments, Current Challenges, and Future Directions

There have been many significant scientific advances in the diagnostics and treatment modalities in the field of male infertility in recent decades. Examples of these include assisted reproductive technologies, sperm selection techniques for intracytoplasmic sperm injection, surgical procedures for sperm retrieval, and novel tests of sperm function. However, there is certainly a need for new developments in this field. In this review, we discuss advances in the management of male infertility, such as seminal oxidative stress testing, sperm DNA fragmentation testing, genetic and epigenetic tests, genetic manipulations, artificial intelligence, personalized medicine, and telemedicine. The role of the reproductive urologist will continue to expand in future years to address different topzics related to diverse questions and controversies of pathophysiology, diagnosis, and therapy of male infertility, training researchers and physicians in medical and scientific research in reproductive urology/andrology, and further development of andrology as an independent specialty.

The reprotoxic adverse side effects of neurogenic and neuroprotective drugs: current use of human organoid modeling as a potential alternative to preclinical models

The management of neurological disorders heavily relies on neurotherapeutic drugs, but notable concerns exist regarding their possible negative effects on reproductive health. Traditional preclinical models often fail to accurately predict reprotoxicity, highlighting the need for more physiologically relevant systems. Organoid models represent a promising approach for concurrently studying neurotoxicity and reprotoxicity, providing insights into the complex interplay between neurotherapeutic drugs and reproductive systems. Herein, we have examined the molecular mechanisms underlying neurotherapeutic drug-induced reprotoxicity and discussed experimental findings from case studies. Additionally, we explore the utility of organoid models in elucidating the reproductive complications of neurodrug exposure. Have discussed the principles of organoid models, highlighting their ability to recapitulate neurodevelopmental processes and simulate drug-induced toxicity in a controlled environment. Challenges and future perspectives in the field have been addressed with a focus on advancing organoid technologies to improve reprotoxicity assessment and enhance drug safety screening. This review underscores the importance of organoid models in unraveling the complex relationship between neurotherapeutic drugs and reproductive health.

The limitations of testicular organoids: are they truly as promising as we believe?

Organoid systems have revolutionised various facets of biological research by offering a three-dimensional (3D), physiologically relevant in vitro model to study complex organ systems. Over recent years, testicular organoids have been publicised as promising platforms for reproductive studies, disease modelling, drug screening, and fertility preservation. However, the full potential of these systems has yet to be realised due to inherent limitations. This paper offers a comprehensive analysis of the current challenges associated with testicular organoid models. Firstly, we address the inability of current organoid systems to fully replicate the intricate spatial organisation and cellular diversity of the in vivo testis. Secondly, we scrutinise the fidelity of germ cell maturation within the organoids, highlighting incomplete spermatogenesis and epigenetic inconsistencies. Thirdly, we consider the technical challenges faced during organoid culture, including nutrient diffusion limits, lack of vasculature, and the need for specialised growth factors. Finally, we discuss the ethical considerations surrounding the use of organoids for human reproduction research. Addressing these limitations in combination with integrating complementary approaches, will be essential if we are to advance our understanding of testicular biology and develop novel strategies for addressing reproductive health issues in males.

Advancing Organoid Engineering for Tissue Regeneration and Biofunctional Reconstruction

Tissue damage and functional abnormalities in organs have become a considerable clinical challenge. Organoids are often applied as disease models and in drug discovery and screening. Indeed, several studies have shown that organoids are an important strategy for achieving tissue repair and biofunction reconstruction. In contrast to established stem cell therapies, organoids have high clinical relevance. However, conventional approaches have limited the application of organoids in clinical regenerative medicine. Engineered organoids might have the capacity to overcome these challenges. Bioengineering-a multidisciplinary field that applies engineering principles to biomedicine-has bridged the gap between engineering and medicine to promote human health. More specifically, bioengineering principles have been applied to organoids to accelerate their clinical translation. In this review, beginning with the basic concepts of organoids, we describe strategies for cultivating engineered organoids and discuss the multiple engineering modes to create conditions for breakthroughs in organoid research. Subsequently, studies on the application of engineered organoids in biofunction reconstruction and tissue repair are presented. Finally, we highlight the limitations and challenges hindering the utilization of engineered organoids in clinical applications. Future research will focus on cultivating engineered organoids using advanced bioengineering tools for personalized tissue repair and biofunction reconstruction.

Anin vitrothree-dimensional (3D) testicular organoid culture system for efficient gonocyte maintenance and propagation using frozen/thawed neonatal bovine testicular tissues

Fertility preservation in prepubertal boys with cancer requires the cryopreservation of immature testicular tissues (ITTs) prior to gonadotoxic treatment. However, the limited number of germ cells in small human ITT biopsies necessitates the development of anin vitroculture system for germ cell expansion using frozen-thawed ITTs. Here, we generated testicular organoids for thein vitromaintenance and expansion of gonocytes from frozen-thawed two-week-old neonatal bovine ITTs. We investigated the effects of different cell-seeding densities, culture serums, seeding methods, and gonadotropin supplementations, on the maintenance and proliferation of enriched gonocytes. Our results demonstrated that enriched gonocytes and testicular cells from frozen-thawed neonatal ITTs could self-assemble into spheroid organoids in three days in an appropriate Matrigel-based culture environment. For the optimal formation of prepubertal testicular organoids, a seeding density of 1 × 106cells/well is recommended over other densities. This strategy results in organoids with a mean diameter of 60.53 ± 12.12 μm; the mean number of organoids was 5.57 ± 1.60/105μm2on day 11. The viability of organoids was maintained at 79.75 ± 2.99% after being frozen and thawed. Supplementing the culture medium with glial cell-derived neurotrophic factor, fibroblast growth factor 2, and leukemia inhibitory factor, increased the proportion of KI67-positive proliferating cells in organoids, elevated the expression ofC-KITbut reduced the expression ofGFRα1at day 28 when compared to those without hormone supplements(p< 0.05). In addition, supplementing the culture medium with follicle-stimulating hormone and testosterone helped to maintain a significantly higher viability (p< 0.05) in ITT organoids at day 28. These organoids could be cryopreserved for storage and thawed as needed. The successful generation of ITT organoids provides a valuable tool for establishingin vitrospermatogenesis, propagating human germ cells, investigating testicular physiology and the origin of germ cell tumors, and testing the toxicity of new drugs in future clinical applications.

Bovine adipose tissue-derived mesenchymal stem cells self-assemble with testicular cells and integrates and modifies the structure of a testicular organoids

Mesenchymal stem cells (MSC) display self-renewal and mesodermal differentiation potentials. These characteristics make them potentially useful for in vitro derivation of gametes, which may constitute experimental therapies for human and animal reproduction. Organoids provide a spatial support and may simulate a cellular niche for in vitro studies. In this study, we aimed at evaluating the potential integration of fetal bovine MSCs derived from adipose tissue (AT-MSCs) in testicular organoids (TOs), their spatial distribution with testicular cells during TO formation and their potential for germ cell differentiation. TOs were developed using Leydig, Sertoli, and peritubular myoid cells that were previously isolated from bovine testes (n = 6). Thereafter, TOs were characterized using immunofluorescence and Q-PCR to detect testicular cell-specific markers. AT-MSCs were labeled with PKH26 and then cultured with testicular cells at a concentration of 1 × 106 cells per well in Ultra Low Attachment U-shape bottom (ULA) plates. TOs formed by testicular cells and AT-MSCs (TOs + AT-MSCs) maintained a rounded structure throughout the 28-day culture period and did not show significant differences in their diameters. Conversely, control TOs exhibited a compact structure until day 7 of culture, while on day 28 they displayed cellular extensions around their structure. Control TOs had greater (P < 0.05) diameters compared to TOs + AT-MSCs. AT-MSCs induced an increase in proportion of Leydig and peritubular myoid cells in TOs + AT-MSCs; however, did not induce changes in the overall gene expression of testicular cell-specific markers. STAR immunolabelling detected Leydig cells that migrated from the central area to the periphery and formed brunches in control TOs. However, in TOs + AT-MSCs, Leydig cells formed a compact peripheral layer. Sertoli cells immunodetected using WT1 marker were observed within the central area forming clusters of cells in TOs + AT-MSCs. The expression of COL1A associated to peritubular myoids cells was restricted to the central region in TOs + AT-MSCs. Thus, during a 28-day culture period, fetal bovine AT-MSCs integrated and modified the structure of the TOs, by restricting formation of branches, limiting the overall increase in diameters and increasing the proportions of Leydig and peritubular myoid cells. AT-MSCs also induced a reorganization of testicular cells, changing their distribution and particularly the location of Leydig cells.

Empowering tomorrow's leaders: the impact of the 15th Network of Young Researchers in Andrology (NYRA) meeting on male reproductive health and interdisciplinary collaboration

The 15th Network of Young Researchers in Andrology (NYRA) meeting, held at the Palace de Caux, Switzerland, served as a valuable platform to disseminate cutting-edge research and facilitate interactions among early-career researchers and trainees in andrology from around the world. Preceding the 22nd European Testis Workshop, the 2-day event brought together participants from a variety of countries to discuss a range of topics pertaining to men's reproductive health and biology. Specific focuses included piRNAs in mammalian reproduction, biomolecules enhancing sperm physiology, advances in in vitro spermatogenesis, reproductive strategies across species, and career development. A dedicated 'scientific speed-dating' social event also stood out, encouraging cross-disciplinary collaborations and strengthening ties within the scientific community. The high participation rate of the meeting highlighted its value in connecting the andrology community. Finally, the announcement of NYRA's merger with the European Academy of Andrology (EAA) marked a pivotal moment, enabling NYRA to support young researchers while collaborating with the EAA to advance andrology research. The 15th NYRA meeting played a crucial role in enhancing knowledge dissemination and andrology research, empowering young researchers, and addressing key challenges in male infertility.

Microphysiological Constructs and Systems: Biofabrication Tactics, Biomimetic Evaluation Approaches, and Biomedical Applications

In recent decades, microphysiological constructs and systems (MPCs and MPSs) have undergone significant development, ranging from self-organized organoids to high-throughput organ-on-a-chip platforms. Advances in biomaterials, bioinks, 3D bioprinting, micro/nanofabrication, and sensor technologies have contributed to diverse and innovative biofabrication tactics. MPCs and MPSs, particularly tissue chips relevant to absorption, distribution, metabolism, excretion, and toxicity, have demonstrated potential as precise, efficient, and economical alternatives to animal models for drug discovery and personalized medicine. However, current approaches mainly focus on the in vitro recapitulation of the human anatomical structure and physiological-biochemical indices at a single or a few simple levels. This review highlights the recent remarkable progress in MPC and MPS models and their applications. The challenges that must be addressed to assess the reliability, quantify the techniques, and utilize the fidelity of the models are also discussed.

In vitro spermatogenesis in artificial testis: current knowledge and clinical implications for male infertility

Men's reproductive health exclusively depends on the appropriate maturation of certain germ cells known as sperm. Certain illnesses, such as Klinefelter syndrome, cryptorchidism, and syndrome of androgen insensitivity or absence of testis maturation in men, resulting in the loss of germ cells and the removal of essential genes on the Y chromosome, can cause non-obstructive azoospermia. According to laboratory research, preserving, proliferating, differentiating, and transplanting spermatogonial stem cells or testicular tissue could be future methods for preserving the fertility of children with cancer and men with azoospermia. Therefore, new advances in stem cell research may lead to promising therapies for treating male infertility. The rate of progression and breakthrough in the area of in vitro spermatogenesis is lower than that of SSC transplantation, but newer methods are also being developed. In this regard, tissue and cell culture, supplements, and 3D scaffolds have opened new horizons in the differentiation of stem cells in vitro, which could improve the outcomes of male infertility. Various 3D methods have been developed to produce cellular aggregates and mimic the organization and function of the testis. The production of an artificial reproductive organ that supports SSCs differentiation will certainly be a main step in male infertility treatment.

Preservation of fertility in female and male prepubertal patients diagnosed with cancer

Over the past two decades, the importance of fertility preservation has grown not only in the realm of medical and clinical patient care, but also in the field of basic and applied research in human reproduction. With advancements in cancer treatments resulting in higher rates of patient survival, it is crucial to consider the quality of life post-cure. Therefore, fertility preservation must be taken into account prior to antitumor treatments, as it can significantly impact a patient's future fertility. For postpubertal patients, gamete cryopreservation is the most commonly employed preservation strategy. However, for prepubertal patients, the situation is more intricate. Presently, ovarian tissue cryopreservation is the standard practice for prepubertal girls, but further scientific evidence is required in several aspects. Testicular tissue cryopreservation, on the other hand, is still experimental for prepubertal boys. The primary aim of this review is to address the strategies available for possible fertility preservation in prepubertal girls and boys, such as ovarian cryopreservation/transplantation, in vitro follicle culture and meiotic maturation, artificial ovary, transplantation of cryopreserved spermatogonia, and cryopreservation/grafting of immature testicular tissue and testicular organoids.

Differentiation of human primary testicular cells in the presence of SCF using the organoid culture system

PURPOSE

Development of organoids using human primary testicular cells has remained a challenge due to the complexity of the mammalian testicular cytoarchitecture and culture methods. In this study, we generated testicular organoids derived from human primary testicular cells. Then, we evaluated the effect of stem cell factor (SCF) on cell differentiation and apoptosis in the testicular organoid model.

METHODS

The testicular cells were harvested from the three brain-dead donors. Human spermatogonial stem cells (SSCs) were characterized using immunocytochemistry (ICC), RT-PCR and flow cytometry. Testicular organoids were generated from primary testicular cells by hanging drop culture method and were cultured in three groups: control group, experimental group 1 (treated FSH and retinoic acid (RA)), and experimental group 2 (treated FSH, RA and SCF), for five weeks. We assessed the expression of SCP3 (Synaptonemal Complex Protein 3) as a meiotic gene, PRM2 (Protamine 2) as a post-meiotic marker and apoptotic genes of Bax (BCL2-Associated X Protein) and Bcl-2 (B-cell lymphoma 2), respectively by using RT-qPCR. In addition, we identified the expression of PRM2 by immunohistochemistry (IHC).

RESULTS

Relative expression of SCP3, PRM2 and Bcl-2 were highest in group 2 after five weeks of culture. In contrast, BAX expression level was lower in experimental group 2 in comparison with other groups. IHC analyses indicated the highest expression of PRM2 as a postmeiotic marker in group 2 in comparison to 2D culture and control groups but not find significant differences between experimental group 1 and experimental group 2 groups. Morphological evaluations revealed that organoids are compact spherical structures and in the peripheral region composed of uncharacterized elongated fibroblast-like cells.

CONCLUSION

Our findings revealed that the testicular organoid culture system promote the spermatogonial stem cell (SSC) differentiation, especially in presence of SCF. Developed organoids are capable of recapitulating many important properties of a stem cell niche.

Tissue engineering studies in male infertility disorder

Infertility is an important issue among couples worldwide which is caused by a variety of complex diseases. Male infertility is a problem in 7% of all men. In vitro spermatogenesis (IVS) is the experimental approach that has been developed for mimicking seminiferous tubules-like functional structures in vitro. Currently, various researchers are interested in finding and developing a microenvironmental condition or a bioartificial testis applied for fertility restoration via gamete production in vitro. The tissue engineering (TE) has developed new approaches to treat male fertility preservation through development of functional male germ cells. This makes TE a possible future strategy for restoration of male fertility. Although 3D culture systems supply the perception of the effect of cellular interactions in the process of spermatogenesis, formation of a native gradient of autocrine/paracrine factors in 3D culture systems have not been considered. These results collectively suggest that maintaining the microenvironment of testicular cells even in the form of a 3D-culture system is crucial in achieving spermatogenesis ex vivo. It is also possible to engineer the testicular structures using biomaterials to provide a supporting scaffold for somatic and stem cells. The insemination of these cells with GFs is possible for temporally and spatially adjusted release to mimic the microenvironment of the in situ seminiferous epithelium. This review focuses on recent studies and advances in the application of TE strategies to cell-tissue culture on synthetic or natural scaffolds supplemented with growth factors.

New Solutions for Old Problems: How Reproductive Tissue Engineering Has Been Revolutionizing Reproductive Medicine

Acquired disorders and congenital defects of the male and female reproductive systems can have profound impacts on patients, causing sexual and endocrine dysfunction and infertility, as well as psychosocial consequences that affect their self-esteem, identity, sexuality, and relationships. Reproductive tissue engineering (REPROTEN) is a promising approach to restore fertility and improve the quality of life of patients with reproductive disorders by developing, replacing, or regenerating cells, tissues, and organs from the reproductive and urinary systems. In this review, we explore the latest advancements in REPROTEN techniques and their applications for addressing degenerative conditions in male and female reproductive organs. We discuss current research and clinical outcomes and highlight the potential of 3D constructs utilizing biomaterials such as scaffolds, cells, and biologically active molecules. Our review offers a comprehensive guide for researchers and clinicians, providing insights into how to reestablish reproductive tissue structure and function using innovative surgical approaches and biomaterials. We highlight the benefits of REPROTEN for patients, including preservation of fertility and hormonal production, reconstruction of uterine and cervical structures, and restoration of sexual and urinary functions. Despite significant progress, REPROTEN still faces ethical and technical challenges that need to be addressed. Our review underscores the importance of continued research in this field to advance the development of effective and safe REPROTEN approaches for patients with reproductive disorders.

Advances of three-dimensional (3D) culture systems for in vitro spermatogenesis

The loss of germ cells and spermatogenic failure in non-obstructive azoospermia are believed to be the main causes of male infertility. Laboratory studies have used in vitro testicular models and different 3-dimensional (3D) culture systems for preservation, proliferation and differentiation of spermatogonial stem cells (SSCs) in recent decades. The establishment of testis-like structures would facilitate the study of drug and toxicity screening, pathological mechanisms and in vitro differentiation of SSCs which resulted in possible treatment of male infertility. The different culture systems using cellular aggregation with self-assembling capability, the use of different natural and synthetic biomaterials and various methods for scaffold fabrication provided a suitable 3D niche for testicular cells development. Recently, 3D culture models have noticeably used in research for their architectural and functional similarities to native microenvironment. In this review article, we briefly investigated the recent 3D culture systems that provided a suitable platform for male fertility preservation through organ culture of testis fragments, proliferation and differentiation of SSCs.

In Vitro and In Vivo Models for Drug Transport Across the Blood-Testis Barrier

The blood-testis barrier (BTB) is a selectively permeable membrane barrier formed by adjacent Sertoli cells (SCs) in the seminiferous tubules of the testes that develops intercellular junctional complexes to protect developing germ cells from external pressures. However, due to this inherent defense mechanism, the seminiferous tubule lumen can act as a pharmacological sanctuary site for latent viruses (e.g., Ebola, Zika) and cancers (e.g., leukemia). Therefore, it is critical to identify and evaluate BTB carrier-mediated drug delivery pathways to successfully treat these viruses and cancers. Many drugs are unable to effectively cross cell membranes without assistance from carrier proteins like transporters because they are large, polar, and often carry a charge at physiologic pH. SCs express transporters that selectively permit endogenous compounds, such as carnitine or nucleosides, across the BTB to support normal physiologic activity, although reproductive toxicants can also use these pathways, thereby circumventing the BTB. Certain xenobiotics, including select cancer therapeutics, antivirals, contraceptives, and environmental toxicants, are known to accumulate within the male genital tract and cause testicular toxicity; however, the transport pathways by which these compounds circumvent the BTB are largely unknown. Consequently, there is a need to identify the clinically relevant BTB transport pathways in in vitro and in vivo BTB models that recapitulate human pharmacokinetics and pharmacodynamics for these xenobiotics. This review summarizes the various in vitro and in vivo models of the BTB reported in the literature and highlights the strengths and weaknesses of certain models for drug disposition studies. SIGNIFICANCE STATEMENT: Drug disposition to the testes is influenced by the physical, physiological, and immunological components of the blood-testis barrier (BTB). But many compounds are known to cross the BTB by transporters, resulting in pharmacological and/or toxicological effects in the testes. Therefore, models that assess drug transport across the human BTB must adequately account for these confounding factors. This review identifies and discusses the benefits and limitations of various in vitro and in vivo BTB models for preclinical drug disposition studies.

Recent advances in endocrine organoids for therapeutic application

The endocrine system, consisting of the hypothalamus, pituitary, endocrine glands, and hormones, plays a critical role in hormone metabolic interactions. The complexity of the endocrine system is a significant obstacle to understanding and treating endocrine disorders. Notably, advances in endocrine organoid generation allow a deeper understanding of the endocrine system by providing better comprehension of molecular mechanisms of pathogenesis. Here, we highlight recent advances in endocrine organoids for a wide range of therapeutic applications, from cell transplantation therapy to drug toxicity screening, combined with development in stem cell differentiation and gene editing technologies. In particular, we provide insights into the transplantation of endocrine organoids to reverse endocrine dysfunctions and progress in developing strategies for better engraftments. We also discuss the gap between preclinical and clinical research. Finally, we provide future perspectives for research on endocrine organoids for the development of more effective treatments for endocrine disorders.

Human organoid systems in modeling reproductive tissue development, function, and disease

Research focused on human reproductive biology has primarily relied upon clinical samples affording mainly descriptive studies with limited implementation of functional or mechanistic understanding. More importantly, restricted access to human embryonic material has necessitated the use of animals, primarily rats and mice, and short-term primary cell cultures derived from human patient material. While reproductive developmental processes are generally conserved across mammals, specific features unique to human reproduction have resulted in the development of human-based in vitro systems designed to retain or recapitulate key molecular and cellular processes important in humans. Of note, major advances in 3D epithelial stem cell-based systems modeling human reproductive organ development have been made. These cultures, broadly referred to as organoids, enable research aimed at understanding cellular hierarchies and processes controlling cellular differentiation and function. Moreover, organoids allow the pre-clinical testing of pharmacological substances, both from safety and efficacy standpoints, and hold large potential in driving aspects of personalized medicine that were previously not possible with traditional models. In this mini-review, we focus on summarizing the current state of regenerative organoid culture systems of the female and male reproductive tracts that model organ development, maintenance, and function. Specifically, we will introduce stem cell-based organoid models of the ovary/fallopian tube, endometrium, cervix, prostate gland, and testes. We will also describe organoid systems of the pre-implanting blastocyst and trophoblast, as the blastocyst and its extraembryonic trophectoderm are central to fetal, maternal, and overall pregnancy health. We describe the foundational studies leading to their development and outline the utility as well as specific limitations that are unique and common to many of these in vitro platforms.

Gradient to sectioning CUBE workflow for the generation and imaging of organoids with localized differentiation

Advancements in organoid culture have led to various in vitro mini-organs that mimic native tissues in many ways. Yet, the bottleneck remains to generate complex organoids with body axis patterning, as well as keeping the orientation of organoids during post-experiment analysis processes. Here, we present a workflow for culturing organoids with morphogen gradient using a CUBE culture device, followed by sectioning samples with the CUBE to retain information on gradient direction. We show that hiPSC spheroids cultured with two separated differentiation media on opposing ends of the CUBE resulted in localized expressions of the respective differentiation markers, in contrast to homogeneous distribution of markers in controls. We also describe the processes for cryo and paraffin sectioning of spheroids in CUBE to retain gradient orientation information. This workflow from gradient culture to sectioning with CUBE can provide researchers with a convenient tool to generate increasingly complex organoids and study their developmental processes in vitro.

Biomaterials for Testicular Bioengineering: How far have we come and where do we have to go?

Traditional therapeutic interventions aim to restore male fertile potential or preserve sperm viability in severe cases, such as semen cryopreservation, testicular tissue, germ cell transplantation and testicular graft. However, these techniques demonstrate several methodological, clinical, and biological limitations, that impact in their results. In this scenario, reproductive medicine has sought biotechnological alternatives applied for infertility treatment, or to improve gamete preservation and thus increase reproductive rates in vitro and in vivo. One of the main approaches employed is the biomimetic testicular tissue reconstruction, which uses tissue-engineering principles and methodologies. This strategy pursues to mimic the testicular microenvironment, simulating physiological conditions. Such approach allows male gametes maintenance in culture or produce viable grafts that can be transplanted and restore reproductive functions. In this context, the application of several biomaterials have been proposed to be used in artificial biological systems. From synthetic polymers to decellularized matrixes, each biomaterial has advantages and disadvantages regarding its application in cell culture and tissue reconstruction. Therefore, the present review aims to list the progress that has been made and the continued challenges facing testicular regenerative medicine and the preservation of male reproductive capacity, based on the development of tissue bioengineering approaches for testicular tissue microenvironment reconstruction.

Organoids of the male reproductive system: Challenges, opportunities, and their potential use in fertility research

Organoids are units of function of a given organ able to reproduce, in culture, a biological structure similar in architecture and function to its counterpart in vivo. Today, it is possible to develop an organoid from a fragment of tissue, a stem cell located in an adult organ, an embryonic stem cell, or an induced pluripotent stem cell. In the past decade, many organoids have been developed which mimic stomach, pancreas, liver and brain tissues, optic cups, among many others. Additionally, different male reproductive system organs have already been developed as organoids, including the prostate and testis. These 3D cultures may be of great importance for urological cancer research and have the potential to be used in fertility research for the study of spermatozoa production and maturation, germ cells-somatic cells interactions, and mechanisms of disease. They also provide an accurate preclinical pipeline for drug testing and discovery, as well as for the study of drug resistance. In this work, we revise the current knowledge on organoid technology and its use in healthcare and research, describe the male reproductive system organoids and other biomaterials already developed, and discuss their current application. Finally, we highlight the research gaps, challenges, and opportunities in the field and propose strategies to improve the use of organoids for the study of male infertility situations. This article is categorized under: Reproductive System Diseases > Stem Cells and Development Reproductive System Diseases > Biomedical Engineering.

In vitro complete differentiation of human spermatogonial stem cells to morphologic spermatozoa using a hybrid hydrogel of agarose and laminin

Spermatogenesis refers to the differentiation of the spermatogonial stem cells (SSCs) located in the base seminiferous tubules into haploid spermatozoa. Prerequisites for in vitro spermatogenesis include an extracellular matrix (ECM), paracrine factors, and testicular somatic cells which play a supporting role for SSCs. Thus, the present study evaluated the potential of co-culturing Sertoli cells and SSCs embedded in a hybrid hydrogel of agarose and laminin, the main components of the ECM. Following the three-week conventional culture of human testicular cells, the cells were cultured in agarose hydrogel or agarose/laminin one (hybrid) for 74 days. Then, immunocytochemistry, real-time PCR, electron microscopy, and morphological staining methods were applied to analyze the presence of SSCs, as well as the other cells of the different stages of spermatogenesis. Based on the results, the colonies with positive spermatogenesis markers were observed in both culture systems. The existence of the cells of all three phases of spermatogenesis (spermatogonia, meiosis, and spermiogenesis) was confirmed in the two groups, while morphological spermatozoa were detected only in the hybrid hydrogel group. Finally, a biologically improved 3D matrix can support all the physiological activities of SSCs such as survival, proliferation, and differentiation.

Human in vitro spermatogenesis as a regenerative therapy - where do we stand?

Spermatogenesis involves precise temporal and spatial gene expression and cell signalling to reach a coordinated balance between self-renewal and differentiation of spermatogonial stem cells through various germ cell states including mitosis, and meiosis I and II, which result in the generation of haploid cells with a unique genetic identity. Subsequently, these round spermatids undergo a series of morphological changes to shed excess cytoplast, develop a midpiece and tail, and undergo DNA repackaging to eventually form millions of spermatozoa. The goal of recreating this process in vitro has been pursued since the 1920s as a tool to treat male factor infertility in patients with azoospermia. Continued advances in reproductive bioengineering led to successful generation of mature, functional sperm in mice and, in the past 3 years, in humans. Multiple approaches to study human in vitro spermatogenesis have been proposed, but technical and ethical obstacles have limited the ability to complete spermiogenesis, and further work is needed to establish a robust culture system for clinical application.

Murine skin-derived multipotent papillary dermal fibroblast progenitors show germline potential in vitro

BACKGROUND

Many laboratories have described the in vitro isolation of multipotent cells with stem cell properties from the skin of various species termed skin-derived stem cells (SDSCs). However, the cellular origin of these cells and their capability to give rise, among various cell types, to male germ cells, remain largely unexplored.

METHODS

SDSCs were isolated from newborn mice skin, and then differentiated into primordial germ cell-like cells (PGCLCs) in vitro. Single-cell RNA sequencing (scRNA-seq) was then applied to dissect the cellular origin of SDSCs using cells isolated from newborn mouse skin and SDSC colonies. Based on an optimized culture strategy, we successfully generated spermatogonial stem cell-like cells (SSCLCs) in vitro.

RESULTS

Here, using scRNA-seq and analyzing the profile of 7543 single-cell transcriptomes from newborn mouse skin and SDSCs, we discovered that they mainly consist of multipotent papillary dermal fibroblast progenitors (pDFPs) residing in the dermal layer. Moreover, we found that epidermal growth factor (EGF) signaling is pivotal for the capability of these progenitors to proliferate and form large colonies in vitro. Finally, we optimized the protocol to efficiently generate PGCLCs from SDSCs. Furthermore, PGCLCs were induced into SSCLCs and these SSCLCs showed meiotic potential when cultured with testicular organoids.

CONCLUSIONS

Our findings here identify pDFPs as SDSCs derived from newborn skin and show for the first time that such precursors can be induced to generate cells of the male germline.

Inheritance of paternal lifestyles and exposures through sperm DNA methylation

Many different lifestyle factors and chemicals present in the environment are a threat to the reproductive tracts of humans. The potential for parental preconception exposure to alter gametes and for these alterations to be passed on to offspring and negatively affect embryo growth and development is of concern. The connection between maternal exposures and offspring health is a frequent focus in epidemiological studies, but paternal preconception exposures are much less frequently considered and are also very important determinants of offspring health. Several environmental and lifestyle factors in men have been found to alter sperm epigenetics, which can regulate gene expression during early embryonic development. Epigenetic information is thought to be a mechanism that evolved for organisms to pass on information about their lived experiences to offspring. DNA methylation is a well-studied epigenetic regulator that is sensitive to environmental exposures in somatic cells and sperm. The continuous production of sperm from spermatogonial stem cells throughout a man's adult life and the presence of spermatogonial stem cells outside of the blood-testis barrier makes them susceptible to environmental insults. Furthermore, altered sperm DNA methylation patterns can be maintained throughout development and ultimately result in impairments, which could predispose offspring to disease. Innovations in human stem cell-based spermatogenic models can be used to elucidate the paternal origins of health and disease.

Tissue hydraulics in reproduction

The development of functional eggs and sperm are critical processes in mammalian development as they ensure successful reproduction and species propagation. While past studies have identified important genes that regulate these processes, the roles of luminal flow and fluid stress in reproductive biology remain less well understood. Here, we discuss recent evidence that support the diverse functions of luminal fluid in oogenesis, spermatogenesis and embryogenesis. We also review emerging techniques that allow for precise quantification and perturbation of tissue hydraulics in female and male reproductive systems, and propose new questions and approaches in this field. We hope this review will provide a useful resource to inspire future research in tissue hydraulics in reproductive biology and diseases.

Se(XY) matters: the importance of incorporating sex in microphysiological models

The development of microphysiological models is currently at the forefront of preclinical research. Although these 3D tissue models are being developed to mimic physiological organ function and diseases, which are often sexually dimorphic, sex is usually neglected as a biological variable. For decades, national research agencies have required government-funded clinical trials to include both male and female participants as a means of eliminating male bias. However, this is not the case in preclinical trials, which have been shown to favor male rodents in animal studies and male cell types in in vitro studies. In this Opinion, we highlight the importance of considering sex as a biological variable and outline five approaches for incorporating sex-specific features into current microphysiological models.

Differentiation of neonate mouse spermatogonia on two-dimensional and three-dimensional culture systems supplemented with d-Serine and Dizocilpine (MK-801)

N-methyl-d-aspartate (NMDA) modulates the spermatogenesis process through stimulating the steroid hormone biosynthesis. The aim of this study was to evaluate the effects of NMDA receptors agonists (d-Serine) and antagonists (MK801) on spermatogonia differentiation on decellularization testicular matrix (DTM) hydrogel scaffold. Four treatment groups were planned: 2D + D-Serine, 3D + D-Serine, 2D + MK801, and 3D + MK801. Results showed that cell viability was significantly decreased after 48 h in the 3D + D-Serine group and after 24 and 48 h in the 3D + MK801 group compared to the controls. The spermatogonia proliferation after two, four, and eight weeks was significantly increased in the 3D + D-Serine culture, while it was significantly reduced in the 2D + MK801 and 3D + MK801 groups after four and eight weeks. Real-time PCR results demonstrated that pre-meiotic gene (Plzf) expression was significantly increased only in the 3D + D-Serine culture compared to the control groups after four weeks of culture. The meiotic gene (Sycp3) expression was significantly increased in the 2D + D-Serine and 3D + D-Serine compared to the 2D controls after four and eight weeks. The post-meiotic gene (Tnp1) level in the 3D + D-Serine was significantly higher than the other groups. Flow-cytometry results indicated that the protein expression of Plzf (after four and eight weeks), Sycp3 (after eight weeks), and Tnp1 (after eight weeks) in the d-Serine-treated groups was significantly increased compared with the 2D control groups. There were not any significant changes in the gene expression of spermatogenic-related markers in MK801 culture media. However, a significant decrease in the protein levels of Plzf after eight weeks and Sycp3 after four and eight weeks was observed. In conclusion, the addition of NMDARs agonists (d-Serine) could be used to regulate the differentiation of spermatogonia in the 3D culture system.

Stem Cells and Organs-on-chips: New Promising Technologies for Human Infertility Treatment

Having biological children remains an unattainable dream for most couples with reproductive failure or gonadal dysgenesis. The combination of stem cells with gene editing technology and organ-on-a-chip models provides a unique opportunity for infertile patients with impaired gametogenesis caused by congenital disorders in sex development or cancer survivors. But how will these technologies overcome human infertility? This review discusses the regenerative mechanisms, applications, and advantages of different types of stem cells for restoring gametogenesis in infertile patients, as well as major challenges that must be overcome before clinical application. The importance and limitations of in vitro generation of gametes from patient-specific human-induced pluripotent stem cells (hiPSCs) will be discussed in the context of human reproduction. The potential role of organ-on-a-chip models that can direct differentiation of hiPSC-derived primordial germ cell-like cells to gametes and other reproductive organoids is also explored. These rapidly evolving technologies provide prospects for improving fertility to individuals and couples who experience reproductive failure.

Generation and Characterization of Bovine Testicular Organoids Derived from Primary Somatic Cell Populations

Organoids are 3D-culture systems composed of tissue-specific primary cells that self-organize and self-renew, creating structures similar to those of their tissue of origin. Testicular organoids (TOs) may recreate conditions of the testicular niche in domestic and wild cattle; however, no previous TO studies have been reported in the bovine species. Thus, in the present study, we sought to generate and characterize bovine TOs derived from primary testicular cell populations including Leydig, Sertoli and peritubular myoid cells. Testicular cells were isolated from bovine testes and cultured in ultra-low attachment (ULA) plates and Matrigel. TOs were cultured in media supplemented from day 3 with 100 ng/mL of BMP4 and 10 ng/mL of FGF2 and from day 7 with 15 ng/mL of GDNF. Testicular cells were able to generate TOs after 3 days of culture. The cells positive for STAR (Leydig) and COL1A (peritubular myoid) decreased (p < 0.05), whereas cells positive for WT1 (Sertoli) increased (p < 0.05) in TOs during a 28-day culture period. The levels of testosterone in media increased (p < 0.05) at day 28 of culture. Thus, testicular cells isolated from bovine testes were able to generate TOs under in vitro conditions. These bovine TOs have steroidogenic activity characterized by the production of testosterone.

Biomaterial strategies for the application of reproductive tissue engineering

Human reproductive organs are of vital importance to the life of an individual and the reproduction of human populations. So far, traditional methods have a limited effect in recovering the function and fertility of reproductive organs and tissues. Thus, aim to replace and facilitate the regrowth of damaged or diseased tissue, various biomaterials are developed to offer hope to overcome these difficulties and help gain further research progress in reproductive tissue engineering. In this review, we focus on the biomaterials and their four main applications in reproductive tissue engineering: in vitro generation and culture of reproductive cells; development of reproductive organoids and models; in vivo transplantation of reproductive cells or tissues; and regeneration of reproductive tissue. In reproductive tissue engineering, designing biomaterials for different applications with different mechanical properties, structure, function, and microenvironment is challenging and important, and deserves more attention.

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Various biomaterials have been developed and used in reproductive tissue engineering.

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3D culture systems can lead to better cell-cell interactions for in vitro production of reproductive cells.

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Reproductive organoids and models are formed by biomaterials to simulate the environment of natural reproductive organs.

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Biomaterials should promote vascular regeneration and resist inflammation for in-situ reproductive tissue regeneration.

Emerging organoid models to study the epididymis in male reproductive toxicology

The importance of the epididymis on sperm maturation and consequently male fertility has been well documented. The pseudostratified epithelium of the epididymis is comprised of multiple cell types, including principal cells, which are the most abundant, and basal cells. The role of basal cells has been unclear and has been a source of discussion in the literature. However, the recent demonstration that these cells are multipotent or adult stem cells has opened new areas of research in epididymal biology. One such avenue is to understand the regulation of these stem cells, and to exploit their properties to develop tools for toxicological studies to elucidate the effects of chemicals on cell differentiation and epididymal function in vitro. Studies in both rat and mouse have shown that purified single epididymal basal cells cultured under 3D conditions can proliferate and differentiate to form organoids, or mini organs. Furthermore, these epididymal basal stem cells can self-renew and differentiate into other epididymal cell types. It is known that during epididymal development, basal cells are derived from undifferentiated columnar cells, which have been reported to share common properties to stem cells. Like basal cells, these undifferentiated columnar cells can also form organoids under 3D culture conditions and can differentiate into basal, principal and clear cells. Organoids derived from either basal cells or columnar cells offer unique models for toxicology studies and represent an exciting and emerging approach to understand the epididymis.

A brief history of testicular organoids: from theory to the wards

In recent years, researchers have successfully generated many human and mammalian organoid models, including organoids representing the intestine, prostate, ovary, bladder, liver, and brain. Therefore, organoids have become an important research model in the fields of regenerative medicine, drug research, and gene therapy, acting as a bridge between in vivo and in vitro experiments. In addition, testicular organoids (TOs) represent the highest level of in vitro culture of spermatogenic cells in a simulated testicular environment. However, the generation of TOs is still in the early stages, and there is still much room for improvement in dealing with the many challenges and prospects to achieve the goal of TOs that simulate the testicular microenvironment in vitro or even reconstruct the process of spermatogenesis without the need to reconstruct seminiferous tubules. We review the brief history of TO generation and some major strategies for functional applications of TOs, which are the main concerns of our clinicians and laboratory researchers.

Perfusion in Organ-on-Chip Models and Its Applicability to the Replication of Spermatogenesis In Vitro

Organ/organoid-on-a-chip (OoC) technologies aim to replicate aspects of the in vivo environment in vitro, at the scale of microns. Mimicking the spatial in vivo structure is important and can provide a deeper understanding of the cell-cell interactions and the mechanisms that lead to normal/abnormal function of a given organ. It is also important for disease models and drug/toxin testing. Incorporating active fluid flow in chip models enables many more possibilities. Active flow can provide physical cues, improve intercellular communication, and allow for the dynamic control of the environment, by enabling the efficient introduction of biological factors, drugs, or toxins. All of this is in addition to the fundamental role of flow in supplying nutrition and removing waste metabolites. This review presents an overview of the different types of fluid flow and how they are incorporated in various OoC models. The review then describes various methods and techniques of incorporating perfusion networks into OoC models, including self-assembly, bioprinting techniques, and utilizing sacrificial gels. The second part of the review focuses on the replication of spermatogenesis in vitro; the complex process whereby spermatogonial stem cells differentiate into mature sperm. A general overview is given of the various approaches that have been used. The few studies that incorporated microfluidics or vasculature are also described. Finally, a future perspective is given on elements from perfusion-based models that are currently used in models of other organs and can be applied to the field of in vitro spermatogenesis. For example, adopting tubular blood vessel models to mimic the morphology of the seminiferous tubules and incorporating vasculature in testis-on-a-chip models. Improving these models would improve our understanding of the process of spermatogenesis. It may also potentially provide novel therapeutic strategies for pre-pubertal cancer patients who need aggressive chemotherapy that can render them sterile, as well asfor a subset of non-obstructive azoospermic patients with maturation arrest, whose testes do not produce sperm but still contain some of the progenitor cells.

Small-Molecule-Driven Direct Reprogramming of Fibroblasts into Functional Sertoli-Like Cells as a Model for Male Reproductive Toxicology

Sertoli cells (SCs) are vital to providing morphological and nutritional support for spermatogenesis. Defects in SCs often lead to infertility. SCs transplantation is a promising potential strategy to compensate for SC dysfunction. However, isolation of SCs from testes is impractical due to obvious and ethical limitations. Here, a molecular cocktail is identified comprising of pan-BET family inhibitor (I-BET151), retinoic acid, and riluzole that enables the efficient conversion of fibroblasts into functional Sertoli-like cells (CiSCs). The gene expression profiles of CiSCs resemble those of mature SCs and exhibit functional properties such as the formation of testicular seminiferous tubules, engulfment of apoptotic sperms, supporting the survival of germ cells, and suppressing proliferation of primary lymphocytes in vitro. Moreover, CiSCs are sensitive to toxic substances, making them an alternative model to study the deleterious effects of toxicants on SCs. The study provides an efficient approach to reprogram fibroblasts into functional SCs by using pure chemical compounds.

Male fertility preservation and restoration strategies for patients undergoing gonadotoxic therapies†

Medical treatments for cancers or other conditions can lead to permanent infertility. Infertility is an insidious disease that impacts not only the ability to have a biological child but also the emotional well-being of the infertile individuals, relationships, finances, and overall health. Therefore, all patients should be educated about the effects of their medical treatments on future fertility and about fertility preservation options. The standard fertility preservation option for adolescent and adult men is sperm cryopreservation. Sperms can be frozen and stored for a long period, thawed at a later date, and used to achieve pregnancy with existing assisted reproductive technologies. However, sperm cryopreservation is not applicable for prepubertal patients who do not yet produce sperm. The only fertility preservation option available to prepubertal boys is testicular tissue cryopreservation. Next-generation technologies are being developed to mature those testicular cells or tissues to produce fertilization-competent sperms. When sperm and testicular tissues are not available for fertility preservation, inducing pluripotent stem cells derived from somatic cells, such as blood or skin, may provide an alternative path to produce sperms through a process call in vitro gametogenesis. This review describes standard and experimental options to preserve male fertility as well as the experimental options to produce functional spermatids or sperms from immature cryopreserved testicular tissues or somatic cells.

Testis on a chip - a microfluidic 3-dimensional culture system for the development of spermatogenesisin-vitro

This research presents a novel Testis-on-a Chip- platform. Testicular cells are enzymatically isolated from the seminiferous tubules of sexually immature mice, seeded in a methylcellulose gel and cultured in a microfluidic chip. The unique design sandwiches the soft methylcellulose between stiffer agar support gels. The cells develop into organoids continuing to proliferate and differentiate. After seven weeks of culture the cells have over 95% viability. Confocal microscopy of the developed organoids reveals a structure containing the various stages of spermatogenesis up to and including meiosis II: premeiotic, meiotic and post-meiotic germ cells. The organoid structure also contains the supporting Sertoli and peritubular cells. The responsiveness of the system to the addition of testosterone and retinoic acid to the culture medium during the experiment are also investigated. As a benchmark, the Testis-on-a-Chip is compared to a conventional three-dimensional methylcellulose cell culture in a well plate. Analysis via FACS (Fluorescence-activated cell sorting) shows more haploid cells in the chip as compared to the plates. Immunofluorescence staining after seven weeks of culture shows more differentiated cells in the chip as compared to the well plate. This demonstrates the feasibility of our platform as well as its advantages. This research opens new horizons for the study and realization of spermatogenesis in-vitro. It can also enable the implementation of microfluidic technologies in future therapeutic strategies for pre pubertal male fertility preservation and adults with maturation arrest. Lastly, it can serve as a platform for drug and toxin testing.

Organoids to model the endometrium: implantation and beyond

Despite advances in assisted reproductive techniques in the 4 decades since the first human birth after in vitro fertilisation, 1–2% of couples experience recurrent implantation failure, and some will never achieve a successful pregnancy even in the absence of a confirmed dysfunction. Furthermore, 1–2% of couples who do conceive, either naturally or with assistance, will experience recurrent early loss of karyotypically normal pregnancies. In both cases, embryo-endometrial interaction is a clear candidate for exploration. The impossibility of studying implantation processes within the human body has necessitated the use of animal models and cell culture approaches. Recent advances in 3-dimensional modelling techniques, namely the advent of organoids, present an exciting opportunity to elucidate the unanswerable within human reproduction. In this review, we will explore the ontogeny of implantation modelling and propose a roadmap to application and discovery.

Fertility preservation in boys facing gonadotoxic cancer therapy

Patient survival following childhood cancer has increased with contemporary radiation and chemotherapy techniques. However, gonadotoxicity associated with treatments means that infertility is a common consequence in survivors. Novel fertility preservation options are emerging, but knowledge about these options amongst urologists and other medical professionals is lacking. Pre-pubertal boys generally do not produce haploid germ cells. Thus, strategies for fertility preservation require cryopreservation of tissue containing spermatogonial stem cells (SSCs). Few centres worldwide routinely offer this option and fertility restoration (including testicular tissue engraftment, autotransplantation of SSCs and in vitro maturation of SSCs to spermatozoa) post-thaw is experimental. In pubertal boys, the main option for fertility preservation is masturbation and cryopreservation of the ejaculate. Assisted ejaculation using penile vibratory stimulation or electroejaculation and surgical sperm retrieval can be used in a sequential manner after failed masturbation. Physicians should inform boys and parents about the gonadotoxic effects of cancer treatment and offer fertility preservation. Preclinical experience has identified challenges in pre-pubertal fertility preservation, but available options are expected to be successful when today's pre-pubertal boys with cancer become adults. By contrast, fertility preservation in pubertal boys is clinically proven and should be offered to all patients undergoing cancer treatment.