From the Cover: An Animal-Free In Vitro Three-Dimensional Testicular Cell Coculture Model for Evaluating Male Reproductive Toxicants

Rapid identification of reproductive toxicants among environmental chemicals using an in vivo evaluation of gametogenesis in budding yeast Saccharomyces cerevisiae

Infertility affects ∼12 % of couples, with environmental chemical exposure as a potential contributor. Of the chemicals that are actively manufactured, very few are assessed for reproductive health effects. Rodents are commonly used to evaluate reproductive effects, which is both costly and time consuming. Thus, there is a pressing need for rapid methods to test a broader range of chemicals. Here, we developed a strategy to evaluate large numbers of chemicals for reproductive toxicity via a yeast, S. cerevisiae high-throughput assay to assess gametogenesis as a potential new approach method (NAM). By simultaneously assessing chemicals for growth effects, we can distinguish if a chemical affects gametogenesis only, proliferative growth only or both. We identified a well-known mammalian reproductive toxicant, bisphenol A (BPA) and ranked 19 BPA analogs for reproductive harm. By testing mixtures of BPA and its analogs, we found that BPE and 17 β-estradiol each together with BPA showed synergistic effects that worsened reproductive outcome. We examined an additional 179 environmental chemicals including phthalates, pesticides, quaternary ammonium compounds and per- and polyfluoroalkyl substances and found 57 with reproductive effects. Many of the chemicals were found to be strong reproductive toxicants that have yet to be tested in mammals. Chemicals having affect before meiosis I division vs. meiosis II division were identified for 16 gametogenesis-specific chemicals. Finally, we demonstrate that in general yeast reproductive toxicity correlates well with published reproductive toxicity in mammals illustrating the promise of this NAM to quickly assess chemicals to prioritize the evaluation for human reproductive harm.

Recent Progress of In Vitro 3D Culture of Male Germ Stem Cells

Male germline stem cells (mGSCs), also known as spermatogonial stem cells (SSCs), are the fundamental seed cells of male animal reproductive physiology. However, environmental influences, drugs, and harmful substances often pose challenges to SSCs, such as population reduction and quality decline. With advancements in bioengineering technology and biomaterial technology, an increasing number of novel cell culture methods and techniques have been employed for studying the proliferation and differentiation of SSCs in vitro. This paper provides a review on recent progress in 3D culture techniques for SSCs in vitro; we summarize the microenvironment of SSCs and spermatocyte development, with a focus on scaffold-based culture methods and 3D printing cell culture techniques for SSCs. Additionally, decellularized testicular matrix (DTM) and other biological substrates are utilized through various combinations and approaches to construct an in vitro culture microenvironment suitable for SSC growth. Finally, we present some perspectives on current research trends and potential opportunities within three areas: the 3D printing niche environment, alternative options to DTM utilization, and advancement of the in vitro SSC culture technology system.

Alternatives to animal testing in toxicity testing: Current status and future perspectives in food safety assessments

The development of alternative methods to animal testing has gained great momentum since Russel and Burch introduced the "3Rs" concept of Reduction, Refinement, and Replacement of animals in safety testing in 1959. Several alternatives to animal testing have since been introduced, including but not limited to in vitro and in chemico test systems, in silico models, and computational models (e.g., [quantitative] structural activity relationship models, high-throughput screens, organ-on-chip models, and genomics or bioinformatics) to predict chemical toxicity. Furthermore, several agencies have developed robust integrated testing strategies to determine chemical toxicity. The cosmetics sector is pioneering the adoption of alternative methodologies for safety evaluations, and other sectors are aiming to completely abandon animal testing by 2035. However, beyond the use of in vitro genetic testing, agencies regulating the food industry have been slow to implement alternative methodologies into safety evaluations compared with other sectors; setting health-based guidance values for food ingredients requires data from systemic toxicity, and to date, no standalone validated alternative models to assess systemic toxicity exist. The abovementioned models show promise for assessing systemic toxicity with further research. In this paper, we review the current alternatives and their applicability and limitations in food safety evaluations.

The role of small GTPases in bisphenol AF-induced multinucleation in comparison with dibutyl phthalate in the male germ cells

The goal of this study is to examine bisphenol AF (BPAF)-induced multinucleation (MNC) in comparison with dibutyl phthalate (DBP), known to induce MNC in mouse gonocytes in vivo. We performed image-based single-cell high content analysis (HCA) in the mouse spermatogonia C18-4 cells treated with various concentrations of BPAF and DBP. BPAF as low as 5 µM was cytotoxic and resulted in 40% cell death of the C18-4 cells after 72 h. HCA revealed that 5 µM of BPAF significantly increased the number of MNC by an average of 3.6-fold. DBP did not induce MNC in the doses we tested. Cytokinesis is tightly regulated by various small GTPase-signaling pathways. We, therefore, tested 5 selective GTPase inhibitors and found that Y27632, a ROCK inhibitor, reduced the BPAF-induced MNC by nearly 30%. Inhibition of Cdc42 by ML141 conversely increased the number of BPAF-induced MNC. We performed a hierarchical cluster analysis of the HCA data and demonstrated that the cytoskeletal disruption by BPAF was reversely modified by Y27632. We found that mRNA expression of genes regulating Rho and Rac GTPase activities, p190RhoGap and MgcRacGap, was altered in BPAF-treated C18-4 cells in a time-dependent manner. Multinucleated gonocytes are often indicators of disease pathologies. Our results provided the first evidence of mechanisms of the dual toxicity by BPAF to male germ cells, which induces chromosome endoreplication without the coordinated cytokinetic cellular components. The unique genotoxic mechanism of forming multinucleated germ cells suggests a novel mode of action in the male repro-toxicity concern over the increasingly ubiquitous presence of BPA analogs.

The toxic effect of bisphenol AF and nanoplastic coexposure in parental and offspring generation zebrafish

Microplastics (MPs) and bisphenol AF (BPAF) are two environmental pollutants that usually coexist in the natural environment. Studies of MPs or BPAF have gradually increased in recent years, but few studies have focused on the combination toxic effects. In this study, the subchronic model of adult zebrafish was exposed to 1 mg/L nanolevel microplastics and 200 μg/L BPAF for 45 days; the parental zebrafish were spawning every 3 days during exposure, and the effects of continuous poisoning were examined on the offspring after 1-9 spawns. The results showed that single BPAF exposure or BPAF and nanoplastic coexposure can both decrease the number of eggs laid and the locomotor behavior of parental zebrafish and impact the hatching rate, mortality, body length and locomotor behavior of offspring zebrafish, especially in 7-9 spawn. BPAF were accumulated in parental zebrafish intestinal in 334.62 ng/g in BPAF group and 594.52 ng/g in nm+BPAF group, and accumulated in whole offspring zebrafish for 281.6 ng/g in BPAF group and 321.46 ng/g in nm+BPAF group. Neurodevelopmental, inflammation, apoptosis and oxidative stress-related genes were also significantly increased after 7-9 spawn. In addition, the exacerbated accumulation in the BPAF+nm group in parental and offspring zebrafish may be the reason for the accelerated toxic effect in the present research. In this study, we investigated the combined effects of nanoplastics and BPAF on parental and offspring zebrafish in the aquatic environment to identify the accumulative toxic effects and provide new experimental support for assessing the effects of coexposure on aquatic organisms.

Cordycepin mitigates spermatogenic and redox related expression in H2O2-exposed Leydig cells and regulates testicular oxidative apoptotic signalling in aged rats

CONTEXT

Cordycepin (COR), from Cordyceps militaris L., (Cordycipitaceae), is a valuable agent with immense health benefits.

OBJECTIVE

The protective effects of COR in ageing-associated oxidative and apoptosis events in vivo and hydrogen peroxide (H₂O₂)-exposed spermatogenesis gene alterations in TM3 Leydig cells was investigated.

MATERIALS AND METHODS

Male Sprague-Dawley rats were divided into young control (YC), aged control (AC) and COR treated (COR-20) aged groups. COR-20 group received daily doses of COR (20 mg/kg) for 6 months. Cell viability and hormone levels were analysed by MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] and enzyme immunoassay kits with COR treated at 1, 5, and 10 μg/mL. Oxidative enzymes, spermatogenic, and apoptotic expression in testis tissues were evaluated by Western blotting and real-time RT-PCR.

RESULTS

COR treatment (1, 5, and 10 μg/mL) significantly (p < 0.05 ∼ p < 0.001) inhibited the H₂O₂-induced decrease in the percentage of viable cells (from 63.27% to 71.25%, 85.67% and 93.97%, respectively), and reduced the malondialdehyde (MDA) content (from 4.28 to 3.98, 3.14 and 1.78 nM MDA/mg protein, respectively). Further, the decreased antioxidant enzymes (glutathione-S-transferase mu5, glutathione peroxidase 4 and peroxiredoxin 3), spermatogenesis-related factors (nectin-2 and inhibin-α) and testosterone levels in H₂O₂-exposed TM3 cells were significantly (p < 0.05 ∼ p < 0.001) ameliorated by COR. In aged rats, COR (20 mg/kg) restored the altered enzymatic and non-enzymatic antioxidative status and attenuated the apoptotic p53 and Bax/Bcl-2 expression significantly (p < 0.05).

CONCLUSION

COR might be developed as a potential agent against ageing-associated and oxidative stress-induced male infertility.

Characterization of primary canine Sertoli cells as a model to test male reproductive toxicant

Sertoli cells play critical roles in regulating spermatogenesis and testis development by providing structural and nutritional support. This study aimed to develop a standard protocol for canine Sertoli cell isolation and culture; and characterize its biological features, functionality, and application of compound toxicity testing. Canine testicles were received from the neuter clinic, and three-step of enzymatic digestion was applied to isolate Sertoli cells. We characterized the growth and purity of Sertoli cells with the expression of SOX9, GATA4, and Clusterin. In addition, we selected cadmium as a model toxicant to evaluate the toxic responses in the newly established Sertoli cells using High-content Analysis (HCA). With our optimized protocol, the purity of isolated Sertoli cells was above 95%, as determined with Sertoli cell-specific protein markers of SOX9 and GATA4. More importantly, primary Sertoli cell populations could be expanded rapidly in vitro, passaged (up to seven), and cryopreserved. The HCA-based assay revealed that cadmium at 1 μM induced both disruptions of cytoskeletal and DNA damage responses. Furthermore, we established an HCA assay with the newly isolated and optimized culture of canine Sertoli cells to evaluate the epigenetic markers of histone modification. We found cadmium-induced differential changes in histone modifications H3Me3K9, H3Me3K36, H4Me3K20, and H4acK5. In summary, we have established the standardized protocol to produce canine Sertoli cells with Sertoli cell-specific phenotype. The isolation and expansion of large quantities of canine Sertoli cells will provide broad applications in studying male infertility, reproductive toxicology, testicular cancer, and cell therapy.

Comparative analysis of the testes from wild-type and Alkbh5-knockout mice using single-cell RNA sequencing

The RNA demethylase ALKBH5 is regarded as the “eraser” in N6-methyladenosine modification. ALKBH5 deficiency causes male infertility in mice; however, the mechanisms that confer disruption of spermatogenesis are not completely clear. In this study, we profiled testis samples from wild-type and Alkbh5-knockout mice using single-cell RNA sequencing. We obtained single-cell RNA sequencing data of 5,596 and 6,816 testis cells from a wild-type and a knockout mouse, respectively. There were differences detected between the transcriptional profiles of the groups at various germ cell developmental stages. This ranged from the development of spermatogonia to sperm cells, in macrophages, Sertoli cells, and Leydig cells. We identified the differentially expressed genes related to spermatogenesis in germ cells and somatic cells (Sertoli cells and Leydig cells) and evaluated their functions and associated pathways, such as chromatin-related functional pathways, through gene ontology enrichment analysis. This study provides the first single-cell RNA sequencing profile of the testes of ALKBH5-deficient mice. This highlights that ALKBH5 is an important gene for germ cell development and spermatogenesis and offers new molecular mechanistic insights. These findings could provide the basis for further research into the causes and treatment of male infertility.

In vitro testicular toxicity of environmentally relevant endocrine-disrupting chemicals: 2D vs. 3D models of prepubertal Leydig TM3 cells

The testis is a priority organ for developing alternative models to assess male reproductive health hazards of chemicals. This study characterized a 3D in vitro model of murine prepubertal Leydig TM3 cells with improved expression of steroidogenesis markers suitable for image-based screening of testicular toxicity. This 3D scaffold-free spheroid model was applied to explore the impact of prototypical endocrine-disrupting chemicals (EDCs) and environmental reprotoxicants (benzo[a]pyrene, 2- and 9-methylanthracenes, fluoranthene, triclosan, triclocarban, methoxychlor) on male reproductive health. The results were compared to the male reprotoxicity potential of EDCs assessed in a traditional monolayer (2D) culture. The testicular toxicity was dependent not only on the type of culture (2D vs. 3D models) but also on the duration of exposure. Benzo[a]pyrene and triclocarban were the most active compounds, eliciting cytotoxic effects in prepubertal Leydig cells at low micromolar concentrations, which might be a mechanism contributing to their male reprotoxicity.

Can nanomaterials induce reproductive toxicity in male mammals? A historical and critical review

The nanotechnology enabled the development of nanomaterials (NMs) with a variety of industrial, biomedical, and consumer applications. However, the mechanism of action (MoA) and toxicity of NMs remain unclear, especially in the male reproductive system. Thus, this study aimed to perform a bibliometric and systematic review of the literature on the toxic effects of different types of NMs on the male reproductive system and function in mammalian models. A series of 236 articles related to the in vitro and in vivo reproductive toxicity of NMs in mammalian models were analyzed. The data concerning the bioaccumulation, experimental conditions (types of NMs, species, cell lines, exposure period, and routes of exposure), and the MoA and toxicity of NMs were summarized and discussed. Results showed that this field of research began in 2005 and has experienced an exponential increase since 2012. Revised data confirmed that the NMs have the ability to cross the blood-testis barrier and bioaccumulate in several organs of the male reproductive system, such as testis, prostate, epididymis, and seminal vesicle. A similar MoA and toxicity were observed after in vitro and in vivo exposure to NMs. The NM reproductive toxicity was mainly related to ROS production, oxidative stress, DNA damage and apoptosis. In conclusion, the NM exposure induces bioaccumulation and toxic effects on male reproductive system of mammal models, confirming its potential risk to human and environmental health. The knowledge concerning the NM reproductive toxicity contributes to safety and sustainable use of nanotechnology.

The Open Challenge of in vitro Modeling Complex and Multi-Microbial Communities in Three-Dimensional Niches

The comprehension of the underlying mechanisms of the interactions within microbial communities represents a major challenge to be faced to control their outcome. Joint efforts of in vitro, in vivo and ecological models are crucial to controlling human health, including chronic infections. In a broader perspective, considering that polymicrobial communities are ubiquitous in nature, the understanding of these mechanisms is the groundwork to control and modulate bacterial response to any environmental condition. The reduction of the complex nature of communities of microorganisms to a single bacterial strain could not suffice to recapitulate the in vivo situation observed in mammals. Furthermore, some bacteria can adapt to various physiological or arduous environments embedding themselves in three-dimensional matrices, secluding from the external environment. Considering the increasing awareness that dynamic complex and dynamic population of microorganisms (microbiota), inhabiting different apparatuses, regulate different health states and protect against pathogen infections in a fragile and dynamic equilibrium, we underline the need to produce models to mimic the three-dimensional niches in which bacteria, and microorganisms in general, self-organize within a microbial consortium, strive and compete. This review mainly focuses, as a case study, to lung pathology-related dysbiosis and life-threatening diseases such as cystic fibrosis and bronchiectasis, where the co-presence of different bacteria and the altered 3D-environment, can be considered as worst-cases for chronic polymicrobial infections. We illustrate the state-of-art strategies used to study biofilms and bacterial niches in chronic infections, and multispecies ecological competition. Although far from the rendering of the 3D-environments and the polymicrobial nature of the infections, they represent the starting point to face their complexity. The increase of knowledge respect to the above aspects could positively affect the actual healthcare scenario. Indeed, infections are becoming a serious threat, due to the increasing bacterial resistance and the slow release of novel antibiotics on the market.

Effects of boric acid on cell death and oxidative stress of mouse TM3 Leydig cells in vitro

BACKGROUND

Boron (B) is an abundant element on earth and presents at physiological pH in the form of boric acid (BA). It has both positive and negative effects on biological systems. BA and sodium borates have been considered as being toxic to the reproduction system in animal experiments. Unfortunately, the molecular mechanism underlying the toxic effects of BA is not fully understood.

METHODS

Here, we demonstrate the influence of BA on mouse TM3 Leydig cells which are male reproductive system cells targeted by BA exposure. The cytotoxicity was evaluated by MTT and NRU assays. Annexin V-FITC/PI double staining kit, mitochondria membrane potential (ΔΨm) assay kit with JC-1 and caspase-3 colorimetric assay kit were used to indicate the cell death pathway. To estimate the role of oxidative stress in BA induced toxicity, glutathione (GSH) level, catalase (CAT) and superoxide dismutase (SOD) activities were measured manually.

RESULTS

The cell viability assays showed that BA was not cytotoxic within the tested concentrations up to 1000 μM. Sub-toxic concentrations were used for detecting oxidative stress status. BA exposure was significantly reduced GSH level at 1000 μM and CAT activity in a concentration-dependent manner. However, SOD activity was increased at the tested concentrations (100-1000 μM). Moreover, ΔΨm was significantly decreased at 500 and 1000 μM of BA, while caspase-3 activity was not changed apparently.

CONCLUSION

These findings demonstrated that BA is not cytotoxic and apoptotic but may slightly induces oxidative stress in TM3 Leydig cells at higher concentrations.

High-Content Image-Based Single-Cell Phenotypic Analysis for the Testicular Toxicity Prediction Induced by Bisphenol A and Its Analogs Bisphenol S, Bisphenol AF, and Tetrabromobisphenol A in a Three-Dimensional Testicular Cell Co-culture Model

Emerging data indicate that structural analogs of bisphenol A (BPA) such as bisphenol S (BPS), tetrabromobisphenol A (TBBPA), and bisphenol AF (BPAF) have been introduced into the market as substitutes for BPA. Our previous study compared in vitro testicular toxicity using murine C18-4 spermatogonial cells and found that BPAF and TBBPA exhibited higher spermatogonial toxicities as compared with BPA and BPS. Recently, we developed a novel in vitro three-dimensional (3D) testicular cell co-culture model, enabling the classification of reproductive toxic substances. In this study, we applied the testicular cell co-culture model and employed a high-content image (HCA)-based single-cell analysis to further compare the testicular toxicities of BPA and its analogs. We also developed a machine learning (ML)-based HCA pipeline to examine the complex phenotypic changes associated with testicular toxicities. We found dose- and time-dependent changes in a wide spectrum of adverse endpoints, including nuclear morphology, DNA synthesis, DNA damage, and cytoskeletal structure in a single-cell-based analysis. The co-cultured testicular cells were more sensitive than the C18 spermatogonial cells in response to BPA and its analogs. Unlike conventional population-averaged assays, single-cell-based assays not only showed the levels of the averaged population, but also revealed changes in the sub-population. Machine learning-based phenotypic analysis revealed that treatment of BPA and its analogs resulted in the loss of spatial cytoskeletal structure, and an accumulation of M phase cells in a dose- and time-dependent manner. Furthermore, treatment of BPAF-induced multinucleated cells, which were associated with altered DNA damage response and impaired cellular F-actin filaments. Overall, we demonstrated a new and effective means to evaluate multiple toxic endpoints in the testicular co-culture model through the combination of ML and high-content image-based single-cell analysis. This approach provided an in-depth analysis of the multi-dimensional HCA data and provided an unbiased quantitative analysis of the phenotypes of interest.

Evaluation of an in vitro mouse testis organ culture system for assessing male reproductive toxicity

BACKGROUND

Development of an in vitro system capable of producing mature sperm remains a challenging goal, with only few successes reported. Such a system, could be used to test agents for potential toxicity to the male reproductive system; to explore this, we exposed immature mouse testis fragments in culture to ethinylestradiol (EE), a well-known testicular toxicant in vivo.

METHODS

Testis fragments from postnatal day 5 mice were cultured in Albumax I medium. After 24 hr of culture, fragments were treated with 0.01, 0.1 or 1 nM EE, then harvested after 20 days in culture and examined for histology or gene expression measures by quantitative PCR.

RESULTS

There was substantial variability between fragments in the degree of spermatogenesis observed. The percentage of seminiferous tubules containing any dead germ cells increased as a result of EE exposure in a dose dependent fashion. This was accompanied with a decreased percentage of tubules with round spermatids. Expression of estrogen receptor 1, cytochrome P450, family 11, subfamily a, and polypeptide 1 also was reduced, depending on the dose.

CONCLUSION

These gene expression changes in the testis fragments are similar to those seen after animals have been exposed to EE. Gene expression changes in testis fragments are encouraging, but the variability across samples will need to be reduced for this in vitro system to become a generally applicable method for assessing testicular toxicants.

Mechanistic Insights into PFOS-Mediated Sertoli Cell Injury

Studies have proven that per- and polyfluoroalkyl substances are harmful to humans, most notably perfluorooctanesulfonate (PFOS). PFOS induces rapid disorganization of actin- and microtubule (MT)-based cytoskeletons in primary cultures of rodent and human Sertoli cells, perturbing Sertoli cell gap junction communication, thereby prohibiting Sertoli cells from maintaining cellular homeostasis in the seminiferous epithelium to support spermatogenesis. PFOS perturbs several signaling proteins/pathways, such as FAK and mTORC1/rpS6/Akt1/2. The use of either an activator of Akt1/2 or overexpression of a phosphomimetic (and constitutively active) mutant of FAK or connexin 43 has demonstrated that such treatment blocks PFOS-induced Sertoli cell injury by preventing actin- and MT-based cytoskeletal disorganization. These findings thus illustrate an approach to manage PFOS-induced reproductive dysfunction.