Low dose of fire retardant, 2,2',4,4'-tetrabromodiphenyl ether (BDE47), stimulates the proliferation and differentiation of progenitor Leydig cells of male rats during prepuberty

Update of the risk assessment of polybrominated diphenyl ethers (PBDEs) in food

The European Commission asked EFSA to update its 2011 risk assessment on polybrominated diphenyl ethers (PBDEs) in food, focusing on 10 congeners: BDE-28, -47, -49, -99, -100, -138, -153, -154, -183 and ‑209. The CONTAM Panel concluded that the neurodevelopmental effects on behaviour and reproductive/developmental effects are the critical effects in rodent studies. For four congeners (BDE-47, -99, -153, -209) the Panel derived Reference Points, i.e. benchmark doses and corresponding lower 95% confidence limits (BMDLs), for endpoint-specific benchmark responses. Since repeated exposure to PBDEs results in accumulation of these chemicals in the body, the Panel estimated the body burden at the BMDL in rodents, and the chronic intake that would lead to the same body burden in humans. For the remaining six congeners no studies were available to identify Reference Points. The Panel concluded that there is scientific basis for inclusion of all 10 congeners in a common assessment group and performed a combined risk assessment. The Panel concluded that the combined margin of exposure (MOET) approach was the most appropriate risk metric and applied a tiered approach to the risk characterisation. Over 84,000 analytical results for the 10 congeners in food were used to estimate the exposure across dietary surveys and age groups of the European population. The most important contributors to the chronic dietary Lower Bound exposure to PBDEs were meat and meat products and fish and seafood. Taking into account the uncertainties affecting the assessment, the Panel concluded that it is likely that current dietary exposure to PBDEs in the European population raises a health concern.

Mechanisms of Male Reproductive Toxicity of Polybrominated Diphenyl Ethers

Polybrominated diphenyl ethers (PBDE) are a group of flame retardants used in a variety of artificial materials. Despite being phased out in most industrial countries, they remain in the environment and human tissues due to their persistence, lipophilicity, and bioaccumulation. Populational and experimental studies demonstrate the male reproductive toxicity of PBDEs including increased incidence of genital malformations (hypospadias and cryptorchidism), altered weight of testes and other reproductive tissues, altered testes histology and transcriptome, decreased sperm production and sperm quality, altered epigenetic regulation of developmental genes in spermatozoa, and altered secretion of reproductive hormones. A broad range of mechanistic hypotheses of PBDE reproductive toxicity has been suggested. Among these hypotheses, oxidative stress, the disruption of estrogenic signaling, and mitochondria disruption are affected by PBDE concentrations much higher than concentrations found in human tissues, making them unlikely links between exposures and adverse reproductive outcomes in the general population. Robust evidence suggests that at environmentally relevant doses, PBDEs and their metabolites may affect male reproductive health via mechanisms including AR antagonism and the disruption of a complex network of metabolic signaling.

Characterization of 2,2'4,4'-Tetrabromodiphenyl ether (BDE47)-induced testicular toxicity via single-cell RNA-sequencing

Background

The growing male reproductive diseases have been linked to higher exposure to certain environmental compounds such as 2,2′,4,4′-tetrabromodiphenyl ether (BDE47) that are widely distributed in the food chain. However, the specific underlying molecular mechanisms for BDE47-induced male reproductive toxicity are not completely understood.

Methods

Here, for the first time, advanced single-cell RNA sequencing (ScRNA-seq) was employed to dissect BDE47-induced prepubertal testicular toxicity in mice from a pool of 76 859 cells.

Results

Our ScRNA-seq results revealed shared and heterogeneous information of differentially expressed genes, signaling pathways, transcription factors, and ligands-receptors in major testicular cell types in mice upon BDE47 treatment. Apart from disruption of hormone homeostasis, BDE47 was discovered to downregulate multiple previously unappreciated pathways such as double-strand break repair and cytokinesis pathways, indicative of their potential roles involved in BDE47-induced testicular injury. Interestingly, transcription factors analysis of ScRNA-seq results revealed that Kdm5b (lysine-specific demethylase 5B), a key transcription factor required for spermatogenesis, was downregulated in all germ cells as well as in Sertoli and telocyte cells in BDE47-treated testes of mice, suggesting its contribution to BDE47-induced impairment of spermatogenesis.

Conclusions

Overall, for the first time, we established the molecular cell atlas of mice testes to define BDE47-induced prepubertal testicular toxicity using the ScRNA-seq approach, providing novel insight into our understanding of the underlying mechanisms and pathways involved in BDE47-associated testicular injury at a single-cell resolution. Our results can serve as an important resource to further dissect the potential roles of BDE47, and other relevant endocrine-disrupting chemicals, in inducing male reproductive toxicity.

Tetramethyl bisphenol a inhibits leydig cell function in late puberty by inducing ferroptosis

Tetramethyl bisphenol A (TMBPA) is a commonly used bisphenol analog, used as a fire retardant. However, whether it inhibits the function of Leydig cells in late puberty remains unclear. In this study, 35-day-old male Sprague-Dawley rats were gavaged with 0, 10, 100, and 200 mg/kg body weight TMBPA for 21 days. TMBPA significantly reduced serum testosterone levels at 10 mg/kg and higher doses without altering serum luteinizing hormone and follicle-stimulating hormone levels. TMBPA significantly increased serum iron concentraion while reducing the ratio of serum glutathione (GSH) and GSH/GSSG (oxidized glutathione disulfide). In addition, TMBPA significantly increased testicular iron amount at 10 mg/kg and higher doses and malondialdehyde level at 200 mg/kg. TMBPA down-regulated the expression of Leydig cell genes, including Nr5a1, Star, Scarb1, Insl3, Cyp11a1, Cyp17a1, Hsd17b3, and Hsd11b1, and their proteins. In addition, TMBPA markedly down-regulated the expression of genes in the ferroptosis pathway (Tp53, Slc7a11, Sod1, Sod2, Cat, Sqstm1, Keap1, and Hmox1). TMBPA significantly reduced the levels of ferroptosis pathway proteins (TP53, SLC7A11, GPX4, SQSTM1, KEAP1, NRF2, and HMOX1) in Leydig cells in vivo. Immature and adult Leydig cell culture in vitro also showed that TMBPA significantly reduced testosterone concentrations in the medium, which can be reversed by a ferroptosis inhibitor. After 24 h of culture in primary Leydig cells at 10 and 50 μM, TMBPA significantly induced reactive oxygen species and lowered the mitochondrial membrane potential. TMBPA also altered protein levels in the ferroptosis pathway in Leydig cells in vitro. In conclusion, TMBPA directly inhibits the activity of rat Leydig cell steroidogenic enzymes and induces the ferroptosis of Leydig cells, thereby inhibiting the testosterone synthesis of Leydig cells in the late puberty.

Research Progress of PCNA in Reproductive System Diseases

Reproductive system diseases have become a public health problem that endangers human physical and mental health. The causes of reproductive diseases are complex and diverse. From a biological point of view, abnormal cell proliferation may affect important physiological functions of reproductive organs and cause various gynecological or andrological diseases. Proliferating cell nuclear antigen (PCNA) is the most commonly used indicator for detecting cell proliferation activity. The up- or downregulation of its expression is of great significance in reproductive system diseases. This review summarizes the significance of the latest research on PCNA expression in reproductive system diseases.