Genotoxic and cytotoxic effects of aflatoxin on the reproductive system: Focus on cell cycle dynamics and apoptosis in testicular tissue

Aflatoxins (AFs) are inevitable environmental contaminants that are detrimental to human and animal health. AFs interfere with metabolic processes, metabolizing into different hydroxylated derivatives in the liver, as well as mechanistically induce ROS accumulation, S-phase arrest, DNA damage, and cell apoptosis. Chronic consumption of aflatoxin-contaminated foods can adversely affect the male reproductive system, cause testicular damage, prevent testosterone synthesis, decline sperm quality, and cause infertility. Oxidative stress is the fundamental pathogenesis of aflatoxin-induced reproductive toxicity. The overproduction of reactive oxygen substances can cause testicular failure and disturb the process of spermatogenesis. Mitochondria are susceptible to being impaired by oxidative stress, and its damage is associated with infertility. AFs also disturb the process of spermatogenesis by disrupting the regulation of genes related to the progression of the cell cycle such as cyclins and inducing genes related to apoptosis, thereby weakening fertility and negatively affecting the testicular endocrine potential by suppressing androgen synthesis. Additionally, AFs downregulate ERα expression, potentially negatively impacting spermatogenesis by enhancing the apoptotic mechanism. In this review, we provide new insights into the genotoxic and cytotoxic effects of AFB1 on the male reproductive system with a focus on the cell cycle and apoptosis destruction of testicular tissue.

Histological differences between the central and peripheral areas of the testes of busulfan-administered mice

Busulfan is an anticancer drug known to cause serious damage to seminiferous tubules in the testes and deplete germ cells in human and animal models. The testicular artery is anastomosed with deferential and cremasteric arteries and is divided into capsular arteries, which give rise to the centripetal arteries and then recurrent arteries. The arterial blood in the testicular tissue is supplied by such a consequent system of arterial vessels, in order from the peripheral to the central area. As anticancer drugs are generally distributed throughout the whole body via the bloodstream and the running and distribution of arteries differ among the testicular areas, we hypothesized that the efficacy of busulfan differs in different testicular areas, particularly between the central and peripheral areas. In this study, busulfan was intraperitoneally injected at 40 mg/kg body weight into C57BL/6J male mice. After 28 days, in busulfan-treated mice, the diameters of seminiferous tubules were significantly higher in the central than in the peripheral area of the testes. The seminiferous tubular areas also significantly decreased in the peripheral areas compared with the central areas. The number of germ cells per seminiferous tubule was significantly higher in the central than in the peripheral area. Sertoli cell nuclei were detached into the lumen in the peripheral area. The number of Leydig cells was significantly lower in the peripheral areas. These data suggest that the effects of busulfan differ between the central and peripheral areas of the testis at 4 weeks after busulfan administration.

Maternal exposure to PM2.5 disrupting offspring spermatogenesis through induced sertoli cells apoptosis via inhibin B hypermethylation in mice

Particulate Matter 2.5 (PM_2.5) disrupts endocrine functions and may negatively affect sperm quality and quantity in males; however, the long-term effects and potential mechanisms of this effect are unknown. This study aimed to investigate the epigenetic mechanism of maternal exposure to PM_2.5-induced inhibin B hypermethylation in male offspring. In this experiment design, pregnant C57BL/6 mice were treated with two doses of PM_2.5 (4.8 and 43.2 mg/kg bw). The membrane control group was given a sampling membrane and the control group received nothing. Following the formation of the vaginal plug, intratracheal instillation of PM_2.5 was administered every three days until delivery of the pups. To assess the effect of PM_2.5 in vitro, TM4 cells, a Sertoli-like cell line, was treated with different concentrations (0, 25, 50, 100 μg/mL) of PM_2.5 for 24 h. The results displayed that Sperm motility, as well as the number of adult offspring, was decreased in the PM_2.5 exposed group relative to the untreated controls. Increased vacuolization was observed in the Sertoli cells of mice that were exposed to PM_2.5 in utero. The levels of inhibin and testosterone were reduced and the levels of LH and FSH increased in the PM_2.5 groups relative to the untreated controls. In vitro, PM_2.5 resulted in cell cycle inhibition as well as increased apoptosis in TM4 cells. Moreover, PM_2.5-induced inhibin B hypermethylation and activation of the p21/Cleaved Caspase-3 pathway resulted in TM4 cell apoptosis that was rescued through the use of a DNA methylation inhibitor. Together, our data suggest that prenatal exposure to PM_2.5 results in inhibin B hypermethylation and can activate the p21/Cleaved Caspase-3 pathway, resulting in Sertoli cell apoptosis, aberrant secretion of androgen binding protein, and decreased testosterone, thus resulting in the inhibition of spermatogenesis.

Induction of autophagy via the ROS-dependent AMPK-mTOR pathway protects copper-induced spermatogenesis disorder

Copper (Cu) is a necessary micronutrient at lower concentration, while excessive Cu exposure or Cu homeostasis disorders can lead to toxicity. The mechanism of male reproductive toxicity induced by Cu is still unknown. This study aims to investigate whether autophagy plays an important role in copper-induced spermatogenesis disorder in vivo and vitro. The present study showed that copper sulfate (CuSO₄) might significantly promote autophagy level in the testis and mouse-derived spermatogonia cell line GC-1 spg cells. Concurrently, CuSO₄ could induce autophagy via AMPK-mTOR pathway that downregulated p-mTOR/mTOR and subsequently upregulated p-AMPKα/AMPKα as well as p-ULK1/ULK1. In the meanwhile, CuSO₄ treatment could also increase expression levels of the autophagy-related proteins. Then, the role of oxidative stress in CuSO₄-induced autophagy was investigated. The findings demonstrated that oxidative stress inhibitor (NAC) attenuated CuSO₄-induced autophagy in vivo and vitro, reversing the activation for AMPK-mTOR pathway. Additionally, the study also investigated how autophagy worked under the spermatogenesis disorder induced by CuSO₄. Inhibition of autophagy could decrease cell viability, and enhance the ROS accumulation and apoptosis in the GC-1 cells, meanwhile, the spermatogenesis disorder, oxidative stress and histopathological changes were increased in the testis. Furthermore, co-treatment with the apoptosis inhibitor (Z-VAD-FMK) could decrease the spermatogenesis disorder but not influence autophagy. Besides, the crosslink between autophagy and ferroptosis were also measured, the data showed that inhibition of autophagy could suppress CuSO₄-induced ferroptosis in in vivo and vitro. Altogether, abovementioned results indicated that CuSO₄ induced autophagy via oxidative stress-dependent AMPK-mTOR pathway in the GC-1 cells and testis, and autophagy activation possibly led to the generation of protection mechanism through oxidative damage and apoptosis inhibition, however, autophagy also aggravate CuSO₄ toxicology through promoting ferroptosis. Overall, autophagy plays a positive role for attenuating CuSO₄-induced testicular damage and spermatogenesis disorder. Our study provides a possible targeted therapy for Cu overload-induced reproduction toxicology.

In vivo and in vitro protective effects of the Wuzi Yanzong pill against experimental spermatogenesis disorder by promoting germ cell proliferation and suppressing apoptosis

ETHNOPHARMACOLOGICAL RELEVANCE

Wuzi Yanzong pill (WZYZP) is a classical traditional Chinese medicine (TCM) formula originated from the Tang dynasty. WZYZP has a long history of use for reinforcing kidney and alleviating male infertility in China.

AIM OF THE STUDY

The effect of WZYZP on male infertility and the mechanism underlying this effect was not clarified clearly. Therefore, this study aimed to investigate the protective effect of WZYZP in experimental spermatogenesis disorder via in vivo and in vitro studies, to promote the use of this formula for the treatment of spermatogenesis disorder.

MATERIAL AND METHODS

Male SD rats were exposed to tripterygium glycosides to induce experimental spermatogenesis disorder, and WZYZP was subsequently administrated at different dosages for treatment. Sperm counts, sperm motility, and serum hormone levels were detected. HE staining and TUNEL staining were performed to evaluate the pathological lesions and apoptosis of testes, respectively. Next, germ cells were isolated from spermatogenesis disorder-model rats and treated with WZYZP- containing serum at different concentrations. CCK-8 assay and flow cytometry assay were performed to detect cell proliferation and apoptosis. Immunofluorescence assay, qRT-PCR and Western blotting analyses were performed to detect the expression of Beclin 1, LC3 and TGF-β-PI3k/AKT-mTOR pathway - related factors, including TGF-β, PI3K, AKT, mTOR, 4 EBP-1 and p70S6K.

RESULTS

In vivo experiments showed that WZYZP protected against spermatogenesis disorder in model rats by improving sperm count and motility, as well as restoring serum hormone levels. HE and TUNEL staining demonstrated that the pathological injuries and cell apoptosis in testes of the model rats were alleviated by WZYZP treatment. Moreover, in vitro experiments of germ cells isolated from spermatogenesis disorder-model rats showed that WZYZP treatment increased the cell proliferation, inhibited cell apoptosis and autophagy. qRT-PCR and Western blotting assay results showed that this protective effect was associated with the regulation of the TGF-β/PI3K/AKT/mTOR signaling pathway. The expression levels of p-PI3K/PI3K, p-AKT/AKT, p-mTOR/mTOR, 4 EBP-1 and p70S6K were increased, while TGF-β was inhibited in the WZYZP treated groups.

CONCLUSION

The results showed that WZYZP could protect against experimental spermatogenesis disorder by increasing the germ cell proliferation and inhibiting their apoptosis. Our support the clinical use of this formula for the management of spermatogenesis disorder.

Mitochondrial damage are involved in Aflatoxin B1-induced testicular damage and spermatogenesis disorder in mice

Aflatoxin B₁ (AFB₁) is an unavoidable environmental pollutants, which seriously endangers human and animal health. AFB₁ has male reproductive toxicity, yet the underlying mechanisms remain inconclusive. Mitochondra are a kind of crucial organelle for maintaining spermatogenesis in testis. Thus, we hypothesized that AFB₁ can impair mitochondria to aggravate testicular damage and spermatogenesis disorder. To verify this hypothesis, 48 male mice were intragastrically administered with 0, 0.375, 0.75 or 1.5 mg/kg body weight AFB₁ for 30 days, respectively. In this study, we found AFB₁ caused testicular histopathological lesions and spermatogenesis abnormalities, with the elevation of oxidative stress (increased H₂O₂, whereas decreased SOD and GSH). Significant mitochondria structure damage of germ cells and Leydig cells, MMP loss, ATP contents reduction, and inhibited activities of mitochondrial complexes I-IV in mice testis were found in AFB₁ treatment groups. Besides, AFB₁ inhibited mitochondrial biogenesis and mitochondrial dynamics, presenting as the decreased mRNA and protein expressions of PGC-1α, Nrf1, Tfam, Drp1, Fis1, Mfn1 and Opa1. The results revealed that the mitochondrial damage were involved in AFB₁-induced testicular damage and spermatogenesis disorder, providing a considerable direction to clarify potential mechanisms of AFB₁ reproductive toxicity.