Cadmium mediated redox modulation in germline stem cells homeostasis affects reproductive health of Drosophila males

Cadmium as a male reproductive toxicant and natural and non-natural ways to tackle it: a review

Cadmium (Cd) is a naturally occurring environmental pollutant, a toxic substance that causes oxidative stress. According to epidemiological studies, the data suggested that environmental and occupational Cd exposure may be related to several diseases and severe testicular damage. However, studies are going on to explore the mechanism of Cd-induced male reproductive toxicity and its treatment strategies. Currently, researchers are focusing on naturally occurring bioactive compounds, plant extracts, and biochemical, which have better efficacy, less toxicity, and high bioavailability. This review focuses on the mechanistic effect of Cd on testicular toxicity and different categories of compounds having a beneficial impact on Cd-induced male reproductive toxicity. Some potent bioactive antioxidants are quercetin, caffeic acid phenethyl ester, cyanidin-3-O-glucoside, curcumin, and silymarin. In comparison, plant extracts are Costus afer leaf methanol extract, methanol root extract of Carpolobia lutea, red carrot methanolic extract, Panax ginseng extract, and biochemicals including melatonin, progesterone, glutamine, L-carnitine, and selenium. Advanced and more detailed studies are needed on these compounds to explore their mechanism in attenuating Cd-induced testicular toxicity and can be potential therapeutics in the future.

Single-cell RNA sequencing analysis to evaluate antimony exposure effects on cell-lineage communications within the Drosophila testicular niche

The increasing production and prevalence of antimony (Sb)-related products raise concerns regarding its potential hazards to reproductive health. Upon environmental exposure, Sb reportedly induces testicular toxicity during spermatogenesis; moreover, it is known to affect various testicular cell populations, particularly germline stem cell populations. However, the cell-cell communication resulting from Sb exposure within the testicular niche remains poorly understood. To address this gap, herein we analyzed testicular single-cell RNA sequencing data from Sb-exposed Drosophila. Our findings revealed that the epidermal growth factor receptor (EGFR) and WNT signaling pathways were associated with the stem cell niche in Drosophila testes, which may disrupt the homeostasis of the testicular niche in Drosophila. Furthermore, we identified several ligand-receptor pairs, facilitating the elucidation of intercellular crosstalk involved in Sb-mediated reproductive toxicology. We employed scRNA-seq analysis and conducted functional verification to investigate the expression patterns of core downstream factors associated with EGFR and WNT signatures in the testes under the influence of Sb exposure. Altogether, our results shed light on the potential mechanisms of Sb exposure-mediated testicular cell-lineage communications.

Molybdenum and cadmium cause blood-testis barrier dysfunction through ROS-mediated NLRP3 inflammasome activation in sheep

In this study, 24 healthy male sheep were divided into four groups: the control group, Mo group (45 mg Mo·kg-1·BW), Cd group (1 mg Cd·kg-1·BW), and Mo + Cd group (45 mg Mo·kg-1·BW + 1 mg Cd·kg-1·BW). The experiment was last for 50 d. The results showed that Mo and Cd co-exposure induced histopathological changes and ultrastructural damage, decreased the mRNA and protein expression levels of BTB (blood-testis barrier)-related factors (CX-43, ZO-1, OCLN) (P < 0.05) and the T-SOD and CAT activity (P < 0.05), increased the MDA content (P < 0.05) and the proinflammatory factors levels (P < 0.05) in sheep testes. Moreover, the results showed that a sharp decline in BTB-related factors and antioxidase activity, and a significant increase in reactive oxygen species (ROS) levels (P < 0.05) and the expression levels of NLRP3 inflammasome-related factors (P < 0.05) in primary Sertoli cells (SCs) under Mo and Cd co-exposure. However, treatment with a ROS scavenger or NLRP3 inflammasome inhibitors could relieve BTB damage and oxidative injury, reduce the production of ROS (P < 0.05) and decrease the level of inflammatory factors (P < 0.05). Overall, these results indicated that Mo and Cd co-exposure reduced BTB-related protein levels and promoted ROS production and inflammatory reactions by activating the ROS/NLRP3 inflammasome pathway in sheep testes, which eventually induced reproductive toxicity.

Cadmium-induced reproductive toxicity combined with a correlation to the oogenesis process and competing endogenous RNA networks based on a Caenorhabditis elegans model

Accumulation of the heavy metal Cadmium (Cd) in the ovaries and placenta can affect the structure and function of these organs and induce female reproductive toxicity. This toxicity may be due to Cd's similarity to estrogen and its ability to disrupt endocrine systems. However, the exact molecular mechanism by which Cd causes reproductive toxicity at the transcriptome level remains poorly understood. Hence, this study aimed to observe Cd-induced reproductive damage at the gene level, scrutinize the repercussions of Cd exposure on oogenesis, and explicate the putative pathogenesis of Cd-induced oogenesis based on Caenorhabditis elegans (C. elegans) as an in vivo model. The results showed that Cd exposure significantly decreased the number of offspring and prolonged the reproductive span of C. elegans. Cd exposure also reduced the number of cells in mitosis and the pachytene and diakinesis stages of meiosis, thereby disrupting oogenesis. Combined with transcriptional sequencing and bioinformatics analysis, a total of 3167 DEmRNAs were identified. Regarding gene expression, cul-6, mum-2, and vang-1 were found to be related to Cd-induced reproductive toxicity, and their competing endogenous RNA networks were constructed. We observed that mutations of mom-2 and vang-1 in the Wnt pathway could induce susceptibility to Cd-caused meiosis injury. In conclusion, the results indicated that Cd could impair the oogenesis of C. elegans and the Wnt pathway might serve as a protective mechanism against Cd reproductive toxicity. These findings contribute to a better understanding of the damaging effects and molecular biological mechanisms of Cd on the human reproductive system.

Single-cell RNA-sequencing reveals the transcriptional landscape of ND-42 mediated spermatid elongation via mitochondrial derivative maintenance in Drosophila testes

During spermatogenesis, mitochondria extend along the whole length of spermatid tail and offer a structural platform for microtubule reorganization and synchronized spermatid individualization, that eventually helps to generate mature sperm in Drosophila. However, the regulatory mechanism of spermatid mitochondria during elongation remains largely unknown. Herein, we demonstrated that NADH dehydrogenase (ubiquinone) 42 kDa subunit (ND-42) was essential for male fertility and spermatid elongation in Drosophila. Moreover, ND-42 depletion led to mitochondrial disorders in Drosophila testes. Based on single-cell RNA-sequencing (scRNA-seq), we identified 15 distinct cell clusters, including several unanticipated transitional subpopulations or differentiative stages for testicular germ cell complexity in Drosophila testes. Enrichments of the transcriptional regulatory network in the late-stage cell populations revealed key roles of ND-42 in mitochondria and its related biological processes during spermatid elongation. Notably, we demonstrated that ND-42 depletion led to maintenance defects of the major mitochondrial derivative and the minor mitochondrial derivative by affecting mitochondrial membrane potential and mitochondrial-encoded genes. Our study proposes a novel regulatory mechanism of ND-42 for spermatid mitochondrial derivative maintenance, contributing to a better understanding of spermatid elongation.

Single-cell RNA sequencing reveals cell landscape following antimony exposure during spermatogenesis in Drosophila testes

Antimony (Sb), is thought to induce testicular toxicity, although this remains controversial. This study investigated the effects of Sb exposure during spermatogenesis in the Drosophila testis and the underlying transcriptional regulatory mechanism at single-cell resolution. Firstly, we found that flies exposed to Sb for 10 days led to dose-dependent reproductive toxicity during spermatogenesis. Protein expression and RNA levels were measured by immunofluorescence and quantitative real-time PCR (qRT-PCR). Single-cell RNA sequencing (scRNA-seq) was performed to characterize testicular cell composition and identify the transcriptional regulatory network after Sb exposure in Drosophila testes. scRNA-seq analysis revealed that Sb exposure influenced various testicular cell populations, especially in GSCs_to_Early_Spermatogonia and Spermatids clusters. Importantly, carbon metabolism was involved in GSCs/early spermatogonia maintenance and positively related with SCP-Containing Proteins, S-LAPs, and Mst84D signatures. Moreover, Seminal Fluid Proteins, Mst57D, and Serpin signatures were highly positively correlated with spermatid maturation. Pseudotime trajectory analysis revealed three novel states for the complexity of germ cell differentiation, and many novel genes (e.g., Dup98B) were found to be expressed in state-biased manners during spermatogenesis. Collectively, this study indicates that Sb exposure negatively impacts GSC maintenance and spermatid elongation, damaging spermatogenesis homeostasis via multiple signatures in Drosophila testes and therefore supporting Sb-mediated testicular toxicity.

Cadmium exposure induces pyroptosis in testicular tissue by increasing oxidative stress and activating the AIM2 inflammasome pathway

High doses of cadmium (Cd) cause irreversible injury to the reproductive system, especially testicular tissue. Studies have shown that pyroptosis is involved in Cd-induced tissue damage, but whether pyroptosis is involved in damage to testicular tissue following Cd exposure remains unclear. To investigate the mechanism of pyroptosis in testicular injury induced by Cd exposure, we used 8-week-old male C57BL/6J mice subjected to consecutive 7 days of intraperitoneal injection of cadmium chloride (CdCl₂) at concentrations of 0, 1.0 and 3.0 mg/kg. The results indicated that 3.0 mg/kg CdCl₂ significantly decreased serum testosterone levels, sperm concentration and sperm motility, while increased LDH and IL-1β levels. Testicular HE staining indicated that Cd exposure damaged the interstitial cells and increased the atypical residual bodies. Fluorescence results indicated that 3.0 mg/kg CdCl₂ increased ROS levels, DNA damage, and the number of TUNEL-positive seminiferous tubule cells in testicular tissue. Transcriptome analysis showed that Cd exposure mainly induced inflammatory and chemokine signaling pathways in testicular tissue, with upregulated mRNA levels of Aim2, and reduced mRNA levels of Nlrp3. Further analysis showed that 3.0 mg/kg CdCl₂ increased the expression of testicular HO-1, SOD2, γH2AX and PARP-1, as well as the pyroptosis-related factors GSDMD, GSDME, Caspase-1, ASC and IL-1β. In conclusion, our results provide a possible mechanism by which Cd exposure activates the AIM2 pathway by increasing oxidative stress injury to induce pyroptosis in testicular tissue. This provides a new perspective on testicular damage caused by Cd exposure.

Single and combined effect of bisphenol A with high sucrose diet on the diabetic and renal tubular dysfunction phenotypes in Drosophila melanogaster

In the present study, effect of exposure of bisphenol A (BPA) and combined exposure of BPA + HSD has been investigated on the glucose homeostasis and associated renal complications in Drosophila. Exposure of 1.0 mM BPA alone induced type 2 diabetes like condition (T2D) in adult male D. melanogaster via oxidative stress. Elevated TGF-β signaling was evident by increased expression of baboon (babo) in BPA exposed organism that stimulated the modulation of extracellular matrix (ECM) component collagen IV resulting in the fibrosis of the Malpighian tubules (MTs). Combined exposure of BPA + HSD (high sucrose diet) resulted in the increased magnitude of T2D and MTs dysfunction parameters. Taken together, the study illustrates that BPA has diabetogenic potential in exposed Drosophila that caused adverse effects on their MTs and combined exposure with BPA and HSD could aggravate the renal tubular dysfunction. The study further suggests the use of Drosophila model to study the environmental chemicals induced diabetes mediated renal dysfunction.

An in-vivo microfluidic assay reveals cardiac toxicity of heavy metals and the protective effect of metal responsive transcription factor (MTF-1) in Drosophila model

Previous toxicity assessments of heavy metals on Drosophila are limited to investigating the survival, development rate, and climbing behaviour by oral administration while cardiac toxicity of these elements have not been investigated. We utilized a microfluidic device to inject known dosages of zinc (Zn) or cadmium (Cd) into the larvae's hemolymph to expose their heart directly and study their heart rate and arrhythmicity. The effect of heart-specific overexpression of metal responsive transcription factor (MTF-1) on different heartbeat parameters and survival of Drosophila larvae was investigated. The heart rate of wild-type larvae decreased by 24.8% or increased by 11.9%, 15 min after injection of 40 nL of 100 mM Zn or 10 mM Cd solution, respectively. The arrhythmicity index of wild-type larvae increased by 58.2% or 76.8%, after injection of Zn or Cd, respectively. MTF-1 heart overexpression ameliorated these effects completely. Moreover, it increased larvae's survival to pupal and adulthood stages and prolonged the longevity of flies injected with Zn and Cd. Our microfluidic-based cardiac toxicity assay illustrated that heart is an acute target of heavy metals toxicity, and MTF-1 overexpression in this tissue can ameliorate cardiac toxicity of Zn and Cd. The method can be used for cardiotoxicity assays with other pollutants in the future.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-022-03336-7.

High-fat diet aggravates prenatal low-dose DEHP exposure induced spermatogenesis disorder: Characterization of testicular metabolic patterns in mouse offspring

Di-(2-ethylhexyl) phthalate (DEHP) is a widely used plasticizer and has been identified as a male prenatal reproductive toxicant. A high fat diet (HFD) has also been suggested as another potential disruptor of male reproductive function. Despite this potential synergism between DEHP exposure and HFD, little is known about the concomitant effects of prenatal DEHP and a subsequent HFD exposure on male offspring reproductive injury. Here we established a mouse model of prenatal exposure to DEHP (0.2 mg/kg/day) to assess the testicular development and spermatogenesis in offspring subjected to obesogenic diet during the pubertal period. Gross phenotype, hormone profiles and the testicular metabolome were analyzed to determine the underlying mechanism. We found that prenatal exposure to low-dose DEHP resulted in decreased sperm density, decreased testosterone (T) levels, increased luteinizing hormone (LH) levels and testicular germ cell apoptosis. Furthermore, these injury phenotypes were aggravated by pubertal HFD treatment. Testicular riboflavin and biotin metabolites were enriched implying their roles in contributing HFD to exacerbate offspring spermatogenesis disorders due to prenatal low-dose DEHP exposure. Our findings suggest that pubertal HFD exacerbates reproductive dysfunction associated with prenatal exposure to low-dose DEHP in male adult offspring.