Cresyl Diphenyl Phosphate exposure induces reproductive functional defects in men and male mice

Cresyl Diphenyl Phosphate (CDP), as a novel organophosphate esters (OPEs), achieves widely used and exposed in multiple industries. However, its male reproductive toxicity and underlying mechanism remains unclear. In vivo, male mice were gavaged with CDP (0, 4, 20, or 100 mg/kg/d) for 8 weeks. And we treated TM3, TM4 and GC-2 cells with 0, 10, 25, and 50 μM CDP for 24 h to detect its reproductive toxicity effect in vitro. In our study, we revealed that CDP inhibited proliferation and induced apoptosis in mice testis and GC-2 cells, thereby leading to the decreased sperm quality. In mechanism, CDP trigger the oxidative stress and ROS production, thus partially causing DNA damage and cell apoptosis. Moreover, CDP exposure causes injury to Ledyig cells and Sertoli cells, thus disturbing the testicular microenvironment and inhibiting spermatogonia proliferation. In conclusion, this research reveals multiple adverse impacts of CDP on the male reproductive system and calls for further study of the toxicological effects of CDP on human health.

The constructive and destructive impact of autophagy on both genders' reproducibility, a comprehensive review

Reproduction is characterized by a series of massive renovations at molecular, cellular, and tissue levels. Recent studies have strongly tended to reveal the involvement of basic molecular pathways such as autophagy, a highly conserved eukaryotic cellular recycling, during reproductive processes. This review comprehensively describes the current knowledge, updated to September 2022, of autophagy contribution during reproductive processes in males including spermatogenesis, sperm motility and viability, and male sex hormones and females including germ cells and oocytes viability, ovulation, implantation, fertilization, and female sex hormones. Furthermore, the consequences of disruption in autophagic flux on the reproductive disorders including oligospermia, azoospermia, asthenozoospermia, teratozoospermia, globozoospermia, premature ovarian insufficiency, polycystic ovarian syndrome, endometriosis, and other disorders related to infertility are discussed as well.Abbreviations: AKT/protein kinase B: AKT serine/threonine kinase; AMPK: AMP-activated protein kinase; ATG: autophagy related; E2: estrogen; EDs: endocrine disruptors; ER: endoplasmic reticulum; FSH: follicle stimulating hormone; FOX: forkhead box; GCs: granulosa cells; HIF: hypoxia inducible factor; IVF: in vitro fertilization; IVM: in vitro maturation; LCs: Leydig cells; LDs: lipid droplets; LH: luteinizing hormone; LRWD1: leucine rich repeats and WD repeat domain containing 1; MAP1LC3: microtubule associated protein 1 light chain 3; MAPK: mitogen-activated protein kinase; MTOR: mechanistic target of rapamycin kinase; NFKB/NF-kB: nuclear factor kappa B; P4: progesterone; PCOS: polycystic ovarian syndrome; PDLIM1: PDZ and LIM domain 1; PI3K: phosphoinositide 3-kinase; PtdIns3P: phosphatidylinositol-3-phosphate; PtdIns3K: class III phosphatidylinositol 3-kinase; POI: premature ovarian insufficiency; ROS: reactive oxygen species; SCs: Sertoli cells; SQSTM1/p62: sequestosome 1; TSGA10: testis specific 10; TST: testosterone; VCP: vasolin containing protein.

Triphenyltin disrupts the testicular microenvironment and reduces sperm quality in adult male rats

Triphenyltin (TPT) is organotin that is widely used as an anti-fouling agent and has been determined to have male reproductive toxicity. The objective of this study was to investigate the effects of TPT on the testicular microenvironment and sperm quality in male rats. Adult male Sprague Dawley rats were daily gavaged with TPT (0, 0.5, 1, and 2 mg/kg body weight) for 28 days. The results showed that TPT dose-dependently decreased sperm count and sperm motility, interfered with sperm histone-protamine replacement process, and significantly increased sperm deformity rate, but did not affect sperm DNA integrity. TPT at 2 mg/kg significantly decreased the gene and protein expressions of testis PCNA and Ki67, and dose-dependently decreased the number of PCNA-positive cells and Ki67-positive cells. TPT at 1 mg/kg and/or 2 mg/kg down-regulated the expression of StAR, SF1, P450scc, FSHR, WT1, DDX4 and PLZF, and up-regulated SOX9 expression. Simultaneously, TPT reduced serum testosterone levels at each dose and dose-dependently decreased the expression of Leydig cells regulators (INSL3, IGF1, inhibin B) and Sertoli cells regulators (GDNF, FGF2, CXCL12, ETV5), altered testicular microenvironment. Further, in vitro, we treated TM3 (Leydig cells), TM4 (Sertoli cells) and GC-1 (spermatogonia) cells with 1-100 nM TPT for 24 h. 100 nM TPT significantly down-regulated the expression of the above indicators in TM3 and TM4 cells but did not directly affect the cell proliferation ability of GC-1. However, after co-culturing TPT-treated TM3 or TM4 cells with GC-1 cells, it was found that TPT-treated TM3 or TM4 cells dose-dependently reduced the gene and protein expression levels of PCNA and Ki67 and increased cytotoxicity in GC-1 cells. In conclusion, TPT impairs the proliferative ability of spermatogonia by disrupting the microenvironment of Leydig cells and Sertoli cells, which in turn leads to low sperm quality in adult male rats.

Water Blooms-A Potential Threat to Male Reproduction: Clues From Aquatics and Rodents

Toxic cyanobacteria blooms are a potential threat to global aquatic ecosystems and human health. Microcystin-leucine-arginine (MC-LR) is the most toxic variant of microcystins (MCs), and exposure to MCs can damage the male reproductive system. Two electronic databases were searched for controlled studies of rodents and fishes published before September 2020. Effect sizes were calculated for eight main reproductive parameters, including sperm count, sperm motility, sperm morphology, serum testosterone, testis weight, serum follicle stimulating hormone (FSH), serum luteinising hormone (LH) and serum estradiol. Nine meta-analyses of individual parameters were conducted using R version 4.0.2. Fifteen studies were included in the meta-analysis. In the studies of rodents, exposure to MC-LR by intraperitoneal injection or intragastric administration yielded statistically significant effects on sperm count (standardised mean difference (SMD) = -1.7426 (95% CI: -2.2098 to -1.2754)), abnormal sperm rate (SMD = 1.6714 (95% CI: 0.9702 to 2.3726)), sper5% CI: -3.9811 to -1.7834)), testis weight (SMD = -2.8822 (95% CI: -3.9811 to -1.7834)) and serum FSH (SMD = 0.4707 (95% CI: 0.0659 to 0.8756) changes in serum testosterone (SMD = 0.5521 (95% CI: 0.1652; 0.9391)) and estradiol (SMD = 0.6398 (95% CI: 0.1896 to 1.0900)) concentrations are considered to be statistically significant. Dose-response analysis reflected the dynamic changes of male reproductive function caused by MC. Short-term exposure to MC-LR can affect the function of the male reproductive system in rodents and fish. Elevated dosage or extended exposure time may worsen the damage. Human-related research on MC-LR exposure is very necessary to protect health and the water environment.

Beneficial Effects of Quercetin on Microcystin-LR Induced Tight Junction Defects

Quercetin has numerous functions including antioxidant and anti-inflammatory effects. The beneficial effect of quercetin against microcystin-LR (MC-LR)-induced testicular tight junctions (TJs) defects in vitro and in vivo were investigated. Significant reductions in transepithelial electrical resistance, occludin, and zonula occludens-1(ZO-1) levels were detected in the MC-LR-treated TM4 cells, and quercetin attenuated these effects. Interestingly, quercetin suppressed MC-LR-induced phosphorylation of protein kinase B (AKT). It effectively inhibited the accumulation of reactive oxygen species (ROS) in cells stimulated by MC-LR. In addition, ROS inhibitors blocked the TJ damage that is dependent on the AKT signaling pathway induced by MC-LR. In conclusion, our results suggest that alleviates MC-LR-impaired TJs by suppressing the ROS-regulated activation of the AKT pathway.

Microcystin-leucine-arginine induces apical ectoplasmic specialization disassembly

Microcystin-leucine-arginine (MC-LR) has been identified to be a hazardous material to cause hepatotoxicity. In this study, mice were exposed to MC-LR dissolved in drinking water at doses of 1, 10, 20 and 30 μg/L for 90 and 180 days, respectively. We validated MC-LR accelerated spermatid exfoliation and caused large vacuoles in testes, reducing sperm count and increasing percentage of morphologically abnormal sperm. Furthermore, we found MC-LR induced the apical ectoplasmic specialization (ES) disassembly by disrupting F-actin organization. Further studies identified that downregulation of Palladin, the actin crosslinking protein, might be associated with disassembly of the apical ES in mice testis following MC-LR exposure. We also confirmed that MC-LR disrupted the interaction between Palladin and other actin-related proteins and thus impeded the F-actin organization. Additionally, we found that autophagy initiated by AMPK/ULK1 signaling pathway mediated the degradation of Palladin in Sertoli cells challenged with MC-LR. Following exposure to MC-LR, reduced PP2A activity and upregulated expression of LKB1 and CAMKK2 could activate AMPK. In conclusion, these results revealed MC-LR induced the degradation of Palladin via AMPK/ULK1-mediated autophagy, which might result in the apical ES disorder and spermatid exfoliation from spermatogenic epithelium. Our work may provide a new perspective to understand MC-LR-induced male infertility.

Influence of microcystins-LR (MC-LR) on autophagy in human neuroblastoma SK-N-SH cells

Microcystin-LR (MC-LR) variant exposure poses a potential health hazard to ecosystem, animals, and humans. Previously investigators showed that autophagy plays a key role in MC-LR induced cytotoxicity immortalized murine ovarian granular KK-1 cells and rat Sertoli cells. Recently exposure to MC-LR via drinking water was reported to accumulate in mouse brain with associated adverse oxidant and inflammatory responses. However, autophagy the physiological mechanism required for cells to degrade their own impaired organelles to maintain their homeostasis has not been determined with respect to MC-LR actions on the central nervous system (CNS). Thus, the aim of this study was to examine the effects of MC-LR on autophagy using human neuroblastoma SK-N-SH cells as CNS model. Data demonstrated that after treatment with 15 or 30 µmol/L MC-LR for 48 hr significantly reduced survival rate was noted in SK-N-SH cells. MC-LR increased the expression levels of autophagy-related proteins light chain 3 (LC3) II/I and p62 in SK-N-SH cells, resulting in the accumulation of LC3 and increased intracellular free calcium ion levels. Data indicated that MC-LR induced adverse effects on the CNS as evidenced by decreased cellular survival associated with inhibition of autophagy flux and consequent enhanced autophagosomes accumulation.

Anaerobic degradation of microcystin-LR by an indigenous bacterial Enterobacter sp. YF3

Microcystin-LR (MC-LR), a known hepatotoxin present in drinking water, and contaminated food and algal dietary supplements poses a threat to environmental and public health and thus needs to be removed. Previously microbial aerobic degradation was considered the predominant catabolic process for MC-LR inactivation, but the potential role of anaerobic microbes still needs to be determined. In our study an anaerobic MC-degrading bacterium Enterobacter sp. YF3 was isolated and identified that was capable of degrading MC-LR. Under optimal conditions the anaerobic Enterobacter sp. YF3 displayed a MC-degrading rate of 0.34 µg/ml/day. This process was dependent on temperature, pH and MC-LR concentration. Further the extracellular secretion of metabolites of anaerobic bacterium degraded MC-LR at 0.22 µg/ml/day. The parent MC-LR as well as two MC-degrading products was identified by high performance liquid chromatography (HPLC). The anaerobic MC-degrading Enterobacter sp. bacterium metabolized MC-LR independent of MC-degrading genes mlrABCD. Data indicate that anaerobic Enterobacter sp. YF3 produces MC-degrading products via a pathway that acts independently of mlrABCD genes which may add to the arsenal of bacteria to degrade microcystins.

A transcriptomic regulatory network among miRNAs, piRNAs, circRNAs, lncRNAs and mRNAs regulates microcystin-leucine arginine (MC-LR)-induced male reproductive toxicity

Microcystin-leucine arginine (MC-LR) which is produced by cyanobacteria is a potent toxin for the reproductive system. Our previous work has demonstrated that both acute and chronic reproductive toxicity engendered by MC-LR can result in the decline of sperm quality and damage of testicular structures in male mice. The present study was designed to investigate the impact of chronic low-dose exposure to MC-LR on the regulation of RNA networks including mRNA, microRNA (miRNA), piwi-associated RNA (piRNA), covalently closed circular RNA (circRNA) and long non-coding RNA (lncRNA) in testicular tissues. By high-throughput sequencing analysis, 1091 mRNAs, 21 miRNAs, 644 piRNAs, 278 circRNAs and 324 lncRNAs were identified to be significantly altered in testicular tissues treated with MC-LR. We performed gene ontology (GO) analysis to ascertain the biological functions of differentially expressed genes. Among the altered 21 miRNAs and 644 piRNAs, the miRNA chr13_8977, which is a newly discovered species, and the piRNA mmu_piR_027558 were dramatically down-regulated after exposure to MC-LR. Consistently, both mRNA levels and protein expression levels of their predicted targets were increased significantly when chr13_8977 and mmu_piR_027558 were each down-regulated. Testicular structures, germ cell apoptosis and sperm quality were also affected by the altered expression of chr13_8977 and mmu_piR_027558 severally. We further investigated the differential expression of circRNAs and lncRNAs and their biological functions in testicular tissues following treatment with chronic low-dose exposure to MC-LR. We also constructed a competing endogenous RNA (ceRNA) network to predict the functions of the altered expressed RNAs using MiRanda. Our study suggested a crucial role for the potential network regulation of miRNAs, piRNAs, circRNAs, lncRNAs and mRNAs impacting the cytotoxicity of MC-LR in testicular tissues, which provides new perspectives in the development of diagnosis and treatment strategies for MC-LR-induced male reproductive toxicity.

Microcystin-LR disturbs testicular development of giant freshwater prawn Macrobrachium rosenbergii

Microcystins (MCs) are produced by cyanobacterial blooms and known for their hepatotoxicity. They could cause serious damage to the reproduction of higher vertebrate mice and fish. However, few studies have focused on the reproductive toxicity of MCs to invertebrates. Giant freshwater prawn Macrobrachium rosenbergii are highly cultivated in China. During their breeding process, M. rosenbergii are often infested by cyanobacteria blooms. In the present study, to investigate the toxic effect of MCs on the testicular development of M. rosenbergii. Male M. rosenbergii were exposed to environmental relevant concentration of MC-LR for 1, 2 and 3 weeks. Results showed that MC-LR entered M. rosenbergii testis, down-regulated hemolymph testosterone (T) levels, and damaged testicular germ cells, mitochondria and cell junctions, and inhibited testicular development. Moreover, MC-LR could significantly induce the expression of gonadal development related genes in testis and eyestalk). The present results indicate that MC-LR can disrupt the testicular development of M. rosenbergii by affecting T levels and gonadal development related genes in the testis and eyestalk.

From the Cover: Roles of mmu_piR_003399 in Microcystin-Leucine Arginine-Induced Reproductive Toxicity in the Spermatogonial Cells and Testis

Our previous work has demonstrated that microcystin-leucine arginine (MC-LR) is a potent toxin for the reproductive system of male mice and it exerts cytotoxicity in spermatogonial cells, resulting in the constitutional and functional changes of the mouse testis. The present study was designed to investigate the functions of P-element-induced wimpy (piwi)-interacting RNAs (piRNAs) in MC-LR-induced reproductive toxicity in male mice. We observed an increase in the mmu_piR_003399 level in spermatogonial cells and mouse testicular tissues following treatment with MC-LR. Moreover, our data confirmed that cyclin-dependent kinase 6 (CDK6) was the target gene of mmu_piR_003399. Increases in the concentration of mmu_piR_003399 were correlated with the reduced expression of CDK6 both in vitro and in vivo. mmu_piR_003399 induced cell cycle arrest at the G1-phase, down-regulated sperm counts and sperm motility, and compromised sperm morphology. On the contrary, suppressing the expression of mmu_piR_003399 could substantially attenuate MC-LR-induced pathology in mice including cell cycle arrest, reduced mature sperm counts, sperm viability loss and abnormal sperm morphology. Furthermore, our data supported that mmu_piR_003399 existed in mouse serum and plasma, and its level was increased in MC-LR-treated mice. In conclusion, we demonstrate that mmu_piR_003399 plays a crucial role in regulating MC-LR-induced reproductive toxicity.

Subcellular localization of microcystin in the liver and the gonads of medaka fish acutely exposed to microcystin-LR

Among the diverse toxic components produced by cyanobacteria, microcystins (MCs) are one of the most toxic and notorious cyanotoxin groups. Besides their potent hepatotoxicity, MCs have been revealed to induce potential reproductive toxicity in various animal studies. However, little is still known regarding the distribution of MCs in the reproductive organ, which could directly affect reproductive cells. In order to respond to this question, an acute study was conducted in adult medaka fish (model animal) gavaged with 10 μg.g^-1 body weight of pure MC-LR. The histological and immunohistochemical examinations reveal an intense distribution of MC-LR within hepatocytes along with a severe liver lesion in the toxin-treated female and male fish. Besides being accumulated in the hepatocytes, MC-LR was also found in the connective tissue of the ovary and the testis, as well as in oocytes and degenerative spermatocyte-like structures but not spermatocytes. Both liver and gonad play important roles in the reproductive process of oviparous vertebrates. This observation constitutes the first observation of the presence of MC-LR in reproductive cells (female, oocytes) of a vertebrate model with in vivo study. Our results, which provide intracellular localization of MC-LR in the gonad, advance our understanding of the potential reproductive toxicity of MC-LR in fish.

Glutathione peroxidase-1 overexpressing transgenic mice are protected from neurotoxicity induced by microcystin-leucine-arginine

Although it has been well-recognized that microcystin-leucine-arginine (MCLR), the most common form of microcystins, induces neurotoxicity, little is currently known about the underlying mechanism for this neurotoxicity. Here, we found that MCLR (10 ng/μL/mouse, i.c.v.) induces significant neuronal loss in the hippocampus of mice. MCLR-induced neurotoxicity was accompanied by oxidative stress, as shown by a significant increase in the level of 4-hydroxynonenal, protein carbonyl, and reactive oxygen species (ROS). Superoxide dismutase-1 (SOD-1) activity was significantly increased, but glutathione peroxidase (GPx) level was significantly decreased following MCLR insult. In addition, MCLR significantly inhibited GSH/GSSG ratio, and significantly induced NFκB DNA binding activity. Because reduced activity of GPx appeared to be critical for the imbalance between activities of SODs and GPx, we utilized GPx-1 overexpressing transgenic mice to ascertain the role of GPx-1 in this neurotoxicity. Genetic overexpression of GPx-1 or NFκB inhibitor pyrrolidine dithiocarbamate (PDTC) significantly attenuated MCLR-induced hippocampal neuronal loss in mice. However, PDTC did not exert any additive effect on neuroprotection mediated by GPx-1 overexpression, indicating that NFκB is a neurotoxic target of MCLR. Combined, these results suggest that MCLR-induced neurotoxicity requires oxidative stress associated with failure in compensatory induction of GPx, possibly through activation of the transcription factor NFκB.

N-acetylcysteine protects against microcystin-LR-induced endoplasmic reticulum stress and germ cell apoptosis in zebrafish testes

Previous studies have shown that microcystin-LR (MCLR) is a reproductive toxicant that induces germ cell apoptosis in the testes, but the underlying mechanisms have not been well understood. In this study, we investigated that MCLR induces germ cell apoptosis is through activation of endoplasmic reticulum (ER) stress and N-acetylcysteine (NAC), an antioxidant could protect against germ cell apoptosis by inhibiting the ER stress. Healthy male zebrafish were intraperitoneally injected with NAC (500 nM), beginning at 2 h before different doses of MCLR (0, 50, 100, 200 μg/kg). As expected, acute MCLR exposure resulted in oxidative stress and germ cell apoptosis in zebrafish testes. Further analysis showed that NAC significantly alleviated MCLR-induced testicular germ cell apoptosis and inhibited the caspase-dependent apoptotic proteins. Meanwhile H&E staining showed that NAC could rescue testicular damage induced by MCLR. Moreover, MCLR induced activation of ER stress which consequently triggered apoptosis in zebrafish testes. Interestingly, NAC was effective in improving the total antioxidant capacity (T-AOC) level and activity of antioxidant enzymes in NAC pretreated groups. NAC significantly attenuated MCLR-induced upregulation of GRP78 in testes. In addition, NAC significantly attenuated MCLR-triggered testicular eIF2s1 and MAPK8 activation, indicating that NAC counteracts MCLR-induced unfolded protein response (UPR) in testes. Taken together, the results observed in this study suggested that ER stress plays a critical role in germ cell apoptosis exposed to MCLR and NAC could protect against apoptosis via inhibiting ER stress in zebrafish testes.

Exposure routes and health effects of microcystins on animals and humans: A mini-review

Microcystins (MCs) pollution has quickly risen in infamy and has become a major problem to public health worldwide. MCs are a group of monocyclic hepatotoxic peptides, which are produced by some bloom-forming cyanobacteria in water. More than 100 different MCs variants posing a great threat to animals and humans due to their potential carcinogenicity have been reported. To reduce MCs risks, the World Health Organization has set a provisional guideline of 1 μg/L MCs in human's drinking water. This paper provides an overview of exposure routes of MCs into the human system and health effects on different organs after MCs exposure including the liver, intestine, brain, kidney, lung, heart and reproductive system. In addition, some evidences on human poisoning and deaths associated with MCs exposure are presented. Finally, in order to protect human life against the health threats posed by MCs, this paper also suggests some directions for future research that can advance MCs control and minimize human exposure to MCs.

Genetic overexpression of glutathione peroxidase-1 attenuates microcystin-leucine-arginine-induced memory impairment in mice

Microcystin-leucine-arginine (MCLR) is the most common form of microcystins, which are environmental toxins produced by cyanobacteria, and its hepatotoxicity has been well-documented. However, the neurotoxic potential of MCLR remains to be further elucidated. In the present study, we investigated whether intracerebroventricular (i.c.v.) infusion of MCLR induces mortality and neuronal loss in the hippocampus of mice. Because we found that MCLR impairs memory function in the hippocampus at a low dose (4 ng/μl/mouse, i.c.v.) without a significant neuronal loss, we focused on this dose for further analyses. Results showed that MCLR (4 ng/μl/mouse, i.c.v.) significantly increased oxidative stress (i.e., malondialdehyde, protein carbonyl, and synaptosomal ROS) in the hippocampus. In addition, MCLR significantly increased superoxide dismutase (SOD) activity without corresponding induction of glutathione peroxidase (GPx) activity, and thus led to significant decrease in the ratio of GPx/SODs activity. The GSH/GSSG ratio was also significantly reduced after MCLR treatment. GPx-1 overexpressing transgenic mice (GPx-1 Tg) were significantly protected from MCLR-induced memory impairment and oxidative stress. The DNA binding activity of nuclear factor erythroid-derived 2-related factor 2 (Nrf2) in these mice was significantly enhanced, and the ratios of GPx/SODs activity and GSH/GSSG returned to near control levels in the hippocampus. Importantly, memory function exhibited a significant positive correlation with the ratios of GPx/SODs activity and GSH/GSSG in the hippocampus of MCLR-treated non-transgenic (non-Tg)- and GPx-1 Tg-mice. Combined, our results suggest that MCLR induces oxidative stress and memory impairment without significant neuronal loss, and that GPx-1 gene constitutes an important protectant against MCLR-induced memory impairment and oxidative stress via maintaining antioxidant defense system homeostasis, possibly through the induction of Nrf2 transcription factor.

Microcystin-LR degradation utilizing a novel effective indigenous bacterial community YFMCD1 from Lake Taihu

Microcystins (MC) produced by species of cyanobacteria including Microcystis, Anabaena, and Aphanizomenon are a group of monocyclic hepatotoxins posing serious threat to public health. Microcystin-LR (MC-LR) is the most toxic and frequently encountered microcystin variant in the environment, and thus removal of this toxin using bacteria was shown to be a reliable, efficient, and cost-effective method that avoids utilization of chemicals that may produce potentially harmful by-products. The aim of this study was to determine whether a novel indigenous bacterial community designated YFMCD1 was effective in destroying MC. In addition, the influence of environmental factors such as temperature, MC concentration, and pH was examined on the effectiveness of YFMCD1 to degrade MC-LR. MC-degradation products were identified by high performance liquid chromatography coupled with an ultra-high resolution LTQ Orbitrap Velos Pro ETD mass spectrometry equipped with electrospray ionization interface (HPLC-ESI-MS). MC-LR underwent maximal degradation at rate of 0.5 µg/ml/hr with YFMCD1 containing Klebsiella sp. termed YFMCD1-1 or Stenotrophomonas sp. termed YFMCD1-2. Moreover, Adda (3-amino-9-methoxy-2, 6, 8-trimethyl-10-phenyldeca-4, 6-dienoic acid) is a constituent within the MC-LR molecule found to be responsible for biological activity expression and critical for MC-induced toxicity, which is also degraded by YFMCD1. The results showed that YFMCD1 effectively degraded MC-LR. The degradation rate was significantly affected by temperature, pH, and MC-LR concentrations. Data indicate that this bacterial community may prove beneficial in bioremediation of lakes containing MC.

Characterization of in vitro effects of microcystin-LR on intestinal epithelial cells

The intestinal epithelium is a single-cell layer that provides an important barrier against natural toxins. Microcystin-LR (MC-LR), a cyclic heptapeptide, is one of the best known toxins able to alter the functions of intestine. This study evaluated the toxic effects and the possible mechanisms of MC-LR on barrier function of the intestinal epithelial cells. Intestinal epithelial cells (IEC-6) were exposed to 0, 6.25, 12.5, 25 and 50 μM MC-LR. Cell viability significantly decreased, while the ratio of apoptotic cells increased after exposure to 12.5μM and higer concentration of MC-LR. As expected, the integrity of a polarized IEC-6 monolayer was affected by MC-LR exposure, as demonstrated by a decrease in the transepithelial electrical resistance (TEER) values, becoming most pronounced at 50μM, 24 h. No effects were detected on the protein expression levels of the tight junction protein claudin at 50μM. However, the expression of occludin and zonula occludens-1 (ZO-1) declined. Furthermore, MC-LR can immigrate into IEC-6 cells. The activity of protein phosphatases 2A (PP2A) decreased from the concentration of 12.5 μM, showing a dose-dependent decline. These results provide new information that strengthens the concept that the intestinal epithelium is important targets for toxic effects of water contaminants like MC-LR. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 1539-1547, 2017.

Roles of piRNAs in microcystin-leucine-arginine (MC-LR) induced reproductive toxicity in testis on male offspring

In the present study, we evaluated the toxic effects on the testis of the male offspring of MC-LR exposure during fetal and lactational periods. Pregnant females were distributed into two experimental groups: control group and MC-LR group which were exposed to 0 and 10 μg/L of MC-LR, respectively, through drinking water separately during fetal and lactational periods. At the age of 30 days after birth, the male offspring were euthanized. The body weight, testis index, and histomorphology change were observed and the global changes of piwi-interacting RNA (piRNA) expression were evaluated. The results revealed that MC-LR was found in the testis of male offspring, body weight and testis index decreased significantly, and testicular tissue structure was damaged in the MC-LR group. In addition, the exposure to MC-LR resulted in an altered piRNA expression profile and an increase of the cell apoptosis and a decrease of the cell proliferation in the testis of the male offspring. It was reasonable to speculate that the toxic effects on reproductive system of the male offspring in MC-LR group might be mediated by piRNAs through the regulation of the target genes. As far as we are aware, this is the first report showing that MC-LR could play a role in disorder of proliferative and cell apoptosis in the testis of the male offspring by the maternal transmission effect of toxicity.

miR-541 Contributes to Microcystin-LR-Induced Reproductive Toxicity through Regulating the Expression of p15 in Mice

Microcystin-leucine arginine (MC-LR) is a harmful cyanotoxin produced by cyanobacteria. MC-LR can exert endocrine-disrupting activities in many organisms. We have previously demonstrated that MC-LR exerts both acute and chronic reproductive toxicity in male mice, resulting in a decline in sperm quality and damage to testicular structure. Moreover, we also observed extensive alterations in a panel of microRNAs in spermatogonial cells after exposure to MC-LR. In this study, we have confirmed that miR-541 was significantly increased both in GC-1 cells (in vitro) and in mouse testes (in vivo) after exposure to MC-LR. Our data support that p15 was the target gene of miR-541. Increase in miR-541 led to a reduction of p15 and murine double minute2 (MDM2), promoting the activation of p53 signaling and MC-LR-mediated cell apoptosis. Moreover, cells responded to MC-LR with reduced viability and increased apoptosis. Consistently, inhibiting miR-541 could upregulate the expression of p15 and MDM2, resulting in the downregulation of phospho-p53. Downregulation of miR-541 promoted cell viability by reducing MC-LR-induced cell apoptosis. In conclusion, we demonstrate here a crucial role for miR-541 in MC-LR-induced toxic effects on the reproductive system, in an attempt to provide a rational strategy for the diagnosis and treatment of MC-LR-induced impairment in the reproductive system.

Microcystin-LR induces mitochondria-mediated apoptosis in human bronchial epithelial cells

The present study aimed to investigate the toxicity of microcystin-LR (MC-LR) and to explore the mechanism of MC-LR-induced apoptosis in human bronchial epithelial (HBE) cells. HBE cells were treated with MC-LR (1, 10, 20, 30 and 40 µg/ml) alone or with MC-LR (0, 2.5, 5 and 10 µg/ml) and Z-VAD-FMK (0, 10, 20, 40, 60, 80, 100, 120 and 140 µM), which is a caspase inhibitor, for 24 and 48 h. Cell viability was assessed via an MTT assay and the half maximal effective concentration of MC-LR was determined. The optimal concentration of Z-VAD-FMK was established as 50 µm, which was then used in the subsequent experiments. MC-LR significantly inhibited cell viability and induced apoptosis of HBE cells in a dose-dependent manner, as detected by an Annexin V/propidium iodide assay. MC-LR induced cell apoptosis, excess reactive oxygen species production and mitochondrial membrane potential collapse, upregulated Bax expression and downregulated B-cell lymphoma-2 expression in HBE cells. Moreover, western blot analysis demonstrated that MC-LR increased the activity levels of caspase-3 and caspase-9 and induced cytochrome c release into the cytoplasm, suggesting that MC-LR-induced apoptosis is associated with the mitochondrial pathway. Furthermore, pretreatment with Z-VAD-FMK reduced MC-LR-induced apoptosis by blocking caspase activation in HBE cells. Therefore, the results of the present study suggested that MC-LR is capable of significantly inhibiting the viability of HBE cells by inducing apoptosis in a mitochondria-dependent manner. The present study provides a foundation for further understanding the mechanism underlying the toxicity of MC-LR in the respiratory system.

Sex-dependent effects of microcystin-LR on hypothalamic-pituitary-gonad axis and gametogenesis of adult zebrafish

While microcystins (MCs) have been reported to exert reproductive toxicity on fish with a sex-dependent effect, the underlying mechanism has been rarely investigated. In the present study, zebrafish were exposed to 1, 5 and 20 μg/L MC-LR for 30 d. The gonad-somatic index declined in all treated males. 17β-estradiol (E2), testosterone (T), 11-keto testosterone (11-KT) and follicle-stimulating hormone (FSH) levels increased in serum from all treated females, while T, FSH and luteinizing hormone (LH) levels changed in all treated males. Histomorphological observation showed that MC-LR exposure evidently retarded oogenesis and spermatogenesis. Transcriptional changes of 22 genes of the hypothalamic-pituitary-gonad (HPG) axis exhibited sex-specific responses, and the relationship between gene transcriptions and gametogenesis was evaluated by principle component analysis (PCA). Major contributors to PC1 (gnrh2, gnrhr3, ar, lhr, hmgra, hmgrb and cyp19a) were positively correlated with the number of post-vitellogenic oocytes, while PC1 (gnrh2, lhβ, erβ, fshr, cyp11a and 17βhsd) were positively correlated with the number of spermatozoa. The protein levels of 17βHSD and CYP19a were affected in both females and males. In conclusion, this study first investigated the sex-dependent effects of microcystins on fish reproduction and revealed some important molecular biomarkers related to gametogenesis in zebrafish suffered from MC-LR.

A review of reproductive toxicity of microcystins

Animal studies provide strong evidence of positive associations between microcystins (MCs) exposure and reproductive toxicity, representing a threat to human reproductive health and the biodiversity of wild life. This paper reviews current knowledge of the reproductive toxicity of MCs, with regard to mammals, fishes, amphibians, and birds, mostly in males. Toxicity of MCs is primarily governed by the inhibition of protein phosphatases 1 and 2A (PP1 and PP2A) and disturbance of cellular phosphorylation balance. MCs exposure is related to excessive production of reactive oxygen species (ROS) and oxidative stress, leading to cytoskeleton disruption, mitochondria dysfunction, endoplasmic reticulum (ER) stress, and DNA damage. MCs induce cell apoptosis mediated by the mitochondrial and ROS and ER pathways. Through PP1/2A inhibition and oxidative stress, MCs lead to differential expression/activity of transcriptional factors and proteins involved in the pathways of cellular differentiation, proliferation, and tumor promotion. MC-induced DNA damage is also involved in carcinogenicity. Apart from a direct effect on testes and ovaries, MCs indirectly affect sex hormones by damaging the hypothalamic-pituitary-gonad (HPG) axis and liver. Parental exposure to MCs may result in hepatotoxicity and neurotoxicity of offspring. We also summarize the current research gaps which should be addressed by further studies.

Effects of Microcystin-LR Exposure on Spermiogenesis in Nematode Caenorhabditis elegans

Little is known about the effect on spermiogenesis induced by microcystin-leucine arginine (MC-LR), even though such data are very important to better elucidate reproductive health. In the current work, with the aid of nematode Caenorhabditis elegans (C. elegans) as an animal model, we investigated the defects on spermiogenesis induced by MC-LR. Our results showed that MC-LR exposure induced sperm morphology abnormality and caused severe defects of sperm activation, trans-activation, sperm behavior and competition. Additionally, the expression levels of spe-15 were significantly decreased in C. elegans exposed to MC-LR lower than 16.0 μg/L, while the expression levels of spe-10 and fer-1 could be significantly lowered in C. elegans even exposed to 1.0 μg/L of MC-LR. Therefore, the present study reveals that MC-LR can induce adverse effects on spermiogenesis, and those defects of sperm functions may be induced by the decreases of spe-10, spe-15 and fer-1 gene expressions in C. elegans.

NF-κB plays a key role in microcystin-RR-induced HeLa cell proliferation and apoptosis

Microcystins (MCs) are well-known cyanobacterial toxins produced in eutrophic waters and can act as potential carcinogens and have caused serious risk to human health. However, pleiotropic even paradoxical actions of cells exposure to MCs have been reported, and the mechanisms of MC-induced tumorigenesis and apoptosis are still unknown. In this study, we performed the first comprehensive in vitro investigation on carcinogenesis associated with nuclear factor kappa B (NF-κB) and its downstream genes in HeLa cells (Human cervix adenocarcinoma cell line from epithelial cells) exposure to MC-RR. HeLa cells were treated with 0, 20, 40, 60, and 80 µg/mL MC-RR for 4, 8, 12, and 24 h. HeLa cells presented dualistic responses to different doses of MCs. CCK8 assay showed that MC-RR exposure evidently enhanced cell viability of HeLa cells at lower MCs doses. Cell cycle and apoptosis analysis revealed that lower MCs doses promoted G1/S transition and cell proliferation while higher doses of MCs induced apoptosis, with a dose-dependent manner. Electrophoretic mobility shift assay (EMSA) revealed that MC-RR could increase/decrease NF-κB activity at lower/higher MC-RR doses, respectively. Furthermore, the expression of NF-κB downstream target genes including c-FLIP, cyclinD1, c-myc, and c-IAP2 showed the same variation trend as NF-κB activity both at mRNA and protein levels, which were induced by lower doses of MC-RR and suppressed by higher doses. Our data verified for the first time that NF-κB pathway may mediate MC-induced cell proliferation and apoptosis and provided a better understanding of the molecular mechanism for potential carcinogenicity of MC-RR.

Regulation of microcystin-LR-induced toxicity in mouse spermatogonia by miR-96

Microcystin (MC)-LR is a cyclic heptapeptide that acts as a potent reproductive system toxin, especially by decreasing sperm quality through affecting spermatogonia. However, the molecular mechanisms of MC-induced spermatogonial cytotoxicity still remain unclear. The present study was designed to investigate changes in microRNA (miRNA) profiles and their potential functions in spermatogonia (GC-1 cell line) following treatment with MC-LR. With microarray analysis, 101 miRNAs were identified to be significantly altered in GC-1 cells treated with MC-LR. Among the 25 miRNAs associated with spermatogenesis, miR-96 was down-regulated most dramatically and thus selected for further functional analysis. Deleted-in azoospermia-associated protein 2 (DAZAP2) was predicted to have a binding sequence for miR-96 within its 3'-untranslated region. Fluorescent reporter assay confirmed that DAZAP2 was the target gene of miR-96. The expression of DAZAP2 decreased significantly when miR-96 was up-regulated. Consistently, down-regulation of miR-96 significantly increased the level of DAZAP2. Up-regulation of miR-96 promoted cell viability in GC-1 cells as a result of exposure to MC-LR. Our study suggested a crucial role for miR-96 in the regulation of cytotoxic effects of MC-LR in spermatogonia, which provides new perspectives in the diagnosis and treatment strategies for MC-induced male infertility.