Environmentally relevant concentrations of oxytetracycline and copper increased liver lipid deposition through inducing oxidative stress and mitochondria dysfunction in grass carp Ctenopharyngodon idella

Regulation of lipid metabolism in grass carp primary hepatocytes by exosomes derived from fatty hepatocytes though GRP78

Exosomes regulate lipid metabolism by carrying miRNAs, nucleic acids, and proteins, thereby influencing the function of receptor cells. Glucose-regulated protein 78 (GRP78) is also involved in the regulation of lipid metabolism. However, it remains unclear whether exosomes derived from fatty hepatocytes (OA-Exo) regulate lipid metabolism through the enrichment of GRP78. In this study, we observed the expression of GRP78 was significantly increased in fatty hepatocytes (incubating hepatocytes with oleic acid (OA) for 24 h) and OA-Exo (P < 0.05). In addition, OA-Exo (50 μg/mL) and GRP78 protein (1 μg/mL) significant increased the content of triacylglycerol (TG) and total cholesterol (TC), as well as up-regulated the expression of GRP78 and inositol-requiring enzyme-1alpha (IRE1α) protein (P < 0.05). We further used YUM70 (an inhibitor of GRP78) to inhibit endogenous GRP78, and compared with the YUM70 group, OA-Exo reversed the effect of YUM70 and increased the content of TG, TC, and the expression of GRP78 protein in hepatocytes (P < 0.05). Furthermore, the inhibition of the IRE1α pathway with 4μ8C resulted in a significant decrease in TG content compared to the control group (P < 0.05). However, when compared with the 4μ8C group, OA-Exo and GRP78 reversed the effect of 4μ8C and significantly increased TG content (P < 0.05). Taken together, these results indicated that OA-Exo activated IRE1α to promote lipid accumulation in hepatocytes through the enrichment of GRP78. This study provided a new perspective for further exploration of exosomal lipid metabolism in fish.

Mitochondria UPR stimulation by pelargonidin-3-glucoside contributes to ameliorating lipid accumulation under copper exposure

Intensification of copper pollution in the environment has led to its excessive accumulation in humans, causing oxidative stress and lipid metabolism disorders. It is necessary to look for effective targets and safe methods to alleviate copper toxicity. Pelargonidin-3-glucoside (Pg3G) is a natural anthocyanin with metal ion chelating ability and multiple physiological activities. In this study, lipid accumulation was investigated under copper exposure in Caenorhabditis elegans which can be improved by Pg3G. Transcriptome analysis revealed that differentially expressed genes are enriched in lipid metabolism and protein folding/degradation. Pg3G activated mitochondrial unfold protein response (UPRmt) to mitigate mitochondrial damage caused by copper and regulated the expression of genes involved in lipid absorption, transport, and synthesis, thereby reducing lipid levels in C. elegans. This improvement disappeared in the ubl-5 knockout strain, indicating that ubl-5 is one target of Pg3G. Meanwhile, in HepG2 cells, Pg3G enhanced the cellular antioxidant capacity by activating UPRmt for maintaining mitochondrial homeostasis, followed by inhibition of excessive lipid accumulation. Overall, these results suggested that UPRmt activation can be a strategy for mitigating lipid disorders induced by copper and Pg3G with excellent ability to resist oxidative stress specially targeted for ubl-5 has a promising application in controlling copper contamination.

Impacts of cattle management and agricultural practices on water quality through different approaches: physicochemical and ecotoxicological parameters

The intensification of livestock farming can pose risks to the environment due to the increased use of veterinary products and the generation of waste in confined areas. The quality of water bodies near livestock establishments (Areco River (A) and Doblado stream (D), San Antonio de Areco, Buenos Aires, Argentina) was studied by physicochemical parameters, metals, pesticides, emerging contaminants, and lethal and sublethal toxicity (neurotoxicity and oxidative stress) in larvae of the native amphibian Rhinella arenarum. Six sites were selected: upstream (S1A and S1D), at the level (S2A and S2D), and downstream (S3A and S3D) from the establishments. A low concentration of dissolved oxygen was observed in Doblado stream (< 2.34 mg/L). Cu, Mn, V, and Zn exceeded the limits for the protection of aquatic life at various sites. Between 24 and 34 pesticides were detected in all sites, with 2,4-D, atrazine, and metolachlor being the most recurrent. In water and sediment, the concentrations of ivermectin (S2A, 1.32 μg/L and 58.18 μg/kg; S2D, 0.8 μg/L and 85.22 μg/kg) and oxytetracycline (S2A, < 1 mg/L and < 1 mg/kg; S2D, 11.8 mg/L and 39 mg/kg) were higher at sites near the establishments. All sites caused between 30 and 38.3% of lethality and produced neurotoxicity and alterations in the reduced glutathione content. Moreover, larvae exposed to samples from all sites incorporated ivermectin. These results demonstrate the degradation of the studied sites in relation to the agricultural activities of the area, highlighting the need to take measures to protect and preserve aquatic ecosystems.

Differential effects of oxytetracycline on detoxification and antioxidant defense in the hepatopancreas and intestine of Chinese mitten crab under cadmium stress

This study aims to evaluate the effects of oxytetracycline (OTC) on detoxification and oxidative defense in the hepatopancreas and intestine of Chinese mitten crab (Eriocheir sinensis) under cadmium (Cd) stress. The crab was exposed to 0.6 μM Cd, 0.6 μM OTC, and 0.6 μM Cd plus 0.6 μM OTC for 42 days. Our results showed that in the intestine, OTC alone enhanced protein carboxylation (PC) and malondialdehyde (MDA) contents, which was associated with the increased OTC accumulation. Compared to Cd alone, Cd plus OTC increased Cd and OTC contents, and reduced detoxification (i.e., glutathione (GSH) content, gene expressions of cytochrome P450 (CYP) isoforms, 7-ethoxyresorufin O-deethylase (EROD) activity, mRNA levels and activities of glutathione peroxidase (GPx), glutathione reductase (GR) and glutathione-S-transferase (GST)), and antioxidant defense (i.e., gene expressions and activities of catalase (CAT) and superoxide dismutase (SOD)) in the intestine, leading to the increased in PC and MDA contents, suggesting that OTC had a synergistic effect on Cd-induced oxidative damage. In the hepatopancreas, although OTC alone increased OTC accumulation, it did not affect PC and MDA contents. Compared to Cd alone, Cd plus OTC reduced MDA content, which was closely related to the improvement of detoxification (i.e., GSH content, mRNA levels of CYP isoforms, EROD activity, gene expressions and activities of GPx, GR and GST), and antioxidant defense (gene expressions and activities of CAT and SOD, metallothionein content). Aryl hydrocarbon receptor (AhR) and nuclear factor E2-related factor 2 (Nrf2) transcriptional expressions were positively correlated with most detoxification- and antioxidant-related gene expressions, respectively, indicating that AhR and Nrf2 were involved in the regulation of these gene expressions. Our results unambiguously demonstrated that OTC had tissue-specific effects on Cd-induced toxicological effect in E. sinensis, which contributed to accurately evaluating Cd toxicity modulated by TCs in crab.

The azole biocide climbazole induces oxidative stress, inflammation, and apoptosis in fish gut

Climbazole is an azole biocide that has been widely used in formulations of personal care products. Climbazole can cause developmental toxicity and endocrine disruption as well as gut disturbance in aquatic organisms. However, the mechanisms behind gut toxicity induced by climbazole still remain largely unclear in fish. Here, we evaluate the gut effects by exposing grass carp (Ctenopharyngodon idella) to climbazole at levels ranging from 0.2 to 20 μg/L for 42 days by evaluating gene transcription and expression, biochemical analyses, correlation network analysis, and molecular docking. Results showed that climbazole exposure increased cyp1a mRNA expression and ROS level in the three treatment groups. Climbazole also inhibited Nrf2 and Keap1 transcripts as well as proteins, and suppressed the transcript levels of their subordinate antioxidant molecules (cat, sod, and ho-1), increasing oxidative stress. Additionally, climbazole enhanced NF-κB and iκBα transcripts and proteins, and the transcripts of NF-κB downstream pro-inflammatory factors (tnfα, and il-1β/6/8), leading to inflammation. Climbazole increased pro-apoptosis-related genes (fadd, bad1, and caspase3), and decreased anti-apoptosis-associated genes (bcl2, and bcl-xl), suggesting a direct reaction to apoptosis. The molecular docking data showed that climbazole could form stable hydrogen bonds with CYP1A. Mechanistically, our findings suggested that climbazole can induce inflammation and oxidative stress through CYP450s/ROS/Nrf2/NF-κB pathways, resulting in cell apoptosis in the gut of grass carp.

Proteomics revealed composition- and size-related regulators for hepatic impairments induced by silica nanoparticles

Along with the growing production and application of silica nanoparticles (SiNPs), increased human exposure and ensuing safety evaluation have progressively attracted concern. Accumulative data evidenced the hepatic injuries upon SiNPs inhalation. Still, the understanding of the hepatic outcomes resulting from SiNPs exposure, and underlying mechanisms are incompletely elucidated. Here, SiNPs of two sizes (60 nm and 300 nm) were applied to investigate their composition- and size-related impacts on livers of ApoE-/- mice via intratracheal instillation. Histopathological and biochemical analysis indicated SiNPs promoted inflammation, lipid deposition and fibrosis in the hepatic tissue, accompanied by increased ALT, AST, TC and TG. Oxidative stress was activated upon SiNPs stimuli, as evidenced by the increased hepatic ROS, MDA and declined GSH/GSSG. Of note, these alterations were more dramatic in SiNPs with a smaller size (SiNPs-60) but the same dosage. LC-MS/MS-based quantitative proteomics unveiled changes in mice liver protein profiles, and filtered out particle composition- or size-related molecules. Interestingly, altered lipid metabolism and oxidative damage served as two critical biological processes. In accordance with correlation analysis and liver disease-targeting prediction, a final of 10 differentially expressed proteins (DEPs) were selected as key potential targets attributable to composition- (4 molecules) and size-related (6 molecules) liver impairments upon SiNPs stimuli. Overall, our study provided strong laboratory evidence for a comprehensive understanding of the harmful biological effects of SiNPs, which was crucial for toxicological evaluation to ensure nanosafety.

An azole fungicide climbazole damages the gut-brain axis in the grass carp

Azole antifungal climbazole has frequently been detected in aquatic environments and shows various effects in fish. However, the underlying mechanism of toxicity through the gut-brain axis of climbazole is unclear. Here, we investigated the effects of climbazole at environmental concentrations on the microbiota-intestine-brain axis in grass carp via histopathological observation, gene expression and biochemical analyses, and high-throughput sequencing of the 16 S rRNA. Results showed that exposure to 0.2 to 20 μg/L climbazole for 42 days significantly disrupted gut microbiota and caused brain neurotoxicity in grass carp. In this study, there was an alteration in the phylum and genus compositions in the gut microbiota following climbazole treatment, including reducing Fusobacteria (e.g., Cetobacterium) and increasing Actinobacteria (e.g., Nocardia). Climbazole disrupted intestinal microbial abundance, leading to increased levels of lipopolysaccharide and tumor necrosis factor-alpha in the gut, serum, and brain. They passed through the impaired intestinal barrier into the circulation and caused the destruction of the blood-brain barrier through the gut-brain axis, allowing them into the brain. In the brain, climbazole activated the nuclear factor kappaB pathway to increase inflammation, and suppressed the E2-related factor 2 pathway to produce oxidative damage, resulting in apoptosis, which promoted neuroinflammation and neuronal death. Besides, our results suggested that this neurotoxicity was caused by the breakdown of the microbiota-gut-brain axis, mediated by reduced concentrations of dopamine, short chain fatty acids, and intestinal microbial activity induced by climbazole.

miRNA-seq analysis of liver tissue from largemouth bass (Micropterus salmoides) in response to oxytetracycline and enzyme-treated soy protein

The specific miRNA regulation triggered by enzyme-treated soybean protein in response to well-known stressors, such as the prophylactic use of the antimicrobial oxytetracycline, remains unknown. Hence, this study aimed to evaluate the regulatory changes of hepatic miRNAs induced by oxytetracycline and enzyme-treated soybean protein in largemouth bass dietary formulations. The experiment was designed with three groups: the normal control (NC), the oxytetracycline exposure treatment group (OTC), and the pre-treatment with enzyme-treated soybean protein before oxytetracycline exposure group (ETSP). miRNA sequencing was employed to characterize the differences between these groups. In conclusion, the NC group exhibited up-regulation of 13 host miRNAs and down-regulation of 1 miRNA compared to the OTC group, whereas the ETSP group showed an increasing trend of 36 host miRNAs and a decreasing trend of 13 host miRNAs compared to the OTC group. Nine miRNAs were identified as prudential targets for enzyme-treated soy protein, protecting the largemouth bass liver from oxytetracycline. Furthermore, gene ontology analysis revealed nine key miRNAs that mediate signaling pathways with significant differences. The cellular lipid metabolic process was identified as the most important biological process, and the propanoate metabolism pathway was highlighted as significant. These results will facilitate further exploration of the mechanism by which enzyme-treated soy protein alleviates the effects of oxytetracycline on largemouth bass in water environments.

Palmitic acid activates NLRP3 inflammasome through NF-κB and AMPK-mitophagy-ROS pathways to induce IL-1β production in large yellow croaker (Larimichthys crocea)

Studies on marine fish showed that vegetable oils substituted for excessive fish oil increased interleukin-1β (IL-1β) production. However, whether the nucleotide-binding oligomerization domain, leucine-rich repeat-containing family, pyrin domain-containing-3 (NLRP3) inflammasome has a substantial role in fatty acid-induced IL-1β production in fish remains unclear. The associated specific mechanism is also unknown. In this study, nlrp3, caspase-1 and apoptosis-associated speck-like protein containing a CARD (asc) were successfully cloned, and NLRP3 inflammasome consisted of NLRP3, caspase-1 and ASC in large yellow croaker. Primary hepatocytes of fish incubated with palmitic acid (PA) exhibited the highest expression of pro-inflammatory genes (il-1β and tnfα) and NLRP3 inflammasome related genes (nlrp3, caspase-1 and asc), caspase-1 activity and IL-1β production among different treatments. Furthermore, PA-induced NLRP3 inflammasome activation was confirmed to require two signals: the first signal was that PA promoted the NF-κB (P65) protein into the nucleus, and NF-κB increased NLRP3 promoter activity and nlrp3 transcription. The second signal was that PA inhibited AMPK phosphorylation and decreased mitophagy by inhibiting the expression of PINK and parkin proteins, thereby damaging the mitochondria that could not be effectively cleared. Mitochondrial damage generated excessive amounts of reactive oxygen species, which activated the NLRP3 inflammasome and then induced caspase-1 activity and IL-1β production. Therefore, excessive dietary PA activated NLRP3 inflammasome through NF-κB and AMPK-mitophagy-ROS pathways to induce IL-1β production, thereby leading to inflammation in fish.

Co-exposure of nanoplastics and arsenic causes neurotoxicity in zebrafish (Danio rerio) through disrupting homeostasis of microbiota-intestine-brain axis

Nanoplastics (NPs) and arsenic (As) are toxic pollutants prevalent on the earth and have gained considerable attention in recent decades. Although numerous studies reported NPs and As can cause neurotoxicity there are still significant knowledge gaps in illustrating their combined toxicity and its mechanism. In this study, the co-exposure of environmentally relevant concentrations of NPs and As caused neurobehavioral toxicity in zebrafish, as evidenced by reduced swimming ability, anxiety and impaired short-term learning memory. Potentially, its toxicity mechanism is through disrupting the homeostasis of microbiota-intestine-brain axis in zebrafish. Specifically, the co-exposure reduced the 5-hydroxytryptamine (5-HT) production in intestine, which led to lower levels of 5-HT transported by the blood circulation to the brain. Ultimately, neurobehavior was adversely affected by the reduced binding of 5-HT to its receptors. Intestine, the primary source of 5-HT, its impaired health (aggravation in oxidative stress, mitochondrial damage and histopathological alterations) induced the dysregulation in the 5-HT system, which may be induced by the increased accumulation of As in the intestine by the co-exposure. Besides, the reduced 5-HT levels were correlated with decreased Firmicutes and Protecbacteria and increased Actinobacteriota and Chloroflexi in intestines. Potentially, intestinal microbiota adversely regulates the intestine-brain axis by reducing SCFAs levels. Thus, the alteration of intestinal microbiota structure may be the other reason for the dysregulation of intestine-brain axis. In summary, co-exposure of NPs and As induced neurobehavior toxicity probably through disrupting the homeostasis of microbiota-intestine-brain axis. This study provides insights into assessing the environmental health risks of the pollution of NPs and As to aquatic organisms.

miR-20a-5p targeting mfn2-mediated mitochondria-lipid droplet contacts regulated differential changes in hepatic lipid metabolism induced by two Mn sources in yellow catfish

Understanding the hazards of different forms of metal elements provided innovative insights into their toxicity and environmental risk assessment. To date, few studies had been conducted to investigate the differential effects and mechanisms of MnO2 NPs and MnSO4, two widely distributed environmental pollutants, on hepatic toxicity and lipid metabolism since lipid metabolism-relevant parameters were broadly used as biomarkers for risk assessment of hazardous contaminants. Thus, using yellow catfish Pelteobagrus fulvidraco, an ecologically and economically important freshwater fish as the model, the present study investigated the differential effects and mechanisms of MnO2 NPs and MnSO4 influencing hepatic lipid metabolism. Compared to MnSO4, MnO2 NPs increased hepatic Mn content, induced lipotoxicity, up-regulated the mRNA expression of lipogenic genes, increased peridroplet mitochondrial (PDM) contents, intensified the contact between mitochondria and lipid droplets (LDs), and downregulated miR-20a-5p abundance. Importantly, miR-20a-5p targeted mfn2, which mediated the contact between mitochondria and LDs and influenced changes in lipid metabolism induced by MnO2 NPs. Mechanistically, the direct Mfn2-Plin2 binding and Mfn2 GTPase activity promoted the MnO2 NPs-induced interactions between mitochondria and LDs, which in turn influenced MnO2 NPs-induced changes in hepatic lipid metabolism. For the first time, our findings indicated the significant differences between the changes in body metabolism induced by nanoparticles and inorganic elements, which helped to illuminate different mechanisms governing the responses of aquatic vertebrates to hazardous metal pollutants (MnO2 NPs and MnSO4).

Zinc attenuates sulfamethoxazole-induced lipotoxicity by reversing sulfamethoxazole-induced mitochondrial dysfunction and lysosome impairment in a freshwater teleost

Sulfamethoxazole (SMZ) and zinc (Zn) are widespread harmful materials in aquatic ecosystems and cause toxic effects to aquatic animals under their individual exposure. Although they often co-exist in aquatic environments, little is known about their joint effects and mechanism influencing aquatic animals. Herein, SMZ induced mitochondrial and lysosomal dysfunction, inhibited autophagy flux, and induced lipotoxicity. However, SMZ-induced changes of these physiological and metabolic processes above were reversed by Zn exposure, indicating the antagonism between Zn and SMZ. SOD1-knockdown abrogated the reversing effects of Zn on mitochondria dysfunction and autophagy flux blockage induced by SMZ, suggesting that SOD1 was essential for Zn to reverse SMZ-induced mitochondria dysfunction and autophagy impairment. Our further investigation found that Zn regulated STAT3 translocation to lysosomes and mitochondria to attenuate SMZ-induced lipotoxicity, and SOD1 was required for these processes. Mechanistically, STAT3 was associated with ATP6V1 A in a coiled-coil domain-dependent manner, and pS710-STAT3-and pY753-STAT3-independent manners. Moreover, SMZ suppressed autophagic degradation of damaged mitochondria via inhibiting interaction between STAT3 and ATP6V1 A and increasing pS710-STAT3 level; SMZ impaired mitochondrial β-oxidation via decreasing pY753-STAT3 level and STAT3 mitochondrial localization. Zn reversed these SMZ-induced effects to alleviate SMZ-induced lipotoxicity. Taken together, our data showed that SMZ impaired mitochondrial β-oxidation and lysosomal acidification via the downregulation of SOD1, leading to lipotoxicity, and that Zn reversed SMZ-induced changes of these important biological processes and attenuated SMZ-induced lipotoxicity. Thus, our study identified previously unidentified mechanisms for the antagonistic mechanisms of Zn and SMZ on aquatic animals, which provided novel insights into the environmental risk assessments of the joint exposure between heavy metals and antibiotics in the aquatic organisms.

Regulation of PGC-1α of the Mitochondrial Energy Metabolism Pathway in the Gills of Indian Medaka (Oryzias dancena) under Hypothermal Stress

Ectothermic fish exposure to hypothermal stress requires adjusting their metabolic molecular machinery, which was investigated using Indian medaka (Oryzias dancena; 10 weeks old, 2.5 ± 0.5 cm) cultured in fresh water (FW) and seawater (SW; 35‱) at room temperature (28 ± 1 °C). The fish were fed twice a day, once in the morning and once in the evening, and the photoperiod was 12 h:12 h light: dark. In this study, we applied two hypothermal treatments to reveal the mechanisms of energy metabolism via pgc-1α regulation in the gills of Indian medaka; cold-stress (18 °C) and cold-tolerance (extreme cold; 15 °C). The branchial ATP content was significantly higher in the cold-stress group, but not in the cold-tolerance group. In FW- and SW-acclimated medaka, the expression of genes related to mitochondrial energy metabolism, including pgc-1α, prc, Nrf2, tfam, and nd5, was analyzed to illustrate differential responses of mitochondrial energy metabolism to cold-stress and cold-tolerance environments. When exposed to cold-stress, the relative mRNA expression of pgc-1α, prc, and Nrf2 increased from 2 h, whereas that of tfam and nd5 increased significantly from 168 h. When exposed to a cold-tolerant environment, prc was significantly upregulated at 2 h post-cooling in the FW and SW groups, and pgc-1α was significantly upregulated at 2 and 12 h post-cooling in the FW group, while tfam and nd5 were downregulated in both FW and SW fish. Hierarchical clustering revealed gene interactions in the cold-stress group, which promoted diverse mitochondrial energy adaptations, causing an increase in ATP production. However, the cold-tolerant group demonstrated limitations in enhancing ATP levels through mitochondrial regulation via the PGC-1α energy metabolism pathway. These findings suggest that ectothermic fish may develop varying degrees of thermal tolerance over time in response to climate change. This study provides insights into the complex ways in which fish adjust their metabolism when exposed to cold stress, contributing to our knowledge of how they adapt.

A lipidomic approach to bisphenol F-induced non-alcoholic fatty liver disease-like changes: altered lipid components in a murine model

Bisphenol A (BPA), a typical environmental endocrine disruptor, is an "obesogen" that can induce lipid accumulation in the liver. Highly similar in structure to BPA, bisphenol F (BPF) is becoming the dominant BPA substitute on the market, which attracts more and more attention due to its potential adverse effects. Recently, BPF exposure is found to cause non-alcoholic fatty liver disease (NAFLD)-like changes; however, the underlying toxic effects remain poorly understood. Therefore, in the current study, we focused on BPF-mediated lipid homeostasis, especially the alterations of lipid components and metabolism. In human serum, the BPF levels in healthy controls and NAFLD patients were assessed by ELISA, and BPF-induced disturbance of lipid metabolism was evaluated in mouse model via non-targeted lipomic methods with ultra-high performance liquid chromatography-quadrupole time-of-flight mass spectrometry. It suggested that BPF exposure was positively correlated with NAFLD severity and triglyceride level in patients. Based on the relationships, lipid metabolites were assessed in mouse livers between control and BPF-treated group, and it revealed that twenty-six lipid metabolites (including phospholipids, sphingolipids, and glycerides) were significantly changed in mouse livers. Phosphatidylcholine, phosphatidylethanolamine, and diglyceryl ester levels were lower than those in the control mice; hexose ceramide content in sphingolipids markedly increased in BPF-treated mouse livers. Noteworthily, the glycerophospholipid metabolic pathway was found to be the most pronounced in BPF-induced disturbance of lipid metabolism. Therefore, the current study, for the first time, is deciphering the BPF-induced lipid metabolic disturbance, which may provide novel intervention strategies for BPF-induced NAFLD-like changes.

MnO2 nanoparticles and MnSO4 differentially affected hepatic lipid metabolism through miR-92a/acsl3-dependent de novo lipogenesis in yellow catfish Pelteobagrusfulvidraco

With the increasing production and use of MnO2 NPs and MnSO4 in various fields, their discharge into the aquatic environment is inevitable, which poses potential threats to aquatic organisms and humans. However, to date, few studies have been conducted to investigate the potential mechanism of the toxicity of MnO2 NPs, and a comprehensive understanding of the differences between this mechanism and the toxicity mechanism of inorganic Mn (MnSO4) is still lacking. Since lipid metabolism-relevant parameters have been widely recognized as novel biomarkers for risk assessment of environmental contaminants, the present study investigated the differential mechanisms of how MnO2 NPs and MnSO4 affect hepatic lipid metabolism in a freshwater fish yellow catfish. Compared to MnSO4, dietary MnO2 NPs caused liver injury, increased hepatic lipid accumulation and induced lipotoxicity, and up-regulated mRNA expression of de novo lipogenic genes. Moreover, MnO2 NPs downregulated the expression of miR-92a and miR-92b-3p, microRNAs involved in regulation of lipid metabolism, in the liver. Mechanistically, we found that acls3, an acetyl-coenzyme A synthetase, is target gene of miR-92a, and miR-92a-acsl3-dependent de novo lipogenesis contributes to lipid accumulation and lipotoxicity induced by MnO2 NPs. Collectively, these findings provided novel insights into mechanism whereby miRNAs mediate nanoparticles- and inorganic Mn-induced hepatic lipotoxicity and changes of lipid metabolism in vertebrates. Our findings also shed new perspective for ecotoxicity and ecological risk of MnO2 NPs and MnSO4 in aquatic environment.

Novel mechanism for zinc inducing hepatic lipolysis via the HDAC3-mediated deacetylation of β-catenin at lysine 311

Zinc (Zn) is a multipurpose trace element indispensable for vertebrates and possesses essential regulatory roles in lipid metabolism, but the fundamental mechanism remains largely unknown. In the current study, we found that a high-Zn diet significantly increased hepatic Zn content and influenced the expression of Zn transport-relevant genes. Dietary Zn addition facilitated lipolysis, inhibited lipogenesis, and controlled β-catenin signal; Zn also promoted T-cell factor 7-like 2 (TCF7L2) to interact with β-catenin and regulating its transcriptional activity, thereby inducing lipolysis and inhibiting lipogenesis; Zn-induced lipid degradation was mediated by histone deacetylase 3 (HDAC3) which was responsible for β-catenin deacetylation and the regulation of β-catenin signal under the Zn treatment. Mechanistically, Zn promoted lipid degradation via stimulating HDAC3-mediated deacetylation of β-catenin at lysine 311 (K311), which enhanced the interaction between β-catenin and TCF7L2 and then transcriptionally inhibited fatty acid synthase (FAS), 2-acylglycerol O-acyltransferase 2 (MOGAT2), and sterol regulatory element-binding protein 1 (SREBP1) expression, but elevated the mRNA abundance of adipose triglyceride lipase (ATGL), hormone-sensitive lipase a (HSLA) and carnitine palmitoyltransferase 1a1b (CPT1A1B). Overall, our research reveals a novel mechanism into the important roles of HDAC3/β-catenin pathway in Zn promoting lipolysis and inhibiting lipogenesis, and highlights the essential roles of K311 deacetylation in β-catenin actions and lipolytic metabolism, and accordingly provides novel insight into the prevention and treatment of steatosis in the vertebrates.

Climbazole causes cell apoptosis and lipidosis in the liver of grass carp

Climbazole, an azole, is widely used in personal care products, pharmaceuticals, and pesticides and is frequently detected in surface water. Climbazole has showed endocrine-disrupting effects. However, the effects of climbazole in fish are still largely unclear. In this study, grass carp (Ctenopharyngodon idella) and liver cell lines (L8824 cells) were treated with climbazole at concentrations ranging from 0.2 to 20 μg/L for 42 days in vivo and 24 h in vitro to evaluate the effects on the liver, respectively. Pathological, biochemical, and gene transcription and expression analyses were conducted to examine the hepatotoxicity. Our results showed that climbazole significantly decreased the hepatosomatic index, caused cell apoptosis in vivo and in vitro, and finally accumulated lipids in the liver. Beside, climbazole increased ROS levels, reduced Nrf2 and Keap1 mRNA and protein levels, and further decreased transcription of Nrf2-dependent downstream antioxidant enzyme genes, causing oxidative stress. Moreover, climbazole increased transcription and protein levels of apoptosis-related genes. Finally, climbazole damaged mitochondrial function and structure, disrupted liver lipid metabolism. Overall, climbazole caused hepatotoxicity, leading to a high ecological risk for aquatic organisms.

Combined transcriptomics and metabolomics analysis reveals lipid metabolic disruption in swamp eel (Monopterus albus) under chronic waterborne copper exposure

Excessive copper can induce many adverse effects although it's an essential trace element in organisms. The effects of copper on the lipid metabolism have aroused increasing attention. This study investigated the liver lipid metabolism in swamp eel (Monopterus albus, M. albus) chronically exposed to 0, 10, 50, and 100 μg/L Cu²⁺ for 56 days. The results showed that copper increased the contents of triglyceride (TG), total cholesterol (T-CHO), non-esterified fatty acids (NEFA), and lipid droplets. Transcriptomic analysis found 1901 differentially expressed genes (DEGs) and 140 differential alternative splicing (DAS) genes in the 50 μg/L Cu²⁺ group, and 1787 DEGs and 184 DAS genes in the 100 μg/L Cu²⁺ group, respectively, which were enriched in peroxisome proliferator-activated receptor (PPAR), adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK), and other signaling pathways. The expression levels of key genes related to PPAR and AMPK signaling pathways were significantly down-regulated after chronic exposure to Cu²⁺. Meanwhile, metabolomics analysis showed that 52 and 110 differentially expressed metabolites (DEMs) were identified, which were mainly enriched in glycerophospholipids metabolism and steroid synthesis. Moreover, combined analysis of transcriptome and metabolome showed that glycerophospholipid metabolism co-enriched 19 down-regulated DEGs and 4 down-regulated DEMs. Taken together, our results suggested that chronic waterborne copper exposure promoted lipid synthesis, disrupted the metabolic homeostasis of glycerophospholipid, and led to excessive hepatic lipid deposition in M. albus. The combined omics approach enhanced our understanding of copper pollution to lipid metabolism.

Copper induces liver lipotoxicity disease by up-regulating Nrf2 expression via the activation of MTF-1 and inhibition of SP1/Fyn pathway

Excessive copper (Cu) intake leads to hepatic lipotoxicity disease, which has adverse effects on health, but the underlying mechanism is unclear. We found that Cu increased lipotoxicity by promoting Nrf2 recruitment to the ARE site in the promoters of five lipogenic genes (g6pd, 6pgd, me, icdh and pparγ). We also found that Cu affected the Nrf2 expression via different pathways: metal regulatory transcription factor 1 (MTF-1) mediated the Cu-induced Nrf2 transcriptional activation; Cu also enhanced the expression of Nrf2 by inhibiting the SP1 expression, which was achieved by inhibiting the negative regulator Fyn of Nrf2. These promoted the enrichment of Nrf2 in the nucleus and ultimately affected lipotoxicity. Thus, for the first time, we elucidated that Cu induced liver lipotoxicity disease by up-regulating Nrf2 expression via the MTF-1 activation and the inhibition of SP1/Fyn pathway. Our study elucidates the Cu-associated obesity and NAFLD for fish and possibly humans.

Long-term waterborne Cu2+ exposure affects collagen metabolism in fish

Copper pollution might have a negative effect on collagen metabolism in fish. To test this hypothesis, we exposed an important economical fish, silver pomfret (Pampus argenteus), to three concentrations of Cu²⁺ for up to 21 days to simulate natural exposure to copper. With increasing copper exposure concentration and time, hematoxylin and eosin staining and picrosirius red staining revealed extensive vacuolization, cell necrosis, and tissue structure destruction, and a change of type and abnormal accumulation of collagen in the liver, intestine, and muscle tissues. To further study the mechanism of collagen metabolism disorder caused by copper exposure, we cloned and analyzed a key collagen metabolism regulation gene, timp, of silver pomfret. The full-length timp2b cDNA was 1035 bp with an open reading frame of 663 bp, encoding a protein of 220 amino acids. Copper treatment significantly increased the expression of akts, erks, and fgfs genes and decreased the mRNA and protein expression of Timp2b and MMPs. Finally, we constructed a silver pomfret muscle cell line (PaM) for the first time and used PaM Cu²⁺ exposure models (450 μM Cu²⁺ exposure for 9 h) to examine regulation function of the timp2b-mmps system. We knocked down or overexpressed timp2b in the model, and found that downregulation of mmps expression and upregulation of akt/erk/fgf were further aggravated in the timp2b^- group (subjected to RNA interference), whereas some recovery was achieved in the timp2b⁺ group (overexpression). These results indicated that long-term excessive copper exposure can lead to tissue damage and abnormal collagen metabolism in fish, which might be caused by the alteration of akt/erk/fgf expression, which disrupts the effects of the timp2b-mmps system on extracellular matrix balance. The present study assessed the impact of copper on the collagen of fish and clarified its regulatory mechanism, providing a basis for toxicity of copper pollution study.

Chronic hypoxia and Cu2+ exposure induce gill remodeling of largemouth bass through endoplasmic reticulum stress, mitochondrial damage and apoptosis

Hypoxia and Cu²⁺ pollution often occur simultaneously in aquatic ecosystems and jointly affect physiology of fish. As the respiratory and ion exchange tissue of fish, how gill responds to the stress induced by these two abiotic environmental factors is still unclear. We have conducted a study by exposing largemouth bass (Micropterus salmoides) to hypoxia (2.0 mg·L^-1) and/or Cu²⁺ (0.5 mg·L^-1) for 28 days to answer this question. We subsequently studied respiratory rate, Cu²⁺ transport, endoplasmic reticulum (ER) stress, mitochondrial damage, and morphology in gill tissue on day 7, 14, 21 and 28. We found that hypoxia exposure increased the respiratory rate of largemouth bass, reflecting the response of largemouth bass to cope with hypoxia. Of note, Cu²⁺ entered gill by specifically binding to CTR1 and its accumulation dramatically in gill disrupted the response of largemouth bass to hypoxia. Hypoxia and/or Cu²⁺ exposure led to ER stress and mitochondrial damage in gills of largemouth bass. ER stress and mitochondrial damage induced apoptosis by activating caspase-8 and caspase-9 signaling pathways, respectively. Apoptosis induced by hypoxia and Cu²⁺ exposure had a positive and synergistic effect on gill remodeling by reducing interlamellar cell masses. In addition, Cu²⁺ exposure induced hypoxia-like remodeling to gill morphology through mechanisms similar to hypoxia exposure. Most of gene expression changed mainly within 21 days and recovered to the control level on day 28, reflecting the acclimation of largemouth bass to hypoxia and/or Cu²⁺ exposure at gene expression level. Overall, our research suggests that chronic hypoxia and Cu²⁺ exposure could induce gill remodeling of largemouth bass through ER stress, mitochondrial damage and apoptosis. The outcomes could provide an insight for fish environmental adaptation and environmental toxicology.

Lead and copper led to the dysregulation of bile acid homeostasis by impairing intestinal absorption in Bufo gargarizans larvae: An integrated metabolomics and transcriptomics approach

Bile acids, as metabolic regulators and signaling molecules, play key roles in the regulation of host metabolism and immune responses. Heavy metals such as lead (Pb) and copper (Cu) are widespread environmental pollutants that threaten public health. However, the effects of heavy metals on bile acid metabolism and the underlying molecular mechanisms remain unclear, particularly for ecologically important amphibian species. In the present research, the effects of exposure to environmentally-relevant concentrations of Pb (250 μg/L), Cu (50 μg/L), and a mixture of both (Mix) on bile acid metabolism and the underlying molecular mechanisms in the intestines of Bufo gargarizans larvae were comprehensively investigated using histopathology, metabolomics and transcriptomics analysis. Our results suggested that Pb and/or Cu caused histopathological damage to the intestine and liver, such as decreased intestinal epithelial cell height and dilated hepatic sinusoid. The total bile acid level was decreased in the Pb and Mix exposure groups but elevated in the Cu treatment. A significant decrease in the ratio of conjugated to unconjugated bile acids was present in all treatment groups. Also, the level of GCA was increased while TCA and TCDCA were decreased in all exposure groups. In addition, exposure to Pb and Cu altered the expression levels of genes related to intestinal absorption. For example, mrp2, mrp3 and aqp4 had higher expression in the Pb and Mix treatment groups, and aqp1 and mrp4 were increased in the Cu treatment group. Overall, we speculated that the dysregulation of bile acid homeostasis induced by Pb and Cu exposure may be due to impaired intestinal absorption. These findings raise further concerns about the hazards of Pb and/or Cu in influencing bile acid metabolism that might lead to the development of metabolic diseases and inflammatory disorders.

Effects of copper exposure on lipid metabolism and SREBP pathway in the Chinese mitten crab Eriocheir sinensis

Copper (Cu) is not only a common metal pollutant in the aquatic environment but also an essential trace element for aquatic organisms such as the Chinese mitten crab (Eriocheir sinensis). Cu is known to regulate lipid metabolism yet exert toxic effects if ingested in excess. However, the molecular regulatory roles of Cu in the lipid metabolism of crabs remains unclear. Thus, this study investigated the potential regulatory mechanism of Cu onto lipid metabolism of E. sinensis following acute Cu exposure. Crabs were exposed to environmental concentration of Cu (50 μg/L) for 96 h, and the expression of sterol regulatory element binding protein (SREBP) was knocked down by RNA interference (RNAi) to test its effect on Cu exposure. The results showed that RNAi significantly attenuated the Cu exposure-induced increase in lipid synthesis and triglycerides (TG) hydrolysis, while significantly inhibited the Cu exposure-induced decrease in fatty acid β-oxidation, suggesting that SREBP is involved in Cu-induced lipid metabolism. Subsequent analyses of the transcriptome results further revealed potential responsive genes of SREBP that were linked to lipid metabolism and immune regulation. Moreover, Cu may affect lipid metabolism through the TOR-SREBP pathway in E. sinensis. This work provides a reference for exploring the effects of Cu on lipid metabolism disorders in crustaceans.

Histological, physiological, and transcriptomic responses of hepatopancreas to air exposure in asian freshwater clam Corbicula fluminea

Corbicula fluminea (C. fluminea) is an important freshwater economy shellfish in China, but it often suffers from air exposure during transportation. In this study, we investigated the histological, physiological (mainly including respiratory metabolism, antioxidant capacity, and immune function), and transcriptomic responses of hepatopancreas in C. fluminea to different times of air exposure. At histological level, air exposure caused vacuolation of digestive cells (24-96 h) and enlargement of digestive tubule lumen (6-96 h) in hepatopancreas. At physiological level, the activities of enzymes related to glycolysis (hexokinase and pyruvate kinase) and anaerobic respiration (lactate dehydrogenase) were increased first (6-24 h) of air exposure, then came back to normal level or even decreased. The activity of aerobic respiration-related enzyme (succinic dehydrogenase) began to reduce from 24 h of air exposure. The activities of antioxidant enzymes (superoxide dismutase and catalase) were enhanced during 6-48 h of air exposure and then returned to control level or even inhibited. The content of malondialdehyde (MDA) increased from 96 h of air exposure. The activities of immune-related enzymes (acid phosphatase and alkaline phosphatase) increased during 6-48 h, then returned to normal or began to decline. At transcriptome level, 44 differentially expressed genes (DEGs) in the hepatopancreas were identified after 96-h air exposure. Among these DEGs, 8 were associated with glycolysis, TCA cycle, immune, and antioxidant, and were downregulated after 96-h air exposure. Taken together, these findings illuminated the response of C. fluminea to air exposure at histological, physiological, and transcriptomic levels, which will be beneficial to the aquaculture and transportation of C. fluminea.

Neurotoxicity of singular and combined exposure of Oreochromis niloticus to methomyl and copper sulphate at environmentally relevant levels: Assessment of neurotransmitters, neural stress, oxidative injury and histopathological changes

Aquatic organisms are concomitantly exposed to multiple noxious chemicals that can be discharged into water bodies. We aimed to investigate the single and simultaneous sub-acute exposure to copper and methomyl on juvenile Oreochromis niloticus. Compared to the controls, the outcomes revealed that brain of methomyl-exposed fish displayed significant declines in the activities of SOD, CAT, and GST in addition to higher MDA and lower GSH levels. Methomyl induced notable declines in levels of GABA and acetylcholine esterase in brain and muscle of exposed fish. Noteworthy downregulated gene expression levels of TNF-α, HSP-70 together with upregulated c-fos were evident in brain of fish expose to either of tested compounds. Marked apoptotic changes were observed in fish brain exposed to copper and methomyl indicated by augmented immune expression of caspase-3. Conclusively, the results indicated the possible interaction between both compounds with subsequent toxic effects that differ from their single exposure.

Iron increases lipid deposition via oxidative stress-mediated mitochondrial dysfunction and the HIF1α-PPARγ pathway

Iron is an essential micro-element, involved in multiple biological activities in vertebrates. Excess iron accumulation has been identified as an important mediator of lipid deposition. However, the underlying mechanisms remain unknown. In the present study, we found that a high-iron diet significantly increased intestinal iron content and upregulated the mRNA expression of two iron transporters (zip14 and fpn1). Intestinal iron overload increased lipogenesis, reduced lipolysis and promoted oxidative stress and mitochondrial dysfunction. Iron-induced lipid accumulation was mediated by hypoxia-inducible factor-1 α (HIF1α), which was induced in response to mitochondrial oxidative stress following inhibition of prolyl hydroxylase 2 (PHD2). Mechanistically, iron promoted lipid deposition by enhancing the DNA binding capacity of HIF1α to the pparγ and fas promoters. Our results provide experimental evidence that oxidative stress, mitochondrial dysfunction and the HIF1α-PPARγ pathway are critical mediators of iron-induced lipid deposition.

Sirt3-Sod2-mROS-Mediated Manganese Triggered Hepatic Mitochondrial Dysfunction and Lipotoxicity in a Freshwater Teleost

Exposure to excessive manganese (Mn) is toxic to humans and animals. However, the toxic effects and mechanisms of excessive Mn influencing the vertebrates have been highly overlooked. In the present study, dietary Mn overload significantly increased hepatic lipid and Mn contents, decreased superoxide dismutase 2 (Sod2) activity, increased the Sod2 acetylation level, and induced mitochondrial dysfunction; Mn induced mitochondrial dysfunction through Mtf1/sirtuin 3 (Sirt3)-mediated acetylation of Sod2 at the sites K55 and K70. Meanwhile, mitochondrial oxidative stress was involved in Mn-induced lipotoxicity. Mechanistically, Mn-induced lipotoxicity was via oxidative stress-induced Hsf1 nucleus translocation and its DNA binding capacity to the regions of a peroxisome proliferator-activated receptor g (pparg) promoter, which in turn induced the transcription of lipogenic-related target genes. For the first time, our study demonstrated that Mn-induced hepatic lipotoxicity via a mitochondrial oxidative stress-dependent Hsf1/Pparg pathway and Mtf1/sirt3-mediated Sod2 acetylation participated in mitochondrial dysfunction. Considering that lipid metabolism and lipotoxicity are widely used as the biomarkers for environmental assessments of pollutants, our study provided innovative and important insights into Mn toxicological and environmental evaluation in aquatic environments.

Transcriptomic Analysis of Hepatotoxicology of Adult Zebrafish (Danio rerio) Exposed to Environmentally Relevant Oxytetracycline

The extensive use of the broad-spectrum antibiotics like oxytetracycline (OTC) has become a serious environmental issue globally. OTC has profound negative effects on aquatic organisms including fishes. In this study, RNA-Seq analysis was employed to examine the possible molecular mechanism of hepatotoxicology in zebrafish induced by OTC exposure. Adult male zebrafish was exposed to 0, 5, 90, and 450 μg/L OTC for 3 weeks. The results showed the decrease in body weight and tail length but the increase in total length of zebrafish under OTC exposure in a dose-dependent way. In addition, severe histopathological damages were featured by increasing tissue vacuolization in the livers of 450 μg/L OTC group. Moreover, RNA-Seq analysis revealed that molecular signaling and functional pathways in the liver were disrupted by OTC exposure. Furthermore, the down-regulation of gene expression after OTC exposure was found on both the genes related to fatty acid degradation and the genes related to lipid synthesis. The present study implied that OTC induced liver malfunction and fish health risks through growth retard, histopathological damages, molecular signaling disruption, genetic expression alteration, and lipid metabolism disturbance.

Physiological and transcriptomic analyses reveal the toxicological mechanism and risk assessment of environmentally-relevant waterborne tetracycline exposure on the gills of tilapia (Oreochromis niloticus)

With the increasing application of tetracycline (TC) in medical treatment, animal husbandry and aquaculture in recent decades, high quantities of TC have been frequently detected in the aquatic environment, and accordingly TC-related toxicity and environmental pollution have become a global concern. The present study was performed to explore the toxicological influences of TC exposure at its environmentally relevant concentrations on the gills of tilapia Oreochromis niloticus, based on the alteration in histopathology, oxidative stress, inflammatory response, cell cycle, mitochondrial function, apoptosis, and transcriptomic analysis. Our findings revealed that TC exposure damaged the structure and function, induced oxidative stress, affected inflammatory responses, and reduced Na⁺/K⁺-ATPase (NKA) activity in the gills. TC also caused the inhibition in cell cycle, resulted in mitochondrial dysfunction and activated apoptosis. Further transcriptomic analysis indicated the extensive influences of TC exposure on the gill function, and immune system was the main target to waterborne TC exposure. These results elucidated that environmental TC had more complex toxicological effects on gills of fish than previously assessed, and provided novel insight into molecular toxicology of TC on fish and good basis for assessing the environmental risk of TC.

Gill physiological and transcriptomic response of the threatened freshwater mussel Solenaia oleivora to salinity shift

Solenaia oleivora, a freshwater shellfish endemic to China, is becoming one of the most threatened freshwater mussels owing to water pollution, habitat fragmentation, and overfishing. Hence, exploring its response to different environmental factors is important for its conservation. In this work, we investigated the physiological and transcriptomic response of S. oleivora to increased salinity. We found that increased salinity caused the death of S. oleivora. High salinity caused shrinking and deformation of gill filaments, reduced gill cilia, and induced cell apoptosis in gills. The activities of superoxide dismutase (SOD), catalase (CAT), acid phosphatase (ACP), alkaline phosphatase (AKP), as well as glutathione (GSH) content were increased at the beginning of salinity stress (3-12 h), while SOD and ACP activities decreased at 48 h. Transcriptome data revealed that high salinity stress (48 h) induced 766 differentially expressed genes (DEGs). Among these DEGs, the majority of the stress response and ion transport-related genes were up-regulated, while most of the immune-related genes were down-regulated. In conclusion, these findings suggest that the antioxidant and immune functions of S. oleivora can be inhibited by high salinity, which may be one of the main reasons for its low survival rate under conditions of increasing salinity.