Microcystin-LR-induced autophagy regulates oxidative stress, inflammation, and apoptosis in grass carp ovary cells in vitro

Microcystin-LR and its health impacts: Chemistry, transmission routes, mechanisms of toxicity and target organs

Microcystin-LR, a hepatotoxin produced by cyanobacteria, poses significant health risks to humans and other animals through various routes of exposure. This review comprehensively explores the chemistry, transmission pathways, mechanisms of toxicity, and target organs affected by MC-LR to provide a detailed understanding of its health impacts on animals and humans. MC-LR exposure occurs through different transmission routes, including ingesting contaminated water and food, algal dietary supplements, direct body contact with harmful algal blooms, and inhalation of aerosolized toxins. In this review, we explored that the toxic effects of MC-LR are mediated through multiple complex mechanisms. A key mechanism of its toxicity is the inhibition of protein phosphatases PP1 and PP2A which results in abnormal cellular signalling pathways. Additionally, MC-LR induces oxidative stress and disrupts cellular homeostasis. The findings suggest that MC-LR modulates the activity of various antioxidant enzymes and also activates apoptosis pathways by different mechanisms. It also induces cytoskeletal disruption, ultimately compromising cellular integrity and function. MC-LR also induces activation of oncogenes such as Gankyrin, PI3K/AKT, HIF-1α, RAC1/JNK and NEK2 pathway and upregulates the inflammatory molecules such as NF-κβ, and TNF-α, hence leading to carcinogenesis. MC-LR has toxicological effects on multiple organs. The liver is the primary target, where MC-LR accumulates and causes hepatotoxicity, but other organs are affected as well. MC-LR shows neurotoxicity, nephrotoxicity, cardiotoxicity and reproductive toxicity.

Oxidative stress and mitochondrial dysfunctions induced by cyanobacterial microcystin-LR in primary grass carp hepatocytes

Microcystin-LR (MC-LR), a cyclic heptapeptide produced by freshwater cyanobacteria, induces a range of liver injuries. However, the mechanisms underlying MC-LR toxicity in primary hepatocytes of aquatic organisms remains poorly understood. In this study, we investigated the effects of MC-LR on oxidative stress and mitochondrial function using primarily cultured grass carp hepatocytes. The results revealed that IC50 of MC-LR on grass carp primary liver cells for 24 hours was 2.40 μmol/L. Based on 24h-IC50, concentrations of 0, 0.30, 0.60, and 1.20 μmol/L were used in subsequent experiments. MC-LR exposure led to a significant reduction in cell viability, induced abnormal cell morphology, and caused plasma membrane rupture, as indicated by elevated LDH activity in a concentration-dependent manner. Additionally, MC-LR exposure induced oxidative stress, resulting in increased ROS levels and downregulation of genes associated with oxidative stress, including keap1, nrf2, cat, sod1, gpx, gst, and gr (P<0.05). Furthermore, the electron microscopy results showed that MC-LR caused damage to the ultrastructure of primary hepatocytes, including mitochondrial membrane rupture, vacuolation, and induction of mitochondrial autophagy. Moreover, MC-LR exposure elevated intracellular Ca2+ concentration, reduced MMP and ATP levels, and inhibited mitochondrial respiratory chain complex I activity (P<0.05). qRT-PCR analysis demonstrated that MC-LR treatment significantly decreased the transcriptional levels of genes related to mitochondrial quality control including pgc-1α, tfam, nrf1, drp1, opa1, mfn1, and mfn2 (P<0.05). Collectively, our findings highlight that MC-LR causes oxidative stress and impairs mitochondrial function, leading to further hepatocyte damage, which provides insights into the mechanisms of MC-LR-induced hepatotoxicity and offers valuable references for further investigations.

MC-LR induced apoptosis in human embryonic kidney (HEK293) cells through activation of TNF-R1/RIPK1 pathway

In recent years, the outbreak of cyanobacterial blooms has become increasingly frequent. Microcystin-LR (MC-LR), a metabolite of cyanobacteria, poses a significant threat to the ecosystem and human health. Several studies have demonstrated that MC-LR might induce renal cell apoptosis, as a consequence of tissue damage. However, the molecular mechanisms underlying MC-LR-initiated renal injury remain to be determined. This investigation aimed to determine the role of apoptosis in MC-LR-induced kidney damage and its potential underlying mechanisms using the human embryonic kidney (HEK293) cell line. The results of TUNEL and immunofluorescence assays indicated that MC-LR induced increased apoptosis in HEK293 cells. Compared to control, the mRNA expression levels of RIPK1, caspase-8, and TNF-α were elevated following incubation with MC-LR, while the mRNA expression level of Bcl-2/Bax was decreased. The protein levels of RIPK1, TNF-R1, and caspase-8 were elevated in the MC-LR-treated HEK293 cells. Data demonstrated that MC-LR induced renal cell apoptosis through activation of the TNF-R1/RIPK1 pathway, providing new insights into understanding the toxic mechanisms attributed to MC-LR.

Attenuation effect of a polysaccharide from large leaf yellow tea by activating autophagy

Chemotherapy, the most common class of anticancer drugs, is considerably limited owing to its adverse side effects. In this study, we aimed to evaluate the protective effect and mechanism of action of large-leaf yellow tea polysaccharides (ULYTP-1, 1.29 × 104 Da) against chemotherapeutic 5-fluorouracil (5-Fu). Structural characterisation revealed that ULYTP-1 was a β-galactopyranouronic acid. Furthermore, ULYTP-1 promoted autolysosome formation, activating autophagy and reducing the oxidative stress and inflammation caused by 5-Fu. Our in vivo study of 4 T1 tumour-bearing mice revealed that ULYTP-1 also attenuated 5-Fu toxicity through modulation of the gut microbiota. Moreover, ULYTP-1 effectively protected immune organs and the liver from 5-Fu toxicity, while promoting its tumour-inhibitory properties. The current findings provide a new strategy for optimising chemotherapy regimens in the clinic.

Integration of Multi-Omics, Histological, and Biochemical Analysis Reveals the Toxic Responses of Nile Tilapia Liver to Chronic Microcystin-LR Exposure

Microcystin-LR (MC-LR) is a cyanobacterial metabolite produced during cyanobacterial blooms and is toxic to aquatic animals, and the liver is the main targeted organ of MC-LR. To comprehensively understand the toxicity mechanism of chronic exposure to environmental levels of MC-LR on the liver of fish, juvenile Nile tilapia were exposed to 0 μg/L (control), 1 μg/L (M1), 3 μg/L (M3), 10 μg/L (M10), and 30 μg/L (M30) MC-LR for 60 days. Then, the liver hepatotoxicity induced by MC-LR exposure was systematically evaluated via histological and biochemical determinations, and the underlying mechanisms were explored through combining analysis of biochemical parameters, multi-omics (transcriptome and metabolome), and gene expression. The results exhibited that chronic MC-LR exposure caused slight liver minor structural damage and lipid accumulation in the M10 group, while resulting in serious histological damage and lipid accumulation in the M30 group, indicating obvious hepatotoxicity, which was confirmed by increased toxicity indexes (i.e., AST, ALT, and AKP). Transcriptomic and metabolomic analysis revealed that chronic MC-LR exposure induced extensive changes in gene expression and metabolites in six typical pathways, including oxidative stress, apoptosis, autophagy, amino acid metabolism, primary bile acid biosynthesis, and lipid metabolism. Taken together, chronic MC-LR exposure induced oxidative stress, apoptosis, and autophagy, inhibited primary bile acid biosynthesis, and caused fatty deposition in the liver of Nile tilapia.

The cytotoxicity of microcystin-LR: ultrastructural and functional damage of cells

Microcystin-LR (MC-LR) is a toxin produced by cyanobacteria, which is widely distributed in eutrophic water bodies and has multi-organ toxicity. Previous cytotoxicity studies have mostly elucidated the effects of MC-LR on intracellular-related factors, proteins, and DNA at the molecular level. However, there have been few studies on the adverse effects of MC-LR on cell ultrastructure and function. Therefore, research on the cytotoxicity of MC-LR in recent years was collected and summarized. It was found that MC-LR can induce a series of cytotoxic effects, including decreased cell viability, induced autophagy, apoptosis and necrosis, altered cell cycle, altered cell morphology, abnormal cell migration and invasion as well as leading to genetic damage. The above cytotoxic effects were related to the damage of various ultrastructure and functions such as cell membranes and mitochondria. Furthermore, MC-LR can disrupt cell ultrastructure and function by inducing oxidative stress and inhibiting protein phosphatase activity. In addition, the combined toxic effects of MC-LR and other environmental pollutants were investigated. This review explored the toxic targets of MC-LR at the subcellular level, which will provide new ideas for the prevention and treatment of multi-organ toxicity caused by MC-LR.

Biological and Chemical Approaches for Controlling Harmful Microcystis Blooms

The proliferation of harmful cyanobacterial blooms dominated by Microcystis aeruginosa has become an increasingly serious problem in freshwater ecosystems due to climate change and eutrophication. Microcystis-blooms in freshwater generate compounds with unpleasant odors, reduce the levels of dissolved O2, and excrete microcystins into aquatic ecosystems, potentially harming various organisms, including humans. Various chemical and biological approaches have thus been developed to mitigate the impact of the blooms, though issues such as secondary pollution and high economic costs have not been adequately addressed. Red clays and H2O2 are conventional treatment methods that have been employed worldwide for the mitigation of the blooms, while novel approaches, such as the use of plant or microbial metabolites and antagonistic bacteria, have also recently been proposed. Many of these methods rely on the generation of reactive oxygen species, the inhibition of photosynthesis, and/or the disruption of cellular membranes as their mechanisms of action, which may also negatively impact other freshwater microbiota. Nevertheless, the underlying molecular mechanisms of anticyanobacterial chemicals and antagonistic bacteria remain unclear. This review thus discusses both conventional and innovative approaches for the management of M. aeruginosa in freshwater bodies.

Toxic cyanobacteria induce coupled changes in gut microbiota and co-metabolite of freshwater gastropods

Frequent outbreaks of harmful cyanobacterial blooms and the microcystins (MCs) they produce seriously affect the survival of aquatic organisms. Interactions between gut microbiota and hosts often play crucial roles in driving the adaptation of aquatic organisms to environmental changes. In this study, we investigated the phenotypic indicators of the freshwater gastropod Bellamya aeruginosa, after uptake of Microcystis aeruginosa and explored its gut microbial composition and gut metabolites in response to toxic cyanobacterial stress. Results showed that the MCs concentration in the hepatopancreas of snails fed with toxic cyanobacteria decreased from 2.64 ± 0.14 μg·g-1 on day 7 to 1.16 ± 0.10 μg·g-1 on day 14. The compositions of the intestinal microbiota of snails fed with different algae significantly differed, and the relative abundance of gut microbes such as Lactobacillus and Sphingobium significantly increased after feeding toxic cyanobacteria. Significant differences also existed in intestinal metabolites, the relative abundance of the following metabolites significantly increased: l-proline, 5,6-DHET, stachyose, raffinose, and 3-isopropylmalate. Sankey network diagrams showing links between gut microbes and gut metabolites. The association of Lactobacillus and Sphingobium with amino acids may be related to host tolerance to toxicity, and the linkages of gut microbes with metabolites such as levan, imidazolepropionic acid, and eicosanoids may be associated with involvement in host immune responses. The association of microbes with stachyose and raffinose can help the host to regulate energy homeostasis. These results reveal the underlying mechanisms of gut microbes in the snail adaptation to toxic cyanobacterial stress. This study could be great important for gaining new insights into toxic cyanobacteria-induced changes in snail gut microbes and metabolites and their roles in snail adaptation to toxic cyanobacterial stress, and may provide important insights into the use of freshwater gastropods for the prevention and control of cyanobacterial blooms.

Microcystin-LR-induced autophagy via miR-282-5p/PIK3R1 pathway in Eriocheir sinensis hepatopancreas

With the intensifying climate warming, blue-green algae blooms have become more frequent and severe, releasing environmental hazards such as microcystin that pose potential threats to human and animal health. Autophagy has been shown to play a crucial role in regulating immune responses induced by environmental hazards, enabling cells to adapt to stress and protect against damage. Although microcystin-LR (MC-LR) has been identified to affect autophagy in mammalian, its impact on aquatic animals has been poorly studied. To investigate the toxicological effects of MC-LR in aquatic ecosystems, we constructed a microRNA profile of acute MC-LR stress in the hepatopancreas of the Chinese mitten crab. Interestingly, we found the MC-LR exposure activated autophagy in the hepatopancreas based on the following evidence. Specifically, mRNA expression level of ATG7, Beclin1 and Gabarap was significantly up-regulated, autophagy regulatory pathways were significantly enriched, and numerous autolysosomes and autophagosomes were observed. Additionally, we found that miR-282-5p and its target gene PIK3R1 played important regulatory roles in autophagy by in vivo and in vitro experiments. Overexpression of miR-282-5p mimicked MC-LR-induced autophagy by inhibiting PIK3R1 expression, while miR-282-5p silencing inhibited autophagy by promoting PIK3R1 expression. Altogether, our findings suggest that MC-LR increases miR-282-5p, which then targets inhibition of PIK3R1 to stimulate autophagy. This study focused on the stress response regulatory mechanisms of juvenile crabs to toxic pollutants in water, offering a potential target for alleviating the toxicity of MC-LR. These findings lay a foundation for reducing the toxicity of MC-LR and environmental hazards in organisms.

Lycopene abolishes typical polyhalogenated carbazoles (PHCZs)-induced hepatic injury in yellow catfish (Pelteobagrus fulvidraco): Involvement of ROS/PI3K-AKT/NF-κB signaling

Aquatic ecosystems are being more contaminated with polyhalogenated carbazoles (PHCZs), which raising concerns about their impact on aquatic organisms. Lycopene (LYC) exhibits several beneficial properties for fish via enhance antioxidant defenses and improve immunity. In this study, we attempted to investigate the hepatotoxic effects of typical PHCZs 3, 6-dichlorocarbazole (3,6-DCCZ) and the protective mechanisms of LYC. In this study, we found that yellow catfish (Pelteobagrus fulvidraco) exposure to 3,6-DCCZ (1.2 mg/L) resulted in hepatic inflammatory infiltration and disordered hepatocyte arrangement. Besides, we observed that 3,6-DCCZ exposure resulted in hepatic reactive oxygen species (ROS) overproduction and excessive autophagosome accumulation, accompanied with inhibition of phosphatidylinositol-3-kinase (PI3K)/protein kinase B (AKT) pathway. Subsequently, we confirmed that 3,6-DCCZ exposure triggered hepatic uncontrolled inflammatory response via activation of nuclear factor-κB (NF-κB) pathway, along with decreased plasma complement C3 (C3) and complement C4 (C4) levels. Meanwhile, yellow catfish exposed to 3,6-DCCZ exhibit an increased hepatic apoptosis phenomenon, as evidenced by the elevated number of positive TUNEL cells and upregulated expression of caspase3 and cytochrome C (CytC). In contrast, LYC treatment could alleviate the 3,6-DCCZ-induced pathological changes, hepatic ROS accumulation, autophagy, inflammatory response and apoptosis. To sum up, this study provided the demonstration that LYC exerts hepatoprotective effects to alleviate 3,6-DCCZ-induced liver damage by inihibiting ROS/PI3K-AKT/NF-κB signaling in yellow catfish.

Integration of Transcriptomics and Microbiomics Reveals the Responses of Bellamya aeruginosa to Toxic Cyanobacteria

Frequent outbreaks of harmful cyanobacterial blooms and the cyanotoxins they produce not only seriously jeopardize the health of freshwater ecosystems but also directly affect the survival of aquatic organisms. In this study, the dynamic characteristics and response patterns of transcriptomes and gut microbiomes in gastropod Bellamya aeruginosa were investigated to explore the underlying response mechanisms to toxic cyanobacterial exposure. The results showed that toxic cyanobacteria exposure induced overall hepatopancreatic transcriptome changes. A total of 2128 differentially expressed genes were identified at different exposure stages, which were mainly related to antioxidation, immunity, and metabolism of energy substances. In the early phase (the first 7 days of exposure), the immune system may notably be the primary means of resistance to toxin stress, and it performs apoptosis to kill damaged cells. In the later phase (the last 7 days of exposure), oxidative stress and the degradation activities of exogenous substances play a dominant role, and nutrient substance metabolism provides energy to the body throughout the process. Microbiomic analysis showed that toxic cyanobacteria increased the diversity of gut microbiota, enhanced interactions between gut microbiota, and altered microbiota function. In addition, the changes in gut microbiota were correlated with the expression levels of antioxidant-, immune-, metabolic-related differentially expressed genes. These results provide a comprehensive understanding of gastropods and intestinal microbiota response to toxic cyanobacterial stress.