Hemeprotein amplifies the innate immune receptors of Ctenopharyngodon idellus kidney cells through NF-κB- and MAPK-dependent reactive oxygen species generation

Hemolysis-associated release of hemoglobin induces mitochondrial oxidative phosphorylation (OXPHOS) disturbance and aggravates cell oxidative damage in grass carp (Ctenopharyngodon idella)

The liver is a key site for the removal of cell-free hemin during hemolysis. However, the mechanism underlying liver damage caused by hemolysis in teleost hemolytic disorderss remains unclear. In this study, the hemin incubation of grass carp liver cells (L8824) and phenylhydrazine (PHZ) injection were employed to simulate in vitro and in vivo hemolysis models. The Cell Counting Kit (CCK) assay results of the L8824 cells showed that the hemin caused obvious cell death and exhibited concentration-dependent characteristics. Furthermore, hemin stimulation significantly increased intracellular iron content, markedly enhanced intracellular ROS (reactive oxygen species) production, triggered the activation of genes linked to iron metabolism, and disrupted mitochondrial structural integrity. The quantitative real-time PCR (qRT-PCR) assay and enzyme activity findings indicated that the hemoglobin (Hb) treatment activated the activity and expression of mitochondrial respiratory chain complexes, while the addition of compound inhibitors I, II, and III could rescue hemin-induced cell death. Finally, a hemolysis model was established via intraperitoneal injection of PHZ in the grass carp. Histopathological analysis and in vivo transcriptome data showed that PHZ-induced hemolysis resulted in liver inflammation and iron and collagen fiber buildup. Additionally, immunofluorescence and immunohistochemical data indicated it enhanced the ROS generation, malondialdehyde (MDA), and 4-hydroxy-2-nonenal (4-HNE), destroyed the mitochondria, and up-regulated the transcription of mitochondrial respiratory chain complexes. In summary, the cell-free Hb released during hemolysis increased iron deposition, disrupted iron metabolism homeostasis, and caused oxidative stress. Consequently, this destroyed mitochondria function and ultimately exacerbated cell death.

Generation of transgenic fish cell line with α-lactalbumin nanocarriers co-delivering Tol2 transposase mRNA and plasmids

Fish cells, such as grass carp (Ctenopharyngodon idella) kidney (CIK) cells, are harder to transfect than mammalian cells. There is a need for an efficient gene delivery system for fish cells. Here, we used CIK cell line as a model to develop a strategy to enhance RNA and plasmid DNA transfection efficiency using a nanocarrier generated from α-lactalbumin (α-NC). α-NC absorbed nucleic acid cargo efficiently and exhibited low cytotoxicity. Plasmid transfection was more efficient with α-NC than with liposomal transfection reagents. We used α-NC to co-transfect Tol2 transposase mRNA and a plasmid containing Cas9 and GFP, generating a stable transgenic CIK cell line. Genome and RNA sequencing revealed that the Cas9 and GFP fragments were successfully inserted into the genome of CIK cells and efficiently transcribed. In this study, we established an efficient transfection system for fish cells using α-NC, simplifying the process of generating stable transgenic fish cell lines.

FerrylHb induces inflammation and cell death in grass carp (Ctenopharyngodon idella) hepatocytes

Grass carp hemorrhagic disease is a significant problem in grass carp aquaculture. It releases highly oxidizing hemoglobin (Hb) into tissues, induces rapid autooxidation, and subsequently discharges cytotoxic reactive oxygen species (ROS). However, the mechanism underlying Hb damage to the teleost remains unclear. Here, we employed ferrylHb and heme to incubate L8824 (grass carp liver) cells and quantitatively analyzed the corresponding molecular regulation using the RNA-seq method. Based on the RNA-seq analysis data, after 12 h of incubation of the L8824 cells with ferrylHb, a total of 3738 differentially expressed genes (DEGs) were identified, 1824 of which were upregulated, and 1914 were downregulated. A total of 4434 DEGs were obtained in the heme treated group, with 2227 DEGs upregulated and 2207 DEGs downregulated. KEGG enrichment analysis data revealed that the incubation of ferrylHb and heme significantly activated the pathways related to Oxidative Phosphorylation, Autophagy, Mitophagy and Protein Processing in Endoplasmic Reticulum. The genes associated with NF-κB, autophagy and apoptosis pathways were selected for further validation by quantitative real-time RT-PCR (qRT-PCR). The results were consistent with the RNA-seq data. Taken together, the incubation of Hb and heme induced the molecular regulation of L8824, which consequently led to programmed cell death through multiple pathways.

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.

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.

Effect of hemoglobin on Nile tilapia (Oreochromis niloticus) kidney (NTK) cell line damage

Bacteria or viral outbreaks can cause tilapia hemorrhage, ensuring considerable volume of hemoglobin (Hb) into the tissue. However, the hemoglobin toxicity on tissue and high doses also effect on tissue this phenomena is still under consideration. Therefore, current study exploited Nile tilapia kidney (NTK) cells to deeply expose the toxic effect of Hb on NTK cells. Toxicity of Hb on NTK cells was determined in terms of cells growth, expression of iron metabolism and inflammation-related genes, consequently examined antioxidant-related enzymes genes expression, intracellular iron and reactive oxygen species (ROS) contents, and apoptosis-related genes expression. The results showed that Hb and heme significantly inhibited NTK cells growth and up-regulated iron metabolism-related genes expression in different degrees. The Hb and heme activated the expression of pro-inflammatory cytokines (TNF-α, tumor necrosis factor-α; IL-1β, interleukin 1β; IL-6, interleukin 6), the anti-inflammatory factor (IL-10, interleukin 10) and the chemotactic factors (IL-4, interleukin 4; IL-8, interleukin 8) through NF-κB pathway, meanwhile activated the expression of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GSH-Px). Moreover, the Hb significantly increased intracellular iron and ROS contents while the expression of apoptosis-related genes was significantly activated by both Hb and heme. Current investigation suggested that high oxidative activity of Hb could activate iron metabolism- and inflammation-related genes expression, and increase intracellular iron and ROS levels, lead to up-regulated the expression of apoptosis genes in NTK cells.

Structural characterization and immunomodulatory effects of extracellular polysaccharide from Lactobacillus paracasei VL8 obtained by gradient ethanol precipitation

In this study, gradient ethanol precipitation method was applied to obtain the extracellular polysaccharides of Lactobacillus paracasei VL8 (VL8-EPS). The yields, physicochemical properties, and immunomodulatory effects of VL8-EPS obtained by precipitation at different ethanol concentrations (30%, 50%, and 70%, v/v) were compared. The results showed that VL8-EPSs were high molecular weight sulfated heteropolysaccharides, composed mainly of glucose and galactose, and the alteration of ethanol concentration had an effect on their chemical compositions, molecular weight distributions, monosaccharide composition, and surface structure, while the primary structure remained the same. Among the three polysaccharide fractions, VL8-EPS50 displayed better immunomodulatory activities compared with VL8-EPS30 and VL8-EPS70. VL8-EPS50 was found to exert immunomodulatory effects by enhancing the phagocytic activity of RAW264.7 cells and to promote their secretion of more nitric oxide; it also showed stronger thermal and solution stability. In summary, there was a correlation between the structural characteristics of polysaccharides and their immunomodulatory activity, and VL8-EPS50 was preferentially used for in vivo immunomodulatory activity. Practical Application This study opens up the source of raw materials for functional foods, which can provide some theoretical basis for the research and development of extracellular polysaccharides of lactic acid bacteria and promote their application in the future development of food industry.

The Oxidative Injury of Extracellular Hemoglobin Is Associated With Reactive Oxygen Species Generation of Grass Carp (Ctenopharyngodon idella)

Intravascular hemolysis is a fundamental feature of hemorrhagic venereal infection or tissue and releases the endogenous damage-associated molecular pattern hemoglobin (Hb) into the plasma or tissues, which results in systemic inflammation, vasomotor dysfunction, thrombophilia, and proliferative vasculopathy. However, how the cytotoxic Hb affects the tissues of grass carp remains unclear. Here, we established a hemolysis model in grass carp by injecting phenylhydrazine (PHZ). The data revealed that the PHZ-induced hemolysis increased the content of Hb and activated the antioxidant system in plasma. The histopathology analysis data showed that the PHZ-induced hemolysis increased the accumulation of Hb and iron both in the head and middle kidney. The results of quantitative real-time PCR (qRT-PCR) detection suggested that the hemolysis upregulated the expressions of iron metabolism-related genes. In addition, the immunofluorescence and immunohistochemistry data revealed that the hemolysis caused an obvious deposition of collagen fiber, malondialdehyde (MDA), and 4-hydroxynonenal (4-HNE) accumulation and increased the content of oxidative-related enzymes such as β-galactosidase (β-GAL), lipid peroxide (LPO), and MDA in both the head and middle kidney. Furthermore, the PHZ-induced hemolysis significantly increased the production of reactive oxygen species (ROS), which resulted in apoptosis and modulated the expressions of cytokine-related genes. Taken together, excess of Hb released from hemolysis caused tissue oxidative damage, which may be associated with ROS and inflammation generation.

Hemoglobin induces inflammation through NF-kB signaling pathway and causes cell oxidative damage in grass carp (Ctenopharyngodon idella)

Hemolytic disease in grass carp (C. idella) leads to hemolysis in vivo, releasing damage-related molecular patterns (DAMPs) hemoglobin (Hb; which is rapidly oxidized to Hb-Fe³⁺ and Hb-Fe⁴⁺) and generating a high level of reactive oxygen species (ROS) that cause oxidative damage. However, the effect of cell-free Hb on tissue cells of grass carp has yet to be elucidated. In this study, western blotting (WB) and immunofluorescence analysis (IFA) results showed that PHZ-induced hemolysis caused Hb and iron accumulation, increased the production of ROS and resulted in apoptosis in head kidney and middle kidney of the grass carp. Quantitative real-time PCR (qRT-PCR), WB, and IFA revealed that PHZ-induced hemolysis significantly upregulated the expression of inflammation-related genes through activation of the NF-κB signaling pathway. To further explore the effect of Hb, three forms of Hb (Hb, MetHb, and FerrylHb) were prepared. The incubation with the different forms of Hb and heme markedly upregulated the expression of cytokine genes through NF-κB signaling pathway, which was further confirmed by a specific inhibitor (caffeic acid phenethyl ester, CAPE). Flow cytometry analysis data showed that the stimulation of different forms of Hb and heme increased the production of ROS, and resulted in apoptosis. In summary, our data suggest that the excess cell-free Hb released during hemolysis modulates the inflammatory response through activation of the NF-κB signaling pathway and causes cell oxidative damage and apoptosis.