Effect of lipopolysaccharide on the hemocyte apoptosis of Eriocheir sinensis

An Interleukin-17 Isoform from Thick Shell Mussel Mytilus coruscus Serves as a Mediator of Inflammatory Response

The inflammatory cytokine interleukin-17 (IL17) plays an important role in innate immunity by binding to its receptors (IL17Rs) to activate immune defense signals. To date, information on members of the IL17 family is still very limited in molluscan species. Here, a novel member of the IL17 family was identified and characterized from thick shell mussel Mytilus coruscus, and this gene was designated as McIL17-1 by predicting structural domains and phylogenetic analysis. McIL17-1 transcripts existed in all examined tissues with high expression levels in gills, hemocytes and digestive glands. After the stimuli of different pathogen associated molecular patterns (PAMPs) for 72 h, transcriptional expression of McIL17-1 was significantly upregulated, except for poly I:C stimulation. Cytoplasm localization of McIL17-1 was shown in HEK293T cells by fluorescence microscopy. Further, in vivo and in vitro assays were performed to evaluate the potential function of McIL17-1 played in immune response. McIL17-1 was either knocked down or overexpressed in vivo through RNA inference (RNAi) and recombinant protein injection, respectively. With the infection of living Vibrio alginolyticus, a high mortality rate was exhibited in the McIL17-1 overexpressed group compared to the control group, while a lower mortality rate was observed in the McIL17-1 knocked down group than control group. In vitro, the flow cytometric analysis showed that the apoptosis rate of McIL17-1 inhibited hemocytes was significantly lower than that of the control group after lipopolysaccharide stimulation. These results collectively suggested that the newly identified IL17 isoform is involved in the inflammatory response to bacterial infection in M. coruscus.

Impact of aluminum exposure on oxidative stress, intestinal changes and immune responses in red swamp crayfish (Procambarus clarkii)

Aluminum (Al) is an abundant metal that has been classified as a threatening pollutant due to indiscriminate use and anthropogenic activities. This study aimed to evaluate the impacts of Al on crayfish (Procambarus clarkii), including biochemical change, histological alteration, gut microbial community diversification, and immune changes. The bioaccumulation of Al was detected in the hemolymph and intestine of crayfish after Al exposure at different time points. Results showed that Al exposure significantly induced oxidative stress and caused pathohistological changes on intestinal barrier structures in crayfish. It was found that the intestinal microbiota was affected by retained Al and the intestinal community diversity was changed after Al treated in the crayfish. Furthermore, Al exposure affected the immunity in crayfish, by altering the expression of a set of immune-related genes, as well as reducing the phenoloxidase and lysozyme activities. Moreover, Al exposure promoted hemocytes apoptosis and impaired hemophagocytic capacity against Vibro parahamolyticus, resulting in higher mortality of crayfish upon bacterial infection. Taken these results together, we conclude that excessive Al exposure caused adverse effects on multiple biological processes of crayfish and Al pollution is a potential threat to crayfish culture.

Oxidative stress and immune response of hepatopancreas in Chinese mitten crab Eriocheir sinensis under lipopolysaccharide challenge

Chinese mitten crab (Eriocheir sinensis; H. Milne Edwards, 1853) is one of the important farmed crustaceans in China. Lipopolysaccharide (LPS), as a harmful factor, is prone to occur during the farming process of crabs. Aiming to test the hypothesis that damage degrees of the hepatopancreas in E. sinensis is correlated to LPS concentrations, in this study, E. sinensis were injected with LPS (50 μg/kg, and 500 μg/kg) and analyzed for the activity of antioxidant and immune-related enzymes, immune-related gene expression, and histopathological of hepatopancreas. As result, the hepatopancreas of E. sinensis immune-related genes, i.e., Dorsal, HSP90, Toll2, TLRs, Tube, and proPO, were significantly affected by LPS challenge. Among immune-related genes, Dorsal and proPO might play key roles in combating the LPS challenge. The activity of CAT gradually decreased with the increase of time, and the total antioxidant capacity was decreased after LPS challenge, indicating the inhibition of LPS on the antioxidant system. Interestingly, the decreasing trend of AKP and ACP activity suggested the immune system of crabs was affected by LPS challenge. The hepatopancreas section showed that the damage degree of hepatopancreas was different under the challenge of LPS with different concentrations, and the damage degree was proportional to the concentration. Our findings provide useful information for understanding the mechanism of hepatopancreas injury of E. sinensis induced by LPS infection.

Microplastics can aggravate the impact of ocean acidification on the health of mussels: Insights from physiological performance, immunity and byssus properties

Ocean acidification may increase the risk of disease outbreaks that would challenge the future persistence of marine organisms if their immune system and capacity to produce vital structures for survival (e.g., byssus threads produced by bivalves) are compromised by acidified seawater. These potential adverse effects may be exacerbated by microplastic pollution, which is forecast to co-occur with ocean acidification in the future. Thus, we evaluated the impact of ocean acidification and microplastics on the health of a mussel species (Mytilus coruscus) by assessing its physiological performance, immunity and byssus properties. We found that ocean acidification and microplastics not only reduced hemocyte concentration and viability due to elevated oxidative stress, but also undermined phagocytic activity of hemocytes due to lowered energy budget of mussels, which was in turn caused by the reduced feeding performance and energy assimilation. Byssus quality (strength and extensibility) and production were also reduced by ocean acidification and microplastics. To increase the chance of survival with these stressors, the mussels prioritized the synthesis of some byssus proteins (Mfp-4 and Mfp-5) to help maintain adhesion to substrata. Nevertheless, our findings suggest that co-occurrence of ocean acidification and microplastic pollution would increase the susceptibility of bivalves to infectious diseases and dislodgement risk, thereby threatening their survival and undermining their ecological contributions to the community.

Time-Course of the Innate Immune Response of the Terrestrial Crustacean Porcellio scaber After Injection of a Single Dose of Lipopolysaccharide

Invertebrates, including crustaceans, rely on cellular and humoral immune responses to protect against extrinsic and intrinsic factors that threaten their integrity. Recently, different immune parameters have been increasingly used as biomarkers of effects of pollutants and environmental change. Here, we describe the dynamics of the innate immune response of the terrestrial crustacean Porcellio scaber to injection of a single dose of lipopolysaccharide (LPS), an important molecular surface component of the outer membrane of Gram-negative bacteria. The aim was to provide a basis for interpretation of change in immune parameters as a result of different challenges, including microplastics and nanoplastics exposure. Changes in total and differential numbers of hemocytes, hemocyte viability, and humoral immune parameters (i.e., phenoloxidase-like activity, nitric oxide levels) were assessed at different times (3, 6, 12, 24, 48 h). An injection of 0.5 μg/μL LPS into the body of P. scaber resulted in a rapid decrease (3 h after LPS injection) in the total number of hemocytes and reduced viability of the hemocytes. This was accompanied by changed proportions of the different hemocyte types, as a decrease in the numbers of semigranulocytes and granulocytes, and a marked increase in the numbers of hyalinocytes. In addition, phenoloxidase-like activity and nitric oxide levels in the hemolymph were increased at 3 h and 6 h, respectively, after the LPS challenge. Forty-eight hours after LPS injection, the immune parameters in the hemolymph of P. scaber had returned to those before the LPS challenge. This suggests that the innate immune system successfully protected P. scaber from the deleterious effects of the LPS challenge. These data indicate the need to consider the dynamics of innate immune responses of P. scaber when effects of infections, pollutants, or environmental changes are studied. We also propose an approach to test the immunocompetence of organisms after different challenges in ecotoxicity studies, based on the dynamics of their immune responses.

Stressor-Dependant Changes in Immune Parameters in the Terrestrial Isopod Crustacean, Porcellio scaber: A Focus on Nanomaterials

We compared the changes of selected immune parameters of Porcellio scaber to different stressors. The animals were either fed for two weeks with Au nanoparticles (NPs), CeO2 NPs, or Au ions or body-injected with Au NPs, CeO2 NPs, or lipopolysaccharide endotoxin. Contrary to expectations, the feeding experiment showed that both NPs caused a significant increase in the total haemocyte count (THC). In contrast, the ion-positive control resulted in a significantly decreased THC. Additionally, changes in phenoloxidase (PO)-like activity, haemocyte viability, and nitric oxide (NO) levels seemed to depend on the stressor. Injection experiments also showed stressor-dependant changes in measured parameters, such as CeO2 NPs and lipopolysaccharide endotoxin (LPS), caused more significant responses than Au NPs. These results show that feeding and injection of NPs caused an immune response and that the response differed significantly, depending on the exposure route. We did not expect the response to ingested NPs, due to the low exposure concentrations (100 μg/g dry weight food) and a firm gut epithelia, along with a lack of phagocytosis in the digestive system, which would theoretically prevent NPs from crossing the biological barrier. It remains a challenge for future research to reveal what the physiological and ecological significance is for the organism to sense and respond, via the immune system, to ingested foreign material.

Gender Differences in Hemocyte Immune Parameters of Hong Kong Oyster Crassostrea hongkongensis During Immune Stress

Gender differences in individual immune responses to external stimuli have been elucidated in many invertebrates. However, it is unclear if gender differences do exist in the Hong Kong oyster Crassostrea hongkongensis, one of the most valuable marine species cultivated along the coast of South China. To clarify this, we stimulated post-spawning adult C. hongkongensis with Vibrio harveyi and lipopolysaccharide (LPS). Gender-based differences in some essential functional parameters of hemocytes were studied via flow cytometry. Obvious gender-, subpopulation-, and immune-specific alterations were found in the hemocyte immune parameters of C. hongkongensis. Three hemocyte subpopulations were identified: granulocytes, semi-granulocytes, and agranulocytes. Granulocytes, the chief phagocytes and major producers of esterase, reactive oxygen species, and nitric oxide, were the main immunocompetent hemocytes. Immune parameter alterations were notable in the accumulation of granulocyte esterase activities, lysosomal masses, nitric oxide levels, and granulocyte numbers in male oysters. These results suggest that post-spawning-phase male oysters possess a more powerful immune response than females. Gender and subpopulation differences in bivalve immune parameters should be considered in the future analysis of immune parameters when studying the impact of pathogenic or environmental factors.

Immunopathogenesis of hematopoietic tissues in response to Vibrio parahaemolyticus (VPAHPND) infection in Macrobrachium rosenbergii

In crustacean, hemocytes are known as crucial components of crustaceans' innate immunity against pathogens. Drastic hemocytes reduction during infectious disease is apparently related to disease severity and calls for a health status evaluation and aquaculture management. The molecular pathogenesis of hemocytes loss during bacterial infection was elucidated with VP_AHPND challenged in M. rosenbergii. We report herein a correlation between hemocyte loss and the pathogenicity and aggressive immune response in hematopoietic tissues of moribund M. rosenbergii. In this study, adult freshwater prawn was administered an LC₅₀ dose of VP_AHPND; bacterial clearance ensued, and success was reached within 24 h. Hemocytes increased in survival, yet drastically decreased in moribund prawn. Pathological analysis of hematopoietic tissue of moribund prawn showed apparent abnormal signs, including the presence of bacteria, a small number of mitotic cells, cellular swelling, loosening of connective tissue, and karyorrhectic nuclei cells. A significant upregulation of a core apoptotic machinery gene, caspase-3, was detected in hematopoietic tissue of moribund shrimp, but not in those of Escherichia coli DH5α (non-pathogenic bacteria) and VP_AHPND survival prawn. The highest level was found in the moribund group, which confirms the occurrence of apoptosis in this hematopoietic tissue. Further, our results suggest that hematopoietic tissue damage may arise from inflammation triggered by an aggressive immune response. Immune activation was indicated by the comparison of immune-related gene expression between controls, E. coli (DH5α)-infected (non-pathogenic), and VP_AHPND-infected survival groups with moribund prawn. RT-PCR revealed a significant upregulation of all genes in hematopoietic tissues and hemocytes within 6-12 h and declined by 24 h. This evident related to the almost VP_AHPND are clearance in survival and E. coli (DH5α) challenged group in contrast with drastic high expression was determined in moribund group. We conclude that a reduction of renewing circulating hemocytes in fatally VP_AHPND-infected prawn was caused by an acute self-destructive immune response by hematopoietic cells.

An inhibitor of apoptosis protein (EsIAP1) from Chinese mitten crab Eriocheir sinensis regulates apoptosis through inhibiting the activity of EsCaspase-3/7-1

Inhibitor of apoptosis proteins (IAPs) maintain the balance between cell proliferation and cell death by inhibiting caspase activities and mediating immune responses. In the present study, a homolog of IAP (designated as EsIAP1) was identified from Chinese mitten crab Eriocheir sinensis. EsIAP1 consisted of 451 amino acids containing two baculoviral IAP repeat (BIR) domains with the conserved Cx2 Cx6 Wx3 Dx5 Hx6 C motifs. EsIAP1 mRNA was expressed in various tissues and its expression level in hemocytes increased significantly (p < 0.01) at 12–48 h after lipopolysaccharide stimulation. In the hemocytes, EsIAP1 protein was mainly distributed in the cytoplasm. The hydrolytic activity of recombinant EsCaspase-3/7-1 against the substrate Ac-DEVD-pNA decreased after incubation with rEsIAP1. Moreover, rEsIAP1 could directly combine with rEsCaspase-3/7-1 in vitro. After EsIAP1 was interfered by dsRNA, the mRNA expression and the hydrolytic activity of EsCaspase-3/7-1 increased significantly, which was 2.26-fold (p < 0.05) and 1.71-fold (p < 0.05) compared to that in the dsGFP group, respectively. These results collectively demonstrated that EsIAP1 might play an important role in apoptosis pathway by regulating the activity of EsCaspase-3/7-1 in E. sinensis.

Classification and characterization of hemocytes from two Asian horseshoe crab species Tachypleus tridentatus and Carcinoscorpius rotundicauda

In present study, transmission electron microscopy and flow cytometry were utilized to investigate the classification, characterization and immune functions of hemocytes from horseshoe crab, Tachypleus tridentatus and Carcinoscorpius rotundicauda. Three types of hemocytes were distinguished respectively: the granular cell, the semi-granular cell and the hyaline cell by transmission electron microscopy, while three hemocyte subpopulations (Gate 1 cell, Gate 2 cell, Gate 3 cell) were classified by flow cytometry. Hyaline cell was the major cell type with the highest nuclear-cytoplasmic ratio and granular cell and semi-granular cell showed lower ratios. Immune parameters of hemocytes in horseshoe crabs were investigated by flow cytometry. Different hemocyte subpopulations respond for diverse functions. Lysosomal contents and hemocyte mortality in Gate 3 cell subpopulation were higher than that in other subpopulations, while reactive oxygen species, phagocytosis and non-specific esterase, in Gate 1 cell subpopulation, were higher than those in other subpopulations. The hemocyte types between the two species had no significant differences in staining or morphology.

A novel effector caspase (Caspase-3/7-1) involved in the regulation of immune homeostasis in Chinese mitten crab Eriocheir sinensis

Caspases are a conserved family of cysteine proteases characterized by specificity for aspartic acid and play an essential role in cell apoptosis. In the present study, a novel effector caspase (designated as EsCaspase-3/7-1) was identified from Chinese mitten crab Eriocheir sinensis. The open reading frame of EsCaspase-3/7-1 cDNA was of 972 bp, encoding a polypeptide of 323 amino acids. EsCaspase-3/7-1 contained an N-terminal prodomain and a conservative C-terminal CASc domain, with the conserved active site "QACRG". The mRNA transcripts of EsCaspase-3/7-1 were constitutively expressed in all the examined tissues with high expression level in hemocytes, hepatopancreas and gill. The EsCaspase-3/7-1 protein was mainly distributed in the cytoplasm of hemocytes. After Aeromonas hydrophila and lipopolysaccharide (LPS) stimulations, the mRNA expression level of EsCaspase-3/7-1 in hemocytes increased significantly. The mRNA expression level of EsCaspase-3/7-1 in hemocytes was significantly up-regulated after H₂O₂ treatment in vitro. The recombinant EsCaspase-3/7-1 protein (rEsCaspase-3/7-1) was capable of hydrolyzing the substrate Ac-DEVD-pNA rather than Ac-YVAD-pNA and Ac-VEID-pNA in vitro, and exhibited binding activity to LPS. These results demonstrated that EsCaspase-3/7-1 might act as an LPS receptor, and play an important role in the regulation of immune homeostasis of E. sinensis.

The cyclin-dependent kinase 2 (CDK2) mediates hematopoiesis through G1-to-S transition in Chinese mitten crab Eriocheir sinensis

Cyclin-dependent kinases (CDKs), a family of cell cycle-related serine/threonine kinases, participate in various biological processes, and play crucial roles in the innate immunity. In the present study, a CDK2 (designed as EsCDK2) with a serine/threonine protein kinase catalytic domain was identified from Chinese mitten crab (Eriocheir sinensis). The full-length cDNA sequence of EsCDK2 was of 2405 bp with an open reading frame (ORF) of 909 bp. EsCDK2 shared 66%-81% sequence similarities with previously identified CDK2s. It was clustered with the CDK2 from Penaeus monodon in the invertebrate branch of the phylogenetic tree. The mRNA transcripts of EsCDK2 were highly expressed in hematopoietic tissue (HPT) and gonad, while lower in hemocytes, heart, gills, and muscle. EsCDK2 protein distributed in both cytoplasm and nucleus of HPT cells. The expression of EsCDK2 mRNA in HPT was significantly up-regulated and peaked at 3 h post stimulations with Aeromonas hydrophila (2.31-fold, p < 0.05) and Lipopolysaccharide (LPS) (2.02-fold, p < 0.05). After exsanguination, the total hemocyte counts (THC) decreased significantly to 0.42 × 10⁷/ml (0.39-fold, p < 0.05) at 0.5 h, then returned to a normal level at 6 h, while the mRNA expression of EsCDK2 in HPT cells was up-regulated at the early phase from 0.5 h to 6 h. After injection of EsCDK2-dsRNA, the mRNA expression level of EsCDK2 in HPT and THC both decreased to 0.53-fold (p < 0.01) and 0.78-fold (p < 0.05) at 24 h, respectively, and the percentage of new-born hemocytes in HPT also decreased significantly from 37.7% to 16.3% (0.43-fold, p < 0.01). After knocking down of EsCDK2, THC decreased dramatically at 6 h (0.65-fold, p < 0.01) post exsanguination, while returned normal at 6 h in PBS group. After interference of EsCDK2 mRNA expression, the percentage of G0-G1 phase cells significantly increased to 85.01% (1.26-fold, p < 0.01), while S phase and G2-M phase cells significantly decreased to 7.92% (0.46-fold, p < 0.01) and 7.07% (0.43-fold, p < 0.01) respectively, indicating that the cell cycle of HPT cells arrested at G1 phase. These results collectively demonstrated that EsCDK2 participated in the regeneration of hemocytes or hematopoiesis by regulating the transition from G1 to S phase in the cell cycle, and involves in the innate immune responses of E. sinensis.

PGC-1α regulates the cell cycle through ATP and ROS in CH1 cells

Peroxisome proliferator-activated receptor-γ coactivator 1α (PGC-1α) is a transcriptional co-activator involved in mitochondrial biogenesis, respiratory capacity, and oxidative phosphorylation (OXPHOS). PGC-1α plays an important role in cellular metabolism and is associated with tumorigenesis, suggesting an involvement in cell cycle progression. However, the underlying mechanisms mediating its involvement in these processes remain unclear. To elucidate the signaling pathways involved in PGC-1α function, we established a cell line, CH1 PGC-1α, which stably overexpresses PGC-1α. Using this cell line, we found that over-expression of PGC-1α stimulated extra adenosine triphosphate (ATP) and reduced reactive oxygen species (ROS) production. These effects were accompanied by up-regulation of the cell cycle checkpoint regulators CyclinD1 and CyclinB1. We hypothesized that ATP and ROS function as cellular signals to regulate cyclins and control cell cycle progression. Indeed, we found that reduction of ATP levels down-regulated CyclinD1 but not CyclinB1, whereas elevation of ROS levels down-regulated CyclinB1 but not CyclinD1. Furthermore, both low ATP levels and elevated ROS levels inhibited cell growth, but PGC-1α was maintained at a constant level. Together, these results demonstrate that PGC-1α regulates cell cycle progression through modulation of CyclinD1 and CyclinB1 by ATP and ROS. These findings suggest that PGC-1α potentially coordinates energy metabolism together with the cell cycle.

Identification, characterization and expression analysis of ERK2 in Chinese mitten crab Eriocheir sinensis after challenge with LPS and Aeromonas hydrophila

Farming of Eriocheir sinensis was seriously threaten by the infection of opportunistic pathogens, especially the gram-negative bacterium. In this paper, we analyzed the sequence of extracellular signal-regulated kinases 2 (ERK2) of E. sinensis (EsERK2) and its expression levels after challenge with LPS and Aeromonas hydrophila in both in vivo and in vitro examination. The full-length cDNA sequence of EsERK2 was 2455 bp in size with an open reading frame (ORF) of 1095 bp, encoding the protein of 365 amino acids. It owned a predicted molecular mass of 42.4 kDa and a theoretical isoelectric point (pI) of 5.93. EsERK2 was distributed in all examined tissues including haemocyte, gonad, hepatopancreas, gill, muscle heart, stomach and intestine, but its expression level was significantly higher in hepatopancreas than it in other examined tissues. The expression level of EsERK2 increased significantly after LPS challenge at 2 h (P < 0.05), and then gradually increased and reached highest at 16 h. However, its expression level decreased significantly after A. hydrophila challenge at 4 h, and then gradually decreased till 24 h (P < 0.05), and returned to its initial value at 36 h. According to the immunofluorescence assay and western blotting assay, EsERK2 was found to be distributed mainly in cytoplasm of haemocyte, and its expression level showed a prominent boost in primary cultured haemocytes after challenge with LPS and A. hydrophila in vitro. These results indicated that the expression of EsERK2 was sensitive to the exterior stimulants and its encoding protein might be associated with the signaling transduction in response to exterior pathogens in E. sinensis.