Functional characterization of hemocytes from Chinese mitten crab Eriocheir sinensis by flow cytometry

Dynamic pathology and pathogen distribution of the yeast Metschnikowia bicuspidata in the Chinese mitten crab (Eriocheir sinensis)

In this study, the "milky disease" model of Eriocheir sinhensis was constructed via intramuscular injection with the pathogenic yeast Metschnikowia bicuspidata. The dynamic pathological changes of E. sinensis after injection were elucidated with two staining methods (haemotoxylin-eosin and alcian blue periodic acid-Schiff) and fluorescence in situ hybridization technology. Anatomical observation revealed three stages of the "milky disease": no clinical signs (1-4 days after infection), the appearance of signs of disease (5-7 days), and significant liquefaction (10 days). Histological observation also revealed three stages of the disease: yeast diffusion (1-2 days after infection), yeast slow development (3-4 days), and yeast rapid proliferation (5 days). And FISH technique was suitable for the early detection of infection with M. bicuspidata in E. sinensis. We found that M. bicuspidata spread to the whole body of the crab through the haemolymph and developed into fungal septicaemia. These results elucidate the systemic pathological characteristics of "milky disease" in E. sinensis and suggest the pathogenic mechanism of M. bicuspidata.

H2O2-Induced Oxidative Stress Responses in Eriocheir sinensis: Antioxidant Defense and Immune Gene Expression Dynamics

Eriocheir sinensis, a key species in China's freshwater aquaculture, is threatened by various diseases, which were verified to be closely associated with oxidative stress. This study aimed to investigate the response of E. sinensis to hydrogen peroxide (H2O2)-induced oxidative stress to understand the biological processes behind these diseases. Crabs were exposed to different concentrations of H2O2 and their antioxidant enzyme activities and gene expressions for defense and immunity were measured. Results showed that activities of antioxidant enzymes-specificallysuperoxide dismutase (SOD), catalase (CAT), total antioxidant capacity(T-AOC), glutathione (GSH), and glutathione peroxidase (GSH-Px)-varied with exposure concentration and duration, initially increasing then decreasing. Notably, SOD, GSH-Px, and T-AOC activities dropped below control levels at 96 h. Concurrently, oxidative damage markers, including malondialdehyde (MDA), H2O2, and 8-hydroxy-2'-deoxyguanosine (8-OHdG) levels, increased with exposure duration. The mRNA expression of SOD, CAT, and GSH-Px also showed an initial increase followed by a decrease, peaking at 72 h. The upregulation of phenoloxidaseloxidase (proPO) and peroxinectin (PX) was also detected, but proPO was suppressed under high levels of H2O2. Heat shock protein 70 (HSP70) expression gradually increased with higher H2O2 concentrations, whereas induced nitrogen monoxide synthase (iNOS) was upregulated but decreased at 96 h. These findings emphasize H2O2's significant impact on the crab's oxidative and immune responses, highlighting the importance of understanding cellular stress responses for disease prevention and therapy development.

Changes in Hemolymph Microbiota of Chinese Mitten Crab (Eriocheir sinensis) in Response to Aeromonas hydrophila or Staphylococcus aureus Infection

The Chinese mitten crab (Eriocheir sinensis) has significant economic potential in both the Chinese domestic and global markets. The hemolymph microbiota is known to play a critical role in regulating physiological and biochemical functions in crustaceans. However, the study of the hemolymph microbiota of E. sinensis in response to infections has not been undertaken. In this study, changes in the composition and function of the hemolymph microbiota in E. sinensis infected with either Staphylococcus aureus (Sa) or Aeromonas hydrophila (Ah) were investigated using 16S rRNA sequencing, with a phosphate buffer saline (PBS) injection serving as the control. Results showed that the dominant hemolymph microbiota of E. sinensis were Proteobacteria, Bacteroidota, and Firmicutes. The relative abundance of the phyla Firmicutes, Bdellovibrionota, and Myxococcota was significantly reduced in both Sa and Ah groups compared to the PBS group. At the genus level, compared to the PBS group, a significant increase in the abundance of Flavobacterium and Aeromonas was found in both Ah and Sa groups. The analysis of the functional profile showed that pathways related to 'cell growth and death', 'metabolism of terpenoids and polyketides', 'cancers', 'lipid metabolism', 'neurodegenerative diseases', 'metabolism of other amino acids', 'xenobiotics biodegradation and metabolism', and 'circulatory system and endocrine system' were predominant in the Ah group. Meanwhile, pathways related to 'metabolism or genetic information progressing', such as 'translation', 'metabolic diseases', and 'cellular processes and signaling', were enriched in the Sa group. This study revealed the effects of pathogens (S. aureus or A. hydrophila) on the maintenance of the hemolymph microbiota in E. sinensis. It shed light on the mechanisms employed by the hemolymph microbiota of E. sinensis under pathogen stimulation.

The involvement of hypoxia inducible factor-1α on the proportion of three types of haemocytes in Chinese mitten crab under hypoxia stress

Hypoxia triggers diverse cell physiological processes, and the hypoxia inducible factors (HIFs) are a family of heterodimeric transcription factors that function as master regulators to respond to hypoxia in different cells. However, the knowledge about the hypoxic responses especially cell alteration mediated by HIFs under hypoxia stress is still limited in crustaceans. In the present study, a hypoxia-inducible factor-1α (HIF-1α) gene was identified (designed as EsHIF-1α). The relative mRNA expression level of EsHIF-1α was highest in hyalinocytes and lowest in granulocytes among three types of haemocytes in crabs. Hypoxia could significantly increase the EsHIF-1α protein expression level in haemocytes. Meanwhile, the proportion of hyalinocytes began to increase from 3 h post hypoxia treatment, and reached the highest level at 24 h. However, the opposite variation in proportion of granulocytes was observed under hypoxia stress. Further investigation showed that the inhibition of EsHIF-1α induced by KC7F2 (HIF-1α inhibitor) could lead to the significant decrease in the proportion of hyalinocytes under hypoxia stress, and also resulted in an increase of granulocytes proportion. While, after EsHIF-1α was activated by IOX4 (HIF-1α activator), the proportion of hyalinocytes was significantly up-regulated and the proportion of granulocytes was significantly down-regulated under post hypoxia treatment. These results collectively suggested that EsHIF-1α was involved in the regulation of proportion of three types of haemocytes induced by hypoxia stress, which provided vital insight into the understanding of the crosstalk between hypoxia and cell development in invertebrates.

A novel c-type lysozyme from Litopenaeus vannamei exhibits potent antimicrobial activity

Lysozyme is relevant to the innate immune system as a vital protein for crustaceans. In the present study, we cloned and characterized a novel c-type lysozyme gene (LvLYZ) from the Pacific white shrimp (Litopenaeus vannamei). The obtained full-length cDNA of LvLYZ was 990 bp and contained an open reading frame of 693 bp. Its deduced amino acid sequence consisted of 230 amino acids (aa) with a 17 aa signal peptide at the N-terminal and 130 aa functional domains. The multiple sequence alignment (MSA) indicated that the typical active sites in LvLYZ were similarly conserved as c-type lysozymes from other species. The transcription of LvLYZ appeared in all detected tissues and had relatively higher expression levels in hemocytes, hepatopancreas, gill and intestine. The mRNA expression profiles of LvLYZ were up-regulated in hemocyte and hepatopancreas post the stimulation of Vibrio parahaemolyticus or white spot syndrome virus (WSSV), respectively. The recombinant protein of LvLYZ (rLvLYZ) exhibited antibacterial activities against various microbes, including Escherichia coli, Vibrio splendidus, Micrococcaus luteus, Vibrio parahaemolyticus and Staphylococcus aureus. These results indicated that LvLYZ could cope with bacteria in L. vannamei and may play a significant role in immune response against invading pathogens.

Flow cytometric characterization of the hemocytes of sea hares from tidal pools in Jeju Island off the south coast of Korea

The members in the family Aplysidae known as sea hares play a crucial role as a grazer in small tidal pools or shallow subtidal hard bottoms. Like other marine gastropods, hemocyte types and functions of sea hares are limitedly known. This study identified and characterized the hemocytes of common Aplysia species Aplysia kurodai, A. juliana, and A. oculifera in rocky tidal pools in Jeju Island off the south coast of Korea using flow cytometry and light microscopy. The flow cytometry identified three different hemocytes in the hemolymph of the three sea hare species: granulocytes, hyalinocytes, and blast-like cells. The granulocytes exhibited pseudopodia on the cell surface and granules in the cytoplasm. Morphology of the hyalinocyte was similar to that of the granulocytes, while they lack cytoplasmic granules. The blast-like cells were small and round, with very thin cytoplasm. The hyalinocytes were the most abundant in the hemolymph, accounting for 89.8-92.6% of the total hemocytes. Flow cytometry indicated that the granulocytes and blast-like cells were less than 5.6% and 5.4% of the total hemocyte populations. Flow cytometry also revealed that the granulocytes and hyalinocytes are engaged in cellular defensive activities such as intra-cellular lysosomal content, phagocytosis, and ROS production. The mean lysosomal contents of the granulocytes (0.4 × 10⁵-0.2 × 10⁵ A U.) were 2-3 times higher than that of hyalinocytes (0.2 × 10⁵-0.6 × 10⁵ A U.). In addition, the ROS production of the granulocytes (0.98 × 10⁶-1.95 × 10⁶ A U.) was about twice higher than that of the hyalinocytes (0.62 × 10⁶-1.14 × 10⁶ A U.). Of the three species of sea hares, the granulocytes showed comparatively higher phagocytosis capacity (70.4-92.3%) than that of the hyalinocytes (34.8-46.0%). Flow cytometry and microscopy indicated that the hemocyte types and their functions were identical, regardless of the species.

Microplastics, chlorpyrifos and their mixtures modulate immune processes in the terrestrial crustacean Porcellio scaber

Microplastics and agrochemicals are common pollutants in terrestrial ecosystems. Their interaction during coexistence in soils may influence their fate and adverse effects on terrestrial organisms. The aim of this study was to investigate how the exposure to two types of microplastics; polyester fibres, and crumb rubber; induce changes in immune parameters of Porcellio scaber and if the co-exposure of microplastics affects the response induced by the organophosphate pesticide chlorpyrifos. A number of immune parameters, such as total haemocyte count, differential haemocyte count, and phenoloxidase-like activity were assessed. In addition, the acetylcholinesterase (AChE) activity in the haemolymph was evaluated as a measure of the bioavailability of chlorpyrifos. After three weeks of exposure, the most noticeable changes in the measured immune parameters and also a significantly reduced AChE activity were seen in chlorpyrifos-exposed animals. Both types of microplastic at environmentally relevant concentrations caused only slight changes in immune parameters which were not dependent on the type of microplastic, although the two types differed significantly in terms of the chemical complexity of the additives. Mixtures of chlorpyrifos and microplastics induced changes that differed from individual exposures. For example, alterations in some measured parameters suggested a reduced bioavailability of chlorpyrifos (AChE activity, haemocyte viability) caused by both types of microplastics exposure, but the increase of haemocyte count was promoted by the presence of fibres implying their joint action. In conclusion, this study suggests that immune processes in P. scaber are slightly changed upon exposure to both types of microplastics and microplastics can significantly modulate the effects of other co-exposed chemicals. Further research is needed on the short-term and long-term joint effects of microplastics and agrochemicals on the immunity of soil invertebrates.

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.

Modulations of immune parameters caused by bacterial and viral infections in the terrestrial crustacean Porcellio scaber: Implications for potential markers in environmental research

The terrestrial crustacean Porcellio scaber (Crustacea: Isopoda) is an established invertebrate model in environmental research. Preceding research using isopods did not widely use immune markers. In order to advance their use in research, knowledge of the reference values in control animals as well as variations during infections is of importance. This study presents, for the first time, the morphology, and ultrastructure of the three main haemocyte types of Porcellio scaber as semigranulocytes (SGCs), granulocytes (GCs), and hyalinocytes (HCs), with the latter having two subtypes, using various light and electron microscopy approaches. The modulation of selected immune cellular and humoral parameters of P. scaber in symptomatic phases of Rhabdochlamydia porcellionis and Iridovirus IIV-31 infections is presented. A clear difference in the immune responses of bacterial and viral infections was shown. Remarkable changes in total haemocyte count (THC) values and the proportions of three different haemocyte types were found in animals with a viral infection, which were not as significant in bacterially infected animals. Modified NO levels and SOD activity were more pronounced in cases of bacterial infection. Knowledge of the morphological and ultrastructural features of distinct haemocyte types, understanding the baseline values of immune parameters in control animals without evident symptoms of infection, and the influence that infections can have on these parameters can serve as a basis for the further use of P. scaber immune markers in environmental research.

Peroxiredoxin 6 modulates Toll signaling pathway and protects DNA damage against oxidative stress in red swamp crayfish (Procambarus clarkii)

Peroxiredoxin 6 (Prx6) is an important member of the peroxiredoxin family that plays critical roles in protecting host against the toxicity of oxidative stress and participates in cell signaling. Herein, we report Prx6 gene from red swamp crayfish, Procambarus clarkii. The cDNA fragment of PcPrx6 was 660 bp, encoding a 219 amino acid residues protein. The quantitative real time PCR analysis showed ubiquitous expression of PcPrx6 mRNA in the tested tissues. The challenge with peptidoglycan and Poly I:C remarkably suppressed the mRNA level of PcPrx6 in hepatopancreas at 3, 12, 48 h compared with the PBS control. However, the expression level significantly increased after 36 h of their treatment. The knockdown of PcPrx6 by small interference RNA significantly enhanced the transcript levels of Toll pathway-responsive genes at 24 h. Recombinant PcPrx6 protein was purified using affinity chromatography and analyzed for its biological role. The results revealed that the recombinant PcPrx6 protein manifested the ability to protect supercoiled DNA damage from oxidative stress elicited by mixed function oxidative assay. Altogether, PcPrx6 may have multiple functional roles in the physiology of P. clarkii, since it negatively regulates the Toll signaling transduction and protects supercoiled DNA damage from oxidative stress.

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.

Dietary fructooligosaccharide can mitigate the negative effects of immunity on Chinese mitten crab fed a high level of plant protein diet

An 8-week feeding trial was carried out under controlled condition to evaluate the effect of dietary fructooligosaccharide (FOS) on growth performance, whole body composition, antioxidant status and immunity of crabs fed high levels of plant protein diets. Thus, six experimental diets were formulated (designated as F₀P₅₀, F₀P₆₀, F₀P₇₀, F_0.2P₅₀, F_0.2P₆₀ and F_0.2P₇₀), which contain two FOS levels (0 or 0.2%) and three plant protein levels (50, 60, or 70%) according to a 2 × 3 factorial design. The results showed that weight gain increased significantly as dietary plant protein level decreased from 70% to 50%. At 50% plant protein level, the addition of 0.2% FOS can significantly elevate weight gain (WG) (P < 0.05). The highest value in survival rate was observed in crabs fed F_0.2P₅₀ and F_0.2P₆₀ diet. Crabs fed F_0.2P₅₀ diet showed significantly higher crude protein content (P < 0.05) compared with those in other groups, but there were no significant differences in the contents of moisture, crude lipid and ash among all groups (P > 0.05). Catalase (CAT) activity in crabs fed F_0.2P₅₀ increased significantly (P < 0.05) compared with crabs fed F₀P₆₀, F₀P₇₀, F_0.2P₆₀ and F_0.2P₇₀, but malondialdehyde (MDA) concentrations decreased significantly (P < 0.05). Meanwhile, nitric oxide (NO) concentration, acid phosphatase (ACP) and alkaline phosphatase (AKP) activities of crabs fed 0.2% FOS diets increased significantly (P < 0.05) compared with crabs fed 0% FOS diets. The expressions of prophenoloxidase (propo) was significantly (P < 0.05) affected only by dietary plant protein levels with the highest values observed in 50% plant protein diet, whereas the opposite was true for Myeloid differentiation factor 88 (myd88). The mRNA expressions of mitochondrial manganese superoxide dismutase (mtmnsod), lipopolysaccharide-induced TNF-α factor (litaf) and toll like receptors (tlrs) were significantly affected (P < 0.05) by both FOS and plant protein levels. The cytosolic manganese superoxide dismutase (cytmnsod) mRNA expressions in F_0.2P₅₀ and F_0.2P₆₀ groups were significantly higher than those in F₀P₇₀ and F_0.2P₇₀ groups. The results in this study indicated that supplementation with 0.2% FOS can enhance growth performance in crabs fed lower plant protein diets and as well improve immunity in those fed with higher plant protein diets.

Molecular characterization of glutaminyl-peptide cyclotransferase(QPCT)in Scylla paramamosain and its role in Vibrio alginolyticus and white spot syndrome virus (WSSV) infection

Glutaminyl-peptide cyclotransferase (QPCT) catalyzes the posttranslational modification of an N-terminal glutamate of proteins to pyroglutamate. This renders the protein more resistant to protease degradation, more susceptible to hydrophobic interactions, aggregation, and neurotoxic. In this study, we evaluated the influence of QPCT in the crab Scylla paramamosain infected with white spot syndrome virus (WSSV) or with Vibrio alginolyticus. A cDNA clone, encompassing the entire 2445 bp of the S. paramamosain QPCT gene, containing a 1113 bp open reading frame (ORF) encoding a 370 amino acid protein was cloned from S. paramamosain. Real-time PCR indicated that QPCT was primarily expressed in the digestive tract of S. paramamosain, was up-regulated in hemocytes after infection with V. alginolyticus, and down-regulated in hemocytes after infection with WSSV. Knockdown of QPCT expression by double-stranded RNA (QPCT-dsRNA) resulted in down-regulation of prophenoloxidase (proPO) and crustin antimicrobial peptide, whereas myosin-II-essential-light-chain-like-protein was significantly up-regulated in hemocytes at 24 h post QPCT-dsRNA treatment. WSSV challenge in crabs treated with QPCT-dsRNA resulted in a reduction in viral burden and in the apoptotic rate of crab hemocytes, while the phagocytic activity of crab hemocytes and overall mortality rate were increased. This suggests that WSSV might take advantage of QPCT to benefit its replication. In contrast, V. alginolyticus infection in crabs treated with QPCT-dsRNA indicated that the apoptotic rate and phagocytic activity of hemocytes, and overall incidence of mortality, were increased compared to mock-treated animals, indicating that QPCT might be a resistance factor in bacterial infection. These results increase our understanding of the function of QPCT and its role in the innate immunity of S. paramamosain.

Transcriptome sequencing reveals the involvement of reactive oxygen species in the hematopoiesis from Chinese mitten crab Eriocheir sinensis

Reactive oxygen species (ROS) produced in vivo during various electron transfer reactions are generally kept at a certain level since they are harmful to cells. However, it can sensitize hematopoietic progenitors to differentiation, and plays a signaling role in the regulation of hematopoietic cell fate. In the present study, the transcriptomes of crab HPT and hemocytes were sequenced using the Ion Torrent Proton sequencing platform. A total of 51,229,690 single end reads were obtained from six single-end libraries, which were assembled into 31346 unireads as reference. After mapping and transcript assembling, 362 differently expressed genes were identified and 301 of them were deemed to be more abundant in HPT. GO annotation revealed that they were mostly implicated in DNA, RNA and protein synthesis, cell division, mitochondria activities and energy metabolism. The expression level of mitochondrial complexes I (mitochondrial NADH-ubiquinone oxidoreductase) which was the main natural producers of mitochondrial ROS was found to be 8.6-fold (p < 0.01) higher in HPT than that in hemocytes. In hemocytes, the proteinase genes associated with proPO activation from the 61 up-regulated genes in hemocytes were the main up-regulated genes which might be the potential markers for mature hemocytes. ROS level in HPT cells was relatively higher which was confirmed with the high expression level of mitochondria related genes identified by transcriptome sequencing. After the ROS level was depressed by N-acetyl-l-cysteine (NAC), the production of hemocytes from HPT was inhibited, and the recovery of the total hemocytes counts was delayed. These results collectively indicated that the genes in redox system were more active in HPT, and ROS could function as an important modulator in the hematopoiesis of crab and promote the production of hemocytes from HPT.