Independent and simultaneous effect of crustacean hyperglycemic hormone and dopamine on the hemocyte intracellular signaling pathways and immune responses in white shrimp Litopenaeus vannamei

The injection of one recombinant C-type lectin (LvLec) induced the immune response of hemocytes in Litopenaeus vannamei

To explore the immune function of C-type lectin in shrimp, one recombinant C-type lectin (LvLec) was injected into Litopenaeus vannamei. There were four treatments in the experiment: saline group (as control group), recombinant C-type lectin group (LvLec, 1 mg mL^-1), Vibrio harveyi group (V. harveyi, 10⁶ cfu mL^-1) and recombinant C-type lectin combined with Vibrio harveyi group (LvLec + V. harveyi, 1 mg mL^-1 + 10⁶ cfu mL^-1). The sampling time was set at 0, 3, 6, 9, 12, 24 h after the injection. The results showed that the total hemocyte count decreased significantly and the phagocytic activity improved notably after the injection of LvLec, V. harveyi or LvLec + V. harveyi. Prophenoloxidase (proPO) activity decreased, while phenoloxidase (PO) activity increased and the changing degree of each group exhibited a significant difference. The hemagglutinating activity and bacteriolytic activity improved significantly, while the antimicrobial activity did not show a remarkable change in all of the groups. There were also changes that occurred in the levels of second messengers (cAMP, cGMP) and protein kinase (PKA, PKG). After the injection of LvLec, V. harveyi or LvLec + V. harveyi, the concentration of cGMP and PKA increased significantly, while the concentration of cAMP and PKG did not change remarkably. The results above suggested that rLvLec could induce nonspecific immune response, including phagocytosis, release of PO, hemagglutination and bacteriolysis through cGMP-PKA pathway in vivo.

The exploration of neuroendocrine regulation of crustacean hyperglycemic hormone (CHH) on innate immunity of Litopenaeus vannamei under ammonia-N stress

To unveil the neuroendocrine-immune (NEI) mechanism of crustaceans under high ambient ammonia-N, crustacean hyperglycemic hormone (CHH) in L. vannamei was knocked down under 20 mg/L ammonia-N exposure. The results showed that the expression of CHH in the eyestalks decreased significantly when CHH was silenced. After CHH was knocked down, the levels of CHH, ACh, DA, NE, and 5-HT in the haemolymph decreased significantly. Correspondingly, the expressions of GC, ACh₇R, DM1, DA₁R, and 5-HT₇R in haemocytes down-regulated significantly, while DA₄R and α₂AR up-regulated significantly. Besides, the expression of Toll3 reduced significantly. And significantly changes occurred in the levels of G protein effectors (AC and PLC), second messengers (cAMP, cGMP, CaM, and DAG), protein kinases (PKA, PKC and PKG), and nuclear transcription factors (CREB, Dorsal, Relish and NKRF). Furthermore, immune defense proteins (BGBP and PPO3, Crustin A, ALF, LYC, TNFα, and IL-16), phagocytosis-related proteins (Cubilin, Integrin, Peroxinectin, Mas-like protein, and Dynamin-1) and exocytosis-related proteins (SNAP-25, VAMP-2 and Syntaxin) changed significantly. Eventually, a significant decrease in the levels of THC, haemocytes phagocytosis rate, plasma PO, antibacterial and bacteriolytic activities was detected. Therefore, these results indicate that under ammonia-N stress, the combination of CHH and GC mainly affects exocytosis of shrimp through the cGMP-PKG-CREB pathway. Simultaneously, CHH stimulates the release of biogenic amines, and then activate G protein effectors after binding to their specific receptors, to regulate exocytosis mainly via the cAMP-PKA-CREB pathway and influence phagocytosis primarily by the cAMP-PKA-NF-κB pathway. CHH can enhance ACh, and then activate G protein effectors after binding to the receptors, and finally regulate exocytosis mainly through the cAMP-PKA-CREB pathway and regulate phagocytosis by the cAMP-PKA-NF-κB pathway. CHH can also promote Toll3-NF-κB pathway, thereby affecting the expressions of immune defense factors. This study contributes to a further understanding of the NEI mechanism of crustacean in response to environmental stress.

Proteomic analysis of hemocyte reveals the immune regulatory mechanisms after the injection of corticosteroid-releasing hormone in mud crab Scylla Paramamosain

Corticosteroid-releasing hormone (CRH) is a crucial neuroendocrine-immune factor regulating the immune response of Scylla paramamosain. To understand the regulatory mechanisms of CRH in S. paramamosain, the hemolymph of S. paramamosain with injection of CRH (1.5 ng/crab) at 24 h were chosen to perform proteomic analysis in this study. Furthermore, quantitative real-time PCR (RT-PCR) method was used to validate the accuracy of proteomic data at 24 h after CRH injection. The proteomic data showed that 255 DEPs were identified, in which 231 and 24 were up- or down-regulated, respectively. Besides, the results of enriched pathways showed that the DEPs were involved in signaling pathways, cellular immunity, humoral immunity and the response of immune related processes. These results revealed that CRH promoted the activation of signal transduction, regulated immune systems and antioxidation, and enhanced the immune related processes (such as protein synthesis, protein transport, carbohydrate mobilization and energy redistribution). These findings will benefit to foster the understanding on the effects of glucocorticoids on neuroendocrine-immune (NEI) networks of crustacean, and supply a substantial material and foundation for further researching of the NEI response. SIGNIFICANCE: Corticotrophin-releasing hormone (CRH) is a 41-amino acid neuropeptide and has been preliminarily studied in aquatic animals. CRH can regulate many important physiological activities comprising protein synthesis, energy metabolism, growth, breeding and behavior in fish, which play an important roles in neuroendocrine-immune (NEI) regulatory network of fish. The neuroendocrine system of crustacean has a primary research, that inspired by fish NEI network. Despite the research on the neuroendocrine system in crustacean has rapidly increased in recent years, our understanding of the regulation between neuroendocrine system and immune system in crustacean is still limited. The research on the strategy of NEI network in crustaceans becomes a significant issue. In the present study, the isobaric tags for relative and absolute quantification (iTRAQ) technology approach were applied to examine the NEI network of Scylla Paramamosain. control group and treatment group (CRH: 1.5 ng/crab) were settled for the iTRAQ experiment, and sampled at 24 h after CRH injection. The study aimed to gain knowledge on the immune response in Scylla Paramamosain after CRH injection and identify related differentially expressed proteins (DEPs) of the crab. The results of this study provide a preliminary resource for analysis the immune mechanism for crustaceans. In general, our work represents the first report of the utilization of the iTRAQ proteomics method for the study of NEI regulatory network in Scylla Paramamosain after CRH injection. We identified a number of DEPs involved in diverse pathways including immune signaling pathways, cellular immunity, humoral immunity, immune related process. These results demonstrated a very complex network involving immune and multiple related metabolic pathways in hemocytes of Scylla Paramamosain and will be of great value in understanding the crab neuroendocrine-immune immune mechanism.

Crustacean hyperglycemic hormone (CHH) regulates the ammonia excretion and metabolism in white shrimp, Litopenaeus vannamei under ammonia-N stress

To understand the adaptation of Litopenaeus vannamei to high environmental ammonia-N, RNA interference was used to investigate the function of crustacean hyperglycemic hormone (CHH) in the physiological process of neuroendocrine signaling transduction, and ammonia excretion and metabolism. The shrimp were exposed to 25 mg/L NH₄Cl and injected with 20 μg/shrimp CHH dsRNA for 72 h. The results showed that hemolymph ammonia content increased under ammonia-N stress and further increased after CHH knockdown, suggesting that CHH can promote ammonia excretion. Moreover, after CHH knockdown, the levels of CHH, DA, and Wnts decreased significantly, the expression of receptor GC, DA1R, Frizzled and LRP 5/6 also decreased, while DA4R increased remarkably. Moreover, PKA and PKG decreased, while PKC markedly increased, and nuclear transcription factors (CREB and TCF) as well as effector proteins (β-catenin, FXYD2, and 14-3-3) were significantly downregulated. Furthermore, ammonia transporters Na⁺/K⁺-ATPase (NKA), K⁺channel, Rh protein, AQP, V-ATPase, and VAMP decreased significantly, while Na⁺/H⁺ exchangers (NHE) and Na⁺/K⁺/2Cl^- cotransporter (NKCC) increased significantly. These results suggest that CHH regulates ammonia excretion in three ways: 1) by mainly regulating ion channels via PKA, PKC, and PKG signaling pathways; 2) by activating related proteins primarily through Wnt signaling pathway; and 3) by exocytosis, mostly induced by the PKA signaling pathway. In addition, the levels of Gln, uric acid, and urea increased in accordance with the activities of GDH/GS, XDH, and arginase, respectively, suggesting that ammonia excretion was inhibited but ammonia metabolism was slightly enhanced. This study deepens our understanding of the mechanism by which crustaceans respond to high environmental ammonia-N.

Transcriptome analysis of hemocytes from the white shrimp Litopenaeus vannamei with the injection of dopamine

As a crucial neuroendocrine-immune factor, dopamine (DA) could regulate the immune system of Litopenaeus vannamei. To understand the immune mechanisms and regulatory pathways of DA in L. vannamei, the transcriptome analysis of hemocytes of L. vannamei with injection of DA (10^-6 mol/shrimp) at 3 and 12 h were performed in this study. Moreover, quantitative real-time PCR (qPCR) method was applied to validate the accuracy of transcriptome sequencing and analyze the expression pattern of candidate differentially expressed genes (DEGs) at different time points (0, 3, 6, 12, and 24 h) after DA injection. The results showed that a total of 51382 unigenes with a N50 length of 2341 bp were generated. And 1397 and 457 DEGs were obtained by comparative transcriptome at 3 and 12h respectively. Moreover, the results of functional annotation and enriched pathway showed that the DEGs were involved in phagosome (ko04145), lysosome (ko04142), Endocytosis (ko04144), and NOD-like receptor signaling pathway (ko04621). Besides, the Pearson's correlation coefficient (R) between transcriptome sequencing and qPCR was 0.845, which confirmed the reliability of the transcriptome sequencing results and the accuracy of assembly. Furthermore, the expression pattern of 15 candidate DEGs, containing 9 up-regulated and 6 down-regulated DEGs at 3 h, indicated the regulation of DA in physiological functions especially in the immune system. Therefore, these results revealed that DA induced the expressions of membrane receptors or proteins, activated intracellular signaling pathways, regulated cellular and humoral immune systems, controlled antioxidation and apoptosis, and was involved in the regulation of neuroendocrine system. These findings are helpful to promote the understanding on the effects of biogenic amines on physiological functions and regulatory networks of crustacean, and offer a substantial material and foundation for researching the immune response of crustacean.

Effects of crustacean hyperglycemic hormone (CHH) on regulation of hemocyte intracellular signaling pathways and phagocytosis in white shrimp Litopenaeus vannamei

Shrimps like other arthropods rely on innate immune system, and may have some form of adaptive immunity in defending against pathogens. Phagocytosis is one of the oldest cellular processes, serving as a development process, a feeding mechanism and especially as a key defense reaction in innate immunity of all multicellular organisms. It is confirmed that crustacean hyperglycemic hormone (CHH) is one of the most important neuropeptides produced by Neuro-endocrine Immune (NEI) regulatory network, which undertakes important roles in various biological processes, especially in immune function and stress response. In this study, the recombinant Litopenaeus vannamei CHH (rLvCHH) was obtained from a bacterial expression system and the intracellular signaling pathways involved in the mechanism of phagocytosis after rLvCHH injection was investigated. The results showed that the contents of adenylyl cyclase (AC), phospholipase C (PLC) and calmodulin (CaM) in hemocytes were increased significantly after rLvCHH injection. Furthermore, the mRNA expression levels of NF-kB family members (relish and dorsal) and phagocytosis-related proteins in hemocytes were basically overexpressed after rLvCHH stimulation, while the expression level of NF-kB repressing factor (NKRF) gene was down-regulated significantly. Eventually, the total hemocyte count and phagocytic activity of hemocyte were dramatically enhanced within 3 h. Collectively, these results indicate that shrimps L. vannamei could carry out a simple but 'smart' NEI regulation through the action of neuroendocrine factors, which could couple with their receptors and trigger the downstream signaling pathways during the phagocytic responses of hemocytes.

Crustacean hyperglycemic hormone (CHH) affects hemocyte intracellular signaling pathways to regulate exocytosis and immune response in white shrimp Litopenaeus vannamei

Recombinant Litopenaeus vannamei CHH (rLvCHH) was obtained from a bacterial expression system and the intracellular signaling pathways involved in exocytosis and immune response after rLvCHH injection (0.2 and 2 μg/shrimp) was investigated in this study. The results showed that CHH contents increased 51.4%-110.2% (0.2 μg/shrimp) and 65.0%-211.3% (2 μg/shrimp) of the control level. And the contents of three biogenic amines in hemolymph presented a similar variation pattern after rLvCHH injection, but reached the highest level at different time points. Furthermore, the mRNA expression levels of membrane-bound guanylyl cyclase (mGC) (1.20-1.93 fold) and biogenic amine receptors, including type 2 dopamine receptor (DA2R) (0.72-0.89 fold), α2 adrenergic receptor (α2-AR) (0.72-0.91 fold) and 5-HT7 receptor (5-HT7R) (1.37-3.49 fold) in hemocytes were changed consistently with their ligands. In addition, the second messenger and protein kinases shared a similar trend and reached the maximum at the same time respectively. The expression levels of nuclear transcription factor (cAMP response element-binding protein, CREB) and exocytosis-related proteins transcripts were basically overexpressed after rLvCHH stimulation, which reached the peaks at 1 h or 3 h. Eventually, the phenoloxidase (PO) activity (37.4%-158.5%) and antibacterial activity (31.8%-122.3%) in hemolymph were dramatically enhanced within 6 h, while the proPO activity in hemocytes significantly decreased (11.2%-62.6%). Collectively, these results indicate that shrimps L. vannamei could carry out a simple but 'smart' NEI regulation by releasing different neuroendocrine factors at different stages after rLvCHH stimulation, which could couple with their receptors and trigger the downstream signaling pathways during the immune responses in hemocytes.

One recombinant C-type lectin (LvLec) from white shrimp Litopenaeus vannamei affected the haemocyte immune response in vitro

C-type lectin has received widespread attention in animal immunomodulation functions since it was discovered, but it is still limited in crustaceans. The present study is to explore effects of one recombinant C-type lectin (LvLec protein) on haemocyte immune response in Litopenaeus vannamei (L. vannamei). The methods of keeping haemocyte immune activity were optimised by the Key Laboratory of Mariculture. The experiment was divided into four groups: control group, recombinant protein group (LvLec protein, 1.0 mg mL^-1), Lipopolysaccharide group (LPS, 1.0 mg mL^-1), and LPS combine with LvLec protein group (LPS + LvLec protein, 1.0 mg mL^-1 + 1.0 mg mL^-1), while each group processes 0, 3, 6, 9, 12, and 24 h respectively. The results showed that the haemocyte count reduced, while the exocytosis PO activity, hemagglutinating activity and phagocytic activity promoted, and the concentration of cGMP and PKA increased after LvLec protein treatment. However, the levels of antibacterial activity and bacteriolytic activity as well as the concentrations of cAMP and PKG did not change significantly after treating with LvLec protein, LPS or LPS + LvLec protein. Therefore, these results suggest that LvLec protein can stimulate the exocytosis PO activity through cGMP-PKA pathway to affect the phagocytic activity and hemagglutinating activity of L. vannamei haemocytes in vitro.