Protein kinase A affectsGalleria mellonella(Insecta: Lepidoptera) larval haemocyte non‐self responses

Effects of α and β-adrenergic signaling on innate immunity and Porphyromonas gingivalis virulence in an invertebrate model

To investigate the role of adrenergic signalling (AS) in the host immune response and Porphyromonas gingivalis virulence, we compared norepinephrine (NE) and isoproterenol (ISO) responses in Galleria mellonella. P. gingivalis infection was evaluated by survival; humoral immune responses (i.e. melanization and cecropin and gloverin mRNA expression); cellular immune responses (i.e. haemocyte count, nodulation by histology); and P. gingivalis recovery (CFU/mL). P. gingivalis was cultivated in the presence of ISO (PgISO) or NE and injected into the larvae for survival evaluation. Finally, we co-injected ISO and PgISO to evaluate the concomitant effects on the immune response and bacterial virulence. None of the ligands were toxic to the larvae; ISO increased haemocyte number, even after P. gingivalis infection, by mobilizing sessile haemocytes in a β-adrenergic-specific manner, while NE showed the opposite effect. ISO treatment reduced larval mortality and the number of recovered bacteria, while NE increased mortality and showed no effect on bacterial recovery. ISO and NE had similar effects on melanization and decreased the expression of cecropin. Although co-cultivation with NE and ISO increased the gene expression of bacterial virulence factors in vitro, only the injection of PgISO increased larval death, which was partially reversed by circulating ISO. Therefore, α- and β-adrenergic signalling had opposite effects after P. gingivalis infection. Ultimately, the catecholamine influence on the immune response overcame the effect of more virulent strains. The effect of AS directly on the pathogen found in vitro did not translate to the in vivo setting.

The Entomopathogenic Nematodes H. bacteriophora and S. carpocapsae Inhibit the Activation of proPO System of the Nipa Palm Hispid Octodonta nipae (Coleoptera: Chrysomelidae)

Entomopathogenic nematodes are biocontrol agents of invasive insect pests in soil and cryptic habitats. Nipa palm hispid, Octodonta nipae, is a pest of palm trees in Sothern China. To address its increasing damage, environmentally friendly control methods are required. This study aimed to test efficacy of Heterorhabditis bacteriophora and Steinernema carpocapsae on O. nipae and investigated the influence of secondary metabolites, nematodes, and their isolated cuticles on the activation of O. nipae’s prophenoloxidase system using qPCR analysis. Our data revealed that O. nipae were less susceptible to H. bacteriophora than S. carpocapsae and penetrations of infective juveniles were higher with S. carpocapsae treatment than H. bacteriophora. Moreover, expression levels of the serine protease P56, prophenoloxidase activation factor 1, PPO and serine protease inhibitor 28 upon S. carpocapsae and H. bacteriophora infections were generally downregulated at all times. However, upon heating, the cuticles lost their inhibitory effects and resulted in upregulation of the PPO gene. Similarly, the addition of arachidonic acid reversed the process and resulted in the upregulation of the PPO gene compared to the control. Further work is needed to identify toxic substances secreted by these EPNs to evade O. nipae’s immune system.

Defective phagocyte association during infection of Galleria mellonella with Yersinia pseudotuberculosis is detrimental to both insect host and microbe

Adhesins facilitate bacterial colonization and invasion of host tissues and are considered virulence factors, but their impact on immune-mediated damage as a driver of pathogenesis remains unclear. Yersinia pseudotuberculosis encodes for a multivalent adhesion molecule (MAM), a mammalian cell entry (MCE) family protein and adhesin. MAMs are widespread in Gram-negative bacteria and enable enteric bacteria to colonize epithelial tissues. Their role in bacterial interactions with the host innate immune system and contribution to pathogenicity remains unclear. Here, we investigated howY. pseudotuberculosis MAM contributes to pathogenesis during infection of the Galleria mellonella insect model. We show that Y. pseudotuberculosis MAM is required for efficient bacterial binding and uptake by hemocytes, the host phagocytes. Y. pseudotuberculosis interactions with insect and mammalian phagocytes are determined by bacterial and host factors. Loss of MAM, and deficient microbe-phagocyte interaction, increased pathogenesis in G. mellonella. Diminished phagocyte association also led to increased bacterial clearance. Furthermore, Y. pseudotuberculosis that failed to engage phagocytes hyperactivated humoral immune responses, most notably melanin production. Despite clearing the pathogen, excessive melanization also increased phagocyte death and host mortality. Our findings provide a basis for further studies investigating how microbe- and host-factors integrate to drive pathogenesis in a tractable experimental system.

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.

Expression analysis of immune-associated genes in hemocytes of mud crab Scylla paramamosain under low salinity challenge

To gain knowledge on the immune response in Scylla paramamosain under low salinity challenge, S. paramamosain we investigated digital gene expression (DEG) in S. paramamosain hemocytes using the deep-sequencing platform Illumina Hiseq XTen. A total of 97,257 high quality unigenes with mean length 786.59 bp were found to be regulated by low salinity challenge, among which 93 unigenes were significantly up regulated, and 71 were significantly down regulated. Functional categorization and pathways analysis of differentially expressed genes revealed that immune signaling pathway including cAMP and cGMP signaling pathway were affected in low salinity stress. Cellular immunity-related genes including low-density lipoprotein receptor-related protein 6 (LRP6) and xanthine dehydrogenase (XDH) were down-regulated, indicating phagocytosis and oxygen dependent mechanism of phagocyte were suppressed in low salinity stress; Humoral immunity-related genes serine proteases and serpins 3 were up- and down-regulated, respectively, suggest that the proPO system was influenced by low salinity significantly; Moreover, processes related to immune response including carbohydrate metabolism, protein synthesis and lipid transport were found differentially regulated, implying the integrity of the immune response in low salinity stress. This study gained comprehensive insights on the immune mechanism of S. paramamosain at low salinity stress at the molecular level. The findings provide a theoretical basis for understanding immune mechanisms of S. paramamosain under low salinity stress, and technical reference for evaluating physiological adaptation in fresh water environment.

Physiological evidence of integrin-antibody reactive proteins influencing the innate cellular immune responses of larval Galleria mellonella hemocytes

Larval Galleria mellonella (L.) hemocytes form microaggregates in response to stimulation by Gram-positive bacteria. Hemocyte adhesion to foreign materials is mediated by the cAMP/ protein kinase A pathway and the β-subunit of cholera toxin using a cAMP-independent mechanism. Cholera toxin-induced microaggregation was inhibited by the integrin inhibitory RGDS peptide, implying integrins may be part of the mechanism. Based on the types of mammalian integrin-antibody reactive proteins affecting hemocyte adhesion and bacterial-induced responses α₅ , α_v , β₁ , and β₃ subunits occurred on both granular cell and plasmatocyte hemocyte subtypes. A fluorescent band representing the binding of rabbit α₅ -integrin subunit antibodies occurred between adhering heterotypic hemocytes. The frequency of the bands was increased by cholera toxin. The α₅ and β₁ rabbit integrin subunit antibodies inhibited removal of Bacillus subtilis (Cohn) from the hemolymph in vivo. A α₅ β₁ -specific synthetic peptide blocker similarly diminished hemocyte function whereas the α_v β₃ -specific inhibitory peptide and the corresponding integrin subunit antibodies did not influence nonself hemocyte activities. Western blots revealed several proteins reacting with a given integrin-antibody subtype. Thus integrin-antibody reactive proteins (which may include integrins) with possible α₅ and β₁ epitopes modulate immediate hemocyte function. Confocal microscopy established plasmatocyte adhesion to and rosetting over substrata followed by granular cell microaggregate adhesion to plasmatocytes during early stage nodulation.

Effects of dopamine on immune signaling pathway factors, phagocytosis and exocytosis in hemocytes of Litopenaeus vannamei

Dopamine (DA) is an important neuroendocrine factor, which can act as neurotransmitter and neurohormone. In this study, we explored the immune defense mechanism in Litopenaeus vannamei with injection of dopamine at 10^-7 and 10^-6 mol shrimp^-1, respectively. The genes expressions of dopamine receptor (DAR), G proteins (Gs, Gi, Gq), phagocytosis and exocytosis-related proteins, as well as intracellular signaling pathway factors, and immune defense parameters were measured. Results showed that mRNA expression levels of dopamine receptor D4 (D4), Gi, nuclear transcription factors and exocytosis-related proteins decreased significantly and reached the minimum at 3 h, while the genes expressions of Gs, Gq and phagocytosis-related proteins reached the highest and lowest levels at 3 h and 6 h, respectively. The second messenger synthetases increased significantly in treatment groups within 3 h. Simultaneously, the second messengers and protein kinases shared a similar trend, which were significantly elevated and reached the peak value at 3 h. Ultimately lead to the total hemocyte count (THC), proPO activity and phagocytic activity decreased significantly, reaching minimum values at 3 h, 3 h and 6 h, respectively. While PO activity showed obvious peak changes, which maximum value reached at 3 h. These results suggested that DA receptor could couple with G protein after DA injection and might regulate immunity through cAMP-PKA, DAG-PKC or CaM pathway.

Hemocyte-hemocyte adhesion and nodulation reactions of the greater wax moth, Galleria mellonella are influenced by cholera toxin and its B-subunit

Nodulation, the lepidopteran insect immune response to large numbers of microbes in the blood (hemolymph) consists of the coordination of the blood cell (hemocyte) types the granular cells and plasmatocytes in terms of granular cell-bacteria adhesion and hemocyte-hemocyte adhesion (microaggregation). Hemocyte-microbe adhesion is influenced by the secondary messenger, cAMP, and cAMP-dependent protein kinase A. In the present study, cholera toxin, an AB5 protein known to indirectly stimulate adenylate cyclase, is used to examine the hemocyte responses to glass, bacteria and hemocyte-hemocyte microaggregates. In vitro, this toxin induces a bimodal hemocyte adhesion response that varies with the holotoxin concentration in terms of the individual and aggregated hemocyte adhesion responses: the lower CTX concentration (1.2 nM) increases microaggregate adhesion and decreases individual hemocyte binding to glass, as does higher concentrations (6-120 nM), however microaggregates induced by lower concentrations do not adhere to glass. Cholera toxin-induced microaggregation is inhibited by RGDS, suggestive of integrin involvement. In vivo, cholera toxin (1.2-120 nM) injected into larvae induces also a bimodal hemocytic response: low levels (1.2-6 nM) cause reduced hemocyte adhesion, while high levels (12-120 nM) increase hemocyte release or mobilization of adhesive hemocyte counts in the hemolymph. Increasing levels of cholera toxin concomitantly injected with the non-pathogenic bacterium, Bacillus subtilis produces a bimodal pattern in bacterial removal from the hemolymph which correlates with nodule frequency in larvae injected with cholera toxin only. The effects of higher concentrations of cholera toxin in vitro (6-120 nM) and in vivo (12-120 nM) are mediated by the B-subunit, whereas the isolated A-subunit has no effect on hemocyte activity. Cholera toxin and its individual subunits did not detectably alter levels of intracellular cAMP in the hemocytes, suggesting a cAMP-independent mechanism stimulating the nodulation response.

Innate hemocyte responses of Malacosoma disstria larvae (C. Insecta) to antigens are modulated by intracellular cyclic AMP

Invertebrate intracellular hemocyte signaling pathways affecting cellular-antigen responses, although defined for molluscs and some arthropods including dipteran insects, is less known for lepidopterans. Hemocytic-antigen responses of the arboreal pest lepidopteran Malacosoma disstria are linked to cAMP-dependent protein kinase A implicating cAMP in cellular hemocyte immune responses. The purpose in the present study was to determine intracellular cAMP effects on larval M. disstria hemocytes adhering to slides and bacteria. Altering adenylate cyclase and phosphodiesterase activities as well as cAMP levels in vitro and in vivo changed hemocyte responses to antigens. Quiescent hemocytes had high cAMP levels due to adenylate cyclase activity and possibly low phosphodiesterase (type 4) activity. Antigen contact diminished hemocytic cAMP levels. Inhibiting adenylate cyclase increased hemocyte-antigen and hemocyte-hemocyte adhesion, the latter producing nodules in vivo without bacterial antigens. Inhibiting phosphodiesterase type 4 produced the reverse effects. Pharmacologically increasing intracellular cAMP in attached hemocytes caused many of the cells to detach. Diminished intracellular cAMP changed hemograms in vivo in bacteria-free larvae comparable to changes induced by the bacterium, Bacillus subtilis, by producing nodules. Lowering cAMP enhanced also the removal of Xenorhabdus nematophila and B. subtilisin vivo.

The antioxidants dimethylsulfoxide and dimethylthiourea affect the immediate adhesion responses of larval haemocytes from 3 lepidopteran insect species

Antioxidants, dimethylsulfoxide (DMSO) and dimethylthiourea (DMTU), at concentrations not affecting the viability of blood cells (haemocytes) from the larval stage of 3 lepidopteran insects - Galleria mellonella, Lymantria dispar, and Malacosoma disstria - differed in their influence on the innate binding of haemocytes to glass, bacteria to haemocytes, and on humoral responses to alien materials. In vitro DMSO had little effect, whereas DMTU substantially impaired the adhesion of the haemocyte types, the plasmatocytes and granular cells, to slides as well as the attachment of Bacillus subtilis to these haemocytes. Although both antioxidants increased lysozyme and phenoloxidase activities, there was no correlation of enzyme activity and haemocyte adhesion responses, possibly reflecting sequestered radicals. Nitric oxide and hydroxyl radicals offset the DMTU effect. In the absence of antioxidants, inactivate protein kinases A (PKA) and C (PKC) enhanced haemocyte aggregation. In general, DMSO, as opposed to DMTU, did not alter the effects of PKA and PKC activators and inhibitors on haemocyte aggregation or of PKC and PKA activities. High concentrations of DMSO and all levels of DMTU, although inhibiting PKA and PKC, inhibited haemocyte adhesion to slides. Comparable results occurred for DMTU-treated haemocytes incubated with B. subtilis. In vivo DMSO, unlike DMTU, did not impair plasmatocyte or granular cell responses to foreign materials, including bacterial removal from the haemolymph and nodulation.

Humoral immune response upon mild heat-shock conditions in Galleria mellonella larvae

Larvae of Galleria mellonella exposed to mild heat-shock (38 degrees C) showed an enhanced humoral immune response after microbial infection in comparison to infected animals grown at 28 degrees C. This enhanced response was manifested by increased expression of antimicrobial peptide (AMP) genes leading to enhanced antimicrobial activity in the hemolymph. We found an increased level of Hsp90 and changes in the level of a 55kDa protein recognized by anti-Hsp90 antibodies in fat bodies of infected animals reared at 28 degrees C as well as in uninfected animals exposed to elevated temperature. Pre-treatment of animals with an inhibitor of Hsp90, 17-DMAG, prior to immunization resulted in increased expression of AMP genes encoding gallerimycin and cecropin at 38 degrees C. This observation was correlated with the changes in Hsp90 protein and increased level of 55kDa protein. Also G. mellonella larvae pre-treated with 17-DMAG and exposed to mild heat-shock for 30min showed an increased survival rate after infection with entomopathogenic bacteria Pseudomonas aeruginosa. We also show the effect of 17-DMAG on the phosphorylation state of ERK MAP kinase. We postulate that Hsp90 may play a significant role in converging pathways involved in the insect immune response and heat-shock.

Protein kinase A activity and protein phosphorylation in the haemocytes of immune-challenged Galleria mellonella larvae

Protein kinase A (PKA) activity was detected in the haemocytes of greater wax moth, Galleria mellonella larvae using a specific peptide substrate--kemptide. The enzyme was activated in vitro by 1 microM concentration of cAMP, 8-Br-cAMP, 8-Chl-cAMP and BzcMP, whereas in the case of cGMP 10 microM concentration was necessary. Immune challenge of G. mellonella larvae with bacteria led to changes in haemocyte PKA activity. Gram-positive M. luteus was a better inducer of PKA activity than Gram-negative E. coli. The kinetics of activity changes was dependent on the bacteria used and considerably differed from that observed in water-treated insects. Inhibition of PKA activity by cell-permeable, specific inhibitor, Rp-8-Br-cAMPS, induced changes in haemocyte morphology resembling those caused by live bacteria. Four potential PKA substrates of 155 kDa, 44 kDa, 40 kDa and 22 kDa were recognized in the haemocytes of naive larvae by phospho-motif antibodies for PKA phosphorylation consensus site. The modification level of 40 kDa protein changed after water treatment and immune challenge of G. mellonella larvae, whereas that of 155 kDa protein changed only after E. coli and LPS injections. Additionally, in the haemocytes of bacteria- and LPS-challenged insects a transient phosphorylation of 36 kDa protein was detected.

Friend and foe: the two faces of Xenorhabdus nematophila

Comparisons of mutualistic and pathogenic relationships are necessary to decipher the common language of microorganism-host interactions, as well as the subtle differences in dialect that distinguish types of symbiosis. One avenue towards making such comparisons is to study a single organism that speaks both dialects, such as the gamma-proteobacterium Xenorhabdus nematophila. X. nematophila inhabits and influences the lives of two host animals, helping one to reproduce optimally while killing the other.

Studies on the role of protein kinase A in humoral immune response of Galleria mellonella larvae

Protein kinase A (PKA) activity was detected in the fat body of Galleria mellonella larvae by a non-radioactive method using a specific peptide substrate-kemptide. The enzyme activity was stimulated by cAMP and its analogues: BzcMP, 8-Chl-cAMP and 8-Br-cAMP in concentrations of 1-4muM. Cyclic GMP was not effective in PKA activation. A two-fold increase in PKA activity was detected in the fat body of G. mellonella LPS-challenged larvae. Selective, membrane-permeable PKA inhibitors, H89 and Rp-8-Br-cAMPS, inhibited protein kinase A activity in the fat body of G. mellonella larvae in vitro and in vivo. The inhibition of PKA activity in vivo was correlated with a considerable lowering of haemolymph antibacterial activity and a decrease in lysozyme content in the fat body of immune challenged larvae. The use of phospho-motif antibodies recognising PKA phosphorylation consensus site allowed identification of four potential PKA phosphorylation substrates of 79, 45, 40 and 36kDa in G. mellonella fat body.

Phagocytosis by Lymnaea stagnalis haemocytes: A potential role for phosphatidylinositol 3-kinase but not protein kinase A

The molecular events that regulate phagocytosis, an important innate immune response, in invertebrate defence cells (haemocytes) are poorly understood. Lymnaea stagnalis haemocytes were used as a model to elucidate the role of cell signalling pathways in phagocytosis by molluscan defence cells. The phosphatidylinositol 3-kinase (PI3-K) inhibitor, LY294002, significantly impaired haemocyte phagocytic activity in a dose-responsive manner with 10 microM LY294002 reducing internalization of fluorescent-conjugated Escherichia coli by 62% (P < or = 0.001). In contrast, the protein kinase A (PKA) inhibitor KT5720 was without effect. Therefore, PI3-K, but not PKA, appears to control phagocytosis by haemocytes in these gastropod molluscs.

Cyclic AMP affects the haemocyte responses of larval Galleria mellonella to selected antigens

Signal transduction of the innate immediate responses of insect haemocytes to foreign matter is rarely considered. Herein using a combination of adenylate cyclase inhibitors and activators and phosphodiesterase inhibitors we determined that cyclic adenosine monophosphate (cAMP) at high levels normally impairs non-self response. Haemocyte contact with glass and bacteria lowered cAMP in vitro. Inactive phosphodiesterases, including type 4, impaired haemocyte reactions in vitro. Using the drugs in vivo to modulate adenylate cyclase and phosphodiesterases altered the total and types of haemocytes. Adenylate cyclase inhibitors and etazolate (a type 4 phosphodiesterase inhibitor) alone produced changes in the haemograms similar to those caused by Bacillus subtilis. Sequential injections of an enzyme modulator followed by B. subtilis impaired bacterial removal due (1) in the case of enzyme inhibitors, to the removal of haemocytes prior to bacterial challenge and (2) in the case of forskolin and IBMX to the shut-down of the haemocytes. Activating adenylate cyclase or inhibiting phosphodiesterase impaired bacterial removal when co-injecting the compounds and bacteria.