The DNA chaperone HMGB1 potentiates the transcriptional activity of Rel1A in the mosquito Aedes aegypti

Spätzle processing enzyme is required to activate dorsal switch protein 1 induced Toll immune signalling pathway in Tenebrio molitor

Dorsal switch protein 1 (DSP1) acts as a damage-associated molecular pattern (DAMP) molecule to activate immune responses in Tenebrio molitor. From a previous study in Spodoptera exigua, we found that DSP1 activates Toll immune signalling pathway to induce immune responses by melanisation, PLA2 activity and AMP synthesis. However, the target site of DSP1 in this pathway remains unknown. The objective of this study was to determine the role of spätzle processing enzyme in the DSP1 induced toll immune signalling pathway. To address this, we analyzed spätzle processing enzyme (Tm-SPE) of the three-step serine protease cascade of T. molitor Toll pathway. Tm-SPE expressed in all developmental stages and larval tissues. Upon immune challenge, its expression levels were upregulated but significantly reduced after RNA interference (RNAi). In addition, the induction of immune responses upon immune challenge or recombinant DSP1 injection was significantly increased. Loss of function using RNA interference revealed that the Tm-SPE is involved in connecting DSP1 induced immune responses like hemocyte nodule formation, phenoloxidase (PO) activity, phospholipase A2 (PLA2) activity and antimicrobial peptide (AMP) synthesis. These suggest that Tm-SPE controls the DSP1 induced activation of Toll immune signalling pathway required for both cellular and humoral immune responses. However, to confirm the target molecule of DSP1 in three-step proteolytic cascade, we have to check other upstream serine proteases like Spatzle activating enzyme (SAE) or modular serine protease (MSP).

Determinants of Chikungunya and O'nyong-Nyong Virus Specificity for Infection of Aedes and Anopheles Mosquito Vectors

Mosquito-borne diseases caused by viruses and parasites are responsible for more than 700 million infections each year. Anopheles and Aedes are the two major vectors for, respectively, malaria and arboviruses. Anopheles mosquitoes are the primary vector of just one known arbovirus, the alphavirus o'nyong-nyong virus (ONNV), which is closely related to the chikungunya virus (CHIKV), vectored by Aedes mosquitoes. However, Anopheles harbor a complex natural virome of RNA viruses, and a number of pathogenic arboviruses have been isolated from Anopheles mosquitoes in nature. CHIKV and ONNV are in the same antigenic group, the Semliki Forest virus complex, are difficult to distinguish via immunodiagnostic assay, and symptomatically cause essentially the same human disease. The major difference between the arboviruses appears to be their differential use of mosquito vectors. The mechanisms governing this vector specificity are poorly understood. Here, we summarize intrinsic and extrinsic factors that could be associated with vector specificity by these viruses. We highlight the complexity and multifactorial aspect of vectorial specificity of the two alphaviruses, and evaluate the level of risk of vector shift by ONNV or CHIKV.

CRISPR mediated transactivation in the human disease vector Aedes aegypti

As a major insect vector of multiple arboviruses, Aedes aegypti poses a significant global health and economic burden. A number of genetic engineering tools have been exploited to understand its biology with the goal of reducing its impact. For example, current tools have focused on knocking-down RNA transcripts, inducing loss-of-function mutations, or expressing exogenous DNA. However, methods for transactivating endogenous genes have not been developed. To fill this void, here we developed a CRISPR activation (CRISPRa) system in Ae. aegypti to transactivate target gene expression. Gene expression is activated through pairing a catalytically-inactive ('dead') Cas9 (dCas9) with a highly-active tripartite activator, VP64-p65-Rta (VPR) and synthetic guide RNA (sgRNA) complementary to a user defined target-gene promoter region. As a proof of concept, we demonstrate that engineered Ae. aegypti mosquitoes harboring a binary CRISPRa system can be used to effectively overexpress two developmental genes, even-skipped (eve) and hedgehog (hh), resulting in observable morphological phenotypes. We also used this system to overexpress the positive transcriptional regulator of the Toll immune pathway known as AaRel1, which resulted in a significant suppression of dengue virus serotype 2 (DENV2) titers in the mosquito. This system provides a versatile tool for research pathways not previously possible in Ae. aegypti, such as programmed overexpression of endogenous genes, and may aid in gene characterization studies and the development of innovative vector control tools.

HMG-Like DSP1 Mediates Immune Responses of the Western Flower Thrips (Frankliniella occidentalis) Against Beauveria bassiana, a Fungal Pathogen

Western flower thrips, Frankliella occidentalis, is a serious pest by directly infesting host crops. It can also give indirect damage to host crops by transmitting a plant virus called tomato spotted wilt virus. A fungal pathogen, Beauveria bassiana, can infect thrips. It has been used as a biopesticide. However, little is known on the defense of thrips against this fungal pathogen. This study assessed the defense of thrips against the fungal infection with respect to immunity by analyzing immune-associated genes of F. occidentalis in both larvae and adults. Immunity-associated genes of western flower thrips were selected from three immunity steps: nonself recognition, mediation, and immune responses. For the pathogen recognition step, dorsal switch protein 1 (DSP1) was chosen. For the immune mediation step, phospholipase A₂ (PLA₂) and prostaglandin E₂ synthase were also selected. For the step of immune responses, two phenoloxidases (PO) genes and four proPO-activating peptidase genes involved in melanization against pathogens were chosen. Dual oxidase gene involved in the production of reactive oxygen species and four antimicrobial peptide genes for executing humoral immune responses were selected. All immunity-associated genes were inducible to the fungal infection. Their expression levels were induced higher in adults than in larvae by the fungal infections. However, inhibitor treatments specific to DSP1 or PLA₂ significantly suppressed the inducible expression of these immune-associated genes, leading to significant enhancement of fungal pathogenicity. These results suggest that immunity is essential for thrips to defend against B. bassiana, in which DSP1 and eicosanoids play a crucial role in eliciting immune responses.

Salicylic Acid, a Plant Hormone, Suppresses Phytophagous Insect Immune Response by Interrupting HMG-Like DSP1

Salicylic acid is a plant hormone that can mediate various plant physiological processes. Salicylic acid can bind to human high mobility group box 1 (HMGB1) and interrupt its role in mediating immune responses. Dorsal switch protein 1 (DSP1) is an insect homolog of HMGB1. In this study, a DSP1 (Se-DSP1) encoded in Spodoptera exigua, a phytophagous insect, was characterized, and its potential role in immune response was explored. Upon bacterial challenge, Se-DSP1 was localized in the nucleus and released into the hemolymph. The released Se-DSP1 could mediate both cellular and humoral immune responses by activating eicosanoid biosynthesis. Salicylic acid could bind to Se-DSP1 with a high affinity. The immune responses of S. exigua were significantly interrupted by SA feeding. Larvae reared on tomatoes with high endogenous SA levels became more susceptible to entomopathogens. Taken together, these results suggest a tritrophic defensive role of plant SA against phytophagous insects.

HMGB1-like dorsal switch protein 1 of the mealworm, Tenebrio molitor, acts as a damage-associated molecular pattern

High-mobility group box 1 (HMGB1) is a nuclear protein highly conserved in eukaryotes and ubiquitously expressed to regulate transcription and chromatin remodeling. Dorsal switch protein 1 (DSP1) is its insect homolog. A lepidopteran DSP1 acts as a damage-associated molecular pattern (DAMP) in response to immune challenge. The objective of this study was to determine the role of DAMP in the mealworm beetle, Tenebrio molitor, a coleopteran insect. DSP1 of T. molitor (Tm-DSP1) encodes 536 amino acids and shares sequence similarities with Homo sapiens HMGB1 (56.3%) and Spodoptera exigua DSP1 (59.2%). An antisera raised against S. exigua DSP1 was cross-reactive to Tm-DSP1. Like other insect DSPs, Tm-DSP1 has a relatively long N-terminal extension in addition to two conserved HMG box domains. It was expressed in all developmental stages of T. molitor and different larval tissues. Upon immune challenge, its expression level was upregulated. Its RNA interference (RNAi) treatment resulted in a significant reduction in immune responses measured by hemocyte nodule formation against bacterial infection. In addition, the induction of some antimicrobial peptide genes to the immune challenge was suppressed by its RNAi treatment. Interestingly, phospholipase A₂ associated with eicosanoid biosynthesis was significantly suppressed in its catalytic activity by the RNAi treatment specific to Tm-DSP1 expression. Without any pathogen infection, injection of a lepidopteran DSP1 induced both cellular and humoral immune responses. These results suggest that Tm-DSP1 in T. molitor can act as a DAMP molecule and mediate immune responses upon immune challenge.

Immune mediation of HMG-like DSP1 via Toll-Spätzle pathway and its specific inhibition by salicylic acid analogs

Xenorhabdus hominickii, an entomopathogenic bacterium, inhibits eicosanoid biosynthesis of target insects to suppress their immune responses by inhibiting phospholipase A₂ (PLA₂) through binding to a damage-associated molecular pattern (DAMP) molecule called dorsal switch protein 1 (DSP1) from Spodoptera exigua, a lepidopteran insect. However, the signalling pathway between DSP1 and PLA₂ remains unknown. The objective of this study was to determine whether DSP1 could activate Toll immune signalling pathway to activate PLA₂ activation and whether X. hominickii metabolites could inhibit DSP1 to shutdown eicosanoid biosynthesis. Toll-Spätzle (Spz) signalling pathway includes two Spz (SeSpz1 and SeSpz2) and 10 Toll receptors (SeToll1-10) in S. exigua. Loss-of-function approach using RNA interference showed that SeSpz1 and SeToll9 played crucial roles in connecting DSP1 mediation to activate PLA₂. Furthermore, a deletion mutant against SeToll9 using CRISPR/Cas9 abolished DSP1 mediation and induced significant immunosuppression. Organic extracts of X. hominickii culture broth could bind to DSP1 at a low micromolar range. Subsequent sequential fractionations along with binding assays led to the identification of seven potent compounds including 3-ethoxy-4-methoxyphenol (EMP). EMP could bind to DSP1 and prevent its translocation to plasma in response to bacterial challenge and suppress the up-regulation of PLA₂ activity. These results suggest that X. hominickii inhibits DSP1 and prevents its DAMP role in activating Toll immune signalling pathway including PLA₂ activation, leading to significant immunosuppression of target insects.

Immune responses of insects are highly effective in defending various entomopathogens. Xenorhabdus hominickii is an entomopathogenic bacterium that uses a pathogenic strategy of suppressing host insect immunity by inhibiting phospholipase A₂ (PLA₂) which catalyzes the committed step for eicosanoid biosynthesis. Eicosanoids mediate both cellular and humoral immune responses in insects. This study discovers an upstream signalling pathway to activate PLA₂ in response to bacterial challenge. Se-DSP1 is an insect homolog of vertebrate HMGB1 that acts as a damage-associated molecular pattern. Upon bacterial infection, Se-DSP1 is released to the circulatory system to activate Spätzle, an insect cytokine that can bind to Toll receptor. Toll immune signalling pathway can activate antimicrobial peptide gene expression and PLA₂. A deletion mutant against a Toll gene abolished immune responses mediated by Se-DSP1. Indeed, X. hominickii can produce and secrete secondary metabolites including salicylic acid analogs that can strongly bind to Se-DSP1. These bacterial metabolites prevented the release of Se-DSP1, which impaired the activation of PLA₂ and resulted in a significant immunosuppression of target insects against bacterial infection.

Molecular and functional characterization of single-box high-mobility group B (HMGB) chromosomal protein from Aedes aegypti

High-mobility group B (HMGB) proteins have highly conserved, unique DNA-binding domains, HMG boxes, that can bind non-B-type DNA structures, such as bent, kinked and unwound structures, with high affinity. HMGB proteins also promote DNA bending, looping and unwinding. In this study, we determined the role of the Aedes aegypti single HMG-box domain protein AaHMGB; characterized its structure, spatiotemporal expression levels, subcellular localization, and nucleic acid binding activities; and compared these properties with those of its double-HMG-box counterpart protein, AaHMGB1. Via qRT-PCR, we showed that AaHMGB is expressed at much higher levels than AaHMGB1 throughout mosquito development. In situ hybridization results suggested a role for AaHMGB and AaHMGB1 during embryogenesis. Immunolocalization in the midgut revealed that AaHMGB is exclusively nuclear. Circular dichroism and fluorescence spectroscopy analyses showed that AaHMGB exhibits common features of α-helical structures and is more stably folded than AaHMGB1, likely due to the presence of one or two HMG boxes. Using several DNA substrates or single-stranded RNAs as probes, we observed significant differences between AaHMGB and AaHMGB1 in terms of their binding patterns, activity and/or specificity. Importantly, we showed that the phosphorylation of AaHMGB plays a critical role in its DNA-binding activity. Our study provides additional insight into the roles of single- versus double-HMG-box-containing proteins in nucleic acid interactions for better understanding of mosquito development, physiology and homeostasis.

Nuclear factor-kappa B activation inhibits proliferation and promotes apoptosis of vascular smooth muscle cells

Objectives

To investigate the role of nuclear factor-kappa B (NF-κB) performed in cell proliferation and apoptosis of vascular smooth muscle cells (VSMCs), and to assess the mechanisms.

Methods

Human aorta VSMCs were divided into control, NF-κB inhibitor, NF-κB overexpression + NF-κB inhibitor, control vector + NF-κB inhibitor, NF-κB overexpression, and control vector groups. NF-κB overexpression vector was constructed and transfected into VSMCs. Proliferation of VSMCs in each group was detected by 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide. Apoptosis of VSMCs was detected by flow cytometry. The expression of NF-κB, FasL, and hypertension-related gene (HRG-1) was measured by Western blotting.

Results

NF-κB overexpression vector was constructed correctly by restriction endonuclease, and the results showed that the activation of NF-κB could inhibit the proliferation of VSMCs. The results of flow cytometry also confirmed that NF-κB overexpression promoted apoptosis of VSMCs. Mechanically, NF-κB overexpression could up-regulate the expression of FasL and HRG-1.

Conclusions

NF-κB overexpression promotes apoptosis and inhibits cell proliferation of VSMCs. The mechanisms might be regulated by promoting FasL and HRG-1 expression.