Bombyx mori ferritin heavy-chain homolog facilitates BmNPV proliferation by inhibiting reactive oxygen species-mediated apoptosis

MicroRNA bmo-miR-31-5p inhibits apoptosis and promotes BmNPV proliferation by targeting the CYP9e2 gene of Bombyx mori

BACKGROUND

Bombyx mori nuclear polyhedrosis virus (BmNPV), as a typical baculovirus, is the primary pathogen that infects the silkworm B. mori, a lepidopteran species. Owing to the high biological safety of BmNPV in infecting insects, it is commonly utilized as a biological insecticide for pest control. Apoptosis is important in the interaction between the host and pathogenic microorganisms. MicroRNAs (miRNAs) influence immune responses and promote stability of the immune system via apoptosis. Therefore, the study of apoptosis-related miRNA in silkworms during virus infection can not only provide support for standardizing the prevention and control of diseases and insect pests, but also reduce the economic losses to sericulture caused by the misuse of biological pesticides.

RESULTS

Through transcriptome sequencing, we identified a miRNA, miR-31-5p, and demonstrated that it can inhibit apoptosis in silkworm cells and promote the proliferation of BmNPV in BmE-SWU1 cells. We identified a target gene of miR-31-5p, B. mori cytochrome P450 9e2 (BmCYP9e2), and demonstrated that it can promote apoptosis in silkworm cells and inhibit the proliferation of BmNPV. Moreover, we constructed transgenic silkworm strains with miR-31-5p knockout and confirmed that they can inhibit the proliferation of BmNPV.

CONCLUSION

These data indicate that miR-31-5p may exert functions of inhibiting apoptosis and promoting virus proliferation by regulating BmCYP9e2. The findings demonstrate how miRNAs influence host cell apoptosis and how they are involved in the host immune system response to viruses, providing important insights into the applications of biological insecticides for pest control. © 2024 Society of Chemical Industry.

Bmo-miR-3351 modulates glutathione content and inhibits BmNPV proliferation by targeting BmGSTe6 in Bombyx mori

MicroRNAs (miRNAs) are small non-coding RNAs that play pivotal roles in the host response to invading pathogens. Among these pathogens, Bombyx mori nucleopolyhedrovirus (BmNPV) is one of the main causes of substantial economic losses in sericulture, and there are relatively few studies on the specific functions of miRNAs in the B. mori-BmNPV interaction. Therefore, we conducted transcriptome sequencing to identify differentially expressed (DE) messenger RNAs (mRNAs) and miRNAs in the midgut of 2 B. mori strains (BmNPV-susceptible strain P50 and BmNPV-resistant strain A35) after BmNPV infection. Through correlation analysis of the miRNA and mRNA data, we identified a comprehensive set of 21 miRNAs and 37 predicted target mRNAs. Notably, miR-3351, which has high expression in A35, exhibited remarkable efficacy in suppressing BmNPV proliferation. Additionally, we confirmed that miR-3351 binds to the 3' untranslated region (3' UTR) of B. mori glutathione S-transferase epsilon 6 (BmGSTe6), resulting in its downregulation. Conversely, BmGSTe6 displayed an opposite expression pattern to miR-3351, effectively promoting BmNPV proliferation. Notably, BmGSTe6 levels were positively correlated with glutathione S-transferase activity, consequently influencing intracellular glutathione content in the infected samples. Furthermore, our investigation revealed the protective role of glutathione against BmNPV infection in BmN cells. In summary, miR-3351 modulates glutathione content by downregulating BmGSTe6 to inhibit BmNPV proliferation in B. mori. Our findings enriched the research on the role of B. mori miRNAs in the defense against BmNPV infection, and suggests that the antiviral molecule, glutathione, offers a novel perspective on preventing viral infection in sericulture.

Regulation of Bombyx mori ferritin heavy-chain homolog on ROS induces multiple effects on BmNPV replication

Ferritin is an iron-binding protein composed of light-chain and heavy-chain homologs with a molecular weight of about 500 kDa. Free iron ions significantly affect reactive oxygen species (ROS) accumulation. Previous research has shown that Bombyx mori nucleopolyhedrosis virus (BmNPV) can increase ROS accumulation, activate autophagy, induce apoptosis, and upregulate the expression of B. mori ferritin heavy-chain homolog (BmFerHCH). However, the mechanism of mutual regulation between BmFerHCH and ROS-mediated autophagy and apoptosis induced by BmNPV remains unclear. In this study, we found that BmNPV induced the time-dependent accumulation of ROS in BmN cells, thereby promoting BmFerHCH expression. Interestingly, in BmFerHCH-overexpressed cells, BmNPV replication was inhibited in the first 18 h after infection but stimulated after 24 h. Further research on H2O2 or antioxidant-treated cells indicated that ROS-induced autophagy slightly increased in the early infection stage and increased BmNPV replication, while in the late stage, a large accumulation of ROS induced apoptosis and inhibited BmNPV replication. In this process, BmFerHCH inhibits BmNPV-induced ROS accumulation by chelating Fe2+. Taken together, BmFerHCH regulates ROS-mediated autophagy and apoptosis to achieve its various effects on BmNPV replication. These findings will help elucidate BmNPV-induced autophagy and apoptosis mediated by ROS and BmFerHCH, as well as the mutually fighting relationship between viruses and hosts.

BmRRS1 Protein Inhibits the Proliferation of Baculovirus Autographa californica Nucleopolyhedrovirus in Silkworm, Bombyx mori

The study of functional genes involved in baculovirus infection is vital for its wide application in pest biocontrol. This study utilized the Autographa californica nucleopolyhedrovirus (AcMNPV) and silkworm as models to elucidate the role of BmRRS1, which has been found to exhibit notable differential expression between resistant and susceptible silkworm strains. The results showed that it was evolutionarily conserved in selected species. Among different tissues, it was expressed at the highest level in the gonads, followed by the hemolymph and silk glands; among the different developmental stages, it was the highest in the second instar, followed by the pupae and adults. Moreover, its vital role in suppressing AcMNPV infection was verified by the decreased expression of lef3 and vp39 protein after overexpression of BmRRS1 as well as by the increased expression of the viral gene lef3 and the viral protein vp39 after siRNA treatment against BmRRS1 expression in BmN cells. Additionally, the direct interaction between BmRRS1 and AcMNPV was detected by the GST pull-down assay. Finally, the homologue of BmRRS1 in Spodoptera frugiperda was found to be involved in larval resistance to AcMNPV. In a word, BmRRS1 plays a vital role in AcMNPV resistance in silkworms, and this might be related to the direct interaction with AcMNPV. The results of this study provide a potential target for protecting silkworm larvae from virus infection and controlling agricultural and forestry pests.

Characterization of a silkworm UFM1 homolog in regulating Bombyx mori unfolded protein response and nucleopolyhedrovirus replication

The Ubiquitin (Ub)-like molecules is essential for animal development and the physiopathology of multiple tissues in the vertebrate. Ubiquitin-fold modifier 1 (UFM1) is one of the newly-identified UBL, which is covalently attached to its substrates through the orchestrated action of a dedicated enzymatic cascade. Bombyx mori nuclear polyhedrosis virus (BmNPV) is one of the main pathogens in sericulture, causing serious economic losses every year. However, there are no studies on UFMylation and the effect of UFMylation on BmNPV replication in silkworm. In this study, we identified BmUFM1 in the B. mori genome. Spatio-Temporal expression profiles showed that BmUFM1 expression was highly in hemocytes and response to various pathogenic stimuli. Furthermore, BmUFM1 is involved in the regulation of ER stress induced Unfolded Protein Response (UPR) and knockdown of BmUFM1 inhibited BmNPV replication. Overall, these results suggest that BmUFM1 plays an important role in facilitating BmNPV proliferation in silkworm. Our findings advance the understanding of UFM1's conjugation machinery, and also provides a potentially molecular target for BmNPV prevention and silkworm breeding.

A Protein Asteroid with PIN Domain in Silkworm Bombyx mori Is Involved in Anti-BmNPV Infection

Nuclease is a type of protein that degrades nucleic acids, which plays an important role in biological processes, including RNA interference efficiency and antiviral immunity. However, no evidence of a link between nuclease and Bombyx mori nucleopolyhedrovirus (BmNPV) infection in silkworm B. mori has been found. In this study, a protein asteroid (BmAst) containing the PIN domain and XPG domain was identified in silkworm B. mori. BmAst gene was highest expressed in hemocytes and fat body of the 5th instar larvae, and high expression in the pupa stage. The transcriptional levels of the BmAst gene in 5th instar larvae were significantly induced by BmNPV or dsRNA. After knocking down BmAst gene expression by specific dsRNA, the proliferation of BmNPV in B. mori was increased significantly, whereas the survival rate of larvae was significantly lower when compared with the control. Our findings indicate that BmAst is involved in silkworm resistance to BmNPV infection.

Apoptosis-related long non-coding RNA LINC5438 of Bombyx mori promotes the proliferation of BmNPV

Apoptosis, as an important part of the immune response, is one of the core events in the host-virus interaction. Studies have shown that long non-coding RNAs (lncRNAs) play important roles in the process of cell apoptosis and pathophysiology. To investigate the apoptosis-related lncRNAs involved in Bombyx mori nucleopolyhedrovirus (BmNPV) infecting silkworms, transcriptome sequencing was conducted based on silkworm cells infected with BmNPV before and after B. mori inhibitor of apoptosis (Bmiap) gene knockout. A total of 23 differentially expressed lncRNAs were identified as being associated with the mitochondrial apoptosis pathway. Moreover, we demonstrated that B. mori LINC5438 has the function of inhibiting apoptosis in silkworm cells. Overexpression of LINC5438 promoted the proliferation of BmNPV, while interference with LINC5438 inhibited its proliferation, indicating that LINC5438 plays an important role in BmNPV infection. Our results also showed that LINC5438 can regulate the expression of Bmiap, BmDronc, BmICE, and its predicted target gene BmAIF, suggesting that LINC5438 may function through the mitochondrial pathway. These findings provide important insights into the mechanisms of virus-host interaction and the applications of baculoviruses as biological insecticides.

Transcriptome analysis reveals that knocking out BmNPV iap2 induces apoptosis by inhibiting the oxidative phosphorylation pathway

Apoptosis is essential for the normal growth, development, and immunity defense of living organisms, and its function and mechanisms have been intensively studied. When viral infection occurs, apoptosis is triggered, causing programmed death of the infected cells. Meanwhile, viruses have also evolved countermeasures to inhibit apoptosis in host cells. We previously constructed a transgenic silkworm line with significantly improved resistance to Bombyx mori nucleopolyhedrovirus (BmNPV) by knocking out the BmNPV inhibitor of apoptosis 2 (iap2) gene. However, the mechanism of how IAP2 induces apoptosis still needs to be further investigated. Here, the transcriptomes of Cas9(-)/sgiap2 (-) and Cas9(+)/sgiap2(+) strains were analyzed at 48 h after BmNPV infection, and a total of 709 differential genes were obtained. A KEGG analysis revealed that the differentially expressed genes were enriched in the oxidative phosphorylation, proteasome, and ribosome pathways. In the oxidative phosphorylation pathway, 41 differentially expressed genes were downregulated, and 12 of these genes were verified by qRT-PCR. More importantly, the knockout of BmNPV iap2 led to the inhibition of the oxidative phosphorylation pathway, followed by activated oxidative stress triggered apoptosis, thereby inhibiting the replication of BmNPV in vitro and vivo. The results provide a basis for the analysis of the initiation of apoptosis that can inhibit virus proliferation, and the study presents new ideas for the subsequent creation of resistant material.

Reactive oxygen species-mediated phosphorylation of JNK is involved in the regulation of BmFerHCH on Bombyx mori nucleopolyhedrovirus proliferation

c-Jun N-terminal kinase (JNK) phosphorylation is widely observed during virus infection, modulating various aspects of the virus-host interaction. In our previous research, we have proved that B. mori ferritin heavy-chain homolog (BmFerHCH), an inhibitor of reactive oxygen species (ROS), facilitates B. mori nucleopolyhedrovirus (BmNPV) proliferation. However, one question remains: Which downstream signaling pathways does BmFerHCH regulate by inhibiting ROS? Here, we first determined that silencing BmFerHCH inhibits BmNPV proliferation, and this inhibition depends on ROS. Then, we substantiated that BmNPV infection activates the JNK signaling pathway. Interestingly, the JNK phosphorylation during BmNPV infection is activated by ROS. Further, we found that the enhanced nuclear translocation of phospho-JNK induced by BmNPV infection was dramatically reduced by pretreatment with the antioxidant N-acetylcysteine (NAC), whereas there was more detectable phospho-JNK in the cytoplasm. Next, we investigated how changes in BmFerHCH expression affect JNK phosphorylation. BmFerHCH overexpression suppressed the phosphorylation of JNK and nuclear translocation of phospho-JNK during BmNPV infection, whereas BmFerHCH knockdown facilitated phosphorylation of JNK and nuclear translocation of phospho-JNK. By measuring the viral load, we found the inhibitory effect of BmFerHCH knockdown on BmNPV infection depends on phosphorylated JNK. In addition, the JNK signaling pathway was involved in BmNPV-triggered apoptosis. Hence, we hypothesize that ROS-mediated JNK phosphorylation is involved in the regulation of BmFerHCH on BmNPV proliferation. These results elucidate the molecular mechanisms and signaling pathways of BmFerHCH-mediated response to BmNPV infection.

Ferritin heavy chain participated in ameliorating 3-nitropropionic acid-induced oxidative stress and apoptosis of goose follicular granulosa cells

Oxidative stress is the major culprits responsible for ovarian dysfunction by damaging granulosa cells (GCs). Ferritin heavy chain (FHC) may participate in the regulation of ovarian function by mediating GCs apoptosis. However, the specific regulatory function of FHC in follicular GCs remains unclear. Here, 3-nitropropionic acid (3-NPA) was utilized to establish an oxidative stress model of follicular GCs of Sichuan white geese. To explore the regulatory effects of FHC on oxidative stress and apoptosis of primary GCs in geese by interfering or overexpressing FHC gene. After transfection of siRNA-FHC to GCs for 60 h, the expressions of FHC gene and protein decreased significantly (P < 0.05). After FHC overexpression for 72 h, the expressions of FHC mRNA and protein upregulated considerably (P < 0.05). The activity of GCs was impaired after interfering with FHC and 3-NPA coincubated (P < 0.05). When overexpression of FHC combined with 3-NPA treatment, the activity of GCs was remarkably enhanced (P < 0.05). After interference FHC and 3-NPA treatment, NF-κB and NRF2 gene expression decreased (P < 0.05), the intracellular reactive oxygen species (ROS) level increased greatly (P < 0.05), BCL-2 expression reduced, BAX/BCL-2 ratio intensified (P < 0.05), the mitochondrial membrane potential decreased notably (P < 0.05), and the apoptosis rate of GCs aggravated (P < 0.05). While overexpression of FHC combined with 3-NPA treatment could promote BCL-2 protein expression and reduce BAX/BCL-2 ratio, indicating that FHC regulated the mitochondrial membrane potential and apoptosis of GCs by mediating the expression of BCL-2. Taken together, our research manifested that FHC alleviated the inhibitory effect of 3-NPA on the activity of GCs. FHC knockdown could suppress the expression of NRF2 and NF-κB genes, reduce BCL-2 expression and augment BAX/BCL-2 ratio, contributing to the accumulation of ROS and jeopardizing mitochondrial membrane potential, as well as exacerbating GCs apoptosis.

Nuclear Factor Kappa B Promotes Ferritin Heavy Chain Expression in Bombyx mori in Response to B. mori Nucleopolyhedrovirus Infection

Ferritin heavy chain (FerHCH) is a major component of ferritin and plays an important role in maintaining iron homeostasis and redox equilibrium. Our previous studies have demonstrated that the Bombyx mori ferritin heavy chain homolog (BmFerHCH) could respond to B. mori nucleopolyhedrovirus (BmNPV) infection. However, the mechanism by which BmNPV regulates the expression of BmFerHCH remains unclear. In this study, BmFerHCH increased after BmNPV infection and BmNPV infection enhanced nuclear factor kappa B (NF-κB) activity in BmN cells. An NF-κB inhibitor (PDTC) reduced the expression of the virus-induced BmFerHCH in BmN cells, and overexpression of BmRelish (NF-κB) increased the expression of virus-induced BmFerHCH in BmN cells. Furthermore, BmNPV infection enhanced BmFerHCH promoter activity. The potential NF-κB cis-regulatory elements (CREs) in the BmFerHCH promoter were screened by using the JASPAR CORE database, and two effective NF-κB CREs were identified using a dual luciferase reporting system and electrophoretic mobility shift assay (EMSA). BmRelish (NF-κB) bound to NF-κB CREs and promoted the transcription of BmFerHCH. Taken together, BmNPV promotes activation of BmRelish (NF-κB), and activated BmRelish (NF-κB) binds to NF-κB CREs of BmFerHCH promoter to enhance BmFerHCH expression. Our study provides a foundation for future research on the function of BmFerHCH in BmNPV infection.