The negative regulation of piscine CD44c in viral and bacterial infection

Role of alternative splicing in fish immunity

Alternative splicing serves as a pivotal source of complexity in the transcriptome and proteome, selectively connecting various coding elements to generate a diverse array of mRNAs. This process encodes multiple proteins with either similar or distinct functions, contributing significantly to the intricacies of cellular processes. The role of alternative splicing in mammalian immunity has been well studied. Remarkably, the immune system of fish shares substantial similarities with that of humans, and alternative splicing also emerges as a key player in the immune processes of fish. In this review, we offer an overview of alternative splicing and its associated functions in the immune processes of fish, and summarize the research progress on alternative splicing in the fish immunity. Furthermore, we review the impact of alternative splicing on the fish immune system's response to external stimuli. Finally, we present our perspectives on future directions in this field. Our aim is to provide valuable insights for the future investigations into the role of alternative splicing in immunity.

Effect of TRAF6-knockout on gene expression and lncRNA expression in Epithelioma papulosum cyprini (EPC) cells

TRAF6 is a key immune gene that plays a significant role in toll-like receptor signal transduction and activates downstream immune genes involved in antiviral immunity in fish. To explore the role of TRAF6 in Epithelioma papulosum cyprini (EPC) cells, we knocked out the TRAF6 gene using the Clustered Regularly Interspaced Short Palindromic Repeats-Cas9 (CRISPR-Cas9) technique and then analyzed the transcriptomes of the knockout cells. In this study, we identified that 232 transcripts were differentially expressed in naive cells. Using the pipeline, we identified 381 novel lncRNAs in EPC cells, 23 of which were differentially expressed. Gene Ontology enrichment analysis demonstrated that differentially expressed genes (DEG) are implicated in various immune processes, such as neutrophil chemotaxis and mitogen-activated protein kinase binding. In addition, the KEGG pathway analysis revealed enrichment in immune-related pathways (Interleukin-17 signaling pathway, cytokine-cytokine receptor interaction, and TNF signaling pathway). Furthermore, the target genes of the differentially expressed lncRNAs were implicated in the negative regulation of interleukin-6 and tumor necrosis factor production. These results indicate that lncRNAs and protein-coding genes participate in the regulation of immune and metabolic processes in fish.

Annexin A2 regulates Mycoplasma bovis adhesion and invasion to embryo bovine lung cells affecting molecular expression essential to inflammatory response

Mycoplasma bovis (M. bovis) is an important pathogen of the bovine respiratory disease complex, invading lower respiratory tracts and causing severe pneumonia. However, its molecular mechanism largely remains unknown. Host annexin A2 (ANXA2) is a calcium-dependent phospholipid-binding protein. The current study sought to determine whether ANXA2 could mediate M. bovis adhesion and invasion thereby affecting its induction of inflammatory response. ANXA2 expression was upregulated in M. bovis-infected bovine lung epithelial cells (EBL), and blocking ANXA2 with an anti-ANXA2 antibody reduced M. bovis adhesion to EBL. Compared with uninfected cells, more ANXA2 was translocated from the cytoplasm to the cell surface after M. bovis infection. Furthermore, RNA interference knockdown of ANXA2 expression in EBL cells resulted in a significant decrease in M. bovis invasion and F-actin polymerization. Next, the transcriptomic study of M. bovis-infected EBL cells with and without ANXA2 knockdown were performed. The data exhibited that ANXA2 knockdown EBL cells had 2487 differentially expressed genes (DEGs), with 1175 upregulated and 1312 downregulated compared to control. According to GO and KEGG analyses, 50 genes potentially linked to inflammatory responses, 23 involved in extracellular matrix (ECM) receptor interaction, and 48 associated with PI3K-AKT signal pathways were upregulated, while 38 mRNA binding genes, 16 mRNA 3′-UTR binding genes, and 34 RNA transport genes were downregulated. Furthermore, 19 genes with various change-folds were selected for qPCR verification, and the results agreed with the RNA-seq findings. Above all, the transcription of two chemokines (IL-8 and CXCL5) and a key bovine β-defensin TAP in IL-17 signaling pathway were significantly increased in ANXA2 knockdown cells. Moreover, ANXA2 knockdown or knockout could increase NF-κB and MAPK phosphorylation activity in response to M. bovis infection. Additionally, ANXA2 knockdown also significantly decreased the CD44 transcripts via exon V3 and V7 skipping after M. bovis infection. We concluded that M. bovis borrowed host ANXA2 to mediate its adhesion and invasion thereby negatively regulating molecular expression essential to IL-17 signal pathway. Furthermore, CD44 V3 and V7 isoforms might contribute to this ANXA2 meditated processes in M. bovis infected EBL cells. These findings revealed a new understanding of pathogenesis for M. bovis infection.

CD44a functions as a regulator of p53 signaling, apoptosis and autophagy in the antibacterial immune response

The cell adhesion molecule CD44 has been implicated in diverse biological functions including the pathological responses to infections and inflammatory diseases. The variable forms of CD44 contribute to functional variations, which are not yet defined in teleost. Here, we show that zebrafish CD44a plays a protective role in the host defense against Edwardsiella piscicida infection. Zebrafish CD44a deficiency inhibits cell growth and proliferation, impairs cell growth and death pathways, and regulates the expression levels of many genes involved in p53 signaling, apoptosis and autophagy. In addition, CD44a gene disruption in zebrafish leads to inhibition of apoptosis and induction of autophagy, with the increased susceptibility to E. piscicida infection. Furthermore, we show that zebrafish CD44a variants including CD44a_tv1 and CD44a_tv2 promote the translocation of p53 from the nucleus to the cytoplasm and interact with p53 in the cytoplasm. Mechanistically, zebrafish CD44a_tv1 mediates the beneficial effect for larvae survival infected with E. piscicida is depending on the CASP8-mediated apoptosis. However, the antibacterial effect of zebrafish CD44a_tv2 depends on the cytoplasmic p53-mediated inhibition of autophagy. Collectively, our results identify that different mechanisms regulate CD44a variants-mediated antibacterial responses.

Histone H2A Nuclear/Cytoplasmic Trafficking Is Essential for Negative Regulation of Antiviral Immune Response and Lysosomal Degradation of TBK1 and IRF3

Histone H2A is a nuclear molecule tightly associated in the form of the nucleosome. Our previous studies have demonstrated the antibacterial property of piscine H2A variants against gram-negative bacteria Edwardsiella piscicida and Gram-positive bacteria Streptococcus agalactiae. In this study, we show the function and mechanism of piscine H2A in the negative regulation of RLR signaling pathway and host innate immune response against spring viremia of carp virus (SVCV) infection. SVCV infection significantly inhibits the expression of histone H2A during an early stage of infection, but induces the expression of histone H2A during the late stage of infection such as at 48 and 72 hpi. Under normal physiological conditions, histone H2A is nuclear-localized. However, SVCV infection promotes the migration of histone H2A from the nucleus to the cytoplasm. The in vivo studies revealed that histone H2A overexpression led to the increased expression of SVCV gene and decreased survival rate. The overexpression of histone H2A also significantly impaired the expression levels of those genes involved in RLR antiviral signaling pathway. Furthermore, histone H2A targeted TBK1 and IRF3 to promote their protein degradation via the lysosomal pathway and impair the formation of TBK1-IRF3 functional complex. Importantly, histone H2A completely abolished TBK1-mediated antiviral activity and enormously impaired the protein expression of IRF3, especially nuclear IRF3. Further analysis demonstrated that the inhibition of histone H2A nuclear/cytoplasmic trafficking could relieve the protein degradation of TBK1 and IRF3, and blocked the negative regulation of histone H2A on the SVCV infection. Collectively, our results suggest that histone H2A nuclear/cytoplasmic trafficking is essential for negative regulation of RLR signaling pathway and antiviral immune response in response to SVCV infection.

NLRC3-like 1 inhibits NOD1-RIPK2 pathway via targeting RIPK2

Both NLRC3 and NOD1 belong to regulatory NLR subfamily based on their best-characterized function. In mammals, NLRC3 was reported to function by attenuating signaling cascades initiated by other families of PRRs. In teleosts, multiple NLRC3-like genes were identified through transcriptome sequencing. However, the functions of many NLRC3-like genes, especially the fish-specific NLRC3-like genes, remain unclear. In the present study, we report the functional characterization of a novel category of NLRC3-like proteins (named as NLRC3-like 1) from the zebrafish, which consists of a fish-specific FISNA, a conserved NACHT and five C-terminal LRRs domains. The expression of zebrafish NLRC3-like 1 was inducible in response to Edwardsiella piscicida infection. During bacterial infection, the in vitro and in vivo studies revealed that zebrafish NLRC3-like 1 overexpression facilitated bacterial growth and dissemination, together with the decreased survival rate of zebrafish larvae infected with E. piscicida. The attenuated response by zebrafish NLRC3-like 1 in response to bacterial infection were characterized by the impaired expression of antibacterial genes, proinflammatory cytokines and Nox genes. Furthermore, zebrafish NLRC3-like 1 interacted with the adaptor protein RIPK2 of NODs signaling via the FISNA (Fish-specific NACHT associated domain) and NACHT domains. However, the interaction between zebrafish NLRC3-like 1 and RIPK2 inhibited the assembly of the NOD1-RIPK2 complex. Importantly, zebrafish NLRC3-like 1 inhibited NOD1-mediated antibacterial activity, NF-κB and MAPK pathways and proinflammatory cytokine production. All together, these results firstly demonstrate that zebrafish NLRC3-like 1 inhibits NOD1-RIPK2 antibacterial pathway via targeting the adaptor protein RIPK2.

The CoV-2 outbreak: how hematologists could help to fight Covid-19

COVID-19 is a medical emergency, with 20 % of patients presenting with severe clinical manifestations. From the pathogenetic point of view, COVID-19 mimics two other well-known diseases characterized by cytokine storm and hyper-activation of the immune response, with consequent organ damage: acute graft-versus-host disease (aGVHD) and macrophage activation syndrome (MAS). Hematologists are confident with these situations requiring a prompt therapeutic approach for switching off the uncontrolled cytokine release; here, we discuss pros and cons of drugs that are already employed in hematology in the light of their possible application in COVID-19. The most promising drugs might be: Ruxolitinib, a JAK1/2 inhibitor, with a rapid and powerful anti-cytokine effect, tyrosine kinase inhibitors (TKIs), with their good anti-inflammatory properties, and perhaps the anti-Cd26 antibody Begelomab. We also present immunological data from gene expression experiments where TKIs resulted effective anti-inflammatory and pro-immune drugs. A possible combined treatment algorithm for COVID-19 is here proposed.

Histone H2A cooperates with RIP2 to induce the expression of antibacterial genes and MHC related genes

An octamer consisting of two copies of histones H2A, H2B, H3 and H4 is the nucleosome core. It is well established that histone derived antimicrobial peptides (AMPs) have anti-microbial properties in various invertebrate and vertebrate species. Different from well-known histone H2A-derived AMPs, the antimicrobial properties of the complete histone H2A are rather limited. In the present study, we report the functional characterization of the complete histone H2A from zebrafish. The expression of zebrafish histone H2A was higher in embryos than in larvae, and inducible in response to bacterial infection. Furthermore, the expression of zebrafish histone H2A was decreased by RIP2 deficiency with and/or without bacterial infection. During Edwardsiella piscicida infection, the overexpression of zebrafish histone H2A inhibited bacterial proliferation and increased the survival rate of zebrafish larvae. The overexpression of zebrafish histone H2A demonstrated an increased transcription of many antibacterial genes and MHC related genes, which was dependent on RIP2, an adaptor protein for signal propagation of the NLRs-mediated antibacterial immune response. In line with this, zebrafish histone H2A cooperated with RIP2 to induce the transcription of many antibacterial genes and MHC related genes. All together, these results firstly demonstrate the antibacterial property of the complete histone H2A against gram-negative bacteria E. piscicida in vivo and the correlation between zebrafish histone H2A and RIP2 adaptor protein on the transcriptional regulation of antibacterial genes and MHC related genes.