Characteristics of CD4-1 gene and its immune responses against Aeromonas veronii infection by activating NF-κB signaling in Qihe crucian carp Carassius auratus

CD4-1 found in bony fish contains four extracellular immunoglobulin (Ig)-like domains similar to that of mammalian CD4, which is crucial for the activation of CD4+ helper T-cell. However, there is limited knowledge regarding the molecular markers, immune functions and regulation mechanism of CD4-1 in teleosts due to their vast diversity. In this study, we cloned and characterized two isoforms of Qihe crucian carp CD4-1, designated as CaCD4-1.1 and CaCD4-1.2. We further explored their expression responses upon stimulation with Aeromonas veronii, and the regulation of their immune responses against A. veronii by NF-κB. The ORF of CaCD4-1.1 and CaCD4-1.2 cDNA encoded 477 and 466 amino acids, respectively. Both proteins contained seven conserved cysteine residues in the extracellular domain, and a CCC motif in their cytoplasm, respectively. However, CaCD4-1.1 exhibited a relatively limited similarity with CaCD4-1.2 in the ectodomain. The quantitative real-time polymerase chain reaction (qRT-PCR) analysis revealed that the mRNA expression of CaCD4-1.1 and CaCD4-1.2 exhibited differential constitutive expression across all examined tissues. Furthermore, the expression level of CD4-1.2 was higher than that of CD4-1.1 in the gills, head kidney, and spleen of Qihe crucian carp subjected to A. veronii challenge, while it was lower in the trunk kidney. Inhibition of NF-κB activity resulted in a decrease in the expression levels of CD4-1.1 and CD4-1.2 mRNA in the gill, while inducing an increase in expression levels in the spleen, in accordance with the observed ultrastructural changes in both organs. Interestingly, the impact of NF-κB on the mRNA expression level of CD4-1.1 appears to be stronger than that of CD4-1.2. Our results suggest that CaCD4-1.1 and CaCD4-1.2 could be expressed on T cells and antigen-sampling cells that exhibit similar characteristics to mammalian M cells, respectively, and differentially regulated by NF-κB in adaptive immune responses against bacterial infection. This research contributes to a better understanding of the crucial role of CD4-1 in the immune response of Qihe crucian carp and provide novel insights for the prevention and treatment of fish diseases in aquaculture.

Role of HIF in fish inflammation

The hypoxia-inducing factor (HIF) is a central transcription factor in cellular oxygen sensing and regulation. It is common that the inflammation always appears in many diseases, like infectious diseases in fishes, and the inflammation is often accompanied by hypoxia, as a hallmark of inflammation. Besides coordinating cellular responses to low oxygen, HIF-mediated hypoxia signaling pathway is also crucial for immune responses such as the regulations of innate immune cell phenotype and function, as well as metabolic reprogramming under the inflammation. However, the understanding of the molecular mechanisms by which HIFs regulate the inflammatory response in fish is still very limited. Here, we review the characteristics of HIF as well as its roles in innate immune cells and the infections caused by bacteria and viruses. The regulatory effects of HIF on the metabolic reprogramming of innate immune cells are also discussed and the future research directions are outlooked. This paper will serve as a reference for elucidating the molecular mechanism of HIF regulating inflammation and identifying treatment strategies to target HIF for fish disease.

The role of CcPTGS2a in immune response against Aeromonas hydrophila infection in common carp (Cyprinus carpio)

Prostaglandin-endoperoxide synthase 2 (PTGS2), a crucial enzyme in prostaglandin synthesis, catalyzes the conversion of arachidonic acid to prostaglandins and plays a significant role in the inflammatory response. This investigation aimed to determine the regulatory role of PTGS2a in the innate immune response to bacterial infection in fish. To achieve this objective, the CcPTGS2a gene was identified and characterized in common carp (Cyprinus carpio), and its function in immune defense was investigated. According to the sequence and structural analysis results, CcPTGS2a had an open reading frame of 1806 bp that encoded 602 amino acids. It was estimated that the protein's theoretical molecular weight was 69.0 kDa, and its isoelectric point was 8.10. The structure of CcPTGS2a was observed to be conserved, with an epidermal growth factor domain and a peroxidase domain present. Moreover, the amino acid sequence of CcPTGS2a exhibited significant homology with the amino acid sequences of several fish species. CcPTGS2a mRNA was detected in the healthy tissues of common carp, with higher expression in the head kidney, spleen, gills, and liver. Following the challenges with Aeromonas hydrophila and lipopolysaccharide, CcPTGS2a mRNA showed unique geographic and temporal expression patterns, with significant increases detected in the head kidney, gills, spleen, and liver. Additionally, the recombinant CcPTGS2a protein exhibited detectable bacterial binding to various bacteria. As determined by subcellular localization analysis, CcPTGS2a was predominantly localized in the nucleus and cytoplasm. Furthermore, it was discovered that the overexpression of CcPTGS2a stimulated the up-regulation of ferroptosis-related genes and inflammatory cytokine mRNA expression in fish and EPC (Epithelioma papulosum cyprinid) cells while concurrently reducing the bacterial load of A. hydrophila. In contrast, the interference of CcPTGS2a decreased the mRNA expression of ferroptosis-related genes and inflammatory cytokines in fish and EPC cells and increased the bacterial load of A. hydrophila. Notably, A. hydrophila stimulation resulted in the up-regulation of CcPTGS2a protein expression in EPC cells. These results suggested that CcPTGS2a was involved in the immune response to bacterial infections in common carp.

Two CcCCL19bs orchestrate an antibacterial immune response in Yellow River carp (Cyprinus carpio haematopterus)

Chemokines are a group of chemotactic cytokines with an essential role in homeostasis as well as immunity via specific G protein-coupled receptors and atypical receptors. In our study, two Yellow River carp (Cyprinus carpio haematopterus) CCL19b genes (CcCCL19bs), tentatively named CcCCL19b_a and CcCCL19b_b, were cloned. The open reading frames (ORFs) of CcCCL19b_a and CcCCL19b_b were both 333 bp that encoded a 12 kDa protein with 110 amino acid residues. CcCCL19bs contained a signal peptide and a SCY domain with four typical conserved cysteine residues. The two CcCCL19b proteins shared high similarities with each other in both secondary and three-dimensional structure. Phylogenetic analysis showed that CcCCL19bs and other CCL19bs from tetraploid cyprinid fish were clustered into one clade. CcCCL19bs were highly expressed in gill and intestine in healthy fish, and a significant up-regulation of gene expression after Aeromonas hydrophila infection and poly(I:C) stimulation was observed in gill, liver, and head kidney. Furthermore, chemotaxis and antibacterial activity of CcCCL19bs were studied. The results indicated that recombinant CcCCL19b_a and CcCCL19b_b protein (rCcCCL19b_a and rCcCCL19b_b) exhibited significant attraction to primary head kidney leukocytes (HKLs). Meanwhile, both of rCcCCL19bs could promote the proliferation of HKLs, and significantly up-regulate the expressions of IL-1β, CCR7, and IL-6, and down-regulate the expression of IL-10 in primary HKLs. In vitro, rCcCCL19bs could bind and aggregate A. hydrophila and Staphylococcus aureus. The rCcCCL19bs exhibited significant antibacterial activity against A. hydrophila, but not S. aureus. Moreover, they inhibited the growth of A. hydrophila and S. aureus. In vivo, overexpression of CcCCL19bs contributed to the bacterial clearance. These studies suggested that CcCCL19bs orchestrate an antibacterial immune response.

Activation Mechanism of CcGSDMEb-1/2 and Regulation for Bacterial Clearance in Common Carp (Cyprinus carpio)

Gasdermin E (GSDME), to date, is considered the only direct executor of the pyroptosis process in teleost and plays an important role in innate immunity. In common carp (Cyprinus carpio), there contains two pairs of GSDME (GSDMEa/a-like and GSDMEb-1/2), and the pyroptotic function and regulation mechanism of GSDME still remain unclear. In this study, we identified two GSDMEb genes of common carp (CcGSDMEb-1/2), which contain a conserved N-terminal pore-forming domain, C-terminal autoinhibitory domain, and a flexible and pliable hinge region. We investigated the function and mechanism of CcGSDMEb-1/2 in association with inflammatory and apoptotic caspases in Epithelioma papulosum cyprinid cells and discovered that only CcCaspase-1b could cleave CcGSDMEb-1/2 through recognizing the sites 244FEVD247 and 244FEAD247 in the linker region, respectively. CcGSDMEb-1/2 exerted toxicity to human embryonic kidney 293T cells and bactericidal activity through its N-terminal domain. Interestingly, after i.p. infection by Aeromonas hydrophila, we found that CcGSDMEb-1/2 were upregulated in immune organs (head kidney and spleen) at the early stage of infection, but downregulated in mucosal immune tissues (gill and skin). After CcGSDMEb-1/2 were knocked down and overexpressed in vivo and in vitro, respectively, we found that CcGSDMEb-1/2 could govern the secretion of CcIL-1β and regulate the bacterial clearance after A. hydrophila challenge. Taken together, in this study, it was demonstrated that the cleavage mode of CcGSDMEb-1/2 in common carp was obviously different from that in other species and played an important role in CcIL-1β secretion and bacterial clearance.

Characterization of hepcidin gene and protection of recombinant hepcidin supplemented in feed against Aeromonas hydrophila infection in Yellow River carp (Cyprinus carpio haematopterus)

Hepcidin is a small peptide of defensins with antibacterial activity, and plays an important role in innate immunity against pathogenic microorganisms, which can also participate in the regulation of iron metabolism. The hepcidin gene in Yellow River carp (Cyprinus carpio haematopterus) (CcHep) was cloned and identified. The total length of CcHep cDNA was 480 bp, containing an open reading frame (ORF) that encoded 91 amino acids (aa), which contained a 24-aa signal peptide, a 42-aa propeptide, and a 25-aa mature peptide. The mature peptide had a typical RX (K/R) R motif and eight conserved cysteine residues forming four pairs of disulfide bonds. Homology and phylogenetic tree analysis showed that CcHep had the closest relationship with that of crucian carp. The expression levels of hepcidin mRNA in healthy and Aeromonas hydrophila stimulated fish were measured by real-time fluorescence quantitative PCR. The results showed that CcHep mRNA was expressed in different tissues of healthy fish with the highest relative expression level in liver, followed by kidney and intestine, and the lowest expression level was observed in heart. The hepcidin gene was extremely significantly up-regulated in head kidney, intestine, liver, skin, spleen, and gill at 6 h and 12 h after A. hydrophila infection. Furthermore, the immunoregulation effect of dietary recombinant protein was evaluated. The recombinant hepcidin protein (rCcHep) was successfully expressed by Pichia pastoris X-33 and showed strong antibacterial activity against A. hydrophila, Escherichia coli, Vibrio anguillarum and Bacillus subtilis in vitro. In order to evaluate the preventive effect of rCcHep, fish were fed with basal diet or diet supplemented with different doses of rCcHep, and then challenged with A. hydrophila. The results showed that immune genes were up-regulated to varying degrees, and feed additive groups exhibited a significantly improved up-regulation expressions of Lysozyme, Toll-like receptor 5 (TLR 5), Major histocompatibility complex classⅡ (MHCⅡ), while inhibited up-regulation expressions of Interleukin 1β (IL-1β), Interleukin 8 (IL-8), and Tumor necrosis factor α (TNF-α) in liver and spleen compared to the control. Meanwhile, the relative immune protection rate in 120 mg/kg feed additive group was 28%, and the bacterial clearance rate in tissues of this group was higher than that of the control. Collectively, these results indicated that rCcHep had antibacterial activity and showed an immune protection effect against A. hydrophila, and could be considered as a dietary supplement to apply in aquaculture.

C-H Functionalization of Heterocycles with Triplet Carbenes by means of an Unexpected 1,2-Alkyl Radical Migration

The C-H functionalization of indole heterocycles constitutes a key strategy to leverage the synthesis of endogenous signaling molecules such as tryptamine or tryptophol. Herein, we report on the photocatalytic reaction of ethyl diazoacetate with indole, which shows an unusual solvent dependency. While C2-functionalization occurs under protic conditions, the use of aprotic solvents leads to a complete reversal of selectivity and exclusive C3-functionalization occurs. To rationalize for this unexpected reactivity switch, we have conducted detailed theoretical and experimental studies, which suggest the participation of a triplet carbene intermediate that undergoes initial C2-functionalization. A distinct cationic [1,2]-alkyl radical migration then leads to formation of C3-functionalized indole. We conclude with the application of this photocatalytic reaction to access oxidized tryptophol derivatives including gram-scale synthesis and derivatization reactions.

Contribution of flagellar cap gene in virulence and pathogenicity of Aeromonas veronii

Aeromonas veronii is an important zoonotic and aquatic pathogen that causes a number of illnesses in both humans and animals. It is related to gastroenteritis, skin and soft tissue infections and bacteremia in humans, as well as causing significant economic losses in aquaculture owing to fish sepsis. Here, we constructed the flagellar cap gene (fliD) mutant strain of A. veronii by suicide plasmid-mediated homologous recombination system and analysed its characteristics. It was found that the deletion of fliD had no effect on growth and biochemical properties and could be inherited stably. However, the motility of A. veronii ΔfliD was significantly reduced, the flagellum was defective and the biofilm formation was attenuated compared with that of A. veronii wild-type strain. In vivo experiments revealed that the colonization capacity of ΔfliD was significantly lower than that of the wild-type strain in the period of first 24 h, and the median lethal dose (LD₅₀ ) was 56 times higher than that of the wild-type strain. The Cyprinus carpio infected with the wild-type strain indicated faster death speed and more severe clinical signs compared to ΔfliD strain. These results suggest that fliD is closely related to the virulence of A. veronii and plays an important role in pathogenicity, providing the foundation for pathogenic mechanism studies of A. veronii.

Induction and potential molecular mechanism of the enhanced immune response in Procambarus clarkii after secondary encountered with Aeromonas veronii

For a long time, it was believed that invertebrates do not possess acquired immunity and mainly rely on innate immunity for protection against pathogens infection. However, an increasing number of studies have suggested that some form of "immune memory" can be initiated in invertebrates after primary exposure to the pathogen, which was defined as "specific immune priming". In the present study, two experiments were carried out to determine whether specific immune priming can be induced in crayfish (Procambarus clarkii) by Aeromonas veronii, if so, to identify the underlying mechanism. Once being "preimmunization" by formalin-killed A. veronii, the survival rate, in vitro antibacterial activity and haemocyte phagocytosis rate of crayfish were enhanced, which indicated that better immune protection was obtained. Furthermore, at some time points, the expression of antimicrobial peptide (AMP) and Down syndrome cell adhesion molecule (Dscam) genes was significantly higher in P. clarkii individuals that underwent stimulation twice than in those that were only stimulated once. Taken together, the results suggest that enhanced specific immune protection can be obtained in primed crayfish and that the Dscam molecule, haemocyte phagocytosis function, and AMPs may be involved in this immune priming. The present study provides a better understanding of the molecular mechanism of immune priming in invertebrates.

Polyfunctionalization of vicinal carbon centers and synthesis of unsymmetric 1,2,3,4-tetracarbonyl compounds

The synthesis and characterization of organic compounds with unusual atom or functional group connectivity is one of the main driving forces in the discovery of new synthetic methods that has raised the interest of chemists for many years. Polycarbonyl compounds are such compounds wherein multiple carbonyl groups are directly juxtaposed and influence each other's chemical reactivity. While 1,2-dicarbonyl or 1,2,3-tricarbonyl compounds are well-known in organic chemistry, the 1,2,3,4-tetracarbonyl motif remains barely explored. Herein, we report on the synthesis of such 1,2,3,4-tetracarbonyl compounds employing a synthetic strategy that involves C-nitrosation of enoldiazoacetates, while the diazo functional group remains untouched. This strategy not only leverages the synthesis of 1,2,3,4-tetracarbonyl compounds to an unprecedented level, it also accomplishes the synthesis of 1,2,3,4-tetracarbonyl compounds, wherein each carbonyl group is orthogonally masked. Combined experimental and theoretical studies provide an understanding of the reaction mechanism and rationalize the formation of such 1,2,3,4-tetracarbonyl compounds.

Characterization of CD3γ/δ gene and its immune response in Qihe crucian carp Carassius auratus after challenged by Aeromonas veronii and Poly(I:C)

CD3γ/δ found in non-mammalian vertebrates is a CD3 homolog with structural characteristics similar to both mammalian CD3γ and CD3δ, and plays important roles in T cell recognization and immune response in fish. In this study, the full-length of CD3γ/δ from Qihe crucian carp (named CaCD3γ/δ) was cloned and characterized, then the expression response profiles and potential immune functions was explored after Aeromonas veronii and Poly(I:C) challenge. The results showed that the full-length of CaCD3γ/δ was 819 bp including a 5'-UTR of 141 bp, a 3'-UTR of 168 bp, and an ORF of 510 bp encoding a putative 169-aa protein with an estimated MW of 18.71 kD and a theoretical pI of 8.77. The protein sequence of CaCD3γ/δ contained a Leu-Leu and a CXXXC motif in the extracellular domain, and an ITAM and a Leu-Ile motif in the cytoplasm, and a residue of Asn in the transmembrane. CaCD3γ/δ was constitutively expressed in the spleen, liver, gill, and blood of Qihe crucian carp. After the carp were challenged with Poly(I:C) and Aeromonas veronii, the mRNA expression levels of CaCD3γ/δ were significantly changed in the spleen, head kidney, intestine and gill, according to the results of qPCR. However, compared with A. veronii, Poly(I:C) challenge can rapidly induce the CaCD3γ/δ expression levels in head kidney, intestine and spleen, which suggested CaCD3γ/δ may be differentially modulated by different pathogens. Moreover, the results of immunohistochemical analysis showed that the CaCD3γ/δ⁺ secreted cells in the spleen and gills of Qihe crucian were increased after challenged with Poly(I:C), as well as the spleen challenged with A. veronii, but at different levels. Combined with the fact that vascular congestion, necrosis of parenchymal cells, and inflammatory cells including lymphocytes infiltration were also observed in the gill and spleen of Qihe crucian carp treated with A. veronii and Poly(I:C) revealed by pathological analysis, it was predicted that CaCD3γ/δ⁺ T lymphocytes may participated in the immune response against pathogens. This study will contribute to understand the important role of CaCD3γ/δ⁺ T lymphocytes in the immune response of Qihe crucian carp, and provide new insights for the prevention and treatment of the diseases of Qihe crucian carp.

Molecular characteristics of interleukin (IL)-17A/F3 and its immune response on the pathogen and functional regulation on cytokines in common carp Cyprinus carpio L

Fish interleukin (IL)-17A/F is homologous with mammalian IL-17A and IL-17F, which plays a key role in regulating inflammatory responses and autoimmune diseases. In fish, IL-17A/F1, 2, and 3 have been identified and described. However, IL-17A/F3 has received little attention in fish. In this study, a homolog of IL-17A/F3 was identified in common carp (Cyprinus carpio L.), which was termed as Cc_IL-17A/F3. The deduced amino acid sequence of Cc_IL-17A/F3 has four conserved cysteine residues, which could form two intrachain disulfide bonds. Homology comparison showed that the Cc_IL-17A/F3 was in the range of 31.7-71.9% of sequence similarity with these of other fishes. The Cc_IL-17A/F3 gene was constitutively expressed in various tissues, with higher expression levels in the skin and gills. After common carp were infected by Aeromonas. hydrophila, the mRNA expression levels of Cc_IL-17A/F3 were significantly up-regulated in the spleen, head kidney, gills, and intestine. Based on the indirect immunofluorescence assay, Cc_IL-17A/F3 proteins were found to be obviously increased in the intestine and spleen upon A. hydrophila infection at 24 h post-infection. The recombinant protein rCc_IL-17A/F3 could enhance the gene expression levels of pro-inflammatory cytokines (IL-1β, IL-6, IFN-γ, and TNF-α) as well as chemokines (CXCL8 and CXCL20) in primary head kidney leukocytes. In vivo and in vitro experiments have similar stimulatory effects. When Cc_IL-17A/F3 was overexpressed in common carp, the expressions of pro-inflammatory cytokines and chemokines were significantly up-regulated in head kidney and spleen. In summary, the results derived from the present study suggested that the Cc_IL-17A/F3 plays an important role in defending against bacterial infections, and probably participates in mucosal immunity of the host.

Photochemical Intermolecular Cyclopropanation Reactions of Allylic Alcohols for the Synthesis of [3.1.0]-Bicyclohexanes

Cyclopropane-fused lactones are highly desirable in drug and natural products synthesis. Herein, we report on a photochemical, chemoselective reaction of aryldiazoacetates with allylic alcohols that furnishes cyclopropane-fused lactone skeletons efficiently in one step. The diastereoselectivity of the protocol was precisely controlled, and chemoselective cyclopropanation of allylic alcohols via free carbene intermediate followed by transesterification constitutes a series of bicyclic lactones in high yield without the formation of ether byproducts via typical O-H insertion reactions.

Molecular characteristics and the roles of CaASC and its restriction to Aeromonas hydrophila in Carassius auratus

Apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC), as a critical adaptor molecule in inflammasome complexes, plays an important role in mediating inflammation reaction. In this study, the complete cDNA of ASC gene with 891 bp was cloned in Qihe crucian carp Carassius auratus (named as CaASC), which was composed of a 5'-UTR of 36 bp, a 3'-UTR of 252 bp, and an ORF of 603 bp encoded 200 amino acids with a predicted isoelectric point of 5.61 and a molecular mass of 22.0 kDa. Multiple sequence alignment and motif analysis revealed that CaASC contained a conserved N-terminal Pyrin domain (PYD) and a C-terminal Caspase recruitment domain (CARD). CaASC mRNA and protein expressions were detected in selected tissues, with the highest mRNA level in the spleen. Meanwhile, CaASC gene expressions were clearly altered in intestine, gill, skin, spleen, liver and head kidney of fish challenged by Aeromonas hydrophila, LPS, and polyI:C, respectively. The recombined proteins of CaASC with fluorescent tag were over-expressed in transfected 293T cells, and the green specks were observed obviously and located in the cytoplasm. Furthermore, knockdown of CaASC reduced the expression of IL-1β and promoted the bacterial colonization in fish tissues, while overexpression of CaASC increased the expression of IL-1β and hampered the bacterial colonization in these tissues. Taken together, these results identified the molecular characteristics of CaASC in C. auratus, and revealed its role in regulating IL-1β expression and restricting bacterial infection in vivo.

Interleukin (IL)-22 in common carp (Cyprinus carpio L.): Immune modulation, antibacterial defense, and activation of the JAK-STAT signaling pathway

Interleukin (IL)-22 is an IL-10 family cytokine secreted by CD4⁺ T cells and plays an important role in regulating inflammation and infection elimination. IL-22 homologues have been reported in the teleost, but the functions of IL-22 are still unclear. In this study, we identified two duplicated IL-22 genes in common carp (Cyprinus carpio L.), termed Cc_IL-22A and Cc_IL-22B. Sequence analysis showed that Cc_IL-22A and Cc_IL-22B had four conserved cysteine residues, which could form two intra-chain disulfide bridges. The Cc_IL-22A and Cc_IL-22B were constitutively expressed in various tissues, with the highest expression in the gill. The mRNA expression levels of Cc_IL-22A and Cc_IL-22B were significantly up-regulated in the gill, intestine, head kidney, and spleen of common carp challenged with Aeromonas. hydrophila. In vivo study showed that the expression levels of pro-inflammatory cytokines were significantly up-regulated in the head kidney and spleen when Cc_IL-22A or Cc_IL-22B were over-expressed. Furthermore, the over-expression of Cc_IL-22A and Cc_IL-22B indicated a protective effect on tissues, with only lymphocytic infiltration observed in comparison to the control and pcN3 groups, without obvious change in tissue morphology. Similar stimulatory effects of rIL-22A and rIL-22B were observed in vitro. When HKLs were stimulated with rIL-22A or rIL-22B, the expression levels of critical signaling molecules in the Janus kinase (JAK) and signal transducer and activator of transcription (STAT) pathway were significantly induced, including JAK1, JAK3, STAT1, and STAT3, as well as pro-inflammatory cytokines (IL-1β and TNF-α). Together, these results suggest that Cc_IL-22A and Cc_IL-22B may regulate inflammatory responses through the JAK-STAT signaling pathway and have a significant impact on the immune defense of common carp against bacterial infection. Therefore, our study provides a new perspective on the functions of Cc_IL-22A and Cc_IL-22B in the immune defense mechanism of fish.

Molecular characterization of NLRC3 and its interaction with other inflammasome components and regulation on the bacterial colonization in Qihe crucian carp Carassius auratus

The NLRC as a very unique subfamily of Nod like receptors (NLRs), is believed to play an important role in the bacterial recognition of animals. However, the molecular characterization and immunological role of NLRC3 in Carassius auratus is little known. In this study, we identified and achieved a complete cDNA sequence of NLRC3 gene in Qihe crucian carp Carassius auratus (named as CaNLRC3). The full-length cDNA sequence of CaNLRC3 was composed of 3823 bp, which contained a 5'-UTR of 251 bp, a 3'-UTR of 158 bp, and an open reading frame (ORF) of 3414 bp encoded 1137 amino acids with a predicted isoelectric point of 8.25 and a molecular mass of 124.1 kDa, characterized with a caspase recruitment domain (CARD) at N-terminus. The mRNA expression of CaNLRC3 was detected to be constitutive in all the examined tissues, with the high expression levels in spleen, skin and intestine. After challenges with bacteria or pathogenic analogue, expression levels of CaNLRC3 gene were strongly induced. Co-localization and co-immunoprecipitation results found that CaNLRC3 can assemble CaASC through CARD domain interaction, then CaASC associated with CaCaspase-1a, presumably to assemble the NLRC3 inflammasome complex. The overexpression of CaNLRC3 could significantly increase the mRNA expression of IL-1β, and promote the bacterial elimination and result in the decrease of bacterial loading in liver, spleen and kidney after bacterial infection. Vice versa, the knockdown of CaNLRC3 could obviously reduce IL-1β expression at mRNA level, and bacterial loading was significantly increased in tissue. Taken together, CaNLRC3 is proved to be a pivotal cytosolic innate immune receptor in this study, which is acted as the potential component of inflammasome to regulate inflammation reaction, and could modify bacterial loading in tissue and restrict bacterial infection in teleost.

Photochemical synthesis of 1,2,4-triazoles via addition reaction of triplet intermediates to diazoalkanes and azomethine ylide intermediates

The reactivity of diazoalkanes most commonly proceeds through the formation of carbene intermediates or dipolar cycloaddition reactions. The reaction of diazoalkanes with intermediates with unpaired electrons, however, is much less elaborated. Herein, we report on the photochemical reaction of acceptor-only diazoalkanes with azodicarboxylates. Photoexcitation of the latter results in the formation of a triplet species, which undergoes an addition reaction with diazoalkanes and formation of an azomethine ylide followed by dipolar cycloaddition reaction with organic nitriles to give a 1,2,4-triazole. The application of this transformation was elaborated in a broad and general substrate scope (48 examples), including scale-up via flow chemistry and downstream transformations. Experimental and computational studies were performed to elucidate the reaction mechanism and to rationalize the reaction outcome.

Genome-wide identification, evolutionary analysis, and antimicrobial activity prediction of CC chemokines in allotetraploid common carp, Cyprinus carpio

Chemokines are a group of secreted small molecules which are essential for cell migration in physiological and pathological conditions by binding to specific chemokine receptors. They are structurally classified into five groups, namely CXC, CC, CX3C, XC and CX. CC chemokine group is the largest one among them. In this study, we identified and characterized 61 CC chemokines from allotetraploid common carp (Cyprinus carpio). The sequence analyses showed that the majority of CC chemokines had an N-terminal signal peptide, and an SCY domain, and all CC chemokines were located in the extracellular region. Phylogenetic, evolutionary and syntenic analyses confirmed that CC chemokines were annotated as 11 different types (CCL19, CCL20, CCL25, CCL27, CCL32, CCL33, CCL34, CCL35, CCL36, CCL39, and CCL44), which exhibited unique gene arrangement pattern and chromosomal location respectively. Furthermore, genome synteny analyses between common carp and four representative teleost species indicated expansion of common carp CC chemokines resulted from the whole genome duplication (WGD) event. Additionally, the continuous evolution of gene CCL25s in teleost afforded a novel viewpoint to explain the WGD event in teleost. Then, we predicted the three-dimensional structures and probable function regions of common carp CC chemokines. All the CC chemokines core structures were constituted of an N-loop, a three-stranded β-sheet, and a C-terminal helix. Finally, 43 CC chemokines were predicted to have probable general antimicrobial activity. Their tertiary structures, cationic and amphiphilic physicochemical property supported the viewpoint. To verify the prediction, six recombinant CCL19s proteins were prepared and the antibacterial activity against Escherichia coli and Aeromonas hydrophila were verified. The results supported our prediction that rCCL19a.1s (rCCL19a.1_a, rCCL19a.1_b) and rCCL19bs (rCCL19b_a, rCCL19b_b), especially rCCL19bs, exhibited extremely significant inhibition to the growth of both E. coli and A. hydrophila. On the contrary, two rCCL19a.2s had no significant inhibitory effect. These studies suggested that CC chemokines were essential in immune system evolution and not monofunctional during pathogen infection.

Identification of Shewanella putrefaciens as a novel pathogen of the largemouth bass (Micropterus salmoides) and histopathological analysis of diseased fish

The largemouth bass (Micropterus salmoides) is an economically important aquaculture species in China, and its production has increased rapidly in recent years. Although Shewanella putrefaciens is known to infect several fish species, its role in infecting M. salmoides is relatively unknown. Here, we isolated a gram-negative bacterial strain (termed XX2021) from farmed largemouth bass. Based on the results of 16S rRNA sequencing and phylogenetic analyses, the isolate was identified as S. putrefaciens. The virulence of XX2021 was dependent on water temperature, such as the LD50 values were 4.21×104, 7.26×105, and 2.47×106 CFU/g fish weight at 10°C, 18°C, and 25°C, respectively. Four virulent genes—including dksA, hem, lonR, and fur—were screened through a PCR assay. The results of an antibiotic resistance test showed that XX2021 was sensitive to kanamycin, cefotaxime, doxycycline, sulfamethoxazole, florfenicol, tetracycline, and gentamicin; showed intermediate susceptibility to streptomycin, ampicillin, and norfloxacin; and was resistant to nalidixic acid and penicillin. XX2021-infected fish showed clinical symptoms typical of S. putrefaciens infection. In addition, we re-isolated XX2021 from infected fish and confirmed its identity using 16S rRNA sequencing. Histopathological changes were observed in the intestine, head kidney, spleen, and liver of diseased fish. This study presents the first report of the pathogenic effects of S. putrefaciens in farmed largemouth bass. Our findings may help develop effective disease control strategies for aquaculture fish and prevent disease outbreaks under low water temperatures.

Significance of diagnosis and prognosis for appendiceal orifice inflammation in ulcerative colitis: a real-world study

OBJECTIVE

Ulcerative colitis (UC) is a chronic inflammatory disease of the large intestine. At present, the significance of appendiceal orifice inflammation (AOI) in UC prognosis is still controversial. This prospective observational study investigated the importance of AOI in UC diagnosis and prognosis. Additionally, it compared the therapeutic efficacy of treatments in UC patients with or without AOI.

DESIGN

This study was a prospective, observational, single-centre, real-world study. Patients with AOI were included in the observation group, and patients without AOI were assigned to the control group. All patients were followed up for 1 year; the disease remission and treatment efficacy were re-examined by colonoscopy. In addition, the clinical, endoscopic and pathological features were collected before and after the treatment.

RESULTS

Patients with endoscopic diffuse inflammatory changes in the distal colorectum accompanied by AOI had a higher positive UC diagnosis rate than those without (96.5% vs 78.0%). Also, AOI had a specificity of 95.2% and a sensitivity of 28.3% for UC diagnosis. However, no difference in the modified Mayo score (p=0.881) or Baron grading was observed between the control and observation groups, indicating that AOI does not affect the treatment outcome of UC patients.

CONCLUSION

In this study, the observation of AOI improved the UC diagnostic accuracy in patients with diffuse lesions in the distal colorectum. Furthermore, the presence of AOI does not affect the treatment efficacies of UC.

TRIAL REGISTRATION NUMBER

ChiCTR1800017753.

Molecular characterizations, immune modulation, and antibacterial activity of interleukin-17A/F1a and interleukin-17A/F1b in common carp Cyprinus carpio

Interleukin-17 (IL-17), as a pro-inflammatory cytokine family, mediates different pro-inflammatory mediators in various cell types (e.g., epithelial cells, macrophages, endothelial cells, and fibroblasts), which play an important role in defending against pathogens. The IL-17A/F1 genes have recently been reported in fish. However, the functions of these genes are still unclear. In this study, we identified two duplicated IL-17A/F1 genes in common carp (Cyprinus carpio L.), namely, CcIL-17A/F1a and CcIL-17A/F1b. Sequence analysis showed that CcIL-17A/F1a and CcIL-17A/F1b proteins had four conserved cysteine residues, which could form two intra-chain disulfide bridges. Homology comparison displayed that the deduced amino acid sequences of CcIL-17A/F1a and CcIL-17A/F1b shared 31.1%-77.3% and 32.5%-75.7% of sequence similarity to IL-17A/F1 homologues from other fish species, respectively. The mRNA expression levels of CcIL-17A/F1a and CcIL-17A/F1b were obviously increased in gill and head-kidney of fish challenged with A. hydrophila. The recombinant protein rCcIL-17A/F1a and rCcIL-17A/F1b could enhance the expression levels of pro-inflammatory cytokines (IL-1β, IL-6, IFN-γ, and TNF-α) and chemokines (CXCL8 and CXCL20). The 3 × Flag eukaryotic expression vectors to express protein rCcIL-17A/F1a (or rCcIL-17A/F1b) were constructed and intramuscularly injected in common carp. The rCcIL-17A/F1a (or rCcIL-17A/F1b) could be successfully expressed in vivo. Four immune-related genes, namely, CD4, CD8, TNF-α, and IgM, were also significantly induced to be expressed at higher mRNA levels compared with the control. The pretreatment with CcIL-17A/F1a or CcIL-17A/F1b could markedly increase the survival rate of common carp challenged with A. hydrophila. Our results demonstrated that CcIL-17A/F1a or CcIL-17A/F1b plays an important role in immune responses and immune defense against bacteria. CcIL-17A/F1a or CcIL-17A/F1b could also be potentially used as an immunopotentiator to prevent diseases in common carp.

Molecular characterization of Rab7 and its involvement in innate immunity in red swamp crayfish Procambarus clarkii

Rab7 is a member of the Rab GTPases protein family, and it plays an essential role in regulating trafficking organelles in higher animals. However, recent studies showed that it also participated in the immune response and cytophagy against pathogens in invertebrates. In the present study, the full-length of Rab7 from Procambarus clarkii (PcRab7) was cloned, and its function during pathogen infection and phagocytosis of haemocytes was also explored. The results showed that the full-length of PcRab7 was 3639 bp, containing a 618 bp open reading frame encoding 155 amino acids. The predicted molecular weight and isoelectric point of PcRab7 were 23.2 kDa and 5.77, respectively. PcRab7 was widely expressed in various tissues including haemocytes, intestine, muscle, gill, and hepatopancreas, and the highest expression level was in haemocytes. The mRNA transcripts of PcRab7 in the main organs (gill, intestine, and hepatopancreas, and haemocytes) were significantly affected by white spot syndrome virus (WSSV) and Aeromonas veronii infection. Subsequently, the prokaryotic and eukaryotic expression vectors were successfully constructed, and polyclonal antibodies, which could specifically recognize the endogenous Rab7 protein, were also obtained. Furthermore, the phagocytosis rate of haemocytes against FITC-labeled A. veronii was significantly decreased when the PcRab7 was silenced, while the over-expression of Rab7 increased the phagocytosis rate of haemocytes. The abnormal expression of Rab7 protein could also affect the survival rate of P. clarkii infected with WSSV or A. veronii. These results could provide a basis for further study on the immunological function of PcRab7.

Visible‐Light‐Induced, Single‐Metal‐Catalyzed, Directed C−H Functionalization: Metal‐Substrate‐Bound Complexes as Light‐Harvesting Agents

C−H functionalization represents one of the most rapidly advancing areas in organic synthesis and is regarded as one of the key concepts to minimize the ecological and economic footprint of organic synthesis. The ubiquity and low reactivity of C−H bonds in organic molecules, however, poses several challenges, and often necessitates harsh reaction conditions to achieve this goal, although it is highly desirable to achieve C−H functionalization reactions under mild conditions. Recently, several reports uncovered a conceptually new approach towards C−H functionalization, where a single transition‐metal complex can be used as both the photosensitizer and catalyst to promote C−H bond functionalization in the absence of an exogeneous photosensitizer. In this Minireview, we will provide an overview on recent achievements in C−H functionalization reactions, with an emphasis on the photochemical modulation of the reaction mechanism using such catalysts.

A Computational Study on the Photochemical O-H Functionalization of Alcohols with Diazoacetates

In this computational study, we provide a detailed analysis of the underlying reaction mechanism and show that a singlet carbene is initially formed. Depending on the pK_A of the alcohol, this singlet carbene can engage in direct protonation or enol formation to yield the O-H functionalization product. On the contrary, propargylic alcohols take up a dual role and form a complex with the carbene intermediate that leads to facile cyclopropenation reactions.

Hydrogen Bonding Networks Enable Brønsted Acid-Catalyzed Carbonyl-Olefin Metathesis

Synthetic chemists have learned to mimic nature in using hydrogen bonds and other weak interactions to dictate the spatial arrangement of reaction substrates and to stabilize transition states to enable highly efficient and selective reactions. The activation of a catalyst molecule itself by hydrogen‐bonding networks, in order to enhance its catalytic activity to achieve a desired reaction outcome, is less explored in organic synthesis, despite being a commonly found phenomenon in nature. Herein, we show our investigation into this underexplored area by studying the promotion of carbonyl‐olefin metathesis reactions by hydrogen‐bonding‐assisted Brønsted acid catalysis, using hexafluoroisopropanol (HFIP) solvent in combination with para‐toluenesulfonic acid (pTSA). Our experimental and computational mechanistic studies reveal not only an interesting role of HFIP solvent in assisting pTSA Brønsted acid catalyst, but also insightful knowledge about the current limitations of the carbonyl‐olefin metathesis reaction.

Proton or Carbene Transfer? On the Dark and Light Reaction of Diazoalkanes with Alcohols

The formal alkylation reaction of OH groups with diazoalkanes under catalyst-free reaction conditions finds broad application in organic synthesis. However, even today, this reaction is mainly limited to the use of diazomethane as reaction partner. In this combined experimental and theoretical study, we aim at a fundamental understanding of the reaction of diazoalkanes with alcohols to make this transformation amenable to a generalized approach towards formal alkylation reactions of alcohols with diazoalkanes. Experimental and theoretical studies suggest a direct proton transfer only in exceptional cases. In a more general setting, such O-H functionalization proceed both under dark and photochemical conditions via a key hydrogen-bonded singlet carbene intermediate that undergoes a protonation-addition mechanism. We conclude with applications of this approach in O-H functionalization reactions of alcohols, including simple fluorinated, halogenated and aliphatic alcohols and showcase functional-group tolerance of this method in the reaction of biologically active and pharmaceutically relevant alcohols.

Photocatalytic gem-Difluoroolefination Reactions by a Formal C-C Coupling/Defluorination Reaction with Diazoacetates

The photolysis of diazoalkanes to conduct singlet carbene transfer reactions of colored diazoalkanes has recently attracted significant interest in organic synthesis. Herein, we describe a photocatalytic approach that allows the access of triplet carbene intermediates via energy transfer to conduct highly efficient gem‐difluoroolefination reactions with α‐trifluoromethyl styrenes. The use of a tertiary amines proved pivotal to unlock this unusual reaction pathway and to prevent undesired cyclopropanation pathways. The amine further facilitates the ultimate abstraction of fluoride to yield gem‐difluoroolefins (43 examples, up to 88 % yield), which is supported by experimental and theoretical mechanistic studies. We explored this synthesis method with a broad substrate scope, ranging from simple olefins and heterocyclic olefins towards the decoration of pharmaceutically relevant building blocks.

Teleost CD4+ helper T cells: Molecular characteristics and functions and comparison with mammalian counterparts

CD4⁺ helper T cells play key and diverse roles in inducing adaptive immune responses in vertebrates. The CD4 molecule, which is found on the surfaces of CD4⁺ helper T cells, can be used to distinguish subsets of helper T cells. Teleosts are the oldest living species with bona-fide CD4 coreceptors. Although some components of immune systems of teleosts and mammals appear to be similar, many physiological differences are represented between them. Previous studies have shown that two CD4 paralogs are present in teleosts, whereas only one is present in mammals. Therefore, in this review, the CD4 molecular structure, expression profiles, subpopulations, and biological functions of teleost CD4⁺ helper T cells were summarized and compared with those of their mammalian counterparts to understand the differences in CD4 molecules between teleosts and mammals. This review provides suggestions for further studies on the CD4 molecular function and regulatory mechanism of CD4⁺ helper T cells in teleost fish and will help establish therapeutic strategies to control fish diseases in the future.

Molecular characterization and biological effect of a C-type lectin receptor in Qihe crucian carp, Carassius auratus

C-type lectin receptors, as the important members of pattern-recognition receptors, play the crucial roles in the innate immune system, which discriminate self and non-self by recognizing and binding the carbohydrates on the surface of microorganism. In this study, we identified a C-type lectin receptor gene in Qihe crucian carp Carassius auratus (named as CaCLR). The full-length cDNA of CaCLR was composed of 1130 bp, with a 226 bp 5'-untranslated region (UTR), a 792 bp ORF encoding a 263aa protein, and a 112 bp 3'-UTR with a polyadenylation signal sequence AATAAA and a poly (A) tail. The predicted amino acid sequence of CaCLR is a single transmembrane receptor with a typical carbohydrate recognition domain (CRD) at its C-terminus. With regard to the mRNA transcript of CaCLR, it was ubiquitously detected in the tested tissues, among which it was the most abundant in head kidney. The temporal expressions of CaCLR were obviously up-regulated in liver, spleen, kidney, and head kidney after Aeromonas hydrophila and poly I: C challenge, respectively, and the patterns of expression changes were in a time-depended manner. The recombinant CaCLR (rCaCLR) purified from Escherichia coli BL21 (DE3), exhibited strong binding ability with lipopolysaccharide (LPS), peptidoglycan (PGN), β-Glucan, and Mannan, as well as five microorganisms including fungus (Saccharomyces cerevisiae), Gram-negative bacteria (A. hydrophila, E. coli and Vibrio anguillarum), and Gram-positive bacteria (Micrococcus lysodeikticus). In the presence of rCaCLR, the eliminating capacity against A. hydrophila could be enhanced in C. auratus. Taken together, CaCLR is involved in the antibacterial defense in C. auratus.

Photochemical Carbene Transfer Reactions of Aryl/Aryl Diazoalkanes-Experiment and Theory*

Controlling the reactivity of carbene intermediates is a key parameter in the development of selective carbene transfer reactions and is usually achieved by metal complexes via singlet metal-carbene intermediates. In this combined experimental and computational studies, we show that the reactivity of free diaryl carbenes can be controlled by the electronic properties of the substituents without the need of external additives. The introduction of electron-donating and -withdrawing groups results in a significant perturbation of singlet triplet energy splitting of the diaryl carbene intermediate and of activation energies of consecutive carbene transfer reactions. This strategy now overcomes a long-standing paradigm in the reactivity of diaryl carbenes and allows the realization of highly chemoselective carbene transfer reactions with alkynes. We could show that free diaryl carbenes can be readily accessed via photolysis of the corresponding diazo compounds and that these carbenes can undergo highly chemoselective cyclopropenation, cascade, or C-H functionalization reactions. Experimental and theoretical mechanistic analyses confirm the participation of different carbene spin states and rationalize for the observed reactivity.

Rhodium-catalyzed cascade reactions of triazoles with organoselenium compounds - a combined experimental and mechanistic study

Herein, we report on our studies on the reaction of organoselenium compounds with triazoles under thermal conditions using simple Rh(ii) catalysts. These reactions do not provide the product of classic rearrangement reactions. Instead two different cascade reactions were uncovered. While allyl selenides react in a cascade of sigmatropic rearrangement and selenium-mediated radical cyclization reaction to give dihydropyrroles, cinnamyl selenides undergo a double rearrangement reaction cascade involving a final aza-Cope reaction to give the product of 1,3-difunctionalization. Theoretical and experimental studies were conducted to provide an understanding of the reaction mechanism of these cascade reactions. The former provide an important insight into fundamental question on the nature of the ylide intermediate in rearrangement reactions and reveal that organoselenium compounds take up multiple roles in rearrangement reactions and mediate a free ylide reaction mechanism.

Herein, we report on our studies on the reaction of organoselenium compounds with triazoles under thermal conditions using simple Rh(ii) catalysts.

Forensic analysis of soman exposure using characteristic fragment ions from protein adducts

The verification of exposure to nerve agents is a serious challenge, especially in cases of soman (GD) poisoning. Protein adducts are reliable biomarkers, that provide forensic information and evidence during incidents of terrorism or sporadic poisoning. Mass spectrometry, coupled with a proteomics approach, was established for the forensic analysis of GD-based protein adducts. The fragmentation pathways of GD-based protein adducts were investigated for the first time using electrospray ionization tandem mass spectrometry. Three abundant natural loss product ions, [M+2H-54]²⁺ (loss of two carbon cations), [M+2H-72]²⁺ (loss of tert-butyl and methyl moieties), and [M+2H-84]²⁺ (loss of the pinacolyl moieties), were observed in each of the GD-labeled adducts, and the product ions were independent of protein structure and exposure route. A unique mechanism for the formation of product ions involving GD-protein adducts is proposed here. These findings support the development of a simple and precise forensic analysis technique to rapidly verify GD poisoning using these three GD-related product ions.

Gold(I)-catalyzed intramolecular cyclization/intermolecular cycloaddition cascade as a fast track to polycarbocycles and mechanistic insights

Metal carbene is an active synthetic intermediate, which has shown versatile applications in synthetic chemistry. Although a variety of catalytic methods have been disclosed for the generation of carbene species from different precursors, there is an increasing demand for the development of efficient and practical approaches for the in-situ formation of metal carbene intermediates with structural diversity and unrevealed reactivity. Herein we report a gold-catalyzed cascade protocol for the assembly of polycarbocyclic frameworks in high yields under mild reaction conditions. Mechanistic studies indicate that the unique β-aryl gold-carbene species, generated via gold-promoted 6-endo-dig diazo-yne cyclization, is the key intermediate in this reaction, followed by a [4 + 2]-cycloaddition with external alkenes. In comparison to the well-documented metal carbene cycloadditions, this carbene intermediate serves as a 4-C synthon in a cycloaddition reaction. A variety of elusive π-conjugated polycyclic hydrocarbons (CPHs) with multiple substituents are readily accessible from the initially generated products by a mild oxidation procedure.

Synthesis of Trifluoromethylated Tetrasubstituted Allenes via Palladium-Catalyzed Carbene Transfer Reaction

Herein, we report on the palladium-catalyzed synthesis of trifluoromethylated, tetrasubstituted allenes from vinyl bromides and trifluoromethylated diazoalkanes in good to excellent yield. This reaction proceeds via oxidative addition of a Pd(0) complex with vinyl bromide. Subsequent base-promoted reductive elimination generates the allene. This methodology provides an efficient strategy even on gram scale to valuable trifluoromethylated, tetrasubstituted allenes under mild reaction conditions. The allene products can be used in acid catalyzed cyclization reactions to give trifluoromethylated indene products.

Identification of a protective epitope in Japanese encephalitis virus NS1 protein

Japanese encephalitis virus (JEV) is one of the most important culex transmitted-flaviviruses, which can cause encephalitis in humans. Although non-structural protein 1 (NS1) of JEV does not stimulate neutralizing antibodies, this protein can provide high immunoprotection in vivo. The protective epitopes and the protective mechanism of NS1 still remain unclear. In this study, we generated five different monoclonal antibodies (mAbs) targeting the NS1 protein of JEV. In vitro experiments revealed that none of these five antibodies neutralized the JEV infection. In mouse protection studies, one of these mAbs, designated 2B8, provided a therapeutic effect against JEV lethal challenge (70% survival rate). Using peptide mapping analysis, we found that mAb 2B8 reacted with the epitope ²²⁵PETHTLWGD²³³ in the NS1 protein, in which any mutations among amino acid residues T²²⁸, H²²⁹, L²³¹ or W²³² could cause binding failure of 2B8 to the NS1 protein. Furthermore, mice immunized with KLH-polypeptide (²²⁵PETHTLWGD²³³) showed reduced mortality following JEV challenge. Collectively, we found a new protective epitope in the JEV NS1 protein. These results may facilitate the development of therapeutic agent and subunit-based vaccines based on the NS1 protein.

Access to gem-Difluoro Olefins via C-H Functionalization and Dual Role of Anilines

In this Letter, we describe a simple, practical approach in which cheap CuI was used as a catalyst to introduce a gem-difluoro olefin onto simple electron-rich aniline derivatives in good yield via direct C-H functionalization and a subsequent HF elimination reaction. Detailed mechanistic studies point at a dual role of aniline derivatives in this reaction, which serve as a substrate and a basic promoter to trigger the HF elimination step.