IκBα phosphorylation and associated NF-κB activation are essential events in lymphocyte activation, proliferation, and anti-bacterial adaptive immune response of Nile tilapia

Regulatory roles of miRNA-530 in the post-transcriptional regulation of NF-κB signaling pathway through targeted modulation of IκBα in Sebastesschlegelii

MicroRNAs (miRNAs) are a crucial type of non-coding RNAs involved in post-transcriptional regulation. The playing essential regulatory roles in the NF-κB signaling pathway and modulate the host immune response to diverse pathogens by targeting IκBα. However, the regulatory mechanism of miRNAs in relation with IκBα in Sebastes schlegelii remains unclear. In our study, we identified two copies of IkBα gene in black rockfish (Sebastes schlegelii), namely IkBα1 and IkBα2. Moreover, we have discovered that miRNA-530 can activate the NF-κB signaling pathway by inhibiting the expression of IκBα, thereby inducing the inflammatory response. This project comprehensively investigated the interactive regulatory roles of miRNA-530 in the NF-κB signaling pathway at both cellular and in vivo levels, while also elucidating the regulatory relationships between miRNA-530 and IκBα. In conclusion, our research confirmed that miRNA-530 can target the 3'UTR region of IκBα, resulting in a decrease in the expression of IκBα at the post-transcriptional level and inhibiting its translation. The findings contribute to the understanding of the regulatory network of non-coding RNA in teleosts and its subsequent regulation of the NF-κB signaling pathway by miRNAs.

Genome-wide identification and functional characterization of inhibitor of nuclear factor-κB (IκB) kinase (IKK) in turbot (Scophthalmus maximus)

The inhibitor of nuclear factor-κB (IκB) kinase (IKK) is involved in a variety of intracellular cell signaling pathways and is an important component of the NF-κB signaling pathway. IKK genes have been suggested to play important roles in the innate immune response to pathogen infection in both vertebrates and invertebrates. However, little information is available about IKK genes in turbot (Scophthalmus maximus). In this study, six IKK genes were identified including SmIKKα, SmIKKα2, SmIKKβ, SmIKKε, SmIKKγ, and SmTBK1. The IKK genes of turbot showed the highest identity and similarity with Cynoglossus semilaevis. Then, phylogenetic analysis showed that the IKK genes of turbot were most closely related to C. semilaevis. In addition, IKK genes were widely expressed in all the examined tissues. Meanwhile, the expression patterns of IKK genes were investigated by QRT-PCR after Vibrio anguillarum and Aeromonas salmonicida infection. The results showed that IKK genes had varying expression patterns in mucosal tissues after bacteria infection, indicating that they may play key roles in maintaining the integrity of the mucosal barrier. Subsequently, protein and protein interaction (PPI) network analysis showed that most proteins interacting with IKK genes were located in the NF-κB signaling pathway. Finally, the double luciferase report and overexpression experiments showed that SmIKKα/SmIKKα2/SmIKKβ involved in the activation of NF-κB in turbot. In summary, our results suggested that IKK genes of turbot played important roles in the innate immune response of teleost, and provide valuable information for further study of the function of IKK genes.

Molecular characterization and immune functions of lipasin in Nile tilapia (Oreochromis niloticus): Involvement in the regulation of tumor necrosis factor-α secretion

Lipasin, the product of the angiopoietin-like 8 (angptl8) gene, is known as a critical regulator of plasma lipid metabolism. However, its immune function in vertebrates is currently poorly understood. By 5'/3'-rapid amplification of cDNA ends (RACE), we established the structural identity of Nile tilapia (Oreochromis niloticus) angptl8. The transcripts of tilapia angptl8 were widely expressed in various tissues, with the highest levels in the liver. Following lipopolysaccharide in vivo challenges, time-dependent angptl8 gene expression was observed in the head kidney and liver. On the basis of the sequence obtained, we produced recombinant lipasin that inhibited lipoprotein lipase activity. Treatment of head kidney leukocytes with lipasin stimulated tumor necrosis factor-α (TNF-α) secretion and gene expression. In addition, lipasin-induced TNF-α secretion could be prevented by inhibiting the nuclear factor-kappa B (NF-κB) signaling pathway. Furthermore, lipasin enhanced the phosphorylation and degradation of IκBα and promoted translocation of the p65 subunit of NF-κB to the nucleus. Collectively, the current findings suggested that lipasin was involved in the immune response of Nile tilapia and stimulated TNF-α secretion by activating the NF-κB pathway in tilapia head kidney leukocytes.

Response of immunoglobulin M in gut mucosal immunity of common carp (Cyprinus carpio) infected with Aeromonas hydrophila

Immunoglobulin (Ig) M is an important immune effector that protects organisms from a wide variety of pathogens. However, little is known about the immune response of gut mucosal IgM during bacterial invasion. Here, we generated polyclonal antibodies against common carp IgM and developed a model of carp infection with Aeromonas hydrophila via intraperitoneal injection. Our findings indicated that both innate and adaptive immune responses were effectively elicited after A. hydrophila infection. Upon bacterial infection, IgM+ B cells were strongly induced in the gut and head kidney, and bacteria-specific IgM responses were detected in high levels both in the gut mucus and serum. Moreover, our results suggested that IgM responses may vary in different infection strategies. Overall, our findings revealed that the infected common carp exhibited high resistance to this representative enteropathogenic bacterium upon reinfection, suggesting that IgM plays a key role in the defense mechanisms of the gut against bacterial invasion. Significantly, the second injection of A. hydrophila induces strong local mucosal immunity in the gut, which is essential for protection against intestinal pathogens, providing reasonable insights for vaccine preparation.

Protective effect of berberine against LPS-induced injury in the intestine: a review

Sepsis is a systemic inflammatory condition caused by an unbalanced immunological response to infection, which affects numerous organs, including the intestines. Lipopolysaccharide (LPS; also known as endotoxin), a substance found in Gram-negative bacteria, plays a major role in sepsis and is mostly responsible for the disease's morbidity and mortality. Berberine is an isoquinoline alkaloid found in a variety of plant species that has anti-inflammatory properties. For many years, berberine has been used to treat intestinal inflammation and infection. Berberine has been reported to reduce LPS-induced intestinal damage. The potential pathways through which berberine protects against LPS-induced intestinal damage by inhibiting NF-κB, suppressing MAPK, modulating ApoM/S1P pathway, inhibiting COX-2, modulating Wnt/Beta-Catenin signaling pathway, and/or increasing ZIP14 expression are reviewed.Abbreviations: LPS, lipopolysaccharide; TLR, Toll-like receptor; MD-2, myeloid differentiation factor 2; CD14, cluster of differentiation 14; LBP, lipopolysaccharide-binding protein; MYD88, myeloid differentiation primary response 88; NF-κB, nuclear factor kappa light-chain enhancer of activated B cells; MAPK, mitogen-activated protein kinase; IL, interleukin; TNFα, tumor necrosis factor-alpha; Caco-2, cyanocobalamin uptake by human colon adenocarcinoma cell line; MLCK, myosin light-chain kinase; TJ, tight junction; IκBα, nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor, alpha; IBS, irritable bowel syndrome; ERK, extracellular signal-regulated kinase; JNK, c-Jun N-terminal kinase (JNK; GVB, gut-vascular barrier; ApoM, apolipoprotein M; S1P, sphingosine-1-phosphate; VE-cadherin, vascular endothelial cadherin; AJ, adherens junction; PV1, plasmalemma vesicle-associated protein-1; HDL, high-density lipoprotein; Wnt, wingless-related integration site; Fzd, 7-span transmembrane protein Frizzled; LRP, low-density lipoprotein receptor-related protein; TEER, transendothelial/transepithelial electrical resistance; COX-2, cyclooxygenase-2; iNOS, inducible nitric oxide synthase; IGF, insulin-like growth factor; IGFBP, insulin-like growth factor-binding protein; ZIP, Zrt-Irt-like protein; PPAR, peroxisome proliferator-activated receptors; p-PPAR, phosphorylated-peroxisome proliferator-activated receptors; ATF, activating transcription factors; SOD, superoxide dismutase; GSH-Px, glutathione peroxidase; SARA, subacute ruminal acidosis; IPEC-J2, porcine intestinal epithelial cells; ALI, acute lung injury; ARDS, acute respiratory distress syndrome.

High-fat diet blunts T-cell responsiveness in Nile tilapia

The reduced stress resistance and increased disease risk associated with high-fat diet (HFD) in animals have attracted increasing attention. However, the effects of HFD on adaptive immunity in early vertebrates, especially non-tetrapods, remain unknown. In this study, using Nile tilapia (Oreochromis niloticus) as a model, we investigated the effects of HFD on the primordial T-cell response in fish. Tilapia fed with an HFD for 8 weeks showed impaired lymphocyte homeostasis in the spleen, as indicated by the decreased number of both T and B lymphocytes and increased transcription of proinflammatory cytokines interferon-γ and interleukin-6. Moreover, lymphocytes isolated from HFD-fed fish or cultured in lipid-supplemented medium exhibited diminished T-cell activation in response to CD3ε monoclonal antibody stimulation. Moreover, HFD-fed tilapia infected by Aeromonas hydrophila showed decreased T-cell expansion, increased T-cell apoptosis, reduced granzyme B expression, and impaired infection elimination. Additionally, HFD attenuated adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK) activity in tilapia lymphocytes, which in turn upregulated fatty acid synthesis but downregulated fatty acid β-oxidation. Altogether, our results suggest that HFD impairs lymphocyte homeostasis and T cell-mediated adaptive immune response in tilapia, which may be associated with the abnormal lipid metabolism in lymphocytes. These findings thus provide a novel perspective for understanding the impact of HFD on the adaptive immune response of early vertebrates.

The improvement of Coreopsis tinctoria essential oil on learning and memory impairment of d-galactose-induced mice through Nrf2/NF-κB pathway

Essential oil of Coreopsis tinctoria (EOC) is a essential substance extracted from Coreopsis tinctoria with the excellent anti-oxidant effect. However, it is still unclear whether EOC can improve learning and memory impairment and its mechanism. The purpose of this study was to investigate the effect of EOC on learning and memory impairment induced by D-galactose (D-gal) in mice and reveal its mechanism. The composition of EOC was analyzed by GC-MS, and the results showed that the highest content was D-limonene. The follow-up experiments were conducted by comparing EOC with D-limonene. The aging model was established by subcutaneous injection of D-gal, and donepezil, D-limonene and EOC were given by intragastric administration. It was found that EOC and D-limonene significantly improved learning and memory impairment induced by D-gal through the Morris water maze and step-through tests. Pathological and biochemical analysis showed that the hippocampal morphologic of mice was damage and the activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) induced by D-gal were decreased, while the content of malondialdehyde (MDA) was increased, while EOC and D-limonene could reverse the morphological changes and reduce oxidative damage. In addition, EOC and D-limonene significantly increased body weight and organ coefficients, including liver, spleen and kidney. Moreover, EOC and D-limonene improved the expression of nuclear factor E2 related factor 2 (Nrf2) pathway and inhibited nuclear transcription factors-κB (NF-κB) pathway. In summary, the results showed that EOC and D-limonene could improve learning and memory impairment induced by D-gal through Nrf2/ NF-κB pathway. It was clear that as a mixture, EOC was better than D-limonene on improving learning and memory impairment.

Matrix metalloproteinase-25 from Japanese sea bass (Lateolabrax japonicus) is involved in pro-inflammatory responses

Matrix metalloproteinases (MMPs) are highly expressed in leukocytes and macrophages, which play a role in the innate immune response. Here, the cDNA sequence of MMP25 from Japanese sea bass (Lateolabrax japonicus) (LjMMP25) was identified. Phylogenetic analysis revealed that LjMMP25 was most closely related to large yellow croaker MMP25. Multiple sequence alignment of LjMMP25 with MMP25 sequences from other teleosts revealed that regions of known functional importance were highly conserved. Expression analysis revealed that LjMMP25 was highly expressed in the head kidney and widely expressed in other tissues including gill, spleen, and liver. LjMMP25 was found to regulate inflammatory cytokine production and promote phagocytosis and bacterial killing in monocytes/macrophages (MO/MФ). Furthermore, LjMMP25 regulated the inflammatory response by modulating NF-κB signaling. These findings reveal new information about the role of LjMMP25 in regulating pro-inflammatory responses in this species.

microRNA-122 regulates NF-κB signaling pathway by targeting IκBα in miiuy croaker, Miichthys miiuy

The inhibitory protein IκBα plays a key role in the inflammatory process and immune response by regulating the activity of the transcription factor NF-κB. microRNA (miR) is a small non-coding RNA that can regulate many biochemical processes, such as cell growth, proliferation, and immune response. In this study, it was first predicted that IκBα is the target of miR-122 through bioinformatics, and it was confirmed by dual fluorescence experiments. Then we found that miR-122 can inhibit the expression of IκBα at the mRNA and protein levels, thereby promoting the p65-activated NF-κB pathway. It is speculated that miR-122 plays an important role in the innate immunity of teleost fish. This study will help to further understand miRNAs regulatory mechanism in teleost fish.

Identification of IκBα in Japanese eel Anguilla japonica that impairs the IKKα-dependent activation of NF-κB, AP1, and type I IFN signaling pathways

As a member of inhibitory κB family (IκB) family, IκBα is best-characterized and plays a central negative feedback regulator of NF-κB pathway in mammals, but the information about IκBα in the regulation of immune responses is still limited in teleost fishes. In the present study, the full-length cDNA of an IκBα homologue, AjIκBα, was cloned by 5' and 3' SMART RACE from Japanese eel, and its characteristics of expression in response to various PAMPs and A. hydrophila infection were investigated both in vivo and in vitro using quantitative real-time polymerase chain reaction (qRT-PCR). In addition, the subcellular localization of AjIκBα GFP fusion protein and the induction of AjIκBα alone or co-expression with Japanese eel IKKα (AjIKKα) in the activation of NF-κB, type I IFN and AP1 performed using Dual-Glo luciferase assay system were also detected. Sequence comparison analysis revealed that AjIκBα has typical conserved domains, including the N-terminal conserved degradation motif, the ankyrin repeats, and the C-terminal PEST domain. The predicted three-dimensional structure of AjIκBα is similar to that of human IκBα. qRT-PCR analysis revealed a broad expression for AjIκBα in a wide range of tissues, with the highest expression in the spleen, followed by intestine, liver, gills, skin, kidney, and with a lower expression in the heart and muscle. The AjIκBα expressions in the kidney, spleen, and especially in liver were significantly induced following injection with Gram-negative bacterial component LPS, the viral mimic poly I:C and Aeromonas hydrophila infection. In vitro, the AjIκBα transcripts of Japanese eel liver cells were significantly enhanced by the treatment of LPS, poly I:C, or the stimulation of different concentration of Aeromonas hydrophil. Luciferase assays demonstrated that not only could the AjIκBα expression significantly decrease the activation of NF-κB, AP1, and IFNβ-responsive promoters in HEK293 cells and EPC cells, but also robustly inhibited the activity of these three promoters in HEK293 cells or NF-κB and AP1-responsive promoters in EPC cells induced by AjIKKα. Additionally, subcellular localization studies showed that AjIκBα was evenly distributed in the cytoplasm and nucleus both in HEK293 cells and EPC cells under natural state. AjIκBα was found to aggregate into spots in the cytoplasm and nucleus stimulated by LPS or mostly aggregate into nucleus with the treatment of poly I:C in HEK293 cells, whereas the elevated expression of AjIκBα was observed in the cytoplasm of EPC cells upon the stimulation of poly I:C. These results collectively indicated that AjIκBα function as an important negative regulation in innate immunity of host against antibacterial and antiviral infection likely via the inhibition of the activation of NF-κB, AP1, and type I IFN signaling pathways.

Astaxanthin attenuates oxidative stress and immune impairment in D-galactose-induced aging in rats by activating the Nrf2/Keap1 pathway and suppressing the NF-κB pathway

As a potential antioxidant, astaxanthin (AST) exhibits anti-aging effects. However, its relationships to oxidative stress and immunity have yet to be sufficiently investigated. In this research, integrated analysis of oxidative stress and immunosenescence was performed to elucidate the efficacy and potential mechanisms of AST in d-galactose-induced aging in rats. The results showed that AST significantly decreased malonaldehyde (MDA) levels and increased antioxidase activity, in addition to demonstrating the ability to repair histopathological injuries to the liver, thereby attenuating oxidative stress. Nuclear factor erythroid 2-related factor 2 (Nrf2) expression was up-regulated by 117.95%, whereas Kelch-like ECH-associated protein-1 (Keap1) expression was simultaneously down-regulated by 51.22%. Moreover, AST significantly reduced interleukin-1β (IL-1β) and interleukin-6 (IL-6) levels, as well as expression of nuclear factor-kappa B (NF-κB) (p65) and i-kappa-B-alpha (IκBα) proteins. Findings of repair of immune organs, as well as elevated levels of interleukin-2 (IL-2), immunoglobulin M (IgM) and immunoglobulin G (IgG), suggest a novel mechanism by which AST could regulate cellular immunity and humoral immunity to attenuate immunosenescence. The anti-aging effects of AST were shown to be due in part to the Nrf2/Keap1 and NF-κB pathways, and AST treatment ameliorated oxidative stress and immune impairment overall.

An atypical KLRG1 in Nile tilapia involves in adaptive immunity as a potential marker for activated T lymphocytes

Killer cell lectin-like receptor G subfamily 1 (KLRG1) is a receptor generally expressed on effector CD8⁺ T cells or NK cells at terminal differentiation stage, and it will be highly induced for lymphocyte cytotoxicity upon pathogen infection or lymphocyte activation. However, little is known about the character or function of KLRG1 in lower vertebrates. In present study, we reappraised a molecule that previously defined as KLRG1 in the genomic sequence of Nile tilapia Oreochromis niloticus, and identified it as an atypical KLRG1-like molecule (defined as On-KLRG1-L), and illustrated its potential function serving as a marker representing effector T lymphocytes of fish species. On-KLRG1-L consists of two C-type lectin-like domains (CTLDs) without transmembrane region, and the tertiary structure of the CTLD is highly alike to that in mouse KLRG1. As a CTLD-containing protein, the recombinant On-KLRG1-L could bind PGN and several microbes in vitro. On-KLRG1-L was widely expressed in immune-associated tissues, with the highest expression level in the gill. Once Nile tilapia is infected by Aeromonas hydrophila, mRNA level of On-KLRG1-L in spleen lymphocytes were significantly up-regulated on 5 days after infection. Meanwhile, On-KLRG1-L protein was also induced on 5 or 8 days after A. hydrophila infection. Furthermore, we found both mRNA and protein levels of On-KLRG1-L were dramatically enhanced within several hours after spleen lymphocytes were activated by T cell-specific mitogen PHA in vitro. More importantly, the ratio of On-KLRG1-L⁺ T cells was also augmented after PHA stimulation. The observations suggested that the KLRG1-like molecule from Nile tilapia participated in lymphocyte activation and anti-bacterial adaptive immune response, and could serve as an activation marker of T lymphocytes. Our study thus provided new evidences to understand lymphocyte-mediated adaptive immunity of teleost.

Akt1/mTORC1 signaling modulates adaptive immune response of Nile tilapia by promoting lymphocyte activation and proliferation

Serving as a significant signaling molecule, RAC-alpha serine/threonine-protein kinase (Akt1) plays indispensable roles in cell cycle, growth, survival, metabolism, as well as immune response. However, how Akt1 regulates adaptive immune response in early vertebrate, especially the teleost, is largely unknown. Here, using a Nile tilapia Oreochromis niloticus model, we investigated the regulatory role of Akt1 in adaptive immunity of teleost. Both sequence and structure of the O. niloticus Akt1 (OnAkt1), were evolutionarily conserved comparing with the counterparts from other vertebrates. mRNA of OnAkt1 was widely expressed in lymphoid organs/tissues of Nile tilapia, with relative higher level in PBL. After Nile tilapia was infected by Aeromonas hydrophila, both transcription and phosphorylation levels of OnAkt1 were obviously elevated in spleen lymphocytes at the adaptive immune stage, suggesting Akt1 participated in primary adaptive immune response of Nile tilapia. Furthermore, OnAkt1 transcript or phosphorylation was dramatically augmented after spleen lymphocytes were activated by T cell specific mitogen PHA or lymphocyte agonist PMA. More critically, inhibition of Akt1 by specific inhibitor crippled the activation of downstream mTORC1 signaling, and impaired the up-regulation of T cell activation markers CD44, IFN-γ and CD122 in spleen lymphocytes upon PHA-induced T cell activation. Meanwhile, blockade of Akt1-activated mTORC1 signaling also decreased the frequency of BrdU⁺ lymphocytes during A. hydrophila infection, indicating the critical role of Akt1 in regulating lymphocyte proliferation of Nile tilapia. Together, our results demonstrated that Akt1 modulated adaptive immune response of Nile tilapia by promoting lymphocyte activation and proliferation via mTORC1 signaling. Our study enriched the regulatory mechanism of lymphocyte-mediated adaptive immunity in teleost, and thus provided novel insights into the evolution of adaptive immune system.

S6K1/S6 axis-regulated lymphocyte activation is important for adaptive immune response of Nile tilapia

Ribosomal protein S6 kinase beta-1 (S6K1) is a serine/threonine kinase downstream of the mechanistic target of rapamycin (mTOR) pathway, and plays crucial roles in immune regulation. Although remarkable progress has been achieved with a mouse model, how S6K1 regulates adaptive immunity is largely unknown in early vertebrates. In this study, we identified an S6K1 from Nile tilapia Oreochromis niloticus (OnS6K1), and further investigated its potential regulatory role on the adaptive immunity of this fish species. Both sequence and structure of OnS6K1 were highly conserved with its homologs from other vertebrates and invertebrates. OnS6K1 was widely expressed in immune tissues, and with a relative higher expression level in the liver, spleen and head kidney. At the adaptive immune stage of Nile tilapia that infected with Aeromonas hydrophila, mRNA expression of OnS6K1 and its downstream effector S6 was significantly up-regulated in spleen lymphocytes. Meanwhile, their phosphorylation level was also enhanced during this process, suggesting that S6K1/S6 axis participated in the primary response of anti-bacterial adaptive immunity in Nile tilapia. Furthermore, after spleen lymphocytes were activated by the T cell-specific mitogen PHA or lymphocytes agonist PMA in vitro, mRNA and phosphorylation levels of S6K1 were elevated, and phosphorylation of S6 was also enhanced. Once S6K1 activity was blocked by a specific inhibitor, both mRNA and phosphorylation levels of S6 were severely impaired. More importantly, blockade of S6K1/S6 axis reduced the expression of T cell activation marker IFN-γ and CD122 in PHA-activated spleen lymphocytes, indicating the essential role of S6K1/S6 axis in regulating T cell activation of Nile tilapia. Together, our study suggests that S6K1 and its effector S6 regulate lymphocyte activation of Nile tilapia, and in turn promote lymphocyte-mediated adaptive immunity. This study enriched the mechanism of adaptive immune response in teleost and provided useful clues to understand the evolution of adaptive immune system.

Effect of berberine on LPS-induced expression of NF-B/MAPK signalling pathway and related inflammatory cytokines in porcine intestinal epithelial cells

Berberine is an alkaloid extracted from medicinal plants such as Coptis chinensis and Phellodendron chinense. It possesses anti-inflammatory, anti-tumour and anti-oxidation properties, and regulates Glc and lipid metabolism. This study explored the mechanisms of the protective effects of berberine on barrier function and inflammatory damage in porcine intestinal epithelial cells (IPEC-J2) induced by LPS. We first evaluated the effects of berberine and LPS on cell viability. IPEC-J2 cells were treated with 5 μg/ml LPS for 1 h to establish an inflammatory model, and 75, 150 and 250 μg/ml berberine were used in further experiments. The expression of IL-1β, IL-6 and TNF-α was measured by RT-PCR. The key proteins of the NF-κB/MAPK signalling pathway (IκBα, p-IκBα, p65, p-p65, c-Jun N-terminal kinase (JNK), p-JNK, p38, p-p38, ERK1/2 and p-ERK1/2) were detected by Western blot. Upon exposure to LPS, IL-1β, IL-6 and TNF-α mRNA levels and p-IκBα p-p65 protein levels were significantly enhanced. Pre-treatment with berberine reduced the expression of inflammatory factors and was positively correlated with its concentration, and dose dependently inhibited the expression of IκBα, p-IκBα, p-p65, p-p38 and JNK. These results demonstrated that pre-treating intestinal epithelial cells with berberine was useful in preventing and treating diarrhoea induced by Escherichia coli in weaned pigs.