Porcine Beta-Defensin 2 Provides Protection Against Bacterial Infection by a Direct Bactericidal Activity and Alleviates Inflammation via Interference With the TLR4/NF-κB Pathway

Intranasal B5 promotes mucosal defence against Actinobacillus pleuropneumoniae via ameliorating early immunosuppression

Actinobacillus pleuropneumoniae (APP) is an important pathogen of the porcine respiratory disease complex, which leads to huge economic losses worldwide. We previously demonstrated that Pichia pastoris-producing bovine neutrophil β-defensin-5 (B5) could resist the infection by the bovine intracellular pathogen Mycobacterium bovis. In this study, the roles of synthetic B5 in regulating mucosal innate immune response and protecting against extracellular APP infection were further investigated using a mouse model. Results showed that B5 promoted the production of tumour necrosis factor (TNF)-α, interleukin (IL)-1β, and interferon (IFN)-β in macrophages as well as dendritic cells (DC) and enhanced DC maturation in vitro. Importantly, intranasal B5 was safe and conferred effective protection against APP via reducing the bacterial load in lungs and alleviating pulmonary inflammatory damage. Furthermore, in the early stage of APP infection, we found that intranasal B5 up-regulated the secretion of TNF-α, IL-1β, IL-17, and IL-22; enhanced the rapid recruitment of macrophages, neutrophils, and DC; and facilitated the generation of group 3 innate lymphoid cells in lungs. In addition, B5 activated signalling pathways associated with cellular response to IFN-β and activation of innate immune response in APP-challenged lungs. Collectively, B5 via the intranasal route can effectively ameliorate the immune suppression caused by early APP infection and provide protection against APP. The immunization strategy may be applied to animals or human respiratory bacterial infectious diseases. Our findings highlight the potential importance of B5, enhancing mucosal defence against intracellular bacteria like APP which causes early-phase immune suppression.

Host defense peptides human β defensin 2 and LL-37 ameliorate murine necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is a leading cause of preterm infant morbidity and mortality. Treatment for NEC is limited and non-targeted, which makes new treatment and prevention strategies critical. Host defense peptides (HDPs) are essential components of the innate immune system and have multifactorial mechanisms in host defense. LL-37 and hBD2 are two HDPs that have been shown in prior literature to protect from neonatal sepsis-induced mortality or adult inflammatory bowel disease, respectively. Therefore, this article sought to understand if these two HDPs could influence NEC severity in murine preclinical models. NEC was induced in P14-16 C57Bl/6 mice and HDPs were provided as a pretreatment or treatment. Both LL-37 and hBD2 resulted in decreased NEC injury scores as a treatment and hBD2 as a pretreatment. Our data suggest LL-37 functions through antimicrobial properties, while hBD2 functions through decreases in inflammation and improvement of intestinal barrier integrity.

Deficiency of immunoglobulin IgSF6 enhances antibacterial effects by promoting endoplasmic reticulum stress and the inflammatory response in intestinal macrophages

Immunoglobulin superfamily (IgSF) members are known for their role as glycoproteins expressed on the surface of immune cells, enabling protein-protein interactions to sense external signals during immune responses. However, the functions of immunoglobulins localized within subcellular compartments have been less explored. In this study, we identified an endoplasmic reticulum (ER)-localized immunoglobulin, IgSF member 6 (IgSF6), that regulates ER stress and the inflammatory response in intestinal macrophages. Igsf6 expression is sustained by microbiota and significantly upregulated upon bacterial infection. Mice lacking Igsf6 displayed resistance to Salmonella typhimurium challenge but increased susceptibility to dextran sulfate sodium-induced colitis. Mechanistically, deficiency of Igsf6 enhanced inositol-requiring enzyme 1α/-X-box binding protein 1 pathway, inflammatory response, and reactive oxygen species production leading to increased bactericidal activity of intestinal macrophages. Inhibition of reactive oxygen species or inositol-requiring enzyme 1α-X-box binding protein 1 pathway reduced the advantage of Igsf6 deficiency in bactericidal capacity. Together, our findings provide insight into the role of IgSF6 in intestinal macrophages that modulate the ER stress response and maintain intestinal homeostasis.

Fecal microbiota transplantation alleviates intestinal inflammatory diarrhea caused by oxidative stress and pyroptosis via reducing gut microbiota-derived lipopolysaccharides

Infancy is a critical period in the maturation of the gut microbiota and a phase of susceptibility to gut microbiota dysbiosis. Early disturbances in the gut microbiota can have long-lasting effects on host physiology, including intestinal injury and diarrhea. Fecal microbiota transplantation (FMT) can remodel gut microbiota and may be an effective way to treat infant diarrhea. However, limited research has been conducted on the mechanisms of infant diarrhea and the regulation of gut microbiota balance through FMT, primarily due to ethical challenges in testing on human infants. Our study demonstrated that elevated Lipopolysaccharides (LPS) levels in piglets with diarrhea were associated with colon microbiota dysbiosis induced by early weaning. Additionally, LPS upregulated NLRP3 levels by activating TLR4 and inducing ROS production, resulting in pyroptosis, disruption of the intestinal barrier, bacterial translocation, and subsequent inflammation, ultimately leading to diarrhea in piglets. Through microbiota regulation, FMT modulated β-PBD-2 secretion in the colon by increasing butyric acid levels. This modulation alleviated gut microbiota dysbiosis, reduced LPS levels, attenuated oxidative stress and pyroptosis, inhibited the inflammatory response, maintained the integrity of the intestinal barrier, and ultimately reduced diarrhea in piglets caused by colitis. These findings present a novel perspective on the pathogenesis, pathophysiology, prevention, and treatment of diarrhea diseases, underscoring the significance of the interaction between FMT and the gut microbiota as a critical strategy for treating diarrhea and intestinal diseases in infants and farm animals.

Porcine β-Defensin 114: Creating a Dichotomous Response to Inflammation

The immunity-related functions of defensins seem to be dependent on environmental stimuli, the cell type, and the concentration of peptides. However, the function and mechanism of porcine β-defensin 114 (pBD114) in regulating the inflammatory response to macrophages are unclear. Therefore, the modulatory effects of porcine pBD114 on the inflammatory response were investigated by treating the mouse monocyte macrophage cell line RAW264.7 with different concentrations of pBD114 with or without lipopolysaccharide (LPS). RNA-seq analysis was performed to investigate the mechanisms underlying pBD114's regulation of inflammatory responses in macrophages. In addition, the inflammatory response-modulating effects of pBD114 were also further verified with a mouse assay. The results showed that 100 μg/mL of pBD114 significantly promoted the secretion of TNF-α and IL-10 in RAW264.7. However, the LPS-induced increase in TNFα in the RAW264.7 cell cultures was significantly decreased with 10 μg/mL of pBD114. These results suggest that pBD114 can exhibit pro-inflammatory activities under normal physiological conditions with 100 μg/mL of pBD114, and anti-inflammatory activities during an excessive inflammatory response with 10 μg/mL of pBD114. RNA-seq analysis was performed to gain further insights into the effects of pBD114 on the inflammatory response. Among the pBD114-promoting RAW264.7 pro-inflammatory responses, pBD114 significantly up-regulated 1170 genes and down-regulated 724 genes. KEGG enrichment showed that the differentially expressed genes (DEGs) were significantly enriched in the immune- and signal-transduction-related signaling pathways. Protein-Protein Interaction (PPI) and key driver analysis (KDA) analyses revealed that Bcl10 and Bcl3 were the key genes. In addition, pBD114 significantly up-regulated 12 genes and down-regulated 38 genes in the anti-inflammatory response. KEGG enrichment analysis revealed that the DEGs were mainly enriched in the "Cytokine-cytokine receptor interaction" signaling pathway, and PPI and KDA analyses showed that Stat1 and Csf2 were the key genes. The results of qRT-PCR verified those of RNA-seq. In vivo mouse tests also confirmed the pro- or anti-inflammatory activities of pBD114. Although the inflammatory response is a rapid and complex physiological reaction to noxious stimuli, this study found that pBD114 plays an essential role mainly by acting on the genes related to immunity, signal transduction, signaling molecules, and interactions. In conclusion, this study provides a certain theoretical basis for the research and application of defensins.

Designing a multi-epitope vaccine to control porcine epidemic diarrhea virus infection using immunoinformatics approaches

Porcine epidemic diarrhea virus (PEDV), a continuously evolving pathogen, causes severe diarrhea in piglets with high mortality rates. However, current vaccines cannot provide complete protection against PEDV, so vaccine development is still necessary and urgent. Here, with the help of immunoinformatics approaches, we attempted to design a multi-epitope vaccine named rPMEV to prevent and control PEDV infection. The epitopes of rPMEV were constructed by 9 cytotoxic T lymphocyte epitopes (CTLs), 11 helper T lymphocyte epitopes (HTLs), 6 linear B cell epitopes (LBEs), and 4 conformational B cell epitopes (CBEs) based on the S proteins from the four representative PEDV G2 strains. To enhance immunogenicity, porcine β-defensin-2 (PBD-2) was adjoined to the N-terminal of the vaccine as an adjuvant. All of the epitopes and PBD-2 were joined by corresponding linkers and recombined into the multivalent vaccine, which is stable, antigenic, and non-allergenic. Furthermore, we adopted molecular docking and molecular dynamics simulation methods to analyze the interaction of rPMEV with the Toll-like receptor 4 (TLR4): a stable interaction between them created by 13 hydrogen bonds. In addition, the results of the immune simulation showed that rPMEV could stimulate both cellular and humoral immune responses. Finally, to raise the expression efficiency, the sequence of the vaccine protein was cloned into the pET28a (+) vector after the codon optimization. These studies indicate that the designed multi-epitope vaccine has a potential protective effect, providing a theoretical basis for further confirmation of its protective effect against PEDV infection in vitro and in vivo studies.

The Contribution of Antimicrobial Peptides to Immune Cell Function: A Review of Recent Advances

The development of novel antimicrobial agents to replace antibiotics has become urgent due to the emergence of multidrug-resistant microorganisms. Antimicrobial peptides (AMPs), widely distributed in all kingdoms of life, present strong antimicrobial activity against a variety of bacteria, fungi, parasites, and viruses. The potential of AMPs as new alternatives to antibiotics has gradually attracted considerable interest. In addition, AMPs exhibit strong anticancer potential as well as anti-inflammatory and immunomodulatory activity. Many studies have provided evidence that AMPs can recruit and activate immune cells, controlling inflammation. This review highlights the scientific literature focusing on evidence for the anti-inflammatory mechanisms of different AMPs in immune cells, including macrophages, monocytes, lymphocytes, mast cells, dendritic cells, neutrophils, and eosinophils. A variety of immunomodulatory characteristics, including the abilities to activate and differentiate immune cells, change the content and expression of inflammatory mediators, and regulate specific cellular functions and inflammation-related signaling pathways, are summarized and discussed in detail. This comprehensive review contributes to a better understanding of the role of AMPs in the regulation of the immune system and provides a reference for the use of AMPs as novel anti-inflammatory drugs for the treatment of various inflammatory diseases.

Mechanisms and regulation of defensins in host defense

As a family of cationic host defense peptides, defensins are mainly synthesized by Paneth cells, neutrophils, and epithelial cells, contributing to host defense. Their biological functions in innate immunity, as well as their structure and activity relationships, along with their mechanisms of action and therapeutic potential, have been of great interest in recent years. To highlight the key research into the role of defensins in human and animal health, we first describe their research history, structural features, evolution, and antimicrobial mechanisms. Next, we cover the role of defensins in immune homeostasis, chemotaxis, mucosal barrier function, gut microbiota regulation, intestinal development and regulation of cell death. Further, we discuss their clinical relevance and therapeutic potential in various diseases, including infectious disease, inflammatory bowel disease, diabetes and obesity, chronic inflammatory lung disease, periodontitis and cancer. Finally, we summarize the current knowledge regarding the nutrient-dependent regulation of defensins, including fatty acids, amino acids, microelements, plant extracts, and probiotics, while considering the clinical application of such regulation. Together, the review summarizes the various biological functions, mechanism of actions and potential clinical significance of defensins, along with the challenges in developing defensins-based therapy, thus providing crucial insights into their biology and potential clinical utility.

Recent Progress in the Characterization, Synthesis, Delivery Procedures, Treatment Strategies, and Precision of Antimicrobial Peptides

Infectious diseases are constantly evolving to bypass antibiotics or create resistance against them. There is a piercing alarm for the need to improve the design of new effective antimicrobial agents such as antimicrobial peptides which are less prone to resistance and possess high sensitivity. This would guard public health in combating and overcoming stubborn pathogens and mitigate incurable diseases; however, the emergence of antimicrobial peptides' shortcomings ranging from untimely degradation by enzymes to difficulty in the design against specific targets is a major bottleneck in achieving these objectives. This review is aimed at highlighting the recent progress in antimicrobial peptide development in the area of nanotechnology-based delivery, selectivity indices, synthesis and characterization, their doping and coating, and the shortfall of these approaches. This review will raise awareness of antimicrobial peptides as prospective therapeutic agents in the medical and pharmaceutical industries, such as the sensitive treatment of diseases and their utilization. The knowledge from this development would guide the future design of these novel peptides and allow the development of highly specific, sensitive, and accurate antimicrobial peptides to initiate treatment regimens in patients to enable them to have accommodating lifestyles.

C5aR antagonist inhibits LPS-induced inflammation in human gingival fibroblasts via NF-κB and MAPK signaling pathways

OBJECTIVE

Abnormal complement activation is associated with periodontitis. W54011 is a novel non-peptide C5aR antagonist (C5aRA) that exhibits favorable anti-inflammatory effects in various inflammatory models. However, whether W54011 inhibits periodontitis has not yet been fully elucidated. To address this, we have investigated the probable anti-inflammatory mechanism of W54011 in LPS-treated inflammation in human gingival fibroblasts (HGFs).

METHODOLOGY

HGFs were isolated from healthy gingival tissue samples using the tissue block method and were identified with immunofluorescence staining. The CCK8 assay and reverse transcription-PCR (RT-PCR) were used to select the optimal induction conditions for Lipopolysaccharide (LPS) and C5aRA (according to supplementary data S1, S2 and S3). The levels of inflammatory cytokines, C5aR, and the activation of NF-κB/MAPK signaling pathways were determined by RT-quantitative PCR (RT-qPCR) and Western blotting.

RESULTS

Immunofluorescence results showed that vimentin and FSP-1 were positive in HGFs and Keratin was negative in HGFs. Immunofluorescence staining demonstrated that C5aRA inhibited LPS-stimulated nuclear translocation of p-p65. RT-qPCR and Western blotting showed that C5aRA reduced the expression of IL-1β, IL-6, TNF-α, C5aR, p-p65, p-IκBα, p-JNK, p-c-JUN, and TLR4 in LPS-induced HGFs.

CONCLUSION

These findings suggested that C5aRA attenuated the release of inflammatory cytokines in LPS-induced HGFs by blocking the activation of the NF-κB and MAPK signaling pathways.

Oral administration of hepcidin and chitosan benefits growth, immunity, and gut microbiota in grass carp (Ctenopharyngodon idella)

Intensive high-density culture patterns are causing an increasing number of bacterial diseases in fish. Hepcidin links iron metabolism with innate immunity in the process of resisting bacterial infection. In this study, the antibacterial effect of the combination of hepcidin (Cihep) and chitosan (CS) against Flavobacterium columnare was investigated. The dosing regimen was also optimized by adopting a feeding schedule of every three days and every seven days. After 56 days of feeding experiment, grass carp growth, immunity, and gut microbiota were tested. In vitro experiments, Cihep and CS can regulate iron metabolism and antibacterial activity, and that the combination of Cihep and CS had the best protective effect. In vivo experiments, Cihep and CS can improve the growth index of grass carp. After challenge with Flavobacterium columnare, the highest survival rate was observed in the Cihep+CS-3d group. By serum biochemical indicators assay and Prussian blue staining, Cihep and CS can increase iron accumulation and decrease serum iron levels. The contents of lysozyme and superoxide dismutase in Cihep+CS-3d group increased significantly. Meanwhile, Cihep and CS can significantly reduce the pathological damage of gill tissue. The 16S rRNA sequencing results showed that Cihep and CS can significantly increase the abundance and diversity of grass carp gut microbiota. These results indicated that the protective effect of consecutive 3-day feeding followed by a 3-day interval was better than that of consecutive 7-day feeding followed by a 7-day interval, and that the protective effect of Cihep in combination with chitosan was better than that of Cihep alone. Our findings optimize the feeding pattern for better oral administration of Cihep in aquaculture.

Chloroform extracts of Atractylodes chinensis inhibit the adhesion and invasion of Salmonella typhimurium

There are 27 million cases of Salmonella Typhimurium (STM) reported worldwide annually, which have resulted in 217,000 deaths to date. Thus, there is an urgent requirement to develop novel antibacterial agents to target the multidrug-resistant strains of STM. We evaluated the inhibitory effect of the chloroform extracts of Atractylodes chinensis (Ac-CE) on the virulence of STM in vitro and develop it as a potential antibacterial agent. First, we determined the in vitro effects of Ac-CE on STM biofilm formation, and swimming, swarming, and adhesion to mucin. Further, we evaluated the effect of Ac-CE on the adhesion and invasion of STM at the gene level. Lastly, we evaluated the inhibitory effect of Ac-CE on STM infectivity at the cellular level. Ac-CE could attenuate both the adhesion and invasion abilities of STM in vitro. At the gene level, it could inhibit the expression of flagella, pilus, biofilm, SPI-1, and SPI-2 genes, which are related to the adhesion and invasion ability of STM in cells. Ac-CE significantly downregulated the expression of inflammatory cytokines and the TLR4/MyD88/NF-κB pathway in an STM infection cell model. It also significantly recovered the expression of intestinal barrier-related genes and proteins in intestinal cells that are damaged during STM infection. Ac-CE is effective as an antivirulence agent in alleviating STM infection. Although the main components of Ac-CE were analyzed.We have not demonstrated the antivirulence effect of the active ingredients in Ac-CE. And the antivirulence effect of Ac-CE and its active ingredients warrant further in vivo studies.

The recombinant defensin/HSA fusion protein that inhibits NF-κb associated with intensive macropinocytosis shows potent efficacy against pancreatic cancer

KRAS mutation and NF-κB both play crucial role in pancreatic cancer; in addition, defensin, the peptide mediator in innate immunity, can inhibit NF-κB. Assuming a strategy that targets both NF-κB and concomitantly the mutated KRAS indirectly via intensive macropinocytosis, we designed and generated a recombinant protein DF2-HSA which consists of two molecules of human beta-defensin 2 (HBD2) and a moiety of human serum albumin (HSA). As shown, the recombinant protein DF2-HSA markedly down-regulated NF-κB in both KRAS mutant MIA PaCa-2 cells and wild type BxPC-3 cells. Determined by confocal microscopy, the uptake of DF2-HSA in MIA PaCa-2 cells was more intense than that in BxPC-3 cells. The uptake was blocked by the specific inhibitor EIPA, indicating that DF2-HSA internalized via macropinocytosis. DF2-HSA displayed more potent cytotoxicity to cancer cells than HBD2. DF2-HSA induced apoptosis in cancer cells. Notably, DF2-HSA inhibited tumor cell spheroid formation, an effect comparable to that of salinomycin. DF2-HSA inhibited tumor cell migration and invasion. As detected with scanning electron microscopy, DF2-HSA strongly depleted filopodia on cell surface; and salinomycin induced similar changes. By in vivo imaging, DF2-HSA displayed intense tumor-site accumulation and lasting retention for over 14 days; however, HBD2 showed much less tumor-site accumulation and a shorter retention time for only 24 h. DF2-HSA suppressed the growth of pancreatic cancer MIA PaCa-2 xenograft in athymic mice; and its combination with gemcitabine achieved higher antitumor efficacy. In summary, the recombinant defensin/HSA fusion protein that inhibits NF-κb associated with intensive macropinocytosis is highly effective against pancreatic cancer.

The Intracellular Interaction of Porcine β-Defensin 2 with VASH1 Alleviates Inflammation via Akt Signaling Pathway

Defensins are a major class of antimicrobial peptides that facilitate the immune system to resist pathogen infection. To date, only β-defensins have been identified in pigs. In our previous studies, porcine β-defensin 2 (PBD-2) was shown to have both bactericidal activity and modulatory roles on inflammation. PBD-2 can interact with the cell surface TLR4 and interfere with the NF-κB signaling pathway to suppress the inflammatory response. In this study, the intracellular functions of PBD-2 were investigated. The fluorescently labeled PBD-2 could actively enter mouse macrophage cells. Proteomic analysis indicated that 37 proteins potentially interacted with PBD-2, among which vasohibin-1 (VASH1) was further tested. LPS, an inflammation inducer, suppressed the expression of VASH1, whereas PBD-2 inhibited this effect. PBD-2 inhibited LPS-induced activation of Akt, expression and release of the inflammatory mediators vascular endothelial growth factor and NO, and cell damage. A follow-up VASH1 knockdown assay validated the specificity of the above observations. In addition, PBD-2 inhibited LPS-induced NF-κB activation via Akt. The inhibition effects of PBD-2 on LPS triggered suppression of VASH1 and activation of Akt, and NF-κB and inflammatory cytokines were also confirmed using pig alveolar macrophage 3D4/21 cells. Therefore, the data indicate that PBD-2 interacts with intracellular VASH1, which inhibits the LPS-induced Akt/NF-κB signaling pathway, resulting in suppression of inflammatory responses. Together with our previous findings, we conclude that PBD-2 interacts with both the cell surface receptor (TLR4) and also with the intracellular receptor (VASH1) to control inflammation, thereby providing insights into the immunomodulatory roles of defensins.

Recombinant porcine beta defensin 2 alleviates inflammatory responses induced by Escherichia coli in IPEC-J2 cells

pBD2 is one of the porcine beta defensins with broad antimicrobial activity, and plays an important role in immune regulation. However, the activities and mechanisms of pBD2 regulating host resistance to Escherichia coli infection are unclear. In this study, the immunomodulatory activity and mechanisms of recombinant pBD2 against Escherichia coli infection were explored in IPEC-J2 cells. Recombinant pBD2 had no obvious effect on the growth of cells below 80 μg/mL, however, it reduced the number of E. coli adhering to cells. Furthermore, pBD2 restored the abnormal expression of ZO-1 and occludin in cells challenged with E. coli. pBD2 treatment also reduced cell apoptosis and decreased the expression of the apoptosis-related genes Cox-2 and Caspase-3, and decreased the expression of the pro-inflammatory IL-6, IL-8, IL-1α and TNF-α, and Cxcl2 and Ccl20. pBD2 also reduced the expression of TAK1, and inhibited the phosphorylation of NF-κB p65 following E. coli infection. In addition, pBD2 was localized in the cytoplasm. Collectively, pBD2 appeared to penetrate cells and alleviate inflammatory responses via the TAK1-NF-κB signaling pathway. Our results revealed the immunomodulatory activity of recombinant pBD2 against E. coli and provided insights into the molecular mechanisms that protected cells from E. coli infection.

Sequence polymorphisms of PR39 cathelicidins and extensive copy variations in commercial pig breeds

Copy number polymorphisms (CNPs) of antimicrobial peptides (AMPs) in livestock can influence the innate immune response of individuals. We conducted a high-resolution analysis of the genomic variations of porcine cathelicidin PR39 using cloned PR39 amplicons corresponding to the 5' untranslated region (UTR) to 3' UTR from four individuals of three different pig breeds. We identified 15 different sequences corresponding to 9 different coding domain sequences (CDSs), encoding 7 different protein sequences consisting of 3 functional and 4 non-functional forms. Subsequently, we developed a PR39 CNP typing method using real-time polymerase chain reaction (PCR) and analyzed the PR39 copy numbers from 44 pigs of six breeds. Significant variations in PR39 copies ranging from 2 to 10 copies, with a mean copy number of 5, were observed among all commercial breeds, except the wild boar. Among the different breeds, the PR39 copy number was highest (10) in Korean native pigs. Gene expression analysis showed that PR39 expression was correlated with the copy number. Moreover, the comparative analysis of the cathelicidin cluster-containing region among eight mammalian species showed the complete evolutionary conservation of the region, except for differences in the degree of cathelicidin expansion in each species. Therefore, characterization of CNPs in AMP genes could aid in improving the genetic potential of innate immune responses in livestock animals.

Porcine β-defensin 2 confers enhanced resistance to swine flu infection in transgenic pigs and alleviates swine influenza virus-induced apoptosis possibly through interacting with host SLC25A4

Swine influenza virus (SIV) not only brings about great economic losses on the global pig industry, it also poses a significant threat to the public health for its interspecies transmission capacity. Porcine β-defensin 2 (PBD-2) is a host defense peptide and our previous study has shown that PBD-2 inhibits proliferation of enveloped pseudorabies virus both in vitro and in transgenic (TG) mice. The aim of this study is to investigate the possible anti-SIV ability of PBD-2 in a TG pig model created in our previous study. The in-contact challenge trial demonstrated that overexpression of PBD-2 in pigs could efficiently alleviate SIV-associated clinical signs. The SIV titers quantified by EID₅₀ in lung tissues of infected TG pigs were significantly lower than that of wild-type littermates. In vitro, the cell viability assay revealed that PBD-2 mainly interfered with viral entry and post-infection stages. It was further confirmed that PBD-2 could enter porcine tracheal epithelial cells. The proteins interacting with PBD-2 inside host cells were identified with immunoprecipitation and the pathways involved were analyzed. Results showed that PBD-2 could interact with pro-apoptotic solute carrier family 25 member 4 (SLC25A4), also known as adenine nucleotide translocase 1, and thereby inhibited SIV-induced cell apoptosis. The molecular docking analysis suggested that PBD-2 interacted with porcine SLC25A4 mainly through strong hydrogen binding, with the predicted binding affinity being -13.23 kcal/mol. Altogether, these indicate that PBD-2 protects pigs against SIV infection, which may result from its role as a SLC25A4 blocker to alleviate cell apoptosis, providing a novel therapeutic and prophylactic strategy of using PBD-2 to combat SIV.

P38 MAPK pathway regulates the expression of resistin in porcine alveolar macrophages via Ets2 during Haemophilus parasuis stimulation

Haemophilus parasuis is a widespread bacterial pathogen causing acute systemic inflammation and leading to the sudden death of piglets. Resistin, a multifunctional peptide hormone previously demonstrated to influence the inflammation in porcine, was extremely increased in H. parasuis-infected tissues. However, the mechanism of resistin expression regulation in porcine, especially during pathogen infection, remains unclear. In the present study, we explored for the first time the transcription factor and signaling pathway mediating the expression of pig resistin during H. parasuis stimulation. We found that H. parasuis induced the expression of pig resistin in a time- and dose-dependent manner via the transcription factor Ets2 in porcine alveolar macrophages during H. parasuis stimulation. Moreover, the expression of Ets2 was mediated by the activation of the p38 MAPK pathway induced by H. parasuis, thus promoting resistin production. These results revealed a novel view of the molecular mechanism of pig resistin production during acute inflammation induced by pathogenic bacteria.

Maternal Supplementation with Artemisia annua L. Ameliorates Intestinal Inflammation via Inhibiting the TLR4/NF-κB and MAPK Pathways and Improves Oxidative Stability of Offspring

Artemisia annua L. (A. annua) contains artemisinin, which attracts attention on account of its anti-inflammatory and anti-oxidant effects. The increased intestinal inflammation, oxidative stress, and hypoimmunity commonly occur in the...

Antimicrobial peptides: mechanism of action, activity and clinical potential

The management of bacterial infections is becoming a major clinical challenge due to the rapid evolution of antibiotic resistant bacteria. As an excellent candidate to overcome antibiotic resistance, antimicrobial peptides (AMPs) that are produced from the synthetic and natural sources demonstrate a broad-spectrum antimicrobial activity with the high specificity and low toxicity. These peptides possess distinctive structures and functions by employing sophisticated mechanisms of action. This comprehensive review provides a broad overview of AMPs from the origin, structural characteristics, mechanisms of action, biological activities to clinical applications. We finally discuss the strategies to optimize and develop AMP-based treatment as the potential antimicrobial and anticancer therapeutics.

Antibiofilm activity of host defence peptides: complexity provides opportunities

Host defence peptides (HDPs) are integral components of innate immunity across all living organisms. These peptides can exert direct antibacterial effects, targeting planktonic cells (referred to as antimicrobial peptides), and exhibit antibiofilm (referred to as antibiofilm peptides), antiviral, antifungal and host-directed immunomodulatory activities. In this Review, we discuss how the complex functional attributes of HDPs provide many opportunities for the development of antimicrobial therapeutics, focusing particularly on their emerging antibiofilm properties. The mechanisms of action of antibiofilm peptides are compared and contrasted with those of antimicrobial peptides. Furthermore, obstacles for the practical translation of candidate peptides into therapeutics and the potential solutions are discussed. Critically, HDPs have the value-added assets of complex functional attributes, particularly antibiofilm and anti-inflammatory activities and their synergy with conventional antibiotics.

Knockdown of TRIM52 alleviates LPS-induced inflammatory injury in human periodontal ligament cells through the TLR4/NF-κB pathway

Tripartite motif-containing (TRIM) 52 (TRIM52) is a vital regulator of inflammation. However, the function and mechanisms of TRIM52 in lipopolysaccharide (LPS)-induced inflammatory injury of human periodontal ligament cells (HPDLCs) in periodontitis remain undefined. In the present research, gene expression was determined using a quantitative polymerase chain reaction and Western blot. The effect of TRIM52 on LPS-induced inflammatory injury was evaluated using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, flow cytometry, and enyzme-linked immunosorbent assay (ELISA). We found that TRIM52 expression was up-regulated in LPS-treated HPDLCs. Knockdown of TRIM52 alleviated LPS-induced proliferative inhibition and apoptosis promotion in HPDLCs, as evidenced by a decrease in cleaved caspase-3 expression and caspase-3 activity. Silencing TRIM52 suppressed LPS-induced inflammatory response of HPDLCs, as indicated by the decrease in interleukin (IL)-6, IL-8, tumor necrosis factor-α (TNF-α) levels, and increase in IL-10 levels. TRIM52 knockdown inhibited LPS-induced activation of TLR4/nuclear factor-κ B (NF-κB) signaling pathway. Taken together, knockdown of TRIM52 mitigated LPS-induced inflammatory injury via the TLR4/NF-κB signaling pathway, providing an effective therapeutic target for periodontitis.

Astaxanthin Alleviates Ochratoxin A-Induced Cecum Injury and Inflammation in Mice by Regulating the Diversity of Cecal Microbiota and TLR4/MyD88/NF-κB Signaling Pathway

Ochratoxin A (OTA) is a common environmental pollutant found in a variety of foods and grains, and excessive OTA consumption causes serious global health effects on animals and humans. Astaxanthin (AST) is a natural carotenoid that has anti-inflammatory, antiapoptotic, immunomodulatory, antitumor, antidiabetes, and other biological activities. The present study is aimed at investigating the effects of AST on OTA-induced cecum injury and its mechanism of action. Eighty C57 mice were randomly divided into four groups, including the control group, OTA group (5 mg/kg body weight), AST group (100 mg/kg body weight), and AST intervention group (100 mg/kg body weight AST+5 mg/kg body weight OTA). It was found that AST decreased the endotoxin content, effectively prevented the shortening of mouse cecum villi, and increased the expression levels of tight junction (TJ) proteins, consisting of occludin, claudin-1, and zonula occludens-1 (ZO-1). AST increased the number of goblet cells, the contents of mucin-2 (MUC2), and defensins (Defa5 and β-pD2) significantly, while the expression of mucin-1 (MUC1) decreased significantly. The 16S rRNA sequencing showed that AST affected the richness and diversity of cecum flora, decreased the proportion of lactobacillus, and also decreased the contents of short-chain fatty acids (SCFAs) (acetate and butyrate). In addition, AST significantly decreased the expression of TLR4, MyD88, and p-p65, while increasing the expression of p65. Meanwhile, the expression of inflammatory factors including TNF-α and INF-γ decreased, while the expression of IL-10 increased. In conclusion, AST reduced OTA-induced cecum injury by regulating the cecum barrier function and TLR4/MyD88/NF-κB signaling pathway.

Antibacterial and pro-osteogenic effects of β-Defensin-2-loaded mesoporous bioglass

The human antimicrobial peptide beta-defensin-2 (hBD2) shows broad antibacterial activity and infrequent bacterial resistance. Here mesoporous bioactive glass (MBG) was loaded with hBD2, forming hBD2-loaded MBG (BD-MBG). The antibacterial and osteogenic effects of BD-MBG were investigated in comparison with MBG and the blank control (BC). The result showed that BD-MBG yielded sustained hBD2 release for more than 7 weeks in vitro, and resulted in significantly lower amounts of viable bacteria and colony forming units, and significantly higher levels of bacterial protein release compared with those in the BC and MBG groups (all p<0.05). Compared with that in the BC group, significantly higher bone marrow stromal cell (BMSC) proliferation rates, alkaline phosphatase (ALP) activity, calcium nodule formation, and expression levels of early and late osteogenic makers were observed after MBG and BD-MBG treatments (p<0.05). Thus, BD-MBG inhibited bacterial growth, damaged their membrane, and promoted early and late osteogenic BMSC differentiation.

Pigs Overexpressing Porcine β-Defensin 2 Display Increased Resilience to Glaesserella parasuis Infection

As the causative agent of Glässer’s disease, Glaesserella (Haemophilus) parasuis has led to serious economic losses to the swine industry worldwide. Due to the low cross-protection of vaccines and increasing antimicrobial resistance of G. parasuis, it is important to develop alternative approaches to prevent G. parasuis infection. Defensins are host defense peptides that have been suggested to be promising substitutes for antibiotics in animal production, while porcine β-defensin 2 (PBD-2) is a potent antimicrobial peptide discovered in pigs. Our previous study generated transgenic (TG) pigs overexpressing PBD-2, which displayed enhanced resistance to Actinobacillus pleuropneumoniae. In this study, the antibacterial activities of PBD-2 against G. parasuis are determined in vitro and in the TG pig model. The concentration-dependent bactericidal activity of synthetic PBD-2 against G. parasuis was measured by bacterial counting. Moreover, after being infected with G. parasuis via a cohabitation challenge model, TG pigs overexpressing PBD-2 displayed significantly milder clinical signs and less severe gross pathological changes than their wild-type (WT) littermates. The TG pigs also exhibited alleviated lung and brain lesions, while bacterial loads in the lung and brain tissues of the TG pigs were significantly lower than those of the WT pigs. Additionally, lung and brain homogenates from TG pigs possessed enhanced antibacterial activity against G. parasuis when compared with those from the WT pigs. Altogether, these proved that overexpression of PBD-2 could also endow pigs with increased resilience to G. parasuis infection, which further confirmed the potential of using the PBD-2 coding gene to develop disease-resistant pigs and provided a novel strategy to combat G. parasuis as well.

Echinacea polysaccharide alleviates LPS-induced lung injury via inhibiting inflammation, apoptosis and activation of the TLR4/NF-κB signal pathway

Lung injury is a common critical life-threatening syndrome. Inflammation is a key factor in the pathogenesis of lung injury. It is reported that Echinacea Polysaccharides (EP) has anti-inflammatory activity. However, the effect of EP on lung injury remains unclear. In our study, murine model of lung injury was induced with 2.5 mg/kg LPS before administration of 5 mg/kg or 10 mg/kg EP. EP ameliorated LPS-induced lung pathological damage, along with reduction in lung wet/dry weight ratio and myeloperoxidase activity. EP decreased the number of leukocytes, eosinophils, neutrophils, lymphocytes and macrophages in bronchoalveolar lavage fluid, and the release of tumour necrosis factor-α (TNF-α), interleukin-6 (IL-6) and interleukin-1β (IL-1β) in LPS-treated lung. EP suppressed LPS-induced apoptosis along with down-regulation of Bcl2-associated X (Bax) and cleaved caspase-3 (CC3), and elevated B-cell lymphoma-2 (Bcl-2). Besides, RAW 264.7 cells were treated with EP 100 μg/ml for 1 h and then incubated with 1 μg/ml LPS for 24 h. TNF-α, IL-6 and IL-1β levels were lowered by treatment of EP in LPS-treated RAW 264.7 cells. Moreover, EP down-regulated the expression of toll-like receptor 4 (TLR4), myeloid differentiating factor 88 (MyD88), p-IκBα, nuclear factor kappa-B (NF-κB), p-NF-κB, and up-regulated the inhibitor of NF-κB (IκBα) in vivo and in vitro following LPS induction, which is consistent with the effect of TAK-242. In conclusion, EP may alleviate LPS-induced lung injury via inhibiting inflammation, apoptosis and activation of TLR4/NF-κB signal pathway.

Generation of Marker-Free pbd-2 Knock-in Pigs Using the CRISPR/Cas9 and Cre/loxP Systems

Porcine β-defensin 2 (PBD-2), expressed by different tissues of pigs, is a multifunctional cationic peptide with antimicrobial, immunomodulatory and growth-promoting abilities. As the latest generation of genome-editing tool, CRISPR/Cas9 system makes it possible to enhance the expression of PBD-2 in pigs by site-specific knock-in of pbd-2 gene into the pig genome. In this study, we aimed to generate marker-free pbd-2 knock-in pigs using the CRISPR/Cas9 and Cre/loxP systems. Two copies of pbd-2 gene linked by a T2A sequence were inserted into the porcine Rosa26 locus through CRISPR/Cas9-mediated homology-directed repair. The floxed selectable marker gene neoR, used for G418 screening of positive cell clones, was removed by cell-penetrating Cre recombinase with a recombination efficiency of 48.3%. Cloned piglets were produced via somatic cell nuclear transfer and correct insertion of pbd-2 genes was confirmed by PCR and Southern blot. Immunohistochemistry and immunofluorescence analyses indicated that expression levels of PBD-2 in different tissues of transgenic (TG) piglets were significantly higher than those of their wild-type (WT) littermates. Bactericidal assays demonstrated that there was a significant increase in the antimicrobial properties of the cell culture supernatants of porcine ear fibroblasts from the TG pigs in comparison to those from the WT pigs. Altogether, our study improved the protein expression level of PBD-2 in pigs by site-specific integration of pbd-2 into the pig genome, which not only provided an effective pig model to study the anti-infection mechanisms of PBD-2 but also a promising genetic material for the breeding of disease-resistant pigs.

Antimicrobial Mechanism of pBD2 against Staphylococcus aureus

Antimicrobial peptides (AMPs) show high antibacterial activity against pathogens, which makes them potential new therapeutics to prevent and cure diseases. Porcine beta defensin 2 (pBD2) is a newly discovered AMP and has shown antibacterial activity against different bacterial species including multi-resistant bacteria. In this study, the functional mechanism of pBD2 antibacterial activity against Staphylococcus aureus was investigated. After S. aureus cells were incubated with different concentrations of pBD2, the morphological changes in S. aureus and locations of pBD2 were detected by electron microscopy. The differentially expressed genes (DEGs) were also analyzed. The results showed that the bacterial membranes were broken, bulging, and perforated after treatment with pBD2; pBD2 was mainly located on the membranes, and some entered the cytoplasm. Furthermore, 31 DEGs were detected and confirmed by quantitative real-time PCR (qRT-PCR). The known functional DEGs were associated with transmembrane transport, transport of inheritable information, and other metabolic processes. Our data suggest that pBD2 might have multiple modes of action, and the main mechanism by which pBD2 kills S. aureus is the destruction of the membrane and interaction with DNA. The results imply that pBD2 is an effective bactericide for S. aureus, and deserves further study as a new therapeutic substance against S. aureus.

Mycoplasma hyopneumoniae Inhibits Porcine Beta-Defensin 2 Production by Blocking the Unfolded Protein Response To Facilitate Epithelial Adhesion and Infection

Mycoplasma hyopneumoniae causes the disease porcine enzootic pneumonia, a highly contagious and chronic disease affecting pigs. Understanding the molecular mechanisms of its pathogenicity is critical for developing effective interventions to control this swine respiratory disease. Here, we describe a novel virulence mechanism by which M. hyopneumoniae interferes with the host unfolded protein response (UPR) and eventually facilitates bacterial adhesion and infection. We observed that M. hyopneumoniae infection suppressed the UPR target molecules GRP78 and CHOP by reducing PKR-like endoplasmic reticulum kinase/eukaryotic initiation factor 2 alpha (PERK/eIF2α) phosphorylation, ATF6 cleavage, and X-box binding protein 1 (XBP1) splicing. Interestingly, further analyses revealed that host UPR inhibition subsequently suppressed the NF-κB pathway, leading to the reduced production of porcine beta-defensin 2 (PBD-2), thus facilitating M. hyopneumoniae adherence and infection. This study provides new insights into the molecular pathogenesis of M. hyopneumoniae and sheds light upon its interactions with the host.

Neutrophil extracellular traps induced by cigarette smoke contribute to airway inflammation in mice

Neutrophil extracellular traps (NETs) were initially identified as an important antimicrobial barrier to capture and kill microorganisms. Emerging evidence suggests that NETs play a crucial role in chronic airway inflammation induced by cigarette smoke (CS). However, how NETs form and the mechanisms by which NETs function in CS-related airway diseases are still unclear. To explore NET formation and its potential role in CS-related airway diseases, we first established a CS-induced subacute airway inflammation model in mice and verified NET formation in the airways. Moreover, NETs degradation by aerosolized DNase I treatment significantly inhibited the airway inflammation induced by CS in mice. More importantly, by in vitro experiments, we found that cigarette smoke extract (CSE) induces NET formation in an NADPH oxidase-dependent manner, and that macrophages and human bronchial epithelial cells (HBEs) are important targets for the NETs-induced secretion of inflammatory cytokines. Therefore, NETs may represent a critical link among neutrophils, macrophages and HBEs under chronic inflammation conditions induced by CS.

l-Arginine Ameliorates Lipopolysaccharide-Induced Intestinal Inflammation through Inhibiting the TLR4/NF-κB and MAPK Pathways and Stimulating β-Defensin Expression in Vivo and in Vitro

Nutritional regulation of endogenous antimicrobial peptide (AMP) expression is considered a promising nonantibiotic approach to suppressing intestinal infection of pathogen. The current study investigated the effects of l-arginine on LPS-induced intestinal inflammation and barrier dysfunction in vivo and in vitro. The results revealed that l-arginine attenuated LPS-induced inflammatory response, inhibited the downregulation of tight junction proteins (TJP) (p < 0.05) by LPS, and maintained intestinal integrity. In porcine intestinal epithelial cells (IPEC-J2), l-arginine obviously suppressed (p < 0.05) the levels of IL-6 (220.63 ± 2.82), IL-8 (333.95 ± 3.75), IL-1β (693.08 ± 2.38), and TNF-α (258.04 ± 4.14) induced by LPS. Furthermore, l-arginine diminished the LPS-induced expression of Toll-like receptor 4 (TLR4) and inhibited activation of TLR4-mediated nuclear factor kappa B (NF-κB) and mitogen-activated protein kinase (MAPK) signaling pathways. Importantly, we proposed a new mechanism that l-arginine had the ability to stimulate the expression of porcine epithelial β-defensins through activating the mammalian target of the rapamycin (mTOR) pathway, which exerts anti-inflammatory influence. Moreover, pBD-1 gene overexpression decreased (p < 0.05) the TNF-α level stimulated by LPS in IPEC-J2 cells (4.22 ± 1.64). The present study indicated that l-arginine enhanced disease resistance through inhibiting the TLR4/NF-κB and MAPK pathways and partially, possibly through increasing the intestinal β-defensin expression.

Effect of Bifunctional β Defensin 2-Modified Scaffold on Bone Defect Reconstruction

Bone tissue engineering has emerged as an effective alternative treatment to the problem of bone defect. To repair a bone defect, antibiosis and osteogenesis are two essential aspects of the repair process. By searching the literature and performing exploratory experiments, we found that β defensin 2 (BD2), with bifunctional properties of antibiosis and osteogenesis, was a feasible alternative for traditional growth factors. The antimicrobial ability of BD2 against Staphylococcus aureus and Escherichia coli was studied by the spread plate and live/dead staining methods (low effective concentration of 20 ng/mL). BD2 was also demonstrated to enhance osteogenesis, with higher messenger RNA (mRNA) and protein expression of the osteogenic markers collagen I (Col1), runt-related transcription factor 2 (Runx2), osteopontin (Opn), and osteocalcin (Ocn) in vitro (1.5-2.5-fold increase compared with the control group in the most effective concentration group), which was consistent with the alkaline phosphatase (ALP) and alizarin red S (ARS) staining results. We implanted poly(sebacoyl diglyceride) (PSeD) combined with BD2 and rat bone tissue-derived mesenchymal stem cells (rBMSCs) under the back skin of rats and found that the inflammatory response was significantly lower with this combination than with the PSeD/rBMSCs scaffold without BD2 and the pure PSeD group and was similar to the control group. Importantly, when assessed in a critical-sized in vivo rat 8 m diameter calvaria defect model, a scaffold we developed combining bifunctional BD2 with porous organic polymer displayed an osteogenic effect that was 160-200% greater than the control group. The in vivo study results revealed a significant osteogenic response and antimicrobial effect and were consistent with the in vitro results. In summary, BD2 displayed a great potential of simultaneously promoting bone regeneration and preventing infection and could provide a viable alternative to traditional growth factors applied in bone defect repair.

Regulation of Macrophage and Dendritic Cell Function by Chondroitin Sulfate in Innate to Antigen-Specific Adaptive Immunity

Chondroitin sulfate (CS), a type of glycosaminoglycan (GAG), is a linear acidic polysaccharide comprised of repeating disaccharides, modified with sulfate groups at various positions. Except for hyaluronan (HA), GAGs are covalently bound to core proteins, forming proteoglycans (PGs). With highly negative charges, GAGs interact with a variety of physiologically active molecules, including cytokines, chemokines, and growth factors, and control cell behavior during development and in the progression of diseases, including cancer, infections, and inflammation. Heparan sulfate (HS), another type of GAG, and HA are well reported as regulators for leukocyte migration at sites of inflammation. There have been many reports on the regulation of immune cell function by HS and HA; however, regulation of immune cells by CS has not yet been fully understood. This article focuses on the regulatory function of CS in antigen-presenting cells, including macrophages and dendritic cells, and refers to CSPGs, such as versican and biglycan, and the cell surface proteoglycan, syndecan.

Porcine β-defensin 2 inhibits proliferation of pseudorabies virus in vitro and in transgenic mice

Background

Porcine β-defensin 2 (PBD-2), produced by host cells, is an antimicrobial cysteine-rich cationic peptide with multi-functions. Previous studies have demonstrated that PBD-2 can kill various bacteria, regulate host immune responses and promote growth of piglets. However, the antiviral role of PBD-2 is rarely investigated. This study aimed to reveal the antiviral ability of PBD-2 against pseudorabies virus (PRV), the causative pathogen of Aujeszky’s disease, in PK-15 cells and in a PBD-2 expressing transgenic (TG) mouse model.

Methods

In this study, the cytotoxicity of PBD-2 on PK-15 cells was measured by CCK-8 assay. PK-15 cells were incubated with PRV pre-treated with different concentrations of PBD-2 and PRV titers in cell culture supernatants were determined by real-time quantitative PCR (RT-qPCR). TG mice and wild-type (WT) mice were intraperitoneally injected with PRV and the survival rate was recorded for 10 days. Meanwhile, tissue lesions in brain, spleen and liver of infected mice were observed and the viral loads of PRV in brain, liver and lung were analyzed by RT-qPCR.

Results

PBD-2 at a maximum concentration of 80 μg/mL displayed no significant cytotoxicity on PK-15 cells. A threshold concentration of PBD-2 at 40 μg/mL was required to inhibit PRV proliferation in PK-15 cells. The survival rate in PBD-2 TG mice was 50% higher than that of WT mice. In addition, TG mice showed alleviated tissue lesions in brain, spleen and liver compared with their WT littermates after PRV challenge, while viral loads of PRV in brain, liver and lung of TG mice were significantly lower than that of WT mice.

Conclusions

PBD-2 could inhibit PRV proliferation in PK-15 cells and protect mice from PRV infection, which confirmed the antiviral ability of PBD-2 both in vitro and in vivo. The application of PBD-2 in developing anti-viral drugs or disease-resistant animals can be further investigated.