Intracellular receptor for human host defense peptide LL-37 in monocytes

The antimicrobial peptide database is 20 years old: Recent developments and future directions

In 2023, the Antimicrobial Peptide Database (currently available at https://aps.unmc.edu) is 20-years-old. The timeline for the APD expansion in peptide entries, classification methods, search functions, post-translational modifications, binding targets, and mechanisms of action of antimicrobial peptides (AMPs) has been summarized in our previous Protein Science paper. This article highlights new database additions and findings. To facilitate antimicrobial development to combat drug-resistant pathogens, the APD has been re-annotating the data for antibacterial activity (active, inactive, and uncertain), toxicity (hemolytic and nonhemolytic AMPs), and salt tolerance (salt sensitive and insensitive). Comparison of the respective desired and undesired AMP groups produces new knowledge for peptide design. Our unification of AMPs from the six life kingdoms into "natural AMPs" enabled the first comparison with globular or transmembrane proteins. Due to the dominance of amphipathic helical and disulfide-linked peptides, cysteine, glycine, and lysine in natural AMPs are much more abundant than those in globular proteins. To include peptides predicted by machine learning, a new "predicted" group has been created. Remarkably, the averaged amino acid composition of predicted peptides is located between the lower bound of natural AMPs and the upper bound of synthetic peptides. Synthetic peptides in the current APD, with the highest cationic and hydrophobic amino acid percentages, are mostly designed with varying degrees of optimization. Hence, natural AMPs accumulated in the APD over 20 years have laid the foundation for machine learning prediction. We discuss future directions for peptide discovery. It is anticipated that the APD will continue to play a role in research and education.

Neutrophil-derived cathelicidin promotes cerebral angiogenesis after ischemic stroke

Neutrophils play critical roles in the evolving of brain injuries following ischemic stroke. However, how they impact the brain repair in the late phase after stroke remain uncertain. Using a prospective clinical stroke patient cohort, we found significantly increased cathelicidin antimicrobial peptide (CAMP) in the peripheral blood of stroke patients compared to that of healthy controls. While in the mouse stroke model, CAMP was present in the peripheral blood, brain ischemic core and significantly increased at day 1, 3, 7, 14 after middle cerebral artery occlusion (MCAO). CAMP-/- mice exhibited significantly increased infarct volume, exacerbated neurological outcome, reduced cerebral endothelial cell proliferation and vascular density at 7 and 14 days after MCAO. Using bEND3 cells subjected to oxygen-glucose deprivation (OGD), we found significantly increased angiogenesis-related gene expression with the treatment of recombinant CAMP peptide (rCAMP) after reoxygenation. Intracerebroventricular injection (ICV) of AZD-5069, the antagonist of CAMP receptor CXCR2, or knockdown of CXCR2 by shCXCR2 recombinant adeno-associated virus (rAAV) impeded angiogenesis and neurological recovery after MCAO. Administration of rCAMP promoted endothelial proliferation and angiogenesis and attenuated neurological deficits 14 days after MCAO. In conclusion, neutrophil derived CAMP represents an important mediator that could promote post-stroke angiogenesis and neurological recovery in the late phase after stroke.

The antimicrobial peptide chensinin-1b alleviates the inflammatory response by targeting the TLR4/NF-κB signaling pathway and inhibits Pseudomonas aeruginosa infection and LPS-mediated sepsis

Excessive inflammatory responses are a major contributor to the high mortality associated with sepsis, a prevalent global complication. Therefore, the potential therapeutic strategy for sepsis involves targeting macrophages and reducing proinflammatory cytokine release. Chensinin-1b, an analog of the natural antimicrobial peptide derived from Rana chensinensis skin secretion, exhibits broad-spectrum antibacterial activity and adopts a random coil conformation in both PBS and membrane solution. By efficiently neutralizing LPS, chensinin-1b holds promise in alleviating LPS-induced inflammatory responses. In this study, we established a mouse septic shock model by exposing mice to multiple-drug-resistant Pseudomonas aeruginosa, as well as an endotoxin-mediated sepsis model induced by LPS. Administering chensinin-1b significantly prolonged the survival of the experimental mice, concurrently mitigating inflammatory responses and reducing organ damage. Additionally, we investigated the anti-inflammatory mechanism of chensinin-1b using a constructed LPS-induced mouse macrophage RAW264.7 inflammatory model. Our findings demonstrated that chensinin-1b effectively mitigated the excessive activation of the TLR4/NF-κB signaling pathway by directly neutralizing extracellular LPS, thus ameliorating the inflammatory response. Moreover, upon blocking the TLR4 signaling pathway, chensinin-1b further reduced the release of proinflammatory cytokines induced by LPS, indicating alternative modes of regulation. Notably, chensinin-1b rapidly entered RAW264.7 cells within 30 min via endocytosis, diffusing into the cytoplasm while retaining its anti-inflammatory properties intracellularly. Although further investigations are warranted to comprehensively elucidate the intracellular anti-inflammatory mechanism of chensinin-1b, our findings substantiate its possession of anti-inflammatory properties both intracellularly and extracellularly. Thus, chensinin-1b emerges as a promising candidate for mitigating excessive inflammatory responses associated with sepsis.

Biological Function of Antimicrobial Peptides on Suppressing Pathogens and Improving Host Immunity

The emergence of drug-resistant genes and concerns about food safety caused by the overuse of antibiotics are becoming increasingly prominent. There is an urgent need for effective alternatives to antibiotics in the fields of livestock production and human medicine. Antimicrobial peptides can effectively replace antibiotics to kill pathogens and enhance the immune functions of the host, and pathogens cannot easily produce genes that are resistant to them. The ability of antimicrobial peptides (AMPs) to kill pathogens is associated with their structure and physicochemical properties, such as their conformation, electrical charges, hydrophilicity, and hydrophobicity. AMPs regulate the activity of immunological cells and stimulate the secretion of inflammatory cytokines via the activation of the NF-κB and MAPK signaling pathways. However, there are still some limitations to the application of AMPs in the fields of livestock production and human medicine, including a restricted source base, high costs of purification and expression, and the instability of the intestines of animals and humans. This review summarizes the information on AMPs as effective antibiotic substitutes to improve the immunological functions of the host through suppressing pathogens and regulating inflammatory responses. Potential challenges for the commercial application of AMPs in animal husbandry and human medicine are discussed.

Regulation of Macrophage Cell Surface GAPDH Alters LL-37 Internalization and Downstream Effects in the Cell

Mycobacterium tuberculosis (M.tb), the major causative agent of tuberculosis, has evolved mechanisms to evade host defenses and persist within host cells. Host-directed therapies against infected cells are emerging as an effective option. Cationic host defense peptide LL-37 is known to internalize into cells and induce autophagy resulting in intracellular killing of M.tb. This peptide also regulates the immune system and interacts with the multifunctional protein glyceraldehyde-3-phosphate dehydrogenase (GAPDH) inside macrophages. Our investigations revealed that GAPDH moonlights as a mononuclear cell surface receptor that internalizes LL-37. We confirmed that the surface levels of purinergic receptor 7, the receptor previously reported for this peptide, remained unaltered on M.tb infected macrophages. Upon infection or cellular activation with IFNγ, surface recruited GAPDH bound to and internalized LL-37 into endocytic compartments via a lipid raft-dependent process. We also discovered a role for GAPDH in LL-37-mediated autophagy induction and clearance of intracellular pathogens. In infected macrophages wherein GAPDH had been knocked down, we observed an inhibition of LL-37-mediated autophagy which was rescued by GAPDH overexpression. This process was dependent on intracellular calcium and p38 MAPK pathways. Our findings reveal a previously unknown process by which macrophages internalize an antimicrobial peptide via cell surface GAPDH and suggest a moonlighting role of GAPDH in regulating cellular phenotypic responses of LL-37 resulting in reduction of M.tb burden.

Cathelicidin-related antimicrobial peptide mediates skeletal muscle degeneration caused by injury and Duchenne muscular dystrophy in mice

BACKGROUND

Cathelicidin, an antimicrobial peptide, plays a key role in regulating bacterial killing and innate immunity; however, its role in skeletal muscle function is unknown. We investigated the potential role of cathelicidin in skeletal muscle pathology resulting from acute injury and Duchenne muscular dystrophy (DMD) in mice.

METHODS

Expression changes and muscular localization of mouse cathelicidin-related antimicrobial peptide (Cramp) were examined in the skeletal muscle of normal mice treated with chemicals (cardiotoxin and BaCl₂ ) or in dystrophic muscle of DMD mouse models (mdx, mdx/Utrn^+/- and mdx/Utrn^-/- ). Cramp penetration into myofibres and effects on muscle damage were studied by treating synthetic peptides to mouse skeletal muscles or C2C12 myotubes. Cramp knockout (KO) mice and mdx/Utrn/Cramp KO lines were used to determine whether Cramp mediates muscle degeneration. Muscle pathophysiology was assessed by histological methods, serum analysis, grip strength and lifespan. Molecular factors targeted by Cramp were identified by the pull-down assay and proteomic analysis.

RESULTS

In response to acute muscle injury, Cramp was activated in muscle-infiltrating neutrophils and internalized into myofibres. Cramp treatments of mouse skeletal muscles or C2C12 myotubes resulted in muscle degeneration and myotube damage, respectively. Genetic ablation of Cramp reduced neutrophil infiltration and ameliorated muscle pathology, such as fibre size (P < 0.001; n = 6) and fibrofatty infiltration (P < 0.05). Genetic reduction of Cramp in mdx/Utrn^+/- mice not only attenuated muscle damage (35%, P < 0.05; n = 9-10), myonecrosis (53%, P < 0.05), inflammation (37-65%, P < 0.01) and fibrosis (14%, P < 0.05) but also restored muscle fibre size (14%, P < 0.05) and muscle force (18%, P < 0.05). Reducing Cramp levels led to a 63% (male, P < 0.05; n = 10-14) and a 124% (female, P < 0.001; n = 20) increase in the lifespan of mdx/Utrn^-/- mice. Proteomic and mechanistic studies revealed that Cramp cross-talks with Ca²⁺ signalling in skeletal muscle through sarcoplasmic/endoplasmic reticulum Ca²⁺ -ATPase1 (SERCA1). Cramp binds and inactivates SERCA1, leading to the activation of Ca²⁺ -dependent calpain proteases that exacerbate DMD progression.

CONCLUSIONS

These findings identify Cramp as an immune cell-derived regulator of skeletal muscle degeneration and provide a potential therapeutic target for DMD.

Cathelicidin-Related Antimicrobial Peptide Negatively Regulates Bacterial Endotoxin-Induced Glial Activation

Recent studies have suggested that mouse cathelicidin-related antimicrobial peptide (CRAMP) and its human homologue leucine leucine-37 (LL-37) play critical roles in innate immune responses. Here, we studied the role of mouse CRAMP in bacterial endotoxin lipopolysaccharide (LPS)-induced neuroinflammation. CRAMP peptide treatment significantly inhibited LPS-mediated inflammatory activation of glial cells in culture. In the animal model of LPS-induced neuroinflammation, CRAMP expression was highly induced in multiple cell types, such as astrocytes, microglia, and neurons. Injection of exogenous CRAMP peptide significantly inhibited inflammatory cytokine expression and the reactivity of glial cells in the mouse brain following intraperitoneal or intracerebroventricular LPS administration. Altogether, results of the study suggest that CRAMP plays an important part in containment of LPS-induced neuroinflammatory responses, and that CRAMP can be exploited for the development of targeted therapies for neuroinflammatory conditions associated with bacterial infection.

Chicken cathelicidin-2 promotes NLRP3 inflammasome activation in macrophages

Chicken cathelicidin-2 (CATH-2) as a host defense peptide has been identified to have potent antimicrobial and immunomodulatory activities. Here, we reported the mechanism by which CATH-2 modulates NLRP3 inflammasome activation. Our results show that CATH-2 and ATP as a positive control induced secretion of IL-1β and IL-1α in LPS-primed macrophages but did not affect secretion of IL-6, IL-12 and TNF-α. Furthermore, CATH-2 induced caspase-1 activation and oligomerization of apoptosis-associated speck-like protein containing a carboxy- terminal caspase recruitment domain (ASC), which is essential for NLRP3 inflammasome activation. However, CATH-2 failed to induce IL-1β secretion in Nlrp3^-/-, Asc^-/- and Casp1^-/- macrophages. Notably, IL-1β and NLRP3 mRNA expression were not affected by CATH-2. In addition, CATH-2-induced NLRP3 inflammasome activation was mediated by K⁺ efflux but independent of the P2X7 receptor that is required for ATP-mediated K⁺ efflux. Gene interference of NEK7 kinase which has been identified to directly interact with NLRP3, significantly reduced IL-1β secretion and caspase-1 activation induced by CATH-2. Furthermore, confocal microscopy shows that CATH-2 significantly induced lysosomal leakage with the diffusion of dextran fluorescent signal. Cathepsin B inhibitors completely abrogated IL-1β secretion and caspase-1 activation as well as attenuating the formation of ASC specks induced by CATH-2. These results all indicate that CATH-2-induced activation of NLRP3 inflammasome is mediated by K⁺ efflux, and involves the NEK7 protein and cathepsin B. In conclusion, our study shows that CATH-2 acts as a second signal to activate NLRP3 inflammasome. Our study provides new insight into CATH-2 modulating immune response.

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.

Antimicrobial Peptides and Cationic Nanoparticles: A Broad-Spectrum Weapon to Fight Multi-Drug Resistance Not Only in Bacteria

In the last few years, antibiotic resistance and, analogously, anticancer drug resistance have increased considerably, becoming one of the main public health problems. For this reason, it is crucial to find therapeutic strategies able to counteract the onset of multi-drug resistance (MDR). In this review, a critical overview of the innovative tools available today to fight MDR is reported. In this direction, the use of membrane-disruptive peptides/peptidomimetics (MDPs), such as antimicrobial peptides (AMPs), has received particular attention, due to their high selectivity and to their limited side effects. Moreover, similarities between bacteria and cancer cells are herein reported and the hypothesis of the possible use of AMPs also in anticancer therapies is discussed. However, it is important to take into account the limitations that could negatively impact clinical application and, in particular, the need for an efficient delivery system. In this regard, the use of nanoparticles (NPs) is proposed as a potential strategy to improve therapy; moreover, among polymeric NPs, cationic ones are emerging as promising tools able to fight the onset of MDR both in bacteria and in cancer cells.

Increased Activities against Biofilms of the Pathogenic Yeast Candida albicans of Optimized Pom-1 Derivatives

Antimicrobial peptides (AMPs) are an alternative group for the therapy of infectious diseases, with activity against a wide range of diverse pathogens. However, classical AMPs have significant side effects in human cells due to their unspecific pore formation in biomembranes. Nevertheless, AMPs are promising therapeutics and can be isolated from natural sources, which include sea and freshwater molluscs. The AMPs identified in these organisms show promising antimicrobial activities, as pathogens are mainly fought by innate defence mechanisms. An auspicious candidate among molluscs is the Cuban freshwater snail Pomacea poeyana, from which the peptides Pom-1 and Pom-2 have been isolated and studied. These studies revealed significant antimicrobial activities for both AMPs. Based on the activities determined, Pom-1 was used for further optimization. In order to meet the emerging requirements of improved anti-biofilm activity against naturally occurring Candida species, the six derivatives Pom-1A to F were developed and investigated. Analysis of the derivatives acting on the most abundant naturally occurring Candida yeast Candida albicans (C. albicans) revealed a strong anti-biofilm activity, especially induced by Pom-1 B, C, and D. Furthermore, a moderate decrease in the metabolic activity of planktonic yeast cells was observed.

Membrane-disruptive peptides/peptidomimetics-based therapeutics: Promising systems to combat bacteria and cancer in the drug-resistant era

Membrane-disruptive peptides/peptidomimetics (MDPs) are antimicrobials or anticarcinogens that present a general killing mechanism through the physical disruption of cell membranes, in contrast to conventional chemotherapeutic drugs, which act on precise targets such as DNA or specific enzymes. Owing to their rapid action, broad-spectrum activity, and mechanisms of action that potentially hinder the development of resistance, MDPs have been increasingly considered as future therapeutics in the drug-resistant era. Recently, growing experimental evidence has demonstrated that MDPs can also be utilized as adjuvants to enhance the therapeutic effects of other agents. In this review, we evaluate the literature around the broad-spectrum antimicrobial properties and anticancer activity of MDPs, and summarize the current development and mechanisms of MDPs alone or in combination with other agents. Notably, this review highlights recent advances in the design of various MDP-based drug delivery systems that can improve the therapeutic effect of MDPs, minimize side effects, and promote the co-delivery of multiple chemotherapeutics, for more efficient antimicrobial and anticancer therapy.

PEGylated Graphene Oxide Carried OH-CATH30 to Accelerate the Healing of Infected Skin Wounds

BACKGROUND

The treatment of Staphylococcus aureus (S. aureus)-infected wounds is difficult. It causes extreme pain to tens of thousands of patients and increases the cost of medical care. The antimicrobial peptide OH-CATH30 (OH30) has a good killing activity against S. aureus and can play a role in accelerating wound healing and immune regulation. Therefore, it shows great potential for wound healing.

PURPOSE

The aim of this study was to overcome the short half-life and easy enzymolysis of OH30 by using graphene oxide conjugated with polyethylene glycol to load OH30 (denoted as PGO-OH30), as well as to evaluate its effect on wounds infected by S. aureus.

METHODS

PGO-OH30 nanoparticles were prepared by π-π conjugation and characterized. Their cell cytotoxicity, cell migration, infectious full-thickness dermotomy models, and histopathology were evaluated.

RESULTS

Characterization and cytotoxicity experiments revealed that the PGO-OH30 drug-delivery system had good biocompatibility and excellent drug-delivery ability. Cell-migration experiments showed that PGO-OH30 could promote the migration of human immortalized keratinocytes (HaCaT) cells compared with the control group (P<0.05). In a mouse model of skin wound infection, PGO-OH30 accelerated skin-wound healing and reduced the amount of S. aureus in wounds compared with the control group (P<0.05). In particular, on day 7, the number of S. aureus was 100 times lower in the PGO-OH30 group than in the control group.

CONCLUSION

The PGO-OH30 drug-delivery system had good biocompatibility and excellent drug-delivery ability, indicating its good therapeutic effect on a skin wound-infection model.

Cathelicidin and PMB neutralize endotoxins by multifactorial mechanisms including LPS interaction and targeting of host cell membranes

Antimicrobial peptides (AMPs) contribute to an effective protection against infections. The antibacterial function of AMPs depends on their interactions with microbial membranes and lipids, such as lipopolysaccharide (LPS; endotoxin). Hyperinflammation induced by endotoxin is a key factor in bacterial sepsis and many other human diseases. Here, we provide a comprehensive profile of peptide-mediated LPS neutralization by systematic analysis of the effects of a set of AMPs and the peptide antibiotic polymyxin B (PMB) on the physicochemistry of endotoxin, macrophage activation, and lethality in mice. Mechanistic studies revealed that the host defense peptide LL-32 and PMB each reduce LPS-mediated activation also via a direct interaction of the peptides with the host cell. As a biophysical basis, we demonstrate modifications of the structure of cholesterol-rich membrane domains and the association of glycosylphosphatidylinositol (GPI)-anchored proteins. Our discovery of a host cell-directed mechanism of immune control contributes an important aspect in the development and therapeutic use of AMPs.

Rational design of innate defense regulator peptides as tumor vaccine adjuvants

The development of adjuvants has been an empirical process. Efforts to develop a new design and evaluation system for novel adjuvants are not only desirable but also necessary. Moreover, composite adjuvants that contain two or more types of adjuvants to synergistically enhance the immune response are important for adjuvant and vaccine design. Innate defense regulator peptides (IDRs) are promising adjuvants for clinical immunotherapy because they exhibit multifaceted immunomodulatory capabilities. However, the rational design and discovery of IDRs that have improved immunomodulatory activities have been hampered by the lack of screening techniques and the great challenges in the identification of their interaction partners. Here, we describe a screening and evaluation system for IDR design. On the basis of in vitro screening, the optimized IDR DP7 recruited neutrophils, monocytes and macrophages to the site of infection. The adjuvant, comprising the DP7 and CpG oligonucleotide (CpG), induced chemokine/cytokine expression, enhanced the antigen uptake by dendritic cells and upregulated surface marker expression in dendritic cells. Vaccination with the NY-ESO-1 or OVA antigens combined with the adjuvant alum/CpG/DP7 strongly suppressed tumor growth in mice which was due to the improvement of antigen-specific humoral and cellular immunity. Regarding the mechanism of action, GPR35 may be the potential interaction partner of DP7. Our study revealed the potential application of the screening and evaluation system as a strategy for rationally designing effective IDRs or composite adjuvants and identifying their mechanism of action.

Beneficial impact of cathelicidin on hypersensitivity pneumonitis treatment-In vivo studies

Cathelicidin (CRAMP) is a defence peptide with a wide range of biological responses including antimicrobial, immunomodulatory and wound healing. Due to its original properties the usefulness of CRAMP in the treatment of pulmonary fibrosis was assessed in a murine model of hypersensitivity pneumonitis (HP). The studies were conducted on mouse strain C57BL/6J exposed to a saline extract of Pantoea agglomerans cells (HP inducer). Cathelicidin was administered in the form of an aerosol during and after HP development. Changes in the composition of immune cell populations (NK cells, macrophages, lymphocytes: Tc, Th, Treg, B), were monitored in lung tissue by flow cytometry. Extracellular matrix deposition (collagens, hydroxyproline), the concentration of cytokines involved in inflammatory and the fibrosis process (IFNγ, TNFα, TGFβ1, IL1β, IL4, IL5, IL10, IL12α, IL13) were examined in lung homogenates by the ELISA method. Alterations in lung tissue morphology were examined in mouse lung sections stained with haematoxylin and eosin as well as Masson trichrome dyes. The performed studies revealed that cathelicidin did not cause any negative changes in lung morphology/structure, immune cell composition or cytokines production. At the same time, CRAMP attenuated the immune reaction induced by mice chronic exposure to P. agglomerans and inhibited hydroxyproline and collagen deposition in the lung tissue of mice treated with bacteria extract. The beneficial effect of CRAMP on HP treatment was associated with restoring the balance in quantity of immune cells, cytokines production and synthesis of extracellular matrix components. The presented study suggests the usefulness of cathelicidin in preventing lung fibrosis; however, cathelicidin was not able to reverse pathological changes completely.

Assessing biofilm inhibition and immunomodulatory activity of small amounts of synthetic host defense peptides synthesized using SPOT-array technology

Peptides are promising drug candidates because of their diversity, biocompatibility and spectrum of activities. Here, we describe a protocol for high-throughput screening of SPOT-peptide arrays to assess the antibiofilm, antimicrobial and immunomodulatory activities of synthetic peptides. It is a Protocol Extension of our previous Nature Protocols article, which describes the synthesis of SPOT-peptide arrays and assays for screening antimicrobial activity. This latest protocol allows the simultaneous assessment of hundreds of synthetic host defense peptides to define their overall activity profiles and identify candidate sequences that are suitable for further characterization and development as anti-infectives. When coupled with the SPOT-array technology for peptide synthesis, the described procedures are rapid, inexpensive and straightforward for peptide library screening. The protocols can be implemented in most microbiology or immunology research laboratories without the need for specialists. The time to complete each step ranges between 1 and 4 h with overnight pauses, and datasets related to the antibiofilm and immunomodulatory activities of a large set of peptide sequences can be generated in a few days.

The neutrophil antimicrobial peptide cathelicidin promotes Th17 differentiation

The host defence peptide cathelicidin (LL-37 in humans, mCRAMP in mice) is released from neutrophils by de-granulation, NETosis and necrotic death; it has potent anti-pathogen activity as well as being a broad immunomodulator. Here we report that cathelicidin is a powerful Th17 potentiator which enhances aryl hydrocarbon receptor (AHR) and RORγt expression, in a TGF-β1-dependent manner. In the presence of TGF-β1, cathelicidin enhanced SMAD2/3 and STAT3 phosphorylation, and profoundly suppressed IL-2 and T-bet, directing T cells away from Th1 and into a Th17 phenotype. Strikingly, Th17, but not Th1, cells were protected from apoptosis by cathelicidin. We show that cathelicidin is released by neutrophils in mouse lymph nodes and that cathelicidin-deficient mice display suppressed Th17 responses during inflammation, but not at steady state. We propose that the neutrophil cathelicidin is required for maximal Th17 differentiation, and that this is one method by which early neutrophilia directs subsequent adaptive immune responses.

Antimicrobial peptide temporin-1CEa isolated from frog skin secretions inhibits the proinflammatory response in lipopolysaccharide-stimulated RAW264.7 murine macrophages through the MyD88-dependent signaling pathway

Temporin-1CEa, which is isolated from the skin secretions of the Chinese brown frog Rana chensinensis, exhibits broad-spectrum antimicrobial activity against gram-positive and gram-negative bacteria and antitumor activity. LK2(6) and LK2(6)A(L) are the analogs of temporin-1CEa obtained by replacing amino acids and displayed an improved anticancer activity. In the present study, the anti-inflammatory activity and mechanism of action of temporin-1CEa and its analogs LK2(6) and LK2(6)A(L) in lipopolysaccharide (LPS)-stimulated RAW264.7 murine macrophages were investigated. The results showed that temporin-1CEa and its analogs decreased the production of the cytokines tumor necrosis factor-α and interleukin-6 by inhibiting the protein expression of nuclear factor-κB and mitogen-activated protein kinase and the MyD88-dependent signaling pathway. Isothermal titration calorimetry studies revealed that temporin-1CEa, LK2(6) and LK2(6)A(L) exhibited binding affinities to LPS, an important inflammatory inducer, with Kd values of 0.1, 0.03 and 0.06 μM, respectively. Circular dichroism and zeta potential experiments showed that temporin-1CEa and its analogs interacted with LPS by electrostatic binding between the positively charged peptides and negatively charged LPS, resulting in the neutralization of LPS toxicity.

Moonlighting Proteins Are Important Players in Cancer Immunology

Plasticity and adaptation to environmental stress are the main features that tumor and immune system share. Except for intrinsic and high-defined properties, cancer and immune cells need to overcome the opponent's defenses by activating more effective signaling networks, based on common elements such as transcriptional factors, protein-based complexes and receptors. Interestingly, growing evidence point to an increasing number of proteins capable of performing diverse and unpredictable functions. These multifunctional proteins are defined as moonlighting proteins. During cancer progression, several moonlighting proteins are involved in promoting an immunosuppressive microenvironment by reprogramming immune cells to support tumor growth and metastatic spread. Conversely, other moonlighting proteins support tumor antigen presentation and lymphocytes activation, leading to several anti-cancer immunological responses. In this light, moonlighting proteins could be used as promising new potential targets for improving current cancer therapies. In this review, we describe in details 12 unprecedented moonlighting proteins that during cancer progression play a decisive role in guiding cancer-associated immunomodulation by shaping innate or adaptive immune response.

Inhalation Delivery of Host Defense Peptides (HDP) using Nano- Formulation Strategies: A Pragmatic Approach for Therapy of Pulmonary Ailments

Host defense peptides (HDP) are small cationic molecules released by the immune systems of the body, having multidimensional properties including anti-inflammatory, anticancer, antimicrobial and immune-modulatory activity. These molecules gained importance due to their broad-spectrum pharmacological activities, and hence being actively investigated. Presently, respiratory infections represent a major global health problem, and HDP has an enormous potential to be used as an alternative therapeutics against respiratory infections and related inflammatory ailments. Because of their short half-life, protease sensitivity, poor pharmacokinetics, and first-pass metabolism, it is challenging to deliver HDP as such inside the physiological system in a controlled way by conventional delivery systems. Many HDPs are efficacious only at practically high molar-concentrations, which is not convincing for the development of drug regimen due to their intrinsic detrimental effects. To avail the efficacy of HDP in pulmonary diseases, it is essential to deliver an appropriate payload into the targeted site of lungs. Inhalable HDP can be a potentially suitable alternative for various lung disorders including tuberculosis, Cystic fibrosis, Pneumonia, Lung cancer, and others as they are active against resistant microbes and cells and exhibit improved targeting with reduced adverse effects. In this review, we give an overview of the pharmacological efficacy of HDP and deliberate strategies for designing inhalable formulations for enhanced activity and issues related to their clinical implications.

The Dual Role of Antimicrobial Peptides in Autoimmunity

Autoimmune diseases (AiDs) are characterized by the destruction of host tissues by the host immune system. The etiology of AiDs is complex, with the implication of multiple genetic defects and various environmental factors (pathogens, antibiotic use, pollutants, stress, and diet). The interaction between these two compartments results in the rupture of tolerance against self-antigens and the unwanted activation of the immune system. Thanks to animal models, the immunopathology of many AiDs is well described, with the implication of both the innate and adaptive immune systems. This progress toward the understanding of AiDs led to several therapies tested in patients. However, the results from these clinical trials have not been satisfactory, from reversing the course of AiDs to preventing them. The need for a cure has prompted many investigators to explore alternative aspects in the immunopathology of these diseases. Among these new aspects, the role of antimicrobial host defense peptides (AMPs) is growing. Indeed, beyond their antimicrobial activity, AMPs are potent immunomodulatory molecules and consequently are implicated in the development of numerous AiDs. Importantly, according to the disease considered, AMPs appear to play a dual role in autoimmunity with either anti- or pro-inflammatory abilities. Here, we aimed to summarize the current knowledge about the role of AMPs in the development of AiDs and attempt to provide some hypotheses explaining their dual role. Definitely, a complete understanding of this aspect is mandatory before the design of AMP-based therapies against AiDs.

Polymorphisms in the P2X7 receptor, and differential expression of Toll-like receptor-mediated cytokines and defensins, in a Canadian Indigenous group

Canadian Indigenous peoples (First Nations and Inuit) exhibit a high burden of infectious diseases including tuberculosis influenced by societal factors, and biological determinants. Toll-like receptor (TLR)-mediated innate immune responses are the first line of defence against infections. We examined the production of a panel of 30 cytokines in peripheral blood-derived mononuclear cells (PBMC) isolated from Indigenous and non-Indigenous participants, following stimulation with five different TLR ligands. The levels of TLR-induced pro-inflammatory cytokines such as IL-12/23p40, IL-16, and IFN-γ, and chemokines (MCP-4, MDC and eotaxin) were different between Indigenous compared to non-Indigenous participants. Antimicrobial cationic host defence peptides (CHDP) induced by TLR activation are critical for resolution of infections and modulate the TLR-to-NFκB pathway to alter downstream cytokine responses. Therefore, we examined the expression of human CHDP defensins and cathelicidin in PBMC. mRNA expression of genes encoding for def-A1 and def-B1 were significantly higher following stimulation with TLR ligands in Indigenous compared to non-Indigenous participants. The purinergic receptor P2X7 known to be activated by ATP released following TLR stimulation, is a receptor for CHDP. Therefore, we further examined single nucleotide polymorphisms (SNP) in P2X7. Indigenous participants had a significantly higher percentage of a P2X7 SNP which is associated with reduced function and lower ability to clear infections. These results suggest that a higher frequency of non-functional P2X7 receptors may influence the activity of downstream immune mediators required for resolution of infections such as pro-inflammatory cytokines and CHDP defensins, thus contributing to higher burden of infections in Indigenous population.

Identification of Key Pathways and Genes of Acute Respiratory Distress Syndrome Specific Neutrophil Phenotype

Despite over 50 years of clinical and basic studies, acute respiratory distress syndrome (ARDS) is still a critical challenge with high mortality worldwide. The severity of neutrophil activation was associated with disease severity. However, the detailed pathophysiology of the circulating polymorphonuclear neutrophil activation in ARDS remains unclear. To identify key pathways and genes in the ARDS-specific neutrophil phenotype distinct from sepsis, the datasets of blood polymorphonuclear neutrophils (PMNs) from patients with ARDS (GSE76293) and from sepsis patients (GSE49757) were chosen from the Gene Expression Omnibus (GEO) and analyzed using bioinformatics methods. A total of 220 differential expressed genes (DEGs) were overlapped between GSE49757 and GSE76293 in a Venn diagram. Pathway enrichment analysis results showed that DEGs in GSE76293 were mainly enriched in the MAPK signaling pathway, FoxO signaling pathway, and AMPK signaling pathway relative to GSE49757. We identified 30 hub genes in the protein-protein interaction network. By comparing with GSE49757, we speculated that GAPDH, MAPK8, PIK3CB, and MMP9 may play important roles in the progression of ARDS-specific circulating neutrophil activation. The findings may provide novel insights into the development of promising targets for the diagnosis and treatment of ARDS in the future.

The putative mature peptide of piscidin-1 modulates global transcriptional profile and proliferation of splenic lymphocytes in orange-spotted grouper (Epinephelus coioides)

Piscidins are important components in protecting microbial infections in teleost. The present study purified and identified a truncated peptide, whose sequence was very close to that of putative mature peptide of epinecidin-1 (piscidin-1) in orange-spotted grouper (Epinephelus coioides), Epi-1 (also named as short form of ecPis-1, ecPis-1S). The immunomodulatory effects of ecPis-1S on splenic lymphocytes of orange-spotted grouper were explored in vitro. The transcriptome study was carried out by De novo transcriptome sequencing (RNA-Seq) in splenic lymphocytes of orange-spotted grouper. Regarding the profiles of gene expressions, 2994 genes were up-regulated and 2679 genes were down-regulated in the splenic lymphocytes stimulated by ecPis-1S. In the case of differential expression genes, 330 genes were involved in immune related pathways. Among them, 34 genes were involved in T cell receptor signaling pathway, 31 genes in natural killer cell mediated cytotoxicity and 23 genes in leukocyte transendothelial migration, respectively. Immune-related genes selected for qRT-PCR verification, such as interleukin-1β (il-1b), tumor necrosis factor α (tnfa), T cell antigen receptor (tcr), major histocompatibility complex class I (mhc I), and mhc II were significantly up-regulated by ecPis-1S (p < 0.05). ecPis-1S could significantly enhance the proliferation of splenic lymphocytes of orange-spotted grouper in vitro (p < 0.05). In addition, the result of qRT-PCR revealed that ecPis-1S also significantly up-regulated cell cycle-related genes, including cyclin A (cyca), cyclin-dependent kinase 2 (cdk2), cdk4, cell division cycle protein 6 (cdc6), and transforming growth factor β (tgfb) (p < 0.05), which suggested that ecPis-1S promoted the proliferation of lymphocytes by activating cell division cycle. In conclusion, the results indicated that the mature peptide of piscidin-1 in orange-spotted grouper could act as immune modulator and play an important role in regulation of the immune response in fish.

Reassessing the Host Defense Peptide Landscape

Current research has demonstrated that small cationic amphipathic peptides have strong potential not only as antimicrobials, but also as antibiofilm agents, immune modulators, and anti-inflammatories. Although traditionally termed antimicrobial peptides (AMPs) these additional roles have prompted a shift in terminology to use the broader term host defense peptides (HDPs) to capture the multi-functional nature of these molecules. In this review, we critically examined the role of AMPs and HDPs in infectious diseases and inflammation. It is generally accepted that HDPs are multi-faceted mediators of a wide range of biological processes, with individual activities dependent on their polypeptide sequence. In this context, we explore the concept of chemical space as it applies to HDPs and hypothesize that the various functions and activities of this class of molecule exist on independent but overlapping activity landscapes. Finally, we outline several emerging functions and roles of HDPs and highlight how an improved understanding of these processes can potentially be leveraged to more fully realize the therapeutic promise of HDPs.

A novel moonlight function of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) for immunomodulation

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is an energy metabolism-related enzyme, which generates NADH in glycolysis. Our previous study revealed a novel role of exogenous GAPDH in the amelioration of lipopolysaccharide (LPS)-induced sepsis-related, severe acute lung injury (ALI) in mice. Here, we show the effect of extracellular GAPDH on the physiological functions of macrophages, which play an important role in the onset of sepsis and ALI. GAPDH has no effect on cell viability, while it strongly suppressed cell adhesion, spreading, and phagocytic function of LPS-stimulated macrophages. GAPDH treatment significantly reduced tumor necrosis factor (TNF)-α, while it induced interleukin (IL)-10 production from LPS-stimulated macrophages in a dose-dependent manner. It is noteworthy that heat inactivation of GAPDH lost its immunomodulatory activity. Correspondingly, NADH significantly inhibited TNF-α and enhanced IL-10 production with elevation of both M1/M2 macrophage markers. These data suggest that extracellular GAPDH induces intermediate M1/M2 macrophages for termination of inflammation, partly through its enzyme activity for generation of NADH. © 2018 BioFactors, 44(6):597-608, 2018.

Cathelicidins: Immunomodulatory Antimicrobials

Cathelicidins are host defense peptides with antimicrobial and immunomodulatory functions. These effector molecules of the innate immune system of many vertebrates are diverse in their amino acid sequence but share physicochemical characteristics like positive charge and amphipathicity. Besides being antimicrobial, cathelicidins have a wide variety in immunomodulatory functions, both boosting and inhibiting inflammation, directing chemotaxis, and effecting cell differentiation, primarily towards type 1 immune responses. In this review, we will examine the biology and various functions of cathelicidins, focusing on putting in vitro results in the context of in vivo situations. The pro-inflammatory and anti-inflammatory functions are highlighted, as well both direct and indirect effects on chemotaxis and cell differentiation. Additionally, we will discuss the potential and limitations of using cathelicidins as immunomodulatory or antimicrobial drugs.

Host Defense Peptide LL-37-Mediated Chemoattractant Properties, but Not Anti-Inflammatory Cytokine IL-1RA Production, Is Selectively Controlled by Cdc42 Rho GTPase via G Protein-Coupled Receptors and JNK Mitogen-Activated Protein Kinase

The human host defense peptide LL-37 promotes immune activation such as induction of chemokine production and recruitment of leukocytes. Conversely, LL-37 also mediates anti-inflammatory responses such as production of anti-inflammatory cytokines, e.g., IL-1RA, and the control of pro-inflammatory cytokines, e.g., TNF. The mechanisms regulating these disparate immunomodulatory functions of LL-37 are not completely understood. Rho GTPases are GTP-binding proteins that promote fundamental immune functions such as chemokine production and recruitment of leukocytes. However, recent studies have shown that distinct Rho proteins can both negatively and positively regulate inflammation. Therefore, we interrogated the role of Rho GTPases in LL-37-mediated immunomodulation. We demonstrate that LL-37-induced production of chemokines, e.g., GRO-α and IL-8 is largely dependent on Cdc42/Rac1 Rho GTPase, but independent of the Ras pathway. In contrast, LL-37-induced production of the anti-inflammatory cytokine IL-1RA is not dependent on either Cdc42/Rac1 RhoGTPase or Ras GTPase. Functional studies confirmed that LL-37-induced recruitment of leukocytes (monocytes and neutrophils) is also dependent on Cdc42/Rac1 RhoGTPase activity. We demonstrate that Cdc42/Rac1-dependent bioactivity of LL-37 involves G-protein-coupled receptors (GPCR) and JNK mitogen-activated protein kinase (MAPK) signaling, but not p38 or ERK MAPK signaling. We further show that LL-37 specifically enhances the activity of Cdc42 Rho GTPase, and that the knockdown of Cdc42 suppresses LL-37-induced production of chemokines without altering the peptide's ability to induce IL-1RA. This is the first study to demonstrate the role of Rho GTPases in LL-37-mediated responses. We demonstrate that LL-37 facilitates chemokine production and leukocyte recruitment engaging Cdc42/Rac1 Rho GTPase via GPCR and the JNK MAPK pathway. In contrast, LL-37-mediated anti-inflammatory cytokine IL-1RA production is independent of either Rho or Ras GTPase. The results of this study suggest that Cdc42 Rho GTPase may be the molecular switch that controls the opposing functions of LL-37 in the process of inflammation.

The respiratory syncytial virus fusion protein formulated with a polymer-based adjuvant induces multiple signaling pathways in macrophages

Respiratory syncytial virus (RSV) causes acute respiratory tract infections in infants, the elderly and immunocompromised individuals. No licensed vaccine is available against RSV. We previously reported that intranasal immunization of rodents and lambs with a RSV vaccine candidate (ΔF/TriAdj) induces protective immunity with a good safety profile. ΔF/TriAdj promoted innate immune responses in respiratory mucosal tissues in vivo, by local chemokine and cytokine production, as well as infiltration and activation of immune cells including macrophages. The macrophage is an important cell type in context of both innate and adaptive immune responses against RSV. Therefore, we characterized the effects of ΔF/TriAdj on a murine macrophage cell line, RAW264.7, and bone marrow-derived macrophages (BMMs). A gene expression study of pattern recognition receptors (PRRs) revealed induction of endosomal and cytosolic receptors in RAW264.7 cells and BMMs by ΔF/TriAdj, but no up-regulation by ΔF in PBS. As a secondary response to the PRR gene expression, induction of several chemokines and pro-inflammatory cytokines, as well as up-regulation of MHC-II and co-stimulatory immune markers, was observed. To further investigate the mechanisms involved in ΔF/TriAdj-mediated secondary responses, we used relevant signal transduction pathway inhibitors. Based on inhibition studies at both transcript and protein levels, JNK, ERK1/2, CaMKII, PI3K and JAK pathways were clearly responsible for ΔF/TriAdj-mediated chemokine and pro-inflammatory cytokine responses, while the p38 and NF-κB pathways appeared to be not or minimally involved. ΔF/TriAdj induced IFN-β, which may participate in the JAK-STAT pathway to further amplify CXCL-10 production, which was strongly up-regulated. Blocking this pathway by a JAK inhibitor almost completely abrogated CXCL-10 production and caused a significant reduction in the cell surface expression of MHC-II and co-stimulatory immune markers. These data demonstrate that ΔF/TriAdj induces multiple signaling pathways in macrophages.

Microglia-derived extracellular vesicles in Alzheimer's Disease: A double-edged sword

Extracellular vesicles (EVs), based on their origin or size, can be classified as apoptotic bodies, microvesicles (MVs)/microparticles (MPs), and exosomes. EVs are one of the new emerging modes of communication between cells that are providing new insights into the pathophysiology of several diseases. EVs released from activated or apoptotic cells contain specific proteins (signaling molecules, receptors, integrins, cytokines), bioactive lipids, nucleic acids (mRNA, miRNA, small non coding RNAs, DNA) from their progenitor cells. In the brain, EVs contribute to intercellular communication through their basal release and uptake by surrounding cells, or release into the cerebrospinal fluid (CSF) and blood. In the central nervous system (CNS), EVs have been suggested as potential carriers in the intercellular delivery of misfolded proteins associated to neurodegenerative disorders, such as tau and amyloid β in Alzheimer's Disease (AD), α-synuclein in Parkinson's Disease (PD), superoxide dismutase (SOD)1 in amyotrophic lateral sclerosis and huntingtin in Huntington's Disease. Multiple studies indicate that EVs are involved in the pathogenesis of AD, although their role has not been completely elucidated. The focus of this review is to analyze the new emerging role of EVs in AD progression, paying particular attention to microglia EVs. Recent data show that microglia are the first myeloid cells to be activated during neuroinflammation. Microglial EVs in fact, could have both a beneficial and a detrimental action in AD. The study of EVs may provide specific, precise information regarding the AD transition stage that may offer possibilities to intervene in order to retain cognition. In chronic neurodegenerative diseases EVs could be a novel biomarker to monitor the progression of the pathology and also represent a new therapeutical approach to CNS diseases.

Importance of phosphoinositide binding by human β-defensin 3 for Akt-dependent cytokine induction

Host defense peptides (HDPs) are well-characterized for their antimicrobial activities but also variously display potent immunomodulatory effects. Human β-defensin 3 (HBD-3) belongs to a well-known HDP family known as defensins and is able to induce leukocyte chemotactic recruitment, leukocyte activation/maturation, proinflammatory cytokine release, and co-stimulatory marker expression. HBD-3-stimulated cytokine induction is NF-κB-dependent and was initially suggested to act via G protein-coupled C-C chemokine receptor phospholipase C (PLC) and/or Toll-like receptor signaling. Subsequent pharmacological inhibition, however, revealed that NF-κB activation by HBD-3 is receptor-independent and instead involves the phosphoinositide 3-kinase (PI3K)-protein kinase B (Akt) pathway, the mechanism of which remains undetermined. Recently, we have shown that HBD-3 can enter mammalian cells and bind to inner membrane phosphoinositide 4,5-bisphosphate [PI(4,5)P₂], an important second lipid messenger of PLC and PI3K-Akt pathways. In this study, we report that the interaction of HBD-3 with PI(4,5)P₂ is important for PI3K-Akt-NF-κΒ-mediated induction of tumor necrosis factor and interleukin-6. These data provide insights into the mechanism of immunomodulation by HBD-3, and more generally, highlight the complex multifaceted signaling roles of HDPs in innate defense. Furthermore, it is suggested that the proposed mode of action may be conserved in other HDPs.

Aggregation and Its Influence on the Immunomodulatory Activity of Synthetic Innate Defense Regulator Peptides

There is increasing interest in developing cationic host defense peptides (HDPs) and their synthetic derivatives as antimicrobial, immunomodulatory, and anti-biofilm agents. These activities are often evaluated without considering biologically relevant concentrations of salts or serum; furthermore certain HDPs have been shown to aggregate in vitro. Here we examined the effect of aggregation on the immunomodulatory activity of a synthetic innate defense regulator peptide, 1018 (VRLIVAVRIWRR-NH₂). A variety of salts and solutes were screened to determine their influence on 1018 aggregation, revealing that this peptide "salts out" of solution in an anion-specific and concentration-dependent manner. Furthermore, the immunomodulatory activity of 1018 was found to be inhibited under aggregation-promoting conditions. A series of 1018 derivatives were synthesized with the goal of disrupting this self-assembly process. Indeed, some derivatives exhibited reduced aggregation while maintaining certain immunomodulatory functions, demonstrating that it is possible to engineer optimized synthetic HDPs to avoid unwanted peptide aggregation.

Immuno-Stimulatory Peptides as a Potential Adjunct Therapy against Intra-Macrophagic Pathogens

The treatment of infectious diseases is increasingly prone to failure due to the rapid spread of antibiotic-resistant pathogens. Antimicrobial peptides (AMPs) are natural components of the innate immune system of most living organisms. Their capacity to kill microbes through multiple mechanisms makes the development of bacterial resistance less likely. Additionally, AMPs have important immunomodulatory effects, which critically contribute to their role in host defense. In this paper, we review the most recent evidence for the importance of AMPs in host defense against intracellular pathogens, particularly intra-macrophagic pathogens, such as mycobacteria. Cathelicidins and defensins are reviewed in more detail, due to the abundance of studies on these molecules. The cell-intrinsic as well as the systemic immune-related effects of the different AMPs are discussed. In the face of the strong potential emerging from the reviewed studies, the prospects for future use of AMPs as part of the therapeutic armamentarium against infectious diseases are presented.

A synthetic cationic antimicrobial peptide inhibits inflammatory response and the NLRP3 inflammasome by neutralizing LPS and ATP

Antimicrobial peptides (AMPs) are one of the most important defense mechanisms against bacterial infections in insects, plants, non-mammalian vertebrates, and mammals. In the present study, a class of synthetic AMPs was evaluated for anti-inflammatory activity. One cationic AMP, GW-A2, demonstrated the ability to inhibit the expression levels of nitric oxide (NO), inducible NO synthase (iNOS), cyclooxygenase-2 (COX-2), tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) in lipopolysaccharide (LPS)-activated macrophages. GW-A2 reduced LPS-induced increases in the phosphorylation of mitogen-activated protein kinase and protein kinase C-α/δ and the activation of NF-κB. GW-A2 also inhibited NLRP3 inflammasome activation induced by LPS and ATP. Furthermore, in the mice injected with LPS, GW-A2 reduced (1) the concentration of IL-1β, IL-6 and TNF-α in the serum; (2) the concentration of TNF-α in the peritoneal lavage; (3) the expression levels of iNOS, COX-2 and NLRP3 in the liver and lung; (4) the infiltration of polymorphonuclear neutrophils in the liver and lung. The underlying mechanisms for the anti-inflammatory activity of GW-A2 were found to be partially due to LPS and ATP neutralization. These results provide insights into how GW-A2 inhibits inflammation and the NLRP3 inflammasome and provide a foundation for the design of rational therapeutics for inflammation-related diseases.

Antimicrobial peptide-gold nanoscale therapeutic formulation with high skin regenerative potential

Chronic skin wounds affect ≈3% of persons aged >60years (Davies et al., 2007) [1]. These wounds are typically difficult to heal by conventional therapies and in many cases they get infected making even harder the regeneration process. The antimicrobial peptide (AMP) LL37 combines antimicrobial with pro-regenerative properties and thus represents a promising topical therapy to address both problems. Here, we investigated the wound healing potential of soluble and immobilized LL37 (LL37-conjugated gold nanoparticles, LL37-Au NPs), both in vitro (migration of keratinocytes) and in vivo (skin wound healing). Our results show that LL37-Au NPs, but not LL37 peptide, have the capacity to prolong the phosphorylation of EGFR and ERK1/2 and enhance the migratory properties of keratinocytes in a large in vitro wound model. We further report that both LL37 and LL37-Au NPs promote keratinocyte migration by the transactivation of EGFR, a process that seems to be initiated at the P2X7 receptor, as confirmed by chemical and genetic inhibition studies. Finally, we show in vivo that LL37-Au NPs have higher wound healing activity than LL37 peptide in a splinted mouse full thickness excisional model. Animal wounds treated by LL37-Au NPs have higher expression of collagen, IL6 and VEGF than the ones treated with LL37 peptide or NPs without LL37. Altogether, the conjugation of AMPs to NPs offers a promising platform to enhance their pro-regenerative properties.

Comparative efficacy analysis of anti-microbial peptides, LL-37 and indolicidin upon conjugation with CNT, in human monocytes

BACKGROUND

Antimicrobial peptides (AMPs) have the potential to serve as an alternative to antibiotic. AMPs usually exert bactericidal activity via direct killing of microbial pathogens. Reports have proposed that by harnessing innate immune activation, AMPs can regulate pathogen invasion and may control infection. It has been reported that AMPs could be utilized to activate the innate mucosal immune response in order to eliminate pathogenic infections. This way of controlling pathogen infection, by activating host immunity, confers the potential to the select AMPs to alleviate the problem of antibiotic resistance. Among various AMPs tested LL-37 and indolicidin, showed promise to be potential candidates for eliciting enhanced host innate immune responses. LL-37 and indolicidin had exhibited substantial innate immune activation in both human and murine macrophages. Dosage for each of the AMPs, however, was high with adverse side effects.

RESULTS

In this study, we reported that upon conjugation with carbon nanotubes (CNT), each AMP remained biologically functional at a concentration that was 1000-fold less than the dosage required for free AMP to remain active in the cells.

CONCLUSIONS

Current study also revealed that while indolicidin induced signalling events mediated through the TNFRSF1A pathway in THP1 cells, followed by activation of NFκB and c-JUN pathways, treatment of cells with LL-37 induced signalling events by activating IL1R, with subsequent activation of NFκB and NFAT2. Thp1 cells, primed with CNT conjugated LL-37 or indolicidin, are protected against Salmonella typhimurium infection at 16 h post challenge.

Evaluation of the Immunomodulatory Activity of the Chicken NK-Lysin-Derived Peptide cNK-2

Chicken NK-lysin (cNK-lysin), the chicken homologue of human granulysin, is a cationic amphiphilic antimicrobial peptide (AMP) that is produced by cytotoxic T cells and natural killer cells. We previously demonstrated that cNK-lysin and cNK-2, a synthetic peptide incorporating the core α-helical region of cNK-lysin, have antimicrobial activity against apicomplexan parasites such as Eimeria spp., via membrane disruption. In addition to the antimicrobial activity of AMPs, the immunomodulatory activity of AMPs mediated by their interactions with host cells is increasingly recognized. Thus, in this study, we investigated whether cNK-lysin derived peptides modulate the immune response in the chicken macrophage cell line HD11 and in chicken primary monocytes by evaluating the induction of chemokines, anti-inflammatory properties, and activation of signalling pathways. cNK-2 induced the expression of CCL4, CCL5 and interleukin(IL)-1β in HD11 cells and CCL4 and CCL5 in primary monocytes. We also determined that cNK-2 suppresses the lipopolysaccharide-induced inflammatory response by abrogating IL-1β expression. The immunomodulatory activity of cNK-2 involves the mitogen-activated protein kinases-mediated signalling pathway, including p38, extracellular signal-regulated kinase 1/2 and c-Jun N-terminal kinases, as well as the internalization of cNK-2 into the cells. These results indicate that cNK-2 is a potential novel immunomodulating agent rather than an antimicrobial agent.

Interspecies cathelicidin comparison reveals divergence in antimicrobial activity, TLR modulation, chemokine induction and regulation of phagocytosis

Cathelicidins are short cationic peptides initially described as antimicrobial peptides, which can also modulate the immune system. Because most findings have been described in the context of human LL-37 or murine CRAMP, or have been investigated under varying conditions, it is unclear which functions are cathelicidin specific and which functions are general cathelicidin properties. This study compares 12 cathelicidins from 6 species under standardized conditions to better understand the conservation of cathelicidin functions. Most tested cathelicidins had strong antimicrobial activity against E. coli and/or MRSA. Interestingly, while more physiological culture conditions limit the antimicrobial activity of almost all cathelicidins against E. coli, activity against MRSA is enhanced. Seven out of 12 cathelicidins were able to neutralize LPS and another 7 cathelicidins were able to neutralize LTA; however, there was no correlation found with LPS neutralization. In contrast, only 4 cathelicidins enhanced DNA-induced TLR9 activation. In conclusion, these results provide new insight in the functional differences of cathelicidins both within and between species. In addition, these results underline the importance not to generalize cathelicidin functions and indicates that caution should be taken in extrapolating results from LL-37- or CRAMP-related studies to other animal settings.

Positive selection in cathelicidin host defense peptides: adaptation to exogenous pathogens or endogenous receptors?

The cause of adaptive protein evolution includes internal (for example, co-evolution of ligand-receptor pairs) and external (for example, adaptation to different ecological niches) mechanisms. Host defense peptides (HDPs) are a class of vertebrate-specific cationic antimicrobial peptides evolving under positive selection. Besides their antibiotic activity, HDPs also exert an effect on multiple host immune cells, thus providing an ideal model to study selective agents driving their evolution. On the basis of a combination of computational and experimental approaches, we studied the evolution of LL-37-type HDPs in mammals, the mature peptide of cathelicidin CAP18 (herein termed CAP18-MP) and investigated the driving force behind the evolution. Using codon-substitution maximum likelihood models, we analyzed CAP18-MPs in 40 species belonging to nine mammalian Orders and identified four positively selected sites (PSSs) that all are located on two terminal unordered regions of CAP18-MPs. Grafting the two positively selected regions of human or whale CAP18-MP to the α-helical scaffold of a rabbit homolog (substituting its corresponding parts) led to no alterations in antibacterial activity, spectrum and action mode. Likewise, further deletion of the two terminal regions did not alter its functional features. Evolutionary conservation analysis of mammalian FPR2, a receptor known to interact with the C-terminal positively selected region of LL-37, revealed high evolutionary variability in its ligand-binding extracellular loop domains, matching sequence diversity of the unordered regions in CAP18-MPs. This is the first report describing that the signature of positive selection of cathelicidins is not associated with their direct bactericidal activity, but rather with the evolutionary variability of their endogenous receptors.

Molecular mechanisms of LL-37-induced receptor activation: An overview

The human cathelicidin peptide LL-37 plays a crucial role in the immune system on many levels, from the first line of defense in epithelial cells to restoring the tissue after infection. On host cells, the majority of the LL-37-induced effects are mediated via the direct or indirect activation of several structurally unrelated cell surface receptors or intracellular targets. How LL-37 is able to affect multiple receptors is currently not well understood. So far, the mechanistic details underlying receptor activation are poorly investigated and evidence for a conventional ligand/receptor interaction is scarce. Over the past few decades, a large number of studies have reported on the activation of a receptor and/or components of the downstream signal transduction pathway induced by LL-37. This review summarizes the current knowledge on molecular mechanisms underlying LL-37-induced receptor activation.

Roles of Mas-related G protein-coupled receptor X2 on mast cell-mediated host defense, pseudoallergic drug reactions, and chronic inflammatory diseases

Mast cells (MCs), which are granulated tissue-resident cells of hematopoietic lineage, contribute to vascular homeostasis, innate/adaptive immunity, and wound healing. However, MCs are best known for their roles in allergic and inflammatory diseases, such as anaphylaxis, food allergy, rhinitis, itch, urticaria, atopic dermatitis, and asthma. In addition to the high-affinity IgE receptor (FcεRI), MCs express numerous G protein-coupled receptors (GPCRs), which are the largest group of membrane receptor proteins and the most common targets of drug therapy. Antimicrobial host defense peptides, neuropeptides, major basic protein, eosinophil peroxidase, and many US Food and Drug Administration-approved peptidergic drugs activate human MCs through a novel GPCR known as Mas-related G protein-coupled receptor X2 (MRGPRX2; formerly known as MrgX2). Unique features of MRGPRX2 that distinguish it from other GPCRs include their presence both on the plasma membrane and intracellular sites and their selective expression in MCs. In this article we review the possible roles of MRGPRX2 on host defense, drug-induced anaphylactoid reactions, neurogenic inflammation, pain, itch, and chronic inflammatory diseases, such as urticaria and asthma. We propose that host defense peptides that kill microbes directly and activate MCs through MRGPRX2 could serve as novel GPCR targets to modulate host defense against microbial infection. Furthermore, mAbs or small-molecule inhibitors of MRGPRX2 could be developed for the treatment of MC-dependent allergic and inflammatory disorders.

Functions of Cationic Host Defense Peptides in Immunity

Cationic host defense peptides are a widely distributed family of immunomodulatory molecules with antimicrobial properties. The biological functions of these peptides include the ability to influence innate and adaptive immunity for efficient resolution of infections and simultaneous modulation of inflammatory responses. This unique dual bioactivity of controlling infections and inflammation has gained substantial attention in the last three decades and consequent interest in the development of these peptide mimics as immunomodulatory therapeutic candidates. In this review, we summarize the current literature on the wide range of functions of cationic host defense peptides in the context of the mammalian immune system.

Human Host Defense Cathelicidin Peptide LL-37 Enhances the Lipopolysaccharide Uptake by Liver Sinusoidal Endothelial Cells without Cell Activation

The liver is a major organ that removes waste substances from the blood, and liver sinusoidal endothelial cells (LSECs) are professional scavenger cells, which incorporate and degrade various endogenous and exogenous molecules including pathogenic factor LPS. Mammalian cells express a number of peptide antibiotics that function as effectors in the innate host defense systems. LL-37, a human cathelicidin antimicrobial peptide, has a potent LPS-neutralizing activity and exhibits protective actions on various infection models. However, the effect of LL-37 on the LPS clearance has not been clarified. In this study, to further understand the host-protective mechanism of LL-37, we evaluated the effect of LL-37 on the LPS clearance in vitro. LL-37 enhanced the LPS uptake by human LSECs. Of interest, LL-37 was similarly incorporated into LSECs both in the presence and the absence of LPS, and the incorporated LPS and LL-37 were colocalized in LSECs. Importantly, the uptake of LPS and LL-37 was inhibited by endocytosis inhibitors, heparan sulfate proteoglycan analogs, and glycosaminoglycan lyase treatment of the cells. Moreover, the uptake of LL-37-LPS did not activate TLR4 signaling in both MyD88-dependent and -independent pathways. In addition, the incorporated LL-37-LPS was likely transported to the lysosomes in LSECs. Together these observations suggest that LL-37 enhances the LPS uptake by LSECs via endocytosis through the complex formation with LPS and the interaction with cell-surface heparan sulfate proteoglycans, thereby facilitating the intracellular incorporation and degradation of LPS without cell activation. In this article, we propose a novel function of LL-37 in enhancing LPS clearance.

Unique features of human cathelicidin LL-37

Cathelicidins are antimicrobial peptides produced by humans and animals in response to various pathogenic microbes. This review intends to provide a brief overview of the expression, structure, properties and function of human cathelicidin LL-37 which may be a therapeutic agent against a variety of bacterial and viral diseases, cancers, and hard-to-heal wounds. Cathelicidins act as a primary defense against bacteria and other pathogens in the case of inflammation. They are able to kill bacteria and fungi, inhibit and destroy bacterial biofilms, and possess antiviral and antiparasitics properties. They can also play a role in angiogenesis, wound healing, and the regulation of apoptosis. The host defense peptide LL-37 has emerged as a novel modulator of tumor growth and metastasis in carcinogenesis of various types of cancers. LL-37 is an antimicrobial peptide able of inducing various effects. It acts as an anti- and pro- inflammatory factor. Cathelicidins are able to directly and selectively destroy membranes of various microbes and cancer cells, but they do not attack normal cells. The role of cathelicidins in cancer is double-sided. They play an important role in killing cancer cells and may provide a new possibility for the development of cancer therapeutics. However, they also can participate in carcinogenesis. Due to its activity spectrum LL-37 could be applied in pharmacotherapy. Cathelicidin peptides could serve as a template for the development of modern anti-microbial and anti-viral drugs. LL-37 is an excellent candidate to develop into therapeutics for infected wounds.

Identifying the Critical Domain of LL-37 Involved in Mediating Neutrophil Activation in the Presence of Influenza Virus: Functional and Structural Analysis

The human cathelicidin LL-37 has been shown to play a role in host defense against influenza A viruses (IAV) through direct antiviral effects and through modulating inflammatory responses to infection. We recently showed that LL-37 increases neutrophil respiratory burst and neutrophil extracellular trap (NET) responses to IAV through engaging formyl peptide receptor 2 (FPR-2). In this paper we show that a fragment of LL-37, GI-20, which is composed of the central helical segment of the peptide, has similar effects as LL-37 on neutrophil activation. In addition to increasing respiratory burst and NET responses of the cells to IAV through an FPR-2 dependent mechanism, it reduces neutrophil IL-8 production to IAV (also like LL-37). The N-terminal fragment, LL-23, did not have similar effects. Both GI-20 and LL-37 increase neutrophil intracellular calcium levels and their ability to increase neutrophil activation responses was calcium dependent and partially inhibited by pertussis toxin. These studies show that the central helix of LL-37 retains the ability of LL-37 to modulate neutrophil responses through FPR-2. Based on our findings we developed a homology model of FPR-2 and performed docking experiments of LL-37 and GI-20 with the receptor.