Protecting the boundary: the sentinel role of host defense peptides in the skin

The Central Roles of Keratinocytes in Coordinating Skin Immunity

The function of keratinocytes (KCs) to form a barrier and produce cytokines is well-known, but recent progress has revealed many different roles for KCs in regulation of skin immunity. In this review, we provide an update on the current understanding of how KCs communicate with microbes, immunocytes, neurons, and other cells to form an effective immune barrier. We catalog the large list of genes and metabolites of KCs that participate in host defense and discuss the mechanisms of immune crosstalk, addressing how KCs simultaneously form a physical barrier, communicate with fibroblasts, and control immune signals. Overall, the signals sent and received by KCs are an exciting group of therapeutic targets to explore in the treatment of dermatologic disorders.

Characterization and mechanism of action of amphibian-derived wound-healing-promoting peptides

Wound-healing-promoting peptides are excellent candidates for developing wound-healing agents due to their small size and low production cost. Amphibians are one of the major sources of bioactive peptides, including wound-healing-promoting peptides. So far, a series of wound-healing-promoting peptides have been characterized from amphibians. We hereby summarized the amphibian-derived wound-healing-promoting peptides and their mechanism of action. Among these peptides, two peptides (tylotoin and TK-CATH) were characterized from salamanders, and twenty five peptides were characterized from frogs. These peptides generally have small sizes with 5-80 amino acid residues, nine peptides (tiger17, cathelicidin-NV, cathelicidin-DM, OM-LV20, brevinin-2Ta, brevinin-2PN, tylotoin, Bv8-AJ, and RL-QN15) have intramolecular disulfide bonds, seven peptides (temporin A, temporin B, esculentin-1a, tiger17, Pse-T2, DMS-PS2, FW-1, and FW-2) are amidated at the C-terminus, and the others are linear peptides without modifications. They all efficiently accelerated the healing of skin wounds or photodamage in mice or rats. They selectively promoted the proliferation and migration of keratinocytes and fibroblasts, recruited neutrophils and macrophages to wounds, and regulated the immune response of neutrophils and macrophages in wounds, which were essential for wound healing. Interestingly, MSI-1, Pse-T2, cathelicidin-DM, brevinin-2Ta, brevinin-2PN, and DMS-PS2 were just antimicrobial peptides, but they also significantly promoted the healing of infected wounds by clearing off bacteria. Considering the small size, high efficiency, and definite mechanism, amphibian-derived wound-healing-promoting peptides might be excellent candidates for developing novel wound-healing-promoting agents in future.

Sodium hyaluronates applied in the face affects the diversity of skin microbiota in healthy people

OBJECTIVE

A healthy and stable microbiome has many beneficial effects on the host, while an unbalanced or disordered microbiome can lead to various skin diseases. Hyaluronic acid is widely used in the cosmetics and pharmaceutical industries; however, specific reports on its effect on the skin microflora of healthy people have not been published. This study aimed to determine the effect of sodium hyaluronate on the facial microflora of healthy individuals.

METHODS

Face of 20 healthy female volunteers between 18 and 24 years was smeared with sodium hyaluronate solution once per day. Cotton swabs were used to retrieve samples on days 0, 14, and 28, and high-throughput sequencing of 16 S rRNA was used to determine the changes in bacterial community composition.

RESULTS

Facial application of HA can reduce the abundance of pathogenic bacteria, such as Cutibacterium and S. aureus, and increase the colonization of beneficial bacteria.

CONCLUSION

This is the first intuitive report to demonstrate the effect of hyaluronic acid on facial microflora in healthy people. Accordingly, sodium hyaluronate was found to have a positive effect on facial skin health.

Small animal models of thermal injury

Burns are a severe form of trauma that account for 1.1 million cases necessitating medical attention and 4500 mortalities annually in the United States alone. Importantly, the initial trauma is succeeded by extensive, prolonged physiological alterations that detrimentally impact multiple organ systems. Given the complexity of post-burn pathophysiology, in vitro experiments are insufficient to model thermal injuries. Therefore, compatible animal burn models are essential for studying burn-related phenomena. In this chapter, we discuss commonly employed small animal burn models and their comparability and applicability to human studies. In particular, we compare post-burn wound healing between the species as well as relevant hypermetabolic and inflammatory characteristics, providing a better understanding of the pros and cons of utilizing a small animal surrogate for human burns. We further provide an overview of the rodent scald burn model methodology as well as a comparison between elderly, aged and young animals, providing a guide for tailoring animal model choice based on the relevant research question.

Host defense peptides as immunomodulators: The other side of the coin

Host defense peptides (HDPs) exhibit a broad range of antimicrobial and immunomodulatory activities. In this sense, both functions are like different sides of the same coin. The direct antimicrobial side was discovered first, and widely studied for the development of anti-infective therapies. In contrast, the immunomodulatory side was recognized later and in the last 20 years the interest in this field has been continuously growing. Different to their antimicrobial activities, the immunomodulatory activities of host defense peptides are more effective in vivo. They offer a great opportunity for new therapeutic applications in the fields of anti-infective therapy, chronic inflammatory diseases treatment, novel vaccine adjuvants development and anticancer immunotherapy. These immune related functions of HDPs includes chemoattraction of leukocytes, modulation of inflammation, enhancement of antigen presentation and polarization of adaptive immune responses. Our attempt with this review is to make a careful evaluation of different aspects of the less explored, but attractive immunomodulatory side of the HDP functional coin.

A proline rich protein from the gingival seal around teeth exhibits antimicrobial properties against Porphyromonas gingivalis

The gingival seal around teeth prevents bacteria from destroying the tooth-supporting tissues and disseminating throughout the body. Porphyromonas gingivalis, a major periodontopathogen, degrades components of the specialized extracellular matrix that mediates attachment of the gingiva to the tooth. Of these, secretory calcium-binding phosphoprotein proline-glutamine rich 1 (SCPPPQ1) protein has a distinctive resistance to degradation, suggesting that it may offer resistance to bacterial attack. In silico analysis of its amino acid sequence was used to explore its molecular characteristics and to predict its two- and three-dimensional structure. SCPPPQ1 exhibits similarities with both proline-rich and cationic antimicrobial proteins, suggesting a putative antimicrobial potential. A combination of imaging approaches showed that incubation with 20 μM of purified SCPPPQ1 decrease bacterial number (p < 0.01). Fluorescence intensity decreased by 70% following a 2 h incubation of Porphyromonas gingivalis with the protein. Electron microscopy analyses revealed that SCPPPQ1 induced bacterial membrane disruption and breaches. While SCPPPQ1 has no effect on mammalian cells, our results suggest that it is bactericidal to Porphyromonas gingivalis, and that this protein, normally present in the gingival seal, may be exploited to maintain a healthy seal and prevent systemic dissemination of bacteria.

Tryptanthrin promotes keratinocyte and fibroblast responses in vitro after infection with Trichophyton benhamiae DSM6916

Exceedingly virulent pathogens and growing antimicrobial resistances require new therapeutic approaches. The zoophilic dermatophyte Trichophyton benhamiae causes highly inflammatory, cutaneous fungal infections. Recently, it could be shown that the plant-derived alkaloid tryptanthrin (TRP) exhibits strong anti-microbial activities against yeasts and dermatophytes. The aim of this study was to analyse the bioactivity of TRP under infectious conditions using an in-vitro dermatophytosis model employing fibroblasts and keratinocytes infected with T. benhamiae DSM6916. Analyses comprised determination of cell viability, effects on the innate immune response including expression and secretion of pro-inflammatory cytokines/chemokines as well as expression of various antimicrobial peptides (AMP), toll-like receptor (TLR) 2 and proliferation marker MKI67. T. benhamiae caused severe inflammation in the cutaneous cell models. TRP almost fully prevented T. benhamiae-derived damage of dermal fibroblasts and substantially reduced it in epidermal keratinocytes. A distinct down-regulation of the expression and secretion of pro-inflammatory cytokines was observed. Further, TRP promoted AMP expression, especially of HBD2 and HBD3, in keratinocytes even without fungal presence. This study provides crucial evidence that TRP is not only a strong antifungal agent but also potentially modulates the innate immune response. This makes it interesting as a natural antimycotic drug for adjuvant treatment and prevention of fungal re-infection.

Innate immune response of human epidermal keratinocytes and dermal fibroblasts to in vitro incubation of Trichophyton benhamiae DSM 6916

BACKGROUND

Superficial cutaneous infection caused by the zoophilic dermatophyte Trichophyton benhamiae is often associated with a highly inflammatory immune response. As non-professional immune cells, epidermal keratinocytes and dermal fibroblasts contribute to the first line of defence by producing pro-inflammatory cytokines and antimicrobial peptides (AMP).

OBJECTIVE

Purpose of this study was to gain a deeper understanding of the pathogenesis and the fungal-host interaction as not much is known about the innate immune response of these cutaneous cells against T. benhamiae.

METHODS

Using a dermatophytosis model of fibroblasts and keratinocytes incubated with T. benhamiae DSM 6916, analyses included determination of cell viability and cytotoxicity, effects on the innate immune response including expression and secretion of pro-inflammatory cytokines/chemokines and expression of AMP, as well as alterations of genes involved in cell adhesion.

RESULTS

Trichophyton benhamiae DSM 6916 infection led to severe cell damage and direct induction of a broad spectrum of pro-inflammatory cytokines and chemokines in both cutaneous cells. Only keratinocytes differentially up-regulated AMP genes expression after T. benhamiae DSM 6916 infection. Expression of AMPs in fibroblasts was not inducible by fungal infection, whereas their absences potentially contributed to a continuous increase in the fungal biomass on fibroblasts, which in turn was reduced in keratinocytes possibly due to the antimicrobial actions of induced AMPs. On mRNA level, T. benhamiae DSM 6916 infection altered cell-cell contact proteins in keratinocytes, indicating that targeting specific cell-cell adhesion proteins might be part of dermatophytes' virulence strategy.

CONCLUSION

This study showed that in addition to immune cells, keratinocytes and fibroblasts could participate in antimicrobial defence against an exemplary infection with T. benhamiae DSM 6916.

The Immunomodulatory and Antimicrobial Properties of the Vertebrate Ribonuclease A Superfamily

The Ribonuclease A Superfamily is composed of cationic peptides that are secreted by immune cells and epithelial tissues. Although their physiological roles are unclear, several members of the vertebrate Ribonuclease A Superfamily demonstrate antimicrobial and immune modulation activities. The objective of this review is to provide an overview of the published literature on the Ribonuclease A Superfamily with an emphasis on each peptide’s regulation, antimicrobial properties, and immunomodulatory functions. As additional insights emerge regarding the mechanisms in which these ribonucleases eradicate invading pathogens and modulate immune function, these ribonucleases may have the potential to be developed as a novel class of therapeutics for some human diseases.

Immune Modulation by Human Secreted RNases at the Extracellular Space

The ribonuclease A superfamily is a vertebrate-specific family of proteins that encompasses eight functional members in humans. The proteins are secreted by diverse innate immune cells, from blood cells to epithelial cells and their levels in our body fluids correlate with infection and inflammation processes. Recent studies ascribe a prominent role to secretory RNases in the extracellular space. Extracellular RNases endowed with immuno-modulatory and antimicrobial properties can participate in a wide variety of host defense tasks, from performing cellular housekeeping to maintaining body fluid sterility. Their expression and secretion are induced in response to a variety of injury stimuli. The secreted proteins can target damaged cells and facilitate their removal from the focus of infection or inflammation. Following tissue damage, RNases can participate in clearing RNA from cellular debris or work as signaling molecules to regulate the host response and contribute to tissue remodeling and repair. We provide here an overall perspective on the current knowledge of human RNases’ biological properties and their role in health and disease. The review also includes a brief description of other vertebrate family members and unrelated extracellular RNases that share common mechanisms of action. A better knowledge of RNase mechanism of actions and an understanding of their physiological roles should facilitate the development of novel therapeutics.

[The epidermal barrier]

The skin acts as an interface between the body and its surrounding environment. The epidermis, the surface layer of the skin, is chiefly responsible for this interactive protective function. The epidermal barrier may be subdivided into three defensive systems: the photoprotective barrier, the immune barrier, and the physical and chemical barrier of the stratum corneum or horny layer. To protect against harmful ultraviolet radiation, the epidermis has absorption factors such as melanin, produced by melanocytes, and urocanic acid, which is a degradation product of filaggrin. The epidermal immune defence system comprises an innate component, which is rapid but non-specific, together with adaptive response, which is systemic and antigen-specific, initiated by Langerhans cells. The stratum corneum, derived from terminal differentiation of epidermal keratinocytes, plays a key role as a physical and chemical permeability barrier. This horny layer is made up of corneocytes, covered with horny envelopes and linked to one another by corneodesmosomes and by extracellular matrix sheets. The epidermal barrier, which is constantly being renewed, is characterised by its extremely great capacity of adaptation to changing conditions in the environment.

Antimicrobial Peptides and Their Therapeutic Potential for Bacterial Skin Infections and Wounds

Alarming data about increasing resistance to conventional antibiotics are reported, while at the same time the development of new antibiotics is stagnating. Skin and soft tissue infections (SSTIs) are mainly caused by the so called ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species) which belong to the most recalcitrant bacteria and are resistant to almost all common antibiotics. S. aureus and P. aeruginosa are the most frequent pathogens isolated from chronic wounds and increasing resistance to topical antibiotics has become a major issue. Therefore, new treatment options are urgently needed. In recent years, research focused on the development of synthetic antimicrobial peptides (AMPs) with lower toxicity and improved activity compared to their endogenous counterparts. AMPs appear to be promising therapeutic options for the treatment of SSTIs and wounds as they show a broad spectrum of antimicrobial activity, low resistance rates and display pivotal immunomodulatory as well as wound healing promoting activities such as induction of cell migration and proliferation and angiogenesis. In this review, we evaluate the potential of AMPs for the treatment of bacterial SSTIs and wounds and provide an overview of the mechanisms of actions of AMPs that contribute to combat skin infections and to improve wound healing. Bacteria growing in biofilms are more resistant to conventional antibiotics than their planktonic counterparts due to limited biofilm penetration and distinct metabolic and physiological functions, and often result in chronification of infections and wounds. Thus, we further discuss the feasibility of AMPs as anti-biofilm agents. Finally, we highlight perspectives for future therapies and which issues remain to bring AMPs successfully to the market.

Cystatin C peptidomimetic derivative with antimicrobial properties as a potential compound against wound infections

A peptidomimetic called A20 (Cystapep 1) structurally based upon the N-terminal fragment of human cystatin C is known to have strong antibacterial properties. A20 is characterized by high activity against several bacterial strains often isolated from infected wounds, including methicillin-resistant S. aureus (MRSA). In this work we wanted to explore the therapeutic potential of A20 in the treatment of wound infections. We examined, cytotoxicity, allergenicity and impact of A20 on the proliferation and viability of human keratinocytes. Furthermore, the previously described antimicrobial action of A20has been confirmed here with reference strains of bacteria and extended by several other species. The A20 was highly active against Gram-positive bacteria with minimal inhibitory (MIC) and minimal bactericidal concentrations (MBC) between 8 and 128μg/mL. A20 did not affect proliferation of primary human keratinocytes in concentrations up to 50μg/mL. At the same time, it did not activate Peripheral Blood Mononuclear Cells (PBMCs), including basophils or neutrophils in vitro. Interestingly A20 was found to display immunomodulatory functions as it influences the production of Th2 cytokines (IL-4 and IL-13) by activated PBMCs. It was also resistant to degradation for at least 48h in human plasma. The results indicate that A20 is effective against the multiantibiotic-resistant bacteria and has a high safety profile, which makes it a promising antimicrobial drug candidate.

Sensing the enemy, containing the threat: cell-autonomous immunity to Chlamydia trachomatis

The bacterium Chlamydia trachomatis is the etiological agent of the most common sexually transmitted infection in North America and Europe. Medical complications resulting from genital C. trachomatis infections arise predominantly in women where the initial infections often remain asymptomatic and thus unrecognized. Untreated asymptomatic infections in women can ascend into the upper genital tract and establish persistence, ultimately resulting in extensive scarring of the reproductive organs, pelvic inflammatory disease, infertility and ectopic pregnancies. Previously resolved C. trachomatis infections fail to provide protective immune memory, and no effective vaccine against C. trachomatis is currently available. Critical determinants of the pathogenesis and immunogenicity of genital C. trachomatis infections are cell-autonomous immune responses. Cell-autonomous immunity describes the ability of an individual host cell to launch intrinsic immune circuits that execute the detection, containment and elimination of cell-invading pathogens. As an obligate intracellular pathogen C. trachomatis is constantly under attack by cell-intrinsic host defenses. Accordingly, C. trachomatis evolved to subvert and co-opt cell-autonomous immune pathways. This review will provide a critical summary of our current understanding of cell-autonomous immunity to C. trachomatis and its role in shaping host resistance, inflammation and adaptive immunity to genital C. trachomatis infections.

Perforin-2 is essential for intracellular defense of parenchymal cells and phagocytes against pathogenic bacteria

Perforin-2 (MPEG1) is a pore-forming, antibacterial protein with broad-spectrum activity. Perforin-2 is expressed constitutively in phagocytes and inducibly in parenchymal, tissue-forming cells. In vitro, Perforin-2 prevents the intracellular replication and proliferation of bacterial pathogens in these cells. Perforin-2 knockout mice are unable to control the systemic dissemination of methicillin-resistant Staphylococcus aureus (MRSA) or Salmonella typhimurium and perish shortly after epicutaneous or orogastric infection respectively. In contrast, Perforin-2-sufficient littermates clear the infection. Perforin-2 is a transmembrane protein of cytosolic vesicles -derived from multiple organelles- that translocate to and fuse with bacterium containing vesicles. Subsequently, Perforin-2 polymerizes and forms large clusters of 100 Å pores in the bacterial surface with Perforin-2 cleavage products present in bacteria. Perforin-2 is also required for the bactericidal activity of reactive oxygen and nitrogen species and hydrolytic enzymes. Perforin-2 constitutes a novel and apparently essential bactericidal effector molecule of the innate immune system.

Purification and modeling amphipathic alpha helical antimicrobial peptides from skin secretions of Euphlyctis cyanophlyctis

Antimicrobial peptides as ancient immune system are found in almost all types of living organisms. Amphibian's skin is an important source of bioactive peptides with strong antibacterial, antiviral, and antitumor properties. They have important role in inducing apoptosis as well as cancer therapy in vitro. In this study, we extracted and purified antimicrobial peptides from skin secretions of Euphlyctis cyanophlyctis and named them brevinin-Eu and cyanophlyctin β. They showed favorable antibacterial properties on both Gram-positive and Gram-negative bacteria with ignorable hemolytic activity of <1.9% and 0.7% at very high concentrations of brevinin-Eu and cyanophlyctin β, respectively. For antibacterial activity and MIC determination, two Gram-positive (Staphylococcus aureus PTCC1431 and B. cereus PTCC1247) and two Gram-negative bacteria (Escherichia coli HP101BA 7601c and Klebsiella pneumoniae PTCC1388) were assayed. MIC values of extracted peptides demonstrated that they can inhibit bacterial growth at very low concentration (17 and 12 μg/mL) for brevinin-Eu and cyanophlyctin β, respectively. Structural prediction suggested that the brevinin-Eu can efficiently bind and destroy bacterial membrane, but cyanophlyctin β uses a diverse mode of action.

Chemical aspects of the preservation and safety control of sea foods

The interest in biopreservation of food has prompted the quest for new natural antimicrobial compounds from different origins.

Host Antimicrobial Peptides in Bacterial Homeostasis and Pathogenesis of Disease

Innate immune responses function as a first line of host defense against the development of bacterial infection, and in some cases to preserve the sterility of privileged sites in the human host. Bacteria that enter these sites must counter host responses for colonization. From the host's perspective, the innate immune system works expeditiously to minimize the bacterial threat before colonization and subsequent dysbiosis. The multifactorial nature of disease further challenges predictions of how each independent variable influences bacterial pathogenesis. From bacterial colonization to infection and through disease, the microenvironments of the host are in constant flux as bacterial and host factors contribute to changes at the host-pathogen interface, with the host attempting to eradicate bacteria and the bacteria fighting to maintain residency. A key component of this innate host response towards bacterial infection is the production of antimicrobial peptides (AMPs). As an early component of the host response, AMPs modulate bacterial load and prevent establishment of infection. Under quiescent conditions, some AMPs are constitutively expressed by the epithelium. Bacterial infection can subsequently induce production of other AMPs in an effort to maintain sterility, or to restrict colonization. As demonstrated in various studies, the absence of a single AMP can influence pathogenesis, highlighting the importance of AMP concentration in maintaining homeostasis. Yet, AMPs can increase bacterial virulence through the co-opting of the peptides or alteration of bacterial virulence gene expression. Further, bacterial factors used to subvert AMPs can modify host microenvironments and alter colonization of the residential flora that principally maintain homeostasis. Thus, the dynamic interplay between host defense peptides and bacterial factors produced to quell peptide activity play a critical role in the progression and outcome of disease.

LL-37 opsonizes and inhibits biofilm formation of Aggregatibacter actinomycetemcomitans at subbactericidal concentrations

Host defense peptides are immediate responders of the innate immunity that express antimicrobial, immunoregulatory, and wound-healing activities. Neutrophils are a major source for oral host defense peptides, and phagocytosis by neutrophils is a major mechanism for bacterial clearance in the gingival tissue. Dysfunction of or reduction in the numbers of neutrophils or deficiency in the LL-37 host defense peptide was each previously linked with proliferation of oral Aggregatibacter actinomycetemcomitans which resulted in an aggressive periodontal disease. Surprisingly, A. actinomycetemcomitans shows resistance to high concentrations of LL-37. In this study, we demonstrated that submicrocidal concentrations of LL-37 inhibit biofilm formation by A. actinomycetemcomitans and act as opsonins and agglutinins that greatly enhance its clearance by neutrophils and macrophages. Improved uptake of A. actinomycetemcomitans by neutrophils was mediated by their opsonization with LL-37. Enhanced phagocytosis and killing of A. actinomycetemcomitans by murine macrophage-like RAW 264.7 cells were dependent on their preagglutination by LL-37. Although A. actinomycetemcomitans is resistant to the bactericidal effect of LL-37, our results offer a rationale for the epidemiological association between LL-37 deficiency and the expansion of oral A. actinomycetemcomitans and indicate a possible therapeutic use of cationic peptides for host defense.

Direct and indirect antimicrobial activities of neuropeptides and their therapeutic potential

As global resistance to conventional antibiotics rises we need to develop new strategies to develop future novel therapeutics. In our quest to design novel anti-infectives and antimicrobials it is of interest to investigate host-pathogen interactions and learn from the complexity of host defense strategies that have evolved over millennia. A myriad of host defense molecules are now known to play a role in protection against human infection. However, the interaction between host and pathogen is recognized to be a multifaceted one, involving countless host proteins, including several families of peptides. The regulation of infection and inflammation by multiple peptide families may represent an evolutionary failsafe in terms of functional degeneracy and emphasizes the significance of host defense in survival. One such family is the neuropeptides (NPs), which are conventionally defined as peptide neurotransmitters but have recently been shown to be pleiotropic molecules that are integral components of the nervous and immune systems. In this review we address the antimicrobial and anti-infective effects of NPs both in vitro and in vivo and discuss their potential therapeutic usefulness in overcoming infectious diseases. With improved understanding of the efficacy of NPs, these molecules could become an important part of our arsenal of weapons in the treatment of infection and inflammation. It is envisaged that targeted therapy approaches that selectively exploit the anti-infective, antimicrobial and immunomodulatory properties of NPs could become useful adjuncts to our current therapeutic modalities.

Two human host defense ribonucleases against mycobacteria, the eosinophil cationic protein (RNase 3) and RNase 7

There is an urgent need to develop new agents against mycobacterial infections, such as tuberculosis and other respiratory tract or skin affections. In this study, we have tested two human antimicrobial RNases against mycobacteria. RNase 3, also called the eosinophil cationic protein, and RNase 7 are two small cationic proteins secreted by innate cells during host defense. Both proteins are induced upon infection displaying a wide range of antipathogen activities. In particular, they are released by leukocytes and epithelial cells, contributing to tissue protection. Here, the two RNases have been proven effective against Mycobacterium vaccae at a low micromolar level. High bactericidal activity correlated with their bacterial membrane depolarization and permeabilization activities. Further analysis on both protein-derived peptides identified for RNase 3 an N-terminus fragment that is even more active than the parental protein. Also, a potent bacterial agglutinating activity was unique to RNase 3 and its derived peptide. The particular biophysical properties of the RNase 3 active peptide are envisaged as a suitable reference for the development of novel antimycobacterial drugs. The results support the contribution of secreted RNases to the host immune response against mycobacteria.

Serine proteolytic pathway activation reveals an expanded ensemble of wound response genes in Drosophila

After injury to the animal epidermis, a variety of genes are transcriptionally activated in nearby cells to regenerate the missing cells and facilitate barrier repair. The range and types of diffusible wound signals that are produced by damaged epidermis and function to activate repair genes during epidermal regeneration remains a subject of very active study in many animals. In Drosophila embryos, we have discovered that serine protease function is locally activated around wound sites, and is also required for localized activation of epidermal repair genes. The serine protease trypsin is sufficient to induce a striking global epidermal wound response without inflicting cell death or compromising the integrity of the epithelial barrier. We developed a trypsin wounding treatment as an amplification tool to more fully understand the changes in the Drosophila transcriptome that occur after epidermal injury. By comparing our array results with similar results on mammalian skin wounding we can see which evolutionarily conserved pathways are activated after epidermal wounding in very diverse animals. Our innovative serine protease-mediated wounding protocol allowed us to identify 8 additional genes that are activated in epidermal cells in the immediate vicinity of puncture wounds, and the functions of many of these genes suggest novel genetic pathways that may control epidermal wound repair. Additionally, our data augments the evidence that clean puncture wounding can mount a powerful innate immune transcriptional response, with different innate immune genes being activated in an interesting variety of ways. These include puncture-induced activation only in epidermal cells in the immediate vicinity of wounds, or in all epidermal cells, or specifically in the fat body, or in multiple tissues.

Antimicrobial peptides (AMPs) from fish epidermis: perspectives for investigative dermatology

Mammalian and fish skin share protective activities against environments that are rich in infectious agents. Fish epidermis is endowed with an extrinsic barrier consisting of a mucus layer and antimicrobial peptides (AMPs). These operate together as a protective chemical shield. As these AMPs are evolutionarily well preserved and also found in higher vertebrate skin (including human epidermis), fish skin offers a unique opportunity to study the origins of innate antimicrobial defense systems. Furthermore, the broad spectrum of fish mucus antimicrobial activities renders piscine AMPs interesting to investigative dermatology, as these may become exploitable for various indications in clinical dermatology. Therefore, this article aims at casting light on fish mucus, the evolutionary relationship between human and fish AMPs, and the latter's antibacterial, antifungal, and even antiviral activities. Moreover, we develop dermatological lessons from, and sketch potential future clinical applications of, fish mucus and piscine AMPs.

The Th17 pathway and inflammatory diseases of the intestines, lungs, and skin

The recent discovery of a new CD4+ T cell subset, Th17, has transformed our understanding of the pathogenetic basis of an increasing number of chronic immune-mediated diseases. Particularly in tissues that interface with the microbial environment-such as the intestinal and respiratory tracts and the skin-where most of the Th17 cells in the body reside, dysregulated immunity to self (or the extended self, the diverse microbiota that normally colonize these tissues) can result in chronic inflammatory disease. In this review, we focus on recent advances in the biology of the Th17 pathway and on genome-wide association studies that implicate this immune pathway in human disease involving these tissues.

The role of moulting in parasite defence

Parasitic infections consist of a succession of steps during which hosts and parasites interact in specific manners. At each step, hosts can use diverse defence mechanisms to counteract the parasite's attempts to invade and exploit them. Of these steps, the penetration of parasites into the host is a key step for a successful infection and the epithelium is the first line of host defence. The shedding of this protective layer (moulting) is a crucial feature in the life cycle of several invertebrate and vertebrate taxa, and is generally considered to make hosts vulnerable to parasites and predators. Here, we used the crustacean Daphnia magna to test whether moulting influences the likelihood of infection by the castrating bacterium Pasteuria ramosa. This parasite is known to attach to the host cuticula before penetrating into its body. We found that the likelihood of successful parasite infection is greatly reduced if the host moults within 12 h after parasite exposure. Thus, moulting is beneficial for the host being exposed to this parasite. We further show that exposure to the parasite does not induce hosts to moult earlier. We discuss the implications of our findings for host and parasite evolution and epidemiology.

Invariant gly residue is important for α-defensin folding, dimerization, and function: a case study of the human neutrophil α-defensin HNP1

The human α-defensins (HNP) are synthesized in vivo as inactive prodefensins, and contain a conserved glycine, Gly(17), which is part of a β-bulge structure. It had previously been shown that the glycine main chain torsion angles are in a D-configuration, and that d-amino acids but not L-alanine could be substituted at that position to yield correctly folded peptides without the help of a prodomain. In this study, the glycine to L-alanine mutant defensin was synthesized in the form of a prodefensin using native chemical ligation. The ligation product folded correctly and yielded an active peptide upon CNBr cleavage. The L-Ala(17)-HNP1 crystal structure depicted a β-bulge identical to wild-type HNP1. However, dimerization was perturbed, causing one monomer to tilt with respect to the other in a dimerization model. Inhibitory activity against the anthrax lethal factor showed a 2-fold reduction relative to wild-type HNP1 as measured by the inhibitory concentration IC(50). Self-association was slightly reduced, as detected by surface plasmon resonance measurements. According to the results of the virtual colony count assay, the antibacterial activity against Escherichia coli, Staphylococcus aureus, and Bacillus cereus exhibited a less than 2-fold reduction in virtual lethal dose values. Prodefensins with two other L-amino acid substitutions, Arg and Phe, at the same position did not fold, indicating that only small side chains are tolerable. These results further elucidate the factors governing the region of the β-bulge structure that includes Gly(17), illuminating why glycine is conserved in all mammalian α-defensins.

Understanding the host inflammatory response to wound infection: an in vivo study of Klebsiella pneumoniae in a rabbit ear wound model

Wound infection development is critically dependent on the complex interactions between bacteria and host. Klebsiella pneumoniae has become an increasingly common wound pathogen, but its natural history within wounds has never been studied. Using a validated, in vivo rabbit ear model, wounds were inoculated with K. pneumoniae at different concentrations (10²-10⁷ colony-forming units) with measurement of viable and nonviable bacterial counts, histological wound-healing parameters, and host inflammatory gene expression at multiple time points postinoculation (48, 96, and 240 hours). Bacteria and wound morphologies were evaluated with scanning electron microscopy. Comparable experiments were performed in ischemic ears to model immune response impairment. All wounds, despite different inoculants, equilibrated to similar bacterial concentrations by 96 hours. With a 10⁶ colony-forming units inoculant, wounds at 240 hours showed decreased bacterial counts (p < 0.01), with a corresponding improvement in healing (p < 0.01) and a decrease in inflammatory response (p < 0.05). In contrast, ischemic wounds revealed impaired inflammatory gene expression (p < 0.05) resulting in higher steady-state bacterial concentrations (p < 0.01), impaired healing (p < 0.05), and biofilm formation on scanning electron microscopy. We conclude that a normal inflammatory response can effectively stabilize and overcome a K. pneumoniae wound infection. An impaired host cannot control this bacterial burden, preventing adequate healing while allowing bacteria to establish a chronic presence. Our novel study quantitatively validates the host immune response as integral to wound infection dynamics.

Activity, expression and genetic variation of canine β-defensin 103: a multifunctional antimicrobial peptide in the skin of domestic dogs

The skin functions as more than a physical barrier to infection. Epithelial cells of the skin can synthesize antimicrobial peptides, including defensins, which exhibit direct antimicrobial activity. Here we characterize the expression pattern, genetic variation and activity of the major β-defensin expressed in canine skin, canine β-defensin 103 (CBD103). The gene encoding CBD103 exhibits two forms of polymorphism: a common 3-basepair deletion allele and a gene copy-number variation. Golden retrievers and Labrador retrievers were the only breeds that encoded the variant allele of CBD103, termed CBD103ΔG23. Both these breeds also exhibited a CBD103 gene copy-number polymorphism that ranged from 2 to 4 gene-copies per diploid genome. Recombinant CBD103 and CBD103ΔG23, as well as the human ortholog human β-defensin 3 (hBD3) and hBD3ΔG23, showed potent and comparable antimicrobial killing against both methicillin-susceptible and methicillin-resistant Staphylococcus pseudintermedius. Skin biopsy specimens from dogs with atopic dermatitis revealed CBD103 expression levels similar to those in healthy controls and comparable at lesional and nonlesional sites. This expression pattern in dogs differs from the previously reported reduced expression of the human ortholog in atopic dermatitis. Overall, the similarities of CBD103 and its human ortholog reported here support the notion that the domestic dog may serve as a valuable model for studying β-defensin biology in the skin.

The antibacterial activity of LL-37 against Treponema denticola is dentilisin protease independent and facilitated by the major outer sheath protein virulence factor

Host defense peptides are innate immune effectors that possess both bactericidal activities and immunomodulatory functions. Deficiency in the human host defense peptide LL-37 has previously been correlated with severe periodontal disease. Treponema denticola is an oral anaerobic spirochete closely associated with the pathogenesis of periodontal disease. The T. denticola major surface protein (MSP), involved in adhesion and cytotoxicity, and the dentilisin serine protease are key virulence factors of this organism. In this study, we examined the interactions between LL-37 and T. denticola. The three T. denticola strains tested were susceptible to LL-37. Dentilisin was found to inactivate LL-37 by cleaving it at the Lys, Phe, Gln, and Val residues. However, dentilisin deletion did not increase the susceptibility of T. denticola to LL-37. Furthermore, dentilisin activity was found to be inhibited by human saliva. In contrast, a deficiency of the T. denticola MSP increased resistance to LL-37. The MSP-deficient mutant bound less fluorescently labeled LL-37 than the wild-type strain. MSP demonstrated specific, dose-dependent LL-37 binding. In conclusion, though capable of LL-37 inactivation, dentilisin does not protect T. denticola from LL-37. Rather, the rapid, MSP-mediated binding of LL-37 to the treponemal outer sheath precedes cleavage by dentilisin. Moreover, in vivo, saliva inhibits dentilisin, thus preventing LL-37 restriction and ensuring its bactericidal and immunoregulatory activities.

Exploring the pharmacological potential of promiscuous host-defense peptides: from natural screenings to biotechnological applications

In the last few years, the number of bacteria with enhanced resistance to conventional antibiotics has dramatically increased. Most of such bacteria belong to regular microbial flora, becoming a real challenge, especially for immune-depressed patients. Since the treatment is sometimes extremely expensive, and in some circumstances completely inefficient for the most severe cases, researchers are still determined to discover novel compounds. Among them, host-defense peptides (HDPs) have been found as the first natural barrier against microorganisms in nearly all living groups. This molecular class has been gaining attention every day for multiple reasons. For decades, it was believed that these defense peptides had been involved only with the permeation of the lipid bilayer in pathogen membranes, their main target. Currently, it is known that these peptides can bind to numerous targets, as well as lipids including proteins and carbohydrates, from the surface to deep within the cell. Moreover, by using in vivo models, it was shown that HDPs could act both in pathogens and cognate hosts, improving immunological functions as well as acting through multiple pathways to control infections. This review focuses on structural and functional properties of HDP peptides and the additional strategies used to select them. Furthermore, strategies to avoid problems in large-scale manufacture by using molecular and biochemical techniques will also be explored. In summary, this review intends to construct a bridge between academic research and pharmaceutical industry, providing novel insights into the utilization of HDPs against resistant bacterial strains that cause infections in humans.