CMAP27, a novel chicken cathelicidin-like antimicrobial protein

Functional characterization of codCath, the mature cathelicidin antimicrobial peptide from Atlantic cod (Gadus morhua)

Cathelicidins are among the best characterized antimicrobial peptides and have been shown to have an important role in mammalian innate immunity. We recently isolated a novel mature cathelicidin peptide (codCath) from Atlantic cod and in the present study we functionally characterized codCath. The peptide demonstrated salt sensitivity with abrogation of activity at physiological salt concentrations. In low ionic strength medium we found activity against marine and non-marine Gram-negative bacteria with an average MIC of 10 μM, weak activity against a Gram-positive bacterium (MIC 80 μM), and pronounced antifungal activity (MIC 2.5 μM). The results suggest the kinetics and mode of action of codCath to be fast killing accompanied by pronounced cell lysis. Extracellular products (ECPs) of three marine bacteria caused breakdown of the peptide into smaller fragments and the cleaved peptide lost its antibacterial activity. Proteolysis of the peptide on the other hand was abolished by prior heat-treatment of the ECPs, suggesting a protease involvement. We observed no cytotoxicity of the peptide in fish cells up to a concentration of 40 μM and the selectivity of activity was confirmed with bacterial and mammalian membrane mimetics. We conclude that the potent broad-spectrum activity of codCath hints at a role of the peptide in cod immune defense.

Improved proteolytic stability of chicken cathelicidin-2 derived peptides by D-amino acid substitutions and cyclization

A truncated version of host defense peptide chicken cathelicidin-2, C1-15, possesses potent, broad spectrum antibacterial activity. A variant of this peptide, F(2,5,12)W, which contains 3 phenylalanine to tryptophan substitutions, possesses improved antibacterial activity and lipopolysaccharide (LPS) neutralizing activity compared to C1-15. In order to improve the proteolytic resistance of both peptides we engineered novel chicken cathelicidin-2 analogs by substitution of l- with D-amino acids and head-to-tail cyclization. Both cyclic and D-amino acid variants showed enhanced stability in human serum compared to C1-15 and F(2,5,12)W. The D-amino acid variants were fully resistant to proteolysis by trypsin and bacterial proteases. Head-to-tail cyclization of peptide F(2,5,12)W resulted in a 3.5-fold lower cytotoxicity toward peripheral blood mononuclear cells. In general, these modifications did not influence antibacterial and LPS neutralization activities. It is concluded that for the development of novel therapeutic compounds based on chicken cathelicidin-2 D-amino acid substitutions and cyclization must be considered. These modifications increase the stability and lower cytotoxicity of the peptides without altering their antimicrobial potency.

A cathelicidin-2-derived peptide effectively impairs Staphylococcus epidermidis biofilms

Staphylococcus epidermidis is a major cause of nosocomial infections owing to its ability to form biofilms on the surface of medical devices. Biofilms are surface-adhered bacterial communities. In mature biofilms these communities are encased in an extracellular matrix composed of bacterial polysaccharides, proteins and DNA. The antibiotic resistance of bacteria present in biofilms can be up to 1000-fold higher compared with the planktonic phenotype. Host defence peptides (HDPs) are considered to be excellent candidates for the development of novel antibiotics. Recently, we demonstrated that a short variant of the HDP chicken cathelicidin-2, peptide F(2,5,12)W, has potent antibacterial and lipopolysaccharide-neutralising activities. This study reports on the antibiofilm activity of peptide F(2,5,12)W against two strains of S. epidermidis, including a multiresistant strain. Peptide F(2,5,12)W potently inhibited the formation of bacterial biofilms in vitro at a low concentration of 2.5 μM, which is below the concentration required to kill or inhibit growth (minimal inhibitory concentration=10 μM). Moreover, peptide F(2,5,12)W also impaired existing S. epidermidis biofilms. A 4-h challenge of pre-grown biofilms with 40 μM F(2,5,12)W reduced the metabolic activity of the wild-type strain biofilm completely and reduced that of the multiresistant strain biofilm by >50%. It is concluded that F(2,5,12)W prevents biofilm formation and impairs mature S. epidermidis biofilms.

Kallikrein-related peptidases: bridges between immune functions and extracellular matrix degradation

Kallikrein-related peptidases (KLKs) constitute a family of 15 highly conserved serine proteases encoded by the largest uninterrupted cluster of protease-encoding genes within the human genome. Recent studies, mostly relying on in vitro proteolysis of recombinant proteins, have suggested that KLK activities are regulated by proteolytic activation cascades that can operate in a tissue-specific manner, such as the semen liquefaction and skin desquamation cascades. The validity of KLK activation cascades in vivo largely remains to be demonstrated. Here, we focus on recent investigations showing that KLKs represent interesting players in the broader field of immunology based on their ability to bridge their inherent ability to degrade the extracellular matrix with major functions of the immune system. More specifically, KLKs assist in the infiltration of immune cells through the skin and the blood brain barrier, whereas they catalyze the generation of antimicrobial peptides by proteolytic activation and further processing of protein precursors. In an attempt to integrate current knowledge, we propose KLK-mediated pathways that are putatively involved in inflammation associated with skin wounding and central nervous system disorders, including multiple sclerosis. Finally, we present evidence of KLK participation in autoimmune diseases and allergies.

Expression of chicken LEAP-2 in the reproductive organs and embryos and in response to Salmonella enterica infection

In recent years host antimicrobial peptides and proteins have been recognised as key mediators of the innate immune response in many vertebrate species, providing the first line of defense against potential pathogens. In chickens a number of cationic antimicrobial peptides have been recently identified. However, although these peptides have been studied extensively in the avian gastrointestinal tract, little is known about their function in the chicken reproductive organs and embryos. Chicken Liver Expressed Antimicrobial Peptide-2 (cLEAP-2) has been previously reported to function in protecting birds against microbial attack. The aim of this study was to investigate the expression of cLEAP-2 gene in the chicken reproductive organs, as well as in chicken embryos during embryonic development, and to determine whether cLEAP-2 expression in the chicken reproductive organs was constitutive or induced as a response to Salmonella enteritidis infection. RNA was extracted from ovary, oviduct, testis and epididymis of sexually mature healthy and Salmonella infected birds, as well as from chicken embryos until day ten of embryonic development. Expression analysis data revealed that cLEAP-2 was expressed in the chicken ovary, testis and epididymis as well as in embryos during early embryonic development. Quantitative real-time PCR analysis revealed that cLEAP-2 expression was constitutive in the chicken epididymis, but was significantly up regulated in the chicken gonads, following Salmonella infection. In addition, expression of cLEAP-2 during chicken embryogenesis appeared to be developmentally regulated. These data provide evidence to suggest a key role of cLEAP-2 in the protection of the chicken reproductive organs and the developing embryos from Salmonella colonization.

Antimicrobial peptides isolated from the blood of farm animals

The development of antimicrobial resistance by pathogenic bacteria has fuelled the search for alternatives to conventional antibiotics. Endogenous antimicrobial peptides have the potential to be used as new antimicrobial substances because they have low minimum inhibitory concentration in vitro, have broad-spectrum activity, neutralise lipopolysaccharides, promote wound healing and have synergistic effects with conventional antibiotics. Farm animals, in particular the blood that is a by-product of the meat and poultry industries, are an abundant, and currently underutilised, source of such antimicrobial peptides. These antimicrobial peptides could be isolated and developed into high-value products such as biopreservatives, topical neutraceutical products and pharmaceuticals. There have been some clinical trials of antimicrobial peptides as pharmaceutical products, but up to now, the trials have shown disappointing results. Further research and development is still needed before such peptides can be commercialised and full advantage taken of this waste product of the meat and poultry industries.

AMPed up immunity: how antimicrobial peptides have multiple roles in immune defense

Antimicrobial peptides (AMPs) are widely expressed and rapidly induced at epithelial surfaces to repel assault from diverse infectious agents including bacteria, viruses, fungi and parasites. Much information suggests that AMPs act by mechanisms that extend beyond their capacity to serve as gene-encoded antibiotics. For example, some AMPs alter the properties of the mammalian membrane or interact with its receptors to influence diverse cellular processes including cytokine release, chemotaxis, antigen presentation, angiogenesis and wound healing. These functions complement their antimicrobial action and favor resolution of infection and repair of damaged epithelia. Opposing this, some microbes have evolved mechanisms to inactivate or avoid AMPs and subsequently become pathogens. Thus, AMPs are multifunctional molecules that have a central role in infection and inflammation.

Interactions between commensal bacteria and the gut-associated immune system of the chicken

The chicken gut-associated lymphoid tissue is made up of a number of tissues and cells that are responsible for generating mucosal immune responses and maintaining intestinal homeostasis. The normal chicken microbiota also contributes to this via the ability to activate both innate defense mechanisms and adaptive immune responses. If left uncontrolled, immune activation in response to the normal microbiota would pose a risk of excessive inflammation and intestinal damage. Therefore, it is important that immune responses to the normal microbiota be under strict regulatory control. Through studies of mammals, it has been established that the mucosal immune system has specialized regulatory and anti-inflammatory mechanisms for eliminating or tolerating the normal microbiota. The mechanisms that exist in the chicken to control host responses to the normal microbiota, although assumed to be similar to that of mammals, have not yet been fully described. This review summarizes what is currently known about the host response to the intestinal microbiota, particularly in the chicken.

Chicken cathelicidin-B1, an antimicrobial guardian at the mucosal M cell gateway

Mucosal epithelial M cells provide an efficient portal of entry for microorganisms. Initially defined by their irregular microvilli and abundant transcytotic channels in the avian bursa of Fabricius, M cells also are found in the lymphoid follicle-associated epithelium of the mammalian appendix, Peyer's patches, and other mucosal surface-lymphoid interfaces. We describe here a previously unrecognized cathelicidin gene in chickens, chCATH-B1, that is expressed exclusively in the epithelium of the bursa of Fabricius. Like the mature peptides of previously identified cathelicidins, the carboxyl-terminal peptide of chCATH-B1 has broad antimicrobial activity against Gram-positive and Gram-negative bacteria. chCATH-B1 expression is restricted to the secretory epithelial cell neighbors of the M cells, whereas its mature peptide is transported to become concentrated on the fibrillar network surrounding basolateral surfaces of the M cells that overlie the bursal lymphoid follicles. We conclude that chCATH-B1 is well placed to serve a protective antimicrobial role at the M cell gateway.

Increased serine protease activity and cathelicidin promotes skin inflammation in rosacea

Acne rosacea is an inflammatory skin disease that affects 3% of the US population over 30 years of age and is characterized by erythema, papulopustules and telangiectasia. The etiology of this disorder is unknown, although symptoms are exacerbated by factors that trigger innate immune responses, such as the release of cathelicidin antimicrobial peptides. Here we show that individuals with rosacea express abnormally high levels of cathelicidin in their facial skin and that the proteolytically processed forms of cathelicidin peptides found in rosacea are different from those present in normal individuals. These cathelicidin peptides are a result of a post-translational processing abnormality associated with an increase in stratum corneum tryptic enzyme (SCTE) in the epidermis. In mice, injection of the cathelicidin peptides found in rosacea, addition of SCTE, and increasing protease activity by targeted deletion of the serine protease inhibitor gene Spink5 each increases inflammation in mouse skin. The role of cathelicidin in enabling SCTE-mediated inflammation is verified in mice with a targeted deletion of Camp, the gene encoding cathelicidin. These findings confirm the role of cathelicidin in skin inflammatory responses and suggest an explanation for the pathogenesis of rosacea by demonstrating that an exacerbated innate immune response can reproduce elements of this disease.

Isolation and characterization of antimicrobial proteins and peptide from chicken liver

Endogenous antimicrobial peptides and proteins are crucial components of the innate immune system and play an essential role in the defense against infection. Antimicrobial activity was detected in the acid extract of livers harvested from healthy adult White Leghorn hens, Gallus gallus. Two antimicrobial proteins and one antimicrobial polypeptide were isolated from the liver extract by cation-exchange and gel filtration chromatography, followed by two-step reverse-phase high-performance liquid chromatography (RP-HPLC). These antimicrobial components were identified as histones H2A and H2B.V, and histone H2B C-terminal fragment using peptide mass fingerprinting and partial sequencing by tandem nanoelectrospray mass spectrometry. The proteins and the peptide identified in the present study, which exhibited antimicrobial activity against both Gram-positive and Gram-negative bacteria, were thermostable and showed salt-resistant activity. The antimicrobial properties of histones and histone fragment in chicken provide further evidence that histones, in addition to their role in nucleosome formation, may play an important role in innate host defense against intracellular or extracellular microbe invasion in a wide range of animal species.

The effects of the BT/TAMUS 2032 cationic peptides on innate immunity and susceptibility of young chickens to extraintestinal Salmonella enterica serovar Enteritidis infection

The BT/TAMUS 2032 (BT) cationic peptides are a group of related cationic peptides produced by a Gram-positive bacterium. Cationic amphiphilic peptides have been found to stimulate or prime the innate immune responses in mammals. The innate immune system of poultry is functionally inefficient during the first week post-hatch enabling pathogens such as Salmonella enterica serovar Enteritidis (SE) to invade and colonize the visceral organs of these immature birds. The objective of the present study was to evaluate the effect of BT as an immunostimulator of the innate immune response of young chickens. BT, provided as a feed additive at three different concentrations (12, 24, or 48 ppm) for 4 days post-hatch, significantly increased protection against SE organ invasion in a concentration-dependent manner. The functional efficiency of heterophils, the avian equivalent to mammalian neutrophils, isolated from chickens fed the BT rations at the three concentrations was significantly up-regulated when compared to heterophils isolated from chickens fed a control starter ration as determined with an array of functional assays. Phagocytosis, oxidative burst, and degranulation were all significantly increased in a concentration-dependent manner in heterophils isolated from chickens fed the BT diets. This is the first report of bacterial cationic peptides inducing the up-regulation of the avian innate immune response and providing protection against extraintestinal Salmonella infections. The significance of these data is that the orally delivered cationic peptides stimulate the innate response at a time of immunologic inefficiency and increased susceptibility to bacterial infections (first week post-hatch). Because of the nonspecific nature of the innate response, we speculate that BT given as a feed additive during the first week post-hatch could provide increased protection against a variety of bacterial pathogens.

The beta-defensin gallinacin-6 is expressed in the chicken digestive tract and has antimicrobial activity against food-borne pathogens

Food-borne pathogens are responsible for most cases of food poisoning in developed countries and are often associated with poultry products, including chicken. Little is known about the role of beta-defensins in the chicken digestive tract and their efficacy. In this study, the expression of chicken beta-defensin gallinacin-6 (Gal-6) and its antimicrobial activity against food-borne pathogens were investigated. Reverse transcription-PCR analysis showed high expression of Gal-6 mRNA in the esophagus and crop, moderate expression in the glandular stomach, and low expression throughout the intestinal tract. Putative transcription factor binding sites for nuclear factor kappa beta, activator protein 1, and nuclear factor interleukin-6 were found in the Gal-6 gene upstream region, which suggests a possible inducible nature of the Gal-6 gene. In colony-counting assays, strong bactericidal and fungicidal activity was observed, including bactericidal activity against food-borne pathogens Campylobacter jejuni, Salmonella enterica serovar Typhimurium, Clostridium perfringens, and Escherichia coli. Treatment with 16 mug/ml synthetic Gal-6 resulted in a 3 log unit reduction in Clostridium perfringens survival within 60 min, indicating fast killing kinetics. Transmission electron microscopy examination of synthetic-Gal-6-treated Clostridium perfringens cells showed dose-dependent changes in morphology after 30 min, including intracellular granulation, cytoplasm retraction, irregular septum formation in dividing cells, and cell lysis. The high expression in the proximal digestive tract and broad antimicrobial activity suggest that chicken beta-defensin gallinacin-6 plays an important role in chicken innate host defense.

Kallikrein-mediated proteolysis regulates the antimicrobial effects of cathelicidins in skin

The presence of cathelicidin antimicrobial peptides provides an important mechanism for prevention of infection against a wide variety of microbial pathogens. The activity of cathelicidin is controlled by enzymatic processing of the proform (hCAP18 in humans) to a mature peptide (LL-37 in human neutrophils). In this study, elements important to the processing of cathelicidin in the skin were examined. Unique cathelicidin peptides distinct from LL-37 were identified in normal skin. Through the use of selective inhibitors, SELDI-TOF-MS, Western blot, and siRNA, the serine proteases stratum corneum tryptic enzyme (SCTE, kallikrein 5) and stratum corneum chymotryptic protease (SCCE, kallikrein 7) were shown to control activation of the human cathelicidin precursor protein hCAP18 and also influence further processing to smaller peptides with alternate biological activity. The importance of this serine protease activity to antimicrobial activity in vivo was illustrated in SPINK5-deficient mice that lack the serine protease inhibitor LEKTI. Epidermal extracts of these animals show a significant increase in antimicrobial activity compared with controls, and immunoabsorption of cathelicidin diminished antimicrobial activity. These observations demonstrate that the balance of proteolytic activity at an epithelial interface will control innate immune defense.

Structure-activity relationships of fowlicidin-1, a cathelicidin antimicrobial peptide in chicken

Cationic antimicrobial peptides are naturally occurring antibiotics that are actively being explored as a new class of anti-infective agents. We recently identified three cathelicidin antimicrobial peptides from chicken, which have potent and broad-spectrum antibacterial activities in vitro (Xiao Y, Cai Y, Bommineni YR, Fernando SC, Prakash O, Gilliland SE & Zhang G (2006) J Biol Chem281, 2858-2867). Here we report that fowlicidin-1 mainly adopts an alpha-helical conformation with a slight kink induced by glycine close to the center, in addition to a short flexible unstructured region near the N terminus. To gain further insight into the structural requirements for function, a series of truncation and substitution mutants of fowlicidin-1 were synthesized and tested separately for their antibacterial, cytolytic and lipopolysaccharide (LPS)-binding activities. The short C-terminal helical segment after the kink, consisting of a stretch of eight amino acids (residues 16-23), was shown to be critically involved in all three functions, suggesting that this region may be required for the peptide to interact with LPS and lipid membranes and to permeabilize both prokaryotic and eukaryotic cells. We also identified a second segment, comprising three amino acids (residues 5-7) in the N-terminal flexible region, that participates in LPS binding and cytotoxicity but is less important in bacterial killing. The fowlicidin-1 analog, with deletion of the second N-terminal segment (residues 5-7), was found to retain substantial antibacterial potency with a significant reduction in cytotoxicity. Such a peptide analog may have considerable potential for development as an anti-infective agent.

Antimicrobial proteins in chicken reproductive system

Antimicrobial activity was detected in the ovary and oviduct tissues of healthy mature White Leghorn hens, Gallus gallus. Two antimicrobial proteins were purified to homogeneity using acid extraction followed by multiple steps of chromatography and the pure proteins were further characterized biochemically. Peptide mixtures obtained after enzymatic digestion of the chicken antimicrobial proteins were analyzed using peptide mass fingerprinting and partial sequencing by tandem nanoelectrospray mass spectrometry and the proteins were identified as histones H1 and H2B. Chicken histone antimicrobial proteins were active against both Gram-positive and Gram-negative bacteria. The abundance of these proteins in the reproductive tissues and their broad-spectrum antimicrobial nature may indicate their defensive role against pathogens during the follicle development in the ovary and egg formation in the oviduct. The discovery of antimicrobial histones in chicken reproductive system provides further evidence that histones may play a role in innate immunity against microorganisms in a wide range of animal species.

Identification and functional characterization of three chicken cathelicidins with potent antimicrobial activity

Cathelicidins comprise a family of antimicrobial peptides sharing a highly conserved cathelin domain. Here we report that the entire chicken genome encodes three cathelicidins, namely fowlicidin-1 to -3, which are densely clustered within a 7.5-kb distance at the proximal end of chromosome 2p. Each fowlicidin gene adopts a fourexon, three-intron structure, typical for a mammalian cathelicidin. Phylogenetic analysis revealed that fowlicidins and a group of distantly related mammalian cathelicidins known as neutrophilic granule proteins are likely to originate from a common ancestral gene prior to the separation of birds from mammals, whereas other classic mammalian cathelicidins may have been duplicated from the primordial gene for neutrophilic granule proteins after mammals and birds are diverged. Similar to ovine cathelicidin SMAP-29, putatively mature fowlicidins displayed potent and salt-independent activities against a range of Gram-negative and Gram-positive bacteria, including antibiotic-resistant strains, with minimum inhibitory concentrations in the range of 0.4-2.0 microm for most strains. Fowlicidin-1 and -2 also showed cytotoxicity, with 50% killing of mammalian erythrocytes or epithelial cells in the range of 6-40 microm. In addition, two fowlicidins demonstrated a strong positive cooperativity in binding lipopolysaccharide (LPS), resulting in nearly complete blockage of LPS-mediated proinflammatory gene expression in RAW264.7 cells. Taken together, fowlicidin-1 and -2 are clearly among the most potent cathelicidins that have been reported. Their broad spectrum and salt-insensitive antibacterial activities, coupled with their potent LPS-neutralizing activity, make fowlicidins excellent candidates for novel antimicrobial and anti-sepsis agents.