Structural and antimicrobial properties of human pre-elafin/trappin-2 and derived peptides against Pseudomonas aeruginosa

Poly-L-Lysine to Fight Antibiotic Resistances of Pseudomonas aeruginosa

Pseudomonas aeruginosa is a major hospital-associated pathogen that can cause severe infections, most notably in patients with cystic fibrosis (CF) or those hospitalized in intensive care units. Given its remarkable ability to resist antibiotics, P. aeruginosa eradication has grown more challenging. Therefore, there is an urgent need to discover and develop new strategies that can counteract P. aeruginosa-resistant strains. Here, we evaluated the efficacy of poly-L-lysine (pLK) in combination with commonly used antibiotics as an alternative treatment option against P. aeruginosa. First, we demonstrated by scanning electron microscopy that pLK alters the integrity of the surface membrane of P. aeruginosa. We also showed using a fluorometry test that this results in an enhanced permeability of the bacteria membrane. Based on these data, we further evaluated the effect of the combinations of pLK with imipenem, ceftazidime, or aztreonam using the broth microdilution method in vitro. We found synergies in terms of bactericidal effects against either sensitive or resistant P. aeruginosa strains, with a reduction in bacterial growth (up to 5-log₁₀ compared to the control). Similarly, these synergistic and bactericidal effects were confirmed ex vivo using a 3D model of human primary bronchial epithelial cells maintained in an air-liquid interface. In conclusion, pLK could be an innovative antipseudomonal molecule, opening its application as an adjuvant antibiotherapy against drug-resistant P. aeruginosa strains.

Elafin and its precursor trappin-2: What is their therapeutic potential for intestinal diseases?

Elafin and its precursor trappin-2 are known for their contribution to the physiological mucosal shield against luminal microbes. Such a contribution seems to be particularly relevant in the gut, where the exposure of host tissues to heavy loads of microbes is constant and contributes to mucosa-associated pathologies. The expression of trappin-2/elafin has been shown to be differentially regulated in diseases associated with gut inflammation. Accumulating evidence has demonstrated the protective effects of trappin-2/elafin in gut intestinal disorders associated with acute or chronic inflammation, or with gluten sensitization disorders. The protective effects of trappin-2/elafin in the gut are discussed in terms of their pleiotropic modes of action: acting as protease inhibitors, transglutaminase substrates, antimicrobial peptides or as a regulator of pro-inflammatory transcription factors. Further, the question of the therapeutic potential of trappin-2/elafin delivery at the intestinal mucosa surface is raised. Whether trappin-2/elafin mucosal delivery should be considered to ensure intestinal tissue repair is also discussed.

A Type Ib Crustin from Deep-Sea Shrimp Possesses Antimicrobial and Immunomodulatory Activity

Crustins are small antimicrobial proteins produced by crustaceans. Of the many reported crustins, very few are from deep sea environments. Crustins are categorized into several types. Recently, the Type I crustin has been further classified into three subtypes, one of which is Type Ib, whose function is unknown. Here, we studied the function of a Type Ib crustin (designated Crus2) identified from a deep-sea crustacean. Crus2 has a whey acidic protein (WAP) domain and a long C-terminal region (named P58). Recombinant Crus2 bound to peptidoglycan (PGN), lipoteichoic acid (LTA), and lipopolysaccharide (LPS), and killed Gram-positive and Gram-negative bacteria by permeabilizing the bacterial cytomembrane. Consistently, Crus2 dramatically attenuated the inflammatory response induced by LPS and LTA. Disruption of the disulfide bonds in the WAP domain abolished the bactericidal ability of Crus2, but had no effect on the bacterial binding ability of Crus2. Deletion of the C-terminal P58 region moderately affected the antimicrobial activity of Crus2 against some bacteria. P58 as a synthesized peptide could bind bacteria and inhibit the bactericidal activity of Crus2. Taken together, these results revealed different roles played by the WAP domain and the P58 region in Type Ib crustin, and provided new insights into the antimicrobial and immunomodulatory functions of crustins.

A Crustin from Hydrothermal Vent Shrimp: Antimicrobial Activity and Mechanism

Crustin is a type of antimicrobial peptide and plays an important role in the innate immunity of arthropods. We report here the identification and characterization of a crustin (named Crus1) from the shrimp Rimicaris sp. inhabiting the deep-sea hydrothermal vent in Manus Basin (Papua New Guinea). Crus1 shares the highest identity (51.76%) with a Type I crustin of Penaeus vannamei and possesses a whey acidic protein (WAP) domain, which contains eight cysteine residues that form the conserved 'four-disulfide core' structure. Recombinant Crus1 (rCrus1) bound to peptidoglycan and lipoteichoic acid, and effectively killed Gram-positive bacteria in a manner that was dependent on pH, temperature, and disulfide linkage. rCrus1 induced membrane leakage and structure damage in the target bacteria, but had no effect on bacterial protoplasts. Serine substitution of each of the 8 Cys residues in the WAP domain did not affect the bacterial binding capacity but completely abolished the bactericidal activity of rCrus1. These results provide new insights into the characteristic and mechanism of the antimicrobial activity of deep sea crustins.

Alarm anti-protease trappin-2 negatively correlates with proinflammatory cytokines in patients with periodontitis

BACKGROUND

Trappin-2 is a potent biologically active serine protease inhibitor with anti-inflammatory properties that has also been characterized as an "alarm anti-protease." Although the importance of trappin-2 in several chronic infections has been demonstrated, its potential involvement in periodontitis remains undefined. This study aims to investigate salivary levels of trappin-2 and interleukin (IL)-1β in periodontally healthy individuals and patients with gingivitis or generalized chronic periodontitis (CP) or aggressive periodontitis (GAgP).

METHODS

Whole unstimulated saliva samples were collected from 80 systemically healthy and non-smoking individuals before full-mouth periodontal examination. Trappin-2 and IL-1β were analyzed by enzyme-linked immunosorbent assay and reported as nanograms per milligram after calibration for total protein levels.

RESULTS

Correlation analysis revealed negative association between trappin-2 and IL-1β levels. Trappin-2 also showed strong negative correlation with clinical periodontal parameters, in contrast to IL-1β, which showed positive correlation. Trappin-2 levels were significantly lower in individuals with CP and GAgP, but not gingivitis, compared with healthy individuals. Reduced salivary concentrations of trappin-2 had high sensitivity and specificity to distinguish health from periodontitis.

CONCLUSIONS

Trappin-2 is abundant in the saliva of individuals with healthy periodontium in line with its role as an "anti-alarm" protease. Decreased salivary trappin-2 and increased IL-1β levels in individuals with periodontitis, compared with healthy individuals, may implicate a potential antiprotease/proinflammatory cytokine imbalance, resulting in impaired host protective capacity.

Antimicrobial peptides secreted by equine mesenchymal stromal cells inhibit the growth of bacteria commonly found in skin wounds

BACKGROUND

The prevalence of chronic skin wounds in humans is high, and treatment is often complicated by the presence of pathogenic bacteria. Therefore, safe and innovative treatments to reduce the bacterial load in cutaneous wounds are needed. Mesenchymal stromal cells (MSC) are known to provide paracrine signals that act on resident skin cells to promote wound healing, but their potential antibacterial activities are not well described. The present study was designed to examine the antibacterial properties of MSC from horses, as this animal model offers a readily translatable model for MSC therapies in humans. Specifically, we aimed to (i) evaluate the in vitro effects of equine MSC on the growth of representative gram-negative and gram-positive bacterial species commonly found in skin wounds and (ii) define the mechanisms by which MSC inhibit bacterial growth.

METHODS

MSC were isolated from the peripheral blood of healthy horses. Gram-negative E. coli and gram-positive S. aureus were cultured in the presence of MSC and MSC conditioned medium (CM), containing all factors secreted by MSC. Bacterial growth was measured by plating bacteria and counting viable colonies or by reading the absorbance of bacterial cultures. Bacterial membrane damage was detected by incorporation of N-phenyl-1-naphthylamine (NPN). Antimicrobial peptide (AMP) gene and protein expression by equine MSC were determined by RT-PCR and Western blot analysis, respectively. Blocking of AMP activity of MSC CM was achieved using AMP-specific antibodies.

RESULTS

We found that equine MSC and MSC CM inhibit the growth of E. coli and S. aureus, and that MSC CM depolarizes the cell membranes of these bacteria. In addition, we found that equine MSC CM contains AMPs, and blocking these AMPs with antibodies reduces the effects of MSC CM on bacteria.

CONCLUSIONS

Our results demonstrate that equine MSC inhibit bacterial growth and secrete factors that compromise the membrane integrity of bacteria commonly found in skin wounds. We also identified four specific AMPs produced by equine MSC. The secretion of AMPs may contribute to the value of MSC as a therapy for cutaneous wounds in both horses and humans.

Complete 1H, 15N and 13C assignment of trappin-2 and 1H assignment of its two domains, elafin and cementoin

Trappin-2 is a serine protease inhibitor with a very narrow inhibitory spectrum and has significant anti-microbial activities. It is a 10 kDa cationic protein composed of two distinct domains. The N-terminal domain (38 residues) named cementoin is known to be intrinsically disordered when it is not linked to the elafin. The C-terminal domain (57 residues), corresponding to elafin, is a cysteine-rich domain stabilized by four disulfide bridges and is characterized by a flat core and a flexible N-terminal part. To our knowledge, there is no structural data available on trappin-2. We report here the complete (1)H, (15)N and (13)C resonance assignment of the recombinant trappin-2 and the (1)H assignments of cementoin and elafin, under the same experimental conditions. This is the first step towards the 3D structure determination of the trappin-2.

Elafin is downregulated during breast and ovarian tumorigenesis but its residual expression predicts recurrence

INTRODUCTION

Elafin is an endogenous serine protease inhibitor. The majority of breast cancer cell lines lack elafin expression compared to human mammary epithelial cells. In this study, we hypothesized that elafin is downregulated during breast and ovarian tumorigenesis.

METHODS

We examined elafin expression by immunohistochemistry (IHC) in specimens of normal breast tissue (n = 24), ductal carcinoma in situ (DCIS) (n = 54), and invasive breast cancer (n = 793). IHC analysis of elafin expression was also performed in normal fallopian tube tissue (n = 20), ovarian cystadenomas (n = 9), borderline ovarian tumors (n = 21), and invasive ovarian carcinomas (n = 216). To understand the significance of elafin in luminal breast cancer cell lines, wild-type or M25G elafin (lacking the protease inhibitory function) were exogenously expressed in MCF-7 and T47D cells.

RESULTS

Elafin expression was downregulated in 24% of DCIS and 83% of invasive breast tumors when compared to elafin expression in the normal mammary epithelium. However, the presence of elafin-positive cells in invasive breast tumors, even at low frequency, correlated with poor recurrence-free survival (RFS), reduced overall survival (OS), and clinicopathological markers of aggressive tumor behavior. Elafin-positive cells were an especially strong and independent prognostic marker of reduced RFS in IHC-defined luminal A-like tumors. Elafin was also downregulated in 33% of ovarian cystadenomas, 43% of borderline ovarian tumors, and 86% of invasive ovarian carcinomas when compared to elafin expression in the normal fallopian tube. In ovarian tumors, elafin-positive cells were correlated with reduced RFS, OS and disease-specific survival (DSS) only in stage I/II patients and not in stage III/IV patients. Notably, exogenous expression of elafin or elafin M25G in the luminal breast cancer cell lines MCF-7 and T47D significantly decreased cell proliferation in a protease inhibitory domain-independent manner.

CONCLUSIONS

Elafin predicts poor outcome in breast and ovarian cancer patients and delineates a subset of endocrine receptor-positive breast cancer patients susceptible to recurrence who could benefit from more aggressive intervention. Our in vitro results suggest that elafin arrests luminal breast cancer cells, perhaps suggesting a role in tumor dormancy.

Elafin Reverses Pulmonary Hypertension via Caveolin-1-Dependent Bone Morphogenetic Protein Signaling

RATIONALE

Pulmonary arterial hypertension is characterized by endothelial dysfunction, impaired bone morphogenetic protein receptor 2 (BMPR2) signaling, and increased elastase activity. Synthetic elastase inhibitors reverse experimental pulmonary hypertension but cause hepatotoxicity in clinical studies. The endogenous elastase inhibitor elafin attenuates hypoxic pulmonary hypertension in mice, but its potential to improve endothelial function and BMPR2 signaling, and to reverse severe experimental pulmonary hypertension or vascular pathology in the human disease was unknown.

OBJECTIVES

To assess elafin-mediated regression of pulmonary vascular pathology in rats and in lung explants from patients with pulmonary hypertension. To determine if elafin amplifies BMPR2 signaling in pulmonary artery endothelial cells and to elucidate the underlying mechanism.

METHODS

Rats with pulmonary hypertension induced by vascular endothelial growth factor receptor blockade and hypoxia (Sugen/hypoxia) as well as lung organ cultures from patients with pulmonary hypertension were used to assess elafin-mediated reversibility of pulmonary vascular disease. Pulmonary arterial endothelial cells from patients and control subjects were used to determine the efficacy and mechanism of elafin-mediated BMPR2 signaling.

MEASUREMENTS AND MAIN RESULTS

In Sugen/hypoxia rats, elafin reduced elastase activity and reversed pulmonary hypertension, judged by regression of right ventricular systolic pressure and hypertrophy and pulmonary artery occlusive changes. Elafin improved endothelial function by increasing apelin, a BMPR2 target. Elafin induced apoptosis in human pulmonary arterial smooth muscle cells and decreased neointimal lesions in lung organ culture. In normal and patient pulmonary artery endothelial cells, elafin promoted angiogenesis by increasing pSMAD-dependent and -independent BMPR2 signaling. This was linked mechanistically to augmented interaction of BMPR2 with caveolin-1 via elafin-mediated stabilization of endothelial surface caveolin-1.

CONCLUSIONS

Elafin reverses obliterative changes in pulmonary arteries via elastase inhibition and caveolin-1-dependent amplification of BMPR2 signaling.

The Role of Serine Proteases and Antiproteases in the Cystic Fibrosis Lung

Cystic fibrosis (CF) lung disease is an inherited condition with an incidence rate of approximately 1 in 2500 new born babies. CF is characterized as chronic infection of the lung which leads to inflammation of the airway. Sputum from CF patients contains elevated levels of neutrophils and subsequently elevated levels of neutrophil serine proteases. In a healthy individual these proteases aid in the phagocytic process by degrading microbial peptides and are kept in homeostatic balance by cognate antiproteases. Due to the heavy neutrophil burden associated with CF the high concentration of neutrophil derived proteases overwhelms cognate antiproteases. The general effects of this protease/antiprotease imbalance are impaired mucus clearance, increased and self-perpetuating inflammation, and impaired immune responses and tissue. To restore this balance antiproteases have been suggested as potential therapeutics or therapeutic targets. As such a number of both endogenous and synthetic antiproteases have been trialed with mixed success as therapeutics for CF lung disease.

Functional characterization of polymorphisms in the peptidase inhibitor 3 (elafin) gene and validation of their contribution to risk of acute respiratory distress syndrome

Elafin (peptidase inhibitor 3 [PI3]) and its biologically active precursor, pre-elafin, are neutrophil serine proteinase inhibitors with an important role in preventing excessive tissue injury during inflammatory events. Recently, we reported an association between single-nucleotide polymorphism (SNP) rs2664581 in the PI3 gene, increased risk of acute respiratory distress syndrome (ARDS) and pre-elafin circulating levels. This study aims to validate the legitimacy of this association by using a cohort of patients who met the criteria for systemic inflammatory response syndrome and were at risk of developing ARDS (n = 840). A comprehensive functional study of SNPs in PI3 gene was also performed. Luciferase assays and electrophoretic mobility shift assays were conducted to determine the functional relevance of promoter region variants. The effect of the coding SNP rs2664581 on the neutrophil elastase inhibitory activity and transglutaminase binding properties of pre-elafin was also investigated. The variant allele of rs2664581 (C) was significantly associated with increased ARDS risk, mainly among subjects with sepsis (odds ratio = 1.44; 95% confidence interval = 1.04-1.99; P = 0.0276, adjusted by age, sex, and Acute Physiology and Chronic Health Evaluation III). Pre-elafin recombinant protein carrying the amino acid change associated with rs2664581 (Thr34Pro, mutant protein [MT]) had greater capacity to undergo transglutaminase-mediated cross-linking to immobilized fibronectin than wild-type protein in vitro (P < 0.003). No differences were observed in the neutrophil elastase inhibitory activities of wild-type versus MT proteins. In addition, the risk allele-promoter construct had significantly lower cytokine-induced transcriptional activity. Electrophoretic mobility shift assay results indicated a differential binding of nuclear proteins to the G and A alleles of SNP -338G > A. Our results confirm the association between SNP rs2664581 and enhanced risk of ARDS, further supporting the role of PI3 in ARDS development. SNPs in the PI3 locus may act synergistically by regulating PI3 gene expression and pre-elafin biological functions.

Anti-HIV-1 activity of elafin depends on its nuclear localization and altered innate immune activation in female genital epithelial cells

Elafin (E) and its precursor trappin-2 (Tr) are alarm antiproteases with antimicrobial and immunomodulatory activities. Tr and E (Tr/E) have been associated with HIV-1 resistance. We recently showed that Tr/E reduced IL-8 secretion and NF-κB activation in response to a mimic of viral dsRNA and contributed to anti-HIV activity of cervicovaginal lavage fluid (CVL) of HIV-resistant (HIV-R) commercial sex workers (CSWs). Additionally, Tr, and more so E, were found to inhibit attachment/entry and transcytosis of HIV-1 in human endometrial HEC-1A cells, acting through virus or cells. Given their immunomodulatory activity, we hypothesized that Tr/E could exert anti-HIV-1 activity at multiple levels. Here, using tagged and untagged Tr/E proteins, we comparatively evaluated their protease inhibitory, anti-HIV-1, and immunomodulatory activities, and cellular distribution. E appeared to function as an autocrine/paracrine factor in HEC-1A cells, and anti-HIV-1 activity of E depended on its unmodified N-terminus and altered cellular innate activation, but not its antiprotease activity. Specifically, exogenously added N-terminus-unmodified E was able to enter the nucleus and to reduce viral attachment/entry and transcytosis, preferentially affecting R5-HIV-1(ADA), but not X4-HIV-1(IIIB). Further, anti-HIV-1 activity of E was associated with significantly decreased HIV-1-triggered IL-8 release, attenuated NF-κB/p65 nuclear translocation, and significantly modulated mRNA expression of innate sensors TLR3 and RIG-I in HEC-1A cells. Most importantly, we found that elevated Tr/E in CVLs of HIV-R CSWs were associated with lower mRNA levels of TLRs 2, 3, 4 and RIG-I in the genital ECs from this cohort, suggesting a link between Tr/E, HIV-1 resistance and modulated innate viral recognition in the female genital mucosa. Collectively, our data indicate that unmodified N-terminus is critical for intranuclear localization and anti-HIV-1 activity of E. We also propose that E-mediated altered cellular innate activation most likely contributes to the HIV-R phenotype of these subjects.

Trappin-2/elafin modulate innate immune responses of human endometrial epithelial cells to PolyI:C

Background

Upon viral recognition, innate and adaptive antiviral immune responses are initiated by genital epithelial cells (ECs) to eradicate or contain viral infection. Such responses, however, are often accompanied by inflammation that contributes to acquisition and progression of sexually transmitted infections (STIs). Hence, interventions/factors enhancing antiviral protection while reducing inflammation may prove beneficial in controlling the spread of STIs. Serine antiprotease trappin-2 (Tr) and its cleaved form, elafin (E), are alarm antimicrobials secreted by multiple cells, including genital epithelia.

Methodology and Principal Findings

We investigated whether and how each Tr and E (Tr/E) contribute to antiviral defenses against a synthetic mimic of viral dsRNA, polyinosine-polycytidylic acid (polyI∶C) and vesicular stomatitis virus. We show that delivery of a replication-deficient adenovector expressing Tr gene (Ad/Tr) to human endometrial epithelial cells, HEC-1A, resulted in secretion of functional Tr, whereas both Tr/E were detected in response to polyI∶C. Moreover, Tr/E were found to significantly reduce viral replication by either acting directly on virus or through enhancing polyI∶C-driven antiviral protection. The latter was associated with reduced levels of pro-inflammatory factors IL-8, IL-6, TNFα, lowered expression of RIG-I, MDA5 and attenuated NF-κB activation. Interestingly, enhanced polyI∶C-driven antiviral protection of HEC-Ad/Tr cells was partially mediated through IRF3 activation, but not associated with higher induction of IFNβ, suggesting multiple antiviral mechanisms of Tr/E and the involvement of alternative factors or pathways.

Conclusions and Significance

This is the first evidence of both Tr/E altering viral binding/entry, innate recognition and mounting of antiviral and inflammatory responses in genital ECs that could have significant implications for homeostasis of the female genital tract.

Coleopteran antimicrobial peptides: prospects for clinical applications

Antimicrobial peptides (AMPs) are activated in response to septic injury and have important roles in vertebrate and invertebrate immune systems. AMPs act directly against pathogens and have both wound healing and antitumor activities. Although coleopterans comprise the largest and most diverse order of eukaryotes and occupy an earlier branch than Drosophila in the holometabolous lineage of insects, their immune system has not been studied extensively. Initial research reports, however, indicate that coleopterans possess unique immune response mechanisms, and studies of these novel mechanisms may help to further elucidate innate immunity. Recently, the complete genome sequence of Tribolium was published, boosting research on coleopteran immunity and leading to the identification of Tribolium AMPs that are shared by Drosophila and mammals, as well as other AMPs that are unique. AMPs have potential applicability in the development of vaccines. Here, we review coleopteran AMPs, their potential impact on clinical medicine, and the molecular basis of immune defense.