Induction of the antimicrobial peptide CRAMP in the blood-brain barrier and meninges after meningococcal infection

Cerebrovascular Endothelial Dysfunction: Role of BACE1

Dysfunctional endothelium is increasingly recognized as a mechanistic link between cardiovascular risk factors and dementia, including Alzheimer disease. BACE1 (β-site amyloid-β precursor protein-cleaving enzyme 1) is responsible for β-processing of APP (amyloid-β precursor protein), the first step in the production of Aβ (amyloid-β) peptides, major culprits in the pathogenesis of Alzheimer disease. Under pathological conditions, excessive activation of BACE1 exerts detrimental effects on endothelial function by Aβ-dependent and Aβ-independent mechanisms. High local concentration of Aβ in the brain blood vessels is responsible for the loss of key vascular protective functions of endothelial cells. More recent studies recognized significant contribution of Aβ-independent proteolytic activity of endothelial BACE1 to the pathogenesis of endothelial dysfunction. This review critically evaluates existing evidence supporting the concept that excessive activation of BACE1 expressed in the cerebrovascular endothelium impairs key homeostatic functions of the brain blood vessels. This concept has important therapeutic implications. Indeed, improved understanding of the mechanisms of endothelial dysfunction may help in efforts to develop new approaches to the protection and preservation of healthy cerebrovascular function.

Role of antimicrobial peptide cathelicidin in thrombosis and thromboinflammation

Thrombosis is a frequent cause of cardiovascular mortality and hospitalization. Current antithrombotic strategies, however, target both thrombosis and physiological hemostasis and thereby increase bleeding risk. In recent years the pathophysiological understanding of thrombus formation has significantly advanced and inflammation has become a crucial element. Neutrophils as most frequent immune cells in the blood and their released mediators play a key role herein. Neutrophil-derived cathelicidin next to its strong antimicrobial properties has also shown to modulates thrombosis and thus presents a potential therapeutic target. In this article we review direct and indirect (immune- and endothelial cell-mediated) effects of cathelicidin on platelets and the coagulation system. Further we discuss its implications for large vessel thrombosis and consecutive thromboinflammation as well as immunothrombosis in sepsis and COVID-19 and give an outlook for potential therapeutic prospects.

Cathelicidin promotes liver repair after acetaminophen-induced liver injury in mice

Background & Aims

Acetaminophen (APAP)-induced acute liver injury (AILI) is a leading cause of acute liver failure (ALF). N-acetylcysteine (NAC) is only effective within 24 h after APAP intoxication, raising an urgent need for alternative approaches to treat this disease. This study aimed to test whether cathelicidin (Camp), which is a protective factor in chronic liver diseases, protects mice against APAP-induced liver injury and ALF.

Methods

A clinically relevant AILI model and an APAP-induced ALF model were generated in mice. Genetic and pharmacological approaches were used to interfere with the levels of cathelicidin in vivo.

Results

An increase in hepatic pro-CRAMP/CRAMP (the precursor and mature forms of mouse cathelicidin) was observed in APAP-intoxicated mice. Upregulated cathelicidin was derived from liver-infiltrating neutrophils. Compared with wild-type littermates, Camp knockout had no effect on hepatic injury but dampened hepatic repair in AILI and reduced survival in APAP-induced ALF. CRAMP administration reversed impaired liver recovery observed in APAP-challenged Camp knockout mice. Delayed CRAMP, CRAMP(1-39) (the extended form of CRAMP), or LL-37 (the mature form of human cathelicidin) treatment exhibited a therapeutic benefit for AILI. Co-treatment of cathelicidin and NAC in AILI displayed a stronger hepatoprotective effect than NAC alone. A similar additive effect of CRAMP(1-39)/LL-37 and NAC was observed in APAP-induced ALF. The pro-reparative role of cathelicidin in the APAP-damaged liver was attributed to an accelerated resolution of inflammation at the onset of liver repair, possibly through enhanced neutrophil phagocytosis of necrotic cell debris in an autocrine manner.

Conclusions

Cathelicidin reduces APAP-induced liver injury and ALF in mice by promoting liver recovery via facilitating inflammation resolution, suggesting a therapeutic potential for late-presenting patients with AILI with or without ALF.

Impact and implications

Acetaminophen-induced acute liver injury is a leading cause of acute liver failure. The efficacy of N-acetylcysteine, the only clinically approved drug against acetaminophen-induced acute liver injury, is significantly reduced for late-presenting patients. We found that cathelicidin exhibits a great therapeutic potential in mice with acetaminophen-induced liver injury or acute liver failure, which makes up for the limitation of N-acetylcysteine therapy by specifically promoting liver repair after acetaminophen intoxication. The pro-reparative role of cathelicidin, as a key effector molecule of neutrophils, in the APAP-injured liver is attributed to an accelerated resolution of inflammation at the onset of liver repair, possibly through enhanced phagocytic function of neutrophils in an autocrine manner.

The antimicrobial peptide cathelicidin drives development of experimental autoimmune encephalomyelitis in mice by affecting Th17 differentiation

Multiple sclerosis (MS) is a highly prevalent demyelinating autoimmune condition; the mechanisms regulating its severity and progression are unclear. The IL-17-producing Th17 subset of T cells has been widely implicated in MS and in the mouse model, experimental autoimmune encephalomyelitis (EAE). However, the differentiation and regulation of Th17 cells during EAE remain incompletely understood. Although evidence is mounting that the antimicrobial peptide cathelicidin profoundly affects early T cell differentiation, no studies have looked at its role in longer-term T cell responses. Now, we report that cathelicidin drives severe EAE disease. It is released from neutrophils, microglia, and endothelial cells throughout disease; its interaction with T cells potentiates Th17 differentiation in lymph nodes and Th17 to exTh17 plasticity and IFN-γ production in the spinal cord. As a consequence, mice lacking cathelicidin are protected from severe EAE. In addition, we show that cathelicidin is produced by the same cell types in the active brain lesions in human MS disease. We propose that cathelicidin exposure results in highly activated, cytokine-producing T cells, which drive autoimmunity; this is a mechanism through which neutrophils amplify inflammation in the central nervous system.

Expression of antimicrobial host defence peptides in the central nervous system during health and disease

Antimicrobial host defence peptides (HDP) are critical for the first line of defence against bacterial, viral, and fungal pathogens. Over the past decade we have become more aware that, in addition to their antimicrobial roles, they also possess the potent immunomodulatory capacity. This includes chemoattracting immune cells, activating dendritic cells and macrophages, and altering T-cell differentiation. Most examinations of their immunomodulatory roles have focused on tissues in which they are very abundant, such as the intestine and the inflamed skin. However, HDP have now been detected in the brain and the spinal cord during a number of conditions. We propose that their presence in the central nervous system (CNS) during homeostasis, infection, and neurodegenerative disease has the potential to contribute to immunosurveillance, alter host responses and skew developing immunity. Here, we review the evidence for HDP expression and function in the CNS in health and disease. We describe how a wide range of HDP are expressed in the CNS of humans, rodents, birds, and fish, suggesting a conserved role in protecting the brain from pathogens, with evidence of production by resident CNS cells. We highlight differences in methodology used and how this may have resulted in the immunomodulatory roles of HDP being overlooked. Finally, we discuss what HDP expression may mean for CNS immune responses.

The Role of Chronic Infection in Alzheimer's Disease: Instigators, Co-conspirators, or Bystanders?

PURPOSE OF REVIEW

Herein, we provide a critical review of the clinical and translational research examining the relationship between viral and bacterial pathogens and Alzheimer's disease. In addition, we provide an overview of the biological pathways through which chronic infection may contribute to Alzheimer's disease.

RECENT FINDINGS

Dementia due to Alzheimer's disease is a leading cause of disability among older adults in developed countries, yet knowledge of the causative factors that promote Alzheimer's disease pathogenesis remains incomplete. Over the past several decades, numerous studies have demonstrated an association of chronic viral and bacterial infection with Alzheimer's disease. Implicated infectious agents include numerous herpesviruses (HSV-1, HHV-6, HHV-7) and various gastric, enteric, and oral bacterial species, as well as Chlamydia pneumonia and multiple spirochetes.

SUMMARY

Evidence supports the association between multiple pathogens and Alzheimer's disease risk. Whether these pathogens play a causal role in Alzheimer's pathophysiology remains an open question. We propose that the host immune response to active or latent infection in the periphery or in the brain triggers or accelerates the Alzheimer's disease processes, including the accumulation of amyloid-ß and pathogenic tau, and neuroinflammation. While recent research suggests that such theories are plausible, additional longitudinal studies linking microorganisms to Aß and phospho-tau development, neuroinflammation, and clinically defined Alzheimer's dementia are needed.

Targeting the Achilles Heel of FtsZ: The Interdomain Cleft

Widespread antimicrobial resistance among bacterial pathogens is a serious threat to public health. Thus, identification of new targets and development of new antibacterial agents are urgently needed. Although cell division is a major driver of bacterial colonization and pathogenesis, its targeting with antibacterial compounds is still in its infancy. FtsZ, a bacterial cytoskeletal homolog of eukaryotic tubulin, plays a highly conserved and foundational role in cell division and has been the primary focus of research on small molecule cell division inhibitors. FtsZ contains two drug-binding pockets: the GTP binding site situated at the interface between polymeric subunits, and the inter-domain cleft (IDC), located between the N-terminal and C-terminal segments of the core globular domain of FtsZ. The majority of anti-FtsZ molecules bind to the IDC. Compounds that bind instead to the GTP binding site are much less useful as potential antimicrobial therapeutics because they are often cytotoxic to mammalian cells, due to the high sequence similarity between the GTP binding sites of FtsZ and tubulin. Fortunately, the IDC has much less sequence and structural similarity with tubulin, making it a better potential target for drugs that are less toxic to humans. Over the last decade, a large number of natural and synthetic IDC inhibitors have been identified. Here we outline the molecular structure of IDC in detail and discuss how it has become a crucial target for broad spectrum and species-specific antibacterial agents. We also outline the drugs that bind to the IDC and their modes of action.

The Dual Role of Antimicrobial Peptides in Autoimmunity

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

In vivo transcriptomes of Streptococcus suis reveal genes required for niche-specific adaptation and pathogenesis

Streptococcus suis is a Gram-positive bacterium and a zoonotic pathogen residing in the nasopharynx or the gastrointestinal tract of pigs with a potential of causing life-threatening invasive disease. It is endemic in the porcine production industry worldwide, and it is also an emerging human pathogen. After invasion, the pathogen adapts to cause bacteremia and disseminates to different organs including the brain. To gain insights in this process, we infected piglets with a highly virulent strain of S. suis, and bacterial transcriptomes were obtained from blood and different organs (brain, joints, and heart) when animals had severe clinical symptoms of infection. Microarrays were used to determine the genome-wide transcriptional profile at different infection sites and during growth in standard growth medium in vitro. We observed differential expression of around 30% of the Open Reading Frames (ORFs) and infection-site specific patterns of gene expression. Genes with major changes in expression were involved in transcriptional regulation, metabolism, nutrient acquisition, stress defenses, and virulence, amongst others, and results were confirmed for a subset of selected genes using RT-qPCR. Mutants were generated in two selected genes, and the encoded proteins, i.e., NADH oxidase and MetQ, were shown to be important virulence factors in coinfection experiments and in vitro assays. The knowledge derived from this study regarding S. suis gene expression in vivo and identification of virulence factors is important for the development of novel diagnostic and therapeutic strategies to control S. suis disease.

Comparing Cathelicidin Susceptibility of the Meningitis Pathogens Streptococcus suis and Escherichia coli in Culture Medium in Contrast to Porcine or Human Cerebrospinal Fluid

Host defense peptides or antimicrobial peptides (AMPs), e.g., cathelicidins, have recently been discussed as a potential new treatment option against bacterial infections. To test the efficacy of AMPs, standardized methods that closely mimic the physiological conditions at the site of infection are still needed. The aim of our study was to test the meningitis-causing bacteria Streptococcus suis and Escherichia coli for their susceptibility to cathelicidins in culture medium versus cerebrospinal fluid (CSF). Susceptibility testing was performed in analogy to the broth microdilution method described by the Clinical and Laboratory Standard Institute (CLSI) to determine minimum inhibitory concentrations (MICs) of antimicrobial agents. MICs were determined using cation-adjusted Mueller-Hinton broth (CA-MHB), lysogeny broth (LB), Roswell Park Memorial Institute medium (RPMI) or Dulbecco's Modified Eagle's Medium (DMEM) (the latter two supplemented with 5% CA-MHB or blood) and compared with MICs obtained in porcine or human CSF. Our data showed that MICs obtained in CA-MHB as recommended by CLSI do not reflect the MICs obtained in the physiological body fluid CSF. However, the MICs of clinical isolates of S. suis tested in RPMI medium supplemented with CA-MHB, were similar to those of the same strains tested in CSF. In contrast, the MICs in the human CSF for the tested E. coli K1 strain were higher compared to the RPMI medium and showed even higher values than in CA-MHB. This highlights the need for susceptibility testing of AMPs in a medium that closely mimics the clinically relevant conditions.

FtsZ inhibitors as a new genera of antibacterial agents

The continuous emergence and rapid spread of a multidrug-resistant strain of bacterial pathogens have demanded the discovery and development of new antibacterial agents. A highly conserved prokaryotic cell division protein FtsZ is considered as a promising target by inhibiting bacterial cytokinesis. Inhibition of FtsZ assembly restrains the cell-division complex known as divisome, which results in filamentation, leading to lysis of the cell. This review focuses on details relating to the structure, function, and influence of FtsZ in bacterial cytokinesis. It also summarizes on the recent perspective of the known natural and synthetic inhibitors directly acting on FtsZ protein, with prominent antibacterial activities. A series of benzamides, trisubstituted benzimidazoles, isoquinolene, guanine nucleotides, zantrins, carbonylpyridine, 4 and 5-Substituted 1-phenyl naphthalenes, sulindac, vanillin analogues were studied here and recognized as FtsZ inhibitors that act either by disturbing FtsZ polymerization and/or GTPase activity. Doxorubicin, from a U.S. FDA, approved drug library displayed strong interaction with FtsZ. Several of the molecules discussed, include the prodrugs of benzamide based compound PC190723 (TXA-709 and TXA707). These molecules have exhibited the most prominent antibacterial activity against several strains of Staphylococcus aureus with minimal toxicity and good pharmacokinetics properties. The evidence of research reports and patent documentations on FtsZ protein has disclosed distinct support in the field of antibacterial drug discovery. The pressing need and interest shall facilitate the discovery of novel clinical molecules targeting FtsZ in the upcoming days.

Cathelicidins prime platelets to mediate arterial thrombosis and tissue inflammation

Leukocyte-released antimicrobial peptides contribute to pathogen elimination and activation of the immune system. Their role in thrombosis is incompletely understood. Here we show that the cathelicidin LL-37 is abundant in thrombi from patients with acute myocardial infarction. Its mouse homologue, CRAMP, is present in mouse arterial thrombi following vascular injury, and derives mainly from circulating neutrophils. Absence of hematopoietic CRAMP in bone marrow chimeric mice reduces platelet recruitment and thrombus formation. Both LL-37 and CRAMP induce platelet activation in vitro by involving glycoprotein VI receptor with downstream signaling through protein tyrosine kinases Src/Syk and phospholipase C. In addition to acute thrombosis, LL-37/CRAMP-dependent platelet activation fosters platelet–neutrophil interactions in other inflammatory conditions by modulating the recruitment and extravasation of neutrophils into tissues. Absence of CRAMP abrogates acid-induced lung injury, a mouse pneumonia model that is dependent on platelet–neutrophil interactions. We suggest that LL-37/CRAMP represents an important mediator of platelet activation and thrombo-inflammation.

Cathelicidins are antimicrobial peptides that eliminate pathogens and contribute to the innate immune response. Here the authors show that neutrophil-derived LL-37/CRAMP induces platelet activation and promotes arterial thrombosis and thrombo-inflammation.

Atopic Dermatitis-like Graft-versus-host Disease and Lichen Planus-like Graft-versus-host Disease: Alterations in Skin Barrier Function and Related Molecules

Background:

Graft-versus-host disease (GVHD) is a common complication of hematopoietic stem cell transplantation. Skin barrier disruption could induce thymic stromal lymphopoietin (TSLP) expression, and the expression of TSLP was increased in lesions of atopic dermatitis (AD)-like GVHD and lichen planus (LP)-like GVHD. This study attempted to investigate the skin barrier function of AD-like GVHD and LP-like GVHD and possible mechanisms.

Methods:

Eighteen AD-like GVHD patients, 12 LP-like GVHD patients, and 14 healthy volunteers were enrolled in this study. Skin biopsy was done in five AD-like GVHD patients, eight LP-like GVHD patients, and eight healthy volunteers. The intensity of pruritus was assessed by visual analog scale itch score and detailed pruritus score. Transepidermal water loss (TEWL) was measured using Tewameter^® TM 300. Immunohistochemistry was used to observe the expression of loricrin, involucrin, LL37, and human β-defensins 2 (hBD2) in skin lesions. Western blot analysis was used for analyzing the protein levels of loricrin and involucrin in skin lesions. Real-time polymerase chain reaction was performed to assess the mRNA levels of LL37 and hBD2 in skin lesions.

Results:

Pruritus score was higher in patients with AD-like GVHD (11.33 ± 5.35) than that of patients with LP-like GVHD (2.58 ± 3.09, P < 0.001). Compared with healthy controls (HCs, 4.52 ± 1.24 g·m⁻²·h⁻¹), TEWL was increased in AD-like GVHD (26.72 ± 9.02 g·m⁻²·h⁻¹, P < 0.001) and LP-like GVHD patients (18.78 ± 4.57 g·m⁻²·h⁻¹, P < 0.001), and expressions of loricrin and involucrin were also increased in skin lesions of AD-like GVHD and LP-like GVHD patients (all P < 0.05). LL37 mRNA expression was decreased in lesions of AD-like GVHD and LP-like GVHD patients (P = 0.005 and P = 0.008, vs. HCs, respectively). hBD2 mRNA expression was increased in skin lesions of AD-like GVHD and LP-like GVHD patients (P = 0.002 and P < 0.001, vs. HCs, respectively).

Conclusions:

Skin barrier dysfunction is present in AD-like GVHD and LP-like GVHD. The immunoreactions, but not the congenital defect, are considered to be the primary cause of skin barrier impairment in AD-like GVHD and LP-like GVHD.

Amyloid-β peptide protects against microbial infection in mouse and worm models of Alzheimer's disease

The amyloid-β peptide (Aβ) is a key protein in Alzheimer's disease (AD) pathology. We previously reported in vitro evidence suggesting that Aβ is an antimicrobial peptide. We present in vivo data showing that Aβ expression protects against fungal and bacterial infections in mouse, nematode, and cell culture models of AD. We show that Aβ oligomerization, a behavior traditionally viewed as intrinsically pathological, may be necessary for the antimicrobial activities of the peptide. Collectively, our data are consistent with a model in which soluble Aβ oligomers first bind to microbial cell wall carbohydrates via a heparin-binding domain. Developing protofibrils inhibited pathogen adhesion to host cells. Propagating β-amyloid fibrils mediate agglutination and eventual entrapment of unatttached microbes. Consistent with our model, Salmonella Typhimurium bacterial infection of the brains of transgenic 5XFAD mice resulted in rapid seeding and accelerated β-amyloid deposition, which closely colocalized with the invading bacteria. Our findings raise the intriguing possibility that β-amyloid may play a protective role in innate immunity and infectious or sterile inflammatory stimuli may drive amyloidosis. These data suggest a dual protective/damaging role for Aβ, as has been described for other antimicrobial peptides.

The Mla pathway is critical for Pseudomonas aeruginosa resistance to outer membrane permeabilization and host innate immune clearance

Pseudomonas aeruginosa is an important opportunistic pathogen that has become a serious problem due to increased rates of antibiotic resistance. Due to this along with a dearth in novel antibiotic development, especially against Gram-negative pathogens, new therapeutic strategies are needed to prevent a post-antibiotic era. Here, we describe the importance of the vacJ/Mla pathway in resisting bactericidal actions of the host innate immune response. P. aeruginosa tn5 transposon mutants in genes from the VacJ/Mla pathway showed increased susceptibility to killing by the host cathelicidin antimicrobial peptide, LL-37, when compared to the wild-type parent strain. The P. aeruginosa vacJ - mutant demonstrated increased membrane permeability upon damage as well as sensitivity to killing in the presence of the detergent sodium dodecyl sulfate and the divalent cation chelator EDTA. When exposed to human whole blood and serum complement, the vacJ - mutant was killed more rapidly when compared to the wild-type parent strain and complemented mutant. Finally, in an in vivo mouse lung infection model, infection with the vacJ - mutant resulted in reduced mortality, lower bacterial burden, and reduced lung damage when compared to the wild-type strain. This study highlights the potential in therapeutically targeting the VacJ/Mla pathway in sensitizing P. aeruginosa to killing by the host innate immune response.

KEY MESSAGES

• The Mla pathway regulates outer membrane dynamics in human pathogen Pseudomonas aeruginosa (PA). • Disruption of Mla pathway gene vacJ sensitizes PA to host cathelicidin antimicrobial peptide LL-37. • Loss of vacJ expression renders PA more sensitive to human whole blood and serum killing. • Loss of vacJ expression reduces PA survival and virulence in a murine lung infection model. • The Mla pathway merits exploration as a pharmacologic target to sensitize PA to host innate immunity.

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

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

Friends or Foes? Host defense (antimicrobial) peptides and proteins in human skin diseases

Host defense peptides/proteins (HDPs), also known as antimicrobial peptides/proteins (AMPs), are key molecules in the cutaneous innate immune system. AMPs/HDPs historically exhibit broad-spectrum killing activity against bacteria, enveloped viruses, fungi and several parasites. Recently, AMPs/HDPs were shown to have important biological functions, including inducing cell proliferation, migration and differentiation; regulating inflammatory responses; controlling the production of various cytokines/chemokines; promoting wound healing; and improving skin barrier function. Despite the fact that AMPs/HDPs protect our body, several studies have hypothesized that these molecules actively contribute to the pathogenesis of various skin diseases. For example, AMPs/HDPs play crucial roles in the pathological processes of psoriasis, atopic dermatitis, rosacea, acne vulgaris, systemic lupus erythematosus and systemic sclerosis. Thus, AMPs/HDPs may be a double-edged sword, promoting cutaneous immunity while simultaneously initiating the pathogenesis of some skin disorders. This review will describe the most common skin-derived AMPs/HDPs (defensins, cathelicidins, S100 proteins, ribonucleases and dermcidin) and discuss the biology and both the positive and negative aspects of these AMPs/HDPs in skin inflammatory/infectious diseases. Understanding the regulation, functions and mechanisms of AMPs/HDPs may offer new therapeutic opportunities in the treatment of various skin disorders.

Human β-Defensin 3 Reduces TNF-α-Induced Inflammation and Monocyte Adhesion in Human Umbilical Vein Endothelial Cells

The aim of this study was to investigate the role of human β-defensin 3 (hBD3) in the initiation stage of atherosclerosis with human umbilical vein endothelial cells (HUVECs) triggered by tumor necrosis factor- (TNF-) α. The effects of hBD3 on TNF-α-induced endothelial injury and inflammatory response were evaluated. Our data revealed that first, hBD3 reduced the production of interleukin-6 (IL-6), IL-8, monocyte chemoattractant protein-1 (MCP-1), and macrophage migration inhibitory factor (MIF) in HUVECs in a dose-dependent manner. In addition, hBD3 significantly prevented intracellular reactive oxygen species (ROS) production by HUVECs. Second, western blot analysis demonstrated that hBD3 dose-dependently suppressed the protein levels of intracellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) in TNF-α-induced HUVECs. As a result, hBD3 inhibited monocyte adhesion to TNF-α-treated endothelial cells. Additionally, hBD3 suppressed TNF-α-induced F-actin reorganization in HUVECs. Third, hBD3 markedly inhibited NF-κB activation by decreasing the phosphorylation of IKK-α/β, IκB, and p65 subunit within 30 min. Moreover, the phosphorylation of p38 and c-Jun N-terminal protein kinase (JNK) in the mitogen-activated protein kinase (MAPK) pathway were also inhibited by hBD3 in HUVECs. In conclusion, hBD3 exerts anti-inflammatory and antioxidative effects in endothelial cells in response to TNF-α by inhibiting NF-κB and MAPK signaling.

The dual role of cathelicidins in systemic inflammation

Antimicrobial peptides are key components of the innate immune system. They act as broad-spectrum antimicrobial agents against Gram-positive and -negative bacteria, viruses, and fungi. More recently, antimicrobial peptides have been ascribed immunomodulatory functions, including roles in wound healing, induction of cytokines, and altering host gene expression. Cathelicidins are a class of antimicrobial peptide found in humans, mice, and rats, among others. Known as LL-37 in humans and cathelin-related antimicrobial peptide (CRAMP) in rodents, cathelicidins are produced by many different cells, including macrophages, neutrophils, and epithelial cells. The role of cathelicidins is somewhat confounding, as they exhibit both pro-and anti-inflammatory activity. A major obstacle in the study of cathelicidins is the inability of exogenous LL-37 or CRAMP to mimic the activity of their endogenous counterparts. Nevertheless, studies have shown that LL-37 is recognized by multiple receptors, and may stabilize or modulate Toll-like receptor signaling. In addition, cathelicidins play a role in apoptosis, inflammasome activation, and phagocytosis. However, many studies are revealing the dual effects of cathelicidins. For example, CRAMP appears to be protective in models of group A Streptococcus skin infection, pneumonia, and meningitis, but detrimental in cases of severe bacterial infection, such as septic shock. It is becoming increasingly clear that the activity of cathelicidins is modulated by complex interactions with the microenvironment, as well as the disease background. This article reviews what is currently known about the activity of cathelicidins in an attempt to understand their complex roles in systemic diseases.

Recent advances in the discovery and development of antibacterial agents targeting the cell-division protein FtsZ

With the emergence of multidrug-resistant bacterial strains, there is a dire need for new drug targets for antibacterial drug discovery and development. Filamentous temperature sensitive protein Z (FtsZ), is a GTP-dependent prokaryotic cell division protein, sharing less than 10% sequence identity with the eukaryotic cell division protein, tubulin. FtsZ forms a dynamic Z-ring in the middle of the cell, leading to septation and subsequent cell division. Inhibition of the Z-ring blocks cell division, thus making FtsZ a highly attractive target. Various groups have been working on natural products and synthetic small molecules as inhibitors of FtsZ. This review summarizes the recent advances in the development of FtsZ inhibitors, focusing on those in the last 5years, but also includes significant findings in previous years.

Bacterial Evasion of Host Antimicrobial Peptide Defenses

Antimicrobial peptides (AMPs), also known as host defense peptides, are small naturally occurring microbicidal molecules produced by the host innate immune response that function as a first line of defense to kill pathogenic microorganisms by inducing deleterious cell membrane damage. AMPs also possess signaling and chemoattractant activities and can modulate the innate immune response to enhance protective immunity or suppress inflammation. Human pathogens have evolved defense molecules and strategies to counter and survive the AMPs released by host immune cells such as neutrophils and macrophages. Here, we review the various mechanisms used by human bacterial pathogens to resist AMP-mediated killing, including surface charge modification, active efflux, alteration of membrane fluidity, inactivation by proteolytic digestion, and entrapment by surface proteins and polysaccharides. Enhanced understanding of AMP resistance at the molecular level may offer insight into the mechanisms of bacterial pathogenesis and augment the discovery of novel therapeutic targets and drug design for the treatment of recalcitrant multidrug-resistant bacterial infections.

Cationic host defense peptides; novel antimicrobial therapeutics against Category A pathogens and emerging infections

Cationic Host Defense Peptides (HDP, also known as antimicrobial peptides) are crucial components of the innate immune system and possess broad-spectrum antibacterial, antiviral, and immunomodulatory activities. They can contribute to the rapid clearance of biological agents through direct killing of the organisms, inhibition of pro-inflammatory mediators such as lipopolysaccharide, and by modulating the inflammatory response to infection. Category A biological agents and materials, as classified by the United States National Institutes for Health, the US Centers for Disease Control and Prevention, and the US Department of Homeland Security, carry the most severe threat in terms of human health, transmissibility, and preparedness. As such, there is a pressing need for novel frontline approaches for prevention and treatment of diseases caused by these organisms, and exploiting the broad antimicrobial activity exhibited by cationic host defense peptides represents an exciting priority area for clinical research. This review will summarize what is known about the antimicrobial and antiviral effects of the two main families of cationic host defense peptides, cathelicidins, and defensins in the context of Category A biological agents which include, but are not limited to; anthrax (Bacillus anthracis), plague (Yersinia pestis), smallpox (Variola major), tularemia (Francisella tularensis). In addition, we highlight priority areas, particularly emerging viral infections, where more extensive research is urgently required.

Group A Streptococcal M1 Protein Sequesters Cathelicidin to Evade Innate Immune Killing

The antimicrobial peptide LL-37 is generated upon proteolytic cleavage of cathelicidin and limits invading pathogens by directly targeting microbial membranes as well as stimulating innate immune cell function. However, some microbes evade LL-37-mediated defense. Notably, group A Streptococcus (GAS) strains belonging to the hypervirulent M1T1 serogroup are more resistant to human LL-37 than other GAS serogroups. We show that the GAS surface-associated M1 protein sequesters and neutralizes LL-37 antimicrobial activity through its N-terminal domain. M1 protein also binds the cathelicidin precursor hCAP-18, preventing its proteolytic maturation into antimicrobial forms. Exogenous M1 protein rescues M1-deficient GAS from killing by neutrophils and within neutrophil extracellular traps and neutralizes LL-37 chemotactic properties. M1 also binds murine cathelicidin, and its virulence contribution in a murine model of necrotizing skin infection is largely driven by its ability to neutralize this host defense peptide. Thus, cathelicidin resistance is essential for the pathogenesis of hyperinvasive M1T1 GAS.

Intrathecal application of the antimicrobial peptide CRAMP reduced mortality and neuroinflammation in an experimental model of pneumococcal meningitis

Antimicrobial peptides (AP) are important components of the innate immune system. Our previous work revealed a higher mortality rate and up-regulation of proinflammatory gene expression as well as glial cell activation in cathelicidin-related antimicrobial peptide (CRAMP)-deficient mice after bacterial meningitis. However, the influence of CRAMP application on the progression of inflammation and its impact on mortality after bacterial meningitis remains unknown. To assess the effects of continuous CRAMP exposure in the brain, C57BL/6 wildtype mice were given intracerebroventricular infusion of CRAMP to investigate the effects on mortality, glial cell activation and inflammation in a mouse model of pneumococcal meningitis using immunohistochemistry and realtime RT-PCR. Our results revealed a decrease of mortality after CRAMP infusion. The intrathecal CRAMP infusion after pneumococcal meningitis resulted in a decreased mRNA expression of pro-inflammatory cytokines, whereas the immune responses including the expression of pattern recognition receptors and chemokines were increased in bacterial meningitis. Taken together, the results support the important role of CRAMP as part of the innate immune response against pathogens in bacterial CNS infections. The APs may be a promising approach for the development of an adjuvant therapy for bacterial meningitis.

The innate defense antimicrobial peptides hBD3 and RNase7 are induced in human umbilical vein endothelial cells by classical inflammatory cytokines but not Th17 cytokines

Antimicrobial peptides are multifunctional effector molecules of innate immunity. In this study we investigated whether endothelial cells actively contribute to innate defense mechanisms by expression of antimicrobial peptides. We therefore stimulated human umbilical vein endothelial cells (HUVEC) with inflammatory cytokines, Th17 cytokines, heat-inactivated bacteria, bacterial conditioned medium (BCM) of Staphylococcus aureus and Streptococcus sanguinis, and lipoteichoic acid (LTA). Stimulation with single cytokines induced discrete expression of human β-defensin 3 (hBD3) by IFN-γ or IL-1β and of ribonuclease 7 (RNase7) by TNF-α without any effects on LL-37 gene expression. Stronger hBD3 and RNase7 induction was observed after combined stimulation with IL-1β, TNF-α and IFN-γ and was confirmed by high hBD3 and RNase7 peptide levels in cell culture supernatants. In contrast, Th17 cytokines or stimulation with LTA did not result in AMP production. Moreover, only BCM of an invasive S. aureus bacteremia isolate induced hBD3 in HUVEC. We conclude that endothelial cells actively contribute to prevent dissemination of pathogens at the blood-tissue-barrier by production of AMPs that exhibit microbicidal and immunomodulatory functions. Further investigations should focus on tissue-specific AMP induction in different endothelial cell types, on pathogen-specific induction patterns and potentially involved pattern-recognition receptors of endothelial cells.

Complexity of antimicrobial peptide regulation during pathogen-host interactions

Antimicrobial peptides (AMPs) are a key component of the immune system and are expressed by a large variety of organisms. AMPs are capable of eliminating a broad range of micro-organisms, illustrated by murine models where lack of AMP expression resulted in enhanced susceptibility to infection. Despite the importance of AMPs in immune defences, it is not clear whether a change in AMP expression is pathogen-specific or reflects a general response to groups of pathogens. Furthermore, it is unclear how the evoked change in AMP expression affects the host. To fully exploit the therapeutic potential of AMPs - by direct application of peptides or by using AMP-inducers - it is crucial to gain an insight into the complexity involved in pathogen-mediated regulation of AMP expression. This review summarises current knowledge on how AMP expression is affected by pathogens. In addition, the relevance and specificity of these changes in AMPs during infection will be discussed.

Anti-fibrogenic effects of the anti-microbial peptide cathelicidin in murine colitis-associated fibrosis

BACKGROUND AND AIMS

Cathelicidin (LL-37 in human and mCRAMP in mice) represents a family of endogenous antimicrobial peptides with anti-inflammatory effects. LL-37 also suppresses collagen synthesis, an important fibrotic response, in dermal fibroblasts. Here we determined whether exogenous cathelicidin administration modulates intestinal fibrosis in two animal models of intestinal inflammation and in human colonic fibroblasts.

METHODS

C57BL/6J mice (n=6 per group) were administered intracolonically with a trinitrobenzene sulphonic acid (TNBS) enema to induce chronic (6-7 weeks) colitis with fibrosis. mCRAMP peptide (5 mg/kg every 3 day, week 5-7) or cathelicidin gene (Camp)-expressing lentivirus (10⁷ infectious units week 4) were administered intracolonically or intravenously, respectively. 129Sv/J mice were infected with Salmonella typhimurium orally to induce cecal inflammation with fibrosis. Camp expressing lentivirus (10⁷ infectious units day 11) was administered intravenously.

RESULTS

TNBS-induced chronic colitis was associated with increased colonic collagen (col1a2) mRNA expression. Intracolonic cathelicidin (mCRAMP peptide) administration or intravenous delivery of lentivirus-overexpressing cathelicidin gene significantly reduced colonic col1a2 mRNA expression in TNBS-exposed mice, compared to vehicle administration. Salmonella infection also caused increased cecal inflammation associated with collagen (col1a2) mRNA expression that was prevented by intravenous delivery of Camp-expressing lentivirus. Exposure of human primary intestinal fibroblasts and human colonic CCD-18Co fibroblasts to transforming growth factor-beta1 (TGF-beta1) and/or insulin-like growth factor 1 induced collagen protein and mRNA expression, that was reduced by LL-37 (3-5 µM) through a MAP kinase-dependent mechanism.

CONCLUSION

Cathelicidin can reverse intestinal fibrosis by directly inhibiting collagen synthesis in colonic fibroblasts.

Antimicrobial peptide CRAMP (16-33) stalls bacterial cytokinesis by inhibiting FtsZ assembly

A cathelin-related antimicrobial peptide (CRAMP) of 37 amino acid residues is thought to regulate innate immunity and provide a host defense mechanism in mammals. Here, a part of the CRAMP peptide, CRAMP (16-33) (GEKLKKIGQKIKNFFQKL), was found to bind to FtsZ and to inhibit the assembly and GTPase activity of FtsZ in vitro. A computational analysis indicated that CRAMP (16-33) binds in the cavity of the T7 loop of FtsZ. Both hydrophobic and ionic interactions were involved in the binding interactions. Further, CRAMP (16-33) inhibited the formation of the FtsZ ring in bacteria, indicating that it inhibited bacterial cell division by inhibiting FtsZ assembly.

Endogenous cathelicidin production limits inflammation and protective immunity to Mycobacterium avium in mice

The production of antimicrobial peptides, such as the cathelicidins, plays a prominent role in the innate immune response against microbial pathogens. Cathelicidins are widely distributed amongst living organisms, and the antimicrobial peptides generated by proteolysis of the precursor forms are typically cationic and α-helical, a structure that facilitates their interaction and insertion into anionic bacterial cell walls and membranes, causing damage and promoting microbial death. Here, we found that mouse cathelicidin (Camp) expression was induced in bone marrow-derived macrophages by infection with Mycobacterium avium in a TLR2- and TNF-dependent manner. However, the endogenous production of the cathelin-related antimicrobial peptide (CRAMP) was not required for the bacteriostasis of M. avium either in primary cultures of macrophages or in vivo, as shown by the use of CRAMP-null mice. In contrast, the lack of Camp led to a transient improvement of M. avium growth control in the spleens of infected mice while at the same time causing an exacerbation of the inflammatory response to infection. Our data highlight the anti-inflammatory effects of CRAMP and suggests that virulent mycobacteria may possess strategies to escape its antimicrobial activity.

Deciphering the contribution of human meningothelial cells to the inflammatory and antimicrobial response at the meninges

We have investigated the response of primary human meningothelial cells to Neisseria meningitidis. Through a transcriptome analysis, we provide a comprehensive examination of the response of meningothelial cells to bacterial infection. A wide range of chemokines are elicited which act to attract and activate the main players of innate and adaptive immunity. We showed that meningothelial cells expressed a high level of Toll-like receptor 4 (TLR4), and, using a gene silencing strategy, we demonstrated the contribution of this pathogen recognition receptor in meningothelial cell activation. Secretion of interleukin-6 (IL-6), CXCL10, and CCL5 was almost exclusively TLR4 dependent and relied on MyD88 and TRIF adaptor cooperation. In contrast, IL-8 induction was independent of the presence of TLR4, MyD88, and TRIF. Transcription factors NF-κB p65, p38 mitogen-activated protein kinase (MAPK), Jun N-terminal protein kinase (JNK1), IRF3, and IRF7 were activated after contact with bacteria. Interestingly, the protein kinase IRAK4 was found to play a minor role in the meningothelial cell response to Neisseria infection. Our work highlights the role of meningothelial cells in the development of an immune response and inflammation in the central nervous system (CNS) in response to meningococcal infection. It also sheds light on the complexity of intracellular signaling after TLR triggering.

Role of the cathelicidin-related antimicrobial peptide in inflammation and mortality in a mouse model of bacterial meningitis

Antimicrobial peptides (AP) are important components of the innate immune system, yet little is known about their expression and function in the brain. Our previous work revealed upregulated gene expression of cathelicidin-related AP (CRAMP) following bacterial meningitis in primary rat glial cells as well as bactericidal activity against frequent meningitis-causing bacteria. However, the effect of cathelicidin expression on the progression of inflammation and mortality in bacterial meningitis remains unknown. Therefore, we used CRAMP-deficient mice to investigate the effect of CRAMP on bacterial growth, inflammatory responses and mortality in meningitis. Meningitis was induced by intracerebral injection of type 3 Streptococcus pneumoniae. The degree of inflammation was analyzed in various brain regions by means of immunohistochemistry and real-time RT-PCR. CRAMP deficiency led to a higher mortality rate that was associated with increased bacterial titers in the cerebellum, blood and spleen as well as decreased meningeal neutrophil infiltration. CRAMP-deficient mice displayed a higher degree of glial cell activation that was accompanied by a more pronounced proinflammatory response. Taken together, this work provides insight into the important role of CRAMP as part of the innate immune defense against pathogens in bacterial CNS infections.

Rational design of engineered cationic antimicrobial peptides consisting exclusively of arginine and tryptophan, and their activity against multidrug-resistant pathogens

The emergence of multidrug-resistant (MDR) pathogens underscores the need for new antimicrobial agents to overcome the resistance mechanisms of these organisms. Cationic antimicrobial peptides (CAPs) provide a potential source of new antimicrobial therapeutics. We previously characterized a lytic base unit (LBU) series of engineered CAPs (eCAPs) of 12 to 48 residues demonstrating maximum antibacterial selectivity at 24 residues. Further, Trp substitution in LBU sequences increased activity against both P. aeruginosa and S. aureus under challenging conditions (e.g., saline, divalent cations, and serum). Based on these findings, we hypothesized that the optimal length and, therefore, the cost for maximum eCAP activity under physiologically relevant conditions could be significantly reduced using only Arg and Trp arranged to form idealized amphipathic helices. Hence, we developed a novel peptide series, composed only of Arg and Trp, in a sequence predicted and verified by circular dichroism to fold into optimized amphipathic helices. The most effective antimicrobial activity was achieved at 12 residues in length (WR12) against a panel of both Gram-negative and Gram-positive clinical isolates, including extensively drug-resistant strains, in saline and broth culture and at various pH values. The results demonstrate that the rational design of CAPs can lead to a significant reduction in the length and the number of amino acids used in peptide design to achieve optimal potency and selectivity against specific pathogens.

Neutrophil differentiation into a unique hybrid population exhibiting dual phenotype and functionality of neutrophils and dendritic cells

Neutrophils have been reported to acquire surface expression of MHC class II and co-stimulatory molecules as well as T-cell stimulatory activities when cultured with selected cytokines. However, cellular identity of those unusual neutrophils showing antigen presenting cell (APC)-like features still remains elusive. Here we show that both immature and mature neutrophils purified from mouse bone marrow differentiate into a previously unrecognized "hybrid" population showing dual properties of both neutrophils and dendritic cells (DCs) when cultured with granulocyte macrophage-colony-stimulating factor but not with other tested growth factors. The resulting hybrid cells express markers of both neutrophils (Ly6G, CXCR2, and 7/4) and DCs (CD11c, MHC II, CD80, and CD86). They also exhibit several properties typically reserved for DCs, including dendritic morphology, probing motion, podosome formation, production of interleukin-12 and other cytokines, and presentation of various forms of foreign protein antigens to naïve CD4 T cells. Importantly, they retain intrinsic abilities of neutrophils to capture exogenous material, extrude neutrophil extracellular traps, and kill bacteria via cathelicidin production. Not only do our results reinforce the notion that neutrophils can acquire APC-like properties, they also unveil a unique differentiation pathway of neutrophils into neutrophil-DC hybrids that can participate in both innate and adaptive immune responses.

A bacterial pathogen co-opts host plasmin to resist killing by cathelicidin antimicrobial peptides

The bacterial pathogen Group A Streptococcus (GAS) colonizes epithelial and mucosal surfaces and can cause a broad spectrum of human disease. Through the secreted plasminogen activator streptokinase (Ska), GAS activates human plasminogen into plasmin and binds it to the bacterial surface. The resulting surface plasmin protease activity has been proposed to play a role in disrupting tissue barriers, promoting invasive spread of the bacterium. We investigated whether this surface protease activity could aid the immune evasion role through degradation of the key innate antimicrobial peptide LL-37, the human cathelicidin. Cleavage products of plasmin-degraded LL-37 were analyzed by matrix-assisted laser desorption ionization mass spectrometry. Ska-deficient GAS strains were generated by targeted allelic exchange mutagenesis and confirmed to lack surface plasmin activity after growth in human plasma or media supplemented with plasminogen and fibrinogen. Loss of surface plasmin activity left GAS unable to efficiently degrade LL-37 and increased bacterial susceptibility to killing by the antimicrobial peptide. When mice infected with GAS were simultaneously treated with the plasmin inhibitor aprotinin, a significant reduction in the size of necrotic skin lesions was observed. Together these data reveal a novel immune evasion strategy of the human pathogen: co-opting the activity of a host protease to evade peptide-based innate host defenses.

Cathelicidin signaling via the Toll-like receptor protects against colitis in mice

BACKGROUND & AIMS

Cathelicidin (encoded by Camp) is an antimicrobial peptide in the innate immune system. We examined whether macrophages express cathelicidin in colons of mice with experimental colitis and patients with inflammatory bowel disease, and we investigated its signaling mechanisms.

METHODS

Quantitative, real-time, reverse-transcription polymerase chain reaction (PCR), bacterial 16S PCR, immunofluorescence, and small interfering RNA (siRNA) analyses were performed. Colitis was induced in mice using dextran sulfate sodium (DSS); levels of cathelicidin were measured in human primary monocytes.

RESULTS

Expression of cathelicidin increased in the inflamed colonic mucosa of mice with DSS-induced colitis compared with controls. Cathelicidin expression localized to mucosal macrophages in inflamed colon tissues of patients and mice. Exposure of human primary monocytes to Escherichia coli DNA induced expression of Camp messenger RNA, which required signaling by extracellular signal-regulated kinase (ERK); expression was reduced by siRNAs against Toll-like receptor (TLR)9 and MyD88. Intracolonic administration of bacterial DNA to wild-type mice induced expression of cathelicidin in colons of control mice and mice with DSS-induced colitis. Colon expression of cathelicidin was significantly reduced in TLR9(-/-) mice with DSS-induced colitis. Compared with wild-type mice, Camp(-/-) mice developed a more severe form of DSS-induced colitis, particularly after intracolonic administration of E coli DNA. Expression of cathelicidin from bone marrow-derived immune cells regulated DSS induction of colitis in transplantation studies in mice.

CONCLUSIONS

Cathelicidin protects against induction of colitis in mice. Increased expression of cathelicidin in monocytes and experimental models of colitis involves activation of TLR9-ERK signaling by bacterial DNA. This pathway might be involved in the pathogenesis of ulcerative colitis.

Cathelin-related antimicrobial peptide differentially regulates T- and B-cell function

Mammalian antimicrobial peptides (AMPs) play an important role in host defense via direct antimicrobial activity as well as immune regulation. The mouse cathelin-related antimicrobial peptide (mCRAMP), produced from the mouse gene Camp, is the only mouse cathelicidin identified and the ortholog of the human gene encoding the peptide LL-37. This study tested the hypothesis that mouse B and T cells produce and respond to mCRAMP. We show that all mature mouse B-cell subsets, including follicular (FO), marginal zone (MZ), B1a, and B1b cells, as well as CD4(+) and CD8(+) T cells produce Camp mRNA and mCRAMP protein. Camp(-/-) B cells produced equivalent levels of IgM, IgG3, and IgG2c but less IgG1 and IgE, while Camp(-/-) CD4(+) T cells cultured in Th2-inducing conditions produced more IL-4-expressing cells when compared with WT cells, effects that were reversed upon addition of mCRAMP. In vivo, Camp(-/-) mice immunized with TNP-OVA absorbed in alum produced an enhanced TNP-specific IgG1 response when compared with WT mice. ELISpot analysis revealed increased numbers of TNP-specific IgG1-secreting splenic B cells and FACS analysis revealed increased CD4(+) T-cell IL-4 expression. Our results suggest that mCRAMP differentially regulates B- and T-cell function and implicate mCRAMP in the regulation of adaptive immune responses.

The formyl peptide receptor like-1 and scavenger receptor MARCO are involved in glial cell activation in bacterial meningitis

Background

Recent studies have suggested that the scavenger receptor MARCO (macrophage receptor with collagenous structure) mediates activation of the immune response in bacterial infection of the central nervous system (CNS). The chemotactic G-protein-coupled receptor (GPCR) formyl-peptide-receptor like-1 (FPRL1) plays an essential role in the inflammatory responses of host defence mechanisms and neurodegenerative disorders such as Alzheimer's disease (AD). Expression of the antimicrobial peptide cathelicidin CRAMP/LL-37 is up-regulated in bacterial meningitis, but the mechanisms underlying CRAMP expression are far from clear.

Methods

Using a rat meningitis model, we investigated the influence of MARCO and FPRL1 on rCRAMP (rat cathelin-related antimicrobial peptide) expression after infection with bacterial supernatants of Streptococcus pneumoniae (SP) and Neisseria meningitides (NM). Expression of FPRL1 and MARCO was analyzed by immunofluorescence and real-time RT-PCR in a rat meningitis model. Furthermore, we examined the receptor involvement by real-time RT-PCR, extracellular-signal regulated kinases 1/2 (ERK1/2) phosphorylation and cAMP level measurement in glial cells (astrocytes and microglia) and transfected HEK293 cells using receptor deactivation by antagonists. Receptors were inhibited by small interference RNA and the consequences in NM- and SP-induced Camp (rCRAMP gene) expression and signal transduction were determined.

Results

We show an NM-induced increase of MARCO expression by immunofluorescence and real-time RT-PCR in glial and meningeal cells. Receptor deactivation by antagonists and small interfering RNA (siRNA) verified the importance of FPRL1 and MARCO for NM- and SP-induced Camp and interleukin-1β expression in glial cells. Furthermore, we demonstrated a functional interaction between FPRL1 and MARCO in NM-induced signalling by real-time RT-PCR, ERK1/2 phosphorylation and cAMP level measurement and show differences between NM- or SP-induced signal transduction.

Conclusions

We propose that NM and SP induce glial cell activation and rCRAMP expression also via FPRL1 and MARCO. Thus the receptors contribute an important part to the host defence against infection.

Biological roles of host defense peptides: lessons from transgenic animals and bioengineered tissues

Host defense peptides (HDPs) have long been recognized as microbicidal agents, but their roles as modulators of innate and adaptive immunity have only more recently been appreciated. The study of transgenic animal and tissue models has provided platforms to improve our understanding of the immune modulatory functions of HDPs. Here, the characterization of transgenic animals or tissue models that over-express and/or are deficient for specific HDPs is reviewed. We also attempt to reconcile this data with evidence from human studies monitoring HDP expression at constitutive levels and/or in conjunction with inflammation, infection models, or disease states. We have excluded activities ascribed to HDPs derived exclusively from in vitro experiments. An appreciation of the way that HDPs promote innate immunity or influence the adaptive immune response is necessary in order to exploit their therapeutic or adjuvant potential and to open new perspectives in understanding the basis of immunity. The potential applications for HDPs are discussed.

Spotlight on Human LL-37, an Immunomodulatory Peptide with Promising Cell-Penetrating Properties

Cationic antimicrobial peptides are major components of innate immunity and help control the initial steps of the infectious process. They are expressed not only by immunocytes, but also by epithelial cells. They share an amphipathic secondary structure with a polar cationic site, which explains their tropism for prokaryote membranes and their hydrophobic site contributing to the destructuration of these membranes. LL-37 is the only cationic antimicrobial peptide derived from human cathelicidin. LL-37 can also cross the plasma membrane of eukaryotic cells, probably through special domains of this membrane called lipid rafts. This transfer could be beneficial in the context of vaccination: the activation of intracellular toll-like receptors by a complex formed between CpG oligonucleotides and LL-37 could conceivably play a major role in the building of a cellular immunity involving NK cells.

Cloning and expression of genes enocoding antimicrobial peptides and bradykinin from the skin and brain of Oki Tago's brown frog, Rana tagoi okiensis

Previous studies led to the isolation from skin extracts of Oki Tago's brown frog, Rana tagoi okiensis of five antimicrobial peptides belonging to the brevinin-1 (brevinin-1TOa), temporin (temporin-TOa and -TOb), and ranatuerin-2 (ranatuerin-2TOa and -2TOb) families, and bradykinin (BK) identical to mammalian BK. Using the reverse-transcription polymerase chain reaction (RT-PCR), we have now cloned from skin total RNA preparations cDNAs encoding biosynthetic precursors of brevinin-1TOa and brevinin-1TOb (containing the substitution Gly(1)-->Val), temporin-TOa and -TOb, and ranatuerin-2TOa and -2TOb. In addition, three cDNA clones encoding preprobradykinins were obtained that contained either one, two, or three tandem repeats of the sequence of BK followed by the sequence of [Thr(6)]-BK. In tissue expression analyses, preprobrevinin-1, preprotemporin, and preproranatuerin-2 gene transcripts were detected at higher levels in brain compared with peripheral tissues (heart, small intestine, kidney, liver lung, skeletal muscle, stomach, and testis). RT-PCR of brain RNA resulted in the amplification of cDNAs encoding ranatuerin-2TOc and ranatuerin-2TOd that contained the amino acid substitutions Lys(6)-->Arg and Ala(14)-->Thr, respectively compared with ranatuerin-2TOb. cDNAs encoding preprobrevinin-1TOa and preprotemporin-TOa were amplified from brain RNA as well as a second preprotemporin cDNA that contained a 10-nucleotide insertion that introduced a frame shift resulting in a premature stop codon. A cDNA encoding a novel peptide, DK25 (DVNDLKNLCAKTHNLLPMCAMFGKK) was amplified from brain RNA but neither DK25 nor its putative post-translationally modified form, DF22-amide (DVNDLKNLCAKTHNLLPMCAMF.NH(2)) displayed antimicrobial or hemolytic activities.

Antimicrobial peptides in the brain

Antimicrobial peptides (AMPs) are an evolutionarily conserved component of the innate immune system of many species. The brain is an immunologically privileged organ but can produce a robust immune response against pathogens and cell debris, promoting rapid and efficient clearance. AMPs may be critically involved in the innate immune system of the brain. Though the mechanisms of AMPs' action in the brain still need further elucidation, many studies have shown that AMPs are multifunctional molecules in the brain. In addition to antimicrobial action, they take part in congenital and adaptive immune reactions (immunoregulation), function as signaling molecules in tissue repair, inflammation and other important processes through different mechanisms, and they might, in addition, become diagnostic markers of brain disease.

The structure of Neisseria meningitidis lipid A determines outcome in experimental meningococcal disease

Lipopolysaccharide (LPS), a major component of the meningococcal outer membrane, is sensed by the host through activation of Toll-like receptor 4 (TLR4). Recently, we demonstrated that a surprisingly large fraction of Neisseria meningitidis disease isolates are lipid A mutants, due to inactivating mutations in the lpxL1 gene. The lpxL1 mutants activate human TLR4 much less efficiently than wild-type bacteria, which may be advantageous by allowing them to escape from the innate immune system. Here we investigated the influence of lipid A structure on virulence in a mouse model of meningococcal sepsis. One limitation, however, is that murine TLR4 recognizes lpxL1 mutant bacteria much better than human TLR4. We show that an lpxL2 mutant, another lipid A mutant lacking an acyl chain at a different position, activates murine TLR4 less efficiently than the lpxL1 mutant. Therefore, the lpxL2 mutant in mice might be a better model for infections with lpxL1 mutants in humans. Interestingly, we found that the lpxL2 mutant is more virulent in mice than the wild-type strain, whereas the lpxL1 mutant is actually much less virulent than the wild-type strain. These results demonstrate the crucial role of N. meningitidis lipid A structure in virulence.

The Alzheimer's disease-associated amyloid beta-protein is an antimicrobial peptide

Background

The amyloid β-protein (Aβ) is believed to be the key mediator of Alzheimer's disease (AD) pathology. Aβ is most often characterized as an incidental catabolic byproduct that lacks a normal physiological role. However, Aβ has been shown to be a specific ligand for a number of different receptors and other molecules, transported by complex trafficking pathways, modulated in response to a variety of environmental stressors, and able to induce pro-inflammatory activities.

Methodology/Principal Findings

Here, we provide data supporting an in vivo function for Aβ as an antimicrobial peptide (AMP). Experiments used established in vitro assays to compare antimicrobial activities of Aβ and LL-37, an archetypical human AMP. Findings reveal that Aβ exerts antimicrobial activity against eight common and clinically relevant microorganisms with a potency equivalent to, and in some cases greater than, LL-37. Furthermore, we show that AD whole brain homogenates have significantly higher antimicrobial activity than aged matched non-AD samples and that AMP action correlates with tissue Aβ levels. Consistent with Aβ-mediated activity, the increased antimicrobial action was ablated by immunodepletion of AD brain homogenates with anti-Aβ antibodies.

Conclusions/Significance

Our findings suggest Aβ is a hitherto unrecognized AMP that may normally function in the innate immune system. This finding stands in stark contrast to current models of Aβ-mediated pathology and has important implications for ongoing and future AD treatment strategies.

Staphylococcus epidermidis antimicrobial delta-toxin (phenol-soluble modulin-gamma) cooperates with host antimicrobial peptides to kill group A Streptococcus

Antimicrobial peptides play an important role in host defense against pathogens. Recently, phenol-soluble modulins (PSMs) from Staphylococcus epidermidis (S. epidermidis) were shown to interact with lipid membranes, form complexes, and exert antimicrobial activity. Based on the abundance and innocuity of the cutaneous resident S. epidermidis, we hypothesized that their PSMs contribute to host defense. Here we show that S. epidermidis delta-toxin (PSMgamma) is normally present in the epidermis and sparsely in the dermis of human skin using immunohistochemistry. Synthetic delta-toxin interacted with neutrophil extracellular traps (NETs) and colocalized with cathelicidin while also inducing NET formation in human neutrophils. In antimicrobial assays against Group A Streptococcus (GAS), delta-toxin cooperated with CRAMP, hBD2, and hBD3. In whole blood, addition of delta-toxin exerted a bacteriostatic effect on GAS, and in NETs, delta-toxin increased their killing capacity against this pathogen. Coimmunoprecipitation and tryptophan spectroscopy demonstrated direct binding of delta-toxin to host antimicrobial peptides LL-37, CRAMP, hBD2, and hBD3. Finally, in a mouse wound model, GAS survival was reduced (along with Mip-2 cytokine levels) when the wounds were pretreated with delta-toxin. Thus, these data suggest that S. epidermidis-derived delta-toxin cooperates with the host-derived antimicrobial peptides in the innate immune system to reduce survival of an important human bacterial pathogen.

Expression and regulation of antimicrobial peptide rCRAMP after bacterial infection in primary rat meningeal cells

Bacterial meningitis is characterized by an inflammation of the meninges and continues to be an important cause of mortality and morbidity. Meningeal cells cover the cerebral surface and are involved in the first interaction between pathogens and the brain. Little is known about the role of meningeal cells and the expression of antimicrobial peptides in the innate immune system. In this study we characterized the expression, secretion and bactericidal properties of rat cathelin-related antimicrobial peptide (rCRAMP), a homologue of the human LL-37, in rat meningeal cells after incubation with different bacterial supernatants and the bacterial cell wall components lipopolysaccharide (LPS) and peptidoglycan (PGN). Using an agar diffusion test, we observed that supernatants from meningeal cells incubated with bacterial supernatants, LPS and PGN showed signs of antimicrobial activity. The inhibition of rCRAMP expression using siRNA reduced the antimicrobial activity of the cell culture supernatants. The expression of rCRAMP in rat meningeal cells involved various signal transduction pathways and was induced by the inflammatory cytokines interleukin-1, -6 and tumor necrosis factor alpha. In an experimental model of meningitis, infant rats were intracisternally infected with Streptococcus pneumoniae and rCRAMP was localized in meningeal cells using immunohistochemistry. These results suggest that cathelicidins produced by meningeal cells play an important part in the innate immune response against pathogens in CNS bacterial infections.

A protein important for antimicrobial peptide resistance, YdeI/OmdA, is in the periplasm and interacts with OmpD/NmpC

Antimicrobial peptides (AMPs) kill or prevent the growth of microbes. AMPs are made by virtually all single and multicellular organisms and are encountered by bacteria in diverse environments, including within a host. Bacteria use sensor-kinase systems to respond to AMPs or damage caused by AMPs. Salmonella enterica deploys at least three different sensor-kinase systems to modify gene expression in the presence of AMPs: PhoP-PhoQ, PmrA-PmrB, and RcsB-RcsC-RcsD. The ydeI gene is regulated by the RcsB-RcsC-RcsD pathway and encodes a 14-kDa predicted oligosaccharide/oligonucleotide binding-fold (OB-fold) protein important for polymyxin B resistance in broth and also for virulence in mice. We report here that ydeI is additionally regulated by the PhoP-PhoQ and PmrA-PmrB sensor-kinase systems, which confer resistance to cationic AMPs by modifying lipopolysaccharide (LPS). ydeI, however, is not important for known LPS modifications. Two independent biochemical methods found that YdeI copurifies with OmpD/NmpC, a member of the trimeric beta-barrel outer membrane general porin family. Genetic analysis indicates that ompD contributes to polymyxin B resistance, and both ydeI and ompD are important for resistance to cathelicidin antimicrobial peptide, a mouse AMP produced by multiple cell types and expressed in the gut. YdeI localizes to the periplasm, where it could interact with OmpD. A second predicted periplasmic OB-fold protein, YgiW, and OmpF, another general porin, also contribute to polymyxin B resistance. Collectively, the data suggest that periplasmic OB-fold proteins can interact with porins to increase bacterial resistance to AMPs.