Jens-Michael Schröder

A peptide antibiotic from human skin

To avoid opportunistic infections, plants and animals have developed antimicrobial peptides in their epithelia that can form pores in the cytoplasmic membrane of microorganisms. After contact with microorganisms, vertebrate skin, trachea and tongue epithelia are rich sources of peptide antibiotics, which may explain the unexpected resistance of these tissues to infection. Here we report that human skin is protected in a similar way by an inducible, transcriptionally regulated, antibiotic peptide, which resembles those in other mammals.

Plasmacytoid dendritic cells sense self-DNA coupled with antimicrobial peptide

Plasmacytoid dendritic cells (pDCs) sense viral and microbial DNA through endosomal Toll-like receptors to produce type 1 interferons. pDCs do not normally respond to self-DNA, but this restriction seems to break down in human autoimmune disease by an as yet poorly understood mechanism. Here we identify the antimicrobial peptide LL37 (also known as CAMP) as the key factor that mediates pDC activation in psoriasis, a common autoimmune disease of the skin. LL37 converts inert self-DNA into a potent trigger of interferon production by binding the DNA to form aggregated and condensed structures that are delivered to and retained within early endocytic compartments in pDCs to trigger Toll-like receptor 9. Thus, our data uncover a fundamental role of an endogenous antimicrobial peptide in breaking innate tolerance to self-DNA and suggest that this pathway may drive autoimmunity in psoriasis.

NOD2 (CARD15) mutations in Crohn's disease are associated with diminished mucosal alpha-defensin expression.

Background: Mutations in NOD2, a putative intracellular receptor for bacterial peptidoglycans, are associated with a subset of Crohn’s disease but the molecular mechanism linking this protein with the disease pathogenesis remains unclear. Human α defensins (HD-5 and HD-6) are antibiotic effector molecules predominantly expressed in Paneth cells of the ileum. Paneth cells also express NOD2. To address the hypothesis that the function of NOD2 may affect expression of Paneth cell defensins, we compared their expression levels with respect to NOD2 mutations in Crohn’s disease. Methods: Forty five Crohn’s disease patients (24 with NOD2 mutations, 21 with wild-type NOD2) and 12 controls were studied. Real time reverse transcription-polymerase chain reaction was performed with mucosal mRNA for HD-5, HD-6, lysozyme, secretory phospholipase A2 (sPLA2), tumour necrosis factor α, interleukin 8, and human hypoxanthine phosphoribosyltransferase (housekeeping gene). Immunohistochemistry with anti-HD-5 and histological Paneth cell staining were performed in 10 patients with NOD2 mutations or wild-type genotypes. Results: Ileal expression of HD-5 and HD-6, but not sPLA2 or lysozyme, were diminished in affected ileum, and the decrease was significantly more pronounced in patients with NOD2 mutations. In the colon, HD-5, HD-6, and sPLA2 were increased during inflammation in wild-type but not in NOD2 mutated patients. In both the colon and ileum, proinflammatory cytokines and lysozyme were unaffected by NOD2 status. Immunohistochemistry identified Paneth cells as the sole source of HD-5. Conclusion: As alpha defensins are important in the mucosal antibacterial barrier, their diminished expression may explain, in part, the bacterial induced mucosal inflammation and ileal involvement of Crohn’s disease, especially in the case of NOD2 mutations.

Antimicrobial psoriasin (S100A7) protects human skin from Escherichia coli infection

Human healthy skin is continuously exposed to bacteria, but is particularly resistant to the common gut bacterium Escherichia coli. We show here that keratinocytes secrete, as the main E. coli–killing compound, the S100 protein psoriasin in vitro and in vivo in a site-dependent way. In vivo treatment of human skin with antibodies to psoriasin inhibited its E. coli–killing properties. Psoriasin was induced in keratinocytes in vitro and in vivo by E. coli, indicating that its focal expression in skin may derive from local microbial induction. Zn2+-saturated psoriasin showed diminished antimicrobial activity, suggesting that Zn2+ sequestration could be a possible antimicrobial mechanism. Thus, psoriasin may be key to the resistance of skin against E. coli.

NF-κB- and AP-1-Mediated Induction of Human Beta Defensin-2 in Intestinal Epithelial Cells by Escherichia coli Nissle 1917: a Novel Effect of a Probiotic Bacterium

ABSTRACT Little is known about the defensive mechanisms induced in epithelial cells by pathogenic versus probiotic bacteria. The aim of our study was to compare probiotic bacterial strains such as Escherichia coli Nissle 1917 with nonprobiotic, pathogenic and nonpathogenic bacteria with respect to innate defense mechanisms in the intestinal mucosal cell. Here we report that E. coli strain Nissle 1917 and a variety of other probiotic bacteria, including lactobacilli—in contrast to more than 40 different E. coli strains tested—strongly induce the expression of the antimicrobial peptide human beta-defensin-2 (hBD-2) in Caco-2 intestinal epithelial cells in a time- and dose-dependent manner. Induction of hBD-2 through E. coli Nissle 1917 was further confirmed by activation of the hBD-2 promoter and detection of the hBD-2 peptide in the culture supernatants of E. coli Nissle 1917-treated Caco-2 cells. Luciferase gene reporter analyses and site-directed mutagenesis experiments demonstrated that functional binding sites for NF-κB and AP-1 in the hBD-2 promoter are required for induction of hBD-2 through E. coli Nissle 1917. Treatment with the NF-κB inhibitor Helenalin, as well as with SP600125, a selective inhibitor of c-Jun N-terminal kinase, blocked hBD-2 induction by E. coli Nissle 1917 in Caco-2 cells. SB 202190, a specific p38 mitogen-activated protein kinase inhibitor, and PD 98059, a selective inhibitor of extracellular signal-regulated kinase 1/2, were ineffective. This report demonstrates that probiotic bacteria may stimulate the intestinal innate defense through the upregulation of inducible antimicrobial peptides such as hBD-2. The induction of hBD-2 may contribute to an enhanced mucosal barrier to the luminal bacteria.

Human beta-defensin-2

Human beta-defensin-2 (HBD-2) is a cysteine-rich cationic low molecular weight antimicrobial peptide recently discovered in psoriatic lesional skin. It is produced by a number of epithelial cells and exhibits potent antimicrobial activity against Gram-negative bacteria and Candida, but not Gram-positive Staphylococcus aureus. HBD-2 represents the first human defensin that is produced following stimulation of epithelial cells by contact with microorganisms such as Pseudomonas aeruginosa or cytokines such as TNF-alpha and IL-1 beta. The HBD-2 gene and protein are locally expressed in keratinocytes associated with inflammatory skin lesions such as psoriasis as well as in the infected lung epithelia of patients with cystic fibrosis. It is intriguing to speculate that HBD-2 is a dynamic component of the local epithelial defense system of the skin and respiratory tract having a role to protect surfaces from infection, and providing a possible reason why skin and lung infections with Gram-negative bacteria are rather rare.

Antimicrobial skin peptides and proteins

Abstract.Human skin is permanently exposed to microorganisms, but rarely infected. One reason for this natural resistance might be the existence of a ‘chemical barrier’ consisting in constitutively and inducibly produced antimicrobial peptides and proteins (AMPs). Many of these AMPs can be induced in vitro by proinflammatory cytokines or bacteria. Apart from being expressed in vivo in inflammatory lesions, some AMPs are also focally expressed in skin in the absence of inflammation. This suggests that non-inflammatory stimuli of endogenous and/or exogenous origin can also stimulate AMP synthesis without inflammation. Such mediators might be ideal ‘immune stimulants’ to induce only the innate antimicrobial skin effector molecules without causing inflammation.

Psoriatic scales: a promising source for the isolation of human skin-derived antimicrobial proteins

Patients with psoriasis, a chronic, hyperproliferative and noninfectious skin disease, suffer surprisingly fewer cutaneous infections than would be expected. This observation led us to the hypothesis that a local “chemical shield” in the form of antimicrobial proteins provides psoriatic skin with resistance against infection. We subsequently began a systematic analysis of in vitro antimicrobially active proteins in psoriatic‐scale extracts. A biochemical approach with rigorous purification and characterization combined with antimicrobial testing identified a number of mostly new human antibiotic peptides and proteins. In this review, we will focus on the most prominent antimicrobial proteins in psoriatic‐scale extracts, which we identified as the S100‐protein psoriasin, human β‐defensin 2 (hBD‐2), RNase 7, lysozyme, and human neutrophil defensin 1–3. Apart from these cutaneous, antimicrobial proteins, only a few others, including hBD‐3, have been characterized. A great number of minor antimicrobial proteins await further structural characterization.

Enhanced expression and secretion of antimicrobial peptides in atopic dermatitis and after superficial skin injury.

Human skin can defend itself against potentially invading microorganisms by production of antimicrobial peptides (AMPs). The expression of AMPs in atopic dermatitis (AD) is still emerging. To gain more insight into the role of AMPs in AD, we systematically analyzed the expression of ribonuclease 7 (RNase 7), psoriasin, and human beta-defensins (hBD)-2 and -3 in AD compared with psoriatic and healthy control skin as well as after experimental barrier disruption. Immunostaining revealed enhanced expression of all AMPs in the lesional skin of untreated AD and psoriasis when compared with non-lesional skin and controls. Accordingly, induced in vivo secretion of RNase 7, psoriasin, and hBD-2 was detected using ELISA on lesional skin in AD and in even higher concentrations in psoriasis. The secretion of AMPs did not correlate with severity of AD and Staphylococcus aureus colonization. Skin barrier disruption caused enhanced immunoreactivity of hBD-2 and hBD-3 after 24 hours. Strong secretion of RNase 7 was already detected after 1 hour, whereas hBD-2 secretion was significantly enhanced after 24 hours only under occlusion. Thus, a disturbed skin barrier may trigger AMP induction in AD and psoriasis. The functional role of AMP in AD, especially with regard to the control of S. aureus colonization, needs further analysis.

Epithelial peptide antibiotics

Surfaces of higher eukaryotes such as plants, invertebrates, and vertebrates, including humans, are normally covered with microorganisms but usually are not infected by them. The reason, apart from physical barriers, is the production of gene-encoded antimicrobial peptides by epithelial cells. Many novel antimicrobial peptides have been discovered recently in the epithelia of plants, insects, amphibians, and cattle, and, more recently, also in humans. In situ hybridization studies indicate a rather organ-specific expression of the genes for peptide antibiotics, which, due to their antimicrobial spectrum and conditions of expression, may also define the physiologic microflora. Some epithelial antimicrobial peptides are constitutively expressed; others are inducible, either by the presence of microorganisms via as of yet not well characterized elicitor receptors or by endogenous proinflammatory cytokines. Most antimicrobial peptides kill microorganisms by forming pores in the cell membrane, and the sensitivity of some peptide antibiotics towards cholesterol, a major mammalian cell membrane constituent, may indicate why these peptide antibiotics are not toxic for mammalian cells. Thus, it seems to be difficult for microorganisms to acquire resistance, making these peptides very attractive for therapeutic use as antibiotics. The first clinical studies are very promising, and after solving the problems of a large-scale biotechnical synthesis, which is more complicated due to the principally suicidal activity of these peptides, a number of new natural structure-based peptides may be developed. Furthermore, discovery of the inducibility of many antimicrobial peptides may also lead to the development of compounds that elicit epithelial defense reactions by stimulating the synthesis of endogenous peptide antibiotics.