Kazuhisa Ouhara

Induction of Keratinocyte Migration via Transactivation of the Epidermal Growth Factor Receptor by the Antimicrobial Peptide LL-37

The closure of skin wounds is essential for resistance against microbial pathogens, and keratinocyte migration is an important step in skin wound healing. Cathelicidin hCAP18/LL-37 is an innate antimicrobial peptide that is expressed in the skin and acts to eliminate microbial pathogens. Because hCAP18/LL-37 is up-regulated at skin wound sites, we hypothesized that LL-37 induces keratinocyte migration. In this study, we found that 1 μg/ml LL-37 induced the maximum level of keratinocyte migration in the Boyden chamber assay. In addition, LL-37 phosphorylated the epidermal growth factor receptor (EGFR) after 10 min, which suggests that LL-37-induced keratinocyte migration occurs via EGFR transactivation. To test this assumption, we used inhibitors that block the sequential steps of EGFR transactivation, such as OSU8-1, CRM197, anti-EGFR no. 225 Ab, and AG1478. All of these inhibitors completely blocked LL-37-induced keratinocyte migration, which indicates that migration occurs via HB-EGF-mediated EGFR transactivation. Furthermore, CRM197, anti-EGFR no. 225, and AG1478 blocked the LL-37-induced phosphorylation of STAT3, and transfection with a dominant-negative mutant of STAT3 abolished LL-37-induced keratinocyte migration, indicating the involvement of the STAT3 pathway downstream of EGFR transactivation. Finally, we tested whether the suppressor of cytokine signaling (SOCS)/cytokine-inducible Src homology 2-containing protein (CIS) family of negative regulators of STAT3 regulates LL-37-induced keratinocyte migration. Transfection with SOCS1/Jak2 binding protein or SOCS3/CIS3 almost completely abolished LL-37-induced keratinocyte migration. In conclusion, LL-37 induces keratinocyte migration via heparin-binding-EGF-mediated transactivation of EGFR, and SOCS1/Jak 2 binding and SOCS3/CIS3 negatively regulate this migration. The results of this study suggest that LL-37 closes skin wounds by the induction of keratinocyte migration.

Outer membrane protein 100, a versatile virulence factor of Actinobacillus actinomycetemcomitans

Actinobacillus actinomycetemcomitans (Aa) is one of the pathogenic bacteria involved in periodontal diseases. We have previously identified six major outer membrane proteins (Omps) of Aa Y4. Among them is an Omp with high molecular mass, designated Omp100, which has homology to a variety of virulence factors. Electron microscopic observation indicated that Omp100 is randomly localized on the cell surface of Aa. Aa Y4 has been shown to adhere and invade KB or normal human gingival keratinocytes. Anti‐Omp100 antibody inhibited 50% of adhesion and 70% of invasion of Aa Y4 to KB cells. An Omp100 knock‐out mutant had a decreased adhesion and invasion efficiency of 60%, compared with that of the wild type. Escherichia coli HB101 expressing Omp100 adhered twofold and invaded 10‐fold more than the wild‐type E. coli HB101. HB101 expressing Omp100 showed resistance to serum by trapping factor H, an inhibitor for C3b, with Omp100. Omp100 induced inflammatory cytokine responses of interleukin (IL)‐8, IL‐6 and tumour necrosis factor (TNF)α in epithelial cells, and induced IL‐1β and TNFα production in mouse macrophages. These results indicate that Omp100 is a versatile virulence factor that may demonstrate potential significance in the onset of periodontal diseases related to Aa.

Innate immune peptide LL-37 displays distinct expression pattern from beta-defensins in inflamed gingival tissue

Anti‐microbial peptides produced from mucosal epithelium appear to play pivotal roles in the host innate immune defence system in the oral cavity. In particular, human beta‐defensins (hBDs) and the cathelicidin‐type anti‐microbial peptide, LL‐37, were reported to kill periodontal disease‐associated bacteria. In contrast to well‐studied hBDs, little is known about the expression profiles of LL‐37 in gingival tissue. In this study, the anti‐microbial peptides expressed in gingival tissue were analysed using immunohistochemistry and enxyme‐linked immunosorbent assay (ELISA). Immunohistochemistry revealed that neutrophils expressed only LL‐37, but not hBD‐2 or hBD‐3, and that such expression was prominent in the inflammatory lesions when compared to healthy gingivae which showed very few or no LL‐37 expressing neutrophils. Gingival epithelial cells (GEC), however, expressed all three examined anti‐microbial peptides, irrespective of the presence or absence of inflammation. Moreover, as determined by ELISA, the concentration of LL‐37 in the gingival tissue homogenates determined was correlated positively with the depth of the gingival crevice. Stimulation with periodontal bacteria in vitro induced both hBD‐2 and LL‐37 expressions by GEC, whereas peripheral blood neutrophils produced only LL‐37 production, but not hBD‐2, in response to the bacterial stimulation. These findings suggest that LL‐37 displays distinct expression patterns from those of hBDs in gingival tissue.

New mechanisms of skin innate immunity: ASK1‐mediated keratinocyte differentiation regulates the expression of β‐defensins, LL37, and TLR2

Epidermal keratinocytes differentiate and form a multilayered epidermis, which is the primary barrier between the body and the outer environment. As the epidermis is constantly exposed to a variety of microbial pathogens, its function of resisting microbial pathogens is vital. This characteristic feature is formed during differentiation. Immunohistochemical analysis revealed that the upper epidermis of normal human skin expresses β‐defensins 1–3 and LL37. We hypothesized that epidermal keratinocytes develop an innate immune barrier based on human β‐defensins (hBD) and LL37 during differentiation. To prove this, we introduced an active form of the apoptosis signal‐regulating kinase‐1 (ASK1), an intracellular regulator of keratinocyte differentiation, into cultured normal human keratinocytes. Transfection of this active form, ASK1‐ΔN, significantly enhanced the expression of hBD1–3 and LL37. In addition, a p38 inhibitor abolished this induction, indicating that the ASK1‐p38 cascade regulates the expression of hBD1–3 and LL37. Furthermore, the ASK1‐p38 pathway also regulated the expression of Toll‐like receptor (TLR)2 in keratinocytes. Contact between S. aureus and keratinocytes resulted in the phosphorylation of p38 and induced the expression of hBD2 and hBD3. Moreover, the p38 inhibitor reduced this induction. In conclusion, the ASK1‐p38 cascade regulates the innate immunity of the skin by forming an immune barrier consisting of hBD, LL37, and TLR2 during epidermal differentiation.

Actinobacillus actinomycetemcomitans Outer Membrane Protein 100 Triggers Innate Immunity and Production of β-Defensin and the 18-Kilodalton Cationic Antimicrobial Protein through the Fibronectin-Integrin Pathway in Human Gingival Epithelial Cells

ABSTRACT Antimicrobial peptides, human β-defensin (hBD), and the 18-kDa cationic antimicrobial protein (CAP18) are components of innate immunity. These peptides have antimicrobial activity against bacteria, fungi, and viruses. Actinobacillus actinomycetemcomitans is a gram-negative facultative anaerobe implicated in the initiation of periodontitis. The innate immunity peptides have antibacterial activity against A. actinomycetemcomitans. We investigated the molecular mechanism of human gingival epithelial cells (HGEC) responding to exposure to A. actinomycetemcomitans. HGEC constitutively express hBD1 and inducibly express hBD2, hBD3, and CAP18 on exposure to A. actinomycetemcomitans. The level of expression varies among clinical isolates. In the signaling pathway for hBD2 induction by the bacterial contact, we demonstrate that the mitogen-activated protein (MAP) kinase and not the NF-κB transcription factor pathway is used. We found the outer membrane protein 100 (Omp100; identified by molecular mass) is the component inducing the hBD2 response. Omp100 binds to fibronectin, an extracellular matrix inducing hBD2 via the MAP kinase pathway. Anti-integrin α5β1, antifibronectin, genistein, and PP2 suppress the Omp100-induced expression of hBD2, suggesting that Src kinase is involved through integrin α5β1. The inflammatory cytokines, tumor necrosis factor α (TNF-α), interleukin-1β (IL-1β), IL-6 and IL-8, produced by HGEC on contact with A. actinomycetemcomitans also stimulate expression of hBD2. Further, neutralizing antibody against TNF-α or IL-8 partially inhibits the induction of hBD2 on bacterial contact. Therefore, we found that the induction of the antimicrobial peptides is mediated by a direct response principally through an Omp100-fibronectin interaction, and using secondary stimulation by inflammatory cytokines induced by the bacterial exposure.

Syntheses of Prostaglandin E2 and E-Cadherin and Gene Expression of β-defensin-2 by Human Gingival Epithelial Cells in Response to Actinobacillus actinomycetemcomitans

The interaction between epithelial cells and microorganisms is the most important step in bacterial infections. Actinobacillus actinomycetemcomitans was suggested to play a significant role in the initiation of periodontitis because of its bacteriological characteristics. Prostaglandins (PG) mediate the inflammatory response. Human β-defensin-2 (hBD-2) is an antimicrobial peptide and contributes to innate immunity. E-cadherin is responsible for an epithelial intercellular junction. In this study, we investigated the syntheses of PGE2 and E-cadherin and the expression of hBD-2 in human gingival epithelial cells (HGEC) following exposure to A. actinomycetemcomitans. The levels of PGE2 and cyclooxygenase-2, which are responsible for an increase in PGE2, were increased depending on bacteria exposure time. hBD-2 mRNA was induced by A. actinomycetemcomitans, while HGEC exposed to A. actinomycetemcomitans showed a decrease in E-cadherin levels. Etodolac, a selective cyclooxygenase-2 inhibitor reinforced the increase in hBD-2 mRNA levels by A. actinomycetemcomitans. Furthermore, the etodolac suppressed the decrease in E-cadherin levels. Thus, endogenous PGE2 is involved in the hBD-2 and E-cadherin responses of HGEC to A. actinomycetemcomitans. These findings suggest that the inflammatory and antimicrobial response of gingival epithelial cells to A. actinomycetemcomitans is involved in the initiation of periodontal inflammation. A. actinomycetemcomitans may destroy the mechanical epithelial barrier by destroying E-cadherin.

Brain-derived Neurotrophic Factor Stimulates Bone/Cementum-related Protein Gene Expression in Cementoblasts

Brain-derived neurotrophic factor (BDNF), recognized as essential in the developing nervous system, is involved in differentiation and proliferation in non-neuronal cells, such as endothelial cells, osteoblasts, and periodontal ligament cells. We have focused on the application of BDNF to the regeneration of periodontal tissue and indicated that BDNF promotes the regeneration of experimentally created periodontal defects. Cementoblasts form cementum, mineralized tissue, which is key to establishing a functional periodontium. The application of BDNF to the regeneration of periodontal tissue requires elucidation of the mechanism by which BDNF regulates the functions of cementoblasts. In this study, we examined how BDNF regulates the mRNA expression of bone/cementum-related proteins (alkaline phosphatase (ALP), osteopontin (OPN), and bone morphogenetic protein-2 (BMP-2)) in cultures of immortalized human cementoblast-like (HCEM) cells. BDNF elevated the mRNA levels of ALP, OPN, and BMP-2 in HCEM cells. Small interfering RNA (siRNA) for TRKB, a high affinity receptor of BDNF, siRNA for ELK-1, which is a downstream target of ERK1/2, and PD98059, an ERK inhibitor, obviated the increase in the mRNA levels. BDNF increased the levels of phosphorylated ERK1/2 and Elk-1, and the blocking of BDNF signaling by treatment with siRNA for TRKB and PD98059 suppressed the phosphorylation of ERK1/2 and Elk-1. Furthermore, BDNF increased the levels of phosphorylated c-Raf, which activates the ERK signaling pathway. These findings provide the first evidence that the TrkB-c-Raf-ERK1/2-Elk-1 signaling pathway is required for the BDNF-induced mRNA expression of ALP, OPN, and BMP-2 in HCEM cells.

Innate defences against methicillin-resistant Staphylococcus aureus (MRSA) infection

The innate immune system is the primary defence against bacterial infection. Among the factors involved in innate defence, anti‐microbial peptides produced by humans have recently attracted attention due to their relevance to some diseases and also to the development of new chemotherapeutic agents. Staphylococcus aureus is one of the major human pathogens, causing a variety of infections from suppurative disease to food poisoning. Methicillin‐resistant S. aureus (MRSA) is a clinical problem and with the recent emergence of a vancomycin‐resistant strain, this will pose serious problems in the near future. In investigating the molecular biology of S. aureus infections to develop new chemotherapeutic agents against MRSA infections, knowledge of the interaction of innate anti‐microbial peptides with S. aureus is important. In vitro and in vivo experiments demonstrate that exposure of S. aureus to host cells can induce the anti‐microbial peptides β‐defensin‐2 (hBD2), hBD3, and LL37/CAP18. The induction level of these peptides differs among strains, as does the susceptibility of the strains, with MRSA strains exhibiting lower susceptibility. In summary, the susceptibility of S. aureus strains, including MRSA strains, to components of the innate immune system varies, with the MRSA strains showing more resistance to both innate immune factors and chemotherapeutic agents. Copyright

Macrophage inflammatory protein-3α and β-defensin-2 stimulate dentin sialophosphoprotein gene expression in human pulp cells

Abstract Macrophage inflammatory protein (MIP)-3α and β-defensin (BD)-2 have antimicrobial activity and chemotactic activity for immature dendritic cells, natural killer cells, and memory T cells. However, it remains unknown if the widespread effects of these peptides also include an influence on the differentiation of mesenchymal cells. Pulp cells have the capacity to differentiate into odontoblasts and to form dentin. The aim of this study was to determine if inflammatory leukocyte products influence the capacity of pulp cells to differentiate. Dentin sialophosphoprotein (DSPP) is a tooth-specific protein being expressed mostly by odontoblast cells. In the present study, we investigated effects of MIP-3α and BD-2 on the DSPP and osteopontin (OPN) gene expression in cultures of human pulp-derived fibroblastic cells (HP cells). HP cells expressed mRNA for the CC chemokine receptor (CCR) 6 to which both MIP-3α and BD-2 can bind. Real-time PCR showed that MIP-3α and BD-2 significantly increased DSPP mRNA levels, although BD-2 increased DSPP mRNA levels less than MIP-3α. MIP-3α and BD-2 increased OPN mRNA levels very slightly. MIP-3α and BD-2 possessed antibacterial activity against Streptococcus mutans and Lactobacillus casei, which are involved in caries, although the antibacterial activity of MIP-3α was lower than that of BD-2. These findings suggest the MIP-3α and BD-2 have the ability to stimulate odontoblast differentiation in addition to their more traditional role in inflammation and have potential in the removal of bacteria in infected soft dentin and pulp tissues.

Susceptibility of Periodontopathogenic and Cariogenic Bacteria to Defensins and Potential Therapeutic Use of Defensins in Oral Diseases

Antimicrobial peptides play an important role in the human innate immune defense system. In the oral cavity, a number of antimicrobial peptides, including defensins and LL37, are produced from various tissues such as salivary glands, gingival epithelium, tongue and buccal mucosa. These peptides are believed to function as a host defense system by controlling the activities of commensal bacteria and thus preventing the colonization and growth of pathogenic bacteria in oral cavity. Two major oral diseases, dental caries and periodontitis are known as infectious diseases. Therefore, it is of great interest to elucidate the mechanisms underlying the onset and progression of these diseases by investigating the interaction between cariogenic, or periodontopathogenic bacteria and antimicrobial peptides. Since these peptides have a broad antimicrobial spectrum, they are implicated as possible therapeutic agents. Therefore, in this review, we first focus on the susceptibility of oral bacteria, especially cariogenic and periodontopathogenic bacteria, to antimicrobial peptides, and then we discuss their potential diagnostic and clinical therapeutic uses.