Vitamin D triggers hCAP18/LL-37 production: Implications for LL-37-induced human osteoblast cytotoxicity

The human cathelicidin LL-37 shows activity against microorganisms, but it is also cytotoxic to host cells. The CAMP gene codes for the LL-37 precursor hCAP18 which is processed extracellularly to active LL-37. It has previously been shown that vitamin D stimulates CAMP gene activity, but less information is available demonstrating that vitamin D also can increase hCAP18/LL-37 protein production. Here, we show with RT-qPCR that a physiological concentration of vitamin D (50 nM) enhances CAMP mRNA levels by about 170 times in human THP-1 monocyte cells. Stimulation with 50 nM vitamin D increases hCAP18/LL-37 protein contents 3-4 times in THP-1 cell lysates demonstrated by both dot blot analysis and ELISA applying two different hCAP18/LL-37 antibodies. Treatment with the proteasome inhibitor MG132 enhances hCAP18/LL-37 levels, suggesting that turnover of hCAP18/LL-37 protein is regulated by the proteasome. The hCAP18/LL-37 concentration in vitamin D-stimulated THP-1 cells corresponds to 1.04 μM LL-37. Interestingly, synthetic LL-37, at this concentration, reduces viability of human osteoblast-like MG63 cells, whereas the THP-1 cells are less sensitive as demonstrated by the MTT assay. In summary, we show that vitamin D enhances hCAP18/LL-37 production, and that this effect can be of physiological/pathophysiological relevance for LL-37-induced human osteoblast toxicity.

A dual functional polypeptide with antibacterial and anti-inflammatory properties for the treatment of periodontitis

Periodontitis has been reported as the sixth most prevalent disease in human beings. This destructive disease is closely related to systemic diseases. Existing local drug delivery systems for periodontitis suffer from poor antibacterial effect and drug resistance. Inspired by the pathogenesis of periodontitis, we implemented a strategy to construct a dual functional polypeptide LL37-C15, which exhibited remarkable antibacterial effect against P. gingivalis and A. actinomycetemcomitans. In addition, LL37-C15 inhibits the release of pro-inflammatory cytokines by controlling the inflammatory pathway and reversing macrophage M1. Furthermore, the anti-inflammatory effect of LL37-C15 was also verified in vivo in a periodontitis rat model through the morphometry and histological observations of alveolar bone, hematoxylin-eosin, and Trap staining in gingival tissue. The results of molecular dynamics simulations showed that LL37-C15 could selectively destroy the bacterial cell membrane and protect the animal cell membrane in a self-destructive manner. The results showed that the polypeptide LL37-C15, as a novel promising therapeutic agent, exhibited a great potential for the periodontitis management. What's more, this dual functional polypeptide provides a promising strategy for building a multifunctional therapeutic platform against the inflammation and other diseases.

Nanomolar LL-37 induces permeability of a biomimetic mitochondrial membrane

LL-37, the only human host cathelicidin peptide, is proposed to be able to induce host cell apoptosis through mitochondrial membrane permeabilization (MMP). Detailed pathways of the LL-37-triggered MMP are however still disputed. It is generally believed that cationic peptides permeate a membrane mostly in conditions of micromolar peptide concentrations and negatively charged membranes, which are not usually satisfied in the mitochondrial circumstance. Herein, using a variety of single-molecule techniques, we show that nanomolar LL-37 specifically induces permeability of a phosphoethanolamine (PE)-rich biomimetic mitochondrial membrane in a protein-independent manner. The insertion dynamics of single LL-37 molecules exhibit different metastable states in bilayers composed of different lipids. Moreover, the PE lipids significantly facilitate adsorption and accumulation of LL-37 on the PE-rich bilayer, and produce deeper insertion of peptide oligomers, especially tetramers, into the bilayer. This work offers an alternative pathway of the LL-37-triggered MMP and apoptosis.

Microbial resistance to nanotechnologies: An important but understudied consideration using antimicrobial nanotechnologies in orthopaedic implants

Microbial resistance to current antibiotics therapies is a major cause of implant failure and adverse clinical outcomes in orthopaedic surgery. Recent developments in advanced antimicrobial nanotechnologies provide numerous opportunities to effective remove resistant bacteria and prevent resistance from occurring through unique mechanisms. With tunable physicochemical properties, nanomaterials can be designed to be bactericidal, antifouling, immunomodulating, and capable of delivering antibacterial compounds to the infection region with spatiotemporal accuracy. Despite its substantial advancement, an important, but under-explored area, is potential microbial resistance to nanomaterials and how this can impact the clinical use of antimicrobial nanotechnologies. This review aims to provide a better understanding of nanomaterial-associated microbial resistance to accelerate bench-to-bedside translations of emerging nanotechnologies for effective control of implant associated infections.

The antimicrobial peptides LL-37, KR-20, FK-13 and KR-12 inhibit the growth of a sensitive and a metronidazole-resistant strain of Trichomonas vaginalis

The parasite Trichomonas vaginalis is the aetiologic agent of trichomoniasis, the most common non-viral sexually transmitted disease worldwide. This infection often remains asymptomatic and is related to several health complications. The traditional treatment for trichomoniasis uses drugs of the 5-nitroimidazole family, such as metronidazole; however, scientific reports indicate an increasing number of drug-resistant strains. Antimicrobial peptides could be an alternative or complementary treatment. In this sense, one attractive candidate is the human cathelicidin, being LL-37 its active form. LL-37 possesses microbicidal activity against many microorganisms such as bacteria, Candida albicans, and Entamoeba histolytica. Shorter sequences derived from this peptide, such as KR-20, FK-13 and KR-12, have been shown to possess a higher microbicidal effect than LL-37. In this study, we determined the activity of LL-37 and its derivatives against T. vaginalis, which was unknown. The results showed that the four peptides (LL-37, KR-20, FK-13-NH₂ and KR-12) decreased the viability of T. vaginalis on a 5-nitroimidazole-sensitive and a 5-nitroimidazole-resistant strain; however, KR-20 was the most effective peptide, followed by FK-13-NH₂. Low concentrations of all peptides showed a better effect when combined with metronidazole in the sensitive and resistant T. vaginalis strains. These results are promising for potential future therapeutic uses.

LL-37 and Double-Stranded RNA Synergistically Upregulate Bronchial Epithelial TLR3 Involving Enhanced Import of Double-Stranded RNA and Downstream TLR3 Signaling

The human host defense peptide LL-37 influences double-stranded RNA signaling, but this process is not well understood. Here, we investigate synergistic actions of LL-37 and synthetic double-stranded RNA (poly I:C) on toll-like receptor 3 (TLR3) expression and signaling, and examine underlying mechanisms. In bronchial epithelial BEAS-2B cells, LL-37 potentiated poly I:C-induced TLR3 mRNA and protein expression demonstrated by qPCR and Western blot, respectively. Interestingly, these effects were associated with increased uptake of rhodamine-tagged poly I:C visualized by immunocytochemistry. The LL-37/poly I:C-induced upregulation of TLR3 mRNA expression was prevented by the endosomal acidification inhibitor chloroquine, indicating involvement of downstream TLR3 signaling. The glucocorticoid dexamethasone reduced LL-37/poly I:C-induced TLR3 expression on both mRNA and protein levels, and this effect was associated with increased IκBα protein expression, suggesting that dexamethasone acts via attenuation of NF-κB activity. We conclude that LL-37 potentiates poly I:C-induced upregulation of TLR3 through a mechanism that may involve enhanced import of poly I:C and that LL-37/poly I:C-induced TLR3 expression is associated with downstream TLR3 signaling and sensitive to inhibition of NF-κB activity.

In Vitro Delivery of HIV-1 Nef-Vpr DNA Construct Using the Human Antimicrobial Peptide LL-37

BACKGROUND AND OBJECTIVES

DNA-based therapeutic vaccines have been proposed as promising strategy for treatment of established HIV infections. However, these vaccines are often associated with certain shortcomings, such as poor immunogenicity and low transfection efficiency. In this study, we investigated ability of LL-37 to deliver a potential immunogenic fusion construct comprising HIV-1 nef and vpr genes into a mammalian cell line.

METHODS

First, the pEGFP-N1 eukaryotic expression vector harboring the HIV-1 nef-vpr fusion was produced free of endotoxin on large scale. Then, DNA/LL-37 complexes were prepared by co-incubation of pEGFP-nef-vpr with LL-37 for 45 minutes at different nitrogen to phosphate (N/P) ratios. Formation of DNA/peptide complexes was investigated by gel retardation assay. Next, stability and morphological characteristics of the nanoparticles were evaluated. Toxicity of LL-37 and the nanoparticles in HEK-293T cells was assessed by MTT assay. Transfection efficiency of the DNA/LL-37 complexes was studied by fluorescence microscopy, flow cytometry, and western blot analysis.

RESULTS

LL-37 formed stable complexes with pEGFP-nef-vpr (diameter of 150-200 nm) while providing good protection against nucleolytic and proteolytic degradation. The peptide significantly affected cell viability even at low concentrations. However, the LL-37/DNA complexes had no significant cytotoxic effect. Treatment of cells with pEGFP-N1/LL-37 and pEGFP-nef-vpr/LL-37 resulted in transfection of 36.32% ± 1.13 and 25.55% ± 2.07 of cells, respectively.

CONCLUSION

Given these findings and the important immunomodulatory and antiviral activities of LL-37, the use of this peptide can be further exploited in the development of novel gene delivery strategies and vaccine design.

The antimicrobial peptide LL-37 triggers release of apoptosis-inducing factor and shows direct effects on mitochondria

The human antimicrobial peptide LL-37 permeabilizes the plasma membrane of host cells, but LL-37-induced direct effects on mitochondrial membrane permeability and function has not been reported. Here, we demonstrate that LL-37 is rapidly (within 20 min) internalized by human osteoblast-like MG63 cells, and that the peptide co-localizes with MitoTracker arguing for accumulation in mitochondria. Subcellular fractionation and Western blot disclose that stimulation with LL-37 (8 μM) for 2 h triggers release of the mitochondrial protein apoptosis-inducing factor (AIF) to the cytosol, whereas LL-37 causes no release of cytochrome C oxidase subunit IV of the inner mitochondrial membrane, suggesting that LL-37 affects mitochondrial membrane permeability in a specific manner. Next, we investigated release of AIF and cytochrome C from isolated mitochondria by measuring immunoreactivity by dot blot. The media of mitochondria treated with LL-37 (8 μM) for 2 h contained 50% more AIF and three times more cytochrome C than that of control mitochondria, showing that LL-37 promotes release of both AIF and cytochrome C. Moreover, in vesicles reflecting mitochondrial membrane lipid composition, LL-37 stimulates membrane permeabilization and release of tracer molecules. We conclude that LL-37 is rapidly internalized by MG63 cells and accumulates in mitochondria, and that the peptide triggers release of pro-apoptotic AIF and directly affects mitochondrial membrane structural properties.

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LL-37 is internalized by osteoblast-like MG63 cells

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LL-37 accumulates in mitochondria

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LL-37 triggers release of apoptosis-inducing factor from mitochondria

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LL-37 permeabilizes mitochondrial membranes

Exogenous LL-37 but not homogenates of desquamated oral epithelial cells shows activity against Streptococcus mutans

OBJECTIVE

The antimicrobial peptide hCAP18/LL-37 is detected in desquamated epithelial cells of human whole saliva, but the functional importance of this pool of hCAP18/LL-37 is not understood. Here, we assess the impact of homogenates of desquamated oral epithelial cells and exogenous, synthetic LL-37 on two oral bacteria: S. mutans and S. gordonii.

MATERIAL AND METHODS

Desquamated epithelial cells of unstimulated whole saliva were isolated and cellular and extracellular levels of hCAP18/LL-37 analyzed by ELISA. Bacterial viability was determined by BacLight Live/Dead staining and confocal laser scanning microscopy.

RESULTS

Desquamated oral epithelial cells harboured hCAP18/LL-37, and they spontaneously released/leaked the peptide to their medium. Exogenous, synthetic LL-37 showed cytotoxic activity against S. mutans but not S gordonii, suggesting that LL-37 acts differentially on these two types of oral bacteria. Homogenates of desquamated oral epithelial cells had no effect on S. mutans viability. Treatment with exogenous, synthetic LL-37 (8 and 10 μM) reduced S. mutans viability, whereas lower concentrations (0.1 and 1 µM) of the peptide lacked effect.

CONCLUSIONS

Desquamated oral epithelial cells contain hCAP18/LL-37, but their cellular levels of hCAP18/LL-37 are too low to affect S. mutans viability, whereas exogenous, synthetic LL-37 has a strong effect on these bacteria.

LL-37-induced caspase-independent apoptosis is associated with plasma membrane permeabilization in human osteoblast-like cells

The host defense peptide LL-37 is active against both gram-positive and gram-negative bacteria, but it has also been shown to reduce human host cell viability. However, the mechanisms behind LL-37-induced human host cell cytotoxicity are not yet fully understood. Here, we assess if LL-37-evoked attenuation of human osteoblast-like MG63 cell viability is associated with apoptosis, and if the underlying mechanism may involve LL-37-induced plasma membrane permeabilization. MG63 cell viability and plasma membrane permeabilization were investigated by using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) method and by measuring lactate dehydrogenase (LDH) release, respectively. Apoptosis was assessed by the terminal deoxynucleotidyl dUTP nick end labeling (TUNEL) assay and Annexin V flow cytometry, and caspase-3 and poly (ADP-ribose) polymerase (PARP) cleavage were determined by Western blot. LL-37 (4 and 10 μM) reduced both cell number and cell viability, and these effects were associated with a pro-apoptotic effect demonstrated by positive TUNEL staining and Annexin V flow cytometry. LL-37-induced apoptosis was not coupled to either caspase-3 or PARP cleavage, suggesting that LL-37 causes caspase-independent apoptosis in MG63 cells. Both LL-37 and the well-known plasma membrane permeabilizer Triton X-100 reduced cell viability and stimulated LDH release. Triton X-100-treated cells showed positive TUNEL staining, and the detergent accumulated cells in late apoptosis/necrosis. Similar to LL-37, Triton X-100 caused no PARP cleavage. We conclude that LL-37 promotes caspase-independent apoptosis, and that this effect seems coupled to plasma membrane permeabilization in human MG63 cells.

Targeting Infectious Agents as a Therapeutic Strategy in Alzheimer's Disease

Alzheimer's disease (AD) is the most prevalent dementia in the world. Its cause(s) are presently largely unknown. The most common explanation for AD, now, is the amyloid cascade hypothesis, which states that the cause of AD is senile plaque formation by the amyloid β peptide, and the formation of neurofibrillary tangles by hyperphosphorylated tau. A second, burgeoning theory by which to explain AD is based on the infection hypothesis. Much experimental and epidemiological data support the involvement of infections in the development of dementia. According to this mechanism, the infection either directly or via microbial virulence factors precedes the formation of amyloid β plaques. The amyloid β peptide, possessing antimicrobial properties, may be beneficial at an early stage of AD, but becomes detrimental with the progression of the disease, concomitantly with alterations to the innate immune system at both the peripheral and central levels. Infection results in neuroinflammation, leading to, and sustained by, systemic inflammation, causing eventual neurodegeneration, and the senescence of the immune cells. The sources of AD-involved microbes are various body microbiome communities from the gut, mouth, nose, and skin. The infection hypothesis of AD opens a vista to new therapeutic approaches, either by treating the infection itself or modulating the immune system, its senescence, or the body's metabolism, either separately, in parallel, or in a multi-step way.

Salivary human beta-defensins and cathelicidin levels in relation to periodontitis and type 2 diabetes mellitus

Objective: Type 2 diabetes mellitus (T2DM) is a well-defined risk factor of periodontitis and it can affect expression of human beta-defensins (hBDs) and cathelicidin (LL-37) as well. The aim of the present study was to evaluate the impact of periodontitis and T2DM on salivary concentrations of these antimicrobial peptides.Material and methods: Unstimulated saliva samples, together with full-mouth periodontal recordings were collected from 92 individuals with periodontitis (63 with T2DM and 21 smokers) and 86 periodontally healthy controls (58 with T2DM and 21 smokers). Salivary hBD-1, -2, -3, LL-37, and advanced glycalization end products (AGE) concentrations were measured by enzyme-linked immunosorbent assay.Results: Among the periodontitis patients, T2DM group demonstrated lower levels of hBD-1 (p = .006), hBD-2 (p < .001) and hBD-3 (p < .001), and higher levels of LL-37 (p < .001) compared to systemically healthy controls. When only periodontally healthy controls were included into the analysis, higher hBD-1 (p = .002) and LL-37 (p < .001) levels were found in T2DM patients in comparison to systemically healthy controls. Salivary LL-37 levels were associated with HbA1c and periodontitis, while hBD-2, hBD-3 and levels associated only with HbA1c.Conclusion: In the limits of this study, hyperglycaemia can be proposed as a regulator of salivary hBD and cathelicidin levels. Periodontitis, on the other hand, affects only salivary LL-37 levels.

What can we learn about functional importance of human antimicrobial peptide LL-37 in the oral environment from severe congenital neutropenia (Kostmann disease)?

The human antimicrobial peptide LL-37 is produced by neutrophils and epithelial cells, and the peptide can be detected in plasma as well as saliva. LL-37 is active against both gram-positive and gram-negative bacteria including oral pathogens such as Porphyromonas gingivalis and Streptococcus mutans. Besides its antimicrobial properties, LL-37 modulates the innate immune system, and furthermore, it also affects host cell viability. Although, both structural and functional properties of LL-37 have been extensively investigated, its physiological/pathophysiological importance in-vivo is not completely understood. In this review, Kostmann disease (morbus Kostmann) is highlighted since it may represent a LL-37 knockdown model which can provide new important information and insights about the functional role of LL-37 in the human in-vivo setting. Patients with Kostmann disease suffer from neutropenia, and although they are treated with recombinant granulocyte colony-stimulating factor (G-CSF) to normalize their levels of neutrophils, they lack or have very low levels of LL-37 in plasma, saliva and neutrophils. Interestingly, these patients suffer from severe periodontal disease, linking LL-37-deficiency to oral infections. Thus, LL-37 seems to play an important pathophysiological role in the oral environment antagonizing oral pathogens and thereby prevents oral infections.

Human host defense peptide LL-37 facilitates double-stranded RNA pro-inflammatory signaling through up-regulation of TLR3 expression in vascular smooth muscle cells

OBJECTIVE

The importance of human host defense peptide LL-37 in vascular innate immunity is not understood. Here, we assess the impact of LL-37 on double-stranded RNA (dsRNA) signaling in human vascular smooth muscle cells.

MATERIALS AND METHODS

Cellular import of LL-37 and synthetic dsRNA (poly I:C) were investigated by immunocytochemistry and fluorescence imaging. Transcript and protein expression were determined by qPCR, ELISA and Western blot. Knockdown of TLR3 was performed by siRNA.

RESULTS

LL-37 was rapidly internalized, suggesting that it has intracellular actions. Co-stimulation with poly I:C and LL-37 enhanced pro-inflammatory IL-6 and MCP-1 transcripts several fold compared to treatment with poly I:C or LL-37 alone. Poly I:C increased IL-6 and MCP-1 protein production, and this effect was potentiated by LL-37. LL-37-induced stimulation of poly I:C signaling was not associated with enhanced import of poly I:C. Treatment with poly I:C and LL-37 in combination increased expression of dsRNA receptor TLR3 compared to stimulation with poly I:C or LL-37 alone. In TLR3 knockdown cells, treatment with poly I:C and LL-37 in combination had no effect on IL-6 and MCP-1 expression, showing loss of function.

CONCLUSIONS

LL-37 potentiates dsRNA-induced cytokine production through up-regulation of TLR3 expression representing a novel pro-inflammatory mechanism.

The C1q Receptors: Focus on gC1qR/p33 (C1qBP, p32, HABP-1)1

In the past several years, a number of C1q binding surface proteins or receptors have been described. This is not of course surprising considering the complexity of the C1q molecule and its ability to bind to a wide range of cellular and plasma proteins via both its collagen-like [cC1q] region and its heterotrimeric globular heads [gC1q] each of which in turn is capable of binding a specific ligand. However, while each of these "receptor" molecules undoubtedly plays a specific function within its restricted microenvironment, and therefore merits full attention, this review nonetheless, will singularly focus on the structure and function of gC1qR-a multi-functional and multi-compartmental protein, which plays an important role in inflammation, infection, and cancer. Although first identified as a receptor for C1q, gC1qR has been shown to bind to a plethora of proteins found in plasma, on the cell surface and on pathogenic microorganisms. The plasma proteins that bind to gC1qR are mostly blood coagulation proteins and include high molecular weight kininogen [HK], Factor XII [Hageman factor], fibrinogen, thrombin [FII], and multimeric vitronectin. This suggests that gC1qR can play an important role in modulating not only of fibrin formation, particularly at local sites of immune injury and/or inflammation, but by activating the kinin/kallikrein system, it is also able to generate, bradykinin, a powerful vasoactive peptide that is largely responsible for the swelling seen in angioedema. Another important function of gC1qR is in cancer, where it has been shown to play a role in tumor cell survival, growth and metastatic invasion by interacting with critical molecules in the tumor cell microenvironment including those of the complement system and kinin system. Finally, by virtue of its ability to interact with a growing list of pathogen-associated molecules, including bacterial and viral ligands, gC1qR is becoming recognized as an important pathogen recognition receptor [PRR]. Given the numerous roles it plays in a growing list of disease settings, gC1qR has now become a potential target for the development of monoclonal antibody-based and/or small molecule-based therapies.

Antimicrobial peptide LL-37 is bactericidal against Staphylococcus aureus biofilms

Our current challenge in the management of prosthetic joint infection is the eradication of biofilms which has driven the need for improved antimicrobial agents and regimens. In this study, the antimicrobial peptide, LL-37, and silver nanoparticles (AgNPs) were investigated for their antimicrobial efficacies against Staphylococcus aureus (S. aureus), a microorganism commonly implicated in biofilm-related infections. These antimicrobials were compared to conventional antibiotics and combination treatments with rifampin. Using a Centers for Disease Control reactor, 24 h S. aureus biofilms were formed on cobalt-chromium discs and the anti-biofilm activity was determined by quantifying the amount of colony forming units following treatments. We found that LL-37 was the most efficacious antimicrobial agent with a more than 4 log reduction in colony counts. In comparison, silver nanoparticles and conventional antibiotics were not as efficacious, with a less than 1 log reduction in colony counts. Antimicrobial combination treatments with rifampin significantly increased the log reduction for AgNPs and gentamicin, although still significantly less than LL-37 in isolation. Furthermore, kinetic studies revealed the rapid elimination of S. aureus biofilm with LL-37. Collectively, the results of this study demonstrated that LL-37 was an effective agent against S. aureus biofilms and may have potential clinical applications in the eradication of biofilms and treatment of prosthetic joint infection.

Sesquiterpene lactones from Ambrosia arborescens Mill. inhibit pro-inflammatory cytokine expression and modulate NF-κB signaling in human skin cells

BACKGROUND

Ambrosia arborescens has been used in Andean traditional medicine to reduce problems associated with various inflammatory diseases and conditions, although the underlying mechanism is unknown.

HYPOTHESIS/PURPOSE

The sesquiterpene lactones (SLs) coronopilin and damsin, which are major secondary metabolites of A. arborescens, have anti-inflammatory activity by attenuation of IL-6 and MCP-1 expression and inhibition of NF-κB in human dermal fibroblasts (HDFa) and human keratinocytes (HaCaT).

STUDY DESIGN

In order to confirm a high concentration of damsin and coronopilin in the plant material, a quantitative method was developed. The effect of the pure compounds on cytokine and NF-κB expression was examined, as well as their effects on HDFa and HaCaT cell morphology and viability.

METHODS

Coronopilin and damsin were quantified by HPLC-DAD analysis, from EtOAc extracts of the aerial parts of A. arborescens. Cell morphology was investigated by phase-contrast microscopy and cell viability by the MTT assay. IL-6 and MCP-1 cytokine gene expression was assessed by quantitative real-time RT-PCR in LPS stimulated cells. The NF-κB pathway was studied through western blotting of the phosphorylated forms of p65 and p50/p105, as well as the non-phosphorylated IκB. Dexamethasone was used as positive control.

RESULTS

Dry aerial parts contained 12.3  mg/g and 13.4  mg/g of coronopilin and damsin, respectively. Treatment with either compound (1-10 µM) for 24  h attenuated LPS-induced mRNA expression of the pro-inflammatory cytokine IL-6 and the chemokine MCP-1 in HDFa cells. The down-regulation of MCP-1 mRNA induced by coronopilin and damsin was confirmed on the protein level. Damsin reduced phosphorylated p65 and p105 subunits in HDFa cells. Neither coronopilin nor damsin affected HDFa cell morphology and viability within the used concentration range (1-10 µM). Also, in HaCaT cells, treatment with damsin (1-10 µM) for 24  h inhibited the MCP-1 expression, and damsin thereby attenuated cytokine expression both in HDFa and HaCaT cells.

CONCLUSION

We show that coronopilin and damsin from A. arborescens inhibit pro-inflammatory IL-6 and MCP-1 expression in human skin cells via NF-κB inhibition, suggesting that they may be useful for antagonizing inflammatory conditions of the human skin.

The host defense peptide LL-37 triggers release of nucleic acids from human mast cells

The human host defense peptide LL-37 possesses antimicrobial activity but also affects host cell function and viability. Mast cells are involved in innate immunity but no data have been presented on effects of LL-37 on human mast cell viability and export of nucleic acids. Here, we demonstrated by immunofluorescence microscopy that synthesized LL-37 was internalized by human LAD2 mast cells and detected both in cytoplasm and nucleus. Treatment with high (4 and 10 μM) but not low (1 μM) concentrations of LL-37 for 4 h reduced cell viability assessed by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Stimulation with 10 μM LL-37 for 4 h enhanced export of nucleic acids, total protein and lactate dehydrogenase (LDH), suggesting that both nuclear and plasma membranes are permeabilized by LL-37. Although LL-37 triggered release of nucleic acids, no extracellular trap-like structures were observed by laser scanning confocal microscopy of cells incubated with the plasma membrane impermeable nucleic acid fluorophore SYTOX-Green, indicating that LL-37 promotes export of nucleic acids but not formation of extracellular traps. On the other hand, phorbol-12-myristate-13-acetate (PMA), which is a well-known inducer of extracellular traps, stimulated export of nucleic acids and also formation of extracellular trap-like structures. However, PMA had no effect on export of either total protein or LDH. Hence, LL-37 and PMA seem to stimulate export of nucleic acids from LAD2 mast cells through different pathways. In conclusion, we demonstrate that LL-37 triggers release of nucleic acids from human mast cells but not the formation of extracellular trap-like structures.

LL-37 disrupts the Kaposi's sarcoma-associated herpesvirus envelope and inhibits infection in oral epithelial cells

Oral epithelial cells (OECs) represent the first line of defense against viruses that are spread via saliva, including Kaposi's sarcoma-associated herpesvirus (KSHV). Infection of humans by KSHV and viral pathogenesis begins by infecting OECs. One method OECs use to limit viral infections in the oral cavity is the production of antimicrobial peptides (AMPs), or host defense peptides (HDPs). However, no studies have investigated the antiviral activities of any HDP against KSHV. The goal of this study was to determine the antiviral activity of one HDP, LL-37, against KSHV in the context of infecting OECs. Our results show that LL-37 significantly decreased KSHV's ability to infect OECs in both a structure- and dose-dependent manner. However, this activity does not stem from affecting OECs, but instead the virions themselves. We found that LL-37 exerts its antiviral activity against KSHV by disrupting the viral envelope, which can inhibit viral entry into OECs. Our data suggest that LL-37 exhibits a marked antiviral activity against KSHV during infection of oral epithelial cells, which can play an important role in host defense against oral KSHV infection. Thus, we propose that inducing LL-37 expression endogenously in oral epithelial cells, or potentially introducing as a therapy, may help restrict oral KSHV infection and ultimately KSHV-associated diseases.

Globular C1q receptor (p33) binds and stabilizes pro-inflammatory MCP-1: a novel mechanism for regulation of MCP-1 production and function

The protein gC1qR (globular C1q receptor), also named p33, was originally identified as a binding partner of the globular heads of C1q in the complement system. gC1qR/p33 is abundantly expressed in many cell types, but the functional importance of this protein is not completely understood. Here, we investigate the impact of gC1qR/p33 on the production and function of the pathophysiologically important chemokine monocyte chemoattractant protein-1 (MCP-1) and the underlying molecular mechanisms. Knockdown of gC1qR/p33 negatively regulated the production of MCP-1, but had no effect on the expression of transcript for MCP-1 in human periodontal ligament cells, suggesting a translational/post-translational mechanism of action. Laser scanning confocal microscopy showed considerable cytosolic co-localization of gC1qR/p33 and MCP-1, and co-immunoprecipitation disclosed direct physical interaction between gC1qR/p33 and MCP-1. Surface plasmon resonance analysis revealed a high-affinity binding (K_D = 10.9 nM) between gC1qR/p33 and MCP-1. Using a transwell migration assay, we found that recombinant gC1qR/p33 enhances MCP-1-induced migration of human THP-1 monocytes, pointing to a functional importance of the interaction between gC1qR/p33 and MCP-1. An in vitro assay revealed a rapid turnover of the MCP-1 protein and that gC1qR/p33 stabilizes MCP-1, hence preventing its degradation. We propose that endogenous gC1qR/p33 physically interacts with MCP-1 causing stabilization of the MCP-1 protein and stimulation of its activity in human periodontal ligament cells, suggesting a novel gC1qR/p33-mediated pro-inflammatory mechanism of action.

Vitamin D-induced up-regulation of human keratinocyte cathelicidin anti-microbial peptide expression involves retinoid X receptor α

The biologically active form of vitamin D, 1α,25-dihydroxyvitamin D3 (1,25D3), has been reported to positively regulate the human cathelicidin anti-microbial peptide (CAMP) gene coding for LL-37, but the mechanisms are not completely understood. We have determined the expression of CAMP, vitamin D receptor (VDR), and the retinoid X receptor (RXR) isoforms in human skin and gingival tissue biopsies and investigated the signaling pathways involved in 1,25D3-induced upregulation of CAMP. Human skin and gingival biopsies exhibited few VDR-immunoreactive cells within the stratum basale, whereas rat colon enterocytes (positive control) possessed abundant VDR immunoreactivity. Nuclear VDR immunoreactivity was demonstrated in human skin keratinocytes (HaCaT cells). Gene analysis revealed that human skin biopsies expressed higher levels of both CAMP and RXRα mRNA than human gingival biopsies, whereas VDR and RXRβ transcript levels were similar in skin and gingiva. In HaCaT cells, treatment with 1,25D3 (5 nM and 1 μM) for 4 and 24 h up-regulated CAMP mRNA several fold, and treatment with 1,25D3 for 24 h increased protein expression of the pro-form of LL-37 (hCAP-18) by about 13 times. The 1,25D3-evoked stimulation of HaCaT CAMP expression was associated with attenuated VDR mRNA and protein expression. Treatment with RXRα short interfering RNA reversed the 1,25D3-induced CAMP expression in HaCaT cells, showing that RXRα is involved in the up-regulation of CAMP by 1,25D3. We conclude that the 1,25D3-evoked stimulation of CAMP expression in human skin keratinocytes is dependent on RXRα but is not associated with the up-regulation of VDR expression.

HCV core protein binds to gC1qR to induce A20 expression and inhibit cytokine production through MAPKs and NF-κB signaling pathways

Hepatitis C virus (HCV) infection is characterized by a strong propensity toward chronicity. During chronic HCV infection, HCV core protein is implicated in deregulating cytokine expression that associates with chronic inflammation. A20 is known as a powerful suppressor in cytokine signaling, in this study, we explored the A20 expression in macrophages induced by HCV core protein and the involved signaling pathways. Results demonstrated that HCV core protein induced A20 expression in macrophages. Silencing A20 significantly enhanced the secretion of IL-6, IL-1β and TGF-β1, but not IL-8 and TNF. Additionally, HCV core protein interacted with gC1qR, but not TLR2, TLR3 and TLR4 in pull-down assay. Silencing gC1qR abrogated core-induced A20 expression. Furthermore, HCV core protein activated MAPK, NF-κB and PI3K/AKT pathways in macrophages. Inhibition of P38, JNK and NF-κB but not ERK and AKT activities greatly reduced the A20 expression. In conclusion, the study suggests that HCV core protein ligates gC1qR to induce A20 expression in macrophages via P38, JNK and NF-κB signaling pathways, which leads to a low-grade chronic inflammation during HCV infection. It represents a novel mechanism by which HCV usurps the host for persistence.