Antibacterial Peptide LL-37 Research Articles

Renovation as innovation: Repurposing human antibacterial peptide LL-37 for cancer therapy.

In many organisms, antimicrobial peptides (AMPs) display wide activities in innate host defense against microbial pathogens. Mammalian AMPs include the cathelicidin and defensin families. LL37 is the only one member of the cathelicidin family of host defense peptides expressed in humans. Since its discovery, it has become clear that they have pleiotropic effects. In addition to its antibacterial properties, many studies have shown that LL37 is also involved in a wide variety of biological activities, including tissue repair, inflammatory responses, hemotaxis, and chemokine induction. Moreover, recent studies suggest that LL37 exhibits the intricate and contradictory effects in promoting or inhibiting tumor growth. Indeed, an increasing amount of evidence suggests that human LL37 including its fragments and analogs shows anticancer effects on many kinds of cancer cell lines, although LL37 is also involved in cancer progression. Focusing on recent information, in this review, we explore and summarize how LL37 contributes to anticancer effect as well as discuss the strategies to enhance delivery of this peptide and selectivity for cancer cells.

Identification of heptapeptides targeting a lethal bacterial strain in septic mice through an integrative approach

Effectively killing pathogenic bacteria is key for the treatment of sepsis. Although various anti-infective drugs have been used for the treatment of sepsis, the therapeutic effect is largely limited by the lack of a specific bacterium-targeting delivery system. This study aimed to develop antibacterial peptides that specifically target pathogenic bacteria for the treatment of sepsis. The lethal bacterial strain Escherichia coli MSI001 was isolated from mice of a cecal ligation and puncture (CLP) model and was used as a target to screen bacterial binding heptapeptides through an integrative bioinformatics approach based on phage display technology and high-throughput sequencing (HTS). Heptapeptides binding to E. coli MSI001 with high affinity were acquired after normalization by the heptapeptide frequency of the library. A representative heptapeptide VTKLGSL (VTK) was selected for fusion with the antibacterial peptide LL-37 to construct the specific-targeting antibacterial peptide VTK-LL37. We found that, in comparison with LL37, VTK-LL37 showed prominent bacteriostatic activity and an inhibitive effect on biofilm formation in vitro. In vivo experiments demonstrated that VTK-LL37 significantly inhibited bacterial growth, reduced HMGB1 expression, alleviated lesions of vital organs and improved the survival of mice subjected to CLP modeling. Furthermore, membrane DEGP and DEGQ were identified as VTK-binding proteins by proteomic methods. This study provides a novel strategy for targeted pathogen killing, which is helpful for the treatment of sepsis in the era of precise medicine.

IL-33 synergistically promotes the proliferation of lung cancer cells in vitro by inducing antibacterial peptide LL-37 and proinflammatory cytokines in macrophages

Lung cancer is the primary cause of cancer-related deaths, and the persistent inflammation is inextricably linked with the lung cancer tumorigenesis. Pro-inflammatory cytokine interleukin-33 (IL-33) is able to serve as a potent modulator of cancer. Mounting evidence indicates IL-33 has significant effect on lung cancer progression by regulating host immune response, but the current opinions about the function and mechanism of IL-33 in lung cancer are still controversial. Meanwhile, antibacterial peptide LL-37 also exerts a momentous effect on immune responses to lung cancer. LL-37 is regarded as versatile, including antimicrobial activities, chemotaxis and immunoregulation. However, the immunomodulatory mechanism of IL-33 and LL-37 in lung cancer remains thoroughly not defined. Here, we determined the secretion of LL-37 was up-regulated in lung cancer serum samples. Similarly, the expression of CRAMP was enhancive in macrophages after co-cultured with lung cancer cells. Moreover, we expounded that IL-33 could up-regulate LL-37 secretion in macrophages, resulting in the massive releases of IL-6 and IL-1β. Additionally, LL-37 cooperated with IL-33 to increase the phosphorylation of p38 MAPK and NF-κB p65 pathways, and augmented IL-6 and IL-1β secretion, which resulting in the proliferation of lung cancer cells in vitro. In conclusion, our study identified that IL-33 aggravated the inflammation of lung cancer by increasing LL-37 expression in macrophages, thereby promoting lung cancer cell proliferation in vitro. It is contributed to our present understanding of the immunomodulatory relationship between pro-inflammatory cytokines and antibacterial peptides in the tumor immune response, and offer a novel perspective for controlling the progress of lung cancer.

LL-37-Induced Autophagy Contributed to the Elimination of Live Porphyromonas gingivalis Internalized in Keratinocytes.

Porphyromonas gingivalis (P. gingivalis), one of the most important pathogens of periodontitis, is closely associated with the aggravation and recurrence of periodontitis and systemic diseases. Antibacterial peptide LL-37, transcribed from the cathelicidin antimicrobial peptide (CAMP) gene, exhibits a broad spectrum of antibacterial activity and regulates the immune system. In this study, we demonstrated that LL-37 reduced the number of live P. gingivalis (ATCC 33277) in HaCaT cells in a dose-dependent manner via an antibiotic-protection assay. LL-37 promoted autophagy of HaCaT cells internalized with P. gingivalis. Inhibition of autophagy with 3-methyladenine (3-MA) weakened the inhibitory effect of LL-37 on the number of intracellular P. gingivalis. A cluster of orthologous groups (COGs) and a gene ontology (GO) functional analysis were used to individually assign 65 (10%) differentially expressed genes (DEGs) to an “Intracellular trafficking, secretion, and vesicular transport” cluster and 306 (47.08%) DEGs to metabolic processes including autophagy. Autophagy-related genes, a tripartite motif-containing 22 (TRIM22), and lysosomal-associated membrane protein 3 (LAMP3) were identified as potentially involved in LL-37-induced autophagy. Finally, bioinformatics software was utilized to construct and predict the protein–protein interaction (PPI) network of CAMP-TRIM22/LAMP3-Autophagy. The findings indicated that LL-37 can reduce the quantity of live P. gingivalis internalized in HaCaT cells by promoting autophagy in these cells. The transcriptome sequencing and analysis also revealed the potential molecular pathway of LL-37-induced autophagy.

LL-37 restored glucocorticoid sensitivity impaired by virus dsRNA in lung

Glucocorticoids play a key role in treatment of inflammatory lung diseases including both airway and parenchymal lung diseases. RNA viral infections are major causes of chronic lung disease exacerbations and can determine glucocorticoid resistance. The antibacterial peptide LL-37, the only member of human cathelicidin family, also functions as antiviral-activity enhancer. However, whether it can alleviate the glucocorticoid resistance caused by RNA viruses remains unclear. Here, we used type I (BEAS-2B) and type II (A549) lung epithelial cells to assess the effect of LL-37 on dsRNA-induced glucocorticoid resistance. We verified that LL-37 and polyinosinic-polycytidylic acid (poly I:C, a mimic of viral dsRNA) interact and enter both cell lines. Co-treatment with LL-37 and poly I:C increased glucocorticoid-induced expression of promyelocytic leukemia zinc finger (PLZF), an anti-inflammatory protein, compared to poly I:C alone. Pre-treatment with LL-37 also restored transactivation of the glucocorticoid response element (GRE). Moreover, LL-37 rescued poly I:C-induced glucocorticoid resistance by increasing phosphorylation and nuclear translocation of glucocorticoid receptor. Importantly, LL-37 downregulated poly I:C-induced Erk and Akt signaling pathways in lung epithelial cells. Finally, we verified our data in vivo, showing that mCRAMP, the mouse LL-37 ortholog, can alleviate poly I:C-induced glucocorticoid insensitivity in a murine asthma model. In summary, this study showed that LL-37 restored glucocorticoid sensitivity impaired by dsRNA possibly by inhibiting Akt pathway, in addition to Erk1/2 pathway. These findings suggest LL-37 as a therapeutic agent for treatment of viral infections in inflammatory pulmonary diseases.

Clinical significance of antibacterial peptide LL-37 in early diagnosis of patients with sepsis in emergency department

To discuss the clinical significance of antibacterial peptide LL-37 in the early diagnosis of patients with sepsis in emergency department. Forty patients diagnosed with sepsis in the emergency department of the Affiliated Hospital of Zunyi Medical College from December 2017 to March 2018 were enrolled as sepsis group. Twenty healthy volunteers were enrolled contemporaneously in our hospital at medical center as healthy control group. Peripheral blood was collected immediately after diagnosis in sepsis group or during physical examination in healthy control group. The expression of antibacterial peptide LL-37 was determined by enzyme-linked immunosorbent assay (ELISA). Meanwhile, serum procalcitonin (PCT) and C-reactive protein (CRP) levels were determined. The differences in antibacterial peptide LL-37, PCT and CRP levels between the two groups were compared. Pearson correlation method was used to analyze the correlation between antibacterial peptide LL-37, PCT and CRP. Receiver operating characteristic (ROC) curve was drawn, and the early individually or jointly diagnostic value of each detected index for sepsis was analyzed. The levels of antimicrobial peptide LL-37, PCT and CRP in peripheral blood of sepsis group were significantly higher than those of healthy control group [LL-37 (μg/L): 1.34±0.69 vs. 0.10±0.06, PCT (μg/L): 46.67±39.51 vs. 0.03±0.02, CRP (mg/L): 129.68±49.83 vs. 3.16±2.85], with statistically significant differences (all P < 0.05). Pearson correlation analysis showed that the expression of antimicrobial peptide LL-37 was positively correlated with PCT and CRP levels (r1 = 0.835, r2 = 0.932, both P < 0.01). ROC curve analysis showed that the area under ROC curve (AUC) of LL-37, PCT and CRP for early diagnosis of sepsis was 0.885, 0.963 and 0.983, respectively, and the AUC of combined diagnosis of the three parameters was as high as 0.994, indicating that the value of combined diagnosis of sepsis was greater than that of single diagnosis; when the combined prediction probability of the three parameters was 0.92, the sensitivity was 97.5%, and the specificity was 95.0%. Antibacterial peptide LL-37 has certain clinical value in early diagnosis of patients with sepsis, which can be used as early routine monitoring indicators for patients with early sepsis when combined with PCT and CRP.

Evaluation value of human antibacterial peptide LL-37 on the prognosis of elderly patients with sepsis

To evaluate the prognostic value of human antibacterial peptide LL-37 in elderly patients with sepsis. Elderly sepsis patients over 65-year-old satisfied the diagnostic criteria for sepsis and septic shock admitted to intensive care unit of East Hospital of Tongji University from January 2016 to December 2017 were enrolled (elderly sepsis group). Aged community-acquired pneumonia (CAP) patients hospitalized during the same period were enrolled as a control group for pneumonia, and the aged health check-ups served as a healthy control group during the same period. The peripheral blood LL-37 levels of all patients on the 1st, 3rd, 7th day of admission and the results on the day of physical examination in the healthy control group and on the day of admission in aged CAP group were recorded. C-reactive protein (CRP), arterial blood lactate (Lac), procalcitonin (PCT) were monitored, and acute physiology and chronic health evaluation II (APACHE II) and sequential organ failure assessment (SOFA) scores were calculated based on the worst values within 24 hours. The correlation between LL-37 and various indicators was analyzed by Spearman method. According to the 28-day clinical outcome, the elderly patients with sepsis were divided into survival group and non-survival group. The differences in all parameters between the two groups were compared. The statistically significant indicators were analyzed by receiver operating characteristic (ROC) curve, and the predictive value of each indicator for prognosis was evaluated. (1) A total of 113 elderly patients with sepsis were enrolled in the final analysis, including 67 patients in sepsis group and 46 patients in septic shock group. Thirty-two patients were enrolled as healthy controls and 31 elderly patients with CAP as elderly pneumonia group. The PCT, CRP, Lac, APACHE II and SOFA scores of the patients in the three groups were higher than those of the healthy control group, and they were gradually increased with the severity of infection. There was no significant difference in gender or age among the groups. Compared with the healthy control group, the other three groups had higher LL-37 level after admission, the LL-37 levels in the sepsis group and the septic shock group were decreased with the prolongation of the hospitalization time, and they were lower than the pneumonia group at 7 days after admission [LL-37 (μg/L): 1 403.9±501.9, 1 517.1±676.4 vs. 1 608.4±816.2, both P > 0.05]. It was shown by correlation analysis that the LL-37 level in peripheral blood of elderly patients with sepsis was significantly negatively correlated with APACHE II score (r = -0.329, P = 0.007) and SOFA score (r = -0.344, P = 0.005), but no significant correlation with Lac was found (r = -0.128, P = 0.311). (2) The 28-day survival analysis revealed that of the 113 elderly patients with sepsis, 54 (47.8%) survived at 28 days and 59 (52.2%) died. There was no significant difference in gender, age, PCT or CRP levels at 1 day after admission between the two groups. The 1-day Lac, APACHE II and SOFA scores of the patients in the non-survival group were significantly higher than those in the survival group, they were gradually increased with the prolongation of the hospitalization time, and they were significantly higher than those in the survival group at 7 days after admission [Lac (mmol/L): 2.4 (1.4, 4.4) vs. 1.0 (0.8, 1.7), APACHE II score: 21.77±5.85 vs. 13.74±4.99, SOFA score: 9.62±4.78 vs. 3.18±2.71, all P < 0.01]. With the prolongation of admission, there was no significant change in LL-37 level of peripheral blood in the survival group. The LL-37 level in the non-survival group showed a downward tendency, and it was significantly lower than that in the survival group at 7 days after admission (μg/L: 1 277.8±642.6 vs. 1 620.6±461.6, P < 0.05). It was shown by ROC curve analysis that the LL-37 in peripheral blood, Lac, APACHE II score and SOFA score at 7-day of admission of elderly patients with sepsis had predictive value for prognosis, and LL-37 had the best predicted effect for 28-day death, the area under the ROC curve (AUC) of LL-37 was 0.670, 95% confidence interval (95%CI) = 0.513-0.757, when the optimal cut-off value was 1 283.0 μg/L, the sensitivity was 75.7%, and the specificity was 61.5%. The expression of LL-37 increased in the early course of the disease in elderly patients with sepsis. However, as the disease progressed and worsened, the level of LL-37 had a decline tendency and was associated with death. The dynamic monitoring of LL-37 combined with APACHE II and SOFA scores had clinical guidance value in predicting the prognosis of sepsis in the elderly.

Effects of artesunate on rosacea-like inflammation in mouse models

Objective To evaluate effects of artesunate on rosacea-like inflammation in mouse models. Methods Twenty-five male BALB/c mice aged 7 weeks were injected subcutaneously with 40 μl antibacterial peptide LL-37 into the back once every 12 hours for 4 sessions to establish mouse models with rosacea-like inflammation. These 25 mice were randomly and equally divided into 5 groups: after each injection of LL-37, model group were gavaged with sodium chloride physiological solution, treatment groups gavaged with 25, 50 and 100 mg/kg artesunate solution separately, and positive control group gavaged with 30 mg/kg doxycycline hydrochloride solution. Another 5 healthy mice injected subcutaneously with pure water into the back for 4 sessions served as blank control group. Forty-eight hours after the initial injection of LL-37, changes in skin lesions and the intensity of erythema were assessed. Skin tissues at the dorsal injection site were resected and subjected to HE staining, the tissue structure was observed and the number of inflammatory cells was counted. Enzyme-linked immunosorbent assay (ELISA) was performed to estimate the activity of myeloperoxidase (MPO) in skin lesions. Results The model group showed obvious inflammatory reactions, and significantly increased erythema score (3.20 ± 0.84) , inflammatory cell count (517.27 ± 99.43) and MPO activity (0.57 ± 0.08) compared with the blank control group (all P 0.05) . Conclusion Artesunate can inhibit rosacea-like inflammatory reactions in mouse models, especially the middle-and high-dose artesunate. Key words: Rhinophyma; Artemisinins; Doxycycline; Cathelicidins; Disease models, animal; Artesunate; LL-37

Escherichia coli PagP Enzyme-Based De Novo Design and In Vitro Activity of Antibacterial Peptide LL-37.

BackgroundThe aim of this study was to investigate the antimicrobial property of peptide LL-37 sequences.Material/MethodsHumanized antibacterial peptide LL-37 and the mutant were prepared by chemical synthesis. The physicochemical properties of antibacterial peptide LL-37 were analyzed by SWISS-MODEL online prediction tool. Molecular docking between antibacterial peptide LL-37 fragments and palmitoyl transferase PagP was made with Lamarckian genetic algorithm by AutoDock1.5.6.ResultsThe systems contacted each other at 8.75 picosec. After 20 picsec, the system had no trend of dissociation, and the bond energy of weak bond -C-O-H…NH2-CH2- was calculated. The hydrophobic groups were important factors that led to contact and merged the two parts. The contacted weak bond -C-O-H…NH2-CH2- was the bridge for contacting LL-37 with palmitoyl transferase PagP. The binding sites of antibacterial peptide LL-37 and palmitoyl transferase PagP mainly included LYS8, GLU11, LEU28, LYS12, PHE27, ILE13, and PHE6 of antibacterial peptide LL-37 and ARG94, TRP89, ASN65, SER3, GLU90, GLU90, ASN100, HIS102, and THR92 of palmitoyl transferase PagP.ConclusionsAntibacterial peptide LL-37 had stronger antibacterial effect via inhibition of activity of PagP.

Roles of neutrophils in the pathogenesis of psoriasis

Psoriasis is a kind of chronic inflammatory skin disease, and its pathogenesis is mainly related to heredity, immunity, inflammation, neoangiogenesis, keratinocyte hyperproliferation, and so on. Recent studies have indicated that neutrophils are the main source of interleukin (IL)-8, IL-17 and other cytokines in skin lesions of patients with psoriasis. Neutrophil elastase (NE), neutrophil gelatinase-associated lipocalin (NGAL), neutrophil extracellular traps (NETs) and antibacterial peptide LL37 (LL37), which are synthesized and secreted by neutrophils, all play important roles in the pathogenesis of psoriasis. Key words: Psoriasis; Neutrophils; Leukocyte elastase; LL37; Cytokines

PORF5 plasmid protein promotes Chlamydia trachomatis infection through inhibition of the antibacterial peptide LL37: a preliminary study

Objective To investigate whether pORF5 plasmid protein promotes Chlamydia trachomatis (Ct)infection through inhibition of the antibacterial peptide LL37,and to explore its potential molecular mechanism.Methods After expression and purification,the glutathione S-transferase (GST)-pORF5 fusion protein was digested with proteases to obtain pORF5 protein without GST tag.Some Hela cells were classified into four groups:Ct group infected with unpretreated Ct,pORF5 group infected with Ct that had been pretreated with pORF5 of 30 μg/ml for 2 hours,LL37 group infected with Ct that had been pretreated with LL37 of 20 μg/ml for 2 hours,combination group infected with Ct that had been pretreated with pORF5 of 30 μg/ml and LL37 of 20 μg/ml for 2 hours.After additional culture,indirect immunofluorescence assay was performed to count the number of Ct inclusion-forming units (IFUs),and real-time,fluorescence-based quantitative PCR and enzyme-linked immunosorbent assay (ELISA) to detect the protein and mRNA expressions of tumor necrosis factor-α (TNF-α) respectively.Some Hela cells were divided into three groups:blank control group remaining untreated,Ct group infected with unpretreated Ct,pORF5 group infected with Ct that had been pretreated with pORF5 of 30 μg/ml for 2 hours.After 6 hours of additional culture,real-time,fluorescence-based quantitative PCR and ELISA were conducted to measure the mRNA and protein expressions of LL37,respectively.Results The concentration of IFUs was significantly higher in the Ct group,pORF5 group and combination group than in the LL37 group (3.8 × 105/ml,3.0 × 105/ml and 3.1 × 105/ml vs.2.0 × 105/ml,all P ＜ 0.05),with no significant differences between the Ct group,pORF5 group and combination group (P ＞ 0.05).The expressions of TNF-α mRNA and protein were significantly increased in the combination group compared with the LL37 group.The mRNA expression of LL37 was reduced by 19％ in the pORF5 group compared with the Ct group.Conclusions pORF5 plasmid protein could promote Ct infection by counteracting the antibacterial peptide LL37,which may be associated with the up-regulation of TNF-α expression and downregulation of LL37 expression in Ct-infected cells. Key words: Chlamydia trachomatis; pORF5 plasmid protein; LL37; Antimicrobial peptides

Skin Electroporation of a Plasmid Encoding hCAP-18/LL-37 Host Defense Peptide Promotes Wound Healing

Host defense peptides, in particular LL-37, are emerging as potential therapeutics for promoting wound healing and inhibiting bacterial growth. However, effective delivery of the LL-37 peptide remains limiting. We hypothesized that skin-targeted electroporation of a plasmid encoding hCAP-18/LL-37 would promote the healing of wounds. The plasmid was efficiently delivered to full-thickness skin wounds by electroporation and it induced expression of LL-37 in the epithelium. It significantly accelerated reepithelialization of nondiabetic and diabetic wounds and caused a significant VEGFa and interleukin (IL)-6 induction. IL-6 was involved in LL-37-mediated keratinocyte migration in vitro and IL-6 neutralizing antibodies delivered to mice were able to suppress the wound healing activity of the hCAP-18/LL-37 plasmid. In a hindlimb ischemia model, electroporation of the hCAP-18/LL-37 plasmid increased blood perfusion, reduced muscular atrophy, and upregulated the angiogenic chemokines VEGFa and SDF-1a, and their receptors VEGF-R and CXCR-4. These findings demonstrate that a localized gene therapy with LL-37 is a promising approach for the treatment of wounds.

Physiological Relevance of LL-37 Induced Bladder Inflammation and Mast Cells

We established the physiological relevance of LL-37 induced bladder inflammation. We hypothesized that 1) human urinary LL-37 is increased in pediatric patients with spina bifida, 2) LL-37 induced inflammation occurs in our mouse model via urothelial binding and is dose dependent and 3) LL-37 induced inflammation involves mast cells. To test our first hypothesis, we obtained urine samples from 56 pediatric patients with spina bifida and 22 normal patients. LL-37 was measured by enzyme-linked immunosorbent assay. Our second hypothesis was tested in C57Bl/6 mice challenged with 7 LL-37 concentrations intravesically for 1 hour. At 24 hours tissues were examined histologically and myeloperoxidase assay was done to quantitate inflammation. In separate experiments fluorescent LL-37 was instilled and tissues were obtained immediately (time = 0) and at 24hours (time = 24). To test our final hypothesis, we performed immunohistochemistry for mast cell tryptase and evaluated 5 high power fields per bladder to determine the mean number of mast cells per mm(2). Urinary LL-37 was 89-fold higher in patients with spina bifida. Mouse LL-37 dose escalation experiments revealed increased inflammation at higher LL-37 concentrations. Fluorescent LL-37 demonstrated global urothelial binding at time = 0 but was not visible at time = 24. Immunohistochemistry for tryptase revealed mast cell infiltration in all tissue layers. At higher concentrations the LL-37 challenge led to significantly greater mast cell infiltration. Urinary LL-37 was significantly increased in pediatric patients with spina bifida. To our knowledge we report for the first time that LL-37 can elicit profound, dose dependent bladder inflammation involving the urothelium. Finally, inflammation propagation involves mast cells.

The effect of human antibacterial peptide LL-37 in the pathogenesis of chronic obstructive pulmonary disease

Previous research has shown that innate immune system was more important than the acquired immune system in the pathogenesis of COPD. LL-37 is the only human cathelicidin identified so far. As an integral part of the innate immune system, besides antibacterial activity, its chemotactic activity, damage repairing, influencing apoptosis and its cytotoxicity are attracting people's attention. The aim of the present study was to evaluate role of LL-37 in the pathogenesis of COPD. ELISA and immunohistochemistry were applied to investigate the expression of LL-37 in induced sputum and lung tissue of COPD patients. Bronchial epithelial cell (BEP2D) and alveolar epithelial cell (A549) were treated with LL-37 synthesis polypeptide invitro to assess the role of LL-37 in inflammation and apoptosis. We found that increased induced sputum levels of LL-37 in COPD patients were associated with airflow limitation, health status and exercise tolerance and the expressing intensity of LL-37 in both airway district and pulmonary alveoli area in COPD group significantly increased compared with control group. Through stimulation by CSE and LPS, the expression of LL-37 was increased in bronchial epithelial cell and alveolar epithelial cell. LL-37 synthesis polypeptide can promote the releasing of inflammatory factor IL-8 and induce apoptosis of bronchial epithelial cell and alveolar epithelial cell. This study suggested that LL-37 may play important role in the pathogenesis of COPD and may be a possible novel therapeutic target in COPD.

Mas-related Gene X2 (MrgX2) Is a Novel G Protein-coupled Receptor for the Antimicrobial Peptide LL-37 in Human Mast Cells: RESISTANCE TO RECEPTOR PHOSPHORYLATION, DESENSITIZATION, AND INTERNALIZATION

Human LL-37 is a multifunctional antimicrobial peptide that promotes inflammation, angiogenesis, wound healing, and tumor metastasis. Most effects of LL-37 are mediated via the activation of the cell surface G protein-coupled receptor FPR2 on leukocytes and endothelial cells. Although LL-37 induces chemotaxis, degranulation, and chemokine production in mast cells, the receptor involved and the mechanism of its regulation remain unknown. MrgX2 is a member of Mas-related genes that is primarily expressed in human dorsal root ganglia and mast cells. We found that a human mast cell line LAD2 and CD34(+) cell-derived primary mast cells, which natively express MrgX2, responded to LL-37 for sustained Ca(2+) mobilization and substantial degranulation. However, an immature human mast cell line, HMC-1, that lacks functional MrgX2 did not respond to LL-37. shRNA-mediated knockdown of MrgX2 in LAD2 mast cell line and primary CD34(+) cell-derived mast cells caused a substantial reduction in LL-37-induced degranulation. Furthermore, mast cell lines stably expressing MrgX2 responded to LL-37 for chemotaxis, degranulation, and CCL4 production. Surprisingly, MrgX2 was resistant to LL-37-induced phosphorylation, desensitization, and internalization. In addition, shRNA-mediated knockdown of the G protein-coupled receptor kinases (GRK2 and GRK3) had no effect on LL-37-induced mast cell degranulation. This study identified MrgX2 as a novel G protein-coupled receptor for the antibacterial peptide LL-37 and demonstrated that unlike most G protein-coupled receptors it is resistant to agonist-induced receptor phosphorylation, desensitization, and internalization.

Extracellular Gelsolin Binds Lipoteichoic Acid and Modulates Cellular Response to Proinflammatory Bacterial Wall Components

The various functions of gelsolin in extracellular compartments are not yet clearly defined but include actin scavenging and antiinflammatory effects. Gelsolin was recently reported to bind endotoxin (LPS) from various Gram-negative bacteria with high affinity. In this study we investigate whether gelsolin also interacts with bacterial wall molecules of Gram-positive bacteria such as lipoteichoic acid (LTA) and whether gelsolin's interaction with bacterial lipids from Gram-negative or Gram-positive bacteria affects their cellular inflammatory responses. A peptide based on the PPI binding site of gelsolin (160-169) binds purified LTA at the same molecular ratio that it binds phosphatidylinositol 4,5-bisphosphate. The OD of recombinant human plasma gelsolin was found to decrease following the addition of purified LTA, and the binding of gelsolin to LTA inhibits F-actin depolymerization by gelsolin. Simultaneously, the ability of LTA to activate translocation of NF-kappaB, E-selectin expression, and adhesion of neutrophils to LTA-treated human aortic endothelial cells was compromised by gelsolin. Gelsolin was able to partially inhibit LPS- or LTA-induced release of IL-8 from human neutrophils but was unable to prevent Gram-positive Bacillus subtilis or Gram-negative Pseudomonas aeruginosa growth and had no effect on the antibacterial activity of the cathelicidin-derived antibacterial peptide LL37. These data suggest that extracellular gelsolin is involved in the host immune recognition of LTA or LPS following release of these molecules from the bacterial outer membrane during cell division or attack by drugs and immune components.

SufA – a novel subtilisin-like serine proteinase of Finegoldia magna

Finegoldia magna is an anaerobic Gram-positive bacterium and commensal, which is also associated with clinically important conditions such as skin and soft tissue infections. This study describes a novel subtilisin-like extracellular serine proteinase of F. magna, denoted SufA (subtilase of Finegoldia magna), which is believed to be the first subtilase described among Gram-positive anaerobic cocci. SufA is associated with the bacterial cell surface, but is also released in substantial amounts during bacterial growth. Papain was used to release SufA from the surface of F. magna and the enzyme was purified by ion-exchange chromatography and gel filtration. A protein band on SDS-PAGE corresponding to the dominating proteolytic activity on gelatin zymography was analysed by MS/MS. Based on the peptide sequences obtained, the sufA gene was sequenced. The gene comprises 3466 bp corresponding to a preprotein of 127 kDa. Like other members of the subtilase family, SufA contains the catalytic triad of aspartic acid, histidine and serine with surrounding conserved residues. A SufA homologue was identified in 33 of 34 investigated isolates of F. magna, as revealed by PCR and immunoprinting. The enzyme forms dimers, which are more proteolytically active than the monomeric protein. SufA was found to efficiently cleave and inactivate the antibacterial peptide LL-37 and the CXC chemokine MIG/CXCL9, indicating that the enzyme promotes F. magna survival and colonization.

The contact system—a novel branch of innate immunity generating antibacterial peptides

Activation of the contact system has two classical consequences: initiation of the intrinsic pathway of coagulation, and cleavage of high molecular weight kininogen (HK) leading to the release of bradykinin, a potent proinflammatory peptide. In human plasma, activation of the contact system at the surface of significant bacterial pathogens was found to result in further HK processing and bacterial killing. A fragment comprising the D3 domain of HK is generated, and within this fragment a sequence of 26 amino acids is mainly responsible for the antibacterial activity. A synthetic peptide covering this sequence kills several bacterial species, also at physiological salt concentration, as effectively as the classical human antibacterial peptide LL-37. Moreover, in an animal model of infection, inhibition of the contact system promotes bacterial dissemination and growth. These data identify a novel and important role for the contact system in the defence against invasive bacterial infection.

α2-Macroglobulin-Proteinase Complexes Protect Streptococcus pyogenes from Killing by the Antimicrobial Peptide LL-37

The significant human bacterial pathogen Streptococcus pyogenes expresses GRAB, a surface protein that binds alpha(2)-macroglobulin (alpha(2)M), a major proteinase inhibitor of human plasma. alpha(2)M inhibits proteolysis by trapping the proteinase, which, however, still remains proteolytically active against smaller peptides that can penetrate the alpha(2)M-proteinase complex. Here we report that SpeB, a cysteine proteinase secreted by S. pyogenes, is trapped by alpha(2)M bound to protein GRAB. As a consequence, SpeB is retained at the bacterial surface and protects S. pyogenes against killing by the antibacterial peptide LL-37.

The newborn infant is protected by an innate antimicrobial barrier: peptide antibiotics are present in the skin and vernix caseosa.

Peptide antibiotics are part of the surface defences against microbial intruders. However, the presence and significance of these innate immune effectors in the skin barrier of the newborn infant have not yet been appreciated. Erythema toxicum neonatorum is an inflammatory skin reaction of unknown aetiology and significance, commonly present in the healthy newborn infant. As peptide antibiotics are upregulated in inflammatory skin disorders, we hypothesized that this also could be the case in erythema toxicum. We also investigated if the vernix caseosa, a cream-like white substance present on the skin of the infant at birth, might contribute to host defences. The presence of the human antibacterial peptide LL-37 was investigated by immunohistochemistry and confocal imaging of skin biopsies from four 1-day-old infants with an erythema toxicum rash and four matched newborns without the rash. In addition, we analysed the expression of LL-37 and human beta defensin-1, an antibacterial peptide of epithelial origin, by reverse transcriptase-polymerase chain reaction. Finally, we screened for antibacterial components in vernix material obtained from six healthy newborns by inhibition zone assays. All biopsies from the lesions of erythema toxicum showed a dense, nodular infiltrate with numerous LL-37-expressing cells located in the dermal layer and a clear localization of the peptide within CD15-expressing neutrophils, EG2-expressing eosinophils and CD1a-expressing dendritic cells. LL-37 was also found to be located in CD1a-expressing Langerhans cells and a positive staining for the peptide was seen throughout the whole epidermal layer, both in infants with and without the rash. Skin samples from infants with the rash of erythema toxicum showed a constitutive expression of human beta defensin-1, while the expression of LL-37 seemed to be induced. Furthermore, LL-37 and lysozyme were detected in the protein fractions derived from the vernix caseosa, and these fractions exhibited a clear antibacterial activity. Peptide antibiotics are present in the vernix caseosa and in the skin of the healthy newborn infant, indicating effective innate immune protection already during fetal and neonatal life.