CAP37 activation of PKC promotes human corneal epithelial cell chemotaxis

Transforming growth factor-β receptor type 2 is required for heparin-binding protein-induced acute lung injury and vascular leakage for transforming growth factor-β/Smad/Rho signaling pathway activation

Heparin-binding protein (HBP), as a granule protein secreted by polymorphonuclear neutrophils, participates in the pathophysiological process of sepsis. It has been reported that HBP is a biomarker of sepsis related to the severity of septic shock and organ dysfunction. HBP binds to vascular endothelial cells as a primary target site. However, it is still unclear whether HBP-binding protein receptors exist on the surface of endothelial cells. The effect of HBP on vascular permeability in sepsis and its mechanism needs to be explored. We conducted in vivo and in vitro studies and demonstrated that HBP binds to transforming growth factor-β receptor type 2 (TGF-β-R2) as a ligand. Glutathione S-transferase pull-down analysis revealed that HBP mainly interacts with the extracellular domain of TGF-β-R2. HBP induces acute lung injury and vascular leakage via activation of the TGF-β/SMAD2/3 signaling pathway. A permeability assay suggested that TGF-β-R2 is necessary for HBP-induced increased permeability. We also defined the role of HBP and its potential membrane receptor TGF-β-R2 in the blood-gas barrier in the pathogenesis of HBP-related acute lung injury.

Increased CAP37 Expression in Stable Chronic Obstructive Pulmonary Disease

OBJECTIVE

Cationic antimicrobial protein of 37 kDa (CAP37), a neutrophil-derived protein originally identified for its antimicrobial activity, is now known to have many regulatory effects on host cells. However, its role in the pathogenesis of chronic obstructive pulmonary disease (COPD) has not been studied. We therefore investigated the expression of CAP37 in COPD and its effects on airway structural cells, including bronchial epithelial cells, smooth muscle cells, and fibroblasts.

METHODS

CAP37 was detected in the lung tissue, sputum, and plasma of COPD patients and the control subjects, as well as in the neutrophils stimulated by cigarette smoke extract (CSE). BEAS-2B cells, human bronchial smooth muscle cells (HBSMCs), and MRC-5 cells were treated with CAP37 or an anti-CAP37 antibody plus CAP37. Interleukin (IL)-6 and IL-8 were detected in the BEAS-2B cells. The cell proliferation was analyzed in the HBSMCs. Collagens were also detected in the MRC-5 cells.

RESULTS

The expression of CAP37 was increased in the lung tissue and sputum supernatant of the COPD patients compared with the control subjects. The sputum supernatant CAP37 levels were inversely correlated with the forced expiratory volume in the first second percentage predicted in COPD. CAP37 was induced by CSE stimulation in the peripheral blood neutrophils from healthy non-smokers. CAP37 induced expression of IL-6 and IL-8 in BEAS-2B cells, and collagen expression of lung fibroblasts (MRC-5 cells). However, CAP37 did not significantly alter the proliferation of the HBSMCs.

CONCLUSION

Our findings indicated that neutrophil-derived CAP37 may be involved in airway inflammation and fibrosis in COPD via affecting the bronchial epithelial cells, and fibroblasts, thus suggesting a possible role of CAP37 in the development and progression of COPD.

Antimicrobial Peptide Expression at the Ocular Surface and Their Therapeutic Use in the Treatment of Microbial Keratitis

Microbial keratitis is a common cause of ocular pain and visual impairment worldwide. The ocular surface has a relatively paucicellular microbial community, mostly found in the conjunctiva, while the cornea would be considered relatively sterile. However, in patients with microbial keratitis, the cornea can be infected with multiple pathogens including Staphylococcus aureus, Pseudomonas aeruginosa, and Fusarium sp. Treatment with topical antimicrobials serves as the standard of care for microbial keratitis, however, due to high rates of pathogen resistance to current antimicrobial medications, alternative therapeutic strategies must be developed. Multiple studies have characterized the expression and activity of antimicrobial peptides (AMPs), endogenous peptides with key antimicrobial and wound healing properties, on the ocular surface. Recent studies and clinical trials provide promise for the use of AMPs as therapeutic agents. This article reviews the repertoire of AMPs expressed at the ocular surface, how expression of these AMPs can be modulated, and the potential for harnessing the AMPs as potential therapeutics for patients with microbial keratitis.

Antimicrobial Peptides Derived from the Immune Defense Protein CAP37 Inhibit TLR4 Activation by S100A9

Purpose

Corneal abrasion is a common eye injury, and its resolution can be seriously complicated by bacterial infection. We showed that topical application of the cationic antimicrobial protein of 37 kDa (CAP37) promotes corneal re-epithelialization in mice, and peptides derived from CAP37 can recapitulate the antibacterial and wound-healing effects of the full-length protein. The current study was designed to identify the molecular mechanisms mediating the wound-healing effect of CAP37 and derived bioactive peptides.

Methods

We used a TriCEPS-based, ligand-receptor glycocapture method to identify the binding partners of CAP37 on live human corneal epithelial cells using the hTCEpi cell line. We used an ELISA method to confirm binding with identified partners and test the binding with CAP37-derived peptides. We used a reporter cell line to measure activation of the identified membrane receptor by CAP37 and derived peptides.

Results

We pulled down S100 calcium-binding protein A9 (S100A9) as a binding partner of CAP37 and found that CAP37 and four derived peptides encompassing two regions of CAP37 bind S100A9 with high affinities. We found that CAP37 and the S100A9-binding peptides could also directly interact with the Toll-like receptor 4 (TLR4), a known receptor for S100A9. CAP37 and one peptide partially activated TLR4. The other three peptides did not activate TLR4. Finally, we found that CAP37 and all four peptides could inhibit the activation of TLR4 by S100A9.

Conclusions

This study identifies a mechanism of action for CAP37 and derived antimicrobial peptides that may restrain inflammatory responses to corneal injury and favor corneal re-epithelialization.

A Promising Candidate: Heparin-Binding Protein Steps onto the Stage of Sepsis Prediction

Sepsis is a systemic inflammatory response syndrome caused by infection. With high morbidity and mortality of this disease, there is a need to find early effective diagnosis and assessment methods to improve the prognosis of patients. Heparin-binding protein (HBP) is a granular protein derived from polynuclear neutrophils. The biosynthetic HBP in neutrophils is rapidly released under the stimulation of bacteria, resulting in increased vascular permeability and edema. It is reasonable to speculate that the HBP in plasma may serve as a novel diagnostic marker for sepsis, bacterial skin infection, acute bacterial meningitis, leptospirosis, protozoan parasites, and even some noncommunicable diseases. It implies that in the detection and diagnosis of sepsis, it will be possible to make relevant diagnosis through this new indicator in the future. In this review, we summarize the typical biological function of HBP and its latest research progress to provide theoretical basis for clinical prediction and diagnosis of sepsis.

The role of neutrophil granule proteins in neuroinflammation and Alzheimer's disease

Neutrophils are the innate immune system’s first line of defense. Neutrophils play a critical role in protecting the host against infectious pathogens, resolving sterile injuries, and mediating inflammatory responses. The granules of neutrophils and their constituent proteins are central to these functions. Although neutrophils may exert a protective role upon acute inflammatory conditions or insults, continued activity of neutrophils in chronic inflammatory diseases can contribute to tissue damage. Neutrophil granule proteins are involved in a number of chronic inflammatory conditions and diseases. However, the functions of these proteins in neuroinflammation and chronic neuroinflammatory diseases, including Alzheimer’s disease (AD), remain to be elucidated. In this review, we discuss recent findings from our lab and others that suggest possible functions for neutrophils and the neutrophil granule proteins, CAP37, neutrophil elastase, and cathepsin G, in neuroinflammation, with an emphasis on AD. These findings reveal that neutrophil granule proteins may exert both neuroprotective and neurotoxic effects. Further research should determine whether neutrophil granule proteins are valid targets for therapeutic interventions in chronic neuroinflammatory diseases.

Bioactive Antimicrobial Peptides as Therapeutics for Corneal Wounds and Infections

Significance: More than 2 million eye injuries and infections occur each year in the United States that leave civilians and military members with reduced or complete vision loss due to the lack of effective therapeutics. Severe ocular injuries and infections occur in varied settings including the home, workplace, and battlefields. In this review, we discuss the potential of developing antimicrobial peptides (AMPs) as therapeutics for the treatment of corneal wounds and infections for which the current treatment options are inadequate.

Recent Advances: Standard-of-care employs the use of fluorescein dye for the diagnosis of ocular defects and is followed by the use of antibiotics and/or steroids to treat the infection and reduce inflammation. Recent advances for treating corneal wounds include the development of amniotic membrane therapies, wound chambers, and drug-loaded hydrogels. In this review, we will discuss an innovative approach using AMPs with the dual effect of promoting corneal wound healing and clearing infections.

Critical Issues: An important aspect of treating ocular injuries is that treatments need to be effective and administered expeditiously. This is especially important for injuries that occur during combat and in individuals who demonstrate delayed wound healing. To overcome gaps in current treatment modalities, bioactive peptides based on naturally occurring cationic antimicrobial proteins are being investigated as new therapeutics.

Future Directions: The development of new therapeutics that can treat ocular infections and promote corneal wound healing, including the healing of persistent corneal epithelial defects, would be of great clinical benefit.

Heparin-binding protein: a key player in the pathophysiology of organ dysfunction in sepsis

Infectious diseases remain a major health problem, and sepsis and other severe infectious diseases are common causes of morbidity and mortality. There is a need for clinical and laboratory tools to identify patients with severe infections early and to distinguish between bacterial and nonbacterial conditions. Heparin-binding protein (HBP), also known as azurocidin or cationic antimicrobial protein of 37 KDa, is a promising biomarker to distinguish between patients with these conditions. It is biologically plausible that HBP is an early and predictive biomarker because it is prefabricated and rapidly mobilized from migrating neutrophils in response to bacterial infections. HBP induces vascular leakage and oedema formation and has a pro-inflammatory effect on a variety of white blood cells and epithelial cells. The dysregulation of vascular barrier function and cellular inflammatory responses can then lead to organ dysfunction. Indeed, it has been shown that patients with sepsis express elevated levels of HBP in plasma several hours before they develop hypotension or organ dysfunction. HBP has a major role in the pathophysiology of severe bacterial infections and thus represents a potential diagnostic marker and a target for the treatment of sepsis.

Effect of Cationic Antimicrobial Protein CAP37 on Cytokine Profile during Corneal Wound Healing

The cationic antimicrobial protein of 37 kDa (CAP37) mediates proliferation, migration, and adhesion of human corneal epithelial cells and promotes corneal re-epithelialization in mouse. The purpose of this study was to investigate the cytokine profile following abrasion of the corneal epithelium, and to identify the cytokines modulated by topical treatment with CAP37 to determine the mechanism by which CAP37 contributes to the recruitment of inflammatory cells and healing of the cornea. The corneal epithelium in mouse eyes was removed and wounds were treated with a saline vehicle or human recombinant CAP37. Wounds were visualized with fluoresce in staining at 0, 16, 24 and 48 h. Mouse corneas were excised at 0, 6, 16, 24 and 48 h post corneal abrasion. The excised corneas were analyzed by immunohistochemistry for re-epithelialization and infiltration of inflammatory cells while the expression profiles of thirty-two cytokines were investigated by multiplex analysis. Results corroborating previous studies showed accelerated wound closure in corneas treated with CAP37 compared to those treated with the saline vehicle. Immunohistochemistry revealed less neutrophil infiltration in CAP37-treated corneas when compared to controls at 24 h. By 48 h post-wounding, histological analysis revealed more staining for neutrophils than the staining observed in the controls. Modulation of cytokine expression occurred for the majority of the cytokines tested at the time of corneal abrasion, during re-epithelialization, and/or by CAP37 treatment. Cytokines monocyte chemoattractant protein-1 (MCP-1) and regulated on activation, normal T cell expressed and secreted (RANTES) were induced during re-epithelialization, at the early 16 h time point. Interleukin 6 (IL-6), leukemia inhibitory factor (LIF), granulocyte colony-stimulating factor (G-CSF), IL-12p70, macrophage inflammatory protein 1 beta (MIP-1β), and interferon gamma-induced protein 10 (IP-10) were induced at 24 h and unchanged during CAP37 treatment. By contrast, IL-15, monokine induced by gamma interferon (MIG), keratinocyte-derived cytokine (KC), tumor necrosis factor alpha (TNF-α), MIP-1α, IL-1β, and macrophage colony-stimulating factor (M-CSF) were modulated by CAP37 treatment. In general, CAP37 appeared to decrease pro-inflammatory cytokines at 24 h and increase them at 48 h when compared to the control group. These data demonstrate that CAP37 modulates the production of cytokines in the cornea and suggest that limiting the number of neutrophils recruited during the early inflammatory phase may support corneal re-epithelialization.

Heparin-binding protein is important for vascular leak in sepsis

BACKGROUND

Elevated plasma levels of heparin-binding protein (HBP) are associated with risk of organ dysfunction and mortality in sepsis, but little is known about causality and mechanisms of action of HBP. The objective of the present study was to test the hypothesis that HBP is a key mediator of the increased endothelial permeability observed in sepsis and to test potential treatments that inhibit HBP-induced increases in permeability.

METHODS

Association between HBP at admission with clinical signs of increased permeability was investigated in 341 patients with septic shock. Mechanisms of action and potential treatment strategies were investigated in cultured human endothelial cells and in mice.

RESULTS

Following adjustment for comorbidities and Acute Physiology and Chronic Health Evaluation (APACHE) II, plasma HBP concentrations were weakly associated with fluid overload during the first 4 days of septic shock and the degree of hypoxemia (PaO₂/FiO₂) as measures of increased systemic and lung permeability, respectively. In mice, intravenous injection of recombinant human HBP induced a lung injury similar to that observed after lipopolysaccharide injection. HBP increased permeability of vascular endothelial cell monolayers in vitro, and enzymatic removal of luminal cell surface glycosaminoglycans (GAGs) using heparinase III and chondroitinase ABC abolished this effect. Similarly, unfractionated heparins and low molecular weight heparins counteracted permeability increased by HBP in vitro. Intracellular, selective inhibition of protein kinase C (PKC) and Rho-kinase pathways reversed HBP-mediated permeability effects.

CONCLUSIONS

HBP is a potential mediator of sepsis-induced acute lung injury through enhanced endothelial permeability. HBP increases permeability through an interaction with luminal GAGs and activation of the PKC and Rho-kinase pathways. Heparins are potential inhibitors of HBP-induced increases in permeability.

The antimicrobial protein, CAP37, is upregulated in pyramidal neurons during Alzheimer's disease

Inflammation is a well-defined factor in Alzheimer's disease (AD). There is a strong need to identify the molecules contributing to neuroinflammation so that therapies can be designed to prevent immune-mediated neurotoxicity. The cationic antimicrobial protein of 37 kDa (CAP37) is an inflammatory mediator constitutively expressed in neutrophils (PMNs). In addition to antibiotic activity, CAP37 exerts immunomodulatory effects on microglia. We hypothesize that CAP37 mediates the neuroinflammation associated with AD. However, PMNs are not customarily associated with the pathology of AD. This study was therefore designed to identify non-neutrophilic source(s) of CAP37 in brains of AD patients. Brain tissues from patients and age-matched controls were analyzed for CAP37 expression using immunohistochemistry (IHC). To determine factors that induce CAP37 in AD, HCN-1A primary human neurons were treated with tumor necrosis factor-alpha (TNF-α) or amyloid β1-40 (Aβ) and analyzed by IHC. Western blotting and quantitative reverse transcription polymerase chain reaction (qRT-PCR) were used to confirm CAP37 expression in neurons and brain tissues. IHC revealed CAP37 in cortical neurons in temporal and parietal lobes as well as CA3 and CA4 hippocampal neurons in patients with AD. CAP37 was found in more neurons in AD patients compared with age-matched controls. qRT-PCR and Western blotting showed an increase in CAP37 transcript and protein in the AD temporal lobe, a brain region that is highly impacted in AD. qRT-PCR observations confirmed CAP37 expression in neurons. TNF-α and Aβ increased neuronal expression of CAP37. These findings support our hypothesis that neuronal CAP37 may modulate the neuroinflammatory response in AD.

Fungus induces the release of IL-8 in human corneal epithelial cells, via Dectin-1-mediated protein kinase C pathways

AIM

To identify whether Aspergillus fumigatus (A. fumigatus) hyphae antigens induced the release of interleukin-8 (IL-8) in anti-fungal innate immunity of cultured human corneal epithelial cells (HCECs) and determine the involvement of intracellular signalling pathways.

METHODS

HCECs were treated with A. fumigatus hyphae antigens with different concentrations and time. The cytoplasmic calcium of HCECs were assessed by fluorescence imaging. Western blot was used to detect the expression of Ca(2+)-dependent protein kinase C (PKC). The IL-8 levels were determined by specific human IL-8 enzyme-linked immunosorbent assay (ELISA) and reverse transcriptase polymerase chain reaction (RT-PCR). Using a series of pharmacological inhibitors, we examined the upstream signalling pathway responsible for IL-8 expression in response to A. fumigatus hyphae antigens.

RESULTS

Cells exposed to A. fumigatus hyphae antigens showed higher level of IL-8 mRNA expression and protein production. We demonstrated here that stimulation of HCECs with A. fumigatus hyphae triggers an intracellular Ca(2+) flux and results in the activation of Ca(2+)-dependent PKC (α, βI and βII) which can be attenuated by pre-treatment of cells with laminarin, suggesting that Dectin-1 signals pathway induced cytoplasmic calcium and influence the activation of PKC in HCECs. Inhibitors of Ca(2+)-dependent PKC (Ro-31-8220 and Go6976) significantly abolished hyphae-induced expression of IL-8.

CONCLUSION

Our findings suggest that A. fumigatus hyphae-induced IL-8 expression was regulated by the activation of Dectin-1-mediated Ca(2+)-dependent PKC in HCECs.

A multifunctional peptide based on the neutrophil immune defense molecule, CAP37, has antibacterial and wound-healing properties

CAP37, a protein constitutively expressed in human neutrophils and induced in response to infection in corneal epithelial cells, plays a significant role in host defense against infection. Initially identified through its potent bactericidal activity for Gram-negative bacteria, it is now known that CAP37 regulates numerous host cell functions, including corneal epithelial cell chemotaxis. Our long-term goal is to delineate the domains of CAP37 that define these functions and synthesize bioactive peptides for therapeutic use. We report the novel finding of a multifunctional domain between aa 120 and 146. Peptide analogs 120-146 QR, 120-146 QH, 120-146 WR, and 120-146 WH were synthesized and screened for induction of corneal epithelial cell migration by use of the modified Boyden chamber assay, antibacterial activity, and LPS-binding activity. In vivo activity was demonstrated by use of mouse models of sterile and infected corneal wounds. The identity of the amino acid at position 132 (H vs. R) was important for cell migration and in vivo corneal wound healing. All analogs demonstrated antimicrobial activity. However, analogs containing a W at position 131 showed significantly greater antibacterial activity against the Gram-negative pathogen Pseudomonas aeruginosa. All analogs bound P. aeruginosa LPS. Topical administration of analog 120-146 WH, in addition to accelerating corneal wound healing, effectively cleared a corneal infection as a result of P. aeruginosa. In conclusion, we have identified a multifunctional bioactive peptide, based on CAP37, that induces cell migration, possesses antibacterial and LPS-binding activity, and is effective at healing infected and noninfected corneal wounds in vivo.

Corneal wound healing, a newly identified function of CAP37, is mediated by protein kinase C delta (PKCδ)

PURPOSE

The neutrophil-derived granular protein, CAP37, an innate immune system molecule, has antibiotic and immunomodulatory effects on host cells, including corneal epithelial cells. We previously showed that CAP37 modulates corneal epithelial cell migration, adhesion, and proliferation, and that protein kinase C delta (PKCδ) mediates CAP37-induced chemotaxis of these cells. The objective of this study was to investigate the hypothesis that CAP37 facilitates corneal wound healing through the PKC signaling pathway.

METHODS

The standard "scratch" assay performed on monolayers of corneal epithelial cells was used to measure the in vitro effect of CAP37 on wound closure. In vivo wound healing in response to CAP37 was measured using a mouse corneal epithelium abrasion model. In vitro and in vivo wound closure were monitored over 48 hours. The PKCδ was visualized during wound closure in cell monolayers and corneal epithelium by immunohistochemistry. The importance of PKCδ in CAP37-induced corneal wound healing was assessed by siRNA.

RESULTS

We found that CAP37 accelerated wound closure in vitro and in vivo. Maximal closure occurred with concentrations of CAP37 between 250 and 500 ng/mL. Topical applications on mouse cornea led to re-epithelialization of the cornea by 24 hours. Immunohistochemistry of in vitro and in vivo wounds revealed a local increase of PKCδ along the wound edge in CAP37-treated cell monolayers and corneas, compared to untreated controls. CAP37-induced corneal wound healing was significantly reduced in vivo upon treatment with PKCδ siRNA.

CONCLUSIONS

These findings support the hypothesis that CAP37 facilitates corneal wound healing through the activation of PKCδ.