Human β Defensin-3 Increases CD86 Expression on Monocytes by Activating the ATP-Gated Channel P2X7

Immunoinformatic exploration of a multi-epitope-based peptide vaccine candidate targeting emerging variants of SARS-CoV-2

Many countries around the world are facing severe challenges due to the recently emerging variants of SARS-CoV-2. Over the last few months, scientists have been developing treatments, drugs, and vaccines to subdue the virus and prevent its transmission. In this context, a peptide-based vaccine construct containing pathogenic proteins of the virus known to elicit an immune response was constructed. An analysis of the spike protein-based epitopes allowed us to design an "epitope-based subunit vaccine" against coronavirus using the approaches of "reverse vaccinology" and "immunoinformatics." Computational experimentation and a systematic, comprehensive protocol were followed with an aim to develop and design a multi-epitope-based peptide (MEBP) vaccine candidate. Our study attempted to predict an MEBP vaccine by introducing mutations of SARS-CoV-2 (Delta, Lambda, Iota, Omicron, and Kappa) in Spike glycoprotein and predicting dual-purpose epitopes (B-cell and T-cell). This was followed by screening the selected epitopes based on antigenicity, allergenicity, and population coverage and constructing them into a vaccine by using linkers and adjuvants. The vaccine construct was analyzed for its physicochemical properties and secondary structure prediction, and a 3D structure was built, refined, and validated. Furthermore, the peptide-protein interaction of the vaccine construct with Toll-like receptor (TLR) molecules was performed. Immune profiling was performed to check the immune response. Codon optimization of the vaccine construct was performed to obtain the GC content before cloning it into the E. coli genome, facilitating its progression it into a vector. Finally, an in-silico simulation of the vaccine-protein complex was performed to comprehend its stability and conformational behavior.

Human β-defensins are correlated with the immune infiltration and regulated by vitamin D3 in periodontitis

OBJECTIVE

Exploring the correlation between human β-defensins (HBDs) and immune infiltration in periodontitis, and whether it is regulated by vitamin D3 .

BACKGROUND

The human body produces essential antimicrobial peptides called HBDs, which are associated with periodontitis. There is a strong link between periodontal tissue destruction and the immune cell infiltration. Moreover, vitamin D3 has been reported to regulate the expression of immune cell chemokines. However, the relationship between vitamin D3 , HBDs, and immune infiltration in periodontitis remains to be investigated.

METHODS

The Gene Expression Omnibus database was accessed to obtain transcriptomic information of gingival samples taken from periodontitis patients. The expression value of HBD-2 and HBD-3 was calculated. Additionally, using the online program ImmuCellAl, 10 immune cells were scored for immune infiltration in the high-HBDs-expression group and the low-HBDs-expression group, separately. After that, transcriptome sequencing was done based on human gingival fibroblasts that had received vitamin D3 treatment. Furthermore, hGFs were treated by vitamin D3 , tumor necrosis factor-α (TNF-α), and Porphyromonas gingivalis lipopolysaccharide (Pg-LPS). The expressions of HBD-2, HBD-3, interleukin-8 (IL-8), and monocyte chemoattractant protein-1 (MCP-1) were detected. To seek the potential mechanism, CYP27A1 siRNA was employed to reduce the expression of CYP27A1, and nuclear factor-gene binding protein 65 (NF-κB p65) was examined.

RESULTS

In GSE10334, the expressions of HBD-2 and HBD-3 were down-regulated in periodontitis group. Meanwhile, monocyte, macrophage, and CD4_T cell were less infiltrated in low-HBD-2-expression group, while less Gamma-delta T-cell infiltration was found in low-HBD-3-expression group. Transcriptome sequencing found that 21 genes were significantly expressed, of which the function was enriched in response to bacterial origin and TNF signal pathway. Vitamin D3 could significantly up-regulate the expression of HBD-2 and HBD-3, which could be controlled by knocking down CYP27A1 mRNA expression. With prolonged vitamin D3 stimulation, the expression of HBD-2 and HBD-3 increased. TNF-α/Pg-LPS could significantly increase the expression of HBD-2, HBD-3, IL-8, MCP-1, and p65, all of which were reduced by vitamin D3 .

CONCLUSION

HBDs are correlated with immune infiltration in periodontitis. Vitamin D3 inhibits the expression of HBDs and chemokines induced by TNF-α/Pg-LPS, possibly through NF-κB pathway, in human gingival fibroblasts.

The Contribution of Antimicrobial Peptides to Immune Cell Function: A Review of Recent Advances

The development of novel antimicrobial agents to replace antibiotics has become urgent due to the emergence of multidrug-resistant microorganisms. Antimicrobial peptides (AMPs), widely distributed in all kingdoms of life, present strong antimicrobial activity against a variety of bacteria, fungi, parasites, and viruses. The potential of AMPs as new alternatives to antibiotics has gradually attracted considerable interest. In addition, AMPs exhibit strong anticancer potential as well as anti-inflammatory and immunomodulatory activity. Many studies have provided evidence that AMPs can recruit and activate immune cells, controlling inflammation. This review highlights the scientific literature focusing on evidence for the anti-inflammatory mechanisms of different AMPs in immune cells, including macrophages, monocytes, lymphocytes, mast cells, dendritic cells, neutrophils, and eosinophils. A variety of immunomodulatory characteristics, including the abilities to activate and differentiate immune cells, change the content and expression of inflammatory mediators, and regulate specific cellular functions and inflammation-related signaling pathways, are summarized and discussed in detail. This comprehensive review contributes to a better understanding of the role of AMPs in the regulation of the immune system and provides a reference for the use of AMPs as novel anti-inflammatory drugs for the treatment of various inflammatory diseases.

TNAP and P2X7R: New Plasma Biomarkers for Alzheimer's Disease

Over the last few years, intense research efforts have been made to anticipate or improve the diagnosis of Alzheimer's disease by detecting blood biomarkers. However, the most promising blood biomarkers identified to date have some limitations, most of them related to the techniques required for their detection. Hence, new blood biomarkers should be identified to improve the diagnosis of AD, better discriminate between AD and mild cognitive impairment (MCI) and identify cognitively unimpaired (CU) older individuals at risk for progression to AD. Our previous studies demonstrated that both the purinergic receptor P2X7 and the tissue-nonspecific alkaline phosphatase ectoenzyme (TNAP) are upregulated in the brains of AD patients. Since both proteins are also present in plasma, we investigated whether plasma P2X7R and TNAP are altered in MCI and AD patients and, if so, their potential role as AD biomarkers. We found that AD but not MCI patients present increased plasma P2X7R levels. Nevertheless, TNAP plasma activity was increased in MCI patients and decreased in the AD group. ROC curve analysis indicated that measuring both parameters has a reasonable discriminating capability to diagnose MCI and AD conditions. In addition to confirming that individuals progressing to MCI have increased TNAP activity in plasma, longitudinal studies also revealed that CU individuals have lower plasma TNAP activity than stable controls. Thus, we propose that P2X7 and TNAP could serve as new plasma biomarkers for MCI and AD.

Physiologic roles of P2 receptors in leukocytes

Since their discovery in the 1970s, purinergic receptors have been shown to play key roles in a wide variety of biologic systems and cell types. In the immune system, purinergic receptors participate in innate immunity and in the modulation of the adaptive immune response. In particular, P2 receptors, which respond to extracellular nucleotides, are widely expressed on leukocytes, causing the release of cytokines and chemokines and the formation of inflammatory mediators, and inducing phagocytosis, degranulation, and cell death. The activity of these receptors is regulated by ectonucleotidases-expressed in these same cell types-which regulate the availability of nucleotides in the extracellular environment. In this article, we review the characteristics of the main purinergic receptor subtypes present in the immune system, focusing on the P2 family. In addition, we describe the physiologic roles of the P2 receptors already identified in leukocytes and how they can positively or negatively modulate the development of infectious diseases, inflammation, and pain.

Circulating P2X7 Receptor Signaling Components as Diagnostic Biomarkers for Temporal Lobe Epilepsy

Circulating molecules have potential as biomarkers to support the diagnosis of epilepsy and to assist with differential diagnosis, for example, in conditions resembling epilepsy, such as in psychogenic non-epileptic seizures (PNES). The P2X7 receptor (P2X7R) is an important regulator of inflammation and mounting evidence supports its activation in the brain during epilepsy. Whether the P2X7R or P2X7R-dependent signaling molecules can be used as biomarkers of epilepsy has not been reported. P2X7R levels were analyzed by quantitative ELISA using plasma samples from controls and patients with temporal lobe epilepsy (TLE) or PNES. Moreover, blood cell P2X7R expression and P2X7R-dependent cytokine signature was measured following status epilepticus in P2X7R-EGFP reporter, wildtype, and P2X7R-knockout mice. P2X7R plasma levels were higher in TLE patients when compared with controls and patients with PNES. Plasma levels of the broad inflammatory marker protein C-Reactive protein (CRP) were similar between the three groups. Using P2X7R-EGFP reporter mice, we identified monocytes as the main blood cell type expressing P2X7R after experimentally evoked seizures. Finally, cytokine array analysis in P2X7R-deficient mice identified KC/GRO as a potential P2X7R-dependent plasma biomarker following status epilepticus and during epilepsy. Our data suggest that P2X7R signaling components may be a promising subclass of circulating biomarkers to support the diagnosis of epilepsy.

Targeting Cancer Heterogeneity with Immune Responses Driven by Oncolytic Peptides

Accumulating preclinical and clinical evidence indicates that high degrees of heterogeneity among malignant cells constitute a considerable obstacle to the success of cancer therapy. This calls for the development of approaches that operate - or enable established treatments to operate - despite such intratumoral heterogeneity (ITH). In this context, oncolytic peptides stand out as promising therapeutic tools based on their ability to drive immunogenic cell death associated with robust anticancer immune responses independently of ITH. We review the main molecular and immunological pathways engaged by oncolytic peptides, and discuss potential approaches to combine these agents with modern immunotherapeutics in support of superior tumor-targeting immunity and efficacy in patients with cancer.

Antimicrobial peptides: bridging innate and adaptive immunity in the pathogenesis of psoriasis

Antimicrobial peptides (AMPs) are small molecules produced by a myriad of cells and play important roles not only in protecting against infections and sustaining skin barrier homeostasis but also in contributing to immune dysregulation under pathological conditions. Recently, increasing evidence has indicated that AMPs, including cathelicidin (LL-37), human β-defensins, S100 proteins, lipocalin 2, and RNase 7, are highly expressed in psoriatic skin lesions. These peptides broadly regulate immunity by interacting with various immune cells and linking innate and adaptive immune responses during the progression of psoriasis. In this review, we summarize the recent findings regarding AMPs in the pathogenesis of psoriasis with a main focus on their immunomodulatory abilities.

The Dichotomous Responses Driven by β-Defensins

Defensins are short, rapidly evolving, cationic antimicrobial host defence peptides with a repertoire of functions, still incompletely realised, that extends beyond direct microbial killing. They are released or secreted at epithelial surfaces, and in some cases, from immune cells in response to infection and inflammation. Defensins have been described as endogenous alarmins, alerting the body to danger and responding to inflammatory signals by promoting both local innate and adaptive systemic immune responses. However, there is now increasing evidence that they exert variable control on the response to danger; creating a dichotomous response that can suppress inflammation in some circumstances but exacerbate the response to danger and damage in others and, at higher levels, lead to a cytotoxic effect. Focussing in this review on human β-defensins, we discuss the evidence for their functions as proinflammatory, immune activators amplifying the response to infection or damage signals and/or as mediators of resolution of damage, contributing to a return to homeostasis. Finally, we consider their involvement in the development of autoimmune diseases.

Overexpressing ovotransferrin and avian β-defensin-3 improves antimicrobial capacity of chickens and poultry products

Zoonotic and foodborne diseases pose a significant burden, decreasing both human and animal health. Modifying chickens to overexpress antimicrobials has the potential to decrease bacterial growth on poultry products and boost chicken innate immunity. Chickens overexpressing either ovotransferrin or avian β-defensin-3 (AvβD3) were generated using Tol-2 transposons. Transgene expression at the RNA and protein level was seen in egg white, breast muscle, and serum. There were significant differences in the immune cell populations in the blood, bursa, and spleen associated with transgene expression including an increased proportion of CD8+ cells in the blood of ovotransferrin and AvβD3 transgenic birds. Expression of the antimicrobials inhibited the in vitro growth of human and chicken bacterial pathogens and spoilage bacteria. For example, transgene expression significantly reduced growth of aerobic and coliform bacteria in breast muscle and decreased the growth of Salmonella enterica in egg white. Overall these results indicate that overexpression of antimicrobials in the chicken can impact the immune system and increase the antimicrobial capacity of poultry products.

Multifaceted immune functions of human defensins and underlying mechanisms

Defensins have been long recognized as natural antimicrobial peptides, but they also possess diverse and versatile immune functions. Defensins can both induce inflammation and suppress inflammatory responses by acting on specific cells through distinct mechanisms. Defensins can also modulate the immune response by forming a complex with cellular molecules including proteins, nucleic acids, and carbohydrates. The mechanisms of defensin-mediated immune modulation appear to be cell-type and context specific. Because the levels of human defensins are often altered in response to infection or disease states, suggesting their clinical relevance, this review summarizes the complex immune functions of human defensins and their underlying mechanisms of action, which have implications for the development of new therapeutics.

The potential of P2X7 receptors as a therapeutic target, including inflammation and tumour progression

Seven P2X ion channel nucleotide receptor subtypes have been cloned and characterised. P2X7 receptors (P2X7R) are unusual in that there are extra amino acids in the intracellular C terminus. Low concentrations of ATP open cation channels sometimes leading to cell proliferation, whereas high concentrations of ATP open large pores that release inflammatory cytokines and can lead to apoptotic cell death. Since many diseases involve inflammation and immune responses, and the P2X7R regulates inflammation, there has been recent interest in the pathophysiological roles of P2X7R and the potential of P2X7R antagonists to treat a variety of diseases. These include neurodegenerative diseases, psychiatric disorders, epilepsy and a number of diseases of peripheral organs, including the cardiovascular, airways, kidney, liver, bladder, skin and musculoskeletal. The potential of P2X7R drugs to treat tumour progression is discussed.

Importance of phosphoinositide binding by human β-defensin 3 for Akt-dependent cytokine induction

Host defense peptides (HDPs) are well-characterized for their antimicrobial activities but also variously display potent immunomodulatory effects. Human β-defensin 3 (HBD-3) belongs to a well-known HDP family known as defensins and is able to induce leukocyte chemotactic recruitment, leukocyte activation/maturation, proinflammatory cytokine release, and co-stimulatory marker expression. HBD-3-stimulated cytokine induction is NF-κB-dependent and was initially suggested to act via G protein-coupled C-C chemokine receptor phospholipase C (PLC) and/or Toll-like receptor signaling. Subsequent pharmacological inhibition, however, revealed that NF-κB activation by HBD-3 is receptor-independent and instead involves the phosphoinositide 3-kinase (PI3K)-protein kinase B (Akt) pathway, the mechanism of which remains undetermined. Recently, we have shown that HBD-3 can enter mammalian cells and bind to inner membrane phosphoinositide 4,5-bisphosphate [PI(4,5)P₂], an important second lipid messenger of PLC and PI3K-Akt pathways. In this study, we report that the interaction of HBD-3 with PI(4,5)P₂ is important for PI3K-Akt-NF-κΒ-mediated induction of tumor necrosis factor and interleukin-6. These data provide insights into the mechanism of immunomodulation by HBD-3, and more generally, highlight the complex multifaceted signaling roles of HDPs in innate defense. Furthermore, it is suggested that the proposed mode of action may be conserved in other HDPs.

Purinergic Signalling: Therapeutic Developments

Purinergic signalling, i.e., the role of nucleotides as extracellular signalling molecules, was proposed in 1972. However, this concept was not well accepted until the early 1990's when receptor subtypes for purines and pyrimidines were cloned and characterised, which includes four subtypes of the P1 (adenosine) receptor, seven subtypes of P2X ion channel receptors and 8 subtypes of the P2Y G protein-coupled receptor. Early studies were largely concerned with the physiology, pharmacology and biochemistry of purinergic signalling. More recently, the focus has been on the pathophysiology and therapeutic potential. There was early recognition of the use of P1 receptor agonists for the treatment of supraventricular tachycardia and A2A receptor antagonists are promising for the treatment of Parkinson's disease. Clopidogrel, a P2Y12 antagonist, is widely used for the treatment of thrombosis and stroke, blocking P2Y12 receptor-mediated platelet aggregation. Diquafosol, a long acting P2Y2 receptor agonist, is being used for the treatment of dry eye. P2X3 receptor antagonists have been developed that are orally bioavailable and stable in vivo and are currently in clinical trials for the treatment of chronic cough, bladder incontinence, visceral pain and hypertension. Antagonists to P2X7 receptors are being investigated for the treatment of inflammatory disorders, including neurodegenerative diseases. Other investigations are in progress for the use of purinergic agents for the treatment of osteoporosis, myocardial infarction, irritable bowel syndrome, epilepsy, atherosclerosis, depression, autism, diabetes, and cancer.

Effect of naringin on gp120-induced injury mediated by P2X7 receptors in rat primary cultured microglia

Human immunodeficiency virus type-1 (HIV-1) envelope glycoprotein 120 has been shown to activate microglia, causing release of inflammatory and toxic factors. The P2X₇ receptor, primarily expressed on microglia, is closely associated with inflammation. Naringin, a plant bioflavonoid, has anti-inflammatory and anti-oxidative properties. We hypothesized that P2X₇ receptor mediated gp120-induced injury in primary cultured microglia, and that naringin would have a protective effect. We showed that HIV-1 gp120 peptide (V3 loop, fragment 308–331) appeared to induce apoptosis of primary cultured microglia. However, there was a decrease of microglia apoptosis in gp120+naringin group compared with gp120 group. Using qPCR, Western blot, and immunofluorescence, we showed that gp120 stimulated expression of P2X₇ mRNA and receptor protein, and this stimulation was inhibited by naringin. Treatment with gp120 increased concentrations of eATP, TNFα and IL-1β, and these effects were inhibited by naringin. Taken together, these results suggested that gp120 contributed to microglial cell injury and neurotoxic activity by up-regulating expression of P2X₇, in a naringin-protective manner.

Defensins in Viral Infection and Pathogenesis

α, β, and θ defensins are effectors of the innate immune system with potent antibacterial, antiviral, and antifungal activity. Defensins have direct antiviral activity in cell culture, with varied mechanisms for individual viruses, although some common themes have emerged. In addition, defensins have potent immunomodulatory activity that can alter innate and adaptive immune responses to viral infection. In some cases, there is evidence for paradoxical escape from defensin neutralization or enhancement of viral infection. The direct and indirect activities of defensins have led to their development as therapeutics and vaccine components. The major area of investigation that continues to lag is the connection between the effects of defensins in cell culture models and viral pathogenesis in vivo. Model systems to study defensin biology, including more physiologic models designed to bridge this gap, are also discussed.

Immunomodulatory effects of anti-microbial peptides

Anti-microbial peptides (AMPs) were originally thought to exert protecting actions against bacterial infection by disintegrating bacterial membranes. Upon identification of internal bacterial targets, the view changed and moved toward inhibition of prokaryote-specific biochemical processes. However, the level of none of these activities can explain the robust efficacy of some of these peptides in animal models of systemic and cutaneous infections. A rapidly growing panel of reports suggests that AMPs, now called host-defense peptides (HDPs), act through activating the immune system of the host. This includes recruitment and activation of macrophages and mast cells, inducing chemokine production and altering NF-κB signaling processes. As a result, both pro- and anti-inflammatory responses are elevated together with activation of innate and adaptive immunity mechanisms, wound healing, and apoptosis. HDPs sterilize the systemic circulation and local injury sites significantly more efficiently than pure single-endpoint in vitro microbiological or biochemical data would suggest and actively aid recovering from tissue damage after or even without bacterial infections. However, the multiple and, often opposing, immunomodulatory functions of HDPs require exceptional care in therapeutic considerations.

Human beta-defensin-2 and -3 enhance pro-inflammatory cytokine expression induced by TLR ligands via ATP-release in a P2X7R dependent manner

Our previous results indicate that HBD2 and HBD3 are chemotactic for a broad spectrum of leukocytes in a CCR6- and CCR2-dependent manner. In this study we report that pre-stimulation of primary human macrophages or THP-1 cells with HBD2 or HBD3 results in a synergistic, enhanced expression of pro-inflammatory cytokines and chemokines induced by TLR ligand re-stimulation. Experiments using specific inhibitors of the ATP-gated channel receptor P2X7 or its functional ligand ATP, suggest that the enhanced expression of pro-inflammatory cytokines and chemokines seems to be mediated by P2X7R. Furthermore, our data provide evidence that beta-defensins do not directly interact with P2X7R but rather induce the release of intracellular ATP. Interference with ATP release abrogated the synergistic effect mediated by HBD2 and HBD3 pre-stimulation in THP-1 cells. However, extracellular ATP alone seems not to be sufficient to elicit the enhanced synergistic effect on cytokine and chemokine expression observed by pre-stimulation of primary human macrophages or THP-1 cells with HBD2 or HBD3. Collectively, our findings provide new insights into the molecular mechanisms how HBD2 and HBD3 interact with cells of myeloid origin and demonstrate their immuno-modulating functions during innate immune responses.