Defensins in Viral Infection and Pathogenesis

Defensins regulate cell cycle: Insights of defensins on cellular proliferation and division

Defensins are a class of small antimicrobial peptides that play a crucial role against pathogens. However, recent research has highlighted defensins exhibit the ability to influence cell cycle checkpoints, promoting or inhibiting specific phases such as G1 arrest or S/M transition. By regulating the cell cycle, defensins impact the proliferation of normal and cancerous cells, with implications for cancer development and progression. Dysregulation of defensin expression can disrupt the delicate balance of cell cycle regulation, leading to uncontrolled cell growth and an increased risk of tumor formation. Defensins contribute to the resolution of inflammation, stimulate angiogenesis, and enhance the migration and proliferation of cells involved in tissue repair. Furthermore, The ability of defensins to respond to microenvironmental changes further demonstrates the significance of these peptides in host defense mechanisms and immune function. By adjusting their expression, defensins continue to combat pathogens effectively and maintain homeostasis within the body. This review highlights the multifaceted role of defensins in regulating the cell cycle and their broader implications in cancer progression, tissue repair, and microenvironmental response.

TLR4/7-mediated host-defense responses of gingival epithelial cells

Gingival epithelial cells (GECs) are physical and immunological barriers against outward pathogens while coping with a plethora of non-pathogenic commensal bacteria. GECs express several members of Toll-like receptors (TLRs) and control subsequent innate immune responses. TLR4 senses lipopolysaccharide (LPS) while TLR7/8 recognizes single-strand RNA (ssRNA) playing important roles against viral infection. However, their distinct roles in GECs have not been fully demonstrated. Here, we analyzed biological responses of GECs to  LPS and CL075, a TLR7/8 agonist. GE1, a mouse gingival epithelial cell line, constitutively express TLR4 and TLR7, but not TLR8, like primary skin keratinocytes. Stimulation of GE1 cells with CL075 induced cytokine, chemokine, and antimicrobial peptide  expressions, the pattern of which is rather different from that with LPS: higher mRNA levels of interferon (IFN) β, CXCL10, and β-defensin (BD) 14 (mouse homolog of human BD3); lower levels of tumor necrosis factor (TNF), CCL5, CCL11, CCL20, CXCL2, and CX3CL1. As for the intracellular signal transduction of GE1 cells, CL075 rapidly induced significant AKT phosphorylation but failed to activate IKKα/β-NFκB pathway, whereas LPS induced marked IKKα/β-NFκB activation without significant AKT phosphorylation. In contrast, both CL075 and LPS induced rapid IKKα/β-NFκB activation and AKT phosphorylation in a macrophage cell line. Furthermore, specific inhibition of AKT activity abrogated CL075-induced IFNβ, CXCL10, and BD14 mRNA expression in GE1 cells. Thus, TLR4/7 ligands appear to induce rather different host-defense responses of GECs through distinct intracellular signaling mechanisms.

Human β-defensins and their synthetic analogs: Natural defenders and prospective new drugs of oral health

As a family of cationic host defense peptides, human β-defensins (HBDs) are ubiquitous in the oral cavity and are mainly synthesized primarily by epithelial cells, serving as the primary barrier and aiming to prevent microbial invasion, inflammation, and disease while maintaining physiological homeostasis. In recent decades, there has been great interest in their biological functions, structure-activity relationships, mechanisms of action, and therapeutic potential in oral diseases. Meanwhile, researchers are dedicated to improving the properties of HBDs for clinical application. In this review, we first describe the classification, structural characteristics, functions, and mechanisms of HBDs. Next, we cover the role of HBDs and their synthetic analogs in oral diseases, including dental caries and pulp infections, periodontitis, peri-implantitis, fungal/viral infections and oral mucosal diseases, and oral squamous cell carcinoma. Finally, we discuss the limitations and challenges of clinical translation of HBDs and their synthetic analogs, including, but not limited to, stability, bioavailability, antimicrobial activity, resistance, and toxicity. Above all, this review summarizes the biological functions, mechanisms of action, and therapeutic potential of both natural HBDs and their synthetic analogs in oral diseases, as well as the challenges associated with clinical translation, thus providing substantial insights into the laboratory development and clinical application of HBDs in oral diseases.

Alpha-defensin binding expands human adenovirus tropism

Mammalian α-defensins are a family of abundant effector peptides of the mucosal innate immune system. Although primarily considered to be antimicrobial, α-defensins can increase rather than block infection by certain prominent bacterial and viral pathogens in cell culture and in vivo. We have shown previously that exposure of mouse and human adenoviruses (HAdVs) to α-defensins is able to overcome competitive inhibitors that block cell binding, leading us to hypothesize a defensin-mediated binding mechanism that is independent of known viral receptors. To test this hypothesis, we used genetic approaches to demonstrate that none of several primary receptors nor integrin co-receptors are needed for human α-defensin-mediated binding of HAdV to cells; however, infection remains integrin dependent. Thus, our studies have revealed a novel pathway for HAdV binding to cells that bypasses viral primary receptors. We speculate that this pathway functions in parallel with receptor-mediated entry and contributes to α-defensin-enhanced infection of susceptible cells. Remarkably, we also found that in the presence of α-defensins, HAdV tropism is expanded to non-susceptible cells, even when viruses are exposed to a mixture of both susceptible and non-susceptible cells. Therefore, we propose that in the presence of sufficient concentrations of α-defensins, such as in the lung or gut, integrin expression rather than primary receptor expression will dictate HAdV tropism in vivo. In summary, α-defensins may contribute to tissue tropism not only through the neutralization of susceptible viruses but also by allowing certain defensin-resistant viruses to bind to cells independently of previously described mechanisms.

Alpha-defensin binding expands human adenovirus tropism

Mammalian α-defensins are a family of abundant effector peptides of the mucosal innate immune system. Although primarily considered to be antimicrobial, α-defensins can increase rather than block infection by certain prominent bacterial and viral pathogens in cell culture and in vivo . We have shown previously that exposure of mouse and human adenoviruses (HAdVs) to α-defensins is able to overcome competitive inhibitors that block cell binding, leading us to hypothesize a defensin-mediated binding mechanism that is independent of known viral receptors. To test this hypothesis, we used genetic approaches to demonstrate that none of several primary receptors nor integrin co-receptors are needed for human α-defensin-mediated binding of HAdV to cells; however, infection remains integrin dependent. Thus, our studies have revealed a novel pathway for HAdV binding to cells that bypasses viral primary receptors. We speculate that this pathway functions in parallel with receptor-mediated entry and contributes to α-defensin-enhanced infection of susceptible cells. Remarkably, we also found that in the presence of α-defensins, HAdV tropism is expanded to non-susceptible cells, even when viruses are exposed to a mixture of both susceptible and non-susceptible cells. Therefore, we propose that in the presence of sufficient concentrations of α-defensins, such as in the lung or gut, integrin expression rather than primary receptor expression will dictate HAdV tropism in vivo . In summary, α-defensins may contribute to tissue tropism not only through the neutralization of susceptible viruses but also by allowing certain defensin-resistant viruses to bind to cells independently of previously described mechanisms.

Author Summary

In this study, we demonstrate a novel mechanism for binding of human adenoviruses (HAdVs) to cells that is dependent upon interactions with α-defensin host defense peptides but is independent of known viral receptors and co-receptors. To block normal receptor-mediated HAdV infection, we made genetic changes to both host cells and HAdVs. Under these conditions, α-defensins restored cell binding; however, infection still required the function of HAdV integrin co-receptors. This was true for multiple types of HAdVs that use different primary receptors and for cells that are either naturally devoid of HAdV receptors or were engineered to be receptor deficient. These observations suggest that in the presence of concentrations of α-defensins that would be found naturally in the lung or intestine, there are two parallel pathways for HAdV binding to cells that converge on integrins for productive infection. Moreover, these binding pathways function independently, and both operate in mixed culture. Thus, we have found that viruses can co-opt host defense molecules to expand their tropism.

Endoplasmic reticulum stress: A possible connection between intestinal inflammation and neurodegenerative disorders

BACKGROUND

Different studies have shown the key role of endoplasmic reticulum (ER) stress in autoimmune and chronic inflammatory disorders, as well as in neurodegenerative diseases. ER stress leads to the formation of misfolded proteins which affect the secretion of different cell types that are crucial for the intestinal homeostasis.

PURPOSE

In this review, we discuss the role of ER stress and its involvement in the development of inflammatory bowel diseases, chronic conditions that can cause severe damage of the gastrointestinal tract, focusing on the alteration of Paneth cells and goblet cells (the principal secretory phenotypes of the intestinal epithelial cells). ER stress is also discussed in the context of neurodegenerative diseases, in which protein misfolding represents the signature mechanism. ER stress in the bowel and consequent accumulation of misfolded proteins might represent a bridge between bowel inflammation and neurodegeneration along the gut-to-brain axis, affecting intestinal epithelial homeostasis and the equilibrium of the commensal microbiota. Targeting intestinal ER stress could foster future studies for designing new biomarkers and new therapeutic approaches for neurodegenerative disorders.

Defensins: A novel weapon against Mycobacterium tuberculosis?

Tuberculosis (TB) is a serious airborne communicable disease caused by organisms of the Mycobacterium tuberculosis (Mtb) complex. Although the standard treatment antimicrobials, including isoniazid, rifampicin, pyrazinamide, and ethambutol, have made great progress in the treatment of TB, problems including the rising incidence of multidrug-resistant tuberculosis (MDR-TB) and extensively drug-resistant tuberculosis (XDR-TB), the severe toxicity and side effects of antimicrobials, and the low immunity of TB patients have become the bottlenecks of the current TB treatments. Therefore, both safe and effective new strategies to prevent and treat TB have become a top priority. As a subfamily of cationic antimicrobial peptides, defensins are rich in cysteine and play a vital role in resisting the invasion of microorganisms and regulating the immune response. Inspired by studies on the roles of defensins in host defence, we describe their research history and then review their structural features and antimicrobial mechanisms, specifically for fighting Mtb in detail. Finally, we discuss the clinical relevance, therapeutic potential, and potential challenges of defensins in anti-TB therapy. We further debate the possible solutions of the current application of defensins to provide new insights for eliminating Mtb.

Molluscum Contagiosum Virus: Biology and Immune Response

Molluscum contagiosum virus is a poxvirus belonging to the Poxviridae family, which includes Orthopoxvirus, Parapoxvirus, Yantapoxvirus, Molluscipoxvirus, Smallpox virus, Cowpox virus and Monkeypox virus. MCV belongs to the genus Molluscipoxvirus and has a tropism for skin tissue. MCV infects keratinocytes and, after an incubation period of 2 weeks to 6 weeks, causes a breakdown of the skin barrier with the development of papules of variable size depending on the proper functioning of the immune response (both adaptive and acquired). MCV only infects humans and does not cause viraemia. MCV encodes for several inhibitory proteins responsible to circumvent the immune response through different signalling pathways. Individuals who can be infected with MCV are children, immunocompromised individuals such as organ transplant recipients and Human Immunodeficiency Virus (HIV)-infected individuals. Current treatments to manage MCV-induced lesions are different and include the use of immunomodulators, which, however, do not provide an effective response.

Brilacidin as a Broad-Spectrum Inhibitor of Enveloped, Acutely Infectious Viruses

Alphaviruses, belonging to the Togaviridae family, and bunyaviruses, belonging to the Paramyxoviridae family, are globally distributed and lack FDA-approved vaccines and therapeutics. The alphaviruses Venezuelan equine encephalitis virus (VEEV) and eastern equine encephalitis virus (EEEV) are known to cause severe encephalitis, whereas Sindbis virus (SINV) causes arthralgia potentially persisting for years after initial infection. The bunyavirus Rift Valley Fever virus (RVFV) can lead to blindness, liver failure, and hemorrhagic fever. Brilacidin, a small molecule that was designed de novo based on naturally occurring host defensins, was investigated for its antiviral activity against these viruses in human small airway epithelial cells (HSAECs) and African green monkey kidney cells (Veros). This testing was further expanded into a non-enveloped Echovirus, a Picornavirus, to further demonstrate brilacidin's effect on early steps of the viral infectious cycle that leads to inhibition of viral load. Brilacidin demonstrated antiviral activity against alphaviruses VEEV TC-83, VEEV TrD, SINV, EEEV, and bunyavirus RVFV. The inhibitory potential of brilacidin against the viruses tested in this study was dependent on the dosing strategy which necessitated compound addition pre- and post-infection, with addition only at the post-infection stage not eliciting a robust inhibitory response. The inhibitory activity of brilacidin was only modest in the context of the non-enveloped Picornavirus Echovirus, suggesting brilacidin may be less potent against non-enveloped viruses.

Exploring the arsenal of antimicrobial peptides: Mechanisms, diversity, and applications

Antimicrobial peptides (AMPs) are essential for defence against pathogens in all living organisms and possessed activities against bacteria, fungi, viruses, parasites and even cancer cells. AMPs are short peptides containing 12-100 amino acids conferring a net positive charge and an amphiphilic property in most cases. Although, anionic AMPs also exist. AMPs can be classified based on the types of secondary structures, charge, hydrophobicity, amino acid composition, length, etc. Their mechanism of action usually includes a membrane disruption process through pore formation (three different models have been described, barrel-stave, toroidal or carpet model) but AMPs can also penetrate and impair intracellular functions. Besides their activity against pathogens, they have also shown immunomodulatory properties in complex scenarios through many different interactions. The aim of this review to summarize knowledge about AMP's and discuss the potential application of AMPs as therapeutics, the challenges due to their limitations, including their susceptibility to degradation, the potential generation of AMP resistance, cost, etc. We also discuss the current FDA-approved drugs based on AMPs and strategies to circumvent natural AMPs' limitations.

Corrected and republished from: "VP4 Is a Determinant of Alpha-Defensin Modulation of Rotaviral Infection"

IMPORTANCE

Rotavirus is a leading cause of severe diarrhea in young children. Like other fecal-oral pathogens, rotaviruses encounter abundant, constitutively expressed defensins in the small intestine. These peptides are a vital part of the vertebrate innate immune system. By investigating the impact that defensins from multiple species have on the infectivity of different strains of rotavirus, we show that some rotaviral infections can be inhibited by defensins. We also found that rotaviruses may have evolved resistance to defensins in the intestine of their host species, and some even appropriate defensins to increase their infectivity. Because rotaviruses infect a broad range of animals and rotaviral infections are highly prevalent in children, identifying immune defenses against infection and how they vary across species and among viral genotypes is important for our understanding of the evolution, transmission, and zoonotic potential of these viruses as well as the improvement of vaccines.

A review of immune modulators and immunotherapy in infectious diseases

The human immune system responds to harmful foreign invaders frequently encountered by the body and employs defense mechanisms to counteract such assaults. Various exogenous and endogenous factors play a prominent role in maintaining the balanced functioning of the immune system, which can result in immune suppression or immune stimulation. With the advent of different immune-modulatory agents, immune responses can be modulated or regulated to control infections and other health effects. Literature provides evidence on various immunomodulators from different sources and their role in modulating immune responses. Due to the limited efficacy of current drugs and the rise in drug resistance, there is a growing need for new therapies for infectious diseases. In this review, we aim to provide a comprehensive overview of different immune-modulating agents and immune therapies specifically focused on viral infectious diseases.

Mechanisms and regulation of defensins in host defense

As a family of cationic host defense peptides, defensins are mainly synthesized by Paneth cells, neutrophils, and epithelial cells, contributing to host defense. Their biological functions in innate immunity, as well as their structure and activity relationships, along with their mechanisms of action and therapeutic potential, have been of great interest in recent years. To highlight the key research into the role of defensins in human and animal health, we first describe their research history, structural features, evolution, and antimicrobial mechanisms. Next, we cover the role of defensins in immune homeostasis, chemotaxis, mucosal barrier function, gut microbiota regulation, intestinal development and regulation of cell death. Further, we discuss their clinical relevance and therapeutic potential in various diseases, including infectious disease, inflammatory bowel disease, diabetes and obesity, chronic inflammatory lung disease, periodontitis and cancer. Finally, we summarize the current knowledge regarding the nutrient-dependent regulation of defensins, including fatty acids, amino acids, microelements, plant extracts, and probiotics, while considering the clinical application of such regulation. Together, the review summarizes the various biological functions, mechanism of actions and potential clinical significance of defensins, along with the challenges in developing defensins-based therapy, thus providing crucial insights into their biology and potential clinical utility.

Cadmium tolerance and hyperaccumulation in plants - A proteomic perspective of phytoremediation

Cadmium (Cd) is a major environmental pollutant and poses a risk of transfer into the food chain through contaminated plants. Mechanisms underlying Cd tolerance and hyperaccumulation in plants are not fully understood. Proteomics-based approaches facilitate an in-depth understanding of plant responses to Cd stress at the systemic level by identifying Cd-inducible differentially abundant proteins (DAPs). In this review, we summarize studies related to proteomic changes associated with Cd-tolerance mechanisms in Cd-tolerant crops and Cd-hyperaccumulating plants, especially the similarities and differences across plant species. The enhanced DAPs identified through proteomic studies can be potential targets for developing Cd-hyperaccumulators to remediate Cd-contaminated environments and Cd-tolerant crops with low Cd content in the edible organs. This is of great significance for ensuring the food security of an exponentially growing global population. Finally, we discuss the methodological drawbacks in current proteomic studies and propose that better protocols and advanced techniques should be utilized to further strengthen the reliability and applicability of future Cd-stress-related studies in plants. This review provides insights into the improvement of phytoremediation efficiency and an in-depth study of the molecular mechanisms of Cd enrichment in plants.

A Single Surface-Exposed Amino Acid Determines Differential Neutralization of AAV1 and AAV6 by Human Alpha-Defensins

Adeno-associated viruses (AAVs) are being developed as gene therapy vectors due to their low pathogenicity and tissue tropism properties. However, the efficacy of these vectors is impeded by interactions with the host immune system. One potential immune barrier to vector transduction is innate immune host defense peptides, such as alpha-defensins, which are potent antiviral agents against other nonenveloped viruses. To investigate the interaction between AAVs and alpha-defensins, we utilized two closely related AAV serotypes, AAV1 and AAV6. Although their capsids differ by only six residues, these two serotypes exhibit markedly different tissue tropisms and transduction efficiencies. Using two abundant human alpha-defensins, enteric human defensin 5 (HD5) and myeloid human neutrophil peptide 1 (HNP1), we found both serotype-specific and defensin-specific effects on AAV infection. AAV6 infection was uniformly neutralized by both defensins at low micromolar concentrations; however, inhibition of AAV1 infection was profoundly influenced by the timing of defensin exposure to the virus relative to viral attachment to the cell. Remarkably, these differences in the defensin-dependent infection phenotype between the viruses are completely dictated by the identity of a single, surface-exposed amino acid (position 531) that varies between the two serotypes. These findings reveal a determinant for defensin activity against a virus with unprecedented precision. Furthermore, they provide a rationale for the investigation of other AAV serotypes not only to understand the mechanism of neutralization of defensins against AAVs but also to design more efficient vectors. IMPORTANCE The ability of adeno-associated viruses (AAVs) to infect and deliver genetic material to a range of cell types makes them favorable gene therapy vectors. However, AAV vectors encounter a wide variety of host immune factors throughout the body, which can impede efficient gene delivery. One such group of factors is the alpha-defensins, which are a key component of the innate immune system that can directly block viral infection. By studying the impact that alpha-defensins have on AAV infection, we found that two similar AAV serotypes (AAV1 and AAV6) have different sensitivities to inhibition. We also identified a single amino acid (position 531) that differs between the two AAV serotypes and is responsible for mediating their defensin sensitivity. By investigating the effects that host immune factors have on AAV infection, more efficient vectors may be developed to evade intervention by the immune system prior to gene delivery.

Evolutionary trend of bovine β-defensin proteins toward functionality prediction: A domain-based bioinformatics study

Defensins are small cationic cysteine-rich and amphipathic peptides that form of three-dimensional β-strand structure connected by disulfide bonds. Defensins form key elements of the innate immune system of multicellular organisms. They not only possess broad-spectrum antimicrobial activity but also have diverse roles, including cell signaling, ion channel agitation, toxic functions, and enzyme inhibitor activities in various animals. Although the role of β-defensins in immune responses against infectious agents and reproduction could be significant, inadequate genomic information is available to explain the whole β-defensin repertoire in cattle. No domain or motif-based functional analyses have been previously reported. In addition, how do defensins possess this magnitude of functions in the immune system is still not clear. Our present study, therefore, investigated the sequence divergence and evolutionary relations of bovine defensin proteins with those of humans. Our domain-based evolutionary analysis revealed four major clusters with significant domain variation while reserving a main antimicrobial activity. Our study revealed the β-defensin domain as the ancestor domain, and it is preserved in the first group of defensin protein with no α-helix in its structure. Due to natural selection, some domains have evolved independently within clusters II and III, while some proteins have lost their domain characteristics. Cluster IV contains the most recently evolved domains. Some proteins of all but cluster I might have adopted the functional characteristics of α-defensins which is largely absent in cattle. The proteins show different patterns of disulfide bridges and multiple signature patterns which might render them specialized functions in different tissue to combat against various pathogens.

Mouse α-Defensins: Structural and Functional Analysis of the 17 Cryptdin Isoforms Identified from a Single Jejunal Crypt

Mouse α-defensins, better known as cryptdins, are host protective antimicrobial peptides produced in the intestinal crypt by Paneth cells. To date, more than 20 cryptdin mRNAs have been identified from mouse small intestine, of which the first six cryptdins (Crp1 to Crp6) have been isolated and characterized at the peptide level. We quantified bactericidal activities against Escherichia coli and Staphylococcus aureus of the 17 cryptdin isoforms identified by Ouellette and colleagues from a single jejunal crypt (A. J. Ouellette et al., Infect Immun 62:5040-5047, 1994), along with linearized analogs of Crp1, Crp4, and Crp14. In addition, we analyzed the most potent and weakest cryptdins in the panel with respect to their ability to self-associate in solution. Finally, we solved, for the first time, the high-resolution crystal structure of a cryptdin, Crp14, and performed molecular dynamics simulation on Crp14 and a hypothetical mutant, T14K-Crp14. Our results indicate that mutational effects are highly dependent on cryptdin sequence, residue position, and bacterial strain. Crp14 adopts a disulfide-stabilized, three-stranded β-sheet core structure and forms a noncanonical dimer stabilized by asymmetrical interactions between the two β1 strands in parallel. The killing of E. coli by cryptdins is generally independent of their tertiary and quaternary structures that are important for the killing of S. aureus, which is indicative of two distinct mechanisms of action. Importantly, sequence variations impact the bactericidal activity of cryptdins by influencing their ability to self-associate in solution. This study expands our current understanding of how cryptdins function at the molecular level.

Preventing Respiratory Viral Diseases with Antimicrobial Peptide Master Regulators in the Lung Airway Habitat

The vast surface area of the respiratory system acts as an initial site of contact for microbes and foreign particles. The whole respiratory epithelium is covered with a thin layer of the airway and alveolar secretions. Respiratory secretions contain host defense peptides (HDPs), such as defensins and cathelicidins, which are the best-studied antimicrobial components expressed in the respiratory tract. HDPs have an important role in the human body's initial line of defense against pathogenic microbes. Epithelial and immunological cells produce HDPs in the surface fluids of the lungs, which act as endogenous antibiotics in the respiratory tract. The production and action of these antimicrobial peptides (AMPs) are critical in the host's defense against respiratory infections. In this study, we have described all the HDPs secreted in the respiratory tract as well as how their expression is regulated during respiratory disorders. We focused on the transcriptional expression and regulation mechanisms of respiratory tract HDPs. Understanding how HDPs are controlled throughout infections might provide an alternative to relying on the host's innate immunity to combat respiratory viral infections.

Yak DEFB124 alleviates intestinal injury caused by Staphylococcus aureus infection

To investigate the characteristics and functions of yak β-defensin 124 (DEFB124), prokaryotic expression, analysis of gut microbiological and other methods were used in this study. The results showed that the sequence of yak DEFB124 gene was 306 bp in length and 207 bp in open reading frame, which encoded 68 amino acids. Yak DEFB124 protein was highly conserved and had the closest relationship with cattle. Yak DEFB124 protein was a secreted cationic β-defensin. The recombinant expression plasmid pET32a-DEFB124 was constructed, and an about 24 kDa protein was successfully expressed. Yak DEFB124 protein had inhibitory activity against Staphylococcus aureus (S. aureus), and its MIC value was 64 μg/mL. After treating with yak DEFB124 protein, the activities of alkaline phosphatase (AKP) and total superoxide dismutase (T-SOD) were higher (P < 0.01) in the jejunum tissue, but the activity of lysozyme (LZM) was lower (P < 0.01). The number of goblet cells in the duodenum, jejunum, and ileum of the mice in the DEFB124 group was increased (P < 0.01). Besides, the expressions of MUC2 mRNA and protein were increased (P < 0.05) after the treatment with yak DEFB124 protein. Furthermore, the relative abundance of Lactobacillus in jejunum of mice in DEFB124 group was also increased. In summary, yak DEFB124 protein could increase the number of goblet cells in mice intestine and the abundance of intestinal probiotics Lactobacillus, thereby protecting the intestinal tract and alleviating intestinal damage.

Long-term environmental levels of microcystin-LR exposure induces colorectal chronic inflammation, fibrosis and barrier disruption via CSF1R/Rap1b signaling pathway

Microcystin-LR (MC-LR) is a very common toxic cyanotoxins threating ecosystems and the public health. This study aims to explore the long-term effects and potential toxicity mechanisms of MC-LR exposure at environmental levels on colorectal injury. We performed histopathological, biochemical indicator and multi-omics analyses in mice with low-dose MC-LR exposure for 12 months. Long-term environmental levels of MC-LR exposure caused epithelial barrier disruption, inflammatory cell infiltration and an increase of collagen fibers in mouse colorectum. Integrated proteotranscriptomics revealed differential expression of genes/proteins, including CSF1R, which were mainly involved in oxidative stress-induced premature senescence and inflammatory response. MC-LR induced chronic inflammation and fibrosis through oxidative stress and CSF1R/Rap1b signaling pathway were confirmed in cell models. We found for the first time that long-term environmental levels of MC-LR exposure caused colorectal chronic inflammation, fibrosis and barrier disruption via a novel CSF1R/Rap1b signaling pathway. Moreover, MC-LR changed the gut microbiota and microbial-related metabolites in a vicious cycle aggravating colorectal injury. These findings provide novel insights into the effects and toxic mechanisms of MC-LR and suggest strategies for the prevention and treatment of MC-caused intestinal diseases.

Design of Three Residues Peptides against SARS-CoV-2 Infection

The continuous and rapid spread of the COVID-19 pandemic has emphasized the need to seek new therapeutic and prophylactic treatments. Peptide inhibitors are a valid alternative approach for the treatment of emerging viral infections, mainly due to their low toxicity and high efficiency. Recently, two small nucleotide signatures were identified in the genome of some members of the Coronaviridae family and many other human pathogens. In this study, we investigated whether the corresponding amino acid sequences of such nucleotide sequences could have effects on the viral infection of two representative human coronaviruses: HCoV-OC43 and SARS-CoV-2. Our results showed that the synthetic peptides analyzed inhibit the infection of both coronaviruses in a dose-dependent manner by binding the RBD of the Spike protein, as suggested by molecular docking and validated by biochemical studies. The peptides tested do not provide toxicity on cultured cells or human erythrocytes and are resistant to human serum proteases, indicating that they may be very promising antiviral peptides.

Defensins: defenders of human reproductive health

BACKGROUND

Reproductive tract infection is an important factor leading to male and female infertility. Among female infertility factors, microbial and viral infections are the main factors affecting female reproductive health and causing tubal infertility, ectopic tubal pregnancy and premature delivery. Among male infertility factors, 13-15% of male infertility is related to infection. Defensins are cationic antibacterial and antiviral peptides, classified into α-defensins, β-defensins and θ-defensins. Humans only have α-defensins and β-defensins. Apart from their direct antimicrobial functions, defensins have an immunomodulatory function and are involved in many physiological processes. Studies have shown that defensins are widely distributed in the female reproductive tract (FRT) and male reproductive tract (MRT), playing a dual role of host defence and fertility protection. However, to our knowledge, the distribution, regulation and function of defensins in the reproductive tract and their relation to reproduction have not been reviewed.

OBJECTIVE AND RATIONALE

This review summarizes the expression, distribution and regulation of defensins in the reproductive tracts to reveal the updated research on the dual role of defensins in host defence and the protection of fertility.

SEARCH METHODS

A systematic search was conducted in PubMed using the related keywords through April 2022. Related data from original researches and reviews were integrated to comprehensively review the current findings and understanding of defensins in the human reproductive system. Meanwhile, female and male transcriptome data in the GEO database were screened to analyze defensins in the human reproductive tracts.

OUTCOMES

Two transcriptome databases from the GEO database (GSE7307 and GSE150852) combined with existing researches reveal the expression levels and role of the defensins in the reproductive tracts. In the FRT, a high expression level of α-defensin is found, and the expression levels of defensins in the vulva and vagina are higher than those in other organs. The expression of defensins in the endometrium varies with menstrual cycle stages and with microbial invasion. Defensins also participate in the local immune response to regulate the risk of spontaneous preterm birth. In the MRT, a high expression level of β-defensins is also found. It is mainly highly expressed in the epididymal caput and corpus, indicating that defensins play an important role in sperm maturation. The expression of defensins in the MRT varies with androgen levels, age and the status of microbial invasion. They protect the male reproductive system from bacterial infections by neutralizing lipopolysaccharide and downregulating pro-inflammatory cytokines. In addition, animal and clinical studies have shown that defensins play an important role in sperm maturation, motility and fertilization.

WIDER IMPLICATIONS

As a broad-spectrum antimicrobial peptide without drug resistance, defensin has great potential for developing new natural antimicrobial treatments for reproductive tract infections. However, increasing evidence has shown that defensins can not only inhibit microbial invasion but can also promote the invasion and adhesion of some microorganisms in certain biological environments, such as human immunodeficiency virus. Therefore, the safety of defensins as reproductive tract anti-infective drugs needs more in-depth research. In addition, the modulatory role of defensins in fertility requires more in-depth research since the current conclusions are based on small-size samples. At present, scientists have made many attempts at the clinical transformation of defensins. However, defensins have problems such as poor stability, low bioavailability and difficulties in their synthesis. Therefore, the production of safe, effective and low-cost drugs remains a challenge.

In vitro Screening of Herbal Medicinal Products for Their Supportive Curing Potential in the Context of SARS-CoV-2

COVID-19 herbal medicinal products may have the potential for symptom relief in nonsevere or moderate disease cases. In this in vitro study we screened the five herbal medicinal products Sinupret extract (SINx), Bronchipret thyme-ivy (BRO-TE), Bronchipret thyme-primula (BRO TP), Imupret (IMU), and Tonsipret (TOP) with regard to their potential to (i) interfere with the binding of the human angiotensin-converting enzyme 2 (ACE2) receptor with the SARS-CoV-2 spike S1 protein, (ii) modulate the release of the human defensin HBD1 and cathelicidin LL-37 from human A549 lung cells upon spike S1 protein stimulation, and (iii) modulate the release of IFN-γ from activated human peripheral blood mononuclear cells (PBMC). The effect of the extracts on the interaction of spike S1 protein and the human ACE2 receptor was measured by ELISA. The effects on the intracellular IFN-γ expression in stimulated human PBMC were measured by flow cytometry. Regulation of HBD1 and LL-37 expression and secretion was assessed in 25 d long-term cultured human lung A549 epithelial cells by RT-PCR and ELISA. IMU and BRO-TE concentration-dependently inhibited the interaction between spike S1 protein and the ACE2 receptor. SINx, TOP, and BRO-TE significantly upregulated the intracellular expression of anti-viral IFN-γ from stimulated PBMC. Cotreatment of A549 cells with IMU or BRO TP together with SARS-CoV-2 spike protein significantly upregulated mRNA expression (IMU) and release of HBD1 (IMU and BRO TP) and LL-37 (BRO TP). The in vitro screening results provide first evidence for an immune-activating potential of some of the tested herbal medicinal extracts in the context of SARS-CoV-2. Whether these could be supportive in symptom relief or curing from SARS-CoV-2 infection needs deeper understanding of the observations.

Transcriptome Analysis Reveals the Multiple Functions of pBD2 in IPEC-J2 Cells against E. coli

Defensins play an important role in fighting bacteria, and are a good candidate for bactericidal agents. However, the function and mechanism of defensins in regulating host responses against bacteria is unclear. In this study, transcriptome analysis was used to study the comprehensive functions of pBD2 in IPEC-J2 cells against E. coli. In total, 230 differentially expressed genes (DEGs) were identified in IPEC-J2 cells between the control and E. coli groups, and were found by KEGG analysis to be involved in many signaling pathways related to immunity. Furthermore, 812 DEGs were observed between E. coli and E. coli +pBD2 groups, involved in the ribosome, oxidative phosphorylation, and certain disease pathways. Among these, 94 overlapping DEGs were in the two DEG groups, and 85 DEGs were reverse expression, which is involved in microRNA in cancer, while PTEN and CDC6 were key genes according to PPI net analysis. The results of qRT-PCR verified those of RNA-seq. The results indicated that pBD2 plays an important role against E. coli by acting on the genes related to immune response, cell cycle, ribosomes, oxidative phosphorylation, etc. The results provide new insights into the potential function and mechanism of pBD2 against E. coli. Meanwhile, this study provides a certain theoretical basis for research and the development of novel peptide drugs.

Involvement of Porcine β-Defensin 129 in Sperm Capacitation and Rescue of Poor Sperm in Genital Tract Infection

In mammals, β-defensins have been reported to play pivotal roles in sperm protection and fertilization. However, the function and mechanism of porcine β-defensin 129 (pBD129) in the sperm remain unclear. Here, we demonstrate that pBD129 is a glycosylated protein and broadly exists in accessory sex glands and coats the sperm surface. We inhibited the pBD129 protein on the sperm surface with an anti-pBD129 antibody and found that sperm motility was not significantly affected; however, sperm acrosome integrity and tyrosine phosphorylation levels increased significantly with time (p < 0.05) during capacitation. These changes were accompanied by an increase in sperm Ca2+ influx, resulting in a significantly reduced in vitro fertilization cleavage rate (p < 0.05). Further investigation revealed that treatment with recombinant pBD129 markedly restored the sperm motility in semen contaminated with Escherichia coli. The results suggest that pBD129 is not only associated with poor sperm motility after genital tract infection but can also protect the spermatozoa from premature capacitation, which may be beneficial for semen preservation.

Progress of Research into Novel Drugs and Potential Drug Targets against Porcine Pseudorabies Virus

Pseudorabies virus (PRV) is the causative agent of pseudorabies (PR), infecting most mammals and some birds. It has been prevalent around the world and caused huge economic losses to the swine industry since its discovery. At present, the prevention of PRV is mainly through vaccination; there are few specific antivirals against PRV, but it is possible to treat PRV infection effectively with drugs. In recent years, some drugs have been reported to treat PR; however, the variety of anti-pseudorabies drugs is limited, and the underlying mechanism of the antiviral effect of some drugs is unclear. Therefore, it is necessary to explore new drug targets for PRV and develop economic and efficient drug resources for prevention and control of PRV. This review will focus on the research progress in drugs and drug targets against PRV in recent years, and discuss the future research prospects of anti-PRV drugs.

The Antimicrobial Peptides Human β-Defensins Induce the Secretion of Angiogenin in Human Dermal Fibroblasts

The skin produces a plethora of antimicrobial peptides that not only show antimicrobial activities against pathogens but also exhibit various immunomodulatory functions. Human β-defensins (hBDs) are the most well-characterized skin-derived antimicrobial peptides and contribute to diverse biological processes, including cytokine production and the migration, proliferation, and differentiation of host cells. Additionally, hBD-3 was recently reported to promote wound healing and angiogenesis, by inducing the expression of various angiogenic factors and the migration and proliferation of fibroblasts. Angiogenin is one of the most potent angiogenic factors; however, the effects of hBDs on angiogenin production in fibroblasts remain unclear. Here, we investigated the effects of hBDs on the secretion of angiogenin by human dermal fibroblasts. Both in vitro and ex vivo studies demonstrated that hBD-1, hBD-2, hBD-3, and hBD-4 dose-dependently increased angiogenin production by fibroblasts. hBD-mediated angiogenin secretion involved the epidermal growth factor receptor (EGFR), Src family kinase, c-Jun N-terminal kinase (JNK), p38, and nuclear factor-kappa B (NF-κB) pathways, as evidenced by the inhibitory effects of specific inhibitors for these pathways. Indeed, we confirmed that hBDs induced the activation of the EGFR, Src, JNK, p38, and NF-κB pathways. This study identified a novel role of hBDs in angiogenesis, through the production of angiogenin, in addition to their antimicrobial activities and other immunomodulatory properties.

Antiviral Effect of hBD-3 and LL-37 during Human Primary Keratinocyte Infection with West Nile Virus

West Nile virus (WNV) is an emerging flavivirus transmitted through mosquito bites and responsible for a wide range of clinical manifestations. Following their inoculation within the skin, flaviviruses replicate in keratinocytes of the epidermis, inducing an innate immune response including the production of antimicrobial peptides (AMPs). Among them, the cathelicidin LL-37 and the human beta-defensin (hBD)-3 are known for their antimicrobial and immunomodulatory properties. We assessed their role during WNV infection of human primary keratinocytes. LL-37 reduced the viral load in the supernatant of infected keratinocytes and of the titer of a viral inoculum incubated in the presence of the peptide, suggesting a direct antiviral effect of this AMP. Conversely, WNV replication was not inhibited by hBD-3. The two peptides then demonstrated immunomodulatory properties whether in the context of keratinocyte stimulation by poly(I:C) or infection by WNV, but not alone. This study demonstrates the immunostimulatory properties of these two skin AMPs at the initial site of WNV replication and the ability of LL-37 to directly inactivate West Nile viral infectious particles. The results provide new information on the multiple functions of these two peptides and underline the potential of AMPs as new antiviral strategies in the fight against flaviviral infections.

Identification of Novel Disease-Relevant Genes and Pathways in the Pathogenesis of Type 1 Diabetes: A Potential Defect in Pancreatic Iron Homeostasis

Multiple pathways contribute to the pathophysiological development of type 1 diabetes (T1D); however, the exact mechanisms involved are unclear. We performed differential gene expression analysis in pancreatic islets of NOD mice versus age-matched congenic NOD.B10 controls to identify genes that may contribute to disease pathogenesis. Novel genes related to extracellular matrix development and glucagon and insulin signaling/secretion were changed in NOD mice during early inflammation. During "respective" insulitis, the expression of genes encoding multiple chemosensory olfactory receptors were upregulated, and during "destructive" insulitis, the expression of genes involved in antimicrobial defense and iron homeostasis were downregulated. Islet inflammation reduced the expression of Hamp that encodes hepcidin. Hepcidin is expressed in β-cells and serves as the key regulator of iron homeostasis. We showed that Hamp and hepcidin levels were lower, while iron levels were higher in the pancreas of 12-week-old NOD versus NOD.B10 mice, suggesting that a loss of iron homeostasis may occur in the islets during the onset of "destructive" insulitis. Interestingly, we showed that the severity of NOD disease correlates with dietary iron intake. NOD mice maintained on low-iron diets had a lower incidence of hyperglycemia, while those maintained on high-iron diets had an earlier onset and higher incidence of disease, suggesting that high iron exposure combined with a loss of pancreatic iron homeostasis may exacerbate NOD disease. This mechanism may explain the link seen between high iron exposure and the increased risk for T1D in humans.

A trifunctional peptide broadly inhibits SARS-CoV-2 Delta and Omicron variants in hamsters

The emergence of highly transmissible SARS-CoV-2 variants has led to the waves of the resurgence of COVID-19 cases. Effective antivirals against variants are required. Here we demonstrate that a human-derived peptide 4H30 has broad antiviral activity against the ancestral virus and four Variants of Concern (VOCs) in vitro. Mechanistically, 4H30 can inhibit three distinct steps of the SARS-CoV-2 life cycle. Specifically, 4H30 blocks viral entry by clustering SARS-CoV-2 virions; prevents membrane fusion by inhibiting endosomal acidification; and inhibits the release of virions by cross-linking SARS-CoV-2 with cellular glycosaminoglycans. In vivo studies show that 4H30 significantly reduces the lung viral titers in hamsters, with a more potent reduction for the Omicron variant than the Delta variant. This is likely because the entry of the Omicron variant mainly relies on the endocytic pathway which is targeted by 4H30. Moreover, 4H30 reduces syncytia formation in infected hamster lungs. These findings provide a proof of concept that a single antiviral can inhibit viral entry, fusion, and release.

Whole Genome Sequencing Provides New Insights Into the Genetic Diversity and Coat Color of Asiatic Wild Ass and Its Hybrids

The diversity of livestock coat color results from human positive selection and is an indispensable part of breed registration. As an important biodiversity resource, Asiatic wild ass has many special characteristics, including the most visualized feature, its yellowish-brown coat color, and excellent adaptation. To explore the genetic mechanisms of phenotypic characteristics in Asiatic wild ass and its hybrids, we resequenced the whole genome of one Mongolian Kulan (a subspecies of Asiatic wild ass) and 29 Kulan hybrids (Mongolian Kulan ♂×Xinjiang♀), and the ancestor composition indicated the true lineage of the hybrids. XP-EHH (Cross Population Extended Haplotype Homozygosity), θπ-ratio (Nucleotide Diversity Ratio), CLR (Composite Likelihood Ratio) and θπ (Nucleotide Diversity) methods were used to detect the candidate regions of positive selection in Asiatic wild ass and its hybrids. Several immune genes (DEFA1, DEFA5, DEFA7, GIMAP4, GIMAP1, IGLC1, IGLL5, GZMB and HLA) were observed by the CLR and θπ methods. XP-EHH and θπ-ratio revealed that these genes are potentially responsible for coat color (KITLG) and meat quality traits (PDE1B and MYLK2). Furthermore, the heatmap was able to show the clear difference in the haplotype of the KITLG gene between the Kulan hybrids and Asiatic wild ass group and the Guanzhong black donkey group, which is a powerful demonstration of the key role of KITLG in donkey color. Therefore, our study may provide new insights into the genetic basis of coat color, meat quality traits and immunity of Asiatic wild ass and its hybrids.

VP4 Is a Determinant of Alpha-Defensin Modulation of Rotaviral Infection

Fecal-oral pathogens encounter constitutively expressed enteric alpha-defensins in the intestine during replication and transmission. Alpha-defensins can be potently antiviral and antibacterial; however, their primary sequences, the number of isoforms, and their activity against specific microorganisms often vary greatly between species, reflecting adaptation to species-specific pathogens. Therefore, alpha-defensins might influence not only microbial evolution and tissue tropism within a host but also species tropism and zoonotic potential. To investigate these concepts, we generated a panel of enteric and myeloid alpha-defensins from humans, rhesus macaques, and mice and tested their activity against group A rotaviruses, an important enteric viral pathogen of humans and animals. Rotaviral adaptation to the rhesus macaque correlated with resistance to rhesus enteric, but not myeloid, alpha-defensins and sensitivity to human alpha-defensins. While mouse rotaviral infection was increased in the presence of mouse enteric alpha-defensins, two prominent genotypes of human rotaviruses were differentially sensitive to human enteric alpha-defensins. Furthermore, the effects of cross-species alpha-defensins on human and mouse rotaviruses did not follow an obvious pattern. Thus, exposure to alpha-defensins may have shaped the evolution of some, but not all, rotaviruses. We then used a genetic approach to identify the viral attachment and penetration protein, VP4, as a determinant of alpha-defensin sensitivity. Our results provide a foundation for future studies of the VP4-dependent mechanism of defensin neutralization, highlight the species-specific activities of alpha-defensins, and focus future efforts on a broader range of rotaviruses that differ in VP4 to uncover the potential for enteric alpha-defensins to influence species tropism. IMPORTANCE Rotavirus is a leading cause of severe diarrhea in young children. Like other fecal-oral pathogens, rotaviruses encounter abundant, constitutively expressed defensins in the small intestine. These peptides are a vital part of the vertebrate innate immune system. By investigating the impact that defensins from multiple species have on the infectivity of different strains of rotavirus, we show that some rotaviral infections can be inhibited by defensins. We also found that some, but not all, rotaviruses may have evolved resistance to defensins in the intestine of their host species, and some even appropriate defensins to increase their infectivity. Because rotaviruses infect a broad range of animals and rotaviral infections are highly prevalent in children, identifying immune defenses against infection and how they vary across species and among viral genotypes is important for our understanding of the evolution, transmission, and zoonotic potential of these viruses as well as the improvement of vaccines.

Inhibition of SARS-CoV-2 Infection by Human Defensin HNP1 and Retrocyclin RC-101

Severe acute respiratory syndrome coronavirus (SARS-CoV)-2 is an enveloped virus responsible for the COVID-19 pandemic. The emergence of new potentially more transmissible and vaccine-resistant variants of SARS-CoV-2 is an ever-present threat. Thus, it remains essential to better understand innate immune mechanisms that can inhibit the virus. One component of the innate immune system with broad antipathogen, including antiviral, activity is a group of cationic immune peptides termed defensins. The ability of defensins to neutralize enveloped and non-enveloped viruses and to inactivate numerous bacterial toxins correlate with their ability to promote the unfolding of proteins with high conformational plasticity. We found that human neutrophil α-defensin HNP1 binds to SARS-CoV-2 Spike protein with submicromolar affinity that is more than 20 fold stronger than its binding to serum albumin. As such, HNP1, as well as a θ-defensin retrocyclin RC-101, both interfere with Spike-mediated membrane fusion, Spike-pseudotyped lentivirus infection, and authentic SARS-CoV-2 infection in cell culture. These effects correlate with the abilities of the defensins to destabilize and precipitate Spike protein and inhibit the interaction of Spike with the ACE2 receptor. Serum reduces the anti-SARS-CoV-2 activity of HNP1, though at high concentrations, HNP1 was able to inactivate the virus even in the presence of serum. Overall, our results suggest that defensins can negatively affect the native conformation of SARS-CoV-2 Spike, and that α- and θ-defensins may be valuable tools in developing SARS-CoV-2 infection prevention strategies.

Porcine β-defensin 2 confers enhanced resistance to swine flu infection in transgenic pigs and alleviates swine influenza virus-induced apoptosis possibly through interacting with host SLC25A4

Swine influenza virus (SIV) not only brings about great economic losses on the global pig industry, it also poses a significant threat to the public health for its interspecies transmission capacity. Porcine β-defensin 2 (PBD-2) is a host defense peptide and our previous study has shown that PBD-2 inhibits proliferation of enveloped pseudorabies virus both in vitro and in transgenic (TG) mice. The aim of this study is to investigate the possible anti-SIV ability of PBD-2 in a TG pig model created in our previous study. The in-contact challenge trial demonstrated that overexpression of PBD-2 in pigs could efficiently alleviate SIV-associated clinical signs. The SIV titers quantified by EID₅₀ in lung tissues of infected TG pigs were significantly lower than that of wild-type littermates. In vitro, the cell viability assay revealed that PBD-2 mainly interfered with viral entry and post-infection stages. It was further confirmed that PBD-2 could enter porcine tracheal epithelial cells. The proteins interacting with PBD-2 inside host cells were identified with immunoprecipitation and the pathways involved were analyzed. Results showed that PBD-2 could interact with pro-apoptotic solute carrier family 25 member 4 (SLC25A4), also known as adenine nucleotide translocase 1, and thereby inhibited SIV-induced cell apoptosis. The molecular docking analysis suggested that PBD-2 interacted with porcine SLC25A4 mainly through strong hydrogen binding, with the predicted binding affinity being -13.23 kcal/mol. Altogether, these indicate that PBD-2 protects pigs against SIV infection, which may result from its role as a SLC25A4 blocker to alleviate cell apoptosis, providing a novel therapeutic and prophylactic strategy of using PBD-2 to combat SIV.

An experimental in silico study on COVID‐19: Response of neutrophil‐related genes to antibiotics

Background and Aims

All components of the immune system are involved in alleviating severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) infection. Further research is required to provide detailed insights into COVID‐19‐related immune compartments and pathways. In addition, a significant percentage of hospitalized COVID‐19 patients suspect bacterial infections and antimicrobial resistance occurs following antibiotics treatment. The aim of this study was to evaluate the possible effects of antibiotics on the response of neutrophil‐related genes in SARS‐CoV‐2 patients by an experimental in silico study.

Methods

The two data sets GSE1739 and GSE21802 including 10 SARS positive patients and 35 influenza A (H1N1) patients were analyzed, respectively. Differentially expressed genes (DEGs) between these two data sets were determined by GEO2R analysis and the Venn diagram online tool. After determining the hub genes involved in immune responses, the expression of these genes in 30 COVID‐19 patients and 30 healthy individuals was analyzed by real‐time polymerase chain reaction (PCR). All patients received antibiotics, including levofloxacin, colistin, meropenem, and ceftazidime.

Results

GEO2R analysis detected 240 and 120 DEGs in GSE21802 and GSE1739, respectively. Twenty DEGs were considered as enriched hub genes involved in immune processes such as neutrophil degranulation, neutrophil activation, and antimicrobial humoral response. The central nodes were attributed to the genes of neutrophil elastase (ELANE), arginase 1 (ARG‐1), lipocalin 2 (LCN2), and defensin 4 (DEFA4). Compared to the healthy subjects, the expression of LCN2 and DEFA4 were significantly reduced in COVID‐19 patients. However, no significant differences were observed in the ELANE and AGR‐1 levels between COVID‐19 subjects and the control group.

Conclusions

Activation and degranulation of neutrophils were observed mainly in SARS, and H1N1 infection processes and antibiotics administration could affect neutrophil activity during viral infection. It can be suggested that antibiotics can decrease inflammation by restoring the expression of neutrophil‐related genes in COVID‐19 patients.

DeepTI: A deep learning-based framework decoding tumor-immune interactions for precision immunotherapy in oncology

BACKGROUND

Increasing evidence suggests the immunomodulatory potential of genes in oncology. But the identification of immune attributes of genes is costly and time-consuming, which leads to an urgent demand to develop a prediction model.

METHOD

We developed a deep learning-based model to predict the immune properties of genes. This model is trained in 70% of samples and evaluated in 30% of samples. Furthermore, it uncovers 60 new immune-related genes. We analyzed the expression perturbation and prognostic value of these genes in gastric cancer. Finally, we validated these genes in immunotherapy-related datasets to check the predictive potential of immunotherapeutic sensitivity.

RESULT

This model classifies genes as immune-promoted or immune-inhibited based on the human PPI network and it achieves an accuracy of 0.68 on the test set. It uncovers 60 new immune-related genes, most of which are validated in the published literature. These genes are found to be downregulated in gastric cancer and significantly associated with the immune microenvironment in gastric cancer. Analysis of immunotherapy shows that these genes can discriminate between responder and non-responder.

CONCLUSION

This model can facilitate the identification of immune properties of genes, decoding tumor-immune interactions for precision immunotherapy in oncology.

Immunomodulatory and Allergenic Properties of Antimicrobial Peptides

With the growing problem of the emergence of antibiotic-resistant bacteria, the search for alternative ways to combat bacterial infections is extremely urgent. While analyzing the effect of antimicrobial peptides (AMPs) on immunocompetent cells, their effect on all parts of the immune system, and on humoral and cellular immunity, is revealed. AMPs have direct effects on neutrophils, monocytes, dendritic cells, T-lymphocytes, and mast cells, participating in innate immunity. They act on B-lymphocytes indirectly, enhancing the induction of antigen-specific immunity, which ultimately leads to the activation of adaptive immunity. The adjuvant activity of AMPs in relation to bacterial and viral antigens was the reason for their inclusion in vaccines and made it possible to formulate the concept of a “defensin vaccine” as an innovative basis for constructing vaccines. The immunomodulatory function of AMPs involves their influence on cells in the nearest microenvironment, recruitment and activation of other cells, supporting the response to pathogenic microorganisms and completing the inflammatory process, thus exhibiting a systemic effect. For the successful use of AMPs in medical practice, it is necessary to study their immunomodulatory activity in detail, taking into account their pleiotropy. The degree of maturity of the immune system and microenvironment can contribute to the prevention of complications and increase the effectiveness of therapy, since AMPs can suppress inflammation in some circumstances, but aggravate the response and damage of organism in others. It should also be taken into account that the real functions of one or another AMP depend on the types of total regulatory effects on the target cell, and not only on properties of an individual peptide. A wide spectrum of biological activity, including direct effects on pathogens, inactivation of bacterial toxins and influence on immunocompetent cells, has attracted the attention of researchers, however, the cytostatic activity of AMPs against normal cells, as well as their allergenic properties and low stability to host proteases, are serious limitations for the medical use of AMPs. In this connection, the tasks of searching for compounds that selectively affect the target and development of an appropriate method of application become critically important. The scope of this review is to summarize the current concepts and newest advances in research of the immunomodulatory activity of natural and synthetic AMPs, and to examine the prospects and limitations of their medical use.

Theta-Defensins to Counter COVID-19 as Furin Inhibitors: In Silico Efficiency Prediction and Novel Compound Design

Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), was characterized as a pandemic by the World Health Organization (WHO) in Dec. 2019. SARS-CoV-2 binds to the cell membrane through spike proteins on its surface and infects the cell. Furin, a host-cell enzyme, possesses a binding site for the spike protein. Thus, molecules that block furin could potentially be a therapeutic solution. Defensins are antimicrobial peptides that can hypothetically inhibit furin because of their arginine-rich structure. Theta-defensins, a subclass of defensins, have attracted attention as drug candidates due to their small size, unique structure, and involvement in several defense mechanisms. Theta-defensins could be a potential treatment for COVID-19 through furin inhibition and an anti-inflammatory mechanism. Note that inflammatory events are a significant and deadly condition that could happen at the later stages of COVID-19 infection. Here, the potential of theta-defensins against SARS-CoV-2 infection was investigated through in silico approaches. Based on docking analysis results, theta-defensins can function as furin inhibitors. Additionally, a novel candidate peptide against COVID-19 with optimal properties regarding antigenicity, stability, electrostatic potential, and binding strength was proposed. Further in vitro/in vivo investigations could verify the efficiency of the designed novel peptide.

Paneth cells and their multiple functions

The small intestine mucosa is lined by specialized cells that form the crypt-villus axis, which expands its surface. Among the six intestinal epithelial cell types, the Paneth cell is located at the base of the crypt, and it contains numerous granules in its cytoplasm, composed of antimicrobial peptides, such as defensins and lysozyme, and growth factors, such as EGF, TGF-alpha, and Wnt ligands. Together, these elements act in the defense against microorganisms, regulation of intestinal microbiota, maintenance, and regulation of stem cell identity. Pathologies that target Paneth cells can disturb such defense activity, but they also affect the maintenance of stem cell niche. In that way, Crohn's disease, necrotizing enterocolitis, and graft-versus-host disease promote a reduction of Paneth cell population, and consequently of secretion of their products into the lumen of the crypts, making the affected organism predisposed to infections and dysbiosis. Additionally, the emergence of new intestinal cells is also decreased. This review aims to address the main characteristics of Paneth cells, highlighting their multiple functions and the importance of their preservation to ensure bowel homeostasis. This article is protected by copyright. All rights reserved.

Sheep β-Defensin 2 Regulates Escherichia coli F17 Resistance via NF-κB and MAPK Signaling Pathways in Ovine Intestinal Epithelial Cells

Simple Summary

This study was conducted to explore the antibacterial ability of sheep β-defensin 2 (SBD-2) against E. coli F17 infection in ovine intestinal epithelial cells (OIECs). Our data revealed that E. coli F17 induces SBD-2 expression in OIECs in vitro, which appears to be mediated through the activation of the signaling pathways NF-κB and MAPK. Our results provide a novel insight for the functionality of SBD-2, which could be useful for developing anti-infective drugs and/or breeding for E. coli diarrhea disease-resistant sheep.

Abstract

Escherichia coli (E. coli) F17 is a member of enterotoxigenic Escherichia coli, which can cause massive diarrhea and high mortality in newborn lambs. β-defensin is mainly produced by the epithelial tissue of the gastrointestinal tract in response to microbial infection. However, the molecular mechanism of sheep β-defensin 2 (SBD-2) against E. coli F17 remains unclear. This study aims to reveal the antibacterial ability of SBD-2 against E. coli F17 infection in sheep. Firstly, we established the culture system of ovine intestinal epithelial cells (OIECs) in vitro, treated with different concentrations of E. coli F17 for an indicated time. Secondly, we performed RNA interference and overexpression to investigate the effect of SBD-2 expression on E. coli F17 adhesion to OIECs. Finally, inhibitors of NF-κB and MAPK pathways were pre-treated to explore the possible relationship involving in E. coli F17 infection regulating SBD-2 expression. The results showed that E. coli F17 markedly (p < 0.01) upregulated the expression levels of SBD-2 mRNA and protein in a concentration- and time-dependent manner. Overexpression of SBD-2 contributed to enhancing E. coli F17 resistance in OIECs, while silencing SBD-2 dramatically improved the adhesion of E. coli F17 to OIECs (p < 0.05 or p < 0.01). Furthermore, E. coli F17 stimulated SBD-2 expression was obviously decreased by pre-treatment with NF-κB inhibitor PDTC, p38 MAPK inhibitor SB202190 and ERK1/2 MAPK inhibitor PD98095 (p < 0.05 or p < 0.01). Interestingly, adhesion of E. coli F17 to OIECs were highly enhanced by pre-treated with PDTC, SB202190 and PD98095. Our data suggested that SBD-2 could inhibit E. coli F17 infection in OIECs, possibly through NF-κB and MAPK signaling pathways. Our results provide useful theoretical basis on developing anti-infective drug and breeding for E. coli diarrhea disease-resistant sheep.

The seven constitutive respiratory defense barriers against SARS-CoV-2 infection

Before eliciting an adaptive immune response, SARS-CoV-2 must overcome seven constitutive respiratory defense barriers. The first is the mucus covering the respiratory tract's luminal surface, which entraps inhaled particles, including infectious agents, and eliminates them by mucociliary clearance. The second barrier comprises various components present in the airway lining fluid, the surfactants. Besides providing low surface tension that allows efficient gas exchange at the alveoli, surfactants inhibit the invasion of epithelial cells by respiratory viruses, enhance pathogen uptake by phagocytes, and regulate immune cells' functions. The respiratory tract microbiota constitutes the third defense barrier against SARS-CoV-2. It activates the innate and adaptive immune cells and elicits anti-infectious molecules such as secretory IgA antibodies, defensins, and interferons. The fourth defense barrier comprises the antimicrobial peptides defensins, and lactoferrin. They show direct antiviral activity, inhibit viral fusion, and modulate the innate and adaptive immune responses. Secretory IgA antibodies, the fifth defense barrier, besides protecting the local microbiota against noxious agents, also inhibit SARS-CoV-2 cell invasion. If the virus overcomes this barrier, it reaches its target, the respiratory epithelial cells. However, these cells also act as a defense barrier, the sixth one, since they hinder the virus' access to receptors and produce antiviral and immunomodulatory molecules such as interferons, lactoferrin, and defensins. Finally, the sensing of the virus by the cells of innate immunity, the last constitutive defense barrier, elicits a cascade of signals that activate adaptive immune cells and may inhibit the development of productive infection. The subject of the present essay is discussing these mechanisms.

Defensins: The natural peptide antibiotic

Defensins are a family of cationic antimicrobial peptides active against a broad range of infectious microbes including bacteria, viruses and fungi, playing important roles as innate effectors and immune modulators in immunological control of microbial infection. Their antibacterial properties and unique mechanisms of action have garnered considerable interest in developing defensins into a novel class of natural antibiotic peptides to fend off pathogenic infection by bacteria, particularly those resistant to conventional antibiotics. However, serious pharmacological and technical obstacles, some of which are unique to defensins and others are common to peptide drugs in general, have hindered the development and clinical translation of defensins as anti-infective therapeutics. To overcome them, several technologies have been developed, aiming for improved functionality, prolonged circulation time, enhanced proteolytic stability and bioavailability, and efficient and controlled delivery and release of defensins to the site of infection. Additional challenges include the alleviation of potential toxicity of defensins and their cost-effective manufacturing. In this review, we briefly introduce defensin biology, focus on various transforming strategies and practical techniques developed for defensins and their derivatives as antibacterial therapeutics, and conclude with a summation of future challenges and possible solutions.

Age-Related Expression of IFN-λ1 Versus IFN-I and Beta-Defensins in the Nasopharynx of SARS-CoV-2-Infected Individuals

SARS-CoV-2 coronavirus infection induces heterogeneous symptoms, ranging from asymptomatic to lethal forms. Severe forms usually occur in the elderly and/or individuals with comorbidities. Children generally remain asymptomatic to primary infection, suggesting that they may have an effective local innate immune response. IFN-I and -III have non-redundant protective roles against SARS-CoV-2, although sometimes damaging the host. The expression and role of anti-viral peptides during SARS-CoV-2 infection have thus far been little studied. We aimed to identify the innate immune molecules present at the SARS-CoV-2 entry point. We analyzed the mRNA levels of type I (IFN-α and -β) and type III (IFN-λ1-3) interferons and selected antiviral peptides (i.e., β-defensins 1-3, α-defensins [HNP1-3, HD5] pentraxin-3, surfactant protein D, the cathelicidin LL-37 and interleukin-26) in nasopharyngeal swabs from 226 individuals of various ages, either infected with SARS-CoV-2 (symptomatic or asymptomatic) or negative for the virus. We observed that infection induced selective upregulation of IFN-λ1 expression in pediatric subjects (≤15 years), whereas IFN-α, IFN-β, IFN-λ2/λ3, and β-defensin 1-3 expression was unaffected. Conversely, infection triggered upregulation of IFN-α, IFN-β, IFN-λ2/λ3, and β-defensin 1-3 mRNA expression in adults (15-65 years) and the elderly (≥ 65 years), but without modulation of IFN-λ1. The expression of these innate molecules was not associated with gender or symptoms. Expression of the interferon-stimulated genes IFITM1 and IFITM3 was upregulated in SARS-CoV-2-positive subjects and reached similar levels in the three age groups. Finally, age-related differences in nasopharyngeal innate immunity were also observed in SARS-CoV-2-negative subjects. This study shows that the expression patterns of IFN-I/-III and certain anti-viral molecules in the nasopharyngeal mucosa of SARS-CoV-2-infected subjects differ with age and suggests that susceptibility to SARS-CoV-2 may be related to intrinsic differences in the nature of mucosal anti-viral innate immunity.

Host Defense Peptides: Dual Antimicrobial and Immunomodulatory Action

The rapid rise of multidrug-resistant (MDR) bacteria has once again caused bacterial infections to become a global health concern. Antimicrobial peptides (AMPs), also known as host defense peptides (HDPs), offer a viable solution to these pathogens due to their diverse mechanisms of actions, which include direct killing as well as immunomodulatory properties (e.g., anti-inflammatory activity). HDPs may hence provide a more robust treatment of bacterial infections. In this review, the advent of and the mechanisms that lead to antibiotic resistance will be described. HDP mechanisms of antibacterial and immunomodulatory action will be presented, with specific examples of how the HDP aurein 2.2 and a few of its derivatives, namely peptide 73 and cG4L73, function. Finally, resistance that may arise from a broader use of HDPs in a clinical setting and methods to improve biocompatibility will be briefly discussed.

Peptides-based therapeutics: Emerging potential therapeutic agents for COVID-19

SARS-CoV-2 is a positive-sense RNA virus and it is the causative agent of the global COVID-19 outbreak. COVID-19 is similar to the previous outbreaks for instance SARS in 2002-2003 and MERS in 2012. As the peptides have many advantages, peptide-based therapeutics might be one of the possible ways in the development of COVID-19 specific drugs. SARS-CoV-2 enters into a human via its S protein by attaching with human hACE2 present on the cell membrane in the lungs and intestines of humans. hACE2 cleaves S protein into the S1 subunit for viral attachment and the S2 subunit for fusion with the host cell membrane. The fusion mechanism forms a six-helical bundle (6-HB) structure which finally fuses the viral envelope with the host cell membrane. hACE2 based peptides such as SBP1 and Spikeplug have shown their potential as antiviral agents. S protein-hACE2 interaction and the SARS-CoV-2 fusion machinery play a crucial part in human viral infection. It is evident that if these interactions could be blocked successfully and efficiently, it could be the way to find the drug for COVID-19. Several peptide-based inhibitors are potent inhibitors of S protein-hACE2 interaction. Similarly, the antiviral activity of the antimicrobial peptide, lactoferrin makes it an important candidate for the COVID-19 drug development process. A candidate drug, RhACE2-APN01 based on recombinant hACE2 peptide has already entered phase II clinical trials. This review sheds light on different aspects of the feasibility of using peptide-based therapeutics as the promising therapeutic route for COVID-19.

Antimicrobial peptides: mechanism of action, activity and clinical potential

The management of bacterial infections is becoming a major clinical challenge due to the rapid evolution of antibiotic resistant bacteria. As an excellent candidate to overcome antibiotic resistance, antimicrobial peptides (AMPs) that are produced from the synthetic and natural sources demonstrate a broad-spectrum antimicrobial activity with the high specificity and low toxicity. These peptides possess distinctive structures and functions by employing sophisticated mechanisms of action. This comprehensive review provides a broad overview of AMPs from the origin, structural characteristics, mechanisms of action, biological activities to clinical applications. We finally discuss the strategies to optimize and develop AMP-based treatment as the potential antimicrobial and anticancer therapeutics.

Quercetin as an antiviral agent inhibits the Pseudorabies virus in vitro and in vivo

Pseudorabies virus (PRV) accounts for a critical swine disease incurring economic losses worldwide. Several PRV vaccines are commercially available but these vaccines are effective against only certain prevalent PRV strains in China. To prevent PRV-induced latent infection and decrease the pathogenicity, novel anti-PRV drugs are required to prevent PRV infection. Natural products show exceptional structural diversity representing an important source for developing novel therapeutic agents. Quercetin is a flavonoid with anti-oxidant, anti-cancer, anti-bacterial and anti-viral activities. This study involved quercetin for studying the anti-PRV function in vitro and in vivo. Quercetin was found to significantly decrease the PRV virulent strain HNX at a half-maximal inhibitory concentration (IC₅₀) of 2.618 μM and selectivity index 229. This anti-PRV activity of quercetin was found to be dose-dependent. Furthermore, quercetin also inhibited a wide the infections by a spectrum of PRV strains like HNX, Ea, Bartha and Fa strain. These virucidal effects of quercetin suggest the interaction between these molecules and viral particles, and quercetin is responsible for inhibiting the adsorption of PRV infections. The silico assays suggesting that quercetin might interact with the gD-protein on the surface of the PRV important for viral infection. Additional, the quercetin plantar injection protected the mice from the lethal challenge, decreasing the PRV-infected mice's brain viral loads and mortality. These results provides a anti-PRV strategy and contribute to drug discovery and development.

Dealing with MDR bacteria and biofilm in the post-antibiotic era: Application of antimicrobial peptides-based nano-formulation

The rapid development of multidrug-resistant (MDR) bacteria due to the improper and overuse of antibiotics and the ineffective performance of antibiotics against the difficult-to-treat biofilm-related infections (BRIs) have urgently called for alternative antimicrobial agents and strategies in combating bacterial infections. Antimicrobial peptides (AMPs), owing to their compelling antimicrobial activity against MDR bacteria and BRIs without causing bacteria resistance, have attracted extensive attention in the research field. With the development of nanomaterial-based drug delivery strategies, AMPs-based nano-formulations have significantly improved the therapeutic effects of AMPs by ameliorating their hydrolytic stability, half-life in vivo, and solubility as well as reducing the cytotoxicity and hemolysis, etc. This review has comprehensively summarized the application AMPs-based nano-formulation in various bacterial infections models, including bloodstream infections (specifically sepsis), pulmonary infections, chronic wound infections, gastrointestinal infections, among others. The design of the nanomaterial-based drug delivery systems and the therapeutic effects of the AMPs-based nano-formulations in literature have been categorized and in details discussed. Overall, this review provides insights into the advantages and disadvantages of the current developed AMPs-based nano-formulations in literature for the treatment of bacterial infections, bringing inspirations and suggestions for their future design in the way towards clinical translation.