Tribolium castaneum defensin 1 kills Moraxella catarrhalisin an in vitro infection model but does not harm commensal bacteria

Porcine beta defensin 2 attenuates inflammatory responses in IPEC-J2 cells against Escherichia coli via TLRs-NF-κB/MAPK signaling pathway

BACKGROUND

Porcine beta defensin 2 (pBD2) is one of the porcine beta defensins that has antibacterial activity, and plays an important role in the immunomodulatory activity that protects cells from pathogens. It has been reported that pBD2 plays their immunomodulatory functions related to the TLR4-NF-κB signal pathways. However, it is not completely clear how pBD2 reduces the inflammatory response caused by pathogens.

RESULTS

In this study, the effect of pBD2 on the expression of genes in the TLRs signaling pathway was investigated after IPEC-J2 cells were challenged with E. coli. The results showed that pBD2 decreased the expression of IL-8 induced by E. coli (P < 0.05), and pBD2 significantly decreased the expression of TLR4, TLR5 and TLR7 (P < 0.05), as well as the key downstream genes p38 and JNK which activated by E. coli (P < 0.05). In addition, pBD2 inhibited the p-p65, p-p38 and p-JNK which were up-regulated by E. coli.

CONCLUSIONS

pBD2 could reduce the inflammatory response induced by E. coli perhaps by inhibiting the TLRs-TAK1-NF-κB/MAPK signaling pathway which was activated by E. coli in IPEC-J2 cells. Our study further reveals the immunomodulatory activity of recombinant pBD2 against E. coli, and provides insights into the molecular mechanisms that protect cells from E. coli infection.

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.

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.

Combating Escherichia coli O157:H7 with Functionalized Chickpea-Derived Antimicrobial Peptides

The rapid dissemination of antibiotic resistance accelerates the desire for new antibacterial agents. Here, a class of antimicrobial peptides (AMPs) is designed by modifying the structural parameters of a natural chickpea-derived AMP-Leg2, termed "functionalized chickpea-derived Leg2 antimicrobial peptides" (FCLAPs). Among the FCLAPs, KTA and KTR show superior antibacterial efficacy against the foodborne pathogen Escherichia coli (E. coli) O157:H7 (with MICs in the range of 2.5-4.7 µmol L^-1 ) and demonstrate satisfactory feasibility in alleviating E. coli O157:H7-induced intestinal infection. Additionally, the low cytotoxicity along with insusceptibility to antimicrobial resistance increases the potential of FCLAPs as appealing antimicrobials. Combining the multi-omics profiling andpeptide-membrane interaction assays, a unique dual-targeting mode of action is characterized. To specify the antibacterial mechanism, microscopical observations, membrane-related physicochemical properties studies, and mass spectrometry assays are further performed. Data indicate that KTA and KTR induce membrane damage by initially targeting the lipopolysaccharide (LPS), thus promoting the peptides to traverse the outer membrane. Subsequently, the peptides intercalate into the peptidoglycan (PGN) layer, blocking its synthesis, and causing a collapse of membrane structure. These findings altogether imply the great potential of KTA and KTR as promising antibacterial candidates in combating the growing threat of E. coli O157:H7.