The misuse of antibiotics has led our age to a dangerous edge, as antibiotic-resistant pathogens appear to evolve more quickly than antibiotics are invented. Thus, new agents to treat bacterial infection are badly needed. Cationic host defense peptides are on the first line of a host defense system and are thought to be good candidates for treating bacterial infection. Here, a novel cationic host defense peptide, mucroporin, was cloned and characterized from the venom ofLychas mucronatus. The MIC forStaphylococcus aureuswas 25 μg/ml, including antibiotic-resistant pathogens. Based on the molecular template of mucroporin, mucroporin-M1 was designed by amino acid substitution. The MIC forS. aureuswas 5 μg/ml, including the antibiotic-resistant pathogens methicillin-resistantS. aureus, methicillin-resistant coagulase-negativeStaphylococcus, penicillin-resistantS. aureus, and penicillin-resistantS. epidermidis. Moreover, mucroporin-M1 also inhibited gram-negative bacteria. The modes of action of mucroporin and mucroporin-M1 were both rapid killing by disrupting the cell membrane of bacteria, and the number of surviving bacteria was reduced by about 4 to 5 orders of magnitude immediately after peptide delivery. These results showed that mucroporin could be considered a potential anti-infective drug, especially for treating antibiotic-resistant pathogens.

The pace of resistance against antibiotics almost exceeds that of the development of new drugs. As many bacteria have become resistant to conventional antibiotics, new drugs or drug resources are badly needed to combat antibiotic-resistant pathogens, like methicillin-resistant Staphylococcus aureus (MRSA). Antimicrobial peptides, rich sources existing in nature, are able to effectively kill multidrug-resistant pathogens. Here, imcroporin, a new antimicrobial peptide, was screened and isolated from the cDNA library of the venomous gland of Isometrus maculates . The MIC of imcroporin against MRSA was 50 μg/ml, 8-fold lower than that of cefotaxime and 40-fold lower than that of penicillin. Imcroporin killed bacteria rapidly in vitro, inhibited bacterial growth, and cured infected mice. These results revealed that imcroporin could be considered a potential anti-infective drug or lead compound, especially for treating antibiotic-resistant pathogens.

Hepatitis B virus (HBV) is a noncytopathic human hepadnavirus that causes acute, chronic hepatitis and hepatocellular carcinoma (HCC). As the clinical utility of current therapies is limited, new anti-HBV agents and sources for such agents are still highly sought after. Here, we report that Mucroporin-M1, a scorpion venom-derived peptide, reduces the amount of extracellular HBsAg, HBeAg, and HBV DNA productions of HepG2.2.15 cells in a dose-dependent manner and inhibits HBV capsid DNA, HBV intracellular RNA replication intermediates and the HBV Core protein in the cytoplasm of HepG2.2.15 cells. Using a mouse model of HBV infection, we found that HBV replication was significantly inhibited by intravenous injection of the Mucroporin-M1 peptide. This inhibitory activity was due to a reduction in HBV promoter activity caused by a decrease in the binding of HNF4α to the precore/core promoter region. Furthermore, we confirmed that Mucroporin-M1 could selectively activate mitogen-activated protein kinases (MAPKs) and lead to the down-regulation of HNF4α expression, which explains the decreased binding of HNF4α to the HBV promoter. Moreover, when the protein phosphorylation activity of the MAPK pathway was inhibited, both HNF4α expression and HBV replication recovered. Finally, we proved that treatment with the Mucroporin-M1 peptide increased phosphorylation of the MAPK proteins in HBV-harboring mice. These results implicate Mucroporin-M1 peptide can activate the MAPK pathway and then reduce the expression of HNF4α, resulting in the inhibition of HBV replication in vitro and in vivo. Our work also opens new doors to discovering novel anti-HBV agents or sources.

Objectives The generation of systemic lupus erythematosus (SLE)-related autoantibodies have been shown to be T cell dependent and antigen driven with HLA-DR restriction. In this study, the initiating antigen(s) and the mechanism of autoantibody diversification were investigated. Methods T cell epitopes (T-epitopes) of SmD1 (SmD) were mapped by T-T hybridomas generated from DR3⁺AE⁰ mice immunised with SmD and with SmD overlapping peptides. TCRs from the reactive hybridomas were sequenced. The core epitopes were determined. Bacterial mimics were identified by bioinformatics. Sera from DR3⁺AE⁰ mice immunised with SmD peptides and their mimics were analysed for their reactivity by ELISA and immunohistochemistry. Samples of blood donors were analysed for HLA-DR and autoantibody specificities. Results Multiple HLA-DR3 restricted T-epitopes within SmD were identified. Many T-T hybridomas reacted with more than one epitope. Some of them were cross-reactive with other snRNP peptides and with proteins in the Ro60/La/Ro52 complex. The reactive hybridomas used unique TCRs. Multiple T-epitope mimics were identified in commensal and environmental bacteria. Certain bacterial mimics shared both T and B cell epitopes with the related SmD peptide. Bacterial mimics induced autoantibodies to lupus-related antigens and to different tissues. HLA-DR3⁺ blood donors made significantly more SLE-related autoantibodies. Conclusions The unique antigenic structures of the lupus-related autoantigens provide the basis for being targeted and for T and B cell epitope spreading and autoantibody diversification with unique patterns. SLE-related autoantibodies are likely generated from responses to commensal and/or environmental microbes due to incomplete negative selection for autoreactive T cells. The production of SLE-related antibodies is inevitable in normal individuals. The findings in this investigation have significant implications in autoimmunity in general.