A new cryptic cationic antimicrobial peptide from human apolipoprotein E with antibacterial activity and immunomodulatory effects on human cells

Abstract

Cationic antimicrobial peptides (AMPs) possess fast and broad-spectrum activity against both Gram-negative and Gram-positive bacteria, as well as fungi. It has become increasingly evident that many AMPs, including those that derive from fragments of host proteins, are multifunctional and able to mediate various immunomodulatory functions and angiogenesis. Among these, synthetic apolipoprotein-derived peptides are safe and well tolerated in humans and have emerged as promising candidates in the treatment of various inflammatory conditions. Here, we report the characterization of a new AMP corresponding to residues 133-150 of human apolipoprotein E. Our results show that this peptide, produced either by chemical synthesis or by recombinant techniques in Escherichia coli, possesses a broad-spectrum antibacterial activity. As shown for several other AMPs, ApoE (133-150) is structured in the presence of TFE and of membrane-mimicking agents, like SDS, or bacterial surface lipopolysaccharide (LPS), and an anionic polysaccharide, alginate, which mimics anionic capsular exo-polysaccharides of several pathogenic microorganisms. Noteworthy, ApoE (133-150) is not toxic toward several human cell lines and triggers a significant innate immune response, assessed either as decreased expression levels of proinflammatory cytokines in differentiated THP-1 monocytic cells or by the induction of chemokines released from PBMCs. This novel bioactive AMP also showed a significant anti-inflammatory effect on human keratinocytes, suggesting its potential use as a model for designing new immunomodulatory therapeutics.

Human apolipoprotein E as a reservoir of cryptic bioactive peptides: The case of ApoE 133‐167

“…Other reports, focused on monomeric and dimeric synthetic peptides encompassing ApoE amino acids 130 to 169, revealed the importance of α‐helical conformations and of positively charged amino acids . Several recent reports are focused on the study of ApoE‐derived peptide antimicrobial and immunomodulatory properties . They have been identified in the receptor binding region, or they have been obtained by combining clusters of residues identified in the same region.…”

“…The method assigns an antimicrobial score to peptides based on their net charge, hydrophobicity and length, and 2 bacterial strain‐dependent weight factors . By means of this method, we have already reported the characterization of novel human peptides including an exhaustive structural and functional study of a cryptic peptide identified in human ApoE (residues 133‐150) . We deeply characterized the ability of ApoE (133‐150) to assume stable conformations in the presence of membrane mimicking agents and LPS as well as its antibacterial and immunomodulatory properties .…”

Apolipoprotein E - A Multifunctional Protein with Implications in Various Pathologies as a Result of Its Structural Features

“…Overexpression of apoE4 fragment 1–272 induced its binding to various components of mitochondrial complexes and promoted mitochondrial dysfunction in Neuro-2a cells [82]. On the other hand, apoE 133–149 peptide displayed neuroprotective functions, besides its anti-inflammatory properties [83].…”

“…ApoE 133–150 peptide was found to be lethal for several Gram-positive ( Staphylococcus aureus , Bacillus subtilis ) and Gram-negative ( Pseudomonas aeruginosa , Escherichia coli , Klebsiella pneumoniae ) bacteria, but displayed no toxicity on several human cell cultures [83]. Furthermore, this peptide reduced the expression of pro-inflammatory cytokines in LPS-treated THP-1 macrophages.…”

“…Another synthetic peptide, apoE23, generated by joining sequences 141–148 and 135–149, exhibited a higher microbiological activity than apoEdp. ApoE23 includes a linker of five amino acids (RLASH) between the repeated 141–148 apoE domains [83].…”