Dual functions of the human antimicrobial peptide LL-37—Target membrane perturbation and host cell cargo delivery

Abstract

The mechanisms behind target vs. host cell recognition of the human antimicrobial peptide LL-37 remain ill-defined. Here, we have investigated the membrane disruption capacity of LL-37 using large unilamellar vesicles (LUVs) composed of varying mixtures of POPC, POPG and cholesterol to mimic target and host membranes respectively. We show that LL-37 is unable to induce leakage of entrapped calcein from zwitterionic POPC LUVs, whereas leakage from LUVs partially composed of POPG is fast and efficient. In accordance with typical antimicrobial peptide behavior, cholesterol diminished LL-37 induced leakage. By using linear dichroism and flow oriented LUVs, we found that LL-37 orients with the axis of its induced α-helix parallel to the membrane surface in POPC:POPG (7:3) LUVs. In the same system, we also observed a time-dependent increase of the parallel α-helix LD signal on timescales corresponding to the leakage kinetics. The increased LD may be connected to a peptide translocation step, giving rise to mass balance across the membrane. This could end the leakage process before it is complete, similar to what we have observed. Confocal microscopy studies of eukaryotic cells show that LL-37 is able to mediate the cell delivery of non-covalently linked fluorescent oligonucleotides, in agreement with earlier studies on delivery of plasmid DNA (Sandgren et al., J. Biol. Chem. 279 (2004) 17951). These observations highlight the potential dual functions of LL-37 as an antimicrobial agent against bacterial target cells and a cell-penetrating peptide that can deliver nucleic acids into the host cells.

Human Host Defense Cathelicidin Peptide LL-37 Enhances the Lipopolysaccharide Uptake by Liver Sinusoidal Endothelial Cells without Cell Activation

“…Noteworthy, HSPGs are required for the initial recruitment of Tat onto the cell surface, and a scavenger receptor low-density lipoprotein receptor-related protein is responsible for the exact uptake of Tat (53). Importantly, LL-37 is recognized as a CPP (36), and LSECs express various scavenger receptors (54). Thus, it is reasonable to speculate that the LL-37-LPS complex initially interacts with cell-surface HSPGs and subsequently binds with some scavenger receptor(s) on LSECs for the incorporation.…”

“…LL-37 is a potent LPS-binding peptide, thus rapidly forming a complex with LPS (34). Intriguingly, it has been demonstrated that LL-37 is incorporated into immune cells or epithelial cells either by itself (22,35) or by forming a complex with bacterial components (23,36). Based on these aspects, we hypothesized that LL-37 itself is incorporated into LSECs and also enhances the LPS uptake by forming a complex with LPS.…”

Multifunctional cationic host defence peptides and their clinical applications

“…Thus generally speaking, extracellular infections require a humoral (T H 2) immune response for clearance, whereas intracellular infections required a cellmediated (T H 1) response [64]. Appropriate physical interactions between the antigen and adjuvant are important as adjuvants often act by increasing the uptake of antigens and in this regard it is worth noting that HDP peptides have the features of cell-penetrating peptides [124]. An ideal adjuvant should also help elicit a strong immune response, but not cause excessive harmful inflammation or other immunopathologies, a feature of most HDPs.…”

Inactivation of the Antifungal and Immunomodulatory Properties of Human Cathelicidin LL-37 by Aspartic Proteases Produced by the Pathogenic Yeast Candida albicans

“…The physiological concentration of LL-37 varies between different cells and tissues and is often altered at infection sites (9)(10)(11)(12). The main antibacterial functions of LL-37 disrupt the microbial cell membrane, which results in cytoplasm leakage (13). In infections with C. albicans, LL-37 can also reduce infectivity by inhibiting biofilm formation or yeast adhesion to the host cells (14).…”