LL-37/CRAMP and other antimicrobial peptides induce H2S production in bacteria and macrophages, mediating anti-infective function

Antimicrobial peptides (AMPs) are crucial components of the innate immune system, serving as a primary defense against microbial infections across diverse animal species. Despite their well-established role, the full spectrum of mechanisms underlying their anti-infective functions remains an active area of research. Concurrently, hydrogen sulfide (H2S), recognized as a vital gasotransmitter, is implicated in numerous physiological processes, including immune regulation. However, the specific interplay between H2S and the anti-infective actions of AMPs, particularly how H2S might contribute to or modulate AMP efficacy, has been largely unexplored, representing a significant gap in understanding host defense mechanisms.

Researchers investigated the role of H2S in the anti-infective functions of antimicrobial peptides (AMPs), focusing on LL-37/CRAMP, the human cathelicidin family AMP and its mouse homolog. They conducted in vitro experiments using bacterial strains, specifically Escherichia coli and Clostridium perfringens, to assess H2S production. Macrophage cell lines were also utilized to study H2S generation in immune cells. The study employed various biochemical and molecular assays, including enzymatic activity assays for 3-mercaptopyruvate sulfurtransferase (3MST) and cystathionine γ-lyase (CSE), ROS detection assays, and Western blotting to analyze Akt signaling pathway activation and protein expression. In vivo anti-infective activity was confirmed in unspecified animal models.

The study revealed a critical, previously unrecognized role for H2S in mediating the anti-infective functions of AMPs. They found that LL-37/CRAMP induces H2S production predominantly through the enzyme 3-mercaptopyruvate sulfurtransferase (3MST) in bacterial pathogens like Escherichia coli and Clostridium perfringens. This bacterially generated H2S was shown to participate in the accumulation of reactive oxygen species (ROS), ultimately leading to bacterial death via oxidative damage. Furthermore, in macrophages, LL-37 activated the Akt signaling pathway, which subsequently upregulated the expression of cystathionine γ-lyase (CSE), another key enzyme responsible for generating H2S. This macrophage-derived H2S plays a potential role in facilitating the immunomodulatory activity of LL-37/CRAMP. The researchers confirmed that:

H2S is involved in their in vivo anti-infective activity of LL-37. Beyond LL-37/CRAMP, the study demonstrated that AMPs from various other animal species also induce H2S production in both bacteria and macrophages, suggesting a ubiquitous and conserved mechanism.