Antinori, B. | bioRxiv Science

bioRxiv2024

Chronic mycobacteria infection triggers macrophage senescence

Chronic infections with intracellular pathogens such as Mycobacterium abscessus (Mab) pose significant health challenges due to their capacity to persist within host cells and evade immune responses. This study investigates the cellular responses to chronic Mab infection in macrophages, particularly focusing on cellular senescence. Using an in vitro model of chronic infection in murine alveolar-like macrophages, we found that Mab induces a senescent phenotype characterised by decreased proliferation, altered morphology, DNA damage signalling activation, and upregulation of senescence markers such as p21 and SA-{beta}-galactosidase. Intriguingly, senescent macrophages secreted pro-inflammatory cytokines, consistent with a senescence-associated secretory phenotype (SASP), which promoted secondary senescence in neighbouring uninfected cells. This paracrine transmission of senescence underscores a potentially deleterious effect of Mab-induced SASP on tissue microenvironments, fostering a pro-inflammatory niche that may contribute to pathogen persistence. These findings highlight Mab-induced senescence as a key factor in chronic infection pathology, suggesting that targeting senescent cells and SASP-related pathways could enhance treatment outcomes in chronic bacterial infections.

microbiology↗

bioRxiv2023

Endolysin B: A new archetype in M. tuberculosis treatment

So far it is thanks to antibiotics that illnesses, such as Tuberculosis (TB), are treatable. However, antimicrobial misuse combined with Mycobacterium tuberculosis phenotypic plasticity are nullifying the effects of the existing therapies. As a result, increasingly people are dying (one person dies of TB every 20 seconds), especially due to the rise of multi-and extensively drug-resistant strains. There is indeed a urgent need for new and more effective therapies, which should match the requirement of avoiding the rise in drug resistance. Among them, the use of bacteriophage - bacteria-restricted viruses - or simply phage lytic enzyme (i.e., endolysin) represents one of the most promising alternatives. All phages encode for the endolysin A (LysA), which degrades the bacteria cell wall, finally leading to the release of the newly synthesized virions. Nevertheless, mycobacteriophages (bacterial viruses selectively infecting mycobacteria), evolved the additional endolysin B (LysB) to selectively damage the complex mycobacteria cell wall, and to evade from their host. LysB, owing a lipolytic enzyme, can degrade the thick mycolic acid layer, and hence disrupt the integrity of the mycobacterial membrane. Despite its key role in mediating mycobacteria lysis, the molecular mechanism regulating LysB binding to its target remains poorly characterized. Herein, we selected Ms6LysB and created a fluorescent engineered version as a proxy to analyze LysB binding qualitatively and quantitatively to both the fast-growing non-pathogenic Mycobacterium smegmatis and the slow-growing pathogenic M. tuberculosis. Additionally, we shed light on LysB antimicrobial activity upon M. tuberculosis infection, by using alveolar-like mouse macrophages (mAMs) as a cellular model that closely recapitulates the natural niche of M. tuberculosis infection. Our study provides the proof-of-principle that Ms6 LysB binding to the outer mycobacterial membrane can impair M. tuberculosis growth homeostasis and that LysB retain its lytic properties even when internalized by mAMs. This lays the groundwork for the use of LysB as a new therapeutic strategy to undermine M. tuberculosis infection.

microbiology↗