Enhancing antimicrobial pathways in innate immune cells to combat bacterial infections in the lung
Rebecca Cooper grant 021765
Final Report 2021 (download here)
Respiratory infection is the sixth leading cause of death in Australia. Pneumonia caused 43,953 hospital admissions and more than 3,000 deaths in this country in 2002. Such infections are normally treated with antibiotics, but the growing problem of antibiotic resistance highlights an urgent and unmet need for alternative treatments. Macrophages, cells specialized in detecting and eradicating microbes, are the first line of defense. But some pathogens have evolved to evade these sentinels, silently “hitchhiking” them to survive and to disseminate through the organism. Our goal is to target and “boost” alveolar macrophages antimicrobial responses. In particular, our preliminary data showed that inhibiting HDAC6, a cytoplasmic histone deacetylase, enhances the bacterial clearance.
We first endeavour to understand the mechanism in which HDAC6 promotes antimicrobial responses. As HDAC6 interacts with mitochondria upon cellular stress, we investigated mitochondrial dynamics upon infection. These small organelles reside within our cells and are considered as their “powerhouse”. But they also have a wide range of proprieties and are incredibly dynamic organelles. Under different conditions, they can exist as a complex network (driven by fusion) or as fragmented organelles (driven by fission). We found that lipopolysaccharide, the main compound of Gram-negative bacteria, triggers mitochondrial fission, which contributes to the production of pro-inflammatory cytokines, key mediators that alert our organism during infection. We identified a large part of the activation pathway that uses Toll-like receptor 4, MyD88 and DRP-1 proteins. Furthermore, we characterised the role of HDAC6 in mitochondria dynamics, and how modulating this mechanism allows us to enhance acutely the antimicrobial activity of the macrophage, eliminating Salmonella and other Gram-negative bacteria.
We also confirmed that LPS promotes mitochondrial fission in alveolar macrophages and that inhibition of HDAC6 enhances the fission-dependent antimicrobial response against lung pathogen Pseudomonas aeruginosa. To validate our finding, we collaborated with Dr. Steven Zuryn, expert in mitochondria and the animal model C. elegans. Consistent with our previous results in mouse, we found that P. aeruginosa infection in worms triggered mitochondrial fission and that modulating the mitochondrial dynamic benefit the worm’s health.
Part of this work has been published in 2020 as an Outstanding Observation in Immunology & Cell Biology journal, the peer-reviewed journal of the Australian Society of Immunology1. Another part of this work has led to important finding in the role of HDAC6, mitochondrial fission and antibacterial response against Gram-negative bacteria. This large body of work is about to be submitted to a high- impact scientific journal. Finally, we have also investigated the impact of HDAC6 inhibition during infection with Pseudomonas aeruginosa infection, an important lung pathogen. These data are included in two manuscripts in preparation. Our findings have been presented at different international conference, including the Hunter Cell Biology Meeting and the World Congress for Immunology in Sydney, both in 2019. The importance of the Rebecca L. Cooper funding has been acknowledged in all presentations and publications.
At a career development level, this fund helped me to obtain a prestigious research grant in Europe funding my independent position. These findings will also be the foundation of an international collaboration with Australian researchers (e.g. NHMRC-Europe collaboration grant and ARC Discovery grant).
Image: a) LPS, a component of bacterial membrane, induces mitochondria fragmentation and pro- inflammatory cytokine release in macrophage. b) Treatment with HDAC inhibitor or genetic silencing promote bacterial clearance of Pseudomonas aeruginosa in alveolar macrophages.