Autophagy is a fundamental degradative process, maintaining cellular homeostasis and functions in host defense against intracellular pathogens, including mycobacteria and Salmonella. The thesis... Show moreAutophagy is a fundamental degradative process, maintaining cellular homeostasis and functions in host defense against intracellular pathogens, including mycobacteria and Salmonella. The thesis investigated the function of an regulator of antibacterial autophagy, Damage Regulated Autophagy Modulator 1 (DRAM1) against infection and shows that DRAM1 restricts bacterial growth not only through canonical antibacterial autophagy (xenophagy) but also promotes an autophagy-related pathway, named LC3-associated phagocytosis (LAP). The function of DRAM1 in restricting bacterial proliferation is independent from the recognition of bacteria by xenophagy receptors. Mechanistically, DRAM1 promotes the infection-induced activation of autophagy and LAP as well as the maturation of bacteria-containing vesicles in both pathways. This maturation process, stimulated by DRAM1, involves multiple vesicle fusion steps directing bacteria to lysosomes. Through this maturation process, DRAM1 delivers the cytosolic protein Fau to bacteria-containing vesicles, where it serves as a precursor for antimicrobial peptides. The underlying mechanism may be explained by the discovery of an interaction between DRAM1 and the SNARE protein VTI1B. Overall, the work in this thesis contributes to ongoing research into the potential application of autophagy modulation as a host-directed therapy against infectious diseases. Show less
New drugs for use as tuberculosis (TB) treatment are needed due to the constrains of classical antibiotics against TB and the rise of antibiotic-resistant strains, making TB a harder and harder... Show moreNew drugs for use as tuberculosis (TB) treatment are needed due to the constrains of classical antibiotics against TB and the rise of antibiotic-resistant strains, making TB a harder and harder disease to treat. This thesis is focused on using the in vivo whole animalzebrafish embryo model for TB to evaluate potential anti-TB host-directed therapeutics (HDTs) arising from in vitro screens. Although in vitro screens for HDTs using cellular models can be performed at high throughput, a limiting step is the validation in whole animal models and translation of results to clinical applications. Due to the complex infection dynamics of mycobacteria, the use of whole animal models is indispensable in research into TB and the zebrafish model has contributed key findings about host-pathogen dynamics during mycobacterial infection. One of the most promising host targets of HDTs is autophagy, which is recognized as an important host-protective pathway. Boosting autophagy levels using HDTs could be a way to overcome the pathogen’s autophagy evasion strategies and could therefore be a promising therapeutic route. For this thesis we took advantage of the possibilities of the zebrafish embryo model for TB and the zebrafish toolkit to study several autophagy-modulating HDTs as potential anti-TB drugs. Show less
The effective treatment of tuberculosis (TB) remains a major challenge to global health. Drug-resistant Mycobacterium tuberculosis (Mtb) strains and co-infection with HIV further increase the... Show moreThe effective treatment of tuberculosis (TB) remains a major challenge to global health. Drug-resistant Mycobacterium tuberculosis (Mtb) strains and co-infection with HIV further increase the difficulty of controlling TB. Thus, under the current situation, it is essential to develop effective treatment strategies for Mtb infections. Autophagy is a lysosomal degradation process and substantial experimental evidence has demonstrated that autophagy is an important host immune defense mechanism against mycobacterial infection. However, the development of effective therapies requires a better understanding of the interaction between the host and invading pathogens to identify host processes that can be targeted. A useful tool for such studies is the zebrafish model for TB. Zebrafish can be infected with Mycobacterium marinum (Mm), which is closely related to Mtb and causes similar disease characteristics. Taking advantage of the zebrafish TB model, this thesis presents new in vivo evidence for the important function of autophagy to inhibit mycobacterial proliferation inside macrophages. Furthermore, this study supports that stimulating the innate host defense processes that are dependent on the autophagy modulator, Dram1, and the selective autophagy receptors, p62 and Optineurin, could be a useful strategy to explore for adjunctive treatment of antibiotic-resistant TB infections. Show less
This thesis focuses on the recognition of pathogenic bacteria and the defense mechanisms that are activated during the innate immune response to infection. Detection of pathogens, such as bacteria,... Show moreThis thesis focuses on the recognition of pathogenic bacteria and the defense mechanisms that are activated during the innate immune response to infection. Detection of pathogens, such as bacteria, viruses, and parasites, depends on receptors that bind to evolutionary conserved structures on their surface. The most extensively studied class of immune receptors is the Toll-like receptor (TLR) family, which signals via adaptor molecules such as myeloid differentiation factor 88 (MyD88) to initiate gene expression and activate the appropriate response upon recognition of a pathogen. We have used the zebrafish as a model organism to study how MyD88 orchestrates the immune response against intracellular bacterial pathogens like Mycobacterium marinum, the causative agent of tuberculosis disease (TB) in fish. We found that several defense mechanisms against TB are highly dependent on MyD88, including autophagy, cytokine and chemokine production, and the generation of microbe killing radicals. These findings in the zebrafish model will hopefully aid in the development of new therapeutic strategies against multi-drug resistant tuberculosis infections. Show less
