Abstract
Tuberculosis is on the rise due to the increasing prevalence of multi-drug resistant strains. Understanding the host response to the causative pathogen, Mycobacterium tuberculosis, is critical to identify host-derived factors as potential therapeutic targets, circumventing bacterial resistance. However, there is a lack of whole-organism, in vivo, models in which to study host-mycobacterial interactions. In a zebrafish mycobacterial model, we have identified hypoxic signalling, via hypoxia inducible factor 1 alpha (Hif-1α), as a host-derived signalling pathway that modulates the host response to infection.
Hif-α was modulated in zebrafish embryos by expression of dominant active and negative variants. Mycobacterium marinum (Mm), a close relative of Mycobacterium tuberculosis and well-established TB model, was microinjected into Hif-α modulated embryos and the host response to infection was investigated.
Hif-α signalling was observed in infected macrophages early in pathogenesis but was not present at later stages. Stabilisation of Hif-1α led to decreased bacterial burden in an inducible nitric oxide synthase (iNOS) dependent manner (Elks et al., Plos Pathogens, 2013). iNOS is a leukocyte specific enzyme that produces nitric oxide (NO) as a bacterial killing mechanism. An anti-nitrotyrosine antibody assay was developed to investigate NO levels during Mm pathogenesis. Infection with Mm, either live or heat-killed, increased NO production by neutrophils. Hif-1α stabilisation primed neutrophils with NO, allowing them to better deal with Mm upon infection (Elks et al., unpublished). Furthermore, live (but not heat-killed) Mm were able to decrease neutrophil NO levels during pathogenesis, indicative of a reprogramming of leukocytes by Mm to allow for permissive conditions for the bacteria.
Our data show that Hif-1α and iNOS are important host-derived immune modulators that are initially activated after Mm infection only to be downregulated later in pathogenesis. Maintaining Hif-1α/NO levels may be a novel therapeutic strategy that circumvents the problem of multi-drug resistance.
Biography
I am a Vice Chancellor’s Fellow in the Department of Infection and Immunity at the University of Sheffield. Throughout my research career I have used the zebrafish as a model to understand human disease processes. I graduated from the University of Warwick in 2004 with a BSc in Biochemistry.
I moved to The University of Sheffield for the first time in 2004 to pursue a PhD in bone biology in a collaborative project between the, then newly forming, MRC Centre for Developmental and Biomedical Genetics (CDBG) (with Dr Henry Roehl) and the Medical School (with Professor Peter Croucher). During my PhD, I developed a zebrafish model of bone biology in which I went on study the roles of Wnt signalling in osteoblast development.
After my PhD I joined Professor Stephen Renshaw’s lab in The MRC Centre for Developmental and Biomedical Genetics (CDBG) for a post-doc where I developed molecular tools to manipulate hypoxia genetics (Hif) in zebrafish and was able to demonstrate that increased Hif signalling in zebrafish embryos prolongs neutrophilic inflammation.
I left the Renshaw lab in 2011 to pursue a European Respiratory Society Fellowship in the group of Dr Annemarie Meijer at the Cell Observatory, IBL, at Leiden University, The Netherlands to investigate the roles of Hif during bacterial infection. During my stay in Holland, I demonstrated that stabilisation of Hif aids the host after infection with Mycobacterium marinum.
I returned to the University of Sheffield in Summer 2013 as a Vice-Chancellor’s Fellow to set up my own independent research programme in the department of Infection and Immunity.