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Remodelling of Mycobacterial Peptidoglycan During Cell Division and the Epigenetics of Macrophages during M. tuberculosis infection
Tuberculosis (TB) has emerged as the world’s most deleterious infectious disease. The etiological agent of TB, Mycobacterium tuberculosis (Mtb), has evolved the ability to evade the host immune system using several mechanisms; emphasising the need for novel treatment strategies. Peptidoglycan (PG) i...
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| Format: | Thesis |
| Language: | English |
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Institute of Infectious Disease and Molecular Medicine
2021
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| Summary: | Tuberculosis (TB) has emerged as the world’s most deleterious infectious disease. The etiological agent of
TB, Mycobacterium tuberculosis (Mtb), has evolved the ability to evade the host immune system using
several mechanisms; emphasising the need for novel treatment strategies. Peptidoglycan (PG) is an
important immunomodulatory heteropolysaccharide structure that can be shed during mycobacterial
infection with immunological consequences and as such, changes in PG structure are expected to have
important implications on disease progression and host responses. Mycobacterial amidases have been
shown to have important roles in the remodelling of PG during cell division in M. smegmatis and are
implicated in sensitivity to antibiotic treatment. However, their roles in modulating host immunity remain
unknown. Herein, we assess the immune responses to Mtb mutants defective for either one of two
amidases, Ami1 and Ami4, in bone marrow-derived macrophages (BMDM) and the C57BL/6 murine
models of tuberculosis. Both Ami1 and Ami4 deletion resulted in increased pro-inflammatory response in
BMDM. Infection with the Mtb Δami1 mutant in mice resulted in differential induction of proinflammatory cytokines and certain chemokines during the acute phase of the infection, an eff ect that
was abrogated in chronic phase infection. The Δami1mutant was found to be susceptible to antibiotics in
liquid growth culture but this sensitivity was negated in macrophages and reversed to a tolerant
phenotype in mice. The Δami4 mutant, by contrast, did not display differential antibiotic susceptibility
and did not significantly alter cytokine and chemokine responses relative to the wildtype control in mice.
These findings suggest that Ami1 and Ami4 in Mtb play a nonoverlapping role in antibiotic sensitivity and
modulating host immunity during tuberculosis.
Additionally, the specific epigenetic alterations which occur during host-Mtb infection that contribute to
immune evasion remain unknown. Here, we propose a method to elucidate transcriptomic changes in
both human primary monocyte-derived macrophages (MDM) and the Mtb bacillus with which they were
infected. In this study, we exhibit a dual-RNA-seq proof-of-concept methodology where, from a single
donor, we successfully sequence host RNA from infected MDMs as well as Mtb RNA enriched from those
same infected MDMs. Utilizing this optimised methodology, we aim to discover and model epigenetic and
transcriptional alterations as well as their effector proteins in primary human macrophages following Mtb
infection. Further, we aim to identify novel and annotated ncRNAs which are correlated with these
epigenetic modifications. |
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