The impact of mucociliary clearance on Mycobacterium tuberculosis pathogenesis

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Project Summary/Abstract. Over one million people died from tuberculosis in 2021. Current treatments are long, costly, and often induce severe adverse effects, but the current vaccine has not been improved in over 100 years. Improved understanding of the host factors that influence Mtb pathogenesis in the lung may dramatically improve control and transmission of Mtb between individuals. Before entering the alveolar macrophage, Mtb encounters respiratory mucins. Mucins are glycosylated macromolecules that encompass the first line of defense against pathogens. Respiratory mucins MUC5B and MUC5AC protect the lung from pathogens via mucociliary clearance, directly inhibiting antimicrobial growth, and altering macrophage signaling. However, little is known about how these macromolecules influence Mtb susceptibility and severity. In this pilot grant, we will evaluate how respiratory mucins impact Mtb pathogenesis using human genetic studies, combined with interrogation of their mechanism of action via small animal models recapitulating Muc5b or Muc5ac insufficiency, deficiency, or overexpression. Our long-term goal is to identify strategies for effective Mtb killing within the lung and improve mucosal delivery of relevant candidate Mtb vaccines. The objective of this grant is to characterize the mechanisms by which MUC5B and MUC5AC, the two commonest respiratory mucins, influence Mtb susceptibility and severity in human populations. The rationale for this study is that respiratory mucins are essential for mucociliary clearance, support a host of extracellular antimicrobial peptides and proteins in the lung, and coats pathogens to alter their pathogenicity in the lung. Our preliminary data demonstrates that common genetic variants in the MUC5B promoter region are associated with pulmonary TB and MUC5B mRNA expression in the lung, while variation in the MUC5AC gene region is associated with TB meningitis mortality and MUC5AC mRNA expression. The central hypothesis is that MUC5B and MUC5AC are physical barriers to infection and also modulate macrophage function and systemic immune homeostasis to worsen TB disease severity. In this grant, we will test this hypothesis by achieving the following specific aims: 1) We will define the functional SNPs that regulate MUC5B and MUC5AC gene expression in the lung, systemic immune responses to TB meningitis, and susceptibility to and severity of TB in a Vietnamese cohort. 2) We will determine the mechanism by which Muc5b and Muc5ac deficiency, knockout, and overexpression influence clinical and immune responses to Mtb using genetically modified mice infected with Mtb. This contribution is significant because mucins represent the first line of defense against Mtb infection, but their role in Mtb pathogenesis is unknown. The proposed work is innovative because we will investigate the mechanisms and effects of a known TB susceptibility gene using innovative mouse models of disease, combined with the genetic cohorts of TB susceptibility. These studies will provide evidence that Mtb host defense begins prior to macrophage infection and provide clues toward the role of the immune microenvironment on Mtb outcomes.