Regulators of IFN-gamma responses during Mycobacterium tuberculosis infection

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Summary Tuberculosis (TB) is a leading cause of death by infectious disease worldwide. Current therapy requires at least six months of treatment and there is no effective vaccine that prevents pulmonary disease. There is a critical need to develop new therapies that will shorten treatment time and activate protective responses to prevent TB progression. Unfortunately, we continue to lack a fundamental understanding of the host immune pathways that protect against TB. While the cytokine interferon γ (IFNγ) is absolutely required, the precise mechanisms that drive IFNγ-mediated protection remain unclear. This is because IFNγ is a pleotropic mediator that controls both bacterial growth and the inflammatory response in the lungs, while bridging the innate and adaptive immune responses. To dissect the complex regulation of IFNγ responses, we conducted a genome-wide CRISPR Cas9 screens in macrophages to define the networks required for the IFNγ-mediated surface expression of MHCII. This screen uncovered an important role for the glycerol 3 kinase beta (GSK3b) in controlling IFNγ-dependent MHCII expression. Using chemical and genetic approaches coupled with transcriptome analysis we found that GSK3b and the paralog GSK3a contribute to the expression of a subset of IFNγ-inducible genes. Further mechanistic studies found that the loss of GSK3a/b blocks the ability of macrophages to serve as antigen presenting cells to CD4+ T cells ex vivo and results in dysregulated cytokine production by macrophages during M. tuberculosis infection. Thus, GSK3a/b balances the cellular response to IFNγ to protect against infection without driving inflammatory tissue damage. These data lead to the hypothesis that GSK3a/b is a critical mediator of the IFNγ response during TB in vivo. This proposal will use genetic approaches combined with in vivo models to dissect the role of GSK3a/b-mediated control of IFNγ responses and TB. Aim 1 will understand the mechanisms that regulate GSK3a/b control of IFNγ responses and determine how M. tuberculosis modulates GSK3a/b activity. In Aim 2, we will use unique models of bacterial control and inflammation to examine how the loss of myeloid-specific GSK3a and/or GSK3b disrupts the IFNγ-mediated control of M. tuberculosis growth and tissue damage. Finally, in Aim 3 we will use M. tuberculosis specific TCR-transgenic T cell mice to test the hypothesis that the loss of myeloid GSK3a and/or GSK3b results in reduced T cell responses and ineffective protection against TB. Together these aims will dissect the role of GSK3a/b in controlling IFNγ-responses and protecting against TB. These mechanisms can then be leveraged to develop new therapies that may shorten treatment times and prevent TB disease progression.