Abstract
Tuberculosis (TB) caused by Mycobacterium tuberculosis (Mtb) infection is the deadliest infectious disease and a global health problem. Macrophages (Mφs) and neutrophils that can phagocytose Mtb represent the first line of immune response to infection. Glycogen synthase kinase-3α/β (GSK-3α/β) represents a regulatory switch in host immune responses. However, the efficacy and molecular mechanisms of how GSK-3α/β interacts with Mtb infection in Mφs remain undefined. Here, we demonstrated that Mtb infection downregulated GSK-3α/β activity and promoted matrix metalloproteinase-1 (MMP-1) and MMP-9 expressions in Mφs derived from acute monocytic human leukemia THP-1 cells (THP-1-Mφs). We confirmed the upregulation of MMP-9 expression in tissues of TB patients compared with patients of chronic inflammation (CI). In THP-1-Mφs and C57BL/6 mice, GSK-3α/β inhibitor SB216763 significantly increased MMP-1/9 production and facilitated Mtb load, while MMP inhibitors blocked MMP-1/9 expression and Mtb infection. Consistently, GSK-3α/β silencing significantly increased MMP-1/9 expression and Mtb infection, while overexpression of GSK-3α/β and constitutive activated GSK-3α/β mutants significantly reduced MMP-1/9 expression and Mtb infection in THP-1-Mφs. MMP-1/9 silencing reduced Mtb infection, while overexpression of MMP-1/9 promoted Mtb infection in THP-1-Mφs. We further found that GSK-3α/β inhibition increased Mtb infection and MMP-1/9 expression was blocked by ERK1/2 inhibitor. Additionally, we showed that protein kinase C-δ (PKC-δ) and mammalian target of rapamycin (mTOR) reduced GSK-3α/β activity and promoted MMP-1/9 production in Mtb-infected THP-1-Mφs. In conclusion, this study suggests that PKC-δ-mTOR axis suppresses GSK-3α/β activation with acceleration of MMP-1/9 expression through phospho-ERK1/2. These results reveal a novel immune escape mechanism of Mtb and a novel crosstalk between these critical signaling pathways in anti-TB immunity.
Highlights
Tuberculosis (TB) caused by Mycobacterium tuberculosis (Mtb) infection remains a global health problem [1]
The results showed that both Ser21/9 and Tyr216/279 phosphorylation of GSK-3a/b were significantly decreased, making it difficult to estimate how GSK-3a/b activity is affected by Mtb infection
We found that Mtb infection decreased the ratio of phosphorylation level to total protein expression of glycogen synthase (GS), indicating GSK-3a/b activity was inhibited by Mtb infection (Figure 1A)
Summary
Tuberculosis (TB) caused by Mycobacterium tuberculosis (Mtb) infection remains a global health problem [1]. The successful establishment of long-term Mtb infection rests upon its ability to convert Mjs into a permissive cellular niche to circumvent host immune response, which leads to the development of TB [2]. GSK-3a/b is a constitutively active serine/threonine kinase [3]. GSK-3a/b plays vital roles in host immune responses through regulating different signaling pathways of immune cells [3, 4]. On one hand, GSK-3a/b activation can be detrimental to the host response against Francisella tularensis LVS infection by restraining inflammatory cytokine response [5]. GSK-3a/b can be beneficial to the host immune response against virus infection through activating IRF3 and NF-kB signaling pathways and IFN-b induction [6]. The exact efficacy and molecular mechanisms as how GSK-3a/b interacts with Mtb infection in Mjs remain undefined
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