Arabinogalactan enhances Mycobacterium marinum virulence by suppressing host innate immune responses

Abstract

Arabinogalactan (AG) participates in forming the cell wall core of mycobacteria, a structure known as the mAGP complex. Few studies have reported the virulence of inartificial AG or its interaction with the host immune system. Using clustered regularly interspaced short palindromic repeats interference gene editing technology, conditional Mycobacterium marinum mutants were constructed with a low expression of embA or glfT2 (EmbA_KD or GlfT2_KD), which are separately involved in the biosynthesis of AG arabinose and galactose domains. High-performance gel permeation chromatography and high-performance liquid chromatography assays confirmed that the EmbA_KD strain showed a remarkable decrease in AG content with fragmentary arabinose chains, and the GlfT2_KD strain displayed less reduction in content with cut-down galactose chains. Based on transmission and scanning electron microscopy observations, the cell walls of the two mutants were found to be dramatically thickened, and the boundaries of different layers were more distinct. Phenotypes including the over-secretion of extracellular substances and enhanced spreading motility with a concomitant decreased resistance to ethambutol appeared in the EmbA_KD strain. The EmbA_KD and GlfT2_KD strains displayed limited intracellular proliferation after infecting murine J774A.1 macrophages. The disease progression infected with the EmbA_KD or GlfT2_KD strain significantly slowed down in zebrafish/murine tail infection models as well. Through transcriptome profiling, macrophages infected by EmbA_KD/GlfT2_KD strains showed enhanced oxidative metabolism. The cell survival measured using the CCK8 assay of macrophages exposed to the EmbA_KD strain was upregulated and consistent with the pathway enrichment analysis of differentially expressed genes in terms of cell cycle/apoptosis. The overexpression of C/EBPβ and the increasing secretion of proinflammatory cytokines were validated in the macrophages infected by the EmbA_KD mutant. In conclusion, the AG of Mycobacterium appears to restrain the host innate immune responses to enhance intracellular proliferation by interfering with oxidative metabolism and causing macrophage death. The arabinose chains of AG influence the Mycobacterium virulence and pathogenicity to a greater extent.

Syringaldehyde Exhibits Antibacterial and Antioxidant Activities against Mycobacterium marinum Infection

“…In our study, we found that supplementation with SA has no effects on the growth of Mm , while noticeably inhibiting Mm invasion into the lung epithelial cells. This lack of effect on Mm growth may be attributed to the arabinogalactan-containing cell wall of Mm , which serves as a natural barrier between Mycobacterium and antibiotics [ 45 ]. Next, a series of experiments in our study demonstrated that SA suppresses the production of proinflammatory cytokines and inhibits the expression of iNOS and COX-2 in macrophages after Mm infection, parallel to the protective role of SA in isoproterenol-induced cardiotoxicity rats [ 29 ], suggesting it has potential anti-inflammatory properties.…”

Combined clinical significance of MRI and serum mannose-binding lectin in the prediction of spinal tuberculosis

“…Tuberculosis, a widespread global infectious disease, is caused by Mycobacterium tuberculosis [ 1 ]. Spinal tuberculosis (STB) accounts for about 2% of all tuberculosis cases, about 15% of extra-pulmonary tuberculosis, and 50% of all bone tuberculosis, making it the most common form of bone and joint tuberculosis [ 2 ].…”