A Bumpy Ride of Mycobacterial Phagosome Maturation: Roleplay of Coronin1 Through Cofilin1 and cAMP

The expression of Nramp1 modulates the uptake of Mycobacterium tuberculosis by macrophages through alternating inflammatory responses

Natural-resistance-associated macrophage protein-1 (NRAMP1) is a transmembrane protein of the mammalian SLC11 gene family. Previously, genome-wide association study (GWAS) have shown that the single nucleotide polymorphisms (SNPs) of NRAMP1 are associated with human susceptibility to tuberculosis (TB), and the detection of clinical samples have demonstrated that the expression levels of NRAMP1 are concomitant with the susceptibility to TB in humans and cows, but underlying mechanism is unknown. In this study, we completed a series of experiments to investigate how the expression of Nramp1 affects the infection of macrophages with Mycobacterium tuberculosis (Mtb). We found that the increase of Nramp1 expression induced the decrease of Mtb infection efficiency and the higher-level expression of pro-inflammatory cytokines and chemokines, However, the knockdown of Nramp1 promoted the efficiency of bacilli infection to macrophages and induced lower-levels of expression of pro-inflammatory cytokines and chemokines. Collectively, the results in this study demonstrated that the levels of Nramp1 expression affect Mtb infection of macrophage and regulate pro-inflammatory responses of macrophages to Mtb infection, indicating the population with the low-expression level of NRAMP1 predispose to Mtb infection and TB development, and suggesting SNPs in NRAMP1 modulate the host susceptibility to TB through its regulation of NRAMP1 expression.

Cofilin‑1 as a potential biomarker for Mycobacterium tuberculosis infection

Tuberculosis (TB) induced by Mycobacterium tuberculosis (M. tb), is one of the deadliest human infections worldwide. Our previous studies demonstrated cofilin-1 (CFL1) expression was significantly increased in exosomes from Mycobacterium avium (M. avium)-infected macrophages. The expression of CFL1 protein in M. tb infected hosts was investigated in the present study to predict whether CFL1 could have potential as a biomarker for M. tb infection. In the present study, the mRNA and protein expression levels of CFL1 in M. avium-infected macrophages and supernatants were analyzed via reverse transcription-quantitative PCR and western blotting. Furthermore, CFL1 expression in macrophages was knocked down in vivo, and then CFL1 expression levels in M. avium-infected macrophages and supernatant were detected via western blotting and ELISA. In addition, CFL1 was detected in the peripheral blood mononuclear cells and plasma of patients with TB using western blotting and ELISA. The specificity and sensitivity of CFL1 as a biomarker and the association between TB infection and normal individuals were compared and analyzed using GraphPad Prism 5. CFL1 protein expression levels were significantly increased in M. avium-infected macrophages and supernatant. Meanwhile, CFL1 was upregulated in patients with TB. Bioinformatics statistics indicated the high specificity and sensitivity of CFL1 in patients with TB. Thus, these results suggest that CFL1 may act as a potential biomarker of TB infection.