Mycobacterium tuberculosis subverts negative regulatory pathways in human macrophages to drive immunopathology.

Tuberculosis remains a global pandemic and drives lung matrix destruction to transmit. Whilst pathways driving inflammatory responses in macrophages have been relatively well described, negative regulatory pathways are less well defined. We hypothesised that Mycobacterium tuberculosis (Mtb) specifically targets negative regulatory pathways to augment immunopathology.

In an in vitro model of human tuberculosis, monocyte-microglial networks regulate matrix metalloproteinase-1 and -3 gene expression and secretion via a p38 mitogen activated protein kinase-dependent pathway.

Background: Tuberculosis (TB) of the central nervous system (CNS) is characterized by extensive tissue inflammation, driven by molecules that cleave extracellular matrix such as matrix metalloproteinase (MMP)-1 and MMP-3. However, relatively little is known about the regulation of these MMPs in the CNS.

Methods: Using a cellular model of CNS TB, we stimulated a human microglial cell line (CHME3) with conditioned medium from Mycobacterium tuberculosis-infected primary human monocytes (CoMTb).

Important role for Mycobacterium tuberculosis UvrD1 in pathogenesis and persistence apart from its function in nucleotide excision repair.

Mycobacterium tuberculosis survives and replicates in macrophages, where it is exposed to reactive oxygen and nitrogen species that damage DNA. In this study, we investigated the roles of UvrA and UvrD1, thought to be parts of the nucleotide excision repair pathway of M. tuberculosis.

Matrix metalloproteinase-1 is regulated in tuberculosis by a p38 MAPK-dependent, p-aminosalicylic acid-sensitive signaling cascade.

Mycobacterium tuberculosis (M. tb) must cause lung disease to spread. Matrix metalloproteinases (MMPs) degrade the extracellular matrix and are implicated in tuberculosis-driven tissue destruction.

The protonmotive force is required for maintaining ATP homeostasis and viability of hypoxic, nonreplicating Mycobacterium tuberculosis.

The persistence of Mycobacterium tuberculosis despite prolonged chemotherapy represents a major obstacle for the control of tuberculosis. The mechanisms used by Mtb to persist in a quiescent state are largely unknown. Chemical genetic and genetic approaches were used here to study the physiology of hypoxic nonreplicating mycobacteria.

The mycobacterium-specific gene Rv2719c is DNA damage inducible independently of RecA.

The mycobacterium-specific gene Rv2719c was found to be expressed primarily from a promoter that was clearly DNA damage inducible independently of RecA. Upstream of the transcriptional start site for this promoter, sequence motifs resembling those observed previously at the RecA-independent, DNA damage-inducible recA promoter were identified, and the -10 motif was demonstrated by mutational analysis in transcriptional fusion constructs to be important for expression of Rv2719c.

The majority of inducible DNA repair genes in Mycobacterium tuberculosis are induced independently of RecA.

In many species of bacteria most inducible DNA repair genes are regulated by LexA homologues and are dependent on RecA for induction. We have shown previously by analysing the induction of recA that two mechanisms for the induction of gene expression following DNA damage exist in Mycobacterium tuberculosis. Whereas one of these depends on RecA and LexA in the classical way, the other mechanism is independent of both of these proteins and induction occurs in the absence of RecA.

Definition of the mycobacterial SOS box and use to identify LexA-regulated genes in Mycobacterium tuberculosis.

The bases of the mycobacterial SOS box important for LexA binding were determined by replacing each base with every other and examining the effect on the induction of a reporter gene following DNA damage. This analysis revealed that the SOS box was longer than originally thought by 2 bp in each half of the palindromic site. A search of the Mycobacterium tuberculosis genome sequence with the new consensus, TCGAAC(N)(4)GTTCGA, identified 4 sites which were perfect matches and 12 sites with a single mismatch which were predicted to bind LexA.