Mycobacterium tuberculosis canonical virulence factors interfere with a late component of the TLR2 response

Abstract

For many intracellular pathogens, the phagosome is the site of events and interactions that shape infection outcome. Phagosomal membrane damage, in particular, is proposed to benefit invading pathogens. To define the innate immune consequences of this damage, we profiled macrophage transcriptional responses to wild-type Mycobacterium tuberculosis (Mtb) and mutants that fail to damage the phagosomal membrane. We identified a set of genes with enhanced expression in response to the mutants. These genes represented a late component of the TLR2-dependent transcriptional response to Mtb, distinct from an earlier component that included Tnf. Expression of the later component was inherent to TLR2 activation, dependent upon endosomal uptake, and enhanced by phagosome acidification. Canonical Mtb virulence factors that contribute to phagosomal membrane damage blunted phagosome acidification and undermined the endosome-specific response. Profiling cell survival and bacterial growth in macrophages demonstrated that the attenuation of these mutants is partially dependent upon TLR2. Further, TLR2 contributed to the attenuated phenotype of one of these mutants in a murine model of infection. These results demonstrate two distinct components of the TLR2 response and identify a component dependent upon endosomal uptake as a point where pathogenic bacteria interfere with the generation of effective inflammation. This interference promotes tuberculosis (TB) pathogenesis in both macrophage and murine infection models.

Mycobacterium tuberculosis Induces Irg1 in Murine Macrophages by a Pathway Involving Both TLR-2 and STING/IFNAR Signaling and Requiring Bacterial Phagocytosis

“…TLR-2 has been shown to activate both a cytoplasmic and an endosome-dependent signaling pathway ( Dietrich et al., 2010 ; Stack et al., 2014 ; Musilova et al., 2019 ) and based on the near total suppression of Irg1 expression resulting from inhibition of phagocytosis or endosomal acidification we speculate that TLR-2 stimulation of the gene is triggered primarily from the latter cellular site. This hypothesis is consistent with the findings of a recent study ( Hinman et al., 2021 ) that employed Mtb mutants to demonstrate distinct early and late components of the macrophage transcriptional response to Mtb and showed that the late component requires endosomal uptake and phagosome acidification. Importantly, they identify the Irg1 gene as present in this late gene cluster that includes a major set of TLR2 induced transcripts.…”

Single cell preparations ofMycobacterium tuberculosisdamage the mycobacterial envelope and disrupt macrophage interactions

“…2A ), eliciting significantly less Il1b , Il6 , Nos2 , and Tnf expression than the so/sp samples. A variety of Mtb PAMPs have been shown to activate TLR2 (Hinman et al, 2021). In order to establish whether the so/sp samples were activating TLR2-dependent pathways, we infected BMDMs from Tlr2 -/- mice.…”

mTOR-regulated Mitochondrial Metabolism Limits Mycobacterium-induced Cytotoxicity

“…Some studies find that Mtb infection boosts glycolysis while others find that it represses it (Braverman et al, 2016; Cumming et al, 2018; Gleeson et al, 2016; Huang et al, 2018; Lachmandas et al ., 2016; Shi et al, 2015). These conflicting findings may reflect the muted metabolic response to mycobacterial infection in comparison to LPS, perhaps because they largely evade TLR recognition (Cambier et al ., 2014a; Cambier et al ., 2014b; Hinman et al, 2021; Holscher et al, 2008; Mayer-Barber et al, 2010). Indeed, in vivo, we have shown that both Mm- and Mtb-infected macrophages exhibit small increases in mitochondrial respiration early on (Roca, 2022).…”