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How bacterial pathogens exploit host metabolism to promote immune tolerance and persist in infected hosts remains elusive. To achieve this, we show that Pseudomonas aeruginosa (PA), a recalcitrant pathogen, utilizes the quorum sensing (QS) signal 2’-aminoacetophenone (2-AA). Here, we unveil how 2-AA-driven immune tolerization causes distinct metabolic perturbations in murine macrophages’ mitochondrial respiration and bioenergetics. We present evidence indicating that these effects stem from decreased pyruvate transport into mitochondria. This reduction is attributed to decreased expression of the mitochondrial pyruvate carrier (Mpc1), which is mediated by diminished expression and nuclear presence of its transcriptional regulator, estrogenrelated nuclear receptor alpha (Esrra). Consequently, Esrra exhibits weakened binding to the Mpc1 promoter. This outcome arises from the impaired interaction between Esrra and the peroxisome proliferator-activated receptor gamma coactivator 1-alpha (Ppargc1a). Ultimately, this cascade results in diminished pyruvate influx into mitochondria and, consequently reduced ATP production in tolerized murine and human macrophages. Exogenously added ATP in infected macrophages restores the transcript levels of Mpc1 and Esrra and enhances cytokine production and intracellular bacterial clearance. Consistent with the in vitro findings, murine infection studies corroborate the 2-AA-mediated long-lasting decrease in ATP and acetyl-CoA and its association with PA persistence, further supporting this QS signaling molecule as the culprit of the host bioenergetic alterations and PA persistence. These findings unveil 2-AA as a modulator of cellular immunometabolism and reveal an unprecedented mechanism of host tolerance to infection involving the Ppargc1a/Esrra axis in its influence on Mpc1/OXPHOS-dependent energy production and PA clearance. These paradigmatic findings pave the way for developing treatments to bolster host resilience to pathogen-induced damage. Given that QS is a common characteristic of prokaryotes, it is likely that 2-AA-like molecules with similar functions may be present in other pathogens. [ABSTRACT FROM AUTHOR]

Vibrio cholerae activates proinflammatory response in cultured intestinal epithelial cells. In this study, we demonstrate that V. cholerae O395 infection of intestinal epithelial cells results in the activation of Akt. Inhibition of Akt significantly decreases IL-1α, IL-6, and TNF-α production in V. cholerae infected Int407 cells. Analysis of the mechanisms of Akt influences on cytokine response demonstrates that Akt promotes NF-κB activation. We have extended these findings to show that Akt activation may be regulated by bacterial genes associated with virulence, adherence, or motility. Insertion mutants in the virulence genes coding for CtxA, ToxT, and OmpU of V. cholerae modulate the activation of PI3K/Akt signaling pathway, whereas an aflagellate non-motile mutant (O395FLAN) and a adherent and less motile mutant (O395Y3N/O395Y4N) of V. cholerae both show very significant down-regulation of Akt activity in Int407 cells. Together, these observations indicate that Akt promotes proinflammatory cytokine production by V. cholerae infected human intestinal epithelial cells through its influences on NF-κB. [ABSTRACT FROM AUTHOR]

The mechanisms by which pathogens evade elimination without affecting host fitness are not well understood. For the pathogen Pseudomonas aeruginosa, this evasion appears to be triggered by excretion of the quorum sensing (QS) molecule 2-aminoacetophenone (2-AA), which dampens host immune responses and modulates host metabolism, thereby enabling the bacteria to persist at a high burden level. Here, we examined how 2-AA trains host tissues to become tolerant to a high bacterial burden, without compromising host fitness. We found that 2-AA regulates histone deacetylase1 (HDAC1) expression and activity, resulting in hypoacetylation of lysine 18 of histone H3 (H3K18) at pro-inflammatory cytokine loci. Specifically, 2-AA induced reprogramming of immune cells occurs via alterations in histone acetylation of immune cytokines in vivo and in vitro. This host epigenetic reprograming, which was maintained for up to 7 days, dampened host responses to subsequent exposure to 2-AA or other pathogen-associated molecules. The process was found to involve a distinct molecular mechanism of host chromatin regulation. Inhibition of HDAC1 prevented the immunomodulatory effects of 2-AA. These observations provide the first mechanistic example of a QS molecule regulating a host epigenome to enable tolerance of infection. These insights have enormous potential for developing preventive treatments against bacterial infections.

How bacterial pathogens exploit host metabolism to promote immune tolerance and persist in infected hosts remains elusive. To achieve this, we show that Pseudomonas aeruginosa (PA), a recalcitrant pathogen, utilizes the quorum sensing (QS) signal 2-aminoacetophenone (2-AA). Here, we unveil how 2-AA-driven immune tolerization causes distinct metabolic perturbations in macrophages mitochondrial respiration and bioenergetics. We present evidence indicating that these effects stem from decreased pyruvate transport into mitochondria. This reduction is attributed to decreased expression of the mitochondrial pyruvate carrier (MPC1), which is mediated by diminished expression and nuclear presence of its transcriptional regulator, estrogen-related nuclear receptor alpha (ERRα). Consequently, ERRα exhibits weakened binding to the MPC1 promoter. This outcome arises from the impaired interaction between ERRα and the peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α). Ultimately, this cascade results in diminished pyruvate influx into mitochondria and, consequently reduced ATP production in tolerized macrophages. Exogenously added ATP in infected macrophages restores the transcript levels of MPC1 and ERRα and enhances cytokine production and intracellular bacterial clearance. Consistent with the in vitro findings, murine infection studies corroborate the 2-AA-mediated long-lasting decrease in ATP and acetyl-CoA and its association with PA persistence, further supporting this QS signaling molecule as the culprit of the host bioenergetic alterations and PA persistence. These findings unveil 2-AA as a modulator of cellular immunometabolism and reveal an unprecedented mechanism of host tolerance to infection involving the PGC-1α/ERRα axis in its influence on MPC1/OXPHOS-dependent energy production and PA clearance. These paradigmatic findings pave the way for developing treatments to bolster host resilience to pathogen-induced damage. Given that QS is a common characteristic of prokaryotes, it is likely that 2-AA-like molecules with similar functions may be present in other pathogens.

Quorum sensing (QS) systems play global regulatory roles in bacterial virulence. They synchronize the expression of multiple virulence factors and they control and modulate bacterial antibiotic tolerance systems and host defense mechanisms. Therefore, it is important to obtain knowledge about QS modes of action and to test putative therapeutics that may interrupt QS actions in the context of infections. This chapter describes methods to study bacterial pathogenesis in murine acute and persistent/relapsing infection models, using the Gram-negative bacterial pathogen Pseudomonas aeruginosa as an example. These infection models can be used to probe bacterial virulence functions and in mechanistic studies, as well as for the assessment of the therapeutic potential of antibacterials, including anti-virulence agents.