Biology subjects

Helaine, S.

Publications and source records attributed to Helaine, S..

4 recordsLinked to original sources

bioRxiv2026

Multimodal temporal mapping of macrophage transcriptome remodeling during Salmonella infection

Macrophages are equipped to eliminate invading pathogens, yet several intracellular bacteria exploit them as replicative niches. Salmonella enterica serovar Typhimurium subverts host immunity by injecting effector proteins that remodel macrophage functions. While macrophages typically induce a pro-inflammatory program upon bacterial invasion, Salmonella can redirect them toward an anti-inflammatory and replication-permissive state via manipulation of the NF-{kappa}B and STAT3 host transcription factors. How the integration of the effects on these two transcription factors and potentially others underpins this reprogramming remains poorly charted. Here, we use a multipronged approach combining a bacterial reporter, temporal single-cell RNA-seq with RNA metabolic labeling, transcription factor (TF) footprinting, and single-cell CRISPR perturbations to dissect macrophage polarization dynamics during early infection. We catch the bifurcation during infection, where a subset of macrophages transition toward the anti-inflammatory phenotype. This shift involves the activation of Salmonella pathogenicity island 2 (SPI2) leading to both the dampening of the initial NF-{kappa}B-driven inflammatory program and the induction of specific transcriptional modules beyond NF-{kappa}B and STAT3, with possible contributions from AP-1 and Maf family members. Together, our study uncovers host decision points in macrophage polarization circuitry and reveals a vulnerability exploited by Salmonella to modulate host immunity. HIGHLIGHTSO_LITemporal scRNA-seq defines the emergence of inflammatory and anti-inflammatory macrophage states concomitant with Salmonella Typhimurium SPI2 induction. C_LIO_LIA critical decision point for infection outcome is reached by 6 hours post-infection. C_LIO_LIMacrophage reprogramming is associated with widespread chromatin remodeling and dynamic transcription factor binding. C_LIO_LISingle-cell perturb-seq experiment uncovers Cybb and Foxo1 as modulators of infection outcome in Hoxb8 macrophages. C_LI

genomics↗

bioRxiv2024

A host-directed adjuvant resuscitates and sensitizes intracellular bacterial persisters to antibiotics

There are two major problems in the field of antimicrobial chemotherapy-antibiotic resistance and antibiotic tolerance. In the case of antibiotic tolerance, antibiotics fail to kill the bacteria as their phenotypic state affords them protection from the bactericidal activity of the antibiotic. Antibiotic tolerance can affect an entire bacterial population, or a subset of cells known as persister cells. Interaction with the host induces the formation of persister cells in numerous pathogens, with reactive oxygen and nitrogen species production being heavily implicated in the collapse of bacterial energy levels and entrance into an antibiotic tolerant state. Here, we developed a high-throughput screen to identify energy modulators for intracellular Staphylococcus aureus. The identified compound, KL1, increases intracellular bacterial energy and sensitizes the persister population to antibiotics, without causing cytotoxicity or bacterial outgrowth. We demonstrate that KL1 exhibits adjuvant activity in a murine model of S. aureus bacteremia and intracellular infection of Salmonella Typhimurium. Transcriptomic analysis and further studies on its mechanism of action reveal that KL1 modulates host immune response genes and suppresses the production of reactive species in host macrophages, alleviating one of the major stressors that induce antibiotic tolerance. Our findings highlight the potential to target intracellular persister cells by stimulating their metabolism and encourage larger efforts to address antibiotic tolerance at the host-pathogen interface, particularly within the intracellular milieu.

microbiology↗

bioRxiv2022

Identification of two pyruvate transporters in Salmonella enterica serovar Typhimurium and their biological relevance

Pyruvate (CH3COCOOH) is the simplest of the alpha-keto acids and is at the interface of several metabolic pathways both in prokaryotes and eukaryotes. In an amino acid-rich environment, fast-growing bacteria excrete pyruvate instead of completely metabolizing it. The role of pyruvate uptake in pathological conditions is still unclear. In this study, we identified two pyruvate-specific transporters, BtsT and CstA, in Salmonella enterica serovar Typhimurium (S. Typhimurium). Expression of btsT is induced by the histidine kinase/response regulator system BtsS/BtsR upon sensing extracellular pyruvate (threshold 200 M), whereas expression of cstA is maximal in the stationary phase. Both pyruvate transporters were found to be important for the uptake of this compound, but also for chemotaxis to pyruvate, survival under oxidative and nitrosative stress, and persistence of S. Typhimurium in response to gentamicin. Compared with the wild-type, the {Delta}btsT{Delta}cstA mutant has disadvantages in antibiotic persistence in macrophages, as well as in colonization and systemic infection in gnotobiotic mice. These data demonstrate the surprising complexity of the two pyruvate uptake systems in S. Typhimurium.

microbiology↗

bioRxiv2021

A tRNA-acetylating toxin and detoxifying enzyme in Mycobacterium tuberculosis.

Toxin-antitoxin (TA) systems allow bacteria to adapt to changing environments without altering gene expression. Despite being overrepresented in Mycobacterium tuberculosis (Mtb), their individual physiological roles remain elusive. We describe a TA system in Mtb which we have named TacAT due to its homology to previously discovered systems in Salmonella. The toxin, TacT, blocks growth by acetylating glycyl-tRNAs and inhibiting translation. Its effects are reversed by the enzyme peptidyl tRNA hydrolase (Pth), which also cleaves peptidyl tRNAs that are prematurely released from stalled ribosomes. Pth is essential in most bacteria and thereby has been proposed as a promising drug target for complex pathogens like Mtb. Transposon sequencing data suggest that the tacAT operon is nonessential for Mtb growth in vitro, and premature stop mutations in this TA system present in some clinical isolates suggest that it is also dispensable in vivo. We assessed whether TacT modulates pth essentiality in Mtb, as drugs targeting Pth might be ineffective if TacAT is disrupted. We find that pth essentiality is unaffected by the absence of tacAT. These results highlight a fundamental aspect of mycobacterial biology and indicate that Pths essential role hinges on its peptidyl-tRNA hydrolase activity. Our work underscores Pths potential as a viable target for new antibiotics.

microbiology↗