Biology subjects

Santoni, K.

Publications and source records attributed to Santoni, K..

7 recordsLinked to original sources

bioRxiv2026

The capsule of hypervirulent Klebsiella pneumoniae maintains neutrophils in neutral activation state

Hypervirulent Klebsiella pneumoniae (hvKp) cause invasive infections despite robust neutrophil recruitment, yet the mechanisms enabling persistence in neutrophil-rich environments remain poorly defined. Here, we show that hvKp do not simply resist neutrophil antimicrobial mechanisms but instead constrain neutrophils into a neutral functional state characterised by limited bactericidal activity. Using genetic dissection of the rmpADC locus, pharmacological inhibition of neutrophil effector pathways, and analysis of a diverse panel of clinical isolates, we demonstrate that rmpADC-driven capsule properties uncouple neutrophil recognition and activation from bacterial killing. Deletion of rmpADC restores phagocytosis, degranulation, and intraphagosomal killing, whereas loss of individual rmpD or rmpC permits neutrophil activation without bacterial killing. Moreover, hypermucoviscosity alone is sufficient to protect bacteria from neutrophil-mediated killing across multiple genetic backgrounds. Together, these findings identify capsule-driven immune state control as a central mechanism of hvKp neutrophil evasion and reveal distinct thresholds governing neutrophil activation and bactericidal outcome.

immunology↗

bioRxiv2025

Capsule-mediated O-antigen masking protects hypervirulent Klebsiella pneumoniae from neutrophil killing

Klebsiella pneumoniae is listed as a critical priority pathogen by the WHO due to prevalent extended-spectrum {beta}-lactamase and carbapenem resistance and high mortality rates Hypervirulent K. pneumoniae (hvKp) causes life-threatening infections in immunocompetent individuals, while classical K. pneumoniae (cKp) causes nosocomial infections in immunosuppressed patients. The convergence of hypervirulence with antibiotic resistance is now a major global health threat. Using a murine pulmonary infection model, we show that hvKp resisted clearance despite significant neutrophil recruitment. Using clinical hvKp and cKp isolates, bone marrow derived neutrophils, cell biology, pharmacology and imaging (both light and electron microscopy) in ex vivo assays revealed that the hvKp hypermucoviscous capsule prevents bacterial recognition and neutrophil activation, blocking ROS production, degranulation, and neutrophil extracellular traps (NETs) formation. In the absence of capsule ({Delta}wcaJ) or hypermucoid capsule determinants ({Delta}rmpADC), hvKp activates neutrophils, leading to degranulation, NET formation and bacterial killing. While superimposing the absence of O-antigen ({Delta}rfb) on the {Delta}wcaJ abrogates degranulation, neutrophils still elaborate NETs that eliminate the {Delta}wcaJ/{Delta}rfb mutant at high efficiency. This suggests that O-antigen is a double-edged sword, functioning as a PAMP triggering neutrophil degranulation yet assisting the pathogen to evade NET-mediated destruction. These findings shed light on the mechanism underpinning immune evasion by the hypervirulent capsule in hvKp.

microbiology↗

bioRxiv2023

Leishmania infantum-exploited Nrf2 transcription factor as a virulence process to escape macrophage-driven ferroptosis-like leishmanicidal process

Macrophages are the main effector cells during Leishmania infection. They contribute to the detection and elimination of Leishmania spp. and may also promote parasite resilience. Here, we report that the activation of the transcription factor Nrf2 in macrophages plays a pivotal role in the progression of Leishmania infantum infection by controlling inflammation and redox balance of macrophages. We also highlight the involvement of NOX2/ROS axis in the early Nrf2 activation and subsequently of PGE2/EP2r signalling in the sustainment of Nrf2 activation upon L. infantum infection. Moreover, we establish macrophage-driven ferroptosis-like process as a cell death program of L. infantum and the protective effect of Nrf2 in macrophages against L. infantum death. Altogether, these results identify Nrf2 as a critical factor for the susceptibility of Leishmania infantum infection, highlighting Nrf2 as a promising pharmacological target for the development of new therapeutic approaches for the treatment of visceral leishmaniasis.

microbiology↗

bioRxiv2023

EEF2-inactivating toxins engage the NLRP1 inflammasome and promote epithelial barrier disruption upon Pseudomonas infection

The intracellular inflammasome complex have been implicated in the maladaptive tissue damage and inflammation observed in chronic Pseudomonas aeruginosa infection. Human airway and corneal epithelial cells, which are critically altered during chronic infections mediated by P. aeruginosa, specifically express the inflammasome sensor NLRP1. Here, together with a companion study, we report that the NLRP1 inflammasome detects Exotoxin A (EXOA), a ribotoxin released by P. aeruginosa Type 2 Secretion System (T2SS) during chronic infection. Mechanistically, EXOA-driven Eukaryotic Elongation Factor 2 (EEF2) ribosylation and covalent inactivation promotes ribotoxic stress and subsequent NLRP1 inflammasome activation, a process shared with other EEF2-inactivating toxins, Diphtheria Toxin and Cholix Toxin. Biochemically, irreversible EEF2 inactivation triggers ribosome stress-associated kinases ZAK- and P38-dependent NLRP1 phosphorylation and subsequent proteasome-driven functional degradation. Finally, Cystic Fibrosis cells from patients exhibit exacerbated P38 activity and hypersensitivity to EXOA-induced ribotoxic stress-dependent NLRP1 inflammasome activation, a process inhibited by the use of ZAK inhibitors. Altogether, our results show the importance of P. aeruginosa virulence factor EXOA at promoting NLRP1-dependent epithelial damage and identify ZAK as a critical sensor of virulence-inactivated EEF2. KEY POINTSO_LIP. aeruginosa induces NLRP1-dependent pyroptosis in human corneal and nasal epithelial cells C_LIO_LIP. aeruginosa Exotoxin A (EXOA) and other EEF2-inactivating bacterial exotoxins activate the human NLRP1 inflammasome C_LIO_LIEEF2 inactivation promotes ribotoxic stress response and ZAK kinase-dependent NLRP1 inflammasome activation. C_LIO_LIBronchial epithelial cells from Cystic Fibrosis patients show extreme sensitivity to ribotoxic stress-dependent NLRP1 inflammasome activation in response to Exotoxin A C_LIO_LIP38 and ZAK inhibition protects Cystic Fibrosis epithelial cell from EXOA-induced pyroptosis C_LI

immunology↗

bioRxiv2021

Pseudomonas aeruginosa infection reveals a Caspase-1-dependent neutrophil pyroptosis pathway that restrains damaging Histone release

Multiple neutrophil death programs contribute to host defense against infections. Although expressing all necessary components, neutrophils specifically fail to undergo pyroptosis, a lytic form of cell death triggered by the activation of the pro-inflammatory complex inflammasome. In the light of the arm race, we hypothesized that intrinsic neutrophil pyroptosis resistance might be bypassed in response to specific microbial species. We show that Pseudomonas aeruginosa (P. aeruginosa) stimulates Caspase-1-dependent pyroptosis in human and murine neutrophils. Mechanistically, activated NLRC4 inflammasome supports Caspase-1-driven Gasdermin-D (GSDMD) activation, IL-1{beta} cytokine release and neutrophil pyroptosis. Furthermore, GSDMD activates Peptidyl Arginine Deaminase-4 which drives an "incomplete NETosis" where neutrophil DNA fills the cell cytosol but fails crossing plasma membrane. Finally, we show that neutrophil Caspase-1 account for IL-1{beta} production and contributes to various P. aeruginosa strains spread in mice. Overall, we demonstrate that neutrophils are fully competent for Caspase-1-dependent pyroptosis, which drives an unsuspected "incomplete NETosis". SummaryNeutrophils play an essential roles against infections. Although multiple neutrophil death programs contribute to host defense against infections, they fail to undergo pyroptosis, a pro-inflammatory form of cell death. Upon Infections, pyroptosis can be induced in macrophages or epithelial cells upon activation of pro-inflammatory complexes, inflammasomes that trigger Caspase-1-driven Gasdermin dependent plasma membrane lysis. In the light of host-microbe interactions, we hypothesized that yet to find microbial species might hold the capacity to overcome neutrophil resistance to inflammasome-driven pyroptosis. Among several bacterial species, we describe that the bacterium Pseudomonas aeruginosa specifically engages the NLRC4 inflammasome, which promotes Caspase-1-dependent Gasdermin-D activation and subsequent neutrophil pyroptosis. Furthermore, inflammasome-driven pyroptosis leads to DNA decondensation and expansion into the host cell cytosol but not to the so called Neutrophil Extracellular Trap (NET) release as DNA fails breaching the plasma membrane. Finally, in vivo P. aeruginosa infections highlight that Caspase-1-driven neutrophil pyroptosis is functional and is detrimental upon P. aeruginosa infection. Altogether, our results unexpectedly underline neutrophil competence for Caspase-1-dependent pyroptosis, a process that contributes to host susceptibility to P. aeruginosa infection.

immunology↗

bioRxiv2021

Phospholipid peroxidation fuels ExoU phospholipase-dependent cell necrosis and supports Pseudomonas aeruginosa-driven pathology

Regulated cell necrosis supports immune and anti-infectious strategies of the body; however, dysregulation of these processes drives pathological organ damage. Pseudomonas aeruginosa expresses a phospholipase, ExoU that triggers pathological host cell necrosis through a poorly characterized pathway. Here, we investigated the molecular and cellular mechanisms of ExoU-mediated necrosis. We show that cellular peroxidised phospholipids enhance ExoU phospholipase activity, which drives necrosis of immune and non-immune cells. Conversely, both the endogenous lipid peroxidation regulator GPX4 and the pharmacological inhibition of lipid peroxidation delay ExoU-dependent cell necrosis and improve bacterial elimination in vitro and in vivo. Our findings also pertain to the ExoU-related phospholipase from the bacterial pathogen Burkholderia thailandensis, suggesting that exploitation of peroxidised phospholipids might be a conserved virulence mechanism among various microbial phospholipases. Overall, our results identify an original lipid peroxidation-based virulence mechanism as a strong contributor of microbial phospholipase-driven pathology.

immunology↗

bioRxiv2020

Irgm2 and Gate-16 cooperatively dampen targeting of caspase-11 to Gram-negative bacterial products

Inflammatory caspase-11 (rodent) and caspases-4 and -5 (human) detect gram-negative bacterial component LPS in the host cell cytosol, which promotes activation of the non-canonical inflammasome. Although non-canonical inflammasome-induced pyroptosis and IL-1 related cytokine release is of importance to mount an efficient immune response against various bacteria, its unrestrained activation drives sepsis. This suggests that cellular components might tightly control the threshold level of the non-canonical inflammasome in order to ensure efficient but not deleterious inflammatory response. Here we show that the IFN-inducible protein Irgm2 and the ATG8 family member Gate-16 cooperatively slow down non-canonical inflammasome activation both in macrophages and in vivo. Specifically, the Irgm2/Gate-16 axis dampens caspase-11 targeting to intracellular bacteria, which lower caspase-11-mediated pyroptosis and cytokine release. Specifically, deficiency in Irgm2 or Gate16 opens an alternative road for caspase-11 targeting to intracellular bacteria, independently of the classical pathway driven by the Guanylate Binding Proteins (GBPs). Thus, our findings provide new molecular effectors involved at fine-tuning the optimal non-canonical inflammasome response and add novel insights in the understanding of the immune pathways they control.

immunology↗