Biology subjects

Guenot, M.

Publications and source records attributed to Guenot, M..

4 recordsLinked to original sources

bioRxiv2025

GBP1 recruitment to actin-rich pedestals induced by extracellular Gram-negative bacteria promotes pyroptosis.

The IFN{gamma}-induced GTPase guanylate binding protein 1 (GBP1) binds to lipopolysaccharide (LPS) on cytosolic Gram-negative bacteria and promotes pyroptosis via the recruitment and activation of caspase-4 on the bacterial outer membrane. Enteropathogenic and enterohaemorrhagic Escherichia coli (EPEC and EHEC, respectively) are extracellular pathogens that also induce LPS-and caspase-4-dependent pyroptosis. However, whether GBP1 is involved in this process remains unknown. EPEC and EHEC adhere intimately to intestinal epithelial cells via avid interactions between the bacterial adhesin Intimin and Tir (Translocated intimin receptor), a type 3 secretion system effector protein. Intimin-mediated clustering of Tir triggers actin polymerisation, leading to pedestal-like structures at bacterial attachment sites. Here we show that GBP1 is recruited to actin-rich pedestals in human cells infected with EPEC and EHEC in vitro and mouse colonocytes infected with the EPEC-like murine pathogen Citrobacter rodentium in vivo. GBP1-dependent caspase-4 trafficking to these sites leads to pyroptosis and IL-18 release. GBP1 mutants defective in LPS coatomer formation also localised to EPEC pedestals, pointing to LPS-independent mobilisation of GBP1 by actin polymerisation induced by extracellular A/E pathogens. To further dissect the underlying mechanism, we engineered a chimeric receptor (Fc{gamma}R-Tir) by combining the intracellular signalling domain of Tir and the extracellular ligand-binding domain of the Fc{gamma} receptor. Clustering of Fc{gamma}R-Tir with IgG-coated beads produced sterile actin-rich pedestals that were sufficient to recruit GBP1 independently of bacteria. Our findings reveal that cytosolic GBP1 is mobilised to sites of pathogen-induced actin remodelling independently of LPS. We establish that GBP1 not only operates as a pattern-recognition receptor but also orchestrates effector-triggered immunity against pathogens that hijack the actin cytoskeleton. 175-word AbstractThe IFN{gamma}-induced GTPase guanylate binding protein 1 (GBP1) binds to lipopolysaccharide (LPS) on cytosolic Gram-negative bacteria and promotes pyroptosis via the recruitment and activation of caspase-4 on the bacterial outer membrane. Enteropathogenic and enterohaemorrhagic Escherichia coli (EPEC and EHEC, respectively) are extracellular pathogens that adhere to host cells and stimulate dense actin polymerisation underneath their attachment sites, generating structures called actin-rich pedestals. Here we show that GBP1 traffics to actin-rich pedestals in human cells infected with EPEC and EHEC in vitro and mouse colonocytes infected with the EPEC-like murine pathogen Citrobacter rodentium in vivo. GBP1 promotes caspase-4 recruitment to actin-rich pedestals, leading to pyroptosis and IL-18 release. GBP1 mutants defective in LPS coatomer formation also localised to EPEC pedestals. Our novel assay that mimics pathogenic effector activity revealed GBP1 recruitment to sterile actin polymerisation sites. We conclude that cytosolic GBP1 is mobilised to sites of pathogen-induced actin remodelling independently of LPS. Our study establishes that GBP1 not only operates as a pattern-recognition receptor but also orchestrates effector-triggered immunity against pathogens that hijack the actin cytoskeleton.

immunology↗

bioRxiv2025

Persistent Light-Induced Reduction of Neuronal Excitability: Implications for Non-Optogenetic control of Brain Actvity

Visible light is widely used in neuroscience, yet its direct effects on neuronal activity in the absence of optogenetic manipulation remain incompletely understood. Here, we investigated whether light stimulation can induce sustained changes in neuronal excitability. Using ex vivo electrophysiological recordings, we show that repeated pulses of blue light (5 s, 430-495 nm, 19 mW) produce a robust and persistent reduction in evoked firing activity in cortical neurons from both male and female mice, with an average decrease of [~]60% relative to baseline. This inhibitory effect persisted for more than 20 minutes following stimulation and was associated with changes in both passive membrane properties and active ion channel conductance. In human cortical neurons, responses were more heterogeneous. While a subset of neurons exhibited similar inhibitory effects, others showed increased excitability, with this response occurring more frequently in neurons from female patients, suggesting a potential sex-dependent effect. In addition, a transient depolarizing response to light was observed in a minority of human neurons but not in mice. These findings indicate that visible light, independently of exogenous opsins, can induce long-lasting modulation of neuronal activity without evidence of acute cytotoxicity under the conditions tested. This raises the possibility that visible light may provide a previously underappreciated, opsin-independent mechanism for modulating neuronal activity, with potential relevance for disorders characterized by neuronal hyperexcitability. We outline a framework for future investigations, including validation in human systems, in vivo studies, optimization of stimulation parameters, and assessment of therapeutic potential in pathological models.

neuroscience↗

bioRxiv2021

Low grade inflammation in the epileptic hippocampus contrasts with explosive inflammation occurring in the acute phase following status epilepticus in rats: translation to patients with epilepsy

There is still a lack of robust data, acquired identically and reliably from tissues either surgically resected from patients with mesial temporal lobe epilepsy (mTLE) or collected in animal models, to answer the question of whether the degree of inflammation of the hippocampus differs between mTLE patients, and between epilepsy and epileptogenesis. Here, using highly calibrated RTqPCR, we show that neuroinflammatory marker expression was highly variable in the hippocampus and the amygdala of mTLE patients. This variability was not associated with gender, age, duration of epilepsy, seizure frequency, and anti-seizure drug treatments. In addition, it did not correlate between the two structures and was reduced when the inflammatory status was averaged between the two structures. We also show that brain tissue not frozen within minutes after resection had significantly decreased housekeeping gene transcript levels, precluding the possibility of using post-mortem tissues to assess physiological baseline transcript levels in the hippocampus. We thus used rat models of mTLE, induced by status epilepticus (SE), that have the advantage of providing access to physiological baseline values. They indisputably indicated that inflammation measured during the chronic phase of epilepsy was much lower than the explosive inflammation occurring after SE, and was only detected when epilepsy was associated with massive neurodegeneration and gliosis. Comparison between the inter-individual variability measured in patients and that established in all epileptic and control rats suggests that some mTLE patients may have very low inflammation in the hippocampus, close to control values. However, the observation of elevated inflammation in the amygdala of some patients indicates that inflammation should be studied not only at the epileptic hippocampus, but also in the associated brain structures in order to have a more integrated view of the degree of inflammation present in brain networks involved in mesial temporal lobe epilepsy.

neuroscience↗

bioRxiv2019

Slow cortico-cortical connectivity (2-5Hz) is a new robust signature of conscious states

While long-range cortico-cortical functional connectivity has been reported by several studies as a necessary condition of conscious state, precise empirical evidence is still scarce. In the present work we provide such a direct and conclusive evidence in a set of three experiments. In the two first experiments intracranial-EEG was recorded during four distinct states in the same individuals: conscious wakefulness (CW), rapid-eye-movement sleep (REM), stable periods of slow-wave sleep (SWS) and deep propofol anaesthesia (PA). We discovered that long-range FC, computed by the weighted Symbolic-Mutual-Information (wSMI) in the 2-5Hz frequency band was a specific marker of conscious states that could discriminate CW and REM from SWS and PA. In the third experiment, we generalized this original finding on a large cohort of brain-injured patients by revealing that wSMI in the 2-5 Hz range was also able to accurately discriminate patients in the vegetative state (or unresponsive wakefulness syndrome) from patients in the minimally conscious state. Taken together the present results suggest that 2-5Hz FC is a new and robust signature of conscious states.

neuroscience↗