Biology subjects

Jalaber, H.

Publications and source records attributed to Jalaber, H..

3 recordsLinked to original sources

bioRxiv2025

Adenovirus phagocytosis by neutrophils triggers a pro-inflammatory response

Adenoviruses are common pathogens that have been engineered and used for medical purposes. Their recognition by innate immune cells such as macrophages and dendritic cells has been widely studied, but very little information is available on adenovirus interaction with neutrophils. Using cytometry and confocal and electron microscopy, we showed that neutrophils bind to antibody-coated adenoviruses and engulf them in a phagosome. Using a single-cell transcriptomic approach, we found that adenovirus phagocytosis activates a specific transcriptional program in neutrophils. It also triggers calcium entry into neutrophils, reactive oxygen species production in the phagosome, and CXCL8 release. Moreover, 4 hours after adenovirus incubation, 50% of neutrophils undergo calcium- and RIPK3-dependent cell death, accompanied by Neutrophil Extracellular Trap emission. Because of this rapid cell death, engulfed adenoviruses are not fully degraded after 3 hours, and the remaining viruses are still capable of expressing their genome in target cells. Thus, our data suggest that, during adenoviral infection, the neutrophil response may promote a pro-inflammatory environment that could damage host tissues. Author SummaryAdenoviruses are common viruses that trigger mild infections, although they can lead to more severe diseases such as gastroenteritis or respiratory tract infections in immunocompromised patients. Non-replicative adenovirus-derived vectors are widely used in medicine for vaccination and antitumor therapy. In this study, we investigated how adenoviruses affect neutrophils, the first immune cells recruited to the site of infection and crucial players in the immune system. We used various methods to explore this interaction. We found that adenoviruses bind to neutrophils, and that this binding is enhanced by human serum containing antibodies against the viruses. This binding is followed by adenovirus internalization, and we showed that it triggers several responses. These responses include the activation of specific genes, the entry of calcium into the cells, the production of reactive oxygen species (molecules that fight infections), and the release of signaling molecules to attract other immune cells. However, this process also leads to rapid neutrophil death and the release of structures called Neutrophil Extracellular Traps. Because of this quick death, adenoviruses are not fully broken down and can still infect other cells. We suggest that this neutrophil response might create an inflammatory environment that could potentially harm the bodys tissues.

immunology↗

bioRxiv2025

Stiffening cells with light

Fluorescence microscopy is widely used to observe structures and dynamic processes in living cells and organisms and is often used as if it were purely innocuous to the cells or structures of interest. However, it can lead to phototoxicity, which can affect the cellular behavior and lead to erroneous interpretations of the observations. The major cause of cell damage through phototoxicity is the production of reactive oxygen species (ROS), which can form crosslinks between intracellular molecules, including proteins and nucleic acids. By using profile microindentation and atomic force microscopy, we demonstrate that the excitation of various fluorescent probes leads to a large increase in the stiffness of several cell types within seconds of illumination. The stiffening exhibits a dose-dependent response, where longer exposure times to exciting light are correlated with larger stiffening. This photostiffening effect explains why T cells loaded with the Fluo-4 Calcium probe stop emitting a protrusion within seconds after the excitation light is turned on. We observed photostiffening in different cell types and fluorophores. We showed that repeated cell indentation alone led to cell stiffening as well as excitation with blue or UV light in the absence of a fluoroph ore. However, in the latter case, the stiffening was much smaller than that when the fluorophore was excited. We used both sharp and blunt indenters to show that stiffening occurred not only at the cell cortex level but also deeper in the cell interior and that photostiffening is independent of actin cytoskeleton organization. We correlated the increase in cell stiffness with the production of intracellular reactive oxygen species and reproduced cell stiffening by incubating cells with a ROS inducer, H2O2. The excitation of the photosensitizer Pheophorbide a, which induces a specific type of reactive oxygen species, namely singlet oxygen, also led to cell stiffening. This study reminds the experimentalists that it is crucial to perform controls when using fluorescence. It further allows us to propose exploiting photostiffening as a new method for rapidly quantifying phototoxicity. SignificanceThis study reveals a direct relationship between fluorescence excitation and cell mechanical properties. The generality of th is phenomenon across diverse fluorophores and cell types highlights the importance of controlling phototoxicity in fluorescence experiments, in particular in complex, quantitative cell biology and biophysical experiments, but also reveals an unexpected rol e of intracellular reactive oxygen species production and identifies cell stiffness as a proxy for assessing the efficacy of photodynamic therapy.

biophysics↗

bioRxiv2021

Plasticity of the dopaminergic phenotype and of locomotion in larval zebrafish induced by changes in brain excitability during the embryonic period.

During the embryonic period, neuronal communication starts before the establishment of the synapses with alternative forms of neuronal excitability, called here Embryonic Neuronal Excitability (ENE). ENE has been shown to modulate the unfolding of development transcriptional programs but the global consequences for the developing organisms are not all understood. Here we monitored calcium transients in zebrafish embryos as a proxy for ENE to assess the efficacy of transient pharmacological treatments to either increase or decrease ENE. Increasing or decreasing ENE for 24 hours at 2 days post fertilization (dpf), at the end of the embryonic period, promoted respectively an increase or a decrease in the numbers of dopamine (DA) neurons in the telencephalon and in the olfactory bulb of zebrafish larvae at 6 dpf. This plasticity of dopaminergic specification occurs within a stable population of vMAT2-positive cells, hence identifying an unanticipated biological marker for this reserve pool of of DA neurons that can be recruited by increasing ENE. Modulating ENE also affected larval locomotion several days after the end of the treatments. In particular, the increase of ENE from 2 to 3 dpf promoted hyperlocomotion of larvae at 6 dpf, reminiscent of endophenotypes reported for Attention Deficit with Hyperactivity Disorders and schizophrenia in zebrafish. These results provide a convenient framework to identify environmental factors that could disturb ENE as well as to study the molecular mechanisms linking ENE to neurotransmitter specification, with relevance to the pathogenesis of neurodevelopmental disorders. Significance Statement- Spontaneous calcium transients, used as a proxy for Embryonic Neuronal Excitability (ENE), are detected in the forebrain of embryonic zebrafish. - Short-term pharmacological treatments by bath application could increase or decrease ENE. - The post-mitotic differentiation of the dopaminergic phenotype is modulated by ENE in the zebrafish forebrain. - The plasticity of the dopaminergic specification occurs within a reserve pool of vMAT2-positive cells. - Transient increase of ENE at the end of the embryonic period induces hyperlocomotion, a phenotype associated with ADHD and schizophrenia in this model. - Our results open clinically relevant perspectives to study the pathogenesis of neurodevelopmental disorders in zebrafish.

neuroscience↗