Biology subjects

Pionneau, C.

Publications and source records attributed to Pionneau, C..

6 recordsLinked to original sources

bioRxiv2026

Characterisation of the new microalgal protein xATPA related to the F-type ATP synthase α subunit, from the ecosystem to the molecule

Microalgal metabolism relies on their chloroplasts, and involves both nucleus and plastidial-encoded proteins of various evolutionary origins. The plastidial ATP synthase complex is a key player in photosynthesis, and has been extensively studied in plants. However, our knowledge in other photosynthetic eukaryotes remains limited, despite their importance in marine environments. Here, we report the characterisation of a novel homologue of the F-type ATP synthase alpha subunit, hereby named xATPA, widespread in microalgae but absent from other photosynthetic organisms. Comparisons of xATPA sequences and predicted structures revealed a specific feature, the bump domain, and highlighted the absence of an ATP-binding site. We assessed xATPA prevalence in microalgae in the global ocean using environmental data from Tara Oceans, with a particular focus on diatoms, and demonstrate that its expression is associated with polar summer conditions. Using a reverse genetic approach in the model diatom Phaeodactylum tricornutum, we show that xATPAPt has a plastidial localisation, and that xATPA KO mutants exhibit growth deficiencies in a combination of low temperature, low salinity and constant light, consistent with environmental analysis. Surprisingly, both RNAseq and physiological assays suggest that xATPA is not involved in ATP synthase functions. On the other hand, xATPA interacts with other F1 ATP synthase subunits in vitro, which we suggest forms transient unassembled complexes. This study hence represents a comprehensive analysis of a novel protein from the environment to the lab, and reveals a new player in the plastidial physiology of eukaryotic microalgae.

plant biology↗

bioRxiv2026

Integrin beta 1 and mannose receptor 2 are involved in the antifungal activity of bronchial epithelial cells through Aspergillus fumigatus lectin FleA interactions

Aspergillus fumigatus is a world-wide saprophyte filamentous fungus which released conidia, its infectious morphotype, in the atmosphere. These conidia are inhaled daily by humans and can colonize the respiratory tract, where they may develop into hyphae, the invasive morphotype. We previously showed that bronchial epithelial cells (BECs) restrict A. fumigatus virulence by inhibiting conidial germination and filament formation through a process requiring PI3K signaling and the conidial fucose-specific lectin FleA. In the present study, we are looking to identify host factors and cellular partners involved in the BEC antifungal response and to define the molecular interactions underpinning FleA recognition. For this, we analyzed transcriptome of BECs infected with A. fumigatus in the presence or absence of the PI3K inhibitor LY294002. Functional involvement of candidate genes was assessed by siRNA knockdown and readouts of fungal filamentation (microscopic scoring and galactomannan release). FleA-interacting host proteins were identified by biotin-FleA affinity co-precipitation coupled to Tandem mass spectrometry, and validated by surface plasmon resonance and biolayer interferometry. The spatiotemporal dynamics of FleA and candidate partners were analyzed by confocal microscopy and proximity ligation assay We demonstrated that BEC antifungal activity involves at least two complementary pathways: a PI3K/laminin-332 axis promoting conidial adhesion, and a FleA-dependent pathway engaging ITGB1 and MRC2 consistent with lectin uptake and trafficking toward LAMP1-positive compartments. These findings nominate FleA-host receptor interactions as attractive targets for anti-adhesive strategies against A. fumigatus. Author summaryFungal pathogens are an increasing threat to public health, as they are becoming more common and harder to treat due to rising drug resistance. Among them, Aspergillus fumigatus has been classified as a critical pathogen by the World Health Organization (WHO). This filamentous fungus delivers spores in the air daily, which are constantly inhaled by humans. In people with weakened immunity, these spores can cause a range of lung diseases known as aspergillosis, with severity ranging from mild to life-threatening. Lung epithelial cells are the first cells of the respiratory tract to encounter inhaled spores. In a previous study, we showed that bronchial cells can prevent spore from developing into filaments, the invasive form of A. fumigatus that is responsible for tissue damage. This protective effect depends of on the recognition of a fungal protein called FleA. In the present study, we identified host cell proteins that bind to FleA and transport it into intracellular compartments. Our findings suggest that these proteins help bronchial epithelial cells to internalize fungal spores, thereby blocking their transformation into the invasive filamentous form.

cell biology↗

bioRxiv2023

PAK1 and NF2/Merlin jointly drive myelination by remodeling actin cytoskeleton in oligodendrocytes

In the central nervous system (CNS), myelin formation by oligodendrocytes (OLs) relies on actin dynamics. Actin polymerization supports the ensheathment step, when the OL process contacts the axon, while a drastic shift to actin depolymerization is required to enable the following step of wrapping and expansion of myelin membranes. The molecular mechanisms triggering this switch, essential for proper myelination, have yet to be elucidated. Here, we identify P21-activated kinase 1 (PAK1) as a major regulator of actin depolymerization in OLs. We show that PAK1 accumulates in OLs in a kinase inhibited form, triggering actin disassembly and, consequently, myelin expansion. Remarkably, we identify NF2/Merlin as an endogenous inhibitor of PAK1 by proteomics analysis of its binding partners. We found that Nf2 knockdown in OLs results in PAK1 activation and impairs myelin formation, and that pharmacological inhibition of PAK1 in Nf2-knockdown OLs rescues these defects. Moreover, we demonstrate that modulating PAK1 activity in OLs controls myelin expansion and provide compelling evidence indicating that specific Pak1 loss-of-function in oligodendroglia stimulates the thickening of myelin sheaths in vivo. Overall, our data indicate that PAK1-NF2/Merlin duo plays a key role in actin cytoskeleton remodeling in OLs, required for proper myelin formation. These findings have broad mechanistic and therapeutic implications for demyelinating diseases and neurodevelopmental disorders. SignificanceRemodeling actin cytoskeleton plays a crucial role in myelin formation by oligodendrocytes (OLs). Recent studies have shown that expansion and wrapping of myelin membranes around axons depends on actin depolymerization. However, the molecular mechanisms triggering this key step in myelination are not fully elucidated. Using genetic and pharmacological tools as well as proteomics analyses, we found that PAK1 (P21 Activated Kinase 1) kinase activity is maintained inhibited by NF2/Merlin in OLs to allow actin depolymerization and, consequently, myelin membrane expansion. Pak1 loss-of-function in OLs leads to an increase in myelin thickness in the white matter of adult mice, confirming the role of PAK1 inactivation in myelin membrane expansion.

neuroscience↗

bioRxiv2022

CARD9 in Neutrophils Protects from Colitis and Controls Mitochondrial Metabolism and Cell Survival

ObjectivesInflammatory bowel disease (IBD) results from a combination of genetic predisposition, dysbiosis of the gut microbiota and environmental factors, leading to alterations in the gastrointestinal immune response and chronic inflammation. Caspase recruitment domain 9 (Card9), one of the IBD susceptibility genes, has been shown to protect against intestinal inflammation and fungal infection. However, the cell types and mechanisms involved in the CARD9 protective role against inflammation remain unknown. DesignWe used dextran sulfate sodium (DSS)-induced and adoptive transfer colitis models in total and conditional CARD9 knock-out mice to uncover which cell types play a role in the CARD9 protective phenotype. The impact of Card9 deletion on neutrophil function was assessed by an in vivo model of fungal infection and various functional assays, including endpoint dilution assay, apoptosis assay by flow cytometry, proteomics and real time bioenergetic profile analysis (Seahorse). ResultsLymphocytes are not intrinsically involved in the CARD9 protective role against colitis. CARD9 expression in neutrophils, but not in epithelial or CD11c+ cells, protects against DSS-induced colitis. In the absence of CARD9, mitochondrial dysfunction in neutrophils leads to their premature death through apoptosis, especially in oxidative environment. The decrease of fonctional neutrophils in tissues could explain the impaired containment of fungi and increased susceptibility to intestinal inflammation. ConclusionThese results provide new insight into the role of CARD9 in neutrophil mitochondrial function and its involvement in intestinal inflammation, paving the way for new therapeutic strategies targeting neutrophils. Summary boxO_LIWhat is already known about this subject? O_LIInflammatory bowel disease (IBD) results from genetic predisposition, microbiota dysbiosis and environmental factors, but the alterations of the immune response leading to chronic intestinal inflammation are still not fully understood. C_LIO_LICaspase recruitment domain 9 (Card9), one of the IBD susceptibility genes, has been shown to protect against intestinal inflammation and fungal infection. C_LIO_LIHowever, the cell types and cellular mechanisms involved in the CARD9 protective role against inflammation remain unknown. C_LI C_LIO_LIWhat are the new findings? O_LICARD9 expression in neutrophils, but not in lymphocytes, epithelial cells or CD11c+ cells, protects against DSS-induced colitis. C_LIO_LIIn the absence of CARD9, mitochondrial dysfunction in neutrophils leads to their premature death through apoptosis, especially in oxidative environment. C_LIO_LIThe decrease of fonctional neutrophils in tissues could explain the impaired containment of fungi and increased susceptibility to intestinal inflammation. C_LI C_LIO_LIHow might it impact on clinical practice in the foreseeable future? O_LIThese results provide new insight into the role of CARD9 in neutrophil mitochondrial function and its involvement in intestinal inflammation. C_LIO_LIUnderstanding the role of neutrophils in chronic inflammation could lead to innovative therapeutic strategies targeting these key immune cells for various complex diseases. C_LI C_LI

immunology↗

bioRxiv2021

The Autophagy Receptor TAX1BP1 (T6BP) is a novel player in antigen presentation by MHC-II molecules.

CD4+ T lymphocytes play a major role in the establishment and maintenance of immunity. They are activated by antigenic peptides derived from extracellular or newly synthesized (endogenous) proteins presented on the surface of antigen presenting cells (APCs) by the MHC-II molecules. The pathways leading to endogenous MHC-II presentation remain poorly characterized. We demonstrate here that the autophagy receptor, T6BP, influences both autophagy-dependent and -independent endogenous presentation of HIV- and HCMV-derived peptides. By studying the immunopeptidome of MHC-II molecules, we show that T6BP affects both the quantity and quality of peptides presented. T6BP silencing induces the mislocalization of the MHC-II-loading compartments and a rapid degradation of the invariant chain (CD74) without altering the expression and internalization kinetics of MHC-II molecules. We determined the interactome of T6BP, identified calnexin as a T6BP partner and show that CANX cytosolic tail is required for this interaction. Remarkably, calnexin silencing replicates the functional consequences of T6BP silencing: decreased CD4+ T cell activation and exacerbated CD74 degradation. Altogether, we unravel T6BP as a key player of the MHC-II-restricted endogenous presentation pathway and we propose one potential mechanism of action.

immunology↗

bioRxiv2020

In-depth proteomic analysis of Plasmodium berghei sporozoites using trapped ion mobility spectrometry with parallel accumulation-serial fragmentation

Malaria is caused by Plasmodium spp. protozoan parasites, which are transmitted by female anopheline mosquitoes in the form of sporozoites. Once deposited in the dermis during the blood meal of the mosquito, sporozoites rapidly migrate to the liver for an initial and obligatory round of replication inside hepatocytes, before exponential multiplication of the parasite in the blood and onset of the malaria disease. Sporozoites and liver stages provide attractive targets for the development of a malaria vaccine. Until now, a single antigen from Plasmodium falciparum, the deadliest species infecting humans, has been considered for subunit vaccine clinical development, with limited success so far. This emphazises the need to identify novel targets. In this context, defining the parasite proteome is important not only to guide the down-selection of potential candidate antigens, but also to allow a better understanding of the parasite biology. Previous studies have determined the total proteome of sporozoite stages from the two main human malaria parasites, P. falciparum and P. vivax, as well as P. yoelii, a parasite that infects rodents. Another murine malaria parasite, P. berghei, has been widely used to investigate the biology of Plasmodium pre-erythrocytic stages. However, a deep view of the proteome of P. berghei sporozoites is still missing. To fill this gap, we took advantage of a novel highly sensitive timsTOF PRO mass spectrometer, based on trapped ion mobility spectrometry with parallel accumulation-serial fragmentation. Combined with three alternative methods for sporozoite purification, this approach allowed us to identify the deep proteome of P. berghei sporozoites using low numbers of parasites. This study provides a reference proteome for P. berghei sporozoites, identifying a core set of proteins expressed accross species, and illustrates how the unprecedented sensitivity of the timsTOF PRO system enables deep proteomic analysis from limited sample amounts.

microbiology↗