Biology subjects

Rissiek, B.

Publications and source records attributed to Rissiek, B..

6 recordsLinked to original sources

bioRxiv2026

Coupling lysosomal polarity and purinergic signaling regulates B cell activation

B cell activation is initiated by engagement of the B cell receptor (BCR) with immobilized antigens, which triggers changes in cell polarity promoting the establishment of an immune synapse that is further shaped by signals from the microenvironment. However, how cell polarity coordinates the sensing of extracellular cues to regulate B cell activation remains unclear. Here, we investigated the impact of adenosine triphosphate (ATP), a conventional danger signal related to inflammation, on B cell function. We found that ATP released by B cells, as well as exogenously added ATP, acts as a promoter of the extraction and presentation of immobilized antigens. Endogenous ATP was produced by mitochondria recruited at the immune synapse and locally released via Pannexin 1 channels to sustain purinergic signaling at the immune synapse. We identified P2RX4 trafficking to the plasma membrane through the Rab6a+ trans-Golgi network and VAMP7+/LAMP1+ lysosomes as a key step in this response. In addition, the local activation of P2RX4 at the immune synapse triggered a migratory switch from motile to sessile, suggesting that this receptor acts as a negative regulator of B cell migration. These findings reveal ATP as a local enhancer of B cell function, and an unexpected role of P2RX4 as a molecular switch for B cell activation.

immunology↗

bioRxiv2026

CD73-derived adenosine at the blood-brain barrier confers protection in a mouse model of ischemic stroke

Ischemic stroke remains a leading cause of death and disability, and current reperfusion therapies do not address the secondary neuroinflammatory response following blood-brain barrier (BBB) disruption. Purinergic signaling critically regulates this process: extracellular ATP promotes inflammation, whereas its enzymatic conversion into adenosine exerts tissue-protective effects. Notably, the ectonucleotidase CD73 (NT5E), which catalyzes AMP-to-adenosine conversion, is highly expressed by human but not murine brain endothelial cells (BECs). Here, we investigated the role of endothelial CD73 in ischemic stroke using an AAV vector engineered for selective transduction of murine BECs to induce BBB-specific CD73 expression. Endothelial CD73 enhanced extracellular ATP degradation toward adenosine generation and established a purine metabolism profile resembling that of human BECs. In the transient middle cerebral artery occlusion (tMCAO) mouse model, BBB-targeted CD73 expression reduced infarct volume by 40% and prevented early mortality within 48 h after reperfusion. Transcriptomic and flow cytometric analyses revealed altered leukocyte responses, including increased recruitment of monocytes/macrophages whose gene expression signatures were consistent with inflammation-resolving programs. These findings identify endothelial CD73 as an important regulator of post-ischemic neuroinflammation and highlight species-specific differences in BBB purine metabolism with implications for translational stroke research.

neuroscience↗

bioRxiv2022

Microglia and meningeal macrophages depletion delay the onset of experimental autoimmune encephalomyelitis

In multiple sclerosis and the experimental autoimmune encephalomyelitis (EAE) model, both resident microglia and infiltrating macrophages contribute to demyelination as well as spontaneous remyelination. Nevertheless, the specific roles of microglia versus macrophages are unknown. We investigated the influence of microglia in EAE using the colony stimulating factor 1 receptor (CSF-1R) inhibitor, PLX5622, to deplete microglial population and Ccr2RFP/+fmsEGFP/+ mice, to distinguish peripheral macrophages and microglia. PLX5622 treatment depleted microglia and meningeal macrophages, and provoked a massive infiltration of CCR2+ macrophages into demyelinating lesions and spinal cord parenchyma. PLX5622 treatment did not alter EAE chronic phase. In contrast, microglia and meningeal macrophages depletion reduced the expression of CD80 co-stimulatory molecule in dendritic and myeloid cells and reduced T cell reactivation and proliferation in the spinal cord parenchyma, inducing a significant delay in EAE onset. Altogether, these data points to a specific role of CNS microglia meningeal macrophages in antigen presentation and T cell reactivation at initial stages of the EAE model.

neuroscience↗

bioRxiv2022

Macrophages and glia are the dominant P2X7-expressing cell types in the gut nervous system - no evidence for a role of neuronal P2X7 receptors in colitis

SummaryBlockade or deletion of the pro-inflammatory P2X7 receptor channel has been shown to reduce tissue damage and symptoms in models of inflammatory bowel disease (IBD) and P2X7 receptors on enteric neurons were suggested to mediate neuronal death and associated motility changes. Here we used P2X7-specific antibodies and nanobodies as well as a BAC transgenic P2X7-EGFP reporter mouse model and P2rx7-/- controls to perform a detailed analysis of cell type-specific P2X7 expression and possible overexpression effects in the enteric nervous system. In contrast to previous studies, we did not detect P2X7 in neurons but found dominant expression in glia and macrophages which closely interact with the neurons. P2X7 overexpression per se did not induce significant pathological effects. Our data indicate that macrophages and/or glia account for P2X7-mediated neuronal damage in IBD and provide a refined basis for the exploration of P2X7-based therapeutic strategies.

physiology↗

bioRxiv2020

A P2rx7 passenger mutation affects the vitality and function of immune cells in P2X4ko and other transgenic mice

Among laboratory mouse strains many genes are differentially expressed in the same cell population. As consequence, gene targeting in 129-derived embryonic stem cells (ESCs) and backcrossing the modified mice onto the C57BL/6 (B6) background can introduce passenger mutations in the close proximity of the targeted gene. Here, we demonstrate that several 129-originating transgenic mice in which P2rx7-neighboring genes were targeted carry a P2rx7 passenger mutation that affects the vitality and function of T cells. By the example of P2rx4tm1Rass we demonstrate that CD4+ and CD8+ T cells derived from these mice express higher levels of P2X7 when compared to corresponding cell populations in B6-WT mice. The increased T cell sensitivity towards the P2X7 activators adenosine triphosphate (ATP) and nicotinamide adenine dinucleotide (NAD+) rendered these cells more vulnerable towards NAD-induced cell death (NICD) compared to their B6-WT counterparts. The enhanced NICD sensitivity significantly affected the outcome of functional assays e.g. cytokine production and cell migration. For P2rx4tm1Rass, we demonstrate that the expression of P2X7 is diminished in several innate immune cell populations, possibly as a side effect of P2rx4 targeting, and independent of the P2rx7 passenger mutation. These results need to be considered when working with P2rx4tm1Rass mice or other 129-based transgenic strains that target P2rx7 neighboring genes and might have implications for other mouse models.

immunology↗

bioRxiv2019

BRAIN-DERIVED EXTRACELLULAR VESICLES ARE HIGHLY ENRICHED IN THE PRION PROTEIN AND ITS C1 FRAGMENT: RELEVANCE FOR CELLULAR UPTAKE AND IMPLICATIONS IN STROKE

Extracellular vesicles (EVs) are important means of intercellular communication and a potent tool for regenerative therapy. In ischemic stroke, transient blockage of a brain artery leads to a lack of glucose and oxygen in the affected brain tissue, provoking neuronal death by necrosis in the core of the ischemic region. The fate of neurons in the surrounding penumbra depends on the stimuli, including EVs, received during the following hours. A detailed characterization of such stimuli is crucial not only for understanding stroke pathophysiology but also for new therapeutic interventions. In the present study, we characterize the EVs in mouse brain under physiological conditions and 24h after induction of transient ischemia in mice. We show that, in steady-state conditions, microglia are the main source of small EVs (sEVs) whereas after ischemia, the main EV population originates from astrocytes. Moreover, sEVs presented high amounts of the prion protein (PrP) which were increased after stroke. Conspicuously, sEVs were particularly enriched in a truncated PrP fragment (PrP-C1). Because of similarities between PrP-C1 and certain viral surface proteins, we studied the cellular uptake of brain-derived sEVs from mice lacking (PrP-KO) or containing PrP (WT). We show that PrP-KO-EVs are rapidly taken up by neurons and colocalize with lysosomes. Although eventually WT-EVs are also found in lysosomes, the amount taken up by neurons is significantly higher for PrP-KO-EVs. Likewise, microglia and astrocytes were also engulfing PrP-KO-sEVs more efficiently than WT-sEVs. Our results provide information on the relative contribution of brain cell types to the sEV pool in mice and indicate that increased release of sEVs by astrocytes together with elevated levels of PrP in sEVs may play a role in intercellular communication at early stages after stroke. In addition, amounts of PrP (and probably PrP-C1) in brain sEVs seem to contribute to their cellular uptake.

neuroscience↗