Biology subjects

Scheller, A.

Publications and source records attributed to Scheller, A..

7 recordsLinked to original sources

bioRxiv2023

Adenosine triggers astrocyte reactivity to drive the pathogenesis of sepsis-associated encephalopathy

Molecular pathways mediating systemic inflammation entering the brain parenchyma to induce sepsis-associated encephalopathy (SAE) remain elusive. Here, we report that in mice during the first 6 hours of peripheral lipopolysaccharide (LPS)-evoked systemic inflammation (6 hpi), the plasma level of adenosine quickly increased and enhanced the tone of central extracellular adenosine which then provoked neuroinflammation by triggering early astrocyte reactivity. Specific ablation of astrocytic A1 adenosine receptors (A1ARs) prevented this early reactivity and reduced the levels of inflammatory factors (e.g., CCL2, CCL5, and CXCL1) in astrocytes, thereby alleviating microglial activation, ameliorating blood-brain barrier disruption, neuronal dysfunction, and depression-like behaviour in the mice. Chemogenetic stimulation of Gi signaling in A1AR-deficent astrocytes at 2 and 4 hpi of LPS injection could restore neuroinflammation and depression-like behaviour, highlighting astrocytes rather than microglia as early drivers of neuroinflammation. Our results identify early astrocyte reactivity towards peripheral and central levels of adenosine as a novel pathway driving SAE.

neuroscience↗

bioRxiv2022

Novel algorithms for improved detection and analysis of fluorescent signal fluctuations

Fluorescent dyes and genetically encoded fluorescence indicators (GEFI) are common tools for visualizing concentration changes of specific ions and messenger molecules during intra-as well as intercellular communication. Using advanced imaging technologies, fluorescence indicators are a prerequisite for the analysis of physiological molecular signaling. Automated detection and avnalysis of fluorescence signals requires to overcome several challenges, including correct estimation of fluorescence fluctuations at basal concentrations of messenger molecules, detection and extraction of events themselves as well as proper segmentation of neighboring events. Moreover, event detection algorithms need to be sensitive enough to accurately capture localized and low amplitude events exhibiting a limited spatial extent. Here, we present two algorithms (PBasE and CoRoDe) for accurate baseline estimation of fluorescent detection of messenger molecules and automated detection of fluorescence fluctuations. Author summaryAnalyzing molecular signalling is crucial in understanding intra- and intercellular communication. These signals are visualized using fluorescent dyes or genetically encoded fluorescence indicators. In the brain, Ca2+ signals of glial cells are essential in deciphering complex regulatory functions in health and disease. Due to signal heterogeneity, detection and analysis are highly challenging. They can be stationary, with low amplitude and localized in cell processes, occur as prominent somatic signals or propagate as waves across cellular networks. We have developed two algorithms to analyze fluorescence transients, each tackling a specific problem. PBasE performs automatic and adaptive background correction, removing basal fluorescence fluctuations. CoRoDe automatically extracts regions of interest, explicitly including temporal information to obtain a precise segmentation, which is essential for accurate transient extraction. Combined, these algorithms are able to detect regions exhibiting low amplitude transients with small spatial extent as well as large, high amplitude signals. Extracted transients are categorized based on their peak amplitude, allowing detailed analyses by comparing changes of specific properties. In order to make these algorithms accessible, an interactive application, called Msparkles, has been designed.

neuroscience↗

bioRxiv2022

Brain injuries and complex motor learning suppress Olig2 in a subpopulation of oligodendrocyte precursor cells

Oligodendrocyte precursor cells (OPCs) are uniformly distributed in the mammalian brain, however their function is rather heterogeneous in respect to their origin, location, receptor/channel expression and age. The basic helix-loop-helix transcription factor Olig2 is expressed in all OPCs as a pivotal determinant of their differentiation. Here, we identified a subset (2-26%) of OPCs lacking Olig2 in various brain regions including cortex, corpus callosum, CA1 and dentate gyrus. These Olig2 negative (Olig2neg) OPCs were enriched in the juvenile brain and decreased subsequently with age, being rarely detectable in the adult brain. However, the loss of this population was not due to apoptosis or microglia-dependent phagocytosis. Unlike Olig2pos OPCs, these subset cells could not be labelled for the mitotic marker Ki67. And, accordingly, BrdU was incorporated only by a three-day long-term labeling but not by a two-hour short pulse, suggesting these cells do not proliferate any more but were derived from proliferating OPCs. The Olig2neg OPCs exhibited a less complex morphology than Olig2pos ones. Olig2neg OPCs preferentially remain in a precursor stage rather than differentiating into highly branched oligodendrocytes. Changing the adjacent brain environment, e.g. by acute injuries or by complex motor learning tasks stimulated the transition of Olig2pos OPCs to Olig2neg cells in the adult. Taken together, our results demonstrate that OPCs transiently suppress Olig2 upon changes of the brain activity. Table of Contents Image O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=145 SRC="FIGDIR/small/496631v1_ufig1.gif" ALT="Figure 1"> View larger version (51K): org.highwire.dtl.DTLVardef@1f8bc79org.highwire.dtl.DTLVardef@11dd807org.highwire.dtl.DTLVardef@51d2e9org.highwire.dtl.DTLVardef@1edf9a1_HPS_FORMAT_FIGEXP M_FIG C_FIG Main points: A subset of OPCs do not express Olig2, of which population peaks in the juvenile brain while wanes with age. Plastic changes of the brain by acute injuries or complex motor learning stop the expression of Olig2 in OPCs.

neuroscience↗

bioRxiv2022

Specific detection and deletion of the Sigma-1 receptor in neurons and glial cells for functional characterization in vivo

The chaperon protein sigma-1 receptor (S1R) has been discovered over forty years ago. Recent pharmacological studies using S1R exogenous ligands demonstrated a promising therapeutical potential of targeting the S1R for several neurological disorders. Although intensive in vitro studies have revealed S1Rs are mainly residing at the membrane of the endoplasmic reticulum (ER), the cell-specific in vivo expression pattern of S1Rs is still unclear, mainly due to the lack of a reliable detection method which also prevented a comprehensive functional analysis. Here, first, we identified a highly specific antibody using S1R knockout (KO) mice and established an immunohistochemical protocol involving a 1% SDS antigen retrieval step. Second, we characterized the S1R expression in the mouse brain and can demonstrate that the S1R is widely expressed: in principal neurons, interneurons, and all glial cell types. Finally, we generated a novel Cre-dependent S1R conditional KO mouse (S1R flox) to study cell type-specific functions of the S1R. As a proof of concept, we successfully ablated S1R expressions in neurons or microglia employing neuronal and microglial Cre-expressing mice, respectively. In summary, we provide powerful tools to cell-specifically detect, delete and functionally characterize S1R in vivo.

neuroscience↗

bioRxiv2022

Time-lapse Imaging of Microglial Activity and Astrocytic Calcium Signaling Reveals a Neuroprotective Effect of Cannabidiol in the Subacute Phase of Stroke

Pharmacological agents that limit secondary tissue loss and/or improve functional outcomes after stroke are still limited. Cannabidiol, the major non-psychoactive component of Cannabis sativa, has been proposed as a neuroprotective agent against experimental focal cerebral ischemia. The effects of cannabidiol have generally been related to the modulation of neuroinflammation, including the control of glial activation and the toxicity exerted by pro-inflammatory mediators. However, so far, most information concerning cannabidiol neuroprotective effects was obtained from histological and biochemical post-mortem assays. To test whether the effects of cannabidiol on glial cells could be also detected in vivo, we performed time-lapse imaging of microglial activity and astrocytic calcium signaling in the subacute phase of stroke using two-photon laser-scanning microscopy. First, C57BL/6N wild-type mice underwent either sham or transient middle cerebral artery occlusion surgery. The animals received intraperitoneal injection of vehicle or cannabidiol (10 mg/kg) 30 min, 24 h, and 48 h after surgery. One day later the neurological score test was performed. Brain tissue was processed to evaluate the neuronal loss and microglial activation. Transgenic mice with microglial expression of the enhanced green fluorescent protein and astrocyte-specific expression of the calcium sensor GCaMP3 were used to access in vivo microglial activity and astrocytic calcium signaling, respectively. The animals were submitted to the same experimental design described above and to imaging sessions before, 30 min, 24 h and, 48 h after surgery. Astrocytic calcium signaling was also assessed in acutely isolated slices 5 h after transient middle cerebral artery occlusion surgery in the presence of perfusion or cannabidiol solution. Cannabidiol prevented ischemia-induced neurological impairments as well as protected against neuronal loss in ischemic mice. Cannabidiol also reduced ischemia-induced microglial activation, as demonstrated in fixed tissue as well in in vivo conditions. No difference in the amplitude and duration of astrocytic calcium signals was detected before and after the middle cerebral artery occlusion in vivo. Similarly, no significant difference was found in the astrocytic calcium signals between contra and ipsilateral side of acutely isolated brain slices. The present results suggest that the neuroprotective effects of cannabidiol after stroke may occur in the subacute phase of ischemia and reinforce the strong anti-inflammatory property of this compound.

neuroscience↗

bioRxiv2021

After traumatic brain injury oligodendrocytes regain a plastic phenotype and can become astrocytes

After acute brain injuries various response cascades are evoked that direct the formation of the glial scar. Here, we report that acute lesions associated with a disruption of the blood-brain barrier trigger a re-programming within the oligodendrocyte lineage. In PLP-DsRed1/GFAP-EGFP and PLP-EGFPmem/GFAP-mRFP1 transgenic mice with cortical injuries, we transiently found PLP transgene-labelled cells with activated GFAP promoter activity adjacent to the lesion site. We termed them AO cells, based on their concomitant activity of astro- and oligodendroglial genes. By fate mapping using PLP- and GFAP-split Cre complementation and NG2-CreERT2 mice we observed that major portions of AO cells surprisingly differentiated into astrocytes. Using repeated long-term in vivo two-photon laser-scanning microscopy (2P-LSM) we followed oligodendrocytes after injury. We observed their conversion into astrocytes via the AO cell stage with silencing of the PLP promoter and simultaneous activation of the GFAP promoter. In addition, we provide evidence that this oligodendrocyte-to-astrocyte conversion depends on local cues. At the lesion site higher expression levels of various glial differentiation factors were detected. And indeed, local injection of IL-6 promoted the formation of AO cells. In summary, our findings highlight the plastic potential of oligodendrocytes in acute brain trauma. An altered environmental milieu affects gene expression programs of mature oligodendrocytes and induces a plastic differentiation stage with astrogliogenic potential via transitional AO cells.

neuroscience↗

bioRxiv2021

Impaired bidirectional communication between interneurons and oligodendrocyte precursor cells affects cognitive behavior

Cortical neural circuits are complex but very precise networks of balanced excitation and inhibition (E/I). Yet, the molecular and cellular mechanisms that form the E/I balance are just beginning to emerge. Here, using conditional GABAB receptor-deficient mice we identified a GABA/TNF-related cytokine (TNFSF12)-mediated bidirectional communication pathway between Parvalbumin-positive (PV+) fast spiking interneurons and oligodendrocyte precursor cells (OPCs) that determines the density and function of interneurons in the developing medial prefrontal cortex (mPFC). Interruption of the GABAergic signaling to OPCs resulted in reduced myelination and hypoactivity of interneurons, strong changes of cortical network activities and impaired cognitive behavior. In conclusion, glial transmitter receptors are pivotal elements in finetuning distinct brain functions.

neuroscience↗