Biology subjects

Lohr, C.

Publications and source records attributed to Lohr, C..

6 recordsLinked to original sources

bioRxiv2026

Cell-type specific astrocyte activation is driven by cortical top-down modulation

Cortical projections to cortical and subcortical targets provide top-down modulation that shapes neuronal performance, including gain control and excitation-inhibition balance. However, the contribution of astrocytes to this process remains poorly understood. In the olfactory bulb, the first relay station of odor information processing, bottom-up input is transmitted from olfactory sensory neurons to mitral/tufted (M/T) cells, which project to the olfactory cortex. Context- and state-dependent top-down modulation arises from feedback projections originating in the anterior piriform cortex (aPC) that target granule cells (GCs). We examined how astrocytes respond to bottom-up and top-down neuronal activity using confocal Ca{superscript 2} imaging, cell-type-specific optogenetics, electrical stimulation, and single-cell electrophysiology. We found that Ca{superscript 2} signals in astrocytes are selectively triggered by action potential-dependent ATP release from GCs while M/T cells failed to elicit significant astrocytic responses. Although synaptic input from M/T cells depolarized GCs, it was insufficient to induce action potential firing and subsequent astrocyte activation. By contrast, glutamatergic top-down input from the aPC evoked sustained GC firing, leading to ATP-dependent Ca{superscript 2} signaling in astrocytes. Our results reveal an unappreciated level of complexity in neuron-astrocyte communication, highlighting its cell-type specificity as well as its context- and state-dependence.

neuroscience↗

bioRxiv2025

Crosstalk of noradrenergic Ca2+ and cAMP signaling in astrocytes of the murine olfactory bulb

Cyclic adenosine monophosphate (cAMP) and Ca2+ are ubiquitous second messengers that regulate gene expression, metabolism, and synaptic plasticity. Here, we identified a complex interplay between Ca2+ and cAMP signaling pathways in mouse olfactory bulb astrocytes. Norepinephrine (NE) elevated both Ca2+ and cAMP levels via 1 and 2 adrenergic receptors, whereas {beta} receptors triggered only cAMP responses. The 1 receptor agonist phenylephrine increased cAMP, but this effect was suppressed when Ca2+ elevations were blocked by Ca2+ depletion and removal of external Ca2+. We found that 1A and 1D receptors are key targets for phenylephrine, acting through Ca2+/calmodulin-dependent adenylyl cyclases AC1 and AC3 downstream of 1 receptor activation. Moreover, 2 receptor stimulation raised Ca2+ levels, thereby stimulating cAMP production, yet also reduced forskolin-induced cAMP elevations, indicating that 2 receptors can both inhibit adenylyl cyclase via Gi and stimulate AC1/AC3 via Ca2+ signaling. Together, these findings reveal intricate crosstalk between noradrenergic Ca2+ and cAMP signaling in olfactory bulb astrocytes mediated by all three adrenergic receptor subtypes.

neuroscience↗

bioRxiv2024

Microgliosis, astrogliosis and loss of aquaporin-4 polarity in frontal cortex of COVID-19 patients

The severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2), causing human coronavirus disease 2019 (COVID-19), not only affects the respiratory tract, but also impacts other organs including the brain. A considerable number of COVID-19 patients develop neuropsychiatric symptoms that may linger for weeks and months and contribute to "long-COVID". While the neurological symptoms of COVID-19 are well described, the cellular mechanisms of neurologic disorders attributed to the infection are still enigmatic. Here, we studied the effect of an infection with SARS-CoV-2 on the structure and expression of marker proteins of astrocytes and microglial cells in the frontal cortex of patients who died from COVID-19 in comparison to non-COVID-19 controls. Most of COVID-19 patients had microglial cells with retracted processes and rounded and enlarged cell bodies in both gray and white matter, as visualized by anti-Iba1 staining and confocal fluorescence microscopy. In addition, gray matter astrocytes in COVID-19 patients were frequently labeled by intense anti-GFAP staining, whereas in non-COVID-19 controls, most gray matter astrocytes expressed little GFAP. The most striking difference between astrocytes in COVID-19 patients and controls was found by anti-aquaporin-4 (AQP4) staining. In COVID-19 patients, a large number of gray matter astrocytes showed an increase in AQP4. In addition, AQP4 polarity was lost and AQP4 covered the entire cell, including the cell body and all cell processes, while in controls, AQP4 immunostaining was mainly detected in endfeet around blood vessels and did not visualize the cell body. In summary, our data suggest neuroinflammation upon SARS-CoV-2 infection including microgliosis and astrogliosis, including loss of AQP4 polarity.

neuroscience↗

bioRxiv2023

KIF23 regulation by miR-107 controls replicative tumor cell fitness in mouse and human hepatocellular carcinoma

Background & AimsIn hepatocellular carcinoma, there is a lack of successful translation of experimental targets identified in mouse models to human patients. In this study, we used a comprehensive transcriptomic approach in mice to identify novel potential targets for therapeutic intervention in humans. MethodsWe analysed combined genome-wide miRNA and mRNA expression data in three pathogenically distinct mouse models of liver cancer. Effects of target genes on hepatoma cell fitness were evaluated by proliferation, survival and motility assays. TCGA and GEO databases, in combination with tissue microarrays (TMA), were used to validate the mouse targets and their impact on human HCC prognosis. Finally, the functional effects of the identified targets on tumorigenesis and tumor therapy were tested in hydrodynamic tail vein injection (HDTVi)-based preclinical HCC models in vivo. ResultsThe expression of miR-107 was found to be significantly reduced in mouse models of liver tumors of various etiologies and in cohorts of human HCC patients. Overexpression of miR-107 or inhibition of its novel target Kinesin family member 23 (Kif23) significantly reduced proliferation by interfering with cytokinesis, thereby controlling survival and motility of mouse and human hepatoma cells. In humans, KIF23 expression was found to be a prognostic marker in liver cancer, with high expression associated with poor prognosis. HDTVi of vectors carrying either pre-miR- 107 or anti-Kif23 shRNA inhibited the development of highly aggressive cMyc-NRas- induced liver cancers in mice. ConclusionsDisruption of the miR-107/Kif23 axis inhibited hepatoma cell proliferation in vitro and prevented oncogene-induced liver cancer development in vivo, offering a novel potential avenue for the treatment of HCC in humans. Impact and implicationsA comprehensive analysis integrating in silico prediction, miRNA and mRNA data in three pathogenically distinct mouse models provided novel targets for the treatment of human HCC, bridging the translational gap between mouse data and human HCC. Our functional findings on the novel miR-107/Kif23 module provide important new insights into the control of mitosis in liver cancer cells. The findings that miR-107 overexpression or Kif23 inhibition had a dramatic functional effect on inhibiting the growth of liver cancer cells in vitro and in vivo suggest that the miR-107/Kif23 axis may be a promising novel target and potential adjunct to sequential systemic therapy of HCC. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=164 SRC="FIGDIR/small/565448v1_ufig1.gif" ALT="Figure 1"> View larger version (45K): org.highwire.dtl.DTLVardef@afda02org.highwire.dtl.DTLVardef@111da7borg.highwire.dtl.DTLVardef@11eeeecorg.highwire.dtl.DTLVardef@1d7d9f7_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightsO_LImiR-107 is globally downregulated in mouse liver cancers of different etiologies and represents a potential biomarker in human HCC. C_LIO_LIIntegration of in-silico-prediction, miRNA and mRNA transcriptomics identified KIF23, a mitotic spindle-associated protein, as a specific target mediating the biological effects of miR-107. C_LIO_LIThe miR-107/KIF23 module promotes replicative fitness of liver cancer cells through an essential function in cytokinesis C_LIO_LIMice receiving shRNA targeting Kif23 were completely protected from oncogene-induced liver cancer. C_LI

cancer biology↗

bioRxiv2023

Astrocytic uptake of posttranslationally modified amyloid-β leads to endolysosomal system disruption and induction of pro-inflammatory signaling

The disruption of astrocytic catabolic processes contributes to the impairment of amyloid-{beta} (A{beta}) clearance, neuroinflammatory signaling, and the loss of synaptic contacts in late-onset Alzheimers disease (AD). While it is known that the posttranslational modifications of A{beta} have significant implications on biophysical properties of the peptides, their consequences for clearance impairment are not well understood. It was previously shown that N-terminally pyroglutamylated A{beta}3(pE)-42, a significant constituent of amyloid plaques, is efficiently taken up by astrocytes, leading to the release of pro-inflammatory cytokine tumor necrosis factor (TNF) and synapse loss. Here we report that A{beta}3(pE)-42, but not A{beta}1-42, gradually accumulates within the astrocytic endolysosomal system, disrupting this catabolic pathway and inducing formation of heteromorphous vacuoles. This accumulation alters lysosomal kinetics and lysosome-dependent calcium signaling, and upregulates lysosomal stress response. These changes correlate with the upregulation of glial fibrillary acidic protein (GFAP) and increased activity of nuclear factor kappa-light-chain-enhancer of activated B cells (NFB). Treatment with a lysosomal protease inhibitor, E64, rescues GFAP upregulation, NFB activation, and synapse loss, indicating that abnormal lysosomal protease activity is upstream of pro-inflammatory signaling and related synapse loss. Collectively, our data suggest that A{beta}3(pE)-42-induced disruption of the astrocytic endolysosomal system leads to cytoplasmic leakage of lysosomal proteases, promoting pro-inflammatory signaling and synapse loss, hallmarks of AD-pathology.

neuroscience↗

bioRxiv2021

Time-Dependent Image Restoration of Low-SNR Live Cell Ca2+ Fluorescence Microscopy Data

Live cell Ca2+ fluorescence microscopy is a cornerstone of cellular signaling analysis and imaging. The demand for high spatial and temporal imaging resolution is, however, intrinsically linked to a low signal-to-noise ratio (SNR) of the acquired spatio-temporal image data, which impedes subsequent image analysis. Advanced deconvolution and image restoration algorithms can partly mitigate the corresponding problems, but are usually defined only for static images. Frame-by-frame application to spatio-temporal image data neglects inter-frame contextual relationships and temporal consistency of the imaged biological processes. Here, we propose a variational approach to time-dependent image restoration built on entropy-based regularization specifically suited to process low- and lowest-SNR fluorescence microscopy data. The advantage of the presented approach is demonstrated by means of four data sets: synthetic data for in-depth evaluation of the algorithm behavior; two data sets acquired for analysis of initial Ca2+ microdomains in T cells; and, to illustrate transferability of the methodical concept to different applications, one dataset depicting spontaneous Ca2+ signaling in jGCaMP7b-expressing astrocytes. To foster re-use and reproducibility, the source code is made publicly available.

bioinformatics↗