Biology subjects

Armbruster, M.

Publications and source records attributed to Armbruster, M..

12 recordsLinked to original sources

bioRxiv2026

Progressive Post-Acute Gut Microbiome Disruption Following SARS-CoV-2 Infection in Mice

SARS-CoV-2 infection is increasingly recognized to produce long-lasting physiological disturbances that extend beyond the acute phase. The gut microbiome has emerged as a potential contributor to post-infection outcomes, yet the longitudinal progression of microbial disruption following infection remains poorly defined. Here, we used a mouse model of SARS-CoV-2 infection to characterize gut microbiome dynamics at 7 (late acute phase), 14 (early recovery), and 21 (post-COVID condition, PCC) days post-infection (dpi). Viral RNA was detected in the lungs through 21 dpi. Longitudinal microbiome profiling revealed a two-phase restructuring marked by early shifts in Bacillota and Bacteroidota abundance, followed by pronounced post-acute dysbiosis characterized by reduced diversity, expansion of Bacillota, and near-complete loss of Bacteroidota. Functional pathway predictions showed progressive metabolic remodeling, including disruptions in nucleotide turnover, fermentation, and vitamin-related pathways. Together, these findings demonstrate that SARS-CoV-2 infection drives progressive and sustained alterations in gut microbial composition and function after the transition from acute infection through recovery into PCC.

microbiology↗

bioRxiv2026

PAR2 signaling shapes microbial and metabolic remodeling along the gut-lung axis

Introduction: Protease activated receptor (PAR2) is a prominent sensor of environmental and microbial proteases and may serve as an important interface between the host epithelium and mucosal microbes. However, whether PAR2 helps shape microbial community structure and function at barrier surfaces remains unclear. To address this, we examined how PAR2 deficiency or activation affects microbial composition and metabolic potential across the gut lumen, airway lumen, and lung tissue in the context of exposure to protease-rich house dust mite allergen (HDM) exposure. Methods: Wild type and PAR2 deficient littermates of both sexes received a single intranasal challenge with phosphate buffered saline, HDM extract, or a selective PAR2 agonist. Microbial communities from feces, bronchoalveolar lavage fluid (BALF), and lung tissue were profiled using 16S rRNA gene sequencing and PICRUSt2 based functional inference to assess compartment specific taxonomic and metabolic responses. Results: Alpha and beta diversity remained stable across all experimental groups, but distinct conditions resulted in compartment specific remodeling of the microbial population. At baseline, PAR2 deficiency altered multiple genera in the gut and lung and shifted predicted pathways linked to amino acid, lipid, and sulfur metabolism. HDM induced broad taxonomic and functional changes in the gut and lung tissue, including shifts in coenzyme A biosynthesis, reductive TCA activity, lysine fermentation, and nucleotide biosynthesis, while producing only limited taxonomic changes in BALF. PAR2 signaling accounted for a substantial portion of HDM driven remodeling, and direct PAR2 activation reproduced many compartment specific effects, including mucin derived sugar degradation in the gut and suppression of nucleotide biosynthesis in the lung. Sex moderately modified microbial and metabolic responses, with males and females exhibiting divergent, condition dependent functional biases across gut and lung. Conclusion: These findings identify PAR2 as a mucosal niche modifying receptor whose activation or loss reshapes microbial composition and metabolic potential along the gut-lung axis.

microbiology↗

bioRxiv2026

Ratiometric iGluSnFr imaging to assess tonic glutamate in the cerebral cortex

Tonic glutamate signaling by ambient levels of extracellular glutamate has been implicated in development, brain injury, pathologies, and physiological activity. However, it has been difficult to assay extracellular glutamate changes with spatial and temporal resolution. Here, we utilize the rarely used ratiometric excitations properties of the fluorescence glutamate sensor iGluSnFr to enable the characterization of ambient glutamate levels in acute brain slices. This ratiometric imaging enables a spatial, temporal and calibratable assay of ambient glutamate and demonstrates regional differences in ambient glutamate and sensitivity to glutamate transporters and system Xc inhibition.

neuroscience↗

bioRxiv2025

iGABASnFR Imaging Reveals Diffusion-Driven GABA Clearance in the Cerebral Cortex

GABAergic signaling consists of presynaptic release, synaptic and extra-synaptic receptor activation, and signal termination by one of several mechanisms including receptor desensitization, diffusion of GABA, and active clearance by GABA transporters (GATs). Understanding how long GABA is free in the extracellular space is key to understanding how inhibition controls activity but has been technically challenging. Estimates of GABAs persistence from GABAA and GABAB recordings range from tens of milliseconds to multiple seconds, but may reflect receptor properties rather than extracellular GABA dynamics. Using the fluorescent GABA sensor, iGABASnFr, in the mouse cerebral cortex, we show that GABA rapidly disperses (tens of milliseconds) from sites of release sites via diffusion rather than GATs. This GABA then accumulates in the extracellular space, where GATs require hundreds of milliseconds to remove extracellular GABA following its release, and even longer when the local density of GABA release is elevated. This extracellular summation of GABA can act hetero-synaptically by activating and/or desensitizing both extra-synaptic and neighboring synaptic receptors. Together these findings reveal a stark disconnect between phasic IPSC signals, which rapidly depress, and extracellular GABA, which strongly accumulates, raising new questions about how GABAergic inhibition works to shape network function.

neuroscience↗

bioRxiv2025

Evidence for the Transient Presence of Atypical Astrocytes in Mice Following a Single, Closed-Head Mild Traumatic Brain Injury

Mild traumatic brain injury (mTBI) affects roughly 42 million people each year, causes a variety of physical, behavioral, and cognitive symptoms, and increases the risk for developing neurological disorders, including post-traumatic headache (PTH) and Alzheimers disease (AD). Multiple molecular and cellular changes occur following mTBI; here we focus on astrocytes - cells that respond to brain injury and are critical to maintaining neuronal and circuit homeostasis. While some astrocytes become reactive after mTBI, others adopt an atypical state characterized by the loss of multiple functional astrocyte proteins, including glutamate transporters (GLT-1, GLAST) and ion channels (Kir4.1), without upregulation of prototypical reactive astrocyte markers (glial fibrillary acidic protein [GFAP]). Previous studies have shown that repeated mTBI causes atypical astrocytes (AtAs) that can persist for months, but we know much less about whether a single mTBI causes similar astrocyte phenotypes. To address this, we employed a closed-head mild traumatic brain injury (chmTBI) model in male and female mice and quantified the abundance of AtAs both acutely (3-days) and chronically (1-month) after a single injury. We found that 3-days after chmTBI, AtAs were present in areas subject to blunt force trauma (BFT), consistent with previous reports, as well as in other brain regions presumably affected by diffuse injury. One month after chmTBI, however, the proportion of AtAs was similar between chmTBI and sham injured mice, thereby suggesting AtAs do not persist long term in this model. Consistent with previous studies, this chmTBI model did not induce significant GFAP-positive reactive astrocytes as assayed using immunohistochemistry, at either timepoint. Overall, we show an increase in AtAs 3-days after a single chmTBI that returns to sham levels when examined 1-month after injury. This suggests that after a single mTBI, AtAs are present but do not persist long term, unlike in repeated mTBI where AtAs persist for months after injury.

neuroscience↗

bioRxiv2024

Human pulmonary neuroendocrine cells respond to House dust mite extract with PAR-1 dependent release of CGRP

BackgroundPulmonary neuroendocrine cells (PNEC) are rare airway epithelial cells that have recently gained attention as potential amplifiers of allergic asthma. However, studying PNEC function in humans has been challenging due to a lack of cell isolation methods and little is known about human PNEC function in response to asthma relevant stimuli. Here we developed and characterized an in vitro human PNEC model and investigated the neuroendocrine response to extracts of the common aeroallergen house dust-mite. (HDM). MethodsPNEC enriched cultures were generated from human induced pluripotent stem cells (iPNEC) and primary bronchial epithelial cells (ePNEC). Characterized PNEC cultures were exposed to HDM extract, a volatile chemical odorant (Bergamot oil), or the bacterial membrane component, lipopolysaccharide (LPS) and neuroendocrine gene expression and neuropeptide release determined. ResultsBoth iPNEC and ePNEC models demonstrated similar baseline neuroendocrine characteristics and a stimuli specific modulation of gene expression. Most notably, exposure to HDM but not Bergamot oil or LPS, lead to dose dependent induction of the CGRP encoding gene, CALCB, and corresponding release of the neuropeptide. HDM induced CALCB expression and CGRP release could be inhibited by a protease activated receptor 1 (PAR1) antagonist or protease inhibitors and was mimicked by a PAR1 agonist. ConclusionsWe have characterized a novel model of PNEC enriched human airway epithelium and utilized this model to demonstrate a previously unrecognized role for human PNEC in mediating a direct neuroendocrine response to aeroallergen exposure and highlighting CGRP production by these cells as a potential therapeutic target in allergic asthma.

cell biology↗

bioRxiv2024

Glutamate uptake is transiently compromised in the perilesional cortex following controlled cortical impact

Glutamate, the primary excitatory neurotransmitter in the CNS, is regulated by the excitatory amino acid transporters (EAATs) GLT-1 and GLAST. Following traumatic brain injury (TBI), extracellular glutamate levels increase, contributing to excitotoxicity, circuit dysfunction, and morbidity. Increased neuronal glutamate release and compromised astrocyte-mediated uptake contribute to elevated glutamate, but the mechanistic and spatiotemporal underpinnings of these changes are not well established. Using the controlled cortical impact (CCI) model of TBI and iGluSnFR glutamate imaging, we quantified extracellular glutamate dynamics after injury. Three days post-injury, glutamate release was increased, and glutamate uptake and GLT-1 expression were reduced. 7- and 14-days post-injury, glutamate dynamics were comparable between sham and CCI animals. Changes in peak glutamate response were unique to specific cortical layers and proximity to injury. This was likely driven by increases in glutamate release, which was spatially heterogenous, rather than reduced uptake, which was spatially uniform. The astrocyte K+ channel, Kir4.1, regulates activity-dependent slowing of glutamate uptake. Surprisingly, Kir4.1 was unchanged after CCI and accordingly, activity-dependent slowing of glutamate uptake was unaltered. This dynamic glutamate dysregulation after TBI underscores a brief period in which disrupted glutamate uptake may contribute to dysfunction and highlights a potential therapeutic window to restore glutamate homeostasis.

neuroscience↗

bioRxiv2024

Cortical inhibitory parvalbumin interneurons exhibit metabolic specializations coordinated by PGC-1α that are lost in rodents and humans after traumatic brain injury

Parvalbumin-positive interneurons (PV-INs) regulate neuronal and circuit activity, and their dysfunction is observed across neurological conditions, including traumatic brain injury (TBI), epilepsy, Alzheimers disease, and schizophrenia. PV-INs are particularly vulnerable to cell loss, potentially due to their increased metabolic demands arising from their uniquely high level of electrical activity, which render them susceptible to metabolic pressure. Here, we use single-nucleus RNA-sequencing (snRNAseq) data from a rodent model of TBI, as well as human TBI data, and demonstrate PV-INs have unique metabolic specializations that are lost after injury and can be rescued by in vivo treatment with the glycolytic inhibitor, 2-deoxyglucose. We generated a novel PV-IN transcriptional identity module comprised primarily of genes encoding specialized ion channels, metabolic enzymes, and synaptic machinery, that identifies heterogenous subsets of injury-associated PV-INs with loss of PV-IN transcriptional identity. We show that changes in metabolic specialization are coupled to changes in transcriptional identity in PV-INs and implicate the PV-IN-enriched transcriptional co-activator, Ppargc1a, as a key driver of PV-IN transcriptional metabolic dysfunction. We also identify a family of long non-coding RNAs enriched in this subset of transcriptionally dysfunctional PV-INs that negatively correlates with PV-IN metabolic specialization. Lastly, we utilize these tools to interrogate a published human TBI snRNAseq data set and find nearly identical changes, underscoring the importance of PV-IN metabolic dysfunction in the pathology of TBI.

neuroscience↗

bioRxiv2023

Traumatic brain injury disrupts state-dependent functional cortical connectivity in a mouse model

Traumatic brain injury (TBI) is the leading cause of death in young people and can cause cognitive and motor dysfunction and disruptions in functional connectivity between brain regions. In human TBI patients and rodent models of TBI, functional connectivity is decreased after injury. Recovery of connectivity after TBI is associated with improved cognition and memory, suggesting an important link between connectivity and functional outcome. We examined widespread alterations in functional connectivity following TBI using simultaneous widefield mesoscale GCaMP7c calcium imaging and electrocorticography (ECoG) in mice injured using the controlled cortical impact (CCI) model of TBI. Combining CCI with widefield cortical imaging provides us with unprecedented access to characterize network connectivity changes throughout the entire injured cortex over time. Our data demonstrate that CCI profoundly disrupts functional connectivity immediately after injury, followed by partial recovery over 3 weeks. Examining discrete periods of locomotion and stillness reveals that CCI alters functional connectivity and reduces theta power only during periods of behavioral stillness. Together, these findings demonstrate that TBI causes dynamic, behavioral state-dependent changes in functional connectivity and ECoG activity across the cortex.

neuroscience↗

bioRxiv2022

Cortical Parvalbumin-positive Interneuron Development and Function are Altered in the APC Conditional Knockout Mouse Model of Infantile Spasm Syndrome

Infantile Spasms syndrome (ISS) is a childhood epilepsy syndrome characterized by infantile or late onset spasms, abnormal neonatal EEG, and epilepsy. Few treatments exist for IS, clinical outcomes are poor, and the molecular and circuit-level etiologies of IS are not well understood. Multiple human ISS risk genes are linked to Wnt/{beta}-catenin signaling, a pathway which controls developmental transcriptional programs and promotes glutamatergic excitation via {beta}-catenins role as a synaptic scaffold. We previously showed that deleting adenomatous polyposis coli (APC), a component of the {beta}-catenin destruction complex, in excitatory neurons (APC cKO mice, APCfl/fl x CaMKIICre) in mice increased {beta}-catenin levels in developing glutamatergic neurons and led to infantile behavioral spasms, abnormal neonatal EEG, and adult epilepsy. Here, we tested the hypothesis that the development of inhibitory GABAergic interneurons (INs) is disrupted in APC cKOs. IN dysfunction is implicated in human ISS, is a feature of other rodent models of ISS and may contribute to the manifestation of spasms and seizures. We found that parvalbumin positive INs (PV+INs), an important source of cortical inhibition, were decreased in number, underwent disproportionate developmental apoptosis, and had altered dendrite morphology at P9, the peak time of behavioral spasms. PV+INs received excessive excitatory input and their intrinsic ability to fire action potentials was reduced at all timepoints examined (P9, P14, P60). Subsequently, synaptic inhibition of pyramidal neurons was uniquely altered in the somatosensory cortex of APC cKO mice at all ages, with both decreased inhibition at P14 and enhanced inhibition at P9 and P60. These results indicate that inhibitory circuit dysfunction occurs in APC cKOs and, along with known changes in excitation, may contribute to ISS-related phenotypes. Significance StatementInfantile spasms syndrome (ISS) is a devastating epilepsy with limited treatment options and poor clinical outcomes. The molecular, cellular, and circuit disruptions that cause infantile spasms and seizures are largely unknown, but inhibitory GABAergic interneuron dysfunction has been implicated in rodent models of ISS and may contribute to human ISS. Here, we utilize a rodent model of ISS, the APC cKO mouse, in which {beta}-catenin signaling is increased in excitatory neurons. This results in altered parvalbumin-positive GABAergic interneuron development and inhibitory synaptic dysfunction throughout life, showing that pathology arising in excitatory neurons can initiate long-term interneuron dysfunction. Our findings further implicate GABAergic dysfunction in ISS, even when pathology is initiated in other neuronal types.

neuroscience↗

bioRxiv2021

Neuronal activity drives pathway-specific depolarization of astrocyte distal processes

Astrocytes are glial cells that interact with neuronal synapses via their distal processes, where they remove glutamate and potassium (K+) from the extracellular space following neuronal activity. Astrocyte clearance of both glutamate and K+ is voltage-dependent, but astrocyte membrane potential (Vm) has been thought to be largely invariant. As a result, these voltage-dependencies have not been considered relevant to astrocyte function. Using genetically encoded voltage indicators enabling the measurement of Vm at distal astrocyte processes (DAPs), we report large, rapid, focal, and pathway-specific depolarizations in DAPs during neuronal activity. These activity-dependent astrocyte depolarizations are driven by action potential-mediated presynaptic K+ efflux and electrogenic glutamate transporters. We find that DAP depolarization inhibits astrocyte glutamate clearance during neuronal activity, enhancing neuronal activation by glutamate. This represents a novel class of sub-cellular astrocyte membrane dynamics and a new form of astrocyte-neuron interaction. One Sentence SummaryGenetically encoded voltage imaging of astrocytes shows that presynaptic neuronal activity drives focal astrocyte depolarization, contributing to activity-dependent inhibition of glutamate uptake.

neuroscience↗

bioRxiv2019

Effects of fluorescent glutamate indicators on neurotransmitter diffusion and uptake

Genetically encoded fluorescent glutamate indicators (iGluSnFRs) enable neurotransmitter release and diffusion to be visualized in intact tissue. Synaptic iGluSnFR signal time courses vary widely depending on experimental conditions and often last 10-100 times longer than the extracellular lifetime of synaptically released glutamate estimated with uptake measurements. iGluSnFR signals typically also decay much more slowly than the unbinding kinetics of the indicator. To resolve these discrepancies, here we have modeled synaptic glutamate diffusion, uptake and iGluSnFR activation to identify factors influencing iGluSnFR signal waveforms. Simulations suggested that iGluSnFR competes with transporters to bind synaptically released glutamate, delaying glutamate uptake. Accordingly, synaptic transporter currents recorded in iGluSnFR-expressing cortical astrocytes were slower than those in control astrocytes. Simulations also suggested that iGluSnFR reduces free glutamate levels in extrasynaptic spaces, likely limiting extrasynaptic receptor activation. iGluSnFR and lower-affinity variants nonetheless provide linear indications of vesicle release, underscoring their value for optical quantal analysis.

neuroscience↗