Biology subjects

Mueller, S. A.

Publications and source records attributed to Mueller, S. A..

15 recordsLinked to original sources

bioRxiv2026

A reproducible human brain tissue model to study physiological and disease-associated microglia phenotypes

Stem-cell-based in vitro models offer promising potential to elucidate human brain cell functions and interactions under physiological and pathological conditions. However, harnessing this potential is impaired by low reproducibility, maturity, or cell-type diversity of existing models. Especially, prolonged incorporation of mature microglia and studies of neuroinflammation have proven challenging. Here, we developed a 3D cortical brain tissue model (3BTM) containing neurons, astrocytes, and microglia with high reproducibility, maturity, and viability. 3BTMs show morphological, functional, and proteomic maturation of all cell types, leading to high similarity to their in vivo counterparts. Incorporated microglia survive for over 6 months and display mature morphology, functions, and gene expression. Importantly, when engineered to model Alzheimers disease pathology, 3BTMs recapitulate key disease hallmarks including amyloid deposition, increased phospho-Tau levels, and neuroinflammation, with microglia shifting their transcriptional landscape to disease-relevant signatures. Together, our model offers unprecedented possibilities for studying physiological and pathological states of human brain tissue and translational applications.

neuroscience↗

bioRxiv2025

Loss of the Parkinson's disease-associated protein DJ-1 impacts dopamine metabolism in astrocytes

The selective loss of dopaminergic neurons in the substantia nigra is a hallmark of Parkinsons disease (PD), yet the contribution of glial cells to this vulnerability is not fully understood. Studies in rodent models suggest that astrocytes can take up and metabolize dopamine (DA), potentially protecting neurons by detoxifying reactive DA metabolites via glutathione S-transferase mu 2 (GSTM2) release. However, these mechanisms remain underexplored in human systems, particularly in the context of PD. Here, we used CRISPR-engineered iPSC-derived human astrocytes with a PD-linked DJ-1 mutation and isogenic controls to investigate astrocytic DA metabolism. Upon DA exposure, control astrocytes upregulated quinone-reducing enzymes NAD(P)H quinone dehydrogenase 1 (NQO1) and GSTM2, whereas DJ-1 mutant astrocytes failed to adaptively respond. In addition, only control astrocytes presented with increased DA quinone products upon DA exposure, not DJ-1 mutants. These results demonstrate astrocytic DA handling being disrupted in DJ-1-linked PD, implicating astroglial dysfunction as an important contributor to PD pathogenesis and potential target for therapeutic intervention.

neuroscience↗

bioRxiv2025

VMAT2 dysfunction impairs vesicular dopamine uptake, driving its oxidation and α-synuclein pathology in DJ-1-linked Parkinson's disease neurons

Parkinsons disease (PD) is characterized by -synuclein accumulation and dopaminergic neuron degeneration, with dopamine (DA) oxidation emerging as a key pathological driver. However, the mechanisms underlying this neurotoxic process remain unclear. Using PD patient-derived and CRISPR-engineered iPSC midbrain dopaminergic neurons lacking DJ-1, we identified defective sequestration of cytosolic DA into synaptic vesicles, which culminated in DA oxidation and -synuclein accumulation. In-depth proteomics, state-of-the-art imaging, and ultrasensitive DA probes uncovered that decreased VMAT2 protein and function impaired vesicular DA uptake, resulting in reduced vesicle availability and abnormal vesicle morphology. Furthermore, VMAT2 activity and vesicle endocytosis are processes dependent on ATP, which is notably reduced in DJ-1-deficient dopaminergic neurons. ATP supplementation restored vesicular function and alleviated DA-related pathologies in mutant dopaminergic neurons. This study reveals an ATP-sensitive mechanism that regulates DA homeostasis through VMAT2 and vesicle dynamics in midbrain dopaminergic neurons, highlighting enhanced DA sequestration as a promising therapeutic strategy for PD. TeaserLoss of DJ-1 interferes with VMAT2 function and vesicle dynamics, leading to DA oxidation and -synuclein pathology in PD neurons.

neuroscience↗

bioRxiv2025

Multiomic profiling reveals aberrant immunomodulatory signature in β-propeller protein-associated neurodegeneration patient iPSC-derived microglia

Microglia are the primary immune cells of the central nervous system and play a crucial role in maintaining brain homeostasis. In common neurodegenerative diseases such as Alzheimers disease and Parkinsons disease (PD), early and sustained microglial activation has been shown to precede neuronal loss, with elevated levels of microglia-derived inflammatory mediators detected in affected brain regions. In contrast, little is known about the role of microglia in rare neurodegenerative disorders. One such disorder is {beta}-propeller protein-associated neurodegeneration (BPAN), a common subtype of neurodegeneration with brain iron accumulation (NBIA). BPAN shares pathological features with PD, including iron accumulation and selective loss of dopaminergic neurons in the substantia nigra, and is caused by mutations in the WD repeat domain 45 (WDR45) gene encoding an autophagy protein also called WIPI4. However, the pathological role of mutant WDR45 in BPAN and the possible contribution of microglia remain unresolved. We generated the first BPAN patient microglia model system using induced pluripotent stem cells (iPSCs) to identify immune-related alterations and immunomodulatory signaling changes in a disease-relevant context. Integrated transcriptomic and proteomic profiling of iPSC-derived microglia from BPAN patients revealed a consistent shift from a homeostatic to a reactive, disease-associated state. Transcriptomic analysis showed disruption of core microglial pathways, including immune activation, stress response, and autophagy, consistent with a chronic pro-inflammatory phenotype. Complementary secretome analysis identified impaired lysosomal function and increased antigen presentation pathways, further supporting persistent microglial activation. Together this suggests that dysfunctional microglial states may contribute to BPAN pathogenesis. Our findings lay the groundwork for advancing immunomodulatory research in BPAN and may open new avenues for therapeutic development targeting microglial dysfunction.

neuroscience↗

bioRxiv2025

Anti-Aβ immunotherapy-mediated amyloid clearance attenuates microglial activation without inducing exhaustion at residual plaques

Anti-amyloid {beta}-peptide (A{beta}) immunotherapy was developed to reduce amyloid plaque pathology and slow cognitive decline during progression of Alzheimers disease. Efficient amyloid plaque clearance has been proven in clinical trials testing anti-A{beta} antibodies, with the impact on cognitive endpoints correlating with the extent of plaque removal. However, treatment is associated with adverse side-effects, such as oedema and haemorrhages, which are potentially linked to the induced immune response. To improve the safety profile of these molecules, it is imperative to understand the consequences of anti-A{beta} antibody treatment on immune cell function. Here, we investigated the effects of long-term chronic anti-A{beta} treatment on amyloid plaque pathology and microglial response in the APP-SAA triple knock-in mouse model. Mice were treated weekly with anti-A{beta} antibody from 4-8 months of age. Long-term treatment with anti-A{beta} results in a robust and dose-dependent removal of amyloid plaque pathology, with a higher efficiency for removing diffuse over dense-core plaques. Analysis of the CSF proteome indicates a reduction of markers for neurodegeneration including Tau and -Synuclein, as well as immune cell related proteins. Bulk RNA-seq revealed a dose-dependent decrease in brain-wide disease-associated microglial (DAM) and glycolytic gene expression, which is supported by a parallel decrease of glucose uptake and protein levels of Triggering receptor of myeloid cells 2 (Trem2) protein, a major immune receptor involved in DAM activation of microglia. In contrast, DAM activation around remaining plaques remains high regardless of treatment dose. In addition, microglia surrounding remaining plaques display a dose-dependent increase in microglial clustering and a selective increase in antigen presenting and immune signalling proteins. These findings demonstrate that long-term chronic anti-A{beta} mediated removal of A{beta} leads to a dose dependent decrease in brain-wide microglial DAM activation and neurodegeneration, while microglia at residual plaques display a combined DAM and antigen presenting phenotype that suggests a continued treatment response. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=161 SRC="FIGDIR/small/645950v1_ufig1.gif" ALT="Figure 1"> View larger version (46K): org.highwire.dtl.DTLVardef@6d1a49org.highwire.dtl.DTLVardef@d8c14dorg.highwire.dtl.DTLVardef@7ae330org.highwire.dtl.DTLVardef@1d96cc3_HPS_FORMAT_FIGEXP M_FIG Graphical abstract: Schematic overview of the effects of chronic long-term anti-A treatment in APP-SAA mice Schematic was created with BioRender.com C_FIG

neuroscience↗

bioRxiv2024

An improved method for sampling and quantitative protein analytics of cerebrospinal fluid of single mice

Mice are the most commonly used preclinical animal model, but protein analytics of murine cerebrospinal fluid (CSF) remains challenging because of low CSF volume (often <10 {micro}l) and frequent blood contaminations. We developed an improved CSF sampling method that allows routine collection of increased volumes (20-30 {micro}l) of pure CSF from individual mice, enabling multiple protein analytical assays from a single sample. Based on cell counts and hemoglobin ELISAs, we provide an easy quality control workflow for obtaining cell- and blood-free murine CSF. Through mass spectrometry-based proteomics using an absolutely quantified external standard, we estimated concentrations for hundreds of mouse CSF proteins. While repeated CSF sampling from the same mouse was possible, it induced CSF proteome changes. Applying the improved method, we found that the mouse CSF proteome remains largely stable over time in wild-type mice, but that amyloid pathology in the 5xFAD mouse model of Alzheimers disease massively changes the CSF proteome. Neurofilament light chain and TREM2, markers of neurodegeneration and activated microglia, respectively, were strongly upregulated and validated using immunoassays. In conclusion, our refined murine CSF collection method overcomes previous limitations, allowing multiple quantitative protein analyses for applications in biomedicine.

neuroscience↗

bioRxiv2024

Loss of CLN3 in microglia leads to impaired lipid metabolism and myelin turnover

BackgroundMicroglia are the primary brain cell type regulating neuroinflammation and they are important for healthy aging. Genes regulating microglial function are associated with an increased risk of neurodegenerative disease. Loss-of-function mutations in CLN3, which encodes an endolysosomal membrane protein, lead to the most common childhood-onset form of neurodegeneration, featuring early-stage neuroinflammation that long precedes neuronal cell loss. How loss of CLN3 function leads to this early neuroinflammation is not yet understood. MethodsHere, we have comprehensively studied microglia from Cln3{Delta}ex7/8 mice, a genetically accurate CLN3 disease model. Microglia were isolated from young and old Cln3{Delta}ex7/8 mice for downstream molecular and functional studies. ResultsWe show that loss of CLN3 function in microglia leads to classic age-dependent CLN3-disease lysosomal storage as well as an altered morphology of the lysosome, mitochonodria and Golgi compartments. Consistent with these morphological alterations, we also discovered pathological proteomic signatures implicating defects in lysosomal function and lipid metabolism processes at an early disease stage. CLN3-deficient microglia were unable to efficiently turnover myelin and metabolize its associated lipids, showing severe defects in lipid droplet formation and significant accumulation of cholesterol, phenotypes that were corrected by treatment with autophagy inducers and cholesterol lowering drugs. Finally, we observed reduced myelination in aging homozygous Cln3{Delta}ex7/8 mice suggesting altered myelin turnover by microglia impacts myelination in the CLN3-deficient brain. ConclusionOur results implicate a cell autonomous defect in CLN3-deficient microglia that impacts the ability of these cells to support neuronal cell health. These results strongly suggest microglial targeted therapies should be considered for CLN3 disease.

neuroscience↗

bioRxiv2023

A MICROGLIAL ACTIVITY STATE BIOMARKER PANEL DIFFERENTIATES FTD-GRANULIN AND AD FROM CONTROL CASES

SummaryO_ST_ABSBackgroundC_ST_ABSWith the emergence of microglia-modulating therapies there is an urgent need for reliable biomarkers to evaluate microglial activation states. MethodsUsing mouse models and human induced pluripotent stem cell-derived microglia (hiMGL), which were genetically modified to yield the most opposite homeostatic (TREM2- knockout) and disease-associated (GRN-knockout) states, we identified microglia activity-dependent markers. Non-targeted mass spectrometry was used to identify changes in microglial and cerebrospinal (CSF) proteome of Grn- and Trem2-knockout mice. Additionally, we analyzed the proteome of GRN- and TREM2-knockout hiMGL and their conditioned media. Candidate marker proteins were tested in two independent patient cohorts, the ALLFTD cohort with 11 GRN mutation carriers and 12 non-carriers, as well as the proteomic data set available from the European Medical Information Framework Alzheimers Disease Multimodal Biomarker Discovery (EMIF-AD MBD). FindingsWe identified proteomic changes between the opposite activation states in mouse microglia and cerebrospinal fluid (CSF), as well as in hiMGL cell lysates and conditioned media. For further verification, we analyzed the CSF proteome of heterozygous GRN mutation carriers suffering from frontotemporal dementia (FTD). We identified a panel of six proteins (FABP3, MDH1, GDI1, CAPG, CD44, GPNMB) as potential indicators for microglial activation. Moreover, we confirmed three of these proteins (FABP3, GDI1, MDH1) to be significantly elevated in the CSF of AD patients. In AD, these markers differentiated amyloid-positive cases with mild cognitive impairment (MCI) from amyloid-negative individuals. InterpretationThe identified candidate proteins reflect microglia activity and may be relevant for monitoring the microglial response in clinical practice and clinical trials modulating microglial activity and amyloid deposition. Moreover, the finding that three of these markers differentiate amyloid-positive from amyloid-negative MCI cases in the AD cohort suggests that these marker proteins associate with a very early immune response to seeded amyloid. This is consistent with our previous findings in the DIAN (Dominantly Inherited Alzheimers Disease Network) cohort, where soluble TREM2 increases as early as 21 years before symptom onset. Moreover, in mouse models for amyloidogenesis, seeding of amyloid is limited by physiologically active microglia further supporting their early protective role. The biological functions of some of our main candidates (FABP3, CD44, GPNMB) also further emphasize that lipid dysmetabolism may be a common feature of neurodegenerative disorders. FundingThis work was supported by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germanys Excellence Strategy within the framework of the Munich Cluster for Systems Neurology (EXC 2145 SyNergy - ID 390857198 to CH, SFL and DP) and a Koselleck Project HA1737/16-1 (to CH).

neuroscience↗

bioRxiv2023

Targeting the TCA cycle can ameliorate widespread axonal energy deficiency in neuroinflammatory lesions

Inflammation in the central nervous system (CNS) can impair the function of neuronal mitochondria and contributes to axon degeneration in the common neuroinflammatory disease multiple sclerosis (MS). Here we combine cell type-specific mitochondrial proteomics with in vivo biosensor imaging to dissect how inflammation alters the molecular composition and functional capacity of neuronal mitochondria. We show that neuroinflammatory lesions in the mouse spinal cord cause widespread and persisting axonal ATP deficiency, which precedes mitochondrial oxidation and calcium overload. This axonal energy deficiency is associated with impaired electron transport chain function, but also an upstream imbalance of tricarboxylic acid (TCA) cycle enzymes, with several, including key rate-limiting, enzymes being depleted in neuronal mitochondria in experimental models and in MS lesions. Notably, viral overexpression of individual TCA enzymes can ameliorate the axonal energy deficits in neuroinflammatory lesions, suggesting that TCA cycle dysfunction in MS may be amendable to therapy.

neuroscience↗

bioRxiv2023

Explicit Modelling of Antibody Levels for Infectious Disease Simulations in the Context of SARS-CoV-2

Measurable levels of immunoglobulin G antibodies develop after infections with and vaccinations against SARS-CoV-2. These antibodies are temporarily dynamic; due to waning, antibody levels will drop below detection thresholds over time. As a result, epidemiological studies could underestimate population protection, given that antibodies are a marker for protective immunity. During the COVID-19 pandemic, multiple models predicting infection dynamics were used by policymakers to plan public health policies. Explicitly integrating antibody and waning effects into the models is crucial for reliable calculations of individual infection risk. However, only few approaches have been suggested that explicitly treat these effects. This paper presents a methodology that explicitly models antibody levels and the resulting protection against infection for individuals within an agent-based model. This approach can be integrated in general frameworks, allowing complex population studies with explicit antibody and waning effects. We demonstrate the usefulness of our model in two use cases.

immunology↗

bioRxiv2023

Deciphering sources of PET signals in the tumor microenvironment of glioblastoma at cellular resolution

Various cellular sources hamper interpretation of positron-emission-tomography (PET) biomarkers in the tumor microenvironment (TME). We developed immunomagnetic cell sorting after in vivo radiotracer injection (scRadiotracing) in combination with 3D-histology via tissue clearing to dissect the cellular allocation of PET signals in the TME. In SB28 glioblastoma mice, translocator protein (TSPO) radiotracer uptake per tumor cell was higher compared to tumor-associated microglia/macrophages (TAMs). Cellular radiotracer uptake was validated by proteomics and confirmed for in vitro samples of patients with glioblastoma. Regional agreement between PET signals and single cell tracer uptake predicted the individual cell distribution in 3D-histology. In consideration of cellular tracer uptake and cell type abundance, tumor cells were the main contributor to TSPO enrichment in glioblastoma, however proteomics identified potential PET targets highly specific for TAMs. Combining cellular tracer uptake measures with 3D-histology facilitates precise allocation of complex PET signal sources and will serve to validate novel TAM-specific radioligands.

neuroscience↗

bioRxiv2022

Endogenous retroviruses promote prion-like spreading of proteopathic seeds

Endogenous retroviruses, remnants of viral germline infections, make up a substantial proportion of the mammalian genome. While usually epigenetically silenced, retroelements can become upregulated in neurodegenerative diseases associated with protein aggregation, such as amyotrophic lateral sclerosis and tauopathies. Here we demonstrate that spontaneous upregulation of endogenous retrovirus gene expression drastically affects the dissemination of protein aggregates between murine cells in culture. Viral glycoprotein Env mediates membrane association between donor and recipient cells and promotes the intercellular transfer of protein aggregates packaged into extracellular vesicles. Proteopathic seed spreading can be inhibited by neutralizing antibodies targeting Env as well as drugs inhibiting viral protein processing. Importantly, we show that also overexpression of a human endogenous retrovirus Env elevates intercellular spreading of pathological Tau. Our data highlight the potential influence of endogenous retroviral proteins on protein misfolding diseases and suggest that antiviral drugs could represent promising candidates for inhibiting protein aggregate spreading.

neuroscience↗

bioRxiv2021

Expedited gene delivery for osteochondral defect repair in a rabbit knee model: a one-year investigation

ObjectiveTo evaluate a single-step, gene-based procedure for repairing osteochondral lesions. DesignOsteochondral lesions were created in the patellar groove of skeletally mature rabbits. Autologous bone marrow aspirates were mixed with adenovirus vectors carrying cDNA encoding green fluorescent protein (Ad.GFP) or transforming growth factor-{beta}1 (Ad.TGF-{beta}1) and allowed to clot. The clotted marrow was press-fit into the defects. Animals receiving Ad.GFP were euthanized at 2 weeks and intra-articular expression of GFP examined by fluorescence microscopy. Animals receiving Ad.TGF-{beta}1 were euthanized at 3 months and 12 months; repair was compared to empty defects using histology and immunohistochemistry. Complementary in vitro experiments assessed transgene expression and chondrogenesis in marrow clots and fibrin gels. In a subsequent pilot study, repair at 3 months using a fibrin gel to encapsulate Ad.TGF-{beta}1 was evaluated. ResultsAt 2 weeks, GFP expression was seen at variable levels within the cartilaginous lesion. At 3 months, there was a statistically significant improvement in healing of lesions receiving Ad.TGF-{beta}1, although variability was high. At 12 months, there was no difference between the empty defects and those receiving Ad.TGF-{beta}1 in overall score and cartilage score, but the bone healing score remained higher. Variability was again high. In vitro experiments suggested that variability reflected variable transduction efficiency and chondrogenic activity of the marrow clots; using fibrin gels instead of marrow provided more uniformity in healing. ConclusionsThis approach to improving the repair of osteochondral lesions holds promise but needs further refinement to reduce variability and provide a more robust outcome.

genetics↗

bioRxiv2019

Fibrillar Aβ triggers microglial proteome alterations and dysfunction in Alzheimer mouse models

Microglial dysfunction is a key pathological feature of Alzheime[r]s disease (AD), but little is known about proteome-wide changes in microglia during the course of AD pathogenesis and their functional consequences. Here, we performed an in-depth and time-resolved proteomic characterization of microglia in two mouse models of amyloid {beta} (A{beta}) pathology, the overexpression APPPS1 and the knock-in APP-NL-G-F (APP-KI) model. We identified a large panel of Microglial A{beta} Response Proteins (MARPs) that reflect a heterogeneity of microglial alterations during early, middle and advanced stages of A{beta} deposition. Although both mouse models display severe microglial alterations at late stages of amyloid pathology, MARP signatures occur earlier in the APPPS1 mice. Strikingly, the kinetic differences in proteomic profiles correlated with the presence of fibrillar A{beta}, rather than dystrophic neurites, suggesting that fibrillar A{beta} aggregates are the main drivers of the AD-associated microglial phenotype and the observed functional decline. The identified microglial proteomic fingerprints of AD provide a valuable resource for functional studies of novel molecular targets and potential biomarkers for monitoring AD progression or therapeutic efficacy.

neuroscience↗

bioRxiv2019

Tetraspanin Tspan15 is an essential subunit of an ADAM10 scissor complex

A disintegrin and metalloprotease 10 (ADAM10) is essential for embryonic development and impacts on diseases such as cancer, Alzheimers and inflammatory diseases. ADAM10 is a molecular scissor that proteolytically cleaves the extracellular region from over 100 substrates, including Notch, amyloid precursor protein, cadherins, growth factors and chemokines. ADAM10 was recently proposed to function as six distinct scissors with different substrates, depending on its association with one of six regulatory tetraspanins, termed TspanC8s. However, it remains unclear to what degree ADAM10 function is critically dependent on a TspanC8 partner. To address this, we generated the first monoclonal antibodies to Tspan15 as a model TspanC8. These were used to show that ADAM10 is the principal Tspan15-interacting protein, that Tspan15 expression requires ADAM10 in cell lines and primary cells, and that a synthetic ADAM10/Tspan15 fusion protein is a functional scissor. Together these findings suggest that ADAM10 exists as an intimate ADAM10/TspanC8 scissor complex.

cell biology↗