Biology subjects

Schneider, G.

Publications and source records attributed to Schneider, G..

At least 19 recordsLinked to original sources

bioRxiv2026

Reverse engineering Lewy bodies suggests alpha-synuclein pathology as condensatopathy

Understanding how soluble monomeric alpha-synuclein transitions into pathological alpha-synuclein (Lewy bodies) has remained a central challenge in neurodegeneration. Existing models, largely based on treating cells and animals with pre-formed alpha-synuclein fibrils cannot account for the emergence of the first inclusion without pre-existing seeds. Here, we combine in vitro reconstitutions, computational modeling and a minimal cellular system to show that phase separation of alpha-synuclein with an interacting scaffold can recapitulate Lewy body-like structures. An unbiased proteomics screen, live-cell imaging, correlative light-electron microscopy, and soft X-ray tomography show that Lewy body-like structures are associated with redistribution of actin and membrane-bound organelles, with mitochondria accumulating at their periphery in an actin-dependent manner. Structural analyses further indicate that alpha-synuclein condensates provide local environments in which the insoluble beta-sheets can form. Together, these findings support a seed-independent trajectory from soluble alpha-synuclein through condensation and progressive immobilization to Lewy body-like assemblies and, subsequently, insoluble beta-sheet fibrils. This framework offers a new mechanistic route for understanding the disease progression and promises to guide the design of innovative therapeutic interventions.

neuroscience↗

bioRxiv2026

Loss of the Y chromosome drives basal identity and metastatic potential via epigenetic reprogramming in pancreatic cancer

Loss of the Y chromosome (LOY) has been largely unexplored in pancreatic ductal adenocarcinoma (PDAC), and no mechanistic framework previously explained its role in tumor biology. We identify LOY as a recurrent, functionally consequential alteration affecting ~50% of male PDAC patients across two independent cohorts, with strong enrichment in advanced disease and, critically, in the basal subtype, establishing LOY as a clinically actionable biomarker. Comprehensive genomic profiling positions LOY as a distinct genetic event associated with TP53 mutations, implicating it in aggressive tumor evolution. Integrative analyses across bulk tumors, single-cell datasets and CRISPR-engineered PDAC models converge on epithelial-to-mesenchymal transition (EMT) as the dominant LOY-driven program. Y-chromosome deletion alone induces EMT transcriptional states, mesenchymal morphology and enhanced metastatic ability. Mechanistically, LOY disrupts epigenetic regulation through loss of Y-linked chromatin modifiers, reshaping DNA methylation at EMT- and basal-defining loci and reducing chemotherapy sensitivity. These findings establish LOY as a causal genetic driver of PDAC progression and a clinically accessible biomarker with direct therapeutic relevance.

cancer biology↗

bioRxiv2026

Multimodal 3D imaging reveals a central role for lysosomes indissolution of cholesterol crystals by macrophages

Formation of cholesterol crystals (CCs) is a key event during the development of atherosclerosis, but the molecular mechanisms of their degradation within cells are poorly understood. By incorporating the fluorescent cholesterol analogue TopFluor-Cholesterol (TF-Chol) into CCs, we were able to visualize the uptake of CCs in macrophages using correlative fluorescence and soft X-ray microscopy. Using quantitative 3D live-cell imaging, we show that CCs are processed in late endosomes and lysosomes (LE/Lys), resulting in formation of TF-Chol containing lipid droplets (LDs) over time. Inhibition of lysosomal sterol export with U18666A caused accumulation of TF-Chol in LE/Lys, and inhibition of lysosomal acidification with bafilomycin A1 led to reduced dissolution of the CCs. Using a novel assay combined with 3D image processing, we show that large CCs in contact with macrophages are processed via lysosomal exocytosis followed by extracellular and intracellular degradation of CCs. Treating macrophages with a fluorescent version of cyclodextrin (CD) promoted the dissolution of CCs and enhanced the formation of LDs enriched with TF-Chol. The majority of fluorescent CD co-localized with a marker for LE/Lys during this process, suggesting that intracellular delivery to LE/Lys may contribute to the dissolution of CCs. Dehydroergosterol (DHE) is an intrinsically fluorescent sterol closely mimicking the properties and behavior of cholesterol. DHE is known to self-associate into aggregates and crystals, and by using fluorescence spectroscopy and specialized ultraviolet (UV) microscopy, we found that CD enhances the dissolution of DHE crystals in vitro and in cells. Together, our findings highlight the lysosomal pathway as responsible for dissolution of CCs, cholesterol trafficking, and efflux in macrophages.

biochemistry↗

bioRxiv2026

Pre-anaesthetic anxiety phenotype stratifies cortical excitability, learned navigation, and post-anaesthetic sleep in sevoflurane-exposed mice

Trait anxiety is a common pre-surgical phenotype and has been linked to adverse postoperative cognitive outcome, but whether it modulates the response to general anaesthesia has not been tested in a controlled design that isolates the anaesthetic from surgical injury. We classified 42 male C57BL/6N mice as low-anxiety (LA, n = 24) or high-anxiety (HA, n = 18) by unsupervised k-medoids clustering on cued fear-retrieval freezing, and exposed all animals to sevoflurane under live-EEG titration without surgery. At adequate anaesthetic depth, HA mice carried a flatter aperiodic (1/f) cortical slope than LA mice (AUC = 0.85, [0.70, 0.95]). Conventional water-cross-maze scoring returned null at post-anaesthetic re-test, but unsupervised decomposition of the same trial videos localised the effect to loss of a specific learned transition in HA mice (AUC = 0.72, [0.56, 0.86]). The dark-phase REMS response reversed direction, with HA mice losing REMS against their own baseline while LA mice gained it (AUC = 0.82, [0.65, 0.94]). The three effects are directionally consistent with modulation of cortical excitation-to-inhibition balance under sevoflurane. The aperiodic exponent and emergence-phase EEG trajectory, both recoverable from routine frontal EEG, are candidate pre-anaesthetic biomarkers.

neuroscience↗

bioRxiv2026

Modeling pancreatic cancer tumor stroma co-evolution in an in ovo model

Pancreatic ductal adenocarcinoma (PDAC) is characterized by a dense, desmoplastic microenvironment that drives disease progression, yet conventional models fail to capture this complex tumor-stroma coevolution. Here, we utilize the chick chorioallantoic membrane (CAM) platform to investigate tumor-stroma interactions using murine PDAC cell lines and patient-derived organoids (PDOs). Integrating single-cell RNA sequencing and spatial transcriptomics, we show that the CAM microenvironment supports the emergence of complex tumor ecosystems while preserving patient-specific characteristics. Within five days, in ovo tumors faithfully recapitulated the structural and molecular features of parental tumors. Histological analysis revealed the rapid recruitment and spatial organization of heterogeneous host cancer-associated fibroblast (CAF) populations, showcasing distinct myofibroblastic and inflammatory stromal states. Crucially, the model preserved intrinsic tumor heterogeneity and permitted functional interrogation of subtype-specific extracellular matrix remodeling and metastatic dissemination. Together, our findings demonstrate that the CAM provides a highly permissive niche for tumor-stroma coevolution. As a rapid, scalable, and biologically relevant platform, this in ovo model offers a powerful approach for studying stromal composition, metastatic progression, and patient-specific tumor biology in pancreatic cancer.

cancer biology↗

bioRxiv2026

Large-Scale Assessment of Animal-to-Human Drug Translation Using Natural Language Processing

BackgroundLarge-scale estimates of animal-to-human drug translation and the study characteristics associated with successful translation remain limited. The expanding preclinical literature also challenges manual evidence synthesis. We developed a natural language processing (NLP) pipeline to structure and link preclinical and clinical evidence at scale. MethodsIn this retrospective meta-research study, we analysed more than 500,000 neuroscience-related animal drug studies from PubMed and linked them to clinical trial and regulatory approval data. NLP methods extracted drug, disease, and experimental design characteristics from abstracts and full texts. Translation was defined as progression to completed phase III/IV trials or regulatory approval. Logistic regression assessed associations between preclinical study characteristics and successful translation. FindingsAmong 291,624 drug entities identified in animal studies, 6{middle dot}7% entered clinical development and 3{middle dot}1% reached phase III/IV trials or regulatory approval. At the drug-disease level, 4{middle dot}4% entered clinical development and 1{middle dot}9% achieved translation. Restricting analyses to successfully linked ontology entities increased estimates to 11{middle dot}3% and 4{middle dot}1%, respectively. Male-only animal studies predominated, whereas reporting of randomisation, blinding, and sample size calculations remained limited. Testing across multiple species and reporting blinding were associated with higher odds of successful translation. InterpretationOnly a minority of interventions tested in animals progress to advanced clinical development or regulatory approval. Greater species diversity and blinding were associated with improved translational success. NLP-based evidence synthesis may support scalable evaluation of translational research and identification of potentially modifiable research practices. FundingSwiss National Science Foundation, UZH Digital Entrepreneurship Fellowship, Universities Federation for Animal Welfare. Research in contextO_ST_ABSEvidence before this studyC_ST_ABSWe searched the literature for studies quantifying large-scale animal-to-human translation and factors associated with successful translation. Existing work was mainly limited to specific diseases, interventions, or manually curated datasets, and large-scale linkage of animal and clinical evidence remained limited. Added value of this studyWe developed a natural language processing pipeline linking more than 500,000 animal studies to clinical trial and regulatory approval data. The study provides large-scale estimates of translation and identifies experimental characteristics associated with successful translation. Implications of all the available evidenceThe findings suggest that only a minority of interventions tested in animals progress to advanced clinical development or regulatory approval. Greater species diversity and reporting of blinding were associated with improved translation. Automated evidence synthesis may support more systematic evaluation of translational research practices.

bioinformatics↗

bioRxiv2026

Cross-species single-cell atlases chart progression, therapy-driven remodelling and immune evasion in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is typically diagnosed at advanced stages, yet single-cell datasets that capture late-stage and treated disease remain sparse, hindering progress in understanding tumour heterogeneity and therapy resistance. Here, we have generated integrated single-cell transcriptomic atlases of human and mouse PDAC to define the cellular and molecular landscape of the disease, from early to advanced and metastatic stages, including post-treatment disease, and to enable direct cross-species comparison. Using scANVI to harmonize 16 human studies comprising 257 donors and representative mouse models (101 tumours), we compiled over 1.6 million cells and established a four-level hierarchical taxonomy of more than 60 distinct cell states spanning malignant, stromal, immune, endothelial, adipose, exocrine and endocrine compartments. We resolve ten malignant programmes linked to progression and uncover rare immune phenotypes, including CD4CD8 double-positive T cells that remain poorly characterized in PDAC. Notably, we show that radiotherapy (RT) exposure is associated with enrichment of an EMT-persistent malignant state and an immunosuppressive microenvironment characterized by expansion of tumour-associated endothelium, depletion of intratumoral T cells and heightened laminin-CD44 signalling, with RT-associated genes linked to adverse prognosis in independent cohorts. Cross-species mapping reveals that orthotopic syngeneic allografts more faithfully recapitulate the cellular diversity and EMT-enriched states of advanced human PDAC, underrepresented in autochthonous genetically engineered models, with differences driven primarily by cell-type composition rather than pathway divergence. Together, these atlases and pretrained models provide a broadly accessible reference for benchmarking PDAC model fidelity and for interrogating mechanisms of tumour progression, microenvironmental remodelling and therapy response and resistance.

cancer biology↗

bioRxiv2026

Prevalent Gut Phages Encode Modular Adhesins Mediating Epithelial Binding and Endoplasmic Reticulum Trafficking

Bacteriophages are crucial components of the human microbiome and hold promise as therapeutic agents. Yet, their physical interactions with mammalian cells remain poorly understood. Here, we developed a high-throughput platform to identify phages that adhere to epithelial layers and the proteins that mediate this interaction. The identified phages encode immunoglobulin (Ig)-like domain-containing proteins that, when displayed on a non-adherent phage, confer epithelial binding and internalization in vitro, and increased phage retention in the mouse gut in vivo. Phages encoding these adhesins are among the most abundant and prevalent human gut phages, including crAss-like phages and a distinct cluster of uncharacterized myophages. Domain sequence variation alters epithelial interaction profiles, and internalized phages traffic to the endoplasmic reticulum through the Golgi apparatus, suggesting access to non-degradative internalization pathways. These findings reveal widespread phage-human interactions in the human virome, with potential impacts on health and implications for next-generation phage therapeutics.

microbiology↗

bioRxiv2025

The Deacetylases HDAC1 and HDAC2 Safeguard BCR-ABL-positive Cells from Replication Stress-Induced Apoptosis via the Nuclear to Mitochondrial p73-NOXA Axis

Histone deacetylases (HDACs) are key epigenetic regulators that are frequently dysregulated in cancer cells. Context-specific dependencies of tumor cell survival on HDACs and the mechanisms through which HDACs determine cell stress responses by specific oncogenic pathways remain to be understood. Here we unravel how the class I deacetylases HDAC1 and HDAC2 control the fate of chronic myeloid leukemia (CML) cells undergoing DNA replication stress. Compared to normal myeloid cells (n=690), CML cells overexpress HDAC1 and HDAC2 (n=234-274). We reveal that HDAC1 and HDAC2 protect cultured and primary CML cells with the hyperactive BCR-ABL tyrosine kinase from programmed cell death through apoptosis upon DNA replication stress. Using transcriptomics and genetically defined knockdown and knockout model systems, we demonstrate that these effects depend on the transcription factor p73 and its pro-apoptotic target gene NOXA. Upon DNA replication stress, p73 binds to the NOXA promoter but only upon additional inactivation of HDAC1/HDAC2 the NOXA gene becomes transcribed. BCR-ABL translocate to the nucleus to catalyze p73 phosphorylation at tyrosine-99 for the induction of p73 and mitochondrial NOXA. Thus, the BCR-ABL oncogene creates a selective vulnerability to HDAC1/HDAC2 inhibitors, driving a cytotoxic shift in replication stress responses towards apoptosis. These data highlight HDAC1/HDAC2 as potential therapeutic targets in CML. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=138 SRC="FIGDIR/small/694110v1_ufig1.gif" ALT="Figure 1"> View larger version (15K): org.highwire.dtl.DTLVardef@1ec0c51org.highwire.dtl.DTLVardef@1cd759org.highwire.dtl.DTLVardef@17e29a8org.highwire.dtl.DTLVardef@1e0fb50_HPS_FORMAT_FIGEXP M_FIG C_FIG

cancer biology↗

bioRxiv2025

Simultaneous Targeting of KRAS and CDK4 Synergistically Suppresses Pancreatic Cancer Cells

Mutant Ras oncoproteins, particularly KRAS, are among the most prevalent drivers of cancer. Small-molecule inhibitors of KRAS have been developed, bearing high potential for cancer therapy but considerable risk of resistance development. To avoid cancer cell adaptation, effective combinatorial partners for increasing immediate efficacy remain to be explored. Here, we demonstrate that combining the KRAS inhibitor Sotorasib with the CDK4/6 inhibitor Palbociclib synergistically eliminates pancreatic ductal adenocarcinoma (PDAC) cells and organoids harboring KRAS G12C mutations. This synergy was particularly pronounced after drug washout, indicating a durable impact. Similar effects were observed in non-small-cell lung cancer (NSCLC) cells. Additionally, MRTX1133, a KRAS G12D inhibitor, synergized with Palbociclib to suppress KRAS G12D-mutant PDAC-derived cells. Mechanistically, these combinations induced sustained cell cycle arrest through reduced RB phosphorylation, decreased E2F1 levels, and increased CDKN1B/p27 expression. Deletion of CDKN1B largely rescued tumor cell proliferation, underscoring its critical role in mediating the observed synergy. These findings support the therapeutic potential of combining KRAS and CDK4/6 inhibitors for treating PDAC and other Ras-driven cancers.

cancer biology↗

bioRxiv2024

Modelling coordinated nocturnal rhythms in ungulates

Studying animal behavior is an important aspect of ethology and behavioral biology and a prerequisite to improving animal management in zoos. As the nocturnal behavior of many ungulate species is, in contrast to the behavior during daylight, poorly studied, a better understanding of nocturnal behavior is necessary to improve animal welfare. We analyse the nocturnal behavior of ungulates recorded in a large number of German and Dutch zoos. These animals show a switching between standing and lying phases, which can be associated with a certain degree of regularity. Interestingly, this regularity is not always captured in the simple length distributions of behavioral phases but shows in the autocorrelation and in the coordination of standing and lying across animals. Particularly, this phenomenon often occurs in younger animals. We provide an explanation to this phenomenon by proposing a stochastic model that can describe these processes. For individual behavior, regular standing cycles are assumed to be potentially interrupted by short lying phases, such that a regular background rhythm appears in the autocorrelation but not necessarily in the raw length distribution of the activity phases. For coordinated behavior, crosscorrelation functions allow to analyse the degree to which pairs of animals that are sharing the same stable box show a synchronization of their standing-lying rhythms. In the data set, our analyses suggest that indeed, baseline regularity does not seem to be reduced in younger animals. Instead, younger animals showed increased probabilities for interruption of standing phases by short lying phases. In addition, the coordination of the standing-lying rhythm between animals in the same box ranged up to 100% and decreased with the distance between boxes. We also found systematic delays between the standing activity of young and adult animals. Author summaryIn this paper, we investigate rhythms observed in the nocturnal behavior of a large number of ungulates housed in zoos. Motivated by the observation that younger individuals, in particular, exhibit irregular standing-lying cycles, we propose and analyze a mathematical model to describe the basic rhythms of the observed animals and quantify the regularity of their standing-lying behavior. Our model enables us to measure both the regularity and synchronization of behavior among individuals. The results suggest that even individuals initially perceived as highly irregular actually follow a strict base rhythm during the night, but single standing phases may be interrupted. Moreover, we observe that animals stalled together typically synchronize their behavior, particularly in the case of a dam and her calf.

animal behavior and cognition↗

bioRxiv2024

Pathogen genomic surveillance as a scalable framework for precision phage therapy

Phage therapy is gaining increasing interest in the fight against critically resistant nosocomial pathogens. However, the narrow host range of bacteriophages hampers the development of broadly effective phage therapeutics and demands precision approaches. Here we combine large-scale phylogeographical analysis with high-throughput phage typing to guide the development of precision phage cocktails targeting carbapenem-resistant Acinetobacter baumannii, a top-priority pathogen. Our analysis reveals that a few strain types dominate infections in each world region, with their geographical distribution remaining stable within six years. As we demonstrate in Eastern Europe, this spatio-temporal distribution enables preemptive preparation of region-specific phage collections that target most local infections. Finally, we showcase the efficacy of a four-phage cocktail against the most prevalent strain type in both in vitro and in vivo animal infection models. Ultimately, genomic surveillance identifies patients benefiting from the same phages across geographical scales, thus providing a scalable framework for precision phage therapy. HighlightsO_LIA few carbapenem-resistant Acinetobacter baumannii types dominate infections worldwide C_LIO_LIPhylogeography reveals stable strain composition of individual countries over a six-year period C_LIO_LIThis spatio-temporal distribution allows preemptive preparation of region-specific phage collections C_LIO_LIA four-phage cocktail is efficacious against the most prevalent strain type in Europe. C_LI

microbiology↗

bioRxiv2024

Large Language Models to process, analyze, and synthesize biomedical texts - a scoping review

The advent of large language models (LLMs) such as BERT and, more recently, GPT, is transforming our approach of analyzing and understanding biomedical texts. To stay informed about the latest advancements in this area, there is a need for up-to-date summaries on the role of LLM in Natural Language Processing (NLP) of biomedical texts. Thus, this scoping review aims to provide a detailed overview of the current state of biomedical NLP research and its applications, with a special focus on the evolving role of LLMs. We conducted a systematic search of PubMed, EMBASE, and Google Scholar for studies and conference proceedings published from 2017 to December 19, 2023, that develop or utilize LLMs for NLP tasks in biomedicine. LLMs are being applied to a wide array of tasks in the biomedical field, including knowledge management, text mining, drug discovery, and evidence synthesis. Prominent among these tasks are text classification, relation extraction, and named entity recognition. Although BERT-based models remain prevalent, the use of GPT-based models has substantially increased since 2023.

bioinformatics↗

bioRxiv2023

Ergosterol mediates aggregation of natamycin in the yeast plasma membrane

Polyene macrolides are antifungal substances, which interact with cells in a sterol-dependent manner. While being widely used, their mode of action is poorly understood. Here, we employ ultraviolet-sensitive (UV) microscopy to show that the antifungal polyene natamycin binds to the yeast plasma membrane (PM) and causes permeation of propidium iodide into cells. Right before membrane permeability becomes compromised, we observed clustering of natamycin in the PM that was independent of PM protein domains. Aggregation of natamycin was paralleled by cell deformation and membrane blebbing as revealed by soft X-ray microscopy. Substituting ergosterol for cholesterol decreased natamycin binding and resulted in reduced clustering of natamycin in the PM. Blocking of ergosterol synthesis necessitates sterol import via the ABC transporters Aus1/Pdr11 to ensure natamycin binding. Quantitative imaging of dehydroergosterol (DHE) and cholestatrienol (CTL), two analogs of ergosterol and cholesterol, respectively, revealed a largely homogeneous lateral sterol distribution in the PM, ruling out that natamycin binds to pre-assembled sterol domains. Depletion of sphingolipids using myriocin increased natamycin binding to yeast cells, likely by increasing the ergosterol fraction in the outer PM leaflet. We conclude that ergosterol-specific aggregation of natamycin in the yeast PM underlies its antifungal activity, which can be synergistically enhanced by inhibitors of sphingolipid synthesis. SignificanceErgosterol is the major sterol in the membranes of fungi and a major target for antifungal treatments. Polyene macrolides, such as natamycin, are known to target ergosterol but the underlying mechanisms for their preference for this yeast sterol compared to mammalian cholesterol is not understood. This study shows that natamycin forms aggregates when associated with yeast S. cerevisiae in an ergosterol-dependent manner. Cholesterol can only partially substitute for ergosterol with respect to natamycin binding and aggregation. Membrane-associated aggregation of natamycin is not the result of pre-formed sterol domains in the cell membrane, as we show by direct visualization of minimally modified ergosterol and cholesterol analogs. Inhibiting sphingolipid synthesis increased membrane association and antifungal activity of natamycin, suggesting that targeting sphingolipids in combination with polyene macrolides could lead to novel drug treatment approaches against fungal infections.

biophysics↗

bioRxiv2023

Nociception in chicken embryos, Part II: Embryonal development of electroencephalic neuronal activity in ovo as a prerequisite for nociception

Chicken culling is forbidden in Germany since 2022, male/female selection and male elimination must be brought to an embryonic status prior to the onset of nociception. The present study evaluated the ontogenetic point when noxious stimuli potentially could be perceived/processed in the brain in ovo. EEG-recordings from randomized hyperpallial brain sites were recorded in ovo and noxious stimuli were applied. Temporal and spectral analyses of the EEG were performed. The onset of physiological neuronal signals could be determined at developmental day 13. ERP/ERSP/ITC analysis did not reveal phase-locked nociceptive responses. Although no central nociceptive responses were documented, adequate EEG-responses to noxious stimuli from other brain areas cannot be excluded. The extreme stress impact on the embryo during the recording may overwrite the perception of noniceptive stimuli. The results suggest developmental day 13 as the earliest embryonal stage being able to receive and process nociceptive stimuli.

neuroscience↗

bioRxiv2023

Global neuronal activity drives cerebrospinal fluid motion mediated by brain blood volume changes in humans

In the mammalian brain, the directed motion of cerebrospinal fluid (CSF-flux) is instrumental in the distribution and removal of solutes. Changes in total cerebral blood volume (CBV) have been hypothesized to drive CSF-flux. We tested this hypothesis in two multi-modal brain imaging experiments in healthy humans, in which we drove large changes in total CBV by neuronal burst-suppression under anesthesia, or by transient global vasodilation in a hypercapnic challenge. We developed a technique to monitor CBV changes based on associated changes in total brain volume by functional MRI (fMRI) and measured cerebral blood flow by arterial spin-labeling. Relating CBV-sensitive signals to fMRI-derived measures of macroscopic CSF flow across the basal cisternae, we demonstrate that increasing total CBV extrudes CSF from the skull and decreasing CBV allows its influx. Moreover, CSF largely stagnates when CBV is stable. Together, our results establish the direct coupling between total CBV changes and CSF-flux.

neuroscience↗

bioRxiv2023

Automated quantification of lipophagy in Saccharomyces cerevisiae from fluorescence and cryo-soft X-ray microscopy data using deep learning

Lipophagy is a form of autophagy by which lipid droplets (LDs) become digested to provide nutrients as a cellular response to starvation. Lipophagy is often studied in yeast, Saccharomyces cerevisiae, in which LDs become internalized into the vacuole. There is a lack of tools to quantitatively assess lipophagy in intact cells with high resolution and throughput. Here, we combine soft X-ray tomography (SXT) with fluorescence microscopy and use a deep learning computational approach to visualize and quantify lipophagy in yeast. We focus on yeast homologs of mammalian Niemann Pick type C proteins, whose dysfunction leads to Niemann Pick type C disease in humans, i.e., NPC1 (named NCR1 in yeast) and NPC2. We developed a convolutional neural network (CNN) model which classifies ring-shaped versus lipid-filled or fragmented vacuoles containing ingested LDs in fluorescence images from wild-type yeast and from cells lacking NCR1 ({Delta}ncr1 cells) or NPC2 ({Delta}npc2 cells). Using a second CNN model, which performs automated segmentation of LDs and vacuoles from high-resolution reconstructions of X-ray tomograms, we can obtain 3D renderings of LDs inside and outside of the vacuole in a fully automated manner and additionally measure droplet volume, number, and distribution. We find that cells lacking functional NPC proteins can ingest LDs into vacuoles normally but show compromised degradation of LDs and accumulation of lipid vesicles inside vacuoles. This phenotype is most severe in{Delta} npc2 cells. Our new method is versatile and allows for automated high-throughput 3D visualization and quantification of lipophagy in intact cells.

bioinformatics↗

bioRxiv2023

Kinetic modelling of sterol transport between plasma membrane and endo-lysosomes based on quantitative fluorescence and X-ray imaging data

Niemann Pick type C1 and C2 (NPC1 and NPC2) are two sterol-binding proteins which, together, orchestrate cholesterol transport through late endosomes and lysosomes (LE/LYSs). NPC2 can facilitate sterol exchange between model membranes severalfold, but how this is connected to its function in cells is poorly understood. Using fluorescent analogs of cholesterol and quantitative fluorescence microscopy, we have recently measured the transport kinetics of sterol between plasma membrane (PM), recycling endosomes (REs) and LE/LYSs in control and NPC2 deficient fibroblasts. Here, we employ kinetic modeling of this data to determine rate constants for sterol transport between intracellular compartments. Our model predicts that sterol is trapped in intraluminal vesicles (ILVs) of LE/LYSs in the absence of NPC2, causing delayed sterol export from LE/LYSs in NPC2 deficient fibroblasts. Using soft X-ray tomography, we confirm, that LE/LYSs of NPC2 deficient cells but not of control cells contain enlarged, carbon-rich intraluminal vesicular structures, supporting our model prediction of lipid accumulation in ILVs. By including sterol export via exocytosis of ILVs as exosomes and by release of vesicles - ectosomes - from the PM, we can reconcile measured sterol efflux kinetics and show that both pathways can be reciprocally regulated by the intraluminal sterol transfer activity of NPC2 inside LE/LYSs. Our results thereby connect the in vitro function of NPC2 as sterol transfer protein between membranes with its in vivo function.

biophysics↗