Biology subjects

Klein, L.

Publications and source records attributed to Klein, L..

17 recordsLinked to original sources

bioRxiv2026

GPNMB enables lysosomal adaptation required for myelin clearance and nerve regeneration after peripheral nerve injury

Recovery from peripheral nerve injury involves coordinated axonal and immune repair programs that promote tissue regeneration. However, the mechanisms regulating immune-mediated repair remain incompletely understood. Here, we demonstrate that glycoprotein non-metastatic melanoma protein B (GPNMB) is a key regulator of repair processes following peripheral nerve injury. In a mouse sciatic nerve crush model, loss of Gpnmb impaired functional recovery after injury. MRI and histological analyses revealed persistent myelin debris accumulation, defective debris clearance, and impaired macrophage lysosomal function within injured nerves. Mechanistic studies showed that GPNMB-deficient human iPSC-derived macrophages exhibited impaired lysosomal adaptation, reduced lysosomal fitness, and defective processing of myelin-associated cargo, resulting in inefficient degradation of injury-associated material. These defects were accompanied by impaired acquisition of repair-associated cellular programs. Together, our findings identify GPNMB as a critical regulator of lysosome-dependent repair programs during nerve regeneration and demonstrate that efficient GPNMB-dependent myelin processing is required for functional recovery following peripheral nerve injury.

neuroscience↗

bioRxiv2026

Temporal cortex astrocytic Gi-GPCR signaling regulates learned threat responses

Astrocytes are increasingly recognized as dynamic modulators of brain circuit function, memory processing, and behavior. Emerging evidence suggests that astrocytic G-protein-coupled receptors (GPCRs) are key regulators of these processes through their influence on intracellular signaling and neuron-glia interactions. Here, we show that the repertoire of functionally expressed GPCRs in cortical astrocytes is broader than previously appreciated. Yet, how distinct GPCR pathways contribute to behavioral regulation remains unknown for most brain areas and behavioral contexts. We therefore investigated the role of astrocytic GPCR signaling in the temporal cortex, a region that integrates multimodal sensory information and learned fear associations. Using chemogenetic tools to selectively activate distinct GPCR pathways in astrocytes, we demonstrate that Gi-coupled GPCR signaling, but not Gs- or Gq-coupled signaling, enhances fear memory retrieval. In vivo fiber photometry revealed that temporal cortex astrocytes exhibit robust Ca2+ transients to neutral, conditioned auditory and aversive sensory stimuli. Notably, astrocytic Gi-GPCR activation attenuated cue-evoked Ca2+ transients during memory retrieval. Together, these findings identify astrocytic GPCR signaling as a pathway-specific regulator of fear memory retrieval and suggest that astrocytic Gi-GPCR signaling modulates the processing of sensory cues to drive defensive behavior.

neuroscience↗

bioRxiv2025

Deep Multi-modal Species Occupancy Modeling

Effective conservation and restoration of species is an increasingly urgent priority. To design management strategies that improve species success, we need a solid understanding of the habitat characteristics that support it. Occupancy models are statistical tools that ecologists use to model these relationships from data. Yet, current models represent habitats with coarse-scale environmental variables that fail to capture important microhabitat features. We show that these limitations can be addressed by incorporating AI-derived, multimodal habitat representations from overhead satellite imagery and ground-level camera-trap imagery. Across geography and species, these representations yield more accurate out-of-sample predictions than models based on conventional covariates alone, and combining satellite and ground-level views provides complementary gains. To translate improved prediction into actionable ecological insight, we further introduce a method that makes black-box AI-derived habitat representations interpretable by summarizing key factors contributing to occupancy probability into text-based descriptions. We then generate a per-site score for each description, which can replace black-box features to transparently link discovered habitat elements to species occurrence while maintaining predictive performance. Our approach provides a path toward microhabitat-aware and interpretable species-habitat models that support restoration planning and management decisions. We implement our method in an open-source Python package bridging AI and statistical ecology.

ecology↗

bioRxiv2025

Entry and exit of Fragilariopsis cylindrus diatoms from the polar night: evidence for chromatin-mediated genome control

Regulation of the epigenome landscape plays a crucial role in adaptation to environmental changes. However, the molecular mechanisms by which epigenome landscapes are established and tuned to adjust the cellular status to environmental cues remain poorly understood, especially in unicellular photosynthetic eukaryotes. Polar microalgae must adapt to extreme variations in light and temperature for survival and therefore represent excellent models to understand the diversity of gene regulatory mechanisms, yet chromatin-based mechanisms have never been explored in these organisms. In this study, we combined genome-wide profiling of histone and DNA modifications with transcriptomic analyses of the marine polar diatom Fragilariopsis cylindrus upon entry and exit of a 3-month-long polar night. We show that, in agreement with its established role in transcription facilitation, histone H2B monobiquitination (H2Bub) is modulated at active genes upon prolonged darkness to light re-exposure. In contrast, histone H3 lysine 27 trimethylation (H3K27me3) and DNA cytosine methylation (CG methylation), two modifications typically associated with the silencing of genes or transposable elements (TEs), remained stable throughout the transitions, reinforcing their role in transcriptional repression, particularly at TEs but also at a few genes. We further demonstrate that H3K27me3 and DNA methylation are physically associated at TEs, probably reflecting a dual locking system enabling F.cylindrus cells to cope with the invasive nature of these genetic elements under extreme environmental conditions. These findings enhance our understanding of genome and epigenome regulation in diatoms in response to environmental variability and open new avenues for exploring the role played by chromatin-level regulation in the unique evolutionary history of polar unicellular eukaryotes.

genomics↗

bioRxiv2024

Dependence of aerosol-borne influenza A virus infectivity on relative humidity and aerosol composition

We describe a novel biosafety aerosol chamber equipped with state-of-the-art instrumentation for bubble-bursting aerosol generation, size distribution measurement, and condensation-growth collection to minimize sampling artifacts when measuring virus infectivity in aerosol particles. Using this facility, we investigated the effect of relative humidity (RH) in very clean air without trace gases (except [~]400 ppm CO2) on the preservation of influenza A virus (IAV) infectivity in saline aerosol particles. We characterized infectivity in terms of 99%-inactivation time, t99, a metric we consider most relevant to airborne virus transmission. The viruses remained infectious for a long time, namely t99 > 5 h, if RH < 30% and the particles effloresced. Under intermediate conditions of humidity (40% < RH < 70%), the loss of infectivity was the most rapid (t99 {approx} 15-20 min, and up to t99 {approx} 35 min at 95% RH). This is more than an order of magnitude faster than suggested by many previous studies of aerosol-borne IAV, possibly due to the use of matrices containing organic molecules, such as proteins, with protective effects for the virus. We tested this hypothesis by adding sucrose to our aerosolization medium and, indeed, observed protection of IAV at intermediate RH (55 %). Interestingly, the t99 of our measurements are also systematically lower than those in 1-L droplet measurements of organic-free saline solutions, which cannot be explained by particle size effects alone.

microbiology↗

bioRxiv2024

Cross-species analyses reveal RORγt-expressing dendritic cells are a lineage of antigen presenting cells conserved across tissues

Conventional dendritic cells (cDCs) are potent antigen presenting cells (APCs) that exhibit tissue and age-specific diversity allowing them to direct situation-adapted immunity. Thereby they harbor great potential for being targeted in vaccination and cancer. Here, we resolve conflicting data about expression of retinoic acid receptor-related orphan receptor-{gamma}t (ROR{psi}t) in cDCs. We show that ROR{psi}t+ DCs exist in murine lymphoid and non-lymphoid tissues across age. Fate mapping, functional assays and single cell multiomic profiling reveal these cells as ontogenetically and transcriptionally distinct from other well characterized cDC subtypes, as well as from ROR{psi}t+ type 3 innate lymphocytes (ILC3s). We show that ROR{psi}t+ DCs can migrate to lymph nodes and activate naive CD4+ T cells in response to inflammatory triggers. Comparative and cross-species transcriptomics revealed homologous populations in human spleen, lymph nodes and intestines. Further, integrated meta-analyses aligned ROR{psi}t+ DCs identified here with other emerging populations of ROR{psi}t+APCs, including R-DC-like cells, Janus cells/extrathymic Aire expressing cells (eTACs) and subtypes of Thetis cells. While ROR{psi}t+APCs have primarily been linked to T cell tolerance, our work establishes ROR{psi}t+ DCs as unique lineage of immune sentinel cells conserved across tissues and species that expands the functional repertoire of ROR{psi}t+ APCs beyond promoting tolerance. One sentence summaryROR{gamma}t+ DC exhibit versatile APC functions and are a distinct immune lineage conserved across age, tissues and species that entails Thetis cells, Janus cells/ROR{gamma}t+ eTACs and R-DC-like cells.

immunology↗

bioRxiv2023

Spatial tumor immune heterogeneity facilitates subtype co-existence and therapy response via AP1 dichotomy in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) displays a high degree of spatial subtype heterogeneity. This intratumoral co-existence of classical and basal-like programs is evident in multi-scale transcriptomic and spatial analyses of resected, advanced-stage and chemotherapy-treated specimens and reciprocally linked to a diverse stromal immune microenvironment as well as worse clinical outcome. However, the underlying mechanisms of intratumoral subtype heterogeneity remain largely unclear. Here, by combining preclinical models, multi-center clinical, bulk and compartment-specific transcriptomic, proteomic, and bioimaging data from human specimens, we identified an interplay between neoplastic intrinsic AP1 transcription factor dichotomy and extrinsic CD68+ macrophages as a driver of intratumoral subtype co-existence along with an immunosuppressive tumor microenvironment with T cell exclusion. Our ATAC-, ChIP-, and RNA-seq analyses revealed that JUNB/AP1- and HDAC-mediated epigenetic programs repress pro-inflammatory immune signatures in tumor cells, antagonizing cJUN/AP1 signaling to favor a therapy-responsive classical neoplastic identity. Through the tumor microenvironment, this dichotomous regulation was further amplified via regional macrophage populations. Moreover, CD68+/TNF-+ cells associated with a reactive phenotype and reduced CD8+ T cell infiltration in human PDAC tumors. Consequently, combined anti-TNF- immunotherapy and chemotherapy resulted in reduced macrophage counts and promoted CD3+/CD8+ T cell infiltration in basal-like PDAC, leading to improved survival in preclinical murine models. We conclude that tumor cell intrinsic epigenetic programs, together with extrinsic microenvironmental cues, facilitate intratumoral subtype heterogeneity and disease progression.

cancer biology↗

bioRxiv2023

Neutrophil-derived complement factor P induces cytotoxicity in basal-like cells via caspase 3/7 activation in pancreatic cancer

Due to profound heterogeneity within stromal immune tumor microenvironment (TME), pancreatic ductal adenocarcinoma (PDAC) remains a hard to treat disease, with the lowest 5-year survival below 10%. Large-scale transcriptomic analysis has revealed two main, clinically relevant PDAC signatures: therapy responsive Classical subtype with better prognosis, and poorly-differentiated Basal-like with poor prognosis. It has also become evident that the cellular and humoral components in the immune TME considerably influence the outcome of tumorigenesis. Complement system, a potent humoral innate immune mechanism, also forms a part of this immune TME. In addition to the regular production of various complement components in the liver, certain infiltrating immune cells such as macrophages, dendritic cells and neutrophils, can produce a few complement components locally at the site of infection and inflammation including TME, and modulate tumorigenic outcomes. Neutrophils are the most prevalent innate immune cells in the PDAC TME; however, its role has been attributed as either pro-tumorigenic or anti-tumorigenic. Neutrophils, when stimulated or under stress, are capable of releasing their secretory granules that also contain the only known up-regulator of the complement alternative pathway, Complement Factor P (CFP) or properdin. Properdin can not only facilitate alternative pathway activation by stabilising the C3 convertase, but also act as a pattern recognition receptor on its own and modify inflammatory response. Here, by combining multicenter transcriptome analysis of PDAC patient tumors, single-cell-RNA-seq analysis, preclinical mouse models and human PDAC specimens, we show that properdin expression and neutrophil surveillance are linked to better prognosis in PDAC patients. Furthermore, properdin expression is substantially higher in well-to-moderately differentiated Classical subtype compared to the highly aggressive basal-like PDAC tumours. Mechanistically, exogenous properdin binds to the cell membrane and activates caspase 3/7 to induce apoptosis in basal-like PDAC cells. Together, these findings suggest that the complement protein, properdin, could be a favorable prognostic factor and exhibit anti-tumorigenic functions in PDAC.

immunology↗

bioRxiv2023

Paying attention to natural scenes in area V1

Natural scene responses in the primary visual cortex are modulated simultaneously by attention and by contextual signals about scene statistics stored across the connectivity of the visual processing hierarchy. Here, we hypothesized that attentional and contextual top-down signals interact in V1, in a manner that primarily benefits the representation of natural visual stimuli, rich in high-order statistical structure. Recording from two macaques engaged in a spatial attention task, we found that attention enhanced the decodability of stimulus identity from population responses evoked by natural scenes but, critically, not by synthetic stimuli in which higher-order statistical regularities were eliminated. Population analysis revealed that neuronal responses converged to a low dimensional subspace for natural but not for synthetic images. Critically, we determined that the attentional enhancement in stimulus decodability was captured by the dominant low dimensional subspace, suggesting an alignment between the attentional and natural stimulus variance. The alignment was pronounced for late evoked responses but not for early transient responses of V1 neurons, supporting the notion that top-down feedback was required. We argue that attention and perception share top-down pathways, which mediate hierarchical interactions optimized for natural vision.

neuroscience↗

bioRxiv2022

Inactivation of Influenza A virus by pH conditions encountered in expiratory aerosol particles results from localized conformational changes within Haemagglutinin and Matrix 1 proteins.

Multiple respiratory viruses including Influenza A virus (IAV) can be transmitted via expiratory aerosol particles, and aerosol pH was recently identified as a major factor influencing airborne virus infectivity. For indoor air, small exhaled aerosols undergo rapid acidification to pH [~]4. IAV is known to be sensitive to mildly acidic conditions encountered within host endosomes, however, it is unknown whether the same mechanisms could mediate viral inactivation within the more acidic aerosol micro-environment. Here, we identified that transient exposure to pH 4 caused IAV inactivation by a two-stage process, with an initial sharp decline in infectious titers that was mainly attributed to premature attainment of the post-fusion conformation of viral protein haemagglutinin (HA). Changes to HA were observed by hydrogen-deuterium exchange coupled to mass spectrometry (HDX-MS) as early as 10 seconds post-exposure to acidic conditions. In addition, virion integrity was partially but irreversibly affected by acidic conditions. This was attributed to a progressive unfolding of the internal matrix protein 1 (M1), and aligned with a more gradual decline in viral infectivity with time. In contrast, no acid-mediated changes to the genome or lipid envelope were detected. Our HDX-MS data are in agreement with other more labor-intensive structural analysis techniques such as X-ray crystallography, highlighting the usefulness of whole-virus HDX-MS for multiplexed protein analyses, even within enveloped viruses such as IAV. Improved understanding of respiratory virus fate within exhaled aerosols constitutes a global public health priority, and information gained here could aid development of novel strategies to control the airborne persistence of seasonal and/or pandemic influenza in the future.

microbiology↗

bioRxiv2022

P38 kinases mediate NLRP1 inflammasome activation after ribotoxic stress response and virus infection

Inflammasomes integrate cytosolic evidence of infection or damage to mount inflammatory responses. The inflammasome sensor NLRP1 is expressed in human keratinocytes and coordinates inflammation in the skin. We found that diverse stress signals converge on the activation of p38 kinases to initiate human NLRP1 inflammasome assembly: UV irradiation and microbial molecules that initiate the ribotoxic stress response critically relied on the MAP3 kinase ZAK to activate p38 and ultimately human NLRP1. Infection with insect-transmitted alphaviruses, including Semliki Forest, Ross River, and Chikungunya virus, also activated NLRP1 in a p38-dependent manner. In the absence on ZAK, inflammasome assembly was maintained, although at reduced levels, indicating contribution of other upstream kinases. NLRP1 activation by direct nanobody-mediated ubiquitination was independent of p38 activity. Stimulation of p38 by overexpression of MAP2 kinases MKK3 or MKK6 is sufficient for NLRP1 activation, and NLRP1 is directly phosphorylated by p38. Taken together, we define p38 activation as a unifying signaling hub that controls NLRP1 inflammasome activation by integrating a variety of cellular stress signals relevant to the skin.

immunology↗

bioRxiv2021

A unique cerebellar pattern of microglia activation in a mousemodel of encephalopathy of prematurity

Preterm infants often show pathologies of the cerebellum, which are associated with impaired motor performance, lower IQ and poor language skills at school ages. Because 1 in 10 babies is born preterm cerebellar injury is a significant clinical problem. The causes of cerebellar damage are yet to be fully explained. Herein, we tested the hypothesis that perinatal inflammatory stimuli may play a key role in cerebellar injury of preterm infants. We undertook our studies in an established mouse model of inflammation-induced encephalopathy of prematurity driven by systemic administration of the prototypic pro-inflammatory cytokine interleukin-1{beta} (IL-1{beta}). Inflammation is induced between postnatal day (P) 1 to day 5, timing equivalent to the last trimester for brain development in humans the period of vulnerability to preterm birth related brain injury. We investigated acute and long-term consequences for the cerebellum on brain volume expansion, oligodendroglial maturation, myelin levels and the microglial transcriptome. Perinatal inflammation induced global mouse brain volume reductions, including specific grey and white matter volume reductions in cerebellar lobules I and II (5% FDR) in IL-1{beta} versus control treated mice from P15 onwards. Oligodendroglia damage preceded the MRI-detectable volume changes, as evidenced by a reduced proliferation of OLIG2+ cells at P10 and reduced levels of the myelin proteins MOG, MBP and MAG at P10 and P15. Increased density of Iba1+ cerebellar microglia was observed at P5 and P45, with evidence for increased microglial proliferation at P5 and P10. Comparison of the transcriptome of microglia isolated from P5 cerebelli and cerebrum revealed significant enrichment of pro-inflammatory markers in microglia from both regions, but in the cerebellum microglia displayed a unique type I interferon signalling dysregulation. Collectively, these data suggest that in our model that systemic inflammation causes chronic activation of microglia and maldevelopment of cerebellum that includes myelin deficits which is driven in the cerebellum by type I interferon signalling. Future protective strategies for preterm infants should consider sustained type I interferon signalling driven cerebellar inflammation as an important target.

neuroscience↗

bioRxiv2020

Stimulus-specific plasticity of macaque V1 spike rates and gamma

When a visual stimulus is repeated, average neuronal responses typically decrease, yet they might maintain or even increase their impact through increased synchronization. Previous work has found that many repetitions of a grating lead to increasing gamma-band synchronization. Here we show in awake macaque area V1 that both, repetition-related reductions in firing rate and increases in gamma are specific to the repeated stimulus. These effects showed some persistence on the timescale of minutes. Further, gamma increases were specific to the presented stimulus location. Importantly, repetition effects on gamma and on firing rates generalized to natural images. These findings suggest that gamma-band synchronization subserves the adaptive processing of repeated stimulus encounters, both for generating efficient stimulus responses and possibly for memory formation.

neuroscience↗

bioRxiv2018

Peripartum cardiomyopathy and hypertensive disorders of pregnancy and cardiovascular events among 1.6 million California pregnancies

BackgroundCardiovascular complications during and soon after pregnancy present an opportunity to assess risk for subsequent cardiovascular disease. We sought to determine whether peripartum cardiomyopathy and hypertensive disorder of pregnancy subtypes predict future myocardial infarction, heart failure, or stroke independent of one another and independent of other risks like gestational diabetes, preterm birth, and intrauterine growth restriction.\n\nMethods and ResultsThe California Healthcare Cost and Utilization Project database was used to identify all hospitalized pregnancies from 2005-2009, with follow-up through 2011, for a retrospective cohort study. Pregnancies, exposures, covariates and outcomes were defined by ICD-9 codes. Among 1.6 million pregnancies (mean age 28y; median follow-up time to event 2.7y), 558 cases of peripartum cardiomyopathy, 123,603 cases of hypertensive disorders of pregnancy, 107,636 cases of gestational diabetes, 116,768 preterm births, and 23,504 cases of intrauterine growth restriction were observed. Using multivariable Cox proportional hazards models, peripartum cardiomyopathy was independently associated with a 13.0-fold increase in myocardial infarction [95%CI, 4.1-40.9], a 39.2-fold increase in heart failure [95%CI, 30.0-51.9], and a 7.7-fold increase in stroke [95%CI, 2.4-24.0]. Hypertensive disorders of pregnancy were associated with a 1.4 [95%CI, 1.0-2.0] to 7.6 [95%CI, 5.4-10.7] fold higher risk of myocardial infarction, heart failure, and stroke. Gestational diabetes, preterm birth, and intrauterine growth restriction had more modest associations with CVD.\n\nConclusionsThese findings support close monitoring of women with cardiovascular pregnancy complications for prevention of early subsequent cardiovascular events and further study of mechanisms underlying their development.

epidemiology↗

bioRxiv2017

Stimulus content shapes cortical response statistics

Spike count correlations (SCCs) are ubiquitous in sensory cortices, are characterized by rich structure and arise from structured internal interactions. Yet, most theories of visual perception focus exclusively on the mean responses of individual neurons. Here, we argue that feedback interactions in primary visual cortex (V1) establish the context in which individual neurons process complex stimuli and that changes in visual context give rise to stimulus-dependent SCCs. Measuring V1 population responses to natural scenes in behaving macaques, we show that the fine structure of SCCs is stimulus-specific and variations in response correlations across-stimuli are independent of variations in response means. Moreover, we demonstrate that stimulus-specificity of SCCs in V1 can be directly manipulated by controlling the high-order structure of synthetic stimuli. We propose that stimulus-specificity of SCCs is a natural consequence of hierarchical inference where inferences on the presence of high-level image features modulate inferences on the presence of low-level features.

neuroscience↗

bioRxiv2017

Persistent homology demarcates a leaf morphospace

Current morphometric methods that comprehensively measure shape cannot compare the disparate leaf shapes found in seed plants and are sensitive to processing artifacts. We explore the use of persistent homology, a topological method applied across the scales of a function, to overcome these limitations. The described method isolates subsets of shape features and measures the spatial relationship of neighboring pixel densities in a shape. We apply the method to the analysis of 182,707 leaves, both published and unpublished, representing 141 plant families collected from 75 sites throughout the world. By measuring leaves from throughout the seed plants using persistent homology, a defined morphospace comparing all leaves is demarcated. Clear differences in shape between major phylogenetic groups are detected and estimates of leaf shape diversity within plant families are made. This approach does not only predict plant family, but also the collection site, confirming phylogenetically invariant morphological features that characterize leaves from specific locations. The application of a persistent homology method to measure leaf shape allows for a unified morphometric framework to measure plant form, including shape and branching architectures.

plant biology↗

bioRxiv2017

ADAM17 Is The Main Sheddase For The Generation Of Human Triggering Receptor Expressed In Myeloid Cells (hTREM2) Ectodomain And Cleaves TREM2 After Histidine 157

Triggering receptor expressed in myeloid cells (TREM2) is a member of the immunoglobulin superfamily and is expressed in macrophages, dendritic cells, microglia, and osteoclasts. TREM2 plays a role in phagocytosis, regulates release of cytokine, contributes to microglia maintenance, and its ectodomain is shed from the cell surface. Using both pharmacological and genetic approaches we report here that the main protease contributing to the release of TREM2 ectodomain is ADAM17, (a disintegrin and metalloproteinase domain containing protein, also called TACE, TNF converting enzyme) while ADAM10 plays a minor role. Using mutational analysis, we demonstrate that the main cleavage site of the sheddases is located within the stalk region of TREM2 proximal to the plasma membrane. Complementary biochemical experiments reveal that cleavage occurs between histidine 157 and serine 158. Shedding is not altered for the R47H-mutated TREM2 protein that confers an increased risk for the development of Alzheimers disease. O-glycosylation is detected within the stalk region, but distant to the cleavage site. These findings reveal a link between shedding of TREM2 and its regulation during inflammatory conditions or chronic neurodegenerative disease like AD in which activity or expression of sheddases might be altered.

cell biology↗