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Olsen, L.

Publications and source records attributed to Olsen, L..

At least 19 recordsLinked to original sources

Glucose restriction reduces systemic, but not cardiac, inflammation during neonatal sepsis in preterm pigs

Introduction: Preterm infants are highly susceptible to sepsis and hyperglycemia may exacerbate inflammation and worsen outcomes. We examined how glucose provision influences systemic and cardiac responses during neonatal sepsis in preterm pigs. Methods: Preterm piglets (90 % gestation) were infused with Staphylococcus epidermidis to induce sepsis. In Experiment 1, three ventilated and anesthetized piglets were continuously monitored for mean arterial pressure (MAP) and blood gases to characterize acute cardiovascular and metabolic deterioration. In Experiment 2, thirty-three piglets were randomized to standard (14 g/kg/day) or reduced (3.5 g/kg/day) glucose provision, with or without infection, and followed for 20h. Results: Infection in Experiment 1 caused progressive hypotension, acidosis, and hypoxia, mirroring clinical neonatal sepsis. In Experiment 2, reduced glucose provision improved survival (77 % vs 46 %, p = 0.06) and attenuated systemic inflammation, with lower IL-6 and higher IL-10 concentrations. Infection induced mild cardiac neutrophil infiltration, without affecting plasma troponin T but clearly reduced cardiomyocyte mitotic density and triggered upregulation of inflammatory transcriptional pathways (NF-{kappa}B, JAK-STAT) and suppression of oxidative phosphorylation. In infected animals. glucose restriction preserved cardiomyocyte mitotic density but did not alter cardiac structure, injury markers or gene expression. Conclusion: Neonatal infection induced circulatory failure, suppression of cardiomyocyte proliferation and upregulation of inflammatory genes in cardiac tissue, while reduced glucose provision mitigated systemic immune responses and preserved cardiomyocyte proliferation.

immunology↗

Highly Pathogenic Avian Influenza Viruses H5N1 and H5N5 in Red Foxes (Vulpes vulpes) in Norway during 2022-2024

Since 2020, highly pathogenic avian influenza (HPAI) A(H5Nx) clade 2.3.4.4b viruses have spread globally, causing extensive outbreaks in domestic and wild birds. Increased circulation has resulted in frequent spillover to mammals, and occasional mammal-to-mammal transmission. Although human infections remain rare, the zoonotic potential of these viruses continues to be a public health concern. We investigated six cases of HPAI in red foxes (Vulpes vulpes) in Norway during 2022-2024 and identified infections with H5N1 and H5N5 viruses. Pathological and virological investigations demonstrated systemic infection, with prominent lesions in the brain and/or lungs. Phylogenetic analyses showed high similarity between viruses detected in foxes and those concurrently circulating in wild birds. The mammalian adaptation marker PB2:E627K was identified in one H5N1 virus and as a minority variant in a second H5N1 virus.

microbiology↗

Serological Evidence of Widespread Exposure to H5 Avian Influenza Virus in Arctic Foxes in Svalbard, Norway

The continued circulation of H5 clade 2.3.4.4b highly pathogenic avian influenza virus (HPAIV) has caused extensive mortality in wild bird populations worldwide with increasing spillover to mammals. In 2022, H5 HPAIV emerged in Svalbard, Norway, with subsequent detections in wild birds, walruses, polar bears, and arctic foxes. To understand the population-level exposure among Svalbard arctic foxes, we analysed body fluids from carcasses trapped in 2006-2015 (n = 56), 2023-2024 (n = 112), and 2024-2025 (n = 94) for antibodies to H5 avian influenza (anti-H5), influenza A nucleoprotein (anti-NP), and neuraminidase subtypes using ELISAs, haemagglutination inhibition (HI), and a multiplex assay. Only three samples from 2006-2015 tested positive for anti-H5 and were interpreted as false positives. In 2023-2024, seropositivity for anti-H5 was high (95%), supported by a lower anti-NP seropositivity (85%) and antibody profiles consistent with mixed H5N1 (42%) and H5N5 (52%) exposure. In 2024-2025, anti-H5 and anti-NP seroprevalences remained high (83% and 57%), with H5N5 (87%) exposure predominating over H5N1 (3%). A subset of anti-H5-positive samples tested positive by HI (2023-2024: 30%; 2024-2025: 14%). Juveniles with exposure limited to the previous season had higher odds of anti-H5 seropositivity in 2023-2024 than in 2024-2025 (OR 5.5). Analysis of paired lung extracts from a subset of individuals (n = 63) yielded results concordant with body fluids, using an indirect anti-H5 ELISA adapted for carnivores. Our findings demonstrate widespread H5 virus exposure. Together with occasional reports of progression to fatal HPAI, this highlights the need for continued population monitoring to evaluate ecological consequences.

microbiology↗

Quantification of compensatory motor neuron sprouting at the Drosophila larval neuromuscular junction

Following nervous system injury, surviving bystander neurons may rewire and form synapses with new postsynaptic targets to restore circuit function. This protocol quantifies compensatory motor neuron sprouting at the Drosophila larval neuromuscular junction. We describe larval dissection, immunostaining, Airyscan imaging, image masking, muscle-specific region-of-interest selection, and Fiji-based quantification of Dlg-positive area, bouton number, mean Dlg-positive area per bouton, NMJ arbor length, axonal versus NMJ branch points, ectopic muscle acquisition, and sprouting penetrance. For complete details on the use and execution of this protocol, please refer to Olsen et al.1

neuroscience↗

CyStainer: A transformer-based variational autoencoder for robust marker imputation in high-parameter cytometry

High parameter cytometry is essential for clinical diagnostics through precise immune cell profiling, improved patient stratification, and monitoring, while also enhancing the understanding of cellular responses in disease and therapeutic contexts. The amount of cytometry data is growing fast, and with that, the need to merge different datasets for unified analysis. Here, we present CyStainer, a transformer-based variational autoencoder that demonstrates competitive or superior performance to existing methods on several key tasks related to marker prediction. As a key novelty, we demonstrate that CyStainer can impute markers without having a set of shared backbone markers. We performed several benchmarks using real-world FACS, CyTOF, InfinityFlow and CITE-seq datasets to show that CyStainer is a robust and flexible tool for panel merging, marker imputation, dataset integration and virtual staining of unseen samples. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=43 SRC="FIGDIR/small/735235v1_ufig1.gif" ALT="Figure 1"> View larger version (15K): org.highwire.dtl.DTLVardef@1e76266org.highwire.dtl.DTLVardef@1ed5303org.highwire.dtl.DTLVardef@1e4ff76org.highwire.dtl.DTLVardef@13faa48_HPS_FORMAT_FIGEXP M_FIG C_FIG

bioinformatics↗

Impaired non-shivering thermogenesis in the desert-dwelling antelope ground squirrel

Adaptations in animals occupying environments of extreme cold or heat offer unique insights into thermoregulation. The antelope ground squirrel, a desert-dwelling rodent situated within a clade of hibernators, provides a notable example of these thermoregulatory extremes. As a non-hibernator closely related to hibernators, antelope ground squirrels may represent a rare case of trait reversal, with a striking ability to maintain core body temperatures exceeding 43{degrees}C while displaying poor tolerance to prolonged cold. Here, we explore the genetic and phenotypic basis of these unique traits by generating the first genome assembly for this species, which we use to conduct comparative genomics across the squirrel family. We complement this with acute and chronic cold-exposure experiments coupled with transcriptomic profiling of thermogenic organs: brown adipose tissue, white adipose tissue, and skeletal muscle. Together, these findings reveal a shift away from non-shivering thermogenesis toward metabolically demanding shivering thermogenesis, a perilous strategy for sustained heat generation.

evolutionary biology↗

Reconfiguration of Premotor Excitation and Inhibition Drives Behavior-Specific Protopodium Dynamics in Drosophila Larvae

Animals use shared muscles and motor neurons to generate distinct movements, but how premotor circuits differentially recruit these neuromuscular components remains unclear. Drosophila larvae crawl forward and backward using overlapping motor pools, yet the timing of ventral oblique (VO) muscle activity differs between these behaviors. Here, we show that VO muscles are major contributors to the movement of protopodia, limb-like structures that help larvae interact with the crawling surface. Muscle imaging, perturbation, and modeling indicate that VO activity is particularly important for protopodium folding, whereas contractions of both VO and ventral longitudinal (VL) muscles contribute to protopodium stride length and crawling efficiency. We identify a tri-segmental premotor motif--comprising excitatory (A27h, A18b3) and inhibitory (A06c) neurons--that shapes VO timing during forward crawling. A06c exhibits two activity peaks during forward fictive locomotion, defining a constrained window of VO MN activation, whereas during backward locomotion the early A06c peak is absent and the excitatory PMNs A27h and A18b3 are inactive. Disrupting this motif shifts VO activity earlier, reduces intersegmental timing delays, increases temporal overlap of VO activity, and impairs forward protopodium folding, stride, and crawling efficiency. These findings show how premotor excitation and inhibition coordinate muscle timing to shape locomotor mechanics.

neuroscience↗

Exercise intensity modulates the human plasma secretome and interorgan communication

Exercise is recognized as first-line therapy for many cardiometabolic diseases, including obesity, type 2 diabetes, and hypertension. Despite the abundant health-promoting effects of exercise, in-depth characterization of circulatory factors that mediate these benefits in humans remains incomplete. Moreover, how different modes and intensities of exercise uniquely regulate these processes is unclear. Here, we address these questions by conducting a multi-cohort human exercise intervention, incorporating sprint-interval exercise (SIE) and moderate-intensity exercise (MIE) to analyze intensity-dependent regulation of interorgan crosstalk. We find that exercise intensity distinctly influences the plasma proteome and metabolome in both untrained and trained participants. SIE led to immediate and robust changes to the plasma proteome, whereas MIE resulted in delayed secretory kinetics. By leveraging large, multi-organ gene and protein expression datasets, in combination with in vitro and in vivo tissue sampling, we map the differentially regulated proteins to their predicted tissue of origin and destination. We find that adipocytes are particularly sensitive to exercise intensity, undergoing broad transcriptomic remodeling following in vitro incubation with SIE as compared to MIE plasma. These findings underscore the integrated whole-body response following acute exercise and highlight exercise intensity as a key factor influencing interorgan communication.

physiology↗

Suppression of interferon signaling via small molecule modulation of TFAM

The mitochondrial transcription factor A (TFAM) is essential for mitochondrial genome maintenance. It binds to mitochondrial DNA (mtDNA) and determines the abundance, packaging and stability of the mitochondrial genome. Because its function is tightly associated with mtDNA, TFAM has a protective role in mitochondrial diseases and supportive studies demonstrate reversal of disease phenotypes by TFAM overexpression. In addition, TFAM deficiency has been shown to cause release of mtDNA into the cytosol and activation of the cGAS/STING innate immune response pathway. As such, TFAM presents as a unique target for therapeutic intervention, but limited efforts for activators have been reported. Herein we disclose novel TFAM small molecule modulators with sub-micromolar activity. Our results demonstrate that these compounds result in increase of TFAM protein levels and mtDNA copy number. This results in inhibition of a mtDNA stress-mediated inflammatory response by preventing mtDNA escape into the cytosol. Furthermore, we see beneficial effects in cellular disease models in which boosting TFAM activity has been advanced as a disease modifying strategy including improved energetics in MELAS cybrid cells and a decrease of fibrotic markers in Systemic Sclerosis (SSc) fibroblasts. These results highlight the therapeutic potential of using small molecule TFAM activators in indications characterized by mitochondrial dysfunction.

cell biology↗

A Drosophila Tonic Motor Neuron Reinnervates Ectopic Muscles Fully Deprived of Native Tonic and Phasic Inputs

Motor neurons (MNs) form precise neuromuscular junctions (NMJs) during development, but the extent to which individual MNs can reinnervate fully denervated muscles in vivo remains poorly understood. In the Drosophila larva, each muscle is co- innervated by a tonic and a phasic glutamatergic MN. Here, we show that the tonic MN1 undergoes robust heterosynaptic sprouting and forms ectopic NMJs when neighboring muscles are deprived of both their native tonic and phasic inputs. This structural plasticity is not induced by silencing, but instead requires the physical ablation of adjacent MNs. Live imaging of the same MN1 axons in individual animals reveals that sprouting initiates early and expands progressively across larval stages. In contrast, phasic MNs show minimal remodeling, indicating that tonic MNs possess a greater intrinsic capacity for neuroplasticity. Notably, as MN1 establishes new synapses on targets it does not normally innervate, it redistributes pre-synaptic territory across both native and ectopic muscles. These findings identify a subtype-specific, injury-induced rewiring program in an intact motor circuit.

neuroscience↗

Motor Neurons Decode Cholinergic Inputs via Spatially Distinct nAChR Subunits to Drive Locomotion in Drosophila larvae

Neural circuits consist of neurons that differ not only in their neurotransmitter identities but also in the types and subcellular localization of neurotransmitter receptors (NRs) they express. This receptor diversity enables distinct responses to the same neurotransmitter, highlighting the need to understand NR distribution and function to fully interpret circuit logic. Here, we focus on nicotinic acetylcholine receptors (nAChRs), the primary mediators of fast excitatory transmission in the Drosophila central nervous system (CNS). Functional nAChRs are pentamers assembled from a pool of 10 subunits (1-7, {beta}1-{beta}3), yet their in vivo expression and function remain poorly defined. We used T2A-Gal4 lines and endogenous protein tagging to examine nAChR expression in larval motor neurons (MNs) and identified eight subunits (1-3, 5-7, {beta}1, {beta}2) expressed in these cells. MN-specific knockdown of individual subunits caused distinct locomotor defects, indicating their functional importance. Co-localization analysis revealed some subunit pairs are frequently co-expressed at the same synapses, while others localize to distinct subcellular domains. Supporting this, double knockdown of co-localized subunits did not worsen locomotor phenotypes compared to single knockdowns, whereas knockdown of non-co-localized subunit pairs produced additive defects. These results suggest that different nAChR subtypes are strategically positioned in discrete synaptic domains within single MNs, where they serve non-redundant roles. Our findings provide new insight into the spatial organization and functional diversity of nAChRs in motor circuits that drive locomotion. Significance StatementMotor circuits rely on precise neurotransmitter signaling, yet the diversity and subcellular organization of neurotransmitter receptors remain poorly understood. Using Drosophila larvae, we show that motor neurons express multiple nicotinic acetylcholine receptor (nAChR) subunits, which localize to distinct synaptic domains and play non-redundant roles in locomotion. These findings reveal a previously underappreciated level of receptor compartmentalization within single neurons and demonstrate that spatially organized nAChRs are essential for coordinated movement. By integrating genetic, imaging, and behavioral approaches, our work provides a new framework for understanding how receptor diversity shapes motor output and highlights the importance of mapping receptor localization to decode circuit function in both health and disease.

neuroscience↗

Kermut: Composite kernel regression for protein variant effects

Reliable prediction of protein variant effects is crucial for both protein optimization and for advancing biological understanding. For practical use in protein engineering, it is important that we can also provide reliable uncertainty estimates for our predictions, and while prediction accuracy has seen much progress in recent years, uncertainty metrics are rarely reported. We here provide a Gaussian process regression model, Kermut, with a novel composite kernel for modeling mutation similarity, which obtains state-of-the-art performance for supervised protein variant effect prediction while also offering estimates of uncertainty through its posterior. An analysis of the quality of the uncertainty estimates demonstrates that our model provides meaningful levels of overall calibration, but that instance-specific uncertainty calibration remains more challenging.

synthetic biology↗

Cross-species comparison of pregnancy-induced GDF15

GDF15 (growth differentiation factor 15) is a stress-induced cytokine. Although the exact physiological function of GDF15 is not yet fully comprehended, the significant elevation of circulating GDF15 levels during gestation suggests a potential role for this hormone in pregnancy. This is corroborated by genetic association studies in which GDF15 and the GDF15 receptor, GDNF Family Receptor Alpha Like (GFRAL) have been linked to morning sickness and hyperemesis gravidarum (HG) in humans. Here, we studied GDF15 biology during pregnancy in mice, rats, macaques, and humans. In contrast to macaques and humans, mice and rats exhibited an underwhelming induction in plasma GDF15 levels in response to pregnancy ([~]75-fold increase in macaques vs. [~]2-fold increase in rodents). The changes in circulating GDF15 levels were corroborated by the magnitude of Gdf15 mRNA and GDF15 protein expression in placentae from mice, rats, and macaques. These species-specific findings may help guide future studies focusing on GDF15 in pregnancy and on the evaluation of pharmacological strategies to interfere with GDF15-GFRAL signaling to treat severe nausea and HG.

physiology↗

The Mexican Cavefish Mount a Rapid and Sustained Regenerative Response Following Skeletal Muscle Injury

Physical injury and tissue damage is prevalent throughout the animal kingdom, with the ability to quickly and efficiently regenerate providing a selective advantage. The skeletal muscle possesses a uniquely large regenerative capacity within most vertebrates, and has thus become an important model for investigating cellular processes underpinning tissue regeneration. Following damage, the skeletal muscle mounts a complex regenerative cascade centered around dedicated muscle stem cells termed satellite cells. In non-injured muscle, satellite cells remain in a quiescent state, expressing the canonical marker Pax7 (Chen et al. 2020). However, following injury, satellite cells exit quiescence, enter the cell cycle to initiate proliferation, asymmetrically divide, and in many cases terminally differentiate into myoblasts, ultimately fusing with surrounding myoblasts and pre-existing muscle fibers to resolve the regenerative process (Chen et al. 2020).

evolutionary biology↗

Circadian rhythm disruption is associated with skeletal muscle dysfunction within the blind Mexican Cavefish

Circadian control of physiology and metabolism is pervasive throughout nature, with circadian disruption contributing to premature aging, neurodegenerative disease, and type 2 diabetes (Musiek et al. 2016; Panda, 2016). It has become increasingly clear that peripheral tissues, such as skeletal muscle, possess cell-autonomous clocks crucial for metabolic homeostasis (Gabriel et al. 2021). In fact, disruption of the skeletal muscle circadian rhythm results in insulin resistance, sarcomere disorganization, and muscle weakness in both vertebrates and non-vertebrates - indicating that maintenance of a functional muscle circadian rhythm provides an adaptive advantage. We and others have found that cavefish possess a disrupted central circadian rhythm and, interestingly, a skeletal muscle phenotype strikingly similar to circadian knock-out mutants; namely, muscle loss, muscle weakness, and insulin resistance (Olsen et al. 2022; Riddle et al. 2018; Mack et al. 2021). However, whether the cavefish muscle phenotype results from muscle-specific circadian disruption remains untested. To this point, we investigated genome-wide, circadian-regulated gene expression within the skeletal muscle of the Astyanax mexicanus - comprised of the river-dwelling surface fish and troglobitic cavefish - providing novel insights into the evolutionary consequence of circadian disruption on skeletal muscle physiology.

evolutionary biology↗

Metabolic reprogramming underlies cavefish muscular endurance despite loss of muscle mass and contractility

Physical inactivity - specifically the lack of moderate-to-vigorous activity - is a scourge to human health, promoting metabolic disease and muscle wasting. Interestingly, multiple ecological niches have relaxed investment into physical activity, providing unique evolutionary insight into adaptive physical inactivity. The Mexican cavefish Astyanax mexicanus lost moderate-to-vigorous activity following cave colonization, reaching basal swim speeds ~3-fold slower than their river-dwelling counterpart. We found that this was accompanied by a marked shift in body composition, decreasing muscle mass by 30% and increasing fat mass by 40%. This shift persisted at the single muscle fiber level via increased lipid and sugar accumulation at the expense of myofibrillar volume. Transcriptomic analysis of laboratory-reared and wild-caught cavefish indicated this shift in investment is driven by increased expression of ppar{gamma} - the master regulator of adipogenesis - with a simultaneous decrease in fast myosin heavy chain expression. Ex vivo and in vivo analysis confirmed these investment strategies come with a functional trade-off, decreasing cavefish muscle fiber shortening velocity, time to maximal force, and ultimately maximal swimming velocity. Despite this, cavefish displayed a striking degree of muscular endurance, reaching maximal swim speeds ~3.5-fold faster than their basal swim speeds. Multi-omics analysis indicated metabolic reprogramming, specifically increased phosphoglucomutase-1 abundance, phosphorylation, and activity, as contributing mechanisms enhancing cavefish glycogen utilization under metabolically strenuous conditions. Collectively, we reveal broad skeletal muscle reprogramming following cave colonization, displaying an adaptive skeletal muscle phenotype reminiscent to mammalian disuse and high-fat models while simultaneously maintaining a unique capacity for sustained muscle contraction under fatiguing conditions. SignificanceThe evolutionary consequence of decreased physical activity upon skeletal muscle physiology remains unexplored. Using the Mexican cavefish, we find loss of moderate-to-vigorous swimming following cave colonization has resulted in broad shifts in skeletal muscle investment - away from muscle mass and instead toward fat and sugar accumulation - ultimately decreasing muscle fiber twitch kinetics. Surprisingly though, cavefish possessed marked muscular endurance, reaching maximal swimming speeds rivaling their river-dwelling counterpart. Multi-omics analysis revealed carbohydrate metabolic reprogramming as a contributing component, most notably elevated abundance and phosphorylation of the glycogenolytic enzyme Phosphoglucomutase-1 - a likely adaptation to cave-specific hypoxia. These findings emphasize the impact multiple selective pressures have on skeletal muscle physiology, providing the first evolutionary insight into skeletal muscle adaptation following decreased activity.

evolutionary biology↗

Liver-derived cell lines from cavefish Astyanax mexicanus as an in vitro model for studying metabolic adaptation

Cell lines have become an integral resource and tool for conducting biological experiments ever since the Hela cell line was first developed (1). They not only allow detailed investigation of molecular pathways but are faster and more cost-effective than most in vivo approaches. The last decade saw many emerging model systems strengthening basic science research. However, lack of genetic and molecular tools in these newer systems pose many obstacles. Astyanax mexicanus is proving to be an interesting new model system for understanding metabolic adaptation. To further enhance the utility of this system, we developed liver-derived cell lines from both surface-dwelling and cave-dwelling morphotypes. In this study, we provide detailed methodology of the derivation process along with a comprehensive biochemical and molecular characterization of the cell lines, which reflects key metabolic traits of cavefish adaptation. We anticipate these cell lines to become a useful resource for the Astyanax community as well as researchers investigating fish biology, comparative physiology, and metabolism.

evolutionary biology↗

Enhanced lipogenesis through Pparγ helps cavefish adapt to food scarcity.

Nutrient availability varies seasonally and spatially in the wild. The resulting nutrient limitation or restricted access to nutrients pose a major challenge for every organism. While many animals, such as hibernating animals, evolved strategies to overcome periods of nutrient scarcity, the cellular mechanisms of these strategies are poorly understood. Cave environments represent an extreme example of nutrient deprived environments since the lack of sunlight and therefore primary energy production drastically diminishes the nutrient availability. Here, we used Astyanax mexicanus, which includes river-dwelling surface fish and cave adapted cavefish populations to study the genetic adaptation to nutrient limitations. We show that cavefish populations store large amounts of fat in different body regions when fed ad libitum in the lab. We found higher expression of lipogenesis genes in cavefish livers when fed the same amount of food as surface fish, suggesting an improved ability of cavefish to use lipogenesis to convert available energy into triglycerides for storage into adipose tissue. Moreover, the lipid metabolism regulator, Peroxisome proliferator-activated receptor {gamma} (Ppar{gamma}), is upregulated at both transcript and protein levels in cavefish livers. Chromatin Immunoprecipitation sequencing (ChIP seq) showed that Ppar{gamma} binds cavefish promoter regions of genes to a higher extent than surface fish. Finally, we identified two possible regulatory mechanisms of Ppar{gamma} in cavefish: higher amounts of ligands of the nuclear receptor, and nonsense mutations in per2, a known repressor of Ppar{gamma}. Taken together, our study reveals that upregulated Ppar{gamma} promotes higher levels of lipogenesis in the liver and contributes to higher body fat accumulation in cavefish populations, an important adaptation to nutrient limited environments.

evolutionary biology↗