Biology subjects

Ostergaard, L.

Publications and source records attributed to Ostergaard, L..

At least 19 recordsLinked to original sources

bioRxiv2026

Sex shapes capillary flows and oxygen extraction in the middle-aged mouse brain

Sex differences in brain aging are well documented, but their origin within the cerebrovascular hierarchy remains unclear. Here we show that cortical blood flow is higher in female than male mice at 15 months of age, at a point when an earlier sex difference in pulsatility and resistance indices has already converged, pial vessel diameter shows no difference between sexes, and estrogen levels are similar between sexes. Using an indicator-dilution and intravascular oxygen measurements using two-photon microscopy, we found that capillary transit-time heterogeneity (CTH) scales more steeply with mean transit time in females, consistent with a passively regulated capillary network, and that this is accompanied by reduced oxygen extraction fraction (OEF) without deficit in arterial oxygen delivery. Spatial transcriptomics reveals that sex differences are organized into distinct regional programs, most prominently in white matter, where a male-associated myelin and axonogenesis signature accompanies reduced white matter volume in females. These molecular and structural differences coincide with elevated hippocampal microglial reactivity and an altered spatial search strategy in females, without any detectable differences in circulating markers of stress, blood-brain barrier integrity, or immunity. Together, these findings indicate that sex differences in the aging brain are expressed at the level of capillary flow regulation and regional tissue programs rather than through bulk cerebral blood flow alone, and that elevated blood flow in females can mask, rather than reflect, adequate tissue oxygenation.

neuroscience↗

bioRxiv2026

Pial arteries bend with every heartbeat

Arterial pulsations are thought to drive perivascular transport by displacing vessel walls radially. In 11 awake mice, all pial arteries also bend with each heartbeat, displacing the wall by three times the pulse-related dilatation per wall, while veins barely move. The bend has a spatial period of about 20 diameters, arrives with the dilatation, at above 1.6 m/s, and dissipates 450 times less energy in the wall.

neuroscience↗

bioRxiv2024

Microvascular pulsatility of the ageing brain and confounding effects of anaesthesia

Microvascular pulsatility in the brain is crucial for sustaining the delicate balance between the brains metabolic demands and blood supply, as it affects nutrient exchange, waste removal and blood-brain barrier permeability. Abnormal pulsatility, associated with ageing or vascular risk factors, may impair the clearance of metabolic waste or contribute to conditions such as cerebral small vessel disease, ultimately leading to dementia and increasing the risk of stroke. In the present study, we introduce a new approach for robust full-field characterization of microvascular pulsatility and apply it to study cerebral perfusion and pulsatility across nearly the entire lifespan of awake and anaesthetized C57BL/6 mice. Our findings in awake animals reveal remarkably stable perfusion and pulsatility from 18 to 81 weeks, with pulsatility starting to change only in the final weeks of observation. In contrast, measurements taken under anaesthesia display a range of age-dependent and age-independent changes. We show that isoflurane affects the perfusion in an age-dependent manner, and both isoflurane and ketamine-xylazine, despite their distinct mechanisms, double the perfusion pulsatility and affect vascular diameter pulsatility in a complex manner, highlighting a previously overlooked detrimental effect of anaesthesia on assessing brain function.

physiology↗

bioRxiv2024

Mitomycin C Retains Efficacy after Adaptive Laboratory Evolution of Staphylococcus aureus

Antibiotic resistance is one of the greatest threats against human health and the misuse and overuse of antibiotics is a key factor driving resistance development. During prolonged antibiotic treatment of chronic infections, the antimicrobial pressure facilitates selection of antibiotic resistance mutations. It has been suggested that using antibiotics in combinations may reduce the emergence of resistance. Furthermore, antibiotic tolerant persister cells may be a reservoir for resistance development, so targeting persister cells with anti-persister drugs could also reduce the emergence of resistance. In this study, we conducted a 42-day adaptive laboratory evolution experiment using Staphylococcus aureus exposed to common antibiotics and the anti-persister drug mitomycin C, either alone or in combination. We monitored susceptibility daily and assessed phenotypic changes in growth and biofilm formation in evolved strains. Whole-genome sequencing revealed mutations linked to antibiotic resistance and phenotypic shifts. Resistance developed rapidly against rifampicin, while ciprofloxacin and daptomycin showed slower resistance emergence. Treatments with vancomycin or mitomycin C resulted in minimal changes in susceptibility. Combination therapies generally delayed resistance, though resistance was not fully prevented. Notably, mitomycin C combined with rifampicin effectively suppressed rifampicin resistance. Sub-inhibitory antibiotic concentrations were associated with both known and novel mutations, including in the nucleotide excision repair system and azoreductase, following mitomycin C treatment--mutations not previously reported. While combination therapy delayed resistance, mitomycin Cs efficacy and ability to prevent rifampicin resistance highlights its potential in combating antibiotic resistance. Further investigation is needed to evaluate the broader application of anti-persister drugs in resistance prevention.

microbiology↗

bioRxiv2024

ETTIN-mediated auxin signalling is an angiosperm-specific neofunctionalization for carpel development

The phytohormone auxin affects processes throughout plant growth and development. While auxin signalling has been mainly attributed to a repressor degradation-based pathway, numerous alternative mechanisms for how auxin mediates its effect have been revealed in recent years. One such mechanism involves a direct auxin-induced switch in the transcriptional regulatory activity of the Auxin Response Factor (ARF) ETTIN (ETT). ETT lacks a conserved C-terminus domain involved in canonical pathway interactions but contains a middle region domain mediating auxin binding. As the ETT clade only exists in the angiosperms, it remains unknown when the pathway evolved. Here we provide evidence for a two-step origin of the ETT clade and its neofunctionalisation through the gain of auxin perception in gynoecium patterning. Phylogenetic analyses reveal the structural divergence of ETT and its paralogue ARF4 after their duplication from an ancestral euphyllophyte ARF3/4 clade. Auxin sensitivity was identified as an ETT-specific innovation that likely originated in the last common angiosperm ancestor. Furthermore, in planta complementation experiments demonstrated the full genetic redundancy of ETT and ARF4 in leaf and ovary development, but a specialised role for the ETT-mediated auxin signalling pathway in style development. Our work thus provides evidence that ETT was recruited from an ancestral role in leaf development and subsequently underwent neofunctionalisation through the acquisition of direct auxin sensing for a novel role in gynoecium patterning.

evolutionary biology↗

bioRxiv2024

Carbonic anhydrase inhibitors prevent presymptomatic capillary flow disturbances in a model of cerebral amyloidosis

Structured abstractO_ST_ABSINTRODUCTIONC_ST_ABSDisturbances in microvascular flow dynamics are hypothesized to precede the symptomatic phase of Alzheimers disease (AD). However, evidence in presymptomatic AD remains elusive, underscoring the need for therapies targeting these early vascular changes. METHODSWe employed a multimodal approach, combining in vivo optical imaging, molecular techniques, and ex vivo MRI, to investigate early capillary dysfunction in Tg-SwDI mice without memory impairment. We also assessed the efficacy of carbonic anhydrase inhibitors (CAIs) in preventing capillary flow disturbances. RESULTSOur study revealed capillary flow disturbances associated with alterations in capillary morphology, adhesion molecule expression, and Amyloid-{beta} (A{beta}) load in 9-10-month-old Tg-SwDI mice without memory impairment. CAI treatment ameliorated these capillary flow disturbances, enhanced oxygen availability, and reduced A{beta} load. DISCUSSIONThese findings underscore the importance of capillary flow disturbances as early biomarkers in presymptomatic AD and highlight the potential of CAIs for preserving vascular integrity in the early stages of AD.

neuroscience↗

bioRxiv2024

SHOOTMERISTEMLESS autoactivation: A prerequisite for fruit metamorphosis

In animals and plants, organ shape is primarily determined during primordium development by carefully coordinated growth and cell division1-3. Rare examples of post-primordial change in morphology (reshaping) exist that offer tractable systems to study mechanisms required for organ-shape determination and diversification. One such example is the heart-shape formation of Capsella fruits that occurs by reshaping the ovate spheroid gynoecium upon fertilization4. Here we use whole-organ live-imaging to show that dynamic changes in growth and cell division coupled with local maintenance of meristematic identity drives Capsella fruit-shape formation. At the molecular level, we reveal an auxin-induced mechanism ultimately descending on a single cis regulatory element to mediate morphological alteration. This element resides in the promoter of the Capsella rubella SHOOTMERISTEMLESS5 (CrSTM) gene. The CrSTM meristem identity factor positively regulates its own expression through binding to this element thereby providing a feed-forward loop at the position and time when protrusions emerge to form the heart. Independent evolution of the STM-binding element in STM promoters across Brassicaceae species correlates with those undergoing a gynoecium-to-fruit metamorphosis. Accordingly, genetic and phenotypic studies showed that the STM-binding element is required to facilitate the shape transition and reveals a conserved molecular mechanism for organ morphogenesis.

plant biology↗

bioRxiv2023

Per-ischemic changes in penumbral blood supply and its microscopic distribution

Acute ischemic stroke (AIS) is a frequent cause of death and adult disability. AIS patient management targets the ischemic penumbra: Hypoperfused, electrically silent brain tissue, which can be salvaged by restoring blood flow during the first, critical hours after symptom onset. Neuroimaging studies in AIS patients suggest that penumbral tissue is characterized not only by hypoperfusion, but also by microvascular flow disturbances that strongly affect tissue outcome. Here, we demonstrate that microvascular flows become increasingly chaotic in the ischemic penumbra in the hours after middle cerebral artery occlusion in a rat model of AIS. Biophysical models suggest that these disturbances are accompanied by increasing hypoxia in the absence of blood flow changes. Unlike findings in severe ischemia, pericyte constrictions do not appear to occlude penumbral capillaries. We propose that microvascular flow disturbances represent a critical feature of penumbral tissue, and a potential target for neuroprotective therapy after AIS.

neuroscience↗

bioRxiv2023

Integrated Phenomics and Genomics reveals genetic loci associated with inflorescence growth in Brassica napus

A fundamental challenge to the production of climate-resilient crops is how to measure dynamic yield-relevant responses to the environment, such as growth rate, at a scale which informs mechanistic understanding and accelerates breeding. The timing, duration and architectural characteristics of inflorescence growth are crucial for optimising crop productivity and have been targets of selection during domestication. We report a robust and versatile procedure for computationally assessing environmentally-responsive flowering dynamics. In the oilseed crop, Brassica napus, there is wide variation in flowering response to winter cold (vernalization). We subjected a diverse set of B. napus accessions to different vernalization temperatures and monitored shoot responses using automated image acquisition. We developed methods to computationally infer multiple aspects of flowering from this dynamic data, enabling characterisation of speed, duration and peaks of inflorescence development across different crop types. We input these multiple traits to genome- and transcriptome-wide association studies, and identified potentially causative variation in a priori phenology genes (including EARLY FLOWERING3) for known traits and in uncharacterised genes for computed traits. These results could be used in marker assisted breeding to design new ideotypes for improved yield and better adaptation to changing climatic conditions.

plant biology↗

bioRxiv2023

Canonical and ETT-mediated auxin signalling pathways synergistically promote gynoecium development in Arabidopsis thaliana

Gynoecium polarity establishment is regulated by auxin, a phytohormone whose signal is transduced through several pathways. The relationship between the ETT and canonical TIR1/AFB pathways, and their relevance for carpel development beyond Arabidopsis thaliana, have not been investigated. The data presented here show that the expression patterns of canonical and ETT-mediated signalling components, and phenotypes of higher order mutants are shared between Arabidopsis and Capsella rubella. tir1 afb2 ett mutants partially phenocopy ett arf4 double mutants, suggesting a role for AUXIN RESPONSE FACTOR 4 (ARF4) in the integration of canonical and ETT-mediated signalling. Comparative transcriptomics revealed that the auxin-independent mis-regulation of YABBY genes correlate with patterning defects observed in Arabidopsis ett arf4 mutants. Together, the data presented suggest conserved synergism between canonical and ETT-mediated pathways in gynoecium polarity establishment in the Brassicaceae. Finally, the data suggest that ETT/ARF4 function to prevent the auxin-induced expression of a range of targets in Arabidopsis, consistent with activator-repressor ARF antagonism, and implying that the maintenance of auxin insensitivity by repressive ARFs is important for a range of biological processes. Summary StatementHere the relationship between canonical and ETT-mediated auxin signalling machineries is investigated in Arabidopsis and Capsella revealing conserved synergism between these two pathways in Brassicaceae with distinct fruit shapes.

plant biology↗

bioRxiv2023

Antibody-drug conjugates to treat bacterial biofilms

Implant-associated infections remain a grand unmet medical need because they involve biofilms that protect bacteria from the immune system and harbour antibiotic-tolerant persister cells. There is an urgent need for new biofilm-targeting therapies with antimicrobials, to treat these infections via a non-surgical way. In this work, we address this urgent medical need and engineer antibody-drug conjugates (ADC) that kill bacteria in suspension and in biofilms, in vitro and in vivo. The ADC contains an anti-neoplastic drug mitomycin C, which is also a potent antimicrobial against biofilms. While most ADCs are clinically validated as anti-cancer therapeutics where the drug is released after internalisation of the ADC in the target cell, the ADCs designed herein release the conjugated drug without cell entry. This is achieved with a novel mechanism of drug, which likely involves an interaction of ADC with thiols on the bacterial cell surface. ADC targeted towards bacteria were superior by the afforded antimicrobial effects compared to the non-specific counterpart, in suspension and within biofilms, in vitro and in vivo. An implant-associated murine osteomyelitis model was then used to demonstrate the ability of the antibody to reach the infection, and the superior antimicrobial efficacy compared to standard antibiotic treatment in vivo. Our results illustrate the development of ADCs into a new area of application with a significant translational potential.

microbiology↗

bioRxiv2022

Extracting Mitochondrial Cristae Characteristics from 3D Focused Ion Beam Scanning Electron Microscopy Data

1Mitochondria are the main suppliers of energy for cells and their bioenergetic function is regulated by mitochondrial dynamics: the constant changes in mitochondria size, shape, and cristae morphology to secure cell homeostasis. Although mitochondrial dysfunction is implicated in a wide range of diseases, our understanding of mitochondrial function remains limited by the complexity of inferring these spatial features from 2D electron microscopical (EM) images of intact tissue. Here, we present a semi-automatic method for segmentation and 3D reconstruction of mitochondria, cristae, and intracristal spaces based on 2D EM images of the murine hippocampus. We show that our method provides a more accurate characterization of mitochondrial ultrastructure in 3D than common 2D approaches and propose an operational index of mitochondrias internal organization. We speculate that this tool may help increase our understanding of mitochondrial dynamics in health and disease.

neuroscience↗

bioRxiv2022

Anesthesia-related brain microstructure modulations detected by diffusion MRI

Brain clearance has been found to be greatly enhanced during sleep and anesthesia. Studies using optical microscopy have attributed this to an anesthesia-related expansion of the brains extra-cellular space. These results, however, have been based on invasive experiments with a limited field of view. Here, we employ diffusion kurtosis magnetic resonance imaging to assess brain microstructure in the awake and anesthetized mouse brain. We find both mean diffusivity and mean kurtosis to be significantly decreased in the anesthetized mouse brain compared to the awake state. This effect is observed in both gray matter and white matter. Our findings are consistent with the reports of brain ECS volume increase in sleep and anesthesia. Based on simple simulations, we discuss how an ECS volume increase (cell shrinkage) during sleep and anesthesia can coexist with other aspects of brain physiology. Our study demonstrates that diffusion kurtosis MRI can be used in the study of the glymphatic system. Importantly, our study shows an overlooked effect of anesthesia on brain microstructure which is relevant to preclinical MRI as a whole.

neuroscience↗

bioRxiv2022

FDA-approved carbonic anhydrase inhibitors reduce Amyloid beta pathology and improve cognition, by ameliorating cerebrovascular health and glial fitness

Alzheimers disease (AD) is a devastating neurodegenerative disorder with no effective cure. Cerebrovascular and neurovascular pathology are early and causal hallmarks of AD, where cerebral amyloid angiopathy (CAA), the deposition of amyloid {beta} (A{beta}) at the cerebral vasculature, is present in about 90% of cases. Our previous work has uncovered the protective effect of carbonic anhydrase (CA) inhibition against A{beta}-mediated mitochondrial dysfunction, production of reactive oxygen species (ROS) and apoptosis in vascular, glial and neuronal cells in culture. Here, we tested for the first time in a transgenic model of AD and cerebrovascular amyloidosis, the TgSwDI mice, a therapeutic regimen employing the FDA-approved CA inhibitors (CAIs), methazolamide (MTZ) and acetazolamide (ATZ). These drugs are used in humans for glaucoma, high altitude sickness, and other disorders, and can cross the blood-brain barrier. We found that both CAIs were non- toxic, significantly reduced cerebral amyloidosis, vascular, microglial and astrocytic A{beta} accumulation, and ameliorated cognition. MTZ and ATZ treatment prevented caspase-3 activation in endothelial cells, microglia and astrocytes, reverted capillary constriction and microhemorrhages, reduced gliosis, and induced glial pro-clearance pathways, which are likely responsible for the reduction of A{beta} deposition. Notably, we unveiled a critical new druggable target, revealing that the mitochondrial isozyme CA-VB is specifically upregulated in TgSwDI mouse brains, as well as in human brains of CAA and AD (with CAA) patients. Importantly, A{beta} challenge induced CA-VB overexpression in human cerebral endothelial cells, and CA-VB silencing, mimicking CAIs effects, reduced A{beta}-mediated endothelial apoptosis. This work paves the way for the application of CAIs in clinical trials for AD and CAA and uncovers CA-VB as a mediator of cerebral amyloid toxicity.

neuroscience↗

bioRxiv2022

mRNA decapping machinery targets LBD3/ASL9 transcripts to allow developmental changes in Arabidopsis

Multicellular organisms perceive and transduce multiple cues to optimize development. Key transcription factors drive developmental changes, but RNA processing also contributes to tissue development. Here, we report that multiple decapping deficient mutants share developmental defects in apical hook, primary and lateral root growth. More specifically, LATERAL ORGAN BOUNDARIES DOMAIN 3 (LBD3)/ASYMMETRIC LEAVES 2-LIKE 9 (ASL9) transcripts accumulate in decapping deficient plants and can be found in complexes with decapping components. Accumulation of ASL9 inhibits apical hook, primary root growth and lateral root formation. Interestingly, exogenous auxin application restores lateral roots formation in both ASL9 over-expressors and mRNA decay-deficient mutants. Likewise, mutations in the cytokinin transcription factors type-B ARABIDOPSIS RESPONSE REGULATORS (B-ARRs) ARR10 and ARR12 restore the developmental defects caused by over-accumulation of capped ASL9 transcript upon ASL9 overexpression. Most importantly, loss-of-function of asl9 partially restores apical hook and lateral root formation in decapping deficient mutants. Thus, the mRNA decay machinery directly targets ASL9 transcripts for decay, possibly to interfere with cytokinin/auxin responses, during development.

developmental biology↗

bioRxiv2022

Nanobody-mediated Complement Activation to Kill HIV-infected Cells

The complement system which is part of the innate immune response against invading pathogens, represents a powerful mechanism for killing of infected cells. Utilizing direct complement recruitment for complement-mediated elimination of HIV-1-infected cells is underexplored. We developed a novel therapeutic modality to direct complement activity to the surface of HIV-1-infected cells. This bispecific complement engager (BiCE) is comprised of a nanobody recruiting the complement-initiating protein C1q, and single-chain variable fragments of broadly neutralizing antibodies (bNAbs) targeting the HIV-1 envelope (Env) protein. Here, we show that two anti-HIV BiCEs targeting the V3 loop and the CD4 binding site, respectively, increase C3 deposition and mediate complement-dependent cytotoxicity (CDC) of HIV-1 Env expressing Raji cells. Furthermore, anti-HIV BiCEs trigger complement activation on primary CD4 T cells infected with laboratory-adapted HIV-1 strain and facilitates elimination of HIV-1-infected cells over time. In summary, we present a novel approach to direct complement deposition to the surface of HIV-1-infected cells leading to complement-mediated killing of these cells.

immunology↗

bioRxiv2020

SARS-CoV-2 Elicits Robust Adaptive Immune Responses Regardless of Disease Severity

The SARS-CoV-2 pandemic currently prevails worldwide. To understand the immunological signature of SARS-CoV-2 infections and aid the search for treatments and vaccines, comprehensive characterization of adaptive immune responses towards SARS-CoV-2 is needed. We investigated the breadth and potency of antibody-, and T-cell immune responses, in 203 recovered SARS-CoV-2 infected patients who presented with asymptomatic to severe infections. We report very broad serological profiles with cross-reactivity to other human coronaviruses. Further, >99% had SARS-CoV-2 epitope specific antibodies, with SARS-CoV-2 neutralization and spike-ACE2 receptor interaction blocking observed in 95% of individuals. A significant positive correlation between spike-ACE2 blocking antibody titers and neutralization potency was observed. SARS-CoV-2 specific CD8+ T-cell responses were clear and quantifiable in 90% of HLA-A2+ individuals. The viral surface spike protein was identified as the dominant target for both neutralizing antibodies and CD8+ T cell responses. Overall, the majority of patients had robust adaptive immune responses, regardless of disease severity. Author summarySARS-CoV-2 can cause severe and deadly infections. However, the immunological understanding of this viral infection is limited. Currently, several vaccines are being developed to help limit transmission and prevent the current pandemic. However, basic understanding of the adaptive immune response developed during SARS-CoV-2 infections is needed to inform further vaccine development and to understand the protective properties of the developed immune response. We investigated, the adaptive immune response developed during SARS-CoV-2 infections in recovered patients experiencing a full spectrum of disease severity, from asymptomatic infections to severe cases requiring hospitalization. We used a novel multiplex serological platform, cell-based neutralization assays and dextramer flow cytometry assays to characterize a broad and robust humoral and cellular immune response towards SARS-CoV-2. We found that the vast majority of recovered individuals have clear detectable and functional SARS-CoV-2 spike specific adaptive immune responses, despite diverse disease severities. The detection of both a humoral and cellular functional spike specific immune response in the vast majority of the individuals, irrespective of asymptomatic manifestations, supports vaccine designs currently underway, and encourages further exploration of whether primary infections provide protection to reinfection.

immunology↗

bioRxiv2020

The Effect of Introgression of an R2R3 MYB Transcription Factor on Sulphur Metabolism in Brassica oleracea

BackgroundA diet rich in cruciferous vegetables is reported to have beneficial health effects, partially mediated by 4-methylsulfinylbutyl glucosinolate, or glucoraphanin, which is predominantly found within broccoli (Brassica oleracea var italica). We describe the downstream effects on transcription and metabolism in broccoli following the introgression of a genetic variant of MYB28 into broccoli from a wild Brassica relative which has previously been associated with enhancement of glucoraphanin. ResultsWhole genome sequencing, RNA expression and metabolite analyses were used to characterise the consequences of the introgression of either one or two copies of a genetic variant of the MYB28 transcription factor into a commercial broccoli genetic background. The introgression of the variant of MYB28 resulted in enhanced expression of genes involved in primary sulphate assimilation, sulphur metabolism and aliphatic glucosinolate biosynthesis, and enhanced accumulation of 4-methylsulphinyl butyl glucosinolate in florets. Other changes in transcription that may be related to non-targeted introgression events are reported. There were no consistent effects upon sulphur metabolites pools, apart from methionine-derived glucosinolates. ConclusionThis study illustrates the downstream effects on transcription and metabolism of the introgression of a genetic variant of MYB28 from a wild species into a commercial broccoli genotype.

plant biology↗