Biology subjects

O'Brown, N. M.

Publications and source records attributed to O'Brown, N. M..

5 recordsLinked to original sources

bioRxiv2026

In vivo discovery of blood-brain barrier opening small molecules with FishNAP

The blood-brain barrier (BBB) is crucial for neural homeostasis, tightly regulating molecular exchange between the circulation and brain. However, this selective protection also greatly limits drug delivery to the central nervous system, posing a major challenge for treating neurological disorders. Pharmacological strategies that transiently and safely increase BBB permeability could therefore transform brain drug delivery, yet systematic discovery of such modulators remains hampered by the limitations of current in vitro and in vivo approaches. Here we present FishNAP, a non-invasive, high-throughput zebrafish platform for real-time assessment of BBB permeability in vivo. FishNAP captures developmental changes in barrier function and detects dysfunction in genetic mutants. Using this platform, we screened 2,320 FDA-approved small molecules for compounds capable of opening an intact BBB and identified 11 that reproducibly increased permeability. Seven of these allowed entry of a 1 kDa tracer into brain tissue, and five also permitted passage of a larger 10 kDa Dextran. Barrier integrity recovered within 24 hours for all seven compounds, indicating reversible modulation. Finally, testing three representative molecules (Calcitriol, Lovastatin, and Sunitinib) in adult mice revealed increased BBB permeability and reduced Claudin-5 expression, demonstrating conserved mechanisms of BBB-regulation across vertebrates. FishNAP thus enables systematic discovery of BBB modulators with direct translational potential for brain drug delivery.

neuroscience↗

bioRxiv2024

Zebrafish glial-vascular interactions progressively expand over the course of brain development

Glial-vascular interactions are critical for the formation and maintenance of brain blood vessels and the blood-brain barrier (BBB) in mammals, but their role in zebrafish is not well understood. Our previous work has detailed the timeline of BBB functional maturation in zebrafish, revealing a conserved mechanism of BBB induction through the suppression of endothelial transcytosis. Yet, as opposed to extensive research on glial-vascular interactions in rodents, such interactions remain largely overlooked in the zebrafish model system. Here, we focus on glial-vascular development in the zebrafish brain, leveraging three glial gene promoters: gfap (glial fibrillary acidic protein), glast (an astrocyte-specific glutamate transporter), and glastini (a new, shortened, equally effective version of the Glast promoter). Using these glial promoters, sparse labeling revealed fewer glial-vascular interactions during early larval stages, with both glial coverage and contact area increasing as the zebrafish brain matured. We then generated stable transgenic lines for both the Glast and Glastini promoters and observed similar increases in glial coverage during larval development, starting at [~]30% coverage at 3 days post-fertilization (dpf) and peaking at [~]60% at 10 dpf. Ultrastructural assessment of glial-vascular interactions using electron microscopy (EM) confirmed a progressive increase in glial coverage over larval development, with maximal coverage reaching [~]70% in adult zebrafish, significantly lower than the nearly 100% coverage observed in mammals. Finally, immunogold-EM labeling confirmed that cells identified as glia in aforementioned morphological analyses were indeed Glast-positive. Taken together, our results identify the temporal profile of glial-vascular maturation in the zebrafish brain.

developmental biology↗

bioRxiv2024

Astrocytic RIPK3 exerts protective anti-inflammatory activity during viral encephalitis via induction of serpin protease inhibitors.

Flaviviruses pose a significant threat to public health due to their ability to infect the central nervous system (CNS) and cause severe neurologic disease. Astrocytes play a crucial role in the pathogenesis of flavivirus encephalitis through their maintenance of blood-brain barrier (BBB) integrity and their modulation of immune cell recruitment and activation within the CNS. We have previously shown that receptor interacting protein kinase-3 (RIPK3) is a central coordinator of neuroinflammation during CNS viral infection, a function that occurs independently of its canonical function in inducing necroptotic cell death. To date, however, roles for necroptosis-independent RIPK3 signaling in astrocytes are poorly understood. Here, we use mouse genetic tools to induce astrocyte-specific deletion, overexpression, and chemogenetic activation of RIPK3 to demonstrate an unexpected anti-inflammatory function for astrocytic RIPK3. RIPK3 activation in astrocytes was required for host survival in multiple models of flavivirus encephalitis, where it restricted neuropathogenesis by limiting immune cell recruitment to the CNS. Transcriptomic analysis revealed that, despite inducing a traditional pro-inflammatory transcriptional program, astrocytic RIPK3 paradoxically promoted neuroprotection through the upregulation of serpins, endogenous protease inhibitors with broad immunomodulatory activity. Notably, intracerebroventricular administration of SerpinA3N in infected mice preserved BBB integrity, reduced leukocyte infiltration, and improved survival outcomes in mice lacking astrocytic RIPK3. These findings highlight a previously unappreciated role for astrocytic RIPK3 in suppressing pathologic neuroinflammation and suggests new therapeutic targets for the treatment of flavivirus encephalitis.

immunology↗

bioRxiv2021

The secreted neuronal signal Spock1 regulates the blood-brain barrier

The blood-brain barrier (BBB) is a unique set of properties of the brain vasculature which severely restricts its permeability to proteins and small molecules. Classic chick-quail chimera studies showed that these properties are not intrinsic to the brain vasculature but rather are induced by surrounding neural tissue. Here we identify Spock1 as a candidate neuronal signal for regulating BBB permeability in zebrafish and mice. Mosaic genetic analysis shows that neuronally-expressed Spock1 is cell non-autonomously required for a functional BBB. Leakage in spock1 mutants is associated with altered extracellular matrix (ECM), increased endothelial transcytosis, and altered pericyte-endothelial interactions. Furthermore, a single dose of recombinant SPOCK1 partially restores BBB function in spock1 mutants by quenching gelatinase activity and restoring vascular expression of BBB genes including mcamb. These analyses support a model in which neuronally secreted Spock1 induces BBB properties by altering the ECM, thereby regulating pericyte-endothelial interactions and downstream vascular gene expression. One-Sentence SummarySpock1 is a signal secreted by neurons that induces barrier properties in the brain vasculature

neuroscience↗

bioRxiv2019

Suppression of transcytosis regulates zebrafish blood-brain barrier development

As an optically transparent model organism with an endothelial blood-brain barrier (BBB), zebrafish offer a powerful tool to study the vertebrate BBB. However, the precise developmental profile of functional zebrafish BBB acquisition and the subcellular and molecular mechanisms governing the zebrafish BBB remain poorly characterized. Here we find a spatiotemporal gradient of barrier acquisition. Moreover, we capture the dynamics of developmental BBB leakage using live imaging, revealing a combination of steady accumulation in the parenchyma and sporadic bursts of tracer leakage. Electron microscopy studies further reveal that this steady accumulation results from high levels of transcytosis that are eventually suppressed, sealing the BBB. Finally, we demonstrate a key mammalian BBB regulator Mfsd2a, which inhibits transcytosis, plays a conserved role in zebrafish. Mfsd2aa mutants display increased larval and adult BBB permeability due to increased transcytosis. Our findings indicate a conserved developmental program of barrier acquisition between zebrafish and mice.

developmental biology↗