Biology subjects

Johnsen, K. B.

Publications and source records attributed to Johnsen, K. B..

3 recordsLinked to original sources

bioRxiv2024

Dietary iron deficiency in the adult mouse increases brain endothelial uptake and blood-brain barrier transport of a high-affinity, anti-transferrin receptor antibody

Background and objectivesBrain capillary endothelial cells (BCECs) express transferrin receptor 1 (TfR1) to ensure sufficient iron transport into the brain across the blood-brain barrier (BBB). Our main objective was to examine adult mice subjected to dietary iron deficiency (ID) for possible changes in the content of TfR1 in BCECs and the influence thereof on the uptake and transport of high-affinity anti-transferrin receptor IgG1 antibodies (clone Ri7217). Material and methodsWe subjected adult, female mice to dietary ID for 8 weeks. Iron and copper were measured using inductively coupled plasma mass spectrometry (ICP-MS) in various tissues, including total brain and isolated brain capillaries. Possible effects of ID on cerebral angioarchitecture were estimated using 3D confocal microscopy of optically cleared brain samples with endothelium labelled using intravenous injection of wheat germ agglutinin with subsequent machine learning-based segmentation and vascular tracing. TfR1 was quantified using ELISA. Ri7217 antibodies were conjugated with 1 nm nanogold and brain uptake quantified using ICP-MS. ResultsID significantly reduced the iron content in isolated brain capillaries, liver, spleen, kidney, heart and skeletal muscles. ID increased the copper content in the brain. Analysis of cerebral cortex angioarchitecture revealed no changes following dietary ID except for a minor increase in tortuosity of small-caliber vessels. TfR1 protein was unchanged in the total brain and isolated brain capillaries. In contrast, uptake of nanogold-conjugated Ri7217 increased in the total brain, the supernatant fraction of isolated brain capillaries representing the post-vascular compartment, liver, spleen, and dissected retinae. ConclusionsTargeting TfR1 in ID revealed increased uptake and transport across the BBB of Ri7217 antibodies. Possibly the elevated transport of transferrin receptors through BCECs is due to the increased trafficking of transferrin receptor-containing vesicles in ID, which appeared to have no major effects on the brain angioarchitecture.

neuroscience↗

bioRxiv2024

Remodeling of the brain angioarchitecture in experimental chronic neurodegeneration

BackgroundChronic neurodegenerative diseases are characterized by substantial neuroinflammation with accumulation of macrophages, reactive microglia, and reactive astrocytes. Impairment of the brain vasculature is also commonly seen in chronic neurodegeneration with causal links warranting further investigation. MethodsTo address the effects of chronic neurodegeneration on regional vasculature, we performed a unilateral injection of a glutamate receptor agonist ibotenic acid into striatum of adult rats, which caused excitotoxicity in the substantia nigra pars reticulata (SNpr) due to imbalance between inhibitory inputs from the striatum and excitatory signals from the subthalamic nucleus. Brains were examined at 28 days (short-term neurodegeneration) and 91 days (long-term neurodegeneration). Dissected brain samples were analyzed for protein and gene expression using immunohistochemistry and qPCR. Brains were further analyzed for remodeling of vasculature labeled with wheat germ agglutinin (WGA) Alexa Fluor 647 conjugate using 3D deep confocal microscopy of optically cleared samples combined with machine learning-based image analysis. ResultsThe resulting neurodegeneration was accompanied by neuroinflammation, verified by the expression of inflammatory markers with gradual, regional loss of brain tissue. An in-depth analysis of the angioarchitecture of the degenerating SNpr revealed substantial changes of the vasculature with higher density, increased diameter, and number of tortuous vessels already after 28 days continuing at 91 days. Interestingly, the vascular remodeling changes occurred without changes in the expression of endothelial tight junction proteins, vascular basement membrane proteins, or markers of angiogenesis. ConclusionsThese results demonstrate how neurodegeneration causing prominent tissue loss in SNpr also leads to substantial remodeling of the angioarchitecture, while not altering the structural integrity of the vessel wall judged from the continuous expression of hallmarks of brain endothelial cells and the vascular basement membrane. We propose that this remodeling occurs as a consequence of the loss of brain tissue and with the resulting changes leaving the vasculature prone to additional vascular pathologies like vessel occlusion or formation of aneurysms.

neuroscience↗

bioRxiv2020

Post-capillary venules is the locus for transcytosis of therapeutic nanoparticles to the brain.

Treatments of neurodegenerative diseases require biologic drugs to be actively transported across the blood-brain barrier (BBB). To answer outstanding questions regarding transport mechanisms, we determined how and where transcytosis occurs at the BBB. Using two-photon microscopy, we characterized the transport of therapeutic nanoparticles at all steps of delivery to the brain and at the nanoscale resolution in vivo. Transferrin receptor-targeted nanoparticles were taken up by endothelium at capillaries and venules, but not at arterioles. The nanoparticles moved unobstructed within endothelial cells, but transcytosis across the BBB occurred only at post-capillary venules, where endothelial and glial basement membranes form a perivascular space that can accommodate biologics. In comparison, transcytosis was absent in capillaries with closely apposed basement membranes. Thus, post-capillary venules, not capillaries, provide an entry point for transport of large molecules across the BBB, and targeting therapeutic agents to this locus may be an effective way for treating brain disorders. HIGHLIGHTSO_LIIntegration of drug carrier nanotechnology with two-photon microscopy in vivo C_LIO_LIReal-time nanoscale-resolution imaging of nanoparticle transcytosis to the brain C_LIO_LIDistinct trafficking pattern in the endothelium of cerebral venules and capillaries C_LIO_LIVenules, not capillaries, is the locus for brain uptake of therapeutic nanoparticles C_LI

neuroscience↗