Injection of Evans blue dye to fluorescently label and image intact vasculature

Altered renal vascular patterning reduces ischemic kidney injury and limits age-associated vascular loss

The kidney vasculature has a complex arrangement, which runs in both series and parallel to perfuse the renal tissue and appropriately filter plasma. Recent studies have demonstrated that the development of this vascular pattern is dependent on netrin-1 secreted by renal stromal progenitors. Mice lacking netrin-1 (Ntn1) from these cells develop an arterial tree with stochastic branching, particularly of the large interlobar vessels. The current study investigated whether abnormalities in renal vascular patterning altered kidney function or response to injury. To examine this, we analyzed kidney function at baseline as well as in response to a model of bilateral ischemic injury and measured vascular dynamics in 7- to 8-mo-old mice. We found no differences in kidney function or morphology at baseline between mice with an abnormal arterial pattern compared with control. Interestingly, male and female mutant mice with stochastic vascular patterning showed a reduction in tubular injury in response to ischemia. Similarly, mutant mice also had a preservation of perfused vasculature with increased age compared with a reduction in the control group. These results suggest that guided and organized patterning of the renal vasculature may not be required for normal kidney function, but uncovers new implications for patterning in response to injury. Understanding how patterning and maturation of the arterial tree affects physiology and response to injury has important implications for enhancing kidney regeneration and tissue engineering strategies.NEW & NOTEWORTHY Kidney vascular patterning is established through responses to guidance cues such as netrin-1; however, the significance of proper patterning to function and injury response remains unexplored. Here, utilizing a conditional knockout of netrin-1 (Ntn1) that displays persistent abnormal arterial patterning, we identify no significant disruptions to normal kidney physiology in adult animals but, surprisingly, less tubular damage in response to ischemic injury. This study uncovers new and significant implications for proper kidney vascular patterning.

Wearable Photonic Device for Multiple Biomarker Sampling and Detection without Blood Draws

Needle-based blood draws or phlebotomy practice in clinics for centuries, often causing pain, discomfort, and inconvenience. Here, a wearable photonic device is presented by integrating a microlens array (MLA) and an optic microneedle array (OMNA) functionalized with immunobinding for safe and needle-free biomarker sampling and detection. The MLA-integrated OMNA amplifies and transmits LED light at 595 nm into skin through the OMNA, bypassing the light-absorbing melanin in the epidermal layer, and evenly distributing it in the capillary-enriched dermis independent of the skin colors. The 595 nm light is absorbed by hemoglobin (Hb) and oxygen-Hb within the capillaries, triggering thermal dilation of capillaries without damaging them or causing petechiae. The light illumination remarkably increases in the concentrations of various blood biomarkers in the skin through biomarker extravasation. These biomarkers bound specifically to the capture antibodies on OMNA with each microneedle covalently immobilized with one specific antibody. The OMNA is extensively modified to amplify the immunobinding signals and achieve sensitivity superior to that of enzyme-linked immunosorbent assay (ELISA) kits. As proof of concept, the functionality of the prototype for minimally invasive sampling and precise multiplexed blood biomarker detection in two mouse models is validated to quantify acute inflammation and specific antibody production.

The role of transcytosis in the blood-retina barrier: from pathophysiological functions to drug delivery

The blood-retina barrier (BRB) serves as a critical interface that separates the retina from the circulatory system, playing an essential role in preserving the homeostasis of the microenvironment within the retina. Specialized tight junctions and limited vesicle trafficking restrict paracellular and transcellular transport, respectively, thereby maintaining BRB barrier properties. Additionally, transcytosis of macromolecules through retinal vascular endothelial cells constitutes a primary mechanism for transporting substances from the vascular compartment into the surrounding tissue. This review summarizes the fundamental aspects of transcytosis including its function in the healthy retina, the biochemical properties of transcytosis, and the methodologies used to study this process. Furthermore, we discuss the current understanding of transcytosis in the context of pathological BRB breakdown and present recent findings that highlight significant advances in drug delivery to the retina based on transcytosis.

TRPM2 overactivation drives hyperlipidemia-induced dysfunction of myeloid cells and neurovascular units

Hyperlipidemia induces cellular dysfunction and is strongly linked to various diseases. The transient receptor potential channel melastatin 2 (TRPM2) plays a critical role in endothelial injury, immune cell activation, and neuronal death. We reveal that TRPM2 expression in human peripheral leukocytes strongly correlates with plasma lipid levels. In middle-aged Apoe-/- mice, global, myeloid, and endothelial TRPM2 knockout or TRPM2 inhibition abolishes the hyperlipidemia-induced exacerbation of ischemic brain injury suggesting that TRPM2 overactivity caused by hyperlipidemia predisposes these cells to dysfunction during ischemia. Using a clinically relevant ischemic brain injury mouse model, we demonstrate TRPM2's pivotal role in mediating hyperlipidemia's detrimental effects on myeloid cells and neurovascular units. Our findings suggest that TRPM2 is a promising therapeutic target for alleviating neurodegenerative diseases exacerbated by hyperlipidemia, such as ischemic stroke. These results also highlight TRPM2 expression in peripheral blood as a potential biomarker for predicting stroke outcomes in hyperlipidemic patients.

Anxiety-like behavior and altered hippocampal activity in a transgenic mouse model of Fabry disease

BACKGROUND

Fabry disease (FD) patients are known to be at high risk of developing neuropsychiatric symptoms such as anxiety, depression and cognitive deficits. Despite this, they are underdiagnosed and inadequately treated. It is unknown whether these symptoms arise from pathological glycosphingolipid deposits or from cerebrovascular abnormalities affecting neuronal functions in the central nervous system. We therefore aimed to fill this knowledge gap by exploring a transgenic FD mouse model with a combination of behavior, transcriptomic, functional and morphological assessments, with a particular focus on the hippocampus.

RESULTS

Male FD mice exhibited increased anxiety-like behavior in the open field test, accompanied by a reduced exploratory drive in the Barnes maze, which could be related to the increased deposition of globotriaosylceramide (Gb3) identified in the dentate gyrus (DG). Hippocampus single-cell sequencing further revealed that Gb3 accumulation was associated with differential gene expression in neuronal and non-neuronal cell populations with granule, excitatory and interneurons, as well as microglia and endothelial cells as the main clusters with the most dysregulated genes. Particularly FD hippocampal neurons showed decreased electrical baseline activity in the DG and increased activity in the CA3 region of acutely dissected hippocampal slices.

CONCLUSIONS

Our study highlights transcriptional and functional alterations in non-neuronal and neuronal cell clusters in the hippocampus of FD mice, which are suggested to be causally related to anxiety-like behavior developing as a consequence of FD pathology in mouse models of the disease and in patients.

Preclinical and First-in-Human Study of a Compact Radionuclide Labeled Self-Assembly Nanomedicine for Chemo-Radio-Theranostics of Cancer

The emerging combination of chemotherapy and radionuclide therapy has been actively investigated to overcome the limitations of monotherapy and augment therapeutic efficacy. However, it remains a challenge to design a single delivery vehicle that can incorporate chemotherapeutics and radionuclides into a compact structure. Here, a chelator DOTA- or NOTA-modified Evans blue conjugated camptothecin molecule (EB-CPT) nanoprodrug was synthesized, which could self-assemble into nanoparticles due to its inherent amphiphilicity. The nanoparticles could then be effectively labeled with therapeutic radionuclide lutetium-177 (177Lu) or diagnostic radionuclides gallium-68 (68Ga)/copper-64 (64Cu) with high radiolabeling efficiency and radiochemical stability. Impressively, a single-dose chemoradiation therapy of [177Lu]Lu-DOTA-EB-CPT plus EB-CPT effectively inhibited tumor growth in HCT116 tumor-bearing mice compared to the respective individual therapeutic approach. The [64Cu]Cu-NOTA-EB-CPT nanoparticles also exhibited excellent in vivo characteristics including favorable blood circulation properties and prolonged tumor retention in tumor-bearing mice. The safety, feasibility, tolerability, and biodistribution of [68Ga]Ga-NOTA-EB-ss-CPT were also preliminarily characterized in a first-in-human study. This study presents a simple but robust EB-CPT radiopharmaceutical that leverages EB as an albumin binder to strike a delicate balance between enhanced tumor accumulation, safety, and diagnostic efficacy, facilitating an integrated theranostic strategy within a single molecular structure. This radionuclide-labeled EB-CPT nanomedicine presents a step toward clinical translation of the combination of chemotherapy and radiotheranostics.

Notch dimerization provides robustness against environmental insults and is required for vascular integrity

The Notch intracellular domain (NICD) regulates gene expression during development and homeostasis in a transcription factor complex that binds DNA either as monomer, or cooperatively as dimers. Mice expressing Notch dimerization-deficient (NDD) alleles of Notch1 and Notch2 have defects in multiple tissues that are sensitized to environmental insults. Here, we report that cardiac phenotypes and DSS (Dextran Sodium Sulfate) sensitivity in NDD mice can be ameliorated by housing mice under hypo-allergenic conditions (food/bedding). However, compound heterozygote NDD mice (N1RA/-; N2RA/-) in hypo-allergenic conditions subsequently develop severe hydrocephalus and hemorrhages. Further analysis revealed multiple vascular phenotypes in NDD mice including leakage, malformations of brain vasculature, and vasodilation in kidneys, leading to demise around P21. This mouse model is thus a hypomorphic allele useful to analyze vascular phenotypes and gene-environment interactions. The possibility of a non-canonical Notch signal regulating barrier formation in the gut, skin, and blood systems is discussed.

Multiscale Three-Dimensional Evaluation and Analysis of Murine Lung Vasculature From Macro- to Micro-Structural Level

The pulmonary vasculature plays a pivotal role in the development and progress of chronic lung diseases. Due to limitations of conventional two-dimensional histological methods, the complexity and the detailed anatomy of the lung blood circulation might be overlooked. In this study, we demonstrate the practical use of optical serial block face imaging (SBFI), ex vivo microcomputed tomography (micro-CT), and nondestructive optical tomography for visualization and quantification of the pulmonary circulation's 3D architecture from macro- to micro-structural levels in murine lung samples. We demonstrate that SBFI can provide rapid, cost-effective, and label-free visualization of mouse lung macrostructures and large pulmonary vessels. Micro-CT offers high-resolution imaging and captures microvascular and (pre)capillary structures, with microstructural quantification. Optical microscopy techniques such as optical projection tomography (OPT) and light sheet fluorescence microscopy, allows noninvasive, mesoscopic imaging of optically cleared mouse lungs, still enabling 3D microscopic reconstruction down to the precapillary level. By integrating SBFI, micro-CT, and nondestructive optical microscopy, we provide a framework for detailed and 3D understanding of the pulmonary circulation, with emphasis on vascular pruning and rarefaction. Our study showcases the applicability and complementarity of these techniques for organ-level vascular imaging, offering researchers flexibility in selecting the optimal approach based on their specific requirements. In conclusion, we propose 3D-directed approaches for a detailed whole-organ view on the pulmonary vasculature in health and disease, to advance our current knowledge of diseases affecting the pulmonary vasculature.

Altered renal vascular patterning reduces ischemic kidney injury and limits vascular loss associated with aging

The kidney vasculature has a complex arrangement, which runs in both series and parallel to perfuse the renal tissue and appropriately filter plasma. Recent studies have demonstrated that the development of this vascular pattern is dependent on netrin-1 secreted by renal stromal progenitors. Mice lacking netrin-1 develop an arterial tree with stochastic branching, particularly of the large interlobar vessels. The current study investigated whether abnormalities in renal vascular pattern altered kidney function or response to injury. To examine this, we analyzed kidney function at baseline as well as in response to recovery from a model of bilateral ischemic injury and measured vascular dynamics in aged mice. We found no differences in kidney function or morphology at baseline between mice with an abnormal arterial pattern compared to control. Interestingly, male and female mutant mice with stochastic vascular patterning showed a reduction in tubular injury in response to ischemia. Similarly, mutant mice also had a preservation of perfused vasculature with aging compared to a reduction in the control group. These results suggest that guided and organized patterning of the renal vasculature may not be required for normal kidney function; thus, modulating renal vascular patterning may represent an effective therapeutic strategy. Understanding how patterning and maturation of the arterial tree affects physiology and response to injury or aging has important implications for enhancing kidney regeneration and tissue engineering strategies.

Fluorescent Water-Soluble Polycationic Chitosan Polymers as Markers for Biological 3D Imaging

Over the last decades, various tissue-clearing techniques have broken the ground for the optical imaging of whole organs and whole-organisms, providing complete representative data sets of three-dimensional biological structures. Along with advancements in this field, the development of fluorescent markers for staining vessels and capillaries has offered insights into the complexity of vascular networks and their impact on disease progression. Here we describe the use of a modified water-soluble chitosan linked to cyanine dyes in combination with ethyl cinnamate-based optical tissue clearing for the 3D visualization of tissue vasculature in depth. The water-soluble fluorescent Chitosans have proven to be an optimal candidate for labeling both vessels and capillaries ex vivo thanks to their increased water solubility, high photostability, and optical properties in the near-infrared window. In addition, the nontoxicity of these markers broadens their applicability to in vitro and in vivo biological applications. Despite the availability of other fluorescent molecules for vascular staining, the present study, for the first time, demonstrates the potential of fluorescent chitosans to depict vessels at the capillary level and opens avenues for advancing the diagnostic field by reducing the complexity and costs of the currently available procedures.

YAP/TAZ signaling in allantois-derived cells is required for placental vascularization

Normal placental development and angiogenesis are crucial for fetal growth and maternal health during pregnancy. However, molecular regulation of placental angiogenesis has been difficult to study due to a lack of specific genetic tools that isolate the placenta from the embryo and yolk sac. To address this gap in knowledge we recently developed Hoxa13 Cre mice in which Cre is expressed in allantois-derived cells, including placental endothelial and stromal cells. Mice lacking the transcriptional regulators Yes-associated protein (YAP) and PDZ-binding motif (TAZ) in allantois-derived cells exhibit embryonic lethality at midgestation with compromised placental vasculature. snRNA-seq analysis revealed transcriptional changes in placental stromal cells and endothelial cells. YAP/TAZ mutants exhibited significantly reduced placental stromal cells prior to the endothelial architectural change, highlighting the role of these cells in placental vascular growth. These results reveal a central role for YAP/TAZ signaling during placental vascular growth and implicate Hoxa13 -derived placental stromal cells as a critical component of placental vascularization.

Three Dimensional Multiscalar Neurovascular Nephron Connectivity Map of the Human Kidney Across the Lifespan

The human kidney is a vital organ with a remarkable ability to coordinate the activity of up to a million nephrons, its main functional tissue unit (FTU), and maintain homeostasis. We developed tissue processing and analytical methods to construct a 3D map of neurovascular nephron connectivity of the human kidney and glean insights into how this structural organization enables coordination of various functions of the nephron, such as glomerular filtration, solute and water absorption, secretion by the tubules, and regulation of blood flow and pressure by the juxtaglomerular apparatus, in addition to how these functions change across disease and lifespans. Using light sheet fluorescence microscopy (LSFM) and morphometric analysis we discovered changes in anatomical orientation of the vascular pole, glomerular density, volume, and innervation through postnatal development and ageing. The extensive nerve network exists from cortex FTUs to medullary loop of Henle, providing connectivity within segments of the same nephron, and between separate nephrons. The nerves organize glomeruli into discreet communities (in the same network of nerves). Adjacent glomerular communities are connected to intercommunal "mother glomeruli" by nerves, a pattern repeating throughout the cortex. These neuro-nephron networks are not developed in postnatal kidneys and are disrupted in diseased kidneys (diabetic or hydronephrosis). This structural organization likely poises the entire glomerular and juxtaglomerular FTUs to synchronize responses to perturbations in fluid homeostasis, utilizing mother glomeruli as network control centers.

Protocol for optical, aqueous-based clearing of murine tissues using EZ Clear

Tissue clearing is an essential prerequisite for 3D volumetric imaging of larger tissues or organs. Here, we present a detailed protocol for optical, aqueous-based clearing of adult murine tissues using EZ Clear. We describe steps to ensure successful perfusion and fixation of organs from the adult mouse and supply guidelines for optimal lipid removal, refractive index matching, and tissue clearing. Finally, we provide imaging parameters for visualizing both exogenous perfused fluorescent dyes and endogenous fluorescence reporters in the adult mouse. For complete details on the use and execution of this protocol, please refer to Hsu et al.1.

Whole-Body and Whole-Organ 3D Imaging of Hypoxia Using an Activatable Covalent Fluorescent Probe Compatible with Tissue Clearing

Elucidation of biological phenomena requires imaging of microenvironments in vivo. Although the seamless visualization of in vivo hypoxia from the level of whole-body to single-cell has great potential to discover unknown phenomena in biological and medical fields, no methodology for achieving it has been established thus far. Here, we report the whole-body and whole-organ imaging of hypoxia, an important microenvironment, at single-cell resolution using activatable covalent fluorescent probes compatible with tissue clearing. We initially focused on overcoming the incompatibility of fluorescent dyes and refractive index matching solutions (RIMSs), which has greatly hindered the development of fluorescent molecular probes in the field of tissue clearing. The fluorescent dyes compatible with RIMS were then incorporated into the development of activatable covalent fluorescent probes for hypoxia. We combined the probes with tissue clearing, achieving comprehensive single-cell-resolution imaging of hypoxia in a whole mouse body and whole organs.

Evaluation of Connexin Hemichannel Activity In Vivo

Connexin hemichannels (Cx HCs) are hexameric structures at the cell plasma membrane, whose function as membrane transport proteins allows for the passive flow of small hydrophilic molecules and ions (≤1 kDa) between the cytosol and the extracellular environment. Activation of Cx HCs is highly dependent on pathological conditions. HC activity provokes changes in the microenvironment, inducing the dissemination of signaling molecules in both an autocrine and paracrine manner. Given the elicitation of a variety of signaling pathways, and assortment of Cx species and dispersion throughout the body, Cx HCs have been implicated in a range of processes such as cell proliferation, differentiation, cell death, and tissue modeling and remodeling. While studying the expression and localization of Cx HCs can be done using traditional laboratory techniques, such as immunoblot analysis, measuring the functionality/activity of the HCs requires a more explicit methodology and is essential for determining Cx-mediated physiological changes. The study of Cx HC function/activity has focused mainly on in vitro measurements through electrophysiological characterization or, more commonly, using HC-permeable dye uptake studies. Here, we describe the use of dye uptake to measure Cx HC activity in vivo using mechanically stimulated osteocytic Cx43 HCs with Evans blue dye as our model.

Reversal of pulmonary veno-occlusive disease phenotypes by inhibition of the integrated stress response

Pulmonary veno-occlusive disease (PVOD) is a rare form of pulmonary hypertension arising from EIF2AK4 gene mutations or mitomycin C (MMC) administration. The lack of effective PVOD therapies is compounded by a limited understanding of the mechanisms driving the vascular remodeling in PVOD. We show that the administration of MMC in rats mediates the activation of protein kinase R (PKR) and the integrated stress response (ISR), which lead to the release of the endothelial adhesion molecule VE-Cadherin in the complex with Rad51 to the circulation, disruption of endothelial barrier, and vascular remodeling. Pharmacological inhibition of PKR or ISR attenuates the depletion of VE-Cadherin, elevation of vascular permeability, and vascular remodeling instigated by MMC, suggesting potential clinical intervention for PVOD. Finally, the severity of PVOD phenotypes was increased by a heterozygous BMPR2 mutation that truncates the carboxyl tail of BMPR2, underscoring the role of deregulated BMP signal in the development of PVOD.

Netrin 1 directs vascular patterning and maturity in the developing kidney

The intricate vascular system of the kidneys supports body fluid and organ homeostasis. However, little is known about how vascular architecture is established during kidney development. More specifically, how signals from the kidney influence vessel maturity and patterning remains poorly understood. Netrin 1 (Ntn1) is a secreted ligand that is crucial for vessel and neuronal guidance. Here, we demonstrate that Ntn1 is expressed by Foxd1+ stromal progenitors in the developing mouse kidney and conditional deletion (Foxd1GC/+;Ntn1fl/fl) results in hypoplastic kidneys with extended nephrogenesis. Wholemount 3D analyses additionally revealed the loss of a predictable vascular pattern in Foxd1GC/+;Ntn1fl/fl kidneys. As vascular patterning has been linked to vessel maturity, we investigated arterialization. Quantification of the CD31+ endothelium at E15.5 revealed no differences in metrics such as the number of branches or branch points, whereas the arterial vascular smooth muscle metrics were significantly reduced at both E15.5 and P0. In support of our observed phenotypes, whole kidney RNA-seq revealed disruptions to genes and programs associated with stromal cells, vasculature and differentiating nephrons. Together, our findings highlight the significance of Ntn1 to proper vascularization and kidney development.

Effects of Five Coumarins and Standardized Extracts from Tagetes lucida Cav. on Motor Impairment and Neuroinflammation Induced with Cuprizone

Multiple sclerosis (MS) is an autoimmune disease of the central nervous system (CNS) with no curative treatment, and the available therapies aim to modify the course of the disease. It has been demonstrated that extracts of Tagetes lucida have immunomodulatory and neuroprotective effects. This work induced motor damage and neuroinflammation in male BALB/c mice by oral administration of cuprizone (CPZ) (40 mg/kg) for five weeks. In addition, the extracts and coumarins of Tagetes lucida (25 mg/kg) were used to control these damage variables; during the experiment, animals were subject to behavioral tests, and at the end of 5 weeks, mice from each group were used to measure the integrity of biological barriers (brain, kidneys, and spleen) through the extravasation test with blue Evans dye. In another group of animals, the ELISA method measured the brain concentrations of IL-1β, IL-4, IL-10, and TNF-α. The results presented here allow us to conclude that the extracts and coumarins IC, HN, PE, DF, and SC of Tagetes lucida exert a neuroprotective effect by controlling the motor damage and neuroinflammation by increasing the expression of IL-4 and IL-10 and decreasing IL-1β and TNF-α; notably, these treatments also protect organs from vascular permeability increase, mainly the BBB, in mice with CPZ-induced experimental encephalomyelitis (VEH * p < 0.05). However, more studies must be carried out to elucidate the molecular mechanisms of the pharmacological effects of this Mexican medicinal plant.

Extravasation of Blood and Blood Toxicity Drives Tubular Injury from RBC Trapping in Ischemic AKI

Red blood cell (RBC) trapping is common in ischemic acute kidney injury (AKI) and presents as densely packed RBCs that accumulate within and engorge the kidney medullary circulation. In this study, we tested the hypothesis that "RBC trapping directly promotes tubular injury independent of extending ischemia time." Studies were performed on rats. Red blood cell congestion and tubular injury were compared between renal arterial clamping, venous clamping, and venous clamping of blood-free kidneys. Vessels were occluded for either 15 or 45 min with and without reperfusion. We found that RBC trapping in the medullary capillaries occurred rapidly following reperfusion from renal arterial clamping and that this was associated with extravasation of blood from congested vessels, uptake of blood proteins by the tubules, and marked tubular injury. To determine if this injury was due to blood toxicity or an extension of ischemia time, we compared renal venous and arterial clamping without reperfusion. Venous clamping resulted in RBC trapping and marked tubular injury within 45 min of ischemia. Conversely, despite the same ischemia time, RBC trapping and tubular injury were minimal following arterial clamping without reperfusion. Confirming the role of blood toward tubular injury, injury was markedly reduced in blood-free kidneys with venous clamping. Our data demonstrate that RBC trapping results in the rapid extravasation and uptake of blood components by tubular cells, causing toxic tubular injury. Tubular toxicity from extravasation of blood following RBC trapping appears to be a major component of tubular injury in ischemic AKI, which has not previously been recognized.

Netrin-1 directs vascular patterning and maturity in the developing kidney

Blood filtering by the kidney requires the establishment of an intricate vascular system that works to support body fluid and organ homeostasis. Despite these critical roles, little is known about how vascular architecture is established during kidney development. More specifically, how signals from the kidney influence vessel maturity and patterning remains poorly understood. Netrin-1 (Ntn1) is a secreted ligand critical for vessel and neuronal guidance. Here, we demonstrate that Ntn1 is expressed by stromal progenitors in the developing kidney, and conditional deletion of Ntn1 from Foxd1+ stromal progenitors (Foxd1GC/+;Ntn1fl/fl) results in hypoplastic kidneys that display extended nephrogenesis. Despite expression of the netrin-1 receptor Unc5c in the adjacent nephron progenitor niche, Unc5c knockout kidneys develop normally. The netrin-1 receptor Unc5b is expressed by embryonic kidney endothelium and therefore we interrogated the vascular networks of Foxd1GC/+;Ntn1fl/fl kidneys. Wholemount, 3D analyses revealed the loss of a predictable vascular pattern in mutant kidneys. As vascular patterning has been linked to vessel maturity, we investigated arterialization in these mutants. Quantification of the CD31+ endothelium at E15.5 revealed no differences in metrics such as the number of branches or branch points, whereas the arterial vascular smooth muscle metrics were significantly reduced at both E15.5 and P0. In support of these results, whole kidney RNA-seq showed upregulation of angiogenic programs and downregulation of muscle-related programs which included smooth muscle-associated genes. Together, our findings highlight the significance of netrin-1 to proper vascularization and kidney development.

Disruption of the Blood-Spinal Cord Barrier using Low-Intensity Focused Ultrasound in a Rat Model

Low-intensity focused ultrasound (LIFU) uses ultrasonic pulsations at lower intensities than ultrasound and is being tested as a reversible and precise neuromodulatory technology. Although LIFU-mediated blood-brain barrier (BBB) opening has been explored in detail, no standardized technique for blood-spinal cord barrier (BSCB) opening has been established to date. Therefore, this protocol presents a method for successful BSCB disruption using LIFU sonication in a rat model, including descriptions of animal preparation, microbubble administration, target selection and localization, as well as BSCB disruption visualization and confirmation. The approach reported here is particularly useful for researchers who need a fast and cost-effective method to test and confirm target localization and precise BSCB disruption in a small animal model with a focused ultrasound transducer, evaluate the BSCB efficacy of sonication parameters, or explore applications for LIFU at the spinal cord, such as drug delivery, immunomodulation, and neuromodulation. Optimizing this protocol for individual use is recommended, especially for advancing future preclinical, clinical, and translational work.

A versatile vessel casting method for fine mapping of vascular networks using a hydrogel-based lipophilic dye solution

Efficient labeling of the vasculature is important for understanding the organization of vascular networks. Here, we propose VALID, a vessel-labeling method that enables visualization of vascular networks with tissue clearing and light-sheet microscopy. VALID transforms traditional lipophilic dye solution into hydrogel by introducing gelatin and restrains the dye aggregation, resulting in complete and uniform vessel-labeling patterns with high signal-to-background ratios. VALID also enhances the compatibility of lipophilic dyes with solvent-based tissue-clearing protocols, which was hard to achieve previously. Using VALID, we combined lipophilic dyes with solvent-based tissue-clearing techniques to perform 3D reconstructions of vasculature within mouse brain and spinal cord. We also employed VALID for 3D visualization and quantification of microvascular damage in a middle cerebral artery occlusion mouse model. VALID should provide a simple, cost-effective vessel-labeling protocol that would significantly widen the applications of lipophilic dyes in research on cerebrovascular complications.

Optical Tissue Clearing to Study the Intra-Pulmonary Biodistribution of Intravenously Delivered Mesenchymal Stromal Cells and Their Interactions with Host Lung Cells

Mesenchymal stromal cells (MSCs) injected intravenously are trapped in the capillaries of the lungs and die within the first 24 h. Studying the biodistribution and fate of labelled therapeutic cells in the 3D pulmonary context is important to understand their function in this organ and gain insights into their mechanisms of action. Optical tissue clearing enables volumetric cell tracking at single-cell resolution. Thus, we compared three optical tissue-clearing protocols (Clear, Unobstructed Brain/Body Imaging Cocktails and Computational analysis (CUBIC), modified stabilised 3D imaging of solvent-cleared organs (s-DISCO) and ethyl cinnamate (ECi)) to evaluate their potential to track the biodistribution of human umbilical cord MSCs expressing the tdTomato fluorescence reporter and investigate how they interact with host cells in the mouse lung. The results showed that although CUBIC clearing is the only method that enables direct imaging of fluorescently labelled MSCs, combining s-DISCO or ECi with immunofluorescence or dye labelling allows the interaction of MSCs with endothelial and immune cells to be studied. Overall, this comparative study offers guidance on selecting an optical tissue-clearing method for cell tracking applications.