A novel method to visualise the three-dimensional organisation of the human cerebral cortical vasculature

Semi-automated protocol to quantify and characterize fluorescent three-dimensional vascular images

The microvasculature facilitates gas exchange, provides nutrients to cells, and regulates blood flow in response to stimuli. Vascular abnormalities are an indicator of pathology for various conditions, such as compromised vessel integrity in small vessel disease and angiogenesis in tumors. Traditional immunohistochemistry enables the visualization of tissue cross-sections containing exogenously labeled vasculature. Although this approach can be utilized to quantify vascular changes within small fields of view, it is not a practical way to study the vasculature on the scale of whole organs. Three-dimensional (3D) imaging presents a more appropriate method to visualize the vascular architecture in tissue. Here we describe the complete protocol that we use to characterize the vasculature of different organs in mice encompassing the methods to fluorescently label vessels, optically clear tissue, collect 3D vascular images, and quantify these vascular images with a semi-automated approach. To validate the automated segmentation of vascular images, one user manually segmented one hundred random regions of interest across different vascular images. The automated segmentation results had an average sensitivity of 83±11% and an average specificity of 91±6% when compared to manual segmentation. Applying this procedure of image analysis presents a method to reliably quantify and characterize vascular networks in a timely fashion. This procedure is also applicable to other methods of tissue clearing and vascular labels that generate 3D images of microvasculature.

Lectin Histochemistry: Historical Perspectives, State of the Art, and Future Directions

Lectins, discovered more than 100 years ago and defined by their ability to selectively recognize specific carbohydrate structures, are ubiquitous in living organisms. Their precise functions are as yet under-explored and incompletely understood but they are clearly involved, through recognition of their binding partners, in a myriad of biological mechanisms involved in cell identity, adhesion, signaling, and growth regulation in health and disease. Understanding the complex "sugar code" represented by the "glycome" is a major challenge and at the forefront of current biological research. Lectins have been widely employed in histochemical studies to map glycosylation in cells and tissues. Here, a brief history of the discovery of lectins and early developments in their use is presented along with a selection of some of the most interesting and significant discoveries to emerge from the use of lectin histochemistry. Further, an evaluation of the next generation of lectin-based technologies is presented, including the potential for designing recombinant lectins with more precisely defined binding characteristics, linking lectin-based studies with other technologies to answer fundamental questions in glycobiology and approaches to exploring the interactions of lectins with their binding partners in more detail.

Advanced high resolution three-dimensional imaging to visualize the cerebral neurovascular network in stroke

As an important method to accurately and timely diagnose stroke and study physiological characteristics and pathological mechanism in it, imaging technology has gone through more than a century of iteration. The interaction of cells densely packed in the brain is three-dimensional (3D), but the flat images brought by traditional visualization methods show only a few cells and ignore connections outside the slices. The increased resolution allows for a more microscopic and underlying view. Today's intuitive 3D imagings of micron or even nanometer scale are showing its essentiality in stroke. In recent years, 3D imaging technology has gained rapid development. With the overhaul of imaging mediums and the innovation of imaging mode, the resolution has been significantly improved, endowing researchers with the capability of holistic observation of a large volume, real-time monitoring of tiny voxels, and quantitative measurement of spatial parameters. In this review, we will summarize the current methods of high-resolution 3D imaging applied in stroke.

Tissue optical clearing for 3D visualization of vascular networks: A review

Reconstruction of the vasculature of intact tissues/organs down to the capillary level is essential for understanding the development and remodeling of vascular networks under physiological and pathological conditions. Optical imaging techniques can provide sufficient resolution to distinguish small vessels with several microns, but the imaging depth is somewhat limited due to the high light scattering of opaque tissue. Recently, various tissue optical clearing methods have been developed to overcome light attenuation and improve the imaging depth both for ex-vivo and in-vivo visualizations. Tissue clearing combined with vessel labeling techniques and advanced optical tomography enables successful mapping of the vasculature of different tissues/organs, as well as dynamically monitoring vessel function under normal and pathological conditions. Here, we briefly introduce the commonly-used labeling strategies for entire vascular networks, the current tissue optical clearing techniques available for various tissues, as well as the advanced optical imaging techniques for fast, high-resolution structural and functional imaging for blood vessels. We also discuss the applications of these techniques in the 3D visualization of vascular networks in normal tissues, and the vascular remodeling in several typical pathological models in clinical research. This review is expected to provide valuable insights for researchers to study the potential mechanisms of various vessel-associated diseases using tissue optical clearing pipeline.

Optimizing tissue clearing and imaging methods for human brain tissue

Objectives

To identify optimum sample conditions for human brains, we compared the clearing efficiency, antibody staining efficiency, and artifacts between fresh and cadaver samples.

Methods

Fresh and cadaver samples were cleared using X-CLARITY™. Clearing efficiency and artifact levels were calculated using ImageJ, and antibody staining efficiency was evaluated after confocal microscopy imaging. Three staining methods were compared: 4-day staining (4DS), 11-day staining (11DS), and 4-day staining with a commercial kit (4DS-C). The optimum staining method was then selected by evaluating staining time, depth, method complexity, contamination, and cost.

Results

Fresh samples outperformed cadaver samples in terms of the time and quality of clearing, artifacts, and 4′,6-diamidino-2-phenylindole (DAPI) staining efficiency, but had a glial fibrillary acidic protein (GFAP) staining efficiency that was similar to that of cadaver samples. The penetration depth and DAPI staining improved in fresh samples as the incubation period lengthened. 4DS-C was the best method, with the deepest penetration. Human brain images containing blood vessels, cell nuclei, and astrocytes were visualized three-dimensionally. The chemical dye staining depth reached 800 µm and immunostaining depth exceeded 200 µm in 4 days.

Conclusions

We present optimized sample preparation and staining protocols for the visualization of three-dimensional macrostructure in the human brain.

Optical Tissue Clearing: Illuminating Brain Function and Dysfunction

Tissue optical clearing technology has been developing rapidly in the past decade due to advances in microscopy equipment and various labeling techniques. Consistent modification of primary methods for optical tissue transparency has allowed observation of the whole mouse body at single-cell resolution or thick tissue slices at the nanoscale level, with the final aim to make intact primate and human brains or thick human brain tissues optically transparent. Optical clearance combined with flexible large-volume tissue labeling technology can not only preserve the anatomical structure but also visualize multiple molecular information from intact samples in situ. It also provides a new strategy for studying complex tissues, which is of great significance for deciphering the functional structure of healthy brains and the mechanisms of neurological pathologies. In this review, we briefly introduce the existing optical clearing technology and discuss its application in deciphering connection and structure, brain development, and brain diseases. Besides, we discuss the standard computational analysis tools for large-scale imaging dataset processing and information extraction. In general, we hope that this review will provide a valuable reference for researchers who intend to use optical clearing technology in studying the brain.