Delivery and kinetics of immersion optical clearing agents in tissues: Optical imaging from ex vivo to in vivo.

Advanced optical imaging provides a powerful tool for the structural and functional analysis of tissues with high resolution and contrast, but the imaging performance decreases as light propagates deeper into the tissue. Tissue optical clearing technique demonstrates an innovative way to realize deep-tissue imaging and have emerged substantially in the last two decades. Here, we briefly reviewed the basic principles of tissue optical clearing techniques in the view of delivery strategies via either free diffusion or external forces-driven advection, and the commonly-used optical techniques for monitoring kinetics of clearing agents in tissue, as well as their ex vivo to in vivo applications in multiple biomedical research fields.

SOLID: minimizing tissue distortion for brain-wide profiling of diverse architectures.

Brain-wide profiling of diverse biological components is fundamental for understanding complex brain pathology. Despite the availability in whole-brain imaging, it is still challenging to conduct multiplexed, brain-wide analysis with current tissue clearing techniques. Here, we propose SOLID, a hydrophobic tissue clearing method that can minimize tissue distortion while offering impressive clearing performance.

A robust vessel-labeling pipeline with high tissue clearing compatibility for 3D mapping of vascular networks.

The combination of vessel-labeling, tissue-clearing, and light-sheet imaging techniques provides a potent tool for accurately mapping vascular networks, enabling the assessment of vascular remodeling in vascular-related disorders. However, most vascular labeling methods face challenges such as inadequate labeling efficiency or poor compatibility with current tissue clearing technology, which significantly undermines the image quality. To address this limitation, we introduce a vessel-labeling pipeline, termed Ultralabel, which relies on a specially designed dye hydrogel containing lysine-fixable dextran and gelatins for double enhancement.

Dual-Channel in Spatial-Frequency Domain CycleGAN for perceptual enhancement of transcranial cortical vascular structure and function.

Observing cortical vascular structures and functions using laser speckle contrast imaging (LSCI) at high resolution plays a crucial role in understanding cerebral pathologies. Usually, open-skull window techniques have been applied to reduce scattering of skull and enhance image quality. However, craniotomy surgeries inevitably induce inflammation, which may obstruct observations in certain scenarios.

Tau induces inflammasome activation and microgliosis through acetylating NLRP3.

Background: Alzheimer's disease (AD) and related Tauopathies are characterised by the pathologically hyperphosphorylated and aggregated microtubule-associated protein Tau, which is accompanied by neuroinflammation mediated by activated microglia. However, the role of Tau pathology in microglia activation or their causal relationship remains largely elusive.

Methods: The levels of nucleotide-binding oligomerisation domain (NOD)-like receptor pyrin domain containing 3 (NLRP3) acetylation and inflammasome activation in multiple cell models with Tau proteins treatment, transgenic mice with Tauopathy, and AD patients were measured by Western blotting and enzyme-linked immunosorbent assay.

Rapid 3D isotropic imaging of whole organ with double-ring light-sheet microscopy and self-learning side-lobe elimination.

Bessel-like plane illumination forms a new type of light-sheet microscopy with ultra-long optical sectioning distance that enables rapid 3D imaging of fine cellular structures across an entire large tissue. However, the side-lobe excitation of conventional Bessel light sheets severely impairs the quality of the reconstructed 3D image. Here, we propose a self-supervised deep learning (DL) approach that can completely eliminate the residual side lobes for a double-ring-modulated non-diffraction light-sheet microscope, thereby substantially improving the axial resolution of the 3D image.

Transcranial photobiomodulation for brain diseases: review of animal and human studies including mechanisms and emerging trends.

The brain diseases account for 30% of all known diseases. Pharmacological treatment is hampered by the blood-brain barrier, limiting drug delivery to the central nervous system (CNS). Transcranial photobiomodulation (tPBM) is a promising technology for treating brain diseases, due to its effectiveness, non-invasiveness, and affordability.

Photostimulation of lymphatic clearance of β-amyloid from mouse brain: a new strategy for the therapy of Alzheimer's disease.

Alzheimer's disease (AD) is an age-related neurodegenerative disorder that poses a significant burden on socio-economic and healthcare systems worldwide. However, the currently available therapy of AD is limited, and new strategies are needed to enhance the clearance of β-amyloid (Aβ) protein and improve cognitive function. Photobiomodulation (PBM) is a non-invasive and effective therapeutic method that has shown promise in treating various brain diseases.

Transcranial photobiomodulation improves insulin therapy in diabetic microglial reactivity and the brain drainage system.

The dysfunction of microglia in the development of diabetes is associated with various diabetic complications, while traditional insulin therapy is insufficient to rapidly restore the function of microglia. Therefore, the search for new alternative methods of treating diabetes-related dysfunction of microglia is urgently needed. Here, we evaluate the effects of transcranial photobiomodulation (tPBM) on microglial function in diabetic mice and investigate its mechanism.

Protocol for fine casting, imaging, and analysis of murine vascular networks with VALID.

The majority of fluorescent vessel labeling techniques currently available are limited by their expense, incomplete labeling, or complexity. Here, we present VALID (vessel labeling via gelatin-based lipophilic dye solution)-a protocol for complete labeling of different vascular networks. We describe steps for preparing different dye hydrogels, murine vascular casting and tissue harvesting, immunolabeling, tissue clearing, and imaging, as well as detailed analysis of the vascular networks.

skin optical clearing for improving imaging and light-induced therapy: a review.

Significance: Skin is the largest organ and also the first barrier of body. Skin diseases are common, and cutaneous microcirculation is relative to various diseases. Researchers attempt to develop novel imaging techniques to obtain the complex structure, components, and functions of skin.

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.

A labeling strategy for the three-dimensional recognition and analysis of microvascular obstruction in ischemic stroke.

Large vessel recanalization in ischemic stroke does not always go along with tissue reperfusion, a phenomenon called "no-reflow". However, knowledge of the mechanism of no-reflow is limited because identifying microvascular obstruction across the cortex and subcortex both in clinical and experimental models is challenging. In this study, we developed a smart three-dimensional recognition pipeline for microvascular obstruction during post-ischemia reperfusion to examine the underlying mechanism of no-reflow.

Optimal combinations of fluorescent vessel labeling and tissue clearing methods for three-dimensional visualization of vasculature.

Significance: Visualization of intact vasculatures is crucial to understanding the pathogeneses of different neurological and vascular diseases. Although various fluorescent vessel labeling methods have been used in combination with tissue clearing for three-dimensional (3D) visualization of different vascular networks, little has been done to quantify the labeling effect of each vessel labeling routine, as well as their applicability alongside various clearing protocols, making it difficult to select an optimal combination for finely constructing different vasculatures. Therefore, it is necessary to systematically assess the overall performance of these common vessel labeling methods combined with different tissue-clearing protocols.

Three-dimensional mapping reveals heterochronic development of the neuromuscular system in postnatal mouse skeletal muscles.

The development of the neuromuscular system, including muscle growth and intramuscular neural development, in addition to central nervous system maturation, determines motor ability improvement. Motor development occurs asynchronously from cephalic to caudal. However, whether the structural development of different muscles is heterochronic is unclear.

Optical clearing imaging assisted evaluation of urokinase thrombolytic therapy on cerebral vessels with different sizes.

Ischemic stroke is caused by occlusion of the blood vessels in the brain, where intravenous thrombolytic therapy is the most effective treatment. Urokinase is a commonly used drug for intravenous thrombolytic therapy, while the effect of vessel size has not been thoroughly studied on urokinase. In this work, using the thrombin-combined photothrombosis model and craniotomy-free skull optical clearing window, we studied the recanalization of different cortical vessels after urokinase treatment.

In vivo tissue optical clearing assisted through-skull targeted photothrombotic ischemic stroke model in mice.

Significance: Photothrombotic stroke is an important and widely used model for ischemic stroke research. However, the significant scattering of the skull during the procedure limits the light's ability to penetrate and focus on its target. Targeted photothrombosis uses surgery-based skull windows to obtain optical access to the brain, but it renders the brain's environment unnatural even before a stroke is established.

Transmissive-detected laser speckle contrast imaging for blood flow monitoring in thick tissue: from Monte Carlo simulation to experimental demonstration.

Laser speckle contrast imaging (LSCI) is a powerful tool to monitor blood flow distribution and has been widely used in studies of microcirculation, both for animal and clinical applications. Conventionally, LSCI usually works on reflective-detected mode. However, it could provide promising temporal and spatial resolution for in vivo applications only with the assistance of various tissue windows, otherwise, the overlarge superficial static speckle would extremely limit its contrast and resolution.

Dec-DISCO: decolorization DISCO clearing for seeing through the biological architectures of heme-rich organs.

The tissue optical clearing technique plays an important role in three-dimensional (3D) visualization of large tissues. As a typical solvent-based clearing method, 3DISCO can achieve the highest level of tissue transparency with favorable clearing speed. However, 3DISCO cannot deal with the residual blood within tissues, leading to tissue brownness or redness after clearing, thus greatly influencing the tissue transparency and image quality due to the strong absorption of residual blood.

FDISCO+: a clearing method for robust fluorescence preservation of cleared samples.

The recently reported solvent-based optical clearing method FDISCO can preserve various fluorescent signals very well. However, the strict low-temperature storage condition of FDISCO is not conducive to long-time or repetitive imaging usually conducted at room temperature. Therefore, it is important to solve the contradiction between fluorescence preservation and imaging condition.

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.

An Approach to Maximize Retrograde Transport Based on the Spatial Distribution of Motor Endplates in Mouse Hindlimb Muscles.

Knowledge regarding the relationship between muscles and the corresponding motor neurons would allow therapeutic genes to transport into specific spinal cord segments. Retrograde tracing technique by targeting the motor endplate (MEP), a highly specialized structure that offers direct access to the spinal motor neurons, has been used to elucidate the connectivity between skeletal muscles and the innervating motor neuron pools. However, current injection strategies mainly based on blind injection or the local MEP region might lead to an underestimation of the motor neuron number due to the uneven distribution of MEP in skeletal muscles.

Physical and chemical mechanisms of tissue optical clearing.

Advanced optical methods combined with various probes pave the way toward molecular imaging within living cells. However, major challenges are associated with the need to enhance the imaging resolution even further to the subcellular level for the imaging of larger tissues, as well as for studies. High scattering and absorption of opaque tissues limit the penetration of light into deep tissues and thus the optical imaging depth.

MACS: Rapid Aqueous Clearing System for 3D Mapping of Intact Organs.

Tissue optical clearing techniques have provided important tools for large-volume imaging. Aqueous-based clearing methods are known for good fluorescence preservation and scalable size maintenance, but are limited by long incubation time, insufficient clearing performance, or requirements for specialized devices. Additionally, few clearing methods are compatible with widely used lipophilic dyes while maintaining high clearing performance.

Three-dimensional visualization of intramuscular innervation in intact adult skeletal muscle by a modified iDISCO method.

Three-dimensional visualization of the innervation in skeletal muscles is helpful for understanding the morphological structure and function. iDISCO, a whole-mount immunolabeling and clearing technique, provides a valuable tool for volume imaging of intramuscular nerve fibers but suffers from the nonspecific staining caused by the anti-mouse secondary antibody when using the murine primary antibody. We developed a modified iDISCO method by introducing pretreatment of ScaeCUBIC-1 reagent, termed m-iDISCO.