Achieving optical transparency in live animals with absorbing molecules

Biotechnological production and emerging applications of betalains: A review

Betalains are food-grade hydrophilic pigments with antioxidant and biological activities, predominantly found in plants. Betanin is a red-violet betalain synthesized from tyrosine through L-DOPA formation, its subsequent aromatic ring-opening, spontaneous cyclization to betalamic acid, and then pH-dependent condensation with i) cyclo-DOPA-5-O-glucoside or ii) cyclo-DOPA followed by 5-O-glucosylation. This short pathway in plants for betanin biosynthesis has been heterologously expressed in other organisms (e.g. non-betalainic plants, yeasts, and fungi) using CYP76AD1, DOD1, and cDOPA5GT or B5GT, corresponding to the enzymatic steps mentioned above. For the red-violet color formation through heterologous expression of the pathway genes in non-betalainic plants, a simplified reporter gene called RUBY has been developed recently. Without any systems engineering, expression of RUBY in non-betalainic plants resulted in accumulation of up to 203 mg betalains/100 g fresh weight of peanut leaves. In yeasts, Saccharomyces cerevisiae and Yarrowia lipolytica, and fungus Fusarium venenatum, betanin production has been achieved through overexpression of the pathway genes, with productivity reaching up to 0.62 mg/L/h, 26 mg/L/h, and 26.4 mg/L/h from d-glucose as carbon source, respectively, after considerable systems engineering and gene copy number augmentation. This review critically analyzes recent biotechnological production of betalains to highlight the advancements and strategies for improvement in the technology. Also, emerging applications of betalain biosynthetic gene products or betalains as biosensors, fluorescent probes, meat analog colors, and others are discussed to strengthen the need for systems engineering and process optimization for large-scale industrial production of these pigments.

Proposal for a simple and easy-to-implement protocol for three-dimensional tissue imaging that is compatible with observation using a confocal microscope

Tissue observation has traditionally been limited to obtaining two-dimensional information from thinly sliced tissues due to issues with light transmission and antibody penetration. In recent years, three-dimensional tissue observation methods combining tissue clearing and deep immunostaining methods have been reported. However, due to the significantly different procedures in these methods from conventional immunostaining methods and the requirement for an expensive and specialized light-sheet microscope for tissue observation, the widespread adoption of these methods has been limited. To promote the shift from the current two-dimensional tissue observation to three-dimensional tissue observation using a combination of tissue clearing and immunostaining, it is essential to establish a simple and easy-to-implement protocol that is compatible with observation using a confocal microscope, which is available in many facilities. In this study, we first examined the effects of tissue clearing and staining conditions of immunostaining with thin tissue slices. We showed that CUBIC-L enhances immunolabeling without diminishing the immunoreactivity of antigens. We also showed that high detergent concentrations enhance the intensity of immunoreactivity and that a two-step staining procedure is suitable for our proposed protocol. Based on the results, we propose a simple protocol that can be easily adapted from conventional methods and is compatible with confocal microscopes. The results of this study are expected to facilitate a shift from traditional methods to three-dimensional tissue observation techniques that combine tissue clearing and immunostaining, contributing to the broader adoption of three-dimensional tissue observation.

Fabrication of Microgel-Reinforced Hydrogels via Vat Photopolymerization

We report a facile method for the vat photopolymerization (i.e., digital light processing, DLP) of microgel-reinforced hydrogels that leverages both light and dark polymerization for curing. As an example, norbornene modified hyaluronic acid (NorHA) microgels at varying volume fractions swollen in acrylamide monomer are implemented as resins. When processed with DLP, acrylamide polymerization and cross-linking results in the formation of a secondary, continuous network that percolates through the microgels. At even low volume fractions (e.g., 30% v/v), the addition of microgels results in up to 4-fold increases in the stress at failure and work of fracture and a reduction in hydrogel swelling. The microgel-reinforced hydrogels are 3D printed into intricate shapes (e.g., metamaterial lattices) while maintaining uniform microgel distributions, and microgels with varied cross-link densities, cross-linkers, and fabrication methods are also investigated. This work expands the potential of microgel-reinforced hydrogels across applications where geometric freedom is essential.

Accessing the viscera: Technologies for interoception research

Interoception, or the perception and regulation of body signals by the central nervous system, is critical for maintaining homeostasis and coordination of behaviors. Deciphering the mechanisms of interoception requires identifying pathways and decoding of diverse signals across the brain-body axis. These studies are enabled by tools to modulate and record physiological processes in the brain and visceral organs. While numerous advanced neurotechnologies are well-established in the brain, these techniques often offer limited utility for other organs, such as the gastrointestinal tract, heart, liver, or bladder. In this review, we highlight recent advances in technologies for recording and modulation of visceral organ physiology in small animals in vivo, with a focus on implantable bioelectronic organ interfaces that can be deployed in behaving animals. We discuss how such interfaces are made possible through innovations in materials and electronics and outline unmet technological challenges in interoception research.

Achieving transient and reversible optical transparency in live mice with tartrazine

Optical imaging provides real-time visualization of tissues and cells at high spatial and temporal resolutions through techniques such as fluorescence microscopy, optical coherence tomography and photoacoustic imaging. However, overcoming light scattering, caused by mismatches in the refractive indices of tissue components such as water and lipids, still represents a major challenge, particularly when imaging through the thicker biological tissues of living animals. Despite advances in deep-tissue imaging, many optical methods struggle to achieve diffraction-limited resolution at depth or are unsuitable for use in live animals. Here we introduce a noninvasive approach to achieving transient and reversible optical transparency in live mice using absorbing dye molecules, using tartrazine as a representative example. Rooted in the fundamental physics of light-matter interactions, this approach enables reversible optical transparency in live animals and can be further applied ex vivo in freshly dissected tissues. In this Protocol, we detail the procedures for visualizing in vivo internal organs and muscle sarcomeres in the mouse abdomen and hindlimb through their respective transparency windows, showcasing a versatile approach for a variety of optical imaging applications in live animals. The entire protocol for an in vivo application can be implemented in just over 2 weeks by users with expertise in optical imaging and animal handling.

Dark-based optical sectioning assists background removal in fluorescence microscopy

In fluorescence microscopy, a persistent challenge is the defocused background that obscures cellular details and introduces artifacts. Here, we introduce Dark sectioning, a method inspired by natural image dehazing for removing backgrounds that leverages dark channel prior and dual frequency separation to provide single-frame optical sectioning. Unlike denoising or deconvolution, Dark sectioning specifically targets and removes out-of-focus backgrounds, stably improving the signal-to-background ratio by nearly 10 dB and structural similarity index measure of images by approximately tenfold. Dark sectioning was validated using wide-field, confocal, two/three-dimensional structured illumination and one/two-photon microscopy with high-fidelity reconstruction. We further demonstrate its potential to improve the segmentation accuracy in deep tissues, resulting in better recognition of neurons in the mouse brain and accurate assessment of nuclei in prostate lesions or mouse brain sections. Dark sectioning is compatible with many other microscopy modalities, including light-sheet and light-field microscopy, as well as processing algorithms, including deconvolution and super-resolution optical fluctuation imaging.

Ultrafiltration and Fluid Excretion in Echinoids Involves the Axial Organ with Elimination via the Intestine

Many animals display nephridial structures for the ultrafiltration of metabolic waste. However, a nephridial equivalent and an excretory system are not generally recognized for echinoderms. Podocytes are nephridial cells that function in ultrafiltration of body fluids. Limited ultrastructural analyses of echinoderms identify cells with podocyte morphology in the axial organ and in the left coelom of larval sea urchins. Echinoid internal anatomy suggests that the excretory system functions by ultrafiltration in the axial organ, as well as filtrate flow via the water vascular system for excretion through the madreporite; however, these reports are based on morphology. To verify podocytes in the axial organ, orthologues of podocyte-specific genes were evaluated in the sea urchin genome and RNAseq data sets. To verify excretion from the madreporite, fluorescein was used as a tracer for nephridial clearance, and was injected into the main body cavity of sea urchins. Results showed that genes encoding proteins that function in podocytes of vertebrates are expressed specifically in the axial organ of sea urchins, in agreement with orthologue expression in the nurse shark kidney. However, fluorescein clearance from the body cavity shows elimination from the anus rather than the madreporite. This leads to the hypothesis that fluorescein and metabolic waste clearance occur through ultrafiltration by podocytes in the axial organ, but that the filtrate flows into the haemal system and the haemal capillaries in the intestinal walls, from which fluid is transferred to the intestinal lumen for elimination through the anus. Future testing is proposed to evaluate fluorescein filtration from the blastocoel of larvae into the left coelom, and for excretion by small or juvenile echinoids that have undergone tissue clearance to visualize the route of fluorescein flow within the internal anatomy of cleared, intact sea urchins.

Imaging-Guided Microscale Photothermal Stereolithography Bioprinting

Stereolithography bioprinting relies heavily on costly photoinitiators for polymerization, limiting its potential for further technical advancement to meet growing needs in tissue engineering and regenerative medicine. Thermal initiators, in contrast, are low cost, and rapid growth of the photothermal conversion field offers a wide range of materials and tools to convert light into heat. However, high-resolution photothermal stereolithography bioprinting remains unattainable due to the difficulty of confining heat in an aqueous environment. Here, this challenge has been fully addressed by establishing imaging-guided microscale photothermal stereolithography bioprinting (ImPSB). This technique is achieved through building a novel imaging-guided stereolithography system that provides depth-resolved visualization of the printing dynamics, creating a unique photothermal initiator in the second near-infrared window, and developing a new bioink by seeing and controlling the photothermal gelation process. ImPSB achieves a printing resolution of ≈47 µm and generates smooth lines of arbitrarily designed shapes with a cross-sectional diameter as small as ≈104 µm, representing an unprecedented scale from photothermal aqueous stereolithography. Its cellular biocompatibility in printing both bioscaffold and cell-laden hydrogel is demonstrated, and its feasibility of transdermal printing is also shown. This work sets a new path for high-resolution stereolithography bioprinting where the vast photothermal resources can be utilized.

Hyperbranched Polyborophosphate towards Transparent Epoxy Resin with Ultrahigh Toughness and Fire Safety

Inherent transparency makes epoxy resins ideal for aircraft windows, yet their brittleness and flammability remain challenges. Existing strategies for these issues often compromise transparency, with limited research on the mechanisms involved. Herein, a novel strategy is proposed for fabricating transparent epoxy resin by tuning the electrostatic potential distribution via hyperbranched polyborophosphate. Electron-deficient boron and relatively electron-rich phosphorus atoms work synergistically to increase the highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) energy gap, preventing visible light absorption. Meanwhile, the hyperbranched structure facilitates polymer network interpenetration to reduce porosity for decreased light scattering. This synergy results in a nearly colorless material with over 80% transmittance at 550 nm even at 4 mm thickness, along with full-band UV shielding. Notably, the material demonstrates a 114.7% increase in impact toughness (45.2 kJ m-2) due to dual dynamic B─O and P─O linkages. Besides, it yields a limiting oxygen index of 33% and a V0 rating in the underwriter laboratories vertical burning test, along with significant reductions in heat, smoke, and toxic gas release. The outstanding performance makes it stand out compared to reported advanced transparent epoxy resins, highlighting the significance of this work.

Nanocarrier Drug Release and Blood-Brain Barrier Penetration at Post-Stroke Microthrombi Monitored by Real-Time Förster Resonance Energy Transfer

Nanotechnology holds great promise for improving the delivery of therapeutics to the brain. However, current approaches often operate at the organ or tissue level and are limited by the lack of tools to dynamically monitor cargo delivery in vivo. We have developed highly fluorescent lipid nanodroplets (LNDs) that enable tracking of nanocarrier behavior at the subcellular level while also carrying a Förster resonance energy transfer (FRET)-based drug delivery detection system (FedEcs) capable of monitoring cargo release in vivo. Using two-photon microscopy, we demonstrate that circulating LNDs in naïve mouse brain vasculature exhibit 3D real-time FRET changes, showing size-dependent stability over 2 h in blood circulation. Further, in the Nanostroke model, dynamic intravital two-photon imaging revealed that LNDs accumulated within cerebral postischemic microthrombi, where they released their cargo significantly faster than in normal blood circulation. Furthermore, the blood-brain barrier (BBB) became permeable at the microclot sites thereby allowing accumulated FedEcs-LNDs to cross the BBB and deliver their cargo to the brain parenchyma. This microthrombi-associated translocation was confirmed at the ultrastructural level via volume-correlative light-electron microscopy. Consequently, FedEcs represents an advanced tool to quantitatively study the biodistribution and cargo release of nanocarriers at high resolution in real-time. By enabling us to resolve passive targeting mechanisms poststroke, specifically, accumulation, degradation, and extravasation via poststroke microthrombi, this system could significantly enhance the translational validation of nanocarriers for future treatments of brain diseases.

Advancing super-resolution microscopy with metal complexes: functional imaging agents for nanoscale visualization

Super-resolution microscopy (SRM) has transformed biological imaging by overcoming the diffraction limit, offering nanoscale visualization of cellular structures and processes. However, the widespread use of organic fluorescent probes is often hindered by limitations such as photobleaching, short photostability, and inadequate performance in deep-tissue imaging. Metal complexes, with their superior photophysical properties, including exceptional photostability, tuneable luminescence, and extended excited-state lifetimes, address these challenges, enabling precise subcellular targeting and long-term imaging. Beyond imaging, their theranostic potential unlocks real-time diagnostics and treatments for diseases such as cancer and bacterial infections. This review explores recent advancements in applying metal complexes for SRM, focusing on their utility in visualizing intricate subcellular structures, capturing temporal dynamics in live cells and elucidating in vivo spatial organization. We emphasize how rational design strategies optimize biocompatibility, organelle specificity, and deep-tissue penetration, expanding their applicability in multiplexed imaging. Furthermore, we discuss the design of various metal nanoparticles (NPs) for SRM, along with emerging hybrid nanoscale probes that integrate metal complexes with gold (Au) scaffolds, offering promising avenues for overcoming current limitations. By highlighting both established successes and potential frontiers, this review provides a roadmap for leveraging metal complexes as versatile tools in advancing SRM applications.

Absorbing molecules as optical clearing agents improve the resolution and sensitivity of photoacoustic microscopy

Photoacoustic microscopy (PAM) offers high resolution and 100% sensitivity to optical absorption, making it promising for biomedicine. However, strong light scattering in tissues limits its imaging depth, intensity, and resolution. Optical clearing agents (OCA) can reduce light scattering. However, traditional methods often use toxic substances or damage tissue components, restricting their application in living tissues. Recently, tartrazine, a common food pigment, has been shown to significantly improve tissue optical transparency while maintaining good biosafety. However, it is unclear whether tartrazine as an absorbing molecule is suitable for use in PAM. In this study, we show that tartrazine, despite its strong light absorption, can significantly enhance the performance of PAM, when used at an appropriate concentration. Our ex vivo experiments demonstrate tartrazine solution enables PAM to achieve an optical resolution of 21 μm even through the skin. A 0.6 M tartrazine solution improves resolution by 3.5 times and the imaging intensity by 4.5 times. Finally, in vivo brain imaging of a mouse with an intact scalp reveals that tartrazine not only increases the imaging intensity by about 4 times but also allows PAM to achieve an optical resolution of brain through the scalp and skull, revealing much more details of the microvasculature in the brain.

Beyond the EPR effect: Intravital microscopy analysis of nanoparticle drug delivery to tumors

Delivery of nanoparticles (NPs) to solid tumors has long relied on enhanced permeability and retention (EPR) effect, involving permeation of NPs through a leaky vasculature with prolonged retention by reduced lymphatic drainage in tumor. Recent research studies and clinical data challenge EPR concept, revealing alternative pathways and approaches of NP delivery. The area was significantly impacted by the implementation of intravital optical microscopy, unraveling delivery mechanisms at cellular level in vivo. This review presents analysis of the reasons for EPR heterogeneity in tumors and describes non-EPR based concepts for drug delivery, which can supplement the current paradigm. One of the approaches is targeting tumor endothelium by NPs with subsequent intravascular drug release and gradient-driven drug transport to tumor interstitium. Others exploit various immune cells for tumor infiltration and breaking endothelial barriers. Finally, we discuss the involvement of active transcytosis through endothelial cells in NP delivery. This review aims to inspire further understanding of the process of NP extravasation in tumors and provide insights for developing next-generation nanomedicines with improved delivery.

Surface-Enhanced Raman Spectroscopy for Biomedical Applications: Recent Advances and Future Challenges

The year 2024 marks the 50th anniversary of the discovery of surface-enhanced Raman spectroscopy (SERS). Over recent years, SERS has experienced rapid development and became a critical tool in biomedicine with its unparalleled sensitivity and molecular specificity. This review summarizes the advancements and challenges in SERS substrates, nanotags, instrumentation, and spectral analysis for biomedical applications. We highlight the key developments in colloidal and solid SERS substrates, with an emphasis on surface chemistry, hotspot design, and 3D hydrogel plasmonic architectures. Additionally, we introduce recent innovations in SERS nanotags, including those with interior gaps, orthogonal Raman reporters, and near-infrared-II-responsive properties, along with biomimetic coatings. Emerging technologies such as optical tweezers, plasmonic nanopores, and wearable sensors have expanded SERS capabilities for single-cell and single-molecule analysis. Advances in spectral analysis, including signal digitalization, denoising, and deep learning algorithms, have improved the quantification of complex biological data. Finally, this review discusses SERS biomedical applications in nucleic acid detection, protein characterization, metabolite analysis, single-cell monitoring, and in vivo deep Raman spectroscopy, emphasizing its potential for liquid biopsy, metabolic phenotyping, and extracellular vesicle diagnostics. The review concludes with a perspective on clinical translation of SERS, addressing commercialization potentials and the challenges in deep tissue in vivo sensing and imaging.

Integrated Study of Fluorescence Enhancement in the Y176H Variant of Cyanobacterial Phytochrome Cph1

Phytochromes are red-light-sensitive biliprotein photoreceptors that control a variety of physiological processes in plants, fungi, and bacteria. Lately, greater attention has been paid to these photoreceptors due to their potential as fluorescent probes for deep-tissue microscopy. Such fluorescing phytochromes have been generated by multiple amino acid substitutions in weakly fluorescent wild-type (WT) proteins. Remarkably, the single substitution of conserved Tyr176 by His in cyanobacterial phytochrome Cph1 increases the fluorescence quantum yield from 2.4 to 14.5%. In this work, we studied this Y176H variant by crystallography, MAS NMR, resonance Raman spectroscopy, and ultrafast absorption spectroscopy complemented by theoretical methods. Two factors were identified to account for the strong fluorescence increase. First, the equilibrium between the photoactive and fluorescent substates of WT Cph1 was shown to shift entirely to the fluorescent substate in Y176H. Second, structural flexibility of the chromophore is drastically reduced and the photoisomerization barrier is raised, thereby increasing the excited-state lifetime. The most striking finding, however, is that Y176H includes the structural properties of both the dark-adapted Pr and the light-activated Pfr state. While the chromophore adopts the Pr-typical ZZZssa configuration, the tongue segment of the protein adopts a Pfr-typical α-helical structure. This implies that Tyr176 plays a key role in coupling chromophore photoisomerization to the sheet-to-helix transition of the tongue and the final Pfr structure. This conclusion extends to plant phytochromes, where the homologous substitution causes light-independent signaling activity akin to that of Pfr.

Light-driven plasmonic microrobot for nanoparticle manipulation

Recently light-driven microdrones have been demonstrated, making use of plasmonic nanomotors based on directional resonant chiral light scattering. These nanomotors can be addressed individually, without requiring the tracking of a focused laser, leading to exceptional 2D maneuverability which renders microdrones a versatile robotic platform in aqueous environments. Here, we incorporate a light-operated manipulator, a plasmonic nano-tweezer, into the microdrone platform, rendering it a microrobot by enabling precise, all-optical transport and delivery of single nanoparticles suspended in solution. The plasmonic nano-tweezer consists of a resonant cross-antenna nanostructure exhibiting a central near-field hot spot, extending the ability of traditional optical tweezers based on focused laser beams to the trapping of nanoparticles. However, most of plasmonic nano-tweezers are fixed to the substrates and lack mobility. Our plasmonic microrobot utilizes circularly polarized light to control both motors and for stable trapping of a 70-nanometer fluorescent nanodiamond in the cross-antenna center. Complex sequences of microrobot operations, including trap-transport-release-trap-transport actions, demonstrate the microrobot's versatility and precision in picking up and releasing nanoparticles. Our microrobot design opens potential avenues in advancing nanotechnology and life sciences, with applications in targeted drug delivery, single-cell manipulation, and by providing an advanced quantum sensing platform, facilitating interdisciplinary research at the nanoscale.

From morphology to single-cell molecules: high-resolution 3D histology in biomedicine

High-resolution three-dimensional (3D) tissue analysis has emerged as a transformative innovation in the life sciences, providing detailed insights into the spatial organization and molecular composition of biological tissues. This review begins by tracing the historical milestones that have shaped the development of high-resolution 3D histology, highlighting key breakthroughs that have facilitated the advancement of current technologies. We then systematically categorize the various families of high-resolution 3D histology techniques, discussing their core principles, capabilities, and inherent limitations. These 3D histology techniques include microscopy imaging, tomographic approaches, single-cell and spatial omics, computational methods and 3D tissue reconstruction (e.g. 3D cultures and spheroids). Additionally, we explore a wide range of applications for single-cell 3D histology, demonstrating how single-cell and spatial technologies are being utilized in the fields such as oncology, cardiology, neuroscience, immunology, developmental biology and regenerative medicine. Despite the remarkable progress made in recent years, the field still faces significant challenges, including high barriers to entry, issues with data robustness, ambiguous best practices for experimental design, and a lack of standardization across methodologies. This review offers a thorough analysis of these challenges and presents recommendations to surmount them, with the overarching goal of nurturing ongoing innovation and broader integration of cellular 3D tissue analysis in both biology research and clinical practice.

Brain-wide immunolabeling and tissue clearing applications for engram research

In recent years, there has been significant progress in memory research, driven by genetic and imaging technological advances that have given unprecedented access to individual memory traces or engrams. Although Karl Lashley argued since the 1930s that an engram is not confined to a particular area but rather distributed across the entire brain, most current studies have focused exclusively on a single or few brain regions. However, this compartmentalized approach overlooks the interactions between multiple brain regions, limiting our understanding of engram mechanisms. More recently, several studies have begun to investigate engrams across the brain, but research is still limited by a lack of standardized techniques capable of reconstructing multiple ensembles at single-cell resolution across the entire brain. In this review, we guide researchers through the latest technological advancements and discoveries in immediate early gene (IEG) techniques, tissue clearing methods, microscope modalities, and automated large-scale analysis. These innovations could propel the field forward in building brain-wide engram maps of normal and disease states, thus, providing unprecedented new insights. Ultimately, this review aims to bridge the gap between research focused on single brain regions and the need for a comprehensive understanding of whole-brain engrams, revealing new approaches for exploring the neuronal mechanisms underlying engrams.

Towards deciphering the bone marrow microenvironment with spatial multi-omics

The tissue microenvironment refers to a localised tissue area where a complex combination of cells, structural components, and signalling molecules work together to support specific biological activities. A prime example is the bone marrow microenvironment, particularly the hematopoietic stem cell (HSC) niche, which is of immense interest due to its critical role in supporting lifelong blood cell production and the growth of malignant cells. In this review, we summarise the current understanding of HSC niche biology, highlighting insights gained from advanced imaging and genomic techniques. We also discuss the potential of emerging technologies such as spatial multi-omics to unravel bone marrow architecture in unprecedented detail.

Color-neutral and reversible tissue transparency enables longitudinal deep-tissue imaging in live mice

Light scattering in biological tissue presents a significant challenge for deep in vivo imaging. Our previous work demonstrated the ability to achieve optical transparency in live mice using intensely absorbing dye molecules, which created transparency in the red spectrum while blocking shorter-wavelength photons. In this paper, we extend this capability to achieve optical transparency across the entire visible spectrum by employing molecules with strong absorption in the ultraviolet spectrum and sharp absorption edges that rapidly decline upon entering the visible spectrum. This new color-neutral and reversible tissue transparency method enables optical transparency for imaging commonly used fluorophores in the green and yellow spectra. Notably, this approach facilitates tissue transparency for structural and functional imaging of the live mouse brain labeled with yellow fluorescent protein and GCaMP through the scalp and skull. We show that this method enables longitudinal imaging of the same brain regions in awake mice over multiple days during development. Histological analyses of the skin and systemic toxicology studies indicate minimal acute or chronic damage to the skin or body using this approach. This color-neutral and reversible tissue transparency technique opens new opportunities for noninvasive deep-tissue optical imaging, enabling long-term visualization of cellular structures and dynamic activity with high spatiotemporal resolution and chronic tracking capabilities.

Pharmacodynamics of Akt drugs revealed by a kinase-modulated bioluminescent indicator

Measuring pharmacodynamics (PD)-the biochemical effects of drug dosing-and correlating them with therapeutic efficacy in animal models is crucial for the development of effective drugs but traditional PD studies are labor and resource intensive. Here we developed a kinase-modulated bioluminescent indicator (KiMBI) for rapid, noninvasive PD assessment of Akt-targeted drugs, minimizing drug and animal use. Using KiMBI, we performed a structure-PD relationship analysis on the brain-active Akt inhibitor ipatasertib by generating and characterizing two novel analogs. One analog, ML-B01, successfully inhibited Akt in both the brain and the body. Interestingly, capivasertib, ipatasertib and ML-B01 all exhibited PD durations beyond their pharmacokinetic profiles. Furthermore, KiMBI revealed that the PD effects of an Akt-targeted proteolysis-targeting chimera degrader endured for over 3 days. Thus, bioluminescence imaging with Akt KiMBI provides a noninvasive and efficient method for in vivo visualization of the PD of Akt inhibitors and degraders.

Optical, contact-free assessment of brain tissue stiffness and neurodegeneration

Dementia affects a large proportion of the world's population. Approaches that allow for early disease detection and non-invasive monitoring of disease progression are desperately needed. Current approaches are centred on costly imaging technologies such as positron emission tomography and magnetic resonance imaging. We propose an alternative approach to assess neurodegeneration based on diffuse correlation spectroscopy (DCS), a remote and optical sensing technique. We employ this approach to assess neurodegeneration in mouse brains from healthy animals and those with prion disease. We find a statistically significant difference in the optical speckle decorrelation times between prion-diseased and healthy animals. We directly calibrated our DCS technique using hydrogel samples of varying Young's modulus, indicating that we can optically measure changes in the brain tissue stiffness in the order of 60 Pa (corresponding to a 1 s change in speckle decorrelation time). DCS holds promise for contact-free assessment of tissue stiffness alteration due to neurodegeneration, with a similar sensitivity to contact-based (e.g. nanoindentation) approaches.

Bioprinted optoelectronically active cardiac tissues

Electrical stimulation of existing three-dimensional bioprinted tissues to alter tissue activities is typically associated with wired delivery, invasive electrode placement, and potential cell damage, minimizing its efficacy in cardiac modulation. Here, we report an optoelectronically active scaffold based on printed gelatin methacryloyl embedded with micro-solar cells, seeded with cardiomyocytes to form light-stimulable tissues. This enables untethered, noninvasive, and damage-free optoelectronic stimulation-induced modulation of cardiac beating behaviors without needing wires or genetic modifications to the tissue solely with light. Pulsed light stimulation of human cardiomyocytes showed that the optoelectronically active scaffold could increase their beating rates (>40%), maintain high cell viability under light stimulation (>96%), and negligibly affect the electrocardiogram morphology. The seeded scaffolds, termed optoelectronically active tissues, were able to successfully accelerate heart beating in vivo in rats. Our work demonstrates a viable wireless, printable, and optically controllable tissue, suggesting a transformative step in future therapy of electrically active tissues/organs.

Versatile application of fast green FCF as a visible cholangiogram in adult mice to medium-sized mammals

An aqueous solution of a common food dye, Fast Green FCF (FG), mimics cholyl-lysyl-fluorescein to visualize embryonic bile flow via single peritoneal injection into intrauterine mouse embryos. Despite its efficacy in embryos, its suitability for adult mice and small to medium-sized mammals remained uncertain. In this study, we investigated FG cholangiography in adult mice, dogs, and goats. The results demonstrate that FG injection enables progressive cholangiography in these species, highlighting its versatility across different animal models without necessitating specialized equipment. To further evaluate diagnostic utility, FG cholangiography was performed in various mouse models of bile flow disorders. FG successfully visualized dilated lumina in the extrahepatic bile duct of BDL mice and revealed aberrant luminal structures in the gallbladder walls of Sox17+/- or Shh-cre; Sox17flox/- mice. In Mab21l1-/- mice with contracted gallbladders, FG influx was limited to the gallbladder neck. Moreover, stereomicroscopic video analysis of FG influx into the gallbladder post-fasting revealed differences in gallbladder wall state and its bile composition between Sox17+/- and wild-type mice, suggesting the potential for detecting variations in gallbladder stored bile properties. These findings underscore the efficacy of FG in facilitating progressive cholangiography across mammalian species.

Unveiling nanoparticle-immune interactions: how super-resolution imaging illuminates the invisible

Nanoparticles (NPs) have attracted considerable attention in nanomedicine, particularly in harnessing and manipulating immune cells. However, the current understanding of the interactions between NPs and immune cells at the nanoscale remains limited. Advancing this knowledge guides the design principles of NPs. This review offers a historical perspective on the synergistic evolution of immunology and optical microscopy, examines the current landscape of NP applications in immunology, and explores the advancements in super-resolution imaging techniques, which provide new insights into nanoparticle-immune cell interactions. Key findings from recent studies are discussed, along with challenges and future directions in this rapidly evolving field.

Strongly absorbing molecules make tissue transparent: a new insight for understanding tissue optical clearing

Optical imaging plays a central role in the field of biomedicine, but it suffers from the light scattering of tissues. The research group from Stanford University has reported a counterintuitive observation that strongly absorbing molecules could achieve optical transparency in live animals, providing a new insight for understanding tissue optical clearing. It empowers scientists to leverage optical imaging techniques for in vivo observation of a wide range of deep-seated structures and activities.

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. With future efforts on the even distribution of both clearing agents and probes, excavation of more effective clearing agents, and automation of tissue clearing processes, tissue optical clearing should provide more insights into the fundamental questions in biological events clinical diagnostics.

Concurrent optogenetic motor mapping of multiple limbs in awake mice reveals cortical organization of coordinated movements

BACKGROUND

Motor mapping allows for determining the macroscopic organization of motor circuits and corresponding motor movement representations on the cortex. Techniques such as intracortical microstimulation (ICMS) are robust, but can be time consuming and invasive, making them non-ideal for cortex-wide mapping or longitudinal studies. In contrast, optogenetic motor mapping offers a rapid and minimally invasive technique, enabling mapping with high spatiotemporal resolution. However, motor mapping has seen limited use in tracking 3-dimensonal, multi-limb movements in awake animals. This gap has left open questions regarding the underlying organizational principles of motor control of coordinated, ethologically-relevant movements involving multiple limbs.

OBJECTIVE

Our first objective was to develop Multi-limb Optogenetic Motor Mapping (MOMM) to concurrently map motor movement representations of multiple limbs with high fidelity in awake mice. Having established MOMM, our next objective was determine whether maps of coordinated and ethologically-relevant motor output were topographically organized on the cortex.

METHODS

We combine optogenetic stimulation with a deep learning driven pose-estimation toolbox, DeepLabCut (DLC), and 3-dimensional triangulation to concurrently map motor movements of multiple limbs in awake mice.

RESULTS

MOMM consistently revealed cortical topographies for all mapped features within and across mice. Many motor maps overlapped and were topographically similar. Several motor movement representations extended beyond cytoarchitecturally defined somatomotor cortex. Finer articulations of the forepaw resided within gross motor movement representations of the forelimb. Moreover, many cortical sites exhibited concurrent limb coactivation when photostimulated, prompting the identification of several cortical regions harboring coordinated and ethologically-relevant movements.

CONCLUSIONS

The cortex appears to be topographically organized by motor programs, which are responsible for coordinated, multi-limbed, and behavior-like movements.

Aggregation-Induced Emission Luminogen Based Wearable Visible-Light Penetrator for Deep Photodynamic Therapy

Photodynamic therapy (PDT) has emerged as a preferred nonsurgical treatment in clinical applications due to its capacity to selectively eradicate diseased tissues while minimizing damage to normal tissue. Nevertheless, its clinical efficacy is constrained by the limited penetration of visible light. Although near-infrared (NIR) lasers offer enhanced tissue penetration, the dearth of suitable photosensitizers and a pronounced imaging-treatment disparity pose challenges. Additionally, clinical implementation via optical fiber implantation carries infection risks and necessitates minimally invasive surgery, contradicting PDT's noninvasive advantage. In this study, we introduce a brilliant approach utilizing aggregation-induced emission luminogens (AIEgen) to develop a visible-light penetrator (VLP), coupled with wireless light emitting diodes (LEDs), enabling deep photodynamic therapy. We validate the therapeutic efficacy of this visible-light penetrator in tissues inaccessible to conventional PDT, demonstrating significant suppression of inflammatory diffusion in vivo using AIEgen TBPPM loaded within the VLP, which exhibits a transmittance of 86% in tissues with a thickness of 3 mm. This innovative visible-light penetrator effectively overcomes the substantial limitations of PDT in clinical settings and holds promise for advancing phototherapy.

Optical Clearing with Tartrazine Enables Deep Transscleral Imaging with Optical Coherence Tomography

Suprachoroidal injections are a relatively new method of drug delivery to treat retinal disease. At present, it is difficult to visualize the distribution of injection-delivered product beneath the sclera into the suprachoroidal space. Imaging the suprachoroidal space with OCT is hindered by scattering of light from densely packed collagen fibers of the sclera, limiting depth penetration of the OCT light. In this Letter, we demonstrate the first use of tartrazine (Yellow 5) as an optical clearing agent for suprachoroidal research imaging with OCT in an ex vivo eye model. Our results show that this clearing agent dramatically improves visualization of the choroid and suprachoroidal space with transscleral OCT and allows for improved imaging of the location and extent of delivered suprachoroidal fluid. We believe these methods will enable use of optical techniques such as OCT to image through a variety of previously optically inaccessible, highly scattering tissue samples.

Neutrophils under the microscope: neutrophil dynamics in infection, inflammation, and cancer revealed using intravital imaging

Neutrophils rapidly respond to inflammation resulting from infection, injury, and cancer. Intravital microscopy (IVM) has significantly advanced our understanding of neutrophil behavior, enabling real-time visualization of their migration, interactions with pathogens, and coordination of immune responses. This review delves into the insights provided by IVM studies on neutrophil dynamics in various inflammatory contexts. We also examine the dual role of neutrophils in tumor microenvironments, where they can either facilitate or hinder cancer progression. Finally, we highlight how computational modeling techniques, especially agent-based modeling, complement experimental data by elucidating neutrophil kinetics at the level of individual cells as well as their collective behavior. Understanding the role of neutrophils in health and disease is essential for developing new strategies for combating infection, inflammation and cancer.

Enhancing Bioluminescence Imaging of Cultured Tissue Explants Using Optical Telecompression

Long-term observation of single-cell oscillations within tissue networks is now possible by combining bioluminescence reporters with stable tissue explant culture techniques. This method is particularly effective in revealing the network dynamics in systems with slow oscillations, such as circadian clocks. However, the low intensity of luciferase-based bioluminescence requires signal amplification using specialized cameras (e.g., I-CCDs and EM-CCDs) and prolonged exposure times, increasing baseline noise and reducing temporal resolution. To address this limitation, we implemented a cost-effective optical enhancement technique called telecompression, first used in astrophotography and now commonly used in digital photography. By combining a high numerical aperture objective lens with a magnification-reducing relay lens, we significantly increased the collection efficiency of the bioluminescence signal without raising the baseline CCD noise. This method allows for shorter exposure times in time-lapse imaging, enhancing temporal resolution and enabling more precise period estimations. Our implementation demonstrates the feasibility of telecompression for enhancing bioluminescence imaging for the tissue-level network observation of circadian clocks.