Deciphering perivascular macrophages and microglia in the retinal ganglion cell layers.

Introduction: The classically defined two retinal microglia layers are distributed in inner and outer plexiform layers. Although there are some reports that retinal microglia are also superficially located around the ganglion cell layer (GCL) in contact with the vitreous, there has been a lack of detailed descriptions and not fully understood yet. Methods: We visualized the microglial layers by using CX3CR1-GFP (C57BL6) transgenic mice with both healthy and disease conditions including NaIO3-induced retinal degeneration models and IRBP-induced auto-immune uveitis models. Result: We found the GCL microglia has two subsets; peripheral (pph) microglia located on the retinal parenchyma and BAM (CNS Border Associated Macrophage) which have a special stretched phenotype only located on the surface of large retinal veins. First, in the pph microglia subset, but not in BAM, Galectin-3 and LYVE1 are focally expressed. However, LYVE1 is specifically expressed in the amoeboid or transition forms, except the typical dendritic morphology in the pph microglia. Second, BAM is tightly attached to the surface of the retinal veins and has similar morphology patterns in both the healthy and disease conditions. CD86+ BAM has a longer process which vertically passes the proximal retinal veins. Our data helps decipher the basic anatomy and pathophysiology of the retinal microglia in the GCL. Discussion: Our data helps decipher the basic anatomy and pathophysiology of the retinal microglia in the GCL.

FITC-Labeled RGD Peptides as Novel Contrast Agents for Functional Fluorescent Angiographic Detection of Retinal and Choroidal Neovascularization.

The development of choroidal neovascularization (CNV) is a crucial factor in the pathophysiology and prognosis of exudative age-related macular degeneration (AMD). Therefore, the detection of CNV is essential for establishing an appropriate diagnosis and treatment plan. Current ophthalmic imaging techniques, such as fundus fluorescent angiography and optical coherence tomography, have limitations in accurately visualizing CNV lesions and expressing CNV activity, owing to issues such as excessive dye leakage with pooling and the inability to provide functional information. Here, using the arginine-glycine-aspartic acid (RGD) peptide's affinity for integrin αvß3, which is expressed in the neovascular endothelial cells in ocular tissues, we propose the use of fluorescein isothiocyanate (FITC)-labeled RGD peptide as a novel dye for effective molecular imaging of CNV. FITC-labeled RGD peptides (FITC-RGD2), prepared by bioconjugation of one FITC molecule with two RGD peptides, demonstrated better visualization and precise localization of CNV lesions than conventional fluorescein dyes in laser-induced CNV rodent models, as assessed using various imaging techniques, including a commercially available clinical fundus camera (Optos). These results suggest that FITC-RGD2 can serve as an effective novel dye for the diagnosis of neovascular retinal diseases, including AMD, by enabling early detection and treatment of disease occurrence and recurrence after treatment.

In vivo longitudinal 920†nm two-photon intravital kidney imaging of a dynamic 2,8-DHA crystal formation and tubular deterioration in the adenine-induced chronic kidney disease mouse model.

Chronic kidney disease (CKD) is one of the most common renal diseases manifested by gradual loss of kidney function with no symptoms in the early stage. The underlying mechanism in the pathogenesis of CKD with various causes such as high blood pressure, diabetes, high cholesterol, and kidney infection is not well understood. In vivo longitudinal repetitive cellular-level observation of the kidney of the CKD animal model can provide novel insights to diagnose and treat the CKD by visualizing the dynamically changing pathophysiology of CKD with its progression over time. In this study, using two-photon intravital microscopy with a single 920 nm fixed-wavelength fs-pulsed laser, we longitudinally and repetitively observed the kidney of an adenine diet-induced CKD mouse model for 30 days. Interestingly, we could successfully visualize the 2,8-dihydroxyadenine (2,8-DHA) crystal formation with a second-harmonics generation (SHG) signal and the morphological deterioration of renal tubules with autofluorescence using a single 920 nm two-photon excitation. The longitudinal in vivo two-photon imaging results of increasing 2,8-DHA crystals and decreasing tubular area ratio visualized by SHG and autofluorescence signal, respectively, were highly correlated with the CKD progression monitored by a blood test showing increased cystatin C and blood urea nitrogen (BUN) levels over time. This result suggests the potential of label-free second-harmonics generation crystal imaging as a novel optical technique for in vivo CKD progression monitoring.

Establishment of the reproducible branch retinal artery occlusion mouse model and intravital longitudinal imaging of the retinal CX3CR1-GFP+ cells after spontaneous arterial recanalization.

Animal models of retinal artery occlusion (RAO) have been widely used in many studies. However, most of these studies prefer using a central retinal artery occlusion (CRAO) which is a typical global ischemia model of the retina, due to the technical limitation of producing single vessel targeted modeling with real-time imaging. A focal ischemia model, such as branch retinal artery occlusion (BRAO), is also needed for explaining interactions, including the immunological reaction between the ischemic retina and adjacent healthy retina. Accordingly, a relevant model for clinical RAO patients has been demanded to understand the pathophysiology of the RAO disease. Herein, we establish a convenient BRAO mouse model to research the focal reaction of the retina. As a photo-thrombotic agent, Rose bengal was intravenously injected into 7 week-old transgenic mice (CX3CR1-GFP) for making embolism occlusion, which causes pathology similarly to clinical cases. In an optimized condition, a 561 nm laser (13.1 mw) was projected to a targeted vessel to induce photo-thrombosis for 27 s by custom-built retinal confocal microscopy. Compared to previous BRAO models, the procedures of thrombosis generation were naturally and minimal invasively generated with real-time retinal imaging. In addition, by utilizing the self-remission characteristics of Rose bengal thrombus, a reflow of the BRAO with immunological reactions of the CX3CR1-GFP+ inflammatory cells such as the retinal microglia and monocytes was monitored and analyzed. In this models, reperfusion began on day 3 after modeling. Simultaneously, the activation of CX3CR1-GFP+ inflammatory cells, including the increase of activation marker and morphologic change, was confirmed by immunohistochemical (IHC) staining and quantitative real-time PCR. CD86 and Nox2 were prominently expressed on day 3 after the modeling. At day 7, blood flow was almost restored in the large vessels. CX3CR1-GFP+ populations in both superficial and deep layers of the retina also increased around even in the BRAO peri-ischemic area. In summary, this study successfully establishes a reproducible BRAO modeling method with convenient capabilities of easily controllable time points and selection of a specific single vessel. It can be a useful tool to analyze the behavior of inflammatory cell after spontaneous arterial recanalization in BRAO and further investigate the pathophysiology of BRAO.

Intravital longitudinal cellular visualization of oral mucosa in a murine model based on rotatory side-view confocal endomicroscopy.

Oral mucosa is a soft tissue lining the inside of the mouth, protecting the oral cavity from microbiological insults. The mucosal immune system is composed of diverse types of cells that defend against a wide range of pathogens. The pathophysiology of various oral mucosal diseases has been studied mostly by ex vivo histological analysis of harvested specimens. However, to analyze dynamic cellular processes in the oral mucosa, longitudinal in vivo observation of the oral mucosa in a single mouse during pathogenesis is a highly desirable and efficient approach. Herein, by utilizing micro GRIN lens-based rotatory side-view confocal endomicroscopy, we demonstrated non-invasive longitudinal cellular-level in vivo imaging of the oral mucosa, visualizing fluorescently labeled cells including various immune cells, pericytes, nerve cells, and lymphatic and vascular endothelial cells. With rotational and sliding movement of the side-view endomicroscope on the oral mucosa, we successfully achieved a multi-color wide-area cellular-level visualization in a noninvasive manner. By using a transgenic mouse expressing photoconvertible protein, Kaede, we achieved longitudinal repetitive imaging of the same microscopic area in the buccal mucosa of a single mouse for up to 10 days. Finally, we performed longitudinal intravital visualization of the oral mucosa in a DNFB-derived oral contact allergy mouse model, which revealed highly dynamic spatiotemporal changes of CSF1R or LysM expressing immune cells such as monocytes, macrophages, and granulocytes in response to allergic challenge for one week. This technique can be a useful tool to investigate the complex pathophysiology of oral mucosal diseases.

Multimodal evaluation of an interphotoreceptor retinoid-binding protein-induced mouse model of experimental autoimmune uveitis.

We aimed to characterize the vascular phenotypes of an experimental autoimmune retinal uveitis (EAU) model induced by interphotoreceptor retinoid-binding protein (IRBP) using multimodal imaging techniques. We systemically administered IRBP or vehicle to adult C57BL/6 mice. Fundus photography, optical coherence tomography (OCT), in vivo live confocal imaging using different tracers, OCT angiography (OCTA), and electroretinography (ERG) were performed after IRBP immunization. Hematoxylin and eosin and immunofluorescence staining were performed to characterize the immune response and vascular permeability. Mice with EAU exhibited perivascular inflammation, vitritis, and superficial retinal inflammation on fundus photography and OCT. H&E revealed immune cell infiltration in the perivascular area of the retina and choroid accompanied by a significant degree of perivasculitis that subsequently damaged photoreceptors 3 weeks postimmunization. Immunofluorescence staining showed subsequent transcytosis induction after local microglial activation followed by neutrophil recruitment in the perivascular area. Transcytosis in the superficial and deep vascular areas was improved by immune cell suppression. Intravital in vivo confocal imaging showed signs of neutrophil infiltration and obstructive vasculitis with perivascular leakage 3 weeks postimmunization. OCTA revealed a significant decrease in vascular flow in the deep capillary layer of the retina. Functional analysis showed that scotopic responses were intact at 2 weeks; however, normal photopic and scotopic responses were hardly detected in mice with EAU mice at 3 weeks postimmunization. Our data suggest that inflammatory cell activation and subsequent transcytosis induction in endothelial cells might be a major pathogenic factor for vascular leakage in uveitis, providing new insights into the pathophysiology of retinal vasculitis in noninfectious uveitis.

3D Visualization of Dynamic Cellular Reaction of Pulpal CD11c+ Dendritic Cells against Pulpitis in Whole Murine Tooth.

In dental pulp, diverse types of cells mediate the dental pulp immunity in a highly complex and dynamic manner. Yet, 3D spatiotemporal changes of various pulpal immune cells dynamically reacting against foreign pathogens during immune response have not been well characterized. It is partly due to the technical difficulty in detailed 3D comprehensive cellular-level observation of dental pulp in whole intact tooth beyond the conventional histological analysis using thin tooth slices. In this work, we validated the optical clearing technique based on modified Murray's clear as a valuable tool for a comprehensive cellular-level analysis of dental pulp. Utilizing the optical clearing, we successfully achieved a 3D visualization of CD11c+ dendritic cells in the dentin-pulp complex of a whole intact murine tooth. Notably, a small population of unique CD11c+ dendritic cells extending long cytoplasmic processes into the dentinal tubule while located at the dentin-pulp interface like odontoblasts were clearly visualized. 3D visualization of whole murine tooth enabled a reliable observation of these rarely existing cells with a total number less than a couple of tens in one tooth. These CD11c+ dendritic cells with processes in the dentinal tubule were significantly increased in the dental pulpitis model induced by mechanical and chemical irritation. Additionally, the 3D visualization revealed a distinct spatial 3D arrangement of pulpal CD11c+ cells in the pulp into a front-line barrier-like formation in the pulp within 12 h after the irritation. Collectively, these observations demonstrated the unique capability of optical clearing-based comprehensive 3D cellular-level visualization of the whole tooth as an efficient method to analyze 3D spatiotemporal changes of various pulpal cells in normal and pathological conditions.

Intravital Imaging of Circulating Red Blood Cells in the Retinal Vasculature of Growing Mice.

Purpose: To establish a custom-built, high-speed 90 frame-per-second laser-scanning confocal microscope for real-time in vivo retinal imaging of individual flowing red blood cells (RBCs) in retinal vasculature of live mouse model. Methods: Fluorescently labeled RBCs were injected into mice of different ages (3 to 62 weeks old). Anti-CD31 antibody conjugated with Alexa Fluor 647 was injected to visualize retinal endothelial cells (ECs). Longitudinal and cross-sectional intravital retinal imaging of flowing RBCs and ECs was performed in two strains (C57BL/6 and Balb/c) by using the custom-built confocal microscope. Results: Simultaneous tracking of the routes of many fluorescently labeled individual RBCs flowing from a large artery and vein to a single capillary in the retina of live mice was achieved, which enabled in vivo measurement of retinal RBC flow velocities in each vessel type in growing mice from 3 to 62 weeks after birth. Average RBC flow velocities were gradually increased during growing from 3 to 14 weeks by more than two times. Then the average RBC flow velocity was maintained at about 20 mm/s in artery and 16 mm/s in vein until 62 weeks. Conclusions: Our study successfully established a custom-built high-speed 90-Hz retinal confocal microscope for measuring RBC flow velocity at the single cell level. It could be a useful tool to investigate the pathophysiology of various retinal diseases associated with blood flow impairment. Translational Relevance: This technological method could be a valuable assessment tool to help the development of novel therapeutics for retinal diseases.

Intravital two-photon imaging and quantification of hepatic steatosis and fibrosis in a live small animal model.

Nonalcoholic fatty liver disease (NAFLD) is one of the most common chronic liver diseases closely associated with the metabolic system, including obesity and type 2 diabetes. The progression of NAFLD with advanced fibrosis is associated with an increased risk of liver cirrhosis and cancer as well as various extra-hepatic diseases. Yet, the underlying mechanism is not fully understood partly due to the absence of effective high-resolution in vivo imaging methods and the appropriate animal models recapitulating the pathology of NAFLD. To improve our understanding about complex pathophysiology of NAFLD, the need for an advanced imaging methodology to visualize and quantify subcellular-level features of NAFLD in vivo over time is ever-increasing. In this study, we established an advanced in vivo two-photon imaging technique to visualize and quantify subcellular-level pathological features of NAFLD in a live mouse animal developing hepatic steatosis, fibrosis, and disrupted microvasculature.