Intravital Microscopy of the Beating Murine Heart to Understand Cardiac Leukocyte Dynamics

Small Extracellular Vesicles from Breast Cancer Cells Induce Cardiotoxicity

Cardiovascular diseases and cancer are leading global causes of morbidity and mortality, necessitating advances in diagnosis and treatment. Doxorubicin (Doxo), a potent chemotherapy drug, causes long-term heart damage due to cardiotoxicity. Small extracellular vesicles (sEVs) carry bioactive molecules-such as proteins, lipids, and nucleic acids-that can modulate gene expression and signaling pathways in recipient cells, including cardiomyocytes. Through the delivery of cytokines, microRNAs, and growth factors, sEVs can influence cell survival, which plays a critical role in the development of cardiotoxicity. This study investigates the role of sEVs derived from breast cancer cells treated or not with Doxo and their potential to induce cardiomyocyte damage, thereby contributing to cardiotoxicity. We isolated sEVs from MCF-7 cells treated or not to Doxo using ultracentrifugation and characterized them through Nanoparticle Tracking Analysis (NTA), Scanning Electron Microscopy (SEM), and Western Blotting (WB) for the markers CD63, CD81, and TSG101. We analyzed cytokine profiles using a Multiplex Assay and Cytokine Membrane Array. We exposed Guinea pig cardiomyocytes to different concentrations of sEVs. We assessed their viability (MTT assay), shortening, reactive oxygen species (ROS-DHE dye) production, mitochondrial membrane potential (JC-1 dye), and calcium dynamics (FLUO-4 dye). We performed statistical analyses, including t-tests, ANOVA, Cohen's d, and η2 to validate the robustness of the results. Treatment of MCF-7 cells with 0.01 μM Doxorubicin resulted in increased sEVs production, particularly after 48 h of exposure (~1.79 × 108 ± 2.77 × 107 vs. ~5.1 × 107 ± 1.28 × 107 particles/mL, n = 3, p = 0.0019). These sEVs exhibited protein profiles in the 130-25 kDa range and 93-123 nm sizes. They carried cytokines including TNF-α, IL-1β, IL-4, IFN-γ, and IL-10. Exposure of cardiomyocytes to sEVs (0.025 μg/mL to 2.5 μg/mL) from both Doxo-treated and untreated cells significantly reduced cardiomyocyte viability, shortened cell length by up to 20%, increased ROS production, and disrupted calcium homeostasis and mitochondrial membrane potential, indicating severe cellular stress and cardiotoxicity. These findings suggest that Doxo enhances sEVs production from breast cancer cells, which plays a key role in cardiotoxicity through their cytokine cargo. The study highlights the potential of these sEVs as biomarkers for early cardiotoxicity detection and as therapeutic targets to mitigate cardiovascular risks in chemotherapy patients. Future research should focus on understanding the mechanisms by which Doxorubicin-induced sEVs contribute to cardiotoxicity and exploring their diagnostic and therapeutic potential to improve patient safety and outcomes in cancer therapy.

Viscocohesive hyaluronan gel enhances stability of intravital multiphoton imaging with subcellular resolution

Multiphoton microscopy (MPM) has become a preferred technique for intravital imaging deep in living tissues with subcellular detail, where resolution and working depths are typically optimized utilizing high numerical aperture, water-immersion objectives with long focusing distances. However, this approach requires the maintenance of water between the specimen and the objective lens, which can be challenging or impossible for many intravital preparations with complex tissues and spatial arrangements. We introduce the novel use of cohesive hyaluronan gel (HG) as an immersion medium that can be used in place of water within existing optical setups to enable multiphoton imaging with equivalent quality and far superior stability. We characterize and compare imaging performance, longevity, and feasibility of preparations in various configurations. This combination of HG with MPM is highly accessible and opens the doors to new intravital imaging applications.

Intravital imaging of the functions of immune cells in the tumor microenvironment during immunotherapy

Cancer immunotherapy has developed rapidly in recent years and stands as one of the most promising techniques for combating cancer. To develop and optimize cancer immunotherapy, it is crucial to comprehend the interactions between immune cells and tumor cells in the tumor microenvironment (TME). The TME is complex, with the distribution and function of immune cells undergoing dynamic changes. There are several research techniques to study the TME, and intravital imaging emerges as a powerful tool for capturing the spatiotemporal dynamics, especially the movement behavior and the immune function of various immune cells in real physiological state. Intravital imaging has several advantages, such as high spatio-temporal resolution, multicolor, dynamic and 4D detection, making it an invaluable tool for visualizing the dynamic processes in the TME. This review summarizes the workflow for intravital imaging technology, multi-color labeling methods, optical imaging windows, methods of imaging data analysis and the latest research in visualizing the spatio-temporal dynamics and function of immune cells in the TME. It is essential to investigate the role played by immune cells in the tumor immune response through intravital imaging. The review deepens our understanding of the unique contribution of intravital imaging to improve the efficiency of cancer immunotherapy.

Intravital Imaging of Thrombosis Models in Mice

Intravital microscopy is a powerful tool to study thrombosis in real time. The kinetics of thrombus formation and progression in vivo is studied after inflicting damage to the endothelium through mechanical, chemical, or laser injury. Mouse models of atherosclerosis are also used to induce thrombus formation. Vessels of different sizes and from different vascular beds such as carotid artery or vena cava, mesenteric or cremaster arterioles, can be targeted. Using fluorescent dyes, antibodies, or reporter mouse strains allows to visualize key cells and factors mediating the thrombotic processes. Here, we review the latest literature on using intravital microscopy to study thrombosis as well as thromboinflammation following transient middle cerebral artery occlusion, infection-induced immunothrombosis, and liver ischemia reperfusion.

Multiphoton microscopy providing pathological-level quantification of myocardial fibrosis in transplanted human heart

Multiphoton microscopy (MPM), a high-resolution laser scanning technique, has been shown to provide detailed real-time information on fibrosis assessment in animal models. But the value of MPM in human histology, especially in heart tissue, has not been fully explored. We aimed to evaluate the association between myocardial fibrosis measured by MPM and that measured by histological staining in the transplanted human heart. One hundred and twenty samples of heart tissue were obtained from 20 patients consisting of 10 dilated cardiomyopathies (DCM) and 10 ischemic cardiomyopathies (ICM). MPM and picrosirius red staining were performed to quantify collagen volume fraction (CVF) in explanted hearts postoperatively. Cardiomyocyte and myocardial fibrosis could be clearly visualized by MPM. Although patients with ICM had significantly greater MPM-derived CVF than patients with DCM (25.33  ± 12.65 % vs. 19.82  ± 8.62 %, p = 0.006), there was a substantial overlap of CVF values between them. MPM-derived CVF was comparable to that derived from picrosirius red staining based on all samples (22.58 ± 11.13% vs. 21.19 ± 11.79%, p = 0.348), as well as in DCM samples and ICM samples. MPM-derived CVF was correlated strongly with the magnitude of staining-derived CVF in both all samples and DCM samples and ICM samples (r = 0.972, r = 0.963, r = 0.973, respectively; all p < 0.001). Intra- and inter-observer reproducibility for MPM-derived CVF and staining-derived CVF were 0.995, 0.989, 0.995, and 0.985, respectively. Our data demonstrated that MPM can provide a pathological-level assessment of myocardial microstructure in transplanted human heart.

Genetically engineered mice for combinatorial cardiovascular optobiology

Optogenetic effectors and sensors provide a novel real-time window into complex physiological processes, enabling determination of molecular signaling processes within functioning cellular networks. However, the combination of these optical tools in mice is made practical by construction of genetic lines that are optically compatible and genetically tractable. We present a new toolbox of 21 mouse lines with lineage-specific expression of optogenetic effectors and sensors for direct biallelic combination, avoiding the multiallelic requirement of Cre recombinase -mediated DNA recombination, focusing on models relevant for cardiovascular biology. Optogenetic effectors (11 lines) or Ca²⁺ sensors (10 lines) were selectively expressed in cardiac pacemaker cells, cardiomyocytes, vascular endothelial and smooth muscle cells, alveolar epithelial cells, lymphocytes, glia, and other cell types. Optogenetic effector and sensor function was demonstrated in numerous tissues. Arterial/arteriolar tone was modulated by optical activation of the second messengers InsP₃ (optoα1AR) and cAMP (optoß2AR), or Ca²⁺-permeant membrane channels (CatCh2) in smooth muscle (Acta2) and endothelium (Cdh5). Cardiac activation was separately controlled through activation of nodal/conducting cells or cardiac myocytes. We demonstrate combined effector and sensor function in biallelic mouse crosses: optical cardiac pacing and simultaneous cardiomyocyte Ca²⁺ imaging in Hcn4^BAC-CatCh2/Myh6-GCaMP8 crosses. These experiments highlight the potential of these mice to explore cellular signaling in vivo, in complex tissue networks.

Label-Free Multiphoton Microscopy for the Detection and Monitoring of Calcific Aortic Valve Disease

Calcific aortic valve disease (CAVD) is the most common valvular heart disease. CAVD results in a considerable socio-economic burden, especially considering the aging population in Europe and North America. The only treatment standard is surgical valve replacement as early diagnostic, mitigation, and drug strategies remain underdeveloped. Novel diagnostic techniques and biomarkers for early detection and monitoring of CAVD progression are thus a pressing need. Additionally, non-destructive tools are required for longitudinal in vitro and in vivo assessment of CAVD initiation and progression that can be translated into clinical practice in the future. Multiphoton microscopy (MPM) facilitates label-free and non-destructive imaging to obtain quantitative, optical biomarkers that have been shown to correlate with key events during CAVD progression. MPM can also be used to obtain spatiotemporal readouts of metabolic changes that occur in the cells. While cellular metabolism has been extensively explored for various cardiovascular disorders like atherosclerosis, hypertension, and heart failure, and has shown potential in elucidating key pathophysiological processes in heart valve diseases, it has yet to gain traction in the study of CAVD. Furthermore, MPM also provides structural, functional, and metabolic readouts that have the potential to correlate with key pathophysiological events in CAVD progression. This review outlines the applicability of MPM and its derived quantitative metrics for the detection and monitoring of early CAVD progression. The review will further focus on the MPM-detectable metabolic biomarkers that correlate with key biological events during valve pathogenesis and their potential role in assessing CAVD pathophysiology.

Intravital Imaging Allows Organ-Specific Insights Into Immune Functions

Leukocytes are among the most mobile and versatile cells that have many essential functions in homeostasis and survival. Especially cells from the innate immune system, i.e., neutrophils and macrophages, play an important role as rapid first responders against invading microorganisms. With the advent of novel imaging techniques, new ways of visualizing innate immune cells have become available in recent years, thereby enabling more and more detailed discoveries about their nature, function and interaction partners. Besides intravital spinning-disc and 2-photon microscopy, clearing and 3D-imaging techniques provide new insights into the mechanism of innate immune cell behavior in their natural environment. This mini review focuses on the contributions of novel-imaging techniques to provide insight into the functions of neutrophils and macrophages under homeostasis and in infections. Imaging setups for different organs like the liver, kidney, heart, lung, and the peritoneal cavity are discussed as well as the current limitations of these imaging techniques.

Long term intravital single cell tracking under multiphoton microscopy

Visualizing and tracking cells over time in a living organism has been a much-coveted dream before the invention of intravital microscopy. The opaque nature of tissue was a major hurdle that was remedied by the multiphoton microscopy. With the advancement of optical imaging and fluorescent labeling tools, intravital high resolution imaging has become increasingly accessible over the past few years. Long-term intravital tracking of single cells (LIST) under multiphoton microscopy provides a unique opportunity to gain insight into the longitudinal changes in the morphology, migration, or function of cells or subcellular structures. It is particularly suitable for studying slow-evolving cellular and molecular events during normal development or disease progression, without losing the opportunity of catching fast events such as calcium signals. Here, we review the application of LIST under 2-photon microscopy in various fields of neurobiology and discuss challenges and new directions in labeling and imaging methods for LIST. Overall, this review provides an overview of current applications of LIST in mammals, which is an emerging field that will contribute to a better understanding of essential molecular and cellular events in health and disease.

Label-free optical biomarkers detect early calcific aortic valve disease in a wild-type mouse model

Background

Calcific aortic valve disease (CAVD) pathophysiology is a complex, multistage process, usually diagnosed at advanced stages after significant anatomical and hemodynamic changes in the valve. Early detection of disease progression is thus pivotal in the development of prevention and mitigation strategies. In this study, we developed a diet-based, non-genetically modified mouse model for early CAVD progression, and explored the utility of two-photon excited fluorescence (TPEF) microscopy for early detection of CAVD progression. TPEF imaging provides label-free, non-invasive, quantitative metrics with the potential to correlate with multiple stages of CAVD pathophysiology including calcium deposition, collagen remodeling and osteogenic differentiation.

Methods

Twenty-week old C57BL/6J mice were fed either a control or pro-calcific diet for 16 weeks and monitored via echocardiography, histology, immunohistochemistry, and quantitative polarized light imaging. Additionally, TPEF imaging was used to quantify tissue autofluorescence (A) at 755 nm, 810 nm and 860 nm excitation, to calculate TPEF 755–860 ratio (A_860/525/(A_755/460 + A_860/525)) and TPEF Collagen-Calcium ratio (A_810/525/(A_810/460 + A_810/525)) in the murine valves. In a separate experiment, animals were fed the above diets till 28 weeks to assess for later-stage calcification.

Results

Pro-calcific mice showed evidence of lipid deposition at 4 weeks and calcification at 16 weeks at the valve commissures. The valves of pro-calcific mice also showed positive expression for markers of osteogenic differentiation, myofibroblast activation, proliferation, inflammatory cytokines and collagen remodeling. Pro-calcific mice exhibited lower TPEF autofluorescence ratios, at locations coincident with calcification, that correlated with increased collagen disorganization and positive expression of osteogenic markers. Additionally, locations with lower TPEF autofluorescence ratios at 4 and 16 weeks exhibited increased calcification at later 28-week timepoints.

Conclusions

This study suggests the potential of TPEF autofluorescence metrics to serve as a label-free tool for early detection and monitoring of CAVD pathophysiology.