In vivo optogenetics for light-induced oxidative stress in transgenic zebrafish expressing the KillerRed photosensitizer protein

Advances in the Genetically Engineered KillerRed for Photodynamic Therapy Applications

Photodynamic therapy (PDT) is a clinical treatment for cancer or non-neoplastic diseases, and the photosensitizers (PSs) are crucial for PDT efficiency. The commonly used chemical PSs, generally produce ROS through the type II reaction that highly relies on the local oxygen concentration. However, the hypoxic tumor microenvironment and unavoidable dark toxicity of PSs greatly restrain the wide application of PDT. The genetically encoded PSs, unlike chemical PSs, can be modified using genetic engineering techniques and targeted to unique cellular compartments, even within a single cell. KillerRed, as a dimeric red fluorescent protein, can be activated by visible light or upconversion luminescence to execute the Type I reaction of PDT, which does not need too much oxygen and surely attract the researchers’ focus. In particular, nanotechnology provides new opportunities for various modifications of KillerRed and versatile delivery strategies. This review more comprehensively outlines the applications of KillerRed, highlighting the fascinating features of KillerRed genes and proteins in the photodynamic systems. Furthermore, the advantages and defects of KillerRed are also discussed, either alone or in combination with other therapies. These overviews may facilitate understanding KillerRed progress in PDT and suggest some emerging potentials to circumvent challenges to improve the efficiency and accuracy of PDT.

Genetically Encoded Photosensitizer for Destruction of Protein or Cell Function

There are several paths when excited molecules return to the ground state. In the case of fluorescent molecules, the dominant path is fluorescence emission that is greatly contributing to bioimaging. Meanwhile, photosensitizers transfer electron or energy from chromophore to the surrounding molecules, including molecular oxygen. Generated reactive oxygen species has potency to attack other molecules by oxidation. In this chapter, we introduce the chromophore-assisted light inactivation (CALI) method using a photosensitizer to inactivate proteins in a spatiotemporal manner and development of CALI tools, which is useful for investigation of protein functions and dynamics, by inactivation of the target molecules. Moreover, photosensitizers with high efficiency make it possible optogenetic control of cell ablation in living organisms and photodynamic therapy. Further development of photosensitizers with different excitation wavelengths will contribute to the investigation of multiple proteins or cell functions through inactivation in the different positions and timings.

Animal Models of Hypertension: A Scientific Statement From the American Heart Association

Hypertension is the most common chronic disease in the world, yet the precise cause of elevated blood pressure often cannot be determined. Animal models have been useful for unraveling the pathogenesis of hypertension and for testing novel therapeutic strategies. The utility of animal models for improving the understanding of the pathogenesis, prevention, and treatment of hypertension and its comorbidities depends on their validity for representing human forms of hypertension, including responses to therapy, and on the quality of studies in those models (such as reproducibility and experimental design). Important unmet needs in this field include the development of models that mimic the discrete hypertensive syndromes that now populate the clinic, resolution of ongoing controversies in the pathogenesis of hypertension, and the development of new avenues for preventing and treating hypertension and its complications. Animal models may indeed be useful for addressing these unmet needs.

Cardiac optogenetics: a novel approach to cardiovascular disease therapy

Optogenetics is a cell-type specific and high spatial-temporal resolution method that combines genetic encoding of light-sensitive proteins and optical manipulation techniques. Optogenetics technology provides a novel approach for research on cardiac arrhythmia treatment, including pacing, recovering the conduction system, and achieving cardiac resynchronization with precise and low-energy optical control. Photosensitive proteins, which usually act as ion channels, pumps, or receptors, are delivered to target cells, where they respond to light pulses of specific wavelengths, evoke transient flows of transmembrane ion currents, and induce signal transmission. With the development of gene technology, the in vivo efficiency of optogenetics in cardiology has been trialed, and in vitro experiments have been performed to test its potential in cardiac electrophysiology. Challenges for applying optogenetics in large animals and humans include the effectiveness, safety, and long-term expression of photosensitive proteins, unscattered and unattenuated exogenous light stimulation, and the need for implantable miniature light stimulators. Photosensitive proteins, genetic engineering technology, and light equipment are essential for experiments in cardiac optogenetics. Optogenetics may provide an alternative method for evaluating the mechanism of cardiac arrhythmias, testing hypotheses, and treating cardiovascular diseases.

Real-time visualization of oxidative stress-mediated neurodegeneration of individual spinal motor neurons in vivo

Generation of reactive oxygen species (ROS) has been shown to be important for many physiological processes, ranging from cell differentiation to apoptosis. With the development of the genetically encoded photosensitiser KillerRed (KR) it is now possible to efficiently produce ROS dose-dependently in a specific cell type upon green light illumination. Zebrafish are the ideal vertebrate animal model for these optogenetic methods because of their transparency and efficient transgenesis. Here we describe a zebrafish model that expresses membrane-targeted KR selectively in motor neurons. We show that KR-activated neurons in the spinal cord undergo stress and cell death after induction of ROS. Using single-cell resolution and time-lapse confocal imaging, we selectively induced neurodegeneration in KR-expressing neurons leading to characteristic signs of apoptosis and cell death. We furthermore illustrate a targeted microglia response to the induction site as part of a physiological response within the zebrafish spinal cord. Our data demonstrate the successful implementation of KR mediated ROS toxicity in motor neurons in vivo and has important implications for studying the effects of ROS in a variety of conditions within the central nervous system, including aging and age-related neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease and amyotrophic lateral sclerosis.

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Motor neurons can be targeted for oxidative stress using optogenetics in zebrafish.

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KillerRed expressing neurons undergo characteristic sequence of neurodegeneration.

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Targeted neurons show microglial activation as part of the physiological response.

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ROS toxicity has important implications for mechanisms driving neurodegeneration.

Novel procedures for whole organism detection and quantification of fluorescence as a measurement for oxidative stress in zebrafish (Danio rerio) larvae

The modes of action of pollutants are diverse, and a common consequences to pollutant exposure is oxidative stress. This phenomenon is caused by an imbalance or disurption in the control of Reactive Oxygen Species (ROS) resulting in an accumulation of free radicals. Oxidative stress may cause damages to the DNA, phospholipids and proteins, and lead to cell death. Due to the possible contribution of oxidative stress to pollutant toxicity, it is valuable to assess its occurrence, role and mechanism. Detection of oxidative stress at low concentrations soon after the onset of exposure can be a sensitive, general marker for contamination. This study aimed at developing and benchmarking a set of novel fluorescence-based procedures to assess the occurrence of oxidative stress in zebrafish larvae (96 hpf) by measuring the antioxidant glutathione (GSH) and general ROS. Zebrafish larvae were exposed to tert-butyl hydroperoxide (t-BHP). ROS and GSH were made visible by means of specific fluorescent molecular probes in different experimental scenarios. The induction was qualified using microscopy and quantified through photometric measurement. For quantitative assessment, an approach based on homogenized larvae and a non-invasive plate assay were developed. The novel procedures proved suitable for oxidative stress detection. Comparisons of qualitative to quantitative data showed that the orientation of the larvae in the well can influence fluorescence data evaluation. The non-invasive quantitative assay proved robust against any influence of the orientation of the larvae. The developed protocols promise to be useful tools for the detection of oxidative stress in zebrafish larvae.

Responsive mesoporous silica nanoparticles for sensing of hydrogen peroxide and simultaneous treatment toward heart failure

Chronic heart failure is often characterized by the elevated amounts of reactive oxygen species such as hydrogen peroxide (H₂O₂) in the heart. Thus, it is of importance that selective release of therapeutic drugs occurs at the heart failure site to maximize therapeutic effects. In this work, functional mesoporous silica nanoparticles (MSNPs) were developed for detection of H₂O₂, selective drug release and controlled treatment toward heart failure. The H₂O₂-sensitive probe was attached to the surface of the MSNPs, and a therapeutic drug of heart failure, captopril, was loaded within the pores of the MSNPs and retained by the binding of α-cyclodextrin to the probe. H₂O₂ present in tissue could react with the probe and enable the dissociation of α-cyclodextrin present on the nanoparticle surface, so that captopril could be successfully released along with "turn-on" of the probe fluorescence. In vivo experiments using the KillerRed heart failure transgenic zebrafish model demonstrated that this therapeutic system is physiologically responsive. Captopril-loaded MSNPs showed high therapeutic efficacy, improving the heartbeat rate and cardiac output in zebrafish experiencing acute KillerRed-induced heart failure.