A synthetic BRET-based optogenetic device for pulsatile transgene expression enabling glucose homeostasis in mice

Lighting up arginine metabolism reveals its functional diversity in physiology and pathology

Arginine is one of the most metabolically versatile amino acids and plays pivotal roles in diverse biological and pathological processes; however, sensitive tracking of arginine dynamics in situ remains technically challenging. Here, we engineer high-performance fluorescent biosensors, denoted sensitive to arginine (STAR), to illuminate arginine metabolism in cells, mice, and clinical samples. Utilizing STAR, we demonstrate the effects of different amino acids in regulating intra- and extracellular arginine levels. STAR enabled live-cell monitoring of arginine fluctuations during macrophage activation, phagocytosis, efferocytosis, and senescence and revealed cellular senescence depending on arginine availability. Moreover, a simple and fast assay based on STAR revealed that serum arginine levels tended to increase with age, and the elevated serum arginine level is a potential indicator for discriminating the progression and severity of vitiligo. Collectively, our study provides important insights into the metabolic and functional roles of arginine, as well as its potential in diagnostic and therapeutic applications.

Optogenetic Strategies for Optimizing the Performance of Phospholipids Biosensors

High-performance biosensors play a crucial role in elucidating the intricate spatiotemporal regulatory roles and dynamics of membrane phospholipids. However, enhancing the sensitivity and imaging performance remains a significant challenge. Here, optogenetic-based strategies are presented to optimize phospholipid biosensors. These strategies involves presequestering unbound biosensors in the cell nucleus and regulating their cytosolic levels with blue light to minimize background signal interference in phospholipid detection, particularly under conditions of high expression levels of biosensor. Furthermore, optically controlled phase separation and the SunTag system are employed to generate punctate probes for substrate detection, thereby amplifying biosensor signals and enhancing visualization of the detection process. These improved phospholipid biosensors hold great potential for enhancing the understanding of the spatiotemporal dynamics and regulatory roles of membrane lipids in live cells and the methodological insights in this study might be valuable for developing other high-performance biosensors.

Optogenetic therapeutic strategies for diabetes mellitus

Diabetes mellitus (DM) is a common chronic disease affecting humans globally. It is characterized by abnormally elevated blood glucose levels due to the failure of insulin production or reduction of insulin sensitivity and functionality. Insulin and glucagon-like peptide (GLP)-1 replenishment or improvement of insulin resistance are the two major strategies to treat diabetes. Recently, optogenetics that uses genetically encoded light-sensitive proteins to precisely control cell functions has been regarded as a novel therapeutic strategy for diabetes. Here, we summarize the latest development of optogenetics and its integration with synthetic biology approaches to produce light-responsive cells for insulin/GLP-1 production, amelioration of insulin resistance and neuromodulation of insulin secretion. In addition, we introduce the development of cell encapsulation and delivery methods and smart bioelectronic devices for the in vivo application of optogenetics-based cell therapy in diabetes. The remaining challenges for optogenetics-based cell therapy in the clinical translational study are also discussed.

Systems for Targeted Silencing of Gene Expression and Their Application in Plants and Animals

At present, there are a variety of different approaches to the targeted regulation of gene expression. However, most approaches are devoted to the activation of gene transcription, and the methods for gene silencing are much fewer in number. In this review, we describe the main systems used for the targeted suppression of gene expression (including RNA interference (RNAi), chimeric transcription factors, chimeric zinc finger proteins, transcription activator-like effectors (TALEs)-based repressors, optogenetic tools, and CRISPR/Cas-based repressors) and their application in eukaryotes-plants and animals. We consider the advantages and disadvantages of each approach, compare their effectiveness, and discuss the peculiarities of their usage in plant and animal organisms. This review will be useful for researchers in the field of gene transcription suppression and will allow them to choose the optimal method for suppressing the expression of the gene of interest depending on the research object.

Spatiotemporal control of RNA metabolism and CRISPR-Cas functions using engineered photoswitchable RNA-binding proteins

RNA molecules perform various crucial roles in diverse cellular processes, from translating genetic information to decoding the genome, regulating gene expression and catalyzing chemical reactions. RNA-binding proteins (RBPs) play an essential role in regulating the diverse behaviors and functions of RNA in live cells, but techniques for the spatiotemporal control of RBP activities and RNA functions are rarely reported yet highly desirable. We recently reported the development of LicV, a synthetic photoswitchable RBP that can bind to a specific RNA sequence in response to blue light irradiation. LicV has been used successfully for the optogenetic control of RNA localization, splicing, translation and stability, as well as for the photoswitchable regulation of transcription and genomic locus labeling. Compared to classical genetic or pharmacologic perturbations, LicV-based light-switchable effectors have the advantages of large dynamic range between dark and light conditions and submicron and millisecond spatiotemporal resolutions. In this protocol, we provide an easy, efficient and generalizable strategy for engineering photoswitchable RBPs for the spatiotemporal control of RNA metabolism. We also provide a detailed protocol for the conversion of a CRISPR-Cas system to optogenetic control. The protocols typically take 2-3 d, including transfection and results analysis. Most of this protocol is applicable to the development of novel LicV-based photoswitchable effectors for the optogenetic control of other RNA metabolisms and CRISPR-Cas functions.

[Research advances in neuromodulation techniques for blood glucose regulation and diabetes intervention]

Diabetes and its complications that seriously threaten the health and life of human, has become a public health problem of global concern. Glycemic control remains a major focus in the treatment and management of patients with diabetes. The traditional lifestyle interventions, drug therapies, and surgeries have benefited many patients with diabetes. However, due to problems such as poor patient compliance, drug side effects, and limited surgical indications, there are still patients who fail to effectively control their blood glucose levels. With the development of bioelectronic medicine, neuromodulation techniques have shown great potential in the field of glycemic control and diabetes intervention with its unique advantages. This paper mainly reviewed the research advances and latest achievements of neuromodulation technologies such as peripheral nerve electrical stimulation, ultrasound neuromodulation, and optogenetics in blood glucose regulation and diabetes intervention, analyzed the existing problems and presented prospects for the future development trend to promote clinical research and application of neuromodulation technologies in the treatment of diabetes.

A Bioluminescent Activity Dependent (BLADe) Platform for Converting Neuronal Activity to Photoreceptor Activation

We developed a platform that utilizes a calcium-dependent luciferase to convert neuronal activity into activation of light sensing domains within the same cell. The platform is based on a Gaussia luciferase variant with high light emission split by calmodulin-M13 sequences that depends on influx of calcium ions (Ca2+) for functional reconstitution. In the presence of its luciferin, coelenterazine (CTZ), Ca2+ influx results in light emission that drives activation of photoreceptors, including optogenetic channels and LOV domains. Critical features of the converter luciferase are light emission low enough to not activate photoreceptors under baseline condition and high enough to activate photosensing elements in the presence of Ca2+ and luciferin. We demonstrate performance of this activity-dependent sensor and integrator for changing membrane potential and driving transcription in individual and populations of neurons in vitro and in vivo.

LOV2-based photoactivatable CaMKII and its application to single synapses: Local Optogenetics

Optogenetic techniques offer a high spatiotemporal resolution to manipulate cellular activity. For instance, Channelrhodopsin-2 with global light illumination is the most widely used to control neuronal activity at the cellular level. However, the cellular scale is much larger than the diffraction limit of light (<1 μm) and does not fully exploit the features of the "high spatial resolution" of optogenetics. For instance, until recently, there were no optogenetic methods to induce synaptic plasticity at the level of single synapses. To address this, we developed an optogenetic tool named photoactivatable CaMKII (paCaMKII) by fusing a light-sensitive domain (LOV2) to CaMKIIα, which is a protein abundantly expressed in neurons of the cerebrum and hippocampus and essential for synaptic plasticity. Combining photoactivatable CaMKII with two-photon excitation, we successfully activated it in single spines, inducing synaptic plasticity (long-term potentiation) in hippocampal neurons. We refer to this method as "Local Optogenetics", which involves the local activation of molecules and measurement of cellular responses. In this review, we will discuss the characteristics of LOV2, the recent development of its derivatives, and the development and application of paCaMKII.

Light-stimulated insulin secretion from pancreatic islet-like organoids derived from human pluripotent stem cells

Optogenetic techniques permit non-invasive, spatiotemporal, and reversible modulation of cellular activities. Here, we report a novel optogenetic regulatory system for insulin secretion in human pluripotent stem cell (hPSC)-derived pancreatic islet-like organoids using monSTIM1 (monster-opto-Stromal interaction molecule 1), an ultra-light-sensitive OptoSTIM1 variant. The monSTIM1 transgene was incorporated at the AAVS1 locus in human embryonic stem cells (hESCs) by CRISPR-Cas9-mediated genome editing. Not only were we able to elicit light-induced intracellular Ca2+ concentration ([Ca2+]i) transients from the resulting homozygous monSTIM1+/+-hESCs, but we also successfully differentiated them into pancreatic islet-like organoids (PIOs). Upon light stimulation, the β-cells in these monSTIM1+/+-PIOs displayed reversible and reproducible [Ca2+]i transient dynamics. Furthermore, in response to photoexcitation, they secreted human insulin. Light-responsive insulin secretion was similarly observed in monSTIM1+/+-PIOs produced from neonatal diabetes (ND) patient-derived induced pluripotent stem cells (iPSCs). Under LED illumination, monSTIM1+/+-PIO-transplanted diabetic mice produced human c-peptide. Collectively, we developed a cellular model for the optogenetic control of insulin secretion using hPSCs, with the potential to be applied to the amelioration of hyperglycemic disorders.

A Single-Component Optogenetic Gal4-UAS System Allows Stringent Control of Gene Expression in Zebrafish and Drosophila

The light-regulated Gal4-UAS system has offered new ways to control cellular activities with precise spatial and temporal resolution in zebrafish and Drosophila. However, the existing optogenetic Gal4-UAS systems suffer from having multiple protein components and a dependence on extraneous light-sensitive cofactors, which increase the technical complexity and limit the portability of these systems. To overcome these limitations, we herein describe the development of a novel optogenetic Gal4-UAS system (ltLightOn) for both zebrafish and Drosophila based on a single light-switchable transactivator, termed GAVPOLT, which dimerizes and binds to gene promoters to activate transgene expression upon blue light illumination. The ltLightOn system is independent of exogenous cofactors and exhibits a more than 2400-fold ON/OFF gene expression ratio, allowing quantitative, spatial, and temporal control of gene expression. We further demonstrate the usefulness of the ltLightOn system in regulating zebrafish embryonic development by controlling the expression of lefty1 by light. We believe that this single-component optogenetic system will be immensely useful in understanding the gene function and behavioral circuits in zebrafish and Drosophila.

Coelenterazine-Type Bioluminescence-Induced Optical Probes for Sensing and Controlling Biological Processes

Bioluminescence-based probes have long been used to quantify and visualize biological processes in vitro and in vivo. Over the past years, we have witnessed the trend of bioluminescence-driven optogenetic systems. Typically, bioluminescence emitted from coelenterazine-type luciferin–luciferase reactions activate light-sensitive proteins, which induce downstream events. The development of coelenterazine-type bioluminescence-induced photosensory domain-based probes has been applied in the imaging, sensing, and control of cellular activities, signaling pathways, and synthetic genetic circuits in vitro and in vivo. This strategy can not only shed light on the mechanisms of diseases, but also promote interrelated therapy development. Here, this review provides an overview of these optical probes for sensing and controlling biological processes, highlights their applications and optimizations, and discusses the possible future directions.

A glucose-blue light AND gate-controlled chemi-optogenetic cell-implanted therapy for treating type-1 diabetes in mice

Exogenous insulin therapy is the mainstay treatment for Type-1 diabetes (T1D) caused by insulin deficiency. A fine-tuned insulin supply system is important to maintain the glucose homeostasis. In this study, we present a designed cell system that produces insulin under an AND gate control, which is triggered only in the presence of both high glucose and blue light illumination. The glucose-sensitive GIP promoter induces the expression of GI-Gal4 protein, which forms a complex with LOV-VP16 in the presence of blue light. The GI-Gal4:LOV-VP16 complex then promotes the expression of UAS-promoter-driven insulin. We transfected these components into HEK293T cells, and demonstrated the insulin was secreted under the AND gate control. Furthermore, we showed the capacity of the engineered cells to improve the blood glucose homeostasis through implantation subcutaneously into Type-1 diabetes mice.

The Roles of Optogenetics and Technology in Neurobiology: A Review

Optogenetic is a technique that combines optics and genetics to control specific neurons. This technique usually uses adenoviruses that encode photosensitive protein. The adenovirus may concentrate in a specific neural region. By shining light on the target nerve region, the photosensitive protein encoded by the adenovirus is controlled. Photosensitive proteins controlled by light can selectively allow ions inside and outside the cell membrane to pass through, resulting in inhibition or activation effects. Due to the high precision and minimally invasive, optogenetics has achieved good results in many fields, especially in the field of neuron functions and neural circuits. Significant advances have also been made in the study of many clinical diseases. This review focuses on the research of optogenetics in the field of neurobiology. These include how to use optogenetics to control nerve cells, study neural circuits, and treat diseases by changing the state of neurons. We hoped that this review will give a comprehensive understanding of the progress of optogenetics in the field of neurobiology.

Precise Thermal Regulation of Engineered Bacteria Secretion for Breast Cancer Treatment In Vivo

For the biomedical application of engineered bacteria, strictly regulating the function of engineered bacteria has always been the goal pursued. However, the existing regulation methods do not meet the needs of the in vivo application of engineered bacteria. Therefore, the exploration of the precise regulation of engineered bacteria is necessary. Herein, heat-sensitive engineered bacteria that can respond to thermal stimuli within 30 min were constructed, and the precise control of functions was verified in the intestines of various model organisms (including C. elegans, bees, and mice). Subsequently, heat-sensitive engineered bacteria were shown to colonize the mouse tumor microenvironment. Finally, thermal stimulation was proven to control engineered bacteria to produce the therapeutic protein tumor necrosis factor α (TNF-α) in the tumor. After three heat stimulation treatments, the growth of the tumor was significantly inhibited, suggesting that heat can be used as a strategy to precisely control engineered bacteria in vivo.

Neurophotonic tools for microscopic measurements and manipulation: status report

Neurophotonics was launched in 2014 coinciding with the launch of the BRAIN Initiative focused on development of technologies for advancement of neuroscience. For the last seven years, Neurophotonics' agenda has been well aligned with this focus on neurotechnologies featuring new optical methods and tools applicable to brain studies. While the BRAIN Initiative 2.0 is pivoting towards applications of these novel tools in the quest to understand the brain, this status report reviews an extensive and diverse toolkit of novel methods to explore brain function that have emerged from the BRAIN Initiative and related large-scale efforts for measurement and manipulation of brain structure and function. Here, we focus on neurophotonic tools mostly applicable to animal studies. A companion report, scheduled to appear later this year, will cover diffuse optical imaging methods applicable to noninvasive human studies. For each domain, we outline the current state-of-the-art of the respective technologies, identify the areas where innovation is needed, and provide an outlook for the future directions.

Advanced Optogenetic-Based Biosensing and Related Biomaterials

The ability to stimulate mammalian cells with light, brought along by optogenetic control, has significantly broadened our understanding of electrically excitable tissues. Backed by advanced (bio)materials, it has recently paved the way towards novel biosensing concepts supporting bio-analytics applications transversal to the main biomedical stream. The advancements concerning enabling biomaterials and related novel biosensing concepts involving optogenetics are reviewed with particular focus on the use of engineered cells for cell-based sensing platforms and the available toolbox (from mere actuators and reporters to novel multifunctional opto-chemogenetic tools) for optogenetic-enabled real-time cellular diagnostics and biosensor development. The key advantages of these modified cell-based biosensors concern both significantly faster (minutes instead of hours) and higher sensitivity detection of low concentrations of bioactive/toxic analytes (below the threshold concentrations in classical cellular sensors) as well as improved standardization as warranted by unified analytic platforms. These novel multimodal functional electro-optical label-free assays are reviewed among the key elements for optogenetic-based biosensing standardization. This focused review is a potential guide for materials researchers interested in biosensing based on light-responsive biomaterials and related analytic tools.

Riboswitches for Controlled Expression of Therapeutic Transgenes Delivered by Adeno-Associated Viral Vectors

Vectors developed from adeno-associated virus (AAV) are powerful tools for in vivo transgene delivery in both humans and animal models, and several AAV-delivered gene therapies are currently approved for clinical use. However, AAV-mediated gene therapy still faces several challenges, including limited vector packaging capacity and the need for a safe, effective method for controlling transgene expression during and after delivery. Riboswitches, RNA elements which control gene expression in response to ligand binding, are attractive candidates for regulating expression of AAV-delivered transgene therapeutics because of their small genomic footprints and non-immunogenicity compared to protein-based expression control systems. In addition, the ligand-sensing aptamer domains of many riboswitches can be exchanged in a modular fashion to allow regulation by a variety of small molecules, proteins, and oligonucleotides. Riboswitches have been used to regulate AAV-delivered transgene therapeutics in animal models, and recently developed screening and selection methods allow rapid isolation of riboswitches with novel ligands and improved performance in mammalian cells. This review discusses the advantages of riboswitches in the context of AAV-delivered gene therapy, the subsets of riboswitch mechanisms which have been shown to function in human cells and animal models, recent progress in riboswitch isolation and optimization, and several examples of AAV-delivered therapeutic systems which might be improved by riboswitch regulation.