Reward-based hypertension control by a synthetic brain-dopamine interface

Involvement of D1 dopamine receptor in the nucleus of the solitary tract of rats in stress-induced hypertension and exercise

OBJECTIVE

Chronic stress can cause hypertension, whereas daily exercise promotes healthy well being through destressing. Although the nucleus of the solitary tract (NTS) is involved in the development of hypertension, the molecular and physiological mechanisms of stress and exercise remain unclear. In this study, we tested whether gene expression in the NTS is altered by stress and daily exercise and whether this is involved in cardiovascular regulation.

METHODS

We have performed RT2 Profiler PCR arrays targeting a panel of neurotransmitter receptor genes in the NTS of Wistar rats subjected to chronic restraint stress (1 h a day over 3 weeks) with or without voluntary wheel exercise. We also performed immunohistochemistry to determine whether the identified molecules were expressed at the protein level. Additionally, microinjection studies in anesthetized rats were performed to examine whether validated molecules exhibit physiological roles in cardiovascular regulation of the NTS.

RESULTS

We observed that blood pressure was significantly increased by stress and the increase was suppressed by exercise. Using PCR analysis, we determined that the expression levels of four genes in the NTS, including the dopamine receptor D1 gene (Drd1), were significantly affected by stress and suppressed by exercise. We also examined dopamine D1 receptor (D1R) expression in NTS neurons and found significantly greater expression in the stressed than nonstressed animals. Furthermore, the microinjection of a D1R agonist into the NTS in anesthetized rats induced hypotensive effects.

CONCLUSION

These results suggest that NTS D1R plays a role in the counteracting processes of stress-induced hypertension.

Enhancing cell-based therapies with synthetic gene circuits responsive to molecular stimuli

Synthetic biology aims to contribute to the development of next-generation patient-specific cell-based therapies for chronic diseases especially through the construction of sophisticated synthetic gene switches to enhance the safety and spatiotemporal controllability of engineered cells. Indeed, switches that sense and process specific cues, which may be either externally administered triggers or endogenous disease-associated molecules, have emerged as powerful tools for programming and fine-tuning therapeutic outputs. Living engineered cells, often referred to as designer cells, incorporating such switches are delivered to patients either as encapsulated cell implants or by infusion, as in the case of the clinically approved CAR-T cell therapies. Here, we review recent developments in synthetic gene switches responsive to molecular stimuli, spanning regulatory mechanisms acting at the transcriptional, translational, and posttranslational levels. We also discuss current challenges facing clinical translation of cell-based therapies employing these devices.

Synthetic biology in multicellular organisms: Opportunities in nematodes

Synthetic biology has mainly focused on introducing new or altered functionality in single cell systems: primarily bacteria, yeast, or mammalian cells. Here, we describe the extension of synthetic biology to nematodes, in particular the well-studied model organism Caenorhabditis elegans, as a convenient platform for developing applications in a multicellular setting. We review transgenesis techniques for nematodes, as well as the application of synthetic biology principles to construct nematode gene switches and genetic devices to control motility. Finally, we discuss potential applications of engineered nematodes.

Applications of synthetic biology in medical and pharmaceutical fields

Synthetic biology aims to design or assemble existing bioparts or bio-components for useful bioproperties. During the past decades, progresses have been made to build delicate biocircuits, standardized biological building blocks and to develop various genomic/metabolic engineering tools and approaches. Medical and pharmaceutical demands have also pushed the development of synthetic biology, including integration of heterologous pathways into designer cells to efficiently produce medical agents, enhanced yields of natural products in cell growth media to equal or higher than that of the extracts from plants or fungi, constructions of novel genetic circuits for tumor targeting, controllable releases of therapeutic agents in response to specific biomarkers to fight diseases such as diabetes and cancers. Besides, new strategies are developed to treat complex immune diseases, infectious diseases and metabolic disorders that are hard to cure via traditional approaches. In general, synthetic biology brings new capabilities to medical and pharmaceutical researches. This review summarizes the timeline of synthetic biology developments, the past and present of synthetic biology for microbial productions of pharmaceutics, engineered cells equipped with synthetic DNA circuits for diagnosis and therapies, live and auto-assemblied biomaterials for medical treatments, cell-free synthetic biology in medical and pharmaceutical fields, and DNA engineering approaches with potentials for biomedical applications.

Relationship between plasma dopamine concentration and temperament in horses

Dopamine (DA) is a neurotransmitter associated with animal behaviors. Along with other neurotransmitters such as oxytocin (OXT) and serotonin (5-HT), DA is also involved in determining the temperament of animals. However, the involvement of DA in horse temperament has not been well elucidated. Therefore, in this study, we aimed to determine the correlation between plasma DA concentration and OXT and 5-HT concentrations and behavioral temperament (eg, docility and friendliness, fearfulness, dominance, and trainability) of horses. Blood samples were collected from 31 horses and the concentrations of DA, OXT, and 5-HT were measured using enzyme-linked immunosorbent assay. The temperament of horses was assessed and scored by 3 researchers. The correlation between the plasma concentration of DA and OXT or 5-HT was statistically analyzed using SPSS software and linear regression analysis was performed to determine the association between DA concentration and OXT and 5-HT concentrations. Meanwhile, the DA concentration associated with each type of temperament was analyzed via one-way analysis of variance with LSD post hoc analysis as well as Student's t-test (for trainability). Plasma DA concentration was not found to be correlated with either OXT or 5-HT concentrations. Furthermore, we found no correlation between plasma DA concentration and dominance and trainability. However, our results suggest the possibility of predicting the degree of fearfulness of horses using plasma DA concentrations. We conclude that plasma DA concentration has a potentiality to be used as a biomarker to predict the fearfulness of horses.

Regulation of Transgene Expression by the Natural Sweetener Xylose

Next-generation gene and engineered-cell therapies benefit from incorporating synthetic gene networks that can precisely regulate the therapeutic output in response to externally administered signal inputs that are safe, readily bioavailable and pleasant to take. To enable such therapeutic control, a mammalian gene switch is designed to be responsive to the natural sweetener xylose and its functionality is assessed in mouse studies. The gene switch consists of the bacterial transcription regulator XylR fused to a mammalian transactivator, which binds to an optimized promoter in the presence of xylose, thereby allowing dose-dependent transgene expression. The sensitivity of SWEET (sweetener-inducible expression of transgene) is improved by coexpressing a xylose transporter. Mice implanted with encapsulated SWEET-engineered cells show increased blood levels of cargo protein when taking xylose-sweetened water or coffee, or highly concentrated apple extract, while they do not respond to intake of a usual amount of carrots, which contain xylose. In a proof-of-concept therapeutic application study, type-1 diabetic mice engineered with insulin-expressing SWEET show lowered glycemia and increased insulin levels when administered this fairly diabetic-compliant sweetener, compared to untreated mice. A SWEET-based therapy appears to have the potential to integrate seamlessly into patients' life-style and food habits in the move toward personalized medicine.

Biomarker-driven feedback control of synthetic biology systems for next-generation personalized medicine

Many current clinical therapies for chronic diseases involve administration of drugs using dosage and bioavailability parameters estimated for a generalized population. This standard approach carries the risk of under dosing, which may result in ineffective treatment, or overdosing, which may cause undesirable side effects. Consequently, maintaining a drug concentration in the therapeutic window often requires frequent monitoring, adversely affecting the patient’s quality of life. In contrast, endogenous biosystems have evolved finely tuned feedback control loops that govern the physiological functions of the body based on multiple input parameters. To provide personalized treatment for chronic diseases, therefore, we require synthetic systems that can similarly generate a calibrated therapeutic response. Such engineered autonomous closed-loop devices should incorporate a sensor that actively tracks and evaluates the disease severity based on one or more biomarkers, as well as components that utilize these molecular inputs to bio compute and deliver the appropriate level of therapeutic output. Here, we review recent advances in applications of the closed-loop design principle in biomedical implants for treating severe and chronic diseases, highlighting translational studies of cellular therapies. We describe the engineering principles and components of closed-loop therapeutic devices, and discuss their potential to become a key pillar of personalized medicine.

An Account of Models of Molecular Circuits for Associative Learning with Reinforcement Effect and Forced Dissociation

The development of synthetic biology has enabled massive progress in biotechnology and in approaching research questions from a brand-new perspective. In particular, the design and study of gene regulatory networks in vitro, in vivo, and in silico have played an increasingly indispensable role in understanding and controlling biological phenomena. Among them, it is of great interest to understand how associative learning is formed at the molecular circuit level. Mathematical models are increasingly used to predict the behaviours of molecular circuits. Fernando's model, which is one of the first works in this line of research using the Hill equation, attempted to design a synthetic circuit that mimics Hebbian learning in a neural network architecture. In this article, we carry out indepth computational analysis of the model and demonstrate that the reinforcement effect can be achieved by choosing the proper parameter values. We also construct a novel circuit that can demonstrate forced dissociation, which was not observed in Fernando's model. Our work can be readily used as reference for synthetic biologists who consider implementing circuits of this kind in biological systems.

Therapeutic cell engineering: designing programmable synthetic genetic circuits in mammalian cells

Cell therapy approaches that employ engineered mammalian cells for on-demand production of therapeutic agents in the patient's body are moving beyond proof-of-concept in translational medicine. The therapeutic cells can be customized to sense user-defined signals, process them, and respond in a programmable and predictable way. In this paper, we introduce the available tools and strategies employed to design therapeutic cells. Then, various approaches to control cell behaviors, including open-loop and closed-loop systems, are discussed. We also highlight therapeutic applications of engineered cells for early diagnosis and treatment of various diseases in the clinic and in experimental disease models. Finally, we consider emerging technologies such as digital devices and their potential for incorporation into future cell-based therapies.

Far-red light-activated human islet-like designer cells enable sustained fine-tuned secretion of insulin for glucose control

Diabetes affects almost half a billion people, and all individuals with type 1 diabetes (T1D) and a large portion of individuals with type 2 diabetes rely on self-administration of the peptide hormone insulin to achieve glucose control. However, this treatment modality has cumbersome storage and equipment requirements and is susceptible to fatal user error. Here, reasoning that a cell-based therapy could be coupled to an external induction circuit for blood glucose control, as a proof of concept we developed far-red light (FRL)-activated human islet-like designer (FAID) cells and demonstrated how FAID cell implants achieved safe and sustained glucose control in diabetic model mice. Specifically, by introducing a FRL-triggered optogenetic device into human mesenchymal stem cells (hMSCs), which we encapsulated in poly-(l-lysine)-alginate and implanted subcutaneously under the dorsum of T1D model mice, we achieved FRL illumination-inducible secretion of insulin that yielded improvements in glucose tolerance and sustained blood glucose control over traditional insulin glargine treatment. Moreover, the FAID cell implants attenuated both oxidative stress and development of multiple diabetes-related complications in kidneys. This optogenetics-controlled "living cell factory" platform could be harnessed to develop multiple synthetic designer therapeutic cells to achieve long-term yet precisely controllable drug delivery.

Recent Advances in Cellular and Molecular Bioengineering for Building and Translation of Biological Systems

In January of 2020, the Biomedical Engineering Society (BMES)- Cellular and Molecular Bioengineering (CMBE) conference was held in Puerto Rico and themed “Vision 2020: Emerging Technologies to Elucidate the Rule of Life.” The annual BME-CMBE conference gathered worldwide leaders and discussed successes and challenges in engineering biological systems and their translation. The goal of this report is to present the research frontiers in this field and provide perspectives on successful engineering and translation towards the clinic. We hope that this report serves as a constructive guide in shaping the future of research and translation of engineered biological systems.

A guide to the design of synthetic gene networks in mammalian cells

Synthetic biology aims to harness natural and synthetic biological parts and engineering them in new combinations and systems, producing novel therapies, diagnostics, bioproduction systems, and providing information on the mechanism of function of biological systems. Engineering cell function requires the rewiring or de novo construction of cell information processing networks. Using natural and synthetic signal processing elements, researchers have demonstrated a wide array of signal sensing, processing and propagation modules, using transcription, translation, or post-translational modification to program new function. The toolbox for synthetic network design is ever-advancing and has still ample room to grow. Here, we review the diversity of synthetic gene networks, types of building modules, techniques of regulation, and their applications.

Engineering precision therapies: lessons and motivations from the clinic

In the past decade, gene- and cell-based therapies have been at the forefront of the biomedical revolution. Synthetic biology, the engineering discipline of building sophisticated ‘genetic software’ to enable precise regulation of gene activities in living cells, has been a decisive success factor of these new therapies. Here, we discuss the core technologies and treatment strategies that have already gained approval for therapeutic applications in humans. We also review promising preclinical work that could either enhance the efficacy of existing treatment strategies or pave the way for new precision medicines to treat currently intractable human conditions.

Intracranial self-stimulation-reward or immobilization-aversion had different effects on neurite extension and the ERK pathway in neurotransmitter-sensitive mutant PC12 cells

Various actions trigger pleasure (reward) or aversion (punishment) as emotional responses. Emotional factors that negatively affect brain neural control processes for long periods of time might cause various mental diseases by inducing neuronal changes. In the present study, newly developed PC12m12 cells which are　highly sensitivity to neurotransmitters such as acetylcholine (ACh), were used. Exposing the cells to plasma from rats that had been subjected to intracranial self-stimulation (ICSS) markedly upregulated neurite outgrowth. In addition, voluntary running in a wheel or forced on a rotating rod was used to induce behavioral excitation in rats, and examinations of their plasma confirmed that the ICSS-induced neurite outgrowth was not associated with the ICSS behavior itself. Furthermore, immunoblotting and treatment with U0126, an ERK (extracellular signal-regulated kinase) antagonist, showed that the ICSS-induced neurite outgrowth was related to neuronal ERK activity. Exposing the same cells to plasma from rats that had been subjected to immobilization (IMM) also increased neurite outgrowth. Although the degree of enhancement was not as great as that seen after the ICSS rat plasma treatment, it was less than that observed after treatment with ACh as a positive control. These results indicate that ICSS or IMM lead to varying degrees of morphological changes, such as enhanced neurite outgrowth, in PC12m12 cells, but the neuronal signal transduction pathways underlying these effects differ; i.e.,the former morphological change might involve the activation of the ERK pathway, whereas the latter changes might not. Using PC12m12 cells which exhibit sensitivity to neurotransmitters, it might be possible to clarify the pathogeneses of mental diseases at the neuronal level and search for therapeutic drugs.

Building sophisticated sensors of extracellular cues that enable mammalian cells to work as "doctors" in the body

Mammalian cells are inherently capable of sensing extracellular environmental signals and activating complex biological functions on demand. Advances in synthetic biology have made it possible to install additional capabilities, which can allow cells to sense the presence of custom biological molecules and provide defined outputs on demand. When implanted/infused in patients, such engineered cells can work as intrabody "doctors" that diagnose disease states and produce and deliver therapeutic molecules when and where necessary. The key to construction of such theranostic cells is the development of a range of sensor systems for detecting various extracellular environmental cues that can be rewired to custom outputs. In this review, we introduce the state-of-art engineering principles utilized in the design of sensor systems to detect soluble factors and also to detect specific cell contact, and we discuss their potential role in treating intractable diseases by delivering appropriate therapeutic functions on demand. We also discuss the challenges facing these emerging technologies.

Segregated Nanocompartments Containing Therapeutic Enzymes and Imaging Compounds within DNA-Zipped Polymersome Clusters for Advanced Nanotheranostic Platform

Nanotheranostics is an emerging field that brings together nanoscale-engineered materials with biological systems providing a combination of therapeutic and diagnostic strategies. However, current theranostic nanoplatforms have serious limitations, mainly due to a mismatch between the physical properties of the selected nanomaterials and their functionalization ease, loading ability, or overall compatibility with bioactive molecules. Herein, a nanotheranostic system is proposed based on nanocompartment clusters composed of two different polymersomes linked together by DNA. Careful design and procedure optimization result in clusters segregating the therapeutic enzyme human Dopa decarboxylase (DDC) and fluorescent probes for the detection unit in distinct but colocalized nanocompartments. The diagnostic compartment provides a twofold function: trackability via dye loading as the imaging component and the ability to attach the cluster construct to the surface of cells. The therapeutic compartment, loaded with active DDC, triggers the cellular expression of a secreted reporter enzyme via production of dopamine and activation of dopaminergic receptors implicated in atherosclerosis. This two-compartment nanotheranostic platform is expected to provide the basis of a new treatment strategy for atherosclerosis, to expand versatility and diversify the types of utilizable active molecules, and thus by extension expand the breadth of attainable applications.

The rise of bio-inspired polymer compartments responding to pathology-related signals

Self-organized nano- and microscale polymer compartments such as polymersomes, giant unilamellar vesicles (GUVs), polyion complex vesicles (PICsomes) and layer-by-layer (LbL) capsules have increasing potential in many sensing applications. Besides modifying the physicochemical properties of the corresponding polymer building blocks, the versatility of these compartments can be markedly expanded by biomolecules that endow the nanomaterials with specific molecular and cellular functions. In this review, we focus on polymer-based compartments that preserve their structure, and highlight the key role they play in the field of medical diagnostics: first, the self-assembling abilities that result in preferred architectures are presented for a broad range of polymers. In the following, we describe different strategies for sensing disease-related signals (pH-change, reductive conditions, and presence of ions or biomolecules) by polymer compartments that exhibit stimuli-responsiveness. In particular, we distinguish between the stimulus-sensitivity contributed by the polymer itself or by additional compounds embedded in the compartments in different sensing systems. We then address necessary properties of sensing polymeric compartments, such as the enhancement of their stability and biocompatibility, or the targeting ability, that open up new perspectives for diagnostic applications.

Gene networks that compensate for crosstalk with crosstalk

Crosstalk is a major challenge to engineering sophisticated synthetic gene networks. A common approach is to insulate signal-transduction pathways by minimizing molecular-level crosstalk between endogenous and synthetic genetic components, but this strategy can be difficult to apply in the context of complex, natural gene networks and unknown interactions. Here, we show that synthetic gene networks can be engineered to compensate for crosstalk by integrating pathway signals, rather than by pathway insulation. We demonstrate this principle using reactive oxygen species (ROS)-responsive gene circuits in Escherichia coli that exhibit concentration-dependent crosstalk with non-cognate ROS. We quantitatively map the degree of crosstalk and design gene circuits that introduce compensatory crosstalk at the gene network level. The resulting gene network exhibits reduced crosstalk in the sensing of the two different ROS. Our results suggest that simple network motifs that compensate for pathway crosstalk can be used by biological networks to accurately interpret environmental signals.

Crosstalk between genetic circuits is a major challenge for engineering sophisticated networks. Here the authors design networks that compensate for crosstalk by integrating, not insulating, pathways.

Optogenetic Medicine: Synthetic Therapeutic Solutions Precision-Guided by Light

Gene- and cell-based therapies are well recognized as central pillars of next-generation medicine, but controllability remains a critical issue for clinical applications. In this context, optogenetics is opening up exciting new opportunities for precision-guided medicine by using illumination with light of appropriate intensity and wavelength as a trigger signal to achieve pinpoint spatiotemporal control of cellular activities, such as transgene expression. In this review, we highlight recent advances in optogenetics, focusing on devices for biomedical applications. We introduce the construction and applications of optogenetic-based biomedical tools to treat neurological diseases, diabetes, heart diseases, and cancer, as well as bioelectronic implants that combine light-interfaced electronic devices and optogenetic systems into portable personalized precision bioelectronic medical tools. Optogenetics-based technology promises the capability to achieve traceless, remotely controlled precision dosing of an enormous range of therapeutic outputs. Finally, we discuss the prospects for optogenetic medicine, as well as some emerging challenges.

Designing cell function: assembly of synthetic gene circuits for cell biology applications

Synthetic biology is the discipline of engineering application-driven biological functionalities that were not evolved by nature. Early breakthroughs of cell engineering, which were based on ectopic (over)expression of single sets of transgenes, have already had a revolutionary impact on the biotechnology industry, regenerative medicine and blood transfusion therapies. Now, we require larger-scale, rationally assembled genetic circuits engineered to programme and control various human cell functions with high spatiotemporal precision in order to solve more complex problems in applied life sciences, biomedicine and environmental sciences. This will open new possibilities for employing synthetic biology to advance personalized medicine by converting cells into living therapeutics to combat hitherto intractable diseases.

Promises of Nanotherapeutics in Obesity

The application of nanotechnology to medicine promises a wide range of new tools and possibilities, from earlier diagnostics and improved imaging, to better, more efficient, and more targeted therapies. This emerging field could help address obesity, with advances in drug delivery, nutraceuticals, and genetic and epigenetic therapeutics. Its application to obesity is still largely in the development phase. Here, we review the novel angle of nanotech applied to human consumable products and their specific applications to addressing obesity through nutraceuticals, with respect to benefits and limitations of current nanotechnology methods. Further, we review potential future applications to deliver genetic and epigenetic miRNA therapeutics. Finally, we discuss future directions, including theranostics, combinatory therapy, and personalized medicine.

Synthetic Biology and the Translational Imperative

Advances at the interface between the biological sciences and engineering are giving rise to emerging research fields such as synthetic biology. Harnessing the potential of synthetic biology requires timely and adequate translation into clinical practice. However, the translational research enterprise is currently facing fundamental obstacles that slow down the transition of scientific discoveries from the laboratory to the patient bedside. These obstacles including scarce financial resources and deficiency of organizational and logistic settings are widely discussed as primary impediments to translational research. In addition, a number of socio-ethical considerations inherent in translational research need to be addressed. As the translational capacity of synthetic biology is tightly linked to its social acceptance and ethical approval, ethical limitations may-together with financial and organizational problems-be co-determinants of suboptimal translation. Therefore, an early assessment of such limitations will contribute to proactively favor successful translation and prevent the promising potential of synthetic biology from remaining under-expressed. Through the discussion of two case-specific inventions in synthetic biology and their associated ethical implications, we illustrate the socio-ethical challenges ahead in the process of implementing synthetic biology into clinical practice. Since reducing the translational lag is essential for delivering the benefits of basic biomedical research to society at large and promoting global health, we advocate a moral obligation to accelerating translational research: the "translational imperative."

Light-Controlled Mammalian Cells and Their Therapeutic Applications in Synthetic Biology

The ability to remote control the expression of therapeutic genes in mammalian cells in order to treat disease is a central goal of synthetic biology-inspired therapeutic strategies. Furthermore, optogenetics, a combination of light and genetic sciences, provides an unprecedented ability to use light for precise control of various cellular activities with high spatiotemporal resolution. Recent work to combine optogenetics and therapeutic synthetic biology has led to the engineering of light-controllable designer cells, whose behavior can be regulated precisely and noninvasively. This Review focuses mainly on non-neural optogenetic systems, which are often used in synthetic biology, and their applications in genetic programing of mammalian cells. Here, a brief overview of the optogenetic tool kit that is available to build light-sensitive mammalian cells is provided. Then, recently developed strategies for the control of designer cells with specific biological functions are summarized. Recent translational applications of optogenetically engineered cells are also highlighted, ranging from in vitro basic research to in vivo light-controlled gene therapy. Finally, current bottlenecks, possible solutions, and future prospects for optogenetics in synthetic biology are discussed.

Synthetic gene circuits for the detection, elimination and prevention of disease

In living organisms, naturally evolved sensors that constantly monitor and process environmental cues trigger corrective actions that enable the organisms to cope with changing conditions. Such natural processes have inspired biologists to construct synthetic living sensors and signalling pathways, by repurposing naturally occurring proteins and by designing molecular building blocks de novo, for customized diagnostics and therapeutics. In particular, designer cells that employ user-defined synthetic gene circuits to survey disease biomarkers and to autonomously re-adjust unbalanced pathological states can coordinate the production of therapeutics, with controlled timing and dosage. Furthermore, tailored genetic networks operating in bacterial or human cells have led to cancer remission in experimental animal models, owing to the network's unprecedented specificity. Other applications of designer cells in infectious, metabolic and autoimmune diseases are also being explored. In this Review, we describe the biomedical applications of synthetic gene circuits in major disease areas, and discuss how the first genetically engineered devices developed on the basis of synthetic-biology principles made the leap from the laboratory to the clinic.

Programming gene and engineered-cell therapies with synthetic biology

Gene and engineered-cell therapies promise to treat diseases by genetically modifying cells to carry out therapeutic tasks. Although the field has had some success in treating monogenic disorders and hematological malignancies, current approaches are limited to overexpression of one or a few transgenes, constraining the diseases that can be treated with this approach and leading to potential concerns over safety and efficacy. Synthetic gene networks can regulate the dosage, timing, and localization of gene expression and therapeutic activity in response to small molecules and disease biomarkers. Such "programmable" gene and engineered-cell therapies will provide new interventions for incurable or difficult-to-treat diseases.

Systems-synthetic biology in understanding the complexities and simple devices in immunology

Systems and synthetic biology in the coming era has the ability to manipulate, stimulate and engineer cells to counteract the pathogenic immune response. The inherent biological complexities associated with the creation of a device allow capitalizing the biotechnological resources either by simply administering a recombinant cytokine or just reprogramming the immune cells. The strategy outlined, adopted and discussed may mark the beginning with promising therapeutics based on the principles of synthetic immunology.

Mammalian Synthetic Biology: Engineering Biological Systems

The programming of new functions into mammalian cells has tremendous application in research and medicine. Continued improvements in the capacity to sequence and synthesize DNA have rapidly increased our understanding of mechanisms of gene function and regulation on a genome-wide scale and have expanded the set of genetic components available for programming cell biology. The invention of new research tools, including targetable DNA-binding systems such as CRISPR/Cas9 and sensor-actuator devices that can recognize and respond to diverse chemical, mechanical, and optical inputs, has enabled precise control of complex cellular behaviors at unprecedented spatial and temporal resolution. These tools have been critical for the expansion of synthetic biology techniques from prokaryotic and lower eukaryotic hosts to mammalian systems. Recent progress in the development of genome and epigenome editing tools and in the engineering of designer cells with programmable genetic circuits is expanding approaches to prevent, diagnose, and treat disease and to establish personalized theranostic strategies for next-generation medicines. This review summarizes the development of these enabling technologies and their application to transforming mammalian synthetic biology into a distinct field in research and medicine.

Engineering Mammalian Designer Cells for the Treatment of Metabolic Diseases

Synthetic biology applies engineering principles to biological systems and has significantly advanced the design of synthetic gene circuits that can reprogram cell activities to perform new functions. The ability to engineer mammalian designer cells with robust therapeutic behaviors has brought new opportunities for treating metabolic diseases. In this review, the authors highlight the most recent advances in the development of synthetic designer cells uploaded with open- or closed-loop gene circuits for the treatment of metabolic disorders including diabetes, hypertension, hyperuricemia, and obesity, and discuss the current technologies and future perspectives in applying these designer cells for clinical applications. In the future, more and more rationally designed cells will be constructed and revolutionized to treat a number of metabolic disorders in an intelligent manner.

Sensing and responding to allergic response cytokines through a genetically encoded circuit

While constantly rising, the prevalence of allergies is globally one of the highest among chronic diseases. Current treatments of allergic diseases include the application of anti-histamines, immunotherapy, steroids, and anti-immunoglobulin E (IgE) antibodies. Here we report mammalian cells engineered with a synthetic signaling cascade able to monitor extracellular pathophysiological levels of interleukin 4 and interleukin 13, two main cytokines orchestrating allergic inflammation. Upon activation of transgenic cells by these cytokines, designed ankyrin repeat protein (DARPin) E2_79, a non-immunogenic protein binding human IgE, is secreted in a precisely controlled and reversible manner. Using human whole blood cell culturing, we demonstrate that the mammalian dual T helper 2 cytokine sensor produces sufficient levels of DARPin E2_79 to dampen histamine release in allergic subjects exposed to allergens. Hence, therapeutic gene networks monitoring disease-associated cytokines coupled with in situ production, secretion and systemic delivery of immunomodulatory biologics may foster advances in the treatment of allergies.

The standard treatment for an allergic response is anti-histamines, steroids and anti-IgE antibodies. Here the authors present a genetic circuit that senses IL-4 and IL-13 and responses with DARPin production to bind IgE.

Quorum-Quenching Human Designer Cells for Closed-Loop Control of Pseudomonas aeruginosa Biofilms

Current antibiotics gradually lose their efficacy against chronic Pseudomonas aeruginosa infections due to development of increased resistance mediated by biofilm formation, as well as the large arsenal of microbial virulence factors that are coordinated by the cell density-dependent phenomenon of quorum sensing. Here, we address this issue by using synthetic biology principles to rationally engineer quorum-quencher cells with closed-loop control to autonomously dampen virulence and interfere with biofilm integrity. Pathogen-derived signals dynamically activate a synthetic mammalian autoinducer sensor driving downstream expression of next-generation anti-infectives. Engineered cells were able to sensitively score autoinducer levels from P. aeruginosa clinical isolates and mount a 2-fold defense consisting of an autoinducer-inactivating enzyme to silence bacterial quorum sensing and a bipartite antibiofilm effector to dissolve the biofilm matrix. The self-guided cellular device fully cleared autoinducers, potentiated bacterial antibiotic susceptibility, substantially reduced biofilms, and alleviated cytotoxicity to lung epithelial cells. We believe this strategy of dividing otherwise coordinated pathogens and breaking up their shielded stronghold represents a blueprint for cellular anti-infectives in the postantibiotic era.

Synthetic biology-inspired therapies for metabolic diseases

Our ability to engineer mammalian cells with effective therapeutic behaviors has brought new hope for treating metabolic diseases. Synthetic gene networks have been customized to interface with the host metabolism, discriminate between healthy and diseased states, and respond by producing an adjusted dose of the therapeutic molecule. Such devices have the potential to treat a range of dysfunctions that are simply not addressable using conventional therapies. Recently, the repurposing of native signaling pathways has formed the basis of autonomous therapeutic programs genetically installed in mammalian cells and has greatly expanded the possibilities to effectively tackle metabolic disorders. Here, we outline network topologies that have been successfully validated in animal models of metabolic diseases and discuss future developments that will be important for bringing this technology closer to clinical application.

A Synthetic-Biology-Inspired Therapeutic Strategy for Targeting and Treating Hepatogenous Diabetes

Hepatogenous diabetes is a complex disease that is typified by the simultaneous presence of type 2 diabetes and many forms of liver disease. The chief pathogenic determinant in this pathophysiological network is insulin resistance (IR), an asymptomatic disease state in which impaired insulin signaling in target tissues initiates a variety of organ dysfunctions. However, pharmacotherapies targeting IR remain limited and are generally inapplicable for liver disease patients. Oleanolic acid (OA) is a plant-derived triterpenoid that is frequently used in Chinese medicine as a safe but slow-acting treatment in many liver disorders. Here, we utilized the congruent pharmacological activities of OA and glucagon-like-peptide 1 (GLP-1) in relieving IR and improving liver and pancreas functions and used a synthetic-biology-inspired design principle to engineer a therapeutic gene circuit that enables a concerted action of both drugs. In particular, OA-triggered short human GLP-1 (shGLP-1) expression in hepatogenous diabetic mice rapidly and simultaneously attenuated many disease-specific metabolic failures, whereas OA or shGLP-1 monotherapy failed to achieve corresponding therapeutic effects. Collectively, this work shows that rationally engineered synthetic gene circuits are capable of treating multifactorial diseases in a synergistic manner by multiplexing the targeting efficacies of single therapeutics.

Synthetic Biology-The Synthesis of Biology

Synthetic biology concerns the engineering of man-made living biomachines from standardized components that can perform predefined functions in a (self-)controlled manner. Different research strategies and interdisciplinary efforts are pursued to implement engineering principles to biology. The "top-down" strategy exploits nature's incredible diversity of existing, natural parts to construct synthetic compositions of genetic, metabolic, or signaling networks with predictable and controllable properties. This mainly application-driven approach results in living factories that produce drugs, biofuels, biomaterials, and fine chemicals, and results in living pills that are based on engineered cells with the capacity to autonomously detect and treat disease states in vivo. In contrast, the "bottom-up" strategy seeks to be independent of existing living systems by designing biological systems from scratch and synthesizing artificial biological entities not found in nature. This more knowledge-driven approach investigates the reconstruction of minimal biological systems that are capable of performing basic biological phenomena, such as self-organization, self-replication, and self-sustainability. Moreover, the syntheses of artificial biological units, such as synthetic nucleotides or amino acids, and their implementation into polymers inside living cells currently set the boundaries between natural and artificial biological systems. In particular, the in vitro design, synthesis, and transfer of complete genomes into host cells point to the future of synthetic biology: the creation of designer cells with tailored desirable properties for biomedicine and biotechnology.

Drug delivery with living cells

The field of drug delivery has grown tremendously in the past few decades by developing a wide range of advanced drug delivery systems. An interesting category is cell-based drug delivery, which includes encapsulation of drugs inside cells or attached to the surface and subsequent transportation through the body. Another approach involves genetic engineering of cells to secrete therapeutic molecules in a controlled way. The next-generation systems integrate expertise from synthetic biology to generate therapeutic gene networks for highly advanced sensory and output devices. These developments are very exciting for the drug delivery field and could radically change the way we administer biological medicines to chronically ill patients. This review is covering the use of living cells, either as transport system or production-unit, to deliver therapeutic molecules and bioactive proteins inside the body. It describes a wide range of approaches in cell-based drug delivery and highlights exceptional examples.

Toward a world of theranostic medication: Programming biological sentinel systems for therapeutic intervention

Theranostic systems support diagnostic and therapeutic functions in a single integrated entity and enable precise spatiotemporal control of the generation of therapeutic molecules according to the individual patient's disease state, thereby maximizing the therapeutic outcome and minimizing side effects. These systems can also incorporate reporter systems equipped with a disease-sensing module that can be used to estimate the efficacy of treatment in vivo. Among these reporter systems, biological sentinel systems, such as viruses, bacteria, and mammalian cells, have great potential for use in the development of novel theranostic systems because of their ability to sense a variety of disease markers and secrete various therapeutic molecules. Furthermore, recent advances in biotechnology and synthetic biology have made it possible to treat these biological systems as true programmable entities capable of conducting complex operations, to accurately identify each individual patient's disease state. In this review, we introduce the basic design principles of these rapidly expanding classes of biological sentinel system-based theranostic agents, with a focus on recent advances, and we also discuss potential enabling technologies that can further improve these systems and provide more sophisticated therapeutic interventions in the near future. In addition, we consider the possibility of synergistic use of theranostic agents that use different modalities and discuss the prospects for next-generation theranostic agents.

Engineering Gene Circuits for Mammalian Cell-Based Applications

Synthetic gene switches are basic building blocks for the construction of complex gene circuits that transform mammalian cells into useful cell-based machines for next-generation biotechnological and biomedical applications. Ligand-responsive gene switches are cellular sensors that are able to process specific signals to generate gene product responses. Their involvement in complex gene circuits results in sophisticated circuit topologies that are reminiscent of electronics and that are capable of providing engineered cells with the ability to memorize events, oscillate protein production, and perform complex information-processing tasks. Microencapsulated mammalian cells that are engineered with closed-loop gene networks can be implanted into mice to sense disease-related input signals and to process this information to produce a custom, fine-tuned therapeutic response that rebalances animal metabolism. Progress in gene circuit design, in combination with recent breakthroughs in genome engineering, may result in tailored engineered mammalian cells with great potential for future cell-based therapies.

A synthetic biology-based device prevents liver injury in mice

BACKGROUND & AIMS

The liver performs a panoply of complex activities coordinating metabolic, immunologic and detoxification processes. Despite the liver's robustness and unique self-regeneration capacity, viral infection, autoimmune disorders, fatty liver disease, alcohol abuse and drug-induced hepatotoxicity contribute to the increasing prevalence of liver failure. Liver injuries impair the clearance of bile acids from the hepatic portal vein which leads to their spill over into the peripheral circulation where they activate the G-protein-coupled bile acid receptor TGR5 to initiate a variety of hepatoprotective processes.

METHODS

By functionally linking activation of ectopically expressed TGR5 to an artificial promoter controlling transcription of the hepatocyte growth factor (HGF), we created a closed-loop synthetic signalling network that coordinated liver injury-associated serum bile acid levels to expression of HGF in a self-sufficient, reversible and dose-dependent manner.

RESULTS

After implantation of genetically engineered human cells inside auto-vascularizing, immunoprotective and clinically validated alginate-poly-(L-lysine)-alginate beads into mice, the liver-protection device detected pathologic serum bile acid levels and produced therapeutic HGF levels that protected the animals from acute drug-induced liver failure.

CONCLUSIONS

Genetically engineered cells containing theranostic gene circuits that dynamically interface with host metabolism may provide novel opportunities for preventive, acute and chronic healthcare.

LAY SUMMARY

Liver diseases leading to organ failure may go unnoticed as they do not trigger any symptoms or significant discomfort. We have designed a synthetic gene circuit that senses excessive bile acid levels associated with liver injuries and automatically produces a therapeutic protein in response. When integrated into mammalian cells and implanted into mice, the circuit detects the onset of liver injuries and coordinates the production of a protein pharmaceutical which prevents liver damage.

Implantable synthetic cytokine converter cells with AND-gate logic treat experimental psoriasis

Psoriasis is a chronic inflammatory skin disease characterized by a relapsing-remitting disease course and correlated with increased expression of proinflammatory cytokines, such as tumor necrosis factor (TNF) and interleukin 22 (IL22). Psoriasis is hard to treat because of the unpredictable and asymptomatic flare-up, which limits handling of skin lesions to symptomatic treatment. Synthetic biology-based gene circuits are uniquely suited for the treatment of diseases with complex dynamics, such as psoriasis, because they can autonomously couple the detection of disease biomarkers with the production of therapeutic proteins. We designed a mammalian cell synthetic cytokine converter that quantifies psoriasis-associated TNF and IL22 levels using serially linked receptor-based synthetic signaling cascades, processes the levels of these proinflammatory cytokines with AND-gate logic, and triggers the corresponding expression of therapeutic levels of the anti-inflammatory/psoriatic cytokines IL4 and IL10, which have been shown to be immunomodulatory in patients. Implants of microencapsulated cytokine converter transgenic designer cells were insensitive to simulated bacterial and viral infections as well as psoriatic-unrelated inflammation. The designer cells specifically prevented the onset of psoriatic flares, stopped acute psoriasis, improved psoriatic skin lesions and restored normal skin-tissue morphology in mice. The antipsoriatic designer cells were equally responsive to blood samples from psoriasis patients, suggesting that the synthetic cytokine converter captures the clinically relevant cytokine range. Implanted designer cells that dynamically interface with the patient's metabolism by detecting specific disease metabolites or biomarkers, processing their blood levels with synthetic circuits in real time, and coordinating immediate production and systemic delivery of protein therapeutics may advance personalized gene- and cell-based therapies.

Prolonged Subcutaneous Administration of Oxytocin Accelerates Angiotensin II-Induced Hypertension and Renal Damage in Male Rats

Oxytocin and its receptor are synthesised in the heart and blood vessels but effects of chronic activation of this peripheral oxytocinergic system on cardiovascular function are not known. In acute studies, systemic administration of low dose oxytocin exerted a protective, preconditioning effect in experimental models of myocardial ischemia and infarction. In this study, we investigated the effects of chronic administration of low dose oxytocin following angiotensin II-induced hypertension, cardiac hypertrophy and renal damage. Angiotensin II (40 μg/Kg/h) only, oxytocin only (20 or 100 ng/Kg/h), or angiotensin II combined with oxytocin (20 or 100 ng/Kg/h) were infused subcutaneously in adult male Sprague-Dawley rats for 28 days. At day 7, oxytocin or angiotensin-II only did not change hemodynamic parameters, but animals that received a combination of oxytocin and angiotensin-II had significantly elevated systolic, diastolic and mean arterial pressure compared to controls (P < 0.01). Hemodynamic changes were accompanied by significant left ventricular cardiac hypertrophy and renal damage at day 28 in animals treated with angiotensin II (P < 0.05) or both oxytocin and angiotensin II, compared to controls (P < 0.01). Prolonged oxytocin administration did not affect plasma concentrations of renin and atrial natriuretic peptide, but was associated with the activation of calcium-dependent protein phosphatase calcineurin, a canonical signalling mechanism in pressure overload-induced cardiovascular disease. These data demonstrate that oxytocin accelerated angiotensin-II induced hypertension and end-organ renal damage, suggesting caution should be exercised in the chronic use of oxytocin in individuals with hypertension.

Synthetic Biology--Toward Therapeutic Solutions

Higher multicellular organisms have evolved sophisticated intracellular and intercellular biological networks that enable cell growth and survival to fulfill an organism's needs. Although such networks allow the assembly of complex tissues and even provide healing and protective capabilities, malfunctioning cells can have severe consequences for an organism's survival. In humans, such events can result in severe disorders and diseases, including metabolic and immunological disorders, as well as cancer. Dominating the therapeutic frontier for these potentially lethal disorders, cell and gene therapies aim to relieve or eliminate patient suffering by restoring the function of damaged, diseased, and aging cells and tissues via the introduction of healthy cells or alternative genes. However, despite recent success, these efforts have yet to achieve sufficient therapeutic effects, and further work is needed to ensure the safe and precise control of transgene expression and cellular processes. In this review, we describe the biological tools and devices that are at the forefront of synthetic biology and discuss their potential to advance the specificity, efficiency, and safety of the current generation of cell and gene therapies, including how they can be used to confer curative effects that far surpass those of conventional therapeutics. We also highlight the current therapeutic delivery tools and the current limitations that hamper their use in human applications.

Novel theranostic agents for next-generation personalized medicine: small molecules, nanoparticles, and engineered mammalian cells

Modern medicine is currently undergoing a paradigm shift from conventional disease treatments based on the diagnosis of a generalized disease state to a more personalized, customized treatment model based on molecular-level diagnosis. This uses novel biosensors that can precisely extract disease-related information from complex biological systems. Moreover, with the recent progress in chemical biology, materials science, and synthetic biology, it has become possible to simultaneously conduct diagnosis and targeted therapy (theranostics/theragnosis) by directly connecting the readout of a biosensor to a therapeutic output. These advances pave the way for more advanced and better personalized treatment for intractable diseases with fewer side effects. In this review, we describe recent advances in the development of cutting-edge theranostic agents that contain both diagnostic and therapeutic functions in a single integrated system. By comparing the advantages and disadvantages of each modality, we discuss the future challenges and prospects of developing ideal theranostic agents for the next generation of personalized medicine.