Mingqi Xie

β-cell–mimetic designer cells provide closed-loop glycemic control

Engineering cells to regulate glucose Diabetes mellitus affects hundreds of millions of people worldwide. Blood glucose levels are chronically deregulated in diabetics, and this can lead to many serious disorders, including cardiovascular disease and renal failure. Xie et al. engineered a synthetic circuit into human cells that can sense the glucose concentration and respond to correct deregulation. Implants containing designer cells improved glucose regulation in diabetic mice. Science, this issue p. 1296 A synthetic circuit provides effective glucose regulation by designer mammalian cells in diabetic mice. Chronically deregulated blood-glucose concentrations in diabetes mellitus result from a loss of pancreatic insulin-producing β cells (type 1 diabetes, T1D) or from impaired insulin sensitivity of body cells and glucose-stimulated insulin release (type 2 diabetes, T2D). Here, we show that therapeutically applicable β-cell–mimetic designer cells can be established by minimal engineering of human cells. We achieved glucose responsiveness by a synthetic circuit that couples glycolysis-mediated calcium entry to an excitation-transcription system controlling therapeutic transgene expression. Implanted circuit-carrying cells corrected insulin deficiency and self-sufficiently abolished persistent hyperglycemia in T1D mice. Similarly, glucose-inducible glucagon-like peptide 1 transcription improved endogenous glucose-stimulated insulin release and glucose tolerance in T2D mice. These systems may enable a combination of diagnosis and treatment for diabetes mellitus therapy.

Self-adjusting synthetic gene circuit for correcting insulin resistance

By using tools from synthetic biology, sophisticated genetic devices can be assembled to reprogram mammalian cell activities. Here, we demonstrate that a self-adjusting synthetic gene circuit can be designed to sense and reverse the insulin-resistance syndrome in different mouse models. By functionally rewiring the mitogen-activated protein kinase (MAPK) signalling pathway to produce MAPK-mediated activation of the hybrid transcription factor TetR-ELK1, we assembled a synthetic insulin-sensitive transcription-control device that self-sufficiently distinguished between physiological and increased blood insulin levels and correspondingly fine-tuned the reversible expression of therapeutic transgenes from synthetic TetR-ELK1-specific promoters. In acute experimental hyperinsulinemia, the synthetic insulin-sensing designer circuit reversed the insulin-resistance syndrome by coordinating expression of the insulin-sensitizing compound adiponectin. Engineering synthetic gene circuits to sense pathologic markers and coordinate the expression of therapeutic transgenes may provide opportunities for future gene- and cell-based treatments of multifactorial metabolic disorders.

A synthetic biology-based device prevents liver injury in mice

Graphical abstract

Smartphone-controlled optogenetically engineered cells enable semiautomatic glucose homeostasis in diabetic mice

Optogenetically engineered cells maintain blood glucose homeostasis in mice by semiautonomous, wirelessly regulated exposure to far-red light. Wireless diabetes control? There’s an app for that In an elegant feat of synthetic biology, Shao et al. were able to remotely control release of glucose-lowering hormones by engineered cells implanted into diabetic mice. These designer cells were transfected with optogenetic circuits, which enabled them to produce the hormones in response to far-red light. A smartphone could adjust far-red light intensity and duration with the help from a control box. Implanting hydrogel capsules containing both engineered cells and light-emitting diode light sources provided a semiautonomous system that maintained glucose homeostasis over several weeks in the diabetic mice. This study illuminates the potential of cell-based therapies. With the increasingly dominant role of smartphones in our lives, mobile health care systems integrating advanced point-of-care technologies to manage chronic diseases are gaining attention. Using a multidisciplinary design principle coupling electrical engineering, software development, and synthetic biology, we have engineered a technological infrastructure enabling the smartphone-assisted semiautomatic treatment of diabetes in mice. A custom-designed home server SmartController was programmed to process wireless signals, enabling a smartphone to regulate hormone production by optically engineered cells implanted in diabetic mice via a far-red light (FRL)–responsive optogenetic interface. To develop this wireless controller network, we designed and implanted hydrogel capsules carrying both engineered cells and wirelessly powered FRL LEDs (light-emitting diodes). In vivo production of a short variant of human glucagon-like peptide 1 (shGLP-1) or mouse insulin by the engineered cells in the hydrogel could be remotely controlled by smartphone programs or a custom-engineered Bluetooth-active glucometer in a semiautomatic, glucose-dependent manner. By combining electronic device–generated digital signals with optogenetically engineered cells, this study provides a step toward translating cell-based therapies into the clinic.

Antagonistic control of a dual-input mammalian gene switch by food additives

Synthetic biology has significantly advanced the design of mammalian trigger-inducible transgene-control devices that are able to programme complex cellular behaviour. Fruit-based benzoate derivatives licensed as food additives, such as flavours (e.g. vanillate) and preservatives (e.g. benzoate), are a particularly attractive class of trigger compounds for orthogonal mammalian transgene control devices because of their innocuousness, physiological compatibility and simple oral administration. Capitalizing on the genetic componentry of the soil bacterium Comamonas testosteroni, which has evolved to catabolize a variety of aromatic compounds, we have designed different mammalian gene expression systems that could be induced and repressed by the food additives benzoate and vanillate. When implanting designer cells engineered for gene switch-driven expression of the human placental secreted alkaline phosphatase (SEAP) into mice, blood SEAP levels of treated animals directly correlated with a benzoate-enriched drinking programme. Additionally, the benzoate-/vanillate-responsive device was compatible with other transgene control systems and could be assembled into higher-order control networks providing expression dynamics reminiscent of a lap-timing stopwatch. Designer gene switches using licensed food additives as trigger compounds to achieve antagonistic dual-input expression profiles and provide novel control topologies and regulation dynamics may advance future gene- and cell-based therapies.

Synthetic biology — application-oriented cell engineering

Synthetic biology applies engineering principles to biological systems and reprograms living cells to perform novel and improved functions. In this review, we first provide an update of common tools and design principles that enable user-defined control of mammalian cell activities with spatiotemporal precision. Next, we demonstrate some examples of how engineered mammalian cells can be developed towards biomedical solutions in the context of real-world problems.

Cosmetics-triggered percutaneous remote control of transgene expression in mice

Synthetic biology has significantly advanced the rational design of trigger-inducible gene switches that program cellular behavior in a reliable and predictable manner. Capitalizing on genetic componentry, including the repressor PmeR and its cognate operator OPmeR, that has evolved in Pseudomonas syringae pathovar tomato DC3000 to sense and resist plant-defence metabolites of the paraben class, we have designed a set of inducible and repressible mammalian transcription-control devices that could dose-dependently fine-tune transgene expression in mammalian cells and mice in response to paraben derivatives. With an over 60-years track record as licensed preservatives in the cosmetics industry, paraben derivatives have become a commonplace ingredient of most skin-care products including shower gels, cleansing toners and hand creams. As parabens can rapidly reach the bloodstream of mice following topical application, we used this feature to percutaneously program transgene expression of subcutaneous designer cell implants using off-the-shelf commercial paraben-containing skin-care cosmetics. The combination of non-invasive, transdermal and orthogonal trigger-inducible remote control of transgene expression may provide novel opportunities for dynamic interventions in future gene and cell-based therapies.

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.

Mammalian designer cells: Engineering principles and biomedical applications

Biotechnology is a widely interdisciplinary field focusing on the use of living cells or organisms to solve established problems in medicine, food production and agriculture. Synthetic biology, the science of engineering complex biological systems that do not exist in nature, continues to provide the biotechnology industry with tools, technologies and intellectual property leading to improved cellular performance. One key aspect of synthetic biology is the engineering of deliberately reprogrammed designer cells whose behavior can be controlled over time and space. This review discusses the most commonly used techniques to engineer mammalian designer cells; while control elements acting on the transcriptional and translational levels of target gene expression determine the kinetic and dynamic profiles, coupling them to a variety of extracellular stimuli permits their remote control with user‐defined trigger signals. Designer mammalian cells with novel or improved biological functions not only directly improve the production efficiency during biopharmaceutical manufacturing but also open the door for cell‐based treatment strategies in molecular and translational medicine. In the future, the rational combination of multiple sets of designer cells could permit the construction and regulation of higher‐order systems with increased complexity, thereby enabling the molecular reprogramming of tissues, organisms or even populations with highest precision.

Treatment of chronic pain by designer cells controlled by spearmint aromatherapy

Current treatment options for chronic pain are often associated with dose-limiting toxicities, or lead to drug tolerance or addiction. Here, we describe a pain management strategy, based on cell-engineering principles and inspired by synthetic biology, consisting of microencapsulated human designer cells that produce huwentoxin-IV (a safe and potent analgesic peptide that selectively inhibits the pain-triggering voltage-gated sodium channel NaV1.7) in response to volatile spearmint aroma and in a dose-dependent manner. Spearmint sensitivity was achieved by ectopic expression of the R-carvone-responsive olfactory receptor OR1A1 rewired via an artificial G-protein deflector to induce the expression of a secretion-engineered and stabilized huwentoxin-IV variant. In a model of chronic inflammatory and neuropathic pain, mice bearing the designer cells showed reduced pain-associated behaviour on oral intake or inhalation-based intake of spearmint essential oil, and absence of cardiovascular, immunogenic and behavioural side effects. Our proof-of-principle findings indicate that therapies based on engineered cells can achieve robust, tunable and on-demand analgesia for the long-term management of chronic pain.Cells engineered to produce an analgesic in response to spearmint aroma and implanted in mouse models of chronic pain reduce the pain-associated behaviour after oral intake of spearmint essential oil with no adverse effects.