Respiring Saccharomyces cerevisiae cells respond to a sudden increase in glucose concentration by a pronounced drop of their adenine nucleotide content. Transient accumulation of the purine salvage pathway intermediate inosine accounts for the apparent loss of adenine nucleotides.Inosine formation in response to perturbations of cellular energy balance depends on the presence of a fermentable carbon source. Under respiratory conditions, AMP accumulates instead and no inosine is formed.Conversion of AXPs into inosine is facilitated by AMP deaminase, Amd1, and IMP-specific 5'-nucleotidase, Isn1. Inosine recycling into the AXP pool is facilitated by the purine nucleoside phosphorylase, Pnp1, and joint action of the phosphoribosyltransferases, Hpt1 and Xpt1.Impaired inosine formation results in altered metabolite pool dynamics in response to glucose addition, but does not change glycolytic flux. However, mutants blocked in inosine formation exhibit delayed growth acceleration after glucose addition.

Diet-induced obesity is a lifestyle-associated medical condition that increases the risk of developing cardiovascular disease, type 2 diabetes and certain types of cancer. Here we report the design of a closed-loop genetic circuit that constantly monitors blood fatty acid levels in the setting of diet-associated hyperlipidemia and coordinates reversible and adjustable expression of the clinically licensed appetite-suppressing peptide hormone pramlintide. Grafting of the peroxisome proliferator-activated receptor-α onto the phloretin-responsive repressor TtgR produces a synthetic intracellular lipid-sensing receptor (LSR) that reversibly induces chimeric TtgR-specific promoters in a fatty acid-adjustable manner. Mice with diet-induced obesity in which microencapsulated cells engineered for LSR-driven expression of pramlintide are implanted show significant reduction in food consumption, blood lipid levels and body weight when put on a high-fat diet. Therapeutic designer circuits that monitor levels of pathologic metabolites and link these with the tailored expression of protein pharmaceuticals may provide new opportunities for the treatment of metabolic disorders.

Synthetic biology has significantly advanced the design of synthetic trigger-controlled devices that can reprogram mammalian cells to interface with complex metabolic activities. In the brain, the neurotransmitter dopamine coordinates communication with target neurons via a set of dopamine receptors that control behavior associated with reward-driven learning. This dopamine transmission has recently been suggested to increase central sympathetic outflow, resulting in plasma dopamine levels that correlate with corresponding brain activities. By functionally rewiring the human dopamine receptor D1 (DRD1) via the second messenger cyclic adenosine monophosphate (cAMP) to synthetic promoters containing cAMP response element-binding protein 1 (CREB1)-specific cAMP-responsive operator modules, we have designed a synthetic dopamine-sensitive transcription controller that reversibly fine-tunes specific target gene expression at physiologically relevant brain-derived plasma dopamine levels. Following implantation of circuit-transgenic human cell lines insulated by semipermeable immunoprotective microcontainers into mice, the designer device interfaced with dopamine-specific brain activities and produced a systemic expression response when the animal's reward system was stimulated by food, sexual arousal, or addictive drugs. Reward-triggered brain activities were able to remotely program peripheral therapeutic implants to produce sufficient amounts of the atrial natriuretic peptide, which reduced the blood pressure of hypertensive mice to the normal physiologic range. Seamless control of therapeutic transgenes by subconscious behavior may provide opportunities for treatment strategies of the future.