Abstract
The human circadian clock integrates external environmental changes and internal physiological signals to generate natural oscillations of secreted endocrine signals to regulate diverse biological processes. Here, we explore human receptors responsive to molecules displaying in vivo oscillatory patterns and identify melatonin receptor 1A (MTNR1A) as a promising molecular sensor to trigger transgene expression. We engineer a melatonin-inducible gene switch consisting of ectopically expressed MTNR1A linked to an amplifier module utilizing the native Gαs protein-mediated cell signaling cascade, which involves adenylyl cyclase, cAMP, protein kinase A and the cAMP-responsive transcription factor CREB, to drive transgene expression from a synthetic promoter. This system operates within the physiological melatonin concentration range, selectively responding to night-phase levels of the diurnal rhythm, while remaining unresponsive to day-phase levels. Such temporal control suggests its potential for personalized cell- and gene-based therapies requiring once-per-day dosing regimen. As proof-of-concept, we show that alginate-encapsulated engineered cells implanted in C3H/HeJ male mice can translate circadian inputs or clinically licensed MTNR1A agonists into regulated GLP-1 expression as a therapeutic output exclusively secreted during nighttime, highlighting potential as an experimental cell therapy for obesity-dependent type-2 diabetes.