Fully Autonomous Diffusion-Based Reporters for MRI
In 2016, we led the development of a new class of genetic reporters for MRI based on aquaporins, channel proteins that facilitate water exchange across cell membranes. Unlike normal cells, where plasma membranes restrict water diffusion, cells engineered to express aquaporins allow for free (and safe) transmembrane exchange of water molecules, resulting in increased net diffusivity that can be visualized using diffusion-weighted imaging, a widely used MRI technique. By using aquaporins as a starting point and integrating synthetic biology, diffusion biophysics, protein engineering, and chemical biology, we aim to discover new (and often unorthodox) solutions to the decades-long challenges of creating specific, sensitive, and biologically responsive MRI reporters.​
Ultrasensitive Dual-Gene Reporters for MRI
A persistent challenge in molecular MRI is the lack of reporters with sufficient cellular sensitivity to observe critical biological processes involving sparse cell populations, such as metastasis, cancer stemness, and immune cell states. To address this challenge, we pursue the development of ultrasensitive genetic reporters that operate through the co-expression of aquaporins with membrane proteins that facilitate the transport of paramagnetic metals or metal complexes into cells. The metal-transporting protein renders cells "MRI-visible" by accumulating paramagnetic contrast agents, which interact with water molecules, thereby increasing their magnetic relaxation rate. Concurrently, aquaporins amplify the resultant MRI signals by allowing the intracellularly accumulated metals to interact with a greater number of water molecules than in the native environment, where water exchange is limited. Presently, we are endeavoring to implement this system for imaging the cell states and tracking immune cells using MRI.
Programmable Genetically Encoded Biosensors
​The advent of fluorescent protein (FP) engineering revolutionized biological research, yielding a vast array of genetically encoded fluorescent sensors that are used in numerous imaging applications to monitor biological events with molecular precision. Unlike optical imaging, which benefits from universal reporter motifs (e.g., GFP and luciferase) and broadly adaptable engineering strategies (e.g., FRET and circular permutation) to create hundreds of diverse genetic indicators, MRI lacks both versatile reporter templates and generalized sensor engineering strategies. Consequently, the creation of genetically encoded MRI sensors for each new target typically necessitates bespoke, capital-, and time-intensive engineering. To date, the repertoire of genetically encoded MRI sensors remains critically limited to approximately 4-5 analytes, a stark contrast to the hundreds available for fluorescence – despite both modalities seeing their first reporter proteins emerge concurrently. To overcome this decades-long bottleneck, we develop methods to create truly modular biosensors that can be easily and rapidly reconfigured to detect diverse biological targets using MRI, thereby eliminating the need for laborious de novo customization for each new application.