Development of a Biosensor for Real-Time Detection of GPCR Signaling in Response to Mechanical Stimuli via Red Fluorescence
Background
Cells are constantly exposed to various physical forces such as shear stress from blood flow, changes in blood pressure, and tissue expansion, in addition to external chemicals. The approximately 800 types of G protein-coupled receptors (GPCRs) in the human genome serve as the central axis of cellular signaling and are known to sense physical stimuli in addition to chemical ligands. Receptors on the surface of vascular endothelial cells or cardiomyocytes receive mechanical forces to regulate blood pressure and induce tissue remodeling.
However, the mechanism by which receptors sense external physical tension and transmit signals into the cell has long remained unclear. Existing fluorescence resonance energy transfer (FRET) sensors exhibited structural limitations, including low signal-to-noise ratios and slow response times of several seconds or more. Phototoxicity in the short-wavelength visible light region and reduced tissue penetration also hinder long-term live biological observation. There was an urgent need for a new measurement tool capable of tracking receptor conformational changes in milliseconds at the moment physical stimuli occur.
Key Findings
Researchers designed 'mechanoLight,' a genome-encoded biosensor that emits red fluorescent signals in real-time upon receiving mechanical stimuli. The structure involves inserting a circularly permuted red fluorescent protein into the third intracellular loop (ICL3) of the mechanosensitive Angiotensin II Type 1 receptor (AT1R). When physical tension is applied to the cell membrane, subtle twisting of the transmembrane helical structure changes the electrostatic environment around the fluorescent chromophore, immediately amplifying the red fluorescence.
Experimental results showed that mechanoLight recorded a fluorescence intensity increase of over 140% (ΔF/F₀ > 1.4) compared to the baseline within just 150 milliseconds (ms) after the application of mechanical stimuli. Considering that the fluorescence change rate of existing FRET-based complex sensors remained at the 15–20% level, this represents a signal sensitivity exceeding sevenfold. Because it absorbs light at a wavelength of 560 nanometers (nm) and emits red fluorescence in the 610 nm region, it minimizes interference from the cell's intrinsic autofluorescence. Analysis shows that simultaneous real-time tracking of multiple signals is possible even when injected into cells with green calcium indicators, as there is no wavelength overlap.
It also excels in quantitative analysis capabilities based on the physical nature of mechanical stimuli. When shear stress was applied stepwise to vascular endothelial cells from 0.5 dyn/cm² to 25 dyn/cm², a linear increase in fluorescence proportional to the force intensity was observed. The activation kinetics caused by physical tension showed a distinctly different pattern from the structural changes occurring upon the administration of chemical agonists. This effectively demonstrates through imaging that physical external forces trigger biased signals that preferentially stimulate the β-arrestin axis instead of the classical G-protein pathway.
Significance and Outlook
This technology, which combines mechanobiology and receptor pharmacology, is regarded as a tool that will change the paradigm of mechanotransduction research. It opens a way to directly identify what molecular modifications GPCRs undergo in pathological physical environments, such as vascular thickening in hypertensive patients, turbulent blood flow in atherosclerotic lesions, and cardiomyocyte overstretching in heart failure. Beyond the cardiovascular system, it is expected to be widely utilized in studying microenvironments where changes in physical pressure promote cancer cell metastasis.
Additional verification challenges for in vivo application remain. To stably observe deep biological tissues for extended periods within a beating heart or inside microcirculation vessels, beyond the cultured cell environment, combination technology with two-photon microscopy is essential. Further protein engineering optimization to minimize the potential impact of fluorescent protein binding on the receptor's intrinsic tertiary structure or natural ligand affinity remains an outstanding challenge.
Proceedings of the National Academy of Sciences, Volume 123, Issue 43, October 2026. SignificanceG protein–coupled receptors (GPCRs) respond to diverse extracellular signals, yet how they sense and transduce mechanical stimuli remains poorly understood. Here, we develop mechanoLight, a red fluorescent biosensor that directly visualizes ...
In drug development, mechanoLight is directly applied to a high-throughput screening (HTS) platform for selecting biased agonists or mechanosensitive blockers that respond to mechanical stimuli. Loading mechanoLight into an organ-on-a-chip system that mimics the shear stress experienced by vascular endothelial cells allows for the immediate determination, via fluorescent signals, of how selectively drug candidates inhibit the excessive response of vasoconstriction receptors under physical blood flow stress. It is expected to serve as an alternative that significantly accelerates the discovery of cardiovascular therapeutics that selectively block pathological vascular wall remodeling without inducing increased blood pressure.