Imaging the uptake of specific amino acids by deuterium labeling and stimulated Raman scattering

Amino acids, renowned as essential metabolic building blocks, play an important role in fundamental processes such as protein synthesis, while the non-invasive visualization of their subcellular distribution has remained a challenge. In this study, we introduce a method for monitoring the intracellular uptake of specific amino acids, including Methionine, within live cells and tissues using stimulated Raman scattering (SRS) microscopy combined with deuterium labeling. Our approach employs a straightforward background subtraction technique to detect the SRS signal of methionine enriched with eight deuterium atoms (d8-Met). Notably, our findings indicate that d8-Met metabolism appears to be minimally invasive and yields a more robust signal when compared to the previously employed alkyne-labeled methionine analog, homopropargyl glycine (Hpg). This enhanced performance can be attributed to the minimally disruptive labeling characteristics of deuterium, making it a promising biorthogonal probe with potential applications for long-term imaging. Furthermore, we extend the applicability of this technique by introducing a synthetic diet containing d8-Met to living Drosophila, enabling us to visualize systemic incorporation of d8-Met. Our imaging efforts encompass various dissected tissues, including the brain, wing disc, fat body, and gut, revealing systemic integration within the organism. These results unveil the capability of SRS imaging to discern previously unseen variations in methionine distribution at a subcellular level within tissues, shedding light on cell-to-cell heterogeneity. In conclusion, d8-Met and analogous deuterated biomolecules hold significant potential for investigating metabolism and molecular fate at subcellular resolutions.