Fingerprint Stimulated Raman Scattering Imaging Reveals Retinoid Coupling Lipid Metabolism and Survival.

Retinoids play critical roles in development, immunity, and lipid metabolism, and their deficiency leads to various human disorders. Yet, tools for sensing retinoids in vivo are lacking, which limits the understanding of retinoid distribution, dynamics and functions in living organisms. Here, using hyperspectral stimulated Raman scattering microscopy, we discover a previously unknown cytoplasmic store of retinoids in Caenorahbditis elegans. Following the temporal dynamics of retinoids, we reveal that their levels are positively correlated with fat storage, and their supplementation slows down fat loss during starvation. We also discover that retinoids promote fat unsaturation in response to high-glucose stress, and improve organism survival. Together, our studies report a new method for tracking the spatiotemporal dynamics of retinoids in living organisms, and suggest the crucial roles of retinoids in maintaining metabolic homeostasis and enhancing organism fitness upon developmental and dietary stresses.