Optical imaging of metabolic dynamics in ALS under methionine regulation.

SIGNIFICANCE: Excessive reactive oxygen species (ROS) in dysfunctional mitochondria, combined with inefficient antioxidant defenses, can drive amyotrophic lateral sclerosis (ALS) progression. L-methionine (Met) can neutralize ROS by modulating metabolism and activating antioxidants; however, its impact on ALS remains unknown. AIM: We aim to investigate the influence of excess Met on cellular metabolism and ROS accumulation and its role in ALS using multimodal optical imaging techniques. APPROACH: We applied deuterium oxide-probed stimulated Raman scattering imaging to study metabolic changes of lipids, proteins, and cytochrome c and two-photon excitation fluorescence imaging to assess mitochondrial redox state (nicotinamide adenine dinucleotide and flavin adenine dinucleotide ratio) in ALS cellular models under excess Met treatment. With three-dimensional (3D) image reconstruction, we investigated morphological changes of lipid droplets (LDs) and stress granules (SGs) in ALS models. RESULTS: Excess Met not only promoted syntheses of lipids and unsaturated lipid membranes but also reduced protein synthesis, cytochrome c oxidation, and oxidative stress. Moreover, 3D image reconstruction showed that LDs increased in volume and number to promote cellular repair, whereas SGs decreased in volume but increased in number in response to reduced cellular stress. CONCLUSIONS: Excess Met offers a protective mechanism against oxidative stress and promotes cellular repair in ALS.