Single-Cell Transcriptomics and Metabolomics Reveal Glutamate Dehydrogenase as a Central Regulator of Nitrogen Metabolic Remodeling During Alkalinity Adaptation in Crustaceans.

Alkaline environments disrupt ammonia excretion and challenge nitrogen metabolism in aquatic invertebrates, but the underlying cellular mechanisms remain unclear. To elucidate the adaptive mechanisms of crustaceans in highly alkaline environments, the responses of Macrobrachium hainanense to acute carbonate alkalinity stress are characterized using single-cell RNA sequencing. High alkalinity inhibits normal ammonia excretion, leading to ammonia accumulation in the hemolymph, gill injury, mitochondrial dysfunction, and elevated oxidative stress. Marked heterogeneous remodeling occurs across distinct cell populations; pillar cells, nephrocytes, and semi-granulocytes play primary roles in nitrogen metabolic regulation, acid-base homeostasis, and immune defense, respectively. Further analyses identify glutamate dehydrogenase (GDH) as a key regulator of alkalinity adaptation. Inhibition of GDH significantly reduces alkaline tolerance, exacerbating tissue damage and metabolic disturbances while impairing ATP maintenance and inducing mitochondrial dysfunction under alkaline stress. Furthermore, GDH suppression inhibits urea metabolism while enhancing purine catabolism, indicating an adaptive shift in nitrogen metabolic strategy. This study provides a single-cell resolution of crustacean alkalinity adaptation and identifies GDH-mediated metabolic remodeling as a determinant of the environmental stress response. These findings offer theoretical insights into the regulatory mechanisms underlying stress adaptation in invertebrates.