Elevation-associated shifts in plasma metabolite abundance and lung gene expression in the Xizang plateau frog, Nanorana parkeri

Compared to other amphibians, the Xizang plateau frog, Nanorana parkeri, is the highest elevation-dwelling amphibian species known to date (up to 5,100 m), offering a valuable model for understanding ectotherm adaptation to extreme environments. Here, we compared plasma metabolomes and lung transcriptomes of frogs between higher (4,600 m) and lower (3,400 m) elevations. We also assayed key metabolites (glucose, lactate, NADH, β-hydroxybutyrate) in the plasma and inferred the metabolic flux of central metabolic pathways. Plasma metabolomics revealed significant elevation-related differences, identifying 222 differential metabolites. High-elevation frogs exhibited 37% higher glucose but 32% and 33% lower lactate and β-hydroxybutyrate, respectively, alongside reduced glycolytic and fatty acid metabolism fluxes. Lung transcriptomic analysis identified 1,618 differentially expressed genes, with broad down-regulation of glycolysis, TCA cycle, oxidative phosphorylation, fatty acid oxidation, and PPAR signaling in high-elevation frogs, indicating metabolic rate depression. Canonical hypoxia sensors (HIF1A, EGLN1-3) showed no differential expression, but transcription factors (ATF3, JUN, ARNT2) and stress-response pathways (Wnt, MAPK, and G protein-coupled receptor signaling) were up-regulated in high-elevation frogs. Increased expression of fibroblast growth factors and IGFBP2 in high-elevation individuals may indicate vascular remodeling. At higher elevation, the up-regulation of potassium/calcium channels, TRP channels, and aquaporins (AQP1, AQP4) may be linked to ion and water homeostasis. Moreover, higher expression of DNA repair-related genes (RAD18, RAD51), heat shock proteins (HSPB6, HSP40), and adhesion molecules (ADAM22, cadherins) was consistent with enhanced cellular stress tolerance under high-elevation conditions. These results reveal that N. parkeri shows coordinated shifts in metabolite abundance and gene expression associated with higher elevation, providing new insights into molecular mechanisms of ectotherm adaptation to extreme environments.