Integration of Metabolomics and Transcriptomics to Reveal the Metabolic Characteristics of Exercise-Improved Bone Mass

1) Background: Exercise is effective in promoting and maintaining bone mass. The aim of this study was to detect the exercise-induced metabolic changes in bone tissue of zebrafish. (2) Methods: Thirty-eight zebrafish (Danio rerio, six months old) were analyzed. The exercise group (n = 19) received 8 weeks of counter-current swimming training. The control group (n = 19) was not subjected to exercise. Mineralization was quantified, and alkaline phosphatase (Alp) and antitartrate acid phosphatase (Trap) activities were estimated (n = 12). The metabolomics (n = 12) and transcriptomics (n = 14) data of bone tissue were used for the integration analyses. (3) Results: The results showed that the exercise training improved the bone mineralization of zebrafish, e.g., the exercise group (5.74 x 10(4) +/- 7.63 +/- 10(3)) had a higher mean optical density than the control group (5.26 x 10(4) +/- 8.56 +/- 10(3), p = 0.046) for the caudal vertebrae. The amount of mineralized matrix in scales of the exercised zebrafish was also higher (0.156 +/- 0.012 vs. 0.102 +/- 0.003, p = 0.005). Both histological staining and biochemical analysis revealed increased Alp activity (0.81 +/- 0.26 vs. 0.76 +/- 0.01, p = 0.002) and decreased Trap activity (1.34 +/- 0.01 vs. 1.36 +/- 0.01, p = 0.005) in the exercise group. A total of 103 different metabolites (DMs, VIP >= 1, fold change (FC) >= 1.20 or <= 0.83, p < 0.050) were identified. Alanine, aspartate and glutamate metabolism, fi-alanine metabolism, pyrimidine metabolism, and pantothenate and CoA biosynthesis were the significantly enriched metabolic pathways (p < 0.050). A total of 35 genes (q <= 0.050 (BH), |Log2FC| >= 0.5) were coenriched with the 103 DMs in the four identified pathways. Protein-protein interaction network analysis of the 35 genes showed that entpd3, entpd1, and cmpk2 were the core genes. (4) Conclusions: The results of this study suggest that alanine, aspartate and glutamate metabolism, fi-alanine metabolism, pyrimidine metabolism, and pantothenate and CoA biosynthesis contributed to exercise-induced improvements in bone mass.