[Glutamine-induced autophagy exacerbates muscle atrophy in cachectic nude mice: a multi-omics analysis]

To clarify whether glutamine induces autophagy to promote skeletal muscle atrophy in cancer cachexia through integrated transcriptomic and metabolomic analyses.

Twenty male BALB/c nude mice were randomized into control and model groups (n=10), and in the latter group cachexia was induced by subcutaneous implantation of CT-26 colon carcinoma cells. Tumor-free body mass and grip strength/body mass ratio of the mice were measured, myofiber transverse diameter was observed using HE staining, and muscle atrophy-related proteins (MuRF1 and atrogin-1) were detected. Transcriptomic and metabolomic analyses were used to identify the differentially expressed genes (DEGs) and differentially expressed metabolites (DEMs), respectively, and the metabolic pathways were mapped. Autophagosomes and gastrocnemius morphology were observed with transmission electron microscopy (TEM), and the autophagic markers (ULK1, LC3, and P62) and signaling pathway proteins (AMPK, FOXO3a, and mTOR) were assayed using Western blotting. The key findings were validated in C2C12 myoblasts treated with glutamine (Gln) and an AMPK inhibitor.

Compared with the control mice, the mice in the model group had significantly decreased tumor-free body mass, grip strength/body mass ratio and myofiber area with elevated atrogin-1 and MuRF1 expressions. The DEGs were mainly enriched in arginine/proline metabolism, AMPK, mTOR, autophagy and FOXO signaling pathways. Metabolomic analysis showed significantly increased glutamine and glutamate in the cachectic muscle. In the tumor-bearing mice, the number of autophagosomes increased significantly with blurred and fragmented myofibrils, upregulated AMPK/FOXO3a pathway proteins and ULK1, and downregulated mTOR pathway proteins and P62. In C2C12 myoblasts, treatment with glutamine obviously promoted autophagy, activated AMPK/FOXO3a signaling and inhibited the mTOR pathway, and these effects were strongly blocked by the AMPK inhibitor.

Glutamine promotes autophagy through activation of the AMPK/FOXO3a signaling axis and suppression of the mTOR pathway, leading to skeletal muscle atrophy in cancer cachexia.