ITCH ‐Mediated Ubiquitination and Degradation of THBS1 : A Key Mechanism for Enhancing Mitochondrial Biogenesis and Alleviating Mouse Skeletal Muscle Atrophy

AIM: Skeletal muscle atrophy is tightly associated with maladaptive alterations in mitochondrial function and morphology. Itchy E3 ubiquitin-protein ligase (ITCH) modulates mitochondria, and thrombospondin 1 (THBS1) positively regulates muscle atrophy, but their roles in muscle atrophy are unclear. METHODS: A muscle atrophy model was established in C57BL/6 mice via daily intraperitoneal injection of dexamethasone (Dex, 20 mg/kg). ITCH overexpression in skeletal muscle was achieved by adeno-associated virus serotype 9 injection. C2C12 cells were treated with 50 μM Dex to mimic in vitro muscle atrophy. Skeletal muscle atrophy in mice was evaluated using hematoxylin-eosin staining and immunofluorescence staining. Mitochondrial damage was assessed via transmission electron microscopy, succinate dehydrogenase staining, and JC-1 staining. Immunoprecipitation-liquid chromatography/mass spectrometry, molecular docking, and co-immunoprecipitation were used to investigate the interaction between ITCH and THBS1. Phosphoproteomics analysis was performed to detect the THBS1 downstream proteins. RESULTS: Dex treatment downregulated ITCH expression in skeletal muscle. ITCH overexpression increased body weight, muscle mass, and muscle strength, downregulated the expression of atrophy-related genes (Atrogin-1, Mstn, MuRF-1), and promoted mitochondrial biogenesis. The results of the C2C12 cells were consistent with those obtained in vivo. Proteomic profiling and Co-IP confirmed ITCH-THBS1 interaction and subsequent THBS1 ubiquitination. THBS1 knockdown reduced the expression of Atrogin-1 and MuRF-1 and inhibited the phosphorylation of JUN and Map3k7, whereas THBS1 overexpression reversed the ITCH-mediated improvement in mitochondrial biogenesis. CONCLUSION: ITCH enhances mitochondrial biogenesis and mitigates Dex-induced muscle atrophy by promoting the ubiquitin-dependent degradation of THBS1 and subsequent inhibition of downstream JUN/Map3k7 phosphorylation.