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.