TWEAK causes myotube atrophy through coordinated activation of ubiquitin-proteasome system, autophagy, and caspases

Area of Science:

• Biochemistry
• Cell Biology
• Physiology

Background:

• Tumor necrosis factor-like weak inducer of apoptosis (TWEAK) is implicated in skeletal muscle wasting during catabolic states.
• The precise molecular mechanisms driving TWEAK-induced muscle proteolysis are not fully elucidated.

Purpose of the Study:

• To investigate the roles of the ubiquitin-proteasome system, autophagy, and caspases in TWEAK-mediated skeletal muscle atrophy.
• To identify key molecular players and signaling pathways involved in TWEAK-induced muscle protein degradation.

Main Methods:

• Utilized C2C12 myotubes as an in vitro model system.
• Applied TWEAK treatment, proteasome inhibitors (MG132, lactacystin), autophagy inhibitors, and RNA interference (MuRF1 knockdown).
• Assessed myosin heavy chain (MyHC) ubiquitination and degradation, myotube atrophy, E3 ligase expression (MuRF1), autophagy-related molecules, caspase activity, and NF-κB activation.

Main Results:

• TWEAK treatment increased MyHC ubiquitination and MuRF1 expression, leading to MyHC degradation and myotube atrophy.
• Proteasome inhibition or MuRF1 knockdown prevented TWEAK-induced MyHC loss and atrophy.
• TWEAK elevated autophagy-related molecules, and autophagy inhibition preserved MyHC levels.
• Caspase activation was observed, and caspase inhibition attenuated TWEAK-induced MyHC loss and reduced myotube diameter.
• NF-κB was critical for TWEAK-induced MuRF1 and Beclin1 expression, with caspases partially mediating NF-κB activation.

Conclusions:

• TWEAK induces skeletal muscle wasting through coordinated activation of the ubiquitin-proteasome system, autophagy, and caspases.
• NF-κB signaling is essential for TWEAK-induced expression of key muscle-wasting genes (MuRF1, Beclin1).
• Caspase activity contributes to NF-κB activation, highlighting a complex interplay in TWEAK-driven muscle catabolism.