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Medical AI Inquiry: You was designed to assist in medical decision-making based on the provided user questions. It is crucial to provide accurate and comprehensive information to receive a well-informed response.  Labels: BACKGROUND, METHODS, RESULTS. Meshes: Alkalies, Animals, Atrophy, Autophagy, Cathepsin B, Cathepsin L, Cathepsins, Cell Line, Cysteine Endopeptidases, Cytosol, Dexamethasone, Down-Regulation, Insulin, Lysosomes, Mice, Muscle Fibers, Skeletal, Neuraminidase, Protein Processing, Post-Translational, Rats, Tumor Necrosis Factor-alpha.
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Is the cytosolic sialidase Neu2 degraded by autophagy during myoblast atrophy? Context: The sialidase Neu2 is a cytosolic enzyme which is fully expressed in mature muscle myofibers. To investigate Neu2 expression during muscle atrophy, we employed an in vitro model consisting of terminally differentiated C2C12 myotubes exposed to different pro-atrophic stimuli that triggered catabolic pathways involved in proteasome activation or autophagy. Neu2 expression was unchanged in myotubes treated with TNF-alpha, a cytokine known to activate the proteasome. However, Neu2 transcript levels and enzymatic activity were downregulated in starved or dexamethasone-treated myotubes that showed proteosomal activation and several hallmarks of macroautophagy, such as formation of autophagosomes, the accumulation of LC3 dots and bulk degradation of long-lived proteins. Neu2 activity and protein levels were rescued upon cotreatment with the lysosomotropic agent NH4Cl, the autophagy inhibitor 3-methyladenine or cathepsin inhibitors, as well as by insulin administration, but were unaffected upon pharmacological inhibition of the proteasome. Moreover, HA- or GST-Neu2 recombinant fusion proteins were rapidly degraded in vitro by purified cathepsin L and B. Overall, we may conclude that Neu2 is degraded by lysosomal enzymes in myotubes undergoing autophagy-mediated atrophy.
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This study demonstrates that Neu2 enzyme degradation occurs in atrophic myotubes via macroautophagy and independently of proteasome activation. Final Decision: yes