The cytosolic sialidase Neu2 is degraded by autophagy during myoblast atrophy

Biochim Biophys Acta. 2009 Aug;1790(8):817-28. doi: 10.1016/j.bbagen.2009.04.006. Epub 2009 Apr 14.

Abstract

Background: The sialidase Neu2 is a cytosolic enzyme which is fully expressed in mature muscle myofibers.

Methods: 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.

Results: 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.

General significance: This study demonstrates that Neu2 enzyme degradation occurs in atrophic myotubes via macroautophagy and independently of proteasome activation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Alkalies / metabolism
  • Animals
  • Atrophy
  • Autophagy* / drug effects
  • Cathepsin B / metabolism
  • Cathepsin L
  • Cathepsins / metabolism
  • Cell Line
  • Cysteine Endopeptidases / metabolism
  • Cytosol / drug effects
  • Cytosol / enzymology*
  • Dexamethasone / pharmacology
  • Down-Regulation / drug effects
  • Insulin / pharmacology
  • Lysosomes / drug effects
  • Lysosomes / enzymology
  • Lysosomes / ultrastructure
  • Mice
  • Muscle Fibers, Skeletal / drug effects
  • Muscle Fibers, Skeletal / enzymology*
  • Muscle Fibers, Skeletal / pathology*
  • Muscle Fibers, Skeletal / ultrastructure
  • Neuraminidase / metabolism*
  • Protein Processing, Post-Translational* / drug effects
  • Rats
  • Tumor Necrosis Factor-alpha / pharmacology

Substances

  • Alkalies
  • Insulin
  • Tumor Necrosis Factor-alpha
  • Dexamethasone
  • Neu2 protein, rat
  • Neuraminidase
  • Cathepsins
  • Cysteine Endopeptidases
  • Cathepsin B
  • Cathepsin L
  • Ctsl protein, mouse
  • Ctsl protein, rat