Mechanism suppressing glycogen synthesis in neurons and its demise in progressive myoclonus epilepsy.

Abstract

Glycogen synthesis is normally absent in neurons. However, inclusion bodies resembling abnormal glycogen accumulate in several neurological diseases, particularly in progressive myoclonus epilepsy or Lafora disease. We show here that mouse neurons have the enzymatic machinery for synthesizing glycogen, but that it is suppressed by retention of muscle glycogen synthase (MGS) in the phosphorylated, inactive state. This suppression was further ensured by a complex of laforin and malin, which are the two proteins whose mutations cause Lafora disease. The laforin-malin complex caused proteasome-dependent degradation both of the adaptor protein targeting to glycogen, PTG, which brings protein phosphatase 1 to MGS for activation, and of MGS itself. Enforced expression of PTG led to glycogen deposition in neurons and caused apoptosis. Therefore, the malin-laforin complex ensures a blockade of neuronal glycogen synthesis even under intense glycogenic conditions. Here we explain the formation of polyglucosan inclusions in Lafora disease by demonstrating a crucial role for laforin and malin in glycogen synthesis.

• Authors: David Vilchez, Susana Ros, Daniel Cifuentes, Lluís Pujadas, Jordi Vallès, Belén García-Fojeda, Olga Criado-García, Elena Fernández-Sánchez, Iria Medraño-Fernández, Jorge Domínguez, Mar García-Rocha, Eduardo Soriano, Santiago Rodríguez de Córdoba, Joan J Guinovart
• Journal: Nature neuroscience (Nat Neurosci) Vol. 10 Issue 11 Pg. 1407-13 (Nov 2007) ISSN: 1097-6256 [Print] United States
• PMID: 17952067 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Carrier Proteins
• Glial Fibrillary Acidic Protein
• Tubulin
• beta3 tubulin, mouse
• Glycogen
• NHLRC1 protein, human
• Ubiquitin-Protein Ligases
• Glycogen Phosphorylase
• Glycogen Synthase
• Protein Tyrosine Phosphatases, Non-Receptor
• EPM2A protein, human

Topics

• Animals
• Apoptosis (physiology)
• Astrocytes (physiology)
• Carrier Proteins (pharmacology)
• Cells, Cultured
• Cerebral Cortex (cytology)
• Embryo, Mammalian
• Gene Expression Regulation (drug effects, physiology)
• Glial Fibrillary Acidic Protein (metabolism)
• Glycogen (metabolism)
• Glycogen Phosphorylase (metabolism)
• Glycogen Synthase (metabolism)
• Humans
• In Situ Nick-End Labeling (methods)
• Mice
• Mutation (physiology)
• Neurons (metabolism)
• Protein Tyrosine Phosphatases, Non-Receptor (pharmacology)
• RNA Interference (physiology)
• Transfection
• Tubulin (metabolism)
• Ubiquitin-Protein Ligases