1. Department of Neurology, Hadassah‐Hebrew University Medical Center, Ein Kerem, , Jerusalem, Israel;2. Electron Microscope Unit, Interdepartmental Core Facility, Faculty of Medicine, The Hebrew University of Jerusalem, Ein Kerem, , Jerusalem, Israel;3. Bio‐imaging Unit, The Alexander Silverman Institute of Life Sciences, The Hebrew University of Jerusalem, Edmund Safra Campus, , Jerusalem, Israel;4. Center for Cancer and Immunology Research, Children's National Medical Center, , Washington, District of Columbia, USA;5. Section of Biology, Department of Oral Function & Molecular Biology, School of Dentistry, Ohu University, , Fukushima, Japan;6. Maxillofacial Anatomy, Tokyo Medical and Dental University, , Tokyo, Japan;7. Department of Neurology, Columbia University Medical Center, , New York, New York, USA
Abstract:
Uncontrolled elongation of glycogen chains, not adequately balanced by their branching, leads to the formation of an insoluble, presumably neurotoxic, form of glycogen called polyglucosan. To test the suspected pathogenicity of polyglucosans in neurological glycogenoses, we have modeled the typical glycogenosis Adult Polyglucosan Body Disease (APBD) by suppressing glycogen branching enzyme 1 (GBE1, EC 2.4.1.18) expression using lentiviruses harboring short hairpin RNA (shRNA). GBE1 suppression in embryonic cortical neurons led to polyglucosan accumulation and associated apoptosis, which were reversible by rapamycin or starvation treatments. Further analysis revealed that rapamycin and starvation led to phosphorylation and inactivation of glycogen synthase (GS, EC 2.4.1.11), dephosphorylated and activated in the GBE1‐suppressed neurons. These protective effects of rapamycin and starvation were reversed by overexpression of phosphorylation site mutant GS only if its glycogen binding site was intact. While rapamycin and starvation induce autophagy, autophagic maturation was not required for their corrective effects, which prevailed even if autophagic flux was inhibited by vinblastine. Furthermore, polyglucosans were not observed in any compartment along the autophagic pathway. Our data suggest that glycogen branching enzyme repression in glycogenoses can cause pathogenic polyglucosan buildup, which might be corrected by GS inhibition.
