Deep morphological analysis of muscle biopsies from type III glycogenesis (GSDIII), debranching enzyme deficiency, revealed stereotyped vacuolar myopathy and autophagy impairment

Philippe Labrune,Evelyne Goillot,Norma B Romero,Michio Inoue,Aleksandra Nadaj‐Pakleza ,C Labasse ,Carola Hedberg‐Oldfors ,Benedikt Schöser ,José C Milisenda ,A Madelaine ,Sarah Léonard-Louis ,Louisa Jauze,Giuseppe Ronzitti,Sabrina Sacconi,Umut Cagin,Nathalie Streichenberger,Edoardo Malfatti,Anders Oldfors,Pascal Laforêt,Federico Mingozzi,Guy Brochier,Julien Fabregue,François Petit,Ichizo Nishino,John Vissing,Thomas Krag,Claire Lefeuvre

doi:10.1186/s40478-019-0815-2

Abstract

Glycogen storage disorder type III (GSDIII), or debranching enzyme (GDE) deficiency, is a rare metabolic disorder characterized by variable liver, cardiac, and skeletal muscle involvement. GSDIII manifests with liver symptoms in infancy and muscle involvement during early adulthood. Muscle biopsy is mainly performed in patients diagnosed in adulthood, as routine diagnosis relies on blood or liver GDE analysis, followed by AGL gene sequencing. The GSDIII mouse model recapitulate the clinical phenotype in humans, and a nearly full rescue of muscle function was observed in mice treated with the dual AAV vector expressing the GDE transgene.In order to characterize GSDIII muscle morphological spectrum and identify novel disease markers and pathways, we performed a large international multicentric morphological study on 30 muscle biopsies from GSDIII patients. Autophagy flux studies were performed in human muscle biopsies and muscles from GSDIII mice. The human muscle biopsies revealed a typical and constant vacuolar myopathy, characterized by multiple and variably sized vacuoles filled with PAS-positive material. Using electron microscopy, we confirmed the presence of large non-membrane bound sarcoplasmic deposits of normally structured glycogen as well as smaller rounded sac structures lined by a continuous double membrane containing only glycogen, corresponding to autophagosomes. A consistent SQSTM1/p62 decrease and beclin-1 increase in human muscle biopsies suggested an enhanced autophagy. Consistent with this, an increase in the lipidated form of LC3, LC3II was found in patients compared to controls. A decrease in SQSTM1/p62 was also found in the GSDIII mouse model.In conclusion, we characterized the morphological phenotype in GSDIII muscle and demonstrated dysfunctional autophagy in GSDIII human samples.These findings suggest that autophagic modulation combined with gene therapy might be considered as a novel treatment for GSDIII.

Highlights

Muscle glycogenoses are rare inherited conditions presenting with muscle symptoms sometimes associated with other organ involvement
Laforêt et al Acta Neuropathologica Communications (2019) 7:167 (Continued from previous page). These findings suggest that autophagic modulation combined with gene therapy might be considered as a novel treatment for Glycogen storage disease type III (GSDIII)
Monitoring autophagy in GSDIII patient muscle To investigate whether autophagy was involved in GSDIII muscle pathology, we studied muscle biopsies from patients with GSDIII and controls for autophagy core protein expression

Summary

Introduction

Muscle glycogenoses are rare inherited conditions presenting with muscle symptoms sometimes associated with other organ involvement. Patients present a liver metabolic disorder with hepatomegaly and severe fasting hypoglycemia, hyperlipidemia, and hyperketonemia. Patients develop a progressive myopathy that can be accompanied by muscle weakness and exercise intolerance [3, 20]. In this phase, the metabolic impairment is less prominent and the patients are referred to muscle specialists [3,4,5,6,7,8,9]. Hepatocellular adenomas (HCA) and carcinomas (HCC) have previously been described in GSDIII patient [9]

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Conclusion