GNE-Myopathie – Warum ist nur der Muskel betroffen?
Zusammenfassung der Projektergebnisse
GNE myopathy is an inheritable disease caused by a dysfunction of the first enzyme in the sialic acid pathway. Sialic acids are the key sugars that terminate glycosylation of proteins and lipids and are therefore crucial for cellular interactions. Disruptions in the sialic acid pathway have been associated with common diseases such as cancer and with genetic defects causing neurological phenotypes. As sialic acid synthesis is ubiquitous, it remains unsolved why only the muscle is affected in GNE myopathy. To tackle this issue, the aim of the project was to apply muscle cells derived from human induced pluripotent stem cells (hiPSC) to analyze the putatively crucial role of the intermediate product of the sialic acid pathway, N-acetylmannosamine (ManNAc). The project originally consisted of three Key Objectives: 1) Generation and functional characterisation of hiPSC-derived heart and skeletal muscle models from patients with GNE myopathy. 2) Glycoproteomic and metabolomic analysis of the GNE deficient heart and skeletal muscle models. 3) Metabolic repair of the biochemical and functional consequences of GNE deficiency. With this, it was expected to elucidate the role of ManNAc and its putatively muscle-specific metabolism to aid diagnostics and therapeutic intervention in GNE myopathy. During the course of the project, patient-derived hiPSCs from GNE myopathy patients were successfully generated and differentiated to cardiomyocytes. However, skeletal muscle differentiation turned out to be not efficiently possible with the cell lines generated due to a potential impairment of muscle differentiation of hiPSCs generated by lentiviral reprogramming. Therefore, alternative approaches to study the sialic acid metabolism were being sought. For instance, a panel of synthetic sugar analogues was applied on control hiPSC-derived myoblasts received from a collaboration partner both in the myoblast stage and during differentiation to myotubes. Moreover, generation of a hiPSC knockout line of NPL, the gene encoding for the sialic acid degrading enzyme N-acetylneuraminate pyruvate-lyase (NPL), was generated and is now being used in a collaboration project with my current group to study the role of NPL and metabolic implications of a defective sialic acid degradation machinery in hiPSC-derived cardiomyocytes as a model for dilated cardiomyopathy.
