Role of the ER-to-Golgi SNAREs BET1 and GOSR2 in muscular dystrophies

• Applicant: Privatdozent Dr. Michael Schwake
• Subject Area: Cell Biology ; Biochemistry
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 515695323

Congenital muscular dystrophies (CMDs) are a group of degenerative muscle disorders, characterized by early age of onset and can be classified by function and cellular localization of affected proteins. For example, pathogenic variants in subunits of the dystrophin-glyco-protein complex (DGC) have been identified, including Duchenne muscular dystrophy and dystroglycanopathies, caused by mutations in the genes encoding dystrophin and dystro-glycan, respectively. Both proteins are central for the DGC, which is an important cell adhesion receptor complex maintaining muscle integrity by linking the actin cytoskeleton to the basal lamina in skeletal muscle cells. Dystroglycan is a protein precursor and is cleaved into peripheral, highly glycosylated a- and a transmembrane b-dystroglycan. Glycosylation of a-dystroglycan is vital for its function, underscored by the findings that also variants in glycosyl¬transferases that modify a-dystroglycan cause muscular dystrophy. Furthermore, variants affecting components of the Endoplasmic Reticulum (ER)-to-Golgi membrane trafficking machinery such as TRAPPC11, GOSR2 and BET1 have been added recently to the list of inherited CMDs. GOSR2 and BET1 are complex partners and SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) proteins that are essential for docking and fusion of vesicle-mediated membrane trafficking between the ER, the ER-Golgi intermediate com-part¬ment (ERGIC) and the Golgi. We and others have shown that biallelic variants in BET1 and GOSR2 are loss-of-function mutations, causing CMD/epilepsy syndromes. However, the molecular mechanism of disease progression remained elusive. The experiments in this proposal will focus on the role of BET1 and GOSR2 in membrane trafficking of the DG complex in myotubes and in vivo to provide molecular insights into the pathogenesis of muscular disorders. In particular, we will analyze on a molecular level novel biallelic variants of unknown significance identified in GOSR2 in patients presented with congenital microcephaly, epilepsy and myopathy with elevated creatine kinase and lactate levels. We will perform a comparative analysis of GOSR2 and BET1 deficient myoblasts and myotubes to identify common disease pathways. Finally, the characterization of the phenotype of muscle specific GOSR2 deficient mice will allow us to analyze the role of ER-to-Golgi SNAREs in vivo. We expect that the outcome of this proposal will establish if the CMDs caused by the ER-to Golgi SNAREs BET1 and GOSR2 are belonging to the dystroglycanopathies or to another subtype.

• DFG Programme: Research Grants