Mechanical stress-induced pathomechanisms in BAG3-associated myopathies

• Applicant: Dr. Michael Hesse
• Subject Area: Cell Biology
• Term: since 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 388932620

The cochaperone BAG3 (Bcl-2 associated athanogene 3) is strongly expressed in cross striated muscles and plays a key role in maintaining muscle architecture and function under mechanical stress owing to its ability to balance transcription, translation, and autophagy. The proline to leucine substitution at position 209 within BAG3 leads to severe and progressively restrictive cardiomyopathy and skeletal muscle dystrophy in patients, followed by death due to heart failure or respiratory insufficiency. Hallmarks of this BAG3-associated myofibrillar myopathy are Z-disc disintegration and protein aggregation. In the first funding period, we finished the thorough analysis of our humanized BAG3P209L overexpressing mice, which suffer from restrictive cardiomyopathy and skeletal muscle myofibrillar myopathy, thereby recapitulating the human disease phenotype. We were able to demonstrate that the disease mechanism is due to the accumulation of BAG3 and sequestering of components of the protein quality control system and autophagy machinery leading to a reduction of the stability and functional organization of Z-disc components. In patients suffering from BAG3P209L-myofibrillar myopathy reported so far there is a large degree of heterogeneity. Accordingly, it is not clear which factors influence the development of the life-threatening cardiac and skeletal muscle phenotype and whether and how the cardiac phenotype influences the skeletal muscle phenotype and vice versa. Therefore, in the second funding period, we will use inducible mouse lines for heart and skeletal muscle-specific induction of hBAG3P209L-expression to analyze if and how the skeletal muscle phenotype influences the cardiac phenotype and vice versa and how the onset of hBAG3P209L expression influences the development of the cardiac/skeletal muscle phenotype. Furthermore, we will subject heart and skeletal muscle-specific hBAG3P209L-expressing mice to mechanical stress induced by physical exercise on a treadmill and investigate the formation of aggregates and the distortion of sarcomeric structures in cardiac and skeletal muscle cells.We will further test therapeutic approaches for BAG3P209L-myofibrillar myopathy in our hBAG3P209L mouse model by using adeno-associated viruses (AAVs) to either knockout hBAG3P209L by CRISPR/Cas9 or knockdown hBAG3P209L by RNA-interference.To understand the full spectrum of BAG3-related muscular diseases we will analyze patient-derived or genome-edited human iPS cell lines with the BAG3P209L mutation, differentiate them to cardiomyocytes and skeletal myotubes, characterize their phenotype, and test therapeutic approaches to treat the disease. The proposed work aims to clarify whether and to what extent mechanical stress contributes to the pathology of BAG3P209L-myofibrillar myopathy and whether gene-therapy approaches are suitable for the treatment of this lethal disease.

• DFG Programme: Research Units
• Subproject of: FOR 2743: Mechanical Stress Protection