Cellular mechanisms leading to desminopathy: Segregation, aggregation and proteostasis imbalance of desmin mutants in muscle cells and tissue

• Applicants: Professor Dr. Harald Herrmann; Professor Dr. Rolf Schröder
• Subject Area: Cell Biology
• Term: from 2016 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 320437777

Mutations of the human desmin gene of chromosome 2q35 (DES) cause autosomal dominant, recessive and sporadic protein aggregate myopathies and cardiomyopathies. Desmin is an intermediate filament protein, which is an essential component of the extra-sarcomeric cytoskeleton in striated muscle cells. Our earlier work demonstrated that distinct desmin mutations have different functional consequences in the complex assembly process of the desmin filaments. However, with regard to human desminopathies it is still unclear if the molecular pathogenesis is related to one or a combination of the following three scenarios: a toxic gain of function of the mutated desmin, the loss of functions executed by wildtype desmin and/or the sequestration of desmin-associated and unrelated important cellular components into the aggregates. To study the disease mechanisms, we have generated R349P desmin knock-in mice, which harbor the ortholog of the most frequent human desmin mutation R350P. By crossbreeding these mice with p53 knock-out mice, we further generated the first immortalized heterozygous and homozygous R349P desmin knock-in muscle cell lines, which can be efficiently differentiated into myotubes. Exploiting these mouse and cell models, we now aim to clarify the cellular mechanisms that cause the observed segregation of wildtype from mutant desmin, the desmin aggregation process itself as well as the associated proteostasis imbalance in striated muscle cells and tissues. By a combination of biochemical and cell biological approaches, we will address the following key questions: 1. Which cellular factors mediate the formation of functional wildtype desmin tetramers? 2. Do mutated desmins utilize the same set of factors or are they recognized by different ones? 3. Which specific factors mediate the sorting of wildtype and mutant desmin? 4. How is the proteolytic activity coupled to the specific processing of wildtype and mutant desmin? Beyond the elucidation of the initial key steps of the molecular pathology our study may provide the basis for novel targeted treatment strategies. Last but not least, our study will set the stage and serve as a paradigm for the characterization of new desmin mutants with respect to their impact in desminopathies.

• DFG Programme: Research Grants