Research Report 2010 - MDC

Michael GotthardtStructure of the GroupGroup LeaderProf. Dr. med. Michael GotthardtScientistsMichael RadkeYu Shi*Padmanabhan Vakeel*Graduate StudentsChen ChenUta WrackmeyerUlrike LisewskiThirupugal GovindarajanKatharina Rost*Neuromuscular and CardiovascularCell BiologyOur long-term goal is to establish how mechanical input is translated into molecularsignals. We focus on titin, the largest protein in the human body and the multi -functional coxsackie-adenovirus receptor (CAR).To lay the groundwork for the in vivo analysis of titin’s multiple signaling, elastic, andadaptor domains, we have generated various titin deficient mice (knock-in and conditionalknockout animals) and established a tissue culture system to study titin’s muscle and nonmusclefunctions. We utilize a combination of cell-biological, biochemical, and genetic toolsto establish titin as a stretch sensor converting mechanical into biochemical signals.Using a comparable loss of function approach we have created a conditional knockout ofthe coxsackie-adenovirus receptor. With these mice, we have demonstrated that CAR iscrucial for embryonic development and determines the electrical properties of the heart.Titin based mechanotransductionMichael Radke, Thirupugal Govindarajan, Martin Liss,Padmanabhan VakeelTitin is a unique molecule that contains elastic springelements and a kinase domain, as well as multiplephosphorylation sites. Therefore, it has been frequentlyspeculated that titin and invertebrate giant titin-likemolecules could act as a stretch sensor in muscle. Morerecently, this concept has been supported by studies onhuman dilative cardiomyopathies which suggest animpaired interaction of titin with its regulatory ligandssuch as Tcap. So far it has remained unknown how thestretch signal is processed, i.e. how the mechanicalstimulus stretch is converted into a biochemical signal.To investigate the stretch signaling pathway, we applymechanical strain in vivo (plaster cast for skeletal muscle;aortic banding for the heart) and in tissue culture(cultivation of primary cells on elastic membranes). Theresulting changes in protein expression and localizationin our titin kinase and spring element deficient animalsare used to map the mechanotransduction pathway.Sarcomere assemblyNora Bergmann, Katharina Rost, ThirupugalGovindarajanOverlapping titin molecules form a continuous filamentalong the muscle fiber. Together with the multiplebinding sites for sarcomeric proteins, this makestitin a suitable blueprint for sarcomere assembly. Theuse of transgenic techniques does not only allow us toaddress the function of titin’s individual domains in sarcomereassembly, but also to follow sarcomere assemblyand disassembly using fluorescently tagged proteins.Understanding the structural and biomechanicalfunctions of titin will help elucidate the pathomechanismsof various cardiovascular diseases and ultimatelyaid the development of suitable therapeutic strategies.Smooth muscle and non-muscle titinsNora Bergmann, Katharina RostRecently titin has been proposed to perform non-musclefunctions following its localization to various cell16 Cardiovascular and Metabolic Disease Research