Poster abstracts
Poster number 4 submitted by Casey Beard
Sarcomere generation is localized to intercalated disk and dependent on store operated calcium entry in a model of rapid onset (Takotsubo) hypertrophy
Casey M. Beard (Biophysics), Vladimir Bogdanov (Department of Physiology and Cell Biology), Benjamn Hernandez Orengo (Department of Physiology and Cell Biology), Galina Sakuta, Svetlana Tikunova (Department of Physiology and Cell Biology), Jonathan P. Davis (Department of Physiology and Cell Biology), Sandor Gyorke (Department of Physiology and Cell Biology)
Abstract:
To achieve hypertrophic growth, a cardiomyocyte must incorporate new sarcomeres within the cell. The location and manner of this growth during either physiologic or pathologic hypertrophy is uncertain. We have recently shown a relationship between hypertrophic processes and store operated calcium entry (SOCE) that occurs near the intercalated disk (ID) of cardiomyocytes. We therefore hypothesize that incorporation of new sarcomeres during hypertrophy occurs at the ID and is impacted by SOCE. We developed a novel mouse model possessing the gain-of-function mutation H109R+/- in the SOCE protein STIM1 that has been linked to human stress-induced cardiomyopathy, also called Takotsubo cardiomyopathy (TCM). STIM1 H109R+/- mice implanted with isoproterenol (ISO) osmotic minipumps developed left ventricular (LV) ballooning and reduced LV ejection fraction reminiscent of TCM and showed premature deaths. Cardiomyocytes derived from STIM1 H109R+/- evidenced a significant increase in length 2-3 days after ISO pump implantation. Confocal Ca2+ imaging in STIM1 H109R+/- myocytes showed increased SOCE localized to IDs. To determine the location of new sarcomere generation during hypertrophy, we employed a myofibril-integrated biomarker through introduction of GFP-tagged troponin C (TnC-GFP) in the described STIM1 H109R+/- mouse model. Myocytes were isolated 70 hours later and confocally imaged to determine regional concentrations of TnC-GFP associated with new sarcomeric growth. Our data suggest intense fluorescent signals localized at myocyte ends, consistent with higher expression of TnC-GFP adjacent to IDs. These results suggest that genetic upregulation of STIM1 under adrenergic stress can cause rapid-onset LV dilation similar to TCM. The longitudinal growth of myocytes under these conditions involves SOCE-dependent sarcomere addition to myocytes at IDs.
Keywords: store operated calcium entry, Takotsubo cardiomyopathy, sarcomerogenesis