Abstract 2576: Activation of Stim1-mediated Store-operated Calcium (SOC) Influx in Calcineurin-dependent Cardiac Hypertrophy
Background: Calcium (Ca2+) signaling is a central regulator of cardiac hypertrophy. Stim1-mediated store-operated Ca2+ entry (SOC), a process triggered by depletion of sarco-endoplasmic reticulum (SR/ER) Ca2+ stores, plays an important role in physiology and pathology in many cell types. However, little is known regarding SOC in heart or its role in cardiac development and hypertrophy.
Methods and Results: Using fluorescent dye measurements of intracellular Ca2+, we detected the presence of SOC channels in cultured neonatal cardiomyocytes. Furthermore Stim1, a recently identified molecular component of the SOC channel, was readily detected by immuno-staining and Western blot analysis. Interestingly, SOC influx was much more robust in neonatal rat ventricular myocytes (NRVMs) than in adult myocytes, as were Stim1 mRNA and protein levels (6.9±0.4, 7.5±0.6 fold, p<0.01, respectively). Furthermore, in two in vivo models of cardiac hypertrophy, thoracic aortic constriction (TAC) and cardiomyocyte-specific over-expression of calcineurin (Cn), we found that Stim1 protein was significantly up-regulated (1.9±0.4-fold, 2.1±0.3-fold, p<0.05 each). Consistent with this, Stim1 levels were increased in NRVMs exposed to multiple growth agonists such as angiotension II (100 nM) and PE (100 μM) (2.3±0.2, 3.1±0.3, p<0.01, respectively). To probe the molecular basis of cardiac SOC current, we expressed mutant (D76A, constitutively active; ΔERM, dominant negative) forms of human Stim1 in NRVMs. D76A markedly increased SOC influx triggered by thapsigargin (Tg) or cyclopiazonic acid. In contrast, ΔERM blocked SOC. Finally, Stim1 over-expression elicited robust, dose-dependent increases in NFAT-dependent luciferase reporter activity and triggered an exaggerated SOC response on Tg stimulation. RNAi-mediated knock-down of Stim1 blocked Tg-triggered luciferase activity.
Conclusion: Stim1-mediated SOC entry is active in neonatal cardiomyocytes and down-regulated in adult cells. Stim1 is up-regulated during hypertrophic transformation of the myocardium, possibly participating in Cn-NFAT activation. We conclude that SOC currents are part of the fetal gene program in heart and may contribute to the sustained Ca2+ overload of heart failure.
This research has received full or partial funding support from the American Heart Association, South Central Affiliate (Arkansas, New Mexico, Oklahoma & Texas).