Abstract 39: CD47 Regulates Aberrant Ca2+ Channel Current in Cardiac Myocytes

Abstract

Background: Left ventricular (LV) heart failure (HF) affects over 5 million Americans with 50% of HF patients dying within 5 years of diagnosis. Therapeutics, while only relieving symptoms and have multiple side effects, have not completely resolved this process. HF is associated with cardiac myocyte cytosolic Ca2+ overload due to impaired sarcoplasmic reticulum (SR) and/or membrane Ca2+ handling. We recently found that a widely expressed cell surface receptor CD47 and its high affinity ligand, thrombospondin-1 (TSP1), are expressed on cardiac myocytes. We further showed that activated CD47 increases isolated neonatal cardiac myocyte cytosolic Ca2+ levels in part through SR Ca2+ channels. We postulated that TSP1-CD47 signaling may in part play a role in LV HF secondary to dysregulation of Ca2+, though the specific Ca2+ dynamics through which TSP1-CD47 signaling controls cardiac Ca2+ remains to be determined. Methods: Isolated hearts from mutated mice lacking CD47 (CD47-/-) and wild type (WT) mice with and without 4 weeks of transverse aortic constriction (TAC) were studied in ex vivo perfused heart Langendorff using dual optical mapping of Cai transients and action potential or voltage measurements. Isolated cardiac myocyte experiments were performed using whole cell voltage-clamp analysis. Results: In TAC-stressed WT murine hearts studied in the Landendorff system, tetracaine (an inhibitor of SR ryanodine receptor2) blunted arrhythmia induced by electrical stimulation. Isoproterenol-induced Ca2+ transient irregularities in hearts from WT mice were ameliorated in CD47-/- mice. Further, hearts from WT mice treated with peptide 7N3, a TSP1 mimetic, showed induced Ca2+ transient irregularities and elicited early after depolarization which was also attenuated with K2O1 (ryanodine receptor2 stabilizer) treatment. Voltage-clamp studies of isolated adult mouse cardiac myocytes showed that 7N3 peptide increased the L-type Ca2+ channel current (ICa,L) whereas the scrambled control peptide did not alter ICa,L. Conclusion: These data demonstrate that CD47 activation may be a trigger for aberrant myocyte Ca2+ handling typically associated with HF. Targeting of TSP1-CD47 signaling may open a new therapeutic avenue to be further studied in HF.