Abstract 18897: iPSC-derived Cardiomyocytes From a Patient With Hypertropic Cardiomyopathy Exhibit Imparied SR Ca Handling but No Change in Cytosolic Buffering Properties
Introduction: A recent report suggests that human induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) from a familial hypertrophic cardiomyopathy (HCM) patient carrying a MYH7 mutation (R663H) exhibit altered Ca handling, but the underlying mechanisms remain unclear. We recently reported that HCM mutations can increase cytosolic Ca binding affinity, which could explain the abnormal Ca handling of HCM iPSC-CMs.
Hypothesis: To test the hypothesis that the MYH7-R663H mutation alters cytosolic Ca buffering.
Methods and Results: Human iPSCs derived from a healthy subject (CON) and a HCM patient (HCM: MYH7-R663H) were plated 21 days after cardiac induction at low density on Matrigel-coated dishes. iPSC-CMs were studied 3-4 days after plating using the ratiometric Ca indicator Fura-2AM at room temperature in Tyrode’s solution (2 mM Ca). HCM iPSC-CMs exhibited reduced Ca transients (measured during field-stimulation at 0.5 Hz) and SR Ca content (measured by caffeine spritz). Importantly, cytosolic Ca buffering was not significantly different between CON (Bmax=100±14μM/Lcytosol, Kd=0.61±0.09μM, n=25) and HCM iPSC-CMs (Bmax=115±10μM/Lcytosol, Kd=0.64±0.06μM, n=17). The rate constant of SR Ca uptake was significantly reduced in the HCM group (KSERCA: CON, 0.89±0.2s-1 vs. HCM, 0.45±0.1s-1, p=0.024) while Ca extrusion via the Na-Ca exchanger (KNCX) was only modestly reduced in HCM iPSC-CM (CON, 0.36±0.03s-1 vs. HCM, 0.26±0.03s-1, p=0.04). As a result, the relative contribution of Ca flux pathways was shifted from the SR to the cell membrane in HCM-iPSC-CM (Figure).
Conclusions: Human iPSC-CMs from patients with HCM exhibit reduced SR Ca flux, but no change in cytosolic buffering.
Author Disclosures: H. Hwang: None. D.O. Kryshtal: None. V. Sánchez-Freire: None. J.C. Wu: Consultant/Advisory Board; Modest; Consultant for Merck, Takeda, and Novartis, Scientific advisory board for Stem Cell Theranostics. B.C. Knollmann: None.
This research has received full or partial funding support from the American Heart Association.
- © 2014 by American Heart Association, Inc.