Chen, S. R. WayneLiu, Yingjie2017-05-012017-05-0120172017Liu, Y. (2017). Molecular Basis and Regulation of Ca2+ Release Termination and its Role in Cardiomyopathies (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca. doi:10.11575/PRISM/26981http://hdl.handle.net/11023/3789It is known that sarcoplasmic reticulum (SR) Ca2+ release in cardiac muscle is initiated via cardiac ryanodine receptor (RyR2) through a mechanism called Ca2+-induced Ca2+ release. However, how the SR Ca2+ release is terminated is undetermined. The objective of the current study is to understand the molecular basis and regulation of RyR2-mediated Ca2+ release termination and its role in the pathogenesis of cardiac diseases. Based on recent 3D structural analyses, the NH2-terminal region of RyR2 interacts with the channel domain via the central domain and undergoes dynamic conformational changes during channel gating. It has also been discovered that the NH2-terminal region consists of three distinct domains. HEK293 cell studies on domain deletions and disease mutations demonstrate that the different domains play different roles in RyR2 function. The NH2-terminal region is a major determinant of Ca2+ release activation and termination. Enhanced luminal Ca2+ activation of RyR2 has been linked to catecholaminergic polymorphic ventricular tachycardia (CPVT). However, in addition to CPVT, many RyR2 mutations can also cause cardiomyopathies. Knock-in mouse models harboring cardiomyopathy- associated RyR2 mutations have been generated to investigate the causal mechanisms of cardiomyopathies. The exon-3 deletion mouse model exhibited markedly reduced RyR2 expression level and no characteristic phenotype. The RyR2-R420W mouse model showed enhanced susceptibility to CPVT and altered cytosolic Ca2+ transient properties, suggesting that the abnormal cytosolic Ca2+ transient may be a key factor in the pathogenesis of cardiomyopathies. Calmodulin (CaM) is a regulatory protein that binds and inhibits RyR2 in the presence of cytosolic Ca2+. The inhibitory effect depends on the affinity of CaM for Ca2+ and RyR2. CaM mutations affecting either aspect may result in aberrant regulation of RyR2 activity, hence abnormal Ca2+ release termination. Indeed, arrhythmogenic mutations and most newly discovered CaM variants delayed Ca2+ release termination while others enhanced it, indicating that CaM is a major modulator of RyR2-mediated Ca2+ release termination. Overall, Ca2+ release termination is an intrinsic property of RyR2 that can be regulated by modulators such as CaM. Altered Ca2+ release termination is critically involved in the pathogenesis of cardiac diseases.engUniversity of Calgary graduate students retain copyright ownership and moral rights for their thesis. You may use this material in any way that is permitted by the Copyright Act or through licensing that has been assigned to the document. For uses that are not allowable under copyright legislation or licensing, you are required to seek permission.Biology--CellBiology--MolecularPhysiologyPharmacologydoctoral thesis10.11575/PRISM/26981