Defective Regulation of Interdomain Interactions Within the Ryanodine Receptor Plays a Key Role in the Pathogenesis of Heart Failure

Abstract

Background-According to our hypothesis, 2 domains within the ryanodine receptor (RyR) of sarcoplasmic reticulum (SR) (N-terminal [0 to 600] and central [2000 to 2500] domains), where many mutations have been found in patients with polymorphic ventricular tachycardia, interact with each other as a regulatory switch for channel gating. Here, we investigated whether the defective FKBP12.6-mediated stabilization of RyR in heart failure is produced by an abnormal interdomain interaction. Methods and Results-SR vesicles were isolated from dog left ventricular muscles, and then the RyR moiety of the SR was fluorescently labeled with methylcoumarin acetate (MCA) using DPc10, a synthetic peptide corresponding to Gly 2460 -Pro 2495 of RyR (one of the mutable domains in polymorphic ventricular tachycardia), as a site-directing carrier; the carrier was removed from the RyR after MCA labeling. Addition of DPc10 induced an unzipped state of the interacting N-terminal and central domains, as evidenced by an increase in the accessibility of the RyR-bound MCA fluorescence to a large fluorescence quencher. Domain unzipping resulted in Ca 2ϩ leak through the RyR and facilitated cAMP-dependent hyperphosphorylation of RyR and FKBP12.6 dissociation from RyR. When DPc10 was introduced into the isolated myocytes, the magnitude of intracellular Ca 2ϩ transient decreased, and its decay time was prolonged. In the SR isolated from pacing-induced dog failing hearts, the domain unzipping has already occurred, together with FKBP12.6 dissociation and Ca 2ϩ leak. Conclusions-The specific domain interaction within the RyR regulates the channel gating property, and the defectiveness in the mode of the interdomain interaction seems to be the initial critical step of the pathogenesis of heart failure.

IP3 Receptors: Toward Understanding Their Activation

“…Several mutations associated with malignant hyperthermia and central core disease (RyR1) or catecholaminergic polymorphic ventricular tachycardia (RyR2), all of which impair the normal regulation of gating, are clustered in an exposed loop (b8-b9) of the N-terminal of RyR (Amador et al 2009). Furthermore, and consistent with the N-terminal of the RyR mediating essential interdomain interactions, a peptide derived from this region causes RyR2 to open spontaneously, apparently by uncoupling an interaction between the endogenous loop and a central region of the RyR that includes residues 2460 -2495 (Oda et al 2005;Tateishi et al 2009). In light of the conservation of structure between IP 3 R and RyR, it is tempting to speculate that the same loop in the SD of the IP 3 R (b8-b9, red in Fig.…”

“…Yet, in this location the N-terminal is too far from the pore to interact directly with the TMD4-5 loop, consistent perhaps with evidence that in RyR the N-terminal may interact directly with a neighboring domain that includes residues from the central part of the primary sequence (Wang et al 2007). These observations and the evidence that the uncoupling peptide derived from the N-terminal of RyR2 appears to interact with residues remote from the pore (Oda et al 2005;Tateishi et al 2009), suggest that the links between the SD and pore may, at least for RyR, be indirect.…”

Correction of Defective Interdomain Interaction Within Ryanodine Receptor by Antioxidant Is a New Therapeutic Strategy Against Heart Failure

“…10 In diseased conditions, a mutation in either of these domains weakens the interdomain interaction even in resting or nonactivating conditions, and diseased channels remain partially open. As shown in our recent study of the pacing-induced heart failure model, 11 abnormal interdomain interaction as well as dissociation of the RyR2-bound FKBP12.6 destabilizes the channel gating of the RyR2 and then produces Ca 2ϩ leak, suggesting that the weakened interdomain interaction is one of the key mechanisms underlying the pathogenesis of ARVD/C2, polymorphic ventricular tachycardia, and heart failure.…”

Mechanisms of Ca2+-Triggered Arrhythmias

“…For example, defective RyR2 interdomain interactions (also called domain unzipping) between the N-terminal domain and central domain in the context of RyR2 mutations weaken this interaction and destabilize the closed state of the RyR2 (Ikemoto & Yamamoto, 2000;Tateishi et al, 2009). Weakening of these interdomain interactions occurs transiently on a beat-to-beat basis during excitationcontraction coupling, but permanently in both CPVT-associated RyR2 mutations and in pacing-induced failing hearts (Oda et al, 2005). Destabilisation of the zipped state may alter the sensitivity of RyR2 to luminal or cytosolic Ca 2+ and contribute to abnormal SR Ca 2+ leak.…”

“…Emerging evidence suggests that defective interdomain interactions within RyR2 play a key role in abnormal channel gating of RyR2 in failing hearts and RyR2 mutations Oda et al, 2005). Therefore, correction of the defective interdomain interaction may represent a new therapeutic strategy against heart failure and possibly cardiac arrhythmia.…”