Decreased pacemaker activity in aged sinoatrial node

老年窦房结起搏器活动减少

基本信息

批准号：
8335801
负责人：
Edward Lakatta
金额：
$ 11.03万
依托单位：
NATIONAL INSTITUTE ON AGING
依托单位国家：
美国
项目类别：
财政年份：
资助国家：
美国
起止时间：
至
项目状态：
未结题

来源：
https://reporter.nih.gov/project-details/8335801
关键词：
ATP2A2 Age Aging Animal Model Arrhythmia Artificial cardiac pacemaker Baltimore Cardiac Cells Coupled Coupling Cyclic AMP Cyclic AMP-Dependent Protein Kinases Deterioration Effector Cell Elderly Exercise Exhibits Functional disorder Future Heart Heart Rate Human Incidence Ion Channel Kinetics Link Longitudinal Studies Measures Mechanics Mediating Membrane Membrane Potentials Modeling Mus Muscle Muscle Cells Nodal Oryctolagus cuniculus Pacemakers Participant Pathway interactions Phosphoric Monoester Hydrolases Phosphorylation Preparation Process Protein phosphatase Proteins Pump Rattus Regulation Relaxation Risk Scientist Seminal Signal Transduction Signaling Molecule Sinoatrial Node Stress Surface Properties System Time Ventricular Western Blotting age related aged base blood pump calmodulin-dependent protein kinase II chronotropic cost density human old age (65+)improved indexing male meetings nodal myocyte novel therapeutics phospholamban physical conditioning receptor response success theories

项目摘要

How does the General Theory of Cardiac Chronotropy and Inotropy Apply to Aging? Both our earlier and very recent studies have contributed seminal perspectives toward understanding age-associated deterioration of both cardiac contractility and heart rate in both humans, and in animal models. Our studies of healthy participants in the Baltimore Longitudinal Study of Aging (BLSA) demonstrated substantial age-associated changes in the ability to increase heart rate and reduce end systolic volume in response to graded exercise stress. (Of note, only the latter, but not the former, can be improved by physical conditioning.) We subsequently demonstrated that deficits both in contractility and heart rate in humans are due, in part, to reduced -AR stimulation response of cAMP-PKA. 1. Contractility In isolated rat cardiac ventricular muscle, we had directly demonstrated a reduction in the Ca2+ cycling and contractile response to -AR stimulation. The relaxation time of the Ca2+ transient and contraction in the absence of -AR stimulation were prolonged, that we traced to a reduced expression of SERCA2. The AP was also markedly prolonged, due to age-associated changes in L-type Ca2+ and K+ currents. In single VM, in addition to numerous properties of surface membrane ion channels, we documented an age-associated reduction in the VM Ca2+ clock, manifest as a prolonged time for restitution of the excitation- Ca2+ release-contraction coupling process, was due to a prolonged restitution time for SR Ca2+ release via RyRs in response to activation by an L-type Ca2+ current. We also showed that SR Ca2+ loading and the amplitude of the Ca2+ transient were preserved in myocytes from the old heart, by virtue of the prolonged AP. 2. Heart rate Our discovery of heart rate regulation by a coupled-clock system in rabbit SANC enabled progress, finally (after 25 years), on the elucidation of potential cellular mechanisms of the age-associated reduction in chronotropic reserve. Specifically, our conceptual breakthrough that regulation of basal pacemaker cell automaticity requires Ca-PKA-CaMKII signaling regulated by PDE and phosphatase activities, and that stimulation of receptors merely extended this regulation, led us to hypothesize that mechanisms involved in the deterioration of mechanisms that regulate of intrinsic heart rate that accompanies advancing age and that those regulating heart rate reserve may involve a slowing of the Ca2+ clock of SANC and linked, in some respects, at least, to the age-associated deterioration of mechanisms that regulate Ca2+ cycling and contractility in VM. Phospholamban (PLB) phosphorylation at Ser16 (PLB/total PLB) immunolabeling in control did not differ with age, increased 2.20.2 fold after incubation with 10 M IBMX in young, but did not increase in old SANC. The intrinsic SR Ca2+ cycling and its response to PDE inhibition decline with aging, and are candidate mechanisms to explain, in part at least, the age-associated decrease in IHR. We had failed for five years in our attempts to isolate single mouse sinoatrial node cells that exhibited stable normal automaticity. Recently, we have met with some success. Our initial results indicate that: the spontaneous AP firing rate of single SANC declines with age; the maximum RyR Ca release flux in response to an AP (indexed as d Ca/dt max) declines with age; and the kinetics of relaxation of the Ca2+ transient become reduced with age. Our results suggest that the intrinsic cAMP-PKA-Ca2+ signaling is deficient in the aged mice. This deficiency may result from: 1.)reduced amount or function of Ca2+ cycling proteins e.g. SR Ca2+ pump, phospholamban (PLB), RyRs. and/or 2.) reduced phosphorylation of Ca2+ cycling proteins e.g.PLB, in response to an increase in cAMP-mediated-PKA dependent phosphorylation. 3.) These deficiencies may explain why the aged heart cannot beat as fast as the young heart. Future plans are: 1) to employ western blotting in cells from young and old SANs to measure Ca2+ cycling protein density; 2) to directly measure the downstream signaling of cAMP-PKA- Ca2+ pathway i.e. PKA-dependent protein phosphorylation and phosphatase activity.

心脏变时性和正性肌力的一般理论如何应用于衰老？我们早期和最近的研究都为理解人类和动物模型中与年龄相关的心肌收缩力和心率恶化提供了开创性的视角。我们在巴尔的摩纵向衰老研究 (BLSA) 中对健康参与者进行的研究表明，随着分级运动压力的增加，心率增加和收缩末期容积减少的能力与年龄相关，发生了显着变化。（值得注意的是，只有后者，不能通过身体调理来改善前者。）我们随后证明，人类收缩力和心率的缺陷部分是由于 cAMP-PKA 的 -AR 刺激反应减少所致。 1. 收缩性在离体大鼠心室肌中，我们直接证明了 Ca2+ 循环和对 -AR 刺激的收缩反应的减少。在没有-AR刺激的情况下，Ca2+瞬态的弛豫时间和收缩时间延长，我们追踪到SERCA2表达的减少。由于 L 型 Ca2+ 和 K+ 电流与年龄相关的变化，AP 也显着延长。在单个VM中，除了表面膜离子通道的众多特性之外，我们还记录了VM Ca2+时钟与年龄相关的减少，表现为兴奋-Ca2+释放-收缩耦合过程的恢复时间延长，这是由于响应 L 型 Ca2+ 电流的激活，通过 RyRs 释放 SR Ca2+ 的恢复时间延长。我们还表明，由于 AP 时间延长，旧心脏的肌细胞中保留了 SR Ca2+ 负荷和 Ca2+ 瞬变幅度。 2.心率我们在兔子 SANC 中发现了耦合时钟系统对心率的调节，最终（25 年后）在阐明与年龄相关的变时储备减少的潜在细胞机制方面取得了进展。具体来说，我们的概念性突破是基础起搏细胞自动性的调节需要由 PDE 和磷酸酶活性调节的 Ca-PKA-CaMKII 信号传导，并且受体的刺激仅仅延长了这种调节，使我们假设涉及调节机制恶化的机制伴随年龄增长的内在心率的变化以及心率储备的调节可能涉及 SANC 的 Ca2+ 时钟减慢，并且至少在某些方面与年龄相关调节机制的恶化有关VM 中的 Ca2+ 循环和收缩性。对照中的磷酸化 Ser16（PLB/总 PLB）免疫标记不随年龄而变化，在年轻人中与 10 M IBMX 孵育后增加 2.20.2 倍，但在老年 SANC 中没有增加。内在的 SR Ca2+ 循环及其对 PDE 抑制的反应随着年龄的增长而下降，并且是至少部分解释与年龄相关的 IHR 下降的候选机制。五年来，我们一直试图分离表现出稳定的正常自动性的单个小鼠窦房结细胞，但一直失败。最近，我们取得了一些成功。我们的初步结果表明：单个 SANC 的自发 AP 放电率随着年龄的增长而下降；响应 AP 的最大 RyR Ca 释放通量（指数为 d Ca/dt max）随着年龄的增长而下降； Ca2+瞬变的弛豫动力学随着年龄的增长而降低。我们的结果表明，老年小鼠内在的 cAMP-PKA-Ca2+ 信号传导存在缺陷。这种缺陷可能是由于： 1.) Ca2+ 循环蛋白的数量或功能减少，例如SR Ca2+ 泵、受磷蛋白 (PLB)、RyRs。和/或 2.) Ca2+ 循环蛋白（例如 PLB）的磷酸化减少，以响应 cAMP 介导的 PKA 依赖性磷酸化的增加。 3.) 这些缺陷可以解释为什么衰老的心脏不能像年轻的心脏那样跳动快。未来的计划是： 1) 在年轻和年老 SAN 的细胞中采用蛋白质印迹法来测量 Ca2+ 循环蛋白密度； 2) 直接测量cAMP-PKA-Ca2+通路的下游信号传导，即PKA依赖性蛋白磷酸化和磷酸酶活性。