Seidel Thomas, Navankasattusas Sutip, Ahmad Azmi, Diakos Nikolaos A, Xu Weining David, Tristani-Firouzi Martin, Bonios Michael J, Taleb Iosif, Li Dean Y, Selzman Craig H, Drakos Stavros G, Sachse Frank B
From Nora Eccles Harrison Cardiovascular Research and Training Institute (T.S., A.A., M.T.-F., S.G.D., F.B.S.), Molecular Medicine Program (S.N., N.A.D., D.Y.L., C.H.S.), Department of Bioengineering (A.A., F.B.S.), Division of Cardiovascular Medicine (W.D.X., M.J.B., I.T., D.Y.L., S.G.D.), and Division of Cardiothoracic Surgery (C.H.S.), University of Utah, Salt Lake City. Dr Seidel is currently at the Institute for Cellular and Molecular Physiology, Friedrich-Alexander-Universitaet Erlangen-Nuernberg, Germany.
Circulation. 2017 Apr 25;135(17):1632-1645. doi: 10.1161/CIRCULATIONAHA.116.024470. Epub 2017 Jan 10.
Cardiac recovery in response to mechanical unloading by left ventricular assist devices (LVADs) has been demonstrated in subgroups of patients with chronic heart failure (HF). Hallmarks of HF are depletion and disorganization of the transverse tubular system (t-system) in cardiomyocytes. Here, we investigated remodeling of the t-system in human end-stage HF and its role in cardiac recovery.
Left ventricular biopsies were obtained from 5 donors and 26 patients with chronic HF undergoing implantation of LVADs. Three-dimensional confocal microscopy and computational image analysis were applied to assess t-system structure, density, and distance of ryanodine receptor clusters to the sarcolemma, including the t-system. Recovery of cardiac function in response to mechanical unloading was assessed by echocardiography during turndown of the LVAD.
The majority of HF myocytes showed remarkable t-system remodeling, particularly sheet-like invaginations of the sarcolemma. Circularity of t-system components was decreased in HF versus controls (0.37±0.01 versus 0.46±0.02; <0.01), and the volume/length ratio was increased in HF (0.36±0.01 versus 0.25±0.02 µm; <0.0001). T-system density was reduced in HF, leading to increased ryanodine receptor-sarcolemma distances (0.96±0.05 versus 0.64±0.1 µm; <0.01). Low ryanodine receptor-sarcolemma distances at the time of LVAD implantation predicted high post-LVAD left ventricular ejection fractions (<0.01) and ejection fraction increases during unloading (<0.01). Ejection fraction in patients with pre-LVAD ryanodine receptor-sarcolemma distances >1 µm did not improve after mechanical unloading. In addition, calcium transients were recorded in field-stimulated isolated human cardiomyocytes and analyzed with respect to local t-system density. Calcium release in HF myocytes was restricted to regions proximal to the sarcolemma. Local calcium upstroke was delayed (23.9±4.9 versus 10.3±1.7 milliseconds; <0.05) and more asynchronous (18.1±1.5 versus 8.9±2.2 milliseconds; <0.01) in HF cells with low t-system density versus cells with high t-system density.
The t-system in end-stage human HF presents a characteristic novel phenotype consisting of sheet-like invaginations of the sarcolemma. Our results suggest that the remodeled t-system impairs excitation-contraction coupling and functional recovery during chronic LVAD unloading. An intact t-system at the time of LVAD implantation may constitute a precondition and predictor for functional cardiac recovery after mechanical unloading.
左心室辅助装置（LVAD）机械卸载后心脏恢复的情况已在慢性心力衰竭（HF）患者亚组中得到证实。HF的特征是心肌细胞中横管系统（t系统）的耗竭和紊乱。在此，我们研究了终末期HF患者t系统的重塑及其在心脏恢复中的作用。
从5名供体和26名接受LVAD植入的慢性HF患者中获取左心室活检组织。应用三维共聚焦显微镜和计算机图像分析来评估t系统结构、密度以及包括t系统在内的兰尼碱受体簇与肌膜的距离。通过LVAD调低期间的超声心动图评估机械卸载后心脏功能的恢复情况。
大多数HF心肌细胞显示出显著的t系统重塑，尤其是肌膜的片状内陷。与对照组相比，HF中t系统成分的圆形度降低（0.37±0.01对0.46±0.02；<0.01），HF中的体积/长度比增加（0.36±0.01对0.25±0.02 µm；<0.0001）。HF中t系统密度降低，导致兰尼碱受体与肌膜的距离增加（0.96±0.05对0.64±0.1 µm；<0.01）。LVAD植入时较低的兰尼碱受体与肌膜距离预测LVAD植入后较高的左心室射血分数（<0.01）以及卸载期间射血分数的增加（<0.01）。LVAD植入前兰尼碱受体与肌膜距离>1 µm的患者在机械卸载后射血分数未改善。此外，在电场刺激的离体人心肌细胞中记录钙瞬变，并根据局部t系统密度进行分析。HF心肌细胞中的钙释放局限于肌膜附近区域。与t系统密度高的细胞相比，t系统密度低的HF细胞中局部钙上升延迟（23.9±4.9对10.3±1.7毫秒；<0.05）且更不同步（18.1±1.5对8.9±2.2毫秒；<0.01）。
终末期人类HF中的t系统呈现出一种由肌膜片状内陷组成的特征性新表型。我们的结果表明，重塑的t系统损害慢性LVAD卸载期间的兴奋 - 收缩偶联和功能恢复。LVAD植入时完整的t系统可能是机械卸载后心脏功能恢复的前提条件和预测指标。
