Department of Cardiovascular, Renal and Metabolic Medicine, Sapporo Medical University School of Medicine, Sapporo, Japan.
Department of Cellular Physiology and Signal Transduction, Sapporo Medical University School of Medicine, Sapporo, Japan.
J Mol Cell Cardiol. 2021 May;154:21-31. doi: 10.1016/j.yjmcc.2021.01.002. Epub 2021 Feb 4.
We previously reported that upregulated AMP deaminase (AMPD) contributes to diastolic ventricular dysfunction via depletion of the adenine nucleotide pool in a rat model of type 2 diabetes (T2DM), Otsuka Long-Evans-Tokushima Fatty rats (OLETF). Meanwhile, AMPD promotes the formation of substrates of xanthine oxidoreductase (XOR), which produces ROS as a byproduct. Here, we tested the hypothesis that a functional link between upregulated AMPD and XOR is involved in ventricular dysfunction in T2DM rats.
Pressure-volume loop analysis revealed that pressure overloading by phenylephrine infusion induced severer left ventricular diastolic dysfunction (tau: 14.7 ± 0.8 vs 12.5 ± 0.7 msec, left ventricular end-diastolic pressure: 18.3 ± 1.5 vs 12.2 ± 1.3 mmHg, p < 0.05) and ventricular-arterial uncoupling in OLETF than in LETO, non-diabetic rats, though the baseline parameters were comparable in the two groups. While the pressure overload did not affect AMPD activity, it increased XOR activity both in OLETF and LETO, with OLETF showing significantly higher XOR activity than that in LETO (347.2 ± 17.9 vs 243.2 ± 6.1 μg/min/mg). Under the condition of pressure overload, myocardial ATP level was lower, and levels of xanthine and uric acid were higher in OLETF than in LETO. Addition of exogenous inosine, a product of AMP deamination, to the heart homogenates augmented XOR activity. OLETF showed 68% higher tissue ROS levels and 47% reduction in mitochondrial state 3 respiration compared with those in LETO. Overexpression of AMPD3 in H9c2 cells elevated levels of hypoxanthine and ROS and reduced the level of ATP. Inhibition of XOR suppressed the production of tissue ROS and mitochondrial dysfunction and improved ventricular function under the condition of pressure overload in OLETF.
The results suggest that increases in the activity of XOR and the formation of XOR substrates by upregulated AMPD contribute to ROS-mediated diastolic ventricular dysfunction at the time of increased cardiac workload in diabetic hearts.
我们之前的研究表明，在 2 型糖尿病（T2DM）大鼠模型（Otsuka Long-Evans-Tokushima Fatty rats，OLETF）中，上调的 AMP 脱氨酶（AMPD）通过耗尽腺嘌呤核苷酸池导致舒张性心室功能障碍，同时，AMPD 促进黄嘌呤氧化还原酶（XOR）底物的形成，后者产生 ROS 作为副产物。在这里，我们验证了 AMPD 和 XOR 之间功能联系与 T2DM 大鼠心室功能障碍有关的假说。
压力-容积环分析显示，苯肾上腺素输注引起的压力超负荷在 OLETF 中引起更严重的左心室舒张功能障碍（tau：14.7±0.8 对 12.5±0.7 毫秒，左心室舒张末期压力：18.3±1.5 对 12.2±1.3 毫米汞柱，p<0.05）和心室-动脉解偶联，而两组的基础参数相当。虽然压力超负荷不影响 AMPD 活性，但它增加了 OLETF 和 LETO 中的 XOR 活性，OLETF 中的 XOR 活性明显高于 LETO（347.2±17.9 对 243.2±6.1 微克/分钟/毫克）。在压力超负荷下，心肌 ATP 水平降低，黄嘌呤和尿酸水平升高，OLETF 高于 LETO。向心脏匀浆中添加外源性肌苷，即 AMP 脱氨的产物，可增强 XOR 活性。OLETF 的组织 ROS 水平比 LETO 高 68%，线粒体状态 3 呼吸降低 47%。在 H9c2 细胞中过表达 AMPD3 可升高次黄嘌呤和 ROS 水平，并降低 ATP 水平。在 OLETF 中，XOR 抑制可抑制组织 ROS 的产生和线粒体功能障碍，并改善压力超负荷下的心室功能。
结果表明，在糖尿病心脏增加心脏工作量时，XOR 活性的增加和上调的 AMPD 形成 XOR 底物导致 ROS 介导的舒张性心室功能障碍。
