Liver Study Unit, Veterans Affairs Medical Center, San Francisco, CA 94121, USA.
Oxid Med Cell Longev. 2011;2011:961059. doi: 10.1155/2011/961059. Epub 2011 Apr 18.
Sphingosine kinase (SphK) exhibits two isoforms, SphK1 and SphK2. Both forms catalyze the synthesis of sphingosine 1-phosphate (S1P), a sphingolipid involved in ischemic preconditioning (IPC). Since the ratio of SphK1:SphK2 changes dramatically with aging, it is important to assess the role of SphK2 in IR injury and IPC. Langendorff mouse hearts were subjected to IR (30 min equilibration, 50 min global ischemia, and 40 min reperfusion). IPC consisted of 2 min of ischemia and 2 min of reperfusion for two cycles. At baseline, there were no differences in left ventricular developed pressure (LVDP), ± dP/dtmax, and heart rate between SphK2 null (KO) and wild-type (WT) hearts. In KO hearts, SphK2 activity was undetectable, and SphK1 activity was unchanged compared to WT. Total SphK activity was reduced by 53%. SphK2 KO hearts subjected to IR exhibited significantly more cardiac damage (37 ± 1% infarct size) compared with WT (28 ± 1% infarct size); postischemic recovery of LVDP was lower in KO hearts. IPC exerted cardioprotection in WT hearts. The protective effect of IPC against IR was diminished in KO hearts which had much higher infarction sizes (35 ± 2%) compared to the IPC/IR group in control hearts (12 ± 1%). Western analysis revealed that KO hearts had substantial levels of phosphorylated p38 which could predispose the heart to IR injury. Thus, deletion of the SphK2 gene sensitizes the myocardium to IR injury and diminishes the protective effect of IPC.
鞘氨醇激酶（SphK）有两种同工酶形式，SphK1 和 SphK2。这两种形式都能催化合成鞘氨醇 1-磷酸（S1P），S1P 是一种参与缺血预处理（IPC）的鞘脂。由于 SphK1：SphK2 的比例随着年龄的增长而剧烈变化，因此评估 SphK2 在 IR 损伤和 IPC 中的作用非常重要。Langendorff 小鼠心脏进行 IR（30 分钟平衡，50 分钟整体缺血和 40 分钟再灌注）。IPC 由 2 分钟缺血和 2 分钟再灌注两个周期组成。在基线时，SphK2 缺失（KO）和野生型（WT）心脏之间的左心室发展压（LVDP）、±dp/dtmax 和心率没有差异。在 KO 心脏中，SphK2 活性无法检测到，与 WT 相比 SphK1 活性不变。总 SphK 活性降低了 53%。与 WT 心脏（28 ± 1%梗死面积）相比，IR 后 SphK2 KO 心脏表现出明显更多的心脏损伤（37 ± 1%梗死面积）；KO 心脏的 LVDP 再灌注后恢复较低。IPC 在 WT 心脏中发挥心脏保护作用。在 KO 心脏中，IPC 对 IR 的保护作用减弱，KO 心脏的梗死面积（35 ± 2%）明显高于对照心脏的 IPC/IR 组（12 ± 1%）。Western 分析显示，KO 心脏有大量磷酸化的 p38，这可能使心脏易受 IR 损伤。因此，SphK2 基因缺失使心肌对 IR 损伤敏感，并降低了 IPC 的保护作用。
