Department of Nephrology and Chest Surgery, Nanjing First Hospital affiliated to Nanjing Medical University, Nanjing, China.
Am J Nephrol. 2010;31(1):1-8. doi: 10.1159/000252844. Epub 2009 Oct 23.
Although recent studies indicate that renal ischemia preconditioning (IPC) protects the kidney from ischemia-reperfusion (I/R) injury, the precise protection mechanism is still unknown. It has been widely recognized that the activity of nuclear factor-kappaB (NF-kappaB) is altered upon I/R injury. However, few studies have focused on the compositional change of NF-kappaB complexes. In the current study, we observed different NF-kappaB dimers in I/R and IPC, and postulated that p50 homodimers might represent the predominant NF-kappaB activation in renal IPC.
24 male SD rats were treated with a sham operation, I/R or IPC. While the right kidney was removed in all animals, I/R was induced by left renal artery clamping for 45 min, and IPC was induced by left renal artery clamping for 2 min, reperfused for 5 min, and repeated for 3 cycles before 45 min occlusion. After 24 h of reperfusion, we assessed NF-kappaB activities, composition of NF-kappaB, and expression of IL-18.
Compared to the I/R group, NF-kappaB activity decreased significantly in the IPC group. Supershift assays were then performed to examine the NF-kappaB subunits in the binding complexes. In both the I/R and IPC groups, the composition of NF-kappaB contained p65 and p50. The densities of these two supershift bands were almost equivalent in the I/R group, suggesting the NF-kappaB composition was p50/p65 dimers. However, the densities of p50 bands were more than twice that of p65 in the IPC group and the levels of Bcl-3 increased in parallel in these rats, suggesting that p50/p50 homodimers might dominate the NF-kappaB activities in renal IPC. Finally, the expression of IL-18, a marker of acute kidney injury, was significantly increased in the area of tubulointerstitium in the I/R group and attenuated in the IPC group.
In conclusion, our investigation suggests that: (1) the general activity of NF-kappaB is attenuated in IPC kidneys, and (2) the remaining activation of NF-kappaB is dominated with p50/p50 homodimer. Both of these effects might subsequently downregulate IL-18 expression, as well as provide renal protective effects of IPC. Though we focused on the phenomenological observations in this study, the detailed mechanism is still to be determined.
尽管最近的研究表明，肾缺血预处理（IPC）可保护肾脏免受缺血再灌注（I/R）损伤，但确切的保护机制尚不清楚。人们普遍认为，核因子-κB（NF-κB）的活性在 I/R 损伤时发生改变。然而，很少有研究关注 NF-κB 复合物的组成变化。在本研究中，我们观察到 I/R 和 IPC 中存在不同的 NF-κB 二聚体，并推测 p50 同源二聚体可能代表肾 IPC 中 NF-κB 的主要激活形式。
24 只雄性 SD 大鼠分别接受假手术、I/R 或 IPC 处理。所有动物均切除右肾，左肾动脉夹闭 45 分钟诱导 I/R，左肾动脉夹闭 2 分钟、再灌注 5 分钟，重复 3 个循环，然后再夹闭 45 分钟。再灌注 24 小时后，我们评估 NF-κB 活性、NF-κB 组成和 IL-18 的表达。
与 I/R 组相比，IPC 组 NF-κB 活性显著降低。然后进行超迁移分析以检查结合复合物中的 NF-κB 亚基。在 I/R 和 IPC 组中，NF-κB 的组成均包含 p65 和 p50。在 I/R 组中，这两个超迁移带的密度几乎相等，表明 NF-κB 的组成是 p50/p65 二聚体。然而，在 IPC 组中，p50 带的密度是 p65 的两倍以上，并且这些大鼠中的 Bcl-3 水平平行增加，表明 p50/p50 同源二聚体可能主导肾 IPC 中的 NF-κB 活性。最后，急性肾损伤标志物 IL-18 的表达在 I/R 组的肾小管间质区域显著增加，并在 IPC 组中减弱。
总之，我们的研究表明：（1）IPC 肾脏中 NF-κB 的总体活性减弱，（2）剩余的 NF-κB 激活被 p50/p50 同源二聚体主导。这两种作用都可能随后下调 IL-18 的表达，并提供 IPC 的肾脏保护作用。虽然我们在这项研究中专注于现象学观察，但详细的机制仍有待确定。
