The Early Activation of Toll-Like Receptor (TLR)-3 Initiates Kidney Injury after Ischemia and Reperfusion

Acute kidney injury (AKI) is one of the most important complications in hospitalized patients and its pathomechanisms are not completely elucidated. We hypothesize that signaling via toll-like receptor (TLR)-3, a receptor that is activated upon binding of double-stranded nucleotides, might play a crucial role in the pathogenesis of AKI following ischemia and reperfusion (IR). Male adult C57Bl6 wild-type (wt) mice and TLR-3 knock-out (-/-) mice were subjected to 30 minutes bilateral selective clamping of the renal artery followed by reperfusion for 30 min 2.5h and 23.5 hours or subjected to sham procedures. TLR-3 down-stream signaling was activated already within 3 h of ischemia and reperfusion in post-ischemic kidneys of wt mice lead to impaired blood perfusion followed by a strong pro-inflammatory response with significant neutrophil invasion. In contrast, this effect was absent in TLR-3-/- mice. Moreover, the quick TLR-3 activation resulted in kidney damage that was histomorphologically associated with significantly increased apoptosis and necrosis rates in renal tubules of wt mice. This finding was confirmed by increased kidney injury marker NGAL in wt mice and a better preserved renal perfusion after IR in TLR-3-/- mice than wt mice. Overall, the absence of TLR-3 is associated with lower cumulative kidney damage and maintained renal blood perfusion within the first 24 hours of reperfusion. Thus, we conclude that TLR-3 seems to participate in the pathogenesis of early acute kidney injury.急性肾损伤（AKI）是住院患者最严重的并发症之一，其发病机制尚未完全阐明。我们提出假说：Toll样受体（TLR-3）——一种可通过结合双链核苷酸激活的受体——介导的信号通路，可能在缺血再灌注（IR）相关AKI的发病过程中发挥关键作用。本研究选用成年雄性C57BL6野生型（wt）小鼠与TLR-3基因敲除（-/-）小鼠，分别给予30分钟双侧选择性肾动脉夹闭，随后分别再灌注30分钟、2.5小时及23.5小时，另设假手术组作为对照。实验结果显示，野生型小鼠的缺血再灌注肾脏内，TLR-3下游信号通路在缺血再灌注3小时内即被激活，进而导致血液灌注受损，随后引发强烈的促炎反应，并伴随显著的中性粒细胞浸润。与之相反，此类效应在TLR-3基因敲除小鼠中并未出现。此外，TLR-3的快速激活会引发肾损伤，在组织形态学上表现为野生型小鼠肾小管的凋亡与坏死率显著升高。这一发现得到了两项实验指标的验证：野生型小鼠的肾损伤标志物NGAL水平显著升高，且TLR-3基因敲除小鼠在缺血再灌注后的肾脏灌注保留情况优于野生型小鼠。总体而言，在再灌注最初24小时内，TLR-3的缺失与更低的累积肾损伤及良好的肾脏血液灌注维持相关。因此，我们得出结论：TLR-3似乎参与了早期AKI的发病过程。