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Mechanisms Underlying Increased TIMP2 and IGFBP7 Urinary Excretion in Experimental AKI
Journal of the American Society of Nephrology ( IF 13.6 ) Pub Date : 2018-08-01 , DOI: 10.1681/asn.2018030265
Ali C.M. Johnson , Richard A. Zager

Background Recent clinical data support the utility/superiority of a new AKI biomarker (“NephroCheck”), the arithmetic product of urinary TIMP × IGFBP7 concentrations. However, the pathophysiologic basis for its utility remains ill defined.

Methods To clarify this issue, CD-1 mice were subjected to either nephrotoxic (glycerol, maleate) or ischemic AKI. Urinary TIMP2/IGFBP7 concentrations were determined at 4 and 18 hours postinjury and compared with urinary albumin levels. Gene transcription was assessed by measuring renal cortical and/or medullary TIMP2/IGFBP7 mRNAs (4 and 18 hours after AKI induction). For comparison, the mRNAs of three renal “stress” biomarkers (NGAL, heme oxygenase 1, and p21) were assessed. Renal cortical TIMP2/IGFBP7 protein was gauged by ELISA. Proximal tubule–specific TIMP2/IGFBP7 was assessed by immunohistochemistry.

Results Each AKI model induced prompt (4 hours) and marked urinary TIMP2/IGFBP7 increases without an increase in renal cortical concentrations. Furthermore, TIMP2/IGFBP7 mRNAs remained at normal levels. Endotoxemia also failed to increase TIMP2/IGFBP7 mRNAs. In contrast, each AKI model provoked massive NGAL, HO-1, and p21 mRNA increases, confirming that a renal “stress response” had occurred. Urinary albumin rose up to 100-fold and strongly correlated (r=0.87–0.91) with urinary TIMP2/IGFBP7 concentrations. Immunohistochemistry showed progressive TIMP2/IGFBP7 losses from injured proximal tubule cells. Competitive inhibition of endocytic protein reabsorption in normal mice tripled urinary TIMP2/IGFBP7 levels, confirming this pathway’s role in determining urinary excretion.

Conclusions AKI-induced urinary TIMP2/IGFBP7 elevations are not due to stress-induced gene transcription. Rather, increased filtration, decreased tubule reabsorption, and proximal tubule cell TIMP2/IGFBP7 urinary leakage seem to be the most likely mechanisms.



中文翻译:

实验性AKI中TIMP2和IGFBP7尿排泄增加的机制

背景技术最近的临床数据支持了新型AKI生物标志物(“ NephroCheck”)的实用性/优越性,该标志物是尿TIMP×IGFBP7浓度的算术乘积。然而,其效用的病理生理学基础仍然不清楚。

方法为了澄清这个问题,对CD-1小鼠进行了肾毒性(甘油,马来酸盐)或缺血性AKI的治疗。在损伤后4小时和18小时测定尿中TIMP2 / IGFBP7的浓度,并将其与尿白蛋白水平进行比较。通过测量肾皮质和/或髓质TIMP2 / IGFBP7 mRNA(AKI诱导后4和18小时)评估基因转录。为了进行比较,评估了三种肾脏“应激”生物标志物(NGAL,血红素加氧酶1和p21)的mRNA。肾皮质TIMP2 / IGFBP7蛋白通过ELISA测定。通过免疫组织化学评估近端小管特异性TIMP2 / IGFBP7。

结果每个AKI模型诱导的提示(4小时)和明显的尿TIMP2 / IGFBP7升高,而肾皮质浓度却没有升高。此外,TIMP2 / IGFBP7 mRNA保持正常水平。内毒素血症也未能增加TIMP2 / IGFBP7 mRNA。相反,每个AKI模型都引起大量NGAL,HO-1和p21 mRNA的增加,从而证实发生了肾脏“应激反应”。尿白蛋白上升至100倍,并与尿TIMP2 / IGFBP7浓度高度相关(r = 0.87–0.91)。免疫组织化学显示损伤的近端小管细胞逐渐发生TIMP2 / IGFBP7丢失。正常小鼠中竞争性抑制内吞蛋白的重吸收使尿TIMP2 / IGFBP7水平增加了三倍,证实了该途径在确定尿排泄中的作用。

结论AKI引起的尿中TIMP2 / IGFBP7升高并不是由于应激引起的基因转录。相反,增加的过滤,减少的肾小管重吸收和近端肾小管细胞TIMP2 / IGFBP7尿液渗漏似乎是最可能的机制。

更新日期:2018-08-01
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