Largo R, Gómez-Garre D, Soto K, Marrón B, Blanco J, Gazapo R M, Plaza J J, Egido J
Renal and Vascular Research Laboratory, Fundación Jiménez Díaz, Universidad Autónoma, Madrid, Spain.
Hypertension. 1999 Feb;33(2):732-9. doi: 10.1161/01.hyp.33.2.732.
Persistent proteinuria is considered a deleterious prognostic factor in most progressive renal diseases. However, the mechanisms by which proteinuria induces renal damage remain undetermined. Since proximal tubular cells possess all the machinery to generate angiotensin II (Ang II), we approached the hypothesis that proteinuria could elicit the renal activation of the renin-angiotensin system in a model of intense proteinuria and interstitial nephritis induced by protein overload. After uninephrectomy (UNX), Wistar-Kyoto rats received daily injections of 1 g BSA or saline for 8 days. The mean peak of proteinuria was observed at the fourth day (538+/-89 versus 3+/-1 mg/24 h in UNX controls; n=12; P<0.05) and was increased during the whole study period (at the eighth day: 438+/-49 mg/24 h; n=12; P=NS). Morphological examination of the kidneys at the end of the study showed marked tubular lesions (atrophy, vacuolization, dilation, and casts), interstitial infiltration of mononuclear cells, and mesangial expansion. In relation to UNX control rats, renal cortex of BSA-overloaded rats showed an increment in the gene expression of angiotensinogen (2.4-fold) and angiotensin-converting enzyme (ACE) (2.1-fold), as well as a diminution in renin gene expression. No changes were observed in angiotensin type 1 (AT1) receptor mRNA expression in both groups of rats. By in situ reverse transcription-polymerase chain reaction and immunohistochemistry, ACE expression (gene and protein) was mainly localized in proximal and distal tubules and in the glomeruli. By immunohistochemistry, angiotensinogen was localized only in proximal tubules, and AT1 receptor was localized mainly in proximal and distal tubules. In the tubular brush border, an increase in ACE activity was also seen (5. 5+/-0.5 versus 3.1+/-0.7 U/mg protein x10(-4) in UNX control; n=7; P<0.05). Our results show that in the kidney of rats with intense proteinuria, ACE and angiotensinogen were upregulated, while gene expression of renin was inhibited and AT1 was unmodified. On the whole, these data suggest an increase in Ang II intrarenal generation. Since Ang II can elicit renal cell growth and matrix production through the activation of AT1 receptor, this peptide may be responsible for the tubulointerstitial lesions occurring in this model. These results suggest a novel mechanism by which proteinuria may participate in the progression of renal diseases.
持续性蛋白尿被认为是大多数进行性肾脏疾病中的一个有害预后因素。然而，蛋白尿诱发肾损伤的机制仍未明确。由于近端肾小管细胞具备生成血管紧张素II（Ang II）的所有机制，我们探讨了这样一个假说：在蛋白质负荷诱导的严重蛋白尿和间质性肾炎模型中，蛋白尿可能引发肾素-血管紧张素系统的肾脏激活。单侧肾切除（UNX）后，Wistar-Kyoto大鼠每日注射1 g牛血清白蛋白（BSA）或生理盐水，共8天。蛋白尿的平均峰值在第4天观察到（UNX对照组为538±89 vs 3±1 mg/24 h；n = 12；P<0.05），且在整个研究期间均升高（第8天：438±- 49 mg/24 h；n = 12；P =无显著差异）。研究结束时肾脏的形态学检查显示明显的肾小管病变（萎缩、空泡化、扩张和管型）、单核细胞间质浸润和系膜扩张。与UNX对照大鼠相比，BSA负荷过重大鼠的肾皮质血管紧张素原基因表达增加（2.4倍），血管紧张素转换酶（ACE）基因表达增加（2.1倍），而肾素基因表达减少。两组大鼠的血管紧张素1型（AT1）受体mRNA表达均未观察到变化。通过原位逆转录-聚合酶链反应和免疫组织化学，ACE表达（基因和蛋白）主要定位于近端和远端肾小管以及肾小球。通过免疫组织化学，血管紧张素原仅定位于近端肾小管，而AT1受体主要定位于近端和远端肾小管。在肾小管刷状缘，也观察到ACE活性增加（5.5±0.5 vs UNX对照组3.1±0.7 U/mg蛋白×10⁻⁴；n = 7；P<0.05）。我们的结果表明，在严重蛋白尿大鼠的肾脏中，ACE和血管紧张素原上调，而肾素基因表达受到抑制，AT1未改变。总体而言，这些数据提示肾脏内Ang II生成增加。由于Ang II可通过激活AT1受体引发肾细胞生长和基质产生，该肽可能是此模型中发生的肾小管间质病变的原因。这些结果提示了蛋白尿可能参与肾脏疾病进展的一种新机制。
