Rampoldi Luca, Caridi Gianluca, Santon Daniela, Boaretto Francesca, Bernascone Ilenia, Lamorte Giuseppe, Tardanico Regina, Dagnino Monica, Colussi Giacomo, Scolari Francesco, Ghiggeri Gian Marco, Amoroso Antonio, Casari Giorgio
DIBIT-San Raffaele Scientific Institute, Via Olgettina 58, 20132 Milan, Italy.
Hum Mol Genet. 2003 Dec 15;12(24):3369-84. doi: 10.1093/hmg/ddg353. Epub 2003 Oct 21.
The disease complex medullary cystic disease/familial juvenile hyperuricemic nephropathy (MCKD/FJHN) is characterized by alteration of urinary concentrating ability, frequent hyperuricemia, tubulo-interstitial fibrosis, cysts at the cortico-medullary junction and renal failure. MCKD/FJHN is caused by mutations of the gene encoding uromodulin, the most abundant protein in urine. Here, we describe new missense mutations in three families with MCKD/FJHN and demonstrate allelism with a glomerulocystic kidney disease (GCKD) variant, showing association of cyst dilatation and collapse of glomeruli with some clinical features similar to MCKD/FJHN as hyperuricemia and impairment of urine concentrating ability. Furthermore, we provide the first functional characterization of uromodulin mutations. The four newly identified mutants were characterized by immunofluorescence and FACS analysis on transfected cells. These experiments showed that all uromodulin mutations cause a delay in protein export to the plasma membrane due to a longer retention time in the endoplasmic reticulum. Immunohistochemistry on GCKD and MCKD/FJHN kidney biopsies revealed dense intracellular accumulation of uromodulin in tubular epithelia of the thick ascending limb of Henle's loop. Electron microscopy demonstrated accumulation of dense fibrillar material within the endoplasmic reticulum. Consistently, patient urines show a severe reduction of excreted uromodulin. The maturation impairment is consistent with the clinical findings and suggests a pathogenetic mechanism leading to these kidney diseases.
髓质囊性疾病/家族性青少年高尿酸血症肾病（MCKD/FJHN）这一疾病复合体的特征为尿浓缩能力改变、频繁高尿酸血症、肾小管间质纤维化、皮质-髓质交界处囊肿及肾衰竭。MCKD/FJHN由编码尿调节蛋白（尿液中最丰富的蛋白质）的基因突变引起。在此，我们描述了三个MCKD/FJHN家族中的新错义突变，并证明其与肾小球囊性肾病（GCKD）变体的等位性，显示囊肿扩张和肾小球塌陷与一些类似于MCKD/FJHN的临床特征相关，如高尿酸血症和尿浓缩能力受损。此外，我们首次对尿调节蛋白突变进行了功能表征。通过对转染细胞进行免疫荧光和流式细胞术分析，对四个新鉴定的突变体进行了表征。这些实验表明，所有尿调节蛋白突变均导致蛋白质向质膜输出延迟，原因是在内质网中的保留时间延长。对GCKD和MCKD/FJHN肾活检组织进行免疫组织化学分析显示，亨氏袢厚升支肾小管上皮细胞内尿调节蛋白密集积聚。电子显微镜显示内质网内有致密纤维状物质积聚。同样，患者尿液中排出的尿调节蛋白严重减少。成熟障碍与临床发现一致，并提示了导致这些肾脏疾病的发病机制。
