Raggi Claudia, Luciani Alessandro, Nevo Nathalie, Antignac Corinne, Terryn Sara, Devuyst Olivier
Division of Nephrology, Université catholique de Louvain, Brussels, Belgium.
Hum Mol Genet. 2014 May 1;23(9):2266-78. doi: 10.1093/hmg/ddt617. Epub 2013 Dec 6.
Nephropathic cystinosis, a lysosomal storage disease caused by mutations in the CTNS gene encoding the lysosomal cystine transporter cystinosin, is characterized by generalized proximal tubule (PT) dysfunction that progresses, if untreated, to end-stage renal disease. The pathogenesis of defective PT cellular transport in nephropathic cystinosis remains unclear. We characterized a recently generated line of C57BL/6 Ctns mice and analyzed endocytic uptake, lysosome function, and dedifferentiation and proliferation markers using primary cultures of PT epithelial cells derived from Ctns(-/-) and Ctns(+/+) littermates. Metabolic studies revealed that Ctns(-/-) mice show a progressive PT dysfunction characterized by low-molecular-weight (LMW) proteinuria, glucosuria and phosphaturia, before structural damage and in the absence of renal failure. These changes are related to decreased expression of the multi-ligand receptors megalin and cubilin and to increased dedifferentiation (ZONAB transcription factor) and proliferation (PCNA and Cyclin D1) rates. Studies on PT cells derived from Ctns(-/-) kidneys confirmed cystine overload, with accumulation of enlarged, dysfunctional lysosomes and reduced expression of endocytic receptors reflected by decreased uptake of specific ligands. These changes were related to a loss of integrity of tight junctions with a nuclear translocation of ZONAB and increased proliferation, as observed in Ctns(-/-) kidneys. These data reveal that the absence of cystinosin in PT cells triggers aberrations of the endolysosomal compartment, transport defects and an abnormal transcription program in the early stage of nephropathic cystinosis. Insights into the early manifestations of cystinosis may offer new targets for intervention, before irreversible renal damage.
肾病性胱氨酸贮积症是一种溶酶体贮积病，由编码溶酶体胱氨酸转运体胱氨酸转运蛋白的CTNS基因突变引起，其特征是广泛性近端肾小管（PT）功能障碍，若不治疗，会进展为终末期肾病。肾病性胱氨酸贮积症中PT细胞转运缺陷的发病机制仍不清楚。我们对最近培育出的C57BL/6 Ctns小鼠品系进行了表征，并使用来自Ctns（-/-）和Ctns（+/ +）同窝小鼠的PT上皮细胞原代培养物分析了内吞摄取、溶酶体功能以及去分化和增殖标志物。代谢研究表明，Ctns（-/-）小鼠在结构损伤之前且在无肾衰竭的情况下，表现出以低分子量（LMW）蛋白尿、糖尿和磷酸盐尿为特征的进行性PT功能障碍。这些变化与多配体受体巨蛋白和立方蛋白的表达降低以及去分化（ZONAB转录因子）和增殖（PCNA和细胞周期蛋白D1）率增加有关。对来自Ctns（-/-）肾脏的PT细胞的研究证实了胱氨酸过载，表现为扩大的、功能失调的溶酶体积累以及内吞受体表达降低，这通过特定配体摄取减少得以体现。这些变化与紧密连接完整性丧失、ZONAB核转位以及增殖增加有关，正如在Ctns（-/-）肾脏中所观察到的那样。这些数据表明，PT细胞中胱氨酸转运蛋白的缺失在肾病性胱氨酸贮积症早期引发了内溶酶体区室异常、转运缺陷和异常转录程序。在不可逆的肾脏损伤之前，对胱氨酸贮积症早期表现的深入了解可能会提供新的干预靶点。
