Zhang Shao-Yu, Marlier Arnaud, Gribouval Olivier, Gilbert Thierry, Heidet Laurence, Antignac Corinne, Gubler Marie Claire
INSERM U574, Université René Descartes, Hôpital Necker-Enfants Malades, Paris, France.
Kidney Int. 2004 Sep;66(3):945-54. doi: 10.1111/j.1523-1755.2004.00840.x.
Mutations in NPHS2, encoding podocin, are a prevalent cause of autosomal-recessive steroid-resistant nephrotic syndrome (SRNS). Podocin is a protein associated with the slit diaphragm that interacts with nephrin and CD2-associated protein (CD2AP) within lipid rafts.
Using renal biopsies of six patients, we analyzed the in vivo consequences of different types of NPHS2 mutations on (1) the podocyte expression and distribution of podocin using in situ hybridization and immunohistology and (2) the distribution of related podocyte proteins and glomerular extracellular matrix components.
In two patients with homozygous 855_856delAA or 419delG mutation, absence of podocyte labeling with the antibodies against the C-terminal domain contrasted with the normal expression of the N-terminal domain of the protein along the glomerular basement membrane (GBM). In patients carrying compound heterozygous mutations or variants (R168S/467_468insT, R138Q/V180M, and R291W/R229Q), or single heterozygous 976_977insA, podocin transcription appeared unchanged but the distribution of the protein was modified. Podocin was restricted to the podocyte body in the patient carrying the R168S/467_468insT mutation whereas strong immunolabeling of the podocyte body was associated with discrete labeling along the GBM in the three others. In all cases, podocin defect was associated with changes in the distribution of nephrin, CD2AP, and alpha-actinin: the proteins were mainly detected in the podocyte body, with mild expression along the GBM. There were no detectable changes in the distribution of other podocyte proteins or glomerular extracellular matrix components.
NPHS2 mutations result in profound alteration of podocin expression and/or distribution. Secondary changes in the distribution of nephrin, CD2AP, and alpha-actinin are additional evidences for the scaffolding role of podocin in the organization of the slit diaphragm.
编码足突蛋白的NPHS2基因突变是常染色体隐性遗传性类固醇抵抗型肾病综合征（SRNS）的常见病因。足突蛋白是一种与裂孔隔膜相关的蛋白质，在脂筏内与nephrin及CD2相关蛋白（CD2AP）相互作用。
利用6例患者的肾活检组织，我们分析了不同类型NPHS2突变在体内的影响，包括：（1）利用原位杂交和免疫组织学分析足细胞中足突蛋白的表达及分布；（2）分析相关足细胞蛋白及肾小球细胞外基质成分的分布。
在两名携带纯合855_856delAA或419delG突变的患者中，针对C端结构域的抗体未显示足细胞标记，而该蛋白的N端结构域沿肾小球基底膜（GBM）呈正常表达。在携带复合杂合突变或变异（R168S/467_468insT、R138Q/V180M及R291W/R229Q）或单杂合976_977insA的患者中，足突蛋白转录似乎未变，但蛋白分布发生改变。携带R168S/467_468insT突变的患者中，足突蛋白局限于足细胞体，而在其他三名患者中，足细胞体的强免疫标记与沿GBM的离散标记相关。在所有病例中，足突蛋白缺陷均与nephrin、CD2AP及α辅肌动蛋白的分布改变相关：这些蛋白主要在足细胞体中检测到，沿GBM有轻度表达。其他足细胞蛋白或肾小球细胞外基质成分的分布未检测到变化。
NPHS2突变导致足突蛋白表达和/或分布的深刻改变。nephrin、CD2AP及α辅肌动蛋白分布的继发性变化是足突蛋白在裂孔隔膜组织中起支架作用的额外证据。
