Cell Biology, Department of Anatomy, Aarhus University, Aarhus, Denmark.
Nephrol Dial Transplant. 2010 Aug;25(8):2458-67. doi: 10.1093/ndt/gfq044. Epub 2010 Mar 2.
A well-characterized dog model of the X-linked collagen disease Alport syndrome (XLAS) was used to study the effect of progressive glomerular disease on megalin-mediated endocytosis. In XLAS, altered structure and function of the glomerular basement membrane induces a progressive proteinuric nephropathy.
The investigation was performed in male XLAS dogs and age-matched normal male littermates. The urine profile and megalin-mediated endocytosis in the proximal tubule of six healthy and six XLAS dogs were examined at 2, 4, 6, 8 and 10 months of age using SDS-PAGE, immunoblotting and immunohistochemistry.
Gradually increasing urinary excretion of proteins over time and a reduced content of the same proteins in proximal tubule cells were found. Besides the glomerular component of the proteinuria, a significant tubular component was seen, which is due to a progressive change in the uptake of low-molecular-weight (LMW) ligands by megalin. Furthermore, the protein overload present in the lumen of the proximal tubule exceeds the reabsorption capacity of megalin and the co-receptor cubilin and results in a combined low- and high-molecular-weight (HMW) proteinuria. Also, a shift in the distribution of lysosomes was seen in the XLAS dogs suggesting changes in the lysosomal degradation pattern in response to the altered endocytosis.
The present study shows that the increased glomerular permeability and the subsequently altered megalin-mediated and megalin-dependent cubilin-mediated endocytosis lead to a partial LMW proteinuria and partial HMW proteinuria.
本研究使用一种特征明确的犬 X 连锁胶原蛋白疾病 Alport 综合征（XLAS）模型，研究进行性肾小球疾病对 megalin 介导的内吞作用的影响。在 XLAS 中，肾小球基底膜结构和功能的改变会导致进行性蛋白尿肾病。
本研究在雄性 XLAS 犬和年龄匹配的正常雄性同窝仔犬中进行。在 2、4、6、8 和 10 月龄时，通过 SDS-PAGE、免疫印迹和免疫组化检查 6 只健康犬和 6 只 XLAS 犬的尿谱和近端肾小管中 megalin 介导的内吞作用。
随着时间的推移，尿蛋白逐渐增加，近端肾小管细胞中同一蛋白的含量减少。除了蛋白尿的肾小球成分外，还观察到明显的肾小管成分，这是由于 megalin 对低分子量（LMW）配体的摄取逐渐发生变化。此外，近端肾小管管腔中存在的蛋白过载超过了 megalin 和协同受体 cubilin 的重吸收能力，导致低分子量（LMW）和高分子量（HMW）蛋白尿的混合。此外，还观察到 XLAS 犬溶酶体分布发生转移，表明溶酶体降解模式发生变化，以应对改变的内吞作用。
本研究表明，肾小球通透性增加，随后改变的 megalin 介导和 megalin 依赖性 cubilin 介导的内吞作用导致部分 LMW 蛋白尿和部分 HMW 蛋白尿。
