| Summary: | 博士 === 國立臺灣大學 === 臨床醫學研究所 === 103 === Childhood idiopathic nephrotic syndrome (INS) is mainly caused by minimal change disease because only subtle ultrastructural alteration could be observed at electron microscopic level in the pathological examination. Glomerular podocytes are currently presumed to be the target cells in nephrotic syndrome whose protein sieving capability is compromised by a yet unidentified permeability perturbing factor.
For the majority of INS cases in children, they manifest minimal change disease and lack apparent direct targets specific for podocytes. Other components of the glomerular protein sieving apparatus, such as the glomerular endothelial cells might play any functional role in childhood nephrotic syndrome remains to be undetermined.
INS pediatric patients who were diagnosed in National Taiwan University Hospital during 2008-2012 were enrolled in this study and a human cytokine antibody array was exploited to analyze the cytokine profiles. In animal model establishment, six-week-old male ICR mice were treated with normal saline and recombinant mouse C5a respectively with the dose of 10 μg/kg every three days through tail vein injection. Blood and urine samples were collected. After 21 days, mice were sacrificed for pathology study. The glomeruli were isolated from minced kidneys, and the kidney endothelial cells bound to the magnetic beads were isolated and preparing for protein permeability assay on endothelial monolayer, immunofluorescence and F-actin staining and GTP-Rho pull-down assay. All the data were expressed as mean ± SD. Comparisons for continuous data between relapse and remission in INS patients were made by paired t-test. In animal studies, a two-tailed t-test was used in analysis of biochemical data between two groups. In cell study, a two-tailed t-test was statistically significant differences between two groups. A p < 0.05 was statistically significant cut-off value.
In a cohort study of INS children, we found the complement fragment C5a was elevated in their sera during relapse status. Administration of recombinant C5a induced profound proteinuria and minimal change nephrotic syndrome in mice. Purified glomerular endothelial cells, instead of podocytes, were demonstrated to be responsible for the proteinuric effect elicited by C5a. Further studies depicted a signaling pathway involving Rho/Rho-associated kinase/myosin activation leading to endothelial cell contraction and cell adhesion complex breakdown. Significantly, application of Rho-associated kinase inhibitor, Y27632, prevented the protein leaking effects observed in both C5a-treated purified endothelial cells and mice.
Our study identifies a previously unknown mechanism causing pediatric INS and provides a new insight toward identifying Rho-associated kinase in kidney endothelial cells as a possible pathogenesis induced proteinuria in INS and a considerable alternative therapeutic option for children with nephrotic syndrome.
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