| Project/Area Number |
16590809
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Kidney internal medicine
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| Research Institution | Osaka Medical Center and Research Institute for Maternal and Child Health, Osaka Hospital Organization |
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Principal Investigator |
MICHIGAMI Toshimi Osaka Medical Center and Research Institute for Maternal and Child Health, Osaka Hospital Organization, Department of Environmental Medicine, Chief, 環境影響部門, 部長 (00301804)
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| Co-Investigator(Kenkyū-buntansha) |
KONDOU Hiroki Osaka Medical Center and Research Institute for Maternal and Child Health, Osaka Hospital Organization, Senior Researcher, 主任研究員 (10373515)
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| Project Period (FY) |
2004 – 2005
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| Project Status |
Completed (Fiscal Year 2005)
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| Budget Amount *help |
¥3,000,000 (Direct Cost: ¥3,000,000)
Fiscal Year 2005: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 2004: ¥2,300,000 (Direct Cost: ¥2,300,000)
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| Keywords | megalin / endocytosis / phosphate / reabsorption / sodium / phosphate co-transporter / receptor associated protein (RAP) / vitamin D |
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| Research Abstract |
Megalin is a multifunctional endocytic receptor expressed in renal proximal tubules, and plays critical roles in the renal uptake of various proteins. We hypothesized that megalin-dependent endocytosis might play a role in renal reabsorption of inorganic phosphate. To address the short-term effects of altered megalin function, we administered a recombinant protein for the soluble form of 39-kD receptor associated protein (RAP) intraperitoneally to 7-wk-old mice. The recombinant protein was prepared as histidine-tagged soluble RAP (aa 39-356) lacking the amino-terminal signal peptide and the carboxyl terminal endoplasmic reticulum (ER) retention signal, which was designated as His-sRAP. After the direct interaction between His-sRAP and megalin was confirmed, mice were given a single intraperitoneal injection of His-sRAP (3.5 mg/dose). Immunostaining and Western blot analyses demonstrated that the uptake of His-sHAP and the accelerated internalization of megalin in proximal tubular cells 1 hour after administration. Interestingly, internalization of the type II sodium/phosphate co-transporter (NaPi-II) was observed. Three sequential administrations of His-sRAP (3.5 mg/dose, three doses with 4-hr intervals) increased the urinary excretion of low molecular weight proteins including vitamin D-binding protein. In addition, the urinary excretion of phosphate was also increased, and the protein level of NaPi-II in the brush border was decreased. Serum 25-hydroxyvitamin D was decreased, while the plasma level of intact parathyroid hormone was not altered. These results suggest that the His-sRAP induced acceleration of megalin-mediated endocytosis caused phosphaturia via altered subcellular distribution of NaPi-II.
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