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Kidney-specific inactivation of the megalin gene impairs trafficking of renal inorganic sodium phosphate cotransporter (NaPi-IIa).


Bachmann, S; Schlichting, U; Geist, B; Mutig, K; Petsch, T; Bacic, D; Wagner, C A; Kaissling, B; Biber, J; Murer, H; Willnow, T E (2004). Kidney-specific inactivation of the megalin gene impairs trafficking of renal inorganic sodium phosphate cotransporter (NaPi-IIa). Journal of the American Society of Nephrology (JASN), 15(4):892-900.

Abstract

Renal reabsorption of inorganic phosphate is mediated by the type IIa sodium phosphate cotransporter (NaPi-IIa) of the proximal tubule. Changes in renal phosphate handling are mainly attributable to altered NaPi-IIa brush border membrane (BBM) expression. Parathyroid hormone (PTH) induces inactivation of NaPi-IIa by endocytic membrane retrieval and degradation. The key elements triggering this process are not clear to date. Megalin serves as a receptor for the endocytosis of multiple ligands and is coexpressed with NaPi-IIa in the proximal tubule. Investigated was the role of megalin in the regulation of NaPi-IIa in steady state and during inactivation. Kidneys and tubular BBM fractions from mice with a renal-specific megalin gene defect and from controls were analyzed by light and electron microscopic histochemical techniques and Western blot test. Steady-state levels of NaPi-IIa in BBM were significantly enhanced, mRNA levels preserved, and phosphaturia reduced in the absence of megalin. Fluid-phase endocytosis was prevented and the apical endocytic apparatus markedly reduced. Systemic administration of PTH resulted in a defective retrieval and impaired degradation of NaPi-IIa. In vitro, the application of various stimuli of the PTH-induced signaling cascade had no effect either. Adequate steady-state expression of NaPi-IIa and the capacity of the proximal tubule cell to react on PTH-driven inactivation of NaPi-IIa by endocytosis and intracellular translocation require the presence of megalin.

Renal reabsorption of inorganic phosphate is mediated by the type IIa sodium phosphate cotransporter (NaPi-IIa) of the proximal tubule. Changes in renal phosphate handling are mainly attributable to altered NaPi-IIa brush border membrane (BBM) expression. Parathyroid hormone (PTH) induces inactivation of NaPi-IIa by endocytic membrane retrieval and degradation. The key elements triggering this process are not clear to date. Megalin serves as a receptor for the endocytosis of multiple ligands and is coexpressed with NaPi-IIa in the proximal tubule. Investigated was the role of megalin in the regulation of NaPi-IIa in steady state and during inactivation. Kidneys and tubular BBM fractions from mice with a renal-specific megalin gene defect and from controls were analyzed by light and electron microscopic histochemical techniques and Western blot test. Steady-state levels of NaPi-IIa in BBM were significantly enhanced, mRNA levels preserved, and phosphaturia reduced in the absence of megalin. Fluid-phase endocytosis was prevented and the apical endocytic apparatus markedly reduced. Systemic administration of PTH resulted in a defective retrieval and impaired degradation of NaPi-IIa. In vitro, the application of various stimuli of the PTH-induced signaling cascade had no effect either. Adequate steady-state expression of NaPi-IIa and the capacity of the proximal tubule cell to react on PTH-driven inactivation of NaPi-IIa by endocytosis and intracellular translocation require the presence of megalin.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:04 Faculty of Medicine > Institute of Physiology
07 Faculty of Science > Institute of Physiology
Dewey Decimal Classification:570 Life sciences; biology
Language:English
Date:1 April 2004
Deposited On:11 Feb 2008 12:22
Last Modified:05 Apr 2016 12:18
Publisher:American Society of Nephrology
ISSN:1046-6673
Publisher DOI:10.1097/01.ASN.0000120389.09938.21
PubMed ID:15034091

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