Premium
Mathematical model of megalin trafficking in differentiated proximal tubule cells and its application in Dent disease
Author(s) -
Shipman Katherine,
Long Kimberly R,
Rbaibi Youssef,
Baty Catherine J,
Weisz Ora A
Publication year - 2019
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.2019.33.1_supplement.751.5
Subject(s) - endocytic cycle , endocytosis , microbiology and biotechnology , chemistry , receptor , endosome , proximal tubule , biology , kidney , biochemistry , endocrinology
The polarized epithelial cells that comprise the proximal tubule (PT) have a specialized apical endocytic pathway that allows for high‐capacity endocytosis which is necessary to recover essential nutrients and to maintain a protein‐free urine. Megalin, a multi‐ligand receptor at the apical surface of the epithelial cells, binds proteins in the ultrafiltrate and internalizes them via receptor‐mediated endocytosis. Ligands are sorted from receptors in endocytic compartments, and the receptors are recycled back to the surface. The molecular identities of the compartments involved in sorting and recycling in PT cells and the kinetics of megalin trafficking through them are unknown. When endocytosis in the proximal tubule is dysfunctional, tubular proteinuria results. Dent disease, an X‐linked disorder characterized by tubular proteinuria that progresses to renal failure, is caused by mutations in the Cl‐/H+ exchanger CLC‐5. Loss of CLC‐5 has been shown to reduce endocytic uptake and to decrease megalin protein expression without altering mRNA levels. However, the mechanism by which this occurs is unclear. We previously discovered that OK cells cultured under continuous fluid shear stress develop morphological and functional features similar to that of the PT in vivo , including high apical endocytic capacity and increased megalin expression. We used data obtained through biochemical approaches to estimate endocytic and recycling rates and the half‐life of surface megalin in untreated and CLC‐5 knockdown OK cells. These rates were used to construct a simplified model of megalin trafficking in differentiated PT cells. We present an ordinary differential equation (ODE) model of megalin trafficking describing surface and internalized pools of megalin with estimated kinetic parameters. We observed a greater fraction of internalized megalin compared to the surface pool due to an endocytic rate that is much faster than the recycling rate. We have quantified decreases in megalin expression and surface half‐life with loss of CLC‐5 expression. Current and future work includes quantifying alterations in megalin trafficking in CRISPR/Cas9 mediated CLC‐5 KO models and defining the structure and markers of the apical endocytic pathway by quantitative imaging to expand our model to include additional trafficking steps. This model will then be used to predict which steps in megalin trafficking are altered in Dent disease. Support or Funding Information ASN Pre‐Doctoral Fellowship, NIH R01‐DK101484, NIH P30‐DK079307 This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .