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Mathematical model of megalin trafficking in differentiated proximal tubule cells
Author(s) -
Shipman Katherine E.,
Long Kimberly R.,
Rbaibi Youssef,
Baty Catherine J.,
Weisz Ora A.
Publication year - 2018
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.2018.32.1_supplement.850.4
Subject(s) - endocytic cycle , endocytosis , microbiology and biotechnology , receptor , chemistry , receptor mediated endocytosis , apical membrane , biology , biochemistry , membrane
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 the endocytosis in the proximal tubule is dysfunctional, low molecular weight (LMW) proteinuria results. LMW proteinuria is often an early sign of kidney damage and is observed in many clinical settings, including genetic disorders, diabetes, sickle cell disease, and after renal transplantation. A significant barrier to understanding the regulation of receptor‐mediated apical endocytosis of filtered proteins has been the lack of a highly differentiated cell culture model that retains the organization and high capacity of the PT apical endocytic pathway. 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 present an ordinary differential equation (ODE) model of megalin trafficking describing surface and internalized pools of megalin with kinetic parameters estimated from experiments using this system. Using biochemical techniques, we have estimated endocytic and recycling rates and the half‐life of surface megalin. The model is capable of achieving a steady‐state with a much larger pool of internalized megalin compared to surface within a range of realistic parameters; this is consistent with observations made by our biochemical assays and by indirect immunofluorescence of endogenous megalin. Future work includes estimated surface delivery kinetics and defining the structure and markers of the apical endocytic pathway in OK cells and mouse kidney sections using quantitative imaging. With these data, our model can be expanded and used to predict changes in megalin trafficking in response to changes in filtration rates, hormones, and in disease states. Support or Funding Information NIH R01 DK101484, R01 DK100357 This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .