Characterization of Atp6ap2 ((Pro)‐Renin Receptor) in Receptor Mediated Endocytosis by the Renal Proximal Tubule

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Atp6ap2 may be an accessory subunit of the V‐type H+ ATPase regulating organellar, cellular, and systemic acid‐base homeostasis. Here we examine whether the knock‐down of Atp6ap2 affects renal V‐ATPase function in the proximal tubule. There, V‐ATPases are important for receptor‐mediated endocytosis of low molecular weight proteins from urine via the megalin/cubilin receptors. In order to elucidate the role of Atp6ap2 in this function we used an inducible shRNA Atp6ap2 rat model and a doxycyline‐inducible kidney specific Atp6ap2 KO mouse model. Knock‐down of Atp6ap2 reduced Atp6ap2 expression by approximately 90 %. Atp6ap2 knock‐down animals showed higher proteinuria (albumin and Vitamin D binding protein).To further examine proximal tubular endocytosis, we injected animals with markers for fluid phase endocytosis (FITC‐ dextran, 10 kDa) and a for receptor mediated endocytosis (human transferrin). Immunofluorescence of kidney slices from both animal groups did not show a difference in FITC‐dextran intensity or localization. Furthermore, evaluation of receptor mediated endocytosis of human transferrin, showed in immunofluorescence stainings no differences between the animal groups but the knock‐down animals excreted human transferrin in the urine while control animal did not so. Hence, our data suggests a possible role for ATP6ap2 for proximal tubule function in the kidney; however, the defect in receptor‐mediated endocytosis is mild in rats and mice.Funded by the Swiss National Science Foundation.