Am. J. Respir. Cell Mol. Biol., Volume 27, Number 1, July, 2002 57-63

HDL-Holoparticle Uptake by Alveolar Type II Cells
Effect of Vitamin E Status

Ingrid Kolleck, Heide Wissel, Florian Guthmann, Michael Schlame, Pranav Sinha, and Bernd Rüstow

Department of Neonatology, University Hospital Charité, Humboldt-University of Berlin, Berlin; Institute of Laboratory Medicine and Pathobiochemistry, Humboldt-University of Berlin, Berlin, Germany; and Department of Anesthesiology, Hospital for Special Surgery, Cornell University Medical College, New York, New York

Alveolar type II cells accumulate vitamin E preferentially from high-density lipoproteins (HDL) and express at least three receptors that are specific for HDL. The expression of these receptors increases in response to vitamin E deficiency. Beside receptors for specific lipid transfer from HDL, cubilin and megalin, several other receptors that mediate HDL-particle uptake were found in the lung. We hypothesize that alveolar type II cells also exhibit the HDL-particle uptake and that this process can be regulated by the vitamin E status. By confocal laser microscopy and flow cytometry we showed that type II cells accumulate protein-labeled HDL-particle. Vitamin E depletion in rats increased HDL-particle uptake in alveolar type II cells and the expression of megalin. The expression of cubilin did not change. Refeeding with vitamin E reversed HDL-particle uptake and megalin expression. Long-time incubation of type II cells with phorbol myristyl acetate (PMA) reduced HDL-holoparticle uptake and megalin expression. We assume that alveolar type II cells exhibit HDL-holoparticle uptake mediated by megalin and cubilin. Megalin represents the regulated element of the megalin/cubilin receptor-cooperation and can be modulated by protein kinase C.

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