9.B.87 The Selenoprotein P Receptor (SelP-Receptor) Family
Selenoprotein P (SelP) contains most of the selenium in blood plasma, and it is utilized by the kidney, brain and testis as a selenium source for selenoprotein synthesis. Apolipoprotein E receptor-2 (ApoER2) is required for SelP uptake by the testis, and deletion of ApoER2 reduces testis and brain, but not kidney, selenium levels. Neither the C-terminus selenocysteine-rich domain of SelP nor ApoER2 were required for SelP uptake by proximal tubules. SelP binds megalin, a lipoprotein receptor localized to the proximal tubule epithelium. Proximal tubules don't take up SelP in megalin null mice. Thus, kidney selenium homeostasis is mediated by a megalin-dependent SelP uptake pathway in the proximal tubule (Olson et al., 2008) that may use an endocytic mechanism (Thévenod, 2010).