Figure 2.

Megalin ablation in Ctns^−/− kidneys prevents cystine accumulation and crystal deposition. (A) Comparison of cystine content in kidneys, liver, and spleen between Ctns^−/− and double KO mice at 9 months of age for males (filled squares) or females (filled circles) (**P<0.01). Red and orange symbols refer to Ctns^−/− mice with either two floxed megalin alleles but no Wnt4-CRE, or one Wnt4-CRE but no floxed megalin allele, respectively. For time course of cystine accumulation between 6 and 9 months, see Supplemental Figure 2. (B) Histologic evidence of cystine crystals (red arrowheads) by polarized light (top panel) and green pseudo-color (bottom panel) in Ctns^−/− kidneys (a, b, c, d) versus their absence in double KO kidneys at 7.5 months (e, f). For large fields, see Supplemental Figure 3. (C) Triple confocal fluorescence imaging of N-fucosyl glycosides (LT-lectin, blue), megalin (red), and late-endosome/lysosome membrane (LAMP-1, green) at 6 months. In control PTCs, brush border is uniformly purple (combined blue and red emissions); lysosomes are all round and of similar size. In Ctns^−/− PTCs, notice several enlarged and deformed lysosomes due to cystine crystal buildup (red arrowheads); brush border is preserved here. In double KO PTCs, brush border is only labeled in blue in most cells, reflecting megalin absence, and LAMP-1 signal is much reduced by comparison with controls as a consequence of abrogation of endocytic uptake. LT-lectin, L. tetragonolobus lectin.