Dents disease is a renal proximal tubular Fanconi disorder characterised by generalised loss of solutes incuding insulin, glucose, PTH, amino acids and vitamin-D binding protein and is associated with rickets in 25% and phosphaturia in ~40% of patients. Dents disease is caused by mutations in the chloride/proton antiporter CLC-5, which, with megalin and cubilin has a role in receptor-mediated endocytosis and vesicle trafficking. To further elucidate the role of CLC-5 in endosomal trafficking, we performed gene expression profiling using Illuminas Human-HT2v4 BeadChip utilising three human conditionally-immortalised proximal tubular epithelial cell-lines (ciPTECs) that harboured one of three CLC-5 mutations: an in-frame histidine insertion at codon 30 (30:insHis), a deletion of codons 132 to 241 (del132241) and a nonsense mutation (Arg637Stop) (n=5 for each ciPTEC). Differentially expressed genes with a minimal fold-change of 1.5 and a P<0.05 were further analysed. Sixty-seven genes were differentially expressed in all three Dents disease ciPTECs, and individually, the ciPTECs had 107 (30:insHis), 272 (del132-241) and 375 (Arg637Stop) differentially expressed genes. Pathway analysis revealed that two functional pathways, which involved endocytosis/actin dynamics and solute transport, were commonly affected. Quantitative PCR and Western blot analysis confirmed that promoters of actin polymerization were upregulated and inhibitors of actin polymerisation were downregulated in Dents disease ciPTECs; these would lead to increased plasma membrane directed vesicular movement, and reduced trafficking from membrane to early endosome. In addition, several small GTPases that regulate early endosomal trafficking were downregulated. Furthermore, Dents disease ciPTECs had decreased expression of a number of solute transport genes including SLC38A5, an amino acid transporter, and glucose transporters, which may contribute to the observed aminoaciduria and glycosuria in patients. Investigation of these dysregulated pathways may help to elucidate the mechanisms by which CLC-5 mutations cause Dents disease.
Declaration of funding: Yes.
Details: This work was supported by the Medical Research Council (grants G9825289 and G1000467), Kidney Research UK (KRUK), EuFP6-EuReGene, (05085) and Fund for Scientific Research, Flanders (Fundamental Clinical Investigatorship, 1801110N).