Endo-lysosomal dysfunction in human proximal tubular epithelial cells deficient for lysosomal cystine transporter cystinosin.

Ekaterina A Ivanova,Maria Antonietta De Matteis,Henry Dijkman,Anna Pastore,Elena N Levtchenko,Lambertus Van Den Heuvel,Maria Giovanna De Leo,Benedetta Bussolati

doi:10.1371/journal.pone.0120998

Abstract

Nephropathic cystinosis is a lysosomal storage disorder caused by mutations in the CTNS gene encoding cystine transporter cystinosin that results in accumulation of amino acid cystine in the lysosomes throughout the body and especially affects kidneys. Early manifestations of the disease include renal Fanconi syndrome, a generalized proximal tubular dysfunction. Current therapy of cystinosis is based on cystine-lowering drug cysteamine that postpones the disease progression but offers no cure for the Fanconi syndrome. We studied the mechanisms of impaired reabsorption in human proximal tubular epithelial cells (PTEC) deficient for cystinosin and investigated the endo-lysosomal compartments of cystinosin-deficient PTEC by means of light and electron microscopy. We demonstrate that cystinosin-deficient cells had abnormal shape and distribution of the endo-lysosomal compartments and impaired endocytosis, with decreased surface expression of multiligand receptors and delayed lysosomal cargo processing. Treatment with cysteamine improved surface expression and lysosomal cargo processing but did not lead to a complete restoration and had no effect on the abnormal morphology of endo-lysosomal compartments. The obtained results improve our understanding of the mechanism of proximal tubular dysfunction in cystinosis and indicate that impaired protein reabsorption can, at least partially, be explained by abnormal trafficking of endosomal vesicles.

Highlights

Nephropathic cystinosis (MIM 219800) is an autosomal recessive disorder caused by mutations in the CTNS gene encoding cystinosin, a lysosomal cystine transporter [1, 2]
We confirmed the results in conditionally immortalized PTEC (ciPTEC) that were established as described previously from living exfoliated cells extracted from urine of a cystinosis patient bearing the 57-kb deletion and of a healthy volunteer [19]
We found that surface binding of GST-RAP was reduced by ~30% (p

Summary

Introduction

Nephropathic cystinosis (MIM 219800) is an autosomal recessive disorder caused by mutations in the CTNS gene encoding cystinosin, a lysosomal cystine transporter [1, 2]. A second isoform of cystinosin has been described, in which the C-terminal targeting motif is substituted by a longer sequence. This isoform has a different localization within the cell, being found on the plasma membrane, in the lysosomes and on other cytosolic structures such as endoplasmic reticulum and Golgi apparatus [4, 5]. Cysteamine enters the lysosome and splits cystine molecule into cysteine and cysteine-cysteamine mixed disulphide. Both products can be released from the lysosome through cysteine and PQLC2 transporters respectively [9]

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Results

Conclusion