The redox status of cystinotic fibroblasts

Abstract

A key unresolved question in the pathogenesis of phenotype development in nephropathic cystinosis is whether intralysosomal cystine, the hallmark of this lethal inborn error of metabolism, alters cytoplasmic redox potential. Variable findings on this issue have been reported. This study of fetal and non-fetal skin and lung-derived cystinotic fibroblasts compared to origin and age-matched normal control fibroblasts reveals that cystinotic cells do not exhibit redox perturbations. We find that the steady-state redox status as assessed by the [GSH]/[GSSG] ratio, an indicator of the intracellular redox poise, is unchanged in cystinotic cells. Furthermore, the dependence of the intracellular GSH and cysteine pool sizes and the [GSH]/[GSSG] ratio are similarly dependent on the two major sources of cysteine, i.e. the transsulfuration pathway and the plasma membrane cystine transporter, xc(-), in both cystinotic and control cells, and the presence of lysosomal cystine has no measurable effect on the redox status of these cells. Hence, mechanisms other than cytosolic redox perturbations are involved in the etiology of nephropathic cystinosis.

Fig. 1

Outline of the GSH biosynthetic pathway and the sites of action of the inhibitors used in this study. Propargylglycine (PPG) inhibits cystathionine γ-lyaseCGL) preventing cysteine synthesis from methionine (Met) via the transsulfuration pathway. Sulfasalazine (SAS) inhibits the transmembrane cystine transporter xc^-. Both inhibitors can decrease the intracellular cysteine concentration and thus cause a decrease in intracellular GSH concentration. CBS denotes cystathionine -synthase, the first enzyme or transsulfuration pathway.

Fig. 2

The influence of propargylglycine and sulfasalazine on thiols in normal and cystinotic non-fetal human skin fibroblasts. Data are the average of two measurements.

Fig. 3

The influence of propargylglycine and sulfasalazine on thiol metabolites in normal and cystinotic fetal human lung fibroblasts. Data are the average of two measurements.