High-resolution mapping of the gene for cystinosis, using combined biochemical and linkage analysis.

Infantile nephropathic cystinosis is an autosomal recessive disorder characterized biochemically by an abnormally high intracellular content of free cystine in different organs and tissues due to a transport defect of cystine through the lysosomal membrane. Affected children present with the Fanconi syndrome and usually develop progressive renal failure within the 1st decade of life. Measurement of free cystine in purified polymorphonuclear leukocytes provides an accurate method for diagnosis and detection of heterozygous carriers. In order to localize the gene locus for cystinosis we performed linkage analysis in 18 cystinosis families. However, since 17 of these were simplex families, we decided to include the phenotypes of the heterozygous carriers previously determined by their leukocyte cystine content in the linkage analysis. This approach allowed us to obtain highly significant results, confirming the localization of the cystinosis gene locus recently mapped to the short arm of chromosome 17 by the Cystinosis Collaborative Research Group. Crucial recombination events allowed us to refine the interval of the cystinosis gene to a genetic distance of 1 cM. No evidence of genetic heterogeneity was found. Our results demonstrate that the use of the previously determined phenotypes of heterozygous carriers in linkage analysis provides a reliable method for the investigation of simplex families in autosomal recessive traits.     

Lysosomal cystine counter-transport in heterozygotes for cystinosis.

Heterozygotes for cystinosis exhibited approximately half the normal rate of cystine counter-transport into isolated leukocyte lysosomes. This gene-dosage effect strongly supports previous findings demonstrating that the basic defect in cystinosis is impaired cystine transport across the lysosomal membrane. The method was used to determine the cystinosis carrier status for siblings of affected children in two families with cystinosis.     

Comparative study of cystine clearance in cystinotic and I-cell fibroblasts upon exposure to cystine dimethyl ester

I-cell fibroblasts can accumulate cystine at levels comparable to those seen in homozygous cystinotic fibroblasts. Cystine accumulation in cystinosis is accounted for cystine clearance defect in situ. To unravel the question whether the same clearance defect or two different mechanisms cause cystine accumulation in I-cell disease, we used the cystine loading technique upon exposure of skin fibroblasts to radioactive cystine dimethyl ester. Normal, cystinotic and I-cell fibroblasts were exposed to radioactive cystine dimethyl ester, and the clearance of the generated radioactive cystine was measured. Cystinotic cells showed a marked defect in cystine clearance in situ, as compared to normal fibroblasts. In I-cell fibroblasts, we observed slow hydrolysis of cystine dimethyl ester to cystine, indicating low esterase activity, but no defect in clearance of the generated cystine. Cysteine production from the exogenous cystine dimethyl ester, presumably by cytoplasmic hydrolysis of the generated cystine, is normal in I-cell fibroblasts. Thus, our results indicate that, unlike cystinosis, there is no cystine clearance defect in situ for cystine in I-cell disease, and probably unrelated mechanisms cause cystine storage in cystinosis and I-cell disease.     

pH-profile of cystine and glutamate transport in normal and cystinotic human fibroblasts

In the human recessive condition cystinosis, cystine transport has been reported to be normal in the plasma membrane but defective in the lysosome membrane. A possible explanation is that the transport systems at the two cellular sites are identical and that the defect in cystinosis affects the porter's ability to operate at the low pH of the lysosome. To test this hypothesis the uptake of 3H-labelled cystine and glutamate by normal and cystinotic human skin fibroblasts has been measured in vitro at pH 5.8, 6.5, 7.0, 7.4 and 8.0. Uptake of glutamate was more rapid than that of cystine. Uptake of cystine increased with increasing pH, but uptake of glutamate showed no marked pH-dependence. Transport in cystinotic cells was similar to that in normal cells, and similarly affected by pH. This finding is incompatible with the hypothesis proposed above. It is concluded that the cystine porters of the plasma membrane and the lysosome membrane are probably genetically distinct.     

Proton-translocating ATPase and lysosomal cystine transport

A proton-translocating ATPase was identified in highly purified lysosomes from Epstein-Barr virus-transformed human lymphoblasts. Activity of this ATPase caused acidification of highly purified, fluorescein isothiocyanate dextran-loaded lysosomes and correlated with the ATP-dependent efflux of lysosomal cystine. The lysosomal ATPase was distinct from mitochondrial F1-ATPase in its responses to a variety of inhibitors. Although ATP-dependent lysosomal cystine efflux is not demonstrable in cultured lymphoblasts from individuals with nephropathic cystinosis, ATPase activity and acidification in lysosomes from these cells is comparable to that in noncystinotic lysosomes. ATPase activity in lymphoblasts from normal individuals was 543 +/- 79 nmol/mg/min while in lymphoblasts from cystinotic individuals this activity was 541 +/- 25 nmol/mg/min. ATP-dependent acidification of lysosomes from normals was -0.5 +/- 0.1 pH units compared to -0.5 +/- 0.1 pH units in cystinotic lysosomes. Activity of the lysosomal proton-translocating ATPase is a necessary, but not sufficient, condition for lysosomal cystine efflux.     

Purification and characterization of a membrane-bound NADPH-cytochrome c reductase capable of catalyzing menadione-dependent O2- formation in guinea pig polymorphonuclear leukocytes

A membrane-bound NADPH-cytochrome c reductase, which is capable of forming the superoxide anion (O2-) in the presence of menadione, was highly purified from membrane fractions of disrupted guinea pig polymorphonuclear leukocytes by solubilization with 0.2% Triton X-100 and chromatographies on Sephacryl S-300 and 2',5'-ADP-agarose. The overall purification from the membrane fraction was over 110-fold, with a yield of about 6%. The purified preparation did not contain two other pyridine nucleotide-oxidizing enzymes: NADH- and NAD(P)H-oxidizing enzymes (J. Biochem. 94, 931-936, 1983). Besides cytochrome c, the purified enzyme was able to reduce menadione, Nitroblue tetrazolium (NBT) and 2,6-dichlorophenolindophenol. The reduction of menadione alone resulted in the formation of O2-. The purified enzyme preparation contained FAD. When assayed by measuring O2--generation in the presence of menadione, the enzyme showed an optimum pH at 7.0-7.4, and Km values for NADPH, NADH, and menadione were 25, 230, and 5.3 microM, respectively. The enzyme activity was not inhibited by NaN3 or dicumarol, but was by N-ethylmaleimide, EDTA, and quercetin; these inhibition profiles agree with those observed for the NADPH oxidase in the membrane fraction of phorbol-myristate acetate-stimulated leukocytes. Furthermore, when compared by means of the NBT-staining method combined with disc gel electrophoresis, the purified enzyme was electrophoretically indistinguishable from the NADPH-NBT reductase in the plasma membrane as well as phagosomes of the leukocytes. These results suggest that the purified NADPH-cytochrome c reductase is the putative flavoprotein of the NADPH oxidase system responsible for the respiratory burst.     

Uptake of cystine by cystine-depleted fibroblasts from patients with cystinosis

[³⁵S]L-cystine uptake was measured in cultured skin fibroblasts from patients with nephropathic cystinosis, pretreated with cysteamine to deplete their cystine pools. The uptake was greater in the cystinotic cells than in normal cells. The data suggest that the enhanced [³⁵S]-cystine uptake observed in cystinotic cells is not a consequence of disulfide exchange with stored cystine and may be related to the underlying abnormality in this enigmatic disorder.     

Zur Beziehung zwischen Hautleistenverlauf und Morbus Wilson

Summary The content of free cystine was measured in cultures of fibroblasts from heterozygotes and children homozygous for the infantile type of cystinosis and from normal controls by a modified procedure. The values in 4 homozygotes ranged between 4.2–8.0 moles 1/2 cystine/g protein; those in 7 heterozygotes between 0.2–0.7 moles 1/2 cystine/g protein; and those in the 5 normal controls between less than 0.1–0.25 moles 1/2 cystine/g protein. This means that in the individual case normals and heterozygotes cannot be differentiated excactly in the lower heterozygote range. This fact should be taken into account in genetic counseling.

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Zusammenfassung In kultivierten Fibroblasten von Heterozygoten und Homozygoten für Cystinose vom frühkindlichen Typ und von Normalpersonen wurde der Gehalt an freiem Cystin mit einer methodisch modifizierten Aufarbeitung gemessen. Die Werte für 4 untersuchte Homozygote liegen im Bereich von 4,2–8,0 Mol 1/2 Cystin/g Protein, die von 7 Heterozygoten zwischen 0,2–0,7 Mol und die von 5 Normalkontrollen zwischen weniger als 0,1–0,25 Mol 1/2 Cystin/g Protein. Während die Gesamtgruppe der Heterozygoten signifikant über der der Normalpersonen liegt, ist im Einzelfall in einem Grenzbereich eine klare Unterscheidung zwischen Normalen und Heterozygoten nicht möglich. Bei der Familienberatung muß dies berücksichtigt werden.

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Supported by the Deutsche Forschungsgemeinschaft (SFB 35).     

Impaired clearance of free cystine from lysosome-enriched granular fractions of I-cell-disease fibroblasts.

Cultured fibroblasts from patients with I-cell disease (mucolipidosis II) accumulate excessive amounts of free cystine, similarly to cells from patients with nephropathic cystinosis, a disorder of lysosomal cystine transport. To clarify whether the intralysosomal accumulation of cystine in I-cell-disease fibroblasts was due to a defective disposal mechanism, we measured the rates of clearance of free [35S]cystine from intact normal, cystinotic and I-cell-disease fibroblasts. Loss of radioactivity from the two mutant cell types occurred slowly (t 1/2 = 500 min) compared with the rapid loss from normal cells (t 1/2 = 40 min). Lysosome-rich granular fractions isolated from three different cystine-loaded normal, cystinotic and I-cell-disease fibroblast strains were similarly examined for non-radioactive cystine egress. Normal granular fractions lost cystine rapidly (mean t 1/2 = 43 min), whereas cystinotic granular fractions did not lose any cystine (mean t 1/2 = infinity). I-cell-disease granular fractions displayed prolonged half-times for cystine disposal (mean = 108 min), suggesting that I-cell-disease fibroblasts, like cystinotic cells, possess a defective carrier mechanism for cystine transport.     

Decrease of intracellular cystine content in cystinotic fibroblasts by inhibitors of gamma-glutamyl transpeptidase

Cystine content of skin fibroblasts derived from patients with cystinosis was decreased by inhibitors of gamma-glutamyl transpeptidase, the initial enzyme in glutathione catabolism. The addition of maleate or the gamma-glutamyl hydrazone of alpha-ketobutyric acid to culture medium (1-20 mM) resulted in dose-dependent decreases of up to 55% on intracellular cystine content of cystinotic cells in 24 h. L-Serine in sodium borate buffer (40 mM each) produced similar results and further decreased cystine levels to 14% of cystinotic control values after 10 days incubation. Analysis of intracellular amino acids showed that, in general, other amino acids remained unchanged following serine-borate treatment. These results suggest that cystine storage in cystinotic tissues may be related to metabolism of glutathione.     

Effect of prostaglandin E1 on chemiluminescence response and adherence of human polymorphonuclear leukocytes to human cultured endothelial cells of prostaglandin E1 treated polytraumatized patients

We investigated the effect of prostaglandin E1 on human polymorphonuclear leukocytes, in vivo. Polymorphonuclear leukocytes of a prostaglandin E1 and placebo study group were harvested and their function, as production of oxygen-derived metabolites and adherence to human cultured endothelial cells, was compared. Additionally, data obtained from polymorphonuclear leukocytes of a prostaglandin E1 and placebo group were compared with data obtained from polymorphonuclear leukocytes from 28 blood donors, who served as a control group. Production of oxygen-derived metabolites by polymorphonuclear leukocytes during contact with endothelial cells was measured by chemiluminescence. Chemiluminescence was significantly (p < 0.01) increased in the placebo group in comparison to the control group decreasing to values of control group after 6 d (post-trauma). Chemiluminescence response was not significantly suppressed in patients treated with prostaglandin E1 in comparison to the placebo group. Adherence of polymorphonuclear leukocytes (placebo group) to endothelial cells was significantly increased (p < 0.01) within the first 6 d post-trauma Following day 6, values were in the same range as values for the control group. Adherence was not significantly suppressed in patients treated with prostaglandin E1 in comparison to the placebo group. In conclusion, prostaglandin E1 at a dose of 20 ng/kg bw/min does not influence production of oxygenderived metabolites and adherence in polytraumatized patients in comparison to a placebo group. Additionally, production of oxygen-derived metabolites by polymorphonuclear leukocytes in response to endothelial cells is shown and it is evident that endothelial cells might influence production of oxygen derived metabolites by polymorphonuclear leukocytes.     

Cystine storage in cultured myotubes from patients with nephropathic cystinosis.

Sorted muscle cells, cultured from a patient with nephropathic cystinosis, stored 100 times normal amounts of cystine. Subcellular fractionation and density-gradient centrifugation confirmed that the cystine was located in a lysosomal compartment. 2. Myoblasts from cystinotic patients in culture underwent fusion to myotubes in a normal fashion. 3. The free thiol cysteamine effectively depleted cystinotic-muscle cells of cystine. 4. Cultured myoblast and myotubes offered a unique system for investigating the effects of lysosomal storage on differentiated cell functions.     

Iduronate sulfatase analysis of hair roots for identification of Hunter syndrome heterozygotes.

Iduronate sulfatase, the enzyme deficient in Hunter syndrome, can be readily measured in individual hair roots. Samples from Hunter syndrome hemizygotes had activities at or near the limits of detection. Samples from two mothers of Hunter syndrome patients, one an obligate heterozygote, had lower average iduronate sulfatase activity than the normal mean, and a significant number of hair roots had activity in the pathognomic range. A third mother showed a normal distribution of enzyme activity, and no hair roots were in the range of those from an affected individual. These results are similar to studies on the distribution of other X-linked enzymes in individual hair root samples from heterozygotes. This suggests that hair root iduronate sulfatase assessment is useful in the detection of Hunter syndrome carrier status, but further refinement of the test system is necessary.     

Transformation of skin fibroblast cells of a cystinotic patient by simian virus 40: evidence for an establishment of a permanent cell clone which retains the original metabolism defect.

Human skin fibroblast cells derived from a juvenile patient with nephropathic cystinosis were transformed by simian virus 40. Transformed cell clones were isolated and established in tissue culture. In comparison to the parental cystinotic cells, the newly isolated, transformed cell clones had a higher plating efficiency, a modal chromosome number of 68, grew in soft agar, and showed a nuclear immunofluorescence typical for SV 40-specific tumor (T) antigen. The content of intracellular, unbound cystine in the transformed cell clone was of the same level (6.1 nmol 1/2 cystine/mg protein) as in the parental cystinotic cells (7.4 nmol). Control cells (SV 80 and WI-38) contained normal levels of cystine (0.31 and 0.47 nmol 1/2 cystine/mg protein). The growth characteristics make the transformed cystinotic cell clone suitable for large scale preparation of cellular constituents, i.e. lysosomes which seem to be affected in cystinotic patients.     

The effect of chloroquine on the metabolism of [35S]cystine in normal and cystinotic human skin fibroblasts.

The present study concerns the effect of the lysosomotropic drug chloroquine on the uptake and metabolism of [35S]cystine in vitro by normal human fibroblasts and those from patients suffering from the lysosomal storage disease cystinosis. When the cells were cultured with [35S]cystine for periods in excess of 4 h, it was found that chloroquine considerably increased (up to 30-fold) the labelling of the intracellular cystine pool in cystinotic cells, with no increase or a much smaller increase in normal cells. For this effect chloroquine had an optimum concentration of 20 microM, with a small effect still being noticeable at 1 microM. A quinoline analogue, 4-(dimethylaminoethylamino)-7-iodoquinoline, had a similar effect to chloroquine. However, NH4Cl at concentrations of between 100 microM and 50 mM showed either no effect (at the lower concentrations) or a depression of intracellular cystine labelling (at the higher concentrations). The differences between the effects of the quinolines on cystinotic acid normal cells were not due to differences in total cell uptake of drug.     

Transformation of human cystinotic fibroblasts by SV40: characteristics of transformed cells with limited and unlimited growth potential.

Human skin fibroblasts derived from patients with nephropathic cystinosis were transformed with SV40 virions, cloned and permitted to enter the degenerative stage of growth termed "crisis," characteristic of SV40 transformed human cells. Nephropathic cystinosis is an autosomal recessively inherited metabolic disorder resulting in the intracellular accumulation of the amino acid cystine. A transformed cystinotic cell line which was recovered from the crisis stage was indistinguishable from its transformed precrisis parental cell strain in growth rate in media containing either 1% or 10% serum, cloning efficiency on plastic, in semisolid media, or upon confluent monolayers of normal skin fibroblasts, expression of SV40 T antigen, or production of virus. However, the modal DNA content of the recovered postcrisis transformed cystinotic cell line was different from that of the cloned parental precrisis transformed cell strain, suggesting that the postcrisis line was derived from a small subpopulation of the precrisis strain. The DNA content of the established cystinotic cell line continued to be unstable during subsequent subculturing and gave rise to subclones with both more and less DNA per cell. This line now has an apparently infinite growth potential and still has the hallmark of the cystinotic parental line, the storage of abnormally large amounts of intracellular nonprotein cystine.     

Respiratory burst as a biomarker for stress responses

A module for the detection of immunotoxic events within the test system Triple-Lux to be used during spaceflights was developed. It is based on the production of reactive oxygen species within the respiratory burst during phagocytosis or after stimulation of the phagocytes with phorbol 12-myristate 13-acetate (PMA). For this purpose, luminol-dependent chemiluminescence was measured. The assays were carried out with polymorphonuclear leukocytes purified from sheep peripheral blood. The influence of hydrocortisone and Cd2+ on the respiratory burst in polymorphonuclear leukocytes was assayed. Hydrocortisone in concentrations between 10(-4) and 10(-9) mol/liter showed an immunostimulating effect after PMA treatment. An immunosuppressive effect was observed for Cd2+ in concentrations between 10(-4) and 10(-7) mol/liter. Cryoconservation, which has often been critical for primary cells, can be accomplished without any subsequent loss of function by freezing the cells in dimethyl sulfoxide-containing medium.     

A potential new prodrug for the treatment of cystinosis: design, synthesis and in-vitro evaluation

Nephropathic cystinosis is a rare autosomal recessive disease characterised by raised lysosomal levels of cystine in the cells of most organs. The disorder is treated by regular administration of the aminothiol, cysteamine, an odiferous and unpleasant tasting compound that along with its metabolites is excreted in breath and sweat, leading to poor patient compliance. In an attempt to improve patient compliance a series of novel prodrugs has been designed and evaluated as a potential new treatment for nephropathic cystinosis. The first of the prodrugs tested, 3a, was found to decrease the levels of intracellular cystine in cystinotic fibroblasts. This is the first report of a potential new therapeutic treatment for nephropathic cystinosis since the advent of cysteamine bitartrate.     

Increased free-cystine content of fibroblasts cultured from patients with cystinosis

The presence of a significantly increased content of free-cystine in skin fibroblasts from both homozygotes and heterozygotes for cystinosis emphasizes the central role of cystine in this disease, even though the primary defect responsible for cystine accumulation is yet to be determined. The studies described in this communication provide evidence that cystine is compartmentalized in a subcellular location in cystinotic cells. In fact, the very growth of cystinotic fibroblasts in the presence more than 100 times the usual content of free-cystine is evidence that the accumulated cystine is not freely dispersed throughout the cell, since would otherwise inhibit many enzymes requiring free sulfhydryl groups for activity (Patrick, 1965). We have no evidence as to whether the cystine is located in a known subcellular organelle or in a previously unrecognized location. Skin fibroblasts may provide a convenient tool to pursue these questions.     

Intralysosomal cystine accumulation in mice lacking cystinosin,the protein defective in cystinosis

Cystinosis is an autosomal recessive disorder characterized by an accumulation of intralysosomal cystine. The causative gene, CTNS, encodes cystinosin, a seven-transmembrane-domain protein, which we recently showed to be a lysosomal cystine transporter. The most severe and frequent form of cystinosis, the infantile form, appears around 6 to 12 months, with a proximal tubulopathy (de Toni-Debré-Fanconi syndrome) and ocular damage. End-stage renal failure is reached by 10 years of age. Accumulation of cystine in all tissues eventually leads to multisystemic disease. Treatment with cysteamine, which reduces the concentration of intracellular cystine, delays disease progression but has undesirable side effects. We report the first Ctns knockout mouse model generated using a promoter trap approach. We replaced the last four Ctns exons by an internal ribosome entry site-betagal-neo cassette and showed that the truncated protein was mislocalized and nonfunctional. Ctns(-/-) mice accumulated cystine in all organs tested, and cystine crystals, pathognomonic of cystinosis, were observed. Ctns(-/-) mice developed ocular changes similar to those observed in affected individuals, bone defects and behavioral anomalies. Interestingly, Ctns(-/-) mice did not develop signs of a proximal tubulopathy, or renal failure. A preliminary therapeutic trial using an oral administration of cysteamine was carried out and demonstrated the efficiency of this treatment for cystine clearance in Ctns(-/-) mice. This animal model will prove an invaluable and unique tool for testing emerging therapeutics for cystinosis.