CYSTINOTIC FIBROBLASTS ACCUMULATE CYSTINE FROM INTRACELLULAR PROTEIN CATABOLISM

Abstract

Nephropathic cystinosis is an autosomal recessive disease characterized clinically by renal tubular and glomerular dysfunction and biochemically by intralysosomal cystine accumulation. We have recently reported that aminothiol treatment of cultured fibroblasts from patients with cystinosis produces rapid and complete removal of the stored cystine (1). Subsequent studies (2) showed that such cystine-depleted cells can reaccumulate cystine during incubation in culture medium lacking cystine. Thus, cystine appears to accumulate in these cells from an intracellular source. Potential intracellular sources include (1) GSH, (2)protein, and (3) cystathionine. No activity of the cystathionase pathway has been found by previous investigations in these cells, and none was found under the conditions of cystine depletion in the current investigations. Cells depleted of >80% of their GSH content reaccumulate cystine to the same extent as non-GSH depleted controls. Cells selectively labelled with 35S-cystine in either the GSH + protein pools or GSH pool alone only reaccumulate labelled cystine when the protein pool is labelled. Known inhibitors of protein degredation (NH4Cl and chloroquin) reversibly inhibit cystine reaccumulation in cystine-depleted cells. We conclude that the intralysosomal cystine accumulation observed in cells cultured from patients with cystinosis is derived from protein catabolism. (1) Thoene, J.G. et al. J.Clin.Invest.58:180, 1976. (2) Oshima, R.G. et al. J.Biol.Chem. 251:4287, 1976.