Chaperone‐mediated autophagy is impaired in the lysosomal storage disorder cystinosis (740.2)

Abstract

Functional lysosomes are essential for autophagosome maturation and clearance of autophagic substrates. Accordingly, Lysosomal Storage Disorders (LSDs) have been associated with autophagy defects. Cell malfunction in the LSD Cystinosis is caused by the accumulation of the amino acid cystine in lysosomes due to genetic defects in the Ctns gene (cystinosin), a lysosomal transporter. Using EM and TIRFM microscopy, we showed that lysosomal number, size and trafficking was affected in Ctns‐/‐ cells. Although the number of autophagosomes was strongly increased in Ctns‐/‐ cells under resting conditions, fusion of autophagosomes with lysosomes, as well as starvation‐induced degradation of the autophagosome marker LC3‐II, was not affected in these cells, indicating that autophagic flux is increased but not impaired in cystinosis. Interestingly, the receptor for chaperone‐mediated autophagy (CMA) LAMP2a, the rate limiting step for CMA, was downregulated and mislocalized in Ctns‐/‐ cells and tissues. Lysosomal translocation and degradation of CMA substrates was defective in Ctns‐/‐ lysosomes, suggesting defective CMA in cystinosis. Reconstitution of Ctns‐/‐ cells with EGFP‐CTNS normalized macroautophagy and partially rescued LAMP2a expression but not localization suggesting underlying trafficking defects in Ctns‐/‐ cells. We propose that defects in CMA contribute to the pathogenesis of cystinosis.Grant Funding Source: Supported by Cystinosis Research Foundation and NIH