Use of human iPSCs and kidney organoids to develop a cysteamine/mTOR inhibition combination therapy to treat cystinosis
Cystinosis is a lysosomal storage disease caused by mutations in CTNS, encoding a cystine transporter, and in its severest form is characterized by cystine accumulation, renal proximal tubule dysfunction and kidney failure. Cystinosis is treated with the cystine-depleting drug cysteamine, however this only slows progression of the disease and there is an urgent need for better treatments. Here, we have generated and characterized the first human induced pluripotent stem cell (iPSC) and kidney organoid models of cystinosis. These models exhibit elevated cystine and cysteine levels, enlarged lysosomes and a block in basal autophagy flux. Cysteamine treatment ameliorates this phenotype except for the basal autophagy flux defect. We found that treatment with Everolimus, an inhibitor of the mTOR pathway, reduces the number of large lysosomes and activates autophagy but does not rescue the cystine/cysteine loading defect. However, dual treatment of cystinotic iPSCs or kidney organoids with cysteamine and Everolimus corrects all of the observed phenotypes indicating that a combination therapy has therapeutic potential to improve the treatment of cystinosis.