mTor inhibition in Cystinotic iPSC’s and a new rat model to study Cystinosis

Presented by Dr Jennifer A Hollywood, Department of Molecular Medicine and Pathology, The University of Auckland, New Zealand

CoAuthor: Professor Alan J Davidson, Department of Molecular Medicine and Pathology, The University of Auckland, New Zealand

The lysosomal storage disease nephropathic cystinosis results from mutations in CTNS, encoding a cystine transporter, and initially causes kidney proximal tubule dysfunction followed by kidney failure. Patients receive the drug-based therapy Cysteamine from diagnosis, however, despite long-term treatment, patients still progress to kidney failure with the need for transplant inevitable. There is an urgent need for alternative treatments as there is increasing evidence that secondary complications are associated with loss of CTNS that are unrelated to the accumulation of cystine. Using our stem cell and kidney organoid model we have discovered a drug combination (Cysteamine + Everolimus) that ‘rescues’ cystinotic cells in vitro. To evaluate the therapeutic potential of this therapy, pre-clinical testing in a rodent model of cystinosis is required. As there are limitations associated with current animal models that make them unsuitable for drug trials, we have utilised gene-editing to generate a cystinotic rat model. These rats display classic hallmark characteristics of a cystinosis phenotype within 3-6 months as seen by:  failure to gain weight, excessive thirst (polydipsia) and urination (polyurea), cystine accumulation and kidney dysfunction. In depth urine analysis revealed high levels of glucose, calcium, albumin and total protein are being excreted at 6 months (consistent with the onset of Fanconi syndrome) as well as progressive diminution of urea and creatinine clearance indicative of chronic kidney damage. Slit lamp examination of the eyes of 3 month old animals revealed the presence of cystine crystals, a hallmark of cystinosis disease. Histology shows the presence of ‘swan neck’ lesions in kidney tissues at 6 months of age.

This novel rat model offers the promise of faithfully recapitulating the human disease and facilitating the testing of new treatment regimens.