Cystinosin-deficient rats recapitulate the phenotype of nephropathic cystinosis.

The lysosomal storage disease cystinosis is caused by mutations in CTNS, encoding the cystine transporter cystinosin, and in its severest form leads to proximal tubule dysfunction followed by kidney failure. Patients receive the drug-based therapy cysteamine from diagnosis. However, despite long-term treatment, cysteamine only slows the progression of end-stage renal disease. Preclinical testing in cystinotic rodents is required to evaluate new therapies; however, the current models are suboptimal. To solve this problem, we generated a new cystinotic rat model using CRISPR/Cas9-mediated gene editing to disrupt exon 3 of Ctns and measured various parameters over a 12-mo time course. Ctns-/- rats display hallmarks of cystinosis by 3-6 mo of age, as demonstrated by a failure to thrive, excessive thirst and urination, cystine accumulation in tissues, corneal cystine crystals, loss of LDL receptor-related protein 2 in proximal tubules, and immune cell infiltration. High levels of glucose, calcium, albumin, and protein were excreted at 6 mo of age, consistent with the onset of Fanconi syndrome, with a progressive diminution of urine urea and creatinine from 9 mo of age, indicative of chronic kidney disease. Kidney histology and immunohistochemistry showed proximal tubule atrophy and glomerular damage as well as classic "swan neck" lesions. Overall, Ctns-/- rats show a disease progression that more faithfully recapitulates nephropathic cystinosis than existing rodent models. The Ctns-/- rat provides an excellent new rodent model of nephropathic cystinosis that is ideally suited for conducting preclinical drug testing and is a powerful tool to advance cystinosis research.NEW & NOTEWORTHY Animal models of disease are essential to perform preclinical testing of new therapies before they can progress to clinical trials. The cystinosis field has been hampered by a lack of suitable animal models that fully recapitulate the disease. Here, we generated a rat model of cystinosis that closely models the human condition in a timeframe that makes them an excellent model for preclinical drug testing as well as being a powerful tool to advance research.

In Vitro and In Vivo Models to Study Nephropathic Cystinosis.

The development over the past 50 years of a variety of cell lines and animal models has provided valuable tools to understand the pathophysiology of nephropathic cystinosis. Primary cultures from patient biopsies have been instrumental in determining the primary cause of cystine accumulation in the lysosomes. Immortalised cell lines have been established using different gene constructs and have revealed a wealth of knowledge concerning the molecular mechanisms that underlie cystinosis. More recently, the generation of induced pluripotent stem cells, kidney organoids and tubuloids have helped bridge the gap between in vitro and in vivo model systems. The development of genetically modified mice and rats have made it possible to explore the cystinotic phenotype in an in vivo setting. All of these models have helped shape our understanding of cystinosis and have led to the conclusion that cystine accumulation is not the only pathology that needs targeting in this multisystemic disease. This review provides an overview of the in vitro and in vivo models available to study cystinosis, how well they recapitulate the disease phenotype, and their limitations.