Cystinuria is a hereditary disorder that results in failure to reabsorb the amino acid cysteine in the urinary system. This results in cysteine-urinary stones (commonly known as kidney stones). Cystinuria is a rare type of stone disease caused by mutations in one of two genes (SLC3A1 and SLC7A9). Current treatment options are limited in their effectiveness at preventing stone reoccurrence. Cysteine stones are dense, large, and mostly resistant to shockwave therapy and obstructive stones often require multiple procedures or surgery for removal. Therefore, there is a clear need for novel therapeutic strategies for the clinical treatment of cystinuria.
What is the solution?
Three major issues represent a critical problem; 1. a clear lack of understanding of the mechanisms of stone recurrence, 2.how stones increase susceptibility to chronic kidney disease and 3. the rarity of cystinuria limits randomised controlled trials for effective treatments.
Recent advances in genome editing using CRISPR-Cas9 engineering allows the creation of model ‘avatars’ that replicate the exact mutation found in patients with cystinuria. For the first time these avatars can be used to investigate the exact underlying mechanisms and be highly precise models for testing novel therapeutic options in rare diseases. We have at least two known cystinuria patients in the Hunter region, one paediatric (CIB Deshpande patient) and one adult (donor), whose specific mutations could be used to guide the generation of these targeted ‘avatars’.
We believe the solution to curing kidney stones and related kidney diseases is in harnessing the power of our immune system. Resident within the urinary system are immune cells known as natural helper cells. These cells have been shown to play important roles in the repair of the kidney following acute kidney injury. However, their role in stone recurrence and susceptibility to chronic kidney disease is unknown. Of particular note is the fact that males are more susceptible to stone formation and males naturally have less natural helper cells. Male sex hormones suppress these cells and in doing so removes their ability to regulate the normal function of the urinary system.
CIA Starkey is an expert in natural helper cells and currently holds an Australian Research Council (ARC) Discovery Early Career Researcher Award to investigate the role of these cells in lung development. He also holds a 2016-17 HMRI grant and is the primary supervisor of an honours student investigating the role of these cells in acute kidney injury. CIA Starkey has already established collaborations with CIB Deshpande and CIC Jiang. CIB Deshpande is a practising Paediatric Urologist at the John Hunter Children’s Hospital and a Clinician Researcher in Kidney and Bladder Diseases in Children. He has been the recipient of a NHMRC scholarship and has published over 40 articles in peer reviewed journals, majority on kidney and bladder diseases in children. In his role as the sole Staff specialist in Paediatric urology in Newcastle, he is intimately involved in the care of children in the Hunter New England area with urinary stones including those with cystinuria.
CIC Jiang is an expert in the use of CRISPR-Cas9 generated models of human mutation to investigate disease. He holds an NHMRC grant into use of these models in autoimmunity which was the awarded the top-ranked NHMRC grant for 2016. He also has expertise in the clinical management of genetic and non-genetic stone disease.
HMRI Specific Research Project/Program to address the need and solution
We intend to address the problem with a multi-disciplinary approach that involves a team of basic scientists and clinician scientists. This includes immunologists, urologists and nephrologists from multiple independent sites including Newcastle, Sydney and Canberra.
In our proposed study, we will generate CRISPR-Cas9 models based on mutations identified in key patients with cystinuria. Kidney stones that spontaneously develop in cystinuria patients and additional models of stone formation e.g. calcium stones (the most common type of kidney stone) will be investigated. We will be the first to establish such models at HMRI and the first in Australia to work on these models. We will also be the first to generate patient specific ‘avatars’ for cystinuria. We will use our cutting-edge core flow cytometry and imaging facilities at HMRI, to allow us to identify natural helper cells in both human blood/urine and model urinary tract tissue. This study will provide valuable new insights into how these immune cells contribute to stone recurrence and chronic kidney disease. It will also provide the foundation for us to establish a new research program in the future that will investigate these cells in human diseases of the urinary system and ways to regulate or increase their function to promote optimal immune responses and repair of this vital organ system. Furthermore, these avatars may then offer an alternative to test novel therapeutic options which can then be translated back to the patients in whom the mutations are found. This is a profound and novel advance as the rarity of cystinuria is a substantial impediment to testing and proving of therapeutic interventions – using models replicating the precise mutation causing human disease allows rapid therapeutic trials specific to individuals with cystinuria.
Dr Malcolm Starkey, Dr Aniruddh Deshpande, Dr Simon Jiang