Researchers found that a single normal copy of a defective gene can prevent dangerous cysts from forming in polycystic kidney disease (PKD). This discovery could lead to the development of gene therapy tailored for treating the disease. They also discovered that the type of drug class called ‘glycoside’ can bypass the effects of the defective gene in PKD. These findings could pave the way for new therapeutic approaches to treating PKD, which affects millions of people worldwide. The study, which was partially funded by the National Institutes of Health (NIH), has been published in Cell Stem Cell.
Dr. Vishy and colleagues used gene editing and 3D human cell models called organoids to study the genetics of PKD. PKD is a life-threatening inherited kidney disorder caused by a gene defect, which leads to the expansion of microscopic tubes in the kidneys, forming cysts that can crowd out healthy tissue over time, leading to kidney function problems and eventually kidney failure. Most people with PKD are born with one healthy gene copy and one defective gene copy in their cells.
To better understand the reason for cysts, form in PKD, Vishy and his colleagues determined 3D human mini-kidney organoids with one normal gene copy and one defective copy. They grew organoids from induced pluripotent stem cells, which can become any kind of cell in the body and mimic features of an organ’s structure and function. To generate organoids containing clinically relevant mutations, the researchers used a gene editing technique called base editing to create mutations in certain locations on the PKD1 and PKD2 genes in human stem cells. They focused on four types of mutations in these genes that are known to cause PKD by disrupting the production of polycystin protein. Disruptions in two types of protein – polycystin-1 and polycystin-2 – are associated with the most severe forms of PKD. They then compared cells with two gene copy mutations in organoids to cells with only one gene copy mutation. In some cases, they also used gene editing to correct mutations in one of the two gene copies to see how this affected cyst formation. They found organoids with two defective gene copies always produced cysts and those that carried one good gene copy and one bad copy did not form cysts.
The researchers discovered that cells with one healthy gene copy produce only half the normal amount of polycystin-1 or polycystin-2, which is enough to prevent cysts from developing. They have also found that there is a need for a second trigger that, if prevented, could potentially prevent the disease. The researchers have used organoid models to study the effectiveness of a class of drugs known as eukaryotic ribosomal selective glycoside in preventing PKD cyst formation. These compounds are effective only on single base pair mutations, which are frequently seen in PKD patients, but not on any mouse models or previous organoid models of PKD. To test the efficacy of these drugs, the researchers created experimental models with this type of mutation.
The researchers found that the drugs restored the ability of genes to produce polycystin, leading to a 50% increase in polycystin-1 levels and preventing cyst formation. Furthermore, the drugs were effective in slowing down cyst growth. Based on these promising results, the researchers propose that the next crucial step would involve clinical trials testing existing glycoside drugs in patients. Additionally, they advocate for further exploration of gene therapy as a potential treatment for PKD.
Reference
Vishy CE, Thomas C, Vincent T, Crawford DK, Goddeeris MM, Freedman BS. Genetics of cystogenesis in base-edited human organoids reveal therapeutic strategies for polycystic kidney disease. Cell Stem Cell. 2024 Apr 4;31(4):537-553.e5.