Target for Polycystic Kidney Disease Gene Therapy Might Lie in MicroRNA Binding Sites

Deleting the 3′-untranslated region (3′-UTR) miR-17 microRNA binding site on PKD1 mRNA via CRISPR/Cas9 editing in cellular, ex vivo, and mouse models of autosomal dominant polycystic kidney disease (ADPKD) alleviated cyst growth and increased levels of Polycystin-1 (PC1), the disease-targeted protein, shedding light on a potential gene therapy approach for treating the disease, according to research recently published in Nature Communications.¹

Because there is evidence suggesting that ADPKD is associated with PKD1 gene dose threshold, the study’s investigators decided to look into methods of increasing PKD1 expression. It was noted that miR-17, a microRNA that has a role in silencing the expression of PKD1 and PKD2 mRNA, is more highly expressed in ADPKD models. Thus, the investigators explored the effects of deleting the sites on PKD1 and PKD2 mRNA to which miR-17 binds, referred to as the 3′-UTR miR-17 binding motifs.

“For more than 25 years, we have known that ADPKD is caused by mutations of PKD1 or PKD2 genes. Yet, no therapeutic strategy exists to go after these root causes...” Vishal Patel, MD, associate professor of internal medicine in the Division of Nephrology at UT Southwestern and corresponding author of the paper, said in a statement regarding the study’s publication.² “There are numerous genetic conditions where 1 copy of the causative gene is mutated, but the other copy is still normal. Our approach to harnessing the remaining normal copy is likely applicable to many other diseases besides PKD.”

In addition to the observed effects on cyst growth and PC1 levels, eliminating the microRNA binding site was also shown to improve the stability of the PKD1 mRNA. Furthermore, Patel and colleagues also found that deleting the same microRNA binding site on PKD2 mRNA also slowed cyst growth in Pkd1-mutant models, an unexpected finding implying that increasing PKD2 expression could be an additional area of interest even for AKPKD caused by mutations in the PKD1 gene. The investigators further verified the potential utility of targeting the microRNA binding sites on PKD1 and PKD2 by acutely blocking Pkd1/2 cis-inhibition in the mouse model with RGLS4326, an anti-miR-17 oligonucleotide. This approach similarly attenuated cyst growth in the mice.

“A noteworthy caveat here is that while RGLS4326 raises PC1 levels, its benefits in later stages of disease could be derived from simultaneous derepression of other miR-17 targets, including Polycystin-2 (PC2) and Ppara,” Patel and colleagues wrote.¹ “Another insight from our work is that potentially restoring hypomorphic Pkd1 mutants may be a beneficial therapeutic approach. On a cautionary note, particularly for modalities employing exogenous PKD1 supplementation, raising Pkd1 above wildtype levels produces cystic disease in mice. However, the uniqueness of our method is that, rather than transactivation, it relies on preventing inhibition, making it unlikely that PKD1 will rise to the supratherapeutic range.”

The investigators also noted that treatment with RGLS4326 was associated with higher urinary levels of PC1 in ADPKD patients in a recent phase 1b clinical trial (NCT04536688), and that future clinical studies are planned that will utilize a next-generation anti-miR-17 oligonucleotide referred to as RGLS8429. Patel and colleagues ultimately concluded that miRNAs that are known to function as inhibitors of a relatively small number of disease-associated mRNAs would be of interest for the development of new treatments for diseases. While their study only focused on ADPKD, they speculate that similar modes of cis-inhibitory regulation exist in other diseases which could be useful therapeutic targets, pointing out haploinsufficient monogenetic conditions as an area of particular interest for future research.