Itaconate Controls the Severity of Autosomal Dominant Polycystic Kidney Disease

Background: Autosomal dominant polycystic kidney disease (ADPKD) is a genetically inherited disease in which inflammation plays a role in renal cyst growth. Itaconate has emerged as a key immunoregulatory metabolite with diverse roles in inflammation and immunity. However, the role of itaconate in cyst growth and its therapeutic potential in ADPKD is unknown. Methods: We performed 1) quantitative real-time PCR to examine the expression of aconitate decarboxylase (Acod1) in Pkd1 mutant renal epithelial cells and tissues, 2) clonogenic assay to assess the effects of itaconate derivative 4-octyl itaconate (4-OI) on Pkd1 mutant renal epithelial cell growth, and 3) western blot and immunostaining analysis in Pkd1 homozygous (PN24) renal epithelial and macrophage (RAW264.7) cells treated with 4-OI. Light microscopy was used to assess the effect of 4-OI on RAW264.7 cell activation in a Pkd1 mutant microenvironment. Furthermore, Pkd1RC/RC mice were treated with 4-OI to evaluate its effect on cyst growth. Results: We found that the expression of itaconate-synthesizing enzyme, Acod1, was downregulated in PN24 cells compared to Pkd1 heterozygous (PH2) control cells and in Pkd1RC/RC mouse kidneys compared to wild type kidneys. Treatment with 4-OI decreased 1) PN24 cell proliferation as examined with clonogenic assay, 2) the activation of PKD associated signaling pathways, including Akt, Erk, Stat3, p65, and S6, and 3) the expression of histone modifying enzymes including JMJD2A, a JmjC histone lysine demethylase (KDM), Smyd2 and Smyd3, both histone lysine methyltransferases (KMTs). In addition, we found that treatment with 4-OI altered mitochondrial dynamics by decreasing mitochondrial fission, and increasing mitochondrial fusion as determined by MitoTracker Red staining. Consistent with its immunoregulatory role, 4-OI treatment affected macrophage polarization of RAW264.7 cells stimulated with condition medium from PN24 cells. Importantly, treatment with 4-OI delayed cyst growth in Pkd1RC/RC mice as seen by a decrease in cystic index, kidney weight (KW)/body weight (BW) ratio and blood urea nitrogen (BUN) levels. Conclusion: Collectively, itaconate contributes to ADPKD by modulating epigenetic reprogramming, cell proliferation, mitochondrial dynamics, and immune response/inflammation, and treatment with itaconate derivatives may be a viable therapeutic strategy for ADPKD. Funding: NIDDK Support, Other U.S. Government Support