Methylation-Controlled J Protein as a Target to Alleviate Kidney Fibrosis and Cyst Growth

Background: Kidney mitochondrial function is abnormal in autosomal dominant polycystic kidney disease (ADPKD) with reduced aerobic glycolysis/oxidative phosphorylation (OXPHOS). Methylation-controlled J protein (MCJ) is the only endogenous inhibitor of electron transport chain (ETC) Complex I. Loss of MCJ enhances Complex I activity, increasing OXPHOS/ATP generation, without increasing reactive oxygen species (ROS). In liver injury models, MCJ genetic or siRNA-based (siMCJ) depletion lessens liver pathology by improving OXPHOS. Methods: We mined published/in house single nucleus/cell (sn/sc) RNAseq data of human and murine normal and ADPKD kidney samples to assess MCJ expression and mitochondrial gene set enrichment (GSE). In mice (WT/Pkd1RC/RC), we assessed kidney purine metabolites via LC-MS/MS. Using unilateral ureteral obstruction (UUO) and Pkd1RC/RC mice on the MCJ-/- background, we assessed MCJ’s role in mediating kidney fibrosis and kidney cyst growth. Fluorescence Lifetime Imaging Microscopy (FLIM, quantification of free NADH) and Electron Paramagnetic Resonance Spectroscopy (EPRS) were used to assess kidney OXPHOS and ROS levels. IV injection of naked siMCJ to WT mice was tested as a therapeutic strategy. Results: Analysis of sn/sc RNAseq revealed global MCJ expression in kidney epithelia, with a significant increase in human ADPKD samples. GSE analyses identified OXPHOS, ATP production, and ETC as the most differentially regulated pathways in WT vs Pkd1RC/RC collecting ducts. LC-MS/MS revealed reduced energy charge (1.28-fold) and ATP/ADP ratio in Pkd1RC/RC vs WT kidneys (1.34-fold). MCJ-/- vs MCJ+/+ mice had reduced kidney fibrosis 2wks post UUO (10.2% vs 14.5% fibrosis, p<0.001). 3mo old Pkd1RC/RC;MCJ-/- vs Pkd1RC/RC;MCJ+/+ mice had reduced kidney/body weight (0.77-fold, p<0.001) and computed cyst volume (1.55-fold, p<0.05). FLIM showed increased OXPHOS in Pkd1RC/RC;MCJ-/- vs Pkd1RC/RC;MCJ+/+ mice, but without increasing kidney ROS levels (EPRS). Lastly, IV injected siMCJ resulted in significantly reduced kidney MCJ levels. Conclusion: These findings suggest that targeting MCJ corrects abnormal kidney mitochondrial function and altered metabolic pathways that contribute to kidney fibrosis and cyst growth. Funding: NIDDK Support