Metabolic effects of polycystin-1 C-terminal tail (CTT) expression in Pkd1-KO mice
Authors: Onuchic Laura , Padovano Valeria , Schena Giorgia , Shi Xiaojian , Dong Ke , Rajendran Vanathy , Rai Victoria , Pandya Raj , Gresko Nikolay , Shen Hongying , Somlo Stefan , Caplan Michael 
Published: May 2023

BACKGROUND: Autosomal dominant polycystic kidney disease (ADPKD) is one of the most common life-threatening genetic diseases. Mutations in the PKD1 gene, which encodes polycystin-1, account for ~78% of cases. We have previously shown that transgenic expression of the polycystin-1 CTT in the Pkd1fl/fl;Pax8rtTA;TetO-Cre mouse model of ADPKD suppresses cystic phenotype and preserves renal function. This suppression is dependent upon an interaction between CTT and Nicotinamide Nucleotide Transhydrogenase (NNT). NNT is a mitochondrial enzyme that modulates levels of NAD(P)(H). In the present study we assessed CTT-dependent changes in metabolic profile and redox modulation in Pkd1-KO mice. Furthermore, we evaluated CTT-dependent changes in NNT enzymatic activity. METHODS: Untargeted metabolomics and NAD(P)(H) levels were determined by LC-MS. NNT enzymatic activity was measured using a kinetic spectrophotometric assay. RESULTS: Untargeted metabolomic analyses were performed in Pkd1fl/fl;Pax8rtTA;TetO-Cre +/- CTT mice at pre-cystic (10 weeks) and cystic (16 weeks) stages. At the pre-cystic stage, 8 metabolites were significantly changed meeting both criteria of P value <0.05 and fold change >2. Consistent with the interpretation that the CTT exerts effects on mitochondrial function, it is interesting to note that the most significantly enriched metabolite in kidneys from CTT-expressing mice was ATP. At the cystic time-point, significant changes were detected in 44 metabolites, of which 6 were upregulated and 38 were downregulated in CTT-expressing mice. Interestingly, many of these downregulated metabolites have been previously implicated in ADPKD pathogenesis and some of them are related to potential therapeutic targets such as methionine, lactate and asparagine. NADH/NAD+ and NADPH/NADP+ ratios were increased in CTT-expressing mice at both timepoints. Finally, we show that CTT expression in Pkd1-KO mice can increase NNT enzymatic activity, as measured in mouse renal tissue ex vivo, to the level observed in healthy wild type controls. This same enzymatic activity assay, performed utilizing an in vitro cell culture system, reveals that the PC1-CTT mitochondrial-targeting sequence (residing between aa residues 4134-4154 of the PC1 protein) is necessary for the modulation of NNT enzymatic activity. CONCLUSION: CTT expression can increase NNT enzymatic activity, which leads to changes in mitochondrial redox and metabolic profile at an early pre-cystic timepoint. At the late cystic time-point, the observed changes in a large and different array of metabolites suggests these findings may reflect consequences of the cystic phenotype. Taken together, these metabolic findings support the interpretation that the CTT suppression model exhibits a shift towards normal metabolism in which oxidative phosphorylation serves as the predominant source of ATP generation, and help elucidate the downstream mechanisms of CTT-dependent disease suppression. PKD Foundation Research Fellowship and NIH RC2 DK120534 This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.