Endogenous adenine mediates kidney injury in diabetic models and predicts diabetic kidney disease in patients
Kumar Sharma, et al.
Kumar Sharma, et al.
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Research Article Nephrology

Endogenous adenine mediates kidney injury in diabetic models and predicts diabetic kidney disease in patients

Abstract

Diabetic kidney disease (DKD) can lead to end-stage kidney disease (ESKD) and mortality; however, few mechanistic biomarkers are available for high-risk patients, especially those without macroalbuminuria. Urine from participants with diabetes from the Chronic Renal Insufficiency Cohort (CRIC) study, the Singapore Study of Macro-angiopathy and Micro-vascular Reactivity in Type 2 Diabetes (SMART2D), and the American Indian Study determined whether urine adenine/creatinine ratio (UAdCR) could be a mechanistic biomarker for ESKD. ESKD and mortality were associated with the highest UAdCR tertile in the CRIC study and SMART2D. ESKD was associated with the highest UAdCR tertile in patients without macroalbuminuria in the CRIC study, SMART2D, and the American Indian study. Empagliflozin lowered UAdCR in nonmacroalbuminuric participants. Spatial metabolomics localized adenine to kidney pathology, and single-cell transcriptomics identified ribonucleoprotein biogenesis as a top pathway in proximal tubules of patients without macroalbuminuria, implicating mTOR. Adenine stimulated matrix in tubular cells via mTOR and stimulated mTOR in mouse kidneys. A specific inhibitor of adenine production was found to reduce kidney hypertrophy and kidney injury in diabetic mice. We propose that endogenous adenine may be a causative factor in DKD.

Authors

Kumar Sharma, Guanshi Zhang, Jens Hansen, Petter Bjornstad, Hak Joo Lee, Rajasree Menon, Leila Hejazi, Jian-Jun Liu, Anthony Franzone, Helen C. Looker, Byeong Yeob Choi, Roman Fernandez, Manjeri A. Venkatachalam, Luxcia Kugathasan, Vikas S. Sridhar, Loki Natarajan, Jing Zhang, Varun S. Sharma, Brian Kwan, Sushrut S. Waikar, Jonathan Himmelfarb, Katherine R. Tuttle, Bryan Kestenbaum, Tobias Fuhrer, Harold I. Feldman, Ian H. de Boer, Fabio C. Tucci, John Sedor, Hiddo Lambers Heerspink, Jennifer Schaub, Edgar A. Otto, Jeffrey B. Hodgin, Matthias Kretzler, Christopher R. Anderton, Theodore Alexandrov, David Cherney, Su Chi Lim, Robert G. Nelson, Jonathan Gelfond, Ravi Iyengar, for the Kidney Precision Medicine Project

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Figure 4

Molecular pathways and events implicating the ribonucleoprotein biogenesis and mTOR pathways with adenine in DKD.

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Molecular pathways and events implicating the ribonucleoprotein biogenes...
(A and B) The protein synthesis (ribonucleoprotein [RNP] biogenesis) pathway increased in proximal tubule cells of patients with DKD without proteinuria. Single-cell- transcriptomic data obtained from DKD kidney biopsies from the KPMP study were analyzed for differentially expressed genes in proximal tubules (PTs) of each DKD patient versus healthy reference tissue. Upregulated genes with an adjusted P ≤ 0.01 and ranked among the top 600 significant differentially expressed genes were subjected to pathway enrichment analysis using the Molecular Biology of the Cell Ontology (MBCO). Ranking for the RNP biogenesis pathway (a level-2 pathway canonically regulated by the mTOR pathway) is shown for 28 individual patients. Vertical dashed lines indicate P ≤ 0.01 for pathway ranking. (C) Up to the top 5, 5, 10, and 5 level-1 (dark red), level-2 (red), level-3 (blue), and level-4 (green) pathways, respectively, using MBCO are shown for patient 1 (P ≤ 0.01). See blue lines in A and B. Single-cell-transcriptomic data from patients with T2D (n = 6) with low albuminuria compared with cohort specific healthy samples was analyzed to identify upregulated pathways in PT cells. Note that the RNP biogenesis pathway is the top ranked level-2 pathway in both independent studies. (D–F) Cell culture studies in mouse proximal tubular cells demonstrated an increase in (D) fibronectin and (E) phospho-S6 kinase and (F) that mediation of fibronectin (FN) upregulation is blocked by rapamycin, indicating that mTOR mediates adenine effect. (G–K) Adenine administration to mice increases (G) serum soluble tumor necrosis factor-1 (sTNFR1) and (H) plasma kidney injury marker-1 (KIM-1) and (I) stimulates kidney and (J and K) matrix molecules in the kidney (n = 12 in control group and n = 7 in adenine treated group). *P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001, 2-tailed Student’s t test was used for 2 group comparisons. One-way ANOVA was used for multiple group comparisons. Data represent mean ± SD.