Abstract: FR-PO0345
Nicotinamide N-Methyltransferase (NNMT)-Dependent Enzymatic Activity Drives SOX9-Associated Maladaptive Proximal Tubular (PT) Repair
Session Information
- AKI: Mechanisms - Metabolism and Repair
October 23, 2026 | Location: Exhibit Hall A, Convention Center
Abstract Time: 10:00 AM - 12:00 PM
Category: Acute Kidney Injury
- 103 AKI: Mechanisms
Authors
- Tao, Yu, The University of Texas Southwestern Medical Center Department of Internal Medicine, Dallas, Texas, United States
- Clark, Amanda J., The University of Texas Southwestern Medical Center Department of Internal Medicine, Dallas, Texas, United States
- Taylor, Keegan, The University of Texas Southwestern Medical Center Department of Internal Medicine, Dallas, Texas, United States
- Muto, Yoshiharu, The University of Texas Southwestern Medical Center Department of Internal Medicine, Dallas, Texas, United States
- Gangadharan, Binnu, The University of Texas Southwestern Medical Center Department of Internal Medicine, Dallas, Texas, United States
- Chen, Liping, The University of Texas Southwestern Medical Center Department of Internal Medicine, Dallas, Texas, United States
- Suzuki, Takashi, The University of Texas Southwestern Medical Center Department of Internal Medicine, Dallas, Texas, United States
- Vu, Kyle Q., The University of Texas Southwestern Medical Center Department of Pediatrics, Dallas, Texas, United States
- Parikh, Samir M., The University of Texas Southwestern Medical Center Department of Internal Medicine, Dallas, Texas, United States
Background
Recent studies suggest renal NNMT upregulation in acute kidney injury (AKI) animal models, while other studies associate NNMT with renal fibrosis in chronic kidney disease (CKD) patients, suggesting a potential role for NNMT in AKI-to-CKD transition. NNMT diverts nicotinamide (NAM) from NAD+ salvage and consumes S-adenosylmethionine (SAM)-derived methyl donors; however, whether these metabolic effects contribute to maladaptive PT repair after AKI remains unclear. Failed-repair PT cells are characterized by loss of epithelial polarity and persistent SOX9 upregulation. However, the mechanisms underlying sustained SOX9 upregulation in failed-repair PT cells remain unknown. To address this gap, we investigated whether NNMT-mediated enzymatic activity contributes to failed PT repair through regulation of the SOX9 signaling pathway.
Methods
Single-cell RNA-seq datasets from KPMP were analyzed using Seurat v5.1.0 to evaluate NNMT expression across kidney cell clusters in AKI and CKD. Catalytically inactive NNMT mutants (D197A, Y20A) plasmid were generated. Wild-type (WT) and mutant NNMT plasmids were transfected into HK-2 cells. Intracellular NAD+ levels were measured using a commercial assay kit. Bulk RNA sequencing and gene set enrichment analysis (GSEA) were performed to identify transcription factors and pathways altered by NNMT overexpression(OE). Targeted metabolic supplementation with NAM, SAM, and methionine was used to distinguish the effects of NAD+ depletion from methyl donor consumption. SOX9 expression was quantified by qRT-PCR and western blot.
Results
Single-cell RNA-seq analysis revealed increased NNMT expression in maladaptive and failed-repair PT cells in AKI patients. WT NNMT induction significantly reduced intracellular NAD+ levels and increased SOX9 expression. GSEA showed that WT NNMT OE suppressed pathways related to tight junction assembly and epithelial polarity. Catalytically inactive NNMT mutants had no effect on NAD+ levels or SOX9 expression. NAM supplement, but not SAM or methionine, restored NAD+ levels and reversed SOX9 upregulation induced by WT NNMT OE.
Conclusion
NNMT upregulation is associated with maladaptive PT repair after AKI, and its enzymatic activity contributes to SOX9 upregulation and loss of epithelial polarity. These effects are specifically dependent on NAM and NAD+ depletion rather than methyl donor consumption.
Funding
- NIDDK Support