Kynurenine 3-monooxygenase (KMO) limits < em > de novo < /em > NAD < sup > + < /sup > synthesis through dietary tryptophan in renal proximal tubule epithelial cell models

Am J Physiol Cell Physiol. 2024 Mar 18. doi: 10.1152/ajpcell.00445.2023. Online ahead of print.ABSTRACTNicotinamide adenine dinucleotide (NAD+) is a pivotal coenzyme, essential for cellular reactions, metabolism, and mitochondrial function. Depletion of kidney NAD+ levels and reduced de novo NAD+ synthesis through the tryptophan-kynurenine pathway are linked to acute kidney injury (AKI), while augmenting NAD+ shows promise in reducing AKI. We investigated de novo NAD+ biosynthesis using in vitro, ex vivo and in vivo models to understand its role in AKI. 2D cultures of human primary renal proximal tubule epithelial cells (RPTECs) and HK-2 cells showed limited de novo NAD+ synthesis, likely due to low pathway enzyme gene expression. Employing 3D spheroid culture model improved the expression of tubular-specific markers and enzymes involved in de novo NAD+ synthesis. However, de novo NAD+ synthesis remained elusive in the 3D spheroid culture, regardless of injury conditions. Further investigation revealed that 3D cultured cells couldn't metabolize tryptophan (Trp) beyond kynurenine (KYN). Intriguingly, supplementation of 3-hydroxyanthrilinic acid into RPTEC spheroids was readily incorporated into NAD+. In a human precision-cut kidney slice (PCKS) ex vivo model, de novo NAD+ synthesis was limited due to substantially downregulated kynurenine 3-monooxygenase (KMO), which is responsible for KYN to 3-hydroxykynurenine conversion. KMO overexpression in RPTEC 3D spheroids successfully...
Source: Am J Physiol Cell Ph... - Category: Cytology Authors: Source Type: research