NRK1 controls nicotinamide mononucleotide and nicotinamide riboside metabolism in mammalian cells

Abstract

NAD+ is a vital redox cofactor and a substrate required for activity of various enzyme families, including sirtuins and poly(ADP-ribose) polymerases. Supplementation with NAD+ precursors, such as nicotinamide mononucleotide (NMN) or nicotinamide riboside (NR), protects against metabolic disease, neurodegenerative disorders and age-related physiological decline in mammals. Here we show that nicotinamide riboside kinase 1 (NRK1) is necessary and rate-limiting for the use of exogenous NR and NMN for NAD+ synthesis. Using genetic gain- and loss-of-function models, we further demonstrate that the role of NRK1 in driving NAD+ synthesis from other NAD+ precursors, such as nicotinamide or nicotinic acid, is dispensable. Using stable isotope-labelled compounds, we confirm NMN is metabolized extracellularly to NR that is then taken up by the cell and converted into NAD+. Our results indicate that mammalian cells require conversion of extracellular NMN to NR for cellular uptake and NAD+ synthesis, explaining the overlapping metabolic effects observed with the two compounds.

Administration of nicotinamide riboside prevents oxidative stress and organ injury in sepsis

“…In fact, the present study demonstrates that a single dose of IP NR injection induced a transient increase in NAD + level (about 3 folds) in lungs of mice, which prevented lung and heart injury, and improved the survival in septic mice. Previous evidence showed that administration of NR effectively elevated NAD + levels in liver and muscle in mice [15,28]. Thus, boosting NAD + with NR may also protect other organs in sepsis.…”

“…This is because sepsis induced a rapid reduction of NR kinase 1/2 in lung and liver (data not shown), essential enzymes responsible for conversion of NR to NAD + [14,15]. Although the protection conferred by pretreatment with NR may limit the use of NR as a therapeutic agent for sepsis at this moment, administration of NR can provide a preventive approach for septic organ injury as NR has been widely used as a health supplement [27].…”

“…A single dose of NR (300 mg/kg body weight; Biochempartner, China) or vehicle was intraperitoneally injected into mice 30 min before saline and LPS administration. This dose of NR was chosen based on previous reports that showed that a dose of 300 mg/kg body weight was safe [27] and efficiently increased the content of NAD + in liver and muscle in mice [15,28]. Four groups were included with 10 mice in each group: (1) Saline + Vehicle, (2) Saline + NR, (3) LPS + Vehicle, and (4) LPS + NR.…”

“…It is a pyridine-nucleoside form of vitamin B3 that functions as a precursor to nicotinamide adenine dinucleotide (NAD + ). NR is converted into NAD + sequentially by NR kinase 1/2 and nicotinamide mononucleotide adenylyltransferase [14,15]. Thus, administration of NR efficiently boosts intracellular NAD + levels, and protects against various chronic health issues such as aging and metabolic syndrome [16–19].…”

Nicotinamide mononucleotide requires SIRT3 to improve cardiac function and bioenergetics in a Friedreich’s ataxia cardiomyopathy model

“…Specifically, we observed increased transcript levels of the muscle-specific nicotinamide riboside kinase 2 (Nmrk2) and decreased transcript levels of nicotinamide phosphoribosyltransferase (Nampt) in FXN-KO hearts. Increased Nmrk2 suggests an enhanced capacity of the FXN-KO heart to take up exogenous NAD + precursors NR and NMN (27), and decreased Nampt suggests reduced de novo synthesis of NAD + in the FXN-KO heart. These observations were validated at the protein level by analysis of the FXN-KO cardiac mitochondrial proteome, which revealed a decrease in the mitochondrial levels of NAMPT and increased expression in the mitochondrial isoform of nicotinamide nucleotide adenylyltransferase 3 (NMNAT3), a protein involved in NMN salvage ( Figure 1, C and D, respectively).…”