SLC25A51 is a mammalian mitochondrial NAD+ transporter

Abstract

Summary Mitochondria require nicotinamide adenine dinucleotide (NAD + ) in order to carry out the fundamental processes that fuel respiration and mediate cellular energy transduction. Mitochondrial NAD + transporters have been identified in yeast and plants 1 , 2 but their very existence is controversial in mammals 3 – 5 . Here we demonstrate that mammalian mitochondria are capable of taking up intact NAD + and identify SLC25A51 (an essential 6 , 7 mitochondrial protein of previously unknown function, also known as MCART1) as a mammalian mitochondrial NAD + transporter. Loss of SLC25A51 decreases mitochondrial but not whole-cell NAD + content, impairs mitochondrial respiration, and blocks the uptake of NAD + into isolated mitochondria. Conversely, overexpression of SLC25A51 or a nearly identical paralog, SLC25A52, increases mitochondrial NAD + levels and restores NAD + uptake into yeast mitochondria lacking endogenous NAD + transporters. Together, these findings identify SLC25A51 as the first transporter capable of importing NAD + into mammalian mitochondria.

Mitochondrial NAD+ Controls Nuclear ARTD1-Induced ADP-Ribosylation

“…Similar to SLC12A8 knockdown, knockdown of NMNAT3 also had no effect on mitochondrial ADP-ribosylation dynamics. These findings strongly support the existence of a separate mitochondrial NAD + transporter ( Davila et al., 2018 ; Girardi et al., 2020 ; Kory et al., 2020 ; Luongo et al., 2020 ) and suggest that both transporters (NMN and NAD + ) are important and necessary for the establishment and regulation of different subcellular NAD + pools.

Figure 4 Lack of NMNAT3 and the NMN Transporter SLC12A8 Extends Nuclear ADP-Ribosylation after H 2 O 2 Treatment (A) Schematic overview of compartmentalized NAD + synthesis and breakdown in most transformed cells.

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Epistasis-driven identification of SLC25A51 as a regulator of human mitochondrial NAD import

“…While additional data, including transport assays with reconstituted recombinant protein, will be necessary to definitely prove the role of SLC25A51 as NAD+ transporter and fully define its substrate profile and transport mechanism, the multiple functional links here described convincingly converge on a functional annotation of SLC25A51 as an enabler of NAD+ accumulation in mitochondria. This annotation is corroborated by two recent publications 44,45 providing complementary evidence, including metabolomics analyses and yeast complementation experiments, of SLC25A51 being the longhypothesized mitochondrial NAD+ transporter in human cells. Further studies addressing the interplay between SLC25A51 and the close paralogs SLC25A52, which also showed the ability to transport NAD+ 44,45 , and the orphan SLC25A53 are also expected to shed light on the physiological relevance and regulatory mechanisms of this SLC.…”

“…This annotation is corroborated by two recent publications 44,45 providing complementary evidence, including metabolomics analyses and yeast complementation experiments, of SLC25A51 being the longhypothesized mitochondrial NAD+ transporter in human cells. Further studies addressing the interplay between SLC25A51 and the close paralogs SLC25A52, which also showed the ability to transport NAD+ 44,45 , and the orphan SLC25A53 are also expected to shed light on the physiological relevance and regulatory mechanisms of this SLC. Despite the high degree of functional redundancy displayed by transporters 46 , we show here that informative patterns of genetic interactions can be systematically derived for this family, allowing the generation of testable hypotheses for the de-orphanization of poorly characterized SLCs.…”

Lactate Limits T Cell Proliferation via the NAD(H) Redox State

“…This could be achieved through NAD-oxidizing agents, some of which are already proposed as anti-cancer treatments ( Li et al, 1999 ; Ough et al, 2005 ); supplementation of NAD + precursors, such as nicotinamide riboside ( Liu et al, 2018 ); augmenting NADH oxidation by expressing NADH oxidase ( Titov et al, 2016 ); or by augmenting mitochondrial function and oxidative phosphorylation of T cells ( Kawalekar et al, 2016 ; Scharping et al, 2016 ). Altering NAD + transport between the cytoplasm and mitochondria ( Luongo et al, 2020 ) may modify the ability of T cells to buffer redox stress. In addition, efforts to limit L-lactic acid efflux from tumors can augment anti-tumor immune responses ( Renner et al, 2019 ).…”